sealed bearings
Sealed Ball Bearings while quite similar to the shielded ball bearings in having covers over the balls offer a greater degree of protection because the “Shield” on the sealed ball bearing actually comes into contact with the inner race. This seal in contact with the inner race provides the highest degree of protection against dirt and moisture for a ball bearing. This higher degree of protection does not come without a price, the high contact pressure of the seal against the rotating inner race increases the friction and torque losses and can cause a build up of heat as well.
Selecting the right shielded or, unshielded bearing for your pump’s electric motor can go a long way in ensuring a long service life. But the thing to remember is that once a ball bearing starts to fail the bearing never will get better on its own and the additional contaminants from the indentation, smearing, spalling or flaking, and corrosion of the metal surfaces of the balls and races accelerate the failure process. The time between the first noise the bearing starts making, to when the friction of the failed bearing starts increasing the motor loading and current draw can be quite quick. You should always have the bearings in the motor replaced at the first sign of bearing failure rather than wait until the increased loading causes the motor to burn out or, the sloppiness caused by the wear causes other damage to the motor components.
Sealed bearings differ from shielded or open bearings in that they cannot be relubricated once the lubrication breaks down or leaks out. Although this results in a shorter overall life span than that of properly maintained shielded or open bearings, sealed bearings, when used properly, still have a number of advantages over unsealed bearings.
The seals are inserted in recesses in the outer ring. For smaller bearing sizes, the seals are pressed into the recesseswhile the seals for the larger sizes are held in position by means of retaining rings. The seals have two sealing lips contacting the lead-in at the sides of the inner ring raceway, to provide efficient sealing.
Sealed bearings are lubricated as standard with an extreme pressure bearing grease according to table 1. They should not be heated to temperatures above 80 °C during mounting, and should not be washed.
Sealed bearings do not need to be relubricated when the operating temperature does not exceed 70 °C and the rotational speed is below 50% of the limiting speed listed in the product table. When temperature and/or speeds are high, relubrication with a similar grease with lithium thickener is recommended (table 1). In this case the polymer band, which covers the lubrication holes in the outer ring must be removed before mounting. Note that only a small amount of grease is needed to relubricate sealed bearings. The grease should be pressed in slowly through the lubrication holes in the outer ring while the bearing is rotating. Excessive pressure should be avoided so as not to damage the seals.
