Drying Particles for Fireworks: An Efficient and Automated Approach

Abstract

Currently, the drying process of the particles used in fireworks in our country mostly relies on natural air drying, which has low drying efficiency and cannot achieve continuous production. Some also use hot air drying, which consumes a lot of energy and has a long drying time. Therefore, it is necessary to seek a more effective drying technique to meet the needs of automated fireworks production.

Far-infrared drying is a highly efficient drying procedure that has high drying efficiency and saves energy, making it easier to achieve automated production. In this paper, a combined far-infrared and hot air drying routine is selected. The automated drying requirements of fireworks particles are achieved through design and calculation. The main research contents are as follows:

In terms of structural design, a new type of far-infrared drying box is designed, which is equipped with an axial flow fan and far-infrared electric heating plates. Three drying boxes are placed at equal distances on a conveyor belt and connected by ventilation pipes and dust collectors. When the shelves containing the particles enter the drying box, they form a closed drying system together. The designed surface of the electric heating plate has a maximum operating temperature of not exceeding 60°C, generating far-infrared radiation to dry the particles. With the help of the axial flow fan, hot air is generated to ensure uniform drying. The power used for drying the particles is calculated in the paper, and the result is lower than the installation power of the electric heating plates in the drying box, meeting the design requirements. In the unloading process, the shelves start tilting due to the push of the cylinder rod, and the particles on the shelves fall into the collection box through the click on the button track groove, completing the unloading process.

In terms of control design, PLC is used in this paper to control the drying and unloading actions, regulate the temperature inside the drying box, and implement counting and high-temperature alarms. To have a more intuitive understanding of the motion of the entire drying and unloading process, motion simulation of the mechanism is realized using Pro/E. Finally, finite element analysis is used to analyze the temperature distribution inside the drying box, and the temperatures at various points in the box are consistent, fully demonstrating the rationality of this design.

The automated fireworks drying and unloading system designed in this thesis will greatly improve the current status of fireworks particle drying. This design not only improves drying efficiency but also saves energy, achieves automated production of fireworks particles, and meets the design requirements of the thesis.

Keywords: fireworks production, far-infrared drying, hot air drying, unloading system, finite element analysis

Chapter 1: Introduction

1.1 Introduction

Fireworks are traditional festive products in China with a long history of production and use [1]. As the birthplace of fireworks and firecrackers, China is also the world’s largest producer and exporter of fireworks. According to statistics, China’s export volume of fireworks and firecrackers reached 3.5 billion yuan in 2005, with an annual output value of nearly 13 billion yuan. Nearly 100 countries and regions import fireworks from China, making China a major exporter with an annual export volume of about 250,000 to 300,000 tons. Incomplete statistics show that approximately 7,064 companies in China are currently engaged in producing fireworks and firecrackers, with 140,000 sales enterprises and a workforce of up to 1.5 million people [2]. Most of these enterprises are located in provinces (regions) such as Hunan, Jiangxi, Jiangsu, and Guangxi. Hunan and Jiangxi have the highest production volume, with over 20 million boxes of fireworks and firecrackers coming from these two provinces, accounting for more than 80% of China’s annual production. Guangdong, Hunan, and Guangxi are the main export ports for fireworks and firecrackers [3].

Since 1950, the scale of fireworks production in China has been continuously increasing to a high level, with rapid development in both quantity and quality [4]. Due to the aesthetic and practical value of fireworks and firecrackers and the continuous improvement of people’s living standards, more and more individuals and enterprises purchase fireworks and firecrackers to enhance the festive atmosphere. Some regions that rely on the fireworks and firecracker industry have become prosperous, making it a pillar industry in these areas [5].

However, in our country, the production of fireworks and firecrackers is still a labor-intensive industry, primarily relying on manual labor staff. Therefore, there are many problems in the production process, and safety accidents frequently occur. These problems mainly manifest in the following aspects: outdated fireworks and firecracker production equipment that cannot achieve automated production, especially in high-risk processes such as granulation, charging, mixing, and drying, which still require manual involvement. The knowledge level of practitioners is relatively low, and they often fail to follow operating procedures [6] strictly. Currently, the fireworks industry has played a certain role in promoting the economy in some areas, solving a portion of the employment issues. However, under the condition of manual labor for loading, it isn’t easy to produce high-quality fireworks products and ensure production safety. Although some new types of fireworks machinery and equipment have been continuously developed in recent years, the performance of these devices varies, and their efficiency is relatively low. Only a few devices have a certain level of versatility. Therefore, manual operation remains the mainstream in current fireworks production. Nowadays, companies are beginning to pay attention to the safety issues in fireworks and firecracker production. Under the strict supervision of the government, the chaotic and disorganized production of fireworks, small family workshops, and manual labor-oriented approaches are gradually transitioning to orderly, factory-oriented, mechanized, and standardized operations. Researching and innovating new types of fireworks and firecracker production equipment has become an important task faced by various levels of safety supervision departments, production enterprises, and related research and development institutions. Consequently, gradually realizing the mechanization and automation of fireworks and firecracker production is the main direction for the future development of the fireworks industry [7].

In the drying process, currently, most of the drying of fireworks grains in China is done in the outdoor natural environment, which is inefficient and prone to accidents. Some methods use hot air drying, but the results are unsatisfactory, and they cannot achieve automated fireworks production. Therefore, it is necessary to find an advanced, reliable, and efficient drying process to make it an important component of automated fireworks production. To ensure the safe production of enterprises, it is essential to reduce manual involvement in the drying process. It avoids the probability of unauthorized operations, ensures the personal safety of workers, ensures smooth production, and enhances the competitiveness of enterprises. In the long run, it reduces labor costs for loading and, most importantly, greatly promotes the development of China’s fireworks industry, improves economic benefits, and enhances the competitiveness of the fireworks industry in our country.

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• Unloading is easy – shelves tilt, and particles seamlessly fall into the collection box.
• Precision control with PLC technology, temperature regulation, and safety features.
• For a foolproof design, get a glimpse of the future – motion simulation and finite element analysis.
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• Experience the ultimate solution, exceeding thesis design requirements.

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1.2 Overview of Domestic and International Research on Fireworks Production

1.2.1 Development History of Fireworks

Gunpowder is one of the Four Great Inventions of China, and it has played a significant role in the development of world civilization. When ignited, gunpowder burns rapidly, producing a large amount of heat and generating intense light, leading to fireworks forming.

Gunpowder first appeared during the Sui and Tang Dynasties. Sun Simiao (581-682 AD), known as the “King of Medicine,” was the first to describe the “sulfur ignition method,” which involved mixing saltpeter, sulfur, and carbonaceous materials to create gunpowder. The earliest firecrackers were born during this period when people filled bamboo tubes with black powder, ignited them with a fuse, and observed the bamboo tubes explode with a loud noise. This phenomenon was believed to ward off evil spirits and demons, giving rise to firecrackers. It is said that Sun Simiao retired to Liuyang, and as a result, Liuyang still has place names such as “Sun’s Hidden Cliff” and “Medicine Washing Bridge,” as well as the “Shengchong Temple.” Nowadays, “Simiao Park” has also been newly built.

Not long after, people discovered that flames would shoot out from the top of the bamboo tubes when firecrackers were ignited. It led to the building of fountains, an early form of fireworks. During the Song Dynasty, people wrapped gunpowder in paper tubes and arranged them on strings, building “firecracker whips.” From then on, the general public began to use a dazzling array of fireworks and firecrackers widely. The technology for making fireworks during this period gradually matured and lasted for nearly a thousand years, laying the foundation for future fireworks production. During the Southern Song Dynasty, large-scale fireworks shows began to be held, gradually becoming people’s favorite way to celebrate.

During the Qing Dynasty, fireworks and firecrackers were widely used for various occasions, such as bidding farewell to the old and welcoming the new, as well as weddings and funerals. In the late Qing Dynasty and early Republic of China, various fireworks called “ground rats” became popular. This variety was developed by a merchant named Li Xiya in Liuyang County. Li Xiya revived and developed the early techniques of fireworks production, creating true “fireworks.”

In the early 1980s, Liuyang began developing “fireworks” that met international standards, making a leap from “toy fireworks” to “large-scale fireworks.” Since then, both domestically and internationally, large-scale fireworks displays have been held, adding a brilliant array of colors to the night sky.

After the 1990s, people invented electronic igniters for fireworks, capable of achieving unmanned ignition of fireworks controlled entirely by computers. Fireworks can be ignited remotely through remote control, making the process safer and the displays more magnificent and diverse.

1.2.2 Principle and Manufacturing Process of Firework Launching

Principle of Firework Launching: Fireworks consist of a launching component and a projectile. The fireworks fuse on the launching component is ignited, releasing a large amount of heat and gas from the propellant inside, propelling the projectile into the air. At the same time, the time-delay fuse on the projectile is also ignited. During the fuse burning, the projectile is propelled to a certain high point. Finally, the explosives and granules inside the projectile are ignited, creating splendid colors and beautiful sounds in the sky. Some fireworks also form various patterns in the high sky, enhancing the festive atmosphere and allowing people to appreciate the beautiful scenery.

Regardless of size or shape, fireworks generally consist of two main parts: the projectile and the launching component. As shown in Figure 1.1, the main components include propellant, igniter, time-delay fuse, explosive, granules, and casing.

Figure 1.1: Firework Structure

The production process of fireworks currently consists of the following steps [11]: (1) Compression of the shell; (2) Pharmaceutical production (explosives, components, pellets, etc.); (3) Ball loading; (4) Pasting the ball; (5) Drying; (6) Installation of internal fuses and launching components; (7) Packaging. As shown in Figures 1.2-1.8.

Figure 1.2: Suppressed Ball Shell

Figure 1.3: Pharmaceutical Manufacturing

Figure 1.4: Ball Installation

Figure 1.5: Ball Pasting

Figure 1.6: Drying

Figure 1.7: Installation of Internal Fuse and Launching Components

Figure 1.8: Packaging

1.2.3 Current Status Analysis of Domestic and International Research

1. Current Status of Fireworks Technology

(1) Formulation Technology of Pyrotechnic Composition

Fireworks compositions mainly include illuminants, oxidizers, sound-producing agents, and binders. There is a certain gap between China and foreign countries in applying these fireworks compositions. Compared to similar products abroad, Chinese fireworks differ greatly in manufacturing techniques, quality, and price [12].

1.   Illuminants: Potassium nitrate, potassium chlorate, and barium nitrate have been widely used as colored illuminants in Chinese fireworks, replacing the previous illuminants primarily composed of potassium chlorate and moisture-sensitive sodium nitrate. In contrast, the formulation of illuminants in foreign countries is more advanced. To achieve better flame color effects, foreign countries use high chlorates (potassium, ammonium), nitrates (potassium, sodium, strontium), and chlorides (potassium, barium) as oxidizers in fireworks. Organic chemical raw materials are widely used for reducers, providing good moisture resistance. Some expensive rare earth elements are also applied in illuminants, allowing fireworks to produce certain special effects [13].

2.   Chlorine Agents: In China, chlorinated rubber, polyvinyl chloride, and chlorinated paraffin are commonly used as chlorine agents in fireworks. Previously, the toxic hexachlorobenzene was used, which was also used abroad with the same formula.

3.   Whistling Agents: Chinese and foreign counterparts mostly use the fourth-generation benzoate as whistling agents. This material is easy to ignite, has good moisture absorption, and, most importantly, produces a loud sound.

4.   Binders: The binders used in China mainly comprise epoxy resin, shellac varnish, cellulose acetate butyrate solvent, phenolic resin, and polyvinyl alcohol. The previously used starch binder has been completely eliminated, primarily due to its tendency to absorb moisture and become moldy. The binders mentioned above are also used and improved in foreign countries. A small amount of paraffin oil, stearic acid, etc., are added to this binder, which can increase the brightness and color saturation of the fireworks, reduce moisture absorption, and greatly improve safety, ignitability, and combustion characteristics.

(2) Product Configuration Technology

China possesses the most abundant firework configuration technology, including toy fireworks, large-scale display fireworks, combination types, and rocket fireworks. These fireworks come in a wide variety of colors and have various effects. For example, some shapes can display ordered arrangements similar to mathematical patterns, some can create light trails resembling meteors, and some fireworks produce colors that flicker and dim intermittently. Domestic consumers deeply love these products.

