JP5027682B2 - Method for producing refractory metal ingot - Google Patents

Description

  The present invention relates to a method for producing a refractory metal ingot using an electron beam melting furnace, and more particularly, to a method for producing a refractory metal ingot having an excellent casting surface.

  Titanium metal production has been greatly increased not only in the aircraft industry but also in recent years with the expansion of global demand. Along with this, the demand for not only sponge titanium but also metal titanium ingots is greatly increasing.

  A metal titanium ingot is formed by forming titanium sponge made by a so-called crawl method, which reduces titanium tetrachloride with a reducing metal, into briquettes, and then combining the briquettes into an electrode for melting, and then vacuum arc melting the electrodes. Can be manufactured.

  A metal titanium ingot can be made of not only sponge titanium but also metal titanium scrap that is available in the market, and melting a high-purity metal ingot in an electron beam melting furnace. Unlike a vacuum arc melting furnace, an electron beam melting furnace does not necessarily require a melting raw material to be formed into an electrode, and has a feature that a granular or massive raw material can be melted as it is.

  In addition, in an electron beam melting furnace with a hearth, the molten metal can be supplied to the mold after the raw material is melted in the hearth and the impurities in the raw material are effectively separated, so that a high-purity metal titanium ingot is melted. The effect that it can be manufactured is also produced. Therefore, according to the electron beam melting furnace with a hearth, it is possible to suitably melt a raw material in which impurities are contained not only in titanium scrap but also in a refractory metal such as zirconium, hafnium or tantalum.

  However, although the electron beam melting furnace can effectively melt a high-purity ingot using scrap as described above, the cast ingot which is the surface in contact with the mold is a vacuum arc. May be slightly inferior to melting furnaces.

  This is because the molten metal injected from the above hearth is supplied to a part of the mold pool, so that the temperature of the molten metal in the mold pool is biased, and as a result, the casting surface of the ingot generated in the mold is not good. There is a need for improvement.

  In order to solve this problem, a technique has been disclosed in which a molten titanium melted in an induction melting furnace having a mold continuously provided at the bottom is cooled and solidified in a mold at the bottom to form an ingot, which is extracted while being rotated ( For example, see Patent Document 1). However, the optimum values of the ingot drawing speed and rotation speed are only presented by analyzing the results of the test, and the above conditions are required for melting the ingot size and titanium alloy to be melted. It is difficult to apply as it is.

  Further, there is no disclosure relating to a technique of pulling out an ingot melted in the above-described electron beam melting furnace instead of an induction melting furnace.

  Further, a technique is disclosed in which chromium or a chromium alloy is melted by an induction slag melting method, cooled and solidified in a mold to form an ingot, and continuously drawn while rotating (see, for example, Patent Documents 2 and 3). reference). However, since the rotation speed is numerically defined by the input speed of the raw material per rotation, it is difficult to apply the above conditions to the dissolution of other metals.

As described above, there is a demand for a technique for melting a metal ingot having an excellent casting surface for not only titanium but also a high melting point metal such as zirconium or tantalum using an electron beam melting furnace.
Japanese Patent Laid-Open No. 02-236232 Japanese Patent Laid-Open No. 06-279884 Japanese Patent Laid-Open No. 06-287659

  The present invention is a method for producing a refractory metal ingot using an electron beam, and particularly aims to provide a melting method capable of effectively melting a metal ingot having an excellent casting surface.

  As a result of extensive studies in view of such circumstances, a refractory metal ingot having an excellent casting surface compared to the conventional one is melted by rotating and drawing out the refractory metal ingot melted in the electron beam melting furnace. As a result, the present invention has been completed. In addition to pulling out the refractory metal ingot while rotating it, melting the refractory metal ingot with better casting surface by making the drawing distance per rotation of the ingot smaller than the depth of the mold pool. I also found out that

That is, the present invention relates to titanium and zirconium that supply molten metal into a mold constituting an electron beam melting furnace and irradiate an electron beam to form a mold pool while drawing a cooled and solidified ingot near the mold bottom vertically. , A method for producing a metal ingot selected from hafnium, tantalum and tungsten , step 1: moving the metal ingot vertically downward, step 2: stopping the movement of step 1, step 3: moving the metal ingot Each step of rotating in a horizontal plane, step 4: stopping the rotation of step 3 is repeated, and the drawing distance per horizontal rotation of the ingot is smaller than the maximum depth of the mold pool.

In the present invention, after the cooled and solidified ingot is rotated in a horizontal plane, it is characterized in that withdrawing the ingot while repeating the operation to pull out the rotation was stopped and then the vertical direction.

Further, in the present invention , among the electron beams irradiated to the mold pool surface, the energy density of the electron beam along the peripheral edge of the mold pool adjacent to the mold is increased as compared with the central portion of the mold pool. It is characterized by doing.

