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The New Zealand Railways Magazine, Volume 5, Issue 2 (June 2, 1930)

Unsuitable Lubricants

Unsuitable Lubricants.

(6) The mechanical conditions, the operating conditions, and the lubricant used must conform one to the other in order that correct lubrication may be accomplished. A bearing once correctly lubricated may become incorrectly lubricated through a change in either the conditions or the lubricant.

The use of an oil, too light or too heavy in body for the existing mechanical and operating conditions, is one of the most common sources of bearing trouble that can be ascribed to the lubricant. For low speeds, heavy pressures, and poor film-forming conditions, the heavier-bodied oils are required; since a light-bodied oil would be squeezed out from the pressure area and fail to maintain a complete oil film. High speeds, light pressures, and good film-forming conditions call for oils of lighter body. The use of an oil too heavy in body results in excessive fluid friction and heating of the bearing.

Oil quality not suited to the service is also a frequent cause of trouble. Failure to use the special grades in a circulation or splash system will lead to breakdown of the oil film and the ultimate failure of lubrication. Where special conditions of high or low temperatures exist, the oil selected must have the specific qualities demanded for the service.

The use of a pure mineral oil for wet bearings may result in failure of the oil film, because the mineral oil will not adhere to a wet surface. Correctly compounded oils of suitable body should be used for this purpose. Heavy-bodied compounded oils are frequently advantageous in bearings subjected to excessive loads, on account of the strong adhesive properties resulting from compounding.

The use of grease on bearings subjected to high speeds and moderate loads, frequently leads to excessive film friction and high bearing temperatures. This effect is the same as that of using an oil with a body that is much too heavy.

Troubles caused by the use of an unsuitable lubricant are the result of failure to observe the principles set forth in earlier parts of this article. The application of these principles, through a correct analysis of the mechanical and operating conditions involved, will lead to the selection of the correct lubricants, and the avoidance of bearing troubles.

Two bottle oilers mounted on bearings where cleanliness is demanded.

Two bottle oilers mounted on bearings where cleanliness is demanded.