Bearings play a critical role in ensuring the smooth operation of mechanical systems. However, they are subject to damage over time, specifically impact and oscillatory damage. This can lead to significant consequences, including equipment downtime, repair costs, and even threats to safety through catastrophic damage.
However, bearings and their condition are often among the lowest priorities. It’s quite common for bearings to be damaged by:
- Dropping bearings
- Impacting an interference fit fitment, such as a coupling hub, that’s seized onto a shaft
- Beating a bearing onto a shaft or into a housing
- Striking a machine with a hammer to move it instead of jacking it and approaching it correctly
- Not caring for the condition of spare machines, such as leaving them for years without rotations or in improper environments
The Deterioration of Bearing Conditions
Poor care and maintenance accelerate bearing deterioration and reduce their lifespan. Though they might not receive the same consideration as other equipment and parts, bearings that fail prematurely and require replacement or contribute to greater machine damage are a significant cost that is also largely avoidable.
These effects can be noticed when these signs of bearing damage are observed:
- Visible Wear: Bearings might show signs of surface damage, including pitting and spalling.
- Excessive Vibration: Higher vibration levels can indicate that the bearing is overly worn or the equipment is misaligned.
- Unexpected Noises: Noises such as knocking, grinding, or squealing can be signs that a bearing is damaged.
- Increased Temperatures: Where bearings are overheating, it can signal insufficient lubrication, leading to metal-to-metal contact and excessive friction.
Here, we’ll examine different types of common bearing damage and how to prevent it.
Recognizing and Preventing Common Bearing Damage Types
True Brinelling
True brinelling is the indentation caused by impact, including impact during installation. Metal is displaced when the rolling element strikes the raceway surface. When the bearing is in use, the damaged area will become an outlier for further stress, leading the impacted areas to spall/flake prematurely.
Proper fitting eliminates the need for hammering and minimizes impact during transportation. Using the correct installation tools, including bearing heaters, and practicing precision installation techniques, such as measuring shaft and housing fits correctly, also minimize brinelling damage.
False Brinelling
False brinelling is the rubbing action leading to metal-to-metal contact, e.g., between the rolling element and the raceway surface. This is caused by vibration or an oscillatory source acting on the bearing or machine while stationary. During operation, the bearing surfaces are protected by the oil film of the lubricant. However, this film cannot be maintained and regenerated when stationary. Once the film has been removed, metal-to-metal damage occurs.
The vibratory action between the rolling element and the raceway surface creates axial lines. If the bearing remains in that position long enough, it will create hollow spots. Similar to true brinelling, when active in use, the damaged areas act as stress risers and fatigue failures ensue.
False brinelling can be avoided by reducing the oscillatory source and vibration. During transport, shafts on machines should be secured. Spare parts should be rotated in and out of service.
Material Contamination
Contamination of a machine or mechanical system happens when dirt, dust, or shavings enter into the bearing housing. These cause significant abrasion and wear, leading to premature failures, potential sparking and obstruction of movement. The solution to contamination is to ensure that seals and covers are intact, always use clean tools, and clean housing and bearings during scheduled maintenance.
Improper Installation
Machines and mechanical systems that are not installed with proper equipment, planning, and installation techniques lead to misalignment, uneven load distribution, and repetitive wear on bearings and housing. This can be prevented by ensuring proper tools and techniques are used and by following manufacturers’ guidelines so that equipment fits flush and has proper alignment.
Inadequate Lubrication
Lubrication is vital for bearings to ensure smooth movement and rotation while minimizing friction and wear from metal-to-metal contact. Significant damage can occur when insufficient lubrication or the wrong lubricant is used. This can be prevented by regularly checking and maintaining lubrication levels and using the lubricants recommended by the bearing manufacturer.
Material Fatigue
Fatigue can occur in equipment and machinery using bearings, as well as in the bearings themselves, where repeated stress cycles, such as those brought about by misalignment, lead to repetitive strain, cracks, and spalling. To prevent material fatigue, install bearings rated for their intended use, regularly inspect them for signs of wear, and replace end-of-life units.
Conclusion
Bearings are integral to many machines, mechanical systems, and industrial processes, yet their maintenance is often overlooked. Bearing damage can have a major impact on equipment downtime, repair costs, and even the health and safety of operators. Some of the most significant types of bearing damage include true and false brinelling, contamination, improper lubrication, and material fatigue.
These issues can be prevented by following proper guidelines for transporting and installing equipment, checking for alignment issues, and maintaining lubricant levels. Choosing the right bearings that are fit for purpose and replacing end-of-life bearings is also important.
Reliability Solutions is a world leader in maintenance and operator training, helping clients create a sustainable and productive environment. We work in the field to provide training that improves asset availability, reduces overall maintenance costs, and enhances safety performance.
To learn how we can improve your maintenance performance and planning, contact us here.
