JP6104751B2 - Manufacturing method of ingot by vacuum arc melting method - Google Patents

Description

The present invention relates to a method for producing an ingot by a vacuum arc melting method, and particularly to a method for producing an ingot having a good casting surface quality .

  Conventionally, titanium, zirconium, and the like have a high melting point and extremely high activity at high temperatures. Therefore, consumable electrode type vacuum arc melting (hereinafter referred to as “VAR method”) is used to purify these metals. ) Is used. In the VAR method, a metal to be purified is used as a cylindrical consumable electrode in a vacuum or an inert gas atmosphere, and is placed above a copper crucible at a certain interval, and a current is passed between the consumable electrode and the copper crucible. In this method, arc discharge is generated, a consumable electrode is melted and dripped by the heat, impurities are evaporated, and a metal is solidified in a crucible to form an ingot.

  In the case of titanium, primary dissolution for dissolving a consumable electrode made by pressing and compacting sponge-like titanium and secondary melting for re-dissolving the ingot obtained by the primary dissolution as a consumable electrode are performed as necessary. Tertiary dissolution is also performed.

  In metal refining using the VAR method, the metal to be purified is dissolved and dropped onto a copper crucible cooled by water cooling. The metal dropped into the crucible is cooled by the bottom and side surfaces of the crucible and solidifies sequentially, and the top surface of the formed ingot becomes concave, and there is a dropped metal (molten metal).

  The factor that most affects the yield of ingots manufactured by the VAR method is the quality of the surface of the ingot (hereinafter referred to as “cast skin”). The lower the casting surface quality, the worse the ingot yield. The reason will be described.

  When the consumable electrode is melted by the VAR method, splash is generated from the molten metal surface or the consumable electrode held in the mold. Splash is a splash of molten metal that adheres to the inner surface of the crucible and solidifies. The solidified product of the splash is particularly easy to deposit in the portion directly above the molten metal on the inner surface of the crucible, and is deposited in an annular shape. Therefore, this deposit is also called “crown”.

  As the consumable electrode melts and the ingot grows, most of the crown is redissolved by the molten metal rising in the crucible. However, when the crown is not completely redissolved and remains on the inner surface of the crucible, wrinkles are formed on the casting surface of the ingot, which deteriorates the quality of the casting surface. When an ingot having a flaw on the casting surface is subjected to a processing step such as forging or rolling, a crack starting from this flaw occurs during the processing.

  In order to suppress the occurrence of this crack, the ingot is generally subjected to a machining process after removing wrinkles on the casting surface by cutting with a grinder or the like. Therefore, the lower the casting surface quality and the greater the number of wrinkles, the more man-hours are required to remove the wrinkles, the greater the amount of cutting, and the lower the yield. In addition, the cost increases as the yield deteriorates.

  Therefore, conventionally, there has been proposed a method of manufacturing an ingot having high casting surface quality by leaving no crown on the inner surface of the crucible by the VAR method. Patent Document 1 proposes a method of stirring the molten metal by rotating the arc at a predetermined rotational speed, and Patent Document 2 proposes a method of changing the distance from the lower end of the consumable electrode to the molten metal depending on the type of titanium ingot. Has been.

  However, the thickness and amount of the crown formed on the inner surface of the crucible depend not only on the size of the ingot to be manufactured and the content of impurities in the consumable electrode as a raw material, but also on various conditions such as the state of the inner surface of the crucible and the cooling state. Also fluctuate. Therefore, in these methods, it is not always easy to redissolve the crown, and it is difficult to stably improve the casting surface quality.

  Patent Document 3 proposes a method of rotating a molten metal by applying a magnetic field having a predetermined strength in the vertical direction inside the crucible. However, even with this method, the state of the crown and the solidification interface fluctuates each time an ingot is manufactured, so it is impossible to always set the proper magnetic field conditions, improving the casting surface quality stably. It is difficult to do.

JP 2010-37651 A JP 2010-116581 A JP-A-61-143528

Thus, it has been difficult to stably obtain an ingot having a good casting surface quality by the conventional method. The present invention has been made in view of this problem, the VAR process, an object that you provide a method capable of casting surface quality can be stably good ingot.

  As described above, when the consumable electrode is melted by the VAR method, if the remelting of the crown formed on the inner surface of the crucible is insufficient, the crown remains, and the casting surface quality of the ingot is deteriorated.

