Compressed air is an important energy resource in automotive coating process besides water, electricity, coal, oil, steam and natural gas. Improper use of compressed air system will increase vehicle coating quality and painting cost. This paper mainly discusses the function and application point of compressed air system in automobile painting, the constitution of compressed air system, the quality classification of compressed air, the amount of compressed air, the daily use and maintenance of compressed air system, the defects caused by abnormal compressed air system and their solutions.
1 compressed air system in automotive painting applications
The compressed air system mainly plays the role of conveying paint, atomizing paint, driving pneumatic tools, blowing dry water and dust, and driving pneumatic valves in the automobile painting production process.
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.
2 composition of the compressed air system
The compressed air system is mainly composed of an air compressor, a main pipe, a branch pipe, a gas storage tank, a freeze dryer, a filter, a water separator, an oil-water separator, a pressure regulating valve, a pressure gauge and the like.
Compressed air system
a) Air compressor: The air compressor of the air compressor room is mainly composed 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.
b) Main line: The main line is a fully enclosed loop that is fixedly installed and delivers air to each line to ensure a 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.
c) Branch line: The branch line is the line that is connected to the top of the main line to deliver 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 needs to be considered when adjusting the pressure range.
d) Gas storage tank: pressure vessel installed on the main road, capacity is often selected
e) Freeze dryer: installed at the inlet end of 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.
f) Filter: compressed air sent out by air compressor and dryer
g) Oil-water separator: Installed on the branch line to filter and discharge water and oil.
h) Adsorption oil water separator: It is often used in the paint station, the paint adjustment station and the pre-paint cleaning station before installation. The internal activated carbon can effectively remove the dust and oil contained in the compressed air. And impurities such as silicide.
i) 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 the 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 related to the management level of the line.
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 systems requires attention to the following points:
a) 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 is equipped with an oil drain valve, and some valves are automatic control valves, which can be set by the discharge interval. To achieve a small amount of oil and water generated by the regular discharge of 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, strict management to achieve regular discharge, and avoid industrial compressed air quality grade solid particle size and concentration. 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 level maximum oil content / (mgm-;) due to excess oil and water in the compressed air Lead to shrinkage of the film film Table 6 painted compressed air system filter material replacement cycle disease.
b) Replacement cycle, common coating tools, compressed air usage, filter, tool name, oil-water separator, process use point, 1 time, half-year diameter, equipment, point diameter, adsorption, water separator, nozzle, blow gun, body washing machine, butterfly grinding machine, double-motion grinding Machine Linear Motion Grinding Machine Horizontal Grinder Cutting Grinder Finishing Grinding Machine Polishing Machine Pneumatic Door Pneumatic Lift Table 5 Painting Compressed Air System Oil Water Discharge Interval Device Name Emission Interval Gas Storage Tank 1/Month Filter Oil Water Separation Process use point 1 / d equipment use point 1 / week adsorption oil water separator
c) Regularly change the filter material: filter, oil-water separator and precision oil-water separator are equipped with different types of filter material filter or activated carbon), which need to be based on the inlet and outlet pressure of the filter, oil-water separator and adsorption oil-water separator. The difference is to replace the filter material 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 based on empirical values.
d) Since the cost of filter replacement in the oil-water separator is not much different from the cost of replacing the entire separator, the oil-water separator is usually replaced directly during the use of the replacement filter cycle.
e) 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. It is reasonable to prevent the shrinkage of the paint film due to the unclean filtration of compressed air oil and water, and to avoid the waste of cost caused by frequent replacement of filter materials.
f) 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.
g) Quickly replace the leaking air quick connector: In the grinding station, finishing station, and the compressed air use point of the painting station, the quick-connect connector is generally used to deliver the compressed air to the sander, the light machine and the spray gun. These quick-connect connectors often have a leaking phenomenon caused by poor sealing during use. Therefore, it is necessary to promptly check and replace these parts 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. The quality of the painting has a great influence.