JP3811817B2 - Electromagnetic plugging of hot dipping pan - Google Patents

Abstract

A hot dip coating pot (2) having a strip inlet passage (3) and electro-magnetic plugging means to prevent leakage of bath liquid from the pot through that passage, wherein: the plugging means comprises two magnetic field generators (7) disposed one on each side of the passage; each generator projects an oscillating magnetic field into the passage from at least two poles of opposite polarity that are adjacent the passage and spaced apart in the through direction of the passage; the said at least two poles of each generator are respectively in substantial alignment with the corresponding poles of the other in the transverse direction of the passage; the magnetic fields projected by the generators have flux patterns which are substantially mirror images with reference to a plane of reflection coinciding with a centre plane of the passage; and both generators operate at a frequency of more than seven kiloHertz. When no strip is present the fields combine and extend transversely of the passage. When a strip is present the fields not only plug the passage but also provide restraining forces to prevent deviation of the strip from its intended pass line.

Description

Technical field
The present invention relates to a pan used to hold a bath of molten metal used for continuous hot dipping of metal strips with a liquid metal coating. It was developed for use in continuous hot dip plating of steel strips, where the coating metal is essentially zinc. However, it will be apparent that it can be applied in any situation as long as the substrate strip is metal and the coating is a liquid metal, such as a hypereutectic aluminum zinc alloy or other alloys.
In particular, the present invention is directed to an electromagnetic plug means that prevents the bath agent from leaking out of the pan in the case of a pan having an opening below the surface level of the liquid during normal operation.
Background art
In the conventional continuous galvanizing process, the steel strip is fed from above into a hot dip zinc or zinc-based alloy bath after cleaning and other adjustments to accept the coating adhesion. The strip passes around a so-called “sink roll” submerged in the bath, then exits the bath and passes between the film thickness control devices, which returns the excess liquid coating to the bath. The coating is then allowed to solidify and the coated strip is finally coiled for storage, other processing or sale.
Sink rolls are submerged in tanks and operate in harsh environments, causing problems and reduced reliability unless carefully maintained. Even with proper maintenance, wear and tear are inevitable and require periodic replacement. In addition, the strips can pull up the dregs from the surface of the bath, and the dregs tend to adhere to the sinking roll and form a coarse alloy growth on the surface of the roll. The lines need to be stopped frequently because the scum and growth can damage the strip and remove the sinking roll and replace it with a new or repaired roll. Therefore, it is desirable to remove the sinking roll.
In view of this desirability, the strip to be coated enters the pan from the horizontal or bottom and exits from a similar outlet opening or pan mouth without having to change the direction of the strip's passage line in the bath. It has been proposed to place at least one inlet opening for the pan below the normal use level of the bath.
Needless to say, it is necessary to prevent the bath agent from flowing out from one or more openings, and various electromagnetic plug means have been proposed.
For convenience of description, liquid metal surfaces that are supported or otherwise limited by forces generated by electromagnetic plug means rather than the solid components of the pan will be referred to hereinafter as “exposed” surfaces of the liquid metal. Call it.
Previously proposed electromagnetic obturator means usually use two categories: multi-phase energized windings or multi-pole electromagnets and switching devices that provide a moving magnetic field through the liquid or the space through which the liquid flows. And means similar to electric motors using permanent magnets or DC or single-phase electromagnets in combination with transverse currents. All such electromagnetic obturator devices utilize the interaction of current and magnetic field generated either alone or induced by the other, where the current oscillates at DC or commercial frequency, and the magnetic field oscillates at steady or commercial frequency as well. In either category of plugging means, a magnetic field and / or current passes through the bath near the opening and generates a limiting force.
Previously proposed electromagnetic obturator means of the type described above require a relatively complex assembly of components to be intimately associated with the liquid metal, and therefore all at high temperatures, often in crowded environments. Will work. Therefore, the design is difficult, the size and shape of the opening to be plugged are limited, and the service life is shortened.