  The lack of remelting of the crown is caused by inadequate melting conditions of the consumable electrode. The melting conditions of the consumable electrode that affect the remelting of the crown include the stirring strength of the molten metal in the crucible by the magnetic field, the reversal period of the direction of stirring by the magnetic field, the magnitude of the current applied during arc melting, and the arc The magnitude of the voltage applied when melting is mentioned.

  For example, when the stirring strength of the molten metal in the crucible by the magnetic field is appropriate, the high-temperature molten metal is appropriately covered on the crown, and the remelting of the crown is promoted. On the other hand, when the stirring strength is too weak, since the molten metal covering the crown is insufficient, the ability to remelt the crown is insufficient, and the crown remains. In addition, when the stirring strength is too strong, the flow of the molten metal is fast, the amount of splash is increased, and the amount of newly deposited is larger than the amount to be redissolved. Will remain. Therefore, the present inventor has made the following hypothesis.

  FIG. 1 is a conceptual diagram showing the relationship between the melting condition of the consumable electrode and the remelting state of the crown based on the hypothesis of the present inventor. The present inventor estimated that the relationship between the magnetic field stirring intensity and the remelting state of the crown can be illustrated as shown in FIG. In other words, when the dissolution conditions are appropriate, crown remelting is most promoted, and if the crown is insufficiently remelted when it deviates from the appropriate conditions in any direction (left and right from the peak position in the figure). Estimated. In addition, the present inventor estimated that the appropriate dissolution conditions naturally change with the progress of the production of the ingot. However, there is no method for knowing whether the dissolution conditions at that time are appropriate conditions or deviated from the appropriate conditions, and there is a problem that proper control of the dissolution conditions is difficult.

  The present inventor examined these problems and found that when the consumable electrode was dissolved by the VAR method, when the lack of re-dissolution of the crown was detected by the deposit detection device, the dissolution conditions deviated from the appropriate conditions. In addition, when it was predicted that the re-dissolution of the crown would be insufficient in the future, it was found that the dissolution condition could be deviated from the appropriate condition in the future.

  In addition, when it is found that the dissolution condition has deviated from the appropriate condition or will change in the future, the dissolution condition is changed in one direction, and as a result, when the lack of re-dissolution is still detected or predicted, the dissolution condition is changed to the first. It was found that ingots with good casting surface quality can be obtained stably by maintaining the melting conditions when the re-fluctuation was varied and no remelting was detected or predicted.

The present invention has been accomplished based on these findings and has as its gist in production how the ingot by following VAR method.

A method for producing an ingot by a vacuum arc melting method in which a consumable electrode is melted by an arc using a vacuum arc melting furnace, and a metal dropped into the crucible is solidified to produce an ingot, wherein the vacuum arc melting furnace is the crucible A deposit detecting device for detecting deposits formed by scattering of metal melted by the arc on the inner surface of the crucible, and the deposits on the inner surface of the crucible are increased by the deposit detecting device during manufacture of the ingot. When it is detected or when it is predicted that it will increase in the future, if the melting condition of the consumable electrode is changed in one direction, and after changing the dissolution condition, it is detected that the deposit has increased, Or, if it is predicted that it will increase in the future, change the dissolution conditions in the opposite direction from the previous conditions to change the dissolution conditions. After not detect that the deposit is increased, and if no predicted to increase future, performs control to maintain the dissolved condition, repeatedly control of these dissolution conditions The melting conditions of the consumable electrode to be varied are the intensity of stirring by the magnetic field of the metal dropped on the crucible, the inversion period of the direction of stirring by the magnetic field, the magnitude of the current when performing arc melting, and when performing arc melting. 1 or 2 or more, and the one direction increases or decreases the agitation strength, while the inversion period is increased or decreased. one be possible and reduced to increase the magnitude of the current, as well as by the vacuum arc melting method which is characterized in that it is one of the possible and reduced to increase the magnitude of the voltage Method of manufacturing the ingots.

  In the ingot manufacturing method according to the vacuum arc melting method of the present invention, the deposit detector uses the light having a wavelength of 0.7 to 2.5 μm to observe the light intensity distribution or heat distribution in the vacuum arc melting furnace. It is desirable to use a device that detects the size of the deposit from the light intensity distribution or the heat distribution observed using the deposit detection device.

