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.

Getting To The Bottom Of Vibration Issues

In mid 2011, technicians at Kingsbury's Repair & Service Division in Hatboro, PA were consulted by the owner-operator of a 40-year-old, 114.3 MW vertical pumped storage turbine-generator located on a major river in the southwestern United States. The combination thrust and guide bearing assembly was installed beneath the generator, with a separate guide bearing assembly installed on the turbine. The 76\" diameter twelve-shoe thrust bearing was designed and produced by the original equipment manufacturer and featured a Kingsbury style, pin type, mechanical load equalizing system.

Preventing equalizing thrust bearing misalignment

There is always some degree of thrust bearing misalignment due to housing and bearing machining tolerances, or misalignment between the shaft and housing. This is considered static misalignment since the bearing is misaligned before a load is applied. This static misalignment is different from dynamic misalignment that may occur when thermal expansion and mechanical deflection causes shifts in the housing and shaft position while in operation.

Preventing electrical pitting damage in bearings

Electrical pitting damage, caused by intermediate arcing between stationary and rotating machine components, erodes the babbitted surface of a bearing, causing it to fail. With the right precautions, however, this type of damage can be prevented.

How to determine end-play in thrust bearings

The purpose of thrust bearing end play is to provide axial clearance between the thrust collar and the thrust bearing assemblies. The end play allows room for the formation of an oil film, misalignment, and thermal expansion of the bearing components. End play is the total distance the shaft can move between the two thrust bearings and is sometimes called float, thrust bearing clearance or axial clearance.
Typical values of end play can be calculated by the following formula:
EP (mils) = 0.9 * Babbitt Outside Dia.


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