Current Situation and Requirements of Asphalt Strong Mixing Control System

I. Summary: As a key core technology of large-scale asphalt concrete mixing equipment products, the leading technology of the automatic control system mainly comes from abroad. Domestic professional automatic control technology companies and asphalt mixture mixing equipment manufacturers have also made significant investments in research and development and testing. However, due to the reliance on imported key supporting components and the long process of thinking and application practice verification, technological upgrades have been extremely slow. If domestic enterprises want to enter the high-end product market or promote an internationalization strategy, they cannot escape the influence of international asphalt mixing equipment control systems. Although the so-called "internationalized supporting facilities" advocated by many people can temporarily meet the survival needs of domestic enterprises, it restricts and limits their own research and development. This is because with the advancement and implementation of the localization strategy of foreign-funded enterprises and the large-scale influx of domestic joint ventures and foreign-funded enterprises, domestic enterprises are at a disadvantage in major factors such as technology and brand. Therefore, given the huge potential of the asphalt mixing equipment market in our country, domestic asphalt mixing equipment mainframe manufacturers should join hands with control supporting enterprises, especially powerful professional colleges and universities, to jointly tackle key problems, so as to possess their own core control technologies.

From the perspective of the Chinese market in recent years, domestic users have increasingly accepted asphalt mixing equipment with technologies from Germany, Italy and the UK. Therefore, in the construction and maintenance projects of domestic expressways, the asphalt mixing equipment products of these countries' companies are often seen. The successful application of intelligent control technology for asphalt mixing equipment abroad has further enhanced the technical level of asphalt mixing equipment.

In addition, asphalt mixing equipment in our country is mainly used in the construction and maintenance of expressways. The application of energy-saving technology and mechatronics technology has reached a point where it must be faced. It adopts ergonomic design to enhance the intelligence of operation. Domestic enterprises should fully recognize the technological gap between our current products and those of similar foreign products. Some seemingly insignificant issues will become decisive factors for whether we can further develop in the market and even survive.

Asphalt mixture mixing equipment is a complex comprehensive supporting device. Due to the influence of factors such as fieldwork, harsh working environment, large temperature fluctuations, and multiple interference sources, the design of the control system of this equipment has been greatly increased in difficulty. Especially for the equipment used in high-grade highways, the measurement accuracy requirements for asphalt, granules, powder and temperature are high. Therefore, the hardware and software design requirements for the control system of this equipment are also relatively high. It is necessary to comprehensively consider the above factors and take necessary design measures to meet the requirements of high-grade highway construction.

Asphalt mixture mixing equipment is a comprehensive supporting device with many independently operating components and a complex process flow. The task of its control system is to start up, run, mix materials and shut down each component according to the predetermined program. Under the premise that the overall performance of the machine meets the requirements, it simplifies the operation as much as possible and improves the level of automatic control of the entire machine.

The principles of control system design: (1) Enhance the reliability of the control system, ensuring that the system's reliability indicators meet the national standard requirements and strive to reach or approach the international advanced level.

(2) For the hardware part, high-quality mature products or advanced foreign products should be adopted as much as possible. Under the premise of meeting all performance indicators, efforts should be made to reduce the production cost of the control system.

(3) Adopt international standards, implement the current national and enterprise standards, and strive to enhance the degree of "three modernizations".

(4) Measurement control accuracy: According to the industry standard JT/T270-2002 (standard working conditions) : Asphalt measurement accuracy: ± 0.25% (static measurement with standard weights) Powder measurement accuracy: ± 0.5% (static measurement with standard weights) Aggregate measurement accuracy: ± 0.5% (static measurement with standard weights) Asphalt measurement accuracy: ± 2.0% (dynamic material measurement) Powder measurement accuracy: ± 2.5% (dynamic material measurement) Aggregate measurement accuracy: ± 2.5% (dynamic material measurement) (5) Ergonomics: It adopts a desktop combination control console, with a simple design, novel and beautiful appearance, and convenient operation. The office-style design gives people a sense of comfort, and the spacious operation interface keeps everything under control. (6) Comfort of operation: The control room maximizes the satisfaction of users' operational efficiency and humanized design; Huge glass Windows, heating and air conditioning equipment, etc. ensure a comfortable environment.

