Development and application of domestic asphalt spreading technology

With the advancement of the world industry and the development of highway construction, especially the need for black pavement construction, asphalt sprinklers have been around since the beginning of the last century. In the 1930s and 1940s, they have developed into more functional products. The model is a self-propelled asphalt spreader. Asphalt spread trucks in China, since the 1950s, with the development of highway construction, technological innovation, product performance continues to improve, so far the domestic asphalt spreader has reached intelligent, its technical performance has been Reach the international advanced level. Looking back at the development of asphalt spreaders in China, it can be roughly divided into two stages: the introduction of the improvement period and the innovation period.




Introduction and improvement of asphalt spreader




In the 1950s, China introduced self-propelled asphalt spreader technology from the Soviet Union and began production. The main features of this model are fire tube heating asphalt; volumetric asphalt pump spraying; changing the spray width by changing or lengthening the spray bar; according to the engineering requirements, using the method of adjusting the driving speed and the speed of the asphalt pump to achieve the predetermined sprinkling The amount of cloth (L/m2). Although the quality of the equipment is not high enough, the operation is still cumbersome, but from the industrial level at that time, this type of machine is still advanced, and it plays an important role in road construction, whether it is replacing human labor or improving productivity. effect. Due to the limited level of industrial technology development, the structure and performance of this traditional asphalt spreader has remained unchanged in the country until the end of the last century. Even in the past two years, this type of machine has been produced.




With the rapid development of China's reform and opening up and road construction, especially the construction of expressways and the promotion of modified asphalt and the need for socialization of road maintenance, higher requirements are put forward for the function of asphalt spreaders. To this end, domestic experts and scholars and relevant practitioners have made unremitting efforts to improve the structure and performance of asphalt spreader vehicles, and published a number of papers, the main representative works are: 1. "Improve domestic asphalt spreader Discussion on Partial Structure; 2. "Experimental Study on Spray Performance of Asphalt Spreading Machine Nozzle"; 3. "Power Balance and Design Calculation of Asphalt Spreading Vehicle".




In the same period, he also applied for a number of patents. The main results include: 1. “Use five-wheel speed measurement system on the spreader”; 2. “Asphalt pump drive adopts hydraulic servo speed control system”; 3. “Use asphalt flowmeter and The speed detecting device regulates the speed of the asphalt pump"; 4. "Electrical detecting device for the pressure, temperature and liquid level of the asphalt pump on the asphalt spreader".




Under the efforts of the relevant employees, although the performance of some domestic asphalt spreaders has been improved, due to the limitations of the industrial level, these discussions and achievements have basically not formed an industrial scale. Innovation of asphalt spreader




Since the beginning of the 21st century, with the further strengthening of international technology exchanges and the advancement and popularization of electronic information technology, it has provided technical and material guarantees for the advancement of asphalt spreading technology in China. Xi'an Dagang Highway Electromechanical Technology Co., Ltd. first launched the SX5190GLQ intelligent asphalt spreader with independent intellectual property rights. As the representative of innovation in this period, it led the technical progress of asphalt spreader in China. Compared with traditional asphalt spreaders, the main features of intelligent asphalt spreaders are:




1. The embedded heat-conducting oil heating device uses the heat-conducting oil as the heat-transfer medium to heat the temperature-raising asphalt, which changes the conventional heat pipe heating, so that the asphalt is easy to age. The automatic ignition diesel burner is adopted, the temperature can be set manually according to the need, the asphalt is automatically heated, and the heating speed is fast, which can meet the requirement of the modern modified asphalt spraying temperature ≥ 175 °C.




Using heat-conducting oil as the heat transfer medium, it is also possible to heat and heat the entire asphalt pipeline system until each nozzle, changing the traditional operation method, that is, the nozzle is used to bake the nozzle before spraying, and the troublesome operation of immersing and rinsing with diesel oil after the cloth is sprayed.




