High speed gearing, operating with low viscosity lubricants, is prone to a failure mode called scoring. In contrast
to the classic failure modes, pitting and breakage, which generally take time to develop, scoring occurs early in the
operation of a gear set and can be the limiting factor in the gear's power capability.
Much information has been written on gear inspection, analytical. functional. semiautomatic and automatic. In most
cases, the charts, (if you are lucky enough to have recording
equipment) have been explained.
Material losses and long production times are two areas of conventional spur and helical gear manufacturing in which improvements can be made. Metalforming processes have been considered for manufacturing spur and helical gears, but these are costly due to the development times necessary for each new part design. Through a project funded by the U.S. Army Tank - Automotive Command, Battelle's Columbus
Division has developed a technique for designing spur and helical gear forging and extrusion dies using computer aided
The effect of various lubricant factors on wormgear efficiency has been evaluated using a variety of gear types and conditions. In particular, the significant efficiency improvements
afforded by certain types of synthetic
lubricants have been investigated to determine the cause of these improvements. This paper describes broad wormgear testing, both in the
laboratory and in service, and describes the extent to which efficiency can be affected by
changes in the lubricant; the effects of viscosity, viscosity index improvers and, finally, synthetic lubricants are discussed. The work concludes that lubricant tractional properties
can play a significant role in determining gear efficiency characteristics.
The development of a new gear strength computer program based upon the finite element method, provides a better way to calculate stresses in bevel and hypoid gear teeth. The program incorporates tooth surface geometry and axle deflection data to establish a direct relationship between fillet bending stress, subsurface shear stress,
and applied gear torque. Using existing software links to other gear analysis programs allows the gear engineer to evaluate the strength performance of existing and new gear designs as a function of tooth contact pattern shape, position and axle deflection characteristics. This approach provides a better understanding of how gears react under load to subtle changes in the appearance of the no load tooth
In designing involute gear teeth, it is essential that the fundamental
properties of the involute curve be clearly understood. A review of "the Fundamental Laws of the Involute Curve"
found in last issue will help in this respect. It has previously been shown that the involute curve has its origin at the base circle. Its length, however, may be anything from zero at the origin or starting point on to infinity. The problem, therefore, in designing gear teeth, is to select that portion of the involute, which will best meet all requirements.
The Integral Temperature Method for the evaluation of the scoring load capacity of gears is described. All necessary equations for the practical application are presented. The limit scoring temperature for any oil can be obtained from a gear scoring test.