JPS63317238A - Continuous levitation type casting polyphase power - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates generally to metal melting and casting techniques, and more particularly to a method for magnetically levitating metal for continuous casting of metal articles. The present invention relates to a device for supplying multiphase power to an induction coil.

BACKGROUND OF THE INVENTION Levitation casting of continuous metal articles is a relatively new and original continuous casting technique that uses an electromagnetic levitation field to support and contain solidified metal in the form of a cylinder. It is. By counteracting the gravitational and hydrostatic pressures acting on the metal cylinder, floating casting can completely eliminate friction and adhesion forces at the interface between the solidified metal and the cooling wall of the heat exchanger. Floating casting, combined with the smooth continuous emergence of solidified product from the top of the casting chamber, inherently allows for high speed casting and excellent dimensional control.

Moreover, flotation casting produces intense electromagnetic stirring of the molten metal before and during solidification, allowing for immediate drawing without hot rolling or other expensive additional treatments. ) or other molding operations, resulting in a homogeneous, equiaxed cast product. Floating casting is particularly well suited for the economical continuous casting of various pure metals and alloys into rods or other shapes.

Floating casting is already a known technology. In flotation casting, a column of molten metal is moved into a forming zone where it is slowly cooled and solidified, during which time the column of molten metal is cooled and solidified as needed to remove the resulting cast product from the forming zone. The metal is exposed to an electromagnetic field that reduces the force, thereby casting the metal into continuous lengths. The effect of this electromagnetic field is to suspend and maintain the column of molten metal over a significant portion of its length, especially in the area where solidification occurs, without being in continuous pressure contact with the walls of the container in which it is contained. . The levitation is carried out by means of moving electromagnetic waves supplied to the columnar body upward, such that most of the length of the columnar body is maintained in a state of release from a continuous pressure state;
It is therefore essentially weightless throughout the entire casting operation.

This flotation and retention effect is such that a continuous column of molten metal is established and held essentially weightless over most of its length and out of contact with the physical mold structure. , used at the same time.

[Problem to be Solved by the Invention] The electromagnetic field that provides the levitation force is generated by an induction coil. The levitation force acting on the metal being cast depends on both the magnitude of the current induced in the metal and the frequency of the induced electromagnetic field. The required levitation force is a function of the mass of the metal to be levitated (which is a function of the diameter of the rod being cast) and the resistivity of the metal (which is a function of the particular metal being cast). Therefore, it is necessary to control the frequency of the electromagnetic field and the amplitude of the current induced in the metal being cast so that the proper amount of levitation force can be generated by the induction coil. It would also be desirable to be able to individually adjust the frequency and current of the induction coil to compensate for the mass and resistivity of the molten metal.

OBJECTS OF THE INVENTION Accordingly, the present invention provides a polyphase power source whose frequency and current output can be adjusted to match the resistivity and mass of the molten metal being cast and to create a continuous buoyancy force on the metal. It provides a phase power supply and an induction levitation coil.

Means for Solving the Problems The present invention is an apparatus for supplying multiphase power to an induction coil for magnetically levitating metal.

The apparatus includes input means connected to a polyphase alternating current power source and polyphase rectifier means for rectifying the alternating current (AC) power.
MS) Selectively varying the magnitude of the current by controlling the electrical phase of the rectifier means. Polyphase inverter means is operatively connected to the rectifier means to convert the rectified AC power into a polyphase A having a preselected frequency.
C power and supplies this multiphase power to the induction coil. A second control means, independent of the first control means, controls the frequency of the AC power supplied to the induction coil by controlling the electrical phase of the inverter means.

The invention also includes a levitation casting apparatus for magnetically levitating metal, and includes an induction levitation coil and a power supply means for supplying polyphase power to the coil, the power supply means comprising a polyphase power supply means for supplying multiphase power to the coil. input means connected to an alternating current power source;
multiphase rectifier means for rectifying the C power; first control means for selectively varying the magnitude of the 8MS current supplied to the induction coil by controlling the electrical phase of the rectifier means; polyphase inverter means operatively connected to the rectifier means for converting the rectified AC power into polyphase AC power having a preselected frequency and supplying the polyphase power to the induction coil; A second control means independent of the first control means is provided for controlling the frequency of AC power supplied to the induction coil by controlling the electrical phase of the inverter means. The coil has a plurality of sections, each section being wound to provide a phase rotation of the magnetic force vector over substantially the entire length of the coil to produce a continuous magnetic levitation force.

