Failure analysis and prevention methods of the hot

Failure analysis and prevention methods of rolling bearings, dry goods

failure analysis and prevention methods of rolling bearings, dry goods

June 6, 2019

rolling bearings are one of the indispensable basic components of running machinery. Although the rolling bearing is small in size and low in cost, once the rolling bearing fails, the loss to the operating machinery and even the whole production equipment is huge. With the rapid development of technology, enterprises have higher and higher requirements for the quality of rolling bearings. Especially for enterprises with automatic and continuous production, the requirements for the reliability of rolling bearings are very strict. Therefore, how to improve the reliability of rolling bearings has become one of the main problems urgently needed to be solved by rolling bearing manufacturers and users

the reliability of rolling bearings is closely related to the failure forms of rolling bearings. To improve the reliability of bearings, we must start with the failure forms of bearings and carefully analyze the failure causes of rolling bearings, so as to find out specific measures to solve the failure

I. failure mechanism of bearing

1 Contact fatigue failure

contact fatigue failure refers to the material fatigue failure caused by the alternating stress on the working surface of the bearing

the common form of contact fatigue failure is contact fatigue spalling. Contact fatigue spalling occurs on the working surface of the bearing, often accompanied by fatigue cracks. It first occurs at the maximum alternating shear stress below the contact surface, and then extends to the surface to form different spalling shapes, such as pitting or pitting spalling, and spalling into small flakes is called shallow spalling. Due to the gradual expansion of the spalling surface, it will slowly expand to the deep layer, forming deep spalling. Deep spalling is the fatigue source of contact fatigue failure

2. Wear failure

wear failure refers to the failure caused by the continuous wear of the metal on the working surface caused by the relative sliding friction between the surfaces

continuous wear will cause gradual damage to bearing parts, and eventually lead to loss of bearing dimensional accuracy and other problems. Wear failure is one of the common failure modes of all kinds of bearings. According to the form of wear, it can be divided into abrasive wear and adhesive wear

abrasive wear refers to the wear caused by the relative movement of the contact surface between the working surfaces of bearings with foreign hard particles or hard foreign bodies or wear debris on the metal surface, which often causes furrow like scratches on the working surfaces of bearings

adhesive wear refers to the uneven stress on the friction surface due to the micro bulge or foreign matter on the friction surface. When the lubrication condition is seriously deteriorated, local friction generates heat, which is easy to cause local deformation and friction micro welding of the friction surface. In serious cases, the surface metal may be locally melted, and the force on the contact surface will tear the local friction welding points from the substrate and increase the plastic deformation

3. Fracture failure

the main causes of bearing fracture failure are defects and overload. When the external load exceeds the material strength limit and causes the part to break, it is called overload fracture. The main cause of overload is the sudden failure or improper installation of the host. The defects of bearing parts, such as microcracks, shrinkage cavities, bubbles, large foreign objects, overheated tissues and local burns, will also cause fracture at the defect when they are impacted, overloaded or violently vibrated, which is called defect fracture

it should be pointed out that in the manufacturing process of bearings, 1. What industries are suitable for the use of universal material testing machine? In the factory re inspection, forging and heat treatment quality control, and processing process control, the above defects can be correctly analyzed by instruments. But generally speaking, most of the bearing fracture failures that usually occur are overload failures

4. Corrosion failure

some rolling bearings inevitably come into contact with water, steam and corrosive media during actual operation, which will cause rust and corrosion of rolling bearings. In addition, the rolling bearing will also be affected by micro current and static electricity during operation, resulting in current corrosion of the rolling bearing

the rust and corrosion of rolling bearings will cause pit like rust, pear skin like rust on the surface of ferrules and rolling elements, and pit like rust with the same spacing between rolling elements, full-scale rust and corrosion. Finally, it causes the failure of rolling bearings

5. Clearance change failure

in the work of rolling bearings, due to the influence of external or internal factors, the original matching clearance changes, the accuracy decreases, and even causes "bite", which is called clearance change failure. External factors such as excessive interference, inadequate installation, expansion caused by temperature rise, instantaneous overload, etc; Internal factors, such as residual austenite and residual stress in an unstable state, are the main reasons for the failure of clearance change

II. Common failure modes and Countermeasures of rolling bearings

1 Peeling at the limit position of one side of the channel

peeling at the limit position of one side of the channel is mainly manifested in the serious peeling ring at the junction of the channel and the retaining edge. The reason is that the bearing is not installed in place or sudden axial overload during operation

the countermeasures taken are to ensure that the bearing is installed in place or to change the outer ring fit of the bearing on the free side to clearance fit, in order to compensate the bearing when the bearing is overloaded. If the installation cannot be ensured in place, the direct contact of the bearing can be reduced by increasing the oil film thickness of the lubricant (increasing the viscosity of the lubricant), or reducing the load of the bearing