  Further, from the light intensity distribution or heat distribution observed using the deposit detector, the average light intensity or average temperature of the region including all or part of the deposit is measured, and the measured average light intensity or average temperature is measured. Alternatively, when the moving average value is less than a predetermined value, it is detected that the deposit has increased, and the measured average light intensity or average temperature or the moving average value is determined in advance in the future. It is desirable to predict that the deposit will increase in the future when it is predicted that it will be less than the specified value. The moving average value is preferably calculated from the average light intensity or the average temperature in the range of 10 to 1000 seconds measured at a period of 0.1 to 5 seconds.

Before Symbol metal may be titanium or a titanium alloy.

According to the method for producing an ingot by the vacuum arc melting method of the present invention, it is possible to stably obtain an ingot having good casting surface quality .

It is a conceptual diagram which shows the relationship between the melt | dissolution conditions of a consumable electrode based on this inventor's hypothesis, and the state of remelting of a crown. It is a block diagram of the vacuum arc melting furnace which can apply the manufacturing method of the ingot of this invention. It is a top view in the VAR furnace in operation. It is a flowchart of the control method of the melt | dissolution conditions of the consumable electrode in this invention. It is a figure which shows the heat distribution in the VAR furnace measured with the heat distribution measuring apparatus. It is a figure which shows the relationship between melt | dissolution time and the average temperature of a measurement area | region.

1. Configuration of Vacuum Arc Melting Furnace and Ingot Manufacturing Method FIG. 2 is a configuration diagram of a vacuum arc melting furnace (hereinafter referred to as “VAR furnace”) to which the ingot manufacturing method of the present invention can be applied. The VAR furnace includes a copper crucible 1, a chamber 2 that is disposed above the crucible 1 and maintains an airtight state therein, and a lifting device 5 that moves the stub 3 and the consumable electrode 4 up and down. An exhaust port 6 connected to an exhaust device (not shown) is provided on the side surface of the chamber 2. A coil (not shown) is provided around the crucible 1, and an axial (vertical) magnetic field is applied to the inside of the crucible 1 by this coil. On the upper surface of the chamber 2, a detection device 7 for detecting the internal state of the chamber 2 is provided. In the figure, two detection devices 7 are shown, but one or three or more may be used. A power source (not shown) that applies a voltage between the crucible 1 and the consumable electrode 4 is connected to the crucible 1 and the lifting device 5. A control device (not shown) is connected to the detection device 7, the coil, and the power source, and can be controlled automatically.

  When manufacturing an ingot using a VAR furnace, as shown in FIG. 2, the stub 3 welded to the upper surface of the consumable electrode 4 is welded to the lower end of the elevating device 5. Then, the air inside the chamber 2 is discharged from the exhaust port 6 to create an inert gas atmosphere or a vacuum atmosphere, and a voltage is applied between the crucible 1 and the consumable electrode 4. As the voltage is applied, an arc is generated between the consumable electrode 4 and the crucible 1, and the consumable electrode 4 is melted and dropped from the lower end by the arc heat. The melted and dropped molten metal is cooled and solidified by the water-cooled crucible 1 to form an ingot 8. The dropped molten metal (molten metal) 9 is held on the top of the ingot 8, and the molten metal 9 is stirred by a magnetic field applied by a coil disposed around the crucible 1.

2. Control of Melting Conditions in the Ingot Manufacturing Method of the Present Invention FIG. 3 is a plan view inside the VAR furnace during operation. On the inner surface of the crucible 1, splash splashed with molten metal adheres to form a crown 10 that is a deposit of splash.

  If the melting conditions of the consumable electrode 4 are appropriate, the crown 10 is covered with the molten metal 9 that has risen as the ingot 8 grows and is remelted, so that an ingot 8 with good casting surface quality is obtained. However, when the state in the VAR furnace changes and the melting conditions are not appropriate, the crown 10 is insufficiently remelted, and the crown 10 increases and remains on the inner surface of the crucible 1. Skin quality is reduced.

  In the ingot manufacturing method of the present invention, the state of the crown 10 and its change are detected by the detection device 7 provided on the upper surface of the chamber 2, and the melting conditions are controlled based on the detection result.

2-1. FIG. 4 is a flowchart of a method for controlling the melting condition of the consumable electrode in the present invention. A method for controlling dissolution conditions will be described with reference to FIG. After starting the operation of the VAR furnace, detection of the crown state is started during the operation of the VAR furnace. For example, detection is performed at a period of 0.1 to 5 seconds.

