A study of the tribological behaviour of polyamide 66 with varying injection-moulding parameters

Injection-moulded polyamide 66 has been widely used for gear and bearing applications but the mechanisms of wear in such components are not fully understood. In particular, little attention has been paid to the effects of processing on materials microstructure and tribological performance. Polyamide 66 discs were moulded using a range of mould wall temperatures. The discs in the as-moulded and machined conditions, representing a variety of microstructures and surface conditions, were tested (unlubricated) on a twin-disc wear testing machine, previously shown to be useful for separating the effects of rolling and sliding in non-conformal contacts. The test parameters of speed, load and slip ratio are useful in simulating wear and friction in applications such as gears where the geometry and complex mechanics mask the fundamental materials behaviour. Optical microscopy, between crossed polars, and differential scanning calorimetry were used to determine bulk crystallinity and spherulite morphology as a function of process parameters. The as-moulded (transcrystalline) and fine-machined surfaces were characterised using optical examination and scanning electron microscopy. The different bulk and surface structures were related to wear performance when running against similar and dissimilar (steel) materials.