Improved Test Method for Tribological Evaluation of High Performance Plastics 2019-01-0183
Engineering plastics are widely used in many tribological applications due to their inherent advantages such as reduced weight, ease of manufacturing, improved chemical compatibility, and damping characteristics. However, the process of selecting an appropriate polymeric material system for a specific application involves significant experimentation. Although, standardized methods of evaluating tribological performance of engineered plastics exist, their ability to be indicative of part performance in the end application is rather poor, primarily because of (a) the typically low pressure-velocity combinations used in these tests, (b) their inability to properly differentiate between various failure modes (wear vs creep vs melting of the plastic in case of thermoplastic polymers) and (c) the large number of variables that exist in a tribological system including applied pressure, relative speeds, thermo-mechanical properties of the mating components, surface roughness/hardness parameters, type of lubricant in case of lubricated contacts and most importantly geometry.
In the present work, a four hour test to evaluate dry and lubricated wear of high performance plastics is developed. This allows for multiple repeats to understand variation within samples. A modified multi-grooved test specimen is used to promote two-body wear by removal of wear debris through the grooves. For the four hour lubricated test, the pressure-velocity conditions are chosen to ensure that the test is in the mixed lubrication regime. The experimental set-up is described and tribological data for a range engineering plastics are summarized.
A case study is presented where in a thrust washer molded using a thermoplastic material that was developed using the proposed methodology, is compared to a thrust washer molded from a commercially available material, using test parameters as in the end application. Results show that the proposed test methodology is suitable for rating tribological performance of materials and correlates well to component performance in the end application.