Something about bearings
Origin of development
The early form of linear motion bearings is to place a row of wooden poles under a row of prizing boards. Modern linear motion bearings use the same working principle, but sometimes they replace balls with balls. The simplest rotary bearing is the axle sleeve bearing. It is just a bushing between the wheel and the axle. This design was then replaced by rolling bearings, which replaced the original bushing with many cylindrical rollers, each of which resembled a single wheel.
An early example of a wooden ball bearing was found on a Roman ship built in 40 B.C. on Lake Nami in Italy: a wooden ball bearing used to support a rotating table top. It is said that Leonardoda Da Finch used to describe a ball bearing around 1500. Among the various immature factors of ball bearings, it is very important that there will be collisions between the balls, resulting in additional friction. But it can be prevented by putting balls into small cages. Galileo made the earliest description of ball bearings in seventeenth Century. At the end of the seventeenth century, C. Wallow of Britain designed and manufactured ball bearings, and installed them on mail cars for trial use, and P. Worth of Britain obtained a patent for ball bearings. The earliest practical rolling bearings with cages were invented by watchmaker John Harrison in 1760 for the H3 timepiece. At the end of eighteenth Century, H.R. Hertz published a paper on contact stress of ball bearings in Germany. On the basis of Hertz's achievements, R. Steinbeck of Germany and A. Pamgren of Sweden carried out a large number of experiments, which contributed to the development of design theory and fatigue life calculation of rolling bearings. Subsequently, Russian N.P. Petrov applied Newton's law of viscosity to calculate bearing friction. The first patent on the ditch was acquired by Philip Vaughan of Carmarthen in 1794.
In 1883, Friedrich Fisher put forward the idea of using suitable production machines to grind steel balls of the same size and precise roundness, which laid the foundation for the bearing industry. O. Reynolds of Britain made a mathematical analysis of Toll's discovery and derived the Reynolds equation, which laid the foundation of hydrodynamic lubrication theory.
According to the statistics of the State Bureau of Statistics, there were 1 416 enterprises in China's bearing manufacturing industry in 2011, with an annual output value of 193.211 billion yuan, an increase of 27.59%; sales revenue of 191.097 billion yuan, an increase of 30.30%; profits of 12.523 billion yuan, an increase of 26.54% over the previous year. It is estimated that by 2015, China's bearing production is expected to exceed 28 billion sets, the main business revenue is expected to reach 210 billion yuan, the world's largest bearing production and sales base.
At present, China's bearing industry is mainly faced with three prominent problems: low concentration of industry production, low R&D and innovation capacity, low manufacturing technology level.
First, the concentration of industrial production is low. Among the world's sales of about $30 billion, the world's 8 largest multinational companies account for 75% to 80%. Germany's two largest companies account for 90% of the country's total, Japan's five accounted for 90% of the country's total, the United States one accounted for 56% of the country's total. While the sales of the 10 largest bearing enterprises, such as bushes and axles, account for only 24.7% of the total industry, and the production concentration of the top 30 enterprises is only 37.4%.
Second, R & D and innovation capabilities are low. The industry is weak in basic theoretical research, participation in international standard formulation, less original technology, less patented products.
At present, our design and manufacturing technology is basically imitation, and our product development capability is low. Although the matching rate of domestic mainframe reaches 80%, the matching and maintenance bearings of high-speed railway passenger cars, medium and high-grade cars, computers, air conditioners, high-level rolling mills and other important mainframe basically rely on imports.
Third, low level of manufacturing technology. China's bearing industry manufacturing technology and equipment technology development is slow, turning CNC rate is low, grinding automation level is low, the country has only more than 200 automatic production lines. Advanced heat treatment processes and equipment, such as controlled atmosphere protection heating, double refinement and bainite quenching, which are crucial to bearing life and reliability, have low coverage, and many technical problems have not been solved. The research and development of new bearing steel grades, the improvement of steel quality, the research and development of lubrication, cooling, cleaning and abrasive grinding tools and other related technologies can not meet the requirements of bearing product level and quality improvement. 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.
Under a certain load, the number of rotations or hours that the bearing undergoes before pitting is called bearing life.
The life of a rolling bearing is defined as the number of revolutions (or hours of work at a given speed): bearings within this life shall suffer initial fatigue damage (spalling or defect) on any bearing ring or roller. However, no matter in the laboratory test or in the actual use, it can be clearly seen that under the same working conditions, the appearance of the same bearing, the actual life is very different. In addition, there are several different definitions of bearing "life", one of which is the so-called "working life", which means that the actual life of a bearing before damage can be achieved by wear, damage is usually not caused by fatigue, but by wear, corrosion, seal damage and other reasons.
In order to determine the standard of bearing life, the life and reliability of bearings are linked.
Due to fabrication accuracy, material homogeneity
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