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Bearings - 2021-01-11

NSK high-precision miniature bearings

In dental air turbines, miniature rolling bearings must overcome a very demanding set of challenges. As well as rotating at speeds of up to 500,000 rpm, these bearings must provide extremely quiet operation and meet rigorous hygiene requirements. NSK offers precision miniature bearings made from stainless steel especially for this application.

Driven pneumatically by a turbine wheel, the two bearings in the head of the instrument ensure stable guidance of the drill during dental procedures. Miniature bearings, which have an outer diameter of just 6.35 to 7 mm, need to attain speeds of up to 500,000 rpm and stop very quickly. In addition, the bearings must avoid the generation of micro-vibrations and tolerate frequent cleaning and sterilisation, usually with hot, moist air in an autoclave environment.

For many years NSK has been developing and manufacturing precision miniature bearings for dental air turbines. Historically, these bearings were destined exclusively for the Asian dental equipment market, but today also for Europe.

Among the materials used to make the bearings is ES1, a special stainless steel developed by NSK that provides significantly increased purity and corrosion resistance compared with the commonly selected AISI 440C (equivalent to ISO 1.4125). The high purity of ES1 stainless steel has a positive effect on bearing service life, since any inclusions or structure irregularities can cause stress cracks or flaking on the bearing raceway. Using ES1 also increases corrosion resistance.

The rolling elements of NSK’s miniature bearings for dental drills are made of high-performance ceramics, while the cage material is either PEEK (a high-performance plastic) or Torlon® PAI (a polyamide-imides thermoplastic).

All of the components used within these miniature precision bearings achieve the highest levels of accuracy. This outcome applies equally to the reproducibility of the ball diameter as it does to the surface quality (roughness) of the raceway, and the roundness of the raceway and cage.

NSK also offers dental bearings in the highest accuracy class ABEC9 (P2) while attaining a bore diameter sorted tolerance class from 0.0025 to 0.00125 mm, and from 0.00125 to 0 mm. The consequence: NSK bearings produce significantly less micro-vibration and emit less noise than comparable bearings from other manufacturers. These characteristics derive from factors such as considerable investment and research in production technology, as well as the development of dedicated test and measurement processes for the various bearing sizes and types.

NSK's range of precision miniature bearings for dental air turbines includes four series of deep groove ball bearings and angular contact ball bearings, with more than 40 different types and sizes. Along with typical external diameters of 6.35 to 7 mm, the bearings have a typical bore diameter of 3 mm for widths of 2.3 to 2.8 mm, while the lubricant is CF1, a low-viscosity, high-performance oil.

 

Picture ): Dental air turbines are equipped with two high-precision miniature bearings that reach speeds of up to 500,000 rpm

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