WO2000039514A1 - Method and device for melting rare earth magnet scrap and primary molten alloy of rare earth magnet - Google Patents

Abstract

A magnet for increasing a yield attained during a process in which, when separating metals from scraps occurring during a rare earth magnet production process, alloy materials for rare earth magnet are melt-refined so as to positively separate oxides and then subjected to a secondary melting by using a vacuum high-frequency induction melting furnace; wherein part or all of the scraps (3) are charged into an insulated (2) water-cooled crucible (1) or a refractory crucible (7, 21, 22) and subjected to twin plasma arc (10A, 10b) melting and tungsten arc or migration arc (15) melting.

Description

 Description Rare earth magnet scrap melting method and melting apparatus, and rare earth magnet scrap primary melting alloy

 The present invention relates to a method of reusing an alloy having a high oxygen concentration such as scrap generated in a process of manufacturing a rare-earth magnet by a melting technique, a melting apparatus used in a recycling method, and a secondary melting method. Rare-earth magnet primary molten alloy prepared in such a way that it can be used to produce magnetic alloy materials (hereinafter referred to as “magnet alloys”). Background art

 Recently, the demand for rare earth sintered magnets based on NdFeB and SmCo, which have excellent magnetic properties, has increased, and the amount of scrap generated in the magnet manufacturing process has also increased. I have. These scraps include defective sintering products that occur during the sintering process, defective products that occur due to chipping or the like during cutting, and defects that occur due to pinholes or the like during the plating process. Scraps of non-defective products are included. In addition, when the alloy for rare earth magnets is melted in a high-frequency induction furnace in a vacuum or inert gas atmosphere, the residue with high oxygen concentration adheres to the refractory lining and remains in the crucible. This is molten slag, but is included in scrap in a broad sense. In addition, powdery scrap is generated during the process of cutting and polishing the sintered body. This is a state in which water used for cutting and powder of abrasives are mixed, and as a general method, a method of dissolving and extracting with an acid is used to recover useful metals such as rare earth elements. Already done.

Unsatisfactory sintering, defective shape, and defective plating Some recovery methods have not been found, so some magnet manufacturers may store them in anticipation of the emergence of a reuse method, or they may be expensive, for example, SmCo-based scrap. In the case of an alloy containing a large amount of Co, it was melted using an electric furnace, and Sm, which is easily oxidized, was oxidized and transferred to slag, and only Co was collected as metal. Melting scouring method is adopted. In this case, expensive useful metals such as Sm and Zr were not recovered. Japanese Patent Laid-Open No. 8-31624 discloses a technique for melting the scrap of a rare-earth magnet. According to this description, a rare-earth metal that is extremely active in high-frequency melting, arc melting, and plasma melting is slag. Since it is difficult to separate rare earth metals from slag, a method has been proposed in which the amount of scrap added to virgin raw materials is limited and redissolved.

 However, in both the SmCo-based and NdFeB-based systems, in the process of manufacturing the magnet, an alloy containing a large amount of extremely active rare earth elements is finely pulverized and passed through the forming and sintering process. A large amount of fine oxides are present in the scrap, and even if they are to be melted in a high-frequency induction melting furnace as they are, the metal yield is extremely low. It has not been established yet. In particular, the problem with the melting method is that the surface of the molten metal is covered with the slag due to the large amount of slag generated, making it difficult to observe the state of the molten metal and measure the temperature; this slag adheres firmly to the inner wall of the crucible and grows As a result, the internal volume of the crucible is reduced, which causes a fence of the input material to be hung; the work of periodically removing the slag from the inner wall of the crucible becomes difficult, and the life of the crucible is shortened. And so on.

The present inventors have analyzed the cause of the low yield when the rare-earth magnet scrap is melted using a normal high-frequency induction melting furnace, and as a result, the rare-earth metal originally contained in the scrap was analyzed. When the oxide is separated from the scrap melt, the molten metal is also entrapped in the slag, causing the metal to be suspended in the oxide and the yield to deteriorate. Or high oxygen concentration Slag was present in the form of slag, and the apparent amount of slag increased, resulting in a decrease in yield.

 The method described in the above-mentioned Japanese Patent Application Laid-Open No. 8-31616 is a method in which a metal (alloy) containing a rare earth magnet constituent element as a main component, a so-called virgin raw material, is first dissolved to prepare a seed water, and then the scrap is produced. This method belongs to the re-melting method rather than the scouring method in which oxides are positively removed by melting.

 In the plasma arc, a transfer arc using the torch electrode as the negative electrode and the material to be melted as the anode, and the torch itself using the torch electrode as the negative electrode and the nozzle as the anode. There are two types of non-transitional arcs with. Recently, unlike the above method, a method has been proposed in which a plasma arc is generated by separately providing a cathode torch and an anode torch (Japanese Patent Application Laid-Open Nos. 1991-1990, 3-8). 736, JP-A-7-126019, and JP-A-8-5247). The plasma generated by this method is called twin-plasma.

 For example, the method of Japanese Patent Application Laid-Open No. Hei 7-126109 proposes a method of melting quartz glass in which impurities are not mixed from a container, and that the plasma has a high energy density and a granular silica is added to the container prior to melting. He states that laying down mosquitoes is important in achieving the desired effect. Japanese Patent Application Laid-Open No. 3-25247 states that the twin torch plasma method is excellent in that it is easy to restart when melting waste such as incineration ash. As described above, it has been known that the conventional twin torch plasma dissolution method provides excellent results in dissolving oxide materials and wastes. Disclosure of the invention

The present invention relates to a method of separating oxides from any rare-earth magnet scrap, such as scrap generated in the process of manufacturing the rare-earth magnet and residues in the crucible generated when melting the raw material of the rare-earth magnet. Aggregation / dissolution that actively promotes separation By providing a melting and refining method, oxides can be partially separated and removed, and a very good yield can be achieved when the raw material for rare earth magnets is secondarily melted using the next vacuum high-frequency induction melting furnace. The purpose is to do so.

 The method according to the first aspect of the present invention is the method for obtaining a raw material for producing a rare earth magnet by first melting a scrap of a rare earth magnet, wherein a water-cooled crucible or a refractory crucible in which a part or all of a molten metal holding part is insulated. A scrap of rare earth magnet is charged into the crucible, and the scrap of rare earth magnet is melted by a plasma torch comprising at least one pair of an anode and a cathode provided so as to be located above the crucible. The present invention relates to a method for melting scraps of rare earth magnets.

