JPH08332557A - Centrifugal casting apparatus - Google Patents

Abstract

PURPOSE: To provide a centrifugal casting method excellent in the productivity and the durability of an equipment by rotating a cylindrical mold built-in a reciprocative tundish having plural nozzles in high speed, at the time of casting an alloy having fine micro structure, such as rare earth magnet alloy. CONSTITUTION: The cylindrical casting mold 1 provided with a rotating mechanism in a vacuum chamber 7, is arranged and molten metal 41 flowed out from a sprue of an induction melting furnace 4 is poured into the reciprocative tundish 2 through a fixed tundish 3. This reciprocative tundish 2 has plural nozzles 21 and reciprocatively moves in the axial direction of the cylindrical mold 1 with a rotating shaft 6. While reciprocatively moving this reciprocative tundish 2, the molten metal 1 is dropped to the inner wall of the rotated cylindrical mold 1 from the nozzles 21. A gas injecting hole for blowing cooling gas toward the inner wall of the mold is arranged in the space part in the cylindrical mold 1. Then, the interval between the nozzles 21 is <=200mm and the distance of the reciprocative movement of the reciprocative tundish 2 is made to <=1/2 of the interval between the nozzles 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting apparatus suitable for producing an ingot having a fine structure without segregation. In particular,
Recently, a rare earth sintered magnet or a rare earth bonded magnet that takes advantage of the excellent magnetic properties of the rare earth alloy system has been attracting attention, and the present invention is an alloy casting apparatus suitable for producing an alloy for a raw material used for such a rare earth magnet. It is about. Further, the present invention relates to an apparatus suitable as a casting apparatus for a rare earth transition metal alloy material used as a negative electrode material of a nickel hydrogen battery.

[0002]

2. Description of the Related Art A conventionally known method for casting a rare earth alloy is a method in which a molten metal is poured into a box-shaped mold to solidify it. In recent years, for example, in Nd-Fe-B system magnets, magnets having further improved magnetic characteristics have been developed. In such a high-performance magnet, it is necessary to increase the ratio of Nd ₂ Fe ₁₄ B, which is responsible for magnetism, to reduce the excess amount of Nd and make the composition close to the stoichiometric composition.
By the way, it is known from the equilibrium diagram that Nd ₂ Fe ₁₄ B is generated from the molten metal by the peritectic reaction between the primary crystal γFe and the liquid phase during melt casting.
ΓFe is likely to be generated and remain in the solidification process. Such γFe transforms into αFe during cooling and remains as αFe in the ingot after solidification. If such αFe remains in the ingot, there arises a problem that it cannot be crushed in the crushing process having the highest cost ratio in the magnetizing process.

Further, all the magnetic alloys actually industrially produced have a composition in which the rare earth element is slightly larger than the stoichiometric composition, and the magnetic alloy ingot has a high concentration of rare earth elements such as Nd (R (Rich phase) is also generated. R
In the Nd-based magnet alloy, the rich phase plays a role of enhancing the liquid phase sinterability, increasing the density and increasing the coercive force. The slower the ingot is cooled, the larger the R-rich phase is generated, and the uniform dispersibility is deteriorated. Thus, when a magnet alloy ingot having a poor R-rich phase uniform dispersion is pulverized as a starting material, liquid phase sintering is difficult to proceed, it is difficult to achieve high density, and the crystal grain size is relatively fine and the grain size is uniform. Obtaining a high-performance magnet becomes difficult. Also, αF
As for e, the slower the cooling of the ingot, the more easily it is generated, and the more coarsely and non-uniformly dispersed it is. Such αF
Also, "e" significantly impairs the pulverizability, causes a compositional change during pulverization, and causes deterioration of magnetic properties and increase in variation.

