Randy Blair, age 15, of Santa Fe, N.M., for his question:
WHO WERE THE FIRST TO USE BEARINGS?
Bearings are part of a machine in which another part turns or slides. A bearing serves to support the moving part and to reduce the friction or rubbing as much as possible.
The ancient Egyptians and Assyrians were the first people to use bearings. They used them to roll 'huge blocks of stones from the quarries to build palaces, temples and pyramids.
Bearings have also been used in weapons. The battering rams used by Greek warriers contained bearings. But it wasn't until the Industrial Revolution that bearings found their modern application in the steam engine and in textile machinery.
Today bearings are used in many machines. There are a number of different types.
The plain or oil film bearing contains a revolving pivot, called a journal. This type is often called the sleeve bearing because it fits around the journal like a coat sleeve.
A thin film of oil covers both the bearing and the shaft and helps reduce friction. The bearing speeds up the process by which the revolving shaft transmits power.
The ball bearing is another important type. The journal inside a ball bearing works upon a number of steel balls. These balls roll easily in a track called the ball race. The balls are usually in a frame or case that keeps them apart from each other but allows contact with the moving parts of the machine.
A roller bearing has rollers that are shaped like cylinders or tapered cones. The rollers usually lie side by side around the shaft.
The purpose of both ball and roller bearings is to change the slide action into a rolling action. The friction takes place on a series of points instead of on a flat surface.
Some machines, such as refrigerator motors, use self lubricating bearings. This is because the machine cannot be lubricated after it has been assembled. Self lubricating bearings are also used where oil splashing may interfere with the operation of the machine.
The term "jewel bearing" is applied to the bearings of a watch, but other precision instruments, such as those in airplanes, also use jewel bearings. The pivot is crystal or some precious stone, such as a ruby.
To ensure the finest quality bearings, manufacturers make steel in electric furnaces that provide the exact control over the temperature, proportions and uniformity of the metal.
To produce a seamless tube from which a bearing's cones and cups are made, the ingot is worked on the inside and outside over a circular forge. Next the bearing parts are machined, hardened, ground and honed to a final accuracy that measures to within one one millionth of an inch of the desired size.
Modern civilization moves on bearings. Wheels turn in bearings on their axles. The pistons that drive the wheels of locomotives slide back and forth in bearings. And most of today's modern machines depend on bearings.