What is a bearing
What is a bearing?
Table of Contents
- What is a bearing?
- The origin of bearing development
- Classification of bearings
- Bearing material
- Application of bearings
- Installation and maintenance of bearings
- Quality inspection of bearings
Bearing is an important part of mechanical equipment. Its main function is to support the mechanical rotating body to reduce the friction coefficient of mechanical load in the process of transmission.
The origin of bearing development
Historical development of bearings
The early form of linear motion bearing is to place a row of wooden poles under a row of skid plates. Modern linear motion bearings use the same working principle, but sometimes use balls instead of rollers. The simplest rotating bearing is the sleeve bearing, which is just a bush sandwiched between the wheel and the axle. This design was later replaced by rolling bearings, which used many cylindrical rollers instead of the original bushing, and each roller was like a separate wheel.
An early example of a ball bearing, a wooden ball bearing, was found on a Roman ship built in 40 B.C. in Lake Nemi, Italy. Leonardo da Vinci is said to have described a ball bearing around 1500. Among the immature factors of ball bearing, one of the most important is that the balls will collide with each other, causing extra friction. But it can be prevented by putting the balls in cages. In the 17th century, Galileo made the earliest description of “cage ball” ball bearing. At the end of the 17th century, C. wallow of England designed and manufactured the ball bearing, which was installed on the mail car for trial use, and P. worth of England obtained the patent of the ball bearing. The first practical rolling bearing with cage was invented by watchmaker John Harrison in 1760 for making H3 chronometer. 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. Stribeck of Germany and a. palmgren of Sweden have carried out a large number 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 channeling was obtained by Philip Vaughn of camassen in 1794.
In 1883, Friedrich Fisher put forward the idea of using suitable production machines to grind steel balls with the same size and accurate roundness, which laid the foundation for the bearing industry. O. Reynolds of England made a mathematical analysis of Thor’s discovery and derived Reynolds equation, which laid the foundation of hydrodynamic lubrication theory.
According to the data of the National Bureau of statistics, in 2011, there were 1416 enterprises in China’s bearing manufacturing industry (with annual sales revenue of more than 20 million yuan), and the annual total industrial output value was 193.211 billion yuan, an increase of 27.59% over the same period last year; Sales revenue was 191.097 billion yuan, up 30.30% year on year; The total profit was 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, and its main business income is expected to reach 210 billion yuan, becoming the world’s largest bearing production and sales base.
At present, China’s bearing industry is facing three major problems: low production concentration, low R & D and innovation ability, and low manufacturing technology level.
First, the industrial production concentration is low. In the world’s bearing sales of about 30 billion US dollars, the world’s eight largest multinational companies account for 75% – 80%. Germany’s two largest companies account for 90% of the country’s total, Japan’s five companies account for 90% of the country’s total, and the United States one company accounts for 56% of the country’s total. However, the sales volume of the top 10 bearing enterprises in China, such as bearing axle, accounts for only 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, the participation in the formulation of international standards is weak, and there are few original technologies and patented products.
At present, our design and manufacturing technology is basically imitative, and our product development ability is low, which is reflected in: Although the matching rate of domestic main engines has reached 80%, the matching and maintenance bearings of important main engines such as high-speed railway passenger cars, medium and high-grade cars, computers, air conditioners and high-level rolling mills are basically imported.
Third, the level of manufacturing technology is low. China’s bearing industry manufacturing technology and process equipment technology development is slow, turning CNC rate is low, grinding automation level is low, there are only more than 200 automatic production lines in the country. The advanced heat treatment technology and equipment which are very important to the bearing life and reliability, such as controlled atmosphere protection heating, double refinement, bainite quenching and so on, 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 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 internal quality of the product is unstable, which affects the accuracy, performance, life and reliability of the bearing.
Parameters of bearing
Under a certain load, the number of revolutions or hours that the bearing experiences before pitting is called bearing life.
The service life of rolling bearing is defined by the number of revolutions (or the working hours at a certain speed): for the bearing within this service life, preliminary fatigue damage (spalling or defect) shall occur on any bearing ring or rolling element. 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 is caused 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 bearing life and reliability are connected.
