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Boyan Atanaschev
Bearing lubrication is vital for preserving the performance and lifespan of rolling element bearings. Lubrication helps separate moving parts relative to one another, such as rollers and raceways or balls, to prevent wear and tear and friction.
Though often viewed as a messy, auxiliary process that has been followed since the Industrial Era to some, bearing lubrication is actually a crucial technology that can make or break your manufacturing processes at your facility.
As lubrication experts trusted by major manufacturers, we know finding the correct grease for your bearing application can be a struggle. We can take some of those burdens with our 30+ years of experience and knowledge and be your "go-to" for lubricant optimization.
Because we take extending the life of your bearings enormously, we put together this in-depth guide to discuss the different types of lubricants, the best methods for bearing lubrication, proper procedure for applications, and mistakes you might be making to ensure the long service life of your bearings.
These include "the type of machine, bearing type, size, temperature, load conditions, speed range, operating conditions (such as vibration and horizontal/vertical orientation of the shaft) and external environment," according to Efficient Plant Magazine.
As a general rule, bearings run the coolest and with the least amount of friction when a minimum amount of the lightest-bodied lubricant that will keep the bearing surfaces apart is used, according to knowyourparts.com.
Oil lubricant is generally used for high speed or high-temperature applications that require heat transfer away from working bearing surfaces. The oils consist of either natural mineral oil (with additives that prevent oxidation and rust) or synthetic oil.
Viscosity is one of the key characteristics when specifying the right oil for a bearing. A good rule of thumb: low-viscosity fluids are thinner like water, and high-viscosity fluids are thicker like molasses.
Grease lubricants are made up of three components: additives (usually rust inhibitors), a base oil, and a thickener. When you are selecting a grease lubricant, it's important to note that the viscosity of the base oil (referred to as "base oil viscosity") determines how the lubricating film develops.
It's important to remember that regardless of which type of lubricant you chose, it will naturally lose its lubricating properties over time and if not maintained properly with the help of an experienced lubrication service, will eventually lead to bearing failure.
If you want to learn more about what a bearing failure is and the different types you can come across in your facility, download our guide "What Causes Bearing Failures and Preventative Measures You Need to Know."
As we've touched on already, bearing lubrication plays a critical role in the lifespan and performance of bearings because it helps separate parts moving parts in order to minimize friction and prevent wear.
In addition to providing that separation, it also dissipates frictional heat (which prevents overheating and deterioration of the lubricant) and protects against other known issues like corrosion, moisture, and other contaminants.
Grease is typically applied with special equipment that deposits the grease between the balls, which forces it inside and around the ball or roller raceway interface. Unlike oil, grease is normally denoted as a percentage (e.g. 30% fill), which represents the actual grease volume compared to the free internal space inside the bearing. [source]
Simply put, this method (often called a gravity feed system) "consists of a loosely covered cup or manifold of oil placed above the bearing that meters out oil at a set interval," according to Tech Transfer.
This type of lubrication was applied by hand in the past, but it actually poses risks like over- or under-lubricating. Drip feed lubrication systems are more commonly used for these applications to supply the correct amount of oil at the right intervals.
With this type of lubrication, the bearings are spattered with oil by moving parts that are regularly dipped in the lube oil. This method is preferred when rotation is not fast enough to churn up the oil.
In a force fed lubrication system, an oil pump pressurizes the oil, which is then directed to the rotating component. Examples of systems that use this method include boiler feed pumps, compressors, gearboxes, and turbine generators.
It's no secret that proper lubrication has the largest impact on bearing life. In fact, it's an industry-wide understanding that at least 80% of bearing failures are related to lubrication and contamination issues. [source]
While it's not a difficult process, it does require following specific guidelines that aren't done properly. As a result, many plants or facilities have inadequate lubrication programs and bearing failures.
Loss of lubricant - if a bearing isn't re-greased with proper intervals and the proper amount of grease, loss of lubricant and lubrication can result and contribute to equipment failure.
