Fireworks Display: Enhancing Safety and Efficiency in Chinese Festivals

• Celebrate festivals the traditional Chinese way with spectacular fireworks displays
• Fireworks play a crucial role in national celebrations and various festive occasions
• Safety concerns pose significant challenges in the fireworks production company
• Introducing an automatic production line for firework particles to minimize safety risks
• Focus on the granulation process to optimize safety and efficiency

Key Points:

• Explore the forming mechanism of powder granulation and analyze influential factors.
• Identify interrelationships among various factors affecting granulation.
• Utilize a systematic design approach, considering domestic and foreign granulation equipment.
• Cater to market demands while proposing a design solution for granulation equipment.
• Determine main technical parameters through CAD/CAE technology and simulation.
• Opt for a dry disk granulation method and implement remote control with PLC.
• Detailed mechanical structure design: feeding, granulation, spraying, discharging, and recycling mechanisms
• Develop an electrical system to control the granulation process and design a user-friendly interface.
• Theoretical calculations and analysis to determine the maximum load-bearing capacity of the main spindle
• Employ finite element software to verify the reliability and fatigue life of the main spindle.
• Obtain enhanced safety, liberate manpower, and improve granulation yield and efficiency.

Abstract

The fireworks display is one of the traditional ways for the Chinese people to celebrate festivals, playing a significant role in national celebrations and various festive occasions. The production of fireworks is a high-risk industry that faces significant safety concerns, which have become a major obstacle to its development. This paper aims to reduce the safety risks in fireworks production and designs an automatic production line for firework particles, focusing on the granulation process.

This thesis discusses the forming mechanism of powder granulation and analyzes various factors that affect granulation and the interrelationships among these factors. Based on the analysis results and utilizing a systematic design approach, various granulation equipment from domestic and foreign sources are referenced, market demands are considered, and a design proposal for the granulation equipment is put forward, including determining the main technical parameters of the equipment. During the development process, CAD/CAE technology is utilized to create solid models, assembly, motion simulation, and interference checks for the designed equipment components.

In terms of system design, a dry disk granulation method is adopted, and remote control of the granulation system is achieved using a PLC. The mechanical structure design includes a feeding mechanism, granulation mechanism, spraying mechanism, discharging mechanism, and residual material recycling mechanism. The electrical part of the design formulates the granulation process and develops a control flowchart, along with a user-friendly human-machine interface.

Furthermore, this paper conducts theoretical calculations and analysis on the main spindle of the granulation system to determine its maximum load-bearing capacity. Finite element software is employed to analyze and calculate the fatigue life of the main spindle, verifying the system’s reliability. The granulation system designed and studied in this thesis will effectively address the current safety issues in fireworks production, liberating manpower from production processes and improving granulation yield and efficiency.

Keywords: fireworks, granulation, automation, main spindle, finite element.

Chapter 1: Introduction

1.1 Introduction

1.1.1 Background and Significance of the Topic

Fireworks are a traditional Chinese craft company with a history of nearly 1,400 years, playing an extremely important role in national celebrations and folk festivities. With the technological advancement in our country, fireworks have become more useful and visually appealing. More and more people are appreciating fireworks, resulting in a rising demand for them in the market. In some regions of our country, there is a close connection between the pillar industries that vigorously develop the economy to get poverty alleviation and affluence and the fireworks industry. Nowadays, China is the world’s largest production base for fireworks. According to relevant statistics, the fireworks produced in China are exported to nearly 100 countries and regions worldwide, with an annual export volume of about 300,000 tons, accounting for nearly 90% of the world’s total fireworks production and 80% of the world trade volume [1]. According to statistics from relevant departments, more than 700 fireworks production enterprises are scattered in Guangxi, Jiangxi, Hunan, Jiangsu, and other regions of China. Among these provinces, Jiangxi and Hunan have the highest production volume, producing a combined total of about 20 million boxes per year, accounting for over 80% of the total annual fireworks production in China. Guangxi, Hunan, and Guangdong are the main export regions for Chinese fireworks. The main export destinations for Chinese fireworks are the United States, Japan, Canada, Europe, the Middle East, Southeast Asia, and other regions. China holds a large share of the global fireworks trade volume of 1 billion US dollars. With China’s rapid foreign economic trade development, the export of Chinese fireworks is expected to expand further [2,3]. The fireworks industry belongs to labor-intensive industries. In some economically underdeveloped areas of our country, especially in some old revolutionary base areas, the fireworks industry has solved the employment problems of millions of rural populations, ensured their basic livelihood, and has become the main source of economic income for the people in those areas. It has become the economic lifeline and pillar industry of these regions. The rational and effective solution to surplus rural labor has improved and ensured local farmers’ daily lives, promoted the rural economy’s coordinated development, and played a significant role in promoting social stability in our country [4,5].

1.   Traditional Celebration: Fireworks display as a cherished tradition for Chinese festivals.

2.   Prominent Safety Constraints: Safety issues pose challenges to the fireworks production industry.

3.   Automated Production: Introduction of an automatic production line for firework particles.

4.   Granulation Process: Focus on the crucial granulation process and its factors.

5.   Systematic Design Approach: Utilizing analysis and market considerations for equipment design.

6.   CAD/CAE Technology: Employing advanced technology for equipment modeling and simulation.

7.   Dry Disk Granulation: Adoption of a dry disk method for granulation.

8.   Remote Control: Achieving granulation system control using PLC and remote capabilities.

9.   Comprehensive Mechanical Design: Items including feeding, granulation, spraying, discharging, and recycling mechanisms.

10.   Efficient Electrical Design: Formulating granulation process, control flowchart, and user-friendly interface.

11.   Spindle Load-Bearing Capacity: Theoretical calculations and fatigue life analysis for spindle reliability.

12.   Enhanced Safety: Addressing current safety issues, reducing manual labor, and improving yield and efficiency.

1.1.2 The high frequency of accidents and low productivity in traditional fireworks production

Fireworks bring joy to people and also bring income. However, this stunning and magnificent art brings both joy and heart-stopping injuries. In the production, transportation, storage, and use of fireworks, slight negligence can lead to explosions and fires, causing significant losses to people’s lives and property. Especially in the production process, major explosion accidents often occur. The Manual operation has always been the main method of fireworks production in our country, and most fireworks workshops are small-scale productions. Due to the low investment cost, the production equipment is simple, and the technological content is low, resulting in high safety risks. The workers who carry out manual operations generally have low qualifications and education levels, mostly being farmers, with a majority being female workers. Various factors have posed great challenges to safety production. According to statistics, since the 1980s, there have been more than 10,000 explosion accidents in the cumulative fireworks production in our country, with an average of over 400 incidents per year. Although explosion accidents have decreased in recent years, the casualty rate has shown an upward trend. It is urgent to solve the safety production problem.

China’s economy has made earth-shaking progress in all aspects, and the tremendous progress has driven rapid development in various industries, most of which have achieved automated production operations. However, the fireworks industry has not followed the trend of the times and remains stagnant. Most production methods and approaches are still traditional manual workshops involving manual operations and direct contact with explosives. It poses significant safety hazards and results in very low productivity, greatly hindering productivity improvement and development.

Revolutionize Fireworks Production: Safe & Efficient Automated Granulation System. Discover the cutting-edge solution to safety risks in fireworks manufacturing. Our advanced system optimizes granulation with precision and remote control capabilities. Increase yield and efficiency while ensuring worker safety. Explore the future of fireworks production today.

1.2 Fireworks Production Technology: Current Research Status at Home and Abroad

1.2.1 Overview and Trends of Fireworks Production Technology

(1) Development Status and Trends of Domestic Fireworks Production:

1.   Regarding fireworks production methods, the production has undergone several stages: small workshop production → base production, and industrialized production. Currently, most legitimate fireworks manufacturers in China have achieved industrialized production. In general, the development trend of fireworks production in China is towards standardization, mechanization, and industrialization.

2.   Regarding the scale of fireworks production, previous production was done in small workshops with an annual output value generally between one to two million. However, industrialized production today is different, with modern industrial enterprises having an annual output value exceeding five million and even reaching billions. Regarding the overall development trend, the investment and scale of fireworks production are increasing, and the industry is moving towards consolidation and integrated production, sales, and research.

3.   Regarding the geographical distribution of fireworks production companies and workshops, fireworks production is mainly concentrated in provinces such as Guangxi, Jiangxi, Hunan, and Anhui. Within these provinces, the distribution is mainly concentrated in areas such as Liuyang, Pingxiang, and Liling. Regarding the overall development trend, the government supports some major production areas as the leading industries in those regions. In contrast, in non-major production areas, the government generally does not provide support, and some local governments have even proposed the withdrawal of fireworks production from their regions. Therefore, the regional concentration of fireworks production is expected to increase.

4.   In terms of fireworks production formulations, traditional fireworks production mainly relied on simple black powder, resulting in fireworks products with a single ignition effect and less aesthetic appeal comparison to the diverse and colorful effects of modern fireworks. Nowadays, the formulation of fireworks is moving towards multiple formulas and the development of various chemical materials. For example, replacing old products with nitroglycerin, chlorinated paraffin, PVC, A-type CuO, military-grade nitrocellulose, and other materials to produce a new type of smokeless, non-toxic, and environmentally friendly fireworks. In terms of overall development trends, fireworks production in China is moving towards diversification of formulations and diversification of chemical materials. Ultimately, fireworks production in China is moving towards technological consolidation and centralization, and the reform of fireworks production enterprises is being further accelerated.

(2) Current Situation and Trends in the Development of Fireworks Production Overseas:

Fireworks originated in China and have flourished there. The production of fireworks abroad, being derived from China, has also adopted the manufacturing processes from China. It has resulted in foreign fireworks production processes and types of fireworks being largely consistent with those domestically for a long time. It wasn’t until the previous century that significant advancements in science and IT, and in-depth research on chemistry, led to further progress in utilizing propellants and optimizing fireworks loading processes. As a result, the display effects of fireworks produced abroad underwent new changes, particularly in terms of a broader range and more dazzling colors, representing a significant advancement in fireworks production approaches. The improved processes quickly spread through the distribution of scientific popularization books.

Consequently, the production ways of fireworks overseas have continued to progress with the advancement of technology. Adding metals like magnesium and aluminum greatly enhanced the colorfulness of fireworks. The improved fireworks display with more and brighter colors, higher and farther flights, and a greater variety became more prevalent [15,16]. However, with the development of a market economy, competition has become increasingly intense. Like other businesses, the fireworks industry faces serious challenges, such as rising raw material and transportation costs, leading to a continuous increase in production costs.

Consequently, a considerable number of small-scale production facilities have had to close down. Some larger companies realized that cost reduction was necessary for survival, and they formed alliances, acquired and merged with smaller enterprises, expanded their production scale, and introduced mechanization. Through mergers, the variety of variations of small-scale fireworks products in foreign production has decreased, highlighting the clear characteristics of technologization, consolidation, and centralization in the fireworks industry [17,18].

1.2.2 Development Overview of Powder Granulation Technology and Fireworks Granulation

In recent years, environmental protection and increasing production automation, powder granulation technology, as an important branch of powder and granular processing, has become increasingly significant. The deep processing of powder products through granulation holds great importance, mainly manifested in the following aspects: firstly, maximizing the reduction of dust pollution to improve the working environment for workers; secondly, meeting the process requirements of production, such as improving the transfer properties, increasing the porosity, and enhancing the specific surface area; finally, improving the physical properties of the products, such as consistency, flowability, bulk density, and permeability. It is done to prevent negative effects such as bubbles or agglomerations in subsequent production processes or during usage and to lay a foundation for further improvement of production automation and the automation and sealing of the usage process.

Powder granulation technology can be divided into two main categories. The first category is forming processing, which involves processing powdered materials using specific equipment and process methods to produce agglomerated materials that meet the required shapes, densities, compositions, etc. The second category is particle size enlargement, mainly achieved by agglomeration to form larger particles from the powder.

Powder technology and its manufacturing equipment manufacture are specialized disciplines and independent technologies. This discipline first appeared overseas as early as the 1940s, while China began researching powder technology in the 1980s. The Powder Engineering Research Institute of the Chemical Machinery Research Institute under the former Ministry of Chemical Industry led the initial research work. After years of unremitting research efforts, China has now reached a relatively high level in powder granulation technology. There has been significant progress scale and equipment in production. The existing technology can meet the demand for particle granulation.

Powder technology can be divided into four categories based on the principle of small particle aggregation: mixing method, pressure molding method, spray and dispersion atomization method, and thermal melt molding method.

