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A Brief Discussion on the Installation, Use, and Management of Large Asphalt Mixing Plants Author: Guangdong Changda Highway Engineering Co., Ltd., Xu Shuxiang Abstract: Based on the practical experience of constructing large asphalt mixing plants, this paper summarizes their installation techniques as well as production and cost management methods, providing guidance for the rational use and effective management of such plants. Keywords: large-scale asphalt mixing plant ； Install ； Technology ； Production ； Cost Management 1. Introduction As China’s transportation network continues to expand and extend, the construction equipment used for road construction is also constantly evolving and improving. In the construction of high-grade highways, asphalt concrete is increasingly used by road designers as a surface material, and asphalt mixing plants play the role of producing this asphalt concrete. The pace of road construction is accelerating, and small and medium-sized asphalt mixing plants can no longer meet the demands of road construction. Asphalt mixing plants with a production capacity of 120 t/h from 10 years ago have gradually been phased out of the market competition, replaced by high-capacity models such as those with 360 t/h and 400 t/h capacities, which have increasingly become the mainstream products in the market. 2. Installation of the asphalt mixing plant: As the production capacity of asphalt mixing plants increases, the size of their various components also increases accordingly. As a large-scale machine, great attention should be paid to the foundation of such plants as well as the installation of their equipment. 2.1 Foundation and equipment installation: During the construction and operation of the asphalt mixing plant, the generation of industrial noise and dust is inevitable. When selecting a location and considering the size of the site for the mixing plant, we must ensure that the asphalt mixing plant is placed as far away as possible from residential areas and farmlands, in order to prevent the noise and dust generated by the plant from affecting the lives of residents. Next, resource factors such as electricity and water supplies should be considered. Regarding the site selected for the asphalt mixing plant, we classify it into two types based on geological conditions: soft soil foundations and solid soil foundations. Solid soil foundations generally consist of harder soil; after excavation to the required depth, only basic grading work is needed before proceeding with the concrete construction of the foundation ； For soft foundation soils, after excavation as per the planned layout, it is necessary to carefully examine the degree of compaction resulting from the excavation, before selecting appropriate treatment methods to reinforce the base of the foundation. Generally, plum blossom-shaped wooden piles and vibration protection sleeves are used, or the area of the foundation at the bottom is increased, in order to boost the bearing capacity of the foundation and prevent potential problems for the mixing building equipment and production processes due to cracks or settlement of the foundation in the future. In production, the vibrating screen, mixing cylinder, and aggregate drying drum in the main body of the asphalt mixing plant are the components that generate the strongest vibrations in the entire setup. During the foundation construction, we should pay special attention to the pouring of the foundations for the main building and the aggregate drying cylinders, in order to prevent potential hazards to the equipment caused by factors such as cutbacks in construction quality and failures to meet the required levelness of the foundations. Prolonged mechanical resonance can cause a high-strength M30 screw to develop mechanical fatigue, eventually leading to its breakage. Therefore, during the foundation installation, we must ensure that the same level of the foundation remains within the range of ±2 cm of the specified elevation, in order to minimize the risks caused by equipment resonance. After numerous experiences with disassembling and assembling equipment, I believe the following installation procedure is feasible: starting from the main building and installing components in a radial pattern in all three directions. This approach allows for the clearance of space occupied by large items, while also enabling the completion of the installation using large cranes in a shorter time frame, thus helping to reduce installation costs. Additionally, for the mixing building, any specific installation sequence requirements must be followed. 