Ethnicity
Bearings (6)
The early form of linear motion bearing is to put a row of wooden sticks 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 a sleeve bearing, which is just a bushing sandwiched between the wheel and the axle. This design was later replaced by rolling bearings, that is, many cylindrical rollers were used instead of the original bushings, and each roller was like an independent wheel.
An early example of ball bearing was found on an ancient Roman ship built in Lake Nano, Italy in 40 BC: a wooden ball bearing was used to support a rotating desktop. It is said that Leonardo da Vinci once described a ball bearing with a ratio of 1500. Among all kinds of immature factors of ball bearings, it is very important that the balls will collide and produce extra friction. But putting the ball in a small cage can prevent this phenomenon. /kloc-in the 0/7th century, Galileo first described the "cage ball" ball bearing. /kloc-At the end of 0/7th century, C. Wallow in Britain designed and manufactured ball bearings, and put them on a mail truck for trial use. P. Worth in Britain obtained a patent for ball bearings. The earliest practical rolling bearing with cage was invented by watchmaker john harrison in 1760 for making H3 chronograph. /kloc-at the end of the 8th century, H.R. Hertz of Germany published a paper on contact stress of ball bearings. On the basis of Hertz's achievements, R. Striebeck of Germany and A. Parmgren of Sweden carried out a lot of experiments, which 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 fairway was obtained by Philip Vaughan of Carmarthen in 1794.
1883, Friedrich Fisher put forward the idea of grinding steel balls with the same size and accurate roundness with 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.
General situation of industry
According to the data of the National Bureau of Statistics, in 20 1 1 year, there were 14 16 enterprises in the bearing manufacturing industry in China, and the total industrial output value was 1932.438+0 1 billion yuan, an increase compared with 2008. Sales revenue1910.97 million yuan, up 30.30% year-on-year; The total profit was 654.38+02.523 billion yuan, an increase of 26.54% over the previous year. It is estimated that by 20 15, China's bearing output is expected to exceed 28 billion sets, and its main business income is expected to reach 2 1000 billion yuan, making it the largest bearing production and sales base in the world.
At present, China's bearing industry mainly faces three outstanding problems: low production concentration, low R&D and innovation ability, and low manufacturing technology level.
First, the concentration of industrial production is low. In the global bearing sales of about $30 billion, the world's eight multinational companies account for 75% ~ 80%. Germany's two major companies account for 90% of its national total, Japan's five major companies account for 90% of its national total, and the United States 1 company accounts for 56% of its national total. However, the sales of the largest 10 bearing enterprises in China only account for 24.7% of the whole industry, and the production concentration of the top 30 enterprises is only 37.4%.
Second, the ability of R&D and innovation is low. The basic theoretical research of the whole industry is weak, and the ability to participate 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. Although the matching rate of domestic main engines reaches 80%, 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 advanced rolling mills are basically imported.
Third, the manufacturing technology level is low. The development of manufacturing technology and equipment technology in bearing industry in China is slow, the turning numerical control rate is low and the grinding automation level is low. There are only over 200 automatic production lines in China. Advanced heat treatment technologies and equipment, such as controlled atmosphere protection heating, double refining and bainite quenching, which are crucial for bearing life and reliability, have low coverage, and many technical problems have not been broken. The research and development of new bearing steel, the improvement of steel quality and the research and development of lubrication, cooling, cleaning, abrasive tools and other related technologies 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 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 experienced by the bearing before pitting occurs is called bearing life.
The service life of a rolling bearing is defined by the number of revolutions (or working hours at a certain speed): any bearing ring or rolling body in this service life should have initial fatigue damage (peeling or defect). However, whether in laboratory test or in actual use, it can be clearly seen that the actual service life of bearings with the same appearance varies greatly under the same working conditions. 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 bearing before damage is caused by wear, 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, bearing life is linked with reliability.
Due to the differences in manufacturing accuracy and material uniformity, even bearings with the same batch, 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 and 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 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 of pitting corrosion resistance, it is stipulated 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, which is represented by C.
That is to say, under the rated dynamic load C, the reliability of this bearing working for one million revolutions (106) without pitting failure is 90%, 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. The centripetal thrust bearing refers to the 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 2009 to 20 13. In 20 13 years, the total industrial output value of the whole industry was 249.363 billion yuan, up by 12.92% year-on-year.
By analyzing the data in recent five years, it is found that the sales revenue of bearing manufacturing industry in China is also increasing year by year from 2009 to 20 13. In 20 13 years, the sales revenue was 24901200 million yuan, up1.80% year-on-year.
With the rapid development of China's bearing industry, bearing varieties have increased from less to more, product quality and technical level have increased from low to high, and industry scale has increased from small to large, forming a specialized production system with basically complete product categories and reasonable production layout.
Structural classification
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Azimuth classification
sliding bearing
Sliding bearings have no inner and outer rings and no rolling elements, and are generally made of wear-resistant materials. It is often used in mechanical rotating parts with low speed, light load, lubricating oil filling and 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 bearing
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 0, and the radial contact bearing is a radial bearing with a nominal contact angle greater than 0 to 45. The axial contact bearing is a thrust bearing with a nominal contact angle of 90, and the thrust angle contact bearing is a thrust bearing with a nominal contact angle greater than 45 but less than 90.
