Use of compressed air systems in automotive coating lines
Yan Runjuan (Baoding Changan Bus Manufacturing Co., Ltd., Hebei Dingzhou 073000 gas quality classification, compressed air consumption, compressed air system use points, etc.), I hope to be able to draw on the coating engineers . Compressed air is an important active resource in addition to water, electricity, coal, oil, steam and natural gas in the automotive coating production process. The correct use of the compressed air system directly affects the quality of the car's painting and the cost of painting. This paper describes the role and use point of compressed air system in automotive painting, the composition of compressed air system, the quality classification of compressed air, the amount of compressed air, the daily use and maintenance of compressed air system, and the coating caused by abnormal compressed air system. A brief discussion on the ills and its solutions. 1 Application of compressed air system in automobile painting Compressed air system mainly plays the role of conveying paint, atomizing paint, driving pneumatic tools, blowing dry water and dust, driving pneumatic valves in the process of automobile painting production. The point of use of compressed air is the point of use of the process and the point of tooling and equipment use. The main points of the process are: the paint transfer station, the painting station (the spray gun use point), the blowing net station, the grinding station (the use point of the pneumatic grinding machine), the glue station (the glue gun use point), and the light. Work station (pneumatic light machine use point), etc., tooling equipment use points are: tooling installation and removal station (pneumatic wrench use point), accumulation chain stop installation point, steam line pneumatic valve installation point. 2Compressed air system The compressed air system is mainly composed of air compressor, main pipeline, branch pipeline, gas storage tank, freeze dryer, filter, oil-water separator, adsorption oil-water separator, pressure regulating valve, pressure gauge, etc. As shown. Safety valve drain valve pressure regulating valve pressure gauge a filter main pipe branch pipe, hose road oil moisture i adsorption oil water separator separator compressed air system composition 1 air compressor: air compressor room air compressor, mainly It consists of an electric motor and a compressor. The model number is selected based on the gas consumption of the entire plant. Automobile manufacturers often use air compressors with a displacement of 10, 20, 40 m3/min and an exhaust pressure of 0.8 MPa. Since the quality of the compressed air produced by the screw air compressor is better than that of the piston air compressor, the screw air compressor is often used. 2 Main line: The main line is a fully enclosed loop that is fixedly installed and delivers air to each line to ensure constant air pressure at each point. The segmentation zone is equipped with a disconnect valve for easy segmentation maintenance. The main pipe diameter, air delivery volume and length matching selection are shown in Table 1. In order to ensure the quality of compressed air, the main pipe has a slope of 1A00 toward the direction of compressed air flow. m selected pipe bureau total gas volume 管 pipe diameter mm m pipe length 150m or less m or more correspondingly increase 3 pipes: branch pipe is the pipe from the top of the main pipe to send air to each point of use. The pipeline is usually galvanized pipe or pressure-resistant, anti-static, silicone-free hose. The pressure drop of the hose should be considered when adjusting the pressure range. The pressure drop range can be shown in Table 2. Table 2 Hose pressure drop hose Straight operation air pressure hose length 10m 4 Gas storage tank: Pressure vessel installed on the main line, capacity often Option 5 freeze dryer: installed at the inlet end of the compressed air into the coating production line or installed in the air compressor air compressor, the compressed air is cooled and cooled to make the gaseous water into liquid water. Automobile manufacturers often use a dry dryer with a handling capacity of 10~40m3/min and air compressor. See the working principle of the dryer. 6 Filter: Compressed air 7 oil water separator that is sent out by air compressor and cold dryer: installed on branch pipe to filter and discharge water and oil. 8 adsorption oil water separator: installed in the pipeline oil water filter, often used in painting station, paint adjustment station and pre-paint cleaning station, the internal activated carbon can further effectively remove dust, oil and dirt contained in compressed air Impurities such as silicide. 9) Pressure regulator and pressure gauge: Adjust and display the compressed air pressure. 3 Compressed air quality class Air compressor compresses the air in the atmosphere and raises the temperature to more than 140 ft. Since the compressed air contains moisture, oil and dust, it needs to be treated by the freeze dryer and the oil-water separator to achieve the car coating. The compressed air quality grade required for installation, ie the pressure dew point is not higher than -40T: the dust particles are less than 0.5 4. The compressed air consumption is about 50,000 units per year. 20m3/min. The average value of compressed air usage of common tools for painting is shown in Table 4. These values ​​are only a value, because the actual amount of compressed air used in each coating line is not only related to the tool selected at the point of use, but also to the production line. The level of management is related. 