JP2018189246A - Cold Crucible Melting Furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cold crucible melting furnace having a hearth provided with magnetic flux induction mechanisms securely melting a solidified skull to realize stable tapping, further, to save power regarding the tapping, and simultaneously, to suppress the damage of the furnace side walls of the melting furnace, the additional structures thereof and the hearth.SOLUTION: A cold crucible melting furnace 1 has such a configuration that a hearth 2 composing the bottom part of the cold crucible melting furnace is made of an aggregate obtained by joining segments almost separately formed in a circumferential direction, and induction magnetic field fluxes from a coil 4 at the lower part are introduced into the upper part of the hearth via the released slits among the segments, and an intermediate slit(s) is provided, other than the slits among the segments, for guiding the fluxes generated at the coils 4 in the lower part to the upper part of the hearth, and further flux induction mechanisms 220a, 220b, 221a and 221b are provided concentrating the fluxes from the coils 4 located in positions exceeding the inner circumferences of furnace side walls 11 on the upper and central directions.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a cold crucible melting furnace. In particular, the present invention relates to a melting furnace having a hearth that can secure stable tapping and reduce apparatus damage of the melting furnace by increasing the metal melting efficiency near the orifice of the hearth while saving power.

  The cold crucible induction melting method is a melting method using a water-cooled copper melting furnace as a crucible, and it is possible to dissolve high-melting and active metals such as titanium in a controlled atmosphere chamber without contamination. It is.

  Magnetic flux from the induction heating coil acts on the metal to be melted in the crucible through the slit gap between the segments of the melting furnace side wall. The molten metal becomes a dome shape due to pinch force, the side faces the furnace side wall, and the lower part is also in contact with the copper hearth, but both are water cooled, so the surface is cooled and solidified skull is drawn Form. Since the solidified skull prevents contact between the molten metal inside it and the copper constituting the melting furnace, this melting method is a useful means for obtaining a high-purity metal without contamination.

  Therefore, the cold crucible melting furnace may be used as a small melting furnace that melts a small amount of expensive metal. In particular, when delivering to the next process such as atomization, a thin hot water nozzle is often used. Therefore, it is desirable to use a small melting furnace in consideration of the life in which the nozzle exposed to high heat functions normally.

  In the past, the tilting method in which the crucible was tilted to discharge the molten metal was generally used. However, there are various problems such as the yield of the molten metal, the low temperature, and safety. Many methods have also been devised for direct hot water discharge.

Special table 2008-554585 gazette

  In order to discharge directly from the hearth, it is necessary to dissolve the solidified skull. Therefore, it is necessary to separately provide a high frequency induction heating coil below the hearth and to heat independently from the furnace side wall, but when consuming a large amount of power or heating from the bottom of the hearth, There is a problem that the lower part of the side wall of the melting furnace that falls within the magnetic field of the coil and the structure attached thereto are simultaneously induction-heated and damaged.

  The heating for tapping hot water requires extra energy because the portion being cooled is heated as compared with the heating for melting the metal. Moreover, in a cold crucible melting furnace, as the size of the furnace increases, the basic unit of electric power (melting electric power per unit weight) required for melting the metal from the furnace side wall decreases. The amount of electric power required for heating from the heat source is about the same whether it is large or small. Therefore, in a small melting furnace, it is said that a large amount of electric power equivalent to the heating from the side wall of the furnace is necessary, so that the problem is particularly great.

  When the shape of the hearth is funnel-shaped, induction heating coils are arranged in an oblique direction and a vertical direction corresponding to the funnel-shaped inclined part and the vertical part leading to the orifice part serving as the outlet of the hot water. Therefore, it is difficult to uniformly heat the solidified skull near the tapping outlet of the tapping hearth, and the heating area of the hearth is larger than that of the flat plate shape. Become.

  On the other hand, a flat hearth with a funnel-shaped orifice part at the outlet of the hot water has a feature that it is easy to concentrate the magnetic flux, and can minimize the contact between the molten metal and the hot water structure. There is an advantage that it can be delivered to the next process without being required, and "the required power can be minimized".

  In patent document 1, while using a flat hearth as a structure for delivering titanium to the atomization process of the next process, a uniform magnetic field is formed in the orifice part of the outlet part, and iron powder that is a magnetic substance is used. The structure which makes it easy to concentrate a magnetic flux further by mixing is mixed with the said part is shown.

