While we’ve covered the basics of ball bearings and roller bearings, what you may not be familiar with are bearing closures. Bearing closures are available in two simple types, namely shields and seals. Both are considered integral parts of deep groove bearings as they retain lubrication, prevent contaminants from penetrating the internal surfaces and can ultimately protect and extend the life of the bearing.
There are various types of closures that can be supplied with a single bearing, and some can even be specially designed to suit a particularly unique application. Both shields and seals have their purpose but deciding which one to use or which combination can be tricky. To determine the correct closure for an application, you first need to understand the advantages and disadvantages of each.
Shields are made from either plastic or metal and are secured to the outer race on each side of the bearing. This design effectively retains lubrication and protects against grease contamination. Shields have no limitations when it comes to speed, but their sealing efficiency is low. This is where seals are more efficient, offering a much higher protection from moisture and dirt. The trade-off is that the high-contact pressure against the inner-race causes friction, restricting operating speeds and increasing the temperature.
Common Shield Types
The most popular type of shielded bearing is the Z Type. It features a single metal shield on only one side of the bearing. This design gives the Z Type it a minimal clearance, but it doesn’t handle heavy loads, high speed or high precision. An alternative option is the ZZ Type or ‘2Z’ shielded bearing, which features a metal shield on both sides of its sides. While the ZZ Type cannot be removed once it has been installed, it doesn’t make contact with the inner ring, so there is no impact on the operational speed.
Common Seal Types
A popular type of sealed bearing is the 2RS which features a moulded rubber (nitrate) seal, bonded to a steel insert and fixed into a groove in the outer ring. Since this seal makes contact with the inner ring, it provides far better protection from environmental contaminants than a metal shield. The bearing’s speed capabilities, however, will be limited and rubber tends to react with certain chemicals, so it’s important to be mindful of this when selecting your lubricant. An alternative seal is the 2RU. While similar in design to the 2RS, this type of seal does not make contact with the inner ring, so it does not affect the torque of the bearing.
These are just a couple of the more common closures that are available. There are many other types and variations and, as mentioned, a combined option is also possible. If you’re interested in learning more about seals or shields, or if you’re having trouble deciding on the proper option for your application, make sure you contact your knowledgeable, local supplier. Contact Bearing Centre, we offer all our customers 24/7 support.