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The properties that self-aligning roller bearing materials should possess
1. Friction compatibility
The performance of preventing adhesion and forming boundary lubrication when the shaft diameter is in direct con
The rated load and ultimate speed of bearings are determined under appropriate conditions of wig lubrication, and appropriate lubrication refers to the appropriate selection and dosage of lubricants. Using 3 lithium based grease and not selecting the appropriate grade of lubricating grease based on the working condition of the self-aligning roller bearing. For example, for low speed motors, the viscosity of 3 # lithium-based grease is low, which cannot form a good oil film, resulting in poor lubrication and wear failure of self-aligning roller bearings. Due to the fact that most bearings do not have non-stop grease injection devices, it is not possible to replenish or replace lubricating grease in a timely manner, resulting in insufficient and deteriorated lubricating grease, leading to lubrication damage and bearing wear and failure.
The bearing cage was broken, the bearing was stuck, and during disassembly inspection, it was found that the lubricating grease at the shaft extension end was dry, hard, and deteriorated. The cage was loose, and the self aligning roller bearing was overheated. Due to the outdoor use of the motor and the low ambient temperature, the viscosity of the lubricating grease increased, resulting in poor lubrication and bearing wear and failure.
The temperature seriously affects the viscosity of the lubricating grease, resulting in poor lubrication of the bearings. In summer, when the temperature reaches 37 ° C, the viscosity of the lubricating grease decreases significantly, while in winter, the low temperature below -30 ° C increases the viscosity of the lubricating grease, even causing clumping. This forms a poor oil film, causing lubrication damage and wear failure of the self-aligning roller bearing.
(1) The degree of difficulty in forming alloys in metallurgical materials.
(2) The affinity between materials and lubricants.
(3) The friction coefficient of the paired material in an unlubricated state.
(4) The microstructure of the material.
(5) The thermal conductivity of the material.
(6) The size of the surface energy of the material and the characteristics of the oxide film.
2. Clamping ability
The ability of materials to prevent scratches or (and) abrasive wear by allowing foreign hard particles to clamp into lubricants. For metallic materials, those with low hardness and elastic modulus have good clamping performance, while non-metallic materials may not necessarily have good clamping performance, such as carbon graphite, which has lower elastic modulus but poor clamping performance. Self aligning roller bearings usually use softer and harder materials to form friction amplitudes, and generally use softer materials as bearing shells.
3. Runnability
The ability to reduce machining errors, coaxiality errors, and surface roughness parameter values between the shaft diameter and bearing pads during the running-in process, in order to achieve uniform contact and thereby reduce friction and wear rates.
4. Friction compliance
The material relies on the elastic plastic deformation of the surface layer to compensate for the initial poor fit of the sliding friction surface and the bending performance of the shaft. Materials with low elastic modulus have better compliance.
5. Wear resistance
The ability of paired materials to resist wear and tear. Under specified wear conditions, wear resistance is represented by the reciprocal of wear rate, wear degree, and wear amount.
6. Fatigue resistance
The ability of a material to resist fatigue failure under cyclic loading. At the operating temperature, the strength, hardness, impact strength, and organizational uniformity of the bearing material are crucial for resisting fatigue. Materials with good running-in and clamping properties usually have poor fatigue resistance.
7. Corrosion resistance
The ability of materials to resist corrosion. When lubricating oil is used in the atmosphere, it will gradually oxidize and produce acidic substances. Moreover, most lubricating oils also contain extreme pressure additives, which can corrode bearing materials. Therefore, self aligning roller bearing materials need to have corrosion resistance.
8. Air corrosion resistance
In the state of motion of a solid relative to a liquid, when bubbles in the liquid rupture near the surface of the solid, local impact high pressure or local high temperature are generated, which will lead to cavitation wear. The ability of a material to resist cavitation wear is called cavitation resistance. Generally, copper lead alloy, tin based self-aligning roller bearing alloy, and aluminum zinc silicon alloy have good resistance to cavitation corrosion.
9. Compressive strength
The ability to withstand unidirectional loads without being crushed or changing in size.
Failure caused by poor lubrication of self-aligning roller bearings
The rated load and ultimate speed of bearings are determined under appropriate conditions of wig lubrication, and appropriate lubrication refers to the appropriate selection and dosage of lubricants. Using 3 lithium based grease and not selecting the appropriate grade of lubricating grease based on the working condition of the self-aligning roller bearing. For example, for low speed motors, the viscosity of 3 # lithium-based grease is low, which cannot form a good oil film, resulting in poor lubrication and wear failure of self-aligning roller bearings. Due to the fact that most bearings do not have non-stop grease injection devices, it is not possible to replenish or replace lubricating grease in a timely manner, resulting in insufficient and deteriorated lubricating grease, leading to lubrication damage and bearing wear and failure.
The bearing cage was broken, the bearing was stuck, and during disassembly inspection, it was found that the lubricating grease at the shaft extension end was dry, hard, and deteriorated. The cage was loose, and the self aligning roller bearing was overheated. Due to the outdoor use of the motor and the low ambient temperature, the viscosity of the lubricating grease increased, resulting in poor lubrication and bearing wear and failure.
The temperature seriously affects the viscosity of the lubricating grease, resulting in poor lubrication of the bearings. In summer, when the temperature reaches 37 ° C, the viscosity of the lubricating grease decreases significantly, while in winter, the low temperature below -30 ° C increases the viscosity of the lubricating grease, even causing clumping. This forms a poor oil film, causing lubrication damage and wear failure of the self-aligning roller bearing.