  By the way, for stable tapping, strong induction heating in the vicinity of the orifice serving as a tapping outlet is required, and for that purpose, it is necessary to collect a large amount of magnetic flux from a coil below the hearth in that portion. . However, the unnecessary magnetic flux causes coil loss and damages the furnace side wall, its attached devices, and the hearth itself by induction heating. Therefore, it is desirable that the unnecessary magnetic flux can be corrected.

  In this respect, in the configuration shown in Patent Document 1, the magnetic flux from the lower induction heating coil is not greatly promoted upward, and the magnetic substance mixed in the orifice portion itself slightly corrects the trajectory of the magnetic flux. Although induction heating may be promoted, the effect is weak and it is not preferable for the durability of the orifice part itself.

  In particular, in a small cold crucible melting furnace, a situation has arisen in which the coil size required for induction heating sufficient for skull melting does not fit within the inner surface of the furnace side wall. In addition to being large, damage to the lower part of the furnace side wall and its attached devices due to leakage magnetic flux is also a serious problem, and a method that can correct the trajectory of the magnetic flux is desired.

  An object of the present invention is to solve the above-described problems. Specifically, a stable tapping water can be realized by making it possible to correct the trajectory of the magnetic flux for induction heating the orifice portion of the tapping outlet. At the same time, an object of the present invention is to provide a cold crucible melting furnace having a hearth that can save power and minimize damage to the apparatus.

  In order to achieve this object, the present invention takes the following measures.

  That is, the cold crucible melting furnace of the present invention is a melting furnace surrounded by a furnace side wall into which an object to be melted is charged, a hearth serving as the bottom of the melting furnace, and a melting center located at the circumference center of the hearth. Provided with an orifice portion and a discharge nozzle for discharging the molten metal in the furnace to the outside, the furnace floor is composed of segments that are substantially divided in the circumferential direction, and the upper part of the hearth via the open slit gap between the segments In this configuration, a magnetic flux from a lower coil is introduced, and an induction mechanism is further provided for guiding the magnetic flux from the coil below the hearth to the upper surface of the hearth and toward the center of the hearth.

  Here, the “substantially divided segment” includes not only the case where the entire segment is completely separated, but also the case where the segments are in a partially connected shape.

  As a result, a larger amount of magnetic flux from the coil below the hearth can be transmitted toward the upper surface of the hearth with the tapping orifice and the center of the hearth, so the thickness of the solidified skull on the upper surface of the hearth is reduced. More stable hot water can be obtained.

  The mechanism for guiding the magnetic flux in the central direction is preferably provided so as to be able to cooperate with the slit that mainly promotes the magnetic flux in the upward direction. Specifically, it has a directionality in an oblique direction that is upward and in the central direction. Preferably, the magnetic flux induction space or the magnetic flux induction member is provided below the slit.

  It is most likely to correct the trajectory because it is primarily the leakage flux that goes upwards through the slit gap, which melts the solidified skull and heats the furnace sidewall and its associated equipment, leading to extra losses. Because it is efficient.

  Since it is impossible to induce the upward magnetic flux in the lateral direction toward the circumferential center direction, the correction angle is so large that it is impossible to induce the magnetic flux upward and in the oblique direction that is the central direction.

  In particular, in a small cold crucible melting furnace, it is desirable to use a hearth having a mechanism for concentrating the magnetic flux from the coil located above the inner periphery of the furnace side wall in the upward and central directions.

  All the magnetic flux that goes out of the range of the inner wall of the furnace wall and goes to the upper side of the coil becomes a leakage flux, and at the same time as the induction furnace heats the melting furnace body and its attached structure, it becomes an extra loss. Therefore, by correcting the trajectory of these magnetic fluxes from the inner surface of the furnace side wall toward the circumference center, damage can be reduced and coil loss can be reduced.

  In order to promote induction of coil magnetic flux toward the upper surface of the hearth, it is desirable to provide an intermediate slit that is short-circuited at the center of each segment of the hearth.

  Furthermore, the magnetic flux induction effect can be enhanced by providing the magnetic flux induction space or the magnetic flux induction member by joining below the intermediate slit.

  The hearth is preferably provided with a circulating water cooling mechanism inside the structure.

  In order to prevent damage to the structure, cooling is indispensable especially in the vicinity of the orifice portion that is heated by induction in a concentrated manner.

