The Role Of Bearing Closures

Bearing closures most usually consist of shields or seals and the purpose of these closures is to protect the inside of the bearing from contaminating particles while also helping to keep the lubricant in place. Metal shields are designed to keep larger particles out. There is gap between the shield and the inner ring to avoid metal on metal contact. This means a shielded bearing is not suitable for dusty environments but shields do not create any additional drag. Contact rubber seals consist of a nitrile rubber seal bonded to a metal washer for extra rigidity. The inner lip of the seal drags on the inner ring of the bearing so although a contact seal will keep out smaller particles and effectively prevent lubricant leakage, the bearing torque will be greatly increased. The drag also reduces maximum speed by up to 40%. Contact seals are also available in different materials such as Teflon or Viton. Teflon seals are resistant to high temperatures (+250C) and some chemicals. Viton can also be used for higher temperatures (230C) although the nitrile seal is still the most popular. Another option is the noncontact seal. This type of nitrile seal does not offer the same degree of protection as the contact seal but is an improvement over the metal shield and due to the lack of contact with the inner ring does not increase bearing torque.