Michael L. Killian

Sliding Contact Test for Engineered Surfaces

This article describes a test process for engineered surfaces such as surface treatments, surface coatings, and lubricant performance for both liquid and solid lubrication. Test constraints require that it be rapid enough to allow for easy multiple testing and be of low cost. In addition, the test should have a simple geometry for specimen preparation and ease of interpretation of results and provide key data such as friction, temperature, and wear, and interactions of these as a function of time. Besides lubricated contacts, dry contacts should also be easily tested and evaluated. Products of interest that have a wide variety of tribosurfaces would include heavy-duty truck transmissions (such as gears, bearings, synchronizers), high-pressure hydraulic systems (such as pumps, motors, actuators), and automotive components (such as tappets, valves, gears). Since this tribotesting must easily relate to products and product tribocontacts, the test must have a systematic approach to these tribocontacts. The test geometry is a rotating ring on washer (flat-on-flat) with Kingsbury-type lubricant entryways to ensure adequate lubrication. All conditions of testing are controlled, except for varying rotational speeds and applied loads along a programmed path. The product of pressure and velocity (PV factor) is increased in a way that drives the contact interface from hydrodynamic lubrication toward boundary lubrication, following the Stribeck curve. Test results have provided data that distinguish the performance capability of various surface treatments and coatings and data that measure the range of performance capabilities of various lubricant regimes.