The MAR-MOT piston rings are supplied with hard coatings as well as protective coatings, depending on the Customer’s requirements. The coatings are specified and described below.
To increase the piston ring and the cylinder working surface life, the hard coatings are used. They include: chromium and molybdenum coating.
Chromium coating (Cr)
The chromium coating is the most popular coating characterised by high abrasion resistance. It is used mainly on working surfaces of the compression rings with the highest temperature and pressure and the oil control rings due to the high unit pressure.
Molybdenum coating (Mo)
Molybdenum coating is characterized by extraordinary abrasion resistance and efficient heat conduction, which facilitates heat transmission from the piston to the cylinder and, due to the slightly porous surface which absorbs the oil molecules it prevents the piston ring from seizing in the cylinder.
To improve the operational properties and to protect the piston rings against corrosion the following protective coatings are used: phosphate coating, tin coating and oxidation.
Phosphate coating (P)
Phosphate coating is a soft coating enabling quicker running in of the piston rings in the early stage of operation and protects the surface against corrosion.
Oxidation is applied mostly on the surfaces of the multi-piece oil control ring side plates. The coating is thin and protects the surface against corrosion.
Tin coating (Sn)
The Tin coating is very soft and facilitates the ring operation on the piston by lowering the friction force.