Introduction of slewing bearing technology
1、Overview
Slewing bearing is a kind of large-scale bearing which can bear comprehensive load, and can bear big axial, radial load and overturning moment at the same time. The slewing bearing is widely used in the real industry. It is called“The joint of the machine”, also need to bear the axial force, radial force, tipping moment of the mechanical necessary important transmission components. With the rapid development of machinery industry, slewing bearing has been widely used in marine equipment, engineering machinery, light industry machinery, metallurgical machinery, medical machinery, industrial machinery and other industries.Structural classification of slewing bearings 1) Single Row Four Point Contact Ball Slewing Bearing
Single Row Four Point Contact Ball Slewing Bearing
Characteristic of structure, performance and application
The single row four point contact ball slewing bearing is composed of two seat rings, which design in compact structure and light weight, steel ball contact with the circular raceway at four point, it can bear the axial force, radial force and the tilting moment at the same time . It can be used for slewing conveyer, welding manipulator, light & medium duty crane, excavator, and other construction machinery .
Double Row Ball Slewing Bearing
2) Double Row Ball Slewing Bearing
Characteristic of structure, performance and application
Double row ball slewing bearing has three seat ring, the steel ball and the spacing block can be directly arrange into the upper and lower races, two rows of upper and lower steel balls with different diameter are fitted according to the stress condition .This kind of open assembly is very convenient, for the upper and lower bear raceway arc angles is 90°,which can bear large axial forces and tilting moment . When the radial force is greater than 0.1 times the axial force need to be specially designed the raceway .Double row different ball slewing bearing’s axial and radial size are relatively large and solid in structure, so it is specially suitable for the medium diameter tower cranes, truck mounted cranes etc . loading and unloading machinery .
3) Three Row Roller Slewing Bearing
Characteristic of structure, performance and application
The three row roller slewing bearing has three seat rings, which separate theupper, lower and radialraceways, it made each row of the roller’s load capacity can be specified and can bear different loads simultaneously . The capacity load is the largest one compare with the other three models . Due to the large size in axial and radial dimension & the solid structure, it is specially suitable for the heavy duty machinery such as wheeled excavator, wheeled crane, ship crane, ladle turrets and the heavy duty mobile crane etc .
Three Row Roller Slewing Bearing
4）Cross -roller slewing bearing
Characteristic of structure, performance and application
Cross -roller slewing bearing consists of two seats. The structure is compact, light weight, high manufacturing accuracy, small in assembly gap, and high requirements for installation accuracy. Larger radial force. It is widely used in large rotary devices such as bartebling machines, overweight transportation machinery, port machinery, mining machinery, construction engineering machinery, park entertainment machines, installation machines and missile launchers.
2.Technical requirements
(一) material and technical parameters of slewing bearing1, material1) the ring adopts 42CrMo-GB/T 3077, but also can adopt other materials with good normalizing, quenching and tempering and induction hardening performance2) the rolling body adopts GCCR15, conforms to the GB/T 18254-2002 regulation.2.Hardness1) the hardness of the matrix, the hardness of the quenched and tempered ferrule is 229HB ~ 269HB.2) raceway surface hardness and layer depth, raceway surface hardness after medium frequency induction hardening is 55HRC-62hrc, bearing raceway effective hardened layer depth DS ≥3.5 mm (raceway surface hardness ≥48HRC)3) surface hardness of gear, the hardness of induction hardening of tooth surface and tooth root is 50HRC-60hrc, the effective hardening depth DS of tooth surface is 1.5-3.0 mm, the effective hardening depth DS of tooth root is 1.0-3.0 mm, the effective hardening depth DS (hardness ≥40HRC)
（二）Design, calculation and check of the roller, raceway, Bolt and gear of the slewing bearing1, steel ball diameter,In the raceway cross-section size allowed, the appropriate increase of steel ball diameter, to a certain extent, can improve the bearing capacity of the slewing support.The RacewayCalculating the rated static load and rated dynamic load of the slewing bearing according to ISO76:2006 and ISO281:2007; calculating the equivalent FA and equivalent M of the slewing bearing under static and dynamic conditions, respectively, the static load curve and dynamic load curve of the slewing bearing are used to select the static Factor of safety and fatigue life of the bearing respectively, both the minimum static Factor of safety and the minimum dynamic Factor of safety are required to be greater than or equal to one at their maximum limit loads3, boltsFirstly, the calculated load of bolts is converted into equivalent load, then the ultimate load curve of the bolt (which is determined when the clamping length of the bolt is 5 times the nominal diameter of the bolt and the pre-tightening force is 70% of the yield limit of the bolt material) is used to check the bolt under the condition of maximum ultimate load Then according to VDI2230 under the static or alternating load of the bolt connection to check, to prevent the failure of the connection may cause serious losses.
（三）Four main parameters which affect the bearing capacity of slewing bearingThere are two failure forms of slewing bearing, one is raceway damage, the other is broken teeth. The damage of raceway accounts for more than 98% , so the quality of raceway is the key factor that affects the life of slewing bearing. Raceway hardness, hardened layer depth, raceway curvature radius and contact angle are the four most important factors affecting raceway quality.Rolling road hardnessRaceway hardness, raceway quenching hardness of rotary bearing has great influence on its rated static load. If the rated static load is 1 at 55HRC, the corresponding relationship between the rated static load of bearing and raceway hardness is as follows.