Lubrication periodicity and key factors of damage in self-aligning roller bearings
There are many reasons for the damage of most self-aligning roller bearings, such as exceeding the originally estimated load, ineffective sealing, and excessive bearing clearance caused by tight fits. Any of these factors has its own unique damage pattern and will leave special traces of damage. Therefore, by examining the damaged bearing of the shaft, possible causes can be found in most cases.
For commonly used bearings, the lubricant should be replaced once a year at a working temperature of approximately 50 ℃. If the operating temperature is 100 ℃ or higher, even if its thermal stability is good, the lubricant should be replaced at least every three months. If the oil bath lubrication becomes contaminated with water or external particles, it must be replaced immediately.
Service life of lubricating grease
For impossible or ineffective re lubrication applications, the service life of lubricating grease can be determined by formulas.
Log L=(0.018f-0.025) T-2.77f+6.3
L=Life of lubricating grease (h)
F=(operating speed) (min-1)/ultimate speed of bearing grease
T=operating temperature
There are situations where it is necessary to use more than the recommended amount of grease in practice. When the required torque is low, lubrication can be completed with very little grease. When the speed is very low and exposed to dust or moisture, it may be almost filled. Under high speed and high temperature conditions, more frequent lubrication is usually required than usual.
All bearings basically contain two hardened steel rings, multiple hardened balls or rollers, and a separating or retaining frame for separating the rollers or rollers. These types are further divided into many types in use. Some types, such as needle shaped columns, may not have inner rings and the rollers move directly on the hardened shaft.
Overall, one-third of bearing damage is due to fatigue damage, the remaining one-third is due to poor lubrication, and the remaining one-third is due to contamination entering the bearings or improper installation and handling. However, these types of damage are also related to industry. For example, the pulp and paper industry is mostly caused by poor lubrication or pollution, rather than material fatigue, resulting in damage to self-aligning roller bearings.
The Importance of Lubrication Quality of Self aligning Roller Bearings for Working Conditions
As a type of imported bearing, how to properly lubricate the bearing during normal operation is an important aspect that cannot be ignored in bearing maintenance and upkeep.
Oil bath smoothing is the most common smoothing method among bearings, suitable for smoothing low and medium speed bearings. Immerse a part of the bearing in the groove, and the smooth oil will be carried by the rotating self-aligning roller bearing parts, and then flow back to the oil groove. The oil level should be slightly lower than the center of the lowest rolling element.
Smooth oil dripping is suitable for bearing components that require a quantitative supply of smooth oil. The appropriate amount of oil dripping is once every 3-8 seconds, as excessive oil will cause an increase in bearing temperature.
Use an oil pump to transport the filtered oil into the bearing components, and then filter and cool the smooth oil after passing through the bearings before use. Because circulating oil can take away a certain amount of heat and cool the bearings, this method is applied to self-aligning roller bearing components with higher rotational speeds.
The dry shrinkage air is mixed with the smooth oil through the spray to cause oil mist. In the radial bearing, the air flow can effectively cool the bearing and avoid the intrusion of impurities. This method is suitable for the smoothness of high-speed and low-temperature bearing components.
Use an oil pump to inject low-pressure oil into the bearing through a nozzle, and the oil injected into the bearing flows into the oil groove through the other end of the bearing. When the bearing rotates at high speed, the rolling element and the support frame also cause airflow around the air at a relatively high rotational speed. It is difficult to deliver smooth oil to the bearing using individual smooth methods. At this time, it is necessary to use low-pressure radiation to spray smooth oil into the bearing, and the position of the nozzle should be placed between the inner ring and the center of the support frame.
1) Compared to roller bearings, ball bearings have a higher limit speed, so ball bearings should be preferred at high speeds.
2) Under the same inner diameter conditions, the smaller the outer diameter, the lighter the rolling element. The centrifugal inertia force exerted by the rolling element on the outer ring raceway during operation is also smaller, making it more suitable for working at higher speeds. When placed at high speeds, it is advisable to choose bearings of ultra light, ultra light, and light series. The self aligning roller bearings of the heavy and extra heavy series are only used in low speed and heavy load situations. If a light series bearing is used but the bearing capacity cannot meet the requirements, a wide series bearing can be considered, or two light series bearings can be installed together for use.
3) The material and structure of the cage have a significant impact on the bearing speed. Solid cages allow for higher rotational speeds than stamped cages.
4) The authorized speed of bearings is very low. When the working speed is high, if the axial load is not very large, angular contact ball bearings can be used to withstand pure axial force.
5) If the working speed slightly exceeds the limit speed specified in the sample, measures such as increasing the tolerance level of the self-aligning roller bearing or appropriately increasing the radial clearance of the bearing, selecting circulating lubrication or oil mist lubrication, and strengthening the cooling of the circulating oil can be taken to improve the high-speed performance of the bearing. If the working speed exceeds the limit speed by a large amount, special high-speed rolling bearings should be selected.
At normal speeds, the speed does not have much effect on the selection of type, and only at higher speeds will there be a significant impact. The bearing samples include the limit speed nlim values for various types and sizes of bearings. This speed refers to a bearing with a low load (P ≤ 0.1C, C is the basic rated dynamic load), normal cooling conditions, and a level 0 tolerance
