What a ring-on-ring test tells you
A thrust washer test measures friction and wear when two flat annular faces slide against each other under a distributed load, the way washers, thrust bearings, bushings and face seals run in service. It is used above all to qualify self-lubricating plastics and composites, where performance depends on how the material transfers to and runs against its counterface over a large area.
How the test works
- The lower ring is mounted on the rotating spindle and the upper ring in a stationary holder, faces parallel.
- A controlled normal load presses the faces together, so the whole annulus is in contact.
- The lower ring rotates at the set speed. The friction torque is measured and converted to a coefficient of friction; depth and acoustic emission can be recorded at the same time.
- Wear is evaluated on the rings after the test, as a wear rate.
Why conformal contact behaves differently
Point and line contacts concentrate the load into a small area, so the initial contact pressure is high and drops as a scar forms. A face contact starts conformal: pressure is low and nearly uniform, heat is generated over the whole annulus, and debris must travel across the face to escape. As a result, wear mechanisms, frictional heating and transfer-film formation can differ from what a pin-on-disk test on the same materials would show. For washers and face-contact parts, ring-on-ring is the closer simulation.
Alignment and torque
Two practical points govern a good thrust washer test. First, the faces must stay parallel so the load is spread over the full annulus rather than an edge. Second, the drive must hold speed against a high friction torque, because the friction force acts over the whole face at a significant mean radius. The T2000’s regulated pneumatic loading keeps the face load constant as the washers wear, and its motor supplies up to 14.7 Nm intermittent torque.
Test environments
Many thrust washer applications run hot, lubricated or both. The ring-on-ring module can run inside an oven up to 1000 °C, in a liquid cup heated to 150 °C, or under controlled humidity, inert gas or cooling to -40 °C, so friction and wear can be measured at service conditions rather than only at room temperature.
