Assuring Reliability of Compressors Using HFC Refrigerants

In Japan, the refrigerant used in room air-conditioners has been changed from HCFC-22 (R-22) to R-410A, a blend of HFC-32 and HFC-125 (50/50 vt%), in order to protect the ozone layer. Generally, the miscibility between the refrigerant and refrigeration oil must be assured, because the oil needs to return to the compressor from the refrigeration cycle and lubricate the sliding parts. Alternative oils with good miscibility with HFCs have been developed, because mineral oil, the primary oil used with R-22, has low miscibility with HFC. The chlorine atoms which make up R-22 create excellent extreme pressure performance on the sliding parts in compressors; however, they are the cause of the depletion of the ozone layer. Because HFC does not have any chlorine atoms in its molecular structure, it is essential to prevent the sliding parts from scuffing (seizing) and wearing when using HFC in the compressors,. Therefore, anti-wear additives are added to the oils, and alternative sliding materials and surface treatments have been used in rotary, swing and scroll compressors which are fitted to room air-conditioners in Japan. The problems in using HFC in swing compressors are similar to those for rotary compressors. This paper describes the technical problems of ensuring the reliability of rotary and scroll compressors using R-410A. Background Both rotary compressors and scroll compressors use HFC refrigerants. In Japan air-conditioners, including room air-conditioners, packaged air-conditioners and multi air-conditioners for buildings, and refrigeration machines all use HFC refrigerants. Description of Compressors Figure 1 presents the cross-section views of rotary compressor. The main sliding parts in a rotary compressor are the sliding bearings, located at the upper and lower ends of the cylinder and supporting the crankshaft, and the vane tip in the cylinder. The suction gas is compressed until reaching the required pressure in the cylinder and discharged to the inside of the shell and then discharged to the refrigeration cycle from the discharge port. The reliability of the sliding bearing is ensured by maintaining the viscosity of the oil mixed with the refrigerant and the film thickness under operating conditions. However, the vane tip contacts the outside surface of the rolling piston linearly and high contact pressure is loaded between the two parts and the outside surface of the rolling piston slides on the vane tip. Therefore, anti-wear technology is required for the vane tip.