Friday, May 26, 2017

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.