1.   Mixing Method

Granulation by mixing involves adding a certain liquid or binder to the powder and then stirring it appropriately to enable contact between the powder and the liquid. This interaction results in adhesive forces and the formation of agglomerates. The most commonly used method is often achieved using a cylindrical drum or a rotating disc to induce the tumbling and rolling motion of the powder, completing the mixing action. Depending on the granulation method, it can be classified into rolling-type agglomerates, mixed-type agglomerates, and powder-type agglomerates. Equipment used in the mixing method includes granulation drums, rotary drum granulators, disc granulators, inclined disc granulators, cone drum granulators, powder blending machines, drum mixers, kneaders, etc. The advantages of the mixing method for granulation are its simple equipment, low cost, high production capacity, and the resulting particles having strong wetting properties and rapid dissolution. However, the disadvantages are the inadequate uniformity of the produced particles and relatively low strength.

2. Pressure Molding Method

The pressure molding method is similar to stamping in molds, where the powder is placed in a specific mold and compressed to attain compaction. The key to using this method for particle production lies in the effective transmission and utilization of applied force and the relevant physical properties of the materials. As mentioned earlier, the pressure molding method includes mold pressing similar to molds and extrusion methods.

3. Spray and Dispersion Nebulization Method

The spray and dispersion nebulization method directly converts liquid or semi-liquid materials into solid particles. Production requires placing the material in specific equipment and ensuring that the liquid material is highly dispersed. The corresponding equipment includes spray drying towers, fluidized beds, fluidized beds, dryers, and other devices. During spraying, the liquid material is dispersed in the air, forming particles through heat or mass transfer. The particle generation mechanism of this method mainly involves the liquid material forming small liquid droplets, which then solidify into particles. The liquid material is deposited on the surface of already formed particles and forms solid particles. Small particles agglomerate into granules under the action of a binder. There are the following requirements for granulation using this method: first, the material must be in liquid form, dispersible, and transported using a pump; second, the entire granulation process is generally uninterrupted and typically involves automated large-scale production operations; third, recyclability, meaning the remaining material needs to be recycled for saving material and reducing wear and carryover issues in equipment; fourth, the particle size of the product is generally smaller than 5mm. The advantages of this equipment are short granulation cycles, mainly due to simultaneous granulation and drying, formulation of a suitable for granulation in various industries. The benefit is, the product has a small particle size and low strength [21, 22, 23].

4. Thermal Melting Forming Method

The thermal melting forming method [24] utilizes powdered materials’ low melting point physical properties. It employs special condensation methods to get the desired shapes, such as semi-spherical, cylindrical, or sheet-like shapes. The following are several granulation methods and their granulation processes:

1.   Extrusion Spheronization Method

Figure 1.1: Extrusion Spheronization

As shown in Figure 1.1, the extrusion spheronization method consists of three steps: First, the wet agglomerated material is extruded into rod-shaped particles using a sieve plate. Second, the rod-shaped particles are cut into small granules. Third, the small granules are placed in a rotating disc and rolled into spherical granules [24, 25]. This method of granulation is simple and practical, with high productivity. It achieves the required spherical shape and smoothness of the particles, formulation of the preferred method for high-density granulation.

1.   Reciprocating Granulator

Figure 1.2: Reciprocating Granulator

The reciprocating granulator (as shown in Figure 1.2) is mainly composed of five parts: eccentric mechanism, hot melt tank, granulation hole, granulation rod, and cooling steel belt (not shown in the figure). As shown in the figure, the eccentric mechanism drives the movement of the granulation rod. Due to the motion characteristics of the eccentric mechanism, the granulation rod undergoes harmonic reciprocating motion along with the eccentric mechanism. The four positions shown in Figure 1.2 correspond to the positions when the eccentric mechanism is located at points a, b, c, and d, respectively. When the granulation rod is at position a, it moves downward. Under the extrusion of the granulation rod, the hot melt moves along the granulation rod toward the granulation hole. When the granulation rod is at position b, it can no longer move downward. At this point, the granulation rod has tightly combined with the granulation hole and reached the lowest position. The hot melt no longer flows downward. When the granulation rod is at position c, it starts to move upward, and the hot melt droplets separate from the granulation rod and drop onto the cooling steel belt for cooling and shaping. When the granulation rod is at position d, it comes to its original position, and the hot melt continues to move downward along the granulation rod [26,27].

3. Rotary Granulator

Figure 1.3: Rotary Granulation

Rotary granulator: As shown in Figure 1.3, the hot melt is pumped into the feed hole 8 through a metering pump and then enters the hopper 3 through 8 and 9, respectively. The hot melt flows to the hopper 3. When hole 6 on the granulation drum 1 is connected to hole 10 on hopper 3, the hot melt enters hole 6 and falls onto the cooling steel belt to cool and form granules. The advantage of this granulation method is that it produces uniform and regular granules [28].

1.   Cone-type gear meshing granulator

Figure 1.4: Conical Gear Granulation

Conical gear granulator: As shown in Figure 1.4, a metering pump is used to pump the molten material into the material pool (located on one side of gear 2). With the rotation of the gears, the molten material is extruded into the meshing area between the two gears. As gear 2 continues to rotate, the molten material is squeezed along the teeth and drops onto the cooling plate, where it cools down and forms granules [29].

5. Boiling granulation method

Figure 1.5: Boiling Granulation Method

Figure 1.6: Fluidized Bed Granulation Method

The working is to use airflow to lift the powder particles and make them come into contact and collide with the sprayed slurry from top to bottom, resulting in the agglomeration and the formation of granules, as shown in Figure 1.5. This method has the highest production efficiency among several methods, but the produced granules have relatively low hardness, loose structure, and unsatisfactory surface smoothness and sphericity. This method is more suitable for producing particles with low production requirements or as pre-processing particles [30].

6. Directed Jetting Granulation Method

Directed Jetting Granulation Method: Figure 1.6 shows this granulation method is similar to the fluidized bed granulation method and is derived from it. A core cylinder is arranged directly below the granulation cylinder. To get a state where the hot air is large in the middle and small around it, the equipment sets up a ventilation plate with a center area larger than the surrounding areas at the bottom. The particles float upward along the core cylinder under different airflow forces and come into contact with the binder (which is sprayed out by a spray gun placed at the central bottom), agglomerating with the powder falling from above. Finally, they descend from the outside of the core cylinder, thus achieving the up-and-down circulation of particles and ensuring uniform growth. The advantage of this granulation method is that it provides a good coating effect on the surface of the granules and uniform particle size. However, the disadvantage is that the granules produced by this method have poor hardness.

7. Spray Drying Method

Figure 1.7: Spray Drying Granulation Method

Spray drying method: as shown in Figure 1.7. This method uses a nozzle or a rotary disc to spray highly concentrated slurry, forming smaller diameter microdroplets. The droplets are rapidly dried into granules under the blowing of high-temperature hot air. Due to the quick evaporation of water, the resulting granules have gaps and low hardness. This method has lower productivity in granule production and requires large equipment with a complex overall production process. It is generally used to produce traditional Chinese medicine preparations and instant foods.

1.   Centrifugal Granulation Method

Figure 1.8: Centrifugal Granulation

Centrifugal Granulation: Figure 1.8 shows this method requires the production of master particles in the initial stage. The master particles are then fed onto a centrifugal disc. Through friction, centrifugal force, and a scraping blade, the master particles form a vortex-like particle flow on the disc. At the same time, the atomized binder is continuously sprayed into the particle flow from a nozzle, causing the master particles to adhere to the powder. Additionally, powdered materials are regularly supplied onto the disc. Hot air is continuously blown into the annular gap of the disc, allowing the master particles to grow until they reach the desired particle size. The advantages of centrifugal granulation are uniform particle size, high hardness, and desirable sphericity and surface smoothness.

1.   Rotary Drum Granulator

Figure 1.9: Rotary Drum Granulator

Rotary Drum Granulator: As shown in Figure 1.9, this equipment mainly comprises a rotary drum, motor, gearbox, large gear, front large support wheel, rear large support wheel, and so on. During the granulation process, powdered materials are fed into the inlet 1. The materials, under friction, rotate along with the rotating drum. When the powder reaches a certain height, it slides down along the inner surface of the drum due to the combined effects of gravity and inertia. Within the drum, binding agents are continuously sprayed onto the materials. As the materials roll, they are influenced by the binding agents and agglomerate into particles, continuously growing.

1.   Disc Granulator

Figure 1.10: Disk Granulator

The granulation principle involves adding powder materials into a rotating inclined disk. Due to the effect of friction, the disk rotates and moves the powder materials. When reaching a certain height, the powder materials slide downwards. The adhesive is continuously added during this process, causing the powder materials to adhere and roll together, forming larger particles, as shown in detail in Figure 1.10.

1.2.3 Firework Granulation Technology

Traditional firework production consists of the following steps:

1.   Weighing and Mixing – Specific proportions of various substances are weighed and then mixed evenly.

2.   Granulation – The evenly mixed substances are formed into spherical particles of specific diameters, known as “bright pearls.”

3.   Tray Loading and Transport – The prepared bright pearls are quantitatively loaded onto trays for easy processing in the next step. They are then transported to the next workstation via a conveyor.

4.   Drying and Unloading – The bright pearls are dried in a specially designed drying machine. After drying, they are placed in containers and await further processing.

The granulation process refers to producing bright pearls among the four steps mentioned above. Bright pearls are formed by uniformly mixing different sections of substances according to specific proportions. As most of the substances used in firework granulation are in powder form, it falls under the category of powder granulation. Since the powders used in firework granulation are explosives, which are highly flammable and sensitive to chemical reactions, explosions can be triggered by sparks, pressure, or even friction. To avoid potential accidents caused by collision, pressure, friction, high temperature, and other factors during the granulation process, traditional firework production techniques commonly employ the mixing method, with the inclined disk granulator being a typical equipment choice.

1.3 Problem Statement

Fireworks production belongs to a special industry with high risks due to its highly flammable and explosive chemical properties and the harsh production environment. China is a major producer of fireworks, with tens of thousands of fireworks production companies of all sizes nationwide. According to relevant departments’ statistics, there is an average of more than one safety accident occurring daily, and the alarming number of casualties is heartbreaking and deeply motivating for people to address the hidden safety risks in fireworks production. Moreover, the current mainstream trends in society are urbanization, health, and environmental protection. Therefore, reducing the risk of production accidents and improving the safety level of fireworks production is of utmost importance. Freeing manpower from production is undoubtedly the best solution, formulation of a mechanization and automation [33] the preferred approach to solving the problem.

1.4 Main Content of this Thesis

China is a major producer of fireworks, and traditional fireworks have undergone continuous improvement, resulting in a wide variety of types. Due to the variability in techniques, formulations, and specifications, even for the same type of fireworks product, there are significant differences in production processes. Most production enterprises are small workshops, with no information communication between the industry, and each company produces according to its own standards. It leads to differences in the formulation of chemicals and mechanical equipment used when producing the same product in different companies. It poses challenges to the implementation of automation in fireworks production. This thesis aims to design a fully automatic fireworks production line by studying the application of existing fireworks production equipment. The goal is to get parameterized production, unmanned production, and high-efficiency production. This thesis is mainly responsible for the design of the granulation system of the production line, which is based on the theoretical research of powder granulation principles. The system is divided into mechanical mechanisms and electrical control parts. The mechanical part focuses on the design of the main mechanical structure of the system, including simulation and optimization design based on the analysis of simulation results. The electrical part mainly focuses on the control system’s design and the monitoring interface’s research. The aim is to improve the automation control level of the system, design a user-friendly human-machine interface, and get intelligent, efficient, simple, and convenient application characteristics of the system. Finally, finite element fatigue life analysis is conducted on the main shaft.

Many granulation methods are currently available, such as disc granulation, fluidized bed granulation, centrifugal granulation, etc. These methods can be generally categorized as dry or wet granulation. This paper only uses the dry granulation method, which applies to powder granulation, specifically in fireworks production. Therefore, only the first three granulation methods mentioned are considered. After a comprehensive analysis of these three methods, it is found that centrifugal granulation is similar to disc granulation, but it requires the addition of seed particles before granulation. Fluidized bed granulation has high production efficiency, but the resulting particles are loose and do not meet the requirements for producing bright beads.

On the other hand, disc granulation is not only suitable for fireworks granulation. It has mature technology but also has a relatively simple granulation equipment structure and produces compact particles, which meet the basic production requirements for bright fireworks beads. Therefore, this research project adopts the disc granulation method to design and study the granulator machine.

