The Performance of Ball Bearings in Nitrogen and Carbon Dioxide at Elevated Temperatures

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Abstract
Life tests on ball bearings running at 100 rpm without lubrication in hot gaseous environments under thrust loads show that their performance, worse than when running under lubricated conditions, is significantly affected by the environment. Two gases, nitrogen and carbon dioxide, are considered. In nitrogen, at temperatures of 200 C and 250 C, the load-carrying capacity was only some 2% of the capacity for lubricated operation at normal temperature, the best results being obtained with full type, cageless, angular contact bearings. In carbon dioxide, however, at 325 C and 375 C, loads of up to 30% of the lubricated capacity were achieved with deep groove, caged bearings. Similar bearings in a 16% Cr stainless steel performed even better at up to 50% of the lubricated capacity. Unlike the fatigue failures encountered under lubricated conditions, these bearing failures were by wear. The measured wear is analyzed and related to the shape of the load-life curve. It is postulated that, in carbon dioxide, bearings acquire a “lubricating” film of oxide which accounts for their better performance in this environment. Treatment with molybdenum disulfide had no beneficial effect under these conditions.

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