However, it is undeniable that although China’s fireworks products encompass up to 13 major categories and thousands of varieties, there are few particularly well-known exquisite varieties. Most fireworks are crudely made and lack strong market competitiveness. Conversely, overseas fireworks enterprises can produce professional and exquisite fireworks varieties, occupying a significant share of the high-end fireworks market. They also achieve high production efficiency, generate less pollution, and feature more personalized designs. Examples include Japan’s spherical fireworks, Europe’s cylindrical single-stage or multi-stage fireworks, the torches, mortars, and shell fireworks of the United States, and the rocket fireworks of Germany and Spain.

(3) Production Process Technology

In China, fireworks and firecracker production remains a labor-intensive industry primarily reliant on manual work. Consequently, the production process has many issues and frequent safety accidents. These problems primarily manifest in outdated fireworks and firecracker production equipment that cannot achieve automated production. Manual labor is still required, particularly in high-risk processes such as granulation, charging, mixing, and drying. The knowledge level of practitioners could be higher, and they often need to adhere more strictly to operating procedures.

In comparison, foreign fireworks production adopts advanced manufacturing techniques. Dangerous processes such as charging and pressing the fireworks components have already been fully mechanized and automated, and they have achieved a high level of automation, resulting in minimal casualties. In critical stages, far-infrared or vacuum drying technologies are employed for drying firework powders. In this aspect, China lags behind outdated and inefficient drying techniques. Foreign countries also surpass China in product formulation. For instance, the ratio of propellant weight to launch weight for Japan’s spherical fireworks is 1:18 to 1:20, whereas, in China, it is 1:8 to 1:10. This reveals the gap in the fireworks production process technology level.

1.   Analysis of Firework Technology Development Trends

(1) Product Development Trends

With the improvement in living standards, people are paying increasing attention to environmental protection. Therefore, the public will love smokeless fireworks in the future, and there will be a greater variety of fireworks effects to meet people’s demands [19].

1.   Establishment of a theoretical system

Fireworks have been essential for people to celebrate festivals for thousands of years, but until now, they have yet to develop their own theoretical system. The main reason is that the traditional formula of fireworks used in the past relies on the generational inheritance of fireworks masters, making it difficult to establish an effective theoretical system for fireworks. With the advancement of technology and the continuous improvement of knowledge among fireworks practitioners, a systematic and standardized system will be established.

1.   Development and application of new materials

To replace the previously polluting gunpowder, new types of smokeless fireworks and low-temperature fireworks will use nitrocellulose as the main component. These fireworks varieties are safer, less polluting, and have more colorful fire effects, and they can also be applied on more occasions. Therefore, more environmentally friendly and safe fireworks compositions will be developed and applied in the future.

1.   Breakthrough in product configuration

Currently, there are various configurations of fireworks products. However, more products will be created with the continuous growth of people’s demands. Static, two-dimensional, tangible, and colorful products should be developed in dynamic, three-dimensional, and multi-sensory directions. Research on fireworks’ shapes, patterns, and text effects should be strengthened. In the structure of fireworks, more easily decomposable materials should be used. It reduces environmental pollution and meets larger market demands [20].

(2) Production Process Trends

Currently, most fireworks enterprises in China are small in scale, with low levels of knowledge among employees and outdated equipment, which severely hampers the fireworks industry’s development. Although some new types of fireworks machinery and equipment have been continuously developed in recent years, the performance of these devices varies, and their efficiency is low. Only a very small number of devices have a certain level of versatility. Therefore, manual operations still dominate the current fireworks production. In contrast, fireworks products abroad mostly adopt new processes and technologies with a high level of mechanization and automation. Thus, gradually achieving mechanization and automation in the fireworks industry is the main direction for its future development.

(3) Relevant Technological Trends

In the future, new technologies and processes will undoubtedly be widely applied in the fireworks industry. For example, fireworks display control technology, utilizing computer control, allows for diverse coordination of lights and sounds. Far-infrared drying technology and vacuum drying technology will also be applied in the automated production process of fireworks. Automatic alarm technology and intelligent monitoring technology will be better promoted. Finally, it is important to establish strict quality standards for fireworks and gradually improve the production norms of fireworks enterprises.

1.3 Current Status of Drying Technology

Regarding the drying technology used in fireworks production, the current drying methods mainly include hot air, vacuum freeze, and far-infrared drying technology.

1.3.1 Hot Air Drying Technology

Hot air drying is a commonly used drying method. Its working principle is as follows: the heat source in the drying system continuously heats the surrounding air. The heated air is then transported to the drying chamber or box through a blower’s ventilation ducts. The hot air is blown onto the heated object, and after a while, the temperature of the hot air stabilizes. Excess heat is expelled through the air outlet, completing the drying process. By adjusting the speed of the blower, the airflow and velocity of the hot air can be controlled to change the drying time of the heated object. The hot air velocity should not be too high or too low. If it is too low, the slow heat dissipation on the surface of the duct may cause damage to the heater. If it is too high, it will result in heat loss during the hot air transportation. Therefore, selecting an appropriate airflow velocity is crucial. Generally, hot air drying equipment consists of the following components [23]:

(1) Heat source: The commonly used heat sources for hot air drying are usually divided into electric heating tubes, high-temperature oil pipes, and high-temperature steam pipes. Electric heating tubes have high heating efficiency but are more expensive. High-temperature oil pipes heat the air passing through the pipes by using high-temperature engine oil, which provides stable and cost-effective heating. High-temperature steam pipes produce hot air using high-temperature steam generated by boilers.

(2) Hot air control system: The temperature inside the drying chamber is regulated by controlling the operating speed of the blower. First, a temperature controller measures the temperature inside the drying chamber, compares it with the set temperature, and generates an electrical signal to adjust the frequency of the inverter. It allows changing the fan’s speed, bringing the temperature inside the drying chamber closer to the set value, forming a closed-loop control system.

(3) Hot air drying system: It mainly consists of a blower and ventilation ducts. After the heat source heats the air in the duct, the blower transports the hot air through the ducts to the drying chamber to dry the materials. Finally, the remaining hot air is expelled through the air outlet.

In addition, there is a passive hot air drying technology. Its working principle involves generating hot air through the friction between the blades of a fan and the air. The hot air is then transported to the drying chamber through ventilation ducts. The temperature of this hot air can be regulated by adjusting the fan’s speed. This technology has a simple structure and convenient operation. However, current hot air drying equipment consumes a lot of energy and has long drying times, resulting in low drying efficiency [24]. Figure 1.9 shows a hot air drying machine.

Figure 1.9: Hot Air Drying Machine

1.3.2 Vacuum Freeze Drying Technology

Vacuum freeze drying, also known as sublimation drying, works as follows: when the material is placed in a sealed drying chamber, heating of the material begins, while the vacuum pump continuously works to remove the moisture from the material, achieving the drying purpose. As the vacuum pump operates, the pressure inside the drying chamber decreases, lower than the pressure inside the material. Under the pressure difference, the moisture constantly diffuses to the material’s surface and is finally expelled through pipes. Vacuum freeze-drying equipment generally consists of the following components [25]:

(1) Drying chamber: The chamber is mainly divided into cylindrical and square shapes, each with its own advantages and disadvantages. Cylindrical chambers are easier to manufacture but have lower space (limited) utilization, while square chambers have a larger usable space (limited) but are more difficult to manufacture.

(2) Heating system: High-pressure steam is used as the heat source to heat the material, entering the drying chamber through an inlet pipe. The heating system can also adjust the internal pressure.

(3) Vacuum System: Vacuum pumps mostly extract gas from the drying chamber and create a vacuum. There are two types of vacuum pumps: one is the Roots pump + oil-sealed pump, which requires high efficiency of the cold trap and cannot extract water vapor, but consumes less energy; the other is the Roots pump + atmospheric injection + water ring pump, which does not require high efficiency of the cold trap, can extract some water vapor, but consumes more energy.

(4) Refrigeration system: Consisting of a refrigeration unit and a cooling discharge pipe, it serves as a water vapor collector.

(5) Control system: There are currently two control methods for vacuum freeze drying: manual and automatic. Automatic control mostly uses programmable logic controllers (PLCs), which are technologically advanced and can meet complex operational requirements. They can achieve diverse needs through input or program modification [26].

When continuous production is required, a sealing structure must be set at the inlet and outlet of the vacuum drying equipment. However, these sealing structures are prone to leaks, so regular inspection and maintenance are necessary, which can have some impact on production. In addition, the manufacturing cost and operating expenses of vacuum drying equipment are relatively high, resulting in higher product prices than other drying methods. Figure 1.10 and Figure 1.11 illustrate a vacuum freeze-drying machine’s working principle and diagram.

Figure 1.11: Vacuum Freeze Dryer

1.4 Far-Infrared Drying Technology

1.4.1 Working Principles and Characteristics of Far-Infrared Drying Technology

1. Basic Knowledge of Infrared Radiation

Infrared radiation, also known as infrared light, was discovered by the British astronomer W. Herschel and was found to have thermal effects while studying the solar spectrum. Herschel observed that the thermal effect increased as the light changed from violet to red, and beyond the red boundary, there was an even stronger thermal effect. Therefore, he believed there must be a type of light beyond the red light in the solar spectrum, which is invisible to the naked eye. He referred to this light as “invisible light,” later, it became known as infrared radiation or infrared light [27].

Further scientific research revealed that infrared radiation is an electromagnetic wave with wavelengths ranging from 0.75 μm to 1000 μm. It has longer wavelengths than visible light and shorter wavelengths than microwaves. Infrared radiation follows the laws of wave motion and can be divided into three types based on wavelength: near-infrared, mid-infrared, and far-infrared. Near-infrared radiation has a wavelength of 0.75-1.5 μm, mid-infrared radiation has a wavelength of 1.5-4 μm, and far-infrared radiation has a wavelength of 4-1000 μm [28].

2. Working Principles of Far-Infrared Drying

The working principle of far-infrared drying is as follows: When the far-infrared radiator starts working, it emits electromagnetic waves, namely far-infrared radiation, at the speed of light. These electromagnetic waves carry energy and irradiate the surface of the drying material. Energy loss is minimal since no medium is required for the transmission process. When the far-infrared radiation reaches the material’s surface, part of it is reflected back, while another part penetrates into the material’s interior. The radiation that enters the interior is partly absorbed and converted into heat energy, while the rest is transmitted out of the material. Figure 1.12 illustrates the working principle of far-infrared drying. The reason why the material can absorb far-infrared radiation and complete the drying process is that when the emission frequency of far-infrared radiation matches the inherent frequency of molecular motion in the dried material (i.e., the emission wavelength of far-infrared radiation matches the absorption wavelength of the dried material), the material absorbs a large amount of far-infrared radiation, causing intense molecular vibrations and generating heat through friction within the material, thus achieving drying objectives.

Figure 1.12: Working Principle of Far-Infrared Drying

However, because far-infrared radiation is an electromagnetic wave, only molecules that exhibit polarity can absorb it. Therefore, far-infrared radiation does not have a drying effect on all substances. For example, due to their symmetric molecular structure and lack of polarity, molecules such as oxygen and nitrogen cannot absorb far-infrared radiation. On the other hand, water molecules and paint molecules, with their partially asymmetric structures and polarity, can effectively absorb far-infrared radiation. Most polymers and organic substances can also absorb far-infrared radiation within the wavelength range of far-infrared, resulting in a resonance phenomenon [29].

Water molecules’ structure consists of two hydrogen atoms and one oxygen atom, as shown in Figure 1.13. The normal vibration modes of water molecules are illustrated in Figure 1.14, which can be divided into three types: (a) shearing vibration, (b) stretching vibration, and (c) bending vibration. Based on the known potential energy function and the equal angle between the two bonds, the calculated vibrational frequencies and corresponding wavelengths of water molecules are 2.663 μm, 2.738 μm, and 6.270 μm. Finally, through experimentation, it has been found that water molecules exhibit strong absorption peaks within the wavelength ranges of 3 μm and below, 5-8 μm, and 14-16 μm. Since far-infrared radiation falls within the wavelength range of 4-1000 μm, far-infrared drying has been widely applied in various fields, including medicine, food processing, agriculture, plastics processing, and other industries [30].

Compared to conventional drying techniques, far-infrared drying is more energy efficient. It does not mean that far-infrared drying generates more heat than conventional drying at the same power level. Rather, far-infrared drying has a higher thermal energy utilization rate when drying materials. Far-infrared radiation can directly penetrate the material’s surface without an intermediate medium, reducing energy loss.

Advantages of far-infrared drying technology include:

1.   Energy savings: Far-infrared drying radiation does not require medium transmission, reducing energy loss. It can also reuse reflected and transmitted far-infrared radiation, improving thermal energy utilization.

