JPH03134485A - Cold wall type crucible furnace melting device and melting method - Google Patents

Abstract

PURPOSE:To extend the service life of an inductive crucible furnace and reduce the manufacturing cost of titanium ingot or titanium alloy by coating an inner surface of a water-cooled copper segment with ceramics whose surface is smooth. CONSTITUTION:A plurality of water-cooled copper segments 3, which comprise the walls of a furnace, are separated by adjacent water-cooled copper segments and slots 2 at a specified span. There is internally provided a cavity which forms a water-cooled jacket 11. Except for the upper end, the cavity is vertically divided into two sections by a partition plate 12 which extends substantially vertically, thereby forming the water-cooled jacket 11. Each water-cooled copper segment 3 is connected with each other at the bottom. The lowest end forms a flange 3', which is but-welded with a flange of an inner cooling water chamber 13 and connected. A flange of an outer cooling water chamber 14 is laid out at the outer periphery of the flange of the inner cooling water chamber 13 so that they may be tightly connected with each other, thereby eliminating leakage. A ceramic coating layer 15 is applied to the inner walls of the water-cooled copper segments 3 and their upper edges. The ceramic coating, although hard in quality, is free of scratch, thereby maintaining the inner surface of the crucible furnace under a smooth state.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is directed to high-grade special metals, particularly oxygen (0) and nitrogen (N
), it is difficult to melt-melt it as a high-purity metal or alloy.
TiJ, Mo, Be, called Metalsl.
Zr.

This invention relates to a high frequency crucible melting furnace having a structure suitable for melting V, Sr, etc.

More specifically, it is a crucible used for an induction melting method called a cold wall crucible melting method. This is a crucible melting device consisting of a heating coil.

A feature of this type of crucible is the structure of its side wall, which is divided into a plurality of vertically elongated rectangular side wall segments approximately parallel to the axis on its circumferential surface, approximately 4 to 20. The side wall segments are disposed intermittently with a predetermined gap between adjacent side wall segments so that the side wall portions do not form a continuous coil, and each of the side wall segments is arranged intermittently with a predetermined gap between them to allow cooling water to flow inside each side wall segment. Although there is a gap between the parts, they are joined together and electrically connected at the bottom.

[Prior Art] Structural alloy steels, heat-resistant alloys, etc. are processed using consumable or non-consumable electrode arc furnaces or high-frequency induction melting furnaces.
Even today, it is possible to meet quality demands.

On the other hand, a) High-purity metals, alloys, etc. such as semiconductors, which are called special metals, Ti, N
Metals that easily react with oxygen, nitrogen, carbon, and other elements, such as O, 2R, and their alloys, and metals with extremely high melting temperatures, such as W, Mo, and Ta, and their alloys, etc., were conventionally processed using non-consumable arcs. We have managed to meet requests by melting in furnaces, high-frequency induction furnaces, etc., and also using vacuum melting, atmosphere melting with inert gas, etc. as necessary.

However, most of the above melting devices are metallurgical containers such as furnace bodies, crucibles, or graphite crucibles made of ceramic refractory materials mainly containing metal oxides such as alumina, silica, magnesia, and beryllia. (hereinafter referred to as the furnace body), the metal to be melted was placed inside the furnace body and melted at high temperature. As a result, the ceramic components that make up these refractory materials and the carbon in the graphite crucible are absorbed into the metal to be melted.
The purity of the melted material has decreased and it no longer meets the required specifications.

The most notable example is that when it comes to titanium and its alloys used in spacecraft, graphite from graphite crucibles mixes with the titanium and its alloys, reducing their mechanical properties, but no innovative melting equipment has been developed since then. Since then, the consumable electrode type arc melting method has become mainstream. In the United States, which is most closely associated with the aerospace industry among liberal nations, research is underway to develop melting methods and equipment that can avoid high-temperature contact between the metal to be melted in the furnace and the furnace walls. As a result, the methods proposed include a non-consumable electrode type vacuum arc melting method using a water-cooled copper electrode, an electron beam (EB) melting method, and an electroslag melting method.

