Rolling bearings are an indispensable basic component of operating machinery. Although rolling bearings are small and inexpensive, their failure can cause enormous losses to the machinery and even the entire production equipment. With rapid technological advancements, companies are placing increasingly higher demands on the quality of rolling bearings. This is especially true for companies with automated, continuous production processes, where the reliability requirements for rolling bearings are extremely stringent. Therefore, improving the reliability of rolling bearings has become one of the most pressing issues for both manufacturers and users.
The reliability of rolling bearings is closely related to their failure modes. To improve bearing reliability, it is necessary to start with the failure modes of the bearings and carefully analyze the causes of rolling bearing failure in order to find specific measures to solve the failure.
01
Bearing failure mechanism
1. Contact fatigue failure
Contact fatigue failure refers to the material fatigue failure caused by alternating stress on the working surface of a bearing.
The most common form of contact fatigue failure is contact fatigue spalling. Contact fatigue spalling occurs on the bearing's working surface, often accompanied by fatigue cracks. It initially originates below the contact surface at the point of maximum alternating shear stress, then extends to the surface, forming different spalling shapes, such as pitting or pitting spalling, or spalling into small flakes, called shallow spalling. As the spalling surface gradually expands, it slowly extends deeper, forming deep spalling. Deep spalling is the fatigue source of contact fatigue failure.
2. Wear and tear failure
Wear failure refers to the failure caused by the continuous wear of the metal on the working surface due to the relative sliding friction between surfaces.
Continuous wear will cause gradual damage to bearing components, eventually leading to loss of bearing dimensional accuracy and other problems. Wear failure is one of the common failure modes of various bearings, and can generally be divided into abrasive wear and adhesive wear according to the wear form.
Abrasive wear refers to the wear caused by the intrusion of hard particles, foreign objects, or metal debris between the working surfaces of a bearing, resulting in relative movement of the contact surfaces. It often causes furrow-like scratches on the working surface of the bearing.
Adhesive wear refers to the uneven force on the friction surface caused by micro-protrusions or foreign objects on the friction surface. When lubrication conditions are severely deteriorated, local friction heat can easily cause local deformation and micro-welding of the friction surface. In severe cases, the surface metal may melt locally, and the force on the contact surface will tear the local friction weld points from the substrate, thus increasing plastic deformation.
3. Fracture failure
Bearing fracture failure is mainly caused by two factors: defects and overload. When the applied load exceeds the material's strength limit, causing the component to fracture, it is called overload fracture. Overload is primarily caused by sudden malfunctions in the main unit or improper installation. Defects in bearing components, such as microcracks, shrinkage cavities, bubbles, large foreign matter, overheated structures, and localized burns, can also cause fracture at the defect site under impact overload or severe vibration; this is called defect fracture.
It should be noted that during the manufacturing process of bearings, the presence of the aforementioned defects can be correctly analyzed using instruments during the incoming inspection of raw materials, quality control of forging and heat treatment, and process control. However, generally speaking, most bearing fracture failures are overload failures.
4. Corrosion failure
Some rolling bearings inevitably come into contact with water, moisture, and corrosive media during actual operation, which can cause rust and corrosion. Additionally, rolling bearings are also subjected to microcurrents and static electricity during operation, leading to electrical corrosion.
Rust and corrosion in rolling bearings can cause pitting rust, pear-skin rust, and evenly spaced pitting rust on the rolling elements and raceways, as well as general rust and corrosion. Ultimately, this leads to the failure of the rolling bearing.
5. Failure due to clearance variation
During operation, rolling bearings may experience changes in their original clearance due to external or internal factors, leading to reduced precision and even seizing, a phenomenon known as clearance variation failure. External factors such as excessive interference fit, improper installation, expansion due to temperature rise, and instantaneous overload; and internal factors such as unstable residual austenite and residual stress are all major causes of clearance variation failure.
02
Common failure modes and countermeasures of rolling bearings
1. Peeling at extreme locations on one side of the channel
Peeling at the extreme position on one side of the bearing groove mainly manifests as severe spalling rings at the junction of the groove and the flange. This is caused by improper bearing installation or sudden axial overload during operation.
