Sheath

Abstract

To provide a sheath, even when heat treatment is executed to an object to be fired using a sheath having a storage space, to which the object to be fired is hard to stick by a glass component(s), and with which the glass component(s) is hard to stick even to the object to be fired itself.SOLUTION: A sheath of this invention consists of: an almost horizontally extending ceramic bottom plate 1; and a ceramic side wall 3 extending upward from the bottom plate 1 and forming a storage space 7 for storing an object W to be fired together with the bottom plate 1, and is used for a heat treatment furnace. The object W to be fired is molded by a carbon-containing molding assistant and at least contains silica. The heat treatment furnace is a continuous heat treatment furnace in which a degreasing zone for removing the molding assistant contained in the object W to be fired and a firing zone for firing the object W to be fired are continuous. At least a lower part of the side wall 3 or the bottom plate 1 is formed with communication passages 5 having an external diameter smaller than that of the object W to be fired and communicating the storage space 7 to the outside.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a sheath, also called a refractory container, a crucible, an ingot mold, a mold, a setter, a firing jig, etc.

Background Art

[0002] Patent Document 1 discloses a conventional sheath. This sheath is composed of a bottom plate made of alumina ceramic extending substantially horizontally and a side wall made of alumina ceramic combined with the bottom plate. The side wall extends upward from the bottom plate and forms a housing space together with the bottom plate for housing the object to be fired. A window portion is provided on the upper surface of the side wall to ensure the flow of air between the outside and the inside. In the housing space, an object to be fired used for electronic components, gas sensor elements, or plugs is housed.

[0003] A plurality of sheaths are provided on a base plate to form a bogie, and the bogie is used in a continuous heat treatment furnace. The continuous heat treatment furnace has a plurality of heat treatment zones continuously extending from a first zone at 700°C to a seventh zone at 1490°C. The bogie is sequentially pushed into the continuous heat treatment furnace from the first zone to the seventh zone, and during this time, the object to be fired is heat-treated. The heat-treated object to be fired is recovered, and the sheath is reused.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, according to the inventor's confirmation, when the object to be fired is heat-treated using a sheath having a storage space as described above, the object to be fired may adhere to the sheath due to the glass component, or the glass component may adhere to the object to be fired itself. If the object to be fired adheres to the sheath, it will increase the labor required to peel the object to be fired from the sheath, leading to an increase in manufacturing costs. Also, if the glass component adheres to the object to be fired itself, the composition of the object to be fired will change, and the quality of the object to be fired will be impaired.

[0006] The present invention has been made in view of the above-described conventional circumstances, and even when the object to be fired is heat-treated using a sheath having a storage space, it is an object to be solved to provide a sheath in which the object to be fired hardly adheres due to the glass component and the glass component hardly adheres to the object to be fired itself.

Means for Solving the Problems

[0007] The inventor conducted intensive research to solve the above problems. Then, as described above, when the object to be fired is heat-treated using a sheath having a storage space, the inventor discovered that the reasons for the problems that the object to be fired adheres to the sheath due to the glass component or the glass component adheres to the object to be fired itself are as follows, and completed the present invention.

[0008] That is, the above problems occur when the object to be fired is formed by a molding aid containing carbon such as an organic binder. Also, the object to be fired needs to contain at least silica (silicon oxide). Further, the heat treatment furnace needs to be a specific continuous heat treatment furnace. The continuous heat treatment furnace needs to have a degreasing zone for removing the molding aid contained in the object to be fired and a firing zone for firing the object to be fired in series.

[0009] Therefore, the inventor infers that the following problems occur under the above circumstances. First, when the object to be fired is fired in a specific continuous heat treatment furnace, if the object to be fired contains at least silica and is formed with a molding aid containing carbon, the degreasing in the degreasing zone before firing may be insufficient. In that case, the object to be fired passing through the degreasing zone has the carbon of the molding aid not fully burned into carbon dioxide and remains carbon. This is presumably due to inevitable factors such as a relatively large number of objects to be fired accommodated in the accommodation space of the sheath, the temperature in the degreasing zone not being high enough, the time spent in the degreasing zone not being long enough, the amount of oxygen present in the degreasing zone not being sufficient, or the object to be fired containing a large amount of molding aid. Therefore, in the degreasing zone, the carbon remaining in the object to be fired reduces the silica in the object to be fired, generating a gas component of SiO called haze. The haze diffuses within the sheath and is stored in the accommodation space of the sheath because it is heavier than the ambient gas such as air in the firing zone. In this regard, in the conventional sheath described above, a window portion was provided on the side wall, but since the window portion was on the upper surface of the side wall, the haze was stored in the accommodation space. For this reason, in the accommodation space, the haze oxidizes on the surface of the object to be fired and becomes fine particulate silicon oxide. Firing continues in this state, and the fine particulate silicon oxide melts to become a glass component, causing the object to be fired to adhere to the sheath or the glass component to adhere to the object to be fired itself.

