Bearings that operate smoothly keep the manufacturing processes moving. They are often the overlooked parts of the process, despite the fact that they carry the weight and production load. Bearings often remain invisible until there is a bearing failure in the facility.
So, what is a bearing failure?
A bearing failure occurs when the bearing fails to meet their expected life or performance levels, often causing a machine shaft to fail, and the machine it is apart of can break down.
The consequences of bearing failure are far-reaching for your facility. These can include increased downtime, high-maintenance costs, missed deliveries, loss of revenue and, in some extreme cases, may injure workers.
When a bearing fails, it negatively impacts your facility, your reputation and your bottom line. That said, there are some preventative measures you can take to increase the lifespan of your bearing and prevent improper wear on them.
We know how frustrating it is for a bearing failure at your facility to cause costly downtime and often force you to go outside of your normal supply chain. At Bearing & Drive Systems, we're committed to providing bearing repair services that help you keep your customers through quicker turn-around time.
Whether or not your facility has recently experienced a bearing failure, this guide has everything you need to know regarding bearing failures.
If you're looking for background on what bearing failure means, different types of failures, common reasons why bearings fail, and actionable tips to prevent bearing failures, you'll love this guide.
Simply put, a bearing failure occurs whenever a bearing fails to meet its expected lifespan or calculated performance levels.
Bearing failures are more common than you think, and even with careful planning and normal maintenance, they can still fail unexpectedly or prematurely in an application.
Less than 30% of bearings ever meet their determined fatigue limit and 'wear out' in their application [source].
How does the bearing's fatigue limit and life expectancy factor in to being used for the correct application? It all starts with the original equipment manager (OEM).
According to Flow Control Network, "the OEM selects bearings for each application in conjunction with the manufacturer's designed life expectancy based on a fatigued spall failure."
In general, there are a handful of common reasons why bearings fail:
We'll discuss these common causes of failure in depth later on in the guide.
"Ball bearing damage" by Originalrocket is licensed under CC BY-NC-SA 2.0
Bearings are a critical part of any operating machine in a facility, so when you hear an awful noise coming from one of your most important pieces of equipment, you need to act fast.
Bearing failures require immediate attention because they can cause all kinds of headaches in your facility like:
Not to mention, bearing failures can be costly and can increase operations costs.
However, what's interesting is that the bearing replacement is often the least expensive part of the failure.
Yes, you read that right.
A $50 bearing that fails can cost as much as $25,000-$50,000 per hour when it halts production in a multi-million dollar process, according to IBT.
Examining the "failure mode", known as the ways, or modes, in which something might fail, will help you determine the exact cause of failure.
But sometimes this examination process ends up becoming complicated quickly thanks to the fact that one failure mode can trigger another.
Here's an example from Barden Precision Bearings...
"Corrosion in a ball race leaves rust-an abrasive-which can cause wear, resulting in loss of preload or an increase in radial clearance. The wear debris can, in a grease-lubricated bearing, impede lubrication, resulting in lubrication failure and subsequent overheating."
If you have a bearing failure in your facility, it is critical to thoroughly assess the situation at hand so you can determine the source of the failure, with the ultimate goal of preventing it from occurring again.
Next, let's move on to the four stages of bearing failure and how this often shows up on the spectrum.
Resources:
"Bearing Failure: Causes and Cures" by Barden Precision Bearings
As we've stated already, bearings do not last forever. They can be damaged and have a shortened lifespan if the right preventative measures aren't followed through in the facility.
How do you know if a bearing is about to fail?
For starters, bearing failures are sorted into four unique stages.
Source: ACOEM AB, Conditioning Monitoring Basics: 4 Stages of Bearing Failure
These stages are based on the types of frequencies produced by the bearing's rolling elements impacting defects in the inner and outer races.
Let's dive into the four stages of failure...
In the first stage, you will see small pits begin to appear in the bearing race as well as impacts of rolling elements that show up at ultrasonic frequencies in the spectrum.
It's important to note that this stage is still considered within the normal operation, so here your bearings are functioning normally.
According to Vibralign, defects appear around 20,000-60,000 Hz and while this isn't a cause for replacing a bearing, Stage 1 may indicate a lack of lubrication between the races and rolling elements.
Once you reach stage two of failure, you will commonly find that the bearing's defects begin to ring at its natural frequencies, which ranges from 500 to 2,000 Hz.
Often these frequencies are actually the resonances of the bearing's components (like the races or rolling elements) or the bearing support structures.
It's important to note that repairs should be put on the schedule for critical machines at this stage.
At the third stage, the bearing defect frequencies levels become much more apparent and harmonics show up on the spectrum.
You would clearly see defects on the raceways if you were to remove it, and it's key to determine a deterioration rate at this point.
Furthermore, bearings (in both critical and non-critical machinery) that reach this stage of failure should be replaced, if they're not already.
