Control of material factors affecting bearing life

In order to make the above-mentioned material factors affecting the life of the bearing in an optimal state, it is first necessary to control the original structure of the steel before quenching. The technical measures that can be taken are: high temperature (1050 ° C) austenitizing and cooling to 630 ° C isothermal normalizing to obtain pseudo The pearlite structure is eutectoidally analyzed or cooled to 420 ° C to obtain a bainite structure. It can also be rapidly annealed by wrought residual heat to obtain fine-grained pearlite structure to ensure fine and uniform distribution of carbides in the steel. When the original structure in this state is austenitized by quenching, the undissolved carbides aggregate into fine particles in addition to the carbides dissolved in the austenite.
   
    When the original microstructure in the steel is constant, the carbon content of the quenched martensite (that is, the austenite carbon content after quenching heating), the amount of retained austenite and the amount of undissolved carbide mainly depend on the quenching heating temperature and the holding time. As the quenching heating temperature increases (time is constant), the amount of undissolved carbides in the steel decreases (the carbon content of the quenched martensite increases), the amount of retained austenite increases, and the hardness first increases as the quenching temperature increases. After reaching the peak, it decreases as the temperature increases. When the quenching heating temperature is constant, as the austenitizing time is prolonged, the amount of undissolved carbides decreases, the amount of retained austenite increases, and the hardness increases. When the time is long, the tendency is slowed down. When the carbides in the original structure are fine, since the carbides are easily dissolved into the austenite, the hardness peak after quenching is shifted to a lower temperature and appears in a shorter austenitizing time.

    In summary, after quenching of GCrl5 steel, the amount of undissolved carbide is about 7%, and the retained austenite is about 9% (the average carbon content of cryptocrystalline martensite is about 0.55%). Moreover, when the carbides in the original structure are fine and evenly distributed, when the above-described level of microstructure is reliably controlled, it is advantageous to obtain high comprehensive mechanical properties, thereby having a high service life. It should be noted that the original structure of the finely dispersed carbides, when quenched and heated, the undissolved fine carbides will aggregate and grow to make them coarse. Therefore, for the original tissue bearing parts with such quenching heating time should not be too long, using rapid heating austenitizing quenching process, will obtain higher comprehensive mechanical properties.
   
    In order to make the bearing parts have a large compressive stress on the surface after quenching and tempering, a carburizing or nitriding atmosphere may be introduced during quenching heating to perform surface carburizing or nitriding for a short time. Since the actual austenite carbon content is not high when the steel is quenched and heated, it is much lower than the equilibrium concentration shown on the phase diagram, so carbon (or nitrogen) can be absorbed. When austenite contains higher carbon or nitrogen, its Ms decreases, and the martensite transformation occurs in the surface layer after quenching than in the inner layer and the core, resulting in a large residual compressive stress. After the GCrl5 steel was heated and quenched by carburizing atmosphere and non-carburizing atmosphere (both low temperature tempering), the contact fatigue test showed that the surface carburizing life was 1.5 times higher than that of non-carburizing. The reason is that the surface of the carburized part has a large residual compressive stress.

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Bearing lubrication

The purpose of bearing lubrication:
    The purpose of lubrication of rolling bearings is to reduce internal friction and wear of the bearings, to prevent sticking, and the lubricating effect is as follows.
    (1) Reduce friction and wear.
    In the mutual contact portion of the ferrule, the rolling element and the retainer constituting the bearing, metal contact is prevented, and friction and wear are reduced.
    (2), prolong the fatigue life.
    The rolling fatigue life of the bearing is prolonged when the rolling contact surface is well lubricated during rotation. Conversely, if the oil viscosity is low and the thickness of the lubricating oil film is not good, it is shortened.
    (3), discharge friction heat, cooling.
The circulation oil supply method or the like can be used to discharge heat generated by friction or heat from the outside to cool. Prevent the bearing from overheating and prevent the lubricant from aging itself.
    (4), other
    There is also the effect of preventing foreign matter from entering the inside of the bearing or preventing rust and corrosion.
    Lubrication method:
    The lubrication method of the bearing is divided into grease lubrication and oil lubrication. In order to make the bearing function well, first, choose a lubrication method that suits the conditions of use and the purpose of use. Lubricity of oil lubrication predominates if only lubrication is considered. However, grease lubrication has the advantage of simplifying the structure around the bearing and comparing the advantages and disadvantages of grease lubrication and oil lubrication.