Incorrect grease - Make sure to use the correct grease for your application. Some applications need non-extreme pressure (non-EP) or general purpose (GP) grease, while others may require extreme pressure (EP) grease, according to Machinery Lubrication.
The proper application procedure is as important as selecting the right lubricant. The most important areas in applying a lubricant include bearing cleaning, lubricant fill quality, and bearing run-in.
In this first step, you need to remove any existing oils, anti-corrosion coatings and greases. This part is essential because the operating life and reliability become more critical and help eliminate any potential incompatibilities.
It's common for bearing companies to provide pre-coated products with an oil film or anti-corrosion coating. As long as the coating has both a micro-thickness and is compatible with your chosen lubricant, then pre-cleaning might not be needed, according to Guide to Proper Bearing Lubrication Procedures by Klber Lubrication.
Proper fill quantity ensures that all contact surfaces have a suitable lubricating film. This step is crucial because, as we've discussed already, over- and under-lubrication are both detrimental to bearing operating life.
Over-lubrication can increase internal friction, which leads to extra heat generation while under-lubrication can lead to wear or lubrication starvation due to contact surfaces not having enough lubrication.
Published engineering data - Manufacturers may have done the work for you by determining the free space for a number of their "catalog bearings." This means a simple email or phone call to the manufacturer's engineering department can get you the answers you need.
Published reference charts - Manufacturers have also developed generalized bearing free space charts, which help you calculate a specific bearing's free based on the inner diameter and design configuration.
Rule of thumb equation - This method is one of the more complex ones to determine fill quality, and it's also worth noting that this method is exactly that, a 'rule of thumb' with limited accuracy.
Lubrication mistakes can be far-reaching. Common side effects of incorrect lubrication include overheating or excessive wear, which can lead to bearing failure. And that can lead to unexpected downtime and lost revenue at your facility.
As we've discussed already, too much grease builds up and eventually causes increased friction and pressure, and that causes excess heat. Too little of grease has the same life-shortening effect on bearings too.
You'll want to listen to the bearing and try to measure the drop in friction as the grease begins to flow into the bearing. Keep note as the decibel level approaches a minimum value and stabilizes, add single shots, and if the decibel level begins to increase even slightly, you can stop because your job is done.
You can monitor, measure, and trend friction levels with ultrasound instead of re-lubricating a bearing on a schedule so you can know exactly when it's the right time to grease, according to Maint World.
Audible feedback alone doesn't work because it's too subjective to pull any real conclusions since no two people hear the same thing. It's also too difficult to remember what a bearing could've sounded like months ago based on memory alone.
There are clear benefits to optimizing your bearing lubrication and avoiding these three mistakes. Doing so will extend the life of your bearings, cut down on grease consumption, and decrease time spent re-lubricating when it's not necessary.
Over time, lubricant in a bearing will naturally lose its lubricating properties, but it's still crucial to pay careful attention to the quality of the original lubricant and to take the above steps we've outlined to preserve the bearing, and it's intended lifespan.
If you're looking for lubrication services to help you meet your customers' specifications, Bearing and Drive Systems has over 200 types of grease and oil in stock from all of the top companies to meet your needs. Get a quote today and we can take some of your burdens with our 30+ years of experience and knowledge and be your "go-to" for lubricant optimization.
My name is Dean Payne and I am the Sales Manager at BDS. I have been with BDS for 19 years and started when I was 18 years old in the warehouse. I have learned a little bit about bearings over the years and would consider myself a career-bearing guy at this point. I enjoy the challenges and the constant changing of nomenclature the bearing industry has to offer, you learn something new every single day.
Grease lubrication is widely applied since there is no need for replenishment over a long period once grease is filled, and a relatively simple structure can suffice for the lubricant sealing device.
There are two methods of grease lubrication. One is the closed lubrication method, in which grease is filled in advance into shielded/sealed bearing; the other is the feeding method, in which the bearing and housing are filled with grease in proper quantities at first, and refilled at a regular interval via replenishment or replacement.
Devices with numerous grease inlets sometimes employ the centralized lubricating method, in which the inlets are connected via piping and supplied with grease collectively.