[0010] The sheath of the present invention is composed of a ceramic bottom plate extending substantially horizontally and a ceramic side wall extending upward from the bottom plate to form an accommodation space for accommodating the object to be fired together with the bottom plate, and is a sheath used in a heat treatment furnace, wherein the object to be fired is formed with a molding aid containing carbon and contains at least silica, the heat treatment furnace is a continuous heat treatment furnace in which a degreasing zone for eliminating the molding aid contained in the object to be fired and a firing zone for firing the object to be fired are continuous, characterized in that at least a lower part of the side wall or the bottom plate is formed with a communication passage having an outer diameter smaller than that of the object to be fired and communicating the accommodation space to the outside.

[0011] The sheath of the present invention has an accommodation space, and a communication passage is formed in at least the lower part of the side wall or the bottom plate. Since this communication passage communicates the accommodation space to the outside, even if haze is likely to be stored in the accommodation space, the haze can be discharged to the outside through the communication passage. Therefore, in the accommodation space, the haze does not oxidize on the surface of the object to be fired and turn into fine silicon oxide. Therefore, even if the firing is continued, no glass component is generated in the accommodation space, and it is possible to prevent the object to be fired from adhering to the sheath due to the glass component or the glass component from adhering to the object to be fired itself.

[0012] Also, for example, in a metal sheath disclosed in Japanese Patent Application Laid-Open No. 2000-169243, etc., metal scatters into the atmosphere during degreasing or firing, and there is a risk of depositing on the object to be fired and mixing into the object to be fired as foreign matter. When the object to be fired contains a noble metal, the noble metal may be contaminated by foreign matter. In this regard, since the bottom plate and the side wall of the sheath of the present invention are made of ceramic, unlike a metal sheath or the like, it is difficult for foreign matter to mix into the object to be fired. In addition, since the outer diameter of the communication passage is smaller than that of the object to be fired, the object to be fired in the accommodation space does not move from the accommodation space to the outside through the communication passage.

Advantages of the Invention

[0013] If the object to be fired is heat-treated using the sheath of the present invention, it is difficult for the object to be fired to adhere to the sheath due to the glass component, and it is also difficult for the glass component to adhere to the object to be fired itself. Therefore, it is possible to achieve a reduction in manufacturing cost and maintain the quality of the object to be fired.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0015] The ceramic forming the bottom plate and the side walls may be composed of oxides such as aluminum, zirconium, titanium, and silicon, and may have a heat resistance of about 1600°C. The bottom plate and the side walls may be integral or separate. The bottom plate and the side walls may be made of the same ceramic or different ceramics.

[0016] The bottom plate only needs to extend substantially horizontally, and the periphery may extend upward to form a dish shape. The side walls only need to extend upward from the bottom plate to form an accommodation space together with the bottom plate, and may extend vertically upward from the bottom plate or obliquely upward from the bottom plate. The side walls may be a cylindrical body of a polygon such as a square in plan view, or a cylindrical body of a circle, an ellipse, etc. in plan view. The accommodation space accommodates the object to be fired.

[0017] The molding aid for molding the object to be fired includes various substances as long as they contain carbon. Specifically, cellulose such as methyl cellulose, organic binders such as polyvinyl alcohol and acrylic resin, etc. are applicable.

[0018] The object to be fired needs to contain at least silica. The object to be fired may also contain alumina, magnesia, calcia, etc. The object to be fired may contain a noble metal when it is used as a catalyst carrier in the petrochemical field, as a filter for impurity filtration in the industrial field, or as an electronic component. The shape of the object to be fired is not limited, and in addition to a cylindrical shape, a granular shape, and a powder shape, it may have a specific shape.