2.The hardened layer depth of racewayThe necessary depth of hardened layer is the guarantee that no spalling occurs in the raceway of rotary bearing. When the slewing bearing bears the external load, the steel ball and the raceway change from the point contact to the surface contact, the contact surface is an elliptical surface. In addition to the compressive stress, the raceway is also subjected to shear stress, and the maximum shear stress occurs at a depth of 0.47 a below the surface (the semi-major axis of the contact ellipse) , this is why the standard defines the depth of the hardened layer according to the diameter of the ball rather than the diameter of the slewing bearing. The minimum guaranteed value is given in the standard. The static load C of the bearing is proportional to the depth of hardened layer H0.908. If the depth of hardened layer required to be 4mm is only quenched to 2.5 mm, then the static load C of the bearing will be reduced from 1 to 0.65, the probability of failure of slewing bearing due to fatigue spalling will be greatly increased
3.Radius of curvature of racewayThe radius of curvature of raceway is the radius of curvature of raceway in vertical section, the ratio of“t” to the radius of the steel ball also significantly affects the rated static load and fatigue life of the slewing bearing. If t = 1.04, the rated static load and fatigue life are both 1, then the relationship between the rated static load and fatigue life of the slewing bearing and T is as follows.
As can be seen from the above table, the greater the radius ratio, the lower the rated static load, the shorter the service life.
4, raceway contact anglecontact angle refers to the ball in the raceway on the contact point and the ball center of the line with the rotating support radial section (horizontal plane) between the angle. The rated static load C of the slewing bearing is linearly proportional to SIN α, and the original contact angle is usually 45 ° . When the slewing bearing has gap, the actual contact angle is larger than the original contact angle, the larger the gap, the greater the actual contact angle. In the range of clearance specified in the standard, the contact angle will increase by 2 ° ~ 10 ° , that is, the actual contact angle will reach 47 ° ~ 55 ° , which is a favorable change to the bearing capacity. However, if the original contact angle and the gap are large, the actual contact angle will exceed 60 ° , and the gap will further increase with the wear of the raceway, and the actual contact angle will also increase, the actual stress of the raceway will be higher than the theoretical stress, which will cause the raceway edge collapse and the slewing bearing failure.
（四）(4) for the application environment with large sloshing, the improvement measures of slewing bearing are needed1) proper reduction of bearing clearance, especially axial clearance.2) control the shape of bearing raceway, especially the ellipticity.3) strictly control the surface hardness and hardened layer depth of bearing raceway to prevent the appearance of too low surface hardness, layer depth, too shallow.4) improve the hardness of the base material of the bearing.5) other factors. After using for a period of time, due to the plastic deformation of the bearing raceway and the increase of the clearance, it is normal for the equipment to swing relatively large.
3.Installation and maintenance
1.Avoid any solvents from being exposed to a sealing ring or entering the roller. Do not paint on the seal belt. The surface contact surface connected to the support must be cleaned up.
2.There are no welding tumors, burrs, paint and other adhesives. There should be no lubricating oil on the surface and must be kept dry.
3.During installation, the quenching soft band should be outside the main load area.
4.Pre -bolts should be installed in a star -shaped shape. Symmetrically continuously in the 180 ° direction, and finally pass it through to ensure that the bolts on the circular cycle have the same pre -tightening force.
It is strictly forbidden to use the spring cushion ring.
5.Gear mesh clearanceFor the rotation support of the tooth, the tooth side gap is adjusted according to the highest point of the radial jump of the gear festival (three teeth with red paint). The minimum value of the side gap is generally 0.03 ～ 0.04 × modulus. After the final tight support, the gear meshing of the small gear on the entire circle must be re -inspected.
6.Lubrication
1) on delivery, the raceway is coated with a small amount of No. 2 lithium grease. The user should refill the raceway with new grease according to different working conditions.2）The first lubrication of the teeth must be performed immediately after installation. Tooth surface must have sufficient lubricant film.3) the raceway should be filled with grease regularly. General ball slewing bearing every 100 hours of operation should be added grease, roller slewing bearing every 50 hours of operation should be added grease. In the high temperature or more dust and other special working environment of the support, should be appropriately shortened replenishment period. Equipment before and after a long time to stop running, it must also add sufficient grease. The Raceway must be filled with grease each time until it oozes from the seal.7, check the bolts, installed and put to work in 100 hours of continuous operation, should fully check the installation of bolts pre-tightening force is in line with the requirements, after every 500 hours of continuous operation repeat the above-mentioned inspection.8、Check the seal system. The tape and seal system must be checked at least once every 12 months. In proper operation, the tape must remain undamaged. When cleaning components, the detergent should be avoided contact with the sealing tape or into the raceway system.