Chapter 2: Overall Design of Fireworks Automatic Production Line and Research on Granulation Part

2.1 Overall Structure Design and Theory of Fireworks Production Line

2.1.1 Design of Weighing and Mixing System

The weighing process is the first station of the entire fireworks automatic production line. Its function is to weigh various ingredients according to the specified proportion, with weighing accuracy within the specified requirements. In the weighing process, the design should also follow the design principles mentioned earlier, including explosion-proof, anti-static, and spark-proof measures, to manufacture for safe production of flames. Figure 2.1 below illustrates the weighing and mixing process.

Figure 2.1: Schematic Diagram of Weighing and Mixing

Process flow of weighing and mixing:

1.   After adding the powder material to the hopper, start the system.

2.   The system automatically detects any faults. The stepper motor starts rotating, conveys the powder material from the hopper to the feeder through the screw rod, and then delivers it to the tray.

3.   When the weight of the powder material reaches the set value, the stepper motor stops working.

4.   After the stepper motor stops, send a signal to the electronic scale cylinder. The electronic scale cylinder starts working, extends, and lifts the tray. When the angle between the tray and the horizontal plane exceeds the angle of repose of the powder, the cylinder stops moving, and all the weighed powder slides from the tray into the guide pipe and finally enters the mixer. The tray cylinder retracts and resets, entering the mixing stage.

5.   After the cylinder retracts and resets, send a signal to the mixer. The mixer starts running. After a while, T (T is the required time for uniform mixing of various powders), the discharge valve opens, and the uniformly mixed powder enters the conveyor through the discharge outlet, awaiting the next signal to be transported to the next stage, the granulation stage.

Working principle of the weighing and mixing process:

1.   Conveyance of ingredients: Various ingredients are transported using a worm gear drive.

2.   Weighing of ingredients: Electronic scales are used as weighing sensors, working in conjunction with stepper motors and worm feeders to get high-precision automatic weighing.

3.   Mechanical agitation mixer: In automated production lines, excessive external degrees of freedom are not conducive to production. Mechanical agitation mixers only have internal motion, providing a prerequisite for automation. It is worth noting that during the mixing process, as various powder components gradually mix uniformly according to the given proportion, they become gunpowder. As mixing aims to prepare gunpowder, measures to prevent explosions must be considered, and strict adherence to safety design principles is necessary to avoid major accidents. Regarding the safety issues of gunpowder, the following measures have been taken in the design: 1. Use engineering plastics for all parts in contact with gunpowder as much as possible. 2. When it is unavoidable to use electrical products, explosion-proof types should be selected. 3. If it is unavoidable to use non-explosion-proof electrical products, they should be wrapped in insulating materials.

2.1.2 Granulation system design

The granulation process is the second stage of the production line, and its specific working process is as follows: After the powder is weighed and mixed according to the given ratio, it is conveyed to the feeding port through feeders, electronic scales, pallets, and conveyors. The powder enters the granulation disc through the feeding device. The motor is started upon receiving a signal and operates at the preset speed. At the same time, the slurry system starts and sprays the granulation, and the disc granulator enters the granulation process. The specific conditions of the granulation are monitored remotely through a camera. After the granulation is completed, the discharging and lifting platform cylinders work together to pour the finished pellets into the residual material recovery device. The pellets that meet the required particle size and those that do not, with remaining powder, are separated by the residual material recovery device. The residual material and the pellets that do not meet the requirements slide into the recovery bin, while the pellets that meet the requirements roll into the pallet through a chute and proceed to the stacking process. Figure 2.2 shows a schematic diagram of the granulation process.

Figure 2.2: Granulation Diagram

Mechanism of Powder Granulation:

1.   Formation of Nuclei: The powder rotates in the inclined disc granulator, and when the spray gun sprays the atomized slurry, the material is wetted. Initially, the slurry injection is limited, and the powder material gaps are not thoroughly filled. Air acts as the continuous phase, and the powder particles are interconnected through the slurry’s surface tension, forming small particles. With the increased slurry injection, the gaps between the particles are completely filled. Due to the capillary effect and liquid bridging, the small particles bonded, forming granules.

2.   Increase in Particle Size: After the formation of nuclei, the atomized slurry is continuously sprayed, and the powder adheres to the nuclei without an increase in particle diameter. At the same time, due to the frictional force, the particles rotate along with the disc’s motion. During this movement, the particles rub against each other, and the previously irregular edges and corners of the particles gradually wear off under frictional force, gradually forming spherical particles. It is the main process of pearl growth and the most critical step in granulation.

3.   Polishing and Drying: After the powder supply and liquid spraying are completed, the disc continues to rotate. Under the action of centrifugal and frictional forces, the particle surfaces are further polished and dried, resulting in glossy, high sphericity, and mechanically strong pearls.

Working Principle of Discharging: When granulation is completed, the time relay sends a signal to the motor, discharge cylinder, and support cylinder. The main machine stops, and the discharge cylinder and support cylinder start operating at the set speed. They work together to pour the pearls into the recovery device. When they reach the specified position, a sensor triggers and sends a stop command, halting the discharge and entering the next cycle.

2.1.3 Stacking Systems Design

Stacking is placing items together and using integrated unitization to stack materials in a certain way. It facilitates various logistics operations for the overall material. Stacking is a technology in the field of logistics automation that has seen rapid development in recent years (decades). Firstly, with the increase in enterprise production scale and capacity, stacking efficiency is continuously demanded to improve, leading to the development of high-speed online stacking. Secondly, as enterprises move from the seller’s market to the buyer’s market, production shifts towards multiple varieties and small batches. Enterprises adopt flexible production to get the production of multiple products on the same line. It also requires stacking to have the potential to handle multiple products.

Additionally, with the emergence of large-scale wholesale distribution centers, there is a need for individualized delivery to different customers, which requires stacking machines to have a wide stacking range and strong mixed stacking capabilities. In such environments, stacking robots have received great development opportunities. Nowadays, various types of stacking machines are available on the market, offering a high degree of automation and flexibility. Automatic stacking machines can be classified as stackers, stackers, automatic stackers, automatic stacking machines, stacking robots, and robots, among others.

In this production line, the stacking machine mainly completes the following processes: transporting tray groups, supplying trays, loading materials, transporting racks, and stacking. The amount of gunpowder produced at a time is 5 kilograms. According to the design requirements of the drying equipment, after the 5 kilograms of gunpowder is granulated, it is placed in 4 trays. Therefore, a tray group consists of 4 trays and a rack holds 4 trays. The rack enters the drying box for drying, completing the entire making process.

The working principle design of the stacking component: The entire stacking component consists of 6 parts: conveyor 1, feeder, conveyor 2, stacking machine, conveyor 3, and conveyor 4. The tasks performed by each part are as follows: conveyor 1 places the tray group to supply it to the feeder; the feeder accepts the trays conveyed by conveyor 1 and then supplies the trays one by one to conveyor 2; conveyor 2 transports the trays supplied by the feeder, and at the same time, the granules are loaded onto the conveyor; conveyor 3 transports the racks to the stacking machine; the stacking machine receives the racks and stacks the trays supplied by conveyor 2 layer by layer; conveyor 4 transports the stacked racks to the drying box for drying. The design of the conveyors can be based on the requirements in the design manual. Therefore, the main focus of the principle design is on the feeder and the stacking machine. Figure 2.3 shows a schematic diagram of the stacking process.

Figure 2.3: Stacking Diagram

2.1.4 Design of Drying and Unloading Systems

The drying and unloading systems consists of two parts: the drying and unloading sections. The drying section is responsible for conveying the racks and drying the materials in the trays placed on the racks. The unloading section can also transport the racks, and the unloading device tilts the materials on top of the rack and empties them into a collection box, completing the unloading process. The systems structure is shown in the diagram. The specific working process is as follows: after the granules are placed in the tray, they are stacked in the stacking section and placed on the rack. Then, the rack is transported to the drying section. The control system controls the motor to drive the conveyor belt, which moves the rack. The drying machine system consists of three drying chambers. The temperature of the first chamber is set to 45 degrees, the second chamber is set to 60 degrees, and the third chamber is set to 45 degrees. The rack is sequentially dried in the three drying chambers for 10 minutes each, completing the drying of the granules. Then, the rack enters the unloading stage, and the cylinder in the unloading section tilts the rack to complete the unloading process. After unloading, the rack is transported back to the stacking section for reloading. Figure 2.4 shows a schematic diagram of the drying and unloading process.

Figure 2.4: Drying Diagram

1.   Working principle of the drying system: The drying process combines to make a mixture far-infrared radiation and hot air to dry the fireworks particles. Far-infrared drying is the main method, supplemented by hot air drying. When the far-infrared electric heating plate in the drying chamber is powered on, it starts to heat up. The surface temperature of the far-infrared electric heating film increases, and when it reaches a certain temperature, it emits far-infrared rays. The far-infrared rays are absorbed by the particles in the tray, causing increased molecular motion inside the particles. The temperature of the particles, both internally and externally, begins to rise uniformly, initiating the drying process. At the same time, the axial flow fan supplies air to the drying chamber, generating hot air to dry the particles. The inlet and outlet ducts form a circulating ventilation system through the action of the axial flow fan, ensuring more uniform heating of the particles. This system also effectively collects dust inside the drying chamber, preventing safety accidents and achieving recycling and reuse effects.

The drying process adopts a PID temperature control system, which allows for setting the temperature freely and automatic adjustment. By adjusting the power of the far-infrared electric heating plate, temperature requirements ranging from room temperature to 150 degrees Celsius can be met. An emergency stop switch is installed on the drying chamber to ensure safety during operation.

1.   Working principle of the unloading system: When the conveyor transports the rack to the unloading system, the front, and rear cylinder systems push the unloading rack to the position where it clamps the rack, preventing it from flipping. Then, the up-and-down cylinder systems lift the unloading conveyor and the rack on top of it. The edges of the tray have an inclined angle, which meets the unloading requirements of the material at a certain inclination angle. Once it is detected that the material has been unloaded, the up and down, as well as the front and rear cylinder systems, gradually return to their original positions. Then the conveyor transports the rack to the next stage.

2.   Issues to be considered in the design: (1) The first thing to consider during the drying process is safety. Safety is the primary concern in the design of the entire fireworks production line. Therefore, explosion-proof motors should be selected for the design, and all wires should not be exposed but sealed to prevent contact with powder and fine particles. In addition, the external surface temperature of all parts in the system should not exceed 80°C. Finally, the system should be equipped with an alarm device. (2) The second issue is to ensure sealing. In the drying box, when drying the powder particles, it is necessary to reduce heat loss. In addition to using insulation materials, attention should be paid to sealing the front and rear “doors” after the shelves enter the drying box. (3) Ensure that all parts are in place. Each part should reach the designated position by detecting with sensors and controlling with the control system. (4) For the unloading part, complete unloading should be ensured. It can be achieved in two ways: firstly, by conducting experiments to determine the maximum unloading time and setting it in the control system; secondly, by capturing images of the pallet using a camera and comparing it with the image of the empty pallet to ensure complete unloading. Based on the above four sections, the overall production line is virtually assembled, and the assembly diagram obtained is shown in Figure 2.5.

Figure 2.5: Assembly Diagram

2.2 Study on the Influence and Interconnection of Various Factors on the Granulation Process in Fireworks Production

2.2.1 Working Principle of Disc Granulator

The working principle of the disc granulator is to add the powder material into a rotating inclined disc. Under the action of frictional force, the disc rotates and drives the powder material to move upward. The powder material slides down along the disc surface when reaching a certain height. A continuous binder injection is sprayed onto the powder material during this process. With the action of the binder, the powder material adheres to each other, and then, with rolling, the particles continue to grow. After reaching the target particle size, the powder material and binder supply are stopped. However, the disc still needs to continue rotating to polish the formed particles to improve their surface smoothness, sphericity, and hardness.

2.2.2 Main Factors Affecting Powder Granulation

1.   Binder

The binder is used to enhance the adhesion between powder particles. The binder itself does not have adhesive properties. Its task is to dissolve the adhesive components in the material to achieve the purpose of bonding the powder particles together. Water, ethanol, and their mixtures are the most common binders in the industry. For binders, the more binder used for a given powder material, the greater the viscosity of the material. However, if the binder contains ethanol, the larger the proportion of ethanol in the binder, the weaker its ability to dissolve the adhesive substances in the material. It leads to an increased dosage of the binder. Therefore, binders with different volume fractions of ethanol need to be used for different materials with different viscosities. If the material has a high viscosity, a binder with a higher ethanol content is usually used to facilitate better control of the exhibited viscosity. However, if the material has low viscosity, a binder with a lower ethanol content should be used to prevent the volatilization of ethanol, which would cause the material to become loose and difficult to form particles. Experimental data show a close relationship between the brittleness of bright beads and the ratio of binders used in the production process [34, 35].

