Caring for bearings

April 1, 2000
When you work for years with rolling-element bearings, you learn those "tricks of the trade" you can't find in a textbook or catalog. Here, we continue a regular column of questions and answers to help you.

More about tapered roller bearings

Q: Because tapered roller bearings are so rugged, do I have to be careful about handling them?
A: You are right — tapered roller bearings being rugged, but you still have to handle them with kid gloves, just as you would any bearing. In particular, be careful not to damage the cage by pressing or pulling against it when removing or installing a bearing. A distorted cage may let the rollers skew; a loose cage may cause the cage or rollers, or both, to fall off the cone.

When using a puller to remove a cone, be sure it contacts the bearing face and not the cage. When the puller is properly adjusted and in position, the cage should be free to rotate.

To make removal easier, sometimes you can pour hot oil between the cone outside diameter and the rollers to expand the cone while applying pressure through the puller.

A word of caution, though, when using heat to expand the inner ring when mounting. The hot inner ring will tend to pull away from a colder shaft shoulder. If you can, seat the hot inner ring against the shoulder with a locknut and, after it has cooled, use the locknut to snug the inner ring against the shoulder.

The same general rules regarding protecting the cage from damage apply during bearing assembly. Cups and cones of smaller bearings should be pressed onto shafts or housings with drivers — not a punch or chisel. A driver is a tubularshaped device that fits over the shaft, touching the bearing over the right area to distribute the hammer blow or press force at one end of the driver uniformly around the bearing axially at the other. Drivers press the cups and cones straight, won’t damage the cage, and prevent nicking of bearing parts.

Q: To save money, when we find a worn or damaged cup or cone, we replace it and reuse the undamaged component. This practice OK?
A: Nice try; bad idea. If a cup or cone is damaged, replace the whole bearing. After being run, both cup and cone develop a distinctive pattern of raceway wear. Combining either with a new component could cause edge stresses on races and bring premature failure.

You can inspect a cone race by shining a light through the bearing. You can also use a thin wire to probe a cone race for pitting or spalling. Nicks and gouges on a cup race can be detected by running your fingernail over the suspected area. Light nicks and gouges may be removed with emery cloth; heavier damage requires bearing replacement.

Q: Any special procedures to follow in regreasing a tapered roller bearing?
A: The most obvious requirement is to be sure you regrease a bearing with the lubricant type recommended by the manufacturer. Any of several types of mechanical grease packers are preferred to grease bearings — they keep grease clean and free of shop dirt and dust.

But you can do it by hand. To pack a cone assembly, force grease into the space between the rollers and cone. Be sure you add enough grease to get it between rollers and cage, not just coating their outsides. To ensure proper distribution, push grease into the bearing from the large end of the rollers until it purges out at the small end. After the cup is installed in the housing, fill the cup with enough grease to cover the outer race.

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