  As a mechanism for inducing the magnetic flux, a magnetic flux induction space or a magnetic flux induction member having directionality toward the center of the hearth can be arranged as seamlessly as possible in a ring shape concentric with the circumference of the hearth, This aspect can produce the maximum magnetic flux induction effect by cooperating with the induction mechanism of the magnetic flux above the hearth.

  Since the present invention has the above-described configuration, it is possible to reliably dissolve the solidified skull and realize a stable tapping water, and to save power related to tapping discharge. Can be suppressed.

Front cross section of cold crucible melting furnace and front cross section of hearth Perspective view of the entire hearth Cross section of hearth and coil and schematic diagram of magnetic flux induction Top view showing one segment of hearth with water cooling mechanism

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 a is a front sectional view of the cold crucible melting furnace 1 of the present embodiment. The copper furnace side wall 11 that is water-cooled by a mechanism (not shown) is not shown, but is divided into strip-shaped segments, and a coil 3 for induction heating, whose cross section is shown, is spirally formed on its outer periphery. It has a wound configuration. The magnetic field induced by the current of the coil 3 causes eddy currents in the metal in the crucible through the slit gap between the segments, and the metal self-heats.

  On the other hand, the bottom of the melting furnace 1 is a flat hearth 2 that is larger than the outer periphery of the furnace side wall 11, and an orifice 21 and a hot water nozzle 22 that can discharge molten metal from the center of the melting furnace 1 out of the melting furnace. It has. Similarly to the furnace side wall 11, the hearth 2 is made of water-cooled copper and is an aggregate of segments 201 that are substantially divided in the circumferential direction, although connected in the center. The metal 7 that has been heated and melted solidifies from the outside facing the water-cooled furnace side wall 11 and the contact surface with the hearth 2. The metal lump formed on the upper surface of the hearth after being cooled is called a solidified skull 8. In order to directly discharge the molten metal from the orifice portion 21 of the hearth 2, it is necessary to melt the solidified skull.

  FIG. 1 b is an enlarged view of the vicinity of the hearth 2 in the front cross-sectional view of the cold exclusive melting furnace.

  The funnel-shaped orifice portion 21 corresponding to the outlet of the hot water of the hearth 2 is joined to the center of the circumference of the hearth 2. The funnel-shaped inclined portion 21 a of the orifice portion 21 is in the same plane as the hearth structure, and the structure of the vertical portion 21 b and below protrudes downward from the structure of the hearth 2. A coil 4 is wound around the protruding portion in the same plane. Therefore, when an electric current is passed through the coil 4, the induced magnetic flux can be induction-heated from the bottom of the skull 8 above the hearth to the orifice 21 at the center of the coil 4 through the gap of the slit 210. The orifice portion 21b and the like below the structure can also be induction-heated.

  A plate-like magnetic body 5 and a cooling plate 6 are disposed below the coil 4.

  The hot water nozzle 22 integrally joined to the orifice portion 21 is a cylindrical structure whose inner surface is coated with carbon, and protrudes further downward from the structure of the cooling plate 6 so that the molten metal melted from the hot water The structure is easy to deliver directly to the next process.

  FIG. 2 is a perspective view of the hearth 2.

  The disk-shaped copper hearth 2 is divided into approximately eight in the circumferential direction, and a slit 210 having a width of, for example, 1 mm is formed between the segments 201 so that the magnetic flux from the coil 4 below the hearth is upward. Induce. In the present embodiment, a slit 211 that is opened in a short-circuit manner is provided as a magnetic flux guiding mechanism at the center of the structure of each segment 201 to promote upward induction of magnetic flux from the lower coil 4.

  By adopting such a configuration, a larger amount of magnetic flux from the coil below the hearth can be transmitted to the upper surface of the hearth. Is possible. Since the magnetic flux of the coil is directed toward the coil center, the intermediate slit 211 alone is effective as a magnetic flux guiding mechanism toward the upper surface of the hearth and toward the center.

  As shown in FIG. 2, as a space for inducing magnetic flux in the hearth 2, it does not penetrate upward and obliquely toward the center direction from a position corresponding to the outer peripheral end of the coil below the hearth 2. In shape, a cylindrical concave space (220a) is provided. At the same time, it is provided so that the upper surface of the cylindrical concave space corresponds to the inner side of the inner surface of the furnace side wall above the hearth. The magnetic flux induction space is provided at 16 locations corresponding to the gaps between the slits (210) between the segments or the slit (211) at the center of the segment.

