Rolling friction torque

Here, M is the torque of the rolling object, hr is the coefficient of rolling friction, FL is the normal force (load), Ff is the friction force and R is the radius of the rolling object (see Fig. 11.4). In this case the friction coefficient is not dimensionless but has the unit of length. Other definitions use... 

Wear tests are conducted with a thrust-washer test apparatus. A sample thrust washer is mounted in an antifriction bearing equipped with a torque arm (see Fig. 3-105) [323]. The test-specimen holder is drilled to accept a thermocouple temperature probe. The raised portion of the thrust washer bears against a dry, cold-rolled, carbon-steel wear ring with a 12- to 16-microinch finish at an 18 to 22 Rockwell C scale hardness at room temperature. Each evaluation is conducted with a new wear ring that has been cleaned and weighed on an analytical balance. The bearing temperature and friction torque are continuously monitored. 

Here, M is the torque of the rolling object, is the coefficient of rolling friction, and... 

Powered backup rolls augment the torque transmitted by the chucks and prevent the bolt bowing away from the knife (Figure 11.4c). The additional torque provided by coated, high friction backup rolls means that the torque transmitted by the chucks can be reduced. Backup rolls enable logs to be turned down to 130 mm cores without wood failure at the ends of the bolt that occurs where the chucks spin free. Smaller chucks are possible and the lathe can peel to a smaller core diameter. 

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