2.   High production efficiency: Far-infrared drying provides fast heating and high heating efficiency, shortening drying time.

3.   High product quality: Far-infrared drying ensures uniform internal and external heating, minimizing the occurrence of cracks and other issues, thus improving product quality.

4.   Simple structure and low investment: Far-infrared radiators have a simple structure, low installation costs, and reduced drying costs for materials.

5.   Easier implementation of continuous production.

1.4.2 Development and Application Prospects of Far-Infrared Drying Technology

1. Development of Far-Infrared Drying Technology

In the 1930s, Ford Motor Company in the United States first applied far-infrared lamps to paint curing, achieving good results. It marked the initial attempt at far-infrared drying technology. Nowadays, people are increasingly emphasizing environmental protection, and due to the growing scarcity of existing energy sources, every country is exploring the utilization of new energy. In Canada, based on experiments, Hydro-Québec, a hydroelectric power company, has successfully developed industrial far-infrared drying devices, which have been widely promoted and applied in more than ten companies, including Cascades. Far-infrared drying technology has also made significant progress in countries like Europe and America, with France at the forefront of theoretical research. In Asia, Japan was the first to adopt far-infrared heating technology. Afzal and Abe [31,32], among others, researched the moisture diffusion of potatoes using far-infrared radiation. They mainly studied the influence of factors such as radiation intensity and slice thickness on the moisture diffusion characteristics of potatoes during far-infrared drying and established corresponding mathematical models. In 2001, Mongpraneet, Abe, and Tsurusaki [33] researched Welsh onions using a far-infrared vacuum drying method, achieving good-quality dehydrated onions.

In recent years, far-infrared drying research and application in the field of drying technology in China have developed rapidly and have received significant attention from the industry. Wang Jun, Xu Naizhang [34,35], and others conducted far-infrared drying experiments on fungi such as apples and mushrooms. They studied this drying technology’s influence on dehydration and product quality temperature characteristics. They also analyzed the relationship between the average dehydration rate and product quality after drying. Finally, they established rate models for the two stages of constant speed and deceleration during drying.

2. Prospects of Far-Infrared Drying Technology Application

The application of far-infrared drying technology has great prospects. Currently, countries worldwide are continuously developing new environmentally friendly energy sources to replace petroleum, coal, and other forms of energy, to reduce the impact of energy pollution on the environment. In energy technology utilization, the application of new technologies in the drying industry has received significant attention [36]. Products dried using far-infrared drying exhibit good quality, with stable temperatures throughout the drying process. Research on the drying of agricultural and sideline products such as food and fruits using far-infrared drying has shown significant effects, with no changes in color and better quality, resulting in longer shelf life. In contrast, products dried using natural methods have poorer color, and their quality and overall characteristics cannot be guaranteed [37]. Therefore, it is certain that far-infrared drying technology will receive excellent development and application in the future.

1.5 Main Content of this Paper

This paper explores the design of a novel drying system – the combined drying system using far infrared and hot air, along with the unloading system- to achieve automation in a fireworks production line’s drying and unloading process.

The drying and unloading system design includes mechanical structure design and electrical control design. The system’s motion simulation was conducted, and the temperature field inside the drying chamber was analyzed. The specific contents are provided as follows:

(1) Mechanical structure design: The design of the drying and unloading system’s structure, primarily including the drying chamber, conveyor, and pneumatic transmission system.

(2) Electrical control design: This includes the design of the drying control system, unloading control system, temperature control system, and alarm system.

(3) Motion simulation: Implementing the motion process of drying and unloading to determine if there is any interference between components. Based on the results, optimization designs can be made.

(4) Temperature field analysis: Analyzing the temperature distribution at various points inside the drying chamber to determine if the temperature distribution is uniform.

Chapter 2: Overall Design of Firework Automatic Production Line

2.1 Overview of Firework Production Line

2.1.1 Working Process of Firework Production Line

The working process of the fireworks automatic production line is as follows: First, several types of powder used for firework composition are added to their respective hoppers. The powders are then sent to the weighing tray through a feeder for weighing. The corresponding weights of the powders are measured according to the required proportions. After that, the powder conveying is stopped, and the process proceeds to the mixing stage. The weighted powders slide from the weighing tray into the feeding pipeline and enter the mixer for blending. After the powders are evenly mixed, they go into the granulation stage. The mixed powders are fed into the granulation disc through a feeding equipment. The motor is activated according to the received signal, operating at the set speed. Simultaneously, the spraying system starts and sprays onto the granules during the granulation process. The disc granulator rotates to granulate the materials, and the finished grains roll into the tray through a slide chute, entering the stacking stage. The trays filled with grains are transported to the stacking machine via a conveyor belt. The trays are stacked layer by layer using cylinders, placed on shelves, and proceeded to the drying stage. The stacked shelves are transported into drying chambers by a conveyor belt and undergo drying for 10 minutes in each of the three drying chambers to complete the drying of the grains. Afterward, the shelves enter the unloading stage. The shelves are tilted by cylinders of the unloading mechanism to complete the unloading process. Once unloading is finished, the shelves are transported back to the stacking section for reloading. The structure of the firework production line is shown in Figure 2.1.

Figure 2.1: Fireworks Production Line Structure Diagram

2.1.2 Problems Faced by the Fireworks Production Line

The biggest problem faced by fireworks production is safety. Due to the use of gunpowder, an explosion accident can occur at any stage of the production process [38]. Therefore, the production process should strictly adhere to the following conditions:

1.   Each independent production process should be carried out in separate workshops.

2.   Production equipment should be made of conductive materials, wood, copper, and new materials.

3.   Explosion-proof facilities should be installed.

4.   Adequate heat dissipation should be ensured.

5.   The number of personnel involved should be less than 3.

6.   The temperature in the production workshop should not exceed 80 degrees.

7.   Real-time monitoring and immediate shutdown should continue to be implemented.

8.   Explosion-proof panels, partition walls, and other measures should be installed.

9.   The amount of a single process should not exceed 5 kilograms.

10.   The thickness of the placement of particles in trays should not exceed 2 particle thicknesses.

11.   During the drying process, the temperature of the particles should not exceed 60 degrees.

Based on the requirements of these production conditions, the production line is initially designed with the principles of small-scale production and high efficiency. The total amount of gunpowder is set at 5 kilograms per cycle, and due to the mixing and granulation processes requiring a certain amount of time, it is temporarily set at 5 cycles per hour.

2.2 Introduction to Design of Production Line Components

2.2.1 Design of Weighing and Mixing Section

The overall scheme design for weighing and mixing consists of two parts: weighing and mixing. These two parts are connected by material feeding, which reduces weight loss after weighing and strengthens the overall structure, making it more compact. Additionally, these two parts are supported and connected by a frame. These two parts’ motors, cylinders, feeders, and mixers are all installed on this frame. The design of the frame structure is relatively complex and has certain load-bearing requirements [39, 40].

The working process of the weighing and mixing section includes the following steps:

(1) After the powder material is added to the hopper, the system is started.

(2) After the automatic detection of no faults, the stepper motor starts running. The powder material passes through the feeder and is delivered to the tray.

(3) When the weight of the powder material reaches a certain value, the stepper motor stops working.

(4) At the same time, the cylinder of the electronic scale starts working, lifting the tray. The cylinder stops moving when the tray reaches a certain angle with the horizontal plane. Then the powder material starts sliding from the tray into the material delivery pipeline, entering the mixing process. Additionally, the cylinder retracts to its original position after the powder material has completely fallen.

(5) The mixer starts running When the powder material has completely fallen into the mixer through the pipeline. After a certain amount of time, the cylinder of the mixer starts working, opening the discharge valve and sending the evenly mixed material to the next section.

Figure 2.2: Schematic Diagram of Weighing and Mixing Mechanism

2.2.2 Granulation Section Design

The granulation section is the third step in the production line. Its specific working process is as follows: The powdered material is weighed and mixed according to the given proportion. Then, it is transported to the feeding port through mechanisms such as a feeder, electronic scale, pallet, and conveyor belt. The material enters the granulating pan through the feeding equipment. A signal activates the motor and starts working at the predetermined speed. At the same time, the spraying system is activated to perform the granulation spraying process. The granulation process is monitored remotely by a camera. After the granulation is completed, the discharge and lifting platform cylinders work together to pour the finished granules into the residual material recovery equipment. The residual material recovery equipment separates the granules that meet the required particle size and those that do not, along with the remaining powder. The remaining material and the granules that do not meet the requirements slide into the recovery bin, while the granules that meet the requirements roll into the pallet and proceed to the stacking process. Figure 2.3 illustrates the working process of granulation.

Figure 2.3: Granulation Diagram

Mechanism of Powder Granulation:

(1) Formation of Nuclei: The powdered material rotates in the inclined disc of the granulator. When the spray gun injects atomized slurry, the material becomes wetted. Initially, the amount of slurry sprayed is small, and the gaps between the powdered material are not completely filled. Air acts as a continuous phase, while the powdered material is interconnected through the slurry’s surface tension, forming small particles. As the amount of slurry increases and completely fills the gaps between the particles, the capillary effect and liquid bridging lead to the aggregation of the small particles, forming granules [43].

(2) Increase in particle size. After the formation of the nucleus, the atomized slurry is continuously sprayed, and the powder material adheres to the nucleus without increasing the particle diameter. At the same time, under the action of frictional force, the particles rotate with the rotating disc. During this movement, the particles rub against each other, and the irregular edges and corners on the particle surface are gradually smoothed by the frictional force, gradually forming spherical particles. It is the main process of granule growth and the most crucial step in the granulation process.

(3) Polishing and drying. After the powder supply and liquid spraying are completed, the disc continues to rotate. Under the action of centrifugal force and frictional force, the particle surface is further polished and dried, resulting in a smooth surface, high sphericity, and certain mechanical strength of the granules [44].

Working principle of discharge: When the granulation is completed, a signal is sent from the timer relay to the motor, discharge cylinder, and support cylinder. The main machine stops, and the discharge and support cylinders operate at the set speed. They work together to pour the granules into the recovery equipment. When they reach the specified position, a sensor is triggered, and the sensor sends a stop command. The discharge stops, and the next cycle begins.

2.2.3 Stacking Design

Stacking refers to the process of placing items together using the concept of integrated unitization and stacking them in a certain way. It is beneficial for implementing various logistics operations for handling materials [45].

Stacking is a technology in the field of logistics automation that has experienced rapid development in recent years. Firstly, with the increase in production scale and improvement in production capacity of enterprises, there is a continuous demand for increased stacking efficiency, leading to the development of high-speed stacking. Secondly, in the process of product flow from the selling market to the buying market, enterprises are increasingly moving towards a multi-variety and small-batch production approach, employing flexible production to achieve the production of multiple products on the same line. Consequently, this requires the stacking process to have the ability to handle multiple product types. Additionally, with the emergence of large-scale wholesale distribution centers, there is a need for individualized distribution for different customers, necessitating stacking machines with a wide range of stacking capabilities and strong mixed stacking abilities. Under these circumstances, stacking robots have been provided with excellent development opportunities. Nowadays, the market offers a wide variety of stacking equipment with high levels of automation and flexibility [46]. Automatic stacking equipment can be divided into stacking machines, palletizers, automatic palletizers, automatic stackers, stacking robots, and robots.

In this production line, the main processes performed by the stacking machine include: transporting pallet groups, supplying pallets, loading materials, transporting shelves, and stacking. The production of gunpowder is carried out in batches of 5 kilograms. According to the design requirements of the drying equipment, once the 5 kilograms of powder are granulated, they are placed in 4 trays. Therefore, a pallet group consists of 4 trays, and a shelf can accommodate 4 pallet groups. The shelves are then placed in the drying chamber to complete manufacturing.

Working principle of the stacking system:

The entire stacking system consists of 6 components: Conveyor 1, Feeder, Conveyor 2, Stacking machine, Conveyor 3, and Conveyor 4, as shown in Figure 2.4. The specific functions of each part are as follows: Conveyor 1 places the tray group on it and supplies the tray group to the Feeder. The Feeder receives the trays from Conveyor 1 and supplies them individually to Conveyor 2. Conveyor 2 receives the trays from the Feeder and simultaneously completes the stacking of the tablets on the conveyor. Conveyor 3 transports the shelves to the Stacking machine. The Stacking machine receives the shelves and stacks the trays layer by layer from Conveyor 2. Conveyor 4 transports the stacked shelves to the drying oven for drying. The design of the conveyors can be based on the requirements specified in the design manual, so the main design work lies in the Feeder and the Stacking machine.

