The Importance of Lubricants
Miniature ball bearings are perfect for high stress environments, but require special lubricants to minimize wear and extend service life, performance, and safety of the product. GRW lubricants provide permanent lubrication to minimize the sliding friction between the rolling body and retainer, rings and retainer, or rolling body and rings. This prevents excessive wear and thermal heating, protecting the balls and raceway from micro-seizing and thereby extending service life while reducing running noise. The application of the miniature ball bearings determine the best type of lubrication to use.
Lubrication with grease
Thanks to its ability to dispense a lubricating film over time, grease lubrication offers the advantages of being maintenance-free and used for permanent applications.
Most GRW miniature ball bearings are grease-lubricated, with approximately 300 greases to select from. The standard amount of grease (lubricant quantity) is one-third (33%) of the free space in the ball bearing. Grease quantities deviating from this standard are indicated in the designation before the type of lubricant, preferably in percent or alternatively in milligram.
Furthermore, the customer can choose other special treatments for grease application, for example a dispersion or a thin defined layer of grease. Here, the designation system differentiates between TF (thin film), MF (medium film), and SF (strong film).
Miniature ball bearings lubricated with oil may offer advantages over those lubricated with grease. Lubricating oil is primarily used in applications with minimal torque requirements. In particular, fast rotating spindle ball bearings are typically lubricated with high performance oils. When compared to grease lubrication, oil lubrication sometimes uses a dispersion of oil and a solvent (special benzene) to achieve a better distribution of the oil in the miniature ball bearing.
Choose the oil that perfectly suits your application from a selection of over 100 different types. If no special lubricant is selected, all ball bearings (either open or with one closure) are preserved with oil when they leave our factory.
Introduction of lubricant during assembly
At GRW’s, miniature ball bearings are lubricated during final assembly under clean-room conditions. Since dirt particles will cling to the oiled or greased miniature ball bearings, It is important that the customer maintains a high standard of cleanliness in their application. In addition we recommend using a clean-room for removal of the ball bearings from their package and for assembly.
With greased miniature ball bearings, the defined quantity of lubricant, accurate to the milligram, is injected directly into specified locations on the miniature ball bearing. Usually, the lubricant is injected from one side: however it is also possible to lubricate the miniature ball bearing from both sides for better distribution.
For oil lubrication with standard oils, the oil is poured over the miniature ball bearing which is then spun. Alternatively, an exactly defined oil quantity can be directly introduced into the miniature ball bearing.
Lubrication with solids
Non-lubricated miniature ball bearings may be used in certain applications and are also available from GRW. These non-lubricated bearings are typically required for vacuum systems up to ultra-high vacuum (UHV) temperature extremes, and for applications in aviation and aerospace. Here the operating conditions go beyond the application limits of oil and grease lubricants. The use of a miniature ball bearing without a protective, separating lubricant film will negatively impact its tribological system; however lubrication with solids is a viable alternative.
GRW offers its customers a variety of different coatings. Applying thin layers of precious metals, graphite or Wolfratherm® (MoS2) provides protection and self-lubrication for the ball bearing.
For oil or grease lubricated ball bearings, this process ensures reliable performance in case of starved lubrication (emergency running conditions). In the numbering system, the surface treatment of ball bearing components is indicated by a “B”, followed by a four-digit number code indicating the type of surface treatment.
In addition to varying lubricants and surface treatments, GRW can modify bearing construction to improve tribological behavior. For example, the phenolic retainer can be saturated with oil (up to 5% by weight). The benefit of a vacuum-impregnated retainer is its ability to release small amounts of lubricant continually during operation. This process improves the general lubrication performance and ensures good emergency running properties in case of starved lubrication.
Lubricants in medical engineering
Sterilization (autoclaving) is mandatory for the processing of medical instruments according to the guidelines of the Robert-Koch Institute. This applies to the hygienic treatment of medical angle devices and dental turbines that depend upon miniature ball bearings.
GRW’s stainless chrome steel and retainer materials can easily withstand sterilization in an autoclave with aggressive superheated steam, but most lubricants are not suitable for these requirements. Combined with the extreme high speed stress of dental turbines. These lubricants are required to provide exceptional surface adhesion behavior and sterilization resistance.
As manufactured, GRW miniature ball bearings utilize a range of lubricants that are particularly resistant to the sterilization process and best suited for dental and medical devices. This optimization extends their rated life under extreme environmental conditions.
For more information about GRW Bearings and specialty bearing lubrication requirements please contact us for a consultation.