The Wear of Crankshafts with “Lead-Bronze” Bearings 400131
CASE-HARDENING is a satisfactory means of reducing crankpin wear with “lead-bronze” or copper-lead bearings, the authors reveal. They report the results of tests to determine the relative wearing properties of various crankshaft materials when running against a typical copper-lead alloy bearing at a temperature of 212 F.
In general and contrary to what was observed with the softer crankpin materials, bearing wear occurred more rapidly than crankpin wear, they divulge, this result being due largely to high initial wear of the bearings during the early part of the tests. Variations in composition-percentage of lead and tin, and hardness-of the copper-lead bearings did not have a marked effect on the wear obtained, they find.
The crankpin materials tested, which were all ground-finished, are specified as: a nickel-chrome steel, heat-treated; a nickel steel, not heat-treated; a nickel-chrome-molybdenum steel, both heat-treated and not heat-treated; a carbon steel, both heat-treated and not heat-treated; three cast materials; three chromium-plated materials (two not ground); three other surface-hardening treatments, namely, carburizing, a proprietary hardening process, and nitriding.
The testing machine used for the research is virtually a dummy engine in which the bearing under test was inserted in the big end of the connecting rod so that, when the machine was driven at a given speed by an electric motor, the big end was subjected to inertia forces the magnitude of which could be calculated.