Intermittent molten metal delivery
View Patent ↗Automated processes that dynamically control rate of delivery of molten metal to a mold during a casting process. Such automated processes can use dynamic metal level variation, control pin pulses and/or oscillation during the mold fill and transient portion of the cast. It has been found that such pulses keep metal flowing in a manner that addresses problems, particularly at the beginning of an ingot cast, associated with metal meniscus contracting and pulling away from the mold on the short faces and corners.
1. A mold apparatus for casting metal, comprising:
a mold;
a conduit configured to deliver molten metal to the mold, the conduit controllably occluded by a control pin;
a positioner coupled to the control pin;
a level sensor configured to sense level of molten metal in the mold; and
a controller coupled with the control pin positioner and the level sensor, the controller programmed to:
accept input in the form of at least a metal level setpoint; and
provide to the positioner, a command signal that includes a plurality of pulses that modulate flow or flow rate of molten metal through the conduit such that the level of molten metal in the mold remains in a molten metal level range of between 5 mm above and 3 mm below, inclusive, the metal level setpoint and such that the level of the molten metal in the mold is increased so as to exceed the metal level setpoint by less than 5 mm above the metal level setpoint as a result of each pulse of the plurality of pulses.
2. An apparatus according to claim 1 wherein the controller is configured to provide to the positioner, a command signal that includes a plurality of pulses that modulate flow or flow rate of molten metal through the conduit such that the level of molten metal in the mold remains in a molten metal level range of between 3 mm above and 1 mm below, inclusive, the metal level setpoint.
3. An apparatus according to claim 1 wherein the controller is configured to provide to the positioner, a command signal that includes a plurality of pulses at a frequency of between 3 and 4 pulses per minute, inclusive, or a plurality of pulses with a minimum of between 15 and 20 seconds between pulses, inclusive.
4. An apparatus according to claim 1 wherein the molten metal is molten aluminum.
5. An apparatus according to claim 4 wherein the controller is configured to provide a command signal wherein the pulses begin at a cast length of 50 mm.
6. An apparatus according to claim 4 wherein the controller is configured to provide a command signal wherein the pulses end when the cast length is between 400 and 500 mm.
7. An apparatus according to claim 1 wherein the controller is a proportional-integral-derivative (PID) controller that includes a PID algorithm for casting of aluminum, the controller configured to accept or determine at least one metal level setpoint.
8. An apparatus according to claim 7 wherein the controller is configured to provide a command signal wherein the pulses occur only if (1) the level of molten metal in the mold is at or below a predetermined metal level setpoint AND (2) the controller is not sending a command signal to the positioner of less than or equal to 5% open.
9. An apparatus according to claim 7 wherein the controller is configured to provide a command signal wherein the pulses occur only if (1) the level of molten metal in the mold is at or below a predetermined metal level setpoint AND (2) the controller is not sending a command signal that causes the controller to issue a hangup alarm signal.
10. An apparatus according to claim 7 wherein the controller is configured to set the command signal to 100% open for a duration of 3 seconds during a pulse, after which the command signal returns to control under the PID algorithm.
11. An apparatus according to claim 1 wherein the positioner is configured, in response to at least some of the command signal pulses, to open to between 30% and 50% open in 3 seconds.
12. An apparatus according to claim 1 wherein the controller is configured to cause the level of the molten metal in the mold to rise to about 3 mm above metal level setpoint as a result of each pulse, and between pulses, prior to the next pulse, to drop to about 1 mm below metal level setpoint under the control of the PID algorithm as a result of undershoot.
13. An apparatus according to claim 1 , wherein the command signal is further characterized in that the plurality of pulses modulate flow or flow rate of molten metal through the conduit such that:
between the pulses of the plurality of pulses the level of the molten metal in the mold is maintained less than 3 mm below the metal level setpoint.
14. An apparatus according to claim 2 , wherein the command signal is further characterized in that the plurality of pulses modulate flow or flow rate of molten metal through the conduit such that:
the level of the molten metal in the mold is increased so as to exceed the metal level setpoint by less than 3 mm above the metal level setpoint as a result of each pulse of the plurality of pulses.
15. An apparatus according to claim 1 , wherein the command signal is further characterized in that the plurality of pulses modulate flow or flow rate of molten metal through the conduit such that:
between the pulses of the plurality of pulses the level of the molten metal in the mold is maintained less than 1 mm below the metal level setpoint.