Patent GB-566629-A (GB)
Title: Improved methods and apparatus for electric glass working
IPC: C03B23/24
Filed: 1943-05-24
Abstract: 566,629. Electric supply. HADDAN, R. (Corning Glass Works). May 24, 1943, No. 8246. [Class 38 (iv)] [Also in Groups XI and XXIII] Current is applied to the marginal edges of a sheet of glass to fuse them by resistance of the glass and to unite them to a second sheet to form a hermetically sealed double-glazed unit. The current is applied at the four corners and is at first conducted by conducting strips along the glass edges, which strips are burned off when the glass becomes conducting. Potential is applied successively to each segment of the path to be heated for the time necessary to bring the current to a predetermined value by contacts A1, B1 C1, D1 of relays A, B, C, D, controlled by a step-by-step switch TS. The conductance of the glass is used to determine the duration of the current application to each edge in succession, and after each circuit of the edges a sequence switch SS advances one step and increases the current and consequently the temperature. During the first few cycles before the conducting strips are burned off, current is applied for a definite time and not to a predetermined value. As. the desired temperature approaches, the temperature increments are made smaller. The electrodes E1-E4 of the glass sheet 11 are supplied from an auto-transformer T9 or T11 depending on the dimensions of the glass sheet, connected to an A.C. 440 volt. supply and, through a series reactor SR supplying the primary of a step-up transformer T8, the secondary of which is connected to the electrodes E1-E4 sequentially by relays A, B, C, D. The applied voltage is partially determined by taps on the secondary T8 controlled by relays AC, AD, AE, AF under control of wiper arm W5. The primary voltage on T8 is determined by taps on T9 controlled by relays Q, W, S, T, U under control of wiper arm W4. Switching from one pair of electrodes to another is under control of a thyratron VT1 which fires when the current in the power circuit reaches a predetermined value. The grid circuit includes a transformer T3 with shunt resistance R33 in the primary circuit of T8, a voltage divider VD, and interrupting relay AP. The plate circuit of VT1 actuates relay AM and switch TS. The current value which causes VT1 to function is determined by the voltage tap on VD to which the grid is connected through wiper arm W1. In the first cycles the current is greater than that required to actuate VT1, and another timing device associated with VT2 is provided to control relay AP. Actuation of VT2 is controlled by discharge of condenser C5 through resistance R12 or R13, the former giving an appreciable time interval and the latter a very small one, under control of wiper arm W3. R12 is operative until the resistance strip is burned off and R13 thereafter. A third thyratron VT3 controls the actuation of relays AL, AM to prevent restoration of power to the electrode through relay AA before the various switching operations are completed. A.C. at 110 volts is supplied at points X and Y, and D.C. at points + and -. The circuits are shown in the condition immediately preceding a heating cycle. The cycle is initiated by closing the switch " Start " which energizes relay AN and completes a locking circuit for it. Relay AN energizes relay AA including upper break contacts of relay AM, and connects a Y terminal to cathode of VT2. Relay AA connects the 440 A.C. line to auto-transformer T9 and current is supplied to electrodes E1, E2. Since relay AT is energized, firing of VT1 is delayed. When VT1 fires, relay AM is energized and the cathode circuit of VT3 completed so that it fires after the delay due to discharge of condenser C4. Switch TS is subsequently actuated to advance its wipers 1W to 3W to their second contacts, which results in connection of electrodes E2, E3. When the cycle is completed, sequence switch SS is advanced for the next cycle. Subsequently, VT2 fires relatively quickly to sensitize the trip circuit before the heating current reaches the value to fire VTL Power supply is cut off after the number of cycles necessary to produce the desired temperature. The electrodes E1-E4 are removed by pulling out a thin filament of glass and fusing it by a short pulse of current. The switch SS is restored to the position shown by actuating switch marked "Reset." An additional switch SS1 may be provided for use in sealing together two cell parts of glass requiring a heating schedule differing from that required for heating the edges of a glass sheet.