All these previously proposed plugging means are also defective in operation. For example, the means of using a direct current flowing between electrodes in contact with the liquid metal, for example, to generate buoyancy in the liquid so that it does not fall from the inlet of the strip is inherently unstable. If a downward protrusion localized by chance is formed on the exposed surface of the liquid metal, the current density at the protrusion becomes lower than the average current density of the exposed surface as a whole. Therefore, the upward electromagnetic force applied to the protrusion is reduced and increased by the hydrostatic pressure. The larger it is, the less the recovery force, and the protrusions will eventually detach from the exposed surface as bath drops. After detachment, no current flows through the drop, the resilience applied to it drops to zero, and the drop falls through the opening. In fact, with such plugging means, if the exposed surface is disturbed in any way, it usually produces a continuous drop of rain, which causes enough disturbance each time it drops, and another drop To form.
Also, all such prior art proposals operating at commercial frequencies produce a liquid flow in the tank near the opening. Thus, the bath becomes confused at that location in contact with the strip to be coated, and this disruption significantly degrades the surface quality of the finished coating.
Finally, state that the device under consideration has or generates a strong magnetic pole near the opening, which tends to interact with the iron substrate strip and attract the strip in the direction of the pole. I have to do that. Coincidentally, deviating from the center pass line to one pole and away from the other pole increases the attraction of the strip to one pole and decreases the attraction to the other, thus increasing the deviation As a result, the deviation force increases. Thus, it is clear that the state is inherently unstable. After all, to operate successfully with a steel strip, it is necessary to place an expensive guide roller near the opening to maintain an undesirably high tension on the strip to prevent deviations, which is actually easy Is not achieved.
In view of the above disadvantages and what can be termed zero or commercial frequency embolic devices, such devices are not widely accepted or used in the metallization industry.
According to another prior art proposal, an electromagnetic field that vibrates at high frequency but is spatially fixed is arranged to exclude the bath agent from the opening of the pot. This proposal makes use of the fact that such an electromagnetic field generates a high-frequency overcurrent in the tank. Due to the high frequency, the overcurrent flows only in a thin surface layer of liquid (the so-called “skin effect”). The reaction between the surface current and the electromagnetic field is a type of mutual repulsion, and at sufficiently high frequencies, the electromagnetic field is effectively excluded from penetration into the liquid. In such an environment, the electromagnetic field behaves as an elastic cushion, which is distorted or compressed by the exposed liquid surface, but resists the penetration of liquid into the space occupied by the electromagnetic field. This resistance force is perpendicular to the exposed surface of the liquid and the direction of the electromagnetic flux and is proportional to the degree of distortion or compression of the electromagnetic field. Thus, unlike interactions at relatively low frequencies, if the liquid surface accidentally protrudes into the electromagnetic field space, it will cause local distortion of the electromagnetic field, concomitantly increasing local resistance and further penetration. Is inherently unstable.
Furthermore, if there is no current or electric field in the body of the bath agent, no disruption is induced in the liquid by the operation of the plugging means.
Thus, the high frequency embolic means overcomes the major drawbacks of zero or low frequency embolic means, but are subject to their own inherent limitations.
Especially when generating sufficient force perpendicular to the exposed liquid surface to resist hydrostatic pressure at the bottom of a liquid metal bath deep enough to allow reliable continuous strip coating operations to proceed. A magnetic field of density is required. This requires a high energy generating coil and it is recommended to use pans and pan opening shapes and dimensions that minimize the degree of exposed liquid area to be supported or otherwise limited. . For this reason, at least the inlet opening of the strip needs to provide only a small clearance as the strip passes through. This requires care to ensure that the strip does not deviate significantly from the intended pass line.
A plating pan having a conceptually high-frequency electromagnetic plug means is disclosed in Japanese Patent No. 04-099160 (Japan Steel Pipe). In this case, the “pan” is a rectangular prismatic cell of silicon carbide that is hollow, about 100 mm wide and about 20 mm wide in the floor. The steel plate moves upward through the slot and through the plating tank contained in the cell. The lower part of the cell is surrounded by a solenoid coil, energized at 20 kHz, with a vertical center plane coinciding with the cell center plane. A slot is set on one side of the center plane. For this reason, it is stated that the lower part of the bath is pushed toward the center plane of the cell and leaves the slot, but does not affect the upper part of the tank. The steel strip to be plated is shown moving upward through the slot and the top of the bath.
