Usage of Correct Bearing Seals Improves Equipment Performance

Bearing seals are important in keeping contaminants out of lubricants in the bearing and bearing chambers. Selecting the correct external bearing seals for specific applications involves the following key factors: bearing type (rolling or sleeve), lubricant (oil or grease), seal friction and consequent heating, shaft surface speed and finish, and physical space available. Choosing the appropriate seal for an application involves matching the mentioned factors with the qualities of external seal types as listed below

Rolling bearings usually use the following types of seals 1) contact or lip seals, 2) non-contact seals, 3) multiple types of bearing isolators that combine functions of contact and non-contact seals. Non-contacting type labyrinth seals are normally paired up with sleeve bearings.

Contact seals provide an effective sealed interface with continuous application of pressure to the surface using a resilient material. These seals secure difficult penetration of fluids or solid particles to the sealed area. However, these also lead to direct contact with the shaft, creating friction and heat that results to degraded seals and damaged shaft surface finish.

Non-contact seals yield much less friction and heating compared with a contact type one. Conversely, these seals let lubricants leak out of the bearing chamber and also allow entrance of physically minute contaminants.

Bearing isolator seals bring together functions of contact and non-contact seals in a unit but use contact features to “drive” part of the seal at the shaft’s rotating speed. These seals can provide more protection than individual contact or non-contact seals, can be used with oil lubrication or grease and with either sleeve or rolling bearings. Bearing isolators are a bit more expensive and need more physical space than contact or non-contact seals but these are guaranteed to deliver more effective sealing.

Variations of bearing isolators include contacting isolators and labyrinth-design isolators. Contacting isolators stop all solid and vapor contamination with rare-earth magnets that apply tension to lapped contacting faces. However, these have surface speed limitations, allowing only a maximum of about 4* (100 mm) shaft at 3600 rpm. Labyrinth-design isolators prevent vapor ingress when the machine is turned off and reduce friction/heat when it is running.

Shaft slingers join elements of contact and non-contact seals. These make contact with the end bracket as the equipment is idle and distance away from it by centrifugal force when the shaft is rotating.

Labyrinth seals are non-contact seals for use with rolling or sleeve bearings, and with oil or grease lubrication. Labyrinth clearance must always be greater (0.002” – 0.004”) than bearing clearance.

Contact seals or bearing isolators are best for most oil-lubricated bearings, excluding sleeve bearings for which labyrinth seals are preferred. Non-contact seals are not suitable for most oil-lubricated applications as these permit leakage.

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