 Further, the apparatus for melting the rare earth scrap for carrying out the first method of the present invention is a method for holding a molten metal in a plasma arc melting furnace having a plasma torch comprising at least one pair of anode and cathode. It is characterized in that a water-cooled crucible or a refractory crucible in which part or all of the part is insulated is arranged.

 A method according to a second aspect of the present invention is the method for obtaining a raw material for producing a rare earth magnet by first melting a scrap of the rare earth magnet, wherein the molten metal holding part has a heat insulating part and a water cooling part in a crucible. The present invention relates to a method for dissolving scrap of rare earth magnets, which comprises inserting a lap and dissolving the scrap of rare earth magnets by a tundass arc or a transition type plasma arc.

 Further, in the apparatus for melting a rare earth scrap for performing the second method of the present invention, a crucible in which a molten metal holding section includes a heat insulating part and a water cooling part is disposed in a tungsten arc or transition type plasma arc furnace. It is characterized by what has been done.

The method according to a third aspect of the present invention is the method for obtaining a raw material for producing a rare-earth magnet by first melting a scrap of the rare-earth magnet, wherein the molten-metal holding part is placed in a crucible having a heat insulating structure. And a tungsten arc or a transition type plasma arc is generated between a first electrode which locally covers the heat insulating surface of the crucible and a second electrode disposed above the crucible. And The present invention relates to a rare earth magnet scrap melting method characterized by melting a rare earth magnet scrap.

 Further, the apparatus for melting the rare earth scrap for carrying out the third method of the present invention is a crucible having a heat retaining structure of a molten metal holding part in a tungsten arc or transition type plasma arc furnace, and And a second electrode disposed above the crucible. The first electrode locally covers the heat insulating surface.

 Further, the alloy obtained by primary melting of the rare earth magnet scrap according to the present invention has a total of 10 to 40 wt% of Sm and Ce and 5 wt% of Nd for the SmCo system. Hereafter, Fe force S 25 wt% or less, Cu force 4 to 10 wt%, Zr 1 to 4 wt%, oxygen 0.1 wt% or less, and the balance is mainly Co. In addition, the present invention relates to a primary molten alloy of a rare earth magnet scrap characterized by being an unavoidable impurity due to the rare earth magnet manufacturing process excluding oxygen and an invading element due to primary melting excluding Fe. .

 In addition, for the NdFeB system, Nd, Pr and Dy total 20 to 35 wt%, B force 0.9 to 1.2 wt%, and A1 force; 1 to 1 wt%, Co force 5 wt% or less, Cu force S 0.5 wt% or less, Nb force S 1 wt% or less, oxygen 0.1 wt% or less, balance Fe mainly And an inevitable impurity due to the rare earth magnet manufacturing process excluding oxygen, and an intrusion element due to primary dissolution excluding Fe, which is a primary molten alloy of a rare earth magnet scrap. About.

 The following summarizes the results achieved by these inventions.

 (1) Since the obtained primary molten alloy has advanced agglomeration and separation of oxides, it can be melted using the next vacuum high-frequency induction melting furnace, and the yield when reused can be extremely high.

(2) Since the crucible is partly or wholly insulated, coagulation and separation of oxides As the thermal efficiency improves, the amount of dissolution increases, and the dissolution time is shortened. As a result, power consumption decreases and productivity increases.

 (3) Since the composition of the primary ingot is uniform, the composition of the secondary ingot can be accurately specified, and the quality of the sintered magnet can be maintained well.

 Hereinafter, the means adopted by the present invention to achieve the above-described results will be described in detail.

 First, items common to the first to third methods of the present invention will be described.

 In general, melting by a tungsten arc melting furnace or a transition type plasma arc melting furnace is usually performed by a skull melting method using a copper water-cooled crucible in order to use a melting raw material as a direct counter electrode to an arc torch. In this method, a shell (skull) of a solidified layer is formed on the inner surface of the water-cooled crucible by the raw material itself. As described above, under the condition that the solidified layer coexists, the NdFeB magnet is melted using a normal arc melting furnace or plasma melting furnace to scrap the SmCo magnet. If so, it becomes difficult to sufficiently raise the temperature of the molten metal above the melting point of the alloy. Therefore, if the melting is performed while keeping the temperature of the molten metal low, the deoxidizing scouring effect becomes insufficient. As a result, the yield of secondary melting of the obtained primary ingot is extremely low at 70% or less.

On the other hand, when a scrap of a rare-earth magnet placed in a crucible partially or entirely made of refractory is melted by twin-point plasma, tungsten arc, or transfer-type plasma arc, it melts. It has been found that the material can be heated to a high temperature, and as a result, the coagulation separation and floating of the rare earth oxides present in the scrap are promoted, and the oxygen separation scouring effect is significantly enhanced. In this case, the skull does not remain in the refractory part of the crucible due to the heat insulation effect, and the skull in the water-cooled part becomes thin and the temperature of the molten metal becomes more than 200 ° C above the melting point, sufficiently. Can be increased. In addition, it has been found that the convection of the molten metal, which is essential for the separation and refining of oxides, becomes active when the temperature difference between the melting point and the molten material of the rare earth alloy material is 200 ° C or more. By setting conditions in this way, The oxides that existed in the clamp are separated efficiently. In general, the difference in specific gravity between a rare earth magnet alloy and its rare earth oxide is small, and it is difficult to separate the oxide by flotation. That was one of the reasons why the conventional dissolution method did not reduce oxygen. However, if the temperature is kept high by using an insulated crucible and using a plasma that can concentrate a large amount of energy, the viscosity difference of the alloy from the melting point is 200 ° C or more and the viscosity of the alloy becomes Very degraded. Therefore, it is considered that the separation of oxides by agglomeration and flotation progresses rapidly together with the stirring effect of plasma heating.

 In the present invention, “insulation” generally assumes that a water-cooled crucible is made of a metal that is a good conductor of heat, and indicates the use of a contradictory poor conductor of heat. As a result, there is no skull in this heat insulating part. Specifically, a heat-insulated conductor is fixed to a part of a water-cooled crucible made of copper or the like in the molten metal holding part of the crucible to form an adiabatic part, or the crucible is made of a water-cooled metal part and a heat-insulated conductor part. Or the entire crucible is made of a poor conductor of heat. Examples of poor conductors of heat include refractory materials such as alumina, zirconia, yttria, calcite, magnesia and the like and fired products of composite oxides thereof. Of these, alumina refractories are the most economical and durable. The mixing of aluminum from the refractory into the metal is controlled to a level that is not problematic by controlling the heat input from the plasma arc, etc., so that the temperature of the molten pool does not become too high. can do.

