Bearings, bearings, bearings… the world runs on bearings

To support overall bearing maintenance, addressing careless work habits goes a long way.

By Ed Duda August 26, 2022
Courtesy: Motion.

Gears and Bearings Insights

  • There are many different types of bearing, but they all need to be maintained or they can break down or fail, which can raise the price of fixing them.
  • Proper storage, installation and commissioning, adequate lubrication, contamination mitigation practices and condition monitoring can extend bearing life.
  • One of the main ways that bearings aren’t maintained properly is overgreasing them, which can cause contamination and break them down faster.

Bearings drive the world and distribute load across processes. While there are different types of bearings in various markets, ball and roller bearings make up approximately 90% of them. Driven by automotive, the industrial sector—as second use—consumes these bearings for electric motors, pumps, gearboxes, compressors, etc. Bearings are an essential manufacturing element and continue to be a high-stress point for many plant maintenance personnel.

While bearing costs vary, the financial implications for a bearing failure can be as much as 10–40 times higher. The key to bearing selection is understanding the design and maintenance stage of equipment; however, ignoring this can result in costly failure.

Bearings selection

There are several bearing options, including plain or journal bearings, element bearings (roll, ball and spherical) and tapered bearings. Each type is purposed to ensure maximum load distribution at the defined speed provided in the application.

The two main parameters to consider when selecting a bearing are speed and load. There are additional considerations in bearing selection, such as sealed-for-life versus open or shielded. Sealed-for-life bearings are perfect for applications where high contamination exists and access is difficult; however, they carry a higher initial investment.

This outer ring raceway shows roller skidding when entering and leaving the load zone. This is suspected to be caused by prolonged periods of reduced loading in conjunction with overlubrication. Instances of reduced loading of a cylindrical bearing application combined with excessive grease will increase the likelihood of skidding.

This outer ring raceway shows roller skidding when entering and leaving the load zone. This is suspected to be caused by prolonged periods of reduced loading in conjunction with overlubrication. Instances of reduced loading of a cylindrical bearing application combined with excessive grease will increase the likelihood of skidding. Courtesy: Motion.

Open bearings are more cost-effective and typically run cooler, yet they have a higher risk of contamination ingress and overgreasing. Shielded bearings control contamination and greasing volume, yet overgreasing them can damage the bearing shield causing wear and increased operating temperatures. Each has its costs and advantages, dependent on the industry and overall goals of a maintenance program.

Something to note is that overgreasing bearings happens often and is typically corrected with proper training and adequate tools. If this isn’t fixed, blown seals, higher operating temperatures and grease entering areas it shouldn’t (e.g., electric motor windings) will induce fatigue and component failure.

Bearings health

Bearings fail due to age, wear or human interference. Defect elimination indicates that 84% of all interactions fail due to human interference: any action impacting the bearing itself, beginning with installation, then general maintenance practices and assembly. For example, electric motor studies reveal that specific operating and ongoing maintenance practices are the root causes of failure.

Misalignment and disassembly were found to cause 27% of failures, lubrication-related failures equated to 58% and the remaining failures were a mixture of overloading, corrosion and other miscellaneous failure modes. Of all electric motors, 50% fail from bearing-related issues and 95% fail prematurely, so there is significant opportunity to ensure L10 bearing life (1Bloch, 2014).

Five bearing controls

Proper storage, installation and commissioning, adequate lubrication, contamination mitigation practices and condition monitoring will improve bearings’ overall performance and life. These five controls will extend bearing life throughout a facility and encourage stakeholders to empower local teams to use technology. Without these controls, bearing life can be as short as one to three months instead of 8-12 years.

1. Storage. Proper storage techniques are instrumental in increasing bearing life. Bearings should be stored at room temperature and protected with a rust-inhibiting lubricant. They should also be used on a first-in, first-out (FIFO) basis. If equipment in the MRO storeroom contains bearings, the equipment should be rotated on a schedule to eliminate premature failure mechanisms, such as false brinelling. Additional considerations may depend on the manufacturing process and environment the MRO storeroom is exposed to, such as high humidity, chemical exposure, etc.

2. Shaft alignment. Bearings are delicate and can easily be destroyed if shaft alignment is not performed correctly. Misalignment can occur with missteps in installation procedures, even something as simple as forgetting to apply adhesive to the key in an electric motor keyway. The cost of failure can be 10–40 times the initial bearing cost.

