3. Fracture failure

The main reasons for bearing fracture and failure are defects and overload. When the external load exceeds the material strength limit and causes part fracture, it is called overload fracture. The main cause of overload is sudden failure or improper installation of the host. Defects such as microcracks, shrinkage cavities, bubbles, large foreign objects, overheated tissues, and local burns in bearing parts can also cause fracture at the defect site during impact overload or severe vibration, which is called defect fracture.

It should be pointed out that during the manufacturing process of bearings, the presence of the above-mentioned defects can be correctly analyzed through instruments in the factory re inspection of raw materials, quality control of forging and heat treatment, and processing control. But generally speaking, the most common bearing fracture failures are overload failures.

3. Corrosion failure

Some rolling bearings inevitably come into contact with water, steam, and corrosive media during actual operation, which can cause rust and corrosion of rolling bearings. In addition, the rolling bearing will also be subjected to micro current and static electricity during operation, causing current corrosion of the rolling bearing.

The rusting and corrosion of rolling bearings can cause pit like rust, pear skin like rust on the surface of the rings and rolling elements, as well as pit like rust with the same spacing between rolling elements, as well as comprehensive rusting and corrosion. Ultimately, it causes the failure of the rolling bearing.

5. Failure due to clearance changes

During the operation of rolling bearings, due to external or internal factors, the original fit clearance changes, 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 clearance change failure.

二、Common Failure Modes and Countermeasures of Rolling Bearings

1. Peeling at the extreme position on one side of the channel

peeling at the extreme position on one side of the channel is mainly manifested in a severe peeling ring at the junction of the channel and the retaining edge. The reason for this is that the bearing is not installed properly or there is a sudden axial overload during operation.

The countermeasures taken are to ensure that the bearings are installed in place or to change the free side bearing outer ring fit to a clearance fit, in order to compensate for bearing overload. If it is not possible to ensure proper installation, methods such as increasing the oil film thickness of the lubricant (increasing the viscosity of the lubricant) or reducing the load on the bearing can be used to reduce direct contact with the bearing.

2. The channel peels off symmetrically in the circumferential direction

Symmetrical position peeling is manifested in the inner ring being peeled off by the surrounding ring, while the outer ring is peeled off in a circumferential symmetrical position (i.e. the short axis direction of the ellipse). The main reason is that the shell hole ellipse is too large or the two halves of the shell hole structure are separated, which is particularly evident in motorcycle camshaft bearings. 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 produces an ellipse, and the clearance in the short axis direction is significantly reduced or even negative. Under the action of load, the inner ring of the bearing rotates to produce circumferential peeling marks, while the outer ring only produces peeling marks in the symmetrical position of the short axis direction. This is the main reason for the early failure of the bearing. After inspection of the failed parts of the bearing, it was found that the outer diameter roundness of the bearing had changed from 0.8um controlled by the original process to 27um. This value is much greater than the radial clearance value. Therefore, it can be confirmed that the bearing operates under severe deformation and negative clearance, and abnormal rapid wear and peeling are easily formed on the working surface at an early stage.

The countermeasure taken is to improve the machining accuracy of the shell hole or avoid using a shell hole half separation structure as much as possible.

3. Ramp inclination and peeling

The inclined peeling ring on the working surface of the bearing indicates that the bearing operates in an inclined state. When the inclination angle reaches or exceeds the critical state, abnormal rapid wear and peeling can easily occur in the early stage. The main reasons for this are poor installation, shaft deflection, and low accuracy of shaft neck and shell holes.

Take measures to ensure the installation quality of bearings and improve the axial runout accuracy of shaft and hole shoulders, or increase the viscosity of lubricating oil to obtain a thicker lubricating oil film.

Ferrule fracture failure is relatively rare, usually caused by sudden overload. The causes are relatively complex, such as raw material defects (bubble shrinkage), forging defects (overburning), heat treatment defects (overheating), machining defects (local burns or surface microcracks), host defects (poor installation, poor lubrication, instantaneous overload), etc. Overload impact load or severe vibration may cause the ring to break. The measures taken are to avoid overload impact loads, select appropriate interference amounts, improve installation accuracy, improve usage conditions, and strengthen quality control during bearing manufacturing.

5. Cage broken

The fracture of the cage belongs to an occasional abnormal failure mode. The main reasons for its occurrence are the following five aspects:

a.Abnormal load on the cage. If the installation is not in place, tilted, or the interference is too large, it can easily cause a decrease in clearance, exacerbate friction heat generation, soften the surface, and premature abnormal peeling. As the peeling expands, foreign objects enter the cage pocket, causing the cage to operate slowly and generate additional loads, exacerbating the wear of the cage. Such a deteriorating cycle may cause the cage to fracture.

e. Defects in the material of the cage (such as cracks, large non-metallic inclusions, shrinkage cavities, bubbles), as well as riveting defects (such as missing nails, cushion nails, or gaps in the joint surface of the two halves of the cage, serious riveting damage), may all cause cage fracture.