The objective of the control system design: 1 The system is compatible with the original control mode of the equipment, enabling manual, automatic and computer operation respectively, which is convenient for users' production. At the same time, it can smoothly complete product connection and facilitate future equipment modification.

2 The hardware resources are the latest and best, and the software resources are powerful in function. Supports the application of multiple new technologies, such as touch screens, dual displays, remote diagnosis, redundant control, etc. It has a high performance-to-price ratio.

3 It provides a user-friendly interface and features high control accuracy.

Reliability of control system design: 1 Stable and reliable redundant control system 2 A dual operating system is formed by combining an industrial computer with a human-machine interface.3. The fully computerized control is stable and reliable. It dynamically displays the operation status of each component of the mixing plant (building), and can store a large amount of various data of the mixing plant at the same time, and print various report materials as required. The human-machine interface is fully automatic controlled. What you see is what you use. Touch operation is quick to get started and the control is convenient and reliable.

The advanced nature of the control system design: The computer system software features high stability and reliability, with rapid communication performance. It can accurately control every detail of the production process, meeting the requirements of continuous production. The high-speed screen update makes the screen smoother and more aesthetically pleasing. Meanwhile, the software features powerful database connection, data processing, formula functions and report functions. It can accurately record production data and print it in various ways. Extended functions of the control system design: 1 Powerful remote communication monitoring function 2 Supports mobile phone SMS function, allowing you to keep abreast of production status in a timely manner through your mobile phone. Supporting GRPS/CDMA/ telephone dial-up communication enables timely monitoring of on-site conditions and production data. 4. Video capture equipment can be provided, supporting CDMA and local area network transmission. On-site images can be viewed through the video server and monitoring station.

Ii. Control Technology and Scheme for Asphalt Mixture Mixing Equipment 1. Strong Current Control (1) Low-voltage Electrical Appliances: All low-voltage electrical appliances are selected from original imported ones from abroad and purchased from the original factory. The main suppliers include Siemens, Golden Bell, Omron, Panasonic, Mitsubishi, Toledo, etc. High-quality low-voltage electrical appliances provide a reliable guarantee for providing high-quality performance. The box body adopts a combined integrated control cabinet. The advanced process design and reasonable layout combination provide a guarantee for the electrical components to be durable, stable and reliable in performance.

(2) Variable frequency speed control: Cold aggregates are speed-regulated by a frequency converter, which can achieve stepless, continuous and stable feeding, maintaining a relatively stable material level consistent with the requirements of the hot material silo.

(3) Reasonable reduced-voltage starting methods for high-power motors: For high-power motors, based on their load characteristics, determine a reasonable reduced-voltage starting method, such as star-delta, autotransformer, soft starter, etc., to protect the motor, cables, and transformers.

(4) Interlocking and protection: Each controlled motor should select the protection setting value based on its working nature, and key components should have protection at least two levels. They are interlocked with each other based on the process flow to prevent material accumulation or equipment damage.

(5) Grounding and Shielding: Good grounding and shielding are the guarantees for the stable and safe operation of equipment.

(6) Lightning protection measures: Install lightning arresters to ensure the safety of equipment and personnel.