5 Use of compressed air system Note that the correct use of the compressed air system can avoid the occurrence of coating defects and reduce the waste of painting costs. The correct use of compressed air system should pay attention to the following points: 1 Periodic discharge of oil and water: The lower part of the gas storage tank, filter, oil-water separator and adsorption oil-water separator in the compressed air system are equipped with oil drain valve, and some valves are automatic. The control valve can set a discharge interval time to realize a regular discharge of a small amount of oil and water generated by the compressed air during the transportation process due to changes in temperature and humidity. In general, gas storage tanks and filters use automatic discharge valves. The oil-water separator and the adsorbed oil-water separator often use manual discharge valves, which requires strict emission intervals (see Table 5, through strict management to achieve the purpose of regular discharge, avoiding the industrial compressed air quality rating of Table 3. Solid particle size and concentration grade Maximum particle size maximum concentration / (mgmi air vapor content (pressure dew point and other fine temple level maximum pressure dew point / especially grade oil content grade maximum oil content / (mgm-;) due to residual in compressed air The excessive amount of oil and water leads to the shrinkage of the paint film. Table 6 applies the compressed air system filter material replacement cycle disease. Replacement cycle table 4 commonly used painting tools compressed air usage filter tool name oil water separator process use point 1 / half year caliber equipment use point diameter adsorption oil water separator nozzle blow gun body washing machine butterfly grinding machine double sports grinding machine Linear motion grinder horizontal grinder cutting grinder finishing grinder polishing machine pneumatic door pneumatic lift table 5 painting compressed air system oil water drain interval equipment name discharge interval time storage tank 1 time / month filter oil water separator Process use point 1 time / d equipment use point 1 time / week adsorption oil water separator 2 regularly change filter material: filter, oil water separator and precision oil water separator are equipped with different types of filter material filter or activated carbon), need According to the pressure difference between the inlet and outlet of the filter, the oil-water separator and the adsorption oil-water separator, the filter material is replaced in time to ensure the quality of the compressed air and prevent the occurrence of defects in the shrinkage film. The filter material can be replaced according to the empirical values ​​listed in Table 6. Since the cost of replacing the filter element in the oil-water separator is not much different from the cost of replacing the entire separator, the oil-water separator is often directly replaced during the use of the replacement filter cycle. The replacement period of the filter material is related to the production line, the season and the pipeline installation of the compressed air system. In the long-term use and exploration process, it is necessary to make a scientific replacement cycle for different production lines, and the replacement cycle is determined reasonably. It can prevent the shrinkage of the film shrinkage caused by the unclean filtration of compressed air oil and water, and avoid the waste of cost caused by frequent replacement of filter materials. 3) Check the quality of compressed air: In the process of using compressed air in the cleaning station, it is necessary to develop the habit of checking the quality of compressed air before opening the line. That is, after draining the oil, wear clean jersey gloves, hold the compressed air hose against the palm of your hand, open the compressed air valve and blow for 2~3 minutes. Check the gloves for no oil and water and then start the blowing operation. This can prevent the occurrence of shrinkage of the paint film due to oil and water in the compressed air. 4 Quickly replace the leaking quick joints: In the grinding station, finishing station, and the working point of the compressed air in the painting station, the quick-connect fittings are generally used to deliver the compressed air to the sander, the light machine and the spray gun. In the process of using the quick-connect connector, the leakage is not strict and the air leakage often occurs. Therefore, these parts need to be inspected and replaced in time to avoid the waste of compressed air. 6 Conclusion In summary, the compressed air system is a relatively important system in the automotive painting process, scientifically selecting equipment, rationally arranging pipelines, using compressed air systems correctly, and strict management, and the construction cost and use cost of the coating production line. 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