The origin of the development of bearings

History development of Bearing
Bearings
The early form of Linear Motion bearing is to place a row of wooden rods under a row of skids. Modern linear motion bearings use the same working principle, but sometimes use balls instead of rollers. The simplest rotary bearing is the bush 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 bushing with many cylindrical rollers, each like a separate wheel.
An early example of a ball bearing was found on an ancient Roman ship built in 40 BC at Lake Nami, Italy: a wooden ball bearing was used to support a rotating table top. 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 there will be collisions between the balls, causing additional friction. But this can be prevented by placing the balls in small cages. In the 17th century, Galileo made the earliest description of the "cage ball" ball bearing. At the end of the seventeenth century, British C. Vallo designed and manufactured ball bearings, and installed them on the mail car for trial use, and British P. Worth obtained a patent for ball bearings. The earliest practical rolling bearing with a cage was invented by watchmaker John Harrison in 1760 for the production of the H3 chronograph. At the end of the eighteenth century, H.R. Hertz of Germany published a paper on the contact stress of ball bearings. On the basis of Hertz's achievements, R. Striebeck of Germany, A. Palmgren of Sweden and others have carried out a large number of experiments, which have contributed to the development of the design theory and fatigue life calculation of rolling bearings. Subsequently, N.P. Petrov of Russia applied Newton's law of viscosity to calculate bearing friction. The first patent for a ball channel was obtained by Philip Vaughan of Carmarthen in 1794.
In 1883, Friedrich Fischer proposed the idea of using suitable production machines to grind steel balls of the same size and accurate roundness, laying the foundation for the bearing industry. British O. Reynolds made a mathematical analysis of Thor's discovery and derived the Reynolds equation, which laid the foundation for the theory of hydrodynamic lubrication.
Industry overview
According to the data of the National Bureau of Statistics, in 2011, there were 1,416 enterprises in China's bearing manufacturing industry (annual sales revenue of more than 20 million yuan), with a total industrial output value of 193.211 billion yuan, a year-on-year increase of 27.59%; sales revenue was 191.097 billion yuan, A year-on-year increase of 30.30%; the total profit was 12.523 billion yuan, an increase of 26.54% over the previous year. It is estimated that by 2015, my country's bearing output is expected to exceed 28 billion sets, and the main business income is expected to reach 210 billion yuan, becoming the world's largest bearing production and sales base.
At present, my country's bearing industry is mainly faced with three prominent problems: low concentration of industry production, low R&D and innovation capabilities, and low level of manufacturing technology.
First, the industry's production concentration is low. In the world's bearing sales of about 30 billion US dollars, the world's eight major multinational companies account for 75% to 80%. Two German companies account for 90% of the national total, five Japanese companies account for 90% of the national total, and one US company accounts for 56% of the national total. The sales of the 10 largest bearing companies in my country, including ZWZ, only account for 24.7% of the industry, and the production concentration of the top 30 companies is only 37.4%.
Second, the R&D and innovation capabilities are low. The basic theoretical research of the whole industry is weak, the participation in the formulation of international standards is weak, and there are few original technologies and few patented products.
At present, our design and manufacturing technology is basically imitation, and our product development ability is low. The supporting and maintenance bearings of the main engine are basically imported.
Third, the level of manufacturing technology is low. The development of manufacturing technology and process equipment technology in my country's bearing industry is slow, the numerical control rate of turning is low, and the level of automation in grinding is low. There are only more than 200 automatic production lines in the country. Advanced heat treatment processes and equipment that are critical to bearing life and reliability, such as controlled atmosphere protection heating, double refinement, bainite quenching, etc., have low coverage, and many technical problems have failed to make breakthroughs. The research and development of new steel grades of bearing steel, the improvement of steel quality, and the research and development of related technologies such as lubrication, cooling, cleaning and abrasive tools cannot meet the requirements of improving the level and quality of bearing products. As a result, the process capability index is low, the consistency is poor, the dispersion of product processing dimensions is large, and the inherent quality of the product is unstable, which affects the accuracy, performance, life and reliability of the bearing.
Bearing parameters
life
Under a certain load, the number of revolutions or hours that a bearing experiences before pitting occurs is called bearing life.
The life of a rolling bearing is defined by the number of revolutions (or hours of work at a certain speed): within this life, the bearing should have initial fatigue damage (spalling or chipping) on any of its bearing rings or rolling elements. However, whether in laboratory tests or in actual use, it can be clearly seen that the actual life of bearings with the same appearance under the same working conditions is very different. In addition, there are several different definitions of bearing "life", one of which is the so-called "working life", which indicates the actual life that a bearing can achieve before failure is due to wear, damage is usually not caused by fatigue, but Caused by wear, corrosion, seal damage, etc.
In order to determine the standard of bearing life, the bearing life and reliability are related.
Due to the difference in manufacturing precision and material uniformity, even the same batch of bearings of the same material and size, used under the same working conditions, have different life spans. If the statistical life is 1 unit, the longest relative life is 4 units, the shortest is 0.1-0.2 unit, and the ratio of the longest to the shortest life is 20-40 times. 90% of bearings do not produce pitting corrosion, and the number of revolutions or hours experienced is called bearing rating life [1].
Rated dynamic load
In order to compare the bearing capacity of the bearing against pitting corrosion, when the rated life of the bearing is specified to be one million revolutions (106), the maximum load that can be supported is the basic rated dynamic load, represented by C.
That is to say, under the action of the rated dynamic load C, the reliability of this kind of bearing working for one million revolutions (106) without pitting failure is 90%. The larger the C, the higher the bearing capacity.
For basic dynamic load rating
1. Radial bearing refers to pure radial load
2. Thrust ball bearings refer to pure axial loads
3. Radial thrust bearing refers to the radial component that produces pure radial displacement