2. Signal Acquisition (1) Weighing Signal: The weighing system adopts the world's advanced control devices (Panther weighing display instruments and sensors from METTLERTOLEDO, USA), featuring good stability and high measurement accuracy. The analog signal enters the PLC for control, flying material calculation and automatic drop compensation functions. It also features good working stability and strong anti-interference ability. The precise design of the entire system's center of gravity, the adoption of anti-wear measures, and the fully breathable heat-resistant flexible connection interface ensure that the measurement accuracy is always guaranteed throughout the construction process. (Cumulative measurement accuracy of stone materials ≤±0.5%; cumulative measurement accuracy of powder materials ≤±0.5%; cumulative measurement accuracy of asphalt ≤±0.35%, etc.) (2) Temperature signal: The heat collection silo, asphalt and dust collector are equipped with thermometers, and there are alarm displays, sound and light alarms and important temperature records. When the fuel oil is discharged from the drying drum, a fast-response non-contact infrared thermometer is installed. This signal is fed back to the burner controller, which automatically adjusts the air-oil ratio to track the set temperature of the hot aggregate. The bag filter with a thermometer, on the one hand, shows the exhaust gas temperature to guide the operator to make effective adjustments; On the one hand, it collects signals for secondary temperature control protection (automatically opening the air mixing valve when the primary temperature exceeds the limit, and forcibly stopping the burner when the secondary temperature exceeds the limit).

(3) Material level signal: Material level gauges are installed in the finished product silo, hot aggregate silo, new powder silo, recovered powder silo, overflow silo and waste silo. The display of material levels enables operators to understand the status of each bin, promptly grasp and take corresponding measures for adjustment, and ensure the continuous and stable operation of the equipment.

(4) Position signals: For the opening and closing limits of the powder butterfly valve, the opening and closing limits of the stone discharge, the opening and closing limits of the mixing cylinder door, the opening and closing limits of the valve position, and the signals of each position in the finished product silo, etc. Conducting position detection and feedback, and participating in program control can ensure that each action is interlocked with each other, accurate and reliable.

(5) Negative pressure and differential pressure signals: Measure the negative pressure of the drum and adjust the induced draft damper in time to stabilize it, providing conditions for complete combustion. Detecting the differential pressure at the inlet and outlet of the bag filter can provide a basis for adjusting the reverse blowing time or interval.

3. Weak Current Control (1) Computer (Control + Management) : Control design of configuration software: The program supports the configuration and metering of 6 types of aggregates, 2 types of powders, 2 types of asphalt, and 1 type of additive, as well as metering without screening. Computer-controlled cold storage speed regulation; It can achieve separate start and stop of the motor and automatic sequential start. Real-time monitoring of the temperature at the inlet and outlet of the sand silo, asphalt, chute, dust collector, and the current of important motors such as the mixing pot, as well as the material level changes of the continuous material level gauge; The real-time displayed alarms include functions such as over-time and over-tolerance of ingredients, overweight of scales, empty scales, external faults, motor overload, automatic fault detection and alarm of equipment. .

The management design of the configuration software: It can display and print the set and actual values of the name, quantity parameters and temperature parameters, and can set the weighing error range. When the specified value is exceeded, an alarm signal will be issued. It can store over 200 kinds of formulas and the formulas can be changed conveniently. Store and print all data at any time, including date, time, cumulative production hours, cumulative material consumption and other contents, as well as average hourly productivity and daily, weekly and monthly production reports and corresponding material consumption. (2)PLC A programmable controller is an electronic system for digital operation, specifically designed for industrial environment applications. It uses a type of programmable memory to store programs internally, execute user-oriented instructions such as logical operations, sequential control, timing, counting, and arithmetic operations, and control various types of machinery or production processes through digital or analog input/output. Programmable controllers and their related peripheral devices are all designed in accordance with the principles of being easy to integrate with industrial control systems as a whole and easy to expand their functions.

A programmable controller is a dedicated computer, which is designed and manufactured specifically for industrial environment applications.

Iii. Temperature Control of Asphalt Mixture Mixing Equipment 1 The guarantee of asphalt temperature: The heat transfer oil system and pipeline heating circulation provide the guarantee.

2 The discharge temperature of the drying drum and its control: The temperature of the hot aggregate is the main factor determining the temperature of the finished product. The automatically controlled combustion device can track the required set temperature and quickly adjust when disturbed (flame, moisture content of the material) The temperature of fine materials in the hot material silo: It reflects the temperature of hot aggregates during the mixing process. When the required temperature cannot be reached, it is better to drain it.

