Bearing shields and seals are designed to prevent particles from entering, and to keep the vital grease inside the bearing. Bearing shields do not make contact with the inner ring. This means they do not increase starting or running torque but are not very effective at preventing washout.
For greater protection against contamination and lubrication loss, contact seals made of nitrile rubber can be used to seal the bearing inner ring. It should be noted however that contact seals produce much higher frictional torque levels than shields, so must warrant the added protection.
The middle ground is non-contact seals. These are also made of nitrile rubber, but do not rub against the bearing inner ring. This means these seals don’t affect torque or maximum speed. They offer more protection over metal shields, but if you need the ultimate seal, you may be better off with the contact type.
For the greatest protection against washout, a highly water resistant grease is recommended. Food grade greases are designed to withstand regular steam cleaning or wash-downs with cleaning chemicals. PFPE greases, many of which are also food grade, will perform the same task but have even higher resistance to chemicals.
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