Piston Rings Material Selection

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What ever you use the material has to be softer than the cylinder block itself or so well designed that the pistons rings will wear & not the cylinders.

Pistons Rings come in many different materials and manufactured by different processes. For your type of application, it is better to go for Cast-Iron rings which has 'Flake Graphite' formation in its structure, and manufactured by Spin-Casting method. This method of casting gives a compact grain structure etc. Ofcourse, this is one of the method, amongst many available today. The hardness of piston rings also should be compatible with that of cylinder bore hardness.

The ceramic coated cast iron piston rings, also, give good life but tends to be expensive compared to the other types. There are so many suppliers of such piston rings, oil wiper rings etc. for automobile and motorbike users, so can be readily available at a reasonable price. Also, the compressor manufacturers, for their certain types of compressors, use the same piston rings and oil wiper rings in their products regularly.

one supplier which come to my mind is Perfect Circle. Am sure there are many more.