  By using the method for producing a refractory metal ingot according to the present invention, a metal ingot having an excellent casting surface can be melted. As a result, the cutting yield is improved and a low-cost refractory metal ingot is melted. The effect that it can be done is produced. Moreover, the refractory metal ingot melted by the above method has an effect that the quality is excellent.

  The best embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows a preferred apparatus configuration example for carrying out the present invention. The electron beam melting furnace M used in the present invention shown in FIG. 1 has a mold 1 for holding and cooling and solidifying a molten metal, an electrode 2 as a melting raw material of an ingot, an electron gun 3 for melting the raw material, and a raw material melted. A mold pool 4 made of molten metal, an ingot 5 formed downward from the bottom of the mold pool 4, a stub 6 for pulling out the ingot, a pulling means 7 for the ingot 5, and a suspension means 8 for the electrode 2. Yes.

  The electrode 2 serves as a melting raw material for the ingot produced according to the present invention, and is composed of a metal rod composed of titanium, tantalum, hafnium, etc., a metal scrap, or a rod-shaped melting raw material prepared by powder metallurgy. Can do.

  After the rod-shaped raw material is mounted on the electrode suspension means 8, it is preferable that the inside of the electron beam melting furnace M is sucked under reduced pressure after closing a vacuum chamber (not shown).

  After confirming that the pressure in the electron beam melting furnace M has reached equilibrium, irradiation of the electron beam from the electron gun 3 disposed around the electrode 2 is started, and melting of the tip of the electrode 2 proceeds. The dissolution of the entire electrode 2 can be completed by sequentially lowering the electrode suspension device 8 downward as the electrode tip portion dissolves.

  Prior to the above-described dissolution, the stub 6 placed on the drawing means 7 is preferably inserted into the mold 1 into the mold 1. The top of the stub 6 inserted into the mold 1 preferably receives the electron beam from the electron gun 3 to form the mold pool 4.

  By continuously melting the electrode 2 while the electrode suspension device 8 is successively lowered downward, the mold pool 4 is increased and the molten metal surface is raised, so that the molten metal surface rises. Pull 5 down.

  The depth of the mold pool 4 depends on the diameter of the mold 1 and the energy of the injected electron beam, the sensible heat of the molten metal falling from the tip of the electrode 2, the drawing speed of the ingot formed in the mold 1, and the mold pool 4. It is determined by the balance between the amount of heat removed from the mold 1 and the radiant heat from the mold pool 4.

  The deeper the mold pool 4, the more uniform the composition of the ingot that is melted, but it is also necessary to increase the energy of the electron beam to be injected into the mold pool 4, which increases the cost.

  Therefore, the depth of the mold pool 4 can be set by combining the above factors with the optimum conditions according to the purpose each time in terms of cost or quality. In the present invention, from the viewpoint of the mold and cost, it is preferable that the depth of the mold pool 4 is configured to be in the range of 6% to 7% of the inner diameter of the mold 1.

  After the formation of a stable pool is confirmed under the above conditions, first, the titanium ingot starts rotating and the ingot is also pulled downward. The number of revolutions of the ingot is preferably set in the range of 1 rpm to 5 rpm. By rotating the ingot at such a speed, there is an effect that the casting surface of the titanium ingot formed in the mold 1 can be favorably maintained.

  Further, in the present invention, it is possible to pull out and rotate the ingot 5 downward at the same time to pull out the ingot spirally, but it is more preferable to perform the pulling and rotation separately. That is, in actual operation, it is preferable to rotate the ingot 5 held in the mold 1 a predetermined number of times and then stop the rotation of the ingot 5 and then pull out the ingot 5 by a predetermined amount. . In the present invention, after the ingot 5 is rotated 1 to 5 times, it is preferable to stop the rotation and pull out the ingot 5 by a distance smaller than the depth of the mold pool 4.

  In other words, the surface of the ingot 5 to be melted can be held smoothly by alternately and intermittently performing the rotation and drawing as described above. In addition, the ingot can be melted and pulled out with a relatively simple device.

  More specifically, when the mold diameter is 100 to 200 mm, the drawing speed of the ingot 5 is preferably operated in the range of 0.5 to 2.0 cm / min. By continuing the above-described operation, it is possible to efficiently produce a titanium ingot having an excellent casting surface.

  FIG. 2 is a plan view of the mold 1 and the mold pool 4 as viewed from above, and shows an electron beam irradiation site in the mold pool 4. For the mold pool 4 formed in the mold 1, the irradiation is divided into the peripheral irradiation from the electron gun 3 to the periphery of the mold pool 4 adjacent to the inner wall surface of the mold 1 and the central irradiation to the center of the mold pool 4. It is preferable to do. By employing such an irradiation method, the temperature in the mold pool 4 can be maintained uniformly.

