Suzuki, N. and Hikasa, A., "Evaluation of the Tribological Property of Resin Coating by the Addition of Nylon and Graphite Particles," SAE Technical Paper 2012-32-0090, 2012, doi:10.4271/2012-32-0090.
A resin coating was applied to a piston skirt for use in an internal combustion engine to reduce the frictional resistance on its surface. The purpose of the authors' study was to observe the change in surface states with the addition of nylon and graphite to the coating as solid lubricant particles in order to investigate the tribological properties of the surface. The authors observed self-formed microdimples on the resin surface when nylon particles were added to the polyamide-imide (PAI) coating material. These microdimples functioned as oil reservoirs similar in size to the nylon particles.The authors used PAI as a binder, and graphite particles (5 μm) and two different grades (5 and 10 μm) of nylon-12 particles as additives. These materials were mixed in a solvent, and an aluminum test sample was coated. The test sample was then heated in an oven to cure the PAI. Next, the texture of the surface was observed. The tribological properties were measured with a ball-on-disk tribometer under both oil lubrication and dry conditions.When only graphite particles were added to PAI, microdimples did not form on the surface of the coatings. However, the authors observed microdimples when both nylon and graphite particles were added. Sliding tests under oil lubrication showed a minimum value of the friction coefficient when 3-5 vol% of nylon was added. The addition of nylon particles to the graphite/PAI mixture decreased the friction coefficient at slow sliding speeds. Under the dry condition, the addition of a small amount of nylon did not affect the coefficient, but the friction coefficient decreased as the amount of graphite particles increased.