Patent GB-832120-A (GB)
Title: Improvements in or relating to controlling the flow of molten glass through a furnace forehearth
IPC: C03B7/02
Filed: 1957-11-11
Abstract: 832,120. Delivering molten glass. OWENSILLINOIS GLASS CO. Nov. 11, 1957 [Nov. 9, 1956], No. 35025/57. Class 56. In a forehearth having a channel through which molten glass is conveyed from a furnace to a mould-charge forming apparatus, a movable flow control element is disposed in the channel between the furnace and the forming apparatus and is moved by operating means which are actuated by means responsive to the level of molten glass in the channel in order to maintain a constant predetermined level of molten glass in the channel. As shown a horizontal forehearth 10, Fig. 1, is provided with a channel 11 through which molten glass 12 flows to a conventional gob feeder. The depth of glass in the forehearth and its rate of flow are controlled by a skimmer block 20 which extends downwards into the channel 11. The skimmer block 20 is raised and lowered by a piston motor 22 to which the block is connected by a horizontal lever 23 and screw-threaded telescopic connections. A vertically disposed probe 40, Fig. 3, extends downwards through a hole in the forehearth roof and carries at its lower end a platinum electrode 41 which makes electrical contact with the glass 12. The probe is periodically moved up and down by a motor 44, a rocker bar 411 and link connections 55 and 40c between paralell bars 42-43, the arrangement ensuring that the probe 40 is held vertical during its movements. Cooling fluid may be circulated through the probe. Temperature regulating devices 125 are provided to maintain the temperature of the molten metal in the forehearth at a constant level. The motor 44 not only controls the movement of the probe but also the operation of a pen driving motor of a recording instrument. When the electrode 41 makes contact with the glass the motor 44 is stopped momentarily and the pen driving motor is rotated to move the pen to a position corresponding to the level of the glass. Thus the position of the pen driving motor and its shaft depends upon the glass level. The electrical circuits are shown in Fig. 9. The motor 44 is two winding : application of power between points 2-4 drives the probe downward, and between points 2 and 5 drives the probe upward. Safety switch 151 opens by a cam when the probe reaches an extreme low position, and a similar uplimit safety switch 152 is also provided. Power is supplied from mains a and b. Voltage is supplied through a transformer T having its primary connected across a and b. The transformer T, rectifier tube 130 and condenser 131 constitute a full wave filtered power supply furnishing D.C. voltage for operating the rest of the electronic control unit, which includes relays R1, R2 and a thyratron 132. The contact arm 134 of a potentiometer 133 has a mechanical driving connection 135 with the motor 44 or the probe operated by it, the contact arm 134 oscillating about its pivot with the movement of the motor. The level of the glass in the forehearth is recorded by a recorder 136 operated under the control of motor 44 and potentiometer 133. This recorder includes a pen driving motor 137 and a clockwork operated chart driving motor 138. When the probe 41 touches the molten glass 12 there is a low resistance between the probe and the ground. As soon as the upward motion breaks contact the voltage across resistor 143 supplies a negative bias to the thyratron through resistors 147 and 146. Relay R2 is energised, its' cirucit being closed by contact 148 and contact bar 149, thyratron 132 and up limit switch 150. This limit switch opens on the upward stroke before the extreme limit switch 152 would open. Relay R1 is de-energised at the same time. As switch 150 opens the thyratron is cut off and breaks the circuit for relay R2. Contact bar 159 of relay R2 completes a circuit through lead 160 to point 4 of motor 44. The motor is reversed, probe 41 is driven downwards and limit switch 150 closes, the negative bias on the thyratron preventing energising of the relays R1 and R2. When the probe touches the hot glass the bias to the thyratron is reduced because the resistance between the probe and ground is lower than that of resistor 147. The thyratron conducts, energises relay R1 and charges condenser 161, and the contact bar 162 completes a circuit for relay R2 which operates so that the contact bar 154 opens the circuit of relay R1. Operation of R2 de-energises the downside of motor 44. The charge condenser 161 keeps R1 closed for a brief time, and as soon as this charge is dissipated R1 is de-energised. During the period that the circuit for R1 remains closed, motor 44 is stopped owing to contact bar 158 opening and the pen drive motor 137 is energised, the pen moving to a position corresponding to that of the arm 134 of the potentiometer, that is, to a position corresponding to the level of the glass at the probe tip. When relay R1 opens, contact bar 158 completes the circuit for the motor 44 to move the probe upwards and the cycle repeats. The automatic means by which the operation of the piston motor 22 is controlled by the movement of the pen drive shaft includes an air line control mechanism of known construction.