Figure 2.4: Diagram of the Stacking System

2.2.4 Design of Drying and Unloading Sections

The drying and unloading system consists of two parts: the drying and unloading sections. The drying section is responsible for conveying the racks and drying the materials on the pallets, with trays placed on the racks. Similarly, the unloading section can also convey the racks, and the unloading equipment pours the materials from the top into a collection box, completing the unloading process [47]. The system structure is shown in Figure 2.5.

The specific workflow is as follows: after the pharmaceutical granules are placed in the pallet, they are stacked in the stacking section and placed on the racks. Then the racks are conveyed to the drying section, where the control system controls the motor to operate the conveyor belt, driving the movement of the racks. The drying machine system consists of three drying chambers, with the temperature of the first chamber set at 45 degrees, the second chamber at 60 degrees, and the third chamber at 45 degrees. The racks are sequentially dried for 10 minutes in each chamber to complete the drying of the granules. Afterward, the racks enter the unloading process, where the cylinder in the unloading section tilts the racks to complete the unloading. Once the unloading is done, the racks are conveyed back to the stacking section for reloading.

Figure 2.5: Schematic Diagram of Drying and Unloading Operation

1.   Drying System Operation Principle: The drying process utilizes a combination of far-infrared radiation and hot air to dry the fireworks particles. Far-infrared radiation is mainly used for drying, while hot air is a supplementary method. When the far-infrared electric heating plate in the drying chamber is powered on, it begins to heat up. As the surface temperature of the far-infrared electric heating film rises to a certain level, it emits far-infrared radiation. The far-infrared radiation is absorbed by the particles in the tray, intensifying the molecular movement within the particles. As a result, the temperature inside and outside the particles rises uniformly, facilitating the drying process. Simultaneously, an axial flow fan supplies air volume to the drying chamber, generating hot air to dry the particles. With the assistance of the axial flow fan, the inlet and outlet ducts form a circulation ventilation system, ensuring more even heating of the particles and effectively collecting dust inside the drying chamber. This system helps prevent safety accidents and capable of dust recycling.

The drying process adopts a PID temperature control system, allowing for temperature setting and automatic adjustment. By regulating the power of the far-infrared electric heating plate, temperature requirements ranging from room temperature to 150 degrees can be met. An emergency stop switch is installed on the drying chamber, ensuring safety during operation by pressing the switch in case of an emergency.

1.   Working Principle of Unloading System: When the conveyor delivers the shelf to the unloading system, the front, and rear cylinder systems push the unloading rack to the position where it clamps the shelf to prevent it from flipping. Then, the up-and-down cylinder systems lift the unloading conveyor and the shelf. The edges of the pallet have an inclined angle that meets the unloading requirements of the materials at a certain angle. After detecting that the materials have been unloaded, the up and down front and rear cylinder systems return to their original positions sequentially. Then, the conveyor transports the shelf to the next stage.

2.   Design Considerations: (1) The first thing to consider during the drying process is safety. Safety is the primary guarantee throughout the entire design process of the fireworks production line. Therefore, explosion-proof motors should be used in the design, and all wires should be sealed to prevent contact with powder and fine particles. Additionally, the external surface temperature of all components in the system should not exceed 80℃. Finally, the system should be equipped with an alarm equipment. (2) The second issue is ensuring sealing. To reduce heat loss during the drying of the granules in the drying box, in addition to using insulation materials, attention should be paid to the sealing of the front and rear “doors” when the shelf enters the drying box. (3) Ensure all parts are in place using sensors for detection and control systems to reach the specified positions. (4) For the unloading part, complete unloading should be ensured. It can be achieved by either determining the maximum unloading time through experiments and setting it in the control system or by capturing images of the pallet using a camera and comparing them with the images of the pallet without any granules to ensure complete unloading.

Chapter 2 Summary

This chapter mainly covers the following key points:

(1) Introducing the working process of the automated fireworks production line and the problems encountered during the production process.

(2) Briefly explain the working principles of various production line parts, including the weighing and mixing, granulation, stacking, drying, and unloading parts.

Chapter 3: Design of Drying and Unloading System

3.1 Composition of Drying and Unloading System

The drying and unloading system consists of two parts: the drying and unloading parts. The drying part is responsible for conveying the racks and the materials in the trays placed on the racks. The unloading part also has the function of conveying the racks. When the rack reaches the unloading position, the unloading equipment dumps the materials on top into a collection box, completing the unloading process. Finally, the rack is transported to the stacking section for reloading. The structure is shown in Figure 3.1.

Figure 3.1: Drying and Unloading System Structure

3.2 Drying System Design

The drying system consists of a drying chamber, a drying conveyor, and a drying air pressure transmission system. The drying chamber is designed to be placed above the belt conveyor, with three evenly spaced drying chambers one width apart. The control of the air pressure transmission system ensures that the racks are precisely positioned inside the drying chamber during drying.

The working principle of the drying system is as follows: heat is provided by two far-infrared electric heating plates located at the left and right ends of the drying chamber. Heat radiation is used to achieve the purpose of drying the materials. An axial flow fan provides a certain amount of airflow to ensure uniform heating of the materials in the trays. A dust collector is installed on the side of the middle drying chamber, connected to the inlet and outlet ducts, to collect dust generated during the drying process and prevent safety issues caused by dust scattering.

In the beginning, the stacking system from the previous process sends the rack to a fixed position on the left side of the conveyor, one drying chamber width away from the first drying chamber, after the rack has been dried in the preceding drying chamber for 10 minutes (one cycle), the cylinder and baffle located at the front end of the drying chamber rise, and then the conveyor drives the rack to the next drying chamber. The baffle lowers again to block the rack from entering the drying chamber. The front and rear plates of the rack seal the drying chamber, acting as a “door.” After the drying time elapses, the rack proceeds to the next drying chamber and continues this process until it has been dried in all three drying chambers, signaling the end of the drying process.

The temperatures inside the three drying chambers from left to right are 45℃, 60℃, and 45℃, respectively. The temperature decreases from low to high and then back to low. The purpose of this design is to prevent excessive temperature at the beginning, which would result in a large temperature difference between the surface and the interior of the material. Such temperature difference would reduce the evaporation of moisture inside the material and affect the drying effect later on. To maintain continuous moisture evaporation, it is necessary to establish a certain humidity and temperature difference on the material’s surface. In general, segmented drying can evaporate the moisture in the material faster and achieve better drying results.

3.2.1 Design of the drying chamber

The drying chamber has two layers: an outer steel plate and an inner layer of aluminum silicate insulation board, which helps reduce heat loss. Each side of the chamber is equipped with a far-infrared electric heating plate. A dust collector is installed on the top of the middle drying chamber. With the assistance of an axial flow fan, a closed ventilation circulation system is formed through the air inlet and outlet pipes connected to the drying chamber. When the axial flow fan operates, the air moves downward on both sides of the drying chamber. The side baffles have evenly spaced air holes (limited), allowing air to enter the drying chamber through these holes. The air then flows upward and forms a ventilation circulation through the outlet pipe, ensuring more even drying of the material. The following two figures (Figure 3.2 and Figure 3.3) depict the drying chamber system’s structural diagram and working schematic, respectively.

Figure 3.2: Drying Box System Structure

Figure 3.3: Schematic Diagram of the Drying Chamber

1.   Far-Infrared Electric Heating Plate

The far-infrared electric heating plate designed in this project consists of a front cover, a far-infrared electric heating film, an alumina silicate fiber insulation plate, a rear cover, and electrodes, as shown in Figure 3.4. The electrode terminals of the electric heating plate are connected to the control system through high-temperature resistant wires, allowing the power of the electric heating plate to be adjusted to set the temperature inside the three drying chambers and maintain temperature balance. When the power is turned on, the far-infrared film emits far-infrared rays, which dry the materials on the tray.

Figure 3.4: Composition of Far-Infrared Electric Heating Plate

The selected far-infrared electric heating film used in the design belongs to a low-temperature radiation film. It is a semi-transparent polyester film that can generate heat when powered on. It is a special heating product made by printing and hot pressing a conductive special ink and metal current-carrying bars between two layers of the insulated polyester film [4 8]. The surface temperature of the powered electric heating film does not exceed 60℃, with good temperature uniformity. It also has functions such as flame retardancy, insulation, waterproofing, and moisture resistance. Its thickness is only a few millimeters; specific parameters are shown in Table 3.1.

Table 3.1: Parameters of Far-Infrared Electric Heating Film

In addition, the far-infrared electric heating film has the following advantages:

(1) High safety: The electric heating film has passed CE safety certification and will not experience leakage. It also uses a waterproof design and can withstand immersion in water and other liquids without any issues.

(2) Energy-saving: The electric heating film can quickly convert electrical energy into radiant energy, achieving thermal equilibrium between the heating element and the insulation material in just a few minutes.

(3) Long service life: The performance of the electric heating polyester film is highly stable. Aging only occurs under sustained high temperatures. When the electric heating film operates normally, its surface temperature does not exceed 60 degrees, well below the aging temperature. Therefore, it has a very long service life [49].

Based on the parameters of the electric heating film, two pieces of electric heating film are selected, with dimensions of 500x1250mm and 500x1250mm, respectively. The total area is 1.25 square meters, and the total power is 350 watts.

The dimensions of the two electric heating panels are designed to be 560x1310x40mm and 560x1310x40mm, respectively. The installed structure of the electric heating panels, as shown in Figure 3.5, is 800mm between the left and right panels.

Figure 3.5: Far Infrared Electric Heating Plate

2. Axial Flow Fan

For safety reasons, the BT35 explosion-proof axial flow fan is selected. This model is mainly used in factories, warehouses, offices, residences, and other places for heating, heat dissipation, and ventilation. If the ventilation ducts are installed in series with spacing, it can enhance the wind pressure in the ducts [50].

The BT35 explosion-proof axial flow fan uses explosion-proof motors and explosion-proof switches. Wire connections are not allowed in explosive areas, so keeping them away from explosive points is best. It is mainly used for discharging flammable and explosive gases. The structural dimensions are shown in Figure 3.6 and Table 3.2, and the performance of the axial flow fan is shown in Table 3.3.

Figure 3.6: Structure Diagram of Axial Flow Fan

Table 3.2: Dimension Table for BT35 № 2.8 Axial Flow Fan

Table 3.3: Performance Table for BT35 № 2.8 Axial Flow Fan

3. Dust Collector

The dust collector is generally installed at the exhaust outlet of the air supply or raw material system to prevent dust from entering the atmosphere, playing a role in recycling and environmental protection. The dust collector is divided into single-stage collision type, multi-stage collision type, rotary type, and louver type. The louver type is used in this design, allowing the dust to be collected and reused in the dust collector. The front cover of the dust collector can be opened to remove the dust when it is full. The working principle is as follows: when the air containing dust enters the dust collector through the exhaust pipe from the drying box, the cone-shaped filter on the dust collector allows the air to pass through and re-enter the drying box through the inlet pipe.

In contrast, the dust cannot pass through the filter and flows into the dust collector from the lower end of the filter. The drain hole is used to remove water droplets formed by hot air. The total amount of dust recovered is 16.6kg, which exceeds the required 15kg. Figure 3.7 shows the basic types of dust collectors. The structure of the dust collector is shown in Figure 3.8.

Figure 3.7: Dust Collector Types

Figure 3.8: Dust Collector Structure

4. Calculation of Installation Power for Drying Chamber

The following formula calculates the total heat loss of the drying chamber: Q = Qh1 + Qh2 + Qh3 [51];

Where: Qh1 – Heat loss through the outer wall of the drying chamber (in kJ/h);

Qh2 – Heat loss from the heated goods (medicine particles, pallets, and shelves) (in kJ/h);

Qh3 – Heat loss from the door opening process and gaps (in kJ/h);

(1) Calculation of heat loss through the outer wall of the drying chamber:

Q = Σ(Ai Ki (t1 – t2)) = Σ(3 5.328 0.71 (60 – 25)) = 3 132.4 = 397.2 kJ/h;

Ai – Surface area of the i-th outer wall of the drying chamber (in m^2);

Ki – Heat transfer coefficient of the i-th outer wall (in W/(m^2·K));

t1 – Workshop temperature (in °C);

t2 – Operating temperature of the drying chamber (in °C);

Where:

A1 = 0.71 m^2, K1 = 0.04 W/(m^2·K), δ1 = 0.034 m, λ1 = 0.23 W/(m·K);

A2 = 0.71 m^2, K2 = 0.04 W/(m^2·K), δ2 = 0.034 m, λ2 = 0.23 W/(m·K);

(2) Calculation of heat loss from the heated goods:

Qh2 = [(m1 c1 (t2 – t3)) + (m2 c2 (t2 – t3)) + (m3 c3 (t2 – t3))] / 3

= [(30 1.4 (12 – 1.7)) + (45 0.46 (57.5 – 0.9))] / (45 – 25)

= (1798 + 674.25) / 20

= 2472.25 kJ/h;

m1 – Weight of medicine particles (in kg);

m2 – Weight of pallets (in kg);

m3 – Weight of steel plates on shelves (in kg);

c1, c2, c3 – Specific heat capacities of the respective materials;

t3 – Initial temperature of the heated goods (in °C).