The countermeasures are to ensure the bearing is properly installed or to change the fit of the outer ring of the free-side bearing to a clearance fit, so that the bearing can be compensated for in case of overload. If proper installation cannot be ensured, the direct contact of the bearing can be reduced by increasing the thickness of the lubricant film (increasing the viscosity of the lubricant) or reducing the load on the bearing.
2. The trench peels off symmetrically in the circumferential direction.
Symmetrical spalling manifests as circumferential spalling on the inner ring, while the outer ring exhibits circumferential symmetrical spalling (i.e., spalling along the minor axis of an ellipse). This is primarily due to an excessively large elliptical housing bore or a split housing bore structure, which is particularly evident in motorcycle camshaft bearings. When the bearing is pressed into an excessively large elliptical housing bore or when a split housing is tightened, the outer ring becomes elliptical, resulting in a significant reduction or even negative clearance along the minor axis. Under load, the inner ring rotates, producing circumferential spalling marks, while the outer ring only shows spalling marks symmetrically along the minor axis. This is the main cause of early bearing failure. Inspection of the failed bearing component revealed that the outer diameter roundness had deteriorated from the original process control of 0.8 μm to 27 μm. This value is far greater than the radial clearance value. Therefore, it can be confirmed that the bearing was operating under severe deformation and negative clearance, making it prone to premature and rapid wear and spalling on the working surface.
The countermeasures are to improve the machining accuracy of the outer casing holes or to avoid using a two-part separation structure for the outer casing holes as much as possible.
3. Roller track tilting and peeling
The presence of inclined spalling rings on the bearing's working surface indicates that the bearing is operating in an inclined state. When the inclination angle reaches or exceeds a critical state, abnormal and rapid wear and spalling are prone to occur prematurely. The main causes are improper installation, shaft deflection, and low precision of the journal and housing bore.
Countermeasures include ensuring bearing installation quality and improving the axial runout accuracy of shaft shoulders and bore shoulders, or increasing the viscosity of the lubricating oil to obtain a thicker lubricating oil film.
4. Ring breakage
The presence of inclined spalling rings on the bearing's working surface indicates that the bearing is operating in an inclined state. When the inclination angle reaches or exceeds a critical state, abnormal and rapid wear and spalling are prone to occur prematurely. The main causes are improper installation, shaft deflection, and low precision of the journal and housing bore.
Countermeasures include ensuring bearing installation quality and improving the axial runout accuracy of shaft shoulders and bore shoulders, or increasing the viscosity of the lubricating oil to obtain a thicker lubricating oil film.
5. Cage breakage
Cage fracture is an occasional, abnormal failure mode. Its causes are mainly due to the following five factors:
a. Abnormal load on the cage. Improper installation, tilting, or excessive interference can reduce clearance, increase friction and heat generation, soften the surface, and cause premature abnormal spalling. As the spalling extends, foreign objects enter the cage pockets, causing cage operation to be hindered and generating additional loads, which accelerates cage wear. This vicious cycle can eventually lead to cage breakage.
b. Poor lubrication mainly refers to the bearing operating in a state of insufficient oil, which easily leads to adhesive wear, deteriorates the condition of the working surface, and the tearing material generated by adhesive wear can easily enter the cage, causing abnormal load on the cage and potentially causing cage breakage.
c. Intrusion of foreign objects is a common cause of cage fracture failure. The intrusion of hard foreign objects exacerbates cage wear and generates abnormal additional loads, which can also lead to cage fracture.
d. Creep is also one of the causes of cage fracture. Creep mainly refers to the sliding phenomenon of the raceways. When the interference fit at the mating surfaces is insufficient, the load point moves outwards due to sliding, causing the raceways to deviate circumferentially from the shaft or housing. Once creep occurs, the mating surfaces wear significantly, and wear particles may enter the bearing interior, forming a process of abnormal wear—raceway spalling—cage wear and additional load, which may even lead to cage fracture.
e. Defects in cage material (such as cracks, large foreign metal inclusions, shrinkage cavities, and bubbles) and riveting defects (missing nails, shims, or gaps at the joint surfaces of the two cage halves, severe riveting damage) can all cause cage breakage. The countermeasure is to strictly control these defects during the manufacturing process.
