JP2010116581A - Method for producing titanium ingot using vacuum arc melting furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a titanium ingot using a vacuum arc melting furnace by which a titanium ingot having high purity, good casting surface and high productivity is produced. <P>SOLUTION: The method for producing the titanium ingot uses the vacuum arc melting furnace which generates an arc between molten metal held in a mold and a consumable electrode to melt the consumable electrode, thereby forming the ingot in the mold. The method is characterized in that an arc gap (a distance from the lower end of the consumable electrode to the molten metal surface) is changed according to kinds of titanium to be melted. When the ingot to be produced is titanium alloy, melting is performed with a smaller arc gap than an average arc gap (the arithmetic average of the maximum arc gap value and the minimum arc gap value in a range where the vacuum arc melting can be performed), and when the ingot to be produced is pure titanium, the melting is performed with a larger arc gap than the average arc gap. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a titanium ingot melting method using a vacuum arc melting furnace, and more particularly to a metal melting method capable of melting a titanium ingot having a good casting surface and high productivity.

  A high melting point metal such as titanium is generally melted under vacuum like the vacuum arc melting method or the electron beam melting method because of its high melting point and high reactivity with the atmosphere. In particular, a consumable electrode type vacuum arc melting method is generally used for large ingots of a high melting point metal such as titanium.

  The consumable electrode type vacuum arc melting method (hereinafter sometimes referred to as “VAR method” or “VAR melting”) suspends an electrode in which a melting raw material is formed or processed into a rod shape in a water-cooled copper mold. In this method, an arc is generated between the electrode and the molten metal pool held in the mold to melt the electrode and form an ingot below the electrode.

  In such metal melting by the VAR method, the above-mentioned arc tends to concentrate at the center of the molten metal formed below the electrode, so that heat input to the molten metal pool near the mold is insufficient. As a result, there is a case where the casting surface of the ingot to be melted is adversely affected. Moreover, a casting surface may deteriorate by the solid substance adhering to the inner wall of the mold.

  In order to deal with such problems, a technology is known that aims to improve the casting surface by applying heat to the molten pool from outside and stirring the entire molten metal to promote heat input to the mold vicinity of the molten pool. (For example, refer to Patent Document 1).

  However, this technique requires a separate device for applying a magnetic field to the outside of the melting furnace. In addition to the equipment cost, it is also necessary to monitor the operation of the magnetic field applying device, resulting in an increase in manufacturing cost. There was a problem.

  In addition, a method is disclosed in which the pressure of the atmosphere during VAR melting is set high to suppress metal evaporation from the molten metal pool and thereby suppress adhesion to the inner wall surface of the mold (for example, see Patent Document 2). . Furthermore, a technique for improving the molten pool temperature in the vicinity of the mold by adding magnesium chloride to the molten metal to increase the width of the arc formed between the electrode and the molten pool is disclosed (for example, patents). Reference 3).

  However, when the atmosphere pressure is set high, or when magnesium chloride is added to the molten metal, atmospheric gas components or magnesium chloride may be mixed into the molten metal and become impurities in the ingot. However, the above-described technique is not necessarily suitable, and a metal melting method suitable for producing high-purity metal and having excellent casting surface is desired.

  In addition, with regard to the casting surface of titanium ingot melted by VAR melting, heat supply to the molten metal pool in the vicinity of the mold is promoted by narrowing the gap between the electrode and the mold, and as a result, the casting surface is improved. It is known that there is an effect of being (see, for example, Patent Document 4). However, in the above-described method, an arc is easily generated between the electrode side surface and the mold, and no mention is made regarding damage to the mold.

  There is a need for an ingot melting technique that can solve the above-described problems of the prior art, can melt a high-purity metal, and has a clean casting surface.

Japanese Patent Publication No. 05-037214 Japanese Patent Laid-Open No. 07-118788 JP-A-51-110410 Japanese Patent Laid-Open No. 10-317046

  The present invention is a method for melting a titanium ingot using a vacuum arc melting furnace, and in particular, it is melted using a consumable electrode type vacuum arc melting furnace, with a good casting surface without mixing of impurities, And it aims at providing the manufacturing method of the titanium ingot with high productivity.

  In view of such circumstances, the above-mentioned problems have been intensively studied, and in a titanium ingot melting method using a vacuum arc melting furnace, a different arc gap is selected depending on the type of metal to be melted. It has been found that the titanium ingot can be melted efficiently with excellent skin and quality, and the present invention has been completed.

  That is, the present invention relates to a method for melting a titanium ingot using a vacuum arc melting furnace that generates an arc between a molten metal held in a mold and a consumable electrode and melts the consumable electrode to form an ingot in the mold. The arc gap, which is the distance from the lower end of the consumable electrode to the molten metal surface, is changed according to the type of metal to be melted.

