JPH0432525A - Method for plasma-melting active metal - Google Patents

Abstract

PURPOSE:To prevent scattering of raw material and to improve melting yield by standing up a heat resistant wall material providing the same kind of metal member as the raw material at inner side face so as to surround plasma irradiating range in a vessel for melting the raw material containing sponge material and chip material. CONSTITUTION:The cylindrical type heat resistant wall material 6 providing the wall material 14 having the same composition as the raw material at the inner side face, is stood up on the vessel 4 for melting the raw material. Then, in a sealed case 1, Ar is sealed under vacuum atmosphere with evacuating system 5, and after making near the atmospheric pressure, again this case is made to under reduced pressure inert atmosphere with the system 5. After that, the active metal raw material 11 mixing the Mg-reduced sponge titanium and the chip is melted with a plasma torch 2 while charging into the vessel 4 used to a mold, from a supplying hopper 3. Then, the scattered small drips of molten metal 12 and small pieces of the chip with the plasma flame 9 are stuck and caught to the wall material 14 and in the other, as a large part thereof is returned back in the vessel 4, the scattering inside the melting furnace can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for plasma melting active metals including sponge materials and/or swarf materials. When obtaining a metal ingot, there are many problems such as the droplet scattering phenomenon called the splash phenomenon, a decrease in product yield due to scattering of raw materials, and contamination of the vacuum exhaust system due to evaporation of chlorides etc. remaining in the sponge-like active metal. The present invention relates to a method for plasma melting active metals that can effectively prevent various troubles caused by such problems.

[Conventional technology]

Vacuum arc remelting method (hereinafter referred to as VAR method) has been widely used for melting active metals such as titanium sponge. This VAR method is a method in which an electrode made of an active metal is manufactured in advance, an arc is generated between the electrode and molten metal in a water-cooled crucible under high vacuum (approximately 10-2 to 103 torr), and the electrode is melted by the arc heat. be. However, this VA
As mentioned above, in the R method, it is necessary to manufacture an electrode made of an active metal prior to melting, and the process including electrode manufacturing is complicated and productivity is low.

On the other hand, in recent years, with the progress of vacuum technology and the development of high energy utilization technology, a plasma melting/casting method using a plasma melting method has been proposed and is attracting attention. This method is
Under an inert gas atmosphere or under vacuum (760~1O-2
In this method, a molten raw material is irradiated with plasma at a temperature of about 10.5 torr (about 1.5 torr) to melt the raw material, and the resulting molten metal is sequentially supplied to a water-cooled mold to obtain an ingot. With this method, without manufacturing electrodes, active metal raw materials in the form of scraps (hereinafter referred to as scrap materials) or active metal raw materials in the form of sponges (hereinafter referred to as sponge materials) can be used as melted raw materials in plasma as they are. ? can be understood.

[Problem to be solved by the invention]

By the way, although the plasma melting/casting method described above has various advantages, especially when a sponge material such as sponge titanium is used as a melting raw material, it causes an extremely undesirable phenomenon in which the molten metal scatters while exhibiting a foaming state during melting ( At the same time, a large amount of chlorides (MgC1z, NaC1, etc.) evaporates from the melted raw materials and adheres to the inner walls of the melting furnace, the exhaust valves and exhaust pumps of the vacuum exhaust system, etc. In addition, when chips made by processing scraps into small chips are used as a raw material for melting, when the chips are irradiated with plasma, a phenomenon occurs in which the chips processed into small pieces are scattered due to the blasting force of the plasma. These problems not only cause a decrease in yield during melting, but also cause scattered droplets, chlorides, evaporated substances, etc. to adhere to the inner walls of the melting furnace, obstructing high vacuuming, and preventing plasma irradiation. It causes many troubles, such as adhering to the oil, etc., and causing operational problems, or contaminating the oil in the oil diffusion pump, lorry pump, etc. of the vacuum exhaust system.

Especially IjgC]. Because it has a high hygroscopicity, if the inside of the melting furnace is exposed to the atmosphere when operations are interrupted, it will quickly absorb moisture, which will significantly impede vacuuming when operations are resumed. Therefore, in order to avoid the above-mentioned troubles, maintenance work such as removing deposits must be performed frequently.

