Patent GB-762030-A (GB)
Title: Control system for continuous casting
IPC: B22D11/20
Filed: 1954-06-11
Abstract: 762,030. Continuous-casting machines. BABCOCK & WILCOX CO. June 11, 1954 [June 26, 1953], No. 17262/54. Class 83 (1). [Also in Group XXXV] In continuous-casting apparatus, Figs. 1, 2 and 3, molten-metal prepared in a tilting arc furnace 20 is discharged into a tun-dish 21 delivering a slag-free stream to the open end of a continuous-casting mould 22. A continuouslyoperating motor 62, driving a screw-and-nut 28, 30, increases the angle of tilt of furnace 20 about an axis 25 to maintain the flow of molten metal. To minimize oxidation of the streams, spaces between shields 23, 24 are filled with inert gas to displace oxygen, or a gas which burns to combine with oxygen. Mould 22 is cooled by water supplied through conduits 32, 33 to a chamber 34 at the upper end of the mould. Water leaving the mould is deflected away from the casting by a deflector 35 into a housing 36 surrounding the after-cooling, guiding and supporting section 37 of the mould. For after-cooling, water is withdrawn from the lower portion of housing 36 by a pump 42 and, after passing through filters 44, is supplied through conduits 46, 47 to spray-nozzles in upright pipes 48 impinging directly on the surface of the casting. Steam is discharged through a vent 40 and excess water through a vent 40 and excess water through an overflow pipe 43. Spring-loaded guide-rolls 41 minimize outward expansion of the casting. Automatic control of casting-withdrawal. The casting is withdrawn by rolls 50 driven by a motor 49 operated intermittently. When the molten metal in mould 22 rises to a predetermined level, response of thermocouples 51 at the same level on opposite sides of the mould cause operation of an amplifier-operated electric relay 58 to start a casting-withdrawal-motor 49 and a withdrawal-timer-motor (not shown). In consequence of the withdrawal, the level of molten metal should fall and casting-withdrawal-motor 49 continues to operate until the withdrawaltimer-motor has operated a switch at its limit of travel in one direction. The level of metal then rises again until, at the predetermined level, the next withdrawal, timed by the withdrawal-timer-motor running to a limit in the opposite direction, is initiated. If the deliveryrate of molten metal is such that withdrawal does not lower the surface in the mould below the predetermined level, thermocouple 51 is arranged to maintain continuous operation of motor 49 and, after a predetermined interval, a delayed relay operates a warning-signal-light. If a solidified rim or shell of the freezing metal sticks to the upper regions of the mould during withdrawal, the temperature of thermocouple 51 is high enough for a lower-limit-contact of relay 58 to be closed. This contact co-operates with the previously-mentioned delayed relay to operate a visual or audible warning after a predetermined interval. If the molten-metal rises to a higher predetermined level, a thermocouple 60 associated with another amplifier-operatedrelay prevents overflow by reversing motor 62 to stop the flow from furnace 20. Simultaneously an electromagnetically-controlled, hydraulically-operated gear-change in the drive between motor 62 and screw 28 ensures a more rapid movement of the furnace in the reverse direction. Mechanism (not shown) is also operated to rotate tun-dish 21 about its axis 29 to stop the flow to the mould and to rotate the dish about a vertical axis so that any further discharge is to another, fixed, mould. Automatic control of pouring rate. In order to maintain constant rate of pour, a dwell-timer-motor (not shown) is started as soon as the withdrawal-timer-motor stops. The dwell-timer-motor operates a switch at the limit of its travel, and if this occurs when the withdrawal-timer-motor starts again, due to rise of the molten metal to the predetermined level, the rate of pour has the desired value. If, however, there is a period when the dwelltimer-motor and the withdrawal-timer-motor operate together, indicating that the pouring rate is too high, or if there is a period when neither motor is operating, indicating that the pouring rate is too low, a motor (not shown) runs in the appropriate direction during this period to correct the rate of pour by adjusting a rheostat controlling the speed of tilting-motor 62. To avoid hunting, a continuous comparison is made between each dwell period and the preceding one. Motors (not shown) rotated in opposite directions to an extent determined by the respective dwell-periods, operate through differential gearing to provide additional adjustment of the rheostat controlling the speed of the tilting motor, so that for a given rate of pour the. correction is less when the rate of pour is approaching the desired value than it is when the rate of pour is varying away from the desired value.