Improving technology
Improving technology
Keywords NSK-RHP
The continuous drive to improve technology in all areas of manufacturing,processing, communications, power generation and transport is placing increasing demands on key power transmission, actuation and support components to operate in special environments and under adverse conditions. NSK-RHP believes that it is meeting these requirements with its SPACEATM series (Plate 1), a range of bearings, ball screws and linear guides that reportedly provides high performance and reliability under all types of demanding operating conditions:super-clean, vacuum, non-magnetic, corrosive, high/low temperature, nuclear and high speed.
Plate 1 NSK's SPACEATM range includes bearings, linear guides and ball screws
SPACEA series products are thought to meet the widest range of technical requirements with a programme of high performance materials, surface finishes and specially developed lubricants, including solid types. Depending upon the application, SPACEA bearings can be manufactured from martensitic and austenitic stainless steels, ceramics, or a combination of both. Hybrid SPACEA types can have any combination of ceramic inner/outer rings or balls, the specific configuration depending upon the operating environment, be it corrosive,non-magnetic, high temperature or clean.
Linear guides and ball screws in the SPACEA series are also manufactured from martensitic and austenitic stainless steels, enabling them to be used in a range of challenging environments, from corrosive to radioactive. The use of ceramics also extends to SPACEA series ball screws. These can be hybrids employing austenite stainless steel recirculation components, or of totally ceramic construction for use in corrosive environments, air or vacuum, at temperatures up to 200°C.
Not all applications require the levels of protection provided by ceramics,so a range of surface coatings offering graduated protection against corrosion has also been developed. The first of these is a low cost cold fluoride chrome plating which is available on all SPACEA series products.
Moving upwards along the cost scale, SPACEA bearings can be hard chrome plated, or have a coating of nickel alloy. The latter claims the highest levels of resistance to corrosion and most types of acids at moderate cost. Where the requirement is for cleanliness, rather than protection from corrosion, another specially developed coating is thought to be ideal. Fluororesin, a surface treatment for SPACEA bearings and ball screws, has been developed for clean room environments. It combines low dust count and gas evaporation characteristics with long endurance life.
Lubrication technology for the SPACEA series includes NSK's new LG2 low dust grease for clean rooms. This is said to provide ten times the life of fluorine greases and to offer superior rust prevention. Also new is moulded oil, a polyolefin resin impregnated with oil which reportedly when employed in NSK's KI lubricating transforms the performance of SPACEA series linear guides and ball screws in applications where lubrication is difficult to apply or conditions are arduous.
Extending the range of applications for the SPACEA series into vacuum environments is a range of solid lubricants. These include silver for linear guides; silver and molybdenum disulphide for ball screws and gold, lead, silver,and molybdenum disulphide for SPACEA bearings. The effect of the coatings is graduated. Molybdenum disulphide is said to enable SPACEA ball screws and bearings to operate in air/vacuum environments at temperatures up to 300°C. Above this figure (up to 500°C), and for high vacuum applications only,silver is the preferred solid lubricant.
SPACEA series equipment for use in clean environments can be divided into two groups: one lubricated with LG2 clean grease, and the other lubricated with fluorine grease. SPACEA products lubricated with LG2 clean grease are used in wafer transfer robots operated on semiconductor production lines and in the manufacture of hard disk drives. In addition, fluororesin coated bearings are used on liquid crystal display production lines and on substrate carriages operated in vacuum and high-temperature environments.
In vacuum environments, where ambient temperatures are not high, SPACEA series products may be lubricated with a fluorine grease of low vapour pressure. However, where ambient temperatures are high and may cause fluorine grease to vaporise, the equipment needs to be lubricated with a solid lubricant, such as silver, lead (bearings only) or molybdenum disulphide.
SPACEA equipment that is used in X-ray tubes and turbo-molecular pumps is also coated with these lubricants. Other uses include vacuum producing equipment and aerospace instruments.
SPACEA bearings with rustproof film coatings are used in cleaning machines and on hard disk and semiconductor production lines. Ceramic bearings are used in film cleaning systems and semiconductor polishers.
According to NSK-RHP its SPACEA bearings for high temperature operation employ a graphite lubricant and can be used at temperatures up to 500°C. The radial clearance of bearings for high temperatures is reportedly made larger than that of general bearings to allow expansion and, therefore, ensure long life. SPACEA bearings used at low temperatures are lubricated with a very low-viscosity liquid lubricant, and their cages are lubricated with fluororesin. It is claimed that this type can be used without maintenance over a long period.
Lubricant selection is important for radiation-resistant SPACEA products. They are lubricated with standard grease for service at permissible radiation doses up to 106rad and with radiation-resistant grease for up to 109rad. Non-magnetic bearings and ball screws are made of either non-magnetic stainless steel or ceramic. They are lubricated with either fluorine grease or fluororesin.
Bearings in the range also include high-speed applications; these are hybrid types with steel outer and inner rings and ceramic balls. Owing to the lower friction between the balls and raceways compared to bearings with steel balls,hybrid bearings have a lower temperature rise during high-speed operation. For this reason they are used in machine tool spindles. Recently, NSK created Neo-Brid bearings for machine tool spindles by changing the material of the inner ring of the hybrid bearing from bearing steel to stainless steel. This change is said to have resulted in 30 per cent better high-speed performance than conventional hybrid bearings. In addition, hybrid bearings reportedly have excellent seizure-resistance.
Further details are available from NSK-RHP UK. Tel: +44 (0) 115 936 6600.