In the partial heat insulation of the water-cooled crucible, the molten metal holding part of the crucible is insulated to such an extent that a phenomenon such as the expansion of the molten pool occurs. The heat insulation region is preferably at least 20%, more preferably at least 30%, and even more preferably at least 50% of the inner area of the crucible. Further, the entire inner area of the crucible may be insulated, or the whole may be a refractory crucible. In the case of a refractory crucible, it may be lined with a refractory inside a metal container (shell). S The refractories used for this lining may be fixed refractories or irregular refractories. The shell can be jacket-cooled.

 As described above, this method has the advantage of dissolving rare-earth magnet scraps with a high oxygen concentration, so it is not advisable to add virgin metal to the raw material to be dissolved. However, in a situation where the amount of scrap generated in the magnet manufacturing plant is small and there is room for the melting equipment, part of the virgin metal, preferably 30% by weight or less, is charged to the molten raw material. May be. In this case, as the virgin metal, industrial pure iron, electrolytic iron, rare earth metals such as neodymium, rare earth mother alloys such as ferro neodymium, and ferroboron can be used.

 In the dissolution method of the present invention, the coagulation separation of oxides proceeds even if the molten metal holding time is prolonged, but its contribution is small compared to the temperature, which is not desirable from the viewpoint of productivity. In order to promote separation, it is preferable to maintain the temperature of the molten metal at a high temperature of 200 ° C. or more, more preferably 300 ° C. or more, which is the melting point of the rare earth magnet scrap.

 In this method as well, if there is a water-cooled portion of the crucible, the skull remains, but the skull is thinner than in the case of a normal water-cooled crucible, and no skull is generated at the bottom or other portion where the refractory layer is arranged. You can do more. After tapping, the next raw material can be charged into the remaining skull to continue dissolution. At this time, the skull shrinks by the time the next raw material is charged, and a gap may occur between the skull and the crucible. If the conductivity of the skull and the crucible is poor, an arc is generated during this time, and the crucible may be locally melted.Therefore, to ensure conduction between the anode side crucible and the scalp, a pure iron plate It is better to have a metal energizing section made of such as.

When tapping the molten metal from the crucible, only the part of the molten metal is removed instead of the whole, leaving the rest of the molten metal in the crucible and adding the rare-earth magnet scrap, which is the raw material to be melted, into the molten metal. Fill the space between the additional charge mass, pieces and so on As a result, it is possible to ensure that the tungsten electrode and the entire raw material are energized. This facilitates the restart of energization of the tungsten arc or the transition type plasma arc, enables semi-continuous melting, and improves productivity. In addition, after the conveyed material has melted down, the raw materials are additionally charged as appropriate, and the molten metal is provided at the edge of the crucible and overflows from the tap hole, so that the tilting of the crucible is omitted. It is also possible to continue refining continuously. In the method of the present invention, when the power supply is stopped at the time of tapping, the surface of the molten metal is covered with the oxide slag. However, if the raw material is charged before the molten metal is completely solidified, the slag layer is broken and a current-carrying part is formed by the raw material, so that current can be continuously supplied.

 Next, the features of the first method of the present invention will be described.

 The twin torch plasma is composed of at least one pair of anode and cathode electrodes, so that the crucible does not need to be conductive. Each torch is inserted from the top of the melting furnace chamber into the melting crucible with the tip of the torch inserted into the melting crucible so that the melting atmosphere is not impaired, the insertion angle is variable, and the vertical position can be adjusted. Have been. The selection range of the voltage, current and input of the plasma torch needs to be changed according to the melting amount per batch and melting time. Generally, it is necessary to increase the plasma current and output as the melting time increases and the melting time decreases. For example, when dissolving 50 kg of scrap per batch, 150 to 300 kW is appropriate. When dissolving 200 kg of scrap, 400 to 600 kW is appropriate.

 Next, features of the second method of the present invention will be described.

Generally, melting by a tungsten arc melting furnace or a transition type plasma arc melting furnace is usually performed by a skull melting method using a copper water-cooled crucible in order to make a melting raw material directly opposite an arc torch. In this method, a shell (skull) of a solidified layer is formed by the raw material itself on the inner surface of the water-cooled crucible. The raw material fed into the side is dissolved. If a part of the water-cooled crucible is insulated with refractory, etc., the molten pool will be wide and deep. For this reason, the molten metal temperature can be easily raised. Therefore, convection in the molten metal of the rare-earth magnet scrap or in the crucible residue having a high oxygen concentration is promoted, and the oxides are easily floated. Can be promoted.

 Subsequently, features of the third method of the present invention will be described.

 This method employs a different crucible structure from the second method. In other words, a structure in which the molten metal holding portion of the crucible is covered with a refractory material to form a heat insulating structure, and a structure in which the refractory material is locally covered with a metal electrode (first electrode) is selected. By covering the entire molten metal holding section with the refractory, it is easier to raise the temperature of the molten metal, and the melting efficiency and the effect of separating and producing oxygen can be enhanced. In this case, the refractory surface is locally covered with a metal electrode in order to secure the power supply.

 It is preferable to use a plate electrode for this coating. When a plate-shaped metal electrode is used, if one or more holes are provided at the bottom of the crucible, the temperature of the molten metal rises, and after sufficient separation of oxygen, the metal electrodes on and around the holes become It is possible to extract the molten metal, that is, to tap the molten metal by utilizing the fact that the molten metal disappears. In this case, the timing of tapping can be controlled by controlling the heat input from the tungsten arc or transitional plasma arc during melting, or by selecting the material and thickness of the metal electrode described later. Can also be adjusted. In this way, when the method of extracting molten metal from the bottom is adopted, after the desired amount of molten metal has flowed out, the outlet of the molten metal is closed with a stud and the like, so that the slag is introduced into the molten metal. Since more slag remains in the crucible than it is prevented from being mixed, it is possible to obtain a primary melting ingot with a sufficient refining effect.

As the material of the metal electrode, an iron electrode can be used. In particular, steel with a low content of carbon, which is a harmful impurity as a raw material for rare earth magnets The use of a material makes it possible to prevent the contamination of these elements, so it is desirable to use an electrode made of industrial pure iron. In addition, an electrode made of a high melting point metal such as niobium, molybdenum, tantalum, or an alloy thereof can be used. In this case as well, the heat input from the tungsten arc or the transition type plasma arc is controlled so that the temperature of the molten metal pool does not become too high in the same way as preventing the incorporation of aluminum when using an alumina refractory. By doing so, the incorporation of the metal elements constituting these electrodes into the substance to be dissolved can be suppressed to a level that is not problematic.

