Improving the tightness of end-face seals in compressors

Abstract

The working surfaces of the stationary and moving rings in end-face seals are usually finished by lapping, because other finishing processes do not ensure the desired surface characteristics -- nonparallelism within 1.5 ~ and surface finish within Ra = 0.16-0.04 p. The stationary rings are usually made of antifriction graphite-base material while the moving rings are made of 20Kh steel with a hardened case-carbufized surface of up to 0.8 mm thickness. The lapping process results in impregnation of the rings with abrasive particles (from the lapping paste) and swarf from wear of the lapping plates. Our studies showed that the depth of impregnation was 15-30 ~ for steel rings and 5-60 ~ for graphite rings. In our opinion, the abrasive particles impregnated in the ring surface during lapping cause periodic loss of tightness in end-face seals during operation. Friction and wear of the stationary and moving rings in operation result in periodic displacement of the abrasive particles. Thus, a gap is created between the mating surfaces of the rings and the Khladonoil mixture starts to leak out. The extent of leakage is usually higher than that specified by the USSR standard GOST 7475-77. After some time the dislodged abrasive particles get thrown out of the contact area under the influence of frictional and centrifugal forces, the gap between the mating surfaces is reduced, and steady-state operation with minimal leakage of Khladon-oil mixture is reestablished. The cycle is repeated when new abrasive particles are once again dislodged and start to move freely at the ring interface. At the Odeskhoiodmash plant a new process of finishing [i, 2] has been developed and introduced for machining the mating surfaces of sealing rings. This process ensures the desired parallelism and surface finish while avoiding impregnation of the machined surface with abrasive particles. The new process of finishing the working surfaces of sealing rings (microgrinding)is done with the help of an abrasive stick 4 (Fig. i) which has an oscillating motion in the direction B and a reciprocating motion in the direction C parallel to the surface which is to be machined. The stick is also given a rocking motion (in the direction A around the pivot 5) perpendicular to the directions of oscillation and reciprocation so that the tip of the stick wears out to a curved surface 3. The line of contact 2 between the stick and the component moves along the curved surface 3, while the stick rocks in the direction A. At the same time, the stick moves along a chord of the component i as a result of the reciprocating motion. The high unit pressures at the contact zone and favorable conditions for cleaning the surface by means of a cooling-lubricat