Patent GB-1285881-A (GB)
Title: Improvements in or relating to a shearing machine
Inventor: FJALLING PER ALVAR
IPC: B23D15/08
Filed: 1968-09-27
Abstract: 1285881 Shearing NORSAX AS 23 Sept 1969 [27 Sept 1968] 45998/68 Heading B3W In a reciprocating shear in which a movable blade 6 arranged at an angle to a fixed shear edge 4 on a work table 2 is automatically returned when it reaches the end of its full working stroke, actuating means are operatively connected to blade-return means so as to cause the blade to be raised on completion of the actual shearing of a workpiece if this occurs before the knife completes the full working stroke. An actuator 12 on the blade 6 operates limit switches 14 and 16 at the top and bottom of the full working stroke. The switch 16 when actuated is connected through a self holding relay 20 to a selector valve 22 so as to cause the valve to connect a pump 24 to a pressure pipe 26 leading to the lower end of hydraulic cylinders 10. The valve 22 remains open until a break impulse is received from the switch 14 by the relay 20 via lead 28, the valve then assuming a neutral position. Actuation of a manual switch 18 causes a second relay 34 to open valve 22 to pipe 36 leading to the upper end of cylinders 10 and cause the blade 6 to carry out a working stroke. At the end of the full stroke a break impulse goes to relay 34 via lead 38 from switch 16 and relay 20 is re-activated to cause blade return. Sensor means which are interposed in the line from the valve 22 to the pipe 36 comprises a piston 42, spring loaded downwards as shown and mounted on a rod 44 which carries a magnet 46 at its other end. Spaced from the magnet is an iron member 52 on a movable arm of a switch 50 connected to the relay 20 in parallel with the switch 16. When, at the start of a working stroke, the relay 34 is actuated, fluid is supplied to the top end of the cylinders 10 and to the cylinder 40 of piston 42. Only when the blade engages the workpiece does the pressure in the system cause the piston 42 to move upwards against the action of spring 48 intil the magnet engages the member 52. Immediately the workpiece has been cut through the pressure drop allows the spring to draw the piston and magnet assembly downwards, the member 52 being carried part of the way and in so doing momentarily closing the relay 20 to open the valve and return the blade. In alternative arrangements the magnet control of the switch is replaced by a mechanical snap device, or the piston rod 44 is rigidly connected to the switch 50 and an electric circuit interposed between the switch and the relay 20 to actuate the relay only when the piston is returned to its normal position by its spring. The piston may be replaced by a diaphragm. Instead of registering pressure drop the sensor means may register a change in the mechanical force transmitted to the blade 6 from the cylinders or from other drive means for the blade e.g. screw spindles. In a further alternative, the width of the workpiece is registered, the first of a series of hold downs, spaced across the whole width of the work-table 2, which engages the work-table outside the workpiece coupling in a limit switch which will initiate the return of the blade 6.