Method for storing titanium sponge lumps and method for manufacturing titanium sponge

Abstract

To provide a method for storing a sponge titanium lump which can inhibit the coloration of the sponge titanium lump during storage.SOLUTION: A method for storing a sponge titanium lump includes placing a sponge titanium lump inside a casing, supplying the inside of the casing with dry air at an absolute humidity of 3.5 gH2O / m3 or less, and discharging the internal gas of the casing from the lower side of the casing so that the internal pressure of the casing is kept at a positive pressure relative to the outside.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for storing titanium sponge chunks and a method for producing titanium sponge. [Background technology]

[0002] Titanium sponge can be produced by the so-called Kroll process. In the Kroll process, titanium tetrachloride is dropped into molten metallic magnesium in a metal reduction reaction vessel, causing a reduction reaction to occur, resulting in a titanium sponge mass (hereinafter, this process of producing the titanium sponge mass may be referred to as the "reduction process"). This titanium sponge mass is then crushed using a crushing shear or the like to produce the titanium sponge (hereinafter, this process of crushing the titanium sponge mass into titanium sponge mass may be referred to as the "crushing process"). The titanium sponge obtained by crushing the titanium sponge mass can be used as a melting raw material, and is melted by, for example, the electron beam melting (EB) process or the vacuum arc remelting (VAR) process to produce titanium ingots.

[0003] Currently, in technical fields such as aircraft and electronic components, there is a demand for extremely high-grade, high-purity titanium. Titanium sponge obtained by crushing titanium sponge blocks has the opportunity to come into contact with the atmosphere before being used to manufacture titanium ingots, which increases its oxygen content. Methods for reducing the oxygen content in titanium sponge include techniques such as those described in Patent Documents 1 to 3.

[0004] Patent Document 1 proposes "a method for storing high-purity titanium sponge granules, in which the center of a titanium sponge block produced by the Kroll process is removed, crushed, and the resulting titanium sponge granules are sealed in a storage container, and the pressure inside the storage container filled with the titanium sponge granules is reduced to 40 Pa or less, and then a low-humidity gas is injected into the storage container."

[0005] Patent Document 2 describes "a storage hopper used in the compounding process in which crushed and sized titanium sponge is mixed to ensure uniform quality, the hopper being characterized by having an openable and closable lid at the top inlet that suppresses the upward flow that occurs inside the hopper when the crushed and sized titanium sponge is added," and describes how "with the lid in place, dry air, nitrogen, argon, or the like is introduced into the hopper to replace the normal atmosphere."

[0006] Patent Document 3 describes a titanium material manufacturing method in which a sponge titanium cake manufactured by the Kroll process is cut and sorted, and the sorted sponge titanium is crushed using a tool, and the crushing is carried out under conditions where the absolute humidity is 10 g-H2O / m 3 A method for producing a low-oxygen titanium material, characterized by being carried out under the following atmosphere, is proposed. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-87373 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-291306 [Patent Document 3] Japanese Patent Application Publication No. 10-259432 Summary of the Invention [Problem to be solved by the invention]

[0008] The titanium sponge lump obtained in the reduction process may weigh 7 tons or more per batch. Due to the nature of the manufacturing equipment, the titanium sponge lump may need to be temporarily stored between the time it is removed from the metal reduction reactor and the time it is crushed. During this storage, the titanium sponge lump may become discolored, e.g., yellow. In this case, even if the discolored titanium sponge lump is crushed in the subsequent crushing process, the discoloration cannot be physically removed, and the crushed titanium sponge also remains discolored. Depending on the application, such as high-purity titanium, the discolored titanium sponge may not be usable as a raw material for melting titanium ingots, which inevitably reduces the yield in titanium sponge production.

[0009] It should be noted that Patent Documents 1 to 3 focus on suppressing an increase in the oxygen content in the titanium sponge during or after crushing, and do not consider discoloration that may occur during storage of the titanium sponge mass before crushing. Therefore, the techniques of Patent Documents 1 to 3 still have room for improvement in order to resolve the decrease in yield in the production of titanium sponge.

