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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
The necessary properties of lubricants for axle units, focusing on requirements for gears and bearings, chemical stability, and load capacity.

Identifier  ExFiles\Box 114\1\  scan0083
Date  11th January 1937 guessed
  
It seems unfair and un-American to restrict the development of lubricants by a policy reciting arbitrary specifications either on the part of the automobile manufacturer or by special groups. The answer to this question is not readily apparent so long as confusion exists involved by distribution problems, and ignorance concerning the true requirements of lubrication.

Proper lubrication concerns both the gears and bearings, and should be related to the requirements imposed by normal service of the axle unit and not by abnormally severe demands imposed by arbitrary tests. The impracticability of having one type of lubricant for the gears and another for the bearings is quite obvious, but since the lubrication for the gears is dictated by the requirements for the gears, this lubricant shall not be harmful to the bearings. What constitutes proper lubrication and what is a proper lubricant may be stated simply:

For ordinary normal service we must have:

1. A lubricant which will provide a film between gear teeth to prevent the gears from scoring at all load, speed and temperature conditions.

2. That the lubricant will not cause of itself or contribute to wear of the gear and bearing parts.

3. That the lubricant shall have no harmful chemical activity.

Now it is apparent in analyzing the three requirements that a lubricant to fulfill the pre-requisites of item 1 shall not suffer any diminution of load capacity and shall not suffer any destructive effects from temperature or agitation and certainly shall not be affected by whatever influences that atmospheric conditions may have. In other words we find here that the lubricant must be stable during use and under the conditions with which it is used at least so far as it effects load carrying capacities. To meet the pre-requisites of item 2 over a reasonable period of time, the lubricant must be non-abrasive at the beginning and it shall not develop any abrasiveness during its use. To meet the requirements of item 3 the lubricant must have no chemical activity which will deteriorate the material normally used in axle construction. A more exacting desirability is that it possess no chemical effect beyond that existing with straight mineral oils.

We might reasonably analyze more fully these three pre-requisites, as follows:

LOAD CAPACITY

The load capacity of the lubricant is necessarily a pre-requisite established by size of the axle and its power transmitting capacity and the service to which it is subjected, the last of which only needs elaboration. What is meant by ordinary normal service is that imposed by operating the car at what might be reasonably experienced in the course of use even including those periods of extraordinary severe usage demanded in exigencies. From the designer's point of view the gear capacity is easily rated by and with sufficient accuracy the tooth loading per inch of face.

So far as load capacity of the lubricant is concerned, I am told that this may be measured by the so called "EP{G. Eric Platford - Chief Quality Engineer}" value and I have been warned that this may mean either high "EP{G. Eric Platford - Chief Quality Engineer}" index with true oily film lubrication or that it may mean a measure of the anti-welding properties of a solid film.

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