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Contamination free
Air lubrication has a particular importance in conditions where it is necessary to keep the environment contamination free from conventional lubricants. Such situations arise in semiconductor wafer manufacturing systems. In these situations, it may be costly or impractical to manufacture a system which can effectively seal off contaminants from oil lubricants used in roller slides. The externally pressurized air bearing lends itself well to harsh environments where liquids, dust and contaminants are present. The air bearing's great resilience stems from the fact that with positive pressure existing inside the bearing, all foreign matter is repelled away from the critical bearing surfaces. Unlike some rolling element bearing supports that require periodic maintenance, cleaning, the addition of oil lubricants and sometimes the replacement or re-surfacing of guide ways, the air bearing's self-cleaning nature allows it to be virtually maintenance-free.
Wide Temperature Range
The most exclusive quality of gases as lubricants is their potential for operation over extremely wide ranges of temperature. Complex gases on the other hand will have decomposition limitations at the upper end of their usable temperature range. No difficulty is seen, for example, at the hot end of the scale, in operating the bearings of small steam turbines or circulators upon superheated steam, and, at the cold end, gases approaching their liquefaction temperatures could be employed to lubricate the bearings of, for instance, gas liquefying turbines. In both examples considerable simplification of design could thus be achieved in some situations. It is noted that whereas with liquids bearing performance falls off with rise of temperature due to fall in viscosity, in the case of gases, the load-carrying performance will in general improve due to a rise in viscosity.
Unlimited Service Life
The absence of contact means absence of wear, McCarthy says an air bearing will operate without change for decades. He notes that these bearings have been deployed in the thousands in digital printing systems worldwide over the last ten years, and has demonstrated intrinsically high production reliability. We can also see applications in which high precision is not required, and air bearings are being selected strictly for their unlimited, maintenance-free service life.
THE IMPORTANCE OF BEARING LUBRICATION
The performance of modern plant and machinery depends on the reliability of rolling bearings. Nick Dowding of The Barden Corporation, discusses the importance of bearing lubrication, including the correct selection, application and maintenance of rolling bearing lubricants.
The performance of modern plant and machinery depends to a large extent upon the reliability of rolling bearings. One of the major contributing factors to achieving high reliability is proper lubrication. Bearings operate on very thin films of lubricant, which have to be maintained in order to ensure that the bearing's design life is achieved.
The three primary principles of maximising bearing life are: selecting the correct lubricant, applying the lubricant properly, and maintaining the lubricant in a clean condition. Neglect or failure in any of these three areas will seriously increase the risk of premature bearing failures and will interfere with trouble-free running.
The increased speeds and higher temperatures at which modern bearings routinely operate, combined with the demands placed upon them for improved accuracy and reliability, mean that the process of selecting a suitable bearing lubricant today, is more critical than ever. Correct selection of a lubricant:
• Reduces friction and wear by providing an elasto hydrodynamic film of sufficient strength and thickness to support the load and separate the balls from the raceways, preventing metal-to-metal contact.
• Minimises cage wear by reducing sliding friction in cage pockets and land surfaces.