Please note that the translation aims to accurately convey the content without adding additional information.

m4 – Weight of the aluminum silicate fiber insulation board on the shelf (/) kg h; 1

c – Specific heat capacity of the granules [/ (.)] kJ kg K; 2

c – Specific heat capacity of the pallet [/ (.)] kJ kg K; 3

c – Specific heat capacity of the steel plate on the shelf [/ (.)] kJ kg K; 4

c – Specific heat capacity of the aluminum silicate fiber insulation board on the shelf [/ (.)] kJ kg K;

(3) Calculation of heat loss through open doors and gaps

Q = 0.15Q + 0.15 397.2 60 (/) h h^3 = kJ h;

Finally, the total heat loss is calculated as: 1 2 3 397.2 2472.25 60 = 2929.45

Installed power for each drying box:

1 1 2929.45 301.4 = 3 3600 3 3600*0.9

η – Radiator conversion efficiency;

The calculated required installed power for the drying box is 301.4W, while the total power of the designed far-infrared electric heating plate is 350W. Since the power of the electric heating plate is adjustable, it can fully meet the needs of drying materials.

3.2.2 Design of the drying conveyor

Due to the width of the “door” of the drying box being 500mm, considering the sealing performance, the conveyor’s belt width is 650mm. The available options for the conveyor are QD80 lightweight belt conveyor, TD75 general-purpose belt conveyor, DTⅡ fixed belt conveyor, and U-shaped belt conveyor. Considering the advantages of the QD80 lightweight belt conveyor, such as its lightweight, small size, low cost, and low power consumption, it is designed as a general-purpose fixed continuous conveyor for sectors such as the chemical industry, light industry, food, grain, and postal services. It can convey various bulk materials and items. Therefore, QD80 lightweight belt conveyor is selected as the basis for improvement in this design [52]. Figure 3.9 shows a schematic diagram of the QD80 lightweight belt conveyor.

Figure 3.9: Schematic diagram of QD80 light-duty belt conveyor.

1.   Application Range and Selection of Conveyors

(1) QD80 light-duty belt conveyors are universal fixed continuous conveying machinery designed for sectors such as chemical, light industry, food, grain, and postal services. They can convey various bulk materials and finished items.

(2) QD80 light-duty belt conveyors have seven belt widths available: 300mm, 400mm, 500mm, 650mm, 800mm, 1000mm, and 1200mm. They can meet the requirements of general transport production lines. Here, we will choose the 650mm width.

(3) QD80 light-duty belt conveyors can work continuously under conditions ranging from -15°C to 40°C. They can also meet special requirements such as acid resistance, alkali resistance, oil resistance, heat resistance, non-toxicity, and pollution prevention.

(4) The unit length load allowed for QD80 light-duty belt conveyors should be smaller than the specified requirements. The unit load for a 650mm width belt is found to be 300-400N/m, which meets the design requirements.

(5) After determining the conveyor load, the maximum conveying length of the conveyor should be determined based on the allowable torque [M] (N.m) of the drive drum.

(6) QD80 light-duty belt conveyors have five basic layout forms, as shown in Figure 3.10. Here, we will choose the horizontal layout.

Figure 3.10: Basic Layout Forms

(7) There are two types of conveyors: flat (B = 300-1200mm) and trough (B = 300-1200mm). They are respectively suitable for conveying fabricated items and bulk materials, and the corresponding support rods are flat and trough-shaped. We will use a flat conveyor since we need to convey fabricated items, and the cross-section shape is shown in Figure 3.11.

Figure 3.11: Conveyor Cross-Section Form

(8) The peak point of the horizontal conveyor belt from the ground can be either 500mm or 800mm and here we choose 800mm.

(9) The maximum allowable inclination angle β of the conveyor depends on the nature of the material being transported, and here we initially use 0°.

1.   Component Selection Instructions

(1) Conveyor Belt

Due to the risk of explosion and fire in the work area, a PVC solid-core flame-retardant conveyor belt is selected here. The solid-core flame-retardant conveyor belt has high strength, large capacity, and smooth transportation. It is made from a solid core impregnated, plasticized, or vulcanized with polyvinyl chloride. This product has good flame resistance, anti-static, impact resistance, wear resistance, and corrosion resistance properties. It is commonly used in coal mining enterprises [53].

(2) Drive Device

The QDF series air-cooled explosion-proof electric drum, QD80 light-duty belt conveyor’s drive equipment, is selected. The electric drum has the advantages of a compact structure, lightweight, easy arrangement, and safe operation. Users widely appreciate it. The available power options are 0.55kW, 0.75kW, 1.1kW, 1.5kW, 2.2kW, 3.0kW, 4.0kW, 5.5kW, and 7.5kW.

(3) Transmission Drum

1.   The transmission drum in this series is a steel plate welded structure and uses roller bearings.

2.   The drum can be divided into smooth, rubber-coated, and cast rubber drums. In cases where the power is not high, and the environmental temperature is low, a smooth drum is mostly used. A rubber-coated drum should be used for humid environments and higher power requirements. The cast rubber drum has the best quality, with a thick and wear-resistant rubber layer, so we choose the cast rubber drum [54].

3.   After consulting the standard belt width of the transmission drum, we choose a diameter of 240mm.

4.   The allowable torque for the transmission drum is 1000[M]/N.m. The specific dimensions are shown in Figure 3.12.

Figure 3.12: Dimensions of the Transmission Drum

(4) Reversing Drum

The reversing drum of the conveyor belt is divided into three types: 180 degrees, 90 degrees, and less than 45 degrees. Here, the 180-degree reversing drum is selected, and the specific dimensions are shown in Figure 3.13.

Figure 3.13: Dimensions of Reversed Drum Structure

(5) Idler Roller

The idler roller is divided into upper idler rollers and lower idler rollers. The upper idler rollers are available in flat and trough shapes, while the lower idler rollers are all flat idler rollers.

Only flat upper idler rollers with a diameter of 60mm and a spacing of 250mm are selected here. The specific dimensions are shown in Figure 3.14.

Figure 3.14: Roller Structure Dimensions

(6) Tensioning Device

1.   This series is equipped with four types of tensioning devices: rear spiral tensioning, right-angle tensioning, middle spiral tensioning, and middle vertical tensioning, to meet the requirements of various conveyor layouts.

2.   The rear spiral tensioning equipment has two stroke options: 500mm and 800mm. It is selected as 1% of the conveyor length and is suitable for conveyors with a length of 80m.

3.   The right-angle tensioning equipment vertically installs the spiral tensioning device on the right-angle tail frame, with a stroke S=200mm. It is suitable for light-load conveyors with less than 20m in length.

4.   The middle spiral tensioning device vertically installs the spiral tensioning equipment on the middle frame, with a stroke S=300mm. It is suitable for light-load conveyors with a belt high point (h) above 800mm and less than 30m long.

5.   The middle heavy hammer tensioning equipment has a stroke greater than 500mm and is suitable for conveyors with a length greater than 50m.

We have chosen the middle spiral tensioning device here because it makes the previous process of conveying more convenient. The specific dimensions are shown in Figure 3.15.

Figure 3.15: Tightening Structural Device Dimensions

3. Design Calculation

(1) Original Data

1.   Name of material and maximum conveying capacity Q (t/h) or n (pieces/h);

2.   Layout form and main dimensions of the conveyor;

3.   Number and location of feeding points and discharge points;

4.   Working environment: indoor, dry, clean;

5.   Special requirements for the conveyed material: dust-free, anti-static, etc.

(2) Selection of Conveyor Belt Speed

The belt speed v is generally set to 0.25 m/s when conveying individual items.

(3) Calculation of Conveyor Belt Width

For individual items, the belt width B should generally be 50-100 mm larger than the transverse dimension of the conveyed item. However, for large items with a low center of gravity (such as tires), the belt width B can be equal to or smaller than the transverse dimension of the item, and the selected width must meet the specified allowable load of 300-400 [q] / (N/m).

(4) Calculation of Conveying Capacity

The conveying capacity of individual items is calculated using Equation 1:

Q = (3600n) / (bvkT) + 3QnG/10^3,

where:

n – maximum conveying capacity, pieces/h;

Q – maximum conveying capacity, t/h;

T – clearance limited space of the item on the conveyor belt, m;

b – length of the item along the conveying direction, m;

k1 – loading coefficient, generally set to k1 = 0.5-0.9;

G – mass of a single item, kg.

According to the measurements of the conveyor and shelf dimensions, T = 700mm, b = 700mm, v = 0.25m/s, and k1 = 0.5, the calculated values are n = 321 pieces/h and Q = 46.4t/h, which are much higher than the actual conveying rate of 6 pieces/h, meeting the requirements.

(5) Power Calculation

Calculation of Drive Drum Shaft Power

The power of the drive drum shaft, P0, is calculated using the following formula:

P0 = P1 + P2 + P3 + fWv + fQ + HQ + L + l

P0 – Power of the drive drum shaft (kW)

P1 – No-load power (kW)

P2 – Horizontal load power (kW)

P3 – Vertical load power (kW)

f – Roller resistance coefficient, f = 0.03

L – Horizontal center distance from the drive drum to the tail drum, measured as 6.1m

l0 – Center distance correction value (m), l0 = 49m

H – Vertical lifting high point, measured as 0.5m

1.   W – Sum of the masses of all moving components per unit length of the conveyor, obtained from the table as 30kg/m

Finally, P0 = 0.276kW

2. Motor Power Calculation

P = 1.1 0.276 (0.8 / K)

P – Motor power (kW)

P0 – Power of the drive drum shaft (kW)

η – Overall transmission efficiency, η = 0.8 for QDF-type air-cooled electric drums

K – Reserve factor, K = 1.1 when P0 is less than 5kW

The available power options for the QDF-type air-cooled electric drum are 0.55kW, 0.75kW, 1.1kW, 1.5kW, 2.2kW, 3.0kW, 4.0kW, 5.5kW, and 7.5kW. Therefore, the chosen power is 0.55kW.

3.2.3 Design of the Drying Air Pressure Transmission System

Due to the height of the “door” of the drying chamber is 1010mm, and in order to prevent the forward movement of the shelf, the stroke of the cylinder is chosen as 300mm. The cylinder selected for this design is an SMC series cylinder, model CM2C20, installed in the middle of the front side door of the drying chamber, with one cylinder above each. This arrangement ensures that the shelf is positioned exactly inside the drying chamber. In the design of the cylinder circuit panel, SY3000 electromagnetic valves are selected. Their standard specifications are shown in Tables 3.4 and 3.5.

In the arranged drying pneumatic pressure transmission system, magnetic switches are used to detect the position of the piston at the maximum and initial positions of the cylinder. A speed control valve controls the cylinder speed, and a two-position five-way valve is used for the cylinder’s directional control. There are solenoid valves at both ends of the directional control valve to control the flow of compressed gas. Figure 3.16 shows the schematic diagram of the arranged pneumatic circuit panel in the drying system.

3. Unloading System Design

The arranged unloading system consists of an unloading frame, material collector, unloading conveyor, and arranged pneumatic unloading system. Figure 3.17 shows the structure of the unloading system. The unloading frame includes an unloading plate and a track groove for the material to fall along when unloading. Thanks to the track groove, the loaded material falls into the unloading container smoothly and at a reduced speed, allowing it to be collected in the material collector.

The working principle of the arranged unloading system is as follows: After drying, the pallet rack is conveyed to the middle position of the drying and unloading conveyors. The left and right moving cylinders push the unloading frame to the rack position, securing it to prevent movement. Then, the up-and-down moving cylinders tilt the upper part of the conveyor and the rack. Due to the inclined angle designed on the edge of the tray, unloading begins when the up-and-down moving cylinders reach their maximum position. After the unloading is complete, the up and down and the left and right cylinders return to their initial positions. The unloading conveyor resumes operation to convey the rack to the stacking section, marking the end of the unloading process.

