Heating furnace and method for manufacturing titanium sponge

Abstract

To provide a heating furnace that can reduce the furnace maintenance load. [Solution] The heating furnace 1 according to the present invention is a heating furnace 1 used for manufacturing sponge titanium blocks TS, comprising a furnace body 3 that houses a metal container 2 inside, a plurality of ceramic hooks 4 fixed to the inner side surface 3a of the furnace body 3, and a resistance heating zone 5 hung on the plurality of hooks 4, wherein the plurality of hooks 4 include a plurality of upper hooks 40 and lower hooks 41 which are divided into upper and lower stages and are arranged apart from each other in the circumferential direction D2 of the furnace body 3, and a plurality of stage transition hooks 42 which are provided in the transition portion between the upper and lower stages and are arranged apart from each other in the circumferential direction D2 of the furnace body 3 while being gradually shifted in the vertical direction D1 to connect the upper and lower stages, and the resistance heating zone 5 is hung on the upper hooks 40 and lower hooks 41 in the upper and lower stages, and is hung on the plurality of stage transition hooks 42 which extend in a wave-like manner in the vertical direction D1 in the transition portion.

Description

Technical Field

[0001] The present invention relates to a heating furnace used for manufacturing sponge titanium lumps and a method for manufacturing sponge titanium using the same.

Background Art

[0002] Sponge titanium used as a raw material for metal titanium products can be manufactured by a method based on the so-called Kroll process. In such a method, molten metal magnesium is previously stored in a metal container to form a molten bath, and a reduction step is performed in which titanium tetrachloride is dropped and supplied onto the bath surface. During the reduction step, the metal magnesium acts as a reducing agent and the titanium tetrachloride is reduced to metallic titanium, and the metallic titanium grows as sponge titanium lumps in the container. At this time, magnesium chloride is generated as a by-product in the molten bath. After the reduction step is completed, a bath discharge step may be performed. Here, the molten bath containing the metal magnesium and the by-product magnesium chloride that were not used in the reduction reaction is discharged from the container while maintaining the molten state. Note that the molten bath may be withdrawn from the container during the reduction step. After the bath discharge step, as a pressure reduction separation step, the pressure inside the container is reduced while heating the container to a high temperature. Thereby, residues such as metal magnesium in the container are separated from the sponge titanium lumps. After the pressure reduction separation step is completed, the sponge titanium lumps are taken out from the container and subjected to crushing to obtain granular sponge titanium.

[0003] The following Patent Document 1 shows that a container (reduction container) is disposed inside a heating furnace (reduction furnace) in the reduction step. The following Patent Document 2 shows that a container (separation container) is disposed inside a heating furnace (electric heating furnace) in the pressure reduction separation step.

[0004] As shown in Patent Document 3 below, multiple hooks (joint members, heater support members, and sleeves) are fixed to the inner side surface of the furnace body of the heating furnace, and a resistance heating strip (strip-shaped heater) is hung on these hooks. When current is supplied to the resistance heating strip, the container and its contents stored inside the heating furnace are heated. Patent Document 3 also discloses that the hooks are arranged in multiple stages, and that the resistance heating strip extends in a vertically undulating manner in each stage. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2002-003959 [Patent Document 2] Japanese Patent Publication No. 2001-348629 [Patent Document 3] Japanese Utility Model Publication No. 03-027598 [Overview of the project] [Problems that the invention aims to solve]

[0006] For example, in the vacuum separation process, the reaction vessel is heated to approximately 1000-1050°C by the resistance heating zone. After the vacuum separation process is completed, the resistance heating zone is cooled to room temperature. In other words, the resistance heating zone repeatedly expands when heated and contracts when cooled.

[0007] As shown in Patent Document 3, by extending the resistance heating band in a vertically undulating manner in each stage, it is expected that the deformation of the resistance heating band due to expansion and contraction in each stage will be absorbed within the wave. That is, when the resistance heating band expands, it is expected that the resistance heating band will extend vertically within each wave, and when the resistance heating band contracts, it is expected that the resistance heating band will return to its initial shape or position within each wave.

[0008] On the other hand, in this configuration, resistance heating zones that are not constrained by hooks occur in the transition areas between each stage. The resistance heating zones in the transition areas are relatively long and extend vertically, and as the resistance heating zones repeatedly expand and contract, their position may shift. Specifically, as shown in Figure 7, the resistance heating zone 5 may detach from the hook 4 located at the upper position of the transition area. Such displacement of the resistance heating zones can lead to short circuits (contact between resistance heating zones) or leakage current (contact between the resistance heating zone and the metal container).

