Technikatörténeti szemle 11. (1979)
TANULMÁNYOK - Petik Ferenc: The development of material testing machines
16. Hydraulic testing machine (Factory of Material Testing Machines, Budapest) Manchester had built a machine Where the pressure medium of the hydraulic loading device was used also for load measurement, by means of a spring- type manometer. Packing friction was a source of error, therefore independent hydraulic dynamometer systems were preferred, with so-called hydraulic gauges with connected spring-type, or, in some cases, mercury column manometers. These could be employed only at lower pressures, or measured pressure was reduced by transmission pistons (Amsler). In the 1890s, a jockey- weight balance was connected to the hydraulic measuring gauge of the Emery testing machine in the USA. Hydraulic dynamometers permitted a practically unlimited increase of measuring ranges. By the Phönix Iron Co in America a machine for 1200 tons maximum load was built already in 1891. Concerning measurement accuracy, Professor A. Martens [4] wrote in 1898 as follows: „Published data on the calibration of testing machines indicate that the generally accepted accuracy of 10% can be ensured on machines being in everyday use, but higher requirements can hardly be set.” Today we .already know that in those years the idea was already ripe, which permitted to improve this accuracy value to one tenth, namely to 1%, as current in our days. The invention that revolutionized hydraulic load measurement was Ama- gat’s piston without packing. Between long cylindrical surfaces both sealing and lubrication are ensured by an oil’film. Thus pressure in the hydraulic system exerting the testing load can be directly used for measuring the load, by means of a pendulum manometer. By employing this invention, at the turn of century, the universal testing machine design generally used up to our days (Fig. 1) was developed, first at Amsler’s. The pressure cylinder is arranged atop, below it the compression testing room, while the tensile testing room is at the bottom. Pendulum manometer is assembled as a separate unit. jÄ * 229
