AUTOMOTIVE rear - axle gears present one of the most difficult gear-design and lubrication problems that are known, Mr. Almen emphasizes in this paper. The requirements are exacting, he explains, because (1) the weight must be held to a minimum; (2) the cost must be low; (3) the dimensions must be small; (4) the heat input is great; (5) the temperature is high, and (6) hypoid gears with their greater sliding velocity must be used.
Early in his paper Mr. Almen establishes the hypothesis that lubricant failure in gears and other highly loaded surfaces results in welding of small areas of the mating surface for the following reasons
- 1.
The rubbing action removes weakly adhering films permitting contact between clean metal surfaces.
- 2.
The temperature of a thin surface layer is very high from the friction of sliding under high load.
- 3.
Welding of two surfaces can occur at temperatures considerably below the melting point of a metal if the pressure is great.
- 4.
Welding will not occur if a sufficiently tenacious contaminating film is formed on the rubbing surfaces.
Explaining his title - “The Dimensional Value of Lubricants in Gear Design” - Mr. Almen points out that, as a result of the modern demand for more intensive use of structural materials, many design details are dependent upon specially compounded lubricants, and these lubricants have thus become inseparable parts of the design.
Considerable data, including three-dimensional charts, are presented to show the effect on the scoring limit of the lubricant, the pressure, the temperature, the sliding velocity, and the hardness.
