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Part 12 - Bearings

The earliest bearing were probably plain wood or stone surfaces lubricated with grease or oil used to move heavy weights like the cut stones used to build the pyramids in Egypt. Plain bearing were also used to improve the productivity of potters wheels. The first linear bearing were probably rollers made from tree trunks.

Plain bearings

The use of the wheel for transport required bearings between the wheel and the axle. Initially this was simply a hole in the wooden wheel hub running on a wooden axle shaft. This also had to take some axial load to prevent wheel falling off or rubbing the side of the cart. Animal fat would have been used to minimize wear and the hardest wood was used for both the axle and the hub of the wheel. As these wore down the hole might have been bored out to a larger size and a cylindrical bushing fitted to take up the wear. As the cost of metals declined the axle and the bushing were made from steel or bronze or brass. But wood was still used for some plain bearings until recent times. John Harrison's clocks with bearings made from lignum vitae wood (guayacan or guaiacum) still work well after hundreds of years, while his clocks with metal bearings are rarely run to minimize wear. Lignum vitae was also use for the propeller shaft on steam ships in the 19th century.

Mechanical watch makers still use plain bearings made from sapphire to reduce friction and provide more precise time keeping.

Plain split bearings are still used to support the crankshaft on some multi-cylinder engines where it is difficult to fit a roller or ball bearing.

Plain bearings , usually with a lubricant such as oil or graphite, are still the most common bearings because they often provide acceptable accuracy, life, and friction at minimal cost.

Ball bearings

The first wooden ball bearing supported a rotating table. It was recovered from the wreck of a Roman ship in Lake Nemi, Italy dated to 40 BCE.

Around 1500 CE, Leonardo da Vinci designed a helicopter incorporating ball bearings. About the same time Agostino Ramelli published sketches of roller and thrust bearings.

Cages

The balls or rollers in bearing can rub against each other causing additional friction unless they are separated within a cage. The first practical caged-roller bearing was invented in the mid-1740s by the clock maker John Harrison for his H3 marine timekeeper.

Bearings were very important for the new industrial machinery designed during the Industrial Revolution where they improved efficiency by greatly reducing friction.

The first modern ball bearings patent was issued to Philip Vaughan, a British iron-master in 1794.  

Another patent was awarded to Jules Suriray, a Parisian bicycle mechanic, on 3 August 1869. The radial style ball bearings were fitted to the winning bicycle ridden by James Moore in the world's first bicycle road race, Paris-Rouen, in November 1869.

In 1883 the founder of FAG, Friedrich Fischer, developed an approach for milling and grinding balls of equal size and exact roundness and created a specialized bearing industry.

Sven Wingquist, of the SKF ball-bearing manufacturer in 1907, was awarded Swedish patent No. 25406 for the design of a self-aligning ball bearing which allowed the bearing to tolerate a small angular misalignment caused by shaft deflections or misalignment. The spherical roller thrust bearing is a derivative of this design.

Henry Timken, an innovator in carriage manufacturing, patented the tapered roller bearing in 1898 which carried axial as well as radial loads and permitted more precise machinery alignment. They are normally used in opposed pairs.

Friction

Reducing friction in bearings is necessary to minimize wear, and to avoid overheating and premature failure of the bearing. Bearing life is better when the bearing is kept clean and well lubricated which is difficult in some applications. For example, bearings in a rock crusher conveyor are exposed constantly to hard abrasive particles. A maintenance program might require frequent lubrication without dismantling the bearing housings for cleaning.

Before the 1970s, sealed bearings were not used on most machinery. From the late 1700s through mid 1900s, industries employed workers called oilers to lubricate machinery frequently with oil cans or grease guns. Today most bearings are sealed for life.

Factory machines typically have central pumps to periodically supply oil or grease to the machine's bearing surfaces or bearing housings. This may be controlled manually or automatically by the machine's computer.

Lubricating pumps in internal combustion engines typically supply oil to all bearings continuously from a reservoir (sump).