On the other hand, the United States has developed a melting method and device that uses a split crucible, in which the furnace wall of the crucible is divided into multiple segments in the circumferential direction, extending vertically into strips, and each segment is cooled with water, without using a graphite crucible. Developed by the Bureau of Mines 195
It was patented in 1977.

This melting method is called an induct slab melting method or an induction slag process, and the structure of the apparatus is as shown in FIG.

A feature of this device is that each of the water-cooled copper side wall segments 3, which are divided into a plurality of elongated sections by the slots 2, are joined at the bottom to be integrated, but the side walls do not need to be completely insulated from each other. Based on the knowledge that (to summarize), the molten slag layer 4 and the solidified thin slag layer 4 are formed and are interposed between the metal to be melted and the furnace wall, so there is no need to create an insulating structure in advance. 16 is a stub for starting coagulation, and 17 is a stub for starting coagulation.
is a drawing rod for drawing out solidified metal.

Despite these structural features, high quality slag made of lucium fluoride (CaFzl) is required, and calcium fluoride and aluminum react during melting to generate gas and solidify. The formation of pores in the metal made melting and casting difficult, so it was not put into practical use for quite some time.

Later, using equipment for the intact slab melting method, it was discovered that melting was possible without the use of slag.

For example, the floating melting method carried out by Mr. D.A. Hukin melts lanthanum in vacuum without slag and melts platinum in the atmosphere (USP 37023681゜A summary of this equipment is shown in Figure 2fAl and ( Bl, and in this method, as shown in the above drawings,
The furnace body 3 of the crucible is divided into a plurality of elongated compartments by slots 2, connected together at the bottom 3°, with an open head followed by a hollow cylindrical part, and an inner diameter gradually decreasing between the head and the bottom. This method uses a crucible whose internal shape resembles a wine glass.

On the other hand, a method of melting active metals without slag using the same type of crucible was proposed by Durillon, also of the United States (Japanese Patent Application Laid-open No. 63-14934171. The outline of this device is shown in Fig. 2 (C). This method is as shown in Dl, and is also called the injection skull melting method, but in short, a solidified layer 5 of the metal to be melted called a skull is formed on the furnace wall surface of the water-cooled copper strip segment 3. The idea is that the upper part of the crucible tries to float the molten metal from the side walls by electromagnetic induction, thereby preventing short circuits between the copper strip furnace walls, and the lower part 6 of the crucible is integrally connected to prevent short circuits.

As for electromagnetic action, a part of the high frequency magnetic flux generated by the high frequency current passed through the primary induction coil 8 passes through the water-cooled copper strip segment 3 constituting the crucible and causes a secondary induced current to flow.

However, since the furnace wall of the crucible is divided into strip segments 3, the flow does not circulate around the entire circumferential wall of the crucible (it only flows in each strip segment. Therefore, the current value is small and each strip segment Each strip segment generates some heat due to the electrical resistance of the copper to the current flowing through the segment.
1 is cooled by water flowing inside it.

On the other hand, most of the high-frequency magnetic flux generated by the primary induction coil 8 passes through the melting chamber 9 of the crucible, causing a secondary induction current to flow through the unmelted material or molten metal contained therein, causing it to generate heat. to advance the melting process or increase the temperature of the molten metal.

Inside the molten metal, the high-frequency magnetic flux generated by the primary induction coil and the secondary induced current generated by the magnetic flux generate forces in the direction perpendicular to the direction of the magnetic flux and the direction of the current, respectively. The unbalance stirs the molten metal within the melting chamber of the crucible and mixes the added alloying components.

The advantages of the cold wall melting method described above are: 1) Since the slits are cut, there is little power loss in the copper crucible itself.

2) Contamination due to contamination with ceramic refractories or reactions with them can be avoided.

3) Electromagnetic stirring force allows metals with different specific gravity to be made into a high-quality alloy without causing segregation.

