Bearings are critical for ensuring optimal equipment performance, allowing machinery to move at high speeds and carry heavy loads without the risk of failure or safety issues. This is achieved by constraining relative motion to the desired motion, thereby reducing friction between the moving parts in machinery.
A wide range of bearing types are available to meet specific application and industry needs. Some of the most common bearings are outlined below.
- Plain bearings — The simplest bearing types, plain bearings contain no rolling elements — just the bearing surface. These cost-efficient models allow for high loads and generally have long life spans.
- Roller bearings — Roller bearings carry heavy loads through the use of a rolling element — most commonly, a cylinder — allowing for the load to be distributed over a larger area. This, in turn, enables the bearing to handle heavier weights. Roller bearings are ideal for radial loads, but not well-suited to thrust loads. For small-scale applications, needle roller bearings may be used, which make use of small-diameter cylinders.
- Ball bearings — Allowing for great versatility, ball bearings can handle both radial and thrust loads. However, they cannot handle heavy loads and can easily become deformed if subjected to them. Precision bearings of this kind are designed to meet strict standards and offer reliable precision for critical jobs.
- Ball thrust bearings — Ball thrust bearings are built to handle thrust loads in low-speed, low-weight scenarios.
- Roller thrust bearings — Like ball thrust bearings, these bearings are designed to handle thrust loads. However, this type can handle much higher thrust loads; they’re commonly used in car transmissions, for instance, providing support for helical gears.
- Tapered roller bearings — These versatile bearings can handle large radial and thrust loads. They’re frequently found in car hubs.
- Bush bushing (linear) bearings — These bearings actually restrict radial motion, enabling smooth, efficient linear motion. They’re frequently used in CNC router head and 3D printer applications.
- Cam follower bearings — These radial load bearings feature an attached threaded rod. They’re commonly used to ride on cams, allowing for linear motion.
- Pillow block bearings — These radial load bearings are encased in a housing, which can be attached to surfaces parallel to the axis of rotation.
Many other specialized bearings are available to meet specific needs, and many manufacturers will provide customization options for unusual and complex requirements. Regardless of the quality of a specific bearing, though, eventual failure must be anticipated and, to best address issues as they arise, it’s critical to have a basic understanding of common types of bearing failure and how to address them.
Signs of Bearing Failure and Their Fixes
- Flaking — When flaking occurs, the surface of the raceway and rolling elements peel away in flakes. Conspicuous valleys and hills form shortly afterward. Flaking is most commonly caused by excessive loads, improper handling, contamination, rust, or insufficient lubrication. Improper mounting, inadequate precision in the shaft or housing, and insufficient clearance can also cause flaking, as well as a drop in hardness due to abnormally high temperatures.
To remedy flaking, it’s important to first evaluate whether the right type of bearing is being used. Then, reevaluate the clearance, the conditions inherent in the application at hand, and the design of the area surrounding the bearing. Improving the precision in the shaft or housing may also help eliminate this problem. Also consider reevaluating the lubricant and lubricating methods, as well as the assembly method, clearance, and handling procedures.
- Peeling — Peeling refers to small areas of flaking or peeling caused by hairline cracks. Peeling may be caused by foreign matter infiltration or insufficient lubrication.
To address this issue, reevaluate the type of lubrication and lubrication methods being used. Also consider enhancing the sealing to prevent foreign matter from infiltrating the bearing. Ensure that operations are conducted smoothly.
- Spalling — Spalling may exhibit as score accompanying seizing, mounting score in the axial direction, score on roller-end faces and guide ribs, or scratches in the spinning direction on the raceway and rolling contact surfaces. Spalling is typically the result of poor mounting or removal practices. It may also be caused by oil film discontinuation on the contact surface due to a radial load that is excessive for the bearing's design, foreign object trapping, or excessive preloading. Slippage and poor lubrication of the rolling elements can also cause spalling.
Spalling can be fixed by correcting the preload, improving operating conditions, and reevaluating the lubricant and lubricating systems used. Improving mounting and removal procedures can also eliminate spalling, as can improving sealing efficiency.
- Smearing and scuffing — When smearing and scuffing occurs, the bearing surface becomes rough and deposits may form. Scuffing, in particular, typically refers to roughness on the race collar and ends of the rollers. These problems may be attributed to inadequate lubrication, excessive slippage of rolling elements, roller skewing due to a misaligned bearing, or entrapped foreign particles. Bare spots in the collar film oil caused by large axial loadings can also cause smearing and scuffing.
To eliminate these problems, users should reevaluate the lubricant and lubricating method being used, as well as service conditions and preload. Assembly methods and handling should be improved upon, and sealing performance should be strengthened.
While these are some of the most common bearing issues, a range of other problems may be encountered depending on the specific situation at hand. Wear, speckles and discoloration, electrical pitting, and cage damage, among many other issues, can all cause bearing failure — disrupting operations while leading to increased downtime, costs, and labor needs.
Staying on top of bearing performance and condition is critical for ensuring optimal equipment functioning and process efficiency. To learn more about the common types of bearing failure and how to recognize the signs, download Emerson Bearing’s free comprehensive guide, Bearing Failure Analysis.
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