Bearings are an important part of contemporary machinery and equipment. Its main function is to support the mechanical rotating body, reduce the friction coefficient during its movement, and ensure its rotation accuracy. According to the different friction properties of moving elements, bearings can be divided into rolling bearings and sliding bearings. Among them, the rolling bearing has been standardized and serialized, but compared with the sliding bearing, its radial size, vibration and noise are larger, and the price is also higher.
Rolling bearings are generally composed of four parts: outer ring, inner ring, rolling element and cage. Strictly speaking, it is composed of six parts: outer ring, inner ring, rolling element, cage, seal, and lubricating oil. Mainly equipped with outer ring, inner ring and rolling elements, it can be defined as rolling bearing. According to the shape of the rolling elements, rolling bearings are divided into two categories: ball bearings and roller bearings. The early form of linear motion bearings was to place a row of wooden poles under a row of skid plates. Modern linear motion bearings use the same working principle, but sometimes use balls instead of rollers. The simplest rotary bearing is a bushing bearing, which is just a bushing sandwiched between the wheel and the axle. This design was subsequently replaced by rolling bearings, which replaced the original bushings with many cylindrical rollers, each of which was like a separate wheel. An example of an early ball bearing was discovered on an ancient Roman ship built in 40 BC in Naimi Lake, Italy: a wooden ball bearing was used to support a rotating tabletop. It is said that Leonardo da Vinci once described a ball bearing around 1500. Among the various immature factors of ball bearings, there is a very important point that collisions between the balls will cause additional friction. But this phenomenon can be prevented by putting the balls in small cages one by one. In the 17th century, Galileo made the earliest description of the "cage ball" ball bearing. At the end of the seventeenth century, British C. Wallo designed and manufactured ball bearings, and installed them on mail trucks for trial use, and British P. Worth obtained a patent for ball bearings. The first rolling bearing with a cage to be put into practical use was invented by watchmaker John Harrison in 1760 to make the H3 chronograph. At the end of the eighteenth century, German H.R. Hertz published a paper on the contact stress of ball bearings. On the basis of Hertz's achievements, R. Stribeck in Germany, A. Palmgren in Sweden and others have conducted a large number of experiments, which have contributed to the development of rolling bearing design theory and fatigue life calculation. Subsequently, Russia's N.P. Petrov applied Newton's law of viscosity to calculate bearing friction. The first patent on the ball groove was obtained by Philip Vaughan of Carmarthen in 1794. In 1883, Friedrich Fisher proposed the use of suitable production machines to grind steel balls of the same size and accurate roundness, which laid the foundation for the bearing industry. British O. Reynolds conducted a mathematical analysis of Thor's discovery and derived the Reynolds equation, thus laying the foundation for the theory of hydrodynamic lubrication.