Research on Friction Pair of Micro Piston Oilless Air Compressor

Experience exchange micro-piston type oil-free air compressor friction pair research Foshan City Guangshun Electric Co., Ltd. Huang Zhuangwei gold and filled polytetrafluoroethylene as an oil-free lubrication friction pair, and gave the test results.

1 Overview Oil-free air compressors are used in more and more industries due to their simple structure and excellent performance, especially the ability to produce clean compressed air.

In China, electromagnetic or diaphragm type micro air compressors have formed a certain scale of production. Unfortunately, these air compressors have low pressure, low flow rate and poor durability, and should not be used as oxygen generators or dental equipment. The micro-piston type oil-free air compressor and the high air pressure and flow rate are the most suitable for the gas equipment of the oxygen machine, but it is still in its infancy.

The most important part of the development and production of miniature piston air compressors is how to solve the technical problems of oil-free lubrication. This article will summarize the author's experience in production practice, explain the essentials of oil-free lubrication technology for micro-piston air compressors, and introduce an oil-free lubrication friction scheme.

2 Oil-free lubrication characteristics and basic requirements for oil-free lubricating materials Oil-free lubricating air compressors have the following advantages compared with traditional oil-lubricated air compressors: (1) Elimination of grease contamination and dripping, available Uncontaminated air.

(2) The post-processing equipment such as oil supply tank and oil circuit system and gas purification have been eliminated, which makes the product structure simple and light, saves investment and reduces maintenance.

(3) Adapt to a wide temperature range, adapt to special working conditions, such as radiation resistance under radioactive conditions, high vacuum resistance and corrosion resistance, etc., suitable for occasions where lubricating grease cannot be used.

(4) Increased anti-corrosion ability, which is more important for the southern part of the humid climate.

Of course, oil-free lubricating materials are prone to wear and have a short service life.

For this reason, the following requirements must be met when selecting an oil-free lubricating material: (1) a lower coefficient of friction, a lower shear strength in the sliding direction, and a higher yield limit in the direction of loading, and prevention. The penetrating ability of the surface of the friction surface, that is, the physical properties of the material is anisotropic.

(2) The adhesion is strong, and the adhesion is required to be greater than the shearing force when sliding, so as to prevent the oil-free lubricating material from peeling off from the substrate or the metal surface.

(3) There must be sufficient cohesion between the solid particles to establish a sufficient lubricating film to prevent the peaks from penetrating the friction surface.

(4) The size should be the largest in the direction of low shear strength to ensure that the particles are well oriented between the sliding surfaces.

(5) It can maintain performance in a wide temperature range and does not have a chemical reaction.

3 micro-piston air compressor oil-free lubrication program for the micro-piston air compressor oil-free lubrication material, requires long service life, stable flow, good heat dissipation. The national standard requires that the service life of oil-free compressors be 3000h, while the foreign standards require 10,000h. To this end, we have selected aluminum alloy and filled polytetrafluoroethylene plastic as the material of the friction pair (see Figure 1).

The cylinder liner material is aluminum alloy LD5, and its composition is as follows: This material is a high-strength aluminum alloy, and has good ductility, and can form a dense structure after extrusion, which is favorable for the formation of a surface hardened layer. Unfortunately, the thermal conductivity of aluminum is small, so it is necessary to make a thin-walled cylinder liner (with a wall thickness of 2.5 mm), and a fan can be used to forcibly dissipate heat to obtain a better effect. The processing difficulty of the thin-walled cylinder liner is improved, and the requirement for the roundness is 0.01, the precision is 0.04, and the surface roughness is 0.1. After the cylinder liner is finished and then squeezed with the squeeze ball, the above can be effectively solved. problem.

In order to increase the surface hardness and enhance the wear resistance, it is necessary to use a low temperature anodizing treatment. The temperature is around 0 ° C, helping to form a dense oxide layer. The thickness of the oxide layer should be about 20 μm. Since the thickness of the oxide layer is increased, a large number of micro-cavities can be formed on the surface, which is advantageous for friction with the cup. Generally speaking, the friction coefficient between aluminum and polytetrafluoroethylene is not low, reaching 0.4. However, due to the micro-cavities of the aluminum oxide layer, a small amount of PTFE film is rubbed after a short friction, and the friction coefficient drops sharply to 0.04. Further wear of the Teflon material can be prevented.

The material of the cup is filled with polytetrafluoroethylene. It has high chemical stability and excellent high and low temperature resistance. It is a very self-lubricating material and can be used for a long time in the range of 200-260 °C.

However, pure PTFE has low hardness, low strength, and poor wear resistance. Direct use causes a decrease in flow rate, and materials such as copper powder and graphite must be added to increase hardness and elasticity. After trial production, we successfully made the reinforced filled PTFE, the hardness reached the performance of the material itself, the structure size of the cup also has a great relationship with the performance of the whole machine. Several of the structural parameters shown in Figure 2 are interrelated and must be determined by experimental optimization.

4 Test results on ZW370A air compressor Compressor parameters: cylinder diameter 63.7mm, stroke 11.2mm, input power 370W, input current 1.7A.

After many trials and repeated experiments, we have obtained the best solution for the optimization of the skin structure. The specific data is shown in Table 1.

The original data optimization data of the skin size of the cup is measured by the structure-optimized cup. The overall performance of the measured air compressor is shown in Table 2. In the test, the flow rate can reach a stable value of 3.4 mh after 10 minutes of starting the air compressor, indicating that the performance of the whole machine is improved after the optimization of the cup.

Air compressor performance, exhaust pressure, flow, power, current, starting load. In addition, we have carried out several durability tests to control the exhaust pressure to 0.2 MPa, continuous operation for more than 2000 h, the performance is basically unchanged, disassemble inspection, The skin was found to be almost wear-free. Our company has produced thousands of compressors according to the above scheme. After being put on the market, the users are satisfied and there is no premature wear problem.

5 Conclusion In the miniature piston compressor, the low-temperature anodized aluminum alloy LD5 is used as the cylinder liner, and the reinforced laminated PTFE sheet is used as the piston cup. The oil-free lubricating friction pair is stable and durable. It can meet the oil-free lubrication requirements of miniature piston air compressors.

1 week Xin Xin, Gong Jiufeng. Lubricant material manual. Shanghai: Shanghai Science and Technology Press Huang Zhuangwei 528000 Guangdong Foshan Guangshun Electric Co., Ltd.

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