The early form of linear motion bearing was to place a row of wooden poles under a row of crowbars. Modern linear motion bearings use the same operating principle, except that balls are sometimes used instead of rollers. The simplest swivel bearing is a sleeve bearing, which is simply a bushing sandwiched between the wheel and axle. This design was later replaced by rolling bearings, which replaced the original bushings with many cylindrical rollers, each rolling element acting like a separate wheel.
An early example of a ball bearing was found on an ancient Roman ship built in 40 BC in Lake Nami, Italy: a wooden ball bearing was used to support the rotating tabletop. Leonardo da Vinci is said to have described a ball bearing around 1500. Among the various immature factors of ball bearings, a very important point is that the balls will collide with each other, causing additional friction. But you can prevent this phenomenon by putting the balls into small cages. In the 17th century, Galileo made the earliest description of "cage ball" ball bearings. At the end of the seventeenth century, C. Wallow of England designed and manufactured ball bearings and installed them on mail trucks for trial use. P. Worth of England obtained the patent for ball bearings. The first rolling bearing with a cage that was put into practical use was invented by watchmaker John Harrison in 1760 to make the H3 chronograph. At the end of the 18th century, H.R. Hertz of Germany published a paper on the contact stress of ball bearings. On the basis of Hertz's achievements, R. Strebeck of Germany, A. Pamgren of Sweden and others conducted a large number of experiments and contributed to the development of the design theory and fatigue life calculation of rolling bearings. Subsequently, N.P. Petrov of Russia applied Newton's viscosity law to calculate bearing friction. The first patent for a ball channel was obtained by Philip Vaughan of Carmarthen in 1794.
In 1883, Friedrich Fisher proposed the idea of ??using suitable production machines to grind steel balls of the same size and accurate roundness, which laid the foundation of the bearing industry. O. Reynolds of the United Kingdom conducted a mathematical analysis of Thor's discovery and derived the Reynolds equation, which laid the foundation for hydrodynamic lubrication theory. According to data from the National Bureau of Statistics, there were 1,416 companies in China's bearing manufacturing industry in 2011 (annual sales revenue of more than 20 million yuan). The total industrial output value for the year was 193.211 billion yuan, a year-on-year increase of 27.59%; sales revenue was 1,910.97 billion, a year-on-year increase of 30.30%; the total profit was 12.523 billion yuan, a year-on-year increase of 26.54%. It is estimated that by 2015, my country's bearing output is expected to exceed 28 billion sets, and its main business income is expected to reach 210 billion yuan, becoming the world's largest bearing production and sales base.
Currently, my country's bearing industry is mainly facing three major outstanding problems: low industry production concentration, low R&D and innovation capabilities, and low manufacturing technology levels.
First, the industry’s production concentration is low. Of the approximately US$30 billion in bearing sales worldwide, the world's eight largest multinational companies account for 75% to 80%. Two major companies in Germany account for 90% of the country's total, five companies in Japan account for 90% of the country's total, and one company in the United States accounts for 56% of the country's total. However, the sales of the 10 largest bearing companies such as my country Wa Bearing only account for 24.7% of the entire industry, and the production concentration rate of the top 30 companies is only 37.4%. Second, R&D and innovation capabilities are low. The industry-wide basic theoretical research is weak, participation in the formulation of international standards is weak, there are few original technologies, and there are few patented products. At present, our design and manufacturing technology are basically imitation, and our product development capabilities are low. This is reflected in the following: Although the matching rate for domestic main engines reaches 80%, high-speed railway passenger cars, mid-to-high-end cars, computers, air conditioners, high-level rolling mills, etc. are important Main engine matching and maintenance bearings are basically imported. Third, the level of manufacturing technology is low. my country's bearing industry manufacturing technology and process equipment technology have developed slowly, the CNC rate of turning and processing is low, and the level of grinding and processing automation is low. There are only more than 200 automatic production lines in the country. Advanced heat treatment processes and equipment that are crucial to bearing life and reliability, such as controlled atmosphere protective heating, double refinement, bainite quenching, etc., have low coverage, and many technical problems have failed to achieve breakthroughs. The research and development of new steel types for bearing steel, the improvement of steel quality, and the research and development of related technologies such as lubrication, cooling, cleaning and abrasives cannot yet meet the requirements for improving the level and quality of bearing products.
As a result, the process capability index is low, the consistency is poor, the product processing size dispersion is large, and the inherent quality of the product is unstable, which affects the accuracy, performance, life and reliability of the bearing. Life
Under a certain load, the number of revolutions or hours that a bearing experiences before pitting corrosion occurs is called the bearing life.
The life of a rolling bearing is defined in terms of revolutions (or the number of hours of operation at a certain speed): Bearings within this life should have initial fatigue damage (flaking) on ??any of their bearing rings or rolling elements. or defective). However, whether in laboratory tests or in actual use, it can be clearly seen that bearings with the same appearance under the same working conditions have very different actual lifespans. In addition, there are several different definitions of bearing "life", one of which is the so-called "operating life", which indicates the actual life that a bearing can achieve before it is damaged. Damage is usually not caused by fatigue, but by wear and tear. Caused by wear, corrosion, seal damage, etc.
In order to determine the standard for bearing life, the bearing life and reliability are related.
Due to differences in manufacturing precision and material uniformity, even the same batch of bearings of the same material and size will have different lifespans when used under the same working conditions. If the statistical life is taken as 1 unit, the longest relative life is 4 units, the shortest is 0.1-0.2 units, and the ratio of the longest to the shortest life is 20-40 times. 90% of bearings do not suffer from pitting corrosion, and the number of revolutions or hours experienced is called the bearing rating life.
Rated dynamic load
In order to compare the bearing capacity against pitting corrosion, it is specified that when the rated life of the bearing is one million revolutions (106), the maximum load it can bear is the basic Rated dynamic load, expressed in C.
That is, under the action of the rated dynamic load C, the reliability of this bearing operating for one million revolutions (106) without pitting failure is 90%. The larger the C, the higher the load-bearing capacity.
For basic dynamic load ratings
1. Radial bearings refer to pure radial load
2. Thrust ball bearings refer to pure axial load
3. Radial thrust bearings refer to the radial component that produces pure radial displacement