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When rolling bearings are working, especially when the load is complex and high-speed rotation, the cage has to withstand great centrifugal force, impact and vibration, there is a large sliding friction between the cage and the rolling elements, and a lot of heat is generated. The combined effect of force and heat will cause cage failure, and in severe cases will cause cage burns and fractures, causing the bearing to fail to work normally.
Therefore, in addition to a certain strength, the material of the cage must also have good thermal conductivity, low friction factor, good wear resistance, strong impact toughness, low density, and expansion coefficient close to the rolling element. In addition, the stamping cage needs to withstand more complicated stamping deformation, and the material is also required to have good processing properties. Some extremely demanding cages are also plated with silver.
The expansion coefficient is similar to that of the rolling elements and good processing performance. In addition, the cage is subject to chemical media, such as lubricants, lubricant additives, organic solvents and coolants.
Cages Cages have four basic functions in rolling bearings:
1. Separate rolling elements;
2. Keep the rolling element itself or keep it together with a ferrule;
3. Guide the rolling body to roll on the correct track;
4. Orient the rolling elements to reduce friction.
Cage Materical
Commonly used cages are divided into metal cages and non-metal cages according to the types of materials. There are also composite cages and so on. The types of cage materials are: low carbon steel stainless steel cage, bakelite/plastic (nylon) cage, brass/bronze/aluminum alloy cage, etc.
Bearing cages for special purposes should also meet the requirements of special working conditions. Such as high temperature resistance, corrosion resistance, self-lubricating (used in vacuum) or non-magnetic, etc.
Steel Cage Materical
Due to the characteristics of high strength, good toughness, and easy processing, steel cage materials are commonly used in rolling bearings. It is often cold stamped from 08 and 10 high-quality carbon steel sheets. In addition, it can also be obtained by other mechanical processing methods as needed. Commonly used steel cage materials include 20, 30, 45, 0Cr18Ni9, 1Cr18Ni9Ti, 40CrNiMo, ML15, ML20, etc. Steel cages are generally heat treated to eliminate stress and restore plasticity. Including high temperature tempering, recrystallization annealing, etc. In order to reduce the coefficient of friction of the steel cage, the finished cage must be surface treated if necessary.
Non-ferrous metal cage material
Different from steel, non-ferrous metals have special properties. For example, aluminum alloy has the characteristics of low density, good thermal conductivity, and good corrosion resistance; copper alloy has the characteristics of good thermal conductivity, low friction coefficient, good formability, and high operating temperature; Zinc aluminum alloy has the advantages of low cost, low density and excellent performance.
Non-metallic cage material
Non-metallic cage materials mainly include polymers and their composite materials, including nylon, phenolic tape, polytetrafluoroethylene, etc. The polymer material has good strength and elasticity matching. The good sliding performance enables the polymer cage to produce only a small friction when relative to the surface of the lubricated rolling element, which can minimize the heating and wear of the bearing. In the absence of lubricant, the polymer cage still has excellent movement characteristics. It can be guaranteed that the bearing will continue to run for a period of time without damage. Due to the lower density of the polymer, the cage made from it has a smaller inertia.
In addition to the use of pure materials, the cage also modifies polymer materials. Use other materials for filling or enhancing use.
Brass cage
There are two types of stamping and solid, stamping is only suitable for small and medium-sized. Brass plates, brass castings or brass forgings. Brass has high tensile strength. The mechanical strength is equivalent to that of steel stamping cages, but the density is relatively small and the limit speed is high. Not affected by lubricants, including synthetic oils and greases; brass cages cannot be used in applications above 300°C, and are not suitable for ammonia (such as cooling), because ammonia can cause brass to break seasonally, and the working temperature is required. Below 300°C.
Polyamide (nylon 66) cage
Solid cage (injection molding method), the material is polyamide (nylon 66); polyamide nylon material has the advantages of large elasticity and light weight, this kind of cage has very good sliding and self-lubricating properties. It is especially suitable for vibration and impact stress or high acceleration and deceleration or when the inner and outer rings of the bearing are inclined to each other; the working temperature is lower than 120° and greater than -40°, and the temperature is too low to make nylon lose its elasticity.
Use restrictions:
(1) Polyamide nylon cage may be affected by special lubrication (corrosive additives in lubricant)
(2) It cannot be used in vacuum because it will become brittle due to dehydration.
Reasons for cage fracture
In most cases, the bearing cage will not be damaged under reasonable working conditions, but incorrect operations in daily production will reduce the service life of the bearing cage. Let's take a look at the reasons for the fracture of the bearing cage.
1. Poor bearing lubrication
When the bearing is running in a lean state, it is easy to form adhesive wear and deteriorate the working surface. The tears produced by the adhesive wear can easily enter the cage, causing abnormal load on the cage and possibly causing the cage to break.
2. The phenomenon of bearing creep
Creep refers to the sliding phenomenon of the ferrule. In the case of insufficient interference of the mating surface, the load point moves to the surrounding direction due to the sliding, which causes the ferrule to deviate from the shaft or the housing in the circumferential direction.
3. Abnormal load of bearing cage
Inadequate installation, tilting, excessive interference, etc. will easily reduce the clearance, increase friction and heat generation, soften the surface, and prematurely peel off. As the peeling expands, the peeled foreign matter enters the cage pockets, resulting in the cage The operation is blocked and additional load is generated, which intensifies the wear of the cage. Such a deteriorating cyclic effect may cause the cage to break.
4. Material defects of bearing cage
Cracks, large dissimilar metal inclusions, shrinkage holes, bubbles and riveting defects, missing nails, pad nails or gaps between the two cage halves, severe riveting, etc. may cause the cage to break.
5. Intrusion of bearing hard foreign bodies
The intrusion of foreign hard foreign objects or other impurities aggravates the wear of the cage.
6. The cage is damaged
The main causes of damage are: cage vibration, excessive speed, wear and foreign matter blockage.
7. Cage wear
The wear of imported bearing cage can be caused by insufficient lubrication or abrasive particles.
8. The raceway is blocked by foreign matter
Fragments of flake material or other hard particles may become between the wedge cage and the rolling elements, preventing the latter from going around its own axis.
9. Bearing vibration
When the inlet is exposed to vibration, the inertial force can be large enough to cause fatigue cracks to form in the cage material. Sooner or later, these cracks cause the cage to fracture.
10. The bearing rotation speed is too fast
If the imported bearing is operated at a speed exceeding the design speed of the cage, the inertia received in the cage may cause the cage to break due to gravity. Usually, where very high speeds are relevant, the retainer can be selected with specially designed bearings.