The adhesive also influences the product’s particle size, and the influencing factor is the mass fraction of the adhesive. If the mass fraction of the adhesive is small, the stacking speed during the bright bead formation process will become slow, and even the already stacked parts may detach. This results in a lower content of larger-sized bright beads in the production. On the other hand, when the mass fraction of the adhesive is large, the viscosity of the material increases, causing the particles to bond together and form larger particles. It leads to a higher proportion of larger-sized bright beads in the production.

2.   Main machine speed (disc speed)

Under the centrifugal force generated by the rotation of the main machine, the powder materials collide with each other and agglomerate into granules under the action of the adhesive. The magnitude of the centrifugal force depends on the speed of the main machine, so the main machine’s speed also affects particle production. When the main machine speed is low, the centrifugal force generated by the rotation of the disc decreases, and the powder materials rotate with the disc without relative motion. There is no rolling phenomenon of the materials in the disc. The materials remain stationary, reducing the wetting surface and uneven wetting. Due to the low main machine speed, the rotational speed of the materials is also low, resulting in small kinetic energy (kinetics) and impact force when the materials collide with the scraper plate. It makes it difficult to crush large agglomerates. When the main machine speed increases, the centrifugal force and the impact force between the materials and the scraper plate also increase. As a result, large agglomerates are broken due to impact, and the materials roll inside the disc, resulting in uniform mixing of the adhesive and uniform particle size distribution in the production of bright beads. However, when the main machine speed increases to a certain value, the adhesive mixing becomes less uniform due to excessive speed, the material viscosity becomes insufficient, and some parts of the stacked bright beads may detach. It leads to an increase in the amount of granulated fine powder and a decrease in overall yield [36, 37].

3.   Slurry pump speed

The slurry pump speed [38] affects the spray effect and indirectly affects the balance between the drying and wetting speeds of the materials. Therefore, the slurry pump speed has a crucial influence on particle formation and particle size. When the speed decreases, it causes the adhesive to fail to wet the material effectively. The reason is that the amount of adhesive sprayed is small, and the adhesive has already dried before wetting the material. This results in the production of particles with smaller sizes than the target size and a large amount of fine powder. As the slurry pump speed increases, when it reaches an appropriate speed, the sprayed adhesive has enough time to dissolve the viscous substances in the powder, and the powder has time to bond together into granules. It produces particles with uniform sizes that meet the requirements. However, when the slurry pump speed exceeds a certain value, an excessive amount of adhesive is sprayed quickly, causing the particles to stick together, resulting in a significant increase in the number of larger-sized particles and poor surface smoothness of the produced particles.

The research team conducted experiments using water as a binder and prepared MCC blank pellet cores using the disc pelletization method. They observed particle size distribution when the slurry pump rotational speed was set at 20, 25, and 30 r·min^-1. The experimental results showed that when the speed was set at 25 r·min^-1, the particle size distribution was uniform, and overall, the yield was considered ideal. Additionally, the research team observed two important equilibrium processes during particle production using the disc pelletization method.

The first equilibrium process involved the distribution of surface and internal moisture in the powder material. This phenomenon was closely related to the physical properties of the material itself, primarily influenced by the powder material’s ability to absorb moisture. If there were less moisture on the surface of the powder, the formed particles would be small and difficult to agglomerate. On the other hand, excessive moisture would result in larger particle sizes.

The second equilibrium process was balancing drying and wetting the powder material. This equilibrium was influenced by two factors: the rotational speed of the main machine and the slurry pump. When the rotational speed of the main machine was low, or the slurry pump speed was too fast, the wetting rate of the material exceeded its drying rate. It led to excessive moisture on the surface of the powder material, increased viscosity, and easy agglomeration between powder particles, resulting in larger particles. Conversely, if the moisture content on the powder surface was insufficient, the powder would lack viscosity, formulation of a difficult for the particles to form.

4.   Atomization conditions of the spray gun

The spray gun has two main atomization conditions: the air flow rate and the air pressure. They directly affect the atomization effect of the slurry and indirectly influence the uniform wetting of the powder material, thereby affecting the formation of pellets and the distribution of particle sizes. When the air flow rate is too low, the atomization effect is poor, and the binder wets the material unevenly, forming large particles. If the airflow rate is too high, it may cause dust to fly, leading to material loss and even safety hazards. Increasing the air pressure enlarges the atomization area, resulting in more uniform material wetting. However, excessively high air pressure can cause a large amount of powder material to fly, leading to loss. Therefore, minimizing the air flow rate is necessary while effectively controlling the atomization effect of the binder.

5.   Powder feeding rate

The powder feeding rate also significantly affects the particle size distribution of the pellets. In the pelletization process using the disc pelletization method, it was found that when the powder feeding rate was slow, there was more moisture on the surface of the pellets, making them prone to aggregation and forming larger particles. The growth rate of the pellets was slow, leading to a longer processing time. On the other hand, when the powder feeding rate was too fast, excessive fine powder accumulated in the disc, and when the binder was sprayed onto the disc, the fine powder agglomerated under the action of the binder, often resulting in false nuclei and uneven particle size distribution. It also caused dust to fly, resulting in the waste of raw materials. When the powder feeding rate was appropriate, the pellet size grew uniformly, and the final particle size concentrated within the desired range. Therefore, to ensure the yield and quality of the produced particles, it is necessary to set the slurry and powder feeding rates appropriately, allowing them to complement each other and jointly affect the pelletization process to achieve optimal production results.

6.   Polishing Time

When the particle size of the bright beads reaches the required level, the powder supply and slurry spraying are stopped. However, the bright beads still need to continue rolling inside the disc granulator for a certain time for polishing to improve the mechanical strength and enhance the sphericity of their appearance. Vertommen et al. [39] (Int J Pharm, 1998) confirmed that the bright beads have a porous sponge-like structure based on the determination of pore volume, specific surface area, true density, and scanning electron microscopy observations. It has been shown that appropriately extending the polishing time can reduce the pores’ volume and improve the bright beads’ surface smoothness. Li Xiaoming et al. [40] observed and analyzed the particle size, brittleness, and yield of metformin hydrochloride microspheres prepared using the disc granulation method under different polishing times. The experimental results showed that when the polishing times were 10, 6, and 4 minutes, the brittleness of the microspheres was 0.74%, 0.87%, and 0.96%, respectively, and the yields were 54%, 89%, and 60% respectively. It was found that with longer polishing time, the particle size distribution range of the prepared microspheres became wider, and there was a trend towards smaller particle sizes, indicating an increase in the number of microspheres colliding and breaking each other. Finally, considering all factors, a polishing time of 6 minutes was chosen. Cui et al. [41] used MCC blank microcrystalline cellulose beads with a particle size of 0.3-0.45 mm as the core material to prepare ofloxacin microspheres. Considering the yield and mechanical strength of the microspheres, a polishing time of 4 minutes was selected.

7.   Disc Tilt Angle

During the granulation process using the disc granulation method, as the particles continue to grow, a phenomenon of particle size grading occurs. The faster the disc’s rotation speed, the larger the centrifugal force becomes, which may cause the particles to collide with the disc’s outer wall and fracture. Therefore, the tilt angle of the disc needs to be increased accordingly [42]. To understand the above phenomenon and the impact of the tilt angle on granulation, the following analysis of the force and motion of the particles in the disc was conducted in this study. Please refer to Figure 2.6 for the force analysis.

Figure 2.6: Diagram of Particle Forces in a Disk

m represents the mass of the particle, measured in kg; FL represents the centrifugal force acting on the particle, measured in N; G represents the force of gravity on the particle, measured in N; F represents the force exerted by the edge of the disk on the particle, measured in N; G1 and G2 represent the components of gravity, measured in N; G21 and G22 represent the components of G2, measured in N; Fm1 and Fm2 represent the frictional forces, measured in N; α represents the inclination angle of the disk; β represents the angle at which the particle detaches; n represents the rotational speed of the disk, measured in r/min; R represents the radius of the disk. A particle with mass m is located on the edge of the disk and is subject to external forces, including the centrifugal force FL, the frictional force Fm, the force F exerted by the edge of the disk, and the force of gravity G. For analysis purposes; we assume that the frictional force Fm can be decomposed into two components, Fm1 and Fm2. Fm2 hinders the particle’s downward movement along the disk’s plane under the influence of the component G2 of gravity. At the same time, Fm1 prevents the particle from moving downward along the edge of the disk in the direction of the component G22 of gravity. The particle can be lifted to a certain height as the disk rotates. If the particle rises to point A and remains stationary, the external forces are in equilibrium with each other. That is:

G22 = Fm1

F + G21 = FL + Fm2 cos β — (2.1)

At the moment when the particle detaches from the edge of the disk and starts rolling down along the disk surface, the force exerted by the edge of the disk on the particle, F, becomes 0. Therefore, equation (2.1) can be simplified as follows:

G21 = FL + Fm 2 cos β — (2.2)

In the equation: G21 = mg sinα cosβ; FL = 2mv/R, v = PRn/30 (m/s), where n is the rotational speed of the disk in r/min; Fm2 = mgf cosα, f is the coefficient of friction between the material and the chassis (f = tanW, W is the angle of friction between the material and the chassis). Substituting G21, FL, and Fm2 into equation (2.2) and simplifying, we have:

R n^2 / 900 ≈ (sinα – f cosα) cosβ — (2.3)

cosβ ≈ R n^2 / 900 (sinα – f cosα) — (2.4)

Analysis of equation (2.4) reveals that when the rotational speed and inclination angle of the granulation disk remains constant, the detachment angle β of particles in granulation is only influenced by the friction coefficient f with the material at the bottom of the disk. The friction coefficient varies with changes in the material’s morphology. As a result, particles of different sizes have different friction coefficients and detachment angles β. The detachment angle increases with an increase in particle size, which is manifested in the disk as larger particles having a smaller height of ascent during motion. Therefore, during the process of powder material rolling and granulating in the disk, particles are graded according to their size, as shown in Figure 2.7.

Figure 2.7: Diagram of Particle Segregation

2.2.3 Relationship between Speed and Inclination Angle of Disc Granulator

Particles roll on the disc surface as the disc rotates, and during this rolling process, the particles gradually grow. The particle growth rate is proportional to the number of rolling cycles per unit of time, which means that production efficiency increases with the increase in speed. However, when the speed reaches a certain value, the particles adhere tightly to the disc’s outer wall due to the increased centrifugal force, and they do not roll down. It leads to the formation of funnel-shaped vortices in the granulation disc, which affects the utilization of the disc surface and the granulation efficiency. Therefore, at higher speeds, it is necessary to increase the inclination angle of the granulation disc accordingly. However, the inclination angle of the disc is also related to the final velocity of the particle rolling inside the disc. When the inclination angle is too large, the final velocity is higher, resulting in greater impact forces between particles and the disc edge or other particles. It can cause particle breakage due to collisions. Therefore, the inclination angle of the disc needs to be controlled within a certain limit.

The disc granulator’s optimal inclination angle depends on the disc’s diameter. The inclination angle is limited by the final velocity of the particles, which is directly proportional to the diameter of the disc. Thus, the inclination angle of the disc is inversely proportional to the disc diameter. To determine the relationship between the inclination angle (α) and the diameter (D) of the disc, the following analysis was conducted in this study:

Under the action of the gravitational force component (G2), particles roll along the disc surface. When they overcome the frictional force and reach a displacement of L, the net force applied to the particles performs work denoted as A.

A = mg(sinα – fcosα)L — (2.5)

Because the work done by the resultant force of external forces on the particle will be completely converted into an increase in the particle’s kinetic energy, that is,

A = m(v^2 – v0^2)/2 (where v0 and v are the initial and final velocities of the rolling particle), substituting A into equation (2.5),

and assuming v0 = 0, then equation (2.5) can be simplified to equation (2.6).

mv/2 = -mg (sinα – fcosα)L/2 — (2.6)

When the particle rolls from the highest point on the disk to the endpoint, its velocity reaches its maximum value. At this point, L = D, and equation (2.6) can be simplified to equation (2.7).

v = 2gD (sinα – fcosα) — (2.7)

For the particles to experience the same dynamic compaction stress in different diameters of granulation disks, the particle’s final velocity should be equal. Therefore, we have the equation:

(sinα1 – f) / (sinα2 – f) = D1 / D2 — (2.8)

By analyzing equation (2.8), we can see that if we can find a set of data Di and αi, we can use formula (2.8) to determine the optimal inclination angle for disks of any diameter.

