How Well Do You Handle Bearings? It Makes a Big Difference

Do you handle your ball bearings with kid gloves? The way you do makes a tremendous difference.

Shristi Sharma, an applications engineer for MBP Bearings, lists the various times bearings are handled and how important proper maintenance practices matter. And, he writes, those practices start, fittingly enough, at the beginning.

For any bearing used in rotating machinery, applying best maintenance practices and using the correct enabling tools can help contribute to maximum bearing service life. These practices include proper storage and mounting, adequate lubrication, and close monitoring and inspection that can uncover the root causes of any damage. While certain uses will present unique factors that influence a bearing’s service life, several general maintenance rules can preserve the working condition of bearings regardless of the application.

Shristi Sharma offers advice for the various stages bearings go through in their life beginning with storage and mounting.

Storing Your Bearings

From the outset, proper bearing storage is critical. Bearings should always be stored in a cool, clean, low-humidity environment that is free of dust, shocks, and vibrations—never directly on the floor. Ideally, bearings should be stored flat, rather than on their end, in their original, unopened packages until mounting. If stored in a standing position, bearings are much more likely to experience false brinelling, the wear of raceways and rolling elements caused by residual vibration.

Proper Mounting Techniques for Bearings

When a bearing is ready to be mounted, maintenance personnel should confirm that both the shaft and housing are clean, undamaged and dimensionally accurate (with proper fit and tolerance). They also must confirm that the lubricant is clean and correctly specified, that the necessary tools and equipment are available and that safety precautions are followed.

Because they are precision components, bearings should be handled and mounted with care, and operators should always use correct techniques and technologies. An estimated 16 percent of all premature bearing failures are caused by poor fitting, usually using brute force and lack of awareness of suitable mounting tools and methods. When mounting a bearing, personnel should never strike it directly with any hard object, such as a steel hammer or chisel, or apply the mounting force through the rolling elements.

According to Shristi Sharma, there are two primary ways to properly mount bearings: cold and hot. If the bearings are small or medium-sized, cold mounting is recommended using fitting tools to apply the correct force to both bearing rings, separating the element that roll from the impact force.

If the bearings are larger, preheating the bearings so they expand follows the practice of Hot mounting. Hot mounting provides an easier method of installation and a better fit.

For more information regarding bearing heaters, please read this article from MBP Bearing. According to the article, 16% of premature bearing failures are the result of incorrect mounting methods.

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Maintaining Your Bearings
Predictive maintenance provides excellent tools to take a snapshot of the health of the bearings. Vibration analysis allows technicians to “hear” possible defects. Laser shaft alignment is an example of a corrective service.

Replacing Your Bearings
Removing old bearings may lead to problems with the replacement bearings if not handled correctly. Improper methods may lead to shaft damages.

A damaged shaft can compromise a machine’s efficiency and greatly influence the service life of the new bearing.

Bearings also may be dismounted for maintenance or replacement of other machine components. Because these dismounted bearings will be mounted again (unless they are damaged during dismounting), personnel should enlist proper dismounting methods and tools. Choice of tools will depend on bearing type, size, and fit.

When a bearing must be replaced because of premature failure, bearing and grease analysis can help determine root causes, which can include inadequate lubrication, contamination, errors in mounting or dismounting, and electrical damage. Pinpointing the actual causes will help prevent a repeat failure.

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Design and Characteristics of Ball and Roller Bearings

DOUBLE ROW SELF-ALIGNING BALL BEARINGS utilize an inner ring with two rows of balls, in two deep raceways; and an outer ring with a single spherical raceway.  In this way, the inner and outer rings can be misaligned relative to each other.  The resulting affect is a comparatively large angle imposing moment loads upon the balls.

The boundary dimensions of the 1200 and 1300 series are the same as the 6200 and 6300 single row deep groove bearings.

CYLNDRICAL ROLLER BEARINGS have rollers which are essentially cylindrical in shape.  This provides a modified line contact with the cylindrical inner and outer ring raceways, while the rollers are guided by ground ribs on either the inner or outer ring.  The cylindrical shape allows the inner ring to have axial movement relative to the outer ring (except the NH type).  This is especially important when accommodating thermal expansion when both rings must be press fitted.

In this series, the NJ, NF, and NH types can carry light or intermittent thrust loads.  The bearings utilizing machined bronze cages are suitable for high speed operation.

The NN3000 and NN3000K series are available in high precision tolerances and are well suited for use in machine tool spindles.

TAPERED ROLLER BEARINGS utilize conical rollers and raceways arranged so that the rollers and raceways meet at a common apex.    The rollers are guided by contact between the large end of the roller and a rib on the inner ring.  This provides high capacity for radial and single thrust loads.

SPHERICAL ROLLER BEARINGS have two rows of rollers in separate raceways which allows the bearing to compensate for angular errors.  They have large radial and thrust load capacity for heavy shock and impact loads, suitable for heavy industrial equipment.

DUPLEX BEARINGS use a set of two on a common shaft with the inner and outer rings clamped solidly together.  They are used to gain axial shaft control, rigity and extra capacity.

There are three fundamental combinations n duplex bearings: face to face (DF); back to back (DB); and tandem (DT).

The back to back mounting (DB) has the load lines through the balls converging toward the outside of the bearing.  This arrangement is preferred when the pair of bearings is to resist moment loading.

The face to face mounting (DF) has the load lines through the balls converging  towards the axis of the bearing.  This arrangement is less sensitive to slight angular errors in mounting of the bearings.

The tandem mounting (DT) is arranged so that the load lines through the balls are parallel to each other.  This mounting is used when it is desired to divide a heavy thrust load between the two bearings.  Since this mounting carries thrust load in one direction only, a third bearing should be provided to take thrust load in the reverse direction.

SINGLE DIRECTION THRUST BALL BEARINGS consist of two washers having ball grooves ground into their adjacent faces with balls and cages mounted between these grooves.  They are normally equipped with either pressed or machined cages and are suitable for carrying thrust loads at moderate speeds.

DOUBLE DIRECTION ANGULAR CONTACT THRUST BALL BEARINGS are back to back duplex bearings with a larger contact angle than that of normal angular contact ball bearings.

These bearings have been recently developed, and are primarily designed as thrust bearings for machine tools.  They utilize machined brass cages.

SPHERICAL ROLLER THRUST BEARINGS are similar to double row spherical roller bearings, but have a greater contact angle.  They are guided by ground flanges on the inner ring and operate against the spherical raceway in the outer ring.  The contact angle is approximately 45⁰.  Machined cages are normally used and oil lubrication is recommended.

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