Claims
- 1. A channel-type induction furnace comprising: a crucible having a lower portion housing at least a first and a second induction coil, said induction coils between separated from each other and from said lower portion so to provide at least a dual-channel with the first channel being between the coils themselves, and the second channel being between the induction coils and the lower portion;
- first and second inverters each having switch means with known turn-off-time characteristics for generating an alternating polarity output voltage across a load, the first inverter being connected to said first induction coil, and the second inverter being connected to said second induction coil;
- means associated with the first inverter for monitoring the current and detecting zero-crossing of the current in said first induction coil, and for generating a control signal in response to such detection of zero-crossing, said means generating the control signal at an interval following detection of the zero-crossing which is greater than the turn-off-time characteristic of the switch means;
- means for supplying the control signal to the switch means of the inverters to change the polarity of the inverter voltage in response to said signal;
- means associated with the second inverter for introducing a selectable delay of said control signal to the switch means of the second inverter to produce a relative phase difference between the output voltages of the first and second inverters.
- 2. A channel-type induction furnace according to claim 1, wherein said lower portion of said crucible houses a plurality of induction coils arranged into pairs with one of each of said pairs being connected to said first inverter and the other of each of said pairs being connected to said second inverter.
- 3. A channel type induction furnace according to claim 2, wherein the means associated with the second inverter for introducing a selectable delay of the control signal is capable of producing a relative phase difference of up to approximately 90 degrees between the output voltages of the first and second inverters which, in turn, produces a relative phase difference of up to approximately 90 degrees between each of the coils in each of the pairs of induction coils housed in said crucible.
- 4. A channel-type induction furnace according to claim 1, wherein the means associated with the second inverter for introducing a selectable delay of the control signal is capable of producing a relative phase difference of up to approximately 90 degrees between the output voltages of the first and second inverters.
- 5. An induction furnace comprising:
- a crucible;
- a plurality of induction coils surrounding the crucible;
- first and second inverters each having switch means with known turn-off-time characteristics for generating an alternating polarity output voltage across a load, the first inverter being connected to a first set of the induction coils, and the second inverter being connected to a second set of the induction coils;
- means associated with the first inverter for monitoring the current and detecting the zero-crossing of the current in the first set of induction coils, and for generating a control signal in response to such detection of zero-crossing, said means generating the control signal at an interval following detection of the zero-crossing which is greater than the turn-off-time characteristic of the switch means;
- means for supplying the control signal to the switch means of the inverters to change the polarity of the inverter voltage in response to said signal,
- means associated with the second inverter for introducing a selectable delay of said control signal to the switch means of the second inverter to produce a relative phase difference between the output voltage of the first and second inverters.
- 6. An induction furnace as in claim 5, wherein the switch means are silicon controlled rectifiers, and wherein the control signal is a gate pulse.
- 7. An induction furnace as in claim 5, wherein said means for generating a control signal further comprises:
- means for comparing power supplied to the first set of induction coils to a preset power level and for decreasing the interval when the supplied power is less than the preset power level.
- 8. An induction furnace as in claim 7, wherein the switch means are silicon controlled rectifiers, and wherein the control signal is a gate pulse.
- 9. An induction furnace as in claim 7, further comprising means for preventing further decrease of the interval whenever one or more parameters related to the load of the first inverter exceed a preselected limit.
- 10. An induction furnace as in claim 9, wherein such parameters may be selected from the group comprising:
- load power, inverter current, capacitor voltage, induction coil voltage, and voltage frequency.
- 11. An induction furnace as in claim 9, wherein there are four induction coils vertically separated from each other around the crucible, the first set having two coils and the second set the other two coils, the first set coils connected in parallel to each other but wound in opposite directions around the crucible, the second set coils being connected in parallel to each other but wound in opposite directions around the crucible, and one of the second set coils being located between the first coils such that the coils wound in the same direction are adjacent to each other.
- 12. An induction furnace as in claim 11, wherein the means associated with the second inverter for introducing a selectable delay of the control signal is capable of producing a relative phase difference up to approximately 90 degrees between the output voltage of the first and second inverters.
- 13. An induction furnace as in claim 7, wherein there are four induction coils vertically separated from each other around the crucible, the first set having two coils and the second set the other two coils, the first set coils connected in parallel to each other but wound in opposite directions around the crucible, the second set coils being connected in parallel to each other but wound in opposite directions around the crucible, and one of the second set coils being located between the first coils such that the coils wound in the same direction are adjacent to each other.
- 14. An induction furnace as in claim 13, wherein the means associated with the second inverter for introducing a selectable delay of the control signal is capable of producing a relative phase difference up to approximately 90 degrees between the output voltage of the first and second inverters.
- 15. An induction furnace as in claim 5, wherein there are four induction coils vertically separated from each other around the crucible, the first set having two coils and the second set the other two coils, the first set coils connected in parallel to each other but wound in opposite directions around the crucible, the second set coils being connected in parallel to each other but wound in opposite directions around the crucible, and one of the second set coils wound in the same direction are adjacent to each other.
- 16. An induction furnace as in claim 15, wherein the means associated with the second inverter for introducing a selectable delay of the control signal is capable of producing a relative phase difference up to approximately 90 degrees between the output voltage of the first and second inverters.
