The hottest technology to improve the reliability

2022-08-16
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Technology to improve the reliability of rotary compressor

compressor is the host of air conditioner, just like human heart. The performance, reliability and more than 10 years of service life of the air conditioner must be guaranteed by the compressor. How to improve the reliability of the main engine compressor has always been a concern of the refrigeration industry. The following views are put forward based on my years of technical practice in rotary compressors and the analysis of foreign well-known brands of rotary compressors in recent years

1. Rotary compressors are high-precision, small power machinery. The internal high and low pressure channels of the movement are completely sealed by the gap and oil film, and the friction between slides is also lubricated by the oil film formed in the gap, so as to reduce wear, ensure reliability and prolong service life

1.1 maintaining a uniform and small gap between the sliding parts of the movement is a prerequisite for improving the performance and reliability of the compressor

1.1.1 clearance between cylinder sliding plate groove and sliding plate

the product drawing stipulates that the clearance between general compressors is 20~30 μ m. Small high-speed variable frequency compressor can be reduced to 15~20 μ m。 The technology requires that the sliding plate can pass through the sliding plate groove in the way of free fall to prove that the gap between the two is uniform. The purpose is to realize: the sliding plate groove can not only guide the sliding plate to move up and down freely, form the suction and exhaust cavity together with the rolling piston and cylinder wall and implement sealing, but also create conditions for forming high-pressure oil film, ensuring lubrication, reducing wear, improving reliability and creating conditions. However, the traditional manufacturing process uses three-point welding to connect the cylinder with the shell. The thermal stress of three spot welding causes the shell to shrink and squeeze the cylinder sliding plate groove, causing the sliding plate groove to deform. This not only affects the uniformity of the fit gap between the two, but also may even cause the fault of sticking the sliding plate. Analyze the influencing factors of deformation: it is related to the cylinder structure, material, three spot welding process, and the connection mode between the movement and the shell. The deformation of the traditional axe cylinder (Fig. 1) after welding is the largest, especially when the material strength is low (such as using metal mold eutectic castings), the three spot welding parameters are improperly selected, the three-point parameters are uneven, and the time is not synchronized, and its deformation can even be as high as 15 μ M above. I once saw a factory where more than 1/3 of the compressors came off the production line due to stuck sliding blades after three spot welding. In terms of pressure, the first to improve the cylinder structure and material is Japan's "Mitsubishi Electric". They control the deformation of the sliding vane groove to 5% by using the spoke cylinder (Figure 2) fc25 sand casting μ Within M. In order to ensure that the gap between the two is uniform and provide a prerequisite for appropriately reducing the gap value. In the early 1980s, Mitsubishi Electric changed the welding cylinder to the welding bearing (frame) on the rotary refrigerator compressor, and designed the upper bearing into a spoke shape to reduce the impact of welding thermal stress (Figure 3). Thus, the deformation of the sliding plate groove is completely avoided. At present, the newly developed products of major compressor manufacturers in Japan basically adopt the technology of spoke cylinder and welded bearing. On this basis, Mitsubishi Electric and Panasonic also changed the traditional broaching process of the slide groove to the method of milling + grinding, so that the dimensional accuracy of the slide groove can reach ± 1 μ m. The parallelism and flatness of the two sides also increased from 7 μ M increased to 4 μ m. Thus, the fit gap between the sliding plate and the sliding plate groove is reduced to 15~20 μ Within m, it creates conditions for improving efficiency, reducing wear, avoiding jamming and ensuring reliability. (see Fig. 1, 2, 3)

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1.1.2 properly reducing the fit clearance between the upper (main) bearing and the crankshaft and appropriately increasing the height of the main bearing are effective measures to ensure the stable rotation of the compressor, reduce vibration and noise, and improve reliability. At present, some manufacturers have narrowed the gap between the two to 20 μ M, Panasonic's newly improved 2K series has increased the height of the main bearing to 52 μ m. South Korea LG changed the three spot welding process from welding the cylinder to welding the main bearing, and also increased the height of the main bearing from 47.5mm to 54.7mm, which brought about stable operation and reduced wear. In order to reduce the clearance, increase the height and make the clearance uniform, in addition to improving the machining accuracy of the crankshaft long shaft, the main bearing hole is also honed after internal grinding. In order to avoid raising the machining accuracy of crankshaft and main bearing hole too high, the matching method can be adopted for them

