Prevent These 10 Common Bearing Issues

Bearings are essential for designing applications that run smoothly and efficiently. They support the load, enable motion, and ensure accuracy in various applications. But even the strongest bearings can face difficulties that can disrupt their function and affect the whole design.

You may have encountered those alarming signs: weird vibrations, excessive heat, and abnormal wear, not to mention safety risks. They all show how bearing problems can lead to bigger troubles. These problems can result in costly reworks, production losses, or even warranty claims.

But don’t fret—bearing failure and related issues can be dealt with and minimized effectively. This article gives you the know-how to overcome these challenges and choose bearings for your design with the final goal in mind. By taking care of lubrication, adjusting operating conditions, and preventing contamination and overload, you’ll be on your way to achieving optimal performance and perfect operation.

Whether you’re a seasoned engineer or someone new to mechanical design, this guide has you covered when it comes to bearing woes. Improve your operations, increase your productivity, and strive for continuous progress as we explore 10 common bearing issues and how to avoid them.

Issue #1: Insufficient Lubrication 

• Causes: Lack of lubrication is typically a user error. A maintenance schedule is recommended for relubrication intervals, but one missed interval can cause damage.
  
  Working with a sealed bearing? It is wise to check the condition of the seal during inspection. If a seal becomes damaged during installation or operation, the lubrication may leak from the bearing, leaving it unprotected. 

• Risks: Insufficient lubrication causes metal-to-metal contact, resulting in overheating. Overheating can cause increased operating temperatures, noise, and vibration. Most of the time, these increases are signs that the bearing will have a shorter lifespan.

• Signs of Failure: Elevated operating temperature, noise and even smell, can be the first signs of insufficient lubrication. If your bearing has experienced a catastrophic failure, you can inspect the bearing components for more signs like discoloration or surface galling. 

• Solutions: Establish a strict schedule for bearing relubrication. Ensure that the lubrication you use is appropriate for your application and ensure that bearing seals are not damaged during installation or operation.

It is important to make sure you are using a lubrication recommended for your application. Verify the thickness of the grease is compatible with your application speed and any kind of seals or shields installed on the bearing. 

Issue #2: Over-Lubrication

• Causes: Overpacking a bearing with grease during relubrication intervals, overfilling oil baths, or lubricating the bearing while machinery is static can cause over-lubrication.

• Risks: Just like insufficient lubrication, over-lubrication can also cause an increase in friction and operating temperatures. Overpacking your bearings with grease or running them in an overfilled oil bath causes an increase in friction as the rolling elements fight to pass through the lubricant. 
  
  In a sealed or shielded bearing, this can cause a churning effect which destroys the effectiveness of installed greases. This churning can leave thickened lumps of grease that cause havoc to internal bearing components.
  
  Another risk to sealed bearings includes lubricating while the machinery is static, then suddenly firing the equipment up at full speed. Because the rolling elements inside of the bearing require a channel to pass through, starting the machinery may blow out the seals.
  

• Signs: Over lubrication results in an excess of lube causing a greasy mess. Static oil baths will likely have a visibly high oil level. Sealed or shielded bearings may have grease oozing from them. If a bearing has been washed before the inspection, it may be difficult to discern this particular cause from other causes of overheating or contamination.

• Solution: Ensure that you lubricate your bearing based on manufacturer standards and the unique requirements of your application. Also, avoid lubricating static bearings and instead add grease to a slowly moving machine. At the very least, hand turn bearings after applying lubricant.

Excess grease leads to an operating environment that attracts dirt and contaminants to your bearing. This excess grease can also cause problems for surrounding components, such as when an over-greased bearing is installed in an electric motor. The grease may reach and insulate motor windings causing a decrease in efficiency and an increase in operating temperature that can damage your motor.

Issue #3: Your Application Exceeds the Thermal Rating of the Grease

• Causes: Selecting an inappropriate grease or exceeding thermal rating of the grease can cause damage to your bearing.

• Risks: A bearing that is rotating at a higher RPM will create more heat. This heat can quickly break down an inappropriate grease, rendering it useless. Other times, the viscosity of the grease may not be compatible with the application. This minimizes the effectiveness of a lubricant, increasing operating temperature and causing premature bearing failure. 

• Signs: The signs will resemble those of overheating of your bearing. Also, the grease may be inconsistent in texture or feel. If you need to lubricate your bearing more frequently than usual, your grease may not be rated for the conditions of your bearing or application.

• Solutions: Operate your bearing within recommended RPM limits and select lubrication compatible with the demands of the application. Be sure to review the lubrication manufacturer’s documentation to ensure compatibility. 
  
  If you are selecting a sealed or shielded bearing for use in your design, be sure that the pre-installed grease can stand up to the needs of the application.
  
  Slowing the RPM of the bearing or switching the lubrication from grease to oil may also be an option in certain applications.

Issue #4: Operating Environment is Too Hot or Too Cold

• Causes: This could be an issue with the application design or it could be that the ambient environment is creating issues for the lubricant. 