Figure 3.17: Unloading System Structure

3.3.1 Design of the Unloading Conveyor

The design process of the drying conveyor has been stated in detail earlier. Here, a brief explanation of the design of the unloading conveyor is provided. Since there is no need to consider the sealing of the arranged drying system, and only one shelf needs to be unloaded at a time, a special lightweight belt conveyor is selected. The belt width of the conveyor is 500mm. This conveyor has the characteristics of light load and low linear speed, suitable for continuous conveying of light load assembled items. The machine is arranged in a flat configuration.

The left end of the upper part of the unloading conveyor is connected to the conveyor base through a bearing, and the right end of the upper part is connected to the base through two cylinders, as shown in the schematic diagram in Figure 3.18. There are a total of three movable components and one translating pair, and three rotating pairs in this planar mechanism. Therefore, the degree of freedom of this mechanism is calculated as follows: 3 2 – 3 2 * (1 + 3) = 1. The mechanism’s motion is fully set on since only the piston rod moves as the driving component.

Figure 3.18: Schematic Diagram of Unloading System Mechanism

1.   Component Selection Instructions

(1) Conveyor Belt

The same PVC solid-core flame-retardant conveyor belt is selected, with a tensile strength of 680s.

(2) Drive Device

A especially lightweight air-cooled explosion-proof electric drum is selected as the drive device. The power rating is not specified.

(3) Transmission Drum

The transmission drum is a welded steel plate structure using roller bearings and a cast rubber drum. The drum diameter is 178mm, and the allowable torque of the transmission drum is 150 [M]/N.m. Specific dimensions are shown in Figure 3.19.

Figure 3.19: Dimension of Transmission Drum

(4) Reversing Drum

Here, a 180-degree reversing drum is chosen. The specific dimensions are shown in Figure 3.20.

Figure 3.20: Dimensions of the Modified Drum Structure

2. Design Calculation

(1) Selection of Conveyor Belt Speed

The belt speed is generally set when conveying assembled items as v = 0.25m/s.

(2) Calculation of Conveying Capacity

The maximum conveying capacity for assembled items is n = 642 pieces/h, Q = 23.2t/h, which is much higher than the actual conveying capacity of 6 pieces/h, meeting the requirements.

(3) Power Calculation

Calculation of Power for Drive Drum Shaft

The power of the drive drum shaft, P0, is calculated using the following equation:

P0 = L + l + P + fWv + fQ,

where:

1.   L, l, P, fWv, and fQ are numerical values.

Finally, the calculated value for P0 is 0.098 kW.

Calculation of Motor Power

To calculate the motor power, use the equation:

P = 1.1 * 0.098 / 0.8,

where:

P is the motor power in kW,

0.8 is the numerical value, and

1.   1.1 * 0.098 represents the multiplication of the given values.

Therefore, the motor power, P, is 0.135 kW.

3.3.2 Unloading Pneumatic Transmission System Design

The cylinders required to be installed in the arranged unloading system are the left-right and up-down moving cylinders. We will use the SMC series cylinders, specifically the CM2C20 and CJ2L16 models. Two of each model will be installed, with one set mounted on the base of the unloading conveyor and the other set positioned at the edge of the conveyor. These cylinders will be used for unloading purposes, and their standard specifications are shown in Table 3.6. Figure 3.21 depicts the schematic diagram of the pneumatic circuit for the unloading system.

Figure 3.21: Schematic diagram of the pneumatic circuit of the unloading system

3.4 Design of the shelf pallet

1.   Calculation of pallet dimensions

When black powder ignites, the following chemical reaction occurs 2KNO3 + S + 3C = K2S + N2↑ + 3CO2↑.

From the reaction equation, their respective proportions are potassium nitrate 75%, sulfur 10%, and charcoal 15%.

Density data obtained: potassium nitrate ρ1 (2.109 g/cm3), sulfur ρ2 (2.0 g/cm3), charcoal ρ3 (0.4 g/cm3).

The theoretical density calculation formula for black powder can be derived as follows:

Due to the addition of luminescent agents, colorants, adhesives, etc., the density of the tablets varies with different compositions. The actual density cannot be decided. According to the literature, the density of the tablets is ≥ 1.2 g/cm3, and the minimum value of 1.2 g/cm3 is used for calculations. In this design, the total weight of gunpowder used each time is 5 kg, and the calculated volume V = m/ρ = 4.17×106 mm3. Each granule has a diameter of 10 mm and a radius of 5 mm, with a volume of 4/3πR3 = 523.4 mm3. Therefore, the total number of granules is 7967, rounded to 8000.

Four trays are used, each containing 2000 granules. Considering the dimensions of the drying box’s dimensions, each tray’s dimensions accommodate 44×52 = 2288 granules, with a length and width of 440×520 mm. Considering the margins, a dimension of 460×540 mm is used, with margins of 10×10 mm. It allows a total of 2288×4 = 9152 granules to be accommodated, exceeding the required amount by 15%.

Figure 3.22 shows that the tray’s depth should be less than the height of the granules above it to scrape off the granules on top. Therefore, the height should be less than 12.07 mm, and a value of 12 mm is chosen. Figure 3.23 shows the designed tray.

Figure 3.22: Tray Depth Calculation

Figure 3.23: Tray

1.   Calculation of Tray Edge Angle

To facilitate cleaner unloading, a certain incline angle is designed at the edge of the tray. δ represents the incline angle of the tray’s edge plate. As shown in Figure 3.24, which illustrates the operation of the unloading mechanism, the calculation process of δ is as follows:

Figure 3.24: Schematic of Unloading Mechanism

(1) The requirement that δ should satisfy is: δ ≤ β – φ

Where: φ – Maximum rolling friction angle of the material (known);

β – Tilt angle of the rack;

(2) Solving for β based on the diagram, we have: β = γ – α

In a right-angled triangle, tanα = L/B, α = arctan (L/B):

Where L is – Length of the piston rod, S – Cylinder stroke, B – Width of the conveyor;

1.   Calculation of Shelf Dimensions

The shelf is used to place pallets. Since there are 4 pallets, the shelf is also designed with 4 levels. The spacing between each level is 150mm. There are 6 rollers on each level, with 3 on each side, evenly placed. It facilitates the stacking of pallets by making pushing them onto the shelf easier. The shelf structure consists of two layers: the outer layer is made of a steel plate, and the inner layer is made of an alumina silicate fiber insulation board. It reduces heat loss when the shelf enters the drying oven. The specific dimensions of the shelf and the assembly diagram of the shelf and pallet are shown in Figure 3.25 and Figure 3.26.

Figure 3.25: Dimensions of the Shelf Structure

Figure 3.26: Assembly Diagram of the Shelf and Pallet

3.5 Summary of this chapter

This chapter mainly covers the following aspects:

(1) Design of the drying system, including the structural design of the drying box and drying conveyor, design of the drying air pressure transmission system, and calculation of the installation power of the drying box.

(2) Design of the unloading system, including the structural design of the unloading conveyor and the unloading air pressure transmission system design.

(3) Design of the shelf pallet, including calculation of the pallet dimensions and structural design of the shelf and pallet.

Chapter 4: Control Design of Drying and Discharging System

4.1 System Scheme Design

4.1.1 Process Overview

Figure 4.1: Schematic diagram of the drying and unloading action.

The process of the drying and unloading system studied in this project includes three routes:

(1) Drying route: Drying time reached – Conveyor 1 transportation – Shelf enters the drying chamber for drying.

The specific process is as follows: When the drying time is reached, cylinders 1-1, 1-2, and 1-3 on the drying chamber start to rise to their initial positions. Then, the motor of Conveyor 1 starts running, conveying the shelf. When the shelf leaves the drying chamber, a position sensor sends a signal, and cylinders 1-1, 1-2, and 1-3 start descending to their maximum positions. When the shelf reaches the next drying chamber, a position sensor sends a signal, the motor stops running, and drying begins. The drying time is 10 minutes, and the above actions are repeated in a cycle after the drying time is reached.

(2) Unloading route: Drying time reached – Conveyor 1 and 2 transportation – Shelf arrives at the unloading position for unloading.

The specific process is as follows: When the drying time is reached, Conveyor 1 and 2 motors start running, conveying the dried shelf. When a position sensor detects that the shelf has reached the unloading position, the motor of Conveyor 2 stops, and the stopping of Conveyor 1 is controlled by the drying process building. Cylinders 3-1 and 3-2 on the unloading device start moving to the right to their initial positions, clamping the shelf to prevent its movement. Then, cylinders 2-1 and 2-2 on Conveyor 2 start rising to specified positions to tilt the upper part of Conveyor 2 and the shelf, initiating unloading. When the unloading time is reached, cylinders 2-1 and 2-2 start descending to their initial positions, followed by cylinders 3-1 and 3-2 moving to the left to their maximum positions for unloading reset. The motor of Conveyor 2 starts running again, transporting the shelf to the next stage. After the shelf leaves, the motor stops running, and the cycle repeats when the drying time is reached.

(3) Temperature Control Route: Capable of detecting temperature rise/fall inside the box – regulate electric heating plate – return panel to set temperature.

During the control process, the cylinder is controlled by corresponding capable solenoid valves. The rise/fall and left/right movements are controlled by dual-coil two-position capable solenoid valves. There are 4 position sensors, with 3 at the exits of three drying boxes and 1 at the front end of the unloading device. The temperature sensor is located inside the drying box to measure the temperature, and the internal temperature is maintained by adjusting the power level.

4.1.2 Control Requirements

The drying and unloading process adopts a PLC capable control system, which uses software programs to achieve automatic control between the capable control devices, and the mechanical devices driven by the control devices complete the required production process. The characteristics of PLC are (1) high reliability and strong anti-interference ability; (2) complete matching, comprehensive functions, and strong applicability; (3) small design scope and construction workload, convenient maintenance, and easy modification; (4) small size, lightweight, and low energy consumption [55].

In addition to stable operation and low failure rate, the PLC in this system should have the following functions:

(1) Manual and Automatic Operation

Manual operation is mainly used for debugging and maintenance of equipment. Pressing the start/stop button can activate the conveyor motor. Automatic operation is primarily used during normal operation. Pressing the start button to continue, lets the system perform predefined actions periodically and automatically. If the stop button is pressed, the system will complete one cycle of actions and return to the starting point to stop automatically. In the event of a sudden power failure, the system will immediately shut down and automatically resume operation from the initial state once the power is restored. A selector switch on the upper computer controls the switch between manual and automatic operation [56].

(2) Fault Diagnosis

PLC has strong self-diagnostic capabilities. When there is a malfunction in the PLC itself or in peripheral devices, the diagnostic indicators, such as LEDs, on the PLC can be used to identify the issue [57].

(3) Display and Counting

The system detects the number of dried shelves on the conveyor belt and parameters such as the temperature inside the drying chamber using position sensors and temperature sensors installed on the drying chamber. These signals are transmitted to the PLC for processing and then displayed on the upper computer.

(4) Over Temperature Alarm

Due to the high production hazard of fireworks particles, the PLC control system must include an over-temperature alarm function. When the temperature sensor installed in the drying chamber detects a temperature exceeding 80°C, the system sends an over-temperature alarm signal.

4.1.3 System Structure Composition

The drying and unloading control system consists of input devices (operating switches, host computers, sensors, etc.), output devices (relays, contactors, signal indicator lights, and other executing components), and control objects driven by output devices (motors, solenoid valves, axial flow fans, cylinders, etc.) [58]. Figure 4.2 shows the structure diagram of the drying and unloading control system.

4.2 System Hardware Design

4.2.1 Electrical Schematic Design

Based on the requirements of the drying and unloading tool and its electrical control, an electrical control schematic diagram was designed, as shown in Figure 4.3.

Figure 4.3: Electrical Schematic Diagram of Drying and Unloading System

In the circuit, contactors KM1, KM2, KM3, KM4, KM5, and KM6, respectively, control conveyor motor 1, conveyor motor 2, axial flow motor, air compressor 1, air compressor 2, and air compressor 3. KM7 also controls conveyor motor 2. Thermal relays FR1, FR2, FR3, FR4, FR5, and FR6 provide overload protection, and fuses FU1, FU2, FU3, FU4, FU5, and FU6 respectively provide short circuit protection for each load circuit. QS1 is the main power switch, and QS2 is the power switch for the PLC.

4.2.2 PLC Control System Design

1.   PLC Selection

Due to the relatively simple nature of the drying and unloading control system, the S7-200 model from Siemens AG, Germany, is chosen for the PLC. It has a compact structure, offers a high cost-performance ratio, and is widely suitable for small-scale control systems. It is also highly reliable, has good expandability, provides rich communication commands, and features a simple communication protocol.