[0009] Therefore, as shown in Figure 8, multiple guide members 90 were arranged along the vertical direction D1 in the transition section between the upper and lower sections, and the resistance heating zone 5 was extended between the upper and lower sections along these guide members 90, thereby restricting the deformation or movement of the resistance heating zone 5 in the circumferential direction D2 of the furnace body (see the dashed line in the figure). However, as the resistance heating zone 5 repeatedly expanded and contracted, it also detached from the guide members 90, and the displacement of the resistance heating zone 5 in the transition section could not be sufficiently suppressed.

[0010] Furthermore, as shown in Figure 9, an attempt was made to install a lifting hook 91 in the transition section to temporarily lift the resistance heating band 5, and to apply tension to the resistance heating band 5 in the transition section by hanging it on the lifting hook 91 (see the dashed line in the figure). However, as the resistance heating band 5 repeatedly expanded and contracted, it fell off the lifting hook 91 as well, and the displacement of the resistance heating band 5 in the transition section could not be sufficiently suppressed.

[0011] Furthermore, as shown in Figure 10, an attempt was made to prevent the resistance heating band 5 from falling off the lifting hook 91 by fixing it with a fixing pin 92 near the lifting hook 91 (see the dashed line in the figure). However, the resistance heating band 5 stretched between the lifting hook 91 and the lower section, and the displacement of the resistance heating band 5 in the transition section could not be sufficiently suppressed.

[0012] Furthermore, as shown in Figure 11, an attempt was made to prevent the stretching of the resistance heating band 5 between the lifting hook 91 and the lower section by fixing the resistance heating band 5 with fixing pins 93 (see the dashed line in the figure). However, the resistance heating band 5 buckled between the fixing pins 93, creating a risk of the resistance heating band 5 breaking.

[0013] As mentioned above, various countermeasures were attempted, but a significant furnace repair load remained due to misalignment of the resistance heating zone in the transition area.

[0014] This invention was made to solve the above-mentioned problems, and one of its objectives is to provide a heating furnace and a method for producing sponge titanium that can reduce the furnace maintenance load. [Means for solving the problem]

[0015] The inventors noticed that misalignment of the resistance heating zone occurs in the transition sections between each stage, but this misalignment is not a significant problem in each individual stage. They then discovered that extending the resistance heating zone in a vertically undulating manner even in the transition sections can resolve the above-mentioned problems. This invention is based on these findings.

[0016] [1] In one embodiment, the present invention relates to a heating furnace used for manufacturing a sponge titanium block, comprising: a furnace body housing a metal container inside; a plurality of ceramic hooks fixed to the inner side surface of the furnace body; and a resistance heating strip hung on the plurality of hooks, wherein the plurality of hooks include a plurality of upper hooks and lower hooks arranged apart from each other in the circumferential direction of the furnace body, divided into upper and lower stages; and a plurality of stage transition hooks provided in the transition portion between the upper and lower stages, arranged apart from each other in the circumferential direction of the furnace body while being gradually shifted vertically to connect the upper and lower stages; and the resistance heating strip is hung on the upper hooks and lower hooks in the upper and lower stages, and is hung on the plurality of stage transition hooks while extending in a vertically undulating manner in the transition portion.

[0017] [2] The present invention includes, at least a portion of the plurality of hooks, a hook body fixed to the inner side surface of the furnace body and a ring-shaped member hung on the hook body, The resistance heating band is placed over the ring-shaped member. The heating furnace described in paragraph 1 may be used.

[0018] [3] The present invention may relate to the heating furnace described in paragraph 1 or 2, wherein the stage transition hooks include a first stage transition hook and a second stage transition hook adjacent to each other in the circumferential direction of the furnace body, the second stage transition hook being positioned below the first stage transition hook, and the resistance heating zone includes a first vertical portion extending vertically downward from the first stage transition hook, a lower folded portion connected to the lower end of the first vertical portion, and a second vertical portion extending vertically upward from the lower folded portion to the second stage transition hook, the vertical length of the first vertical portion being 1.3 times or more and 4 times or less the vertical length of the second vertical portion.