  As a result, the magnetic flux in the coil portion that protrudes from the inner periphery of the furnace side wall, which has the greatest influence on the coil loss, is effectively centered from the inner periphery of the furnace side wall through the gap between the slits 210 and 211. Can be directed to the solidified skull 8 in the direction.

  By introducing magnetic bodies 220b and 221b including ferrite into the magnetic flux induction spaces 220a and 221a, a stronger magnetic flux induction effect can be expected.

  By adopting such a configuration, the magnetic flux for inducing the solidified skull is increased by correcting the trajectory of the magnetic flux leakage, and by reducing the magnetic flux leakage, excess heating to the device is reduced and coil loss is reduced. Can do.

  In a small cold crucible melting furnace 1 that is particularly useful for melting high-purity metals, when the number of turns of the coil 4 is to be secured, the range of the furnace side wall 11 where the solidified skull 8 exists is not exceeded. A coil with a small diameter will be selected. Then, as shown in FIG. 3a, the range of the induced magnetic field can be limited to the necessary area, and the skull near the top surface of the hearth can be thinned. However, because of the coil material having a small cross-sectional area, the coil loss increases and the output power There must be a large high frequency power supply.

  On the other hand, when a wide coil 4 is used as shown in FIG. 3b, if the number of turns is secured, the strength and range required for tapping can be obtained, but the induced magnetic field exceeds the range of the furnace side wall 11. Therefore, not only the target metal to be melted, but also the lower part of the furnace side wall 11 at the upper part of the protruding part and its attached structure are heated. Even if an isolator plate or the like is installed to prevent this, an extra loss is inevitable.

  On the other hand, in FIG. 3C schematically showing the present embodiment, the magnetic flux induction spaces 220a and 221a or the magnetic flux induction members 220b and 221b are formed corresponding to the open slits 210 between the segments and the shorted slits 211 described later. As a result, the path of magnetic flux can be effectively guided to the upper surface of the hearth and the orifice portion 21. Compared to the case of FIG. 3b using the same wide coil, a stronger eddy current can be induced in the vicinity of the hot water outlet, so that stable molten metal can be discharged even with a thin hot water nozzle and coil loss can be reduced. . At the same time, as compared with FIG. 3b, extra heating due to induction heating of the furnace side wall 11 structure above the coil 4 can be reduced.

  According to a comparative experiment conducted up to this example, when the number of windings of the wide coil is set to 4 turns in accordance with the outer periphery of the furnace side wall, when it is protruded and turned 6 turns, While the loss increases and the amount of power supplied to the crucible in the melting furnace 1 is reduced by 3%, the introduction of the magnetic flux induction mechanism by the central slit and the magnetic material according to the present invention reduces this to 5%. % Was able to recover.

  FIG. 4 shows a top view of one segment 201 of the hearth 2.

  By providing a slit 211 having a short-circuited central portion as a magnetic flux induction mechanism, the escape path of the magnetic flux directed upward from the coil 4 below the hearth 2 is increased as much as possible, and the inside of the hearth is folded back to the periphery of the central orifice 21. The cooling water channel 230 that can be used can be secured. As a result, the life of the orifice portion 21 having the most severe damage can be extended, and the structure can be cooled within a range that does not affect the temperature of the tapping portion as much as possible by cooling the structure from the inside.

  As described above, the cold crucible melting furnace 1 of the present embodiment includes the melting furnace surrounded by the furnace side wall 11 into which the object to be melted is charged, the hearth 2 serving as the bottom of the melting furnace, and the hearth And an outlet 21 and an outlet nozzle 22 for discharging the molten metal in the melting furnace to the outside, and the hearth 2 is an assembly in which segments 201 that are substantially divided in the circumferential direction are joined together. The induction magnetic field from the lower coil 4 is introduced into the upper part of the hearth via the slits 210 opened between the segments, and the coil located below the hearth in addition to the slits 210 between the segments. 4 further includes an induction mechanism for guiding the magnetic flux generated at 4 toward the upper surface of the hearth and toward the center of the hearth.

  Since it is such a structure, since the magnetic flux from the coil 4 below the hearth can be transmitted more toward the upper surface of the hearth 2 having the tapping orifice portion 21 and the center of the circumference of the hearth 2, 2 The thickness of the solidified skull 8 on the upper surface can be reduced, and a more stable tapping water can be obtained.