[0010] Therefore, an object of the present invention is to provide a method for storing titanium sponge blocks that can suppress discoloration of the titanium sponge blocks during storage. [Means for solving the problem]

[0011] That is, in one aspect, the present invention provides a method for storing a titanium sponge mass in a casing, the inside of which is maintained at an absolute humidity of 3.5 g H2O / m 3 This is a method for storing titanium sponge blocks, in which dry air is supplied as follows, and the gas inside the casing is discharged to the outside from the lower side of the casing so that the inside of the casing is maintained at a positive pressure relative to the outside.

[0012] In one embodiment of the method for storing titanium sponge lumps according to the present invention, the casing has a plurality of dry air inlets, and the air inlets are arranged at least on the top side and the bottom side of the titanium sponge lumps.

[0013] In one embodiment of the method for storing titanium sponge chunks according to the present invention, the amount of dry air supplied to the inside of the casing is 500 L / min or more and 750 L / min or less.

[0014] In one embodiment of the method for storing titanium sponge mass according to the present invention, the internal volume of the casing is 3 m 3 More than 20m 3 The following is the result.

[0015] In one embodiment of the method for storing a titanium sponge mass according to the present invention, the absolute humidity outside the casing is 15.0 gH2O / m 3 That's all.

[0016] In another aspect, the present invention provides a method for producing titanium sponge, which includes a storage step of storing a titanium sponge lump using any of the above-mentioned methods for storing titanium sponge lump, and a crushing step of crushing the titanium sponge lump after the storage step to obtain titanium sponge. [Effects of the Invention]

[0017] According to one embodiment of the present invention, coloration of the titanium sponge mass during storage can be suppressed. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is an example of a casing used in one embodiment of a titanium sponge lump storage method according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention is not limited to the embodiments described below, and the components can be modified and embodied without departing from the spirit of the invention. Furthermore, various inventions can be created by appropriately combining multiple components disclosed in each embodiment. For example, an invention can be created by deleting some of the components shown in the embodiments.

[0020] [1. Storage method for titanium sponge blocks] In one embodiment of the method for storing titanium sponge lumps according to the present invention, the titanium sponge lumps are stored in a casing. More specifically, the titanium sponge lumps are placed inside the casing, dry air having an absolute humidity below a predetermined level is supplied to the inside of the casing, and the gas inside the casing is discharged to the outside from the lower side of the casing so that the inside of the casing is maintained at a positive pressure relative to the outside. In one embodiment, the dry air can be atmospheric air with moisture removed, and therefore contains oxygen and nitrogen. Dry air is not usually composed of 100% nitrogen or 100% argon. Moisture removal from the atmosphere can be achieved appropriately by utilizing factory exhaust heat, etc. Furthermore, since the dry air contains an appropriate amount of oxygen, workers can pass by the casings located indoors in the factory. Furthermore, the storage method of one embodiment is effective in suppressing discoloration of the titanium sponge mass when the absolute humidity outside the casing is higher than the absolute humidity of the dry air. For example, when the absolute humidity outside the casing is 15.0 gH2O / m 3 In the above cases, the storage method of this embodiment is more effective in suppressing coloration of the titanium sponge mass.

[0021] The titanium sponge mass obtained in the reduction step often has magnesium chloride adhering to it. The reason for this is that the titanium sponge mass is porous, and magnesium chloride remains in the pores. After the reduction step, the titanium sponge mass is immersed in a molten bath containing molten magnesium chloride and molten metallic magnesium, and even if these are removed by draining or vacuum separation, it is difficult to completely remove the molten magnesium chloride from within the pores of the titanium sponge mass.

[0022] Furthermore, because magnesium chloride exhibits deliquescent properties, it absorbs moisture from the air when exposed to the air, and the inventors believe that this is the reason why titanium sponge masses in contact with magnesium chloride become discolored over time.

[0023] For example, if an attempt is made to maintain low humidity by reducing the pressure in the atmosphere surrounding the titanium sponge mass by adapting the technology of Patent Document 1, this would require large-scale equipment that is sealed with sealing or the like, which is not realistic in terms of cost and operational load.

[0024] Therefore, the inventors conducted extensive research and came up with the idea of ​​placing a titanium sponge mass inside a casing of relatively simple structure, and in order to suppress discoloration, supplying dry air of a predetermined absolute humidity into the inside of the casing, thereby maintaining a pressurized state between the inside of the casing and the outside. Preferred embodiments will be described below with reference to the drawings.