 Next, the primary molten alloy according to the present invention will be described. Since this is melted as an ingot of 1 to 50 kg that can be directly charged into the secondary melting furnace, it will be referred to as “primary ingot” below. The primary ingot of the present invention has a significantly lower oxygen concentration than the scrap state, and is significantly lower than the conventional vacuum-melted primary ingot. The composition of this primary ingot is analyzed, combined with the virgin raw material, and the composition is determined so that the desired composition is obtained. Secondary melting and fabrication by the method described in (1) above to obtain a magnet alloy.

 Since the amount of oxygen in the metal is reduced by the primary melting, when the secondary melting is performed using a vacuum high-frequency melting furnace, the slag-like metal content due to the unseparated oxide remaining in the metal decreases. It is possible to improve the yield.

At this time, the amount of primary ingot obtained from the rare earth magnet scrap must be determined in consideration of the following points. This is because scrap has a high carbon concentration due to the lubricant used during magnetic field press forming in the magnet manufacturing process, and decarburization is almost expected during primary melting. Therefore, the carbon content in the primary ingot is typically as high as 0.04% or more. Incidentally, the carbon content of the magnet alloy melted from the virgin material alone is usually less than 0.04%, and typically about 0.02%. If the amount of addition of the primary ingot is too large, the secondary dissolution ingot may be added. The carbon content of the magnet also increases, which adversely affects the properties of the magnet obtained from it. Considering this limitation by the amount of carbon, the primary ingot obtained by the present method can be secondary-dissolved as 50% by weight or less, and the remainder can be a virgin raw material ratio. As described above, in the present invention, the secondary ingot obtained by mixing and melting the primary ingot and the virgin raw material is used as the alloy for the magnet. On the other hand, the primary ingot alone may be used as a magnet alloy, and the ratio of this alloy may be limited in the pulverization and mixing step in the subsequent magnet production.

 In the composition of the primary ingot of the present invention, 15 to 40% of the rare earth element and Fe as the main component of the balance define the component range obtained by dissolving the most common grade of scrap. It was done. Oxygen is mixed in as impurities in the manufacturing process of the rare-earth magnet, particularly in the pulverization process or the sintering process. However, since this reduction is an important achievement of the present invention, it is limited to 0.1% or less. The components of the alloy for the magnet include Sm—Fe, Cu, Zr, and Nd (which may be partially replaced by Pr, Dy) of the Co-based magnet, _Fe— There are B-based magnets such as B, A1, Co, Cu, and Nb, and these are used as components of magnet alloys regardless of the quantity. In general, for Sm—Co magnets, Co is 40 to 60%, Fe is 10 to 25%, Cu is 4 to: L0%, Zr is 4% or less. Yes, for Nd-Fe-B magnets, B is 0.9 ~: 1.2%, A1 is 0.1 ~ 1.5%. Furthermore, in the case of a sintered magnet, carbon is mixed in the magnet alloy powder forming process, but as described above, this is hardly removed and remains in the primary ingot as an impurity. However, if the combined use of primary ingot and virgin raw material is adopted as described above, the carbon content can be tolerated up to 0.1%.

In the melting method according to the present invention, a metal such as Fe is mixed from the metal electrode used in the third method, in addition to the trace elements from the various refractories described above, for example, A1 and the like. This Fe is a necessary component of the magnet alloy. A 1 is S m A Co-based magnet is a harmful element for magnetic properties, while a Nd-Fe-B magnet is acceptable as a small alloy element, but too much is harmful to magnetic properties. Therefore, its amount is preferably less than 1%. BRIEF DESCRIPTION OF THE FIGURES

 FIG. 1 is a sectional view showing one embodiment of a water-cooled copper crucible for carrying out the first and second methods of the present invention.

 FIG. 2 is a sectional view showing one embodiment of a refractory crucible for carrying out the first method of the present invention.

FIG. 3 is a diagram showing an embodiment of the first melting apparatus of the present invention using a twin torch plasma arc melting furnace.

 FIG. 4 is a view showing one embodiment of the melting apparatus according to the second and third aspects of the present invention using a transfer type plasma arc melting furnace.

 FIG. 5 is a perspective view showing one embodiment of a water-cooled copper crucible provided with a current-carrying part for carrying out the second method of the present invention.

 FIG. 6 is a drawing showing one embodiment of a refractory crucible for carrying out the third method of the present invention.

 FIG. 7 is a drawing showing another embodiment of a refractory crucible for carrying out the third method of the present invention.

 FIG. 8 is a drawing showing still another embodiment of the refractory crucible for carrying out the third method of the present invention. Description of embodiments of the invention

 Hereinafter, an embodiment of a melting apparatus for carrying out the method of the present invention will be described with reference to the drawings.

FIG. 1 shows a crucible having a water-cooled structure made entirely of copper for carrying out the method of the present invention. In the figure, 1 is a copper crucible, 2 is a refractory plate, 3 is a raw material, 4 is a cooling water inlet, 5 is a cooling water passage, and 6 is a cooling water outlet. As shown in the figure, by using the refractory plate 2 only at the bottom of the crucible 1 and leaving the side wall of the water-cooled copper crucible, the heat input by plasma and the insulation by the refractory plate 2 are balanced. However, the molten pool can be deepened. Also, if only the bottom is insulated, it is possible to reduce the amount of expensive refractory used, the shape of the refractory is simple, the durability is excellent, and the cost is excellent because it is inexpensive. Dissolution method.

 FIG. 2 shows a refractory crucible for carrying out the method of the present invention. Here, a refractory crucible is placed in a metal container. In the figure, 7 is an alumina crucible, and 9 is an iron container. The gap between the crucible and the container is filled with alumina powder 8. FIG. 3 shows an embodiment of a twin torch plasma melting furnace. In the figure, reference numeral 10 denotes a plasma torch, which generates plasma 11 between the anode torch 10a and the cathode torch 10Ob.

 Fig. 4 shows the transfer type plasma arc melting furnace. In the figure, reference numeral 15 denotes a plasma torch, which generates a plasma arc between the torch and the raw material charged in the copper crucible 1. The tungsten arc melting furnace has a structure provided with a tungsten electrode in place of the plasma torch 15 and generates an arc between the electrode and the raw material. 16 is a raw material charging pipe.