Due to the difference of manufacturing accuracy and material uniformity, even if the same batch of bearings of the same material and size are used under the same working conditions, their service life is not the same. If the statistical life is 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 the bearings do not produce pitting corrosion, and the number of revolutions or hours experienced is called the rated life of the bearing.
Rated dynamic load
In order to compare the anti pitting capacity of bearings, the maximum load that the bearing can bear is the basic rated dynamic load when the rated life of the bearing is one million revolutions (106), expressed as C.
That is to say, under the action of 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 is, the higher the bearing capacity is.
For basic dynamic load rating:
- 1. Radial bearing refers to pure radial load.
- 2. Thrust ball bearing refers to pure axial load.
- 3. Radial thrust bearing refers to the radial component which produces pure radial displacement.
Classification of bearings
The sliding bearing is made of wear-resistant materials, which is not divided into inner and outer rings and rolling body. It is often used in the rotating parts of machinery with low speed, light load, lubricating oil filling and difficult maintenance.
The sliding contact surface of joint bearing is spherical surface, which is mainly suitable for swing motion, tilt motion and rotation motion.
- Rolling bearings are divided into centripetal bearings and thrust bearings according to the load direction or nominal contact angle. The radial contact bearing is the radial bearing with the nominal contact angle of 0, and the radial contact bearing is the centripetal bearing with the nominal contact angle greater than 0 to 45. The axial contact bearing is the thrust bearing with the nominal contact angle of 90, and the thrust angle contact bearing is the thrust bearing with the 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 bearings, tapered roller bearings and self-aligning roller bearings.
- According to whether the center adjustment can be divided into the center adjusting bearing, the raceway is spherical, which can adapt to the angular deviation between the two raceways and angular movement bearings and non centering bearings (rigid bearings) – bearings that can resist the offset of the axial angle between raceways.
- According to the number of rolling body columns, it can be divided into single row bearing, double row bearing and multi row bearing.
- According to whether the components (grommets) can be separated into separable bearings and non separable bearings.
- According to its structural shape (if there is no filling groove, whether there is the shape of inner ring, outer ring or not, the structure of edge blocking, and even whether there is a cage, etc.) it can also be divided into many structural types.
- According to the size of outer diameter, they can be divided into micro bearing (< 26mm), small bearing (28-55mm), medium and small bearing (60-115), medium and large bearing (120-190mm), large bearing (200-430mm) and super large bearing (>440mm).
- According to the application field, it can be divided into motor bearing, rolling mill bearing, main bearing, etc.
- According to the material, it can be divided into ceramic bearing, plastic bearing, etc.
Deep groove ball bearing
Deep groove ball bearing is the most representative rolling bearing. Compared with other bearings with the same size, the bearing has the advantages of small friction coefficient, high limit speed, simple structure, low manufacturing cost, high precision, no need to be maintained frequently, and it has a large size range and many forms, which is the most widely used type of bearing. It mainly bears radial load and can 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, the axial displacement of the shaft or shell can be limited within the axial clearance range of the bearing, so axial positioning can be made in two directions. When deep groove ball bearing has large radial clearance, it has the performance of angular contact bearing and can bear large axial load. Under the high speed operation condition with large axial load, deep groove ball bearing is more superior than thrust ball bearing. In addition, the bearing has a certain ability of adjusting the center. When it is inclined 2 ′ – 10 ′ relative to the shell hole, it can still work normally, but it has certain influence on the bearing life.
Angular contact ball bearing
Generally, it is called 36 and 46 bearings as representative six types of bearings, and angular contact is generally 15 degrees, 25 degrees, 45 degrees, etc.