For the purpose of illustrating the invention, the invention is shown in the drawings in a presently preferred form, but the invention lies in the exact construction, arrangement and arrangement shown.
It should also be understood that the invention is not limited to the embodiments.

[Embodiments] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

With reference to the accompanying drawings in which like reference numerals indicate like elements:
One embodiment of a flotation casting apparatus 10 with which the present invention may be used is shown in FIG. Apparatus 10 is generally designated by the reference numeral 12.
It is equipped with a floating casting section as shown in the figure. Floating casting part 1
2 is mounted on the substrate 14 and extends vertically upward from the substrate 14. The molten metal to be cast is passed through a vertical delivery tube 1, as will be explained in more detail later.
6. The delivery tube 16 delivers molten metal to a multiphase levitation coil and heat exchanger assembly 18. The vertical delivery tube 16 is equipped with a conventional induction heating coil 20 for maintaining the molten metal at the required casting temperature.

The levitation coil and heat exchanger assembly 18 includes a multiphase levitation coil, detailed below, and also includes upper and lower annular plenums and a levitation coil and heat exchanger assembly. Although this structure is not shown in FIG. 1 for simplicity, it includes a cylindrical portion that contacts the outer surface of body 18 and fits around the liner of this assembly. It is well known in the technical field. A cooling liquid, for example tap water, is continuously supplied from a source to the upper plenum, flows through the cylindrical part and drains to a drain via the lower plenum. This coolant is supplied to the flotation coil and heat exchanger assembly 18.
through which the heat absorbed from the molten metal and the newly solidified successive casting is discharged together. As one skilled in the art will appreciate from U.S. Pat. No. 4,414,285, the molten metal solidifies in some arrangement within the levitation coil and heat exchanger assembly 18.

The solidified continuous casting emerges from the upper end of the flotation coil and heat exchanger assembly 18 and enters a cooling chamber (not shown). The cooling chamber includes pairs of counter-rotating pinch rollers that continuously cut the cast product to length or coil it, or otherwise further Transport this cast product to a location where it will be processed.

Still referring to FIG. 1, the apparatus 10 includes an air core induction furnace 22.
and a suitably shaped housing containing the housing. Air core induction furnace 22 includes a refractory crucible 24 surrounded by an induction heating coil 26. The air core induction furnace 22 is installed on a base 28. Molten metal may be added to crucible 24 from a conventional melting furnace 30 through crucible inlet 32 .

Molten metal 34 within crucible 24 is supplied to floating casting section 12 through a trough or conduit 36.

This conduit 36 connects the furnace outlet 38 to the vertical delivery pipe 16.
Connect to. Conduit 3 as well as vertical delivery tube 16
6 is equipped with a conventional induction heating coil 40 to maintain the molten metal at the required temperature required for casting.

The level of molten metal 34 within crucible 24 is controlled by a displacer mass 42 . The displacement body 42 may be constructed of a refractory and electrically conductive material so that it can be heated by induction. Suitable materials include, but are not limited to, graphite, carbon-bonded silicon carbide, and refractory metals.
It is lowered into and withdrawn from the molten metal 34 to change the level of molten metal within the molten metal 24. The molten metal in the crucible 24 is in hydrostatic communication with the molten metal in the levitation coil and heat exchanger assembly 18 such that the hydrostatic head created by the level of molten metal 34 in the crucible 24 causes the levitation coil to and the molten metal in the heat exchanger assembly 18 seeks to obtain the same level as the molten metal in the crucible 24. By controlling the level of molten metal in crucible 24, both a constant flow of metal and control of the molten metal level in floating casting section 12 can be achieved.

Although the foregoing description of device 10 is sufficient for understanding the present invention, a more detailed description of device 10 is provided below.
No. 925.013, filed October 30, 1986, and assigned to the same assignee as the present application.

Referring now to Figures 2A and 2B, there is shown in block diagram form a polyphase power supply 5o according to one embodiment of the present invention capable of supplying the required polyphase power to the levitation coils. This device 5o has six main components: input means 52, polyphase rectifier 2 (means 54, first control means 56).
, a multiphase impark means 58, a second control means 60 and an inductive levitation coil 62, as well as a number of secondary components, all of which will be described in detail below.

Input means 52 may be any conventional means for connecting device 50 to a polyphase AC power source, typically a 50Hz or 60Hz three-phase AC power source commonly supplied by a local power company. Although the present invention is illustrated in connection with a conventional three-phase AC power source, it should be understood that any conventional multi-phase AC power source may be used without departing from the present invention.