[0019] Various types of heat treatment furnaces are applicable as long as they are continuous heat treatment furnaces in which a degreasing zone and a firing zone are continuous. The degreasing zone is a zone for heating and eliminating the molding aids contained in the object to be fired, and the firing zone is a zone for heating and firing the object to be fired. The two zones may be partitioned into individual rooms by walls or the like, or may communicate without having a wall. Specifically, roller hearth kilns, bogie type tunnel kilns, mesh belt kilns, chain conveyor kilns, walking beam kilns, etc. are applicable.

[0020] The communication passage may be formed at least in the lower part of the side wall or on the bottom plate. The communication passage may be formed by penetrating the bottom plate or the side wall, or may be formed by continuous bubbles by forming the bottom plate or the side wall into a porous material. When forming the communication passage in the side wall, it is necessary to form it at least in the lower part of the side wall from the viewpoint of easily discharging the haze from the accommodation space to the outside. However, in order to increase the aperture ratio so that the haze is not stored in the accommodation space, it may be formed in other parts of the side wall. It is preferable not to form the communication passage in the bottom plate and to form the communication passage in the side wall. In this case, the shroud moves stably when the bottom plate rolls on the rollers of the roller hearth kiln.

[0021] When the bottom plate and the side wall are separate bodies and the side wall is placed on the bottom plate for use, it is preferable that the communication passage is formed only in the side wall. In this case, by placing the side wall on the bottom plate and rolling it on the rollers of the roller hearth kiln, etc., the shroud can be stably moved, and when the firing of the object to be fired is completed, the object to be fired on the bottom plate can be easily recovered while gripping the side wall with a robot hand or the like, and the workability is excellent. Also, it is possible to reuse the bottom plate and the side wall separately.

[0022] When the bottom plate and the side wall are separate bodies and the side wall is placed on the bottom plate for use, it is preferable that the communication passage is formed throughout the side wall. In this case, it is difficult for the haze to be stored in the storage space, and it is easy to discharge the haze to the outside. Also, the directionality of the side wall is eliminated, and stable firing of the object to be fired can be realized when the bottom plate and the side wall are reused separately.

[0023] The sheath preferably consists of alumina and silica. In that case, the inventor has confirmed the effect of the present invention. Specifically, the inventor has confirmed the effect of the present invention for a sheath in which alumina is 95% by mass and silica is 5% by mass.

[0024] In this case, according to the inventor's test, the aperture ratio is preferably 6.2% or more and preferably 55.9% or less. If the aperture ratio is 6.2% or more, the number of times of reuse is large and it has practical value. If the aperture ratio exceeds 55.9%, the strength becomes weak and it is easily broken when gripped by a robot hand or the like, making it difficult to reuse. That is, in a continuous heat treatment furnace, since degreasing and firing of the object to be fired are performed without the intervention of human hands, the movement of the sheath after firing is often an automatic movement by a machine such as a robot. Therefore, it is preferable that the sheath reused after firing the object to be fired is not easily broken up to the upper limit of use. If the sheath is easily broken by a robot or the like too much in order to prioritize the release of haze during degreasing, it is insufficient. The limitation of the aperture ratio of 6.2% or more to 55.9% or less is defined as being difficult to break even when gripped by a robot during reuse in a sheath in which alumina is 95% by mass and silica is 5% by mass.

[0025] Also, according to the inventor's test, the side wall preferably has a thickness of 6 mm or more and less than 30 mm. If the thickness is 6 mm or more, the strength is also large, the number of times of reuse is large, and it has practical value. If the thickness becomes 30 mm or more, the volume of the accommodation space decreases and the practical value becomes low.

[0026] (Test 1) Hereinafter, in order to confirm the effects according to the presence or absence of communication paths, Examples 1 to 3 will be described together with Comparative Examples. As shown in FIGS. 1 and 2, the sheaths of Examples 1 to 3 and the Comparative Example have a bottom plate 1 and side walls 3 that are separate bodies. The bottom plate 1 is a plate-shaped member that extends substantially horizontally, has a vertical length of 180 mm, a horizontal length of 180 mm, and a thickness of 15 mm. The side wall 3 is a rectangular cylindrical body in plan view, having a vertical length of 160 mm, a horizontal length of 160 mm, a height of 80 mm, and a thickness of 10 mm. Therefore, the area A of one surface of the side wall 3 is 12800 mm 2 ². In the sheaths of Examples 1 to 3, innumerable 5 mm square communication paths 5 are penetratingly provided in the side wall 3. Therefore, the opening area of the communication path 5 is 25 mm 2 ². On the other hand, no communication path 5 is formed in the side wall 3 of the sheath of the Comparative Example.