If the starting position for the material to roll down without forming fines is at the top of the vertical diameter of the disk, then in this case, the granulation on the disk surface can be maximized, and the motion characteristics are also ideal. We can assume that the particle detachment angle β = 0. Additionally, in the case of a certain powder, the internal friction angle is a fixed value and can be determined through experimental measurements. Using equation (2.3), the relationship between the inclination angle of the disk and the rotational speed can be calculated. Figure 2.8 illustrates the relationship between the disk inclination angle and the rotational speed for granulation machines with different diameters. 

Figure 2.8: Relationship between Speed and Inclination Angle

It is worth mentioning that there are many factors that affect the preparation of bright beads using the disc pelletization method. However, these factors do not act in isolation but interact synergistically to produce an impact. Therefore, statistical methods can be used to conduct cross-experiments on the various influencing factors and then create an analysis of the variance table. The optimal combination of various factors for pelletization can be determined by analyzing the experimental results using mathematical methods. Yu Shuxiang et al. [43] used a 4-factor 3-level L9(34) orthogonal experimental design, with the main machine speed (A), slurry spraying speed (B), powder supply speed (C), and polishing time (D) as the factors under investigation. The sphericity of the microspheres (represented by the critical angle Φ) and the yield of microspheres with a particle size of 0.6-0.8 mm (weighted comprehensive score Y-2Φ) were taken as the evaluation indicators for process optimization. The results of the variance analysis showed that the above four factors all impacted the quality of the microspheres, with the order of influence being slurry spraying speed, powder supply speed, main machine speed, and polishing time. The optimal combination of process parameters was determined: slurry spraying speed of 3.0 ml/min, disc speed of 300 r·min-1, polishing time of 7 min, and powder supply speed of 1.0 g/min.

2.3 Summary of this Chapter

Based on the fireworks production process and powder technology, this chapter divides the fireworks automated production line into four stages and elaborates on each stage’s design schemes and principles. The text focuses on the granulation process, and the impact of adhesive, slurry pump speed, spindle speed, atomization conditions of the spray gun, powder supply rate, polishing time, and disc tilt angle on granulation is analyzed sequentially.

Chapter 3: Research on the Structural Design of the Fireworks Automated Production Line Granulation System

3.1 Composition of the Mechanical Structures and Granulation Process of the System

The fireworks automated production line granulation system consists of mechanical and electrical parts. Due to the sensitive chemical properties of the powder used for granulation and the requirement for dry granulation, the disc granulation method was selected after in-depth research and comparison of various granulation methods and processes. The disc granulation method has a high granulation rate, uniform particle size distribution, simple and durable granulation equipment, and stable operation. The design of the mechanical part is mainly based on the principles and processes of disc granulation. The mechanical structure mainly includes granulation, slurry spraying, scraping, feeding, discharge, and real-time monitoring mechanisms, among others.

3.2 Design of Granulation Mechanism

The role of the granulation mechanism is to transform the prepared gunpowder powder into bright beads. The specific process involves adding the materials to the granulation disc from the top of the equipment. The disc rotates, and under frictional force, the powder is driven to rotate along with the disc. When it reaches a certain height, the powder rolls downward under the influence of gravity. During this process, the intermittent atomized adhesive is sprayed into the granulation disc, and the powder adheres to each other and gradually forms particles due to the effect of the adhesive.

3.2.1 Granulation Disc

Considering the various factors that affect granulation during the disc granulation process, such as disc tilt angle, rotation speed, diameter, etc., the determination of disc parameters needs to consider the actual situation. This design aims to process five kilograms of powder in one cycle. The density of gunpowder is approximately 1 kg/L, so the volume of five kilograms of gunpowder powder is approximately 5L. According to relevant literature, the ratio of the volume of the inclined disc granulation disc to the volume of the granulated powder should be greater than 7/1. Therefore, the disc volume should be larger than 35L. Gunpowder is flammable (flame) and explosive, so to eliminate the generation of sparks and static electricity, the disc’s surface is treated with copper plating. While ensuring the strength of the disc, its mass is minimized. The designed bottom diameter of the disc is 760mm, the mouth diameter is 1050mm, and the thickness is 2mm.

Figure 3.1: Disk

3.2.2 Power Mechanism

Solution 1: The motor transmits torque to the main shaft through a reducer, and the main shaft drives the rotation of the disk through a key connection. Due to the small load and no other special requirements, a common cage-type asynchronous motor is selected for the motor, model Y90S-6, with a power of 0.75 kW, a speed of 910 r/min, a maximum torque of 2.2 N·M, and a weight of 33 kg. The motor protection level is rated as level 6, dustproof [44]. The reducer selected is model ZSY160 with a reduction ratio of 50. The design scheme for the granulation power mechanism is shown in Figure 3.2.

Figure 3.2: First Solution

As shown in the above figure, the speed of the motor transmitted to the disc after deceleration is 18.2 r/min, while the recommended speed for firework granulation is between 15-30 r/min. The tilt angle range of the disc is generally between 43° and 45°. The granulation effect is the best when the tilt angle is 45° and the disc speed is 18 r/min. Therefore, the initial setting for the tilt angle of the disc is 45°. This design has a feed rate of five kilograms and a target particle size of 10mm. The various parameters affecting granulation in Solution 1 (spindle speed of 18.2 r/min, tilt angle of 45°, disc diameter of 760mm) are empirical data, and there is no experimental data to prove that they are the optimal parameter combination for a target particle size of 10mm. Therefore, this design requires the adjustability of various parameters affecting granulation. Then cross-experiments can be conducted based on the specific target particle size to find the optimal parameter combination. To achieve adjustable disc speed, the power mechanism designed in Solution 1 cannot meet the requirements, so alternative solutions must be sought to solve this problem.

Solution 2: The power mechanism combines (mixture) a motor and a frequency converter, which controls the motor’s output speed through the frequency converter. The frequency converter combines microelectronics and frequency conversion technology (mixture) to convert the working power supply of 50Hz or 60Hz into an AC power supply of other frequencies, thereby meeting the speed regulation requirements of the motor. Specifically, it adjusts and changes the frequency and voltage of the output power supply by interrupting the internal insulated gate bipolar transistors, thereby achieving speed regulation. The composition of the frequency converter mainly includes a rectifier unit, filter unit, inverter unit, braking unit, drive unit, detection unit, microprocessor unit, etc.

The motor is the control object of the frequency converter, so the selection of the model and specifications of the frequency converter can be made from the perspective of the motor. After consulting the manual, the ACS101-2K1-1 frequency converter from ABB company is selected, with a power of 1.1 kW and a protection level of IP20.

Solution 3: Using a stepper motor

A stepper motor is an actuator that converts electrical pulses into angular displacement by utilizing the principle of electromagnets. Simply put, whenever it receives a pulse signal, the motor rotates a fixed angle in a predetermined direction called a step angle. The angle displacement and the speed and acceleration of the motor rotation can be controlled by manipulating the number and frequency of the pulse signals [47].

Stepper motors have the following characteristics: 1. One pulse corresponds to one step angle. 2. Controlling the pulse frequency allows for controlling the motor’s speed. 3. Changing the pulse sequence alters the rotation direction. 4. The angle or linear displacement is proportional to the number of electrical pulses.

Figure 3.3: Stepper Motor

Considering the three options, we choose option 2 because the production of the light bulb does not require high-speed accuracy and precise positioning. Option 2 can meet the requirements and is economically practical.

3.2.3 Spindle

Spindle: After the motor decelerates, it transfers torque to the spindle, which drives the disc to rotate. During the granulation process, the tilt angle of the disc ranges from 40° to 60°. Therefore, the angle between the spindle and the horizontal plane is also within the range of 40° to 60°. The spindle is subjected to both torque and bending moment. The most common accident in disc granulator production is the spindle’s breakage, caused by excessive shear stress leading to fatigue fracture. Figure 3.4 shows a schematic diagram of the spindle operation.

To prevent similar problems, the material chosen for the shaft in this design is 40Cr. The minimum diameter of the shaft is determined by the formula (3.1):

The obtained value is D ≥ 32.8mm. The minimum selected shaft diameter is 35mm, and the specific dimensions can be seen in Figure 3.5. The chosen key size is B x H x L = 10 x 8 x 30mm.

Figure 3.4: Illustration of the spindle operation

Figure 3.5: Spindle

3.3 Design of Spraying Mechanism

This project adopts dry granulation for the propellant. During the granulation process in the disc, the propellant powder needs to be continuously sprayed with a binder. The binder allows the powder to agglomerate into particles, and as the powder and binder are added, the particles gradually grow in size. Therefore, the binder is particularly important in propellant granulation.

Traditional binders used in propellant granulation are mixtures of water and alcohol sprayed by pouring them into containers. Spraying the binder in this manner results in uneven distribution, leading to inconsistent particle sizes and a low granulation yield. This project uses a spray method to introduce the binder to improve the yield. The spray method ensures even binder distribution, faster particle formation, higher particle hardness, and easier drying.

3.3.1 Working Principle of Atomizer

Working principles of atomizers [48]: Based on their working principles, Atomizers can be categorized into centrifugal, pneumatic, and hydraulic types. Centrifugal atomizers utilize centrifugal force to propel liquid droplets. Pneumatic atomizers employ the Bernoulli principle, while hydraulic atomizers use the principle of high-speed water jets colliding with objects to produce tiny droplets. 1. Bernoulli Principle (Pneumatic)

Bernoulli principle: As shown in Figure 3.6, when high-speed airflow enters through the inlet, the blowing of the air causes a rapid decrease in pressure at the small hole while the pressure inside the bottle remains high. The pressure difference between the inside and outside forces the liquid to flow upward through the narrow tube below the small hole, and then it is blown into a mist by the high-speed airflow. It verifies the Bernoulli principle states that higher flow velocity corresponds to lower pressure. The droplets produced by this method have diameters ranging from 100 to 150 μm.

Figure 3.6: Bernoulli’s Principle Diagram

2. Principle of high-speed water flow splitting into small droplets upon encountering obstacles (hydrodynamic)

A hydrodynamic sprayer works by introducing liquid with a certain pressure into a narrow tube. The liquid flows rapidly inside the tube, and when it encounters an obstacle, it collides with it and splashes into tiny droplets. Most commonly used sprayers operate on this principle and are cost-effective. One such product is an atomizing nozzle, as shown in Figure 3.7. The high-speed flowing liquid collides with the metal plate at the nozzle’s opening, rebounds, and forms mist-like particles, which are then sprayed out of the nozzle. The diameter of the sprayed droplets from the atomizing nozzle typically ranges from about 15 to 60 μm.

Figure 3.7: Atomization Nozzle

3. Principle of Liquid Ejection by Centrifugal Force (Centrifugal Force)

The centrifugal force sprayer utilizes a high-speed rotating atomization disc to eject the sample of internal liquid, similar to the rotating umbrella in the rain, relying on the centrifugal force’s effect. This method’s droplet diameter range sprayed is 20 to 30μm, as shown in Figure 3.8.

Figure 3.8: Centrifugal Sprayer

3.3.2 Design of the Sprayer

The sprayer in this project is mainly used for spraying adhesive onto the powder, requiring the adhesive to form a mist with droplet diameters ranging from 20 to 60μm. The sprayer is installed above the feeding bracket, so the sprayer must have a compact size and minimize vibration and air agitation to prevent powder scattering. At the same time, it is required to have controllable spraying time and spraying velocity. Based on these requirements, the pneumatic sprayer generates airflow during spraying, which easily leads to powder scattering. The centrifugal sprayer has a large and cumbersome volume, making it difficult to install and adjust the spraying direction and angle. Therefore, this article chooses the type of sprayer to be a hydraulic sprayer. As shown in the figure, the designed sprayer for this project mainly consists of the following parts: liquid tank, pump, liquid inlet pipe, shut-off valve, filter, pressure regulating valve, liquid outlet pipe, and atomizing nozzle. The working principle of this sprayer is as follows: the pump provides power to pressurize the liquid, which enters the liquid inlet pipe and waits for the shut-off valve to open. When the shut-off valve receives the command to open, the liquid enters the filter. Then the pressure is adjusted to the specified value by the pressure regulating valve before entering the atomizing nozzle for atomization. The mist is then sprayed onto the designated area of the granulation disc, as shown in Figure 3.9.