The polyphase AC input is preferably, but not necessarily, connected to the rectifier means 54 through a line disconnect and transient protection circuit 64, which is connected to the rectifier means 54 in case of unexpected power surges or other provided on each power line to act as a disconnect and fault protection device to protect the device 50 from potentially dangerous electrical failures.
For example, circuit breakers and fuses may be provided, and if necessary, normal R
A C (resistor-capacitor) snubber circuit and MOV may also be provided.

Rectifier means 54 is an SCR phase control bridge whose purpose is to generate and control direct current (DC) current to inverter means 58. The rectifier means 54 consists of six conventional phase controlled SCRs. Although omitted from Figure 2A for clarity, each SCR may be shunted with a conventional RC snubber circuit for protection against transients and dv/dt! Each SC of the single flow device means 54
The phase control signal for R is the first one in the manner described below.
control means 56.

Although not required, rectifier means 54 is preferably operatively coupled to inverter means 58 through a current limiting and discharging circuit 66, which is illustrated in more detail in FIG. and a conventional current limiting axle 68 connected in series in the positive (+) output line between the inverter means 58 and the inverter means 58 . This current limiting accelerator 68 acts as a filter to supply a constant current to the inverter means 58, and also operates to limit the increase in current in the event of a fault condition. This protects the rectifier means 54 and allows the circuit breaker in the transient protection circuit 64 sufficient time to trip before the fuse blows. The current limiting and discharging circuit 66 also includes a discharging diode to protect against reverse voltage in the event of a power outage. An RC snubber circuit 74 is provided to suppress high voltage transients generated by inverter means 58. Additionally, a discharge resistor 76 provides an electrical path for discharging the capacitor of the snubber circuit.
is provided.

Referring to FIG. 2B, inverter means 58 is preferably a three-phase variable high frequency automatic sequential commutation inverter;
A sinusoidal current with a phase shift of 120" is generated. The inverter means 58 consists of two complete inverters connected in parallel between the DC input side and the AC output side. Each half of the inverter means 58 The three SCRs, diodes, commutating capacitors, and DI/DT reactors present in the circuit have complementary components in the other half. Each half is connected in parallel to provide the required current. 2nd B
Although omitted from the figure for clarity, each SCR and diode is preferably shunted by an RC snubber circuit to suppress dv/dt and transients.

Next, the operation of the inverter means 58 will be explained. The SCR is gated in response to a control signal from the second control means 60. (Generation of control signals will be explained later.) For activation, 5CR6 and 5CRI are gated simultaneously. This charges the commutating capacitor C1 connected between 5cR6 and SCR4, and the 5C of this capacitor CI
The side connected to R6 becomes positive. Commutation capacitor c2 connected between 5CRI and SCR5 is also charged, and the side of this capacitor c2 connected to 5CR5 becomes positive.

Current flows from the positive DC line through 5CR6, diode D6 and their di/dt reactor 78 to transformer connection T1, and then through the load (levitation coil 62) from transformer connection T3 to SCR1, diode DI and their di/dt. dt reactor 80 to the negative DC line.

5CR4 is gated after a delay of 60 electrical degrees. This causes commutation capacitor C1 to apply a reverse voltage across 5CR6, turning 5CR6 off. This results in 5
Commutation capacitor C3 connected between CR4 and SCR2 is charged, and the side of this capacitor C3 connected to 5CR4 becomes positive. The current is now 5CR from the positive DC line
4, diode D4 and their di/dt reactor 82 to transformer connection T2, and load, transformer connection T3.5CRI, diode D1 and their d
It flows through the i/dt reactor 80 to the negative DC line.

5CR5 is gated after a delay of 60 electrical degrees. This allows commutating capacitor C to be connected between SCR1 and SCR5.
2 applies a reverse voltage across SCR1, and this SCR1
turn off. This charges commutation capacitor C4 connected between 5CR5 and 5CRa, and the side of capacitor c4 connected to 5CR3 becomes positive. Here the current is from the positive DC line to 5CR4, diode D4
and through their di/dt reactors 82 to transformer connection T2, and further to the load, transformer connection T1.5CR
5, through diode D5 and their di/dt reactor 84 to the negative DC line.

