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Quarter-turn Bearing Friction Coefficient Testing

Figure 1: Kalsi Engineering Bearing Torque Fixture Allowed for Cost Effective Testing of Multiple Bearing Materials and Service Conditions.
Figure 1: Kalsi Engineering Bearing Torque Fixture Allowed for Cost Effective Testing of Multiple Bearing Materials and Service Conditions.

The bearing friction coefficient test program is an excellent example of how Kalsi Engineering can develop specialized test fixtures to perform cost effective testing to develop key data to support a wide range of valve sizes and designs. Bearing friction is of particular interest because it is a significant torque component for quarter-turn valves. The bearing torque depends on three primary factors: (1) the bearing force, (2) the bearing/shaft friction coefficient, and (3) the shaft diameter.

The bearing friction coefficient is dependent on the material pair as well as on (1) fluid media (clean water, dirty water, dry air, etc.), (2) temperature, (3) contact stress, (4) dwell time, and (5) bearing wear. Contact stress can directly affect the friction coefficient for metal-to-metal material pairs and can indirectly affect friction coefficient for plastic lined bearings through accelerated wear of the lining. Accelerated wear can lead to unanticipated metal-to-metal contact resulting in a significant increase in bearing friction.

To address industry needs, Kalsi Engineering designed a specialized bearing torque fixture (see Figure 1) and performed bearing friction testing as part of a joint effort with the nuclear power industry.

The quarter-turn bearing test program included numerous types of metallic and nonmetallic bearings. Tests were performed using water and air at ambient and elevated temperature conditions. The tested were performed under various bearing loads and each specimen was tested for numerous cycles to ensure a stable friction coefficient was determined and that any galling potentials were identified (see Figure 2). Dwell tests were performed to determine the change in break out friction as a function of time.

The bearing friction test program provided valuable data to the US nuclear power industry, and has helped ensure safe and reliable valve operation.

Figure 2: Galling on bearing and shaft occurred due to high edge load. The presence of galling significantly increases the bearing friction.

a) Galling near edge of bearing
b) Galling on shaft
Figure 2: Galling on bearing and shaft occurred due to high edge load. The presence of galling significantly increases the bearing friction.