What is a rotating bearing!

Bearing is an important part of contemporary mechanical equipment. Its main function is to support the mechanical rotating body, reduce the friction coefficient during its movement, and ensure its rotation accuracy.

historical development

bearings (6 pieces)

The early form of linear motion bearings was to place a row of wooden poles under a row of pry plates. Modern linear motion bearings use the same working principle, but sometimes balls are used instead of rollers. The simplest rotary bearing is the sleeve bearing, which is just a bushing sandwiched between the wheel and the axle. This design was subsequently replaced by rolling bearings, that is, many cylindrical rollers were used to replace the original bushings, and each roller was like a separate wheel.

An early example of ball bearing was found on an ancient Roman ship built in 4 BC in Nano Lake, Italy: a wooden ball bearing was used to support a rotating table top. It is said that leonardo da vinci once described a kind of ball bearing around 15. Among all kinds of immature factors of ball bearings, it is very important that the balls will collide and cause extra friction. But this phenomenon can be prevented by putting 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 17th century, C. Wallow of Britain designed and manufactured ball bearings, and put them on a mail truck for trial use, and P. Worth of Britain obtained a patent for ball bearings. The earliest practical rolling bearing with cage was invented by watchmaker John Harrison in 176 for making 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, German R. Striebeck and Swedish A. Parmgren have carried out a lot of experiments, which have contributed to the development of 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 on ball channel was obtained by Philip Vaughan of Carmarthen in 1794.

in p>1883, Friedrich fischer put forward the idea of grinding steel balls with the same size and accurate roundness by using suitable production machines, which laid the foundation for bearing industry. O. Reynolds of Britain made a mathematical analysis of Thor's discovery and derived Reynolds equation, which laid the foundation of hydrodynamic lubrication theory.

Industry overview

According to the data of National Bureau of Statistics, in 211, there were 1,416 enterprises in the bearing manufacturing industry in China (with annual sales income of more than 2 million yuan), with a total industrial output value of 193.211 billion yuan, a year-on-year increase of 27.59%; Sales revenue was 191.97 billion yuan, a year-on-year increase of 3.3%; The total profit was 12.523 billion yuan, an increase of 26.54% over the previous year. It is estimated that by 215, China's bearing production is expected to exceed 28 billion sets, and its main business income is expected to reach 21 billion yuan, making it the largest bearing production and sales base in the world.

at present, China's bearing industry mainly faces three prominent problems: low concentration of production, low R&D and innovation ability and low manufacturing technology level.

first, the industrial production concentration is low. Among the sales of bearings in the world of about $3 billion, the world's eight multinational companies account for 75% ~ 8%. Germany's two major companies account for 9% of its national total, Japan's five companies account for 9% of its national total, and the United States' one company accounts for 56% of its national total. However, the sales of the 1 largest bearing enterprises in China, such as Wazhou, account for only 24.7% of the whole industry, and the production concentration of the top 3 enterprises is only 37.4%.

second, the ability of R&D and innovation is low. The basic theory research of the whole industry is weak, and the participation in the formulation of international standards is weak, with few original technologies and few patented products.

At present, our design and manufacturing technology is basically imitation, and our product development ability is low, which is manifested in the fact that although the matching rate of domestic main engines reaches 8%, the matching and maintenance bearings of important main engines such as high-speed railway passenger cars, middle and high-grade cars, computers, air conditioners and high-level rolling mills are basically imported.

thirdly, the manufacturing technology is low. In China, the manufacturing technology and equipment technology of bearing industry are developing slowly, the numerical control rate of turning is low, and the automation level of grinding is low. There are only more than 2 automatic production lines in China. Advanced heat treatment technologies and equipment, which are crucial to the life and reliability of bearings, such as controlled atmosphere protection heating, double refining and bainite quenching, have low coverage, and many technical problems have not been broken through. The research and development of new bearing steel grades, the improvement of steel quality and the research and development of related technologies such as lubrication, cooling, cleaning and abrasive tools can not meet the requirements of improving the level and quality of bearing products. Therefore, the process capability index is low, the consistency is poor, the product processing size dispersion is large, and the internal 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 service life of a rolling bearing is defined by the number of revolutions (or the number of working hours at a certain speed): the bearing within this service life should have initial fatigue damage (peeling or defect) on any bearing ring or rolling body. 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 means that the actual life of a bearing before damage is caused by wear and tear, and the 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 bearing life is linked with reliability.