Noting that the 20 kHz electric field is effectively excluded from the bath and strip, it is clear that the field of this device is asymmetric with respect to the strip in the coastal zone just above the slot. In fact, due to the shielding effect of the strip, even if there is an electromagnetic field inside the strip that pushes liquid back from the inside of the strip just above the slot, it is very weak. This prior art proposal has three drawbacks. That is, (i) the above-described asymmetry results in a very unbalanced lateral force on the strip and a special arrangement and undesirably high tension in the strip to ensure that the strip does not come into contact with the narrow slot walls. (Ii) Since there is no electromagnetic field near the inside of the strip, the liquid falls through the slot inside the strip, and (iii) the exposed surface area of the liquid is large, so a large capacity and high density electromagnetic field is required. As a result, a high output is required for the power generation coil. It is thought that (i) and (ii) can be overcome by centering the slot position. In practice, this removes the unbalanced force on the strip caused by the embolic field and can prevent leakage if the strip is in the slot, but the strip is still free from the passing line laterally. It is possible to move. More importantly, the portion with the highest electromagnetic field density in the bore of the coil is nearly vertical in the natural state, so orientation to provide vertical restraint is not successful. Thus, in the absence of a strip, restraining utilizes a relatively low density diverging electromagnetic field at the top of the solenoid. For this reason, in order to effectively prevent leakage, an extremely high output coil that generates an unnecessarily dense electromagnetic field is required.
Disclosure of the invention
The object of the present invention is to provide a hot dipped pan having a high-frequency electromagnetic plug means that overcomes at least the above-mentioned drawback (i) of the previously proposed high-frequency electromagnetic plug-clad pan, and in a preferred embodiment alleviates the drawback (ii). Is to provide.
The present invention provides a stabilizing force to the strip to prevent the strip from deviating from the intended passage line through the plugged opening, and rather than the previously known plugging means of this type. The object is achieved by providing a high-frequency type plugging means that more effectively prevents liquid metal leakage in the absence of liquid metal.
The present invention resides in a hot dipping pan having a strip inlet passage and electromagnetic plug means for preventing leakage of bath agent through the passage.
The plug means comprises two magnetic field generators, one on each side of the passage,
Each generator generates an oscillating magnetic field into the passageway from at least two poles of reflected polarity spaced in the direction through the passageway adjacent to the passageway,
The at least two poles of each generator are each substantially aligned with the other corresponding pole in the transverse direction of the passage;
The magnetic field generated by the generator has a magnetic flux pattern that is approximately a mirror image of the reflective surface that coincides with the central plane of the passageway,
Both generators operate at frequencies above 3 kilohertz.
As a result of mutual alignment with the mirror image flux pattern, the generated magnetic field provides an equivalent repulsive force on the opposite side of the centrally disposed strip when the strip is in the path. As the strip deviates from the center of the passage, the magnetic field further compresses on one side and the other magnetic field expands, generating a restoring force that reduces the repulsive force and returns the strip to the center position.
All magnetic field generators must have at least two magnetic poles spaced apart to generate a magnetic field. The poles are always of opposite polarity, and the generated magnetic field extends along an infinite flux path from one to the other. These poles may be real (the solid body where the magnetic field diverges) or virtual (the location of the space where the magnetic field diverges). Thus, in order to generate a mirror image magnetic field in the passage according to the present invention, each generator is adjacent to the passage and spaced in the direction through the passage, as described above, and the other generator is aligned with the corresponding pole. Must have at least two poles of opposite polarity.
However, there are additional limitations in the preferred embodiment of the present invention. That is, the polarity of each aligned pole is that the generated magnetic fields combine when there is no strip in the path, and the combined magnetic field passes from each pole of one generator to the corresponding pole of the other generator. It must ensure that it extends in the lateral direction.
By using two high frequency generators as described above, such a change in the magnetic field pattern is possible. This change provides a major advantage of the present invention. In one pattern, the combined magnetic field extends laterally through the passage, and ideally this magnetic field is arranged to plug the passage at full width when the passage is open due to the absence of strips. In the other pattern, the magnetic field extending along the passage on each side of the strip not only plugs the narrow passage space on each side of the strip, but also reacts to the strip, making it generally centered in the inlet passage. Maintaining, thereby allowing the use of a narrow inlet passage with low strip tension.
The invention extends to a continuous molten strip coating line or likewise to a metal coating equipment, where the plating pan is a pan according to the invention.
Conventional coating lines must be large enough to accommodate the sinking roll and allow it to be partially or fully immersed in the liquid coating metal. An advantage of the present invention is that the pan can be made much smaller than previously possible. Thus, hereinafter, the term “pan” is a small but elongated bowl-like shape that performs somewhat the same function as before, although somewhat different in shape and size from the conventional concept of conventional prior art pans. Including containers.