Therefore, it is not possible to obtain a high-performance rare earth magnet by conventional casting using a box-shaped mold. In addition, in order to increase the cooling rate in the conventional casting method using a box-shaped mold, it becomes necessary to set the mold so that the thickness of the ingot becomes thin, and in that case, in order to cast a large volume of molten metal. Requires the area to be increased by making the ingot thinner. However, in such a mold, it is necessary to pour a large amount of molten metal into a pouring part having a narrow mold interval, which causes a problem that the mold is easily melted. Further, the temperature of the molten metal decreases as it flows in the mold, while the mold is heated to a higher temperature as the wall surface of the mold is closer to the pouring portion where the molten metal passes through more. Therefore, the cooling form of the molten metal and the ingot after solidification is different in the vicinity of the pouring part and the part away from the pouring part, the resulting ingot is also affected by it, and the structure becomes different depending on the place, and the ingot of the desirable structure as a whole is It will be extremely difficult to do. For example, in a high-performance Nd-Fe-B based magnet alloy, the cooling rate becomes slow in the vicinity of the pouring portion due to the preheating effect of the mold of the molten metal, and αFe is easily generated. on the other hand,
In the part away from the pouring part, the temperature is likely to drop too much by the time the melt reaches that position, and it is likely to drop below the liquidus temperature at which γFe begins to form, so αFe (γFe in the high temperature range) Are easily generated.

Also in the negative electrode alloy for nickel-hydrogen batteries,
If it is attempted to approach the stoichiometric composition in order to improve the properties, in the conventional melt casting method using a box-shaped mold, segregation during solidification may cause Al and Mn to preferentially precipitate at grain boundaries inside the ingot. Are known. When such an alloy is incorporated in a battery, Al and Mn are preferentially dissolved in the battery solution, and the dissolved Al and Mn ions deteriorate the characteristics of the battery. As a method of solving such a problem, using a thin plate continuous casting method (strip casting method) such as a single roll or a twin roll, a thin ingot is continuously cast, a cooling rate is increased, and a fine structure is formed. A method for producing a rare earth magnet alloy or an alloy for a negative electrode material of a nickel-hydrogen battery has been proposed (for example, Japanese Patent Laid-Open No. Hei 5).
-222488, JP-A-5-295490 and JP-A-5-295490
320832). However, in the method using these equipment, casting takes time, and the molten metal containing the highly active rare earth element is held for a long time and is supplied little by little, so that the components change due to the reaction between the crucible, the holding furnace or the tundish and the molten metal. Easy to do. Further, it is extremely difficult to keep the temperature constant and keep stable casting in a steady state, and there is a problem that the yield is low. Further, there is a problem that a special expensive casting equipment is required.

As another method, there has been proposed a method of obtaining a powdered alloy of a rare earth magnet alloy or an alloy for a negative electrode material of a nickel hydrogen battery by using an atmosphere atomizing facility. However, in order to atomize, it is necessary to first create a fine stream of molten metal and apply a high-speed gas stream to it, but rare earth elements are extremely active and easily react with refractories, and there are refractory nozzles that can be used for such applications. Therefore, practical application is extremely difficult. Further, a method for producing an ingot by depositing atomized powder in a semi-solidified state on a substrate using a so-called spray forming method has been proposed. Also in this case, as in the atomizing method described above, there is a problem with the refractory nozzle for obtaining a fine stream of the molten metal, further requires special expensive equipment, and is scattered without being deposited on the substrate, so-called There is a problem that the ratio of overspray powder is high and the yield is low.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above problems and produces a high-performance rare-earth magnet alloy, a rare-earth transition metal alloy for nickel-metal hydride batteries, and other highly functional alloys having a fine structure and free from segregation. And a centrifugal casting device that is suitable for use in production and has excellent equipment durability. The centrifugal casting method is used for casting tubular iron castings, but it is sufficient that the molten metal solidifies on the surface of the casting, and no particular devise is required in the method of supplying the molten metal. Further, there is an example in which the centrifugal casting method is applied to a rare earth alloy (Japanese Patent Laid-Open No. 1-171).
217), in that case, it is only proposed as a method for manufacturing a cylindrical magnet, and no mention is made of a method for supplying molten metal.

[0008]

DISCLOSURE OF THE INVENTION The present invention is an improvement of a centrifugal casting apparatus for making a cast alloy crystal fine and uniform. That is, according to the present invention, a tundish is inserted and installed in a cylindrical mold having a rotating mechanism, and the tundish has a plurality of pouring nozzles and a reciprocating mechanism that operates in the axial direction of the mold. It is a centrifugal casting device.