- 17. A method of controlling the power supplied to an induction furnace by two or more inverters, each having switch means responsive to a control signal for generating an alternating polarity voltage across a load, said switch means having known turn-off-time characteristics, and in which furnace a first inverter is connected to supply power to a first set of induction coils, and each other inverter is connected to supply power to a different associated set of induction coils, comprising the steps of:
- monitoring the current in the induction coils supplied by the first inverter,
- detecting the zero-crossings of said current,
- generating a switch means control signal after a delay interval of predetermined duration following detection of each zero-crossing of the current, the duration of the delay interval being greater than the turn-off time of the switch means,
- supplying the control signal to the switch means of each of the inverters to supply power to each of the induction coils which is essentially in phase coincidence with the power supplied to each other coil,
- operating the induction coils in phase coincidence until a significant portion of a metal charge in the furnace melted, then
- delaying the control signals supplied to the switch means of the inverters other than the first inverter by a selected interval to create a relative phase difference between the induction coils sufficient to produce stirring wave motion in a melted metal charge.
- 18. A method as in claim 17, further comprising the steps of:
- determining the duration of the delay interval by comparing the power supplied to the first set of induction coils to a preset power level, and
- decreasing the duration of the interval when the supplied power is less than the preset power level.
- 19. A method as in claim 18, further comprising the steps of:
- comparing one or more parameters related to the load of the first inverter to a preselected limit, and
- preventing decrease in the duration of the delay interval when a parameter exceeds its preselected limit.
- 20. A method of controlling the power supplied to an induction furnace by two inverters, each having switch means responsive to a control signal for generating an alternating polarity voltage across a load, said switch means having known turn-off-time characteristics, in which furnace there are four induction coils vertically separated from each other around a crucible, a first inverter is connected to supply power to a first pair of the induction coils, and the second inverter is connected to supply power to a second pair of the induction coils, the first pair of coils being connected in parallel to each other but wound in opposite directions around the crucible, the second pair of coils being connected in parallel to each other but wound in opposite directions around the crucible, and one of the second pair coils being located between the first pair coils such that the coils wound in the same direction are adjacent to each other, comprising the steps of:
- monitoring the current in the first pair induction coils,
- detecting the zero-crossings of said current,
- generating a switch means control signal after a delay interval of predetermined duration following detection of each zero-crossing of the current, the duration of the delay interval being greater than the turn-off time of the switch means,
- sending the control signal to the switch means of both inverters to supply the second pairs of induction coils with power that is essentially in phase coincidence with the power supplied to the first pair,
- operating the induction coils in such phase coincidence until a portion of a metal charge in the crucible has melted, then
- delaying the control signals supplied to the switch means of the second inverter by a selected interval to create a relative phase difference between the induction coils sufficient to produce stirring wave motion in the melted metal charge.
- 21. A method as in claim 20, further comprising the step of progressively delaying the control signal supplied to the switch means of the second inverter until the relative phase difference between the induction coils is sufficient to produce a running wave from the bottom of the crucible to the surface of the melted metal.
- 22. A method of controlling the power supplied to an induction furnace by two inverters, each having silicon controlled rectifiers (SCR) responsive to a gate signal for generating an alternating polarity voltage across a load, and said SCRs having a known turn-off-time, in which furnace there are four induction coils vertically separated from each other around a crucible, a first inverter is connected to supply power to a first pair of the induction coils, and the second inverter is connected to supply power to a second pair of the induction coils, the first pair of coils being connected in parallel to each other but wound in opposite directions around the crucible, the second pair of coils being connected in parallel to each other but wound in opposite directions around the crucible, and one of the second pair coils being located between the first pair coils such that the coils wound in the same direction are adjacent to each other, comprising the steps of:
- monitoring the current in the first pair of induction coils,
- detecting the zero-crossings of said current,
- generating a gate signal after a delay interval following the generation of each signal pulse,
- comparing the power supplied to the first pair of induction coils to a preset power level,
- reducing the duration of the delay interval when the power supplied is less than the preset power level,
- limiting the minimum duration of the delay interval to a duration greater than the turn-off time of the SCRs,
- supplying the gate signals to alternating SCRs in each inverter to change the polarity of the inverter voltages at essentially the same time to supply power to the second pair of induction coils which is essentially in phase coincidence with the power supplied to the first pair,
- operating the induction coil pairs essentially in such phase coincidence with each other until a portion of a metal charge in the crucible has melted, then
- progressively delaying the gate signals supplied to the SCRs of the second inverter by a selected interval to create a phase difference between the induction coils sufficient to produce stirring wave motion in the melted metal charge.
Parent Case Info
This application is a continuation-in-part of Ser. No. 07/732,869 filed Jul. 19, 1991, now abandoned, which, in turn, is a continuation-in-part of Ser. No. 07/503,335 filed Apr. 2, 1990, and now abandoned.
US Referenced Citations (12)
Continuation in Parts (2)
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Number |
Date |
Country |
Parent |
732869 |
Jul 1991 |
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Parent |
503335 |
Apr 1990 |
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