According to the shape of the rolling body, it can be divided into ball bearing and roller bearing. Roller bearings are divided into cylindrical roller bearings, needle roller bearings, tapered roller bearings and self-aligning roller bearings.
According to whether it can be self-aligning during work, it can be divided into self-aligning bearings-spherical raceway bearings and non-self-aligning bearings (rigid bearings) that can adapt to the angular deviation and angular movement between two raceway axes-bearings that can resist the angular deviation between raceway axes.
According to the number of rows of rolling elements, it can be 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 the shape of inner ring, outer ring and ferrule, the structure of flange, and even whether there is a cage, etc.). ), can also be divided into various structural types.
According to its outer diameter, it is divided into miniature bearings (440mm).
According to the application field, it is divided into motor bearing, rolling mill bearing and main bearing.
According to materials, it is divided into ceramic bearings and plastic bearings.
Deep groove ball bearing
Deep groove ball bearing
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Deep groove ball bearing is the most representative rolling bearing. Compared with other types of bearings of the same size, this 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 shell in two directions within the axial clearance range of the bearing, so it can be axially positioned in two directions. Deep groove ball bearing has the performance of angular contact bearing when the radial clearance is large, 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 bearing also has a certain self-aligning ability. When it is inclined 2 ′ ~10 ′ relative to the bearing seat hole, it can still work normally, but it has certain influence on the bearing life.
Radial thrust ball bearing
It is generally called six types of bearings represented by type 36 and type 46 bearings, and the angular contact is generally 15 degrees, 25 degrees, 45 degrees, etc.
Self-aligning ball bearing
Self-aligning ball bearing
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Self-aligning ball bearing is a bearing with spherical ball 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 important official and the shell are bent, it can be automatically adjusted 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 bearing capacity and is suitable for heavy load and impact load. Bearings with tapered holes in the inner ring can be installed directly. Or mounted on a cylindrical shaft using a fastening sleeve and a dismounting cylinder. The cage is stamped from steel plate and polyamide. Self-aligning ball bearings are suitable for heavy and impact loads, precision instruments, low-noise motors, automobiles, motorcycles, metallurgy, rolling mills, mines, petroleum, paper making, cement, sugar making and other industries and general machinery.
Axial contact ball bearing
Thrust ball bearings are divided into one-way and two-way types. They can only bear axial load, but never bear any radial load. Thrust bearing is divided into two parts: tight ring and moving ring. The tightening hoop is fastened with the shaft sleeve, and the moving 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 60 ~ 65. Cages are mostly made of low carbon 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 60. The commonly used thrust angular contact ball bearings are generally bidirectional thrust angular contact ball bearings, which are mainly used for the spindle of precision machine tools. Generally, it is used with double-row cylindrical roller bearings, which can bear bidirectional axial load, and has the advantages of high precision, good rigidity, low temperature rise, high rotation speed and convenient disassembly and assembly.
Thrust roller bearing
Comprises a thrust cylindrical roller bearing, a thrust tapered roller bearing, a thrust needle roller bearing and a thrust self-aligning roller bearing.
needle (roller) bearing
needle (roller) bearing
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Needle roller bearings are equipped with slender rollers (the length of the rollers is 3~ 10 times of the diameter, and the diameter is generally less than 5mm), so the radial structure is compact. When the inner diameter and bearing 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. Needle roller bearings can choose bearings without inner ring or needle roller and cage assembly according to different applications. At this time, the journal surface and shell hole surface matched with the bearing are directly used as the inner and outer rolling surfaces of the bearing. In order to ensure the same bearing capacity and running performance as the bearing with 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 consisting of a centripetal needle roller bearing and a thrust bearing. It is compact in structure, small in volume and high in rotary precision, and can bear a certain axial load while bearing a higher radial load. 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, which can make the mechanical system design very compact and dexterous.
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
Self-aligning roller bearing
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Self-aligning roller bearing has two rows of symmetrical spherical rollers, which mainly bear radial load and axial load in any direction, but cannot bear pure axial load. The outer raceway of this bearing is spherical, which has good self-aligning performance and can compensate the coaxiality error. When important parts are bent or installed in different centers, bearings can still be used normally. Self-aligning performance varies with bearing size series. Generally, the allowable self-alignment angle is 1~2.5 degrees. This kind of bearing has large bearing capacity, which can bear not only radial load but also axial load acting in two directions, and has good impact resistance. Suitable for working under heavy load or vibration load.
flange bearing
Flange bearing outer wheel has flange flange. It is characterized by simplifying the structure of the main engine, reducing the volume of the main engine and making the bearing easier to locate.
Rolling bearing unit
A component that combines a centripetal bearing with a base. There is a bottom plate for mounting screws on a supporting surface parallel to the bearing axis.
combination bearing
A group of rolling bearings consists of two or more bearing structures at the same time. Such as needle roller and thrust cylindrical roller combined bearing, needle roller and thrust ball bearing combined bearing, needle roller and angular contact ball bearing combined bearing, etc.