2. The groove peels symmetrically in the circumferential direction

the peeling in the symmetrical position is manifested in that the inner ring peels off from the surrounding ring belt, while the outer ring peels off in the symmetrical position in the circumferential direction (that is, the short axis direction of the ellipse). The main reason is that the ellipse of the shell hole is too large or the two half separated shell hole structure, which is particularly obvious in camshaft bearings for motorcycles. When the bearing is pressed into the shell hole with a larger ellipse or the two halves of the separated shell are tightened, the outer ring of the bearing will produce an ellipse, and the clearance in the direction of the minor axis will be significantly reduced or even negative. Under the action of load, the inner ring rotates to produce circumferential peeling marks, and the outer ring only produces peeling marks at the symmetrical position in the direction of the minor axis. This is the main reason for the early failure of the bearing. The inspection of the failed parts of the bearing shows that the outer diameter roundness of the bearing has changed from 0.8um controlled by the original process to 27um. This value is much larger than the radial clearance value. Therefore, it is certain that the bearing works under serious deformation and negative clearance, and abnormal sharp wear and spalling are easy to form on the working surface in the early stage

the countermeasures taken are to improve the machining accuracy of the shell hole or not to adopt the separation structure of the two halves of the shell hole as far as possible

3. The inclined spalling of the raceway

shows an inclined spalling ring on the working surface of the bearing, which indicates that the bearing works in an inclined state. When the inclination angle reaches or exceeds the critical state, abnormal sharp wear and spalling are easy to form in the early stage. The main reasons are poor installation, shaft deflection, low accuracy of journal and housing hole

countermeasures are taken to ensure the installation quality of bearings and improve the axial runout accuracy of shaft shoulder and hole shoulder, or improve the viscosity of lubricating oil to obtain a thicker lubricating oil film

4. Ferrule fracture

ferrule fracture failure is relatively rare, usually caused by sudden overload. The causes are complex, such as bearing raw material defects (bubble shrinkage), forging defects (overburning), heat treatment defects (overheating), processing defects (local burns or surface microcracks), host defects (poor installation, poor lubrication, instantaneous overload), etc. The ferrule may be broken by overload, impact load or violent vibration

the countermeasures taken are to avoid overload impact load, select appropriate interference, improve installation accuracy, improve service conditions and strengthen quality control in the process of bearing manufacturing

5. Cage fracture

cage fracture belongs to accidental abnormal failure mode. The main reasons are the following five aspects:

11. During the use of wire change experimental machine, 1. We must learn and study the instruction manual of the instrument. A. abnormal load of the cage. If the installation is not in place, inclination, excessive interference, etc., it is easy to reduce the clearance, intensify friction and heat generation, soften the surface, and premature abnormal peeling. With the expansion of spalling, spalling foreign matters enter the cage pocket, causing the cage to block operation and generate additional load, which intensifies the wear of the cage. Such a deteriorating cycle may cause the cage to fracture

b. poor lubrication mainly refers to that the shaft is in a lean oil state, which is easy to form adhesive wear and deteriorate the state of the working surface. Tears caused by adhesive wear are easy to enter the cage, causing abnormal load on the cage, which may cause cage fracture

c. the invasion of foreign matters is a common mode of cage fracture failure. Due to the invasion of foreign hard foreign matters, the wear of the cage is aggravated and abnormal additional load is generated, which may also lead to the fracture of the cage

d. creep is also one of the reasons for cage fracture. The so-called creep mostly refers to the sliding phenomenon of the ferrule. When the interference of the mating surface is insufficient, the load point moves to the surrounding direction due to sliding, resulting in the deviation of the ferrule from the axis or shell to the circumferential direction. Once creep occurs, the mating surface is significantly worn, and the wear powder may enter the interior of the bearing, forming a process of abnormal wear - raceway peeling - cage wear and additional load, which may even cause cage fracture

e. cage material defects (such as cracks, large heterometallic inclusions, shrinkage cavities, bubbles) and riveting defects (lack of nails, backing nails or the gap between the two halves of the cage interface, serious riveting injury) may cause cage fracture

take countermeasures to strictly control in the manufacturing process

6. Card injury

the so-called card injury is the surface damage caused by the collection of minor burns in the part of the sliding surface damage. Linear scars on the circumference of the sliding surface and rolling surface. Cycloid scar on the end face of the roller, and the snap on the shaft ring near the end face of the roller. The main causes of jamming are: excessive load, excessive preloading, poor lubrication, foreign matter biting, inclination of inner ring and outer ring, shaft deflection, poor accuracy of shaft and bearing housing, etc

it can be solved by proper preloading, improving lubricants and lubrication methods, and improving the accuracy of shafts and bearing housings

7. Wear

wear failure refers to the failure caused by the continuous wear of the metal on the working surface caused by the relative sliding friction between the surfaces. The main factors causing wear failure are lubricant failure or lack of lubricant, wrong lubrication method, abrasive particles entering the bearing, excessive load and large shrinkage, etc. The solution can be to improve the lubricant or lubrication method, strengthen the sealing mechanism, etc

8. Scratch

the so-called scratch is the surface damage that occurs on the raceway surface and rolling surface with the collection of minor burns caused by rolling slip and oil film hot cracking. Produce a rough surface with adhesion. The main causes of abrasion are high-speed light load, rapid acceleration and deceleration, inappropriate lubricant, water intrusion, etc

solutions: improve preloading, improve bearing clearance, use lubricants with good oil film, improve lubrication methods, improve sealing devices, etc

9. When the indentation

bites into the small metal powder or foreign matter, the dent on the raceway surface or rotating surface or due to the impact during installation, a concave surface (Brinell hardness indentation) is formed on the spacing of the rolling elements. The main factors causing indentation are: the bite of foreign matters such as metal powder, and the excessive impact load during assembly or transportation

solution: improve the sealing device, filter and moisten