Based on the actual terminal requirements of the control system, the CPU226 module of the S7-200 PLC is selected. Its main technical parameters are shown in the following table:

Table 4.1: Main Technical Parameters of S7-200 PLC CPU

Through analysis of the control system’s control requirements, it is determined that it requires 35 digital input points, 29 digital output points, and an additional 7 analog input points. Therefore, the following expansion modules are needed: 1 EM223 digital input/output mixed module and 2 EM231 analog input modules. With these, the PLC will have 40 digital signal inputs, 32 digital signal outputs, and 8 analog input signals, which will meet the operational requirements. The main technical parameters of the expansion modules are shown in Table 4.2.

Table 4.2: S7-200 Series Expansion Modules

2.   PLC Input/Output Terminal Configuration

(1) PLC Digital Input/Output

The determination of the number of digital input and output points for the PLC is allocated based on the requirements of the control system, as shown in Table 4.3.

Table 4.3: PLC Digital Input/Output Point Allocation Schedule.

(2) Analog Inputs of PLC

The analog input ports of the control system PLC include the temperature signal detected by the temperature sensor in the box and the position signal detected by the position sensor. The allocation of analog input ports is shown in Table 4.4.

Table 4.4: Allocation table for PLC analog I/O points

3.   PLC Wiring Diagram for Input/Output

As mentioned above, the basic unit chosen is the S7-200 type CPU226. The expansion modules consist of 1 EM223 digital input/output mixed module and 2 EM231 analog input modules. Figures 4.4, 4.5, and 4.6 show the wiring diagrams for the CPU226, EM223, and EM231 modules, respectively.

Figure 4.4: CPU226 Input/Output Wiring Diagram

Figure 4.5: EM223 Input/Output Wiring Diagram

Figure 4.6: Wiring Diagram of EM231 Input/Output

4.2.3 Sensor Selection

1.   Temperature Sensor

The temperature sensor uses a resistance temperature detector (RTD) that operates based on the principle of the change in the resistance value of a conductor or semiconductor with temperature. This phenomenon is commonly known as the thermal resistance effect. Currently, RTDs are widely used to measure temperatures within the range of -200 to +800°C. The temperature sensor converts the detected temperature data into measurable temperature values, compares them with the set temperature, and controls the on/off state of the relay and the open/close state of the alarm system [59].

Specifically, the PT100 type temperature sensor is chosen, which uses contact measurement for temperature sensing. The PT100 temperature sensor can convert temperature variables into standardized output signals to measure and control industrial process temperature parameters. The PT100 temperature sensor typically consists of two parts: the sensor itself, a platinum resistance (Pt100), and the signal converter. The signal converter mainly consists of a measuring unit, a signal processing and conversion unit, and some converters may have a display unit and even fieldbus functionality. Figure 4.7 shows the curve of platinum resistance (Pt100) with respect to temperature variation, and the correspondence between Pt100 resistance and temperature is shown in Table 4.5.

Figure 4.7: Graph of Pt100 Platinum Resistance Variation with Temperature

Table 4.5: Correspondence between Pt100 Platinum Resistance Temperature and Resistance Value

2.   Position Sensor

The selected sensor for this application is a through-beam infrared sensor. Its operating principle is that an infrared transmitter and receiver are installed on opposite sides of the drying chamber exit. When there is no obstruction between them, the receiver can detect the infrared beams emitted by the transmitter. However, when an obstruction, such as a shelf, between the transmitter and receiver, the receiver cannot detect the infrared beams emitted by the transmitter [60]. Figure 4.8 shows a schematic diagram of a through-beam infrared sensor.

Figure 4.8: Schematic diagram of a through-beam infrared sensor operation

4.3 System Program Design

According to the control requirements, the overall control flowchart was designed as shown in Figure 4.9. After system startup, the user can select between two operating modes: automatic and manual. The automatic operation includes three parts: automatic unloading, automatic drying, temperature control, and alarm. Once the entire operation is completed, the system will stop running.

Figure 4.9: Overall control flowchart of the system

4.3.1: Program design for the drying control system

Control program compilation based on the analysis of the drying process:

(1) Start, initialize the program, and raise the cylinder to the maximum position.

(2) Start conveyor 1, transport the shelf to the specified position, and stop. When the shelf leaves the drying box during this process, the cylinder descends to its initial position.

(3) Dry the material. When the time is up, proceed to the next cycle.

Figure 4.10 below shows the flowchart of the drying control program. The ladder diagram can be found in Appendix A.

4.3.2 Unloading Control System Program Design

Based on the analysis of the unloading process, the control program is compiled as follows:

(1) Start the robot by initializing the program. Conveyor 2 starts and moves the conveyor rack to the specified position, then stops.

(2) Cylinder 3 series pushes the unloading frame to the rack position, then Cylinder 2 series rises to begin unloading.

(3) When unloading is complete, the unloading device resets, and Conveyor 2 transports the rack to the stacking section, then stop.

(4) Wait for the drying time in the drying section to elapse and enter the next loading loop.

Figure 4.11 below shows the flowchart of building the unloading control program. The ladder diagram can be found in Appendix B.

Figure 4.11: Unloading Control Flowchart

4.3.3 Temperature and Alarm Control System Program Design

The temperature control system mainly consists of the temperature control PID control section based on Siemens S7-200 PLC, temperature measurement section, temperature conversion section, relay output section, and power supply section. The structure of the temperature control system is shown in the following Figure 4.12.

Figure 4.12: Temperature Control System Structure Diagram

This system adopts PID temperature control. The PID temperature control system is a closed-loop system [61]. It uses the output of the PLC to control the heating of the electric heating plate in the drying box. The temperature sensor converts the current actual temperature of the thermistor into an electrical signal. The electrical signal returned by the temperature sensor is then converted into a digital quantity and sent to the CPU for calculation through the analog input terminal of the PLC. By programming the PLC to set the target temperature, the PID adjusts and controls the output of the PLC, gradually approaching the target temperature of the thermistor.

The principle of the PID closed-loop control system is shown in Figure 4.13. The difference (error) between the temperature set value and the temperature feedback value measured by the platinum resistor is processed through proportional P, integral I, and derivative D operations. The relay output signal is used to adjust the heating power of the electric heating plate, thereby maintaining a stable temperature inside the drying box.

Figure 4.13: Schematic diagram of the PID temperature control system.

Control program development based on the analysis of temperature control and alarm control processes:

(1) Start by initializing the program. The heating plate begins to heat, and the temperature sensor detects the temperature inside the drying chamber reaching 60℃. The heating is then stopped.

(2) If the temperature sensor detects a temperature below 60℃, the heating plate continues to heat; otherwise, heating is stopped.

(3) When the sensor detects a temperature higher than 80℃ inside the drying chamber, the system initiates an alarm, and all system actions are halted.

Figures 4.14 and 4.15, respectively, depict the flowcharts for temperature control and alarm control programs.

Figure 4.14: Temperature Control Program Flowchart

Figure 4.15: Alarm Control Program Flowchart

Chapter 4 Summary

This chapter mainly covers the following main aspects:

(1) Analyzed the process and control requirements of the drying and unloading control system.

(2) Designed the hardware of the control system, including the selection of PLC, the configuration of PLC input/output terminals, and the drawing of wiring diagrams, and finally, selected the sensors used in the system.

(3) Designed the control system’s software, including the program design of the drying control system, unloading control system, and temperature and alarm control system.

Chapter 5: Motion Simulation and Temperature Field Analysis of the Drying and Unloading System

5.1 Motion Simulation of the Drying and Unloading System

Pro/E is capable of simulating the motion of mechanisms, allowing for a visual representation of the moving process and working principles of the mechanisms. It is more intuitive than 2D views and significantly shortens mechanisms’ development and design time, saving costs and improving product quality [62].

After simulating the mechanism, animations and parameter tables can be generated. Through the results, it is possible to understand if there are interferences between the components and the extent of these interferences. Users can make corresponding modifications to the components based on the final results until no interferences occur. In the dynamics of the mechanism, electric motors can be used to generate the desired motion types for study. During the motion analysis, values such as position, velocity, acceleration, or force can be observed, recorded, or measured, and these values can be graphically represented. Trajectory curves and motion envelopes can also be building to describe the motion using physical methods.

1.   Work Process Analysis

The entire analysis process is divided into two stages: the movement of the shelf on the drying conveyor and the unloading of the shelf on the unloading conveyor. This process also includes the up and down movement of the drying box cylinder system and the rotation of the axial flow fan. The termination of the first stage marks the beginning of the second stage.

1.   Work Requirements

(1) The axial flow fan should be operational throughout the analysis.

(2) Other components should remain stationary while the shelf moves on the drying conveyor.

(3) Provide the time and speed parameters for each moving part.

(4) Convert the work process into a video file.

3. Connection Methods for Moving Components

Before selecting predefined sets of connections, it is necessary to know how to apply constraints and use degrees of freedom to define motion. Then, appropriate connections can be selected to achieve the desired motion of the mechanism. Each predefined set of connections is associated with specific degrees of freedom, with translational and rotational degrees of freedom used to specify the mechanism’s motion. Table 5.1 lists several types of connections and their degrees of freedom.

Table 5.1: Link Types and Their Degrees of Freedom

(1) Axial Flow Fan: The axial flow fan only rotates during operation, so the connection method is “pin.”

(2) Cylinder System: The cylinder rod moves linearly forward and backward, so the “sliding rod” connection is chosen.

(3) Rack: The rack moves both to the right and rotates throughout the entire operation, so “6DOF” is considered for better analysis during placement.

(4) Material: The material only falls along a fixed trajectory during the unloading process, so it is set to be connected by a “slot.”

4. Design Steps

Step 1: Open the assembly diagram of the drying and unloading system, and select the “Applications”/”Mechanisms” menu to enter the mechanism environment, as shown in Figure 5.1.

Figure 5.1: Design Step 1

Step 2: Check the assembly connection, and select the menu “Edit” / “Reconnect.” As shown in Figure 5.2.

Figure 5.2: Design Step 2

Step 3: Select the menu “Insert” / “Servo Motor” button to define the servo motor’s name, type, and profile.

As shown in Figure 5.3.

Figure 5.3: Design Step 3

Step 4: Select “Analysis” / “Mechanism Analysis” to define the name, type, preferences, and motor for the analysis definition.

As shown in Figure 5.4.

Figure 5.4: Design Step 4

5. Time and Speed Parameters

After the previous design steps, servo motors have been assigned to each moving component, and their speeds have been selected based on their respective strokes. The sequence of movement for each component and the corresponding time intervals have been determined by analyzing the working process. Please refer to Table 5.2 for specific time and speed parameters. The time and speed parameter curves for each moving component can be found in Figures 5.5, 5.6, 5.7, 5.8, 5.9, and 5.10.

Table 5.2: Time and Speed Parameters.

Figure 5.5: Time-Speed Curve of Axial Flow Fan Servo Motor

Figure 5.6: Time-Speed Curve of Shelf Servo Motor

Figure 5.7: Time-Speed Curve of Servo Motor for Pre and Post-Unloading Movement

Figure 5.8: Time-Speed Curve of Servo Motor for Up and Down Movement during Unloading

Figure 5.9: Time-Speed Curve of Servo Motor for Material Movement

Figure 5.10: Time-Speed Curve of Servo Motor for Drying Oven

5.2 Temperature Field Analysis in the Drying Oven

5.2.1 Introduction to ANSYS

ANSYS software, developed by ANSYS Inc. in the United States, is currently the fastest-growing CAE software in the world. It can be used for research in various disciplines, such as structural, thermal, acoustic, fluid, and electromagnetic fields. It has a wide range of applications in industries such as nuclear, railway, petrochemical, aerospace, mechanical manufacturing, energy, automotive, defense, electronics, civil engineering, shipbuilding, biomedicine, light industry, geology, water conservancy, and household appliances. It is a large-scale general-purpose analysis software [63]. ANSYS also provides powerful and user-friendly features, making it internationally the most popular finite element analysis software. The analysis types offered by ANSYS include: (1) Structural static analysis; (2) Structural dynamics analysis; (3) Structural nonlinear analysis; (4) Dynamics analysis; (5) Thermal analysis; (6) Electromagnetic field analysis; (7) Fluid dynamics analysis; (8) Acoustic field analysis; (9) Piezoelectric analysis.