Self aligning ball bearing
The center adjusting ball bearing is a ball bearing which is equipped with a ball ball between the inner ring of two raceways and the outer ring with spherical surface. The curvature center of outer race surface is consistent with the bearing center, so it has the same function as the automatic centering ball bearing. When the shaft and shell are flexed, it can be adjusted automatically without increasing bearing burden. The roller bearing can bear radial load and axial load in two directions. The radial load capacity of the ball bearing is large, which is suitable for the heavy load and impact load. The inner diameter of inner ring is the bearing of taper hole, which can be installed directly. Or install the fixing sleeve and the disassembly cylinder on the cylinder shaft. The cage is made of steel plate stamping cage and polyamide forming. The core adjusting ball bearing is suitable for industries and general machinery such as heavy load and impact load, precision instrument, low noise motor, automobile, motorcycle, metallurgy, rolling mill, mine, oil, paper, cement, sugar pressing, etc.
Thrust ball bearing
Thrust ball bearings are divided into two types: one-way and two-way. They can only bear axial loads and must not bear any radial loads. Thrust bearing is divided into two parts: tightening ring and movable ring. The tightening ring is tight with the shaft sleeve, and the movable ring is supported on the bearing pedestal. The ring and rolling body are usually made of high strength and wear-resistant rolling bearing steel. The surface hardness after quenching should reach hrc60-65. The cage is made of soft steel stamping, and can also be made of copper alloy cloth plywood or plastic.
Two way thrust angular contact ball bearing
Double row tapered roller bearing
The contact angle of thrust angle contact ball bearing is generally 60 °. The commonly used thrust angle contact ball bearing is generally bi-directional thrust angle contact ball bearing, mainly used for precision machine tool spindle. It is generally used with double row cylindrical roller bearing. It can bear bidirectional axial load, with high precision, good rigidity, low temperature rise, high speed, easy installation and disassembly.
Thrust roller bearing
It includes thrust cylindrical roller bearing, thrust tapered roller bearing, thrust needle roller bearing and thrust regulating roller bearing.
Needle bearingNeedle roller bearing
Needle roller bearing is equipped with fine and long rollers (the roller length is 3-10 times of diameter and diameter is not more than 5mm generally). Therefore, the radial structure is compact, its inner diameter and load capacity are the same as other types of bearings, and the outer diameter is the smallest, especially suitable for the supporting structure with limited radial installation size. Needle roller bearing is different according to the use situation, Bearing or needle roller and cage assembly without inner ring can be selected. At this time, the journal surface and shell hole surface matching the bearing can be directly used as the inner and outer rolling surface of the bearing. In order to ensure the same load capacity and operation performance as the bearing with ferrule, the hardness of the surface of the roller channel of the shaft or shell hole is ensured, The machining accuracy and surface quality should be in line with the bearing ring. The purpose of the combined needle roller bearing is a bearing unit which is composed of centripetal needle bearing and thrust bearing components. It has compact structure, small volume and high rotation precision, and can bear certain axial load while bearing high radial load. And the product structure forms are various, adaptability is wide, easy to install. Combined needle roller bearings are widely used in machine tools, metallurgical machinery, textile machinery and printing machinery and other mechanical equipment, and can make the mechanical system design very compact and agile.
Spherical ball bearing
The outer outer diameter surface of the outer sphere ball bearing is spherical, which can play the role of center adjustment.
Spherical Roller Bearings
The roller bearing with the adjustable core has two rows of symmetrical spherical rollers, which mainly bears radial load, and can also bear axial load in any direction, but can not bear pure axial load. The outer race of this type of bearing is spherical, so its core adjustment performance is good, and it can compensate for the coaxiality error. When the shaft is bent or installed in an eccentric way, the bearing can still be used normally. The centring performance varies with the bearing size series. Generally, the allowable adjustment angle is 1-2.5 degrees, and the load capacity of this type of bearing is relatively large, Besides the radial load, the bearing can also bear the axial load of bidirectional action, and has better impact resistance. Generally speaking, the allowable working speed of the roller bearing is lower. It is suitable for working under heavy load or vibration load.
Flange bearing outer wheel with flange. The feature is that it can simplify the structure of the main machine, reduce the size of the main machine, and make the bearing easier to locate.
A component that is combined with a bearing and a seat, having a base plate for mounting screws on the supporting surface parallel to the bearing axis.
A set of rolling bearings which are composed of the above two or more bearing structures at the same time. Such as needle roller and thrust cylindrical roller combination bearing, needle roller and thrust ball combination bearing, needle roller and angle contact ball combination bearing, etc.