Cylindrical Roller Bearings
    The cylindrical roller is in line contact with the raceway, and has a large radial load capacity, which is suitable for bearing heavy loads and impact loads. It is also suitable for high-speed rotation of N-type and NU-type axial movement, and can be adapted to thermal expansion or installation error. The change of the relative position between the shaft and the outer casing is most suitable for the free end bearing type NJ and NF type to withstand a certain degree of unidirectional axial load. The NH type and NUP type can withstand a certain degree of bidirectional axial load inner or outer ring. Separable, easy to assemble and disassemble NNU type and NN type, strong rigidity against radial load, mostly used for machine tool spindle
    Mainly applicable cages:
    Steel stamping cage (Z-shaped), copper alloy cutting cage, pin cage, synthetic resin forming cage
    The main purpose:
    Medium and large motors, generators, internal combustion engines, gas turbines, machine tool spindles, reduction gears, loading and unloading machinery, various industrial machinery
    Solid needle roller bearing
    The basic structure of the inner ring bearing is the same as that of the NU type cylindrical roller bearing, but due to the use of the needle roller, the volume can be reduced, and the large radial load can be withstood without the inner ring bearing. The mounting surface of the shaft with appropriate precision and hardness should be used as the mounting surface. Raceway surface
    Mainly applicable cages:
    Steel stamping cage
    The main purpose:
    Automotive engines, transmissions, pumps, excavator track wheels, hoists, overhead cranes, compressors
    Tapered Roller Bearings
    This type of bearing is equipped with a circular table-shaped roller. The roller is guided by the large rib of the inner ring so that the apexes of the conical surfaces of the inner ring raceway surface, the outer ring raceway surface and the roller rolling surface intersect on the bearing center line. One-point single-row bearing can withstand radial load and one-way axial load. Double-row bearing can withstand radial load and two-way axial load. It is suitable for bearing heavy load and impact load. It is divided into small cone according to contact chest (α). Three types of angle, middle cone angle and large cone angle, the larger the contact angle, the greater the axial load capacity. The outer ring and inner component (inner ring and roller and cage assembly) can be separated for easy assembly and disassembly, rear auxiliary The bearing code "J" or "JR" has international interchangeability. This type of bearing also uses the British series.

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Bearing damage and countermeasures (2)

Bearing damage:

In general, if the bearing is used correctly, it can be used until the fatigue life is reached. However, there will be accidents that are prematurely damaged and cannot be used. This early damage, as opposed to fatigue life, is a quality use limit called a fault or accident. Many of them are caused by inadvertent installation, use, and lubrication, and foreign objects intruding from the outside are insufficiently studied for the thermal effects of the shaft and the outer casing.

Regarding the damage state of the bearing, such as the ferrule of the roller bearing and the jam of the rib, it may be considered as a cause of insufficient lubricant, unsuitability, defects in the oil supply structure, intrusion of foreign matter, bearing installation error, shaft deflection If the song is too big, there will be coincidences of these reasons.

Therefore, it is difficult to know the true cause of the damage by only investigating the bearing damage. However, if you know the mechanical use of the bearing, the conditions of use, the structure around the bearing, and the situation before and after the accident, combined with the damage state of the bearing and several reasons, it can prevent similar accidents from happening again.

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Bearing cooperation

    In the support portion of the machine, in order to prevent the bearing inner ring and the shaft, the outer ring and the outer ring hole from sliding relative to each other during the operation of the machine, a simple and effective method must be adopted. Especially for the thin-walled ferrules of the ultra-light and ultra-light series bearings, the proper tight fit can make the bearing rings have a uniform force during operation, so that the bearing capacity of the bearing rolling elements can be fully utilized. However, the selected bearing fit cannot be too tight, because the elastic expansion of the inner ring and the contraction of the outer ring will reduce the internal clearance of the bearing until it completely disappears, thus affecting the normal operation of the bearing.
    1. Bearing matching
    (1) Bearings with cylindrical bores
    The main factors that should be considered when choosing a bearing fit are as follows:
    1 type of load
    According to the load acting on the bearing, the load on the ferrule can be divided into three types: fixed load, swing load and swing load.
    Fixed load
    The resultant radial load is absorbed by the local area of ​​the ferrule raceway and is correspondingly transmitted to the corresponding local area wind of the shaft or housing mating surface. This load is called a fixed load.
    The fixed load is characterized by a synthetic radial load that is relatively stationary with the ferrule. A ferrule that is subjected to a fixed load is generally available with a looser fit.
    b. swing load
    The resultant radial load vector acting on the bearing ring rotates in the circumferential direction of the raceway, is in turn received by the various parts of the raceway, and is correspondingly transmitted to various parts of the surface of the shaft housing bore. This type of load is called a swing load, also known as a cyclic load.
    The slewing load is characterized by a synthetic radial load vector and a relative rotation of the ferrule. Filters or interference fits should be used for the ferrules that bear the slewing load and the shaft or housing bore. If the gap is used for the installation, slippage will occur between them, which will cause the contact surface to wear and friction, and the temperature will rise sharply and the bearing will be damaged quickly. The size of the wanted excess is determined by the operation. When the bearing is working under load, the principle of “crawling” on the mating surface of the shaft or the casing hole is not caused.
    C. Swing load
    The resultant radial load vector acting on the bearing ring is relatively oscillated in a certain area of ​​the ferrule raceway, is received by a certain area of ​​the raceway, and is transmitted to a certain area of ​​the surface of the shaft or the casing hole, or acts on the bearing The upper load is the impact load and the vibration load, and the load direction or value often changes. This load is called the swing load, and is also called the directional load.

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