The apparatus of the present invention will be described below with reference to the embodiments shown in the drawings. FIG. 1 is a schematic sectional view of the centrifugal casting apparatus of the present invention. 2 is a sectional view taken along the line AA of FIG. In the figure, 1 is a cylindrical mold. As the material of the mold, cast iron and steel materials used for ordinary molds can be used. By using pure copper or a copper-based alloy whose thermal conductivity is higher than those of these materials, thermal diffusion in the mold is accelerated, so that the cooling rate of the ingot can be further increased.
The mold material may be selected according to the alloy to be melt-cast and the required casting speed or the target alloy composition.

In the case of an alloy to be melted by using the apparatus of the present invention, the structure of the ingot is more important than the appearance, and the shape is easy to make equipment, easy to cast,
It can be determined in consideration of workability such as maintenance of casting, ease of setting, and removal of casting ingot. Considering such factors, the inner diameter of the mold should be at least 200m.
It is appropriate that the length is not less than m and the length is not more than 5 times the inner diameter of the mold. Cast thickness is an important factor in increasing the cooling rate. By setting the thickness of the ingot to be three times or more the thickness of the ingot to be cast, the relative heat capacity of the mold with respect to the ingot increases, and the cooling rate can be increased. The mold is placed on the rotating roller 5 and rotates according to the rotation of the roller by a driving device (not shown). The mold must be rotated at least at a speed such that the centrifugal force has a gravity acceleration of 1 G or more so that the poured molten metal does not drop when it reaches the upper part due to the rotation of the mold. By further increasing the centrifugal force, the cast molten metal is easily spread by the centrifugal force, the cooling effect is enhanced, and the homogeneity can be improved. In order to expect such an effect, the centrifugal force is 3 G or more, more preferably 5 G.
The rotation speed is set to be G or higher.

In the mold, the direction of the rotation axis (left and right in the figure)
A tundish 2 that reciprocates is installed in the. The tundish is made of refractory material such as alumina and has a large number of nozzles 2
1 is provided. Nozzle size is 5-20m in diameter
m is suitable. If the distance between the nozzles is too large, it is difficult to make the molten metal have a uniform thickness on the surface of the mold, so 200 mm or less is preferable. The reciprocating distance of this tundish is 1/2 or more of the nozzle interval for the same reason. The reciprocating motion of the tundish supports both ends by the rotary shaft 6,
This can be performed by repeatedly rotating the rotating shaft at a predetermined cycle.

The alloy to be cast is melted by, for example, an induction melting furnace 4, and the molten metal 41 is poured into the reciprocating tundish 2. Although not shown, the induction melting furnace has a structure in which the body is rotatably suspended by a chain and one end of the lower portion is pulled up by the chain, or the molten metal is tilted by using a hydraulic cylinder or the like. The molten metal can be injected into the reciprocating tundish by direct induction melting when the distance between the nozzles provided in the reciprocating tundish is narrow and therefore the reciprocating movement distance can be short. However, especially when the width of the nozzle interval is, for example, 50 mm or more, the moving distance of the tundish becomes long accordingly, and it becomes difficult to always receive the molten metal stably from the melting crucible. Therefore, the fixed tundish 3 is provided, and the molten metal is melted first. It is desirable to receive this fixed tundish and then pour it into the reciprocating tundish. The material of the fixed tundish may be the same as that of the reciprocating tundish. The central part of the reciprocating tundish is suitable for the tip of the fixed tundish so that the molten metal is uniformly dropped on the mold surface.

A gas blowing tube 8 for air cooling is preferably inserted and installed in the mold in the length direction of the mold, and casting in the mold is performed through gas ejection holes 81 provided at predetermined intervals in the length direction. A casting gas is cooled by blowing a cooling gas such as helium or argon toward the body surface. The gas blowing direction is preferably set so that the incident angle with respect to the mold surface is in the range of 95 to 45 °. In the apparatus of the present invention, in the case of an alloy that is easily oxidized, such as a rare earth magnet alloy, it is preferable to install the entire melting and casting apparatus in the vacuum chamber 7.