Figure 3.9: Schematic Diagram of Sprayer Assembly

3.4 Design of Discharging Mechanism

3.4.1 Semi-Circular Seat

After the granulation process, considering the special chemical properties of the propellant, the use of electrical switches should be avoided as much as possible in the design (to prevent spark generation). At the same time, attention should be paid to the extrusion of the powder to avoid accidents. Therefore, the discharging method adopted is dumping. In the design, the granulation mechanism (granulation disc, motor, etc.) is installed on a semi-circular seat, with the centerline of the disc parallel to the seat and the seat forming a 45° angle with the horizontal plane, ensuring a tilt angle of 45° for the disc. At the same time, the seat is connected to the base with dowel pins, allowing the seat to rotate along the pivot axis. It achieves adjustability for the tilt angle of the disc. Additionally, the bottom surface of the semi-circular seat is equipped with a sliding groove, which is a component of the discharging connecting rod mechanism, as shown in Figure 3.10.

Figure 3.10: Semi-circular disc seat

3.4.2 Discharging Connecting Rod Mechanism

The power for rotating the disc seat is provided by the discharging cylinder, which controls the inclination angle of the disc and the tilting action of the discharge by controlling the extension of the cylinder rod. The connecting rod mechanism consists of the cylinder body, cylinder rod, Y-shaped joint, fish-eye joint, disc seat, and bracket. The cylinder rod moves straight upward along the cylinder body, pushing the Y-shaped joint. The Y-shaped joint is connected to the fish-eye joint pin, and the fish-eye joint slides along the track of the disc seat, simultaneously driving the disc seat to rotate around the pivot axis, thus achieving the transformation between linear and rotational motion. As shown in Figure 3.11.

Figure 3.11: Discharging Connecting Rod Mechanism

Through calculations, it is determined that the required cylinder thrust is approximately 2960N, and the air pressure is 0.4MPa. According to the formula, the cylinder diameter is calculated as 100mm, and the cylinder stroke is chosen as 700mm based on the required travel distance. The SI series ISO6431 standard cylinder is selected for the cylinder. The action form is double-acting, the working medium is air, and the fixing form is FA-type. The temperature range of use is 0-70°C, and the speed range of use is 50-800mm/s. Select Y-type fittings and fisheye fittings, as shown in Figures 3.12 to 3.14.

Figure 3.12: Cylinder

Figure 3.13: Y-type fitting

Figure 3.14: Fisheye fitting

3.4.3 Residual Material Recycling Mechanism

During the discharge process, the turntable rotates counterclockwise to pour out the finished luminous beads. Due to the high moisture content of the freshly made beads, their strength is relatively low. To prevent the luminous beads from impacting and breaking when they fall into the slide and to recycle the residual granulation material, the design incorporates a lifting platform with a residual material recycling slide and a discharge mechanism for the discharge process. While the turntable is tilting, the lifting platform (which is equipped with the residual material recycling slide) and the discharge mechanism work together to reduce the vertical drop height of the luminous beads, thus minimizing the risk of impact-induced breakage. The luminous beads roll down the turntable and enter the residual material recycling slide. The recycling slide is equipped with 3mm-wide gaps distributed evenly along its length. The remaining powder and luminous beads with smaller diameters fall into the recycling bin through the gaps during the sliding process. Luminous beads with larger diameters continue to slide along the slide and enter the next workstation for further processing. The specific structure of the residual material recycling slide is shown in Figure 3.15.

Figure 3.15: Residual Material Recovery Slide

In simple terms, the lift table is a type of transportation machinery used primarily for carrying people or objects and performs only vertical lifting and lowering movements. Lift tables are widely used in factories and warehouses. A hydraulic drive generally provides the power for the lift table, also known as a hydraulic lift table. A pneumatic drive is used for this lift table design due to its small load capacity. The selected type is the fixed scissor type. Cylinders power the lifting and lowering action of the lift table, and there are rolling channels on the upper and lower platforms, allowing the wheels on the scissor brackets to move in a straight line along the slide. The specific details are shown in Figures 3.16 to 3.18.

Figure 3.16: Lift platform surface

Figure 3.17: Lift platform support

Figure 3.18: Assembly rendering of the lift platform

Cylinder Selection: Calculating the required output thrust to be approximately 3000N, the calculated cylinder diameter is 100 mm. Select the cylinder stroke as 300 mm. The air pressure is 0.4 MPa. The chosen cylinder is from the SI series ISO6431 standard cylinder. The action type is double-acting, and the working medium is air. The fixed form is CB type. The temperature range of use is 0-70°C, and the speed range of use is 50-800 mm/s.

3.5 Design of the Feeding Mechanism

After the gunpowder particles are weighed and mixed uniformly in the previous process, they are transported to the feeding station via a conveyor belt. Once the granulation process begins, the conveyor receives the instruction to move, and the gunpowder slides into the hopper. The feeding mechanism of this project consists of four parts: a support frame, a hopper, a guide rail, and a cylinder, as shown in Figure 3.19.

3.5.1 Hopper

The design of the hopper is based on a five-kilogram powder load, and the required hopper volume is calculated to be approximately 5 liters based on a powder density of 1 kg/L. The design of the hopper also needs to consider the angle between the hopper slope and the horizontal plane, which should be greater than the angle of repose of the powder. The measured angle of repose of the gunpowder is approximately 30°. In this design, the angle between the hopper slope and the horizontal plane is set to 64°, and the angle between the pipe and the horizontal plane is set to 45°, allowing the powder to slide smoothly into the disc, meeting the requirements. The design of the hopper is shown in Figure 3.20, with a calculated volume of 6.77 liters using Pro/E software.

Figure 3.19: Assembly Rendering of the Feeding Mechanism

Figure 3.20: Hopper

3.5.2 Support and Guide Rails

Due to the material being a powder, close-range feeding is required considering the airborne nature of powders. However, as mentioned earlier, the discharge requires coordination between the discharge mechanism and the lifting platform in the granulation process. Therefore, the design of the feeding mechanism needs to consider the interference between the feeding mechanism, the disc, and the lifting platform. In this project, a hopper is installed on the support frame, with the hopper positioned at the top of the frame, maintaining a certain safe distance from the lifting platform (when the lifting platform is in the highest position) to avoid interference during the production process. The support frame can move forward and backward to adjust the distance between the feeding port and the granulation disc. The movement of the support frame is achieved through guide rails and cylinders. Sliders are installed at the bottom of the support frame, as shown in Figure 3.21. The selection of guide rails [49]: The total weight of the support frame, hopper, etc., is measured to be 302.6 kg, i.e., the load-bearing capacity of the guide rail is 3026 N. A square guide rail with four rows of balls is chosen, with a width of 35 mm and a length of 2000 mm. The number of sliders is 4.

3.5.3 Power Mechanism

The motion of the support frame in this project is provided by a cylinder [50]. The coefficient of friction for a general linear guide rail is 0.01-0.02. The maximum frictional force required for the sliding of the guide rail is calculated to be 64.12 N. The air pressure is 0.4 MPa. A cylinder with a diameter of 20 mm is selected, and the cylinder stroke is chosen as 1200 mm according to the required travel distance. The cylinder used is from the SI series ISO 6431 standard cylinder, with the action form double acting, the medium working air, and the fixed form FA type. The operating temperature range is 0-70 °C, and the operating speed range is 50-800 mm/s, as shown in Figure 3.22.

Figure 3.21: Support Frame

Figure 3.22: support cylinder

3.6 Scraper Mechanism

3.6.1 Scraper Blade

During the granulation process, the powder slides along the bottom surface of the disc. Some powder may adhere to the granulation disc as the binder is continuously sprayed. Over time, the adhesive layer thickens, affecting the granulation process. Therefore, it is necessary to design and install a scraper blade to scrape off the adhered powder and allow it to continue participating in the granulation. A rubber scraper blade is selected because the granulated powder is explosive. Rubber has elasticity and low hardness, which minimizes the squeezing pressure on the explosive powder.

3.6.2 Scraper Mounting Bracket

The scraper is mounted on a scraper mounting bracket, which is then installed on the base of the disc. The mounting bracket is made of welded pipes; its structure is shown in Figure 3.23.

Figure 3.23: Scraper Mechanism

3.7 Design of Real-time Observation Mechanism

During the granulation process, there is always a risk of explosion. Therefore, in the production process, it is advisable to avoid direct contact between humans and the medication as much as possible. However, the time required to form bright beads to reach the specified size varies, and it is necessary to observe the formation of bright beads at close range to determine the start of the next process. To address this situation, the project employs a dual-camera remote monitoring system. The cameras are positioned on both sides of the support bracket.

3.8 Motion Simulation of Granulation System

3.8.1 Introduction to Motion Simulation and Pro/E Software

Motion simulation refers to the simulation and analysis of the motion process of an object under actual assembly conditions in a real environment using a computer. It involves numerical analysis and calculation of the object’s motion trajectory and variation. Through simulation, the mechanism’s actual motion state and interference can be observed, facilitating optimization design and calculation evaluation of the mechanism’s strength and lifespan. Simulation technology has significant guiding significance for modern industrial design, product development, and optimization, formulation of the design process simpler and more intuitive. It greatly reduces and simplifies the product design and development process while improving design quality.

Pro/E software is one of the most successful software in the world. It is a three-dimensional drafting software developed and launched by PTC, a company established in 1985. It integrates multiple functions, including product design and assembly, mechanism simulation, finite element analysis, reverse engineering, NC machining, automatic measurement, and product database. Its powerful features and user-friendly operation make it highly favored by many users.

Pro/E structural design is a module in the software that includes motion. In this module, users can simulate and experiment with the designed products. It includes analyzing the motion of mechanisms, viewing their trajectories, examining the motion speed and acceleration at specific positions, and checking for assembly interference and motion interference.

3.8.2 Motion simulation and interference inspection of granulation system

The workflow of motion simulation in Pro/E is shown in Figure 3.24 below:

Figure 3.24: Motion Simulation Flowchart

1.   Establishing the motion model

In this study, the cylinder body and piston rod are connected by a sliding rod. The fisheye joint slider is connected to the semicircular disc base through a groove connection, and the bracket is connected to the guide rail through a groove connection. A pin links the scissor support between the lifting platform and the bracket. The scissor support and the upper and lower base plates are connected through pin and groove connections. A pin connects the main shaft. Snapshots are added after setting up the motion connections, as shown in Figures 3.25 and 3.26.

Figure 3.25: Snapshot Configuration

Figure 3.26: Adding Motor

1.   Analysis of the motion mechanism

Power is added to the main shaft, bracket cylinder, discharge cylinder, and lifting table cylinder, respectively, and the analysis definition parameters are set. The initial configuration is defined as snapshot1, and the motor parameters are set, as shown in Figure 3.27.

Figure 3.27: Definition of Simulation Parameters

3. Obtaining Analysis Results

Use the replay tools in the software to view the motion interference of the mechanism. After examining the results, no interference points were found. The motion of the granulating mechanism is in good condition, as shown in Figure 3.28.

Figure 3.28: Viewing Simulation Results

Chapter 3 Summary

The main tasks completed in this chapter were:

1.   Completed mechanical structure design and modeling of the parts of the granulation mechanism.

2.   Used Pro/E software for motion simulation and interference testing of the granulation mechanism.

Chapter 4: Research on the Design of Automatic Fireworks Production Line Granulation – Control System

4.1 Introduction to PLC

In the production of automatic fireworks production lines, the production line automatically completes processes such as weighing and mixing drugs, drug granulation, pellet stacking, and drying. Due to the multiple actions involved and the complexity of the movements, the harsh production conditions for granulation, machine vibrations, and airborne dust impact the operation. Based on the actual working conditions, the following two requirements are proposed for the control system of the automatic fireworks production line: 1. High reliability of the system. 2. The system should be capable of self-checking. Only by meeting these two requirements can the granulation process proceed smoothly and orderly. Various production line controls are implemented using switch control [51].

PLC, also known as Programmable Logic Controller, has the following advantages: simple wiring, high reliability, good versatility and flexibility, easy programming, small size, and low power consumption. Therefore, PLC can meet the design requirements of the fireworks production line control system. Therefore, PLC is chosen to control the production line in this design. The production line has multiple actions and many I/O points, mostly controlled by switches. Considering these factors, the FX2N series PLC from Mitsubishi Electric Corporation of Japan is selected. The advantages of PLC control are as follows:

1.   High reliability

(1) the PLC modules are equipped with shielding measures to prevent interference from radiation signals.

(2) PLC has reliable self-fault diagnosis functions.

(3) Each input terminal of the PLC is equipped with a filter to eliminate interference noise.

(4) Strict device selection criteria are implemented.

(5) The switch power supply of the PLC performs well.