due to the differences in manufacturing accuracy and material uniformity, even the same batch of bearings with the same material and size will have different service lives under the same working conditions. If the statistical life is 1 unit, the longest relative life is 4 units, the shortest is .1-.2 units, and the ratio of the longest to the shortest life is 2-4 times. 9% of bearings do not produce pitting corrosion, and the number of revolutions or hours experienced is called the rated life of bearings. [1]? .

rated dynamic load

in order to compare the bearing capacity against pitting corrosion, it is stipulated that when the rated life of the bearing is one million revolutions (16), the maximum load that can be borne is the basic rated dynamic load, which is expressed by C ..

that is to say, under the rated dynamic load c, the reliability of the bearing working for one million revolutions (16) without pitting failure is 9%, and the greater the C, the higher the bearing capacity.

For the basic rated dynamic load

1. Radial bearing refers to pure radial load

2. Thrust ball bearing refers to pure axial load

3. Radial component that produces pure radial displacement

Industry status

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According to the data of "Forecast of Production and Marketing Demand and Analysis Report of Transformation and Upgrading of Bearing Manufacturing Industry in China", the total industrial output value of bearing manufacturing industry in China has been increasing year by year from 29 to 213. In 213, the total industrial output value of the industry reached 249.363 billion yuan, a year-on-year increase of 12.92%.

By analyzing the data in recent five years, it is found that the sales revenue of bearing manufacturing industry in China has also increased year by year from 29 to 213. In 213, the sales revenue reached 249.12 billion yuan, up 11.8% year-on-year.

China's bearing industry has developed rapidly, with bearing varieties from few to many, product quality and technical level from low to high, and industry scale from small to large, and a professional production system with basically complete product categories and reasonable production layout has been formed.

structure classification

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bearing classification

sliding bearing

sliding bearing has no inner and outer rings and no rolling bodies, and is generally made of wear-resistant materials. Commonly used in low speed, light load, lubricating oil filling and mechanical rotating parts with difficult maintenance.

joint bearing

the sliding contact surface of joint bearing is spherical, which is mainly suitable for swinging motion, tilting motion and rotating motion.

rolling bearings

rolling bearings are divided into radial bearings and thrust bearings according to the load direction or nominal contact angle they can bear. The radial contact bearing is a radial bearing with a nominal contact angle of , and the radial contact bearing is a radial bearing with a nominal contact angle greater than to 45. The axial contact bearing is a thrust bearing with a nominal contact angle of 9, and the thrust angle contact bearing is a thrust bearing with a nominal contact angle greater than 45 but less than 9.

according to the shape of rolling elements, it can be divided into ball bearings and roller bearings. Roller bearings are classified into cylindrical roller bearings, needle roller bearings, tapered roller bearings and self-aligning roller bearings.

according to whether it can be self-aligning when working, it can be divided into self-aligning bearings-bearings with spherical raceways, which can adapt to the angular deviation and angular movement between the axes of two raceways, and non-self-aligning bearings (rigid bearings)-bearings that can resist the angular deviation between the axes of raceways.

according to the number of rows of rolling elements, it is divided into single-row bearings, double-row bearings and multi-row bearings.

according to whether its components (rings) can be separated, it can be divided into separable bearings and inseparable bearings.

according to its structural shape (such as whether there is a filling groove, whether there is an inner ring, an outer ring, the shape of the ferrule, the structure of the flange, and even whether there is a cage, etc.), it can also be divided into various structural types.

according to its outside diameter size, it is divided into miniature bearings (<: 26mm), small bearings (28-55mm), medium and small bearings (6-115), medium and large bearings (12-19mm), large bearings (2-43mm) and oversize bearings (>: 44mm）。

according to the application fields, it is divided into motor bearings, rolling mill bearings and main bearings.

according to materials, it can be divided into ceramic bearings and plastic bearings.

deep groove ball bearing

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Deep groove ball bearing is the most representative rolling bearing. Compared with other types of bearings with the same size, this kind of bearing has the advantages of small friction coefficient, high limit speed, simple structure, low manufacturing cost, high precision, no need for frequent maintenance, large size range and many forms, and is the most widely used bearing. It mainly bears radial load and can also bear certain axial load. When it only bears radial load, the contact angle is zero.

after the deep groove ball bearing is installed on the shaft, it can limit the axial displacement of the shaft or the shell in both directions within the axial clearance range of the bearing, so it can be positioned axially in both directions. When the deep groove ball bearing has large radial clearance, it has the performance of angular contact bearing and can bear large axial load. Under the condition of high-speed operation with large axial load, deep groove ball bearing is superior to thrust ball bearing. In addition, this kind of bearing also has a certain self-aligning ability, and it can still work normally when it is tilted 2' ~ 1' relative to the housing hole, but it has a certain impact on the bearing life.

angular contact ball bearings

Generally, they are called six types of bearings represented by type 36 and 46 bearings, and the angular contact is generally 15 degrees, 25 degrees and 45 degrees.

