GB836834A - Improvements in or relating to presses more particulary for shaping plastic materials - Google Patents

Abstract

836,834. Mechanical presses. MASCHINENFABRIK WEINGARTEN A.G. Jan. 7, 1957 [Jan. 10, 1956], No. 567/57. Class 87(2). [Also in Group XXII] A press, particularly for shaping plastics such as glass-fibre reinforced polyester resins, comprises a work table, a ram, crank drive mechanism for driving the r am in an idling stroke whereby the ram may be positioned for a shaping operation, and is characterised by means acting independently of the crank drive to impart a slow working stroke to the press whilst the crank drive for the ram is stopped in the dead centre position of the cranks. As shown, a double-crank press comprises a work table 1, columns and 3 connected at the head of the machine by a cross member 4, and a crankshaft 6 journalled in the cross member 4 and carrying pitmans 7 which act on the ram 5 at two points. The invention may be performed in any one of five ways, in each of which the ram 5 is lowered on the idling stroke to the bottom dead centre position of the cranks and stopped. (i) A worm wheel 11, united with a spindle nut 9 threaded on the spindle of a head 8 to which the lower end of a pitman 7 is pivoted, is rotated by a worm 12 operated by a motor, not shown, through a drive common to both pitmans. The desired slow working stroke is thus given to the ram 5. (ii) The bed 25 is raised by mechanical means, not shown, to give the equivalent of a slow starting stroke to the ram. (iii) Fluid is forced under pressure by a pump 15, through a pipe 13, to the underside of pistons 10, the reaction thus moving the .ram downwards. In this arrangement a differential piston 19 controls the working pressure, since the fluid . pressure forces up the piston against air in a cylinder 20, till a relief channel 21 is uncovered. Air may be admitted to, or released from, the cylinder 20 to adjust the limiting working pressure. At the end of the pressing operation a valve 17 is opened and fluid is returned, from beneath the pistons 10 to a sump by admitting air under pressure to a balancing cylinder 23 and thus raising the ram 5, either before or during the succeeding idling stroke of the cranks. Pressure fluid can also be forced from beneath the pistons 10 by raising the bed 25 by means of fluid pressure in cushions 26. (iv) In a modification of (iii), there may be a separate differential piston for each pitman, thus enabling the pressure over the surface of the ram to be adjusted. (v) The bed 25 is raised by admitting pressure fluid to the cushions 26, to give the equivalent of the required slow working stroke. The desired pressure may be sensed by a contact manometer or by a piezo-electric gauge.