Axial and radial load on bearings due to thermal expansion
Axial and radial load on bearings due to thermal expansion
(OP)
Does anyone out there know how to calculate the axial and radial lods on bearing due to thermal expansion?
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Axial and radial load on bearings due to thermal expansion
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RE: Axial and radial load on bearings due to thermal expansion
RE: Axial and radial load on bearings due to thermal expansion
I will attempt to gather the appropriate information from SKF.
RE: Axial and radial load on bearings due to thermal expansion
RE: Axial and radial load on bearings due to thermal expansion
RE: Axial and radial load on bearings due to thermal expansion
When there is a large thermal growth issue in the axial direction, it is general practice to constrain a shaft at one end (with something like a deep groove ball bearing) and let the other end float (using a roller bearing).
As for radial fit with a large CTE mismatch between bearing race and housing, there are several things you can do. Say you have a magnesium housing and a steel bearing. If you design for a proper fit at room temp, you will have a loose fit (and fretting) at an operating temp of say 200 degF. Coversely, if you design for a proper fit at an operating temp of 200 degF, you may have a condition where the intereference between the housing and bearing at room temp or lower, removes any running clearance in the bearing and causes it to seize. To avoid this problem you can press and pin a steel sleeve into the nonferrous housing, and then machine the steel sleeve for a proper fit with the bearing. If there is room, you can also get bearings that have a bolt flange on the outer race, eliminating the need for a press fit.
Good luck.
Terry
RE: Axial and radial load on bearings due to thermal expansion
Assume steel shaft with a coefficient of thermal expansion equal to 6.5x10^-6 in/in°F. Assume temperature differential equal 200°F. E equal 2.9 x 10^7 lb/in^2.
For convenience sake assume shaft length equal 10 inches and diameter equal 1 in. (area = 0.7854 in^2)
If the shaft is constrained between two fixed bearings then there will be no expansion and thus the strain will be:
e=10in x 6.5 x 10^-6 in/in°F x 200°F
e=.013 in/in
and since stress = e x E
stress = .013in/in x 2.9 x 10^7 lb/in^2
stress = 377,000 lb/in^2
stress = Force / area
then
Force = stress x area
Force = 377,000lb/in^2 x 0.7854 in^2
Force = 296,096 lb
Obviously this is oversimplified. The setscrews on a mounted bearing will slip and/or the shaft will buckle in addition to overloading the bearing, but the forces generated by thermal expansion are very high. You should use an expansion bearing and a fixed bearing for shafts subjected to thermal loads.