Therefore, the present invention has been made to solve the above-mentioned problems, and its purpose is to:
Prevents sponge material, chips, molten metal droplets, etc. from scattering over a wide area, improves melting yield, prevents operational troubles due to adhesion of chlorides and evaporated substances, and removes adhesion. The purpose of the present invention is to provide a method for plasma melting active metals that can facilitate maintenance and ensure stable operation.

[Means for Solving the Problems] In order to achieve the above object, the first invention of the method for plasma melting active metal according to the present invention is a method for plasma melting active metal raw materials including sponge material and/or chip material. In this method, plasma melting is performed by installing a heat-resistant wall material on the inside surface of the melting container, which is equipped with a member made of the same type of active metal as the raw material, so as to surround the plasma irradiation area of the melting container. be. The second invention is a method for plasma melting an active metal raw material including sponge material and/or swarf material, in which a heat-resistant wall material is erected on the melting container so as to surround the plasma irradiation area in the melting container. At the same time, an exhaust system leading to the inside of this heat-resistant wall material is provided for plasma melting.

[For production]

In the first invention, a heat-resistant wall material whose inner surface is equipped with a member made of the same type of active metal as the raw material is erected on the melting container so as to surround the plasma irradiation area of the melting container. Small droplets of molten metal, small pieces of sponge material and/or scrap material scattered by plasma irradiation are attached to and captured by a member installed on the inner surface of the heat-resistant wall material, and most of them are returned to the melting container. Therefore, scattering into the melting furnace is prevented, the melting yield is improved, and operational troubles due to adhesion of flying particles such as small pieces are also reduced. Furthermore, parts that have attached and captured scattered droplets of molten metal and small pieces of sponge material and/or swarf material can be replaced after each melting process and processed into swarf material, which can then be melted during another melting of the same type of active metal. , plasma melting with improved melting yield can be performed. In addition, some of the chlorides and evaporated substances are captured by the members installed on the inner surface of the heat-resistant wall material or by the inner surface of the heat-resistant wall material, so their adhesion to the inside of the melting furnace is reduced. Operational troubles can be reduced.

In the second invention, the heat-resistant wall material is erected on the melting container so as to surround the plasma irradiation head in the melting container, and an exhaust system that communicates with the heat-resistant wall material is installed. Small droplets of molten metal scattered by irradiation,
Small pieces of sponge material and/or chips are trapped on the heat-resistant wall material, and most of them are returned to the melting container, preventing them from scattering into the melting furnace and improving the melting yield. Operational troubles due to adhesion of scattered objects such as small pieces are also reduced. Scattering to the inner wall of the melting furnace is prevented and the melting yield is improved. In addition, chlorides and evaporated substances generated especially when using sponge materials such as sponge titanium are discharged from the exhaust system, thus preventing them from adhering and contaminating the melting furnace and the vacuum exhaust system. Operational troubles are prevented, and maintenance such as removal of deposits becomes easier. Further, it is preferable that a tramp for capturing chlorides, etc. is provided in the exhaust system so as to be replaceable. This protects the exhaust system and facilitates maintenance of the exhaust system. Furthermore, it is preferable to equip the inner surface of the heat-resistant wall material with a member made of the same type of active metal as the raw material.

As a result, as described in the first invention, small droplets of molten metal, small pieces of sponge material and/or scrap material scattered by plasma irradiation can be attached and captured, and this member can be replaced every time melting and processed into scrap material. Plasma melting with improved melting yield can be achieved by melting the same type of active metal during separate melting.

The form of the member made of the same type of active metal as the raw material to be installed on the inner surface of the heat-resistant wall material is not particularly limited, but it may be machined into a cylindrical shape or heat-resistant plate-shaped scrap material. It may be installed on the inner surface of the wall material.