 FIG. 5 shows a crucible provided with a current-carrying part 17. The current-carrying part 17 is formed by bending an iron plate or the like in accordance with the inner shape of the crucible so as to be in contact with the inner wall of the water-cooled copper crucible. Melting by this method · The following rare earth magnet scrap can be charged and melted inside the skull left after tapping.

At this time, a gap is formed between the crucibles due to the shrinkage of the remaining skull, which causes the conductivity to deteriorate and the crucible to be melted. It is preferable to provide an energizing section 17 for ensuring conduction between the crucible on one side and the skull. In Fig. 5, three plasma transistors are used. 1 shows a crucible used in a plasma arc furnace with three conductors, and three conducting parts are provided so that the conducting parts are arranged between two torches, respectively. By providing the energizing section 17 corresponding to the torch in this way, the scalar section can be made smaller and the heat insulation section can be made larger, improving safety and increasing the amount of melting. Can be. Although the metal for the current-carrying part is partially melted in the skull, it does not need to be replaced as long as the skull is not removed and the melting is continued without interruption.

 In FIG. 6 showing an embodiment of the third method of the present invention, the metal electrode 20 is, for example, a plate-like electrode covering the bottom of the crucible, and the crucible is vertically separated into a bottom 21 and a side wall 22. The electrode 20 is sandwiched between the bottom 21 and the side wall 22 so as to ensure that power is supplied from the outer periphery of the electrode 20 to the power supply. Alternatively, it is also possible to provide a hole at the bottom of the crucible and insert a rod-shaped electrode into the hole to ensure current supply. In the case of such a crucible structure, after the rare earth magnet scrap is melted, the crucible is tilted and heated. Further, as shown in FIG. 8, a crucible structure in which a tap hole 25 is provided at the bottom 21 of the crucible may be employed. BEST MODE FOR CARRYING OUT THE INVENTION

Example 1 (Example of the first invention)

 Scrap of NdFeB magnet (analytical value: Nd + Pr-29. 0 wt%, Dy-2.5 wt%, A1-0.332 wt%, B — 1.03 wt%, O — 0.66 wt%, C — 0.04 wt%, Fe remaining) as raw materials and a water-cooled copper crucible (bottom) insulated with a sintered aluminum plate. Argon gas was turned into plasma and melted using a 5 O kW twin-chip plasma arc melting furnace (Fig. 2) to obtain a primary ingot.

Analytical value of primary ingot: Nd + Pr-25. 2 wt%, Dy-2.1 wt%, A1-0.34 wt%, B-1.00 wt%, O — 0.018 wt%, C-0.04 wt%, Fe remaining. The melting amount of each knuckle is 1.5 kg, and the melting point of this alloy is 1200 to 125 ° C, so the melting temperature is more than 300 ° C higher than this. We decided at 1550. The crucible 1 had an inner diameter of 170 mm and a depth of 70 mm, and an alumina sintered plate 2 having a thickness of 2 Omm was disposed at the bottom.

 The primary dissolution yield was calculated by dividing the product weight by the charged raw material weight. The melting time in this twin torch plasma arc melting furnace was 13 minutes, and the melting power of the primary ingot was 2.8 kWh Zkg. Since the crucible bottom is insulated, the melting time is short and the melting power is small.

 The obtained alloy was used as a raw material and melted in an argon gas atmosphere using a vacuum high-frequency induction melting furnace. At this time, the primary ingot is usually added to the virgin raw material to make the magnet alloy composition, but in order to investigate the yield, the entire amount was melted with the primary ingot alone. Table 1 shows the dissolution yield of the obtained primary ingot, the dissolution yield of the secondary dissolution, and the average oxygen analysis value of the primary ingot.

 As shown in Table 1, by melting the scrap by twin torch plasma arc melting the primary ingot with a significantly reduced oxygen concentration by high frequency induction melting, the amount of slag generated is small and only the virgin raw material is used. A secondary dissolution yield close to 95%, which is the average yield when dissolving in water, was obtained.

Example 2 (Example of the second invention)

A scrap of the NdFeB magnet used in Example 1 was used as a raw material, and an alumina crucible (FIG. 2) was arranged. It was melted in a chi-plasma arc furnace to obtain a primary ingot. Analytical value of primary ingot: N d + P r — 25.0 wt%, D y — 2.2 wt%, A 1-0.38 wt%, B-0.99 wt%, O — 0.019 wt%, C-0. ◦ 4 wt%, Fe remaining. The dissolution amount of the batch was 1.5 kg, and the melting temperature was 1550 ° C. The aluminum crucible 7 has an inner diameter of 170 mm, a depth of 70 mm, and a thickness of 30 mm. This solution The solution time was 12 minutes and the dissolution power of the primary ingot was 2.6 kWhkg. As in Example 1, the dissolution time was short and the dissolution power was low. Table 1 shows the dissolution yield and average oxygen concentration at this time. These values were also the same as in Example 1, and an ingot with a high yield and a remarkably reduced oxygen concentration could be obtained.

 Comparative Example 1

 The NdFeB-based magnet scrap and virgin raw material used in Example 1 were melted using a 15 kW vacuum high-frequency induction melting furnace. The amount of dissolution was 5 kg, and the amount of scrap added to the virgin material was 50%. Table 1 shows the dissolution yield and average oxygen analysis value of the obtained primary ingot. The dissolution yield is assumed to be 95%, which is the average yield when dissolving the virgin raw material using only the virgin raw material, and the dissolving yield of only the scrap is adjusted to match the overall yield. The yield was calculated and the value was given.

 As a method of recycling the scrap, if the virgin raw material is melted directly in a high frequency induction furnace to obtain an alloy for magnets, a large amount of slag is generated, and the operation is difficult. Rate was low, and the composition of the obtained alloy was not stable.

Comparative Example 2

 Using the scrap of the NdFeB-based magnet used in Example 1 as a raw material, 5 kg was melted using a 15 kW vacuum high-frequency induction melting furnace to obtain a primary ingot. Analytical value of primary ingot: Nd + Pr-25.0 wt%, Dy-2.3 wt%, A1-0.35 wt%, B-1.01 wt%, O -0.020 wt%, C-0.04 wt%, Fe remaining.