  The present embodiment is a small cold crucible melting furnace 1 and includes 220a, 220b, 221a, and 221b as one of magnetic flux induction mechanisms that concentrate the magnetic flux upward and in the central direction.

  In particular, all the magnetic flux that goes out of the range of the inner periphery of the furnace side wall 11 toward the upper side of the coil 4 becomes a leakage magnetic flux, and inductively heats the melting furnace 1 body and its attached structure, resulting in an extra loss. Therefore, extra losses can be reduced by correcting the trajectory of these magnetic fluxes from the inner surface of the furnace side wall toward the center of the circumference.

  The magnetic flux guiding space 220a or the magnetic flux guiding member 220b is provided mainly in the form of being joined below the slit 210, which is a magnetic flux guiding mechanism that strongly promotes the magnetic flux strongly in the upward direction, and leaks upward through the slit gap. The magnetic flux can be effectively corrected in the trajectory.

  In this embodiment, in addition to the slit 210, a short-circuited intermediate slit 211 provided at the center of the hearth segment 201 is provided as a further magnetic flux guiding mechanism. It is set as the structure provided with the magnetic flux induction space 221a or the magnetic flux induction member 221b provided by joining to.

  With these configurations, the solidified skull 8 is efficiently melted, and the furnace side wall 11 and its attached devices are heated excessively and further upward through the slits 210 and 211 which are the main causes leading to coil loss. The trajectory of the leakage magnetic flux can be corrected.

  In the present embodiment, a circulating water cooling mechanism 230 is provided inside the structure of the hearth 1.

  With such a configuration, it is possible to prevent damage to the structure in the vicinity of the orifice portion 21 that is particularly concentrated and heated for hot water discharge. Although cooling is indispensable, cooling from the outside with a water cooling plate or the like may reduce the temperature at the center of the orifice portion 21 where it is desired to maintain a high temperature, and heating and cooling are performed at the same time. .

  In addition, the specific configuration can be variously modified without departing from the gist of the present invention.

  Theoretically, the greater the number of slits and magnetic flux derivatives, the higher the effect of guiding the magnetic flux upward and toward the center, making it easier to achieve the object of the present invention. Therefore, a configuration in which the number of slits is increased by arranging the magnetic flux induction space and the magnetic flux induction member in a ring shape or increasing the number of hearth segments having the above-described configuration is also conceivable.

DESCRIPTION OF SYMBOLS 1 ... Cold exclusive melting furnace 11 ... Furnace side wall 2 ... Hearth 21 ... Orifice part 21a ... Funnel-shaped orifice inclination part 21b ... Funnel-shaped orifice vertical part 22 ... Hot metal nozzle 3 ... Metal melting heating coil 4 ... Hot water heating coil 5 ... Magnetic plate 6 ... Water cooling plate 61 ... Water cooling passage 7 ... Molten metal 8 ... Solidified skull 201 ... Hearth segment 210 ... Hearth segment segment slit 211 ... Hearth segment central slit 220a, b ... Hearth segment slit Lower magnetic flux induction space, members 221a, b ... hearth segment central slit lower magnetic flux induction space, member 230 ... water cooling passage in the hearth segment structure

Claims (4)

A melting furnace surrounded by a furnace side wall into which an object to be melted is charged, a hearth constituting the bottom of the melting furnace, an orifice part and a hot water nozzle for discharging the object to be melted outside in the hearth Comprising
Furthermore, a coil for performing induction heating for hot water is provided below the hearth,
The hearth is composed of segments that are substantially divided in the circumferential direction, and is configured to introduce magnetic flux generated in the lower coil to the upper part of the hearth through an open slit between the segments,
The cold crucible melting furnace further comprising an induction mechanism in the hearth structure for guiding the coil magnetic flux below the hearth to the upper surface of the hearth and toward the center of the hearth. The cold crucible melting furnace according to claim 1, wherein a magnetic flux induction space or a magnetic flux induction member is provided in the hearth structure as a mechanism for guiding the coil magnetic flux toward the center of the hearth. The cold crucible melting furnace according to claim 1 or 2, wherein an outer diameter of the coil is larger than an inner diameter of the furnace side wall. The cold crucible melting furnace according to any one of claims 1 to 3, further comprising an intermediate slit as a mechanism for guiding the coil magnetic flux to the upper surface of the hearth in addition to the slit.

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