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15 Types Of Failure Modes Of Aviation Bearings And Their Preventive Measures

15 Types Of Failure Modes Of Aviation Bearings And Their Preventive Measures

2021-01-27

1, scratches, scrapes

Due to the lubricating oil filter net, metal particles are worn down, or some impurities mixed with in the process of installation, and the size of the metal particles, may be greater than the minimum oil film thickness, and due to the contact area between sliding phenomenon, exists in between two contact surfaces at this time of hard small clever grain, will scratch the work surface.In addition, during the installation process, due to the bearing parts contact with other belt Angle of rigid objects, and the bearing parts of the workspace score a certain depth, width, length, different ditch OARS called cut or scratch, if the number of rolling contact surface between, falling into local damage, foreign small particles impurities or lubricating oil is combined with the two between the sliding surface, so that the parts work surface appeared a group of tiny scratches, called scratch.

Preventive measures :(1) strictly filter lubricating oil.(2) in the installation process to prevent pollutants into the person.(3) In the process of cleaning and installation, it is strictly prohibited to scratch the surface of bearing surface with hard objects.

2, wear and tear

Under critical lubrication state.When two objects in contact with each other move relative to each other, there will be surface damage. If this damage continues continuously, it will cause denudation, that is, wear.Wear will cause the loss of dimensional accuracy of parts, and the wear surface will show the characteristics of spot erosion.As shown in Figure 1-1.Due to the large amount of heat generated by friction, metal migration between the two contact surfaces will occur, making the wear surface show the feature of phosphorous spalling.

 

Under high stress, or in the condition of lack of oil, the friction between objects will have a lot of friction heat, sometimes, the heat is to contact the local melting state, thus appear instantaneous welded, and then will be torn apart, the consequences are the cause of contact area between metal migration, the wear is called adhesion wear.

Sometimes, due to some foreign impurities mixed into the contact surface, will also cause serious wear, and will cause serious scratches on the surface, this wear is called abrasive wear.

It is almost impossible to safely avoid the occurrence of wear and tear. Only by taking all effective measures to reduce the occurrence of wear and tear are the following measures:

(1) improve the structure and parts of the finishing process, the selection of appropriate lubrication conditions.

(2) Strictly filter the lubricating oil to ensure the cleanliness of the working environment to reduce or avoid abrasive wear.

3, light load skidding

It also belongs to a kind of serious wear and tear, rolling element and raceway contact, when light contact load (or under the condition of excessive lubrication), due to the influence of inertia force, resulting in the differences between two pieces of each contact point of linear velocity, the slide in between two contact bodies appear phenomenon, called light load skid.The occurrence of light load skidding in roller bearings will cause the friction and wear of raceway, surface fatigue, raceway surface damage and other consequences, and the early damage characteristics are surface scratch and full-layer migration phenomenon.

Measures to overcome light-load skidding of ultra-high speed roller bearings:

(1) in order to ensure that the roller has a high enough fatigue life

(2) The cage is made of high strength lightweight materials to reduce its weight.

(3) improve the structure of roller bearings to improve the fluency of lubricating oil in bearings.

(4) the outer ring oval raceway, in order to increase the number of loaded rollers.

(5) Hollow rollers with pre-load are used to cause all rollers in the bearing to be uniformly loaded without elliptical raceway.

(6) Appropriately reduce clearance to increase the number of bearing rollers and increase towing power.

4, rust

The damage caused by chemical or electrochemical action between metal and surrounding medium is called corrosion or corrosion.When corrosion occurs, black or brown rust spots or rust pits are formed on the surface, and corrosion products appear to destroy the luster of the metal.

In bearings, there will also be a kind of friction corrosion phenomenon, its morphology is characterized by: some spot pits appear on the contact surface.The formation mechanism is: in the contact between the rolling body and the ring, the ring will produce a small amount of plastic deformation under the action of positive pressure, so that a small relative motion will appear between the two contact surfaces.The new metal surface formed by friction will be oxidized under the combined action of chemical, mechanical and thermal, and the oxides formed will be piled and pressed onto the surface layer continuously.Also due to the high temperature of the frictional heat, the lubricant will form aldehydes, ketones and carbonic acid, and these products will also react with the material.Therefore, friction corrosion not only causes surface damage of parts but also reduces the contact fatigue strength of parts.