1.1.3 with the improvement of the manufacturing process of rotary compressor and the improvement of equipment level, other matching clearances (such as cylinder and piston (high), cylinder and sliding plate (high), piston inner hole and crankshaft eccentric circle... Etc.) have a further reduction trend. This is also beneficial to improve the performance of the compressor and ensure its reliability.)

1.2 adopting a powerful oil supply system to provide sufficient lubricating oil with a certain pressure to each sliding part of the movement is an important means to ensure sealing, improve performance, ensure lubrication, reduce wear and improve reliability

1.2.1 the design of oil blade shape of compressor pump is very critical, and the selection of torsion angle should be appropriate. Too small, lifting head is not enough; Too large will cause the oil to rotate in the crankshaft hole, which is not conducive to the formation of high oil pressure

1.2.2 the hole of the crankshaft should be designed into a stepped shape, and the fitting part with the blade can be larger, and the part at the top of the passage should be as small as possible (LG is 4mm). This design is not only conducive to the removal of chips and dirt in the process, but also conducive to the formation of higher oil pressure in the hole during the operation of the blade pump oil, so as to improve the oil delivery capacity. Sanyo also inserted a long pin supporting the rotor disc into the small hole. Because the insertion of the pin further reduces the clearance of the hole, it can not only form high oil pressure, but also facilitate the separation of oil and gas, reduce the discharge of oil to the compressor, ensure the stability of the oil level in the oil pool, and achieve the purpose of simple process, which is a good structural design

although the through-hole crankshaft is conducive to the formation of high oil pressure, if the chips and dirt are not discharged cleanly, and the oil and steam are not completely separated, in turn, it will affect the reliability of the compressor

1.2.3 in order to ensure that the oil supply of the upper and lower bearings is sufficient and evenly distributed in the whole bearing, it is advisable to open an active oil supply groove on the inner wall of the upper and lower bearing holes (generally, the upper bearing is left-handed and the lower bearing is right-handed)

1.2.4 in order to reduce the oil discharge as much as possible, some manufacturers also use L-shaped exhaust pipe

1.3 select high-quality refrigeration engine oil to improve the effect of lubrication and sealing and ensure the safety performance of the compressor

the function of refrigeration oil is to minimize the friction of lubricating parts; Maintain the pressure difference between high and low pressure parts; Heat is dissipated to the outside through the high-pressure housing. Therefore, the refrigeration engine oil should have appropriate kinematic viscosity to facilitate the formation of oil film on the friction surface. It is also required that the refrigeration engine oil has high thermal stability. When the temperature in the machine changes greatly, the viscosity change of the oil is still relatively small to ensure that the core components always maintain good sealing and lubrication

it can be seen from table 1 that ms56, an air-conditioning compressor refrigeration oil specially developed by Nippon Oil (the former Mitsubishi Oil) for Mitsubishi Electric, has the best comprehensive performance - the clearest color, the smallest viscosity change at 40 ℃ and 100 ℃, especially in the temperature range (80~100 ℃) where the air-conditioning compressor mainly works, ms56 has the highest kinematic viscosity - that is, it has the best sealing and lubricating performance. At the same time, due to its highest flash point and insulation strength, Therefore, its safety performance for compressors is also the best, and it is a high-quality refrigeration oil worthy of recommendation in the air conditioning industry