• Risks: Selecting a bearing for use in a furnace or deep freezer can create issues for lubricants. A grease that is colder than its intended operating temperature can become hard or brittle while a grease that becomes too warm will thin out or break down. A cold lubricant will create excess friction without providing lubrication and one that is too warm may not provide the required protective film, it may leak from seals or shields, or it may be flung out of the bearing entirely. 

• Signs: Signs of inappropriate operating temperatures may vary. A grease that is too hard may make rolling elements skid in their races, leaving visible marks or patterns. You may not find much lubrication if the viscosity is too low from a high temperature application. Either way, the signs of overheating will likely be evident. Galling, discoloration, or other deformities may be visible.

• Solution: Any intended use of a particular lubrication should be researched. Manufacturer documentation will outline the recommended operating conditions for various types of lubrication. A new lubrication should be selected and installed when the bearing is replaced.

Issue #5: Bearing Contamination

• Causes: Dirty environments are often part of a machine’s daily life. Examples are the gritty environment of the aggregate industry, or the literal soil of the agriculture industry. Either way, contamination of bearings is always a threat. Lubrication leaks around the bearing can attract dust. And lubrication can allow contaminants to “swim” directly into the inner components of the bearing.

• Risk: Foreign substances such as dirt, grit, or shards of metal that enter the bearing can impede the rotation of the bearing. These contaminants often jam rolling elements or get rolled over repeatedly, reducing the bearing’s lifespan. Even small contaminants such as particulate matter or a single grain of sand can cause significant damage to a bearing. 

• Signs: Strange sounds like squealing, clicking, or rumbling may be evident during operation. Adding more lubricant may silence the bearing for a time, but the noises are likely to return. Upon visually inspecting a failure, there are often skid marks, scuffing, or denting. These are caused by a rolling element dragging along the raceway or repeatedly passing over a contaminant. You may also find the contaminant itself, such as a metal shaving wedged between the ball and the retainer.

• Solution: Doing your best to shield a bearing from contaminants is always a good practice when designing an application. Some options for combating particle contamination include:
  • Bearings with shields or seals
  • Designing housings that protect the bearing from outside contaminants
  • Proper type and amount of lubricant
  • Use of a solid polymer lubricant that prevents the ingress of particles all together

Issue #6: Moisture Contamination

• Causes: Moisture contamination is most often caused by condensation or humidity. Environments with high humidity or those with large swings in temperature will create condensation in a bearing. If the bearing sits still, the moisture makes its way to the lowest point of the bearing. There it gathers, creating rust and oxidation. Bursts of activity such as running the bearing at a high speed, then stopping it, can also create condensation.

• Risk: Moisture can quickly cause problems for lubricants and bearing components. Moisture gathers at the lowest points of a bearing causing a puddle for the rolling elements to pass through. This can quickly result in rust and oxidation that breaks down the internal elements of a bearing.

• Signs: A bearing with moisture contamination may make strange sounds while running. It may also show high operational temperatures or increases in vibration. During an inspection, you may find rust or contamination stains, often at rolling element spacing, or that the grease is inconsistent or ineffective.

• Solutions: The best way to avoid moisture contamination is to operate your applications in dry environments with regulated temperatures. Unfortunately, this is not always an option for certain applications. Here are some of our recommendations to best protect against moisture contamination:
  • Protect applications from rain by using covers or housings that keep outside moisture away from your bearing
  • Use the proper amount of grease or consider an increased grease fill
  • Limit bursts of activity
  • Consider implementing long slow-down periods or designing the application in a way that creates more uniform motion

Issue #7: Overloaded Bearings

• Causes: One cause for bearing overloading is simply expecting the bearing to support too much load or exposing it to shock loads that exceed its capacity. Additionally, a bearing may be excessively preloaded. This can happen through erroneous installation. Most frequently, if a bearing has excessive preload it is an issue with the internal clearance or the fit of the bearing in its housing or on its shaft. 

• Risk: Overloaded bearings will have a sharp decrease in life and performance. This means frequent replacements and increased warranty claims. Luckily, this may be one of the easier problems to avoid.

• Signs: An overloaded bearing will be noisy, but the signs during an inspection will be even more obvious. Depending on the type of overloading, you might find dents at specific intervals. You may find deformation of the retainer or ring as well as flaking of the raceway or rolling elements. Signs of heavy loading on one end, or side, may indicate that your bearing has become thrust-loaded.

• Solutions: Always review the manufacturer’s recommendations for bearing load capacities. A different size or style of bearing may be required to meet the load demands of your application.
  
  Installing a bearing in an undersized housing or on an oversized shaft will remove internal clearance from the bearing and can lead to excessive preloading. It is important to understand the nuance of internal clearance to avoid issues. Bearings can be purchased with varying degrees of clearance so select a bearing with the proper amount of internal clearance for the job and fit of the installation.

