Precautions for compressed air systems used in vehicle painting

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Compressed air systems for the spraying industry https://p3-tt.byteimg.com/origin/pgc-image/5838d4880a2b47eaaf568427af1edfe1?from=pc 1. The importance of compressed air systems Compressed air is another important energy source in the painting process, in addition to water, electricity, coal, oil, steam, and natural gas. The proper use of the compressed air system directly affects the quality of painting and the painting costs. A brief discussion is provided on aspects such as the role and application points of compressed air systems in automotive painting, the composition of compressed air systems, the quality classification of compressed air, the consumption volume of compressed air, the daily use and maintenance of compressed air systems, as well as the painting defects caused by abnormalities in compressed air systems and their solutions. 2. Functions and application points of the compressed air system: The main functions of the compressed air system in the automotive painting process are to transport paint, atomize it, power pneumatic tools, remove moisture and dust, and operate pneumatic valves. Points of use for compressed air: there are points of use in the manufacturing process as well as those related to tools and equipment. The main points of use in the manufacturing process include: the paint transfer station, painting stations (where spray guns are used), cleaning stations, grinding stations (where pneumatic grinders are used), sealing stations (where sealant guns are used), and polishing stations (where pneumatic polishers are used). The main points of use for tools and equipment include: stations for installing and removing tools (where pneumatic wrenches are used), locations for installing chain stoppers, and locations for installing pneumatic valves on steam pipelines. 3. Composition of the compressed air system The compressed air system is mainly composed of an air compressor, main pipelines, branch pipelines, air storage tanks, adsorption dryers, filters, oil-water separators, adsorption-type oil-water separators, pressure regulators, pressure gauges, etc. 1) Air compressor: Refers to the air compressor in the air compressor room, which is mainly composed of a motor and a compression mechanism. Its model is selected based on the overall gas consumption of the factory. Automobile manufacturers often choose air compressors with a displacement of 10 m3/min, 20 m3/min, or 40 m3/min, and an exhaust pressure of 0.8 MPa. Since the quality of compressed air produced by screw compressors is better than that produced by reciprocating compressors, screw compressors are now frequently chosen. 2) Main pipeline: The main pipeline is a fully enclosed circular circuit that is fixed in place and used to deliver air to various branch pipelines, ensuring a constant air pressure at all points where air is used. Circuit breakers are installed in segmented zones to facilitate sectional maintenance. The selection of main pipeline diameter, air delivery volume, and length is shown in Table 1 below. During installation, the main pipeline is often tilted at a rate of 1/100 in the direction of the compressed air flow in order to ensure its quality. 3) Branch pipes: Branch pipes are pipes that extend from the top of the main pipe to deliver air to various usage points. Pipelines commonly use galvanized pipes or pressure-resistant, anti-static hoses that are free of silicon; when adjusting the pressure range, the pressure drop of the hoses must be taken into account. 4) Air storage tank: A pressure vessel installed on the main pipeline, with a capacity typically ranging from (1-5) m3. 5) Freeze dryer: Installed at the rear end of the gas storage tank, it removes most of the moisture using freeze-drying technology. However, since it relies on freezing to remove oil, it can only reduce the dew point to 2–10°C; if further water removal is required, an adsorption dryer must be added. 6) Oil removal filter: Installed between the cold dryer and the adsorption dryer, it can effectively remove oil contaminants from the air. It also protects the adsorbent in the adsorption dryer that follows. It is recommended to use a reliable and efficient oil removal filter, such as an activated carbon filter or a catalytic oxidation oil removal filter. 7) Adsorption dryer: Installed at the inlet end of the compressed air supply to the painting production line, or on the compressors in the air compression station; it removes water molecules from the compressed air through adsorbents, thereby achieving drying. The compressed air treated by adsorption dryers is drier, with a dew point typically ranging from -20 to -70°C. 8) Precision filter: Filters the compressed air delivered by the air compressor and refrigerated dryer, removing oil and water from the compressed air and discharging them. 9) Oil-water separator: Installed on the branch pipeline to filter and discharge water and oil. 10) Pressure regulating valve and pressure gauge: Adjust and display the compressed air pressure. 4. Quality grade of compressed air: Air compressors compress air from the atmosphere, raising its temperature to over 140°C. Since compressed air contains moisture, oil, and dust, it must be processed using freeze-dryers and oil-water separators in order to meet the requirements for quality grade II of compressed air used in automotive painting – that is, the pressure dew point should not be higher than -40°C, the dust particle size should be less than (0.5–1) μm, and the oil content should not exceed 0.10 mg/m3. https://p6-tt.byteimg.com/origin/pgc-image/f512fec465fe435fb984e0234ace5ffe?from=pc 5. Precautions for using compressed air systems Proper use of compressed air systems can prevent defects in painting that may arise from their misuse, thereby reducing unnecessary waste of painting costs. To use a compressed air system correctly, the following points should be noted: 1) Regular removal of oil and water: The air storage tanks, filters, and oil-water separators in a compressed air system are all equipped with valves for removing oil and water. Some of these valves are automatically controlled, allowing for regular removal of the small amounts of oil and water that form as a result of changes in temperature and humidity during the transmission of compressed air. Automatic discharge valves are commonly used in gas storage tanks and filters. In oil-water separators and activated carbon filters, manual discharge valves are often used; therefore, it is necessary to establish strict intervals for discharge and to implement rigorous management in order to ensure controlled discharge, thereby preventing the formation of shrinkage defects in the paint film caused by excessive amounts of oil and water remaining in the compressed air. 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, it is common to simply replace the oil-water separator when its filter element needs to be replaced during normal use. The replacement cycle of filter materials is influenced by many factors, such as the production line’s output, season, and the piping installation in the compressed air system. Through long-term use and experimentation, it is essential to establish a scientific replacement cycle for each production line. When this cycle is determined appropriately, it can prevent defects like pinholes in paint films caused by inadequate filtration of oil and water from the compressed air, while also avoiding unnecessary cost expenditures resulting from frequent replacement of filter materials. 2) Check the quality of compressed air: When using compressed air at the cleaning station, it is important to develop the habit of checking its quality before starting work. That is, after draining out the oil and water, use clean canvas gloves; with the palm of the hand, press the compressed air hose in place, open the compressed air valve and blow for 2-3 minutes. Only after checking that there are no traces of oil or water on the gloves should the cleaning process be continued. This prevents the occurrence of paint film defects caused by oil and water in compressed air. 3) Replace leaking quick connectors promptly: At the grinding station, finishing station, and painting station, quick-connect connectors are used to deliver compressed air to grinders, polishers, and spray guns. These connectors often suffer from poor sealing, which leads to air leaks over time; therefore, it is necessary to inspect them regularly and replace them as needed in order to avoid waste of compressed air. 6. In summary, the compressed air system is also a relatively important system in the automotive painting process. The scientific selection of equipment, proper layout of pipelines, correct use of the compressed air system, as well as strict management, have a significant impact on the construction costs, operating costs, and painting quality of the painting production line.