GB1367578A - Safety lock - Google Patents

Abstract

1367578 Safety locks O ROCCHITELLI 27 Nov 1972 [26 Nov 1971 7 March 1972 28 April 1972] 54662/72 Heading E2A A safety lock for looking and belated releasing of closure doors of machines having internal rotating parts, comprises a latch 2 associated with a door closure hook 3, the latch being held locked, during operation of the machine by a pin 6 which retains the latch in the locking position during the whole working cycle of the machine, and releases the latch after a predetermined time delay in respect of interruption of the power supply to a motor of the machine, so as to permit opening of the door only when the members subject to inertial rotation are completely at a stand-still. As shown, in the door closed position a spring- loaded latch 2 slidable in a housing 1 engages the head of a hook 3 and has, in that position, a hole 5 in alignment with a locking pin 6 an extension 9 of which passes through an electromagnet 14 into contact with a movable core 12 formed with a stem 15 mounting a piston 16 slidable in a chamber 17. Upon closing the door, the hook pivots an arm 20 which causes a push button 19 to bring a blade 18 of a microswitch into contact with a terminal 26 to energise the electro-magnet when the core 12 then moves the pin 6 into the hole 5 of the latch; a gasket 11 dampens vibrations of the core. At the end of a working cycle of the machine, a time delay, before the pin is withdrawn from the hole to release the latch, is determined by the rate of flow of air or oil through holes in the piston 16. In a modification, the moving and timing element comprises a cylindrical body 40 filled with a particular wax and surrounded by an electric resistance element 41 which when heated, upon closure of the door, expands the wax which then pushes forward the piston 38, the rod 32 and a cylinder 29 so that the pin 35 engages in the hole 5 of the latch 2. Upon stopping of the machine at the end of a working cycle current to the coil 41 is interrupted and the wax cools whereupon the rod 32 retracts under the action of the spring 36 to withdraw the pin 35.