4.Rotation accuracy of slewing bearings
5.Axial clearance of slewing bearings
Thin Section Bearings
With the development of modern industry, in the design process of rotating equipment, designers usually pursue simplicity, miniaturization, light weight and compactness. BSPD bearing has developed a variety of low-friction bearings with different cross-sectional dimensions to meet the needs of customers. Before Thin Section Bearings was introduced, designers had to use the lightest range of bearings on the market at the time. There are many "light" 19 series, "extra light" 18 series, "ultra light" 17 series, but the section size of these series can not meet the market demand, and they are often heavy. Equal section thin wall bearing Bearings solve the size and weight problems of traditional bearings. The cross-sectional dimensions of all series of bearings do not change with the increase of the inner diameter. This is in stark contrast to standard bearings, whose cross-sectional dimensions always increase with bore diameter. The constant section size of the bearing has special value when designing a certain product based on the shaft diameter and transmission requirements. By selecting products from the same cross-section series of bearings, designers can standardize some common components. As shown in the figure below, the rotary tables of different sizes have the same bearing sealing chamber.
Thin Section Bearings has a compact structure and saves installation space. We can see the design advantages brought by Thin Section Bearings as shown in the figure below. The shaft with large diameter and small section can be designed as a hollow shaft instead of a small diameter solid shaft. Air supply pipes, infusion pipes or wires, collector rings, etc., can be arranged in the hollow shaft, which is cleaner and more efficient. In order to adapt to different working environments, BSPD Thin Section Bearings have stainless steel and surface plated materials in addition to conventional bearing steel materials.
Thin Section Bearings are classified into deep groove ball structure, code C; angular contact ball structure, code A; four-point contact ball structure, code X. These three basic types of bearings provide customers with a wide range of options in distributing loads, maintaining stiffness and accuracy.
C series deep groove ball bearings (below left) are single row radial ball bearings of conventional design. It can withstand radial force and small axial force, but the positioning accuracy of the bearing is inaccurate, because the inner ring and the outer ring will have a slight displacement when they are subjected to axial force (right picture below).
A series angular contact ball bearings (left picture below) are conventional high-speed, large axial load and high-precision design structures. It can bear both radial load and unidirectional axial load. Just because it can only bear the bearing load in a single direction, it is usually necessary to install it in pairs (right below).
X-Series four-point contact ball bearings (pictured below left), the standard bearing product line, are designed to withstand purely radial or axial loads. The X-type four-point contact bearing product features a peach-shaped inner and outer raceway, so that a single bearing can carry three loads (radial load, axial load and moment) at the same time. Because one four-point contact ball bearing can often replace two bearings, it allows for a cleaner design. X-type bearings can provide different internal preloads and clearances according to customer needs, such as high stiffness or zero clearance. This can be achieved by using balls with a larger gap than between the inner and outer ring raceways. Of course, even in the absence of external loads, the balls and raceways will deform elastically to some extent.
The above is a brief introduction to the structural characteristics of Thin Section Bearings. If you need an in-depth understanding, or you need our assistance in the early design stage, you are welcome to discuss with our BSPD engineers.
Bearings for bicycles - bicycle bearing
In recent years, with the rise of shared bicycles, the bicycle industry has developed rapidly for many years. In addition, people's love for cycling and fitness is growing. People are more and more particular about the riding experience of bicycles, and special models are equipped for different working conditions. Such as road bikes, mountain bikes, track bikes, BMX, trick cars, etc. The demand for high-end bicycles or high-end bicycle parts is increasing day by day. Bearings are the core components of bicycles, which are related to the experience, durability, energy saving and safety of the whole vehicle. Bicycle bearings are wearing parts, and the life of the bearings directly determines the life of the vehicle. The bearings in some parts of the bicycle can be easily replaced, but it is particularly difficult to replace the crank, and it cannot be replaced without professional assembly and disassembly equipment. For this reason, bicycle bearings must have the characteristics of low torque and long life. Bicycles are used for outdoor riding, especially for shared bicycles, the sun and rain put forward a higher test for the sealing of bearings. BSPD bicycle bearings have nearly 20 years of experience in design and manufacturing, providing individual solutions for OEMs. Let me share with you the technical characteristics of bicycle bearings:
1. Temperature resistance of bicycle bearings
Bicycles are everywhere in the world, and wherever there are people, there are bicycles. Therefore, the temperature resistance of bicycles is mainly low temperature resistance, and the low temperature resistance must be lower than -40 ℃. When the bicycle starts to ride in a cold area, the torque of the wheel will be too tight. After running for a few minutes, the temperature of the bearing itself will rise, and the rotation will be slowly and smoothly. Ordinary bearings run the risk of being frozen and unable to turn.
2. Water resistance of bicycle bearings
Outdoor riding, it is often rainy, or the bicycle is parked outdoors in rain. Poor sealing performance, water entering the bearing will cause early failure of the bearing. In the bicycle bearing industry, there are clear requirements for the waterproof performance of bearings, and the waterproof level should reach IP68 or above.
3. Durability of bicycle bearings
The durability of bicycles has certain requirements. The durability of the entire vehicle is equivalent to the durability of the bearing. The life of the bearing directly affects the life of the entire vehicle. The key parts are HUB, Bottom Bracket, Front Crankest, and the bearings used need to undergo strict life tests. The life test conditions of different models are different, such as speed and load.