[0019] [4] The present invention may relate to a heating furnace according to any one of paragraphs 1 to 3, wherein the distance between the upper stage and the lower stage is 300 mm or more and 700 mm or less.

[0020] [5] The present invention may further provide a heating furnace according to any one of paragraphs 1 to 4, comprising a pin provided in the transition portion and positioned inside the lower folded portion of the resistance heating band formed by the undulation of the resistance heating band.

[0021] [6] The present invention relates to a method for producing titanium sponge, which in one embodiment includes heating using a heating furnace as described in any one of paragraphs 1 to 5. [Effects of the Invention]

[0022] According to an embodiment of the heating furnace and the method for manufacturing sponge titanium of the present invention, since the resistance heating band is hung on the upper hook and the lower hook in the upper and lower sections and is hung on a plurality of step transition hooks while extending in a vertically wavy manner in the transition section, the furnace repair load can be reduced.

Brief Description of the Drawings

[0023] [Figure 1] It is an explanatory diagram showing a heating furnace according to an embodiment of the present invention. [Figure 2] It is a front view showing the inner side surface and the hook of the furnace body in FIG. 1. [Figure 3] It is a side view of the hook when viewed along line III-III in FIG. 2. [Figure 4] It is an enlarged view showing an enlarged area IV in FIG. 2. [Figure 5] It is an enlarged view showing an enlarged area V in FIG. 2. [Figure 6] It is a side view of the pin when viewed along line VI-VI in FIG. 5. [Figure 7] It is an explanatory diagram showing a first aspect of a heating furnace in the prior art. [Figure 8] It is an explanatory diagram showing a second aspect of a heating furnace in the prior art. [Figure 9] It is an explanatory diagram showing a third aspect of a heating furnace in the prior art. [Figure 10] It is an explanatory diagram showing a fourth aspect of a heating furnace in the prior art. [Figure 11] It is an explanatory diagram showing a fifth aspect of a heating furnace in the prior art.

Embodiments for Carrying Out the Invention

[0024] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The present invention is not limited to each embodiment, and can be materialized by modifying the components without departing from the spirit of the invention. Furthermore, various inventions can be formed by appropriately combining the multiple components disclosed in each embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, components from different embodiments may be appropriately combined.

[0025] Figure 1 is an explanatory diagram showing a heating furnace 1 according to an embodiment of the present invention. The heating furnace 1 shown in Figure 1 is used for the production of sponge titanium ingots TS.

[0026] The manufacturing process for sponge titanium ingots TS includes a reduction step, a bath discharge step, and a vacuum separation step. The reduction step involves storing molten metallic magnesium in a metal container 2 to create a molten bath, and supplying titanium tetrachloride by dropping it onto the surface of the bath. During the reduction step, the metallic magnesium acts as a reducing agent, reducing titanium tetrachloride to metallic titanium, which grows as sponge titanium ingots TS within container 2. At this time, magnesium chloride is produced in the molten bath as a by-product. The bath discharge step is the process of discharging the molten bath Bm, which contains metallic magnesium not used in the reduction reaction and by-products such as magnesium chloride, from container 2 while maintaining it in a molten state. The bath discharge step may be performed concurrently with the reduction step. The vacuum separation step is the process of separating residual materials such as metallic magnesium from the sponge titanium ingots TS by heating container 2 to a high temperature while reducing the pressure inside container 2. In the vacuum separation step, the heating temperature is kept below the eutectic temperature to prevent the eutectic reaction between titanium and iron. On the other hand, from the viewpoint of efficiency in the evaporation and removal of metallic magnesium or magnesium chloride, a high heating temperature is preferable. Examples of heating temperatures are 950°C to 1080°C or 1000°C to 1050°C. After the vacuum separation process is completed, the sponge titanium mass TS is removed from the container and subjected to crushing to obtain granular sponge titanium.

