A cool approach to lube-free bearings

SKF has developed a technique for using a refrigerant rather than oil to lubricate hybrid bearings. This technology is expected to have particular benefits for bearings used in refrigeration or air-conditioning compressors - traditionally an awkward application.

In the past, oil has been mixed with the refrigerant in the compressor to lubricate such bearings. But when the mixture enters the bearing, the refrigerant can "flash" or evaporate, preventing the oil from lubricating the balls and raceways.

This approach has other drawbacks. When the oil is mixed with the refrigerant, it is diluted, lowering its viscosity and resulting in poor lubrication. To overcome this, a separator is sometimes used to collect the oil and "push" it back into the bearings, but this adds to the cost and complexity of the system, and requires maintenance.

SKF set out to find a way of improving lubrication by controlling the oil dilution - and came up with a bearing that uses just refrigerant as the lubricant. "This is a huge step forward, both for the compressor manufacturer and for the owner," says Hans Wallin, SKF`s compressor technology business manager.

The technique also has environmental attractions, he points out. "Because no oil is used inn the application," Wallin says, "leaks, maintenance issues, and the disposal of used oil, no longer pose a threat."

The hybrid bearings used in the compressors, combine steel raceways with silicon-nitride balls. They are stiff, can run faster and last longer than conventional all-steel bearings.