  When it is detected that the crown has increased from the start of detection until a predetermined time (for example, 5 to 30 seconds) has elapsed, or when it is predicted that the crown will increase in the future (YES in step # 1) Changes the dissolution conditions in one direction (step # 2).

  On the other hand, when it is not detected that the crown has increased and is not predicted to increase in the future (NO in step # 1), the dissolution condition is maintained (step # 3), and the dissolution condition is When the control is not finished (NO in step # 6), the detection of the crown state is continued (step # 1). That is, if no crown increase is detected or predicted and normal consumable electrode dissolution is maintained, this loop is repeated.

  After changing the dissolution conditions in one direction in step # 2, the crown state is further detected again (step # 4). When it is detected that the crown has increased from the start of detection until a predetermined time (for example, 5 to 30 seconds) has elapsed, or when it is predicted that the crown will increase in the future (YES in step # 4) Changes the melting condition in the reverse direction from the condition before changing in step # 2 (step # 5), and continues detection of the crown state if the control of the melting condition is not terminated (NO in step # 6). (Step # 1).

  On the other hand, when it is not detected that the crown has increased in step # 4 and it is not predicted that the crown will increase in the future, the dissolution condition is maintained (step # 3), and the control of the dissolution condition is not terminated (step #). 6), the detection of the crown state is continued (step # 1).

  The dissolution condition is controlled until an arbitrary time point (YES in step # 6).

  By controlling the dissolution conditions in this manner, the crown can be stably re-dissolved, and an ingot with good casting surface quality can be obtained. In general, dissolution of the consumable electrode by the VAR method is often performed a plurality of times. Since cutting of the ingot surface is performed after the final melting, a high effect can be obtained by controlling the melting conditions of the present invention during the final melting.

  Further, the dissolution conditions of the present invention may be controlled from the start to the end of the consumable electrode, or may be performed for an arbitrary time from the start to the end of the dissolution. Even when it is performed for an arbitrary time, an ingot having a good casting surface quality can be obtained at a portion solidified during that time. The ingot manufacturing method of the present invention can be suitably applied to titanium or a titanium alloy.

  The detection or prediction of the increase in crown during the control of the melting conditions of the present invention (steps # 1 and # 4) and the variation of the melting conditions based on this (steps # 2 and # 5) are provided in the vacuum arc melting furnace. It is preferable to perform this automatically using a control device. However, the operator may observe the crown condition, detect or predict the crown increase, and manually change the dissolution conditions.

2-2. Melting conditions The melting conditions to be varied as a control target in the present invention are the stirring intensity of the molten metal in the crucible (magnetic field stirring intensity) by the magnetic field, the inversion period of the stirring direction by the magnetic field (stirring inversion period), One or more of the applied current (melting current) and the voltage (melting voltage) applied when arc melting is performed.

(1) Magnetic field stirring intensity When varying the magnetic field stirring intensity, the current applied to the coil disposed around the crucible is varied to vary the intensity of the magnetic field applied to the inside of the crucible. As described above, when the magnetic field stirring intensity is appropriate, the crown is appropriately covered with a high-temperature molten metal, and remelting of the crown is promoted. On the other hand, when the magnetic field stirring intensity is too weak, the amount of molten metal covering the crown is insufficient, and when the magnetic field stirring intensity is too strong, the amount of splash is increased. Dissolution will be insufficient and the crown will increase.

(2) Stirring reversal period When changing the direction of stirring by a magnetic field, the direction of the current applied to the coil arranged around the crucible is changed. When the stirring reversal period is appropriate, due to the fluctuation of the molten metal that occurs during reversal, the liquid surface is appropriately covered with the hot molten metal, and the remelting of the crown is promoted. If the stirring reversal period is too short or too long to be appropriate, the fluctuation of the melt level that occurs during reversal is insufficient or excessive. If there is an excessive change in the liquid level of the molten metal, if there is an insufficient change in the liquid level of the molten metal, there is not enough molten metal to cover the crown, and if there is an excessive change in the liquid level of the molten metal. Since the amount of splash generated increases, in any case, the crown is insufficiently remelted and the crown increases.

(3) Melting current and melting voltage When the melting current or melting voltage is appropriate, arc heat is appropriately supplied, so that remelting of the crown is promoted. On the other hand, when the melting current or the melting voltage is too small, the arc heat is insufficient, the crown is not sufficiently remelted, and the consumable electrode cannot be sufficiently melted. On the other hand, when the dissolution current or the dissolution voltage is too large, the amount of splash is increased, the re-dissolution of the crown is insufficient, and the crown increases.

