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Incidentally, in low-speed, combustion-risk situations, cages can be made from brass as well. This is to help reduce any incidence of “sparking” between balls/rollers and cage itself. The reason for a cage in first place, is to maintain distance between rollers/balls, because it is only in cases of high low to space ratios, where no space is needed that cages are unnecessary and these are low speed applications.
Other low speed bearing/plain bushings are also “steel backed” with a coating of P.T.F.E. or other plastic on them. Again, this is to give some self lubrication properties, as well as to reduce friction. P.T.F.E. happens to be excellent, as it has a low coefficient of friction.
Bearing failure is primarily due to misalignment and contamination. Of course, there are many variables, such as instances where undue load/other mechanical failure happens to be case. A common cause of failure in case of automotives, is lack of oil or insufficient oil pressure. Absence of proper cooling, generally, will bring excessive loads.
Bearing failure is all too often due to improper installation or fitting practices. Indeed, bearings can be “on way out” almost immediately. Induction coil heaters are readily available from manufacturers to ease fitting operation, and spare bearings undue trauma. Mechanical shock from abuse with a hammer has destroyed many new bearings and they are destined to fail, as little actual work will verify. Indeed, I’ve seen a case where a six-year old machine was overdue some maintenance, and got new bearing fitted six times in six months. It would have been best to leave it overdue; such was fitting skill of men involved. Even without hammer, contamination while fitting, poses massive problems. Allowing foreign bodies to migrate into bearing will have a detrimental effect.
Once fitted even, contaminants from its oil/grease/air supply can make running conditions unbearable. Clean lubricants and environments are answer, and in specific case of oil; clean filters, lines and oil itself, will provide an up-time saving.
Seamus Dolly is the webmaster at www.CountControl and his background is in engineering.