Dealing With Bearing Misalignment Issues

How much static misalignment capability does a non-equalizing thrust bearing with spherical supports have?

A misalignment condition is based on the assumptions that the collar (or thrust disc) is perpendicular to the shaft, the collar surface is flat and smooth, and the runout is within an acceptable tolerance.

The geometry of the support is a significant factor in determining how much a non-equalizing thrust bearing can be misaligned. The line contact support cannot tilt in the direction of the misalignment and has minimal deflection under load. A spherical support tilts in both the tangential and radial directions and deflects under load. This deflection greatly improves the misalignment capability of the bearing.

A KingCole size 8225, direct lubricated, non-equalized thrust bearing was reviewed. Note that the "8" refers to the number of pads and the "225" is the radial length of the pad in inches when divided by 100.

The operational performance of this bearing was calculated using ISO VG 32 oil at 50°C inlet temperature at surface speeds of 30, 60, 90 and 110 m/s and thrust unit loads of 1.0, 2.0, and 3.0 MPa. When this bearing is severely misaligned, one pad will take the majority of the thrust load. The criteria used to determine the maximum limits for continuous operation of this pad are a unit loading of 6 MPa and a 125°C pad temperature in the 75/75 location. (If lower temperature limits are applied by specification, the allowable misalignment values will also be lower.)

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Contributed by: David M. Casper, Engineering Service Coordinator, Kingsbury, Inc