[0027] The heating furnace 1 may heat the container 2 (reduction container) in the reduction process, or it may heat the container 2 (separation container) in the vacuum separation process. Separate heating furnaces 1 may be prepared for the reduction process and the vacuum separation process, or one heating furnace 1 may be used for both the reduction process and the vacuum separation process. The vacuum separation process tends to operate the heating furnace 1 at a higher temperature of about 100°C to 250°C than the reduction process, and the degree of deformation of the resistance heating zone 5, described later, also tends to be greater. According to this embodiment, even if the heating furnace 1 is operated at a high temperature repeatedly for a long period of time, displacement of the resistance heating zone 5 can be suppressed, so preferably, the heating furnace 1 of this embodiment is used in the vacuum separation process. Furthermore, the resistance heating zone 5 is more prone to deformation in the heating furnace 1 for the vacuum separation process, as a large current is often passed through it in the initial stages of heating. Also, the resistance heating zone 5 located on the upper side of the heating furnace 1 tends to deform more easily. The reason why it is more prone to deformation on the upper side is presumed to be because it is more affected by gravity. If separate heating furnaces 1 are prepared for the reduction process and the reduced-pressure separation process, the bath discharge process may be carried out at any time; however, it is preferable to carry out the bath discharge process in the heating furnace 1 for the reduction process in order to facilitate the movement of the container containing the sponge titanium mass TS.

[0028] The heating furnace 1 has a furnace body 3, a plurality of hooks 4, and a resistance heating zone 5.

[0029] The furnace body 3 is a structure that houses a metal container 2 inside. The material of the furnace body 3 (furnace wall) is not particularly limited as long as it can be used to manufacture a sponge titanium block TS and exhibits appropriate strength at high temperatures during heating; for example, refractory bricks are used. The furnace body 3 has a cylindrical or other tubular side wall 30 and a bottom 31 that seals one end of the side wall 30 in the axial direction (the lower end in Figure 1). The upper end of the side wall 30 forms an opening, through which the container 2 is inserted into and removed from the furnace body 3.

[0030] The hooks 4 are fixed to the inner side surface 3a (the inner circumferential surface of the side wall 30) of the furnace body 3. As will be explained in detail later, the hooks 4 are positioned at different locations in the vertical direction D1 and spaced apart from each other in the circumferential direction D2 of the furnace body 3. Figure 1 shows a simplified representation with two rows of hooks 4, but there may be more rows of hooks 4 positioned at different locations in the vertical direction D1. The number of rows of hooks 4 in the vertical direction D1 can be appropriately determined depending on the size of the heating furnace 1 and the container 2, etc.

[0031] Hook 4 is made of ceramics. A ceramic hook 4 can be understood as having ceramics as its main component. When the mass ratio of ceramics in each hook 4 exceeds 50%, it can be understood as having ceramics as its main component. Preferably, the mass ratio of ceramics in each hook 4 is 70% or more, more preferably 80% or more, and even more preferably 90% or more. For example, the mass ratio of ceramics in each hook 4 may be 95% or more. Hook 4 may consist of ceramics and unavoidable impurities.

[0032] The ceramics constituting hook 4 may be oxide-based ceramics. Examples of oxide-based ceramics include alumina (aluminum oxide (Al2O3)), magnesia (magnesium oxide (MgO)), silica (silicon dioxide (SiO2)), titania (titanium dioxide (TiO2)), and barium titanate (BaTiO3). As the ceramics constituting hook 4, alumina is preferred because it is inexpensive, and the mass proportion of alumina may be 90% or more. From the viewpoint of low cost, ceramics containing alumina and silica may also be used. Furthermore, the ceramics constituting hook 4 may also be other ceramics such as nitride-based ceramics. An example of a nitride-based ceramic is silicon nitride (Si3N4).

[0033] The resistance heating strip 5 is a strip-shaped member made of a conductor such as an iron-based alloy containing chromium and aluminum (Kanthal AF, A-1, and AP). A single resistance heating strip 5 may be used, or multiple resistance heating strips 5 with different compositions may be welded together. The resistance heating strip 5 is hung on multiple hooks 4. The container 2 is heated by the radiant heat generated when current flows through the resistance heating strip 5. Typically, the resistance heating strip 5 is connected to an external power source.

[0034] Container 2 is a generally cylindrical container with a closed bottom, suitable for manufacturing sponge titanium ingots TS weighing, for example, between 5 tons and 15 tons, and is made of a heat-resistant metal such as SUS316. Container 2 can also be made of clad steel with a carbon steel lining to prevent contamination of the sponge titanium ingots TS with Ni, Cr, etc.

