TRIBOLOGICAL PROPERTIES OF COMPOSITE PISTON RINGS DESIGNED FOR OIL-FREE CONTACTS IN ECOLOGICAL TRANSPORT

The paper presents a comparison of tribological properties for two generations of sliding contacts, i.e. TG15/ Anodic Hard Coating and PASL/AlMC in oil-free piston compressors designed for ecological transport. In the first contact, the piston ring material is Teflon-graphite TG15 (PTFE+15% graphite), and in the other, an acetal-based (PA) sliding composite (PASL) with additional substances acting as solid lubricants (SL), i.e. PTFE, graphite and carbon fibres. Rings made of plastics slide under conditions of technically dry friction against a cylinder liner’s surface made of aluminium alloy and reinforced by an electrolytic oxide coating (AHC) in the case of the first contact and with a cylinder liner surface made of alloy reinforced by the addition of Al2O3fibres (AlMC composite) in the latter contact. During friction, the wear debris of the filler form a sliding film (transfer film) on the cylinder liner’s surface, which results in a friction coefficient from 0.12 to 0.1 without the use of oil or greases.