Hardness values, gears

The viscosity of Newtonian and non-Newtonian materials increases exponentially with an increase in pressure. However, these changes are extremely small, and under atmospheric conditions of lbar, they are hardly detectable. Hence, the pressure is normally not controlled during rheological measurements. In some circumstances, the pressure exerted on, for example, oils and lubricants, can take up values in excess of 1 GPa (oil rigs, lubricants in gears), and the increase in viscosity is substantial. In such applications, it is thus required to consider the pressure as a factor when studying their rheological properties. 

The fineblanking process produces a hardened surface around the formed sections. The resulting value of hardness depends on a distance from the sheared surface and from the die roll side. At the surface, it amounts to an increase of as much as 100% of the core hardness. It decreases as it gets closer to the burr side. This is an advantage when a hardened material is needed for improved function (i.e., gears, cams, holes exposed to pressure and/or wear). 

Table P-7 gives values of Sc for commonly used gear materials. The rating of a gearset should be based on the softer of the two members, which is normally the gear. The Brinell hardness of the pinion in through-hardened gearsets is usually about 1.2 times that of the gear.

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