based on the above, now take the small double cylinder variable frequency compressor of Mitsubishi Electric as an example: under the condition of small fitting clearance, strong oil delivery system and high-quality refrigeration oil (ms56), after the heavy load test of 30Hz and 130 HR, the refrigeration capacity of the compressor has increased (± 0.35%), and the energy efficiency (COP) has not decreased, but increased (± 1.03%), achieving the ideal effect of similar saturation. Anatomical analysis shows that the wear of its sliding parts is also very small. The maximum local wear of the cylinder, sliding vane groove and suction side is only 6 μ m. Only 9 on the discharge side μ m. The maximum wear of slide r surface is only 1.5 μ m. The local wear of the crankshaft's long and short shafts is within 2 μ Within m, the maximum wear of the main bearing is also 2 μ Within m, it can be said to be very small

2. Controlling the range of the series, appropriately increasing the height of the cylinder and reducing the eccentricity of the crankshaft are effective ways to reduce the centrifugal load of the compressor and maintain stable operation. For example, Mitsubishi Electric Corporation of Japan divides its "RH" series movement components into large and small ones in terms of structure. The exhaust volume of the small machine is small, and the cylinder thickness is set at 23.8. The exhaust volume of the mainframe is large, and the thickness of the cylinder is set at 30.8. Due to the division of large and small, this series of minicomputers are more miniaturized. Due to the increase of the thickness of the cylinder, the exhaust volume of the mainframe increases correspondingly, so that the eccentricity of the mainframe crankshaft is relatively reduced, the centrifugal load is reduced, the vibration is reduced, and the reliability is improved. However, at present, in order to expand the range of products, some manufacturers improperly increase the shaft eccentric moment and increase the centrifugal load too much, which sacrifices the reliability of the compressor and damages the interests of consumers

3. In the process of suction and exhaust, the core components of rotary compressor bear alternating load, in order to improve the stress of main components. To reduce vibration, many well-known manufacturers have adopted elastic support structures in their products, with good results

3.1 in order to improve the force on the crankshaft, increase the pressure bearing surface, and make the support elastic to a certain extent, a deep groove (generally about 1.5mm wide and 8mm deep) is opened at the upper and upper bearing end planes of the large capacity compressor near the supporting baby stroller, electric baby stroller, children's bicycle, children's 3-wheel car hole. (Figure 4) Mitsubishi Electric "pH, NH" series large-scale models, compressors with LG capacity greater than 29cc/rev and high-level double cylinder variable-frequency compressors also adopt this structure, with good results. (see Figure 4)

3.2 Japan "Toshiba" changed the crankshaft thrust surface from the annular surface under the eccentric circle to the crankshaft small end face, and adopted the thrust seat (elastic) fixed at the small outer circle of the lower bearing, supported by the thrust plate placed in it and nitrided on the surface (Figure 5). Because of the structure, the bearing surface of the whole rotor of the compressor not only coincides with the center of gravity, which is conducive to stable operation, At the same time, its elastic support absorbs the vibration caused by torque changes during the operation of the crankshaft, thus further improving the reliability of the compressor. (see Figure 5)

3.3 Japan's "Toshiba" three spot welding process adopts a unique transition flange (Figure 6) method in structure (that is, a cast (to be processed) or stamped transition flange is connected with three spot welds on the shell first, and then the cylinder is fixed on the transition flange after the relative position is accurately processed. This structure not only avoids the influence of three spot welding on the sliding blade groove, but also brings about the miniaturization of the cylinder, and can freely adjust the steam gap between the stator and rotor of the motor in the assembly process, so as to improve the starting performance of the compressor. Cast iron transition flanges processed on large compressors also play a role in vibration absorption and noise reduction. (see Figure 6 for angle control and torque control)

4. Selecting materials with high strength and good wear resistance to manufacture the sliding parts of the compressor is an important guarantee to reduce wear and prolong service life

4.1. Since the sliding parts of the compressor core work under lubrication, metal materials with excellent anti-wear performance under lubrication should be selected. The metallography of pearlitic gray cast iron is a composition with hard structure distributed on the soft matrix. After running in, the matrix of this structure is worn to form grooves to maintain oil film,

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