Technikatörténeti szemle 11. (1979)
TANULMÁNYOK - Petik Ferenc: The development of material testing machines
12. Testing machine with power shafting and driving belt placement of the clamps with adjustable speed wtas permitted only by the introduction of hydraulic systems. It is surprizing, however, that in most cases water was used as pressure transmitting medium, oil did not find widespread use before the end of the century. The analogy of power shafting can be recognized in the solution employed by some laboratories, namely a central hydraulic pump with pressure storage vessels, for actuating several testing machines. The high and unstable friction of leather-packing pistons was the reason of using hydraulics only for loading the specimen, while for force measurement a separate system was employed. Maximum loads were increasing steadily. Already in 1865 a machine for the range up to 450 tons had been made for Kirkaldy’s laboratory (Greenwood and Batley). On the balance used for force measuerement, the next step of development was the mechanization of weight application. This solution is still being employed today on force standard machines where only discrete force steps are required [14]. On material testing machines the first solution of continuously increasing load application was the balance with jockey weight (Fig. 13). The jodkey weight was displaced manually by the operator as required. Later, on some machine types,jockey weight movement was mechanized, controlled by simple automatic devices. With increasing .measuring ranges balance systems became more and more complicated, several balance levers were to be employed. Various ingenuous, but mostly very complicated transmission lever systems had been developed. Knife-edge bearings were dimensioned excessively on account of dynamic effects arising at the break of the specimen. 226