[0025] <Casing> The casing 1 shown in Fig. 1 has a framework structure 2 made up of multiple framework members to form a storage space for storing titanium sponge blocks 7, a resin sheet 3 covering the framework members, air intake sections 4a, 4b, and an exhaust section 5. In addition to the above, the casing 1 may also be box-shaped. The casing 1 shown in Fig. 1 is a so-called tent type, and therefore includes a framework structure and a sheet, but the casing can also be constructed as a single unit as long as the shape of the metal or other covering can be maintained. The internal volume of the casing 1 can be determined appropriately taking into consideration the size of the titanium sponge mass 7. 3 More than 20m 3 It is preferable that the mass is within the following range. The size of the titanium sponge lumps 7 is expected to be within the range of 6 tons to 15 tons. The titanium sponge lumps 7 are produced in the reduction step and are not crushed. The titanium sponge lumps obtained by removing the outer periphery of the titanium sponge lumps produced in the reduction step may be stored. In this case, the means for removing the outer periphery of the titanium sponge lumps is not particularly limited, and one example is to use a small rock drill or the like to remove a predetermined depth from the outer periphery toward the center of the titanium sponge lumps that are laid horizontally on multiple rollers.

[0026] (Frame structure, resin sheet) The material of the frame members of the frame structure 2 is not particularly limited as long as it has high strength and corrosion resistance, but is preferably made of steel. Examples of steel include stainless steel, carbon steel, and aluminum alloy. There are no particular restrictions on the material of the resin sheet 3, and any known material may be used. The resin sheet 3 may be transparent so that it is possible to check whether the titanium sponge mass 7 has been colored during storage.

[0027] (Air supply part) The air intake sections 4a and 4b are used to supply dry air to the inside of the casing 1. The air intake sections 4a and 4b include an air intake port for dry air formed by penetrating the casing 1 (more specifically, the resin sheet 3 or the like), and an air intake pipe (not shown) connected to the air intake port. The number of air intake parts 4a and 4b is at least one, but may be multiple. The titanium sponge mass 7 is disposed inside the casing 1, and from the viewpoint of suppressing coloration, air is introduced into the casing 1 from the air intake ports of the air intake parts 4a and 4b at an absolute humidity of 3.5 gH2O / m 3Dry air is supplied as follows. This makes it possible to suppress discoloration of the titanium sponge lumps 7. While the titanium sponge lumps 7 are stored inside the casing 1, dry air may be supplied continuously or intermittently. Furthermore, because dry air is heavier than gas (air) with a higher humidity, the dry air moves to the lower part of the casing 1. Here, the inside of the casing 1 is maintained at a positive pressure relative to the outside, so the inflow of outside air from the exhaust section 5 located on the lower side of the casing 1 is suppressed. Furthermore, if dry air is supplied toward the upper side inside the casing 1, gases such as air that were present inside the casing 1 before the supply of dry air can be efficiently discharged from the exhaust section described below. As described above, the area around the titanium sponge mass 7 placed inside the casing 1 can be filled with the dry air. The absolute humidity can be calculated using the following equations 1 to 3. The method for calculating absolute humidity is applicable not only to dry air in this specification, but also to the inside and outside of a casing.

[0028]

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[0029]

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[0030]