(6) To ensure the accuracy of data transmission, the I/O circuit of the PLC adopts optocouplers.

1.   Various I/O interface modules

There are various field signals in industrial settings, and PLC has different modules corresponding to different signals.

2.   Modular structure

Currently, most PLCs adopt a modular structure to meet various factory requirements. The cables connect the modules to the rack, forming a modular PLC that meets user needs.

3.   Simple and easy-to-learn programming

PLC programming is similar to ladder diagrams. When programming a PLC, users do not need specialized computer programming skills. Therefore, PLC programming is generally easier for technical personnel to learn and use. ⑤Easy installation, convenient maintenance.

4.2 Granulation Process and Design Requirements

The granulation process of the automatic firework production line studied in this project includes the following steps: the mixed gunpowder is transported to the silo location by a conveyor belt, feeding, granulation initiation (rotation of the disc), spraying, spray stop, granulation completion (stoppage of disc rotation), feeder mechanism prepares for discharge, discharge (coordinated movement of discharge cylinder and lifting platform cylinder), reset of discharge mechanism and lifting platform, reset of feeder mechanism. During the production process, real-time monitoring of the granulation process is required to ensure the quality control and timing of granulation. In case of emergencies, it is necessary to be able to stop the granulation process immediately. When various signals are sent to the PLC, it will execute the corresponding actions according to the programmed instructions.

Based on the mentioned granulation process, the main controlled movements include: the start/stop of the conveyor belt, start/stop of the disc rotation, clockwise and counterclockwise rotation of the granulation tray along the axis, start/stop of the sprayer, lifting motion of the lifting platform, and forward/backward movement of the support frame. The structure and process flow of the granulation system is shown in Figure 4.1.

Figure 4.1: Granulation Schematic

4.3 System Control Requirements

(1) Operation modes. The feeding, granulation, spraying, discharging, support, and lifting platforms all have manual/automatic operation modes. When the system operates in automatic mode, the control mechanism will act in sequence according to the programmed instructions. Manual mode is usually selected only for equipment maintenance, debugging, or independent movement of mechanisms.

(2) Real-time display. The operation status, running time, alarm information, processing cycle count, and other information about each process in the system should be displayed on the touch screen. At the same time, the production line is equipped with real-time monitoring mechanisms, which use camera devices to monitor the granulation process in real-time for remote manual control.

(3) Fault detection. The granulation control system automatically detects faults in each workstation during production. The production line operates normally if all workstations are running normally and the touch screen displays no abnormalities. The touch screen will display the fault message and location if a fault occurs.

(4) Emergency stop. In the event of an emergency during system operation, pressing the emergency stop button will cause all devices to stop simultaneously. The emergency stop button is generally used only in dangerous and faulty situations. Each workstation is also equipped with an emergency stop button, which immediately stops the corresponding equipment when pressed.

(5) Safety protection. When programming, special attention should be paid to important processes, focusing on safety precautions and minimizing the risk of accidents [52].

4.4 Control System Design

The control system mainly consists of hardware pieces such as PLCs, industrial computers, frequency converters, limit switches, and solenoid valves, as shown in Figure 4.2.

Figure 4.2: Control System Diagram

1.   The FX2n series PLC from Mitsubishi Corporation is used. Although this series of PLCs has not been on the market for long, its compact size and high performance have been widely appreciated by users. Among the FX series PLCs, the FX2n series is the most advanced.

2.   The ACS101 series inverter from ABB Corporation is used to control the speed. The inverter is utilized to achieve speed control.

3.   The touch screen from Advantech in Taiwan is adapted to provide a human-machine interaction platform for users. It facilitates the setting and modification of parameters in production and allows observation of the equipment’s operating conditions through the touch screen.

4.4.1 Overall Design of Electrical Control System

1.   In the control objects of the granulation system, the conveyor, granulation disc, and water pump are controlled for starting and stopping using AC contactors. The contactors control the extension of the cylinder and the on/off operation of the sprayer by controlling the electromagnetic valve’s power supply.

2.   For the control of cylinder movements using limit switches, considering the dusty working environment, two switches are installed in the same position to prevent accidents caused by a switch failure.

3.   Thermal relays are used for motor overload protection.

4.   Short-circuit protection is achieved through circuit breakers and fuses. The circuit breakers are installed in the main circuit, while the fuses are installed in each circuit, including control and load circuits.

5.   The programmable logic controller (PLC) is installed in the control room. The electrical panels of the control panel and the PLC are connected using BRV-type copper wires, and terminal boards are used to connect the PLC with the execution devices.

6.   Indicator lights indicate the execution status of each process in the granulation system.

7.   A relay output type PLC is selected.

8.   The grounding terminal of the PLC adopts the second grounding method, the multi-branch single-point grounding method, to improve anti-interference capability [54].

4.4.2 Granulation Control System Architecture

The granulation control section of the fireworks automatic production line adopts a modern advanced distributed control approach [55]. This approach enables manual and automatic control of the granulation process and local and remote operation. It also allows for closed-loop operation based on parameters such as feeding, granulation, and discharge times, automatically carrying out granulation actions and processing. This project uses a PLC to design the control system, and communication is established between the human-machine interface and the upper computer.

Figure 4.3: Composition of Granulation System Control Section

All equipment in the control section of the automatic fireworks production line’s granulation system is installed in a programmable logic controller (PLC) cabinet. The core of the control system consists of a PLC and an industrial computer. The PLC selected is Mitsubishi’s FX2N series, and the industrial computer is a slim industrial computer from Advantech in Taiwan. The control system can complete the control of the feeding mechanism, granulation mechanism’s start and stop, adhesive pipeline valve on/off, and display the feeding, granulation, and spraying times. It also collects and displays the spraying flow rate, liquid pressure, working environment temperature, and working environment dust concentration.

Additionally, it provides functions for abnormal alarms and interlocking protection. The control cabinet mainly contains low-voltage electrical devices such as buttons, contactors, and indicator lights. The composition of the control system is shown in Figure 4.3.

The working temperature is measured using a thermocouple, the dust concentration is measured using a dust concentration sensor, and the adhesive pressure is measured using a transmitter. The adhesive flow is measured using a differential pressure transmitter. The on/off control of the adhesive is achieved through solenoid valves and three-position, five-way solenoid valves control the extension and contraction of various cylinders. The pressure, temperature, flow, and other on-site signals are transmitted to the touch screen and industrial computer’s operating interface through PLC modules inside the control cabinet for display.

4.4.3 Electrical Control Schematic Design

(1) Main Circuit Design of the electrical control system for the granulation system is shown in Figure 4.4.

Figure 4.4: Main Circuit of Granulation Control System

1.   In the main circuit, the AC contactor KM1 controls pump M1, and AC contactors KM2 and KM3 control the turntable motor and feeding motor.

2.   Pump M1, motors M2, and M3 are protected against overload by relays FR1, FR2, and FR3.

3.   QF is the main power switch, which provides short-circuit protection for the main circuit, especially in the case of segmented three-phase AC, making it convenient for use and maintenance.

4.   Fuses FU1, FU2, and FU3 provide short-circuit protection for the load circuits. FU5 and FU6 provide short-circuit protection for the AC and PLC control circuits [56].

(2) AC Control Circuit Design The AC control circuit for the granulation system is shown in Figure 4.5.

1.   The control circuit is equipped with power indicator lights. An isolation transformer is used in the power supply circuit to prevent power interference.

2.   Slurry pump M1, granulation motor M2, feeding motor M3, discharge cylinder, bracket cylinder, and lifting table cylinder each have operation indicator lights HL1 to HL9, and illumination is controlled by normally open auxiliary contacts of contactors KM1 to KM9.

3.   The coil of contactors or limit switches provides the triggering signals for each process.

Figure 4.5: AC Control Circuit of Granulation System

(3) PLC Control Circuit Design

I/O Allocation Table and Terminal Wiring Diagram: The defined I/O allocation table is shown in Table 4.1 in this system design. The 33 input signals and 18 output signals are classified according to their functions, and the input and output signals are tabulated with their corresponding I/O points. Refer to Table 5.1 for details. The I/O terminal wiring diagram is shown in Figure 4.6. It can be seen that all input signals of the control system are switch signals. Among them are 22 operation button switches, 6 limit switches, and 1 thermal relay switch. The PLC control system has 18 output signals, with 9 of them used for driving motors, pumps, and solenoid valves through contactors and 9 for indicating lights corresponding to the operation of the equipment. The selected PLC model is FX2N-80MR-001.

Table 4.1: I/O Allocation Table

Table 4.1: I/O Allocation Table (Continued)

Figure 4.6: I/O Terminal Wiring Diagram

4.4.4 PLC Program Development

(1) Granulation System Flowchart

Prepare a control flowchart for the granulation system. The formulation of the flowchart should be based on the actual control requirements. As shown in Figure 4.7, the flowchart provides a detailed and clear representation of the sequential actions of each mechanism and their interconnections.

Figure 4.7: Granulation Process Flowchart

(2) State Transition Diagram

Based on the granulation process flowchart, create a state transition diagram for the granulation system. The state transition diagram is different from ladder diagrams as it is a Sequential Function Chart (SFC) language that conforms to the IEC 1131-3 standard. It is primarily used for developing sequential control programs with complex logic using state-based control flow diagrams. States control the program circuit, which runs strictly in the specified sequence during execution. It is easy to write and has strong readability. Figure 4.8 represents the state transition diagram for granulation.

Figure 4.8: State Transition Diagram

(3) Step Ladder Diagram

Figure 4.9: Stepped Ladder Diagram

4.4.5 HMI Design and Production

This project utilizes Kingview 6.53 configuration software to design the granulation control system’s human-machine interface (HMI), facilitating information exchange and interaction between humans and computers.

Kingview software [57, 58] is a versatile configuration software with a wide range of applications, also known as industrial monitoring software. It can be used for real-time (realistic) monitoring of individual mechanical equipment and large-scale networked systems. Kingview software significantly reduces the difficulty of work for design and development personnel, as it allows them to thoruughly control software coding and design without the need for computer language. The features of Kingview 6.53 include the following:

1.   Comprehensive configuration functionality

Kingview provides users with a rich library of tools and various functional ingredients Users can design and create various control and display functions with these libraries and elements, visualizing industrial production processes through graphical representations. A well-designed human-machine interaction platform incorporates various feedback data and screens, greatly facilitating production control for workers.

1.   Flexible communication and networking capabilities

Kingview software supports multiple communication protocols, enabling communication with PLCs, frequency converters, intelligent instruments and meters, and intelligent modules. Additionally, Kingview’s networking functionality is robust, allowing monitoring of other stations within the network range.

The production of graphic human-machine interaction interfaces is divided into three parts: the title area, the operation display area, and the interface selection area.

The title area mainly includes the interface name and time display, among others. Each interface is named according to its use, its formulation for an easy to differentiate in the interface selection area. In this design, the title area includes a time display and defines the interface as a “Granulation Monitoring System Based on Kingview and PLC.”

The operation display area shows the working environment temperature, liquid pressure, and flow rate. In terms of equipment control, the granulation system can operate automatically, and manual operations can be performed on feeding, granulation, spraying, and other equipment. Additionally, granulation parameters can be configured.

The interface selection area offers “Return to Homepage” and “Exit.” “Return to Homepage” returns the user to the granulation monitoring screen, as shown in Figure 4.10.

Figure 4.10: Main Control Interface

4.5 Chapter Summary

In this chapter, starting from the granulation system process, the electrical part of the granulation system was systematically structured. The electrical control schematic, PLC wiring diagram, PLC program development, and testing of the PLC program were designed and completed. The control part of this design also added an upper computer and achieved data communication between the upper computer and the lower computer through a network. The upper computer monitors and diagnoses the entire granulation system through a human-machine interface, enabling remote control of the production process by the operators. Appropriate alarm settings allow for error detection and timely implementation of control measures.

Chapter 5: Analysis of Axial Mechanics and ANSYS Fatigue Life Analysis

Disc granulator is a common granulation equipment in industrial granulation, widely used in dry granulation of materials such as coal powder, cement, clinker, fertilizers, and explosives. However, during operation, if the spindle is improperly designed, spindle fracture accidents often occur, which bring many inconveniences to production and even pose safety hazards. To solve this problem, this design has reviewed a lot of information and found that the main cause of spindle fracture is excessive shear stress generated by torque [59]. This paper will calculate and analyze the specific situation and verify whether the forces exerted on the spindle by the disc, material, and binder are within a reasonable range to provide a scientific theoretical basis for preventing the recurrence of similar accidents.