4. Rotational flexibility of bicycle bearings
In order to save energy, bicycle bearings require low torque and low friction characteristics. For this reason, the selection of grease is very critical. Under the condition of ensuring the temperature resistance mentioned above, it must have the characteristics of low torque. Followed by the bearing clearance, to ensure that the bearing working clearance is less than 0.005mm after installation. If the working clearance is small or negative, the bearing rotation will be too tight or stuck, and if the working clearance is too large, the bearing will be loose. It is very important to select a reasonable clearance group according to the tolerance of the bearing and the housing hole.
5. Anti-corrosion of bicycle bearings
The steel parts of the whole vehicle except the bearing have surface treatment, or paint or electroplating, but the bearing has no surface treatment. Because the bearing surface treatment will affect the rotational flexibility of the bearing. Bearing steel has stronger corrosion resistance than ordinary carbon steel, and the surface of the bearing is coated with anti-rust oil before leaving the factory, so it will not rust in a non-humid environment in a short period of time. But over time, the bearing surface will rust, and there is grease in the bearing to prevent rust. Water entering the bearing will also cause the raceway and the steel ball to rust. For this reason, the bearing has strict waterproof requirements. Stainless steel bearings have the best corrosion resistance when the cost allows.
The above is a brief introduction to the technical characteristics of bicycle bearings. For in-depth understanding, welcome to discuss with our BSPD engineers.
Plastic coated bearings
The outer ring rotates when the plastic-coated bearing works, and it can be used as a roller. The outer circle of the roller bearing directly rubs against the track. For example, the track of heavy-duty rollers has a certain degree of wear resistance and needs to be lubricated, such as heavy-duty rollers for forklift masts, Telescopic fork rollers, etc.; to ensure that the outer ring of the bearing does not break, the outer ring of the bearing needs to be thickened Design. The hard outer circle of the bearing is easy to damage the track by grinding and pressing, so the outer surface of the outer ring of the heavy-duty roller needs to be lowered or made into a drum structure. For ordinary load rollers, the usual method is to make a shell, and then press the standard bearing into the shell, and the outer circle of the shell rubs against the track. This avoids the cost of making heavy-duty rollers. Light-loaded rollers and plastic-coated bearings came into being. The plastic has a certain degree of self-lubricity, low friction coefficient, low heat generation, and rolling on the track will not wear the raceway. Plastic-coated bearings have simple structure, convenient processing, and high mass production efficiency. Plastic-coated bearings are widely used, such as roller skating, furniture, strollers, automobile tensioners, beverage processing equipment, printing equipment, logistics equipment, etc. BSPD can manufacture all kinds of plastic-coated bearings according to the different needs of customers. Hundreds of plastic-coated bearings are provided for various industries.
Plastic-coated bearing is a layer of plastic on the outer bread of the bearing. The plastic material is generally nylon PA, ABS polyoxymethylene POM and engineering plastics polypropylene, PP, PU, PV, etc. Plastic has certain flexibility, impact resistance, friction resistance and certain self-lubricating type. With the rise of the plastics industry, there are a variety of plastic materials with different hardnesses for us to choose from on the market. According to different application conditions, plastic-coated bearings can choose a variety of different hardness plastics. If the caster needs to bear the weight, the plastic used needs to be harder. The crib needs to improve the anti-vibration performance and needs to be soft. Let's discuss the process requirements of plastic-coated bearings together.
The manufacturing process of overmolded bearings usually involves placing the bearings in an injection mold for injection. Then there are the following requirements for the bearing:
1. The temperature resistance of the bearing, the bearing seal cover and grease must be higher than the temperature of the injection mold. In order to avoid aging of the sealing cap or leakage of grease.
2. The sealing performance of the bearing. During the injection molding process, environmental factors such as dust or dirt will cause the bearing to be contaminated. If the bearing's sealing performance is not good, foreign matter invades into the bearing and affects the rotation flexibility of the bearing. Metal sealing caps are most likely to be invaded by foreign objects, and most plastic-coated bearings are metal sealing caps. For this reason, metal sealing caps need to have a "V" shape in the inner ring, while keeping the injection molding environment clean.
3. Plastic-coated bearings must ensure that after injection, the plastic ring and the bearing are tightly combined and not easy to fall off. For this reason, the plastic-preserving bearing is grooved on the outer circle of the bearing before injection molding. For example, for automobile tensioner bearings, in addition to grooves on the outer circumference of the bearing, knurling is also required at the bottom of the groove. As shown below:
If the hardness of the plastic is too low, we commonly call it soft plastic. The soft plastic ensures that it does not fall off after injection. The outer circle of the bearing needs to be roughed before injection, and then a layer of glue is applied to the rough outer circle. After injection, the plastic ring will be glued to the outer circle of the bearing. Will not fall off easily.