Issue #8: Underloaded Bearings

• Causes: A light load is the most obvious cause of an underloaded bearing. However, another cause may be that the operating speed is too high or that the ramp up to full speed is too short. Running a bearing at high RPMs or ramping up speeds too quickly can cause rolling elements to slip in their races. Using a bearing with too much clearance may also be a factor for underloaded bearing failures.

• Risk: An underloaded bearing will cause rolling elements to slip or skid in their races. It can also create a noticeable lack of precision. This sort of undesired motion will drastically shorten the life of the bearing and may leave new engineers questioning their designs. 

• Signs: Noise, temperature, and vibration are all likely to increase in an underloaded bearing. Bearings may lack precision and cause a wobble or shaking in a shaft. During an inspection of the failed bearing, one might find signs of skidding rolling elements or strange paths of damage that leave patterns around the races or rolling elements. There may also be signs of overheating involved with the excess friction this creates.

• Solutions: Select a bearing that is appropriate for the specific loads and speeds of the bearing’s intended use. In high-speed and high-precision applications, it’s usually recommended that the bearing has an increased amount of preloading to negate looseness and that the ramp up to high speed is adequately controlled. Designing machinery to balance speed and load isn’t only a concern for heavy-load machinery. Speed is a consideration for light-load jobs as well.

Issue #9: Bearing Binding

• Causes: Binding of bearings is usually caused by one of two reasons. Removing too much internal clearance from the bearing or improper bearing alignment are likely causes for bearing binding.
  
  When a bearing has too much clearance removed, the rings of the bearing clamp down on rolling elements. This makes motion difficult and limits a lubricant’s ability to create a protective film between metal parts. It can also increase the amount of force required to rotate the bearing. 
  
  Misalignment is a condition that creates a displacement of a bearing’s inner and outer rings. If the two rings are not in perfect alignment with each other, it affects the path of rolling elements. This means that the load may not be supported optimally while also creating a pinching that requires excessive torque to turn. 

• Risk: A bound bearing will have an extremely short work life. It also causes strain on other attached components. Electric motors are forced to compensate for the issue, requiring more torque and lowering the application’s overall life and efficiency.

• Signs: Binding is usually noticeable even before operation begins. If it is hard to move a shaft by hand, or if it feels completely jammed, that would be the first sign. Running the machinery this way will increase noise and heat in the bearing as well as surrounding equipment like electric motors or belt drives. 
  
  During an inspection, you are likely to find wear and damage in places you wouldn’t expect. Damage to the shoulders of races, strange paths that weave in and out of the optimal path of the race, and deformed retainers. Damage evident in one location (outside of the load zone) is also a telltale sign of a bearing binding.

• Solution: Always check the internal clearance for compatibility. Purchase or design a bearing with increased clearance or determine if another bearing fit would be more suitable. If clearance is not the suspected issue, then it is most likely a misalignment issue caused by the installation or overall assembly of the machinery. Ensure that all bearings and their attached components are aligned and well balanced to avoid binding.

Note: the free rotation of bearings should always be checked before a machine is powered. If the shaft will not rotate freely, corrections are required.

Issue #10: Bearing Noise

• Risk: Noise has been referenced as a sign of numerous problems listed above. The risks associated with bearing noise are numerous and varied. Noise can be a sign of anything from particle contamination to misalignment. No matter the cause, abnormal bearing noise means a decrease in service life.

• Causes: Steady high-pitched tones are typically associated with excessive loads, binding, or misalignment. Intermittent high-pitch tones are signs of skidding rollers, excessive clearance, loose fits, or low loads. Low-pitched tones like growls or rattles are often signs of excessive clearance. Crackling noises are associated with particle contamination.

• Signs: Bearing noises come in a multitude of different sounds as shown above. Each one can be a clue for determining the root cause of a bearing issue.

• Solutions: The solution to the noise depends on the kind of noise. Frequently, users are inclined to pump in more grease which tends to silence the noise for a short time. Because the root problem isn’t being remedied, the sound is likely to return. Instead of adding grease, the sound should be evaluated and the most likely cause should be addressed to ensure bearing life.

Keep Your Bearings Running at Their Best

In the dynamic world of engineering, bearing problems can be a constant headache. These issues often result in productivity decline, increased expenses, and safety risks. Reviewing the solutions given in this article can help you solve the 10 most common bearing issues and keep your designs operating smoothly and efficiently.

Start by ensuring adequate lubrication and maintaining appropriate temperature ranges. Strengthen your designs by being aware of potential particle or moisture contamination and protecting against corrosion.

Under or overloading your bearings can be avoided by understanding internal clearances, preloading, and load capacities. Analyzing bearing noise can help identify an array of operating condition issues. Prolong the life of your bearings by being mindful of potential hazards.

It is important to note that if you encounter a bearing failure you should examine any remaining grease before cleaning the bearing for further inspection. The lubricant itself may reveal clues that indicate the cause of failure.

Keep this handy resource in mind as you face bearing challenges head-on. With these insights, you can improve your systems, enhance your productivity, and keep your machinery running at its best.