4) Since the atmospheric pressure can be increased to 1 atm or more,
Two or more alloying elements with very different boiling points can be alloyed.

5) High purity metals or alloys can be produced by melting in vacuum or under an inert atmosphere, comparable to electron beam (EB) melting.

[Problems to be Solved by the Invention] However, the following drawbacks are recognized in this induction skull melting method.

1) Compared to normal vacuum melting, the power consumption rate is not good, which poses an obstacle when increasing the size of the equipment.

2) It is necessary to further extend the life of the crucible.

Although it has a longer lifespan compared to regular ceramic crucibles,
Since the manufacturing costs for water-cooled segmented crucibles are quite high, extending the life of the crucible is a very important issue.

A common solution is to reduce the amount of radiation heat transfer from the molten metal in the crucible, but to do this, the smoothness of the inner wall surface of the water-cooled segment crucible should be made to the level of a polished surface, and It was necessary to select a material for the inner wall that had a good heat reflection coefficient, and attempts were made to plate the inner surface of the water-cooled copper segment with gold, but since gold is soft by nature, The gold-plated surface is easily scratched when adding the amount of material to be melted into the crucible or when attaching and removing the skull.

It is also possible to use the polished inner surface of the copper segment without gold plating, but even if the initial polishing is satisfactory, as it is used, a copper oxide film is formed on the surface and the absorption of radiant heat is rapid. As the problem continued to increase, a fundamental solution could not be found.

[Means for Solving the Problems] In the present invention, the problems were solved by applying a ceramic coating with a smooth surface to the inner surface of the water-cooled copper segment.

[Function] Ceramic coatings are hard by nature, so they do not get scratched, and the inner surface of the crucible is maintained in a smooth state, which reduces the reduction in power consumption due to absorption of radiant heat, and the thickness of the coating is only a few microns. The temperature difference between the crucible and the copper part that makes up the crucible can be made negligible.

[Example] Figure 1 (Al) and Figure 1 (B) are a side sectional view and a plan view, respectively, of a cold wall melting apparatus to which a ceramic coating according to the present invention is applied. The members will be described with the same reference numerals.

In the figure, reference numeral 3 denotes a plurality of water-cooled copper segments constituting the furnace wall. Adjacent water-cooled copper segments are separated by slots 2 at predetermined intervals, and there is a void inside which becomes a water-cooling jacket 11. The interior, except for the upper end, is partitioned into two parts vertically by a partition plate 12 extending almost vertically.
The water cooling jacket 11 is divided into sections.

The water-cooling jacket 11 directly communicates with the inner cooling water chamber 13, into which cooling water is supplied, and flows upward in a flow path close to the inner wall of the water-cooled copper segment 3, passing over the upper end of the partition plate 12 and passing through the outer flow path. The water flows downward and is discharged to the outside via the outer cooling water chamber 14 which surrounds the inner cooling water chamber 13 and is arranged on the outside.

Each of the water-cooled copper segments 3 is connected together at its bottom, with the lowermost end forming a flange 3' and an inner cooling water chamber 1.
It is connected to the flange of 3, and the inner cooling water chamber 13
The flange of the outer cooling water chamber 14 is arranged on the outer periphery of the flange of the outer cooling water chamber 14 and is fluid-tightly connected to the flange of the outer cooling water chamber 14.

15 is a ceramic coating layer applied alternately to the inner wall portion and the upper edge of the water-cooled copper segment 3, and the thickness thereof is selected within the range of 5 to 500 um.

Although titanium nitride is suitable for dissolving titanium and its alloys, other coating layers with a large thermal infrared reflection coefficient can be used.

Ceramic coatings can be applied using ion blasting or chemical vapor deposition (CVD).
ourDeposition) is preferred. In order to reduce the reduction in the electric power consumption of the crucible due to radiant heat from the molten metal, it is necessary to make the surface of the ceramic coating layer as smooth as possible, and it is necessary to have a smooth surface at least as smooth as a polished finish.

i Reading 1 The water-cooled copper segment crucible melting apparatus of the present invention is suitable for melting active metals, particularly titanium ingots or titanium alloy castings.