  The effect of improving the casting surface quality is highest when the melting current is varied among these melting conditions, followed by the melting voltage, the magnetic field stirring strength, and the stirring inversion cycle in this order. However, since the melting current and the melting voltage have a great influence on the internal quality such as the segregation of ingot components and the positions and sizes of the pores, they are not preferable as conditions for changing for the purpose of improving the casting surface quality during melting. On the other hand, since the magnetic field stirring intensity and the magnetic field stirring cycle have little influence on the internal quality of the ingot, they are preferable as conditions for changing for the purpose of improving the casting surface quality.

2-3. Crown Detection Method The crown detection is performed by the detection device 7 provided on the upper surface of the chamber 2 shown in FIG. When the melting current is as small as several kA and the arc light is weak, a general video camera that observes the inside of the chamber 2 with visible light can be used as the detection device 7. However, in general operation, the melting current is set to several tens of kA. In this case, the arc light is too strong, and it may be difficult to detect the crown state with a video camera using visible light. . As a result of examination by the present inventors, by using light having a wavelength of 0.7 to 2.5 μm instead of visible light, even when the arc light is strong, it is hardly affected by the arc light. It was found that the state, size and shape of the crown can be detected. Therefore, it is preferable to use a device that detects light within a range of 0.7 to 2.5 μm as the detection device. Furthermore, in order to suppress the influence of light outside the range of 0.7 to 2.5 μm, it is preferable to use a filter that blocks light outside the range of 0.7 to 2.5 μm in this apparatus.

  Since the arc light strongly emits short-wavelength light including ultraviolet rays, it is considered that the arc light is affected by the arc light in a wavelength region of less than 0.7 μm. In addition, in the wavelength range longer than 2.5 μm, the intensity of light becomes weak according to Planck's radiation law, so that it is considered that the influence of arc light becomes large.

  The detection device 7 is preferably a light intensity distribution measurement device or a heat distribution measurement device. Since these devices can quantitatively detect the light intensity distribution, the heat distribution, and the like over a wide range, the state of the crown can also be quantitatively detected over a wide range. Light intensity distribution measuring devices and heat distribution measuring devices observe the light intensity distribution and heat distribution using light in the wavelength range of 0.7 to 2.5 μm, so that the influence of arc light is hardly affected. Can detect the crown without receiving it.

  The region detected by the detection device 7 is a region including the entire crown 10 or a part thereof. When a region including a part of the crown 10 is set as a detection region, the region including the inner surface of the crucible 1 and the outer peripheral surface of the consumable electrode 4 is a region having a central angle of 30 ° or more in the cross section of the crucible 1. It is preferable. In FIG. 3, the detection region 11 having a central angle of 60 ° is indicated by a broken line. Most preferably, the detection region is a region including the entire region inside the crucible 1.

  As a reference for the size of the crown 10, the thickness of the crown 10 measured in the detection region 11 (the radial length of the inner surface of the crucible 1) or the ratio of the area of the crown 10 to the detection region 11 is used. Can do. In this case, when an increase in the ratio of the thickness or area of the crown 10 is detected, it is assumed that the crown 10 has been increased. The crown size can be predicted by using the data obtained by continuously performing first-order differentiation with respect to the data obtained by continuously measuring the crown size, or the value obtained by second-order differentiation. .

  FIG. 5 is a diagram showing the heat distribution in the VAR furnace measured by the heat distribution measuring apparatus. The figure shows the heat distribution measured using one heat distribution measuring device that observes the heat distribution using light having a wavelength in the range of 0.7 to 2.5 μm. Due to the limitation of the field of view of the heat distribution measuring device, the measurement range is half of that in the VAR furnace. By using two heat distribution measuring devices, almost the entire area in the VAR furnace can be measured. In the figure, the lower the temperature, the darker the color, and the higher the temperature, the lighter the color is displayed.

  The stub 3 and the crucible 1 have the lowest temperature, and the molten metal 9 has the highest temperature. The consumable electrode 4 is hotter than the stub 3. Further, the crown 10 formed by depositing solid splash generated from the molten metal 9 is lower in temperature than the molten metal 9. As described above, since the temperature is different in each part in the VAR furnace, as shown in FIG. 5, the shape of each part can be clearly discriminated without being substantially affected by the arc light. Therefore, it is possible to detect a change in the shape of the crown 10 by continuously measuring the heat distribution.