Technical requirements for dentist bearings
As people pay more and more attention to the prevention and treatment of dental diseases, the demand for high-speed dental bearings for Dentist handpieces continues to increase. Sellers and manufacturers of dentist bearings continue to flow in, and the quality of dentist bearings on the market is uneven. The dentist bearing is one of the bearings with the highest rotation speed for civilian bearings at present, with a rotation speed of 350,000 rpm. Design and manufacturing capabilities are beyond the reach of ordinary bearing companies. The durability of the product and the environmental protection requirements of the raw materials have special requirements. For this reason, BSPD has made a popularization for everyone according to the technical requirements of dentist bearings.
1. The choice of materials
Because dentist bearings work in dusty and damp mouths, in addition to the environmental protection requirements for dentist bearing materials, they must also have good corrosion resistance and wear resistance.
1.1 Ferrule
Dentist bearing ring materials generally use traditional SUS440C (shown in my country's 9Cr18). A bearing company in the United States has developed a special N-DUR corrosion-resistant stainless steel for medical equipment. Through advanced heat treatment process, the overall quenching hardness can reach above HRC60, which has better corrosion resistance than SUS440C. After precision grinding, the surface roughness of the raceway can reach Ra0.01, which is obviously better than SUS440C. The improvement of the roughness can reduce the bearing noise and also help to improve the corrosion resistance of the product.
1.2 balls
The speed of the dentist's bearing is extremely high, and the high-speed rotating ball has super strong separation force. For this reason, in addition to strong wear resistance and corrosion resistance, dentist bearing balls must also be lightweight. The weight reduction of the ball can directly reduce the centrifugal force and reduce the impact on the cage. We use high-quality silicon nitride Si3N4 ceramic balls. Spherical error, roundness, surface roughness, dimensional accuracy grade G3. The weight of Si3N4 ceramic balls is less than half the weight of steel balls of the same size. The Si3N4 ceramic ball has strong self-lubricity, low heat generation and low thermal expansion coefficient.
1.3 Cage
In addition to the extremely high speed of the dentist bearing, it also has the characteristics of frequent start and stop. During the start and stop process, the acceleration of the ball has a strong impact on the cage. Cages of ordinary materials and structures are obviously not up to the working conditions of dentists' bearings. Dentist bearing cages currently have two structures, one is phenolic laminated cloth tube turning and the other is polyimide Torlon injection molding.
1.4 Grease
The lubrication for dentist bearings must be non-toxic food grade grease. It is not easy to leak and has strong water resistance. It can provide stable lubrication for the bearing even in the environment of air and dust intrusion. Generally, single-sided sealed structure dentist bearings use CHEVRO SRI-2 or Kluberspeed BF72-22 grease. The non-sealed structure dentist bearings use cleaning lubricants, which are attached to the Dentist handpiece, and are cleaned regularly according to the maintenance manual of the Dentist handpiece.
2. Product structure
Different Dentist handpieces are equipped with different dentist bearing structures. There are single-sided cover, with or without cover, deep groove ball structure and angular contact ball structure, with flange and without flange, plus the different cage structure, etc., combination There are more than 100 models of Dentist bearings. The basic models are all R144 (inner diameter 3.175mm, outer diameter 6.35mm).
Common special requirements and solutions for bearings – 2
3、Corrosion resistance of bearings
Bearing rust is a common problem for us. There are many factors that cause bearing rust, such as ambient temperature, temperature, the PH value of coastal air, the performance of anti-rust oil, and packaging protection. Regarding bearing steel, the corrosion resistance of bearing steel from high-quality steel plants is relatively better. Bearing processing and surface roughness also affect the corrosion resistance of the bearing. The smoother the surface, the stronger the corrosion resistance. Industries that have special requirements for corrosion resistance include food, chemical, and medical. The usual solution to improve corrosion resistance is to use stainless steel or non-metallic materials.
1. Martensitic stainless steel
The commonly used SUS440\SUS420 (corresponding to the domestic code is 9Cr18\3Cr13) is martensitic stainless steel. Martensitic stainless steel can obtain high hardness through heat treatment, 420 reaches about HRC55, and SUS440 reaches HRC58 and above. Martensitic stainless steel is actually rusty, commonly known as "stainless iron". The corrosion resistance of stainless steel is evaluated by salt spray test. The SUS440\SUS420 salt spray test will rust in less than 20 hours.
SUS440 and SUS420, improve its corrosion resistance, the solution is passivation treatment. After the passivation treatment, the salt spray test can reach 150 hours without rust, and it can reach 200 hours without rust when done well.
"Bearing steel" is the name of a material family. There are many specifications and models. Steels with a carbon C content of 1% and a chromium Cr content of 1.5% or more can be called bearing steels. We usually consider bearing steels to be GCr15 by default. .The two kinds of stainless steel mentioned above, SUS440 and SUS420, of which SUS440 is a kind of bearing steel, the performance of the product made by it will not be reduced compared with bearing steel. But SUS420 is different, because it has low carbon content and the heat treatment hardness is not up to the standard of bearing steel, and the bearing performance will be lower than that of bearing steel.