[0035] The container 2 comprises a cylindrical or other tubular side wall 20, a bottom 21 that seals one axial end of the side wall 20 (the lower end in Figure 1), and a lid 22 attached to the opening at the other axial end of the side wall 20 (the upper end in Figure 1). The side wall 20 is provided with a discharge pipe 23 connected to a portion of the side wall 20 near the bottom 21, and the lid 22 is provided with a supply pipe 24 for supplying titanium tetrachloride. In the illustrated example, the discharge pipe 23 is connected to the side wall 20, but the discharge pipe 23 may also be connected to the bottom 21. Regardless of where the discharge pipe 23 is connected, it is possible to discharge the molten bath Bm. Generally, on the bottom 21 side of the container 2, as in the illustrated example, a punch 25 is arranged to push up the sponge titanium block TS when removing the sponge titanium block TS from inside the container 2. The punch 25 may be a single molded piece, but it may also have a removable grate in the part on which the sponge titanium block TS is placed. If the punch 25 has a grate, it becomes easier to separate the sponge titanium block TS from the punch 25.

[0036] In container 2, a sponge titanium mass TS can be formed. Specifically, the sponge titanium mass TS is obtained by filling container 2 with molten metallic magnesium (molten magnesium), dropping titanium tetrachloride into the molten magnesium via the supply pipe 24, and reducing the titanium tetrachloride with metallic magnesium. Even after the bath discharge process, impurities such as magnesium chloride and metallic magnesium remain in the sponge titanium mass TS in container 2. By heating container 2, which is under reduced pressure inside the resistance heating zone 5, to a high temperature, the impurities can be evaporated and separated. The evaporated and separated impurities are drawn into a recovery container (not shown). The impurities may be solidified by cooling the recovery container with a cooling device (not shown).

[0037] A space S that can be depressurized is provided between the inner surface of the heating furnace 1 and the outer surface of the container 2. The space S is subjected to a reduced pressure atmosphere when the heating furnace 1 is used in a reduced pressure separation process. The heating furnace 1 is preferably made of a material that can withstand reduced pressure and has a sealed structure with a lid. Specifically, it is preferable to provide a flange on the top of the container 2 and seal the joint surface between this flange and the heating furnace 1 with resin or the like. By adopting such a structure, the pressure inside the container 2 and the pressure in the space S of the heating furnace 1 can be maintained at a controlled predetermined pressure, thereby preventing deformation of the container 2. When the heating furnace 1 is used in a reduction process, the space S may be subjected to an atmospheric pressure. This is because the reduction reaction is an exothermic reaction, and in the reduction process, the internal space of the container 2 decreases as the sponge titanium mass TS grows, so the inside of the container 2 tends to become high pressure.

[0038] Next, Figure 2 is a front view showing the internal side surface 3a and hook 4 of the furnace body 3 in Figure 1, Figure 3 is a side view of hook 4 as seen along line III-III in Figure 2, Figure 4 is an enlarged view showing region IV in Figure 2, Figure 5 is an enlarged view showing region V in Figure 2, and Figure 6 is a side view of pin 6 as seen along line VI-VI in Figure 5.

[0039] As shown in Figure 2, the multiple hooks 4 include multiple upper hooks 40 and lower hooks 41 that are divided into upper and lower sections and are arranged apart from each other in the circumferential direction D2 of the furnace body 3, and multiple stage transition hooks 42 that are provided in the transition section between the upper and lower sections and are arranged apart from each other in the circumferential direction D2 of the furnace body 3, gradually shifting in the vertical direction D1 to connect the upper and lower sections. The stage transition hooks 42 are arranged so as to move downwards in the circumferential direction D2 of the furnace body 3 from one end of the upper section to one end of the lower section (from left to right in the figure).

[0040] These upper hooks 40, lower hooks 41, and step-transition hooks 42 are terms used to describe the arrangement of hooks 4 in the vertical direction D1, and do not imply that the number of hooks 4 is limited to two levels, upper and lower. For example, Figure 2 shows that step-transition hooks 42 are arranged downward to the right at one end (right side in the figure) of the row of upper hooks 40 in the circumferential direction D2 of the furnace body 3. However, another step-transition hook 42 may be arranged upward to the left at the other end (left side in the figure) of the row of upper hooks 40 in the circumferential direction D2, and these other step-transition hooks 42 may connect to hooks 4 of another level that are positioned above the upper hooks 40. In this relationship between the upper hooks 40 and the hooks 4 of another level, the former becomes the lower hook 41, and the latter becomes the upper hook 40. The number and spacing of the upper hooks 40, lower hooks 41, and step-transition hooks 42 can be arbitrarily changed.