Measures to prevent corrosion:

(1) pay attention to the storage of bearings and try to avoid contact with corrosive media.

(2) Clean the bearing carefully when installing it, and wear gloves to avoid sweat stains on the working surface of the bearing.

5. Partial wear and load trajectory downward (climbing)

Partial wear is the wear phenomenon that the bearing is biased to one side in the work, which is more obvious on the inner ring of the roller bearing.That is, in the ball bearing bearing under axial load, the loaded track on the outer ring raceway deviates too much to the other side of the raceway center.

Solutions:

(1) the bearing installation must be in place to make the bearing in a good loading state.

(2) Adjust the clearance of the ball bearing to prevent its value from being too large.

6, pressure pit, collision

Due to the action of static load or impact load, the permanent deformation of the working surface of bearing parts is left at a certain depth, which is called pit or collision.Preventive measures are as follows:

(1) Strictly prevent parts from falling to the ground. It is strictly prohibited to strike with hard objects, which will cause damage to the working surface.

(2) when installing the bearing, keep the ring and the rolling body assembly in a correct position.

7, fatigue peeling

Under the action of alternating contact stress, fatigue spalling occurs not only under the surface but also on the surface.

Fatigue spalling occurs under the surface. Under the action of alternating stress, the maximum shear stress occurs at about 0.2 mm from the surface depth.First of all, the first tiny crack is formed from the weakest point of the material, and then the crack expands and increases in value under the repeated action of alternating stress.The result is the flaking of the metal.

There are two reasons for fatigue spalling originating from the surface:

(1) as raw materials in smelting and bearing parts of forging, stamping, heat treatment and cold working process, such as residue on the surface of non-metallic inclusion, rough granular carbides, pores, wrinkles, pit and metamorphic layer on the surface of the factors, such as in the process of bearing operation, due to the effect of contact stress and cause them to take off, away from the mother or for plastic deformation caused by microporous gathered an enlarged flake form.

(2) On the two rolling surfaces in contact with each other, due to the existence of uneven phenomenon, if the bearing is in the boundary lubrication state when working, the contour peaks of the two surfaces interact, so that those tiny uneven parts produce plastic deformation and fatigue.This phenomenon continues to form a large number of tiny cracks, which then expand and join together to form a tiny spalling.Thus causing surface damage.As the damage spreads, tiny cracks can grow and cover the raceway, forming so-called pitting spots, which in turn grow and join together, causing fatigue spalling on the surface.It has been proved that for the spindle bearing of high speed ship engine, most of the fatigue spalling occurs on the surface.

To overcome or reduce the premature occurrence of fatigue spalling, the following measures can be taken:

(1) improve the lubrication conditions, reduce abrasive wear damage to the working surface.Avoid direct metal-to-metal contact.

(2) adopt new materials or high purity vacuum smelting steel, and optimize the heat treatment process to improve the contact fatigue strength of parts.

(3) improve the surface quality, enhance its wear resistance and corrosion resistance.

(4) Starting from manufacturing, increase the forging ratio, improve the fiber streamline direction, and improve the finishing process.

8, current erosion

Local heating and melting of the metal surface, the damage area by amplification, visible metal after melting and condensation of small spherical particles, this damage is called electrical erosion.The formation mechanism is that the two contact surfaces generate static electricity for some reason, and then an oil film thickness is formed between the two surfaces, and the oil film plays an insulating role.When the electrostatic potential difference between the surfaces of two contacts is high enough to penetrate the insulation layer, a spark discharge occurs and current erosion occurs.

Overcoming method: make the parts keep good grounding state, avoid the occurrence of high potential due to the accumulation of charge in the work, produce spark discharge.

9, cage deformation

Under the action of external force, the shape of the cage is greatly different from the original shape, which is called the cage deformation.The reason for its formation is that the material of the cage is usually light material with low strength, and the lintle size for isolating the rolling body is generally small.Therefore, under the action of external force, it is easy to make the cage produce plastic deformation.

Preventive measures are as follows:

(1) choose high strength light material.

(2) Avoid hitting the cage with hard tools or gravity.

10, crack

When the stress of the bearing parts exceeds the strength limit of the material, the internal or surface of the bearing parts will produce fracture or local fracture phenomenon, and the macro defects are called cracks.It is characterized by sharp roots or edges.The causes of crack are complicated and there are many influencing factors.Therefore, it should be appropriate to the case from all aspects in order to eliminate the generation of cracks.