The domestic market for small and medium stainless steel bearings is mostly SUS420, and it also means to pretend to be SUS440 (because the price of 440 is about 8,000 per ton), the hardness is made high, and the hardness is close to HRC58. The hidden danger that has never been brought is that the ferrule is too brittle Fragile, cracking of the outer ring often occurs when the dust cover is pressed during the manufacturing process.
2. Austenitic stainless steel
Austenitic stainless steel is represented by SUS316 and SUS304, which cannot be obtained by thermal treatment. It is very soft compared to bearing steel, but has super corrosion resistance and will not rust. The public toilet is used Austenitic stainless steel.
Its hardness is not enough, the bearing load capacity is very low, and the speed is also low. The size is not very accurate, and the turning feel is not smooth. Kaka will not rotate flexibly when falling from the table. Bearings made of SUS316 and SUS304 can only be used under conditions where load and speed are not required. The price is many times more expensive than ordinary bearings. There is a small amount of demand in the market for stainless steel bearings like this, and there are also manufacturers who produce them. The price is not cheap. Where can I go about it?
3. Non-metallic materials
The non-metallic materials used for bearings are plastics and ceramics. Plastics and ceramics do not have corrosion problems, but the rotation accuracy, noise, load, and speed performance are much worse than ordinary bearings. It can only be used under conditions that require very low load and speed. The price is many times more expensive than ordinary bearings.
4、High temperature resistance of bearings
The maximum temperature of ordinary bearings does not exceed 140°C. I did a test before and found that when the bearing temperature reaches 140°C, the bearing will burn and turn yellow, and it will fail after less than 10 hours. The long-term operating temperature of the bearing does not exceed 120°C. Like the SKF official website and samples, it states that the working temperature is -20℃~110℃.
The working environment temperature of the bearing, plus the temperature rise of the bearing itself. Bearings whose operating temperature can reach 120°C are not available for ordinary quality products. The temperature rise of the bearing is explained here: when the bearing is running, the temperature of the bearing itself will be higher than the ambient temperature, and the higher the temperature, the worse the quality of the bearing. That is to say, customers often say that your bearings are easy to get hot (that is, the temperature rises). Temperature rise is also an indicator for evaluating bearings. This item is not very popular, and ordinary manufacturers do not have this detection capability. There are standards for temperature rise.
The working environment temperature of the bearing may be higher than the actual data given by the customer. This is also my previous thought. For example, the bearing installation position will be a certain distance from the heat source, and the temperature will be much lower than the heat source, but the customer will regard the heat source temperature as the working temperature of the bearing. For example, for bearings used by customers, the grease added is very poor, and the dropping point is very low. The grease will drip into liquid when the temperature is not high, and the bearing will fail. In this case, high temperature bearings are required. We can replace them. Regular brand high-temperature grease to test. The following summarizes some common methods for high temperature bearings.
1. High temperature tempering
The heat treatment and tempering temperature of bearing steel is 180°C (required in the textbook), but some manufacturers only have 160°C in actual operation. The operating temperature of the bearing is the tempering temperature minus 50°C. High temperature tempering means that the tempering temperature is higher than 180°C. Bearings with high temperature tempering are suffixed with the model name: S1, S2, S3, S4
2. Use ceramic bearings
The working temperature of ceramic material silicon nitride (Si3N4) can reach 1100℃
The working temperature of zirconia (ZrO2) can reach 600℃
The working temperature of ceramic bearings is restricted by the material of the cage. For example, the working temperature of the cage made of PTFE or PEEK is only 260°C. If the working temperature exceeds 260℃, the cage can only be abandoned and a full-ball cageless structure is adopted.
The performance of ceramic bearings is not comparable to other performances of bearing steel materials except for high temperature. Ceramic bearings can only be used under working conditions where low speed, low load and rotation accuracy are not essential.
3. The temperature resistance of the sealing ring and plastic cage of the bearing (commonly used)
3.1 The default material of the sealing ring is nitrile rubber NBR, the maximum working temperature is 120℃,
3.2 The highest working temperature of polyacrylic resin ACM is 160℃, which is widely used in automobile bearings, such as automobile tensioner bearings, automobile generator bearings, and automobile clutch bearings.
3.3 The maximum working temperature of fluorine rubber FKM for automobile bearing seals and microwave ovens is 260℃,
3.4 Nylon cage PA66, the highest working temperature is 120℃,
The maximum working temperature of PA46 is 160℃.
The working temperature of the cage made of PTFE or PEEK is 260℃.
Full ball with loading gap without cage
5、Sealing performance of the bearing
The sealing performance depends on the design and processing quality of the sealing ring and the dust-proof groove. The factors that affect the sealing performance are:
1. Is the sealing ring made according to the drawing? This is very important. At present, domestic manufacturers have the ability to design seal rings, and there are very few seal rings produced according to the design. Most manufacturers, the bearing factory send the prepared open bearing samples to the seal ring manufacturer to open the mold to produce the seal ring. As long as the bearing can be covered, it is not tight or loose, and the bearing does not rotate too tightly. , I don't care if it leaks fat.
2. The rubber material has a considerable influence on the sealing performance. The rubber is too hard to wear and temperature, and it will age when it exceeds 80°C. The same is nitrile rubber. There are 12/kg and 25 yuan/kg on the market.