[Brief description of the drawings]
By way of illustration, some embodiments of the invention described above are described in detail below with reference to the accompanying drawings.
FIG. 1 is a schematic cross-sectional view of the bottom of a coating pan according to the present invention showing the magnetic field pattern established when there are no strips to be coated.
FIG. 2 is a view similar to FIG. 1 showing the magnetic field pattern established when the main objects and strips of that view are present.
FIG. 3 is a perspective view of a pair of electromagnetic field generating coils which are components of the pan of FIG.
FIG. 4 is a view similar to FIG. 3 of an alternative coil pair.
FIG. 5 is a schematic cross-sectional view of the bottom of a coating pan according to another embodiment of the present invention showing the magnetic field pattern established when there are no strips to be coated.
FIG. 6 is a view similar to FIG. 5 showing the magnetic field pattern established in the presence of the main object and strip of the view.
FIG. 7 is an enlarged schematic cross-sectional view of the yokes and strips of the components visible in FIGS. 5 and 6 and showing the dimension designations referred to elsewhere in the description.
FIG. 8 is a view similar to FIG. 6 of another embodiment of the present invention.
Best practice mode of invention
As shown in FIGS. 1 and 2, a hot strip pan in a continuous strip coating line includes a bath 1 of molten metal coating material such as zinc or an alloy of aluminum and zinc. The pan has a floor 2 with a downwardly directed duct 3 of generally rectangular cross section, defining a strip inlet passage 4 that provides clearance for the metal strip 5 to be coated to enter the pan.
The strip 5 is guided by a roll (not shown), enters the pan from below, and moves upward through the tank 1. Prior to reaching the passage 4, the strip 5 may be cleaned to receive the coating and adjusted in other conventional ways. Thus, the steel strip is passed through the passage 4 from a furnace having a controlled reduction state, for example, through a hood (not shown), which also contains a reducing atmosphere or at least an inert atmosphere 6, for example. Supply by conventional methods. As the strip 5 exits the tub 1, it is also completely processed in a conventional manner into a finished product. Therefore, the line device before and after the covering pan may be conventional in all respects except for providing a roll for transporting the strip from the bottom to the pan and the shape of the hood described above.
The pan may be made of ceramic or other refractory material such as alumina stabilized by titanium, silicon carbide or boron nitride.
Two high-frequency electromagnetic field generators composed of the coils 7 are respectively arranged on opposite sides of the duct 3. These coils may be arbitrarily selected from one or the other of the coils shown in FIGS. 3 and 4, for example. This is illustrated in cross-section in FIGS. 1 and 2, the cross-section being taken along line XX in FIGS. 3 and 4.
In each case, each coil 7 is a single-turn coil composed of an upper coil side conductor 8, a lower coil side conductor 9 and a coil end conductor 10. The coils are connected to each other by interconnecting conductors 11 and are fed by a supply conductor 12 that extends to a terminal 13. In the arrangement of FIG. 3, the interconnect conductor 11 is a conductor in which two coils are in series, and in the arrangement of FIG. 4, the coils are in parallel.
In either case, the coil preferably extends firmly from the terminal 13 as a self-supporting cantilever. Thus, the coil can be made from a copper tube, preferably a tube with a non-circular cross-section, such that the coil side conduits 8 and 9 each present a broad flat surface towards the adjacent surfaces of the pan and duct. For example, a coil can be created from a hollow rectangular cross section (HRS). The joint between the coil conductors is preferably brazed with a bronze alloy.
The terminal 13 may be the length of a copper tube adapted to be clamped by a tube pressing formation in or on a rigid power supply bus that extends to the high frequency power transformer. As shown at 14 in FIG. 3, the terminal is cut at an inner thread at the lower end, and a part of the terminal is cut off to receive a coolant supply hose (not shown), so that the coolant during operation of the coil 7 is removed. You can circulate it.
From the above, it is clear that the instantaneous current directions of the two upper coil side conductors 8 are always the same. Similarly, the instantaneous direction of the lower coil side conductor 9 is always the same direction and is always opposite to the direction of the upper conductor.