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[0031] Furthermore, from the viewpoint of more reliably suppressing discoloration of the titanium sponge mass 7 during storage, the supply rate of dry air from the air intake parts 4a, 4b (the total supply rate if there are multiple air intake parts 4a, 4b) is preferably within the range of 500 L / min to 750 L / min. When multiple air intake parts 4a, 4b are arranged in the casing 1, approximately the same amount of dry air may be supplied from each air intake part 4a, 4b, or the supply rates of each air intake part may be different. Furthermore, when multiple air intakes 4a, 4b are arranged in the casing 1, the air intakes 4a, 4b are preferably arranged on both sides of the titanium sponge mass 7 in the casing 1, separating them from each other. For example, they can be arranged on the outer surface of the casing 1 on the top 8 and bottom 9 sides of the titanium sponge mass 7. In this case, the titanium sponge mass 7 is preferably arranged horizontally in the casing 1. Because titanium sponge masses typically have a certain vertical length, placing them vertically poses a risk of tipping over. Therefore, horizontal placement of the titanium sponge mass 7 is preferred. A sheet, pedestal, or the like may be placed underneath the horizontally-placed titanium sponge mass 7 to prevent contamination and ensure safe handling. While the air intakes 4a, 4b are shown in the drawing to be centrally located in the height direction of the casing 1, their placement is not particularly limited. When the air intake sections 4a, 4b are located in the center or lower part of the casing 1 in the height direction, it is preferable that the air intake ports face upward within the casing 1, and dry air is supplied toward a position higher than the titanium sponge mass 7, for example. This allows much of the gas (air, etc.) within the casing 1 to be discharged through the exhaust section by the supplied dry air, and the gas is easily replaced by the dry air. Even in this case, the dry air supplied to the upper side is heavier than gas (air, etc.) with a higher humidity, and therefore subsequently moves downward within the casing 1, thereby more reliably preventing the intrusion of outside air from the exhaust section 5. As a result, yellowing of the titanium sponge mass 7 can be suppressed. It is not always necessary to adjust the temperature of the dry air. For example, the temperature of the dry air may be within ±5°C of the air temperature outside the casing 1.

[0032] The air intake pipe is connected to a dry air supply source that supplies dry air, and a flow rate sensor that measures the flow rate of the dry air may be provided. Examples of dry air supply sources include a compressor that sends out compressed dry air and a tank that stores dry air. From the perspective of production costs, dry air can be generated by drying air using exhaust heat generated by other machines or equipment, but this is not a limitation.

[0033] (Exhaust section) The exhaust section 5 exhausts gas inside the casing 1 from the lower side of the casing 1 to the outside so that the inside of the casing 1 is maintained at a positive pressure relative to the outside. The size and shape of the exhaust section 5 are not particularly limited as long as they maintain a positive pressure inside the casing 1 relative to the outside. For example, the shape of the exhaust section 5 can be appropriately determined in consideration of the amount of dry air supplied to the inside of the casing 1 and the internal volume of the casing 1. The illustrated exhaust section 5 is formed between the bottom edge (e.g., skirt-shaped) of the resin sheet 3 and the bottom surface 6. If the resin sheet 3 is flexible, the pressure inside the casing 1 is made positive relative to the outside, and the resin sheet 3 flexes depending on the magnitude of the positive pressure, thereby functioning as the exhaust section 5. In another embodiment (not shown), the exhaust section may have a through-hole-shaped exhaust port formed in the casing 1 (more specifically, the resin sheet 3, etc.) and an exhaust pipe connected to the exhaust port. By disposing the exhaust section 5 on the lower side of the casing 1, the dry air remaining inside the casing 1 prevents outside air from entering through the exhaust section 5.

[0034] [2. Titanium sponge manufacturing method] One embodiment of the titanium sponge production method according to the present invention includes a storage step in which titanium sponge lumps 7 are stored using the storage method for titanium sponge lumps 7 described above, and a crushing step in which the titanium sponge lumps 7 are removed from the casing 1 after the storage step and crushed. In the crushing step, the titanium sponge lumps 7 may be crushed by a known crushing method. In one embodiment, the method may further include a reduction step in which titanium tetrachloride is reduced with metallic magnesium in, for example, a metallic reduction reactor to produce titanium sponge lumps, and a vacuum separation step in which the molten magnesium chloride and molten magnesium remaining in the metallic reduction reactor are removed from the metallic reduction reactor via a pipe connected to the bottom of the metallic reduction reactor, and then the titanium sponge lumps are subjected to a vacuum separation treatment. The method may also include an outer periphery removal step in which the outer periphery of the titanium sponge lumps removed from the metallic reduction reactor after the vacuum separation step. Note that explanations that overlap with the above-mentioned configuration will be omitted.