2. The maximum sprinkling width is 6m, a total of 48 nozzles are set, and each nozzle can be independently controlled. The advantage is not only that the spraying process starts quickly, but also completely closes, and the sprinkling width can be arbitrarily set within 6m of the maximum sprinkling width ( The step is the pitch of one nozzle).




The unique nozzle design makes the single-spray asphalt spreading angle α meet the requirements of three overlapping sprinkles, namely:



(1) where: α - nozzle spray angle; B - nozzle spacing, mm; H - nozzle height from the ground, mm; β - the angle between the nozzle center line and the spray rod axis.




3. The application of the micro industrial computer enables the function of the asphalt dredging car to realize its dreams, mainly:




1) Sprinkling parameters, such as sprinkling width W, sprinkling density D, and asphalt specific gravity G, can be manually set according to road construction requirements, keyboard input, computer in addition to the set parameters, and provide the driver with reference speed V, Even the gearbox should be geared.




The reference speed V given from the design point of view is an optimized result. It ensures that the machine can work under the best working conditions under the wide range of parameters. Driving the vehicle strictly in accordance with the reference vehicle speed V is actually difficult to achieve. The system allows for a large deviation of the vehicle speed without affecting the accuracy of the amount of sprinkling per square meter.




2) Timely control, when the speed of the vehicle changes, the asphalt spreading system can meet the matching relationship between the asphalt flow rate and the driving speed to meet the requirements of the same amount of sprinkling per square meter, namely:




(2) where: D-set sprinkling density, kg/m2; QL-asphalt pump flow, kg/min; V-dynamic speed, m/min; W-sprinkle width, m. In order to keep the sprinkling density D constant, the automatic control system will ensure that the asphalt pump flow rate QL is adjusted proportionally with the change of the vehicle speed V, which is not difficult to solve in the modern hydraulic transmission and electronic computer era.




3) The adoption of the industrial control machine plus single nozzle independent control technology can realize the trapezoidal surface spraying on the work site, that is, the spraying process can increase or decrease the nozzle one by one, that is, add or reduce the width of the spreading cloth to meet the requirements of the special working surface. The sprinkling width changes and the sprinkling density remains the same.




4) The liquid crystal display can display dynamic parameters such as vehicle speed V, asphalt pump speed nL, sprinkling distance L, and asphalt temperature and liquid level display.




4. Introduce compressed air into the operating system, not only as a power to control the asphalt valves and nozzles through the solenoid valve, but also for the purging of the asphalt pipeline. That is, after the spraying work is finished, the remaining asphalt in the pipeline can be pressed back to the storage tank, and all the nozzles are purged for the next activation.



As can be seen from the above, modern asphalt spreaders generally have four fluid systems, namely a hydraulic drive system, a heat transfer oil heating system, an asphalt spread system, and a compressed air system. Correspondingly, the mechanical design is also required to be high, especially the folding spray pipe, which requires the asphalt and the heat transfer oil to be transmitted through the rotary joint, which makes the structure more complicated. For the first time, the SX5190GLQ intelligent asphalt spreader adopts a double-layer insulated metal hose, and adopts a coaxial rotating double-medium transmission sealing structure and a device for measuring the vehicle speed using Hall originals, which better solves the functional problems of the equipment and has obtained the state. patent.




From the overall perspective of the country, the technical level of asphalt spreading is rapidly increasing. Traditional products are being modified or replaced with new technologies. Market-oriented, some new and old enterprises in China are producing medium and low-end products in addition to different market demands. In terms of technology, it has established a high starting point and produced an intelligent asphalt spreader with advanced domestic level.




Prospect of asphalt spreader




The rapid development of China's highway industry, especially the adoption of new technologies, new materials and the requirements for improving construction quality, has opened up a wide range of use prospects for asphalt spreaders. The “transparent layer”, “lower seal layer” and “adhesive layer” of the newly built expressway require high-quality asphalt spraying; the “layer paving method” adopted by low-grade highways and a large number of township highways requires high-quality asphalt spraying; For the maintenance work, the “single table” or “double table” process also requires high quality asphalt spraying.