[0041] The resistance heating strip 5 is attached to upper hooks 40 and lower hooks 41 in the upper and lower sections, and is attached to multiple section transition hooks 42 in the transition section, extending in a wave-like manner in the vertical direction D1. Wavering in the vertical direction D1 means that the upper and lower positions change periodically as you move in the circumferential direction D2 (for example, as you move from left to right in the figure). Here, "periodic" means that the upper and lower ends of the wave are repeated alternately, and the shape of each wave may be the same or different. Wavering in the vertical direction D1 also includes repeating waves with a shape like the Japanese hiragana character "shi" or the letter "J".

[0042] Here, the resistance heating band 5 repeatedly expands when heated and contracts when cooled. As explained using Figures 7 to 11 as background technology, as the resistance heating band 5 repeatedly expands and contracts, the resistance heating band 5 would sometimes detach from the hooks 4, particularly near the portion that extends relatively long in the vertical direction D1 between the upper and lower stages, causing misalignment of the resistance heating band 5 in the transition area. This misalignment of the resistance heating band 5 is a factor that can cause short circuits (contact between resistance heating bands 5) or leakage current (contact between the resistance heating band 5 and the metal container 2), and when misalignment occurs, it is necessary to repair the heating furnace 1 (furnace repair). In contrast, as in the heating furnace 1 of this embodiment, by having the resistance heating band 5 attached to multiple stage transition hooks 42 while extending in a wave-like manner in the vertical direction D1 in the transition area, the deformation of the resistance heating band 5 due to expansion and contraction in the transition area can be absorbed within the wave. In other words, when the resistance heating zone 5 expands, it extends vertically in the direction D1 within each wave (extending downwards due to the effect of gravity), which prevents the deformation of the resistance heating zone 5 due to expansion from spreading elsewhere. Also, when the resistance heating zone 5 contracts, it can return to its initial shape or position within each wave (the part that extended downwards contracts to return to its initial shape or position). This makes it possible to suppress displacement of the resistance heating zone 5 in the transition area and reduce the furnace maintenance load.

[0043] As shown in Figure 2, the resistance heating band 5 may extend in a wavy manner in the vertical direction D1 in both the upper and lower sections, and be hung on multiple upper hooks 40 and lower hooks 41. In the upper and lower sections, the resistance heating band 5 may form waves with the same amplitude and approximately the same spacing between the peaks.

[0044] As particularly shown in Figure 3, at least some of the multiple hooks 4 include a hook body 400 fixed to the inner side surface 3a of the furnace body 3 and a ring-shaped member 401 hung on the hook body 400, with the resistance heating strip 5 hanging on the ring-shaped member 401. By providing the ring-shaped member 401 in this way, the hook body 400 can be made relatively thin, and the weight on the side wall 30 of the heating furnace 1 can be reduced. In addition, compared to the case where the resistance heating strip 5 is hung directly on the hook body 400, the curvature of the resistance heating strip 5 becomes gentler, and the load on the resistance heating strip 5, especially the curved portion, can be reduced during operation.

[0045] The hook body 400 may have a straight portion 400a, one end of which is embedded in the side wall 30 of the furnace body 3, and a locking portion 400b extending upward from the other end of the straight portion 400a. The ring-shaped member 401 is hooked onto the straight portion 400a, and the locking portion 400b prevents the ring-shaped member 401 and the resistance heating band 5 from falling off the straight portion 400a. The ring-shaped member 401 may have a cylindrical portion 401a and a pair of edges 401b extending radially outward from the outer circumferential surface of the cylindrical portion 401a on both sides of the cylindrical portion 401a in the axial direction. The resistance heating band 5 rests on the outer circumferential surface of the cylindrical portion 401a, and the edges 401b prevent the resistance heating band 5 from falling off the ring-shaped member 401. Note that the edges 401b may be omitted in the ring-shaped member 401. From a material standpoint, both the hook body 400 and the ring-shaped member 401 may be made of ceramics.

[0046] In the illustrated embodiment, all hooks 4 include a hook body 400 and a ring-shaped member 401. However, some hooks 4 may consist only of the hook body 400.

[0047] As particularly shown in Figure 4, the stage transition hooks 42 include a first stage transition hook 421 and a second stage transition hook 422 that are adjacent to each other in the circumferential direction D2 of the furnace body 3. The second stage transition hook 422 is positioned below the first stage transition hook 421. The terms first stage transition hook 421 and second stage transition hook 422 refer to two stage transition hooks 42 that are adjacent to each other in the circumferential direction D2 of the furnace body 3, and do not limit the number of stage transition hooks 42.