As in Example 1, this primary ingot was melted again using a vacuum high-frequency induction melting furnace. As in Example 1, the dissolution yield and average oxygen analysis value were determined and are shown in Tables 1 and 2. Comparative Example 3

 The scrap material of the NdFeB magnet used in Example 1 was used as a raw material in a 50 kW twin torch plasma arc melting furnace using a water-cooled copper crucible without any heat insulation. 5 kg was dissolved to obtain a primary ingot. Analytical value of primary ingot: Nd + Pr—28.0 wt%, Dy-2.4 wt%, A1-0.322 wt%, B-1.02 wt%, O — 0.42 wt%, C-0.04 wt%, Fe remaining. This device can melt scrap with a melting point of 1200 to 125 ° C, but the melting temperature cannot be raised sufficiently because the crucible is not insulated. It stopped at 0 ° C. The skull was also thick, and about half of the charged raw material remained in the crucible as a skull. The melting time in this plasma arc melting furnace was 22 minutes, and the melting power for the primary ingot was 13 kWh / kg. As in the case of Example 1, this primary ingot was melted using a vacuum high-frequency induction melting furnace. In the same manner as in the examples, the dissolution yield and the average oxygen analysis value were determined and are shown in Table 1.

As shown in Table 1, the oxygen analysis value in the primary ingot is very high, and the deoxidizing effect is insufficient. When the scrap is melted in a plasma arc furnace equipped with a normal water-cooled crucible crucible, it is not insulated, and is not kept at a high temperature even if it is melted. It is clear that the oxygen concentration inside remains high. For this reason, the yield in the secondary melting in the high frequency induction furnace was low, and was about the same as when scrap was melted as it was. Ingot dissolution yield, oxygen analysis

Example 3 (Example of the second invention)

 Scrap of the NdFeB magnet used in Example 1 (analytical value: Nd + Pr—29.0 wt%, Dy—2.5 wt%, A1-0.32) wt% B—1.03 wt%, O-0.66 wt%, C—0.04 wt%) Water-cooled copper crucible (6 kg) with the bottom insulated by a sintered alumina plate ( Using a 30 kW tungsten arc melting furnace equipped with (Fig. 1), it was melted in an argon gas atmosphere to obtain a primary ingot. Analytical value of primary ingot: Nd + Pr-25.1 wt%, Dy-2.2 wt%, A1-0.32 wt%, B-1.02 wt%, O — 0.018 wt%, C-0.04 wt%, Fe remaining.

The melting amount per batch is 1.5 kg and the melting point of this alloy is 1300 ° C Therefore, the melting temperature was set to 160 ° C., which is higher by 300 ° C. than this. The crucible 1 had an inner volume of 11 O mm in diameter and a depth of 70 mm, and an alumina sintered plate 2 having a thickness of 20 mm was arranged on the bottom thereof.

 The melting time in this arc melting furnace was 11 minutes, and the melting power of the primary ingot was 1.5 kWh / kg. Because the bottom is insulated, the melting time is short and the melting power is small.

 The obtained alloy was used as a raw material and melted in an argon gas atmosphere using a vacuum high-frequency induction melting furnace. At this time, the primary ingot is usually added to the virgin raw material to make the composition of the magnet alloy, but in order to investigate the yield, the entire amount was melted with the primary ingot alone. Table 2 shows the dissolution yield of the obtained primary ingot, the dissolution yield of the secondary dissolution, and the average oxygen analysis value of the primary ingot.

 As shown in Table 2, high-frequency induction melting of the primary ingot, whose oxygen concentration was significantly reduced by high-temperature arc melting of the scrap, reduced the amount of slag generated and melted using only virgin material. A secondary dissolution yield close to 95%, which is the average yield when performing this, was obtained.

Example 4 (Example of the second invention)

 Instead of the crucible used in Example 3 (Fig. 1), a conductive part made of a pure iron plate (thickness 1 mm x width 15 mm, 3 pieces) was provided in contact with the inner wall of the water-cooled copper crucible shown in Fig. 5 When the scrap of the NdFeB-based magnet used in Example 1 was melted using the crucible, a primary ingot of the following analysis value was obtained. N d + Pr-26.0 wt%, Dy-2.4 wt%, A 1-0.33 wt%, B-1.0 0 0 wt%, O-0.0 16 wt% , C-0.04 wt%, Fe remaining. In addition, there was no melting of the crucible even if it was melted repeatedly 30 times or more.

When the current-carrying part is provided in this manner, arcing between the material to be melted and the water-cooled crucible is minimized, so that the crucible is not easily melted even after repeated melting, and the durability is dramatically improved. Could be improved. Pure iron plate is partially welded to the skull, but remains on the skull side, so the primary ingot The effect on the composition fluctuation due to the penetration into the steel was negligible. Example 5 (Example of the second invention)

 Plasma arc melting using a water-cooled copper crucible shown in Fig. 1 in which the same 5 kg scrap as the NdFeB magnet used in Example 1 was used as a raw material and the bottom was insulated with a sintered alumina plate. Using a furnace, melting was performed in an argon gas atmosphere to obtain a primary ingot. The melting temperature was the same as in the example, 160. I did. The analysis value of the primary ingot was Nd + Pr-24.8 wt%, Dy-2.1 wt%, A1-0.35 wt%, B-0.98 wt%, O -0.018 wt%, C-0.04 wt%, Fe remaining.

 Further, in the same manner as in Example 3, a magnetic alloy was melt-formed using this primary ingot. In the same manner as in Example 1, the dissolution yield was determined, and the average oxygen analysis value of the primary ingot was measured. As shown in Table 2, also in the plasma arc melting furnace, remarkably reducing the oxygen concentration and a high secondary melting yield were obtained as in Example 3 by melting the scrap at a high temperature.

Example 6 (Example of the second invention)

After the raw material of the SmCo-based magnet alloy is melted in a vacuum high-frequency induction melting furnace, the residue remaining in the crucible (Sm—31.6 wt%, Fe-4.6 wt%, Zr — 2.0 wt%, O—2.8 wt%, Co remaining) and a 30 kW tungsten-arc melting furnace with a water-cooled copper crucible (Figure 1) insulated with a sintered aluminum plate at the bottom Metals could be recovered by melting in an argon gas atmosphere using a furnace. The dissolution amount is 1.5 kg, the dissolution yield of the obtained primary ingot is 75%, and the composition analysis value is Sm-15.0 wt%, Fe-28.0 wt% , Cu—4.6 wt%, Zr 2.5 wt%, O—0.021 wt%, Co remaining. As can be seen from the results, the high oxygen concentration residue in the high-frequency induction furnace crucible in the production of SmCo-based magnetic alloys is also significantly reduced in oxygen by high-temperature arc melting. Expensive metals such as Sm and Zr could be recovered in high yield as reusable metal. Example 7 (Example of the second invention)

 To the scrap of the NdFeB magnet used in Example 3, 10% of a virgin material containing Nd metal, which is significantly oxidized, was added, and a primary ingot was obtained in the same manner as in Example 3. Was. The oxygen analysis value of this ingot was sufficiently reduced to no significant difference from Example 1.

