Patent GB-840595-A (GB)
Title: Improvements in or relating to induction heating apparatus
IPC: H05B6/02
Filed: 1957-12-13
Abstract: 840,595. Induction furnaces. WESTING- HOUSE ELECTRIC CORPORATION. Dec. 13, 1957 [Dec. 24, 1956], No. 38778/57. Class 39(3). [Also in Groups XXX and XXXV] An induction furnace for automatically handling and heating bars, billets and like workpieces comprises coil sections 18 secured within a cover 30 by end plates 22 and clamping members 24 Glass fibre tape covered by a layer of insulating varnish may cover the coil sections, which are formed of solid rectangular conductor welded to a hollow water-cooled tube. A stainless, preferably austenitic, steel liner 42 extends between the end plates 22, a layer of heat and electrically insulating material, e.g. ceramic felt or asbestos cloth, being provided between the coil sections and the liner, which is split longitudinally. Apparatus for feeding workpieces 8 into the furnace comprises a shoot 46, an elevator 50, and a trough 48 in axial alignment with the workpiece tunnel 20 formed by the liner ; a mechanism for pushing the workpieces into the furnace comprises a rod 56 reciprocally movable by means of an air cylinder 60. A device for locating the workpieces wholly within the tunnel 20 at the exit end of the furnace consist of an arm 72 connected to an air cylinder piston 92 which, when retracted, causes the free end of the arm to extend slightly into the furnace. A device for clamping the workpieces after they have been positioned in the furnace comprises an arm 87 secured to a rotatable shaft 89, one end of the arm being pressed on a workpiece when the piston rod of an air cylinder 96 is moved outwardly from the cylinder. Also secured to the shaft is an arm 100 carrying two thermo-couple prods 106 which bear on the workpiece nearest the exit end of furnace when the arm 87 is in its clamping position. The prods may comprise a twin prod chromel-ahamel thermocouple and are connected to a temperature controller unit containing low and high temperature thermostat contacts 136 and 138 respectively. After heating, the workpieces are discharged on to a conveyer 64 consisting of rollers 66 driven by an electric motor 70 through a gear reducer. The induction coil sections 18 are energised from transformers 32 supplied from a three-phase sixty-cycle source, the sections being connected such that the centre regions of the workpieces are heated less than the ends of the workpieces. To initiate operation of the apparatus, the circuit to a relay CAR is opened by a push button 110, a solenoid CAS being de-energised and the clamp arm 87 retracted by the piston of the air cylinder 96; the thermocouple arm 100 is also retracted. A clamp arm limit switch LSCA closes and the pusher mechanism is actuated by operation of a relay PFR and a solenoid PFS, a cold workpiece being inserted into the furnace and a heated workpiece being ejected onto the conveyer 64. A limit switch LSBC is operated momentarily by the heated workpiece and a locator arm relay LAR is operated and held, a locator arm solenoid LAS being actuated and the arm 72 extended into the furnace end by operation of the air cylinder 92. Substantially simultaneously the pusher rod 56 begins to retract as a result of de-energisation of the relay PFR and solenoid PFS. When locator arm 72 is fully extended, a limit switch LSLE is actuated, the clamp arm relay CAR and the solenoid CAS are energised and the clamp arm 87 engages with the last inserted workpiece. The contacts of clamp arm limit switch LSCA then open to allow the relay LAR and the solenoid LAS to be de-energised so that the locator arm is retracted. On full retraction of the arm, a cam member 95 associated with the cylinder 92 causes completion of a circuit through limit switch contacts LSLR and interlock relay IMC. A circuit is thus completed through a main contractor relay MCR via contacts 151 of a heat cycle timer TCH, contacts 135 of the relay IMC, high and low temperature thermostat contacts 138, 136, limit switch contacts LSLR, contacts 134 of relay IMC, and a heat-off push button switch 133 ; power is thus supplied to the coil sections 18 through relay contacts 119. When the pusher mechanism reaches the fully retracted position, contacts of a limit switch LSPR are closed to energise an elevator arm relay EAR via closed contacts 82 of a workpiece trough limit switch LSBT, and the elevator arm solenoid EAS is energised to cause a workpiece to be raised so that it will roll into the workpiece trough 48 in front of the retracted pusher rod ready for initiation of the sequence of operations by the push button 110. The heat-on cycle is terminated by opening of the contacts 138 when the temperature of the workpiece within the section 18a reaches a predetermined level as determined by the thermocouple 106. In the event that the high temperature control circuit fails, the heating period is terminated by timers TMH and TCH, and the temperature falls until the thermocouple-controlled contacts 136 close to re-energise relay MCR, and reapply power. TCH again starts timing and the cycle repeats itself until the push button 110 is operated during a cooling period to eject a hot billet. The transformers 32 may be watercooled and the primary windings provided with a tap changing arrangement to enable different sections of a workpiece to be heated to different predetermined temperatures. The coil sections may comprise hollow conductors.