GB681476A - Improvements in and relating to power operated presses, press-brakes, guillotine shears and like machines - Google Patents

Abstract

681,476. Guillotine cutting-machines. CROUCHER, A. H. Feb. 5, 1951. [Feb. 10, 1950] No. 3497/50. Class 31 (i). [Also in Group V] A mechanically-actuated guillotine cutting- machine is provided with a plurality of hydraulic links between the working tool of the machine and the thrust-applying part of the actuating mechanism, each hydraulic link being provided with a relief valve to limit the thrust transmitted thereby and with means including a hydraulic pump, continuously driven when the machine is in operation, for restoring the link to a working condition after an operation of the relief valve. Fig. 2 shows a single link in the case of a press. The actuating mechanism, which may be of a type using a crank, eccentric, toggle or other device, is connected by a member 40 to a closed cylinder 9. The working tool 2 is connected to the piston rod 11 of a piston 10 which works in the cylinder 9, the piston and cylinder constituting the "hydraulic link". The motor which drives the actuating mechanism also drives a pump 6 immersed in a hvdraulic fluid reservoir 8. The relief valve 13 is a "balanced pressure" valve, one side, of smaller area, communicating with the space 14 in the cylinder above the piston and the other side, of larger area, communicating through a conduit 34 with the pump 6. The pump pressure is supplemented by a spring 35. Most of the conduits are flexible, to allow for relative movement between different parts, the hydraulic pressure being low except in the space 14 within the cylinder. The control valve included in the restoring means is essentially a reversing valve for applying hydraulic pressure to one side or other of the piston 10, and comprises a movable member 17 which, in the neutral position shown, closes a number of ports cut in the body of the valve which, as shown, is one with that of the cylinder. The member 17 is operated by movement of the piston through a multiplying lever 19, by which a small movement of the piston causes a large opening of the valve, i.e., the sensivity is increased, one end of the lever 19 being connected by a link to the member 17 and the other pivoted to an arm 24 rigid with the valve and cylinder body. The piston rod is connected to a tube housing a "funk spring" 20, and surrounding a rod 23 which carries an adjustable stop 25. The stop 25 engages a member 26 attached to a pin 27 in the lever 19, and alteration in the position of the stop 25 affects the movement of the valve member 17 and results in adjustment of the working stroke of the machine. Movement of the piston not used in operating the valve is taken up by the funk spring 20. When the operating mechanism bears downwards on the member 40 the "hydraulic link" is constituted by fluid under pressure in the space 14. On the occurrence of overload, such as would be caused by the machine jamming, the fluid pressure rises and is sufficient to open the relief valve 13 against the pressure of the pump, through the conduit 34, and the spring 35. The "hydraulic link" then collapses by the cylinder 9 sliding over the piston 10 and overstrain is thus prevented. The upward movement of the piston rod relative to the cylinder casing is accommodated by the spring 20, which is thus compressed ready to restore the ",hydraulic link" to working condition. On the upstroke the pressure in the space 14 vanishes. Previously this pressure held a plunger 22 against the member 17 and kept it in the neutral position, but at its release the expansion of the spring 20 moves the member 17 to a position where pump pressure is communicated to the space 14 and the original relationship of the piston 10 and cylinder 9 is restored. The weight of the member 2 combined with the pressure above the piston might cause the latter to overshoot its original position, but this is counteracted by the consequent movement of the member 17 bringing the space 12 below the piston into communication with the pump 6, through conduit 38 and the hollow piston rod. A dashpot may also be introduced to controlthe rate of re-positioning of the funk spring or valve, e.g., as at 46, Fig. 4, and so to obviate hunting. To ensura that pressure in excess of the pump pressure cannot be fed back-through the control valve to the pump, which might wipe out pressure difference on which the functioning of the valves depends, a non-return valve 37 is fitted. Expansion of the spaces 14 and 12 might cause cavitation in the fluid therein, and to guard against this suction valves 30, 31 are arranged so that fluid can be temporarily sucked into these spaces from the reservoir. To avoid loss of fluid due to leakage a sump 28 is provided, attached to the piston rod 11 and slidable over the cylinder 9, enclosed by a flexible cover 39, a conduit 29 providing a feed back to the reservoir 8. Where there are double rams, one at each end of the working tool, as in the guillotine cutting-machine, two hydraulic links 3, 3a are used, Fig. 4. If the pressure came on one end only of the tool 2 one ram might collapse under overload but the other would not follow suit, and to obviate the strain which would thus be set up the hydraulic links are mechanically connected by levers 42, 43 so that, if one ram collapses, it operates the control valve of the other which then follows suit under power from the pump. The levers 42, 43 cross one another and are pivoted at their place of intersection to a block which slides on a rod 45 attached to the tool. Provision may be made for tilting the guillotine knife to an adjustable angle by varying the position at which the levers 42, 43 are pivoted by forming in them internally toothed slots 49 and passing a pinion 50 through them where they intersect, the pinion being rotatable by a handle 51. The Specification mentions that the working stroke of the machine may also be made adjustable by mounting the body of the control valve in a slide and varying its position by a nut engaging a screw rotatable by a handwheel, and that the valve may be of the rotary type. Safety guards may be arranged to cause the hydraulic links to collapse in an emergency. The hydraulic power source can be used to operate clutches, brakes and other auxiliary equipment.