  In the present invention, in the case where the titanium ingot to be melted is an alloy, the average value of the arc gap (herein, the average value means “the maximum arc gap and the minimum arc gap that can be selected depending on the apparatus configuration and operating conditions”). It means “arithmetic mean value of arc gap”.) It is preferable to perform melting at an arc gap smaller than that.

  In the present invention, the operation is preferably performed under the condition that the side gap, which is the distance between the side surface of the consumable electrode and the mold, is always larger than the arc gap.

  Moreover, in this invention, it is set as the preferable aspect that the ratio of the side gap with respect to the mold diameter used for vacuum arc melting is 0.01-0.10.

  In this invention, it is set as the preferable aspect that the titanium alloy to melt | dissolve is contained at least 1 or more types from aluminum, vanadium, iron, niobium, tin, and molybdenum.

  By applying the method according to the present invention to the melting of a high melting point metal such as titanium metal, the occurrence of a side arc between the electrode side surface and the mold, which is likely to damage the mold, is suppressed. In addition to being able to melt a titanium ingot with a clean skin, the titanium ingot can be melted while maintaining high productivity.

  The best embodiment of the present invention will be described below with reference to the drawings. FIG. 1 represents a preferred embodiment for carrying out the present invention. In this embodiment, a preferable embodiment will be described below by taking as an example the case where the titanium ingot to be melted is a titanium ingot.

  FIG. 1 shows a situation where a consumable electrode 2 formed by molding sponge titanium is suspended inside a water-cooled copper mold 1 of a vacuum arc melting furnace M. The electrode 2 is disposed opposite to the molten titanium pool 3 disposed below the electrode 2, and the titanium pool 3 and the lower end surface of the electrode 2 are disposed with a predetermined gap AG (arc gap). Yes. The side surface of the electrode 2 is also arranged with a predetermined gap SG (side gap) with the inner wall surface of the mold 1.

  In this invention, it is preferable to change an arc gap according to the kind of metal to melt. When the ingot to be melted is a titanium alloy, it is preferable to melt with an arc gap smaller than the average value of the arc gap defined above. When the arc gap is made small, a titanium pool formed under the electrode disposed inside the vacuum arc melting furnace is formed shallow, and as a result, the alloy components constituting the titanium ingot to be melted are formed. There is an effect that segregation can be efficiently avoided.

  On the other hand, when the metal to be melted is pure titanium, it is preferable that the metal be melted with an arc gap larger than the average value of the arc gap. In the case of constant current operation, as the arc gap increases, the melting voltage increases and the amount of heat generated by the arc increases. As a result, there is an effect that the melting speed of the electrode is increased and the melting time can be shortened.

  In the case where the metal to be melted is pure titanium, even if the titanium pool 3 formed below the electrode 2 is deeply formed, the alloy component is not included, so that segregation does not occur and the alloy is melted. There is no quality problem.

  The average value of the arc gap means the arithmetic average of the maximum arc gap and the minimum arc gap that can be selected according to the apparatus configuration and the operation conditions as described above. For example, as the arc gap is increased, the melting voltage tends to increase as described above, but there is an upper limit somewhere due to restrictions such as the size of the power source. The arc gap at this time corresponds to the maximum value of the arc gap in the present invention. Further, an upper limit value of the arc gap may exist due to other factors. In any case, the arc gap is considered to have an upper limit.

  On the other hand, the minimum value of the arc gap is, for example, that when the arc gap is shortened, the melting voltage decreases and the amount of heat generated in the arc decreases, and the electrode cannot be melted somewhere. it is conceivable that. The arc gap at this time corresponds to the minimum value of the arc gap in the present invention. Other factors may be used, and in any case, it is considered that there is a lower limit value in the arc gap.

  Therefore, the average value of the arc gap as referred to in the present invention is uniquely determined when the apparatus configuration is determined by performing the arithmetic average of the maximum value and the minimum value of the arc gap determined as described above. It is.

  In the present invention, the relationship between the side gap (SG) and the arc gap (AG) shown in FIG. 1 is preferably controlled so that SG> AG. By performing the lowering operation of the electrode under the above-described conditions, there is an effect that generation of a side arc during the melting of the titanium ingot can be effectively suppressed.

  As a result, the occurrence of side arc is avoided, so that the cast surface of the titanium ingot to be melted is not only well maintained, but also damage to the inner surface of the mold is suppressed, effectively reducing the mold maintenance cost and life. There is an effect that it can be improved.