The cast alloy is deposited and solidified in a cylindrical shape on the inner surface of the cylindrical mold. The cast body thus deposited has a laminated structure in which many thin layers are superposed. It has one thin layer of molten metal
During rotation, it solidifies into a semi-solid state, the molten metal is poured onto it, and it becomes a semi-solid state, which is due to this repetition. To take out the laminated and solidified ingot, the vacuum chamber is separated at the flange 71, and the ingot on the inner surface of the mold is scraped.

[0015]

By reciprocating the tundish for pouring the molten metal into the mold, it is possible to perform casting so that the molten metal is uniformly deposited on the inner wall of the mold, and it is possible to manufacture an ingot having a uniform thickness. Furthermore, by controlling the pouring speed using this device, it becomes possible to select the condition that the cast molten metal will proceed to solidification before the next molten metal is poured, and the ingot with a fine structure without segregation can be selected. Can also be manufactured.

(Example of use of the apparatus of the present invention) The alloy composition is Fe-
32 wt% Nd-1.05% B-0.40% Al is mixed with electrolytic iron, Fe-Nd mother alloy, ferroboron and pure aluminum, and an alumina crucible is used in a reduced pressure atmosphere of argon gas 200 Torr. Melted in a high-frequency melting furnace, and immediately before casting, Ar gas was introduced until the pressure in the furnace reached atmospheric pressure.
The value obtained by dividing the molten metal volume flow rate per unit time by the internal area of the mold was 0.03 using a centrifugal casting machine having a length of 1000 mm and a length of 1000 mm.
It was cast so as to be cm / sec. The rotation speed of the mold at this time was set to 267 rpm so that the centrifugal force was 20 G. In addition, the nozzle 21 for pouring the tundish 2 is set to 7
Provided at cm intervals, tundish 2 stroke 6 cm
Then, it was moved in the longitudinal direction of the mold at 1 second / reciprocation. The thickness of the obtained alloy ingot was 5 to 6 mm. further,
As a result of observing the structure of the section with a reflection electron microscope, αF
No e was observed, and the average interval of the Nd-rich phase was as small as 20 μm, and an ingot having a fine and uniform structure was obtained.

[0017]

EFFECTS OF THE INVENTION In casting using a metal fixed mold, if the cast body has a certain thickness, the surface and the inside have different fine structures, and a homogeneous product cannot be obtained. According to the apparatus of the present invention, thin layered casting, solidification, and the same casting are repeated thereon, and thus the obtained cast body can obtain a metal or alloy having a fine and uniform structure from the surface to the inside. The alloy poured into the mold is cooled during one rotation of the cylinder and almost solidifies, so the cycle of pouring and solidification is efficient, and the cast body has a fine structure to the inside even if it has a certain thickness. High productivity because it can.

As for the mold itself, the cylindrical mold has less distortion and deformation of the mold as seen in a box-shaped mold. Further, since the strip casting method of pouring molten metal on the surface of a rotating roll cannot be cast in multiple layers, the contact between the roll and the molten metal is greater than in centrifugal casting, and the damage to the roll is large. In this respect,
In centrifugal casting, the molten metal comes into contact with the mold surface only during one rotation of the cylinder, and the damage to the mold is small.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a centrifugal casting apparatus of the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG. 1;

[Explanation of symbols]

 1 Cylindrical mold 2 Reciprocating motion tundish 21 Nozzle 3 Fixed tundish 4 Induction melting furnace 41 Melt 5 Rotating roller 6 Rotating shaft 7 Vacuum chamber 71 Flange joint 8 Cooling gas spray pipe 81 Gas ejection hole

Claims (4)

[Claims] 1. A tundish is inserted and installed in a cylindrical mold having a rotating mechanism, and the tundish has a plurality of pouring nozzles and a reciprocating mechanism that moves in the axial direction of the mold. Centrifugal casting equipment. 2. The cooling nozzle for blowing gas toward the inner wall of the mold is provided in the space inside the mold.
The described centrifugal casting device. 3. The centrifugal casting apparatus according to claim 1, wherein the centrifugal casting apparatus is provided in a vacuum chamber. 4. The centrifugal casting according to claim 1, wherein the distance between the nozzles is 200 mm or less, and the reciprocating distance of the tundish is 1/2 or more of the nozzle distance. apparatus.