BALL BEARING TYPES

As a group, ball bearings have many uses in trucks, cars, and off-the-road vehicles. Some of the most common are in steering assemblies, transmissions and differentials. In other applications, such as heavy-duty wheel hubs, they have been replaced by roller bearings.

In addition to the inner and outer races, rolling element and separator, there are three accessory components frequently used with ball bearings:

• Snap rings

• Shields

• Seals

Snap rings are separate components used to locate ball bearings in the housing. They hold the bearing in place the same way a shoulder on the shaft or in the housing would.

Shields are circular rims that cover the open space between the two races, on one or both sides of the bearingThey are attached to the edge of only one race, with clearance left at the inner race. Shields prevent dirt and particles from getting in the bearing, while letting excess lubrication flow through the bearing and escape if necessary.

A seal is a metal-based ring lined with a single, double or triple lip made of rubber, elastomers, synthetic or non-synthetic materials. It is a barrier designed to retain lubricants while excluding moisture, fine dirt, dust, or other contaminants from damaging the bearing. Unlike shields, seals prevent lubricants from leaking out of the bearing.

Operation

Though ball bearings and roller bearings share the same objective – to lessen friction – their strategies are quite different. The mechanical forces underlying ball bearing operation are simple to understand. When a ball bearing is inactive and still, the load applied will be distributed evenly through the races and balls on the contact area. Once the bearing is nudged by a moving load, the ball starts to roll. Material in the race bulges out in front of the ball, then flattens out behind the ball. The ball flattens out in the lower front quadrant, then bulges in the lower rear quadrant. This process continues for each ball as long as the load is in motion.

Continual metal-to-metal contact between the balls and races will eventually wear down the parts and result in bearing failure. So even in doing its job – to lessen friction between two surfaces – the bearing creates its own internal friction. This is one reason why lubrication within the bearing is critical in relieving friction. There are four different ball bearing types used in automotive and fleet applications:

• Single row

• Angular contact

• Double row

• Ball thrust

Single row ball bearing

The single row is one of the most popular ball bearing designs. A crescent-shaped cut in both the inner and outer races forms a wide groove in which a single row of balls roll Though designed primarily for radial load capacity, this bearing can support substantial thrust loads in either direction, even at high operating speeds Careful alignment between the shaft and housing is critical to its performance. The bearing is available with seals and shields for extra protection against contaminants, plus retention of lubricant. A variation of the single row bearing is the maximum capacity bearing. Additional balls can be assembled in the bearing for greater radial load

capacity .However, the extra loading area limits the bearing’s thrust load capacity.

Benefits/advantages

 Good performance under radial loads

 Deep groove permits thrust load capacity in either shaft direction

Assures contaminant-free operation when seals are mounted on the bearing

Applications

• Transmission

• Alternator

• Differential

• Steering gear

• Air conditioner clutch

Angular contact ball bearing

The angular contact ball bearing features two high thrust supporting shoulders – one on the inner race, the other at the opposite side on the outer race. The two shoulders form a steep contact angle slanted toward the bearing’s axis, assuring the highest thrust capacity and axial rigidity. This design can support a heavy thrust load in one direction, sometimes combined with a moderate radial load.

Benefits/advantages

High thrust capacity

Axial rigidity

Applications

• Clutch release

Double row ball bearing

The double row ball bearing combines the design principles of the single row and angular contact bearings. Like the angular contact bearing, it has grooves in the outer and inner races which are positioned so that the load lines through the balls form either an outwardly or inwardly converging angle of contact  The two rows of balls assure a lower axial displacement than the single row design. That is, the bearing is less likely to become misaligned on the shaft or in the housing. The double rows can support heavy radial loads and work well under thrust loads in either direction.

Benefits/advantages

 Thrust capacity in either direction

 High radial capacity

 Less axial displacement

Applications

• Air conditioner clutch

Ball thrust

Designed primarily for clutch release applications, the ball thrust bearing has high thrust capacity. The load line runs parallel through its balls to the shaft axis, so there is little axial displacement Flat shoulders on the shaft and housing are recommended under heavy loads.

Benefits/advantages

 High thrust capacity

 Minimal axial displacement

Applications

• Clutch release