  In addition, the irradiation direction of the said outer periphery irradiation does not necessarily need to match with the rotation direction of an ingot, and what is necessary is just to rotate and rotate in arbitrary directions.

  It is preferable to set the rotation speed of the outer periphery irradiation to be larger than the rotation speed of the ingot described above. In this invention, it is preferable to set to the range of 10-100 rpm.

  In the present invention, the rotation direction of the outer periphery irradiation may be periodically reversed with respect to the ingot 5 in the same manner. By irradiating the electron beam from the electron gun 3 along such a method, the ingot can be efficiently melted.

  In the present invention, it is preferable to rotate the ingot 5 prior to the irradiation of the electron beam into the mold pool 4. The molten metal held in the mold pool 4 is partly agitated by such a rotation operation of the ingot 5, and the electron beam energy irradiated thereafter can be distributed and supplied throughout the mold pool 4. As a result, the temperature distribution in the mold pool 4 can be maintained uniformly.

  The metal that can be melted using the present invention is suitable not only for melting metals such as titanium, zirconium, hafnium, tantalum, and tungsten, but also for melting metal ingots belonging to groups 4 to 10 of the periodic table. Applicable. Moreover, it can use suitably also for melting of the alloy ingot of these metals.

  By producing a metal ingot according to the present invention as described above, it is possible to produce a metal ingot having a good casting surface. As a result, it is possible to effectively increase the cutting yield of the ingot.

[Example 1]
The said Example was comprised using the electron beam melting furnace M shown in FIG. The specifications and operating conditions of the constituent equipment of the electron beam melting furnace M are as follows. An ingot was manufactured and pulled out under the following conditions.

1. Electron beam melting furnace 1) Electrode (raw material): It is an ingot raw material and is composed of tantalum scrap. Dimensions are outer diameter 150mm x total length 550mm.
2) Mold: A bottomless cylindrical container made of water-cooled copper. Inner diameter 150 mm x total length 170 mm.
3) Electron gun: Two electron guns for electrode dissolution and template pool formation are arranged. The output for electrode dissolution is 70 kW, and the output for mold pool formation is 150 kW.
4) Rotation / Pulling Device: A driving facility called a stub that can pull the pulling rod fixed to the pulling base while rotating it.
2. After the drawing operation was stopped for 1 minute and the ingot was rotated 3 times, the ingot was then stopped and the operation of drawing 2 cm in the vertical direction for 1 minute was repeated.
1) Drawing speed: 1 cm / min to 2 cm / min 2) Rotation speed: 2 rpm
3. Mold pool depth 1cm

[Comparative Example 1]
The ingot was manufactured and pulled out under the same conditions except that the rotation of the ingot was not applied.

  The tantalum ingot melted in Example 1 had a very good casting surface as compared with the ingot melted in Comparative Example 1. Further, when a required amount of the surface of the ingot melted by the above method was cut into a product ingot, the yield after cutting of the product ingot of Example 1 was improved by 5% compared to the product ingot of Comparative Example 1. It has been confirmed.

  Contributes to efficiency in the production of high quality refractory metal ingots.

FIG. 1 is a schematic cross-sectional view showing an embodiment of an electron beam melting apparatus of the present invention. FIG. 2 is a plan view of the mold and the mold pool portion of the electron beam melting apparatus of FIG. 1 as viewed from above.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Mold, 2 ... Electrode, 3 ... Electron gun, 4 ... Mold pool, 41 ... Outer periphery irradiation part, 42 ... Center irradiation part, 5 ... Ingot, 6 ... Stub, 7 ... Extraction means, 8 ... Electrode suspension means

Claims (3)

Titanium, zirconium, hafnium, tantalum and titanium, zirconium, hafnium, tantalum and A method for producing a metal ingot selected from tungsten,
Steps 1 to 4 below Step 1: Move the metal ingot vertically downward Step 2: Stop the movement of Step 1 Step 3: Rotate the metal ingot in a horizontal plane Step 4: Stop the rotation of Step 3 Repeat and let
A method for producing a metal ingot, wherein a drawing distance per horizontal rotation of the ingot is smaller than a maximum depth of the mold pool.   The electron beam irradiated to the mold pool surface is irradiated with a higher energy density of the electron beam along the peripheral edge of the mold pool adjacent to the mold than the center of the mold pool. Item 2. A method for producing a metal ingot according to Item 1. 3. The refractory metal ingot according to claim 1, wherein the peripheral speed of the electron beam irradiated along the peripheral edge of the mold pool is made larger than the rotational speed of the ingot itself by the drawing means. Method.

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