4 Finished product temperature: Infrared monitoring is installed at the outlet of the mixing tank, or insulation measures are taken for the finished product silo (such as electric heating, heat transfer oil heating, rock wool insulation, etc.).

The discharge temperature of asphalt mixture is an important factor affecting the construction quality. If the temperature is too low, it will affect the quality of the mixture, causing an uneven "flower material" phenomenon, and is not conducive to spreading and rolling. Excessively high temperatures, on the other hand, can lead to significant waste of fuel and, in severe cases, cause asphalt to age and form coke. Therefore, the temperature of the mixture must be strictly controlled, and a reasonable discharge temperature should also be set according to different construction conditions and weather conditions. The temperature in the morning should be slightly higher. Especially for the first vehicle, as the temperature of the paver is very low, it should be about 20℃ higher than the normal mixing temperature. The temperature can be appropriately reduced by 5 to 10 degrees Celsius at noon. Even on windy days, the temperature of the material should be appropriately raised. The temperature of coarse-grained mixture should be 8℃ to 10℃ higher than that of medium-grained mixture to facilitate construction. According to the actual situation, adjust the throttle opening by grasping the changes in the moisture content of the sand and gravel materials, so that the material temperature varies within ±5℃ of the normal temperature. During the rainy season construction, special attention should be paid to controlling the material temperature due to the excessive moisture content of raw materials. The loader operator should be informed to remove materials with excessive moisture content to prevent wet materials from entering the cold material silo. In addition, if abnormal temperature phenomena are found during operation, the cause should be investigated promptly, and mechanical faults and other situations during mixing should be treated separately.

Iv. Oil-to-stone Ratio Control of Asphalt Mixture Mixing Equipment 1. Precision Control of Aggregate Weighing 2. Precision Control of Powder Weighing 3. Asphalt weighing accuracy control 4. Other (recycled materials, SMA) accuracy control 5. Oil-to-stone ratio accuracy and automatic tracking of the oil-to-stone ratio are important indicators of the quality of asphalt mixtures. Too little or too much asphalt content will reduce the strength of asphalt concrete, affecting its compaction degree and stability. Excessive content will also form free asphalt between mineral particles, eventually leading to "oil seepage" on the road surface. Therefore, it is necessary to follow the test data to determine the optimal oil-to-stone ratio and strictly control it during construction to keep the error within ±0.3%. The asphalt metering scale should be frequently checked and calibrated with standard weights and adjusted in a timely manner. In particular, the tightness of the asphalt metering hopper and the discharge valve should be frequently inspected to prevent internal leakage of asphalt, which may cause an excessively high oil-to-stone ratio, resulting in waste and a reduction in the quality of the mixture.

In addition, the mixing parameters should be adjusted in a timely manner according to the mixing process and different situations. For instance, the mixing parameters are not the same when the hot material silo is full or short of materials. At this time, the mass of materials dropped from the air varies greatly. When the silo is full, it is several dozen kilograms, while when it is empty, it is only a few kilograms. This needs to be adjusted in a timely manner during the operation process. One must be well-versed in the performance and principles of the machine. Only by having a thorough understanding can one apply it proficiently to improve the quality of the output materials. Therefore, choosing a control system with reasonable parameters, stable reliability and automatic compensation capability is an important prerequisite for improving the mixing quality.

V. Market Requirements for the Development of Control Systems: The control system of asphalt mixture mixing equipment should be highly humanized in design to meet market demands. Various operations can be completed by the touch screen or mouse, and fully automatic, semi-automatic and manual control can be achieved. It adopts microcomputer monitoring and communication control methods, with a computer color screen display for dynamic monitoring of the production process. It has control and management functions, allowing for parameter and multiple formula Settings, data management, fault diagnosis, remote monitoring and other functions. The metering system adopts imported sensors with a fully sealed structure. The sensor accuracy grade is 0.02%, making it suitable for any harsh working conditions. The control system can automatically compensate for the error of flying materials. Create a clean, moderately temperature-controlled, wide-open, dust-proof and noise-proof operation space that conforms to human-machine coordination. Make work comfortable, convenient and fast.