Self-aligning ball bearing

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Self-aligning ball bearing is a bearing with spherical balls between the inner ring of two raceways and the outer ring with spherical raceway. The curvature center of the raceway surface of the outer ring is consistent with the bearing center, so it has the same self-aligning function as the self-aligning ball bearing. When the shaft and shell are bent, it can be adjusted automatically without increasing the bearing burden. Self-aligning roller bearing can bear radial load and axial load in two directions. Self-aligning ball bearing has large radial load capacity and is suitable for heavy load and impact load. Bearing with tapered bore in inner ring can be installed directly. Or use a fastening sleeve and a dismounting cylinder to mount on the cylindrical shaft. The cage is formed by stamping steel plate and polyamide. Self-aligning ball bearings are suitable for bearing heavy load and impact load, precision instruments, low-noise motors, automobiles, motorcycles, metallurgy, rolling mills, mines, petroleum, paper making, cement, sugar pressing and other industries and general machinery.

thrust ball bearings

thrust ball bearings are divided into one-way and two-way types. They can only bear axial load, and can never bear any radial load. The thrust bearing is divided into two parts: the tight ring and the movable ring. The tight ring is tight with the shaft sleeve, and the movable ring is supported on the bearing seat. Rings and rolling elements are usually made of rolling bearing steel with high strength and good wear resistance, and the surface hardness after quenching should reach HRC 6 ~ 65. Cages are mostly made of mild steel by stamping, and can also be made of copper alloy laminated bakelite or plastic.

bidirectional thrust angular contact ball bearing

double-row tapered roller bearing

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The contact angle of thrust angular contact ball bearing is generally 6. The commonly used thrust angular contact ball bearing is generally a bidirectional thrust angular contact ball bearing, which is mainly used for the spindle of precision machine tools. It is generally used together with double-row cylindrical roller bearing, and can bear bidirectional axial load, with high precision, good rigidity, low temperature rise and rotating speed.

thrust roller bearings

include thrust cylindrical roller bearings, thrust tapered roller bearings, thrust needle roller bearings and thrust self-aligning roller bearings.

needle bearing

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Needle bearing is equipped with thin and long rollers (the length of the rollers is 3~1 times the diameter, and the diameter is generally not more than 5mm), so the radial structure is compact, and when the inner diameter size and load capacity are the same as other types of bearings, the outer diameter is the smallest, which is especially suitable for supporting structures with limited radial installation size. A bearing without inner ring or a needle roller and cage assembly can be selected. At this time, the journal surface and the shell hole surface matched with the bearing are directly used as the inner and outer rolling surfaces of the bearing. In order to ensure that the load capacity and running performance are the same as those of a bearing with a ring, the hardness, machining accuracy and surface quality of the raceway surface of the shaft or shell hole should be the same as that of the bearing ring. Purpose The combined needle roller bearing is a bearing unit composed of a centripetal needle roller bearing and a thrust bearing component, which is compact in structure, small in volume and high in rotation accuracy, and can bear a certain degree of radial load at the same time. And the product has various structural forms, wide adaptability and easy installation. Combined needle bearings are widely used in machine tools, metallurgical machinery, textile machinery, printing machinery and other mechanical equipment, and can make the mechanical system design very compact and smart.

outer spherical ball bearing

The outer diameter surface of the outer ring of the outer spherical ball bearing is spherical, which can play the role of self-aligning.

Self-aligning roller bearing

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Self-aligning roller bearing has two rows of symmetric spherical rollers, which mainly bear radial load and axial load in any direction, but cannot bear pure axial load. The raceway of the outer ring of this kind of bearing is spherical, so its self-aligning performance is good, which can compensate the coaxiality error. The bearing can still be used normally when important official is bent or installed with different centers. The self-aligning performance varies with the bearing size series. Generally, the allowable self-aligning angle is 1~2.5 degrees. This kind of bearing has a large load capacity. Besides radial load, it can also bear axial load acting in two directions, and it has good impact resistance. Generally speaking, self-aligning roller bearings have good impact resistance. Suitable for overloading or