The appearance of modified asphalt, especially rubber asphalt, increases the use temperature of asphalt to above 190 °C, and the dynamic viscosity increases exponentially (above 3Pa.s at 190 °C), which increases the difficulty of asphalt spreading. Therefore, in the future, China will not only increase the demand for asphalt spreaders in terms of quantity, but also further improve the performance of asphalt spreaders.



Internationally, industrial developed countries such as the United States, France, and Germany have introduced advanced models, and some models have entered China. However, due to the different conditions in different countries, the scope of use of machinery is different, the designers have different ideas, and the performance of asphalt spreaders in different countries is still very different. Its main development trends are:




1. Control the computerization, the driver can complete all the settings and operations in the cab with a dedicated micro industrial computer. Through the radar speed measuring system, the proportional control of the amount of sprinkling, uniform distribution, sprinkling accuracy of up to 1%; display can display the necessary dynamic parameters such as vehicle speed, asphalt pump flow, speed, asphalt temperature, liquid level, etc., so that the driver at any time Understand the operation of the equipment.




2. The tank capacity is serialized, and the tank capacity is generally from 1000L to 15000L, or larger. For small-scale maintenance operations, the amount of asphalt used is small, and small tanks can be used to meet the needs. For large-scale highway construction, large-capacity asphalt spreaders are needed to reduce the number of asphalt spills in the construction and improve work efficiency.




3. The width of the spread is serialized, and the width of the spread is generally 2.4 to 6 m, or wider. The independent or group control of the nozzle is a necessary function of the modern asphalt spreader. The actual spread width can be set at any time in the range of the maximum spread width.




4. The spreading density is extended to the two poles. The density of the cloth is determined according to the engineering design. For example, the National Asphalt Technology Center of Auburn University recommends that the surface of the HMA road maintenance stone seal be treated. It is recommended that the amount of asphalt spread can vary from 0.15 to 0.5 gallons per square yard. Change between (1.05~3.5L/m2). Some modified asphalts with rubber particles sometimes require up to 5 L/m2, while some use emulsified asphalt as the permeable oil, the amount of sprinkling is required to be less than 0.3 L/m2.




5. Improving asphalt heating efficiency and reducing heat loss is a new concept of modern asphalt spreader design. It requires that the lower temperature asphalt be rapidly heated in the asphalt spreader to reach the spray temperature. To this end, the asphalt temperature should be above 10 ° C / hour, the average temperature drop of asphalt should be below 1 ° C / hour.




6. Modified asphalt mixture that is easy to isolate, or asphalt mixture that needs to stay in the tank, and the asphalt tank should be equipped with a stirrer.




7. Improving the quality of the starting sprinkles is one of the important performances pursued by asphalt spreaders. The sprinkling quality includes the accuracy of the sprinkling amount from the start to the initial spray distance and the initial sprinkling section (0 to 3 m). Zero spray distance is difficult to achieve, but reducing the initial spray distance is beneficial to the connection of the spray operation. Modern asphalt spreaders should keep the spray distance as short as possible, and start spraying neatly, one line in the horizontal direction. The SX5190GLQ intelligent asphalt spreader produced by Xi'an Dagang Company can be accurately sprayed at a distance of 0.7m after starting, and the horizontal direction is a straight line.




The amount of sprinkling in the initial sprinkling section and its accuracy have a certain relationship with the initial spray distance. Generally speaking, the shorter the initial spray distance, the more difficult it is to control the amount of sprinkling, and the lower the sprinkler accuracy.




In addition, improving the ease of operation, comfort, reliability and reducing production costs of asphalt spreaders is also the pursuit of technological advancement in modern asphalt spreaders.




The development of highway construction has shown a broad development platform for engineering machinery. It is believed that with the efforts of practitioners, the advancement of asphalt spreading technology in China will, together with other construction machinery, quickly catch up with the international advanced level and produce high quality. Products to meet the needs of China's highway construction.

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