5CR2 is gated after a delay of 60 electrical degrees. As a result, commutating capacitor C3 between 5CR4 and SCR2 becomes 5CR
A reverse voltage is applied across 5CR4 to turn off 5CR4. This charges the commutating capacitor C5 connected between 5CR2 and SCR6, and this capacitor C5
The side connected to 5CR2 becomes positive. Now the current flows from the positive DC line to 5CR2, diode D2 and its
to the transformer connection T3 via their di/dt reactor 86 and further to the load, transformer connection T1.5CR5, diode D5 and their di/dt reactor 84.
to the negative DC line.

5CR3 is gated after a delay of 60 electrical degrees. As a result, commutation capacitor C4 between 5CR5 and SCH3 becomes 5CR
A reverse voltage is applied across 5CR5 to turn off 5CR5. This charges the commutating capacitor C6 connected between 5CR3 and SCR1, and this capacitor C6
The side connected to SCR1 becomes positive. Here current flows from the positive DC line through 5CR2, diode D2 and their di/dt reactor 86 to transformer connection T3.
and then through the load, transformer connection T2.5CR83, diode D3 and their di/dt reactor 88 to the negative DC line.

5CR6 is gated after a delay of 60 electrical degrees. As a result, the commutating capacitor C5 between 5CR2 and SCH6 becomes 5CR
A reverse voltage is applied across 5CR2 to turn off 5CR2. This charges the commutating capacitor C1 connected between 5CR6 and SCH4, and this capacitor CI
The side connected to 5CR6 becomes positive. Here the current flows from the positive DC line through the transformer connection T1 through 5CR6, the diode D6 and their di/dt reactor 78.
to the load, transformer connection T2.5CR3, diode D3 and their di/dt reactor 88 to the negative DC line.

SCR1 is gated after a delay of 60 electrical degrees. This allows commutating capacitor C to be connected between 5CR3 and SCR1.
6 applies a reverse voltage across 5CR3, and this 5CR3
turn off. This charges commutation capacitor C2 connected between SCR1 and SCH5, and the side of capacitor C2 connected to 5CR5 becomes positive. The inverter means 58 now returns to the activated state and the gating of the SCR proceeds sequentially as described above until the inverter means turns off.

Although omitted from FIG. 2B for simplicity, those skilled in the art will appreciate that the inverter means 5 is used to prevent the commutating capacitors C1 to C6 from discharging through the load.
It will be noted that a blocking diode may be provided at 8.

The output of the inverter means 58 is preferably connected to the induction coil 62 by an impedance matching transformer 90 which typically matches the load impedance of the induction coil 62 and isolates the induction coil 62 from the inverter means 58. A Y-connection isolation transformer with a variable voltage tap may be used.

The magnitude of the RMS current supplied to the induction coil 62 is controlled by the phasing of the SCR of the rectifier means 54. A phase adjustment signal for the SCH of the rectifier means 54 is generated by the first control means 56. This control means 56 has 12
It is a conventional three-phase gate circuit that generates three sets of output pulses separated by zero electrical degrees. These pulses control the phase of the rectifier means by adjusting the phase of the SCR within the rectifier means. These output gate pulses are phase shifted relative to the input control reference signal from manual control potentiometer 92 or to a computer-generated reference signal from computer control system 94. The reference signal generated by the computer can be selected by switch 96. The output gate pulse is an RM signal that senses the RMS value of the output current of the inverter means by a current sensing transformer 100.
The S vs. D vs. So C feedback circuit 98 is controlled. An ammeter 102 may be provided to display and/or record the sensed current value. A first control means 56 maintains a constant current to the levitation coil, which is necessary for a given casting speed for the particular metal and rod diameter being cast. If the casting parameters change, the controlled current can be adjusted by potentiometer 92 or computer control system 94 to provide the optimum levitation current.

The first control means 56 can also limit the input line current to a maximum predetermined level by limiting the phase angle of the gate pulse. A signal proportional to the input line current value is generated by the current sensing circuit 104 from the output of the current sensing transformer 106 associated with one of the AC input lines to the rectifier means 54. If a fault condition occurs on the load side of the rectifier means 54, the SCR within the rectifier means 54 is turned off by inhibiting or clamping the gate pulse.

The variable frequency gate pulses necessary to control the inverter means 58 are generated by the second control means 60. The frequency of these gate pulses is variable from IKHz to 3KHz. This frequency is manually controlled potentiometer 1
08 or the input reference signal generated by the computer control system 94. This reference control signal can be selected by switch 110. The reference control signal is provided to a voltage controlled oscillator (VCO) 112. If desired, suitable conventional frequency limiting circuitry 114 may be provided to limit the minimum and maximum VCO output frequencies, and a frequency meter 116 may be provided at the output of the VCO to display and/or record the output frequency. .