Thus, the coils are of the same polarity and each coil 7 can be regarded as having three virtual poles spaced longitudinally in the passage 4, that is to say that it is a region 15, a lower part just above the upper coil side 8. An area 16 just below the coil side 9 and an area 17 at the center of the coil. As indicated by the arrows on the magnetic flux lines shown in FIGS. 1 and 2, the electromagnetic fields of the virtual poles 15 and 16 are always in a common direction (that is, the direction toward the passage 4 at a specific moment), and the electromagnetic fields from the virtual pole 17 Is the opposite direction (direction always away from the passage 4 at that moment). Virtual pole 17 can be viewed as a single pole having twice the strength of each of virtual poles 15 and 16 or two adjacent poles corresponding to poles 15 and 16, respectively.
In the absence of strip 5, the corresponding poles of the two generators are closely aligned with each other, and in the case of a simple identical air core coil of an embodiment of the present invention, coincides with the axial alignment of the coils. The electromagnetic field generated by the coil ensures that both coils are linked. Further, in the case of the current of the same coil, the transverse component of the electromagnetic field has a value twice that generated by any one of the coils acting alone.
More importantly, in the absence of a strip, the alignment of the poles 15 prevents a portion of the electromagnetic field from extending from one side to the other laterally relative to the passage and preventing liquid from the bath from descending through the passage. Is to provide. This can be seen in FIG. 1, where the associated flux lines bend downwards depending on the liquid pressure where they cross the passage, but the repulsive force on the exposed surface of the liquid is still essentially higher. Heading to
In general, since the repulsive force between the high-frequency electromagnetic field and the liquid is effective at the boundary surface between the electromagnetic field and the liquid, only the electromagnetic field of the pole 15 is directly effective as a plug, and therefore it is necessary to match the longitudinal direction of the passage. There are only these poles and the part of the pole 17 corresponding to each. Thus, in this embodiment and other embodiments having a simple coil as the electromagnetic field generator, the coil is arranged such that at least its upper coil side conductors are aligned with each other in the direction of travel of the strip. That is, if the strip moves vertically through the duct, the upper coil side is in the same horizontal plane. In particular, the lower coil side can be further away from the passage, for example, it may be on the same horizontal plane as the upper side as appropriate. In other embodiments, the arrangement can be further varied to maximize the electromagnetic field at a position below the pole 17 and utilize the electromagnetic field from that pole to float the liquid.
This complementary polarity and at least the matching of the upper coil sides with each other means that in the absence of strips, the horizontal component of the generated magnetic flux across the duct just below the pan floor 2 is maximized. This is a critical feature of this embodiment of the invention. This maximizes the lift acting on the exposed surface of the liquid metal 1 at the duct entrance.
The coil 7 is energized by an alternating voltage source, preferably with a constant amplitude and a frequency of at least 3 kHz, preferably above 7 kHz.
When strip 5 is present, the electromagnetic field from each generator coil is generally limited to the passage and that portion of the strip on the coil side of the center plane of the strip. Next, the generated electromagnetic field conforms to the mirror image pattern shown in FIG. 2, and the electromagnetic field from each pole 15 enters the passage somewhat in the horizontal direction and then turns, so that the vertical direction of the passage and the strip by a certain distance. After that, the direction is changed again to leave the passage in a slightly lateral direction, and toward the pole 17.
The electromagnetic fields generated from poles 15 and 17 then serve to plug the passages on each side of the strip. In this regard, it must be specified that both the strip and the electromagnetic field provide complete containment of the liquid since the electromagnetic field penetrates the strip, albeit very shallowly.
In any case, the magnitude of the energization voltage required to plug the passage depends on the physical parameters of the equipment (eg, the width of the passage, the width of the strip, the number of turns of the energizing coil, etc.) and the pressure of the liquid. The last mentioned factor depends on the density of the coating material and the depth of the bath.
Select the frequency of the power supply to achieve the optimal balance between the conflicting effects. As the frequency increases, the so-called skin depth of the coil conductor, that is, the thickness of the surface layer in which the current is substantially confined, decreases and the resistance of the coil increases. This increases the resistance loss. In contrast, the repulsive force on the conductor body, i.e. in this case the coating liquid, increases as the eddy current in it is almost restricted to the surface, i.e. the frequency increases. The intersection of the steel strip attraction and repulsion occurs at a frequency in the range of 3-7 Hz. Therefore, frequencies above this range and up to about 100 kHz are preferred.
