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Piston Ring Handbook
Piston Ring Manufacture

Grey cast iron and steel piston rings are manufactured in different processes. At Federal-Mogul grey iron piston rings are cast as individual rings in a noncircular shape; there are other ring manufacturers who cut the individual rings from pots or cuffs. The rings are generally machined to the required shape by means of double cam turning, a process in which the ring blank, already axially ground, is copy turned simultaneously on the inside and outside diameters. After a segment equivalent to the free gap is cut from the ring it assumes the free shape that will give it the required radial pressure distribution when fitted into the cylinder. Once inside the cylinder the ring is completely light tight on its outside diameter and exerts the predefined radial pressure against the cylinder wall.

Besides using double cam turning, ring blanks can also be shaped by machining the inside and outside diameters separately. This involves cam turning the outside diameter of the noncircular blank and machining the inside diameter with the ring in the compressed state. The gap is cut out in a step between O.D. and I.D. machining. Heat forming as a means of shaping piston rings should be mentioned to complete the range of options, but this process is seldom used.

Steel piston rings are made from a profiled wire. The rings are first coiled into a circular shape and then the gap is cut out. The necessary shape is obtained using a heat treatment process in which the rings are mounted onto an arbor appropriately designed to impart the required radial pressure distribution.

Profiling of the running faces of taper faced, Napier and slotted oil rings is carried out, depending on the ring design, on automatic O.D. lathes or profile grinding machines using special profile cutting tools before or after coating.

 
 

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