How Bearings Work

The bearing makes many of the machines we use every day possible. Without bearings we would constantly be replacing parts that wear out from friction.Objects roll more easily than they slide. The wheels on your car are like big bearings. If you had something like skis instead of wheels, your car would be much more difficult to push down the road.

12/01/2001


The bearing makes many of the machines we use every day possible. Without bearings we would constantly be replacing parts that wear out from friction.

Objects roll more easily than they slide. The wheels on your car are like big bearings. If you had something like skis instead of wheels, your car would be much more difficult to push down the road.

When objects slide, friction between them causes a force that tends to slow them down. But if the two surfaces can roll over each other, friction is greatly reduced.

Bearings reduce friction by providing smooth balls or rollers, and smooth inner and outer surfaces for the balls to roll against. These balls or rollers "bear" the load, allowing the device to spin smoothly.

Bearing loads

Bearings typically experience two kinds of loading — radial and thrust. Depending on where the bearing is used, it may see radial loading, thrust loading, or a combination of both.

The bearings in an electric motor and pulley combination face only a radial load. Most of the load comes from the tension in the belt connecting the pulleys.

The bearings in barstools and lazy Susans are totally thrust loaded. The entire load comes from the weight of the objects.

The bearing in the hub of your car wheel must support both radial and thrust loads. The radial load comes from the weight of the car; the thrust load comes from the cornering forces when you go around a turn.

Ball bearings

Ball bearings are the most common type of bearing (see illustration). These bearings can handle both radial and thrust loads, and are usually found in applications where the load is relatively small.

In a ball bearing, the load is transmitted from the outer race to the balls and from the balls to the inner race. Since the ball is a sphere, it only contacts the inner and outer race at a point, which helps it spin smoothly. But it also means that there is not very much contact area carrying that load. If the bearing is overloaded, the balls can deform or crack, ruining the bearing.

Roller bearings

Roller bearings are used in applications such as conveyer belt rollers where they must carry heavy radial loads. In these bearings, the roller is a cylinder. The contact between the inner and outer races is a line instead of a point. This spreads the load over a larger area, allowing the bearing to handle much greater loads than a ball bearing. However, this bearing type is not designed to handle thrust loads.

A needle bearing is a variation of the roller bearing. It uses cylinders that are very small diameter rollers. This allows the bearing to fit into tight places.

Ball thrust bearing

Ball thrust bearings are mostly used for low speed applications and cannot handle much radial load. Swivel chairs and small hand tools use this type of bearing.

Roller thrust bearing

Roller thrust bearings can support large thrust loads. They are often found in gearsets of car transmissions between gears and between the housing and the rotating shafts. The helical gears used in most transmissions have angled teeth. This causes a thrust load, which must be supported by a bearing.

Tapered roller bearings

Tapered roller bearings can support large radial and thrust loads. They are used in car hubs where they are usually mounted in pairs facing opposite directions, so they can handle thrust in both directions.

Magnetic bearings

Some very high-speed devices, such as advanced flywheel energy storage systems, use magnetic bearings. These bearings allow the flywheel to float on a magnetic field created by the bearing.

Some flywheels run at speeds near 50,000 rpm. Ball or roller bearings would melt or explode at these speeds. Magnetic bearings have no moving parts. They can handle these incredible speeds.





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