Bearing Closures

Ball and roller bearings are available with different types of shields and seals. These are commonly referred to as bearing closures. Bearing 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 bearing closures may be supplied on the same bearing. Special designs are also available. The following are descriptions of the most common types we can supply.

Shields (ZZ)

Most sizes are available with metal shields. Shields are designed to prevent larger particles from entering the bearing and also to keep grease inside the bearing. They may be pressed into the bearing’s outer ring (non-removable) or retained by a circlip (removable). As the shields make no contact with the inner ring, they do not  increase starting or running torque. Shields on stainless steel bearings are generally made from AISI 304 grade stainless steel.

• Prevent contamination by larger particles
• Reduce lubricant leakage
• Do not increase torque

 

Contact seals (2RS)

The standard bearing seal consists of nitrile/BUNA-N rubber bonded to a metal washer. High temperature teflon seals (up to 250C) or Viton seals (up to 230C) are available on some sizes. The inner lip of the seal rubs against the bearing inner ring to provide an effective seal against smaller particles such as dust and moisture while preventing lubricant leakage. Contact seals produce much higher frictional torque levels than shields and reduce the maximum speed of a bearing. Below -30°C nitrile rubber and viton will stiffen and provide a less effective seal so teflon seals or metal shields should be considered for very low temperatures.
• Good protection against contamination
• Greatly reduce lubricant leakage
• Reduce maximum speed by approx. 40%
• Greatly increase bearing torque
• Temp. range –40°C/+110°C (nitrile rubber) or up to 230C (Viton) and 250C (Teflon)

Non-contact seals (2RU)

These seals are also made of nitrile rubber bonded to a metal washer but do not rub against the bearing inner ring and therefore do not have the same effect on bearing torque and maximum speed as contact seals so can be used for low torque, high speed applications. They offer superior protection over metal shields but do not provide as effective a seal as the contact type.

• Good protection against contamination
• Reduced lubricant leakage
• No torque increase
• Do not affect maximum speed
• Temp. range –40°C/+110°C

As mentioned previously, it is possible to get a combination of bearing closures on a single bearing. For example, a seal and shield combination, such as RSZ, can provide increased protection from contaminants compared to a double shielded (ZZ or ZZS). The RSZ combination would exhibit less torque than a 2RS configuration. The side of the bearing with seal would be oriented so that it is facing the contaminated environment.

Due to their construction, shields and seals are not typically available on tapered roller bearings or angular contact bearings. External seals are normally incorporated into the design for harsh or extreme environments.