Linear bearings are divided into metal linear bearings and plastic linear bearings.
Metal linear bearing is a linear motion system which is produced at low cost, which is used for the combination of infinite travel and cylindrical shaft. Because the bearing ball contacts the shaft point, the load is small. The ball rotates with minimal friction resistance, thus obtaining high precision and stable motion.
Plastic linear bearing is a linear motion system with self-lubricating characteristics. The biggest difference between the linear bearing and the metal linear bearing is rolling friction, and the point contact between the bearing and the cylindrical shaft is suitable for low load high speed movement; The plastic linear bearing is sliding friction, and the bearing and cylindrical shaft contact each other, so this kind of bearing is suitable for high load and medium and low speed movement.
Characteristics of bearing steel:
1. Contact fatigue strength
Under the action of periodic load, the bearing is easily tired and damaged when contacting the surface, that is, cracks and spalling appear, which is an important failure situation of the bearing. Therefore, in order to improve the service life of bearings, bearing steel must have a high contact fatigue strength.
2. Wear resistance
During the bearing task, the rolling friction not only occurs between the collar, rolling body and the support, but also the sliding friction, which makes the bearing parts wear all the time. In order to increase the wear of bearing parts, maintain the bearing accuracy stability and extend the service life, the bearing steel should have good wear resistance.
Hardness is one of the important quality of bearing quality, which has indirect influence on contact fatigue strength, wear resistance and elastic limit. The hardness of bearing steel in application condition should reach hrc61-65, which makes the bearing obtain high contact fatigue strength and wear resistance.
4. Rust resistance
In order to avoid the corrosion and rust of bearing parts and finished products during processing, placing and application, it is required that bearing steel should have good rust resistance.
5. Processing performance
In the course of consumption, bearing parts must pass many cold and hot working procedures. In order to satisfy the requirements of small quantity, high efficiency and high quality, bearing steel should have good processing performance. For example, cold and hot forming properties, cutting performance, hardenability, etc.
In addition to the above basic requirements, bearing steel shall also meet the requirements of proper chemical composition, average external organization, less non-metallic impurities, external defects and compliance specifications, and the surface decarbonization layer shall not exceed the regular concentration.
Application of bearings
In terms of its function, it should be a support, which is literally used to support the shaft, but it is only a part of its function. The essence of support is to be able to bear radial load. It can also be understood that it is used to fix the shaft. Bearing fast easy excellent automation selection has been included. It is to fix the shaft so that it can only rotate and control its axial and radial movement. The motor can’t work without bearings. Because the shaft may move in any direction, and the motor requires that the shaft can only rotate. Theoretically speaking, it is impossible to realize the function of transmission. Not only that, the bearing will also affect the transmission. In order to reduce this influence, good lubrication must be achieved on the bearings of high-speed shafts. Some bearings have lubrication, which is called pre lubrication bearings. Most bearings must have lubricating oil. When they are in high-speed operation, friction will not only increase energy consumption, What’s more, it’s easy to damage the bearing. It is one-sided to change sliding friction into rolling friction, because there is something called sliding bearing.
The lubrication purpose of rolling bearing is to reduce the internal friction and wear of bearing and prevent burning and sticking; Extend its service life; Discharge friction heat and cooling to prevent bearing overheating and lubricating oil aging; It also has the effect of preventing foreign matters from invading into the bearing, or rust and corrosion.
The lubrication methods of bearings are divided into grease lubrication and oil lubrication. In order to make the bearing function well, first of all, it is necessary to choose the lubrication method suitable for the use condition and purpose. 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 fully affect the bearing life, too much will produce large resistance, affect the speed.
The seal of bearing can be divided into two types: self sealing and external sealing. The so-called bearing with seal is to make the bearing itself into a device with sealing performance. Such as bearing with dust cover, sealing ring, etc. This kind of seal takes up little space, is easy to install and dismantle, and has low cost. The so-called bearing external sealing performance device is a kind of sealing device with various performance made in the installation of end cover. Bearing external seal is divided into non-contact seal and contact seal. The non-contact seal is suitable for high-speed and high-temperature occasions, with clearance type, labyrinth type and gasket type. Contact seal is suitable for medium and low-speed working conditions, commonly used in felt seal, cup seal and other structural forms.
