Patent GB-605443-A (GB)
Title: Improvements in or relating to induction heating apparatus
IPC: H05B6/06
Filed: 1944-09-04
Abstract: 605,443. Heating by electromagnetic induction. BUDD WHEEL CO. Sept. 4, 1944, No. 16847. Convention date, Sept. 2, 1943. [Class 39(iii)] [Also in Groups XXIX and XXXV] Induction heating apparatus, such as that described in Specification 560,630 has a single means for energising successively the starting means for the heating circuit and a yieldable closure means for the feed opening 18 of the heating coil. A fluid pressure valve forms the single starting means, which is operated by a push button and has a spring to return it to preactuating position. The heating circuit is controlled through a relay circuit which may permit removal of the work-piece e.g. a metal bar 20, but prevents re-insertion of the work-piece during the heating cycle by automaticlly closing the feed-opening on removal of the workpiece during heating. The closure means comprise laterally and linearly movable piston rods 27 with end rollers 31 for holding work-pieces of different diameters, and when the workpieces protrude from the coil, the rollers form a ground connection to the workpieces. When the bar 20 lies wholly within the furnace, rollers 31 move into contact to close the opening. Valve - actuating mechanism. - The piston rods 27 are moved apart by coil springs 28 in piston cylinders 24 and are moved together to clamp the bar 20 by fluid pressure applied through pipes 32 from a supply pipe 98 to which fluid is admitted through a threeway valve 41 actuated by a push button 42. The valve has an inlet port 45 connected to a pressure conduit 47, an outlet port 46 connected to a pipe 98 for moving the piston rods 27 and an exhaust port 44. A spring 53 urges a freely floating circular valve member 50 carrying a rubber plate 55 against an apertured side 54 of the inlet chamber 49 to close the aperture. Press button 42 moves axially against a spring 62 a valve rod 56 axially hollowed at the end to form a channel 57 and moves the floating member 50 to allow air to pass into the pipe 98. When the push button returns to its outer position at the end of a heating cycle a spring 62 moves the rod 56 away from the rubber plate 55, and air pressure in the pipe 98 is relieved through the channel 57, through an aperture 58 in its side to an exhaust port 44. Free ends 'of spring arms 65 lie under an annular flange 67 of the push button 42, which, when pushed in, closes the starter switches 124, 125 in casings 63. The button 42 has an internal spring coil 72 engaging a plate 71 slightly spaced from the end of the valve rod 56. The flange 67 of the push button has an inclined edge 76 engaging a similar edge on a pivotal member 77, so that, when the button is pushed in, the edges over-ride and a spring 79 holds the button in until released by a lever arm 80, 81 pivoted at 78. Side plates 83 are pivoted at 82 to the other end of the lever 81 and are joined by a cross pin 84 fitting in an arch 87 of an armature 86, which lifts the levers 83. 81 at the end of a heating cycle to release the push button. Alternatively the button 42 is released manually by a pluuger 93 pushed against the spring 96 to move an arm 90 on the lever 81. An extension 99 on the pipe 98 operates by air pressure a starter switch 184 controlling power supply, which is thus closed shortly after starting the closure means. Terminal bar 100 is also mounted in the valve casing. Current supply system. - Closing the doors of the furnace closes switches 179 and turning on the water cooling system closes pressure switch 117 and water temperature and flow switch 140, 141. The main switch 115 is closed and current flow is indicated by lamps 116, 118 the latter indicating current flow in the heater 119 with thermostat 120 for the cooling water to prevent condensation in the furnace. Operation of the push button closes starting switches 184, 125, 124 in that order, switch 124 being closed only momentarily and being opened on return of the push button to its latching position. Closure of switch 184 makes possible energisation of main contactor relay 181 with pilot light 182 to activate the main power relay 204 through switches 190, 191. Introduction of the workpiece closes load switch 101a and on contact with an ejector rod closes load switches 8a, 8b, thus energising antireset relay 129 with pilot light 136 and closing switches 131, 132. A closed circuit is thus established through main relay contact 127 and pilot contactor relay 121, the latter closing switches 122, 123. As switch 124 is closed only momentarily, switch 123 holds the pilot relay 121 closed. Power is supplied by switch 122 to a sequence switch 148 selecting the particular furnace to be heated and thence to timer section D. Opening of load switch 8b or 101b shifts the anti-reset relay circuit through contact 131, so that if power is withdrawn from this relay permitting opening of contact 131, it cannot again be closed until the furnace is reloaded. Load switch 7 is closed by complete insertion of the workpiece. Lines 112, 172, 175 to the timer section having been energised, locking contacts 153 are closed, timer arms 156 move to closed position at 157 and motors 152 start the timing cycle. Simultaneously relays 154 are energised closing through contacts 155 in series the circuit to contactor relay 181 with pilot light 182, as switch 184 has already been closed by the push-button. Relay 181 closes contacts 190, 191 and opens contact 127 in the starting circuit, so releasing pilot relay 121 which cannot be operated until another cycle is started, thereby releasing the sequence controller 148 from connection with the timers until the machine has been re-loaded. Current passes through contact 191 to a rectifier 192 which supplies direct current to main relay coil 204, which closes a switch 205 in the main induction heating coil circuit, and power from source 207 is applied to heating coil 17. On completion of the heating cycle the motors stop and either timer arm 156 moves from contact 157 to contact 158, the motors stop, relays 154 are de-energised and contacts 155 open to de-energise relay 181 and open contacts 190, 191. Power is thus cut off from the heating coil 17 by switch 205. Movement of either timer arm 156 to contact 158 energises solenoid 169 to open the clamping bars and starter switches 125, 184. The heated workpiece may now be removed by tongs or a foot-pedal, thereby opening the switches 101a, 8b, de-energising relay 129, opening switch 132 and unlocking time relays 151 at contacts 153. The timers cannot be restarted until relays 151 are unlocked. Signal lamps are inserted where shown. If the heating circuit be interrupted by any cause, relay 129 operates to ensure that the machine must be unloaded and reloaded before it can be re-started.