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piston ring face lapping/finishing

piston ring face lapping/finishing

(OP)
I want to do surface finishing of keystone piston rings(has trapezoidal cross-section).The surfaces to be finished are actually the two sides of each ring that are tapered at 7.5 degrees(taper is produced using a lathe).

On the drawing of the ring,it says that lapping machine can be used.But is lapping generally a good choice for tapered surfaces?and if I use lapping,what should be the design considerations for the fabrication of this lapping machine?(material of lapping plates,paste used? rpm of plate etc?after how many rings lapping plates will need to be changed?)

The rings are made up of Molybdenum-tungsten steels heat treated to HRC 19-27.The surface finish achieved should be Delta8(0.63 microns)

The drawing of rings is shown in the accompanied images:

RE: piston ring face lapping/finishing

They may exist, but I've never seen a lapping machine that would work on a conical surface.
Every lapping machine I have used would eventually grind the cone perfectly flat.

I suppose you could lap the rings like you lap engine valves, with a conical brass lap and some abrasive paste. I'd expect to have to face the lap to the desired angle in a lathe after every ring; maybe you could do five or ten rings on a charge, but that depends on how far away from a conical form you can allow the lap, and the workpieces, to become.



Mike Halloran
Pembroke Pines, FL, USA

RE: piston ring face lapping/finishing

(OP)
shouldn't the angle of lap remain at 7.5 degrees?bacause of uniform wear at internal and external diameter of lapping face?

RE: piston ring face lapping/finishing

Uniform wear is a mythical concept, taken seriously mostly by MBAs.

Mike Halloran
Pembroke Pines, FL, USA

RE: piston ring face lapping/finishing

(OP)
ok,can you please tell me which other processes can be used instead of lapping?

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