2.2 Cable Installation: As the production volume of mixing plants increases, the power consumption of these machines also rises; it is now typically between 600kW and 1000kW. The cross-sectional area of the power supply cables is large, and there are numerous control wires as well. Cabling is usually done using cable trays or channels. Before laying the cables, we carefully check for any damage to ensure that no short circuits or open circuits occur. When installing cables for high-power motors, it is essential to wrap the connection terminals tightly with self-adhesive high-voltage tape to prevent the motor’s vibrations from causing the tape to wear out and leading to a short circuit, which could result in damage to the motor. In the control system circuit, the cables connecting the signal screen must be connected in strict accordance with the requirements, in order to reduce the impact of external electromagnetic interference on the control system. At the same time, care should be taken to conceal and protect the wiring, with appropriate safety warning signs in place. The routing of the electrical circuits should be kept as far away as possible from oil pathways as well as areas with high temperatures and high humidity, in order to reduce corrosion and aging of the wires. During the wiring process, if you encounter any ambiguous or unclear wire labels, you must not be careless; making a wrong connection can lead to the damage of electrical components. It’s best to put it aside first, and only when it comes to the final tuning of that section should the circuit be carefully checked to identify any issues and make the necessary improvements one by one. 3. Management of supporting production personnel: In addition to the seven main systems – the main building, storage areas, powder supply system, asphalt supply system, aggregate supply system, control system, and dust removal system – an asphalt mixing plant also has numerous auxiliary components. If any one of these components fails, the entire plant may become dysfunctional. With so many systems and components, each shift requires personnel of appropriate competence to carry out maintenance in order to ensure the proper operation of the mixing plant. After trying several different combinations of team members, we optimized the staffing for each team, thereby ensuring effective production maintenance while also preventing the crew structure from becoming overly large. The optimized staff structure is roughly as follows (two-shift system): Station manager: Responsible for overall coordination of various relationships between the mixing plant and external parties, including submitting reports and summaries to higher-level management ； Team leader: Requires certain proficiency in English reading and writing, knowledge of automatic control as well as coordination skills, and the ability to operate equipment skillfully ； Operator: Understands basic mechanical principles, possesses basic electrical welding and repair skills, and is skilled in operating mixing equipment ； Electrician: Possesses a generator operation certificate, and understands the principles of high-voltage electricity and electric drive control ； Assistant worker: Possesses basic mechanical knowledge, understands the working process of mixing plants, assists in equipment management, and exhibits a high level of responsibility and enthusiasm for work ； 4. Production technology management: The control system for asphalt mixing plants is typically implemented using work servers as terminal industrial computers along with PLCs, resulting in a high degree of automation. During production, operators must follow the operation instructions strictly; it is prohibited to operate the machinery without proper credentials, as well as to start or stop the servers illegally. Before production begins, the crew on duty should carefully check the lubrication of the bearings in all areas, whether there are any leaks in the oil circuits, whether all protective switches and manual valves are in the correct positions, whether the asphalt pump is heated sufficiently, and whether all system parameters fall within the acceptable range. Only after making the necessary safety preparations can the entire machine be started up for preheating. To reduce costs, heavy oil is generally used as an energy source to heat the aggregates. However, since heavy oil does not ignite at room temperature, diesel is needed to assist in ignition before the machine is preheated; once the flame becomes stable, heavy oil is then used for heating. To achieve better fluidity and a lower flash point, heavy oil is usually heated to 100–120°C. The preheating process of the cold aggregate usually takes 10 to 15 minutes. Only after the exhaust gas temperature in the bag filter reaches 90°C and the moisture accumulated inside the bags has evaporated can the cold aggregate be introduced. It is essential not to rush this process; if the bags still contain moisture when the cold aggregate is heated, the water vapor will stick to the dust, blocking the air gaps in the bags and thereby affecting the dust removal efficiency. During this period, it is possible to carry out online operations between the server and the industrial computer, in order to check whether the connection between them is functioning properly, thus preparing for production. Once the server has set all the parameters and production tasks, under the coordinated control of the PLC and industrial computer, the production process in the asphalt mixing plant operates as an automated assembly line process. It moves from cold aggregates to hot materials and then to asphalt mixtures, continuously carrying out the assigned tasks until they are completed. During this process, it is necessary to pay attention to observing (a) the changes in the current of each motor ； (b) Is the aggregate temperature within the allowable deviation range? ； (c) Is the supply between the hot and cold silos balanced? ； (d) Is the powdered asphalt being supplied smoothly? ； (e) Whether all parts of the machinery are operating properly, and if there are any abnormal noises ； (f) Are the material receiving vehicles queuing up to receive materials as required? Once any abnormality is detected, production must be stopped immediately; production can resume only after the fault has been resolved. 