Example 8 (Example of the first invention)

 A scrap of 45 kg of the NdFeB magnet used in Example 1 was used as a raw material, the side was insulated with a sintered alumina cylinder 23, and only the bottom was a water-cooled copper plate 24. Using a 300 kW plasma arc melting furnace in which the crucibles shown in the figure were arranged, melting was performed in an argon gas atmosphere to obtain a primary ingot. Analytical value of primary ingot is Nd + Pr-25.8 wt%, Dy-2.3 wt%, A1-0.34 wt%, B-1.00 wt%, O -0.018 wt%, C-0.04 wt%, Fe remaining.

 The dissolution temperature was set at 160, the same as in Example 3. The crucible 1 was a sintered alumina cylinder 23 having an inner diameter of 32 O mm, a depth of 150 mm and a thickness of 30 mm, and a water-cooled copper plate 24 was disposed at the bottom.

Further, as in Example 3, the magnetic alloy was melt-formed using this primary ingot. As shown in Table 2, in this method, too, by dissolving the scrap at a high temperature, the oxygen concentration was significantly reduced and a high secondary dissolution yield was obtained.

Table 2

 Primary ingot dissolution yield, oxygen analysis

実施例 9 (第 2発明の実施例）

Example 9 (Example of the second invention)

As in Example 6, after the NdFeB-based magnet scrap raw material was melted and discharged, before the molten metal was completely solidified, additional raw materials were added without breaking the argon gas atmosphere. Again, electricity was applied to dissolve. When the molten metal in the crucible became full, a part of the molten metal was poured out by tilting the crucible, and the raw material was added, so that it could be melted continuously. In addition, the metal solidified in the tap at the top of the crucible, and an abnormal arc flew in this part at the beginning of energization, so the solidified metal in this part was cut out slightly to make the tap. The same primary ingot as in Example 8 was obtained by dissolution by such a method.

Example 10 (Example of the third invention)

 Scrap of NdFeB-based magnet used in Example 3 45 kg As a raw material, the sides were insulated with a sintered alumina cylinder, and the bottom was also insulated with a sintered alumina plate. Using a 300 kW plasma arc melting furnace equipped with a crucible as shown in Fig. 6 in which a circular plate made of pure iron was installed as a current-carrying part, melting was performed in an argon gas atmosphere, and the primary ingot was cooled. Obtained.

 The dissolution temperature was set at 160 ° C., the same as in Example 1. The crucible 1 is a sintered alumina cylinder 10 having an inner diameter of 32 O mm, a depth of 15 O mm and a thickness of 30 mm, and an outer diameter of 32 O mm and a thickness of 3 O mm at the bottom thereof. A sintered alumina circular plate was placed, and a 0.5 mm pure iron circular plate was placed inside.

 In this method, the same ingot as in Example 6 was obtained.

Example 1 1 (Example of the third invention)

 Using the scrap of the NdFeB magnet used in Example 3 as a raw material, the side part was insulated with a sintered alumina cylinder 22 and the tap hole 25 was left in the center of the bottom. The crucible shown in FIG. 8 was provided, in which a doughnut-shaped sintered alumina plate 21 was insulated, and a pure iron circular plate 20 was installed as a conducting part inside the pure iron part as a conducting part. Melting was performed in an argon gas atmosphere using a kw plasma arc melting furnace. When melted, the center of the steel plate was broken, and the molten metal flowed to the bottom, and a primary ingot was obtained in the mold installed underneath. The analysis value of the primary ingot was Nd + Pr-25.5 wt%, Dy-2.2 wt%, A1-0.35 wt%, B-1.01 wt%, O — 0.018 wt%, C— 0.04 wt%, Fe remaining.

In this example, the sintered aluminum plate at the bottom was a doughnut having an inner diameter of 10 O mm, an outer diameter of 320 mm, and a thickness of 30 mm under the same conditions as in Example 10. Dissolved. In this method, slag and some metal remained in the crucible, so that a 40 kg ingot with little slag entrainment was obtained. Example 1 2 (Example of the third invention)

 After melting and tapping under the same conditions as in Example 10, the slag on the upper part of the solidified metal remaining in the crucible was partially scraped off, the lower metal layer was exposed and the energized part was secured. Was added, and the method of melting by re-energizing was repeated. At this time, there was also a charge with a hole in the center of the remaining solidified metal. In this case, iron foil or an iron plate was placed to close the hole and the raw material was charged. In this method, the same ingot as in Example 10 was obtained. Industrial applicability

 As explained above, there has been no effective method to lower the oxygen concentration in the rare earth magnet scrap, so it is satisfactory to limit the amount of scrap used and dissolve it with the virgin raw material at best. There was no. According to the present invention, since there is no such restriction, the scrap generated in the magnet manufacturing process can be efficiently and economically reused. For this reason, effective utilization of resources and increase in production can be achieved.