Linear bearing
Linear bearing is divided into metal linear bearing and plastic linear bearing.
Metal linear bearing is a low-cost linear motion system, which is used for infinite travel and cylindrical shafts. Because the bearing ball is in point contact with the shaft, the use load is small. The steel ball rotates with the minimum friction resistance, so that smooth motion with high precision can be obtained.
Plastic linear bearing is a linear motion system with self-lubricating characteristics. The biggest difference between it and metal linear bearing is that the metal linear bearing is rolling friction, and the bearing is in point contact with the cylindrical shaft, so it is suitable for low load and high speed movement. The plastic linear bearing has sliding friction, and the bearing is in surface contact with the cylindrical shaft, which is suitable for high-load medium and low-speed movement.
bearing material
Characteristics of bearing steel:
I. Contact fatigue strength
Under the action of periodic load, the contact surface of bearing is easy to be exhausted and damaged, that is, cracks and peeling appear, which is an important failure situation of bearing. Therefore, in order to improve the service life of bearings, bearing steel must have high contact fatigue strength.
Second, wear resistance.
In the process of bearing work, not only rolling friction but also sliding friction occurs between the ring, roller and maintenance frame, which keeps the bearing parts in a state of wear. In order to increase the wear of bearing parts, maintain the stability of bearing accuracy and prolong the service life, bearing steel should have good wear resistance.
Third, hardness.
Hardness is one of the important qualities of bearing quality, which has an indirect influence on contact fatigue strength, wear resistance and elastic limit. The hardness of bearing steel should reach HRC6 1~65 under working conditions, so that the bearing can obtain high contact fatigue strength and wear resistance.
Four. rust resistance
In order to prevent bearing parts and finished products from being corroded and rusted during processing, storage and use, bearing steel is required to have good antirust performance.
Processing performance of verbs (abbreviation of verb)
Bearing parts have to go through many cold and hot processes during consumption. In order to meet the requirements of small batch, high efficiency and high quality, bearing steel should have good working performance. Such as cold and hot formability, machinability, hardenability, etc.
In addition to the above basic requirements, bearing steel should also meet the requirements of proper chemical composition, general external structure, less nonmetallic impurities, appearance defects conforming to specifications, and decarburization layer on the surface not exceeding the specified concentration.
Purpose application
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Bearing action
Its function should be to support, that is, literally bear the shaft, but this is only part of its function, and its essence is to be able to bear radial load. It can also be understood that it is used to fix the shaft. Include automatically selecte bearings. It is a fixed shaft, so that it can only rotate and control its axial and radial movements. Without bearings, the motor can't run at all. Because the shaft may move in any direction, and the motor requires that the shaft can only rotate when working. It is theoretically impossible to realize the function of transmission. And the bearing will also affect the transmission. In order to reduce this influence, the bearings of high-speed shafts must be well lubricated. Some bearings have been lubricated, which is called pre-lubricated bearings, and most bearings must have lubricating oil, which not only increases energy consumption, but also easily damages bearings due to friction during high-speed operation. Turning sliding friction into rolling friction is one-sided, because there is something called sliding bearing.
lubricate
The lubrication purpose of rolling bearing is to reduce the internal friction and wear of bearing and prevent burning and sticking. Prolong its service life; Exhaust friction heat and cooling to prevent bearing overheating and lubricating oil itself from aging; It also has the function of preventing foreign matter from invading the bearing or preventing rust and corrosion.
Lubrication method
The lubrication methods of bearings can be divided into grease lubrication and oil lubrication. In order to make the bearing play a good role, we must first choose a lubrication method suitable for the use conditions and purposes. If only lubrication is considered, the lubricity of oil lubrication is dominant. However, grease lubrication has the advantage of simplifying the structure around the bearing. The advantages and disadvantages of grease lubrication and oil lubrication are compared. Pay special attention to the amount of lubrication, whether it is oil lubrication or grease lubrication. Too little lubrication will not completely affect the bearing life, too much will produce great resistance and affect the speed.
seal
The sealing of bearings can be divided into self-sealing and external sealing. The so-called bearing self-sealing is to make the bearing itself a device with sealing performance. Such as bearings with dust covers, sealing rings, etc. This kind of seal occupies small space, is convenient to install and disassemble, and has relatively low cost. The so-called bearing external sealing performance device is a sealing device with various properties made inside the mounting end cover. Bearing external seal is divided into non-contact seal and contact seal. Among them, non-contact seal is suitable for high-speed and high-temperature occasions, and there are different structural forms such as gap, labyrinth and gasket. Contact seal is suitable for medium and low speed working conditions, and the common structural forms are felt seal and cup seal.
According to the requirements of bearing working conditions and working environment for sealing degree, various sealing forms are often used comprehensively in engineering design to achieve better sealing effect. The following main factors should be considered when selecting the external seal of the bearing:
Bearing lubricants and types (grease and lubricating oil);
The working environment of the bearing and the size of the occupied space;
Advantages and allowable angle deviation of the supporting structure of the shaft;
Circumferential speed of sealing surface;
Working temperature of bearing;
Manufacturing cost.