(Example〕 Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 [-Above FIG. 1 is a schematic cross-sectional explanatory diagram of a plasma melting/casting apparatus to which the plasma melting method according to the present invention is applied. In times 1, 1 is the shield case, 2 is the plasma torch,
3 is a raw material supply hopper, 4 is a container for melting raw materials, 5 is a vacuum exhaust system, 6 is a cylindrical heat-resistant wall material, 7 is a slab drawing device, 8
1 is a DC power supply, 9 is a plasma flame, 10 is a slab, 11 is an active metal raw material, 12 is a molten metal, 13 is a shooter, and 114 is a wall material having the same composition as the raw material.

Using the device configured as described above, first, the inside of the shield case is operated with the vacuum exhaust system 5 to fill it with Ar gas under a vacuum atmosphere to bring it to near atmospheric pressure, and then the inside of the shield case is closed to the vacuum exhaust system 5 again. 5 to create a reduced pressure inert gas atmosphere. After this, Mg reduced sponge titanium 20% (chloride content 50%)
0 ppm) and 80% of cutting waste are mixed almost evenly into an active metal raw material 11 from a raw material supply hopper 3 into a shooter.
Plasma melting was performed using the plasma torch 2 while charging the raw material into the raw material melting container 4, which also served as a mold, through the tube 13.

After melting, the surface of the refractory wall material 6 was observed, and it was found that in the lower part of the wall material 4 which had the same composition as the raw material near the molten metal 12, chips scattered by the plasma flame 9 were stacked, and the material was due to the splash phenomenon. The adhesion of the scattered molten metal is often seen in the lower part of the wall material 14, and the amount decreases as it goes to the upper part C. In this example, the diameter of the round melting container 4 is 100 m.
m, and the scattered molten metal of the fire-resistant wall material 6 is 48 m from the molten metal surface.
They are hardly seen at a height of 0 mm, and therefore, the height of the fireproof wall material 6 should be at least five times the inner diameter of the melting container 4 to sufficiently capture the scattered objects. In addition, there is no adhesion of scattered I8 molten metal on the inner part of the fireproof wall material 6 that is covered and hidden by the wall material 14, and some amount of scattered molten metal adheres to the upper part of the wall material 6 that is not covered by the wall material 14. It was observed. Furthermore, in the upper part of the fire-resistant wall material 6, there is a lot of contamination such as chloride that evaporates upward, and near the surface of the molten metal of the wall material 14, the contamination of chloride, etc. is higher than in the upper part of the fire-resistant wall material 6. There weren't many. Also, by installing this wall material 6, the shield case 1,
Plasma torch 2, raw material supply hopper 3, vacuum exhaust system 5
The contamination caused by single-shot substances such as chloride was considerably reduced compared to the case where the wall material 6 was not installed. The melting yield at this time is
When the weight of the melted ingot was divided by the weight of the feed material and expressed as a percentage, it was 98%, an improvement of 5% compared to 93% when the wall material 14 was not provided.

In the above embodiment, the shape of the fireproof wall material 6 has been described as being cylindrical, but the shape may be a rectangular tube (quadrangular or polygonal). Further, as shown in the second part, the shape of the upper part 15 may be a conical shape, a constricted L-shape, or a simply capped shape.

Figure 3 is a schematic cross-sectional view of another embodiment of a plasma melting/casting apparatus to which the plasma melting method according to the present invention is applied. In the figure, 1 is a shield case, 2a and 2b are plasma torches, 3 is a raw material supply hopper, 4 is a container for melting raw materials, 5 is a vacuum exhaust system in the furnace, 6 is a heat-resistant wall material, and 7 is a slab drawing device , 8a.

8b is a DC power supply, 9 is a plasma flame, 10 is a slab, 11 is an active metal raw material, 12 is a molten metal, 13 is a shooter 15
16 indicates a water-cooled mold, 16 indicates a water-cooled weir, 17 indicates a chloride trap, and 18 indicates an exhaust system within the heat-resistant wall material 6. The chloride capture trap 17 is connected to an opening in the heat-resistant wall material 6. The exhaust system 18 is installed in the exhaust pipe line 19, and the active metal raw material 11, especially the sponge material, remains in the active metal raw material 11, especially MgC1z and NaCl, by the suction of the exhaust system 18.
It captures chlorides such as

