7 Ways to Avoid Pump-Bearing Misalignment

The diagram shows two typical misalignment situations, compared with a properly aligned bearing. Correctly aligned bearings will exhibit a running path down the center of the inner and outer rings.

Rolling bearings are manufactured with extreme accuracy. For them to perform at their best, great attention must be paid to the mounting and maintenance process. If not, misalignment may occur, leading to bigger problems down the road, including bearing seizure, pump failure, and costly downtime.

Over time, a well-aligned bearing will exhibit a running path down the center of the inner and outer rings, while a misaligned bearing will exhibit uneven running paths. The technical experts at bearing manufacturer NSK Americas, Ann Arbor, MI, offer these helpful tips for preventing and alleviating bearing misalignment in your pump applications.

1. Shaft and housing: The shoulders of the shaft or housing that contact the face of a bearing must be orthogonal to the shaft center line. The fillets should not contact the bearing chamfer, while the supporting shoulder diameter still must be large enough to fully support the face of the bearing.

2. Clean installation: During installation, all mating surfaces should be cleaned and all shaft and shoulder-abutting surface edges should be free of burrs. Bearing mounting methods will vary depending on the bearing type and the type of fit.

3. Proper fit: Most bearings require a tight fit, either with the housing or, most commonly, with the shaft. Depending on the type of fitting surface, different mounting techniques are required. Typically, bearings with cylindrical bores are mounted by pressing through the inner ring onto the shaft (press fit) or heating them to expand their diameter (shrink fit), while bearings with tapered bores can be mounted directly on tapered shafts or on cylindrical shafts using tapered sleeves. Always apply a light film of oil on the fitting surfaces first to prevent scoring. When pressing a bearing into a housing, push on the outer ring of the bearing. When pressing onto a shaft, push on the inner ring.

4. Nylon cages: If you use ball bearings where some degree of misalignment is unavoidable, consider those with nylon cages. Their flexibility allows them to endure misalignment better than steel cages.

5. Internal clearance: Increasing a bearing’s internal clearance will increase its tolerance for misalignment and help mitigate alignment issues.

6. Ball bearings: Self-aligning ball bearings may also be a good alternative. They have a spherical outer ring raceway that allows the axis of the inner ring, balls, and cage to deflect around the bearing center.

7. Follow directions carefully: Rigorously following catalog-recommended assembly tolerances and installation processes is the best way to prevent bearing misalignment.

Remember that reducing or eliminating misalignment is critical for longer bearing and system life. If misalignment cannot be completely avoided in an application, additional calculations are required to determine the effect this condition will have on the life of the bearings.

For more information from NSK experts, including assistance in calculating the impact of unavoidable misalignment on bearing life and other application analyses, visit nskamericas.com.