5.2.2 Thermo-mechanical Finite Element Analysis of the Drying Oven

ANSYS thermal analysis calculates the temperature distribution and other thermal physical parameters of a system or component, such as heat gain or loss, thermal gradients, and heat flux density (heat flux). Thermal analysis plays an important role in many engineering applications, such as internal combustion engines, turbines, heat exchangers, piping systems, electronic components, forging, and casting. ANSYS thermal analysis is based on the energy conservation principle, using the finite element method to calculate the temperatures at various nodes and derive other thermal physical parameters [64].

ANSYS thermal analysis includes the following types: (1) Steady-state heat transfer: the temperature field of the system does not change with time; (2) Transient heat transfer: the temperature field of the system amendments significantly with time.

There are several modes of heat transfer: (1) Conduction: the exchange of energy between two objects in good contact or the internal energy exchange within an object due to temperature gradients; (2) Convection: the heat exchange that occurs between an object and its surrounding medium; (3) Radiation: the exchange of energy between one or two objects through electromagnetic waves.

The temperature transfer method in the drying box belongs to thermal radiation, so a thermal radiation analysis is required. Radiation is a way of transferring energy through electromagnetic waves. Electromagnetic waves propagate at the speed of light and do not require any medium. Thermal radiation is only a small portion of the electromagnetic spectrum. Since the heat flow caused by thermal radiation is directly proportional to the fourth power of the absolute temperature of the object’s surface, thermal radiation analysis is highly nonlinear. The following are the steps for thermodynamic analysis of the drying box:

1.   Problem description

Due to the thermal energy flow inside the drying box not varying with time, it is classified as steady-state heat transfer. The temperature and heat load of the system also do not vary with time, satisfying the first law of thermodynamics.

The CFD module of ANSYS is applied to analyze the thermal radiation of the fluid inside the drying box. The function of the CFD module is to analyze the flow field of two-dimensional and three-dimensional fluids. The cross-sectional dimensions of the drying box are shown in Figure 5-11, and the emissivity of each surface is 0.98. . One end of the drying boxes is selected for analysis, with a temperature of 60℃ or 140 degrees Fahrenheit. The analysis is conducted using the international unit system.

Figure 5.11: Drying Oven Cross-Section Model

2. Problem Analysis

The fluid inside the drying oven is laminar, so the temperature field analysis belongs to steady-state fluid analysis. ANSYS CFD module is used for finite element analysis of steady-state thermal radiation, with the FLUID141 element selected. As shown in Figure 5.12.

Figure 5.12: Steady-state thermal radiation unit types

3. GUI operation steps

(1) Define the analysis file name

Select Utility Menu > File > Change Jobname. In the dialog box that appears, enter “hongganxiang” and click OK.

(2) Define the unit type

Select Main Menu > Preprocessor > Element Type > Add/Edit/Delete. Click the ADD button in the dialog box, select FLOTRAN CFD, 2D FLOTRAN 141, 2D unit, and click OK.

(3) Create a geometric model

Select Main Menu > Preprocessor > Modeling > Create > Areas > Rectangle > By Dimensions. In the dialog box for X1, X2, Y1, and Y2, enter 0, 0.96, 0, 1.45 to create a 2D geometric model.

(4) Set the mesh density

Select Main Menu > Preprocessor > Meshing > Size Cntrls > ManualSize > Global > Size. In the NDIV box, enter 20 and click OK.

(5) Divide the mesh

Select Main Menu > Preprocessor > Meshing > Mesh > Areas > Mapped > 3 to 4-sided. Choose Pick All. Obtain Figure 5.13.

Figure 5.13: Mesh division

Figure 5.14: Applying velocity boundary conditions

(6) Applying boundary constraint conditions

Applying velocity boundary constraint conditions: Select Utility > Select Entities. In the dialog box that appears, choose Nodes, Exterior, From Full, and click OK.

1.   Select Main Menu > Solution > Define Loads > Apply > Fluid/CFD > Velocity > On Nodes. In the dialog box that appears, click Pick All. In the dialog box that appears, click on, enter 0 for VX and 0 for VY, and click OK, as shown in Figure 5.14.

2. Applying temperature boundary constraint conditions:

(1) Applying left boundary temperature constraint conditions: Select Utility Menu > Select > Everything. Select Utility Menu > Select Entities. In the dialog box that appears, choose Lines, By Location, and X-coordinates. Enter 0 for Min and Max, click Apply, then select Nodes, Attached to, Lines, and all.

Select Main Menu > Solution > Define Loads > Apply > Thermal > Temperature > On Nodes. Click Pick All in the dialog box that appears. In the dialog box that appears, select TEMP and enter 140 for VALUE, then click OK, as shown in Figure 5.15.

(2) Apply the right boundary temperature constraint: Select Utility Menu>Select>Everything. Choose Utility Menu>Select Entities. In the dialog box that appears, select Lines, By Location, and X-coordinates. Enter 0.96 for Min and 1.45 for Max. Click Apply. Then select Nodes, Attached to, Lines, all. Choose Main Menu>Preprocessor>Define Loads>Apply>Thermal>Temperature>On Nodes. In the dialog box that appears, click Pick All. In the dialog box that appears, select TEMP and enter 140 in VALUE. Click OK. Select Utility Menu>Select>Everything. Refer to Figure 5.16.

Figure 5.15: Apply the left temperature boundary condition

Figure 5.16: Apply the right temperature boundary condition

(7) Setting FLOTRAN solution options

Select Main Menu > Preprocessor > FLOTRAN Set Up > Solution Options. In the dialog box that appears, choose “Thermal” for TEMP and click OK.

Select Main Menu > Preprocessor > FLOTRAN Set Up > Execution Ctrl. In the dialog box that appears, enter 200 for EXEC and 50 for OVER, then click OK.

(8) Defining fluid material properties

Select Main Menu > Preprocessor > FLOTRAN Set Up > Fluid Properties. Choose “AIR-SI” for FLDATA12, PROP, and DENS. Set FLDATA13, VERY, DENS to “yes.” Choose “AIR-SI” for FLDATA12, PROP, and VISC. Choose “AIR-SI” for FLDATA12, PROP, and COND. Choose “AIR-SI” for FLDATA12, PROP, and SPHT. Click OK and then click OK again in the dialog box that appears.

(9) Applying fluid gravity

Select Main Menu > Preprocessor > FLOTRAN Set Up > Flow Environment > Gravity. In the dialog box, enter 9.8 for ACELY and click OK.

(10) CFD solver control settings

Select Main Menu > Preprocessor > FLOTRAN Set Up > CFD Solver Controls > PRES Solver CFD. In the dialog box that appears, choose “TDMA” and click OK. Accept the default settings in the next dialog box and click OK.

Select Main Menu > Preprocessor > FLOTRAN Set Up > CFD Solver Controls > PRES Solver CFD. In the dialog box that appears, choose “PBCGM” and click OK. Accept the default settings in the next dialog box and click OK.

(11) Thermal radiation parameters and solver settings

Select Main Menu > Solution > Radiation Opts > Solution Opt. In the dialog box that appears, enter 5.67e-8 for STEF. Enter 0.5 for Radiation flux relaxation. Factor in RADOPT. Enter 0.0001 for convergence tolerance. Click OK.

(12) Applying thermal radiation boundary

Select Utility Menu > Select > Everything. Choose Utility Menu > Select Entities. In the dialog box that appears, select Nodes, Exterior, From Full, and click OK.

Select Main Menu > Solution > Define Loads > Apply > Thermal > Surface Rad > On Nodes. In the dialog box that appears, click Pick All. Then, in the subsequent dialog box, enter 0.9 for VALUE and -1 for VALUE2. Click OK. Select Utility Menu > Select > Everything. Choose Utility Menu > Plot > Elements.

(13) Saving

Click on the ANSYS Toolbar and select SAVE_DB.

(14) Solving

Select Main Menu > Solution > Solve > Current LS to start the computation. Refer to Figures 5.17 and 5.18 for reference.

Figure 5.17: Calculation Process

Figure 5.18: Calculation Completed

(15) Explicit Streamline Distribution Cloud Chart

Select Utility Menu>PlotCtrls>Window Controls>Window Options. In the pop-up dialog box,

choose Legend ON in INF0 and click OK.

Select Main Menu>General Postproc>Read Results>Last Set to read the analysis results of the last substep.

Select Main Menu>General Postproc>Plot Results>Contour Plot>Nodal Solu, and choose Other.

FLOTRAN quantities, Stream function-2D. The streamlined distribution cloud chart is shown in Figure 5.19.

Figure 5.19: Streamline Distribution Cloud Map

(16) Explicit Heat Flux Density Distribution Cloud Map

Select Main Menu>General Postproc>Plot Results>Contour Plot>Nodal Solu, choose Other

FLOTRAN quantities, Heat flux. The heat flux density distribution cloud map is shown in Figure 5.20.

Figure 5.20: Heat Flux Density Distribution Cloud Map

(17) Explicit Temperature Field Distribution Cloud Map

Select Main Menu > General Postproc > Plot Results > Contour Plot > Nodal Solu, choose DOF solution, Nodal Temperature. The temperature distribution cloud map is shown in Figure 5.21.

Figure 5.21: Temperature Field Distribution Cloud Map

(18) Exit ANSYS

Click QUIT in the ANSYS Toolbar, select Quit No Save!, and click OK.

Chapter 5 Summary

This chapter mainly accomplished the following main contents:

(1) Conducted motion simulation of the drying and unloading control system, including analysis of the working process, working requirements, connection methods of moving components, design steps, and obtained time and velocity parameter curves.

(2) Analyzed the temperature field inside the drying chamber and obtained a streamline distribution cloud map, heat flux density distribution cloud map, and temperature field distribution cloud map through analysis of the temperature field problem in the drying chamber and GUI operations.

Chapter 6: Conclusion and Outlook

6.1 Conclusion

This study designed a new type of drying and unloading equipment for fireworks particles, which utilizes the conjunction of infrared and hot air drying methods to improve the drying efficiency of the particles. The drying and unloading process is crucial as an integral part of the fireworks automated production line. Due to the high safety requirements in fireworks production, the entire design was carried out while ensuring safety. The main research achievements of this study include the following:

(1) A far infrared electric heating plate was designed with a surface temperature not exceeding 60°C during operation. The electric heating plate is installed inside the drying chamber with a rated power of 350 W, higher than the required power of 301.4 W for drying the particles. Therefore, it meets the needs of the fireworks particle drying process.

(2) The structural design of the drying and unloading system was completed, including the design of the drying chamber, unloading equipment, conveyor, and pallet rack, as well as the design of the pneumatic transmission system.

(3) The control design of the drying and unloading system was completed, including the program design for drying, unloading, temperature control, and alarm control systems, achieving automation control of the entire system.

(4) Motion simulation of the drying and unloading system was performed, and the temperature field inside the drying chamber was analyzed. A temperature field distribution map was obtained, demonstrating the uniform temperature distribution inside the drying chamber.

6.2 Outlook

Although this article has completed the design related to drying and unloading and has achieved certain results, some issues still require further research. The main points to consider are as follows:

(1) While the sealing of the drying chamber cannot be completely guaranteed in the automated production process, this issue still needs further research and improvement.

(2) Due to time constraints and being limited by the complexity of the equipment, this article did not conduct relevant experimental research and only obtained theoretical values. It is hoped that future experimental work can be completed to draw further conclusions.

The combined drying technology of far-infrared and hot air has broad application prospects in fireworks and pyrotechnics drying. Our country’s economically practical and commercialized far-infrared and hot air combined drying equipment has not yet formed a scale. In fact, natural drying and hot air drying methods still account for a large proportion of the drying process of fireworks and pyrotechnic particles in our country. These methods have poor safety, high energy consumption, large pollution, and low efficiency, which cannot meet the requirements of automated fireworks production. Therefore, it is urgent to strengthen in-depth research on the combined drying technology of far-infrared and hot air. It is necessary to actively introduce and absorb advanced foreign experience, strengthen the management of fireworks production, vigorously promote new processes and technologies, and prioritize it in current research work. It is gratifying that our country has made certain progress in theoretical research and experimental work in this area, and it is believed that this technology will achieve better development and application in the future.

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References

• Automatic production device for firework launching barrel
• Fireworks Showrooms
• 1910.109 – Explosives and blasting agents.
• laws and regulations for transportation, use and storage
• Ammunition and Explosives Safety Standards
• Federal Explosives Law and Regulations
• Explosives and Fireworks Act
• Display Fireworks Manual
• Sec. 29.06.01.09. Fireworks and Explosive Materials
• SEC. 57.5605. MANUFACTURE, ASSEMBLY
• International Fire Prevention Code Ordinance