Take measures to strictly control the manufacturing process.

6. Stuck injury

The so-called sticking injury is a surface damage caused by the accumulation of small burns on the sliding surface damage. Linear scars on the circumference of the sliding surface and rolling surface. Cycloidal scars on the end face of the roller, and scratches on the shaft ring surface near the end face of the roller. The main causes of jamming include excessive load, excessive preloading, poor lubrication, foreign object bite, inclination of the inner and outer rings, shaft deflection, and poor accuracy of the shaft and bearing box.

It can be solved by appropriate preloading, improving lubricants and lubrication methods, and improving the accuracy of shafts and bearing boxes.

7. Wear and tear

Wear failure refers to the failure caused by the continuous wear of metal on the working surface due to the relative sliding friction between the surfaces. The main factors causing wear failure include lubricant failure or lack of lubricant, incorrect lubrication method, abrasive particles entering the interior of the bearing, and excessive load. The solution can be achieved by improving lubricants or lubrication methods, enhancing sealing mechanisms, etc.

The so-called scratch refers to the surface damage that occurs on the raceway surface and rolling surface due to the accumulation of small burns caused by rolling slip and oil film thermal cracking. Produce a rough surface with adhesion. The main causes of scratches include high-speed light load, rapid acceleration and deceleration, inappropriate lubricants, and water intrusion.

Solution: Improve preloading, improve bearing clearance, use lubricants with good oil film properties, improve lubrication methods, and improve sealing devices.

When small metal powder or foreign matter is bitten in, the concave surface (Brinell hardness indentation) is formed on the spacing of the rolling element due to the indentation on the raceway surface or the rotating surface or the impact during installation. The main factors causing indentation are: foreign objects such as metal powder biting in, and excessive impact loads received during assembly or transportation.

Solution: Improve sealing devices, filter lubricating oil, improve assembly and usage methods, etc.

10. Burns

The raceway, rolling element, and cage rapidly heat up during rotation until discoloration, softening, deposition, and damage occur. The causes of burns include poor lubrication, excessive load (excessive preload), excessive rotational speed, small clearance, invasion of water and foreign objects, poor accuracy of shafts and bearing boxes, and large deflection of shafts.

This can be solved by improving lubricants and lubrication methods, correcting bearing selection, researching fits, bearing clearances, and preloading, improving sealing devices, checking the accuracy of shafts and bearing boxes, or improving installation methods.

11. Current corrosion

The so-called electrical erosion refers to the phenomenon of local melting and concavity on the surface of the thin lubricating oil film that sparks when the current flows through the contact part between the rotating bearing ring and the rolling element. The main causes of current corrosion are the potential difference between the outer and inner rings, as well as the effect of static electricity. Solution: When setting the circuit, the current does not pass through the bearing, and the bearing is insulated and grounded through static electricity.

12. Rust and corrosion

The rust and corrosion of bearings include pitting rust on the surface of raceways and rolling bodies, as well as comprehensive rust and corrosion. Rust and corrosion of bearings can cause pit like rust on the surface of rings and rolling elements, pear skin like rust, and pit like rust with the same spacing between rolling elements, as well as comprehensive rust and corrosion. There are many reasons for the rust and corrosion failure of rolling bearings, mainly including the invasion of water and corrosive substances (paint, gas, etc.), inappropriate lubricants, water droplets attached due to the condensation of water vapor, stopping operation at high temperatures and high humidity, poor rust prevention during transportation, improper storage status, and improper use.

The solutions include improving the sealing device, researching lubrication methods, taking rust prevention measures during shutdown, improving storage methods, and paying attention when using.

In addition to the common failure modes mentioned above, there are many failure modes of rolling bearings in actual operation, which require further analysis and research. In summary, from the common failure mechanisms and modes of bearings, it can be seen that although rolling bearings are precise and reliable institutional foundations, improper use can also cause early failure. In general, if bearings can be used correctly, they can be used until their fatigue life. The early failure of bearings often occurs due to factors such as manufacturing accuracy, installation quality, usage conditions, lubrication effect, external foreign object invasion, thermal impact, and sudden failure of the host. Therefore, the correct and reasonable use of bearings is a systematic engineering project. In the process of bearing structure design, manufacturing, and installation, corresponding measures should be taken to address the early stages of failure, which can effectively improve the service life of bearings and the host machine.