3. The grease itself is easy to leak. Grease with a low dropping point tends to leak.
4. The bearing product's own structure problem. Larger rolling elements are more prone to leakage than small ones, plastic cages are more prone to leakage than steel cages, and those whose cage is closer to the sealing ring are more prone to leakage.
5. The processing quality of the dust-proof groove. Dimension, roughness, shape and position tolerance.
6. The problem of bearing working conditions. The rotation speed is higher than the lower, and the outer ring is more likely to leak than the inner ring. The higher ambient temperature is more likely to leak.
When encountering customers who have requirements for sealing performance, it is inevitable to choose the right supplier. 1. Sealing ring design and processing capabilities; 2. With dust-proof groove structure in the inner ring, size, roughness, shape tolerance, etc. must be Meet the design requirements; 3. Choose grease with a high dropping point; 4. Add as little as possible within the specified range of the amount of grease.
Common special requirements and solutions for bearings - 1
1、Bearing rotation flexibility
The flexibility of the bearing, as the name implies, is to rotate it flexibly. To rotate it with the same torque, the rotation time is longer and the number of rotations is more. Most customers have this requirement, especially the customers of instrumentation, gyroscope, textile machinery, etc., which are quite demanding on the rotation flexibility of the bearing. Generally, the solutions to improve the flexibility of bearings have the following ideas, depending on the working conditions.
1、Properly increase the working clearance of the bearing to improve the flexibility of bearing rotation Here is an explanation of the working clearance, that is, the clearance after the bearing is installed. The original clearance of the bearing factory, after the interference fit with the seat hole or the shaft, the inner ring of the bearing expands or the outer ring shrinks, then the original clearance will become smaller, and the remaining clearance after the reduction is called the working clearance .
2、Use low-torque grease to improve bearing rotation flexibility If the viscosity of the grease is high, the rotation will be tight, and the torque of the thin grease will be low, and the bearing will rotate fast. Low torque grease such as synergistic SB-M, synergistic PS N2, or use liquid clear oil. Even without lubrication, it is usually a stainless steel mixed ceramic ball or a full ceramic bearing. Ceramic has a certain degree of self-lubricating, such as aircraft models and food machines.
3. Reduce bearing noise and improve bearing rotation flexibility
Under the same conditions, the smaller the bearing noise, the smaller the resistance and the more flexible the rotation. For the motor bearing, the noisy bearing motor drive current will be relatively large during the test, and the noisy bearing needs a larger load to drive it to rotate. Noise is a key item to measure the quality of bearings, and it is closely related to the price of bearings. ZV1~ZV4, the prices of different grades vary greatly. Noise reduction is the eternal goal of bearing manufacturers and users. The following is a brief introduction to the usual methods of noise reduction:
3.1 Improve the cleanliness of the product;
3.2 Use low-noise grease;
3.3 Improve the machining geometric accuracy of the ferrule;
3.4 Improve the waviness, roundness and roughness of the raceway.
3.4 Reduce the contact area between the raceway and the rolling element, increase the curvature of the groove for the ball bearing, and increase the convexity of the roller bearing.
3.5 Use non-metallic cages.
4. Improve the rotation accuracy of the bearing to improve the rotation flexibility of the bearing
The higher the rotation accuracy, the more flexible the rotation. What is rotation accuracy? High rotation accuracy
The bearing does not sway or jump when it rotates, as if it did not move. After the bearing is damaged, the first signal is that the rotation starts to shake and the sound is abnormal.
The precision of the bearing is classified into P0, P6, P5, P4, P2 (ABEC 1~9), and the precision of the bearing
The degree is divided into two parts: dimensional accuracy and rotation accuracy. Bearing accuracy is also a key item to measure the quality of the bearing, and it also has a great relationship with the price of the bearing. P0~P4, the prices of different grades vary greatly.
5. When a sealing ring is required, use a non-contact sealing ring.
Examples of main requirements for bearing rotation flexibility
2、Bearing speed
The rotation speed of the bearing is mainly limited by the temperature rise caused by the friction and heating inside the bearing. When the rotation speed exceeds a certain limit, the bearing will not continue to rotate due to burns, falling frames, etc. This limit value is called the limit speed of the bearing, and there are calculation standards for the limit speed. For this reason, there are standard values for the limit speed of various bearings of different specifications and models. How to increase the speed of the bearing without changing the structure and installation dimensions of the bearing. I summarize the following points.
1. Reduce the weight of the rolling element (but not reduce the size)
When the bearing works, the steel ball rotates in addition to the revolution with the cage. The bearing rotates once, and the steel ball rotates more than 5 times. When the bearing rotates at a high speed, the speed of the steel ball is similar to the bullet shot out of the barrel, which produces a strong centrifugal force and generates a lot of heat. Reducing the weight of the rolling elements can reduce the centrifugal force, reduce the impact on the cage, and reduce the heat generation, thereby increasing the speed of the bearing. The smaller the bearing, the higher the limit speed. The common solution is to change the material of the rolling elements to ceramic materials, such as silicon nitride (Si3N4) and zirconia (ZrO2)
A ceramic ball of the same size is less than half the weight of a steel ball.