5.1 Calculation of the Relationship between Spindle Fracture and Material Quantity

5.1.1 Working Principle

After the motor starts, the spindle is driven to rotate by the disc through the coupling, with the speed regulated by the frequency converter. Figure 5.1 shows the schematic diagram of the transmission mechanism of the disc granulator.

Figure 5.1: Schematic diagram of the transmission mechanism of the disc granulator

5.1.2 Theoretical calculation

1.   Force situation of the main shaft (see Figure 5.2)

(1) Torque at point B of the main shaft:

NB = NDη — (5.1)

In the equation, NB represents the input power at point B of the main shaft, ND represents the rated power of the motor (0.75 kW), and η represents the motor efficiency (0.88). The torque at point B is given by:

NB = 9549 (Nb/M) — (5.2)

In this equation, NM represents the torque multiplier factor at point B.

In equation (5.1), substituting (5.2), we obtain

MNB = 9549 (NDη/n)

In the equation, MNB represents the input torque at point B on the main shaft; n represents the rotational speed of the main shaft, which is 20r/min. Within the AB segment of the main shaft, from the balance of the moment of force couple, we have:

MNB + MNA = 0 — (5.3)

which implies that MNB = -MNA.

Figures 5.2 and 5.3 show that the cross-sectional areas at point A and point B are the same, but the minimum cross-sectional area is more prone to fracture. Therefore, it is necessary to perform a check at this location.

Figure 5.2: Schematic Diagram of Torque Applied to the Main Shaft

Figure 5.3: Torque Diagram

(2) Torque at Point A of the Spindle

When the material is mixed in the disc, it can be abstracted as a particle P with a distance OP = 300mm from the center O of the disc. The torque it generates on the spindle is equivalent to the two forces F’ produced by the material in the disc at the center of mass P, as shown in Figure 5.4, while the force F” does not generate torque.

Figure 5.4: Diagram of the forces acting on a disc

F’ = mg. cosα

M NA = F’OP (5.4)

Substituting F’ = mg·cosa — (5.4), we get

MNA = mg · OP · cosα — (5.5)

In equation (5.5), M NA represents the torque between the material and the disk at point P with respect to the main axis AB; g represents the acceleration due to gravity; OP represents the distance from the center O to the center of gravity P.

1.   Strength calculation

Since point B is the location of the smallest cross-sectional area of the axis within segment AB, the maximum shear stress occurs at the outer edge.

τ max = Mnb/Wn — (5.6)

In equation (5.6), τ max represents the maximum shear stress experienced by the axis. Wn is the torsional section modulus of the axis, and

Wn = πD^3/16 — (5.7)

D represents the diameter of the fracture section.

Substituting equation (7) into equation (6), we obtain τmax = 16 MnB/(πD^3). Therefore, the axis will fracture at point B.

1.   Calculation of the maximum material in the disk

The torque generated by the material in the disk on the main axis should be minimized. If it becomes too large, the maximum shear stress (τ max ) at the outer edge of the main axis may exceed the allowable shear stress of the material τ [max] = (40 MPa), leading to fracture.

τ = MnA/Wn = 16MnA/(πD^3) — (5.8)

substituting (5.5) into (5.8) yields,

m ≤ πD^3 [τ]/(16gOP cosα = 158kg, In the equation, “a” represents the angle between the main axis and the horizontal plane, which is 45 degrees. The total weight of the disc and its accessories is 62 kg, so the amount of material loaded into the disc should be less than 96 kg. Conclusion 5.1.3:

During startup tests, it is recommended to run the equipment without any load initially and then add the material for operation. The amount of material should not exceed the calculated value mentioned above. After each use, the bottom of the disc should be thoroughly cleaned of any adhered material to prevent excessive material accumulation over time.

5.2 Analysis of Spindle Load Fatigue Life

5.2.1 Stress Analysis of the Spindle and Introduction to ANSYS Software

As one of the key units of the granulation system’s mechanical structure, the spindle’s strength and fatigue life significantly impacts the entire mechanical system, affecting not only its operational performance but also its safety performance. Therefore, accurate and reliable prediction of the spindle’s fatigue life is crucial, and it is of great importance in preventing spindle fracture accidents.

This study created a finite element model of the spindle using finite element software. Two types of loads, torsion and bending moments, were applied to the spindle. The stress distribution cloud map of the spindle was obtained through finite element static analysis. The cloud map was used to identify the critical locations of the spindle and extract the stress and strain values at those locations. Finally, the fatigue life of the spindle was analyzed using the FATIGUE[60] module in ANSYS, resulting in the determination of the spindle’s fatigue cycle count and damage factor. ANSYS[61] software is a finite element analysis software that integrates numerous functional modules, including structural analysis, magnetic field analysis, temperature field analysis, electric field analysis, and fluid field analysis, among others. ANSYS can communicate with various high-frequency software, and due to its various advantages, it is a widely popular CAE software among users, especially in the engineering field, such as mechanical, civil, and aerospace domains.

5.2.2 Establishment of Finite Element Model

The material of the spindle is 40Cr medium carbon quenched and tempered steel. The material’s performance parameters are as follows: elastic modulus E = 210 GPa, Poisson’s ratio ν = 0.3. Stress analysis of the spindle was conducted using finite element software. The built-in modeling feature of ANSYS was used, with the element type set as Solide187. The mesh was created using mapped meshing, and the key groove area was refined. The specific details are shown in Figure 5.5.

Figure 5.5: Grid Division

5.2.3 Constraint Conditions and Load Application

The main shaft is subjected to torque and bending moments. The torque is 11 N·m, and the bending moment load is approximately 700 N, acting at one end of the shaft. When applying the load, the end of the main shaft is constrained, with constraints applied at the keyway and shoulder of the shaft, respectively. The torque load is applied using a uniformly distributed load on the side of the keyway. The bending moment load is applied at the center point of the shaft end. The bending moment load is applied in multiple steps using a multi-step loading method [62]. There are a total of 12 load steps, each lasting 0.25 s, with a time step size of 0.05, and the loading method used is a step load. The load-step relationship is additive, as shown in Figures 5.7 and 5.8.

Figure 5.6: Setting Load Step Addition Types

Figure 5.7: Setting Load Parameters

Figure 5.8: Saving Load File

This method sets 12 load steps sequentially and stores them in a file with numbers 1 to 12. The specific load data is shown in Table 5.2, and the loading result is shown in Figure 5.9 after the loading is completed.

Figure 5.9: Load Application Effect Diagram

Table 5.2: Load Data

5.2.4 Finite Element Load File Reading

Read the load file and calculate, as shown in Figure 5.10.

Figure 5.10: Load File Reading

5.3 Spindle Fatigue Life Analysis

5.3.1 ANSYS Fatigue Analysis Steps

ANSYS general post-processing includes a fatigue analysis module called Fatigue. The theoretical basis of this module is linear cumulative damage theory. Using the time history of the applied load on the object and the material’s S-N curve, the stress object’s damage factor and fatigue cycle count can be calculated.

The specific steps for fatigue calculation are as follows:

1.   Enter POST1 and restore the database.

2.   Establish the fatigue calculation scale, define the material fatigue parameters, and set the fatigue calculation parameters.

(1) Define the fatigue calculation parameters.

Set the node positions, number of events, and loadings per event according to the calculation requirements.

(2) Define the fatigue performance of the material.

1.   Store stresses, specify the number of time cycles, and set the scale factor.

2.   Activate the fatigue calculation.

3.   View the calculation results.

The fatigue calculation results are recorded on the output events and can be checked in list form.

5.3.2 Determination of Critical Locations of the Spindle and Fatigue Life Calculation

To perform fatigue analysis, it is necessary to know the load spectrum and critical locations of the spindle. Therefore, static analysis of the spindle needs to be conducted to determine its critical locations.

6. View the results

Enter the post-processor and view the results of stress calculations, as shown in Figures 5.11 to 5.14.

Figure 5.11: Equivalent Stress Contour Map

Figure 5.12: X-direction Stress Contour Map

Figure 5.13: Y-direction Stress Contour Map

Figure 5.14: Z-direction Stress Contour Map

The stress contour map shows that the maximum axial stress point is located in the middle of the key slot.

1.   Input the S-N curve, as shown in Figure 5.15.

2.   Determine the node number based on the coordinates of critical points, as shown in Figure 5.16.

Figure 5.15: Input N-S Curve Dialog Box

Figure 5.16: Input Parameters Dialog Box

4. Specify the stress location, as shown in Figure 5.17.

5. Extract stress values from the database, as shown in Figure 5.18.

Figure 5.17: Recover Node Data from Database Dialog Box

Figure 5.18: Specify Stress Location Dialog Box

1.   Store Node Stress Values, as shown in Figure 5.19.

2.   Set the Number of Event Repetitions, as depicted in Figure 5.20.

Figure 5.19: Node Stress Value Storage Dialog Box

Figure 5.20: Set Event Repetition Count Dialog Box

1.   Fatigue Calculation, as shown in Figure 5.21 for the Fatigue Calculation Dialog Box and Figure 5.22 for the Calculation Results.

Figure 5.21: Fatigue Calculation Dialog Box

Figure 5.22: Calculation Results

From the calculation results, it can be seen that the value in the CYCLES column is ALLOWED = 1.0E+07, which means that the total number of fatigue cycles under the given load condition is 7 times 10 to the power of 7, with a damage factor of 0.66667. It meets the design requirements.

5.4 Summary of this Chapter

The main accomplishments of this chapter are as follows:

1.   The relationship between spindle fracture and material quantity is analyzed through mechanical calculations, and the range of safe production material quantity is determined.

2.   Using the finite element analysis software ANSYS, the critical point of spindle fracture is analyzed, the fatigue life of the spindle is predicted, and its damage factor is determined.

Chapter 6: Conclusion and Prospects

Starting from the perspective of powder granulation technology, this thesis combines the uniqueness of pyrotechnic powder, fully considers the mass production of bright beads in traditional fireworks production, and the advantages and disadvantages of modern production lines, and designs the granulation system of an automatic fireworks production line. The aim is to improve the production efficiency of fireworks production, liberate manpower from traditional fireworks production, and provide a guarantee for safe production.

6.1 Achievements and Conclusions of the Thesis

The main research work of the thesis is as follows:

1.   Analyzing various factors influencing fireworks granulation and their effects on granulation, analyzing the interrelationships among these factors, and proving that the design process of the production line needs to consider factors such as disc diameter, disc tilt angle, spindle speed, slurry mixture pump speed, and polishing time.

2.   Constructing the overall plan of the automatic fireworks production line-granulation system, completing the mechanical structure design of the granulation system, including the feeding mechanism, granulation mechanism, discharging mechanism, residual material recovery mechanism, and scraping mechanism. Using computer-aided design software Pro/E to perform 3D modeling of each mechanism, virtual assembly, and dynamic motion simulation and interference detection test of the virtual prototype, verifying the feasibility of the designed mechanisms.

3.   Based on the granulation process, constructing the overall plan of the granulation system-control system, completing the design and programming of the granulation system’s PLC control system, and testing the program operation using GX Developer. Using Kingview software for the formulation of a user-friendly interface for PLC control. By combining software and hardware, the operation and monitoring of the granulation system are realized.

4.   Calculating the relationship between spindle fracture and material quantity and using finite element analysis software to analyze the fatigue life of the spindle. Completing the ANSYS modeling of the spindle, applying boundary conditions and loads based on the actual stress conditions, calculating the number of fatigue cycles leading to spindle failure, and verifying the reliability of the granulation system application in the production line.

6.2 Future Research and Prospects

For the later stages of this thesis, optimization can be carried out in terms of control methods to obtain interference and dust alarms. Since the parameters of the entire granulation system vary with different material quantities and many factors influence granulation, further experiment is needed to find the optimal combination of system parameters. In addition, improvements need to be made to individual system modules for different material quantities to minimize the system cost and maximize its functionality.

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References

[1] Fireworks: A dynamic workflow system designed for high throughput applications.

[2] REQUIREMENTS FOR REMOTE EXPLOSIVES MANUFACTURING FACILITIES.

[3] Research on technology of safety automatic particle forming equipment for pyrotechnic.

[4] Research on Intelligent Decision System of Fireworks Production Line.

[5] Methods for Improving the Flowability of a Percussion Primer Composition.

[6] Utilization Methods for Explosives Withdrawn from Military Stocks: Designing, Carrying Out and Practical Implementation.

[7] Improved mixing, granulation, and drying of highly energetic premixtures.

[8] Methods for Improving the Flowability of a Percussion Primer Composition.

[9] Research on technology of safety automatic particle forming equipment for pyrotechnic.