Bearings reach this stage when they're at the end of their lifespan, and you will notice that the noise floor is increased at all levels, which in turn produces a random, broadband spectrum.
"Amplitudes of both high-frequency noise floor and HFE may actually decrease, but this is a sign that the bearing is about to fail." [source]
In short, the goal is to prevent bearings from reaching this stage, but if they do, it's imperative that they're replaced immediately.
Utilizing these four stages and identifying which stage a bearing is in is critical because not only will it help you foster an accurate predictive maintenance plan, but it will also help you keep your machines operating efficiently and prevent costly, unplanned downtime.
Speaking of failures, let's move on to discussing in detail the most common reasons why bearings fail that you should keep in mind...
When there is a bearing failure, that means that the bearing motion becomes ineffective. Without proper bearing motion, the machine shaft can ultimately fail, therefore, the machine itself can be damaged and break down.
Regardless if your facility has experienced bearing failure recently, it's not a surprise to say that bearings are being worn down every minute of active process operation.
There are a handful of causes of bearing failures you can experience, and some are more common than others.
In fact, over 70% of bearing failures are due to poor fitting, poor lubrication, or contamination. [source]
Here's a chart that better displays the statistics behind common causes of bearing failures.
Let's dive into further detail about these 13 common reasons why bearings fail as they relate to your manufacturing process.
This should be one of the first reasons considered when inspecting a bearing that has failed. To ensure proper lubrication, adequate viscosity at operating temperature is a must.
Look for highly polished or discolored bearing raceways when troubleshooting to determine if working surfaces are lacking adequate viscosity at operating temperature.
Over-lubricating can be just as detrimental as under-lubricating.
"Under-lubrication risks metal-to-metal contact, over-lubrication causes heat build-up and friction as the rolling elements continuously try to push extra grease out of the way." according to IBT.
There are numerous causes for cage damage. Some of the more common ones include vibration, excessive speed, wear, or blockage.
There are many contaminants that can cause problems with a bearing. Dirt, sand, and water are the most common ones that you run into, but chemicals and corrosives can also damage bearings.
These contaminants reduce viscosity which causes corrosion to the bearing surfaces, disrupts the oil film, and causes erosion, leading to the creation of countless abrasive particles.
Be sure to keep work areas, tools, fixtures, and hands clean, as this prevents and contamination failures. [source]
Also known as "Electric Arc Erosion," this failure occurs when an electric current passes through the bearing and is broken at the contact surface between races and rolling elements, producing high temperatures at localized points. [source]
This can damage the bearing by creating pits on the raceways and rolling elements.
It's vital that the bearing is properly mounted to an accurately sized shaft. If it isn't, it can cause issues in two ways:
1. If the shaft is oversized or expands, it will result in too tight of a fit, reducing the bearing's internal clearance (see more on this below).
2. If the shaft is undersized or has too loose of a fit, the bearing will creep on the shaft and will wear and create heat, which eventually will result in vibration and runout problems.
Often referred to as "spalling," fatigue failure occurs when there's a fracture of the running surfaces, which leads to the removal of tiny, detached particles of bearing material.
Since this type of fatigue is progressive, once it begins, it will continue to spread as the bearing operates. A key indicator of fatigue to keep an eye on is an increase in vibration.
While fatigue may occur at the end of the bearing's normal life expectancy, it frequently occurs before then due to an excessive loads, according to AST Bearings.
This type of failure occurs when loads exceed the elastic limit of the ring material and can be identified as permanent indentation marks in the raceways, which cause increased vibration.
Brinelling falls into two categories:
Misalignments lead to excessive vibration and loads. Some bearings (not all, though) can handle minor misalignments.
According to Bearing Failure: Causes and Cures, the most commonly found causes of misalignment include: bent shafts, dirt or burrs on shaft or housing shoulders, shaft threads that are not square with shaft seats, and locking nuts with faces that are not square to the thread axis.
To prevent misalignment, there are a few best practices you can keep in mind...
Ensure you inspect shafts and housing regularly, use precision-grade locknuts, and shim the housings as needed.
To gain a better idea of the conditions a bearing was operated, it is best to examine the wear path pattern of the dismantled bearing that's already been in service.
Through failure analysis testing and the understanding of normal/ abnormal wear path, one can correctly assess if the bearing has been run under the ideal conditions.
Adequately sealed bearings guard against contamination and ensuring the lubrication isn't destroyed.
Here are some guidelines for selecting and maintaining seals from Flow Control Network:
Putting too much load on a bearing is a common cause of failure.
You can troubleshoot overloading by reducing the load on the bearing or considering using a bearing with a greater capacity.
Simply put, improperly storing bearing causes issues later on because they're exposed to outside elements like dampness, dust, and varying temperatures.
Handling becomes an issue when boxes are opened, or wrappings are torn prematurely because it can expose the bearings to dirt and corrosive elements.
Reliable Plant says to be sure to watch out for dampness and temperatures that could cause rust or uncovered bearings in the storage area.