3. Proper grease or oil lubrication. Two criteria that are fundamental to the survival of all bearings are lubricant selection and lubrication frequency. Many considerations are given to lubricant selection, including speed, load, operating temperature and contamination. Once the proper lubricant is selected, the bearing’s size, type and speed must all be considered to provide appropriate amounts and frequencies.

Overgreasing creates additional heat and failure of equipment, as shown here. This motor bearing and shaft are dripping with grease, while (right) one can see the grease-filled motor end bell housing.

Overgreasing creates additional heat and failure of equipment, as shown here. This motor bearing and shaft are dripping with grease. Courtesy: Motion.

Overgreasing creates additional heat and failure of equipment, as shown here. This motor bearing and shaft are dripping with grease, while one can see the grease-filled motor end bell housing. Courtesy: Motion.

Overgreasing creates additional heat and failure of equipment, as shown here. This motor bearing and shaft are dripping with grease, while one can see the grease-filled motor end bell housing. Courtesy: Motion.

For a grease-lubricated bearing, its size will be used to calculate the grease amount it should hold, and the type and speed will determine how often it should be relubricated. While these parameters are standard practice, the most accurate way to identify how much grease a bearing needs at a defined time is through ultrasonic tools.

Why? A primary example: For an operations and maintenance supervisor, the goal is to keep the plant always running—even at 1:00 in the morning. The night-shift operations crew identifies a noisy bearing and calls the mechanic to investigate. They determine it requires lubrication, so they apply grease to eliminate the noise, solving the problem.

The next day, the day shift receives a preventive maintenance (PM) plan for that same recently greased bearing. However, no documentation was left for the day shift, and the bearing is assumed to need x amount of grease according to the PM plan. The bearing is lubricated, and grease begins to pour out of the dust seal, leading to a failure the next day.

This situation is a common cause of premature bearing failure.

4. Contamination mitigation practices. For oil-lubricated bearings, a contamination control strategy is required. Most of these bearings are for high-impact, high-temperature, high-speed or very large bearing applications, e.g., ball mill pinion bearings, crusher bearings, Babbitt, etc., so oil health is the driving factor for bearing life.

To begin, identify oil health and cleanliness targets. These parameters are most often provided in consultation with a trusted partner in the lubrication space. Second, take action to maintain the set targets. For instance, implement contamination exclusion, desiccant or non-desiccant breather, or contamination removal practices, such as improved inline filtration, kidney loop filtration, etc. Third, take oil samples at intervals conducive to the application and overall strategy for the application. For critical applications, take oil samples at least once per quarter.

5. Condition monitoring. Additional controls to alleviate lubrication-related challenges are continuous vibration and temperature monitoring, continuous oil health and contamination monitoring. Peak-to-peak values, time waveforms and fast Fourier transform (FFT) spectrums support actions when they need to be taken.

For example, suppose a vibration and temperature sensor was on the bearing mentioned above. In the above example, the night-shift maintenance staff could identify a lubrication-related issue and properly grease the bearing. Then, the day-shift maintenance crew would not have overgreased it. Oil health, active oil temperature, ambient temperature, contamination levels and other factors support prescriptive actions for oil-lubricated systems.

Succeeding with a sustainable, predictive approach

Every decision has financial implications, and there are many considerations when selecting a bearing, such as speed, load and environment. Bearings come in many shapes and sizes, but they have one thing in common: failure is imminent if they’re not specifically selected for the application or maintained properly. Various resources guide users through selecting appropriate bearings and properly maintaining them. Understanding that most opportunity comes from addressing careless work habits, industry professionals can leverage resources, trusted partners, and risk management to support overall maintenance and reliability program goals.

References

1. Bloch, H. P., & Budris, A. R. (2014). Pump User’s Handbook: Life Extension. The Fairmont Press, Inc.


Author Bio: Ed Duda is an Industry 4.0 Application Specialist at Motion. He has a multidisciplinary background in operations and maintenance excellence, with several key roles for DTE Energy, Freeport-McMoRan Inc. and Des-Case Corporation. Duda has extensive experience in operational and maintenance strategy execution, lubrication program development and deployment, and applying Industry 4.0 technologies within manufacturing facilities. He has traveled across the United States over the last nine years and continues to drive continuous improvement projects. Duda holds a Master of Business Administration, Bachelor of Science in Chemical Engineering, and several certifications (CMRP, ICML MLT I and MLA I/II).