Linear bearing seals: types, options and applications

Seals used for circulating linear bearings have two functions-preventing contamination and maintaining lubrication-to ensure that the system operates normally without premature wear or failure. Since sealing is critical to linear bearing systems, manufacturers provide a variety of sealing designs and materials to meet a wide range of applications and environments.

Standard linear bearing seals

Most manufacturers of recirculating linear guides provide basic seals in single or double lip styles. These seals form a reliable line contact with the guide rail, which can effectively prevent the entry of fine particles and liquids.

Double lip seals provide two barriers between the external environment and the internal components of the bearing, and are usually used for very fine dust (such as ceramic or glass) and hazardous chemicals. Some manufacturers also provide triple-lip seals as optional accessories.

When the contamination includes large and coarse debris (such as metal or wood chips or welding slag) that may damage the lip seal, a metal scraper can be used in addition to the standard lip seal. Metal scrapers leave a small gap between the seal and the guide rail, but they can wipe or scrape larger debris from the guide rail very well. It is important to note that because they are non-contacting, metal squeegees are generally not suitable for stand-alone use without additional sealing options.

Metal seals or scrapers are used in combination with standard seals to prevent larger contaminants such as wood or metal chips.

Most recirculating linear bearing designs also include internal (sometimes called universal) seals to prevent any contaminants from passing through the front seal or possibly collecting in or around the rail mounting holes.

When we think of linear bearing seals, we usually think of the front seals located at both ends of the bearing housing. But most recirculating linear bearings also include side seals (also called longitudinal or transverse seals) as standard components. These can prevent contaminants from entering from below, along the side of the bearing housing—especially when the component is installed on the side, vertical or upside down. However, while the side seal provides an extra layer of protection, the front seal usually does most of the work in preventing the ingress of contaminants.

Remember, the more the seal is in contact with the running surface, the more force is required to overcome the friction of the seal. This additional friction affects the size and selection of system drive components. The manufacturer usually announces (or can provide) the amount of force required to overcome the friction caused by the seal.

The seal creates friction between the bearing seat and the guide rail, thereby increasing the force required to move the bearing seat. The more contact, the greater the friction. Shown here are low friction, single lip and double lip seals

Although it is recommended to use seals for special-shaped guides and linear guides, due to their importance in maintaining proper lubrication, round-axis linear guides and cam roller guides can operate without seals. Sliding bearing linear guides are also usually used without seals, unless the environment contains serious pollution.

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