How to ward off seal and bearing failure
Ken Thayer | August 01, 2018Bearings and seals are designed for years of service, but improper use or maintenance can lead to premature and costly failures. Many different causes can lead to bearing or seal failure, and most of them are preventable if these best practices are followed.
1. Proper Selection
Fretting corrosion on the inner raceway of a ball bearing. Source: Fabian Schwack
The most important variable is correct component selection. Care should be taken to understand operating conditions and specify the bearing correctly during the design phase. Bearing speed and load has a direct correlation to its life expectancy. Bearing overload is a major cause of premature bearing fatigue.
Proper seal selection is also critical. Speed, temperature, pressure, seal material, chemical compatibility and operating conditions must factor into selecting the correct seal for the application.
2. Machining, Material and Tolerances
Selection and treatment of the shaft and housing material are critical for proper bearing and seal function. The material must be hard enough that it will not become marred during bearing installation. Contact seals generate quite a bit of heat due to friction and can wear grooves in a shaft housing if the material is too soft.
All bearings and seals are designed to operate within specified shaft and housing dimensional tolerances. In addition to these tolerances, surface finish is also an important criterion, typically arithmetic average roughness (Ra) 32 for mounting rolling element bearings. Shafts and housings should be inspected to ensure they are machined to the tolerances specified.
3. Assembly
Once proper bearing or seal selection is complete and the shaft and other components have been machined correctly, the next critical factor is assembly. Selecting the correct component can all be for naught if the installation is not performed correctly. Cleanliness is extremely important for both bearings and seals. All components should be free from dirt and chemicals that could lead to contamination issues.
An important factor for bearing installation is the selection of the proper installation or removal tool. The mounting technique is also important and should follow the manufacturer’s procedures. Care should be taken to apply even force when pressing the bearing onto a shaft or into a housing. Uneven force can lead to brinelling of the surface which can lead to failure.
Seal installation is generally more straightforward than bearing installation as the elastic nature of the seal lips is more forgiving. However, seals lips can be fragile, and they can be turned inside out or damaged if handled improperly. Additionally, the correct type and amount of lubrication should be applied under the seal lip to reduce friction during operation.
All components should be handled with care during assembly. Dropping a bearing can lead to damage or contamination. The workplace should be as clean as possible to avoid any dirt or grit contamination.
4. Operation
Equipment should not be operated beyond the parameters specified for the seal or bearing. If the actual operating conditions exceed those in the original specifications, premature failure may occur.
5. Maintenance
Proper preventive maintenance procedures prolong bearing and seal life and may detect a problem before a catastrophic failure.
Bearing being examined for damage; Source: US Air ForceLubrication is critical to prevent overheating due to friction. Improper lubrication is one of the leading causes of premature bearing failure. Refer to the manufacturer’s specifications for proper lubrication type, amount and frequency. Too much or too little lubrication, incorrect frequency or the wrong lubricant can all lead to failure and may void the manufacturer’s warranty.
Be alert for excess vibration or noise that may indicate contamination or an issue with a bearing. Use of an accelerometer to compare vibration readings to a baseline measurement can easily identify a problem before damage occurs.
If possible, check seal lips for flexibility, hardening or cracking. Also, inspect the seal lip contact surface for scoring or signs of excess heat. Inspect the lip for proper contact and signs of leakage. Look for any signs of dirt or contamination which can indicate a seal has been compromised or dirty lubrication.
If any components are removed for inspection, ensure the area is clean and handle all components with care.
With proper attention during the design phase, adherence to tolerances and machining specifications, careful assembly, and good preventive maintenance processes, bearings and seals should provide years of trouble-free service.
Resources
How to Select the Right Bearing Lubricant
The Challenges of Food Grade Lubricants