6. Stuck
So-called jamming damage is surface damage caused by the accumulation of tiny burns in the sliding surface. Examples include linear scratches on the circumference of the slideway and rolling surfaces, cycloidal scratches on the roller end faces, and jamming damage on the ring surface near the roller end faces. The main causes of jamming damage include: excessive load, excessive preload, poor lubrication, foreign object seizure, misalignment of the inner and outer rings, shaft deflection, and poor precision of the shaft and bearing housing.
This can be solved by applying appropriate preload, improving the lubricant and lubrication method, and increasing the precision of the shaft and bearing housing.
7. Wear and tear
Wear failure refers to the failure caused by the continuous wear of the metal surfaces of the bearings due to relative sliding friction between the surfaces. The main factors contributing to wear failure include lubricant failure or lack of lubricant, improper lubrication methods, abrasive particles entering the bearing, and excessive load. Solutions include improving the lubricant or lubrication method, and strengthening the sealing mechanism.
8. Abrasions
Scratching, also known as abrasion, refers to surface damage on the raceway and rolling surfaces caused by the accumulation of tiny burns resulting from slippage and thermal cracking of the oil film during rolling. This creates a rough surface with adhesive residue. The main causes of scraping include high speed and light load, rapid acceleration and deceleration, inappropriate lubricant, and water intrusion.
Solutions include improving preload, improving bearing clearance, using lubricants with good film properties, improving lubrication methods, and improving sealing devices.
9. Indentation
When small metal powders or foreign objects are embedded, indentations are formed on the raceway or rotating surface, or concave surfaces (Burl hardness indentations) are formed at the spacing of the rolling elements due to impacts during installation. The main factors causing indentations are: the embedding of foreign objects such as metal powders, and excessive impact loads during assembly or transportation.
Solutions include improving sealing devices, filtering lubricating oil, and improving assembly and usage methods.
10. Burns
Raceways, rolling elements, and cages heat up rapidly during rotation, eventually leading to discoloration, softening, melting, and breakage. Causes of burns include poor lubrication, excessive load (excessive preload), excessive speed, insufficient clearance, intrusion of water or foreign matter, poor precision of the shaft and bearing housing, and excessive shaft deflection.
This can be addressed by improving the lubricant and lubrication method, correcting the bearing selection, studying the fit, bearing clearance and preload, improving the sealing device, checking the accuracy of the shaft and bearing housing, or improving the installation method.
11. Electrical corrosion
Electrolytic corrosion (ECC) refers to the phenomenon where an electric current flows through the contact area between the rotating bearing rings and rolling elements, generating sparks through a thin lubricating oil film, resulting in localized melting and unevenness on the surface. The main causes of ECC are the potential difference between the outer and inner rings and the effect of static electricity.
Solution: When setting up the circuit, the current should not pass through the bearing, the bearing should be insulated, and it should be electrostatically grounded.
12. Rust and corrosion
Rusting and corrosion of bearings can manifest as pitting rust on raceways and rolling element surfaces, as well as general rusting and corrosion. Specifically, it can cause pitting rust, pear-skin rust, and evenly spaced pitting rust on the rolling elements, along with general rusting and corrosion. Many factors contribute to the failure of rolling bearings due to rust and corrosion, including: intrusion of water or corrosive substances (paint, gas, etc.); unsuitable lubricants; water droplets due to condensation; failure to rotate under high temperature and humidity; inadequate rust prevention during transportation; improper storage conditions; and improper use.
Solutions include: improving sealing devices, researching lubrication methods, implementing rust prevention measures when the machine is stopped, improving storage methods, and paying attention to usage.
Besides the common failure modes mentioned above, rolling bearings exhibit many other failure modes during actual operation, which require further analysis and research. In summary, based on the common failure mechanisms and modes of bearings, it is clear that although rolling bearings are precise and reliable structural components, improper use can lead to early failure.
Under normal circumstances, if bearings are used correctly, they can be used until their fatigue life. Early bearing failure is often caused by factors such as the manufacturing precision of the mating parts of the host machine, installation quality, operating conditions, lubrication effect, intrusion of external foreign objects, heat-affected zones, and sudden failures of the host machine.
Therefore, the correct and reasonable use of bearings is a systematic project. In the process of bearing structure design, manufacturing and installation, taking corresponding measures for the links that cause early failure can effectively improve the service life of bearings and main equipment.
Disclaimer: This article is a reprint. If it involves copyright issues, please contact us promptly for deletion (QQ: 2737591964). We apologize for any inconvenience.