  In this way, by detecting the crown size from the crown shape with the heat distribution measuring apparatus and using this as a reference, the melting conditions can be controlled with high accuracy with almost no influence of the arc light. Similarly, the light intensity distribution measuring apparatus can detect the shape and size of the crown from the light intensity distribution in the VAR furnace, and can control the melting conditions with high accuracy based on this.

  Furthermore, as a result of the study by the present inventors, the average light intensity of a region including a part or all of the crown 10 measured from the in-furnace light intensity distribution, or a part or all of the crown 10 measured from the in-furnace heat distribution is obtained. It was found that the crown state could be detected from the average temperature of the included region. The average light intensity or average temperature of the measurement region can be calculated by the detection device. If the average light intensity or average temperature of the measurement area falls below a predetermined reference light intensity or reference temperature determined in advance, the crown will not be remelted and the crown will increase, and the average light intensity or average of the measurement area will increase. As the temperature rises above a predetermined reference temperature, crown remelting is facilitated.

  And it turned out that an ingot with more favorable casting surface quality can be obtained by controlling melt | dissolution conditions based on the average light intensity or average temperature of this measurement area | region. Next, control of dissolution conditions based on the average temperature of the measurement region will be described.

2-4. Control of melting conditions based on the average temperature of the measurement area in the furnace The average temperature of the measurement area used to control the dissolution conditions is the average temperature of the measurement area as it is collected, and the value obtained by moving average of the collected average temperature. Either can be used. However, since the surface of the molten metal is constantly fluctuating, the fluctuation with time elapses at the average temperature as it is collected, whereas this fluctuation is gentle at the moving average value. Therefore, it is easier for the moving average value to detect a change in average temperature when a change occurs in the crown state, and it is easier to control the dissolution conditions at an appropriate timing.

  For the control of dissolution conditions based on the average temperature of the measurement area, the above-mentioned reference temperature is used as the target temperature, and when the average temperature of the measurement area falls below the target temperature, it is detected that the crown has increased, and the measurement area When it is predicted that the average temperature will be lower than the target temperature in the future, it is predicted that the crown will increase in the future.

  When using a moving average value, it is preferable to calculate using the temperature of the measurement region in the range of 10 to 1000 seconds collected at a period of 0.1 to 5 seconds. This is because if the range of values used for the moving average is less than 10 seconds, the fluctuation of the moving average value is still fine, and if it exceeds 1000 seconds, it is likely to detect the actual average temperature change later. The range of values used for the moving average is preferably in the range of 30 to 300 seconds. In this range, an ingot with better casting surface quality can be obtained. Hereinafter, control of the melting conditions based on the average temperature of the measurement region during the operation of the VAR furnace will be described with reference to an actually implemented example.

  FIG. 6 is a diagram showing the relationship between the dissolution time and the average temperature in the measurement region. In the figure, the average temperature in the measurement region obtained by moving average in the range of 180 seconds is indicated by a solid line, and the target temperature is indicated by a broken line. The reason why the target temperature rises as the melting time elapses is that the liquid level and crown of the molten metal approach the heat distribution measuring device as the ingot grows, and the measured average temperature rises. The measurement area of the average temperature was the measurement area 11 indicated by the broken line in FIG.

  The object of controlling the melting conditions was the stirring strength of the molten metal in the crucible by the magnetic field, the stirring strength at the initial stage was 100 (relative value), and the first fluctuation direction at the time of control was the direction of increasing. In the following description, reference is made to the flowchart of FIG.

  As shown in FIG. 6, at the initial stage, the temperature gradually increased above the target temperature (NO in step # 1), so the dissolution conditions were maintained (step # 3). Thereafter, the average temperature in the measurement region began to decrease, and at time t1, it was predicted that the temperature would be lower than the target temperature in the future, that is, the crown was predicted to increase (YES in step # 1), and the stirring intensity was increased to 110. (Step # 2). This prediction was performed by using a value obtained by first-order differentiation and a value obtained by second-order differentiation of the change in average temperature in the measurement region.