[0048] The resistance heating strip 5 includes a first vertical section 50 extending vertically downward from the first stage transition hook 421, a lower folded section 51 connected to the lower end of the first vertical section 50, and a second vertical section 52 extending vertically upward from the lower folded section 51 to the second stage transition hook 422. The vertical length L1 of the first vertical section 50 is preferably 1.3 to 4 times the vertical length L2 of the second vertical section 52. For example, the vertical length L1 may be 165 mm and the vertical length L2 may be 85 mm. In this case, the vertical length L1 is 1.9 times the vertical length L2. Each wave formed by the resistance heating strip 5 that is hung on the stage transition hook 42 is not particularly limited as long as it satisfies the above range, and may have the same shape or different shapes.

[0049] In this embodiment, when the first-stage transition hook 421 and the second-stage transition hook 422 include a hook body 400 and a ring-shaped member 401, the resistance heating band 5 has an arc-shaped upper folded portion 53 placed on top of the ring-shaped member 401. The position where the resistance heating band 5 separates from the ring-shaped member 401 (more specifically, the cylindrical portion 401a) is the boundary position between the upper folded portion 53 and the first vertical portion 50 and the second vertical portion 52. The portions extending along the vertical direction D1 from this boundary position are the first vertical portion 50 and the second vertical portion 52, and the lengths of these portions extending along the vertical direction D1 are the vertical lengths L1 and L2. The lower folded portion 51 extends horizontally from the lower ends of the first vertical portion 50 and the second vertical portion 52 with a predetermined radius of curvature. Even when at least one of the first-stage transition hook 421 and the second-stage transition hook 422 consists only of the hook body 400, the portion extending in the vertical direction D1 is the first vertical portion 50 and the second vertical portion 52, and the lengths of the portions extending along this vertical direction D1 are the vertical lengths L1 and L2.

[0050] The number of stages of the stage transition hooks 42 in the transition section can be appropriately determined in consideration of the height of the container 2, etc. As shown in Figure 2, it is preferable that the distance Dis between the upper and lower stages is 300 mm or more and 700 mm or less. Distance Dis is the vertical distance D1 between the apex of the upper folded portion 53 in the upper stage and the apex of the upper folded portion 53 in the lower stage. A distance Dis of 300 mm or more allows for efficient heating of the container 2, and a distance Dis of 700 mm or less reduces the risk of variations in the heating of the container 2.

[0051] The heating furnace 1 of this embodiment further includes a pin 6 provided in the transition section and positioned inside the lower folded portion 51 of the resistance heating zone 5, which is formed by the undulation of the resistance heating zone 5. The pin 6 restricts excessive upward displacement of the lower folded portion 51 when the resistance heating zone 5 contracts, and more reliably suppresses misalignment of the resistance heating zone 5 as it repeatedly expands and contracts.

[0052] The pin 6 may be a rod-shaped member made of ceramic. In the illustrated embodiment, the pin 6 is positioned inside several lower folded portions 51. The frequency at which the pin 6 is positioned is arbitrary. Also, as in the illustrated embodiment, the pin 6 may be positioned inside the lower folded portions 51 of the upper and lower resistance heating zones 5.

[0053] As shown in Figures 5 and 6, the pin 6 may have a rod-shaped pin body 60 with one end embedded in the side wall 30 of the furnace body 3, and a pair of disc bodies 61 attached to the pin body 60 at intervals along its longitudinal direction. The resistance heating zone 5 or the lower folded portion 51 may extend so as not to touch the pin body 60 when the resistance heating zone 5 is contracted to its initial shape or position. The lower folded portion 51 may touch the pin body 60 only when it is excessively displaced upward. The resistance heating zone 5 passes between the pair of disc bodies 61. The disc bodies 61 restrict the movement of the resistance heating zone 5 along the longitudinal direction of the pin body 60. The disc bodies 61 restrict the resistance heating zone 5 from approaching the container 2 when it expands. During expansion during heating and contraction during cooling, the lower side of the wave of the resistance heating zone 5 tends to deform more significantly. Furthermore, this deformation may include deformation along the vertical direction and deformation that moves closer to the container 2. Therefore, by restricting the movement of the lower side of the wave of the resistance heating zone 5 with the pin body 60 and the disc body 61, as in this embodiment, displacement of the resistance heating zone 5 can be suppressed more reliably. The pin body 60 and the disc body 61 may be made of ceramics.

