An Experimental Crank Press

An account is given of the technical problems which arose in the design of an experimental single-action, double-sided crank press of tie-rod construction which has been built for use in the deep-drawing researches carried out in the University of Sheffield. This press was required to have a specified capacity of 20 tons during the second half of the down-stroke and 50 tons during the last inch of the down-stroke. To cover the drawing speeds of industrial practice, a variable speed of 5–60 strokes per min. and a variable stroke of 3–10 inches were specified, and to maintain a close control over the speed, the slowdown at any speed over the whole range was limited to 10 per cent. An air cushion and also an automatic means for stopping the press at top dead centre after each stroke and for interrupting the stroke at any prescribed point in order to obtain partially drawn pressings for examination and measurement were incorporated. Speed variations are obtained through a transmission system consisting of a substantially fixed speed electric motor with a fixed gear to the flywheel, and a variable gearbox between the flywheel and the main gears of the press. It is shown that, from the functional points of view this is the most satisfactory system of power supply and transmission for a variable speed press. Two safety devices are embodied in the press: a shear plate in the ram to protect the crankshaft and a shearing pin in the first reduction gear wheel to protect the gearing. The design of these devices is described in an Appendix.