Using the apparatus configured in this way, first, the vacuum exhaust system 5 is activated to fill the inside of the shield case l with Ar gas under a vacuum atmosphere to bring it to near atmospheric pressure, and then the vacuum exhaust system 5 is turned on again. 5 to create a reduced pressure inert gas atmosphere. After this, Na reduction sponge titanium 85% (chloride content 31%)
500 ppm) and 15% of cutting waste are mixed almost evenly into the raw material melting container 4 from the raw material supply hopper 3 via the chute 13, and the plasma flame 9 from the plasma torch 2a is used as the raw material. 11 to perform plasma melting. The molten metal 12 obtained by this melting is poured into a water-cooled mold 15 while preventing floating substances such as molten slag from flowing out with a water-cooled weir 16, and the top surface of the molten metal poured into the water-cooled mold 15 is heated with a plasma torch 2b. It was then cast.

Even in this type of plasma melting method for active metals, as in the first embodiment, the scattered sponge material and molten metal are captured by the wall material 6, and many of them are stacked on the inner surface of the lower part of the wall material 6. Ta. Further, the dissolution yield at this time was 85% when the wall material 6 was not provided for comparison, due to the large amount of evaporation of chloride, whereas the dissolution yield was significantly improved to 94%. In addition, the trap 17 for trapping chloride was a removable cassette type with a cylindrical double pipe structure and a surface area of 380 cf, and was installed in the exhaust pipe line 19 of the exhaust system 18. A large amount of evaporated matter such as chloride was attached and trapped on the surface. In addition, Tora・7 for chloride capture
The structure of the plate 17 is not limited to the above, and for example, a perforated plate having a large number of through holes can be used.

[Effects of the Invention] As described above, according to the plasma melting method for active metals according to the present invention, active metal raw materials containing sponge material and/or swarf materials are used as melting raw materials, and the melting yield is reduced due to scattering of these raw materials. Plasma melting with improved melting efficiency can be performed without reducing the melting efficiency. Furthermore, what about the raw materials that fly away? 8. The adhesion of evaporated substances such as chlorides from molten metal and molten metal to the plasma torch, furnace inner wall, etc. can be effectively suppressed.
Operational troubles such as breakdowns in the vacuum exhaust system, clogging of the plasma torch, and falling of deposits into different molten metals are reduced, and chlorides and the like can be easily recovered and removed, improving productivity.

[Brief explanation of drawings]

FIG.
FIG. 3, a cross-sectional explanatory view of a heat-resistant wall material according to the present invention, is a schematic cross-sectional view of another embodiment of a plasma melting/casting apparatus to which the plasma melting method according to the present invention is applied. 1 shield case 3 raw material supply hopper 2 2a,
2b Plasma torch 4 Raw material melting container 5 Vacuum exhaust system 6 Heat-resistant wall material 7 Slab drawing device 8, 8a, 8b DC power supply 9 Plasma flame 10 Slab 11
Active metal raw material 12 Molten metal 13
Shooter 14 Wall material with the same composition as the raw material 15 Water-cooled mold 16 Water-cooled weir 17
Chloride trap 18 Exhaust system 19 Exhaust pipe patent applicant Kobe Steel, Ltd.

Claims (4)

[Claims] (1) A method of plasma melting active metal raw materials including sponge materials and/or cutting materials, in which a member made of the same type of active metal as the raw materials is equipped on the inner surface so as to surround the plasma irradiation area in the melting container. A plasma melting method for active metals, which comprises placing a heat-resistant wall material upright on a melting container and performing plasma melting. (2) A method of plasma melting active metal raw materials including sponge material and/or swarf material, in which a heat-resistant wall material is erected on the melting container so as to surround the plasma irradiation area in the melting container, and A plasma melting method for active metals, which is characterized in that plasma melting is carried out by providing an exhaust system leading into this heat-resistant wall material. (3) The method for plasma melting active metals according to claim 2, characterized in that the exhaust system is equipped with a trap for capturing chlorides, etc. (4) A method for plasma melting an active metal according to claim 2 or 3, characterized in that a member made of the same type of active metal as the raw material is provided on the inner surface of the heat-resistant wall material.