[0035] The titanium sponge obtained by the above-mentioned production method can be melted by the VAR method, PAM method, EB method or the like to produce a titanium ingot. [Example]

[0036] The present invention will be specifically described based on examples. The following examples are merely illustrative examples for facilitating understanding of the technical content of the present invention, and the technical scope of the present invention is not limited to these examples. In Example 1 and Comparative Examples 1 and 2, the absolute humidity of the dry air, the inside of the casing 1, and the outside of the casing 1 was calculated by the method described above using a measuring device (WATCH LOGGER Data Logger Temperature and Humidity Stick USB Type KT-255U, manufactured by Fujita Electric Manufacturing Co., Ltd.).

[0037] [Example 1] (reduction and vacuum separation) First, titanium tetrachloride was reduced with metallic magnesium to produce a titanium sponge mass (approximate production volume: 8 tons) in a cylindrical metallic reduction reactor (clad steel with an outer wall made of stainless steel and an inner wall made of carbon steel). The remaining molten magnesium chloride and molten magnesium metal were removed from the metallic reduction reactor through a pipe connected to the bottom of the metallic reduction reactor, and the titanium sponge mass was then subjected to a vacuum separation process. The titanium sponge mass was then removed from the metallic reduction reactor. Next, the outer periphery of the titanium sponge mass (the portion with a high iron content) was chipped off to produce a titanium sponge mass 7 that was approximately cylindrical (φ1.7 m × 2.0 m). Similar operations were performed to produce a total of 30 batches of titanium sponge mass, and approximately cylindrical titanium sponge masses were obtained by chipping.

[0038] (storage) As shown in Figure 1, a frame structure 2 was formed from stainless steel frame members, and then covered with a resin sheet 3 to assemble a casing 1. The inside of the casing 1 (volume: 12 m 3 After placement, as shown in Figure 1, air was supplied from the air supply ports 4a and 4b on the top 8 and bottom 9 sides of the titanium sponge mass at a flow rate of 300 L / min (total 600 L / min) and an absolute humidity of 3.5 gH2O / m 3 The following dry air was supplied into the inside of the casing 1. At this time, the internal gas was discharged from the exhaust section 5, but the inside of the casing 1 was maintained at a positive pressure relative to the outside. In other words, dry air was continuously supplied into the inside of the casing 1, and also continuously discharged from the exhaust section 5, so that the inside of the casing 1 was maintained at a positive pressure relative to the outside. Note that no special temperature adjustment was performed on the dry air supplied into the inside of the casing 1, and the temperature of the dry air was within ±5°C of the air temperature outside the casing 1. After 10 hours had passed since the start of the dry air supply, the supply of dry air was stopped, and the titanium sponge mass 7 was promptly removed from inside the casing 1. Note that, from 2 hours after the start of the dry air supply until the supply of dry air was stopped, the absolute humidity inside the casing 1 was 7 gH2O / m 3 More than 9gH2O / m 3 The absolute humidity outside the casing 1 (outside air) was 15 gH2O / m 3 More than 20gH2O / m 3 It was within the following range: Using the same procedure, a total of 30 titanium sponge lumps were stored in separate casings.

[0039] <Evaluation (presence or absence of yellow coloring and amount of coloring)> An expert visually checked whether the titanium sponge lumps 7 had turned yellow after storage. As a result, no yellow coloring was confirmed in the 30 titanium sponge lumps after storage.

[0040] (Crushing) Thereafter, the titanium sponge mass 7 was crushed to obtain titanium sponge.

[0041] [Comparative Example 1] In Comparative Example 1, the same operations as in Example 1 were carried out to produce titanium sponge blocks in a total of 14 batches, and after chipping, approximately cylindrical titanium sponge blocks were obtained. Next, a total of 14 titanium sponge lumps were stored in the same manner as in Example 1, except that dry air was not used and the titanium sponge lumps were stored exposed to the outside air. The absolute humidity of the outside air at the storage location was 15 gH2O / m 3 More than 20gH2O / m 3 It was within the following range: After 10 hours of storage, the titanium sponge lumps were promptly removed from the room. Then, as in Example 1, it was confirmed whether the titanium sponge lumps had turned yellow after storage. As a result, yellow coloration was confirmed in various parts of the 14 titanium sponge lumps after storage. After crushing the titanium sponge lumps, the colored parts were collected and weighed, and the total weight of the colored parts was found to be 95 tons.