  In the present invention, the ratio of the side gap to the mold diameter used for vacuum arc melting is preferably selected from the range of 0.01 to 0.10. Setting the side gap ratio below the lower limit is not preferable because the side surface of the electrode and the mold are too close to each other and a side arc is generated during the melting of the titanium ingot. On the other hand, if the upper limit of the side gap ratio is exceeded, an arc is generated only in the central portion of the molten titanium pool, the amount of heat at the peripheral portion near the mold is insufficient, and the casting surface is deteriorated, which is not preferable.

  When the diameter of the titanium ingot is 700 mm to 800 mm, the side gap according to the present invention is particularly preferably set in the range of 35 mm to 60 mm and melted. The dissolution current is preferably controlled in the range of 15 KA to 30 KA.

  Moreover, when the diameter of a titanium ingot is 700 mm-800 mm, it is especially preferable to set the range of the arc gap based on this invention to the range of 10 mm-30 mm.

  In addition, as the electrode 2 used in the present invention, an electrode composed of briquette composed of sponge titanium can be used. However, when an ingot formed by primary melting is used as the secondary electrode, the electrode in the circumferential direction is used. The side gap can be kept uniform and the occurrence of side arcs can be further suppressed. As a result, there is an effect that an ingot having a better casting surface can be melted.

  In the present embodiment, the metal to be melted is described by taking titanium as an example, but the side arc suppressing method according to the present invention can be suitably applied to the dissolution of metals such as tantalum and niobium. .

  By following the method for melting a titanium ingot according to the present invention described above, it is possible to effectively satisfy the required characteristics of the titanium ingot to be melted, and to maintain the productivity of the titanium ingot at a high level. Has an effect that the life of the mold for melting the titanium ingot can be effectively extended.

[Example 1]
A melting test of a titanium ingot from the secondary electrode was performed under the following conditions.
1. Melting equipment 1) Mold diameter: 750mm
2) Power supply voltage: 35V, 20KA
3) Secondary electrode diameter: 665 mm
2. Melting raw material 1) Raw material: Pure titanium sponge 2) Electrode type: Secondary electrode made by melting a primary electrode constructed by briquetting a pure titanium sponge.
3) Electrode weight: 4000Kg
3. Arc gap (AG) and side gap (SG)
1) AG: 20mm
2) SG: 42.5 mm (SG / mold diameter ratio = 0.06)
3) Average value of AG: 30 mm
4). Result of melting When the titanium ingot was melted under the above conditions, the surface properties after melting were excellent, and the surface cutting amount was 6.5% of the total titanium ingot.

[Comparative Example 1]
In Example 1, when a titanium ingot was melted under the same conditions except that the side gap was 80 mm (SG / mold diameter ratio = 0.11), a defective portion was found on the casting surface of the titanium ingot. Therefore, the defective portion was removed by surface cutting. As a result, the surface cutting amount reached 8% of the total titanium ingot.

  The casting surface of the titanium ingot or the alloy ingot can be kept good, and the cutting amount can be reduced. As a result, the ingot manufacturing cost can be reduced.

It is a schematic cross section which shows the consumable electrode type vacuum arc melting furnace M of this invention.

Explanation of symbols

M ... vacuum arc melting furnace, 1 ... water-cooled copper mold, 2 ... consumable electrode, 3 ... molten titanium pool, 4 ... ingot, AG ... arc gap, SG ... side gap.

Claims (6)

  In a titanium ingot melting method using a vacuum arc melting furnace, the arc gap, which is the distance from the lower end of the consumable electrode to the molten metal surface, is changed depending on the type of titanium ingot to be melted. Method of melting.   In the case where the titanium ingot to be melted is a titanium alloy, the average value of the arc gap (here, the average value means “the maximum arc gap and the minimum arc gap that can be selected depending on the apparatus configuration and operating conditions”). 2. The method for melting a titanium ingot according to claim 1, wherein melting is performed with an arc gap smaller than “an arithmetic average value”.   2. The method for melting a titanium ingot according to claim 1, wherein when the titanium ingot to be melted is pure titanium, melting is performed with an arc gap larger than an average value of the arc gap.   The method for melting a titanium ingot according to any one of claims 1 to 3, wherein the side gap, which is a distance between the side surface of the consumable electrode and the mold, is operated under a condition that is always larger than the arc gap. .   The method for melting a titanium ingot according to any one of claims 1 to 3, wherein a ratio of the side gap to a mold diameter used for the vacuum arc melting is 0.01 to 0.10.   3. The method for melting a titanium ingot according to claim 1, wherein the titanium alloy includes at least one of aluminum, vanadium, iron, niobium, tin, and molybdenum.

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