The output of VCO 112 controls gate pulse sequencing circuit 118. These circuits 118 divide the VCO output into six phase shifted firing sequence pulses. These pulses drive the ignition circuit 12 which drives the SCR ignition module 122.
given to 0. The SCR ignition module 122 provides appropriate signal levels to the inverter means 58 and isolates the inverter means 58 from the second control means 60.

The induction levitation coil 62 may consist of 3.4.6 or more sections. Each of these sections is wound to provide the correct phase rotation of the magnetic force vector within the coil to create a continuous electromagnetic levitation force on the casting being produced.

For example, the coil 62 may consist of six sections wound and connected as shown in FIG. and six phases φ1, φ2, each separated by 60 electrical degrees as shown in FIG.
φ3, -φ1, -φ2, and -φ3 are generated. This creates a magnetic force vector in the coil that has a continuous phase rotation to provide a continuous upward levitation force on the metal being cast.

Because the current in the coil 62 and the frequency of this current can be independently preset, the present invention allows for easy casting of a wide range of rod sizes and materials, allowing for rapid switching between different metals and between different diameters. becomes.

Since the present invention may be embodied in various other specific forms without departing from its spirit or essential attributes,
The scope of the invention should be determined by the claims, rather than by the foregoing description.

4, ti 8 Fig. 1 is a schematic configuration diagram showing one form of a floating casting device in which the present invention is used, Figs. 2A and 2B are simplified block diagrams of the present invention, and Fig. 3 is a schematic diagram showing one form of a floating casting device in which the present invention is used. FIG. 4 is a simplified circuit diagram of the current limiting circuit used; FIG. 4 is a timing diagram showing the waveforms generated by the circuit shown in the block diagram of FIGS. 2A and 2B.

10: levitation casting apparatus 12: levitation casting section 14: substrate 16: vertical delivery tube 18: levitation coil and heat exchanger assembly 20: induction heating coil 22: air core induction furnace 24: refractory crucible 26 : induction heating coil 28 : base 30 : melting furnace 34 : molten metal 42 : displacement body 50 : polyphase power supply device 52 : input means 54 : polyphase rectifier means 56 : first control means 58 : polyphase inverter means 60 Second control means 62: Inductive levitation coil 64; Line disconnection and transient protection circuit 66: Current limiting and discharging circuit 68: Current limiting actuator 4: RC snubber circuit 90: Impedance matching transformer 94: Computer control system 98: RMS vs. D vs. SoC feedback circuit 100
06: Current sensing transformer 102: Ammeter 104: Current sensing circuit 112: Voltage controlled oscillator (VCO) 114: Frequency limiting circuit 116: Frequency meter 118: Gate pulse sequencing circuit 120: Firing circuit 122: SCR firing module -FIG, 2B Kenichi

Claims (7)

[Claims] (1) an induction levitation coil (60) and a power supply means (50) for supplying multiphase power to the coil, the power supply means being connected to a multiphase AC power source (50);
2) and polyphase rectifier means (5) for rectifying the alternating current power.
4) and first control means (56) for selectively varying the magnitude of the effective current supplied to the induction coil by controlling the electrical phase of the rectifier means;
a polyphase inverter operatively connected to said rectifier means for converting rectified alternating current power into polyphase alternating current power having a preselected frequency and supplying said polyphase alternating current power to said induction coil; means (58) and a second control independent of said first control means for controlling the frequency of alternating current power supplied to said induction coil by controlling the electrical phase of said inverter means. Means (6
0), and the induction coil has a plurality of sections (
φ1 to −φ3), each section being wound to effect a phase rotation of the magnetic force vector over substantially the entire length of the induction coil to generate a continuous magnetic levitation force. Type casting equipment. 2. The flotation casting apparatus of claim 1, wherein said first and second control means are responsive to separate manually selected input signals. 3. The floating casting apparatus of claim 1, wherein said first and second control means are responsive to input signals generated by separate computers. 4. A floating casting apparatus according to claim 1, wherein said first and second control means are selectively responsive to separate manually selected input signals or separate computer generated input signals. . (5) A floating casting apparatus according to claim 1, wherein said rectifier means comprises an SCR phase control bridge circuit. (6) A floating casting apparatus according to claim 1, wherein said inverter means comprises an automatic sequential commutation inverter. (7) The floating casting device according to claim 1, wherein the induction coil has two windings per unit position, and these two windings are connected in series in opposite directions.