[0027] These sheaths were manufactured as follows. First, a 3D printer ("ProJet460Plus" manufactured by 3D Systems) was used to form a shaped body with a molding powder. The composition of the molding powder is 90% by mass of alumina powder ("WA400J" manufactured by Showa Denko KK) and 10% by mass of pulverized PVA ("ASP05" manufactured by Shin-Etsu Chemical Co., Ltd.).

[0028] After taking out the shaped body from the 3D printer, it was dried at 65°C for 3 hours and impregnated with a silane coupling agent ("Silanil919" manufactured by Aika Kogyo Co., Ltd.). Then, they were fired under the following firing conditions to obtain the sheaths of Examples 1 to 3 and the Comparative Example.

[0029] Firing conditions: 500°C (8 hours 20 minutes) → 650°C (10 hours) → 650°C (5 hours) → 1600°C (7 hours 55 minutes) → 1600°C (5 hours)

[0030] For the sheath of Example 1, the interval between each communication passage 5 was set to 1 mm; for the sheath of Example 2, the interval between each communication passage 5 was set to 5 mm; and for the sheath of Example 3, the interval between each communication passage 5 was set to 15 mm. Therefore, as shown in Table 1, for the sheaths of Examples 1 to 3, 32 to 286 communication passages 5 were formed on one surface of the side wall 3, and the total opening area B of the communication passages 5 per surface of the side wall 3 and the closed area C (= A - B) per surface of the side wall 3 were defined. Therefore, the opening ratio D (= B / A) and the closing ratio E (= C / A = 100 - D) of the sheaths of Examples 1 to 3 and the comparative example were obtained.

[0031]

Table 1

[0032] As shown in FIG. 2, the side walls 3 of Examples 1 to 3 and the comparative example were placed on the bottom plate 1 and used as sheaths respectively. Each sheath forms a storage space 7 for storing the object to be fired W by the bottom plate 1 and the side wall 3. The object to be fired W was put into each storage space 7.

[0033] The object to be fired W is in the shape of a short tube with an outer diameter of 10 mm, an inner diameter of 7 mm, and an axial length of 10 mm. Therefore, the outer diameter of the communication passage 5 is smaller than that of the object to be fired W. The composition of the object to be fired W is 75% by mass of aluminum oxide, 20% by mass of silicon oxide, and 5% by mass of a cellulose-based organic binder. Then, the sheaths of Examples 1 to 3 and the comparative example into which the object to be fired W was put into each storage space 7 were degreased and fired over 4 hours from the time they were put into the degreasing zone until they exited the firing zone by a roller hearth kiln as a continuous heat treatment furnace. The roller hearth kiln gradually feeds the sheath and the object to be fired into a firing zone with a maximum temperature of 1400°C, and the degreasing zone and the firing zone are continuous. Degreasing is performed at 600 to 700°C for a certain period of time due to the characteristics of the binder.

[0034] After firing the object to be fired W, while gripping the side wall 3 of the sheaths of Examples 1 to 3 and the comparative example with a robot hand, the object to be fired W on the bottom plate 1 was recovered. During this period, the number of the objects to be fired W attached to the bottom plate 1 in the sheaths of Examples 1 to 3 and the comparative example was confirmed. The number is also shown in Table 1.

[0035] Also, the surface of the bottom plate 1 of the sheath of Example 1 after the fired object W is recovered is shown in FIG. 3, and the surface of the bottom plate 1 of the sheath of the comparative example is shown in FIG. 4. As shown in FIGS. 3 and 4, it can be seen that there is no glass component on the bottom plate 1 of the sheath of Example 1, but there are innumerable glass components scattered on the bottom plate 1 of the sheath of the comparative example.

[0036] Therefore, it can be seen that in the sheath of the comparative example, the fired object W adheres to the sheath due to the glass component, or the glass component adheres to the fired object W itself. For this reason, when using the sheath of the comparative example, the labor for peeling the fired object W from the sheath increases, leading to an increase in manufacturing costs. Also, when using the sheath of the comparative example, the composition of the fired object W changes, and the quality of the fired object W is impaired.