According to the requirements of bearing working conditions and working environment for sealing degree, various sealing forms are often used in engineering design to achieve better sealing effect. The following main factors should be considered in the selection of bearing external seal:
- Bearing lubricants and types (grease and oil);
- The working environment of the bearing and the size of the occupied space;
- The bearing structure of the shaft has the advantages of allowing angle deviation;
- Circumferential velocity of sealing surface;
- Working temperature of bearing;
- Manufacturing costs.
Installation and maintenance of bearings
From the point of view of use, to ensure that the bearing can work reliably, the following points should be paid attention to:
- 1. Improve lubrication quality, control oil pressure, temperature and flow, strengthen oil filtration.
- 2. Use fuel oil and lubricating oil that meet the requirements.
- 3. It is disadvantageous to control the temperature state of diesel generator set and work under the condition of supercooling and overheating. In cold days, the diesel engine should be preheated before starting, and the crankshaft should be turned by hand to make the oil enter the friction surface.
- 4. The surface quality and geometry of bearing and journal should be strictly guaranteed.
- 5. The bearing clearance should be appropriate. If the generator set is too large, it will have impact. If it is too small, it will have poor lubrication and may burn the bearing bush.
How to ensure the reliable operation of bearings
Generally speaking, we should pay attention to the following points from the perspective of use:
- 1. The bearing clearance should be appropriate. If it is too large, impact will occur. If it is too small, poor lubrication will occur and the bearing bush may burn;
- 2. The surface quality and geometry of bearing and journal shall be strictly guaranteed;
- 3. Improve the quality of lubrication, control the pressure, temperature and flow of engine oil, and strengthen the filtration of engine oil;
- 4. Use fuel oil and lubricating oil that meet the requirements.
In order to make the bearing give full play and keep its proper performance for a long time, regular maintenance (regular inspection) must be done. It is very important to improve productivity and economy to detect faults early and prevent accidents in advance through proper regular inspection.
Whether the bearing is installed correctly affects the accuracy, life and performance. Therefore, the design and assembly department should fully study the bearing installation. It is hoped that the installation will be carried out according to the operation standard. The items of operation standard are generally as follows:
- (1) Clean bearings and bearing related parts.
- (2) Check the dimension and finish machining of the related parts.
- (3) Installation.
- (4) Inspection after bearing installation.
- (5) Supply lubricant.
It is hoped that the bearing package will be opened just before installation. General grease lubrication, do not clean, directly filled with grease. Generally, it is not necessary to clean the lubricating oil. However, for instruments or high-speed bearings, it is necessary to clean them with clean oil to remove the rust inhibitor applied on the bearings. The bearing with rust inhibitor removed is easy to rust, so it cannot be placed. Moreover, the bearing that has been sealed with grease can be used directly without cleaning.
The installation method of the bearing varies with the bearing structure, fit and condition. Generally, the inner ring needs interference fit due to the shaft rotation. Cylindrical hole bearing, multi-purpose press in, or multi-purpose hot charging method. In the case of taper hole, it can be directly installed on the taper shaft or installed with sleeve.
When it is installed to the shell, there is usually a lot of clearance fit, and the outer ring has interference. It is usually pressed in by a press, or there is also a cold shrink fit method of installation after cooling. When dry ice is used as the coolant, the moisture in the air will condense on the surface of the bearing. Therefore, appropriate anti rust measures are needed.
The disassembly of the bearing is regular maintenance, and it is carried out when the bearing is replaced. After disassembly, if you continue to use, or need to check the state of the bearing, the disassembly should be as careful as the installation. Pay attention not to damage the bearing parts, especially the disassembly of interference fit bearing, the operation is difficult.
It is also very important to design and make disassembly tools according to needs. During the disassembly, the disassembly method and sequence are studied according to the drawings, and the matching conditions of the bearings are investigated, so as to ensure the safety of the disassembly operation.