Claims

The scope of the claims  1. In a method of obtaining a raw material for manufacturing rare earth magnets by first melting a scrap of a rare earth magnet,  A rare-earth magnet scrap (3) is charged into a water-cooled crucible (1) or a refractory crucible (7) in which part or all of the molten metal holding part is insulated (2). The rare earth magnet scrap is melted by a plasma torch (10) consisting of at least one pair of cathode and cathode, which is provided above the Dissolving method for rare earth magnet scrap.  2. The method according to claim 1, wherein when melting the scrap of the rare earth magnet, the molten metal is kept at a temperature higher than 200 ° C. from the melting point of the scrap of the rare earth magnet. Dissolving method of rare earth magnet scrap described in section.  3. The rare earth magnet scrap according to claim 1 or 2, wherein a virgin raw material made of a metal or an alloy mainly containing at least one of the rare earth magnet constituent elements is added to and dissolved in the rare earth magnet scrap. Rare earth magnet scrap melting method.  4. Dissolve a part of the melted rare-earth magnet scrap and add the rare-earth magnet scrap when the remaining melt is not solidified in the crucible. The method for melting a rare earth magnet scrap according to any one of claims 1 to 3, characterized in that:  5. In the method of obtaining the raw material for rare earth magnet production by primary melting the rare earth magnet scrap,  A scrap (3) of rare earth magnet is charged in a crucible (1) having a heat insulating part (2) and a water-cooled part in the molten metal holding part, and a tungsten arc or a transitional plasma arc (15) A method for dissolving a rare earth magnet scrap, characterized by dissolving the rare earth magnet scrap in (1).  6. The method according to claim 5, wherein after melting the scrap of the rare earth magnet, the molten metal is kept at a high temperature of 200 ° C. or more, which is the melting point of the scrap of the rare earth magnet. Dissolving method of rare earth magnet scrap described. 7. To the scrap of the rare earth magnet, add a virgin material composed of a metal or alloy containing at least one of the rare earth magnet constituent elements as a main component and melt. The method for dissolving a rare earth magnet scrap according to claim 6 or 7, 8. Dissolve a part of the melted rare earth magnet scrap and add the rare earth magnet scrap when the rest of the melt is unsolidified in the crucible. The method for dissolving a rare earth magnet scrap according to any one of claims 5 to 7, characterized in that:  9. In the method of obtaining a raw material for rare earth magnet production by primary melting of the rare earth magnet scrap, the molten metal holding part has a heat insulating structure (21, 22) in a crucible (1). And a second electrode (15) disposed above the crucible and a first electrode (20) for locally covering the heat insulating surface of the crucible. A method for dissolving a rare earth magnet scrap, which comprises dissolving a rare earth magnet scrap by generating an arc or a transition type plasma arc.  10. The method according to claim 1, wherein after the scrap of the rare earth magnet is melted, the molten metal is kept at a high temperature of 200 ° C. or more, which is the melting point of the scrap of the rare earth magnet. 9. The method for dissolving a rare earth magnet scrap according to item 9.  11. The rare earth magnet according to claim 9 or 10, wherein a virgin raw material made of a metal or an alloy containing at least one of the rare earth magnet constituent elements as a main component is added to the rare earth magnet scrap and melted. How to dissolve scrap, 1 2. The power of the first electrode (20) for covering the tap hole penetrating the bottom of the crucible (1) so that the entire amount of the rare earth magnet scrap is dissolved in the molten metal after melting. 12. The method for melting a rare earth magnet scrap according to any one of claims 9 to 11, wherein:  1 3. When the molten metal of the rare-earth magnet scrap is discharged from the tap hole, the slag layer on the molten metal of the rare-earth magnet scrap should not be mixed into the molten metal flow. 13. The method for melting a rare earth magnet scrap according to claim 12, wherein 1 4. In a plasma arc melting furnace equipped with a plasma torch (10) consisting of at least one pair of anode and cathode, a water-cooled crucible (1) or refractory in which part or all of the molten metal holding part is insulated. The crucible (7) A melting device for rare earth magnet scraps.  15. The rare-earth magnet scrap melting apparatus according to claim 14, wherein a refractory plate (2) is disposed so as to cover the entire bottom of the crucible and serves as the heat-insulating portion.  16. A rare-earth magnet scrap, characterized in that a crucible (1) in which a molten metal holding part has an insulating part and a water-cooling part is arranged in a tungsten arc or transition type plasma arc furnace (15). Melting equipment.  17. The rare earth magnet according to claim 16, wherein a metal plate (2) is arranged as a part of the electrode so as to cover a part of the crucible wall of the water-cooled part. Scrap melting equipment.  18. The dissolution of the rare earth magnet scrap according to claim 16 or 17, wherein a refractory plate (2) is disposed so as to cover the entire bottom of the crucible and is used as the heat insulating portion. apparatus.  19. In a tungsten arc or transition type plasma arc furnace, a crucible having a molten metal holding portion having a heat insulating structure (21, 22), and a first electrode (for locally covering the heat insulating surface of the crucible) 20) and a second electrode (15) disposed above the crucible, a melting apparatus for a rare earth magnet scrap, comprising:  20. The apparatus for melting a rare earth magnet scrap according to claim 19, wherein a tap hole penetrating the bottom of the crucible is formed.  2 1. In terms of weight percentage, the sum of 3 111 and 6 is 1041% Nd is 5 wt% or less, Fe force S2 is 5 wt% or less, Cu force S4 〜: I 0 wt% Zr force S 14 wt%, oxygen is 0.1 wt% or less, the balance is mainly Co, and unavoidable impurities and Fe that are caused by the rare earth magnet manufacturing process excluding oxygen Primary melting alloy of rare earth magnet scrap characterized by being an intrusion element caused by primary melting. 22. By weight percentage, Nd, Pr and Dy total 2035 wt% B force S ◦ .91.2 wt% A1 force; 0.1 ~: 1 wt% Co force S 5 wt% or less, Cu power S 0.5 wt% or less, Nb power S 1 wt% or less, oxygen power; 0.1 wt% or less, with the remainder being mainly Fe, inevitable impurities due to the rare earth magnet manufacturing process excluding oxygen, and invading elements caused by primary dissolution excluding Fe, Primary molten alloy with rare earth magnet scrap.  23. The primary molten alloy of a rare earth magnet scrap according to claim 21 or 22, wherein the unavoidable impurity is C of 0.1% or less.  24. The primary molten alloy of the rare earth magnet scrap according to any one of claims 21 to 23, wherein the alloy is in an ingot shape.  25. The primary molten alloy of a rare earth magnet scrap according to claim 24, wherein the weight of the ingot is l to 50 kg.  26. The primary molten alloy of the rare-earth magnet scrap according to any one of claims 21 to 25, wherein the rare-earth magnet is a sintered magnet.  2 7. A rare-earth magnet scrap (3) is placed in a water-cooled crucible (1) or a refractory crucible (7) in which part or all of the molten metal holding part is insulated (2), and the crucible (1) is charged. ) Is formed by melting the scrap of the rare-earth magnet by a plasma torch (10) consisting of at least one pair of anode and cathode provided so as to be located above The primary molten alloy of the rare earth magnet scrap according to any one of claims 21 to 26.  2 8. A scrap (3) of a rare earth magnet is charged into a crucible (1) having a heat insulating part (2) and a water-cooled part in the molten metal holding part, and the rare earth is transferred by a tungsten arc or a transition type plasma arc (15). The primary molten alloy of the rare earth magnet scrap according to any one of claims 21 to 26, produced by melting a scrap of a magnet. 2 9. A rare earth magnet scrap (3) is charged into a crucible (1) having a heat insulating structure (2 1, 2 2) having a molten metal holding section, and a first heat treatment is performed to locally cover the heat insulating surface of the crucible. By generating a tungsten arc or a transition type plasma arc between the second electrode (20) and the second electrode (15) arranged above the crucible, the scrap of the rare earth magnet is melted. 27. The rare-earth magnet disk according to any one of claims 21 to 26, Primary molten alloy in lap,