Shenyang gas compressor factory and lanzhou institute of chemical physics, Chinese academy of sciences are the first to be engaged in the research and development of oil-free filled ptfe ring compressor in China.Since 1964, the experimental research on self-lubricating materials such as piston ring, floating ring, sealing ring and guide sleeve of compressor has been carried out.
* because the gas does not contain oil, so that the work of the air valve in the state of dry friction work, so looking for self-lubricating valve piece material, valve piece structure and heat treatment, such as ring valve piece with its guide pin quenching hardness soon wear;Instead of quenching, the valve will grind out a gap;Using filled teflon guide pin is still not satisfactory;Application of silicone grease with high adsorption capacity can be improved.Change to mesh the valve, its thin place, especially when lower than 0 ℃ air intake, prone to cold brittle fracture.
In order to ensure that the piston ring work, according to the plastic piston ring almost no elastic, in order to ensure the pre-sealing force using tension ring, its specific pressure in the range of 0.1-0.3 KGF /cm2.
In order to prevent the piston in the cylinder, in the process of reciprocating movement and cylinder wall collision must be set floating ring (or guide support ring), the vertical compressor floating ring axial height should be piston ring axial height of 1.5-2 times.
The piston ring, floating ring, seal ring clearance in the material ratio has not yet finalized before the actual test must be determined.
(1) of the piston ring test is to place ring inside diameter is equal to the diameter of the cylinder mould and heated to 150 ℃ between tension ring, according to its thickness is different, heat preservation for 2-3 hours.
(2) floating ring test is place the ring on the outside diameter is equal to the cylinder diameter and inner diameter equal to the piston of floating ring groove bottom diameter heated to 150 ℃ between two fixed slot, according to its thickness is different, heat preservation for 2-3 hours.
(3) seal test is the actual axial thickness of plastic sealing ring (note the test direction and forming in the same direction) heated to 100 ℃ heat 1-2 hours, after the heat preservation of sample measured with micrometer card its deformation, in order to ensure its accuracy, using multi-point measurement, take the average.
In 25 KGF/cm2 secondary compression of air compressor, oil free trial, after 616 hours test the second interview found that when the size of the piston ring, the floating ring:
* the axial thickness of the first-stage piston ring is increased by 0.11-0.22mm;
The thickness of the secondary floating ring is increased by 0.17-0.22mm, and the thickness of the secondary piston ring is increased by 0.08-0.121mm;
* the opening clearance of each ring is larger than before the operation;
U when the expansion coefficient is measured in the constant temperature box also found that the piston ring after the heat insulation, at the same temperature measurements is much less than the calculation, and after cooling to room temperature, opening gap unable to restore to the original state, in the Soviet union book "fluorine plastic" published in working temperature should be above 50-70 ℃ for eliminating stress treatment.
(5) the radial clearance between cylinder and piston should be larger than that of the lubricated cast iron ring, approximately (0.01-0.015) D, D is the cylinder diameter.However, for vertical compressors, the minimum clearance shall not be less than 0.5mm, and for horizontal compressors, it shall not be less than 1mm.
6 cylinder surface roughness, when there are two views in the world: one is that general with 6 advisable, its explanation is: in the plastic ring and cylinder lens movement relative to the friction process, the plastic molecules is transferred to the metal surface, and to the roughness of the 6 most conducive to plastic film formation, after running in the early, from plastic to metal to plastic to plastic, the friction and wear becomes small.