For the outer ring of interference fit, several outer ring screws are set on the circumference of the shell in advance to extrude the screw, and the screw is tightened equally while being disassembled. These screw holes are usually covered with blind plugs, tapered roller bearings and other separate bearings, and several cuts are set on the covering shoulder of the shell, which can be removed by using cushion block, press or tapping gently.
The disassembly of the inner ring can be pulled out with a press. At this time, pay attention to let the inner ring bear its pulling force. Moreover, the drawing fixture shown is mostly used, no matter what kind of fixture, it must be firmly stuck on the side of the inner ring. Therefore, we need to consider the size of the shaft shoulder, or study the processing of the groove at the shoulder, in order to use the drawing fixture.
The inner ring of large bearing is disassembled by oil pressure method. Oil pressure is applied through the oil hole of the bearing to make it easy to draw. For wide bearings, oil pressure method and drawing fixture are used together for disassembly.
The inner ring of cylindrical roller bearing can be disassembled by induction heating method. In a short period of time heating local, so that the inner ring expansion after drawing method. The induction heating method is also used when a large number of such bearing inner rings need to be installed.
When the bearing is removed for inspection, the appearance record shall be made by means of photography. In addition, confirm the amount of remaining lubricant and sample the lubricant before cleaning the bearing.
- a. The cleaning of the bearing is divided into rough cleaning and fine cleaning, and the metal grid can be placed at the bottom of the container in use.
- b. During rough washing, use a brush to remove grease or adhesion in the oil. At this time, if the bearing is rotated in oil, pay attention to the damage of rolling surface due to foreign matters.
- c. During fine cleaning, rotate the bearing slowly in the oil and carefully.
The commonly used cleaning agent is neutral water free diesel or kerosene, and sometimes warm lye is used according to the need. No matter what kind of cleaning agent is used, always filter and keep clean.
After cleaning, apply antirust oil or grease on the bearing immediately.
Inspection and judgment
In order to judge whether the removed bearing can be reused, the dimensional accuracy, rotation accuracy, internal clearance, mating surface, raceway surface, cage and sealing ring should be checked. Since large bearings can not be rotated by hand, pay attention to the appearance of rolling element, raceway surface, cage and flange surface. The more important the bearing is, the more careful it must be inspected.
Causes of rolling bearing heating and its elimination
- Low bearing accuracy: select the bearing with specified accuracy grade.
- Spindle bending or box hole is not concentric: repair spindle or box.
- Poor lubrication: select the specified brand of lubricating material and clean it properly.
- Low assembly quality: improve assembly quality.
- Running ring of inner shell of bearing: replace bearing and relevant wear parts.
- Too large axial force: clean and adjust the clearance of seal ring between 0.2 ~ 0.3mm, correct the diameter of impeller balance hole and check the static balance value.
- Bearing damage: replace the bearing.
Bearings are coated with appropriate amount of antirust oil and packed with antirust paper when they leave the factory. As long as the package is not damaged, the quality of bearings will be guaranteed. However, for long-term storage, it is better to store on the shelf 30cm above the ground when the humidity is lower than 65% and the temperature is about 20 ℃. In addition, the storage place should avoid direct sunlight or contact with cold walls.
Quality inspection of bearings
1. National standard of vibration acceleration (commonly known as Z standard)
The standard was established earlier, and the quality grade of bearing was determined by measuring the vibration acceleration value of bearing rotation, which was divided into Z1, Z2 and Z3 from low to high. At present, the domestic bearing manufacturers are still using the vibration acceleration value to measure the quality of the bearing, which simply reflects the fatigue life of the bearing.
2. Vibration speed standard (commonly known as V standard)
Since the original vibration acceleration standard has not been abolished, the standard is based on the standard issued by the Ministry of machinery industry. It is formulated with reference to the European standard and combined with the actual situation and needs of our country. The quality grade of bearings is divided by detecting the vibration speed of bearings (equivalent to the national standard). It is divided into five quality levels: V, V1, V2, V3 and V4. The quality grades of various ball bearings from low to high are V, V1, V2, V3, v4; The quality grades of roller bearings (cylinder and cone) are V, V1, V2 and V3 from low to high.