2. Improve the impact resistance of the cage to prevent the bearing from falling apart due to high-speed rotation
The impact resistance of the cage is usually done by nitriding the cage or using non-metallic materials such as phenolic resin, nylon PA66, PA46, PTFE, PEEK. Compared with steel cages, non-metallic cages have greater elasticity and impact resistance. Strong, self-lubricating, large contact area with steel ball, small movement. For this reason, the bearing speed is too high to prevent the bearing from falling apart due to the deformation and fracture of the cage. For this reason, our common high-speed bearings are non-metallic cages.
3. Optimize the lubrication method and increase the speed of the bearing
3.1 Grease lubrication, the performance of the grease itself determines the speed of the bearing. Different specifications of grease have different quality focuses, such as: low temperature, high temperature, wear resistance, low torque, compression resistance, high speed, etc. Under the condition of grease lubrication, the only choice to increase bearing speed is high-speed grease.
3.2 Oil lubrication (here refers to liquid)
Oil lubrication has circulating oil lubrication (continuous heat dissipation) and static oil lubrication.
3.3 Oil mist lubrication
Oil mist lubrication, liquid lubricating oil is installed in the atomizer, and high-pressure air is blown in from the air inlet to form a mist of the liquid lubricating oil, which is blown into the bearing from the air outlet. The oil mist lubrication method is the best solution to increase the speed of the bearing. While there is constant new oil to lubricate the bearing, blowing air can cool the bearing heat. The high-speed electronic shafts are all lubricated by oil mist. When we walked into the grinding workshop of the bearing manufacturer, the blowing sound we heard was oil mist lubrication. In some grinding workshops with imperfect exhaust, the whole workshop looked like the next thing. Like mist, this is the oil mist that is not fully discharged and stays in the workshop.
The highest speed bearing I have seen so far is a dental drill bearing with a working speed of 350,000 rpm. The dental drill bearing model is inch miniature deep groove ball bearing SR144ZZ, and its dimensions: 3.175X6.35X2.78, SR144ZZ ordinary bearing limit speed 67000rpm, Dental drill bearings are prepared on the basis of ordinary bearings: inner and outer ring stainless steel, ceramic balls, PEEK material retainer, blowing turbine transmission, no lubrication (no oil in the mouth).
Example of bearing high speed
Angular contact ball bearing structure and principle
1、What is the contact angle?
The contact point between the steel ball and the raceway of the inner ring, and the contact point between the steel ball and the raceway of the outer ring, and the line of the two contact points form an angle with the diameter direction, which is called the contact angle. You must not understand this explanation, so let's break it down.
A、Corner point
1，When a ball is in contact with a plane, it is a point contact。
2，The radius of the arc is greater than the radius of the circle and is tangent to a point.
B、We have learned about the contact point above. The raceway radius of all ball bearings is greater than the radius of the steel ball, and all steel balls and raceways are in point contact.
2、Ball bearing structure
Deep groove ball bearings. The two points where the steel ball contacts the grooves of the inner ring and the outer ring are connected in the diameter direction
The line of the two points where the steel ball contacts the raceways of the inner ring and the outer ring is at an angle relative to the radial tilt type
Angular contact ball bearings are very loose in a free state and can only bear one-way axial loads. If the force is applied in the opposite direction, the bearing will fall apart
4、Oblique wave of angular contact ball bearing
Angular contact ball bearings have the outer ring with oblique waves, and there are also inner and outer rings with oblique waves. Why are there oblique waves? The oblique wave is for installation. The inner ring cage steel balls are grouped together, and the outer ring is expanded by heating and squeezed in from the oblique wave port. You can also squeeze it in in the opposite direction to make it loose
Single row angular contact ball bearings can bear radial load and unidirectional axial load, so single row angular contact ball bearings are generally installed in pairs or 3 sets or 4 sets of bearings together in series.
Angular contact ball bearings are usually installed in pairs. The two bearings each pipe the axial force in one direction. There are two commonly used pairing methods as shown in the figure below.
Pairing method is: back to back, code name DB. Pairing method: face to face, code name DF
Two sets of bearings are connected in series, code-named DT. After the two sets of bearings are used as one set of bearings to increase the load, they can only withstand one-way bearing forces.
Two sets of bearings in series are paired together to become four sets of bearings.
5、Angular contact ball bearings have high speed, can withstand high loads, and have high axial positioning accuracy. It is usually applied to precision parts such as main shafts and workpiece shafts of mechanical equipment. BSPD can carry out targeted design according to the user's special working conditions to improve the bearing's durability, temperature resistance, corrosion resistance and other solutions.
Application examples of angular joint bearings。
1.Regular use
The clearance of the angular contact ball bearing is adjusted when the bearing is installed in the application. As shown, adjust the height of the inner and outer spacers.Or use DT or DF structure to ensure that the thickness of inner and outer spacers is consistent, without adjustment.
2.DB+DB
2.DT+DT+Preload spring
3.（DT+DT）DB+DB
