Characterisation of friction behaviour of flake, spheroidal, and compacted vermicular graphite cast irons

摘要

This paper investigates friction behaviour of flake, spheroidal, and compacted vermicular graphite cast irons used for piston rings of automobile engines. Pin-on-disc friction tests are conducted under dry and room temperature conditions. Pins are made of graphite cast irons, and discs are chromium molybdenum steels. During a test, Coulomb friction coefficient and sliding distance are recorded. Graphite size fraction on the initial surface of the cast iron is determined and its influence on friction coefficient is investigated. Results show that friction coefficient growth rate during the 'running-in' period can be expressed as a power-law function of sliding distance. Two parameters in the power-law form, the damage rate constant and the damage exponent, can describe a friction coefficient evolution during the period. It is identified that graphite size fraction has an influence on a friction coefficient evolution. The influence of graphite size in cast iron is described with the damage rate constant.