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Even with the best design, lubrication and installation failures will occur if the operating environment is not considered. While many potential issues exist, the primary ones are:
- Dust and dirt that can aggressively contaminate a bearing. Great care should be given to use proper sealing techniques
- Aggressive media or water. Once again sealing is primary. The use of specialty type seals is recommended such as pump mechanical or labyrinth style seals that do not score the shaft.
- External Heat. The ambient operating temperature mandates many choices in radial internal clearance, high temperature lubricants, intermittent or continuous running and others that affect bearing life.
- Current passage or electrolytic corrosion. If current is allowed to flow through the rolling elements, sparks can create pitting or fluting on the bearing surfaces. This should be corrected by creating a bypass circuit for the current or through the use of insulation on or within the bearing. This should be an inherent design consideration in applications such as wind turbines and all power generating equipment.
Mounting & Installation of Bearings
It is critical in the mounting and installation process to pay strict attention to:
- Use of proper tools and ovens/induction heaters. Use a sleeve to impact the entire inner ring face of the ring that is being press fit.
- Verify the shaft and housing tolerances. If fit is too tight, too much preload is created. If the fit is too loose, too little resulting preload may allow the shaft to rotate or creep in the bearing. Check for proper diameters, roundness and chamfer radius.
- Avoid misalignment or shaft deflection. This is especially critical in mounting bearings that have separable components such a cylindrical roller bearings where successful load bearing and optimal life are established or diminished at installation.
- Be aware of radial internal clearance. It is critical to maintain the proper RIC established in the original design. The standard scale in order of ascending clearance is C2, C0, C3, C4, C5. The proper clearance for the application is critical in that it allows for challenges of:
- Lubrication. A proper film of lubricant must be established between the rolling elements. Reducing internal clearance and impending lubricant flow can lead to premature failure.
- Shift fit. A reduction in the radial internal clearance is inevitable when the bearing is press fit.
- Heat. In normal bearing operation, heat is produced that creates thermal expansion of the inner and outer rings. This can reduce the internal clearance, which will reduce the optimal bearing life.
Adapted from NTN Corporation – Care and Maintenance of Bearings pp.