A tapered roller bearing from a manual transmission
Have you ever wondered how things like inline skate wheels and electric motors spin so smoothly and quietly? The answer can be found in a neat little machine called a bearing.
The bearing makes many of the machines we use every day possible. Without bearings we would be constantly replacing parts that wore out from friction. Now, we'll learn how bearings work, we'll look at some different kinds of bearings and explain their common uses, and we'll explore some other interesting uses of bearings.
A simple bearing, like the kind found in a skate wheel
Bearings reduce friction by providing smooth metal balls or rollers, and a smooth inner and outer metal surface for the balls to roll against. These balls or rollers "bear" the load, allowing the device to spin smoothly.
The bearings that support the shafts of motors and pulleys are subject to a radial load.
The bearings in the electric motor and the pulley pictured above face only a radial load. In this case, most of the load comes from the tension in the belt connecting the two pulleys.
The bearings in this stool are subject to a thrust load.
The bearing above is like the one in a barstool. It is loaded purely in thrust, and the entire load comes from the weight of the person sitting on the stool.
The bearings in a car wheel are subject to both thrust and radial loads.
The bearing above is like the one in the hub of your car wheel. This bearing has to support both a radial load and a thrust load. The radial load comes from the weight of the car, the thrust load comes from the cornering forces when you go around a turn.
In a ball bearing, the load is transmitted from the outer race to the ball, and from the ball to the inner race. Since the ball is a sphere, it only contacts the inner and outer race at a very small point, which helps it spin very smoothly. But it also means that there is not very much contact area holding that load, so if the bearing is overloaded the balls can deform or squish, ruining the bearing.
Roller Bearings Roller bearings like the one illustrated below are used in applications like conveyer belt rollers, where they must hold heavy radial loads. In these bearings, the roller is a cylinder, so the contact between the inner and outer race is not a point but a line. This spreads the load out over a larger area, allowing the bearing to handle much greater loads than a ball bearing. However, this type of bearing is not designed to handle much thrust loading.
A variation of this type of bearing, called a needle bearing, uses cylinders with a very small diameter. This allows the bearing to fit into tight places.
Cutaway view of a roller bearing
Ball Thrust Bearing Ball thrust bearings like the one shown below are mostly used for low-speed applications and cannot handle much radial load. Barstools and Lazy Susan turntables use this type of bearing.
Ball thrust bearing
Roller Thrust Bearing Roller thrust bearings like the one illustrated below can support large thrust loads. They are often found in gearsets like 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 that must be supported by a bearing.
Roller thrust bearing
Tapered Roller Bearings Tapered roller bearings can support large radial and large thrust loads.
Cutaway view of a tapered roller bearing and a double tapered roller bearing
Tapered roller bearings are used in car hubs, where they are usually mounted in pairs facing opposite directions so that they can handle thrust in both directions.
The new San Francisco International Airport uses many advanced building technologies to help it withstand earthquakes. One of these technologies involves giant ball bearings.
Click on "Earthquake!" to see the earthquake bearing support system at work.
The 267 columns that support the weight of the airport each ride on a 5-foot-diameter steel ball bearing. The ball rests in a concave base that is connected to the ground. In the event of an earthquake, the ground can move 20 inches in any direction. The columns that rest on the balls move somewhat less than this as they roll around in their bases, which helps isolate the building from the motion of the ground. When the earthquake is over, gravity pulls the columns back to the center of their bases.
For more information on bearings and related topics, check out the links on the next page!