In this embodiment, not only the electromagnetic fields of poles 15 and 17, but also all of the electromagnetic fields from the individual poles protrude into the passage and mirror each other, so the electromagnetic fields protruding into the passage from poles 17 and 16 are It also contributes to the resilience that prevents the strip pass line from deviating from the desired center position.
Coil 7 is effectively in air or other medium that cannot be magnetized, as shown. Alternatively, the generator coil may be partially surrounded by a magnetizable outer shell with a C-shaped cross section. Such an outer shell increases the magnetic flux at any energization current, which is advantageous, but also increases the inductance of the coil, which is disadvantageous because it requires a higher energization voltage. Thus, if an outer shell is present, the design must be balanced in order to optimize the efficiency of the plugging means.
FIGS. 5-7 illustrate another preferred embodiment of the present invention, wherein each electromagnetic field generator is an electromagnet consisting essentially of a current coil wound around a preferably G-shaped ferromagnetic core.
In this case, the pan has a floor 20 which houses two high-frequency magnetic field generators 21 in elongated recesses formed in opposite faces of the floor 20 that define the strip inlet passage 22 of the pan. It is thick enough.
Each of the generators 21 comprises an energizing coil 23 surrounding a web of a ferromagnetic or ferrimagnetic core 24 having a C or G cross section, and preferably shields 25 and 26 of pans or other non-ferrous conductors. These shields constrain the high frequency magnetic field so that almost all the magnetic field generated by the coil 23 exits from the elongated end faces 27 and 28 of the core 24. Therefore, these surfaces 27 and 28 become the poles of the magnetic field generator 21.
Each of the coils 7 is preferably energized from an AC voltage source which is preferably common and preferably has a constant amplitude and a frequency exceeding 7 kHz. This is connected to the power supply to produce a preferred polarity, such as when one pole 27 is the north pole and the other pole is the south pole and vice versa.
In these situations, if there is no strip in the passage, a magnetic flux pattern as shown in FIG. 5 is generated, whereby the magnetic field extending between poles 27 plugs passage 22 and the magnetic field extending between poles 28 is Other than completing the magnetic flux path, it does not play a direct role in the operation of the pan.
If strip 29 is present, the flux pattern is assumed to be as shown in FIG. 6, and from the description of the embodiment of FIG. 1, this not only plugs the passage, but also centers the strip in passage 22. It is also obvious to place.
Each side of the passage 22 is lined with a non-metallic, refractory or other refractory insulating faceplate 30 that provides a barrier between the molten metal in the bath 31 and the top of the shield 25 and core 24. To do.
Various aspects of the design of the components of this example are discussed below.
Each core 24 is made of a material with high magnetic permeability, high saturation magnetization, and low loss. For example, high density ferrite, magnetic metallic glass, or iron powder can be used. Since the core 24 has a high magnetic permeability, the magnetic field is concentrated in the gap G adjacent to the surface 27 of the upper pole, thereby preventing excessive “consumption” of the magnetic field to the outside of the gap. The yoke preferably has a G-shape so that the window occupied by the coil 23 can be arbitrarily increased regardless of the pole separation distance S, and the coil maintains a sufficiently compact cross-sectional shape.
Since the coil window is large, a large conductor can be used for a predetermined number of turns, so that the current density can be lowered and the resistance power loss of the coil 23 is reduced. On the other hand, when the size of the coil is increased by increasing the size of the conductor, the leakage magnetic field in the coil increases, so that most of the generated magnetic field does not pass through the surface 27 of the upper pole. When determining the size and shape of the core 24, the two competing effects must be balanced.
When the pole separation distance S is reduced, the magnetic resistance of the magnetic path is reduced, so that when the number of amperes of the coil 23 is a predetermined number, the entire passing magnetic field increases. However, if the pole separation distance S is too small, the magnetic field concentrates in a small region near the pole, and does not enter the strip 29 across the gap G with full force. In this case, the area where the magnetic field near the strip is weak does not form an effective plug and the liquid-coated metal may escape. In general, the pole separation distance S should be about three times the gap G, and preferably greater. Therefore, the distance between the poles in the passage direction of the passage may be in the range of 2 to 10 times the width of the gap between the strip to be coated and the side of the passage.