Last but not least, this failure impacts friction, load zone size, and fatigue life of a bearing. If the clearance of the bearing is inadequate, excessive heat will build up.
As we've discussed already, high temperatures do not fare well for bearings and can cause other problems already listed as in lubrication and internal friction.
Now that you know more about the most common types of bearing failures you can witness in your facility, how exactly can you prevent a bearing failure?
Keep on reading to find out about our top preventative measures that you can implement at your facility today!
Under normal operating conditions, bearings have a substantial service life, but since they do have a fixed lifespan, it's inevitable that a bearing will eventually fail.
Actually, less than 1 percent (0.35 percent specifically) of rolling bearings do not reach their expected life. [source]
The key to preventing downtime and lost productivity in your facility is to prevent premature failure, which stems from damage that occurs to the bearing that usually could have been halted.
Doing so can not only help you prevent premature failure, but it can also help keep your process moving smoothly as well.
The majority of bearing failures we've discussed above (think pitting, spalling, unusual wear patterns, rust, corrosion, etc.) trace back to a small group of causes that are not only interrelated but are fixable too.
These causes are mounting/ alignment, lubrication, operational stress, environmental influence, and improper storing.
Let's dive in...
It's imperative that the proper tools, ovens, and induction heaters are used during the mounting and installation process of bearings.
Be considerate of avoiding misalignment or shaft deflection, as this is significant in mounting bearings with separate parts. Without proper alignment between components, the bearings will end up experiencing abnormal wear.
Once you've completed installation based on manufacturer's instructions, a best practice to keep in mind is giving the bearing a solid flushing and cleaning out with lubricant. Additionally, be sure to apply the final proper amount of lubrication before the machine is used.
This leads us to the next preventable measure... lubrication!
Lubrication is used on bearings to cover the rolling completely and sliding surfaces with a thin oil film to prevent metal-to-metal contact.
Grease is more commonly used because it's easy to handle, while oil lubrication is frequently used with high-temperature or high-speed applications.
Common lubrication failures occur due to:
According to Machinery Lubrication, when applied correctly and effectively, lubrication helps reduce issues like friction and abrasion, transports heat generated by friction, prolonging service life, prevents rust and corrosion, and keeps foreign objects and contamination away from rolling elements.
Operational stress on a bearing can impact bearing life.
Normally, the first sign of issues like these is unusual noises and/or elevated temperatures. The desirable bearing temperature is somewhere below 100 degrees Celsius.
It's important to note that bearing temperatures usually increase with start-up and level off at a temperature slightly lower than the start-up (ranging from 10 to 40 degrees Celsius higher than room temperature).
That is why it's crucial to make sure vibrations are isolated in associated equipment because if they're not isolated, they can cause unusual noises and uneven running.
Source: Machinery Lubrication "5 Ways to Prevent Bearing Failures"
If not taken into consideration, there are numerous operating environments that can bring down even the best bearing and cause a failure. Here is a list of the primary issues you should have on your radar...
Dust and dirt, which can contaminate a bearing at an aggressive rate. Be sure to use proper sealing techniques to prevent this type of contamination.
Aggressive media or water - This is another instance where proper sealing is crucial.
External heat - Ambient operating temperature mandates many choices in radial internal clearance, high-temperature lubricants, intermittent or continuous running and other factors that affect bearing life. [source]
Current passage or electrolytic corrosion - Sparks can create pitting or fluting on bearing surfaces if current is allowed to flow through the bearing's rolling elements. You can fix this by using insulation on or within the bearing or creating a bypass circuit for the current.
Present-day, a majority of facilities keep the number of spares they have in stores a minimum.
Why?
Thanks to preventative maintenance (like the other measures we've mentioned above), facilities can detect potential failures earlier.
This means facilities can order and replace the damaged bearings before an entire machine breaks down, making the need for spare bearings to sit on shelves practically obsolete.
When you need to have bearings being stored in your facility and sitting on shelves, be sure to store them actively. This can be accomplished by rotating or spinning them frequently.
If bearings don't receive occasional rotations, it can cause false brinelling to occur, which is a premature failure we discussed in Chapter 3.
Bearings are typically very reliable, even under the most rigorous conditions, and under normal running conditions, a bearing's service life is substantial.
When a bearing does fail prematurely, it's often due to causes that can be avoided. For this reason, it's crucial to be able to identify the root causes to prevent future failures with preventative measures and the issues that follow them.
Accurately diagnosing and troubleshooting bearing failures in order to get ahead of them will help prevent repeat failures and additional pain-points your facility might be experiencing, such as decreased operating efficiency, increased downtime and lost revenue.
As a premier source of bearings and power transmission products to the global distribution market, Bearing & Drive Systems is committed to delivering a quality, authentic product to meet our customer's expectations.
If you’re looking for a solution that very few vendors provide that offers a significant cost saving, our bearing repair services could be a great way to get your foot in the door or build your existing relationship with your customers.