11. Cage coating falls off or bulges and bubbles

Due to the improper handling of the cage before the silver plating process, or some problems in the silver plating process, the bonding strength between the coating and the parent material is reduced, resulting in the coating falling off and other defects during work.

Preventive measures: improve the silver plating process, enhance the bonding strength of the coating and the parent metal.

12, bipolar wear (cat eye ring)

The morphology features are as follows: concentric circles with a certain area are formed at the two poles of the steel ball.

Causes of the wear between: operate at a high speed and withstand the axial load of three contact ball bearing, the ball will produce a lot of dynamic load a centrifugal force and gyroscopic moment of inertia and centrifugal force role Yu Gangqiu, always make the ball to the outer ring, cause the outer contact Angle decreases, and the inner ring of contact Angle increases, with the increase of speed within one and a half circle by partial discharge to completely uninstall, the bearing should be changed from three contact to two contact, if the bearing is still not out of three contacts, due to the effect of gyro moment, the ball will be half a circle in the load of the severe sliding channel, the cause of bearing parts abrasion or wear.

Its typical manifestation is that many concentric circles (" cat's eye ") with a certain area appear on the steel ball.

The ways to overcome this are as follows:

(1) Increase clearance and strictly control the diameter difference of the steel ball, so as to ensure that the bearing can break away from the third contact after running.

(2) in the design of the appropriate Shan two inner rings, the design of gasket Angle.

13, heat discoloration

After the bearing works for a period of time, there is a light brown sediment or gry-black (or purple) surface on the bearing surface, and the original metallic luster has been lost.

The reasons for the discoloration are as follows:

(1) Because the bearing surface is exposed to hot air and the temperature rises, the oil film attached to the bearing surface produces the oxidation phenomenon of oil, forming a light brown oxide film, which is deposited on the surface of the bearing.

(2) if the bearing is in an abnormal working state, resulting in a sudden rise in the working environment temperature, at this time the temperature has greatly exceeded the tempering temperature of the bearing parts, resulting in serious burns, and the bearing surface becomes gray and black.

Preventive measures: ensure smooth oil pipeline, timely supply of oil required by the bearing.

14, size enlargement or reduction

After a certain period of operation of the bearing, clearance decreases (reflecting the increase or decrease of the size of the inner and outer rings or the diameter of the rolling body). If the size change is large, it is likely to appear the phenomenon of bearing axle holding.

The reason for size swelling or shrinkage is that a certain amount of residual austenite is retained in the heat treatment process of bearing parts. With the change of time and temperature, it will gradually become a more stable martensite. In this transformation process, volume swelling phenomenon will occur, and the size of bearing parts will swell at this time.In addition, if the working temperature of the bearing is higher than the tempering temperature of the bearing, there will be the decomposition process of martensite and the shrinkage of the size.Sometimes the stress relaxation phenomenon in the bearing parts is also one of the reasons for the size change.

Preventive measures: after quenching, the method of cold treatment to reduce the number of residual austenite;The tempering temperature is higher than the operating temperature, and the additional tempering is used for many times to eliminate the residual austenite.

15, the marks

The occurrence of vibration marks can be divided into two situations:

(1) Vibration marks generated by the engine when it is working

In the local area of the raceway surface of the inner or outer ring, there are some axial parallel stripes closely arranged along the rolling direction, which are called vibration stripes.

Formation mechanism: in high-speed centripetal cylindrical roller bearings, due to the raceway roundness of inner and outer rings or the roller diameter difference is large, resulting in the reduction of bearing rotation accuracy, is the main reason for the formation of vibration marks.

Preventive measures: reduce the deformation of the inner and outer rings and reduce the difference between the diameter of the rolling body, improve the accuracy of bearing rotation.

(2) Vibration of the engine at rest

Under the static condition of the engine, due to the occurrence of continuous non-rotating vibration, under the action of static load, it leads to the freaking wear marks formed by the roller pitch on the inner raceway of the cylindrical roller bearing. This type of vibration marks does not affect the performance of the bearing, so it is also called false surface deformation, so it is allowed to exist.

Bearing in the non-rotating state, due to the heavy vibration load or overload, the ball or roller on the raceway to produce a permanent shallow and smooth pit, such deformation - as not allowed to exist.

Preventive measures: to prevent vibration in transportation, strengthen anti-vibration measures.


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