  Then, it is predicted that the average temperature of the measurement region will be lower than the target temperature again in the future after 30 seconds have passed from the change of the stirring intensity (YES in Step # 4), and therefore the stirring intensity varies in Step # 2. It was weakened to 80, which was weaker than before (Step # 5). At this time, since the operation of the VAR furnace was not finished, the control of the melting conditions was not finished (NO in Step # 6), and the temperature measurement was continued (Step # 1).

  Even after the stirring intensity was weakened, the average temperature in the measurement region continued to decrease and once fell below the target temperature. However, since it was predicted that the target temperature would be exceeded by 30 seconds after the stirring intensity was weakened (NO in step # 1), the dissolution condition was maintained (step # 3). The average temperature started to rise and again exceeded the target temperature.

  Thereafter, the temperature rose above the target temperature for a while (NO in step # 1), so the dissolution conditions were maintained (step # 3). Before the time t3, the average temperature in the measurement region began to decrease, and it was predicted that the temperature would be lower than the target temperature at the time t3 (YES in step # 1), and the stirring intensity was increased to 110 (step # 2).

  And, since it was predicted that the average temperature of the measurement region will be lower than the target temperature in the future until 30 seconds have passed since the change of the stirring intensity (YES in Step # 4), the stirring intensity was reduced to 80 (Step) # 5). At this time, since the operation of the VAR furnace was not finished, the control of the melting conditions was not finished (NO in Step # 6), and the temperature measurement was continued (Step # 1). Although the average temperature in the measurement region continued to decrease for a while, the temperature did not fall below the target temperature until 30 seconds had passed since the change in the stirring intensity, and it was not predicted that the temperature would fall below the target temperature (Step # 1). NO). Therefore, when the dissolution conditions were maintained (step # 3), the temperature began to increase at time t4 without becoming below the target temperature.

  After that, when the target temperature or higher was maintained, it was predicted that the average temperature in the measurement region began to decrease again and became lower than the target temperature at time t5. Therefore, it was predicted that the crown would increase (YES in Step # 1), and the stirring intensity was increased to 110 (Step # 2). And since 30 seconds passed from the change of the stirring intensity, it was not less than the target temperature, and it was not predicted that the temperature would be lower than the target temperature (NO in Step # 1), so the dissolution conditions were maintained (Step #). 3) However, it started to increase at time t6 without becoming below the target temperature. After that, since it was not predicted that the target temperature was maintained or lower than the target temperature (NO in Step # 1), the melting condition was maintained (Step # 3), and then the operation of the VAR furnace was terminated. Control of dissolution conditions was terminated (YES in step # 6).

  The control similar to the control of the dissolution condition based on the average temperature of the measurement region described above can also be performed based on the average light intensity of the measurement region. In this case, in the above description, “reference temperature” and “target temperature” are respectively referred to as “reference light intensity” and “target light intensity”.

  In order to confirm the effect of the method for producing an ingot by the vacuum arc melting method of the present invention, the following tests were conducted and the results were evaluated.

1. Test conditions The VAR furnace shown in FIG. 2 was used. Further, a heat distribution measuring device was used as the detection device. The manufactured ingot was made of titanium, and dissolution was performed twice: primary dissolution and secondary dissolution (final dissolution). As the consumable electrode, a sponge titanium sponge was used for primary dissolution, and an ingot manufactured by primary dissolution was used for final dissolution. The test conditions were as shown in Table 1.

  In the comparative example, the production method of the present invention was not applied, and an ingot was produced without changing the dissolution conditions. In the present invention example, the production method of the present invention was applied, and the melting conditions were controlled based on the average temperature of the measurement region in the furnace. The measurement region was the region 11 shown in FIG. 3, and a value obtained by moving and averaging the average temperature of the measurement region collected at a cycle of 1 second over a range of 180 seconds was used for control.

  In Invention Examples 1 to 4, the production method of the present invention was applied only in the final dissolution of the two dissolutions, and in Invention Example 5, the production method of the present invention was applied only in the primary dissolution. The ingot after the final dissolution removed wrinkles generated on the surface by cutting. In Example 6, the production method of the present invention was applied both in the primary dissolution and the final dissolution.

  The fusing conditions varied were magnetic field stirring intensity in inventive examples 1, 5 and 6; stirring inversion period in inventive example 2, dissolving current in inventive example 3, and dissolving voltage in inventive example 4.