It reflects the quality of the bearing by detecting the vibration velocity of the bearing at different frequencies (low frequency, medium frequency and high frequency). It can be generally analyzed whether the bearing has geometric dimension problems (such as steel ring ellipse), the quality problems of raceway / rolling element, and the quality problems of cage. Compared with the vibration acceleration, the bearing quality has been significantly improved. At present, bearings exported to Europe, China’s military and aerospace industry all carry out bearing quality inspection according to the standard. At the same time, it provides a feasible means to detect the quality of bearings imported from Europe and distinguish counterfeit bearings.
There are two standards parallel situation in bearing quality inspection, while the bearing with high quality grade of “Z standard” may not have good quality performance when tested with “V standard”, and there is no corresponding relationship between them. This should be paid special attention in the quality inspection of bearings.
We usually identify the quality of equipment bearings from the following aspects:
1. Is the outer package clear
In general, the brands produced by regular manufacturers have their own special designers to design the external packaging, and arrange the factories with qualified production conditions to make the production. Therefore, the packaging of products should be very clear and unambiguous no matter from lines to color blocks.
2. Is the steel seal clear
Every bearing product will be printed with its brand, label, etc. Although the font is very small, the products produced by regular manufacturers all use steel seal technology to print, and they are pressed before overheating treatment. Therefore, although the font is small, it is deeply concave and very clear. In general, the font of counterfeit products is not only fuzzy, but also floating on the surface due to the rough printing technology. Some of them can be easily erased by hand or have serious manual marks.
3. Is there any noise
The left hand holds the inner sleeve of the bearing, and the right hand moves the sleeve back and forth in a small range to make it rotate. Listen to whether there is any noise during the operation of the bearing. Due to the backward production conditions of most counterfeit products and completely manual workshop operation, the bearing body will inevitably be mixed with dust, sand and other impurities in the production process, so there will be noise or unsmooth operation when the bearing rotates. This is the key to judge whether the products come from the brand products of regular manufacturers with strict production standards and machine operation.
Whether there is muddy oil on the surface, which requires us to pay special attention when buying imported bearings. Because there is a certain gap between the domestic anti rust technology and foreign advanced manufacturing countries, it is easy to leave a thick oil mark when the bearing body is treated with anti rust treatment, and feel sticky when touching by hand, while almost no traces of anti rust oil can be seen on the imported bearings. According to industry insiders, people who are particularly careful can smell a special smell on imported bearings, which is the smell of antirust oil.
5. Whether the chamfer is uniform
The so-called bearing chamfering, that is, the intersection of the horizontal and vertical planes, the counterfeit bearing products due to the limitations of production technology, in these parts of the corner processing is not satisfactory, we can easily identify this.
Bearing packaging is divided into inner packaging and outer packaging
After the bearing is manufactured and inspected to be qualified, it shall be cleaned and antirust treated, and then put into the inner package, so as to achieve the purpose of waterproof, moisture-proof, dust-proof, anti impact, maintaining the quality and accuracy of the bearing, and facilitating the use and sales.
According to the antirust period, the inner packing of bearings can be divided into three categories:
- ① Short antirust period packaging: antirust period of 3-6 months, suitable for mass delivery to the same subscriber, put into use in a short time. According to the agreement of both parties, simple packing is adopted on the principle of convenient use.
- ② General anti rust period packaging: anti rust period of one year, suitable for general purpose bearings.
- ③ Long antirust period packaging: antirust period of two years, suitable for special and precision bearings.
The inner packing materials of bearings include polyethylene plastic cylinder (box), kraft paper, plain and wrinkled polyethylene composite paper, paper box, polyethylene or polyethylene plastic film, nylon fastening belt or plastic woven fastening belt, waterproof high-strength plastic belt, linen bag, etc. All the above materials shall be qualified in the corrosion resistance test.
Source: China Bearing Manufacturer – Yaang Pipe Industry (www.epowermetals.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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