It was interesting that I got the same question two days in a row from two different sources. But this is not the first time that I have had to answer this question.
Today most SRACBBs are flush ground or universally ground. This means that at the factory the bearing manufacturer precisely grinds both side faces of both sides of the bearing such that they can be mated together in any orientation. As well, they can be used as single bearings.
When assembled face to face or back to back, the bearings will achieve a factory set preload or clearance (axial play) when both the inner ring and outer ring faces touch. Generally speaking in the market today, most manufacturers offer two versions, one with nearly zero axial play and one with some axial play.
When I discussed the question with the millwrights at these two facilities, they reported that they tighten the bearing inner ring (in a back-to-back arrangement) just enough to still allow the outer rings to rotate independently. What was troubling about this question is that it suggests that they are not properly mounting the bearing by driving the inner rings together and thus achieving the intended factory set clearance.
The proper way to mount a pair of angular ball bearings is to ensure that the outer rings are clamped together in a face to face arrangement as illustrated in the centre image in the gallery above.
The gap “C” must be removed by squeezing the inner rings together. The same principle holds true for a face to face arrangement in which you squeeze together the outer rings. Don’t worry that the outer rings may not rotate separately, this is the way the bearings were designed and selected to work.
View a video that explains mounting at: SKF Angular Contact Ball Bearings – Mounting and dismounting.
Douglas Martin is a heavy industry engineer based in Vancouver. He specializes in the design of rotating equipment, failure analysis and lubrication. Reach him by email at email@example.com.
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