Lubrication

Bearing lubrication is primarily intended to reduce friction and wear of the bearing, but also serves a variety of other purposes such as heat dissipation and corrosion protection. There are three main categories of lubrication: grease, oil, and dry-film lubricants.

Grease is the appropriate choice of lubricant for most applications. Grease has less tendency for migration which allows for a simpler/lower profile design and often allows bearings to be “lubed for life”. Silverthin sealed bearings are always supplied with grease.

Oil can support much higher bearing speeds, but usually requires a more involved lubrication system. The general rule is that the bearing should not be fully submerged and that the oil level should only reach the midpoint of the lowest rolling element when mounted vertically.

Dry-Film Lubricants are typically considered only when environmental considerations prevent grease or oil from being appropriate. Dry-lubes commonly used include dicronite (WS2), graphite and MoS2 platings. Dry-film lubricants have drawbacks of excessive particulate generation which may cloud optics or other sensitive components if not taken into consideration.

Selection of the correct lubricant is entirely application driven and should consider the following:

  • Desired bearing speeds
  • Bearing loads
  • Limiting torque development
  • Intended service intervals
  • Dithering or oscillating rotation
  • Environment considerations such as:
    • Temperature extremes
    • Vacuum applications
    • External Radiation
    • Chemical interactions
    • Water washout or miscibility with other liquids

Open Bearings shipped without grease are coated with a MIL-PRF 6085 preservative oil. This is intended to protect Silverthin bearings from corrosion but is not intended for operation. Silverthin recommends that bearings be cleaned and relubricated prior to use.

Sealed Bearings are shipped ready for installation with the external surfaces of the bearing protected using a light layer of the grease used for lubrication. Unless otherwise requested sealed bearings are greased with a 20-30% fill of MIL-G-81322 general purpose grease. Shelf life for sealed bearings is generally 2 years, after which the bearings should be serviced or returned to Silverthin for relubrication.

Silverthin bearings can be shipped with alternative lubricants and custom fill amounts to support your application. In addition to customized bearing lubrication Silverthin on-site assembly processes can control cleanliness and perform other specialized lubrication processed such as:

  • Cleaning & relubrication to either refresh or change lubricant
  • Processing in a Class 1000 clean room environment
  • Grease plating
  • Vacuum impregnation of ball retainers

Lubricant selection can have a large impact on performance, cost, and lead time. Please contact Silverthin Engineering for lubricant review and product suitability.

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