Ball and roller bearings are available with different types of shields and seals, commonly referred to as closures. Closures can extend bearing life by preventing contaminants from reaching the critical surfaces inside the bearing, and they help retain the lubricant in the bearing. Different types of closures may be supplied on the same bearing. Special designs are also available. The following are descriptions of the most common types AST can supply.
Type ZZS – Removable non-contact metal shield retained in the outer ring with a snap wire. This type of shield is manufactured from 300 series stainless steel and is available only on miniature and instrument series bearings. Max operating temperature is 600° F. Since there is no contact made with the inner ring there is no appreciable impact on torque or speed and operation can be compared to that of an open bearing. The removable closure allows for cleaning and re-lubrication. The code for a single shield is ZS.
Type ZZ – Non-removable, non-contact metal shield retained in the outer ring via crimping, or pressing. This type of shield cannot be removed once installed. This type of shield can also be manufactured from 300 series stainless steel. On larger bearings, this type of shield is manufactured from 1008 or 1010 strip steel. Max operating temperature is 450° F. Since there is no contact made with the inner ring there is no appreciable impact on torque or speed and operation can be compared to that of an open bearing. The code for a single shield is Z.
Type 2RS – Molded rubber seal. This type of seal is Buna-N bonded to a steel insert. The seal is fixed into a groove in the outer ring. This type of seal can be removed but care must be used not to bend or cut the seal lip. Max operating temperature is 240° F. This type of seal makes contact with the inner ring providing better protection in contaminated environments than a metal shield. However, this results in an increase in torque and reduces the max speed capability of the bearing. Certain lubricants and chemicals react with rubber. The code for a single seal is RS.
Stay tuned for part II of our bearing closure blog series, which will focus on types 2RU, 2VS and TTS.
AST’s consultants and engineers are ready to provide further information about ball bearing cages and any other bearing questions you may have – contact them here.