[0037] On the other hand, according to the sheath of Example 1, it can be seen that the fired object W is difficult to adhere to the sheath due to the glass component, and it is also difficult for the glass component to adhere to the fired object W itself. For this reason, it can be seen that according to the sheaths of Examples 1 to 3, it is possible to achieve a reduction in manufacturing costs and maintain the quality of the fired object W. The sheaths of Examples 2 and 3 were the same as those of Example 1.

[0038] If the number of adherences is 10 or less, the number of times of reuse is large and it can pass the inspection. For this reason, the sheaths of Examples 1 to 3 are satisfactory. Therefore, if the fired object W is heat-treated using the sheaths of Examples 1 to 3, it is possible to achieve a reduction in manufacturing costs and maintain the quality of the fired object W.

[0039] However, since the number of adherences was 9 in the sheath of Example 3, the sheaths of Examples 1 and 2 are superior to the sheath of Example 3. For this reason, it can be understood that the aperture ratio of the side wall 3 of the sheath is preferably more than 6.2% or 20.5% or more. In other words, it can be understood that the closing ratio of the side wall 3 of the sheath is preferably less than 93.8% or 79.5% or less. However, according to the confirmation of the inventor, when the aperture ratio of the side wall 3 of the sheath exceeds 55.9, the strength becomes weak, it is easily broken when gripped by a robot hand or the like, and it becomes difficult to reuse. For this reason, in the case of a sheath in which alumina is 95% by mass and silica is 5% by mass, the aperture ratio is preferably 6.2% or more and 55.9% or less.

[0040] (Test 2) Next, the relationship between the thickness (mm) of the side wall 3 and the number of durabilities (times) of the side wall 3, and the relationship between the thickness (mm) of the side wall 3 and the input amount (ratio magnification) of the object to be fired W were obtained.

[0041] First, in the sheaths of Test Pieces 1 to 9 manufactured in the same manner as in Test 1, the thickness of the side wall 3 was changed from 5 to 50 mm. The number of durabilities was also obtained in the same manner as in Test 1. The input amount of the object to be fired W was the ratio to the input amount of Test 1. The results are shown in Table 2 and FIG. 5.

[0042]

Table 2

[0043] As can be seen from Table 2 and FIG. 5, if the thickness of the side wall 3 is 6 mm or more, the strength is large, the number of times of reuse is large, and it has practical value. On the other hand, when the thickness exceeds 30 mm, the volume of the accommodation space 7 decreases and the practical value decreases. For this reason, in the case of a sheath in which alumina is 95% by mass and silica is 5% by mass, the side wall 3 preferably has a thickness of 6 mm or more and less than 30 mm.

[0044] In the above, the present invention has been described with reference to Examples 1 to 3 and Test Pieces 1 to 9. However, the present invention is not limited to the above Examples 1 to 3 and Test Pieces 1 to 9, and it goes without saying that it can be appropriately changed and applied without departing from the gist thereof.

Industrial Applicability

[0045] The present invention can be used in the manufacturing methods for electronic components, gas sensor elements, plugs, etc.

Explanation of Signs

[0046] 1... bottom plate W... object to be fired 7... accommodation space 3... side wall 5... communication path

Claims

1. It consists of a ceramic bottom plate extending substantially horizontally and a ceramic side wall extending upward from the bottom plate to form an accommodation space for accommodating an object to be fired together with the bottom plate, and is a sheath used in a heat treatment furnace, The object to be fired is molded by a molding aid containing carbon and contains at least silica, The heat treatment furnace is a continuous heat treatment furnace in which a degreasing zone for removing the molding aid contained in the object to be fired and a firing zone for firing the object to be fired are continuous, A sheath characterized in that at least a lower part of the side wall or the bottom plate is formed with a communication passage having an outer diameter smaller than that of the object to be fired and communicating the accommodation space to the outside.

2. The bottom plate and the side wall are separate bodies, The side wall is placed on the bottom plate and used, The sheath according to claim 1, wherein the communication passage is formed only in the side wall.

3. The sheath according to claim 2, wherein the communication passage is formed in the entire side wall.

4. The sheath according to any one of claims 1 to 3, which consists of alumina and silica.

5. The sheath according to claim 4, wherein alumina is 95% by mass and silica is 5% by mass.

6. The sheath according to claim 5, having an aperture ratio of 6.2% or more and 55.9% or less.

7. The sheath according to claim 5, wherein the side wall has a thickness of 6 mm or more and less than 30 mm.

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