[0042] Comparative Example 2 In Comparative Example 2, the same procedure as in Example 1 was carried out to produce a total of 30 batches of titanium sponge blocks, which were then chipped to obtain roughly cylindrical titanium sponge blocks. Next, in Comparative Example 2, a titanium sponge mass 7 was placed so that it lay flat inside the casing 1 shown in Fig. 1. After placement, as shown in Fig. 1, air was introduced from the air inlets of the air inlets 4a and 4b at 300 L / min (total 600 L / min) and an absolute humidity of 3.5 gH2O / m 3 The following dry air is supplied to the inside, and the absolute humidity inside is 9gH2O / m from the start of supply. 3 A total of 30 titanium sponge lumps were stored in the same manner as in Example 1, except that the supply of dry air was stopped and storage was carried out when it was confirmed that the pressure inside the casing 1 reached the pressure below. After the supply of dry air was stopped, exhaust from the inside to the outside of the casing 1 ceased, and the pressure inside and outside the casing 1 became the same. Eight hours had passed since the supply of dry air was stopped (a total of 10 hours including the time for supplying dry air), so the titanium sponge lumps 7 were promptly removed from the casing 1. Then, as in Example 1, it was checked whether the titanium sponge lumps had turned yellow after storage. As a result, yellow coloration was confirmed in various parts of the five titanium sponge lumps after storage. After crushing the titanium sponge lumps, the colored parts were collected and weighed, and the total weight of the colored parts was found to be 25 tons.

[0043] [Table 1]

[0044] (Considerations based on examples) In Example 1, the coloring of the titanium sponge mass during storage was suppressed, so the titanium sponge mass was placed inside a casing and the inside of the casing was kept at an absolute humidity of 3.5 g H2O / m 3 It was confirmed that it was useful to supply dry air as follows and to vent the gas inside the casing from the lower side of the casing to the outside so that the inside of the casing was maintained at a positive pressure relative to the outside. The storage method in Example 1 was mainly a simple process of constructing and removing the casing and then supplying dry air. In other words, unlike when the atmosphere around the titanium sponge mass is reduced in pressure, the storage method in Example 1 did not involve the workload of constructing an airtight warehouse or rigorously sealing the entire warehouse, and therefore the workload was small. On the other hand, it is presumed that the titanium sponge mass in Comparative Example 1 was discolored because it was exposed to the outside air for as long as 10 hours. Observation during the crushing process confirmed that the titanium sponge mass was discolored yellow not only on the surface but also inside. Furthermore, in Comparative Example 2, unlike Example 1, the supply of dry air was stopped, and therefore the inside of the casing could not maintain a positive pressure relative to the outside. Therefore, in Comparative Example 2, it is presumed that the coloring of the titanium sponge mass during storage was caused by the stoppage of the supply of dry air. [Explanation of symbols]

[0045] 1 casing 2. Frame structure 3 Resin sheet 4a, 4b Air supply section 5 Exhaust section 6 Bottom 7 Titanium sponge block 8 top 9 Bottom

Claims

1. A method for storing titanium sponge mass, comprising: The titanium sponge mass was placed inside a casing, and the inside of the casing was kept at an absolute humidity of 3.5 gH 2 O / m 3 A method for storing titanium sponge masses, comprising: supplying dry air as described below; and discharging gas inside the casing from the lower side of the casing to the outside so that the inside of the casing is maintained at a positive pressure relative to the outside.

2. the casing has a plurality of dry air inlets, 2. A method for storing titanium sponge lumps according to claim 1, wherein the air inlets are arranged at least on the top side and the bottom side of the titanium sponge lumps.

3. 3. The method for storing titanium sponge chunks according to claim 1, wherein the amount of dry air supplied to the inside of the casing is 500 L / min or more and 750 L / min or less.

4. The internal volume of the casing is 3 m 3 More than 20m 3 The method for storing a titanium sponge mass according to any one of claims 1 to 3, wherein:

5. The absolute humidity outside the casing is 15.0 gH 2 O / m 3 The method for storing titanium sponge mass according to any one of claims 1 to 4.

6. a storage step of storing the titanium sponge lump by the method for storing the titanium sponge lump according to any one of claims 1 to 5; a crushing step of crushing the titanium sponge mass to obtain titanium sponge after the storing step.

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