Analysis of the Ball Clutch Mechanism of D-Type Shore Hardness Tester

Abstract

It is observed by means of a differential transformer how the hammer of D-type Shore hardness tester is caught in the ball clutch at its height of rebound. The observations made under various conditions show that the hammer vibrates up and down at a frequency of 140∼280c/s before it stops at a little lower height than the height of rebound. The difference between the height of rebound and that of stop is dependent on the tester and hammer and is 0.02∼0.11mm. The variation of the difference over a long period is significantly greater than that over a short period, which amounts to the greater part of the dispersion of shore hardness number usually observed. A crude theory on the mechanism of the ball clutch is developed to explain the observed movement of the hammer in it.