2. Test results Table 1 shows the evaluation together with the test conditions. The evaluation was described as a relative value with the yield of the comparative example and the deviation calculated from the weight of the ingot after cutting the surface and the weight of the consumable electrode in which sponge titanium was pressed and its deviation as 100. The smaller the deviation in yield, the smaller the variation in yield for each ingot, which is desirable for quality control.

  As shown in Table 1, each of Examples 1 to 6 had better casting surface quality than the comparative example, so that the yield was good and the deviation in yield was small. In addition, the inventive examples 1 to 4 applied only in the final dissolution had a better yield and the yield deviation was smaller than the inventive example 5 in which the production method of the present invention was applied only in the primary dissolution. In addition, Example 6 of the present invention applied in the primary dissolution and final dissolution had the best yield, and the yield deviation was the smallest.

  From Examples 1 to 4, it can be seen that the effect of improving the casting surface quality by controlling the melting conditions was the highest in the melting current, and then in the order of the melting voltage, the magnetic field stirring intensity, and the magnetic field stirring cycle.

According to the method for producing an ingot by the vacuum arc melting method of the present invention, it is possible to stably obtain an ingot having good casting surface quality . Therefore the present invention is a useful technique in the field of ingot production using a vacuum arc melting method.

1: crucible, 2: chamber, 3: stub, 4: consumable electrode, 5: lifting device,
6: exhaust port, 7: detection device, 8: ingot, 9: molten metal, 10: crown,
11: Detection area

Claims (6)

A method for producing an ingot by a vacuum arc melting method in which a consumable electrode is melted by an arc using a vacuum arc melting furnace, and a metal dropped into a crucible is solidified to produce an ingot,
The vacuum arc melting furnace includes a deposit detection device that detects deposits formed by scattering metal melted by the arc on the inner surface of the crucible,
When an increase in the deposit on the inner surface of the crucible is detected or predicted to increase in the future by the deposit detector during manufacturing of an ingot, the melting condition of the consumable electrode is changed in one direction. ,
When it is detected that the deposit has increased after the dissolution condition is changed, or when it is predicted that the deposit will increase in the future, the dissolution condition is changed in the reverse direction from the condition before the change in the one direction. Fluctuate,
After changing the dissolution conditions, if it does not detect that the deposit has increased, and did not expect to increase in the future, control to maintain the dissolution conditions,
Just repeat control of these dissolution conditions,
The conditions for melting the consumable electrode to be varied are the strength of stirring by the magnetic field of the metal dropped on the crucible, the inversion period of the direction of stirring by the magnetic field, the magnitude of the current when performing arc melting, and the time when performing arc melting. 1 or 2 or more of the magnitudes of the voltage,
The one direction is one of increasing and decreasing the intensity of the stirring, one of increasing and decreasing the reversal period, one of increasing and decreasing the magnitude of the current, And a method for producing an ingot by a vacuum arc melting method, wherein the voltage is one of increasing and decreasing the magnitude of the voltage .   The said deposit detection apparatus is an apparatus which observes the light intensity distribution or heat distribution in the said vacuum arc melting furnace using the light of a wavelength of 0.7-2.5 micrometers. Ingot manufacturing method by vacuum arc melting method.   The method of manufacturing an ingot by the vacuum arc melting method according to claim 2, wherein the size of the deposit is detected from a light intensity distribution or a heat distribution observed using the deposit detector. From the light intensity distribution or heat distribution observed using the deposit detector, the average light intensity or average temperature of the region including all or part of the deposit is measured,
When the measured average light intensity or average temperature is less than a predetermined value, it is detected that the deposit has increased,
3. The deposit according to claim 2, wherein the deposit is predicted to increase in the future when the measured average light intensity or average temperature is predicted to be less than the predetermined value in the future. Ingot manufacturing method by vacuum arc melting method. From the light intensity distribution or heat distribution observed using the deposit detector, the average light intensity or average temperature of the region including all or part of the deposit is measured, and the average light intensity or average temperature is set to 0. 0. Measured at a period of 1 to 5 seconds, and calculated a moving average value for the average light intensity or average temperature for 10 to 1000 seconds,
When the moving average value is less than a predetermined value, it is detected that the deposit has increased,
The vacuum arc melting method according to claim 2, wherein when the moving average value is predicted to be less than the predetermined value in the future, the deposit is predicted to increase in the future. Ingot manufacturing method. The method for producing an ingot by a vacuum arc melting method according to any one of claims 1 to 5 , wherein the metal is titanium or a titanium alloy.

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