After charging an appropriate amount of raw materials, the primary induction coil is energized to start the shore melting. Once the molten metal reaches a predetermined amount, the skull that forms on the inner wall of the crucible will have the appropriate thickness and shape. However, if there is a reaction due to components in the atmosphere, the operation should be carried out in a vacuum exhaust facility or a vacuum chamber, including replacement with an inert gas.

[Effects] l) There is no need to use slag such as calcium fluoride, so there is no need to consider the quality of the slag.

2) High quality products such as active metals, especially titanium ingots and titanium alloys, can be obtained.

3) The ceramic coating layer can significantly extend the life of the induction crucible furnace, which is an assembly of many water-cooled copper segments and is a high-cost structure to manufacture, thereby contributing to reducing the cost of titanium ingots or titanium alloys.

[Brief explanation of the drawing]

1(A) is a schematic side sectional view of a cold wall type crucible melting furnace of the present invention, FIG. 1(B) is a plan view taken along line BB in FIG. 1(A), and FIG. Figures (A) and (B) are a schematic side sectional view and perspective view of crucibles manufactured by 1 (ukin) as a conventional technique, and Figures 2 (C) and (D) are a schematic side sectional view and a perspective view of a crucible as a conventional technique by Durilon. Fig. 3 is a schematic side sectional view and plan view of an induction skull and crucibles, and Fig. 3 is a schematic side sectional view of an induction slab and crucibles as conventional technology. Reference numbers 2 in the drawings, 3: water-cooled copper Segment, 3”: Bottom of water-cooled copper segment, 5 Niscal, 8: High frequency primary induction coil, 11: Water cooling jacket, 12: Partition plate. 13: Inner cooling water chamber, 14: Outer cooling water chamber, 15: Ceramic coating layer.

Claims (6)

[Claims] 1. A plurality of rectangular hollow spaces whose upper ends are closed and which have gaps that serve as passages for the circulation of a cooling medium inside, and which are divided in the circumferential direction at predetermined intervals and extend vertically parallel to the axis. an intermediate side wall portion comprising side wall segments; and a bottom portion formed by integrally joining the lower ends of the rectangular hollow side wall segments, the inner surfaces of the intermediate side wall portion and the bottom portion comprising:
a crucible body made of a conductive metal such as copper and having an open top and forming a melting chamber for the metal or alloy to be melted inside; an induction heating coil disposed around the outer periphery of the intermediate side wall; A cold wall type crucible melting device having a ceramic coating layer with a smooth surface applied to a portion of the inner surface of the crucible body substantially in contact with the metal or alloy to be melted. 2. 2. The cold wall type crucible melting apparatus according to claim 1, wherein said ceramic coating is titanium nitride deposited by ion plating and has a thickness of 5 to 500 um. 3. 3. The crucible melting apparatus according to claim 1, wherein the ceramic coating is made of titanium nitride and has a thickness of 5 to 500 um, deposited by a CVD method. 4. 4. A method for melting an active metal or an alloy thereof using the cold wall type crucible melting device according to any one of claims 1 to 3, wherein a material to be melted is charged into the crucible melting device, cooling water is While introducing electricity, the material to be melted in the crucible melting device is melted by applying electricity to the induction heating coil, while a skull layer is formed between the inner wall of the crucible, which is composed of water-cooled copper side wall segments coated with ceramics, and the molten material to be melted. 1. A method for melting active metals or their alloys using a cold wall type crucible melting apparatus, characterized in that the molten metal is suspended in the upper part of the crucible and stirred to make the molten metal components uniform. 5. 5. The method for melting active metals or alloys thereof using a cold wall type crucible melting apparatus, wherein the material to be melted is titanium or an alloy thereof. 6. 6. A method for melting active metals or alloys thereof using a cold wall type crucible melting apparatus, wherein the melting method according to claim 4 or 5 is characterized in that the melting is carried out in a vacuum or in an inert gas atmosphere.