The shields 25 and 26 are made of a highly conductive material such as copper, aluminum or silver. If the energizing coil is very large, an additional shield can be placed between the coil conductors to reduce internal magnetic flux leakage. Such an embodiment is shown in FIG. 8 and such additional shields are shown at 32 and 33. Eddy currents are induced in the shield. Therefore, the inside of the shield is heated, and it goes without saying that the environment becomes high temperature. Thus, for example, forced cooling of the shield may be necessary, such as by flowing a coolant in a manner that transfers heat to a tube that is brazed or otherwise joined to the shield. The embodiment of FIG. 8 includes such a tube, shown at 34 in that figure.
In the preferred embodiment, the number of conductor turns in each coil 23 is small, for example 10 or less, preferably 1 to 4 times, depending on the frequency of operation, component geometry, and power supply characteristics. As is well known, a multifilament type conductor is more efficient than a single filament type conductor at high frequencies if the cross-sectional area is the same. In other words, if the other elements are equal, the multifilament type conductor has less output loss than the single filament type conductor. This is because the high-frequency current is restricted by the skin of the conductor surface, and the ratio of the surface to the cross-sectional area of the multifilament type conductor is larger than that of the single filament type conductor. Thus, in the preferred embodiment, each turn of coil 23 is comprised of a plurality of parallel tubular conductors. These conductors are preferably cooled by a cooling fluid that is pumped through the bore.
For reasons detailed with respect to the first described embodiment, the frequency of the magnetic field is preferably in the range of 7 kHz to 100 kHz, although higher frequencies are fully feasible.
By way of illustration, the details of the appropriate design of a plating pan with plug means according to the last mentioned embodiment of the invention and holding a 0.5 m normal depth zinc or aluminum and zinc bath are described below. Show.

Claims (17)

A hot dipping pan having a strip inlet passage and electromagnetic plug means for preventing the bath agent from leaking through the passage,
The plug means comprises two magnetic field generators, one on each side of the passage,
Each generator generates an oscillating magnetic field into the passageway from at least two poles of opposite polarity spaced in the direction through the passageway adjacent to the passageway,
The at least two poles of each generator are respectively aligned with the other corresponding pole in the transverse direction of the passage;
The magnetic field generated from the generator has a magnetic flux pattern that is a mirror image of the reflective surface that coincides with the central plane of the passageway,
Both hot-dipped pans operate at frequencies above 3 kilohertz. The hot dipping pan of claim 1, wherein the pan has a floor with a rectangular cross-section downward duct defining a strip inlet passage. The hot dipping pan according to claim 2, wherein the pan is a refractory material. The hot dipping pan according to claim 3, wherein the refractory material is any one of alumina stabilized by titanium, silicon carbide, and boron nitride. The hot dipping pan according to claim 1, wherein each of the generators is constituted by a coil of a conductor, and the coil extends as a self-supporting cantilever beam from terminals at two ends. The hot dipping pan according to claim 5, wherein the coil is a single coil. The hot dipping pan according to claim 5, wherein the conductor is tubular and the terminal is connected to a coolant supply source so that the coolant flows through the conductor. The hot-dip plating pan according to claim 1, wherein each of the magnetic field generators is composed of an energization coil wound around a magnetic core having an end face toward the passage, and the end face constitutes the pole of the generator. The hot dipped pan of claim 8, wherein the core is G-shaped, whereby one end face is smaller than the other. The hot dipping pan according to claim 9, wherein the generator includes a non-ferrous conductive shield, and the non-conductive shield extends around the energizing coil. 9. The method of claim 8, wherein each side of the passage is lined with a non-metallic, refractory or other refractory insulating faceplate, which provides a barrier between the molten metal in the vessel and the top of the generator. Hot dipping pan. The hot dipping pan according to claim 8, wherein the core is made of any one of high-density ferrite, magnetic metallic glass, and iron powder. The hot dipping pan according to claim 1, wherein the distance between at least two poles in the passage direction of the passage is in the range of 2 to 10 times the width of the gap between the strip to be coated and the side of the passage. The hot dipping pan according to claim 8, wherein each energizing coil is a coil of a multifilament type conductor having 10 or fewer turns. The hot dipping pan according to claim 1, wherein the frequency is in a range of 7 kHz to 100 kHz. The hot dipping pan according to any one of claims 1 to 15, wherein the magnetic fields generated by the generators are combined, and the combined magnetic fields extend in the transverse direction of the passage between the aligned poles of the respective generators. An apparatus for continuously hot dipping a metal strip with metal plating, including the plating pan according to claim 1.

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