[0054] The method for producing sponge titanium according to an embodiment of the present invention includes heating using the heating furnace 1 described above. The production method includes a reduction step, a bath discharge step, and a reduced-pressure separation step. Each step is as described above. Furthermore, as described above, granular sponge titanium is obtained by crushing the sponge titanium mass TS removed from the metal container 2.

[0055] Although preferred embodiments of the present invention have been described in detail above with reference to the attached drawings, the present invention is not limited to these examples. It is clear to any person with ordinary skill in the art to which the present invention belongs that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these are also understood to fall within the technical scope of the present invention. [Examples]

[0056] The present invention will be described more specifically below with reference to examples. The present invention is not limited to these examples.

[0057] As shown in Figure 7, when a resistance heating band was placed vertically in the transition section between the upper and lower stages (comparative example), displacement of the resistance heating band occurred within one year, requiring furnace repair. Similarly, even when the countermeasures shown in Figures 8 to 11 were adopted (comparative example), displacement of the resistance heating band occurred within one year, requiring furnace repair. On the other hand, as shown in Figure 2, when the resistance heating band was extended vertically in a wave-like manner in the transition section and attached to multiple stage transition hooks (example), no furnace repair was required even after 3 years and 6 months of operation. In the example and comparative example, the total length of the resistance heating band in the upper stage, transition section, and lower stage was the same (i.e., the total electrical resistance was the same), and the energization conditions for the heating furnace were the same. [Explanation of symbols]

[0058] 1:Heating furnace 2: Container 20: Side wall 21: Bottom 22: Lid 23: Discharge pipe 24: Supply pipe 25: Punch 3: Furnace body 3a: Internal side 30: Side wall 31: Bottom 4: Hook 40: Upper hook 41: Lower hook 42: Hook for transitioning between levels 421: Hook for transition to the first stage 422: Hook for transition to the second stage 400: Hook body 400a: Straight section 400b: Locking part 401: Ring-shaped member 401a: Cylindrical section 401b :Edge 5: Resistance heating zone 50: First vertical section 51: Bottom folding part 52: Second vertical section 53: Upper folding part 6: Pin 60: Pin body 61: Disc

Claims

1. A heating furnace used for manufacturing sponge titanium blocks, A furnace body that houses a metal container inside, Multiple ceramic hooks fixed to the inner side surface of the furnace body, The resistance heating strip hung on the aforementioned multiple hooks and Equipped with, The aforementioned multiple hooks, Multiple upper hooks and lower hooks are arranged in upper and lower sections, separated from each other in the circumferential direction of the furnace body, A plurality of stage transition hooks are provided in the transition section between the upper and lower stages, and are arranged apart from each other in the circumferential direction of the furnace body, gradually shifting vertically to connect the upper and lower stages. Includes, The resistance heating strip is hung on the upper hook and the lower hook in the upper and lower sections, and extends vertically in a wave-like manner in the transition section, while being hung on the multiple section transition hooks. Heating furnace.

2. At least a portion of the plurality of hooks includes a hook body fixed to the inner side surface of the furnace body and a ring-shaped member hung on the hook body, The resistance heating band is placed over the ring-shaped member. The heating furnace according to claim 1.

3. The stage transition hooks include a first stage transition hook and a second stage transition hook that are adjacent to each other in the circumferential direction of the furnace body, the second stage transition hook being positioned below the first stage transition hook. The resistance heating zone includes a first vertical portion extending vertically downward from the first stage transition hook, a lower folded portion connected to the lower end of the first vertical portion, and a second vertical portion extending vertically upward from the lower folded portion to the second stage transition hook. The vertical length of the first vertical section is 1.3 times or more and 4 times or less the vertical length of the second vertical section. The heating furnace according to claim 1.

4. The distance between the upper and lower sections is 300 mm or more and 700 mm or less. The heating furnace according to claim 1.

5. The transition portion is provided with a pin located inside the lower folded portion of the resistance heating band, which is formed by the undulation of the resistance heating band. The heating furnace according to claim 1.

6. A method for producing titanium sponge, comprising heating using a heating furnace as described in any one of claims 1 to 5.

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