5. Cost control management: During the process of loading mixtures onto transport vehicles, there is a risk of waste resulting from the spillage of these mixtures. The processing cost for one ton of asphalt mixture is generally around 400 to 500 yuan. The more waste there is, the higher the cost of the project will be. If 10 tons of mixture are wasted per day over a project duration of 60 days, it’s possible to end up with 600 tons of asphalt mixture wasted, resulting in direct economic losses of over 300,000 yuan. Therefore, cost control in asphalt mixing plants starts with minimizing unnecessary waste of mixture; a dedicated vehicle coordinator can be appointed for this purpose. In the construction of engineering projects, a significant amount of funds is required for energy materials used to heat asphalt aggregates; proper and effective control of these energy materials can further enhance cost savings. The automatic combustion control system for asphalt mixing plants has, over the years, given rise to a range of different models, such as those using light diesel, heavy oil, coal powder, as well as models that can operate on gas or a combination of gas and oil. In our country, natural gas and coal are not yet abundant enough. Due to the specific conditions of road construction and the locations where such work is carried out, the industry tends to rely on fuel-based burners. In recent years, due to the rising prices of light diesel, this traditional fuel used for heating aggregates has gradually been replaced by heavier oil, which is cheaper. Many asphalt mixing plant operators and end-users, in order to enhance their competitiveness and reduce costs, have modified and optimized their combustion systems to accommodate the use of heavier oil. For a decent burner capable of heating aggregates to 180°C, approximately 8 liters per ton is required. To achieve the same level of heating, heavy oil needs about 9–10 liters per ton. If 200,000 tons of aggregates are produced, using diesel at 4.26 yuan per liter would result in costs of 6.816 million yuan, while using heavy oil at 3 yuan per liter would cost between 5.4 million and 6 million yuan. Thus, projects that use heavy oil can save 816,000 to 1.416 million yuan in costs. Therefore, choosing the appropriate fuel type while ensuring the stable operation of the equipment can enhance overall efficiency and minimize production costs. Before mass-producing mixtures, the temperature of the mixing tank in an asphalt mixing plant is low; as a result, the first batch of mixture produced is often wasted due to this low temperature. Sometimes, several tons to a dozen tons of hot aggregates have to be removed from the hot storage bin before the plant can start operating properly. Such improper practices and waste represent major issues when it comes to cost control. By anticipating this situation, we can first increase the temperature of the hot aggregates appropriately, carry out manual mixing control, and supply cold materials slowly. Once 3 to 4 batches have been produced and the temperature of the mixing tank as well as that of the hot material bin have risen, mass production can begin, thereby preventing unnecessary waste of raw materials. Furthermore, optimizing the production mix, as well as the accuracy of each weighing system, are all related to cost control. 6. Archiving and management of production equipment: An asphalt mixing plant is a set of equipment that combines mechanical and electrical components, and there are numerous technical performance parameters for these components. In many cases, we need to use these parameter data to carry out maintenance and repairs on the equipment. In regular production, it is necessary to pay attention to collecting, recording, and organizing all relevant documents, as well as keeping track of the model numbers of important components in various parts and the structure of those components, for future reference. It is also important to back up programs and the computer system on the computer. At the start of operations, records are kept of the daily production and maintenance status of the machinery in use. 7. Conclusion This article is a summary of the author’s many years of experience in operating large-scale asphalt mixing plants; it is intended solely as a reference for colleagues. Please point out any errors or inaccuracies.