The development of lead-free, soft metal bearings has attracted a radical upsurge in interest among TWI's Industrial Members of late.
It is thought that this is due to a combination of factors, most significantly the legislative trend towards reducing or eliminating toxic materials from future products and the requirement for better technical performance.
Ideally, soft metal bearings should have most, if not all, of the following properties:
- Resistance to high speed, dry lubrication and metal-to-metal contact
- Abrasion resistance
- Embedibility of abrasive and dirt particles
- Thermal dissipation
Whilst many of these can be satisfied using leaded bearings, it is believed that the multiple properties required in new bearing designs will require composite, lead-free materials that cannot be made by conventional castingprocesses.
The use of thermal spraying for manufacture of simple bearings is well-established using a range of available alloys that are representative of soft and hard bearings, such as Babbitt, aluminium-bronze, 13Cr steel and tungstencarbide. It is, however, possible to go a further step by spraying more than one material at a time and to vary the material feed rate with time, and thereby produce composite, multi-layer and graded coatings by continuous spraying.For instance, one can spray a wear resistant alloy with a low melting point alloy to produce a seizure-resistant bearing material.
Fig.2. HVOF metal-ceramic graded coating Many thermal spraying processes, including flame, arc and cold spraying, can be used to produce composite bearing alloys from wire or powder consumables and from a range of materials including metals, metal alloys, ceramics, metalcarbides and polymers.
To learn more about this fascinating work call Andrew Sturgeon. , ITSC 2003, May 2003
