Mold and method for manufacturing quartz crucible

Abstract

To provide a mold for manufacturing a quartz crucible by a rotation mold method, capable of efficiently preventing shape defects due to wavy deformation occurring in a bent part of the quartz crucible during fusion when forming a quartz powder molding.SOLUTION: A bottomed cylindrical mold includes: a straight body part; a first bent part continued to the lower end of the straight body part and having a curvature radius r of 50-300 mm; and a bottom continued to the first bent part and having a second bent part having a curvature radius R of 350-2000 mm. The inner surface of the first bent part has a concave groove being a non-penetration groove without penetrating the mold; and the inner surface in a range of at least 35 mm does not have the concave groove in a direction toward the bottom center along a curved shape from a position contacting the first bent part in the second bent part and has smoothness having an arithmetic surface roughness Ra of 20 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a mold for manufacturing a quartz crucible, and to a method for manufacturing a quartz crucible using the mold. [Background technology]

[0002] The rotating mold method is known as a method for manufacturing a quartz crucible for pulling silicon single crystals, in which quartz powder deposited along the inner surface of a rotating mold is heated and melted to vitrify it, and then molded into the shape of a crucible (for example, Patent Document 1).

[0003] In the rotating mold method, quartz powder is molded into a desired shape before the quartz crucible is melted. The molding process is carried out by spraying quartz powder onto the inner surface of the straight body of a mold rotating at high speed, and depositing the quartz powder on the straight body by centrifugal force.

[0004] Patent Document 2 discloses a mold having a plurality of grooves concentric with the mold rotation axis on at least the straight body portion of the inner surface of the mold. By using such a mold having grooves on the straight body portion, the adhesive force of the raw material powder is improved, and an attempt is made to reduce the amount of raw material powder used and shorten the working time by improving the powder adhesion.

[0005] Furthermore, when quartz powder is heated, melted and vitrified to produce a quartz crucible, the molten part corresponding to the straight body of the quartz crucible cannot withstand its own weight (load), and the molten part corresponding to the small R part (the curved part between the straight body and the bottom) of the quartz crucible slides toward the bottom, causing a wavy deformation from the large R part (the R part with a larger radius of curvature adjacent to the small R part) to the bottom of the quartz crucible (see Figure 5).If the deformation becomes too large, the crucible will be discarded as having a defective shape. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2004-026609 A [Patent Document 2] JP 2019-104647 A Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been developed in consideration of the above-mentioned circumstances, and aims to provide a mold for manufacturing a quartz crucible by a rotational mold method, which can efficiently prevent shape defects caused by wavy deformation that occurs in the curved portion of the quartz crucible when melted when forming a quartz powder molding body. [Means for solving the problem]

[0008] The present invention has been made to solve the above-mentioned problems, and provides a mold for manufacturing a quartz crucible by a rotational mold method, the mold being a bottomed cylindrical mold having a straight body portion, a first curved portion that is continuous with the lower end of the straight body portion and has a radius of curvature r of 50 mm to 300 mm, and a second curved portion that is continuous with the first curved portion and has a radius of curvature R of 350 mm to 2000 mm, the inner surface of the first curved portion having a concave groove, the groove being a non-through groove that does not penetrate the mold, the second curved portion having an inner surface within a range of at least 35 mm in a direction from a position tangent to the first curved portion along the curved shape toward the center of the bottom portion does not have the concave groove, and the inner surface within that range has a smoothness with an arithmetic surface roughness Ra of 20 μm or less.

[0009] In the mold of the present invention, the grooves in the first curved portion form a shape that catches the raw material quartz powder on the inner surface of the mold. This improves the adhesion of the quartz powder and makes it less likely to slip. This also prevents slippage of the molten part corresponding to the small R part of the quartz crucible. Furthermore, by smoothing at least the part of the second curved portion that continues from the first curved portion, the raw material powder supplied to the second curved portion is subjected to a centrifugal force in the direction of the first curved portion, so that slippage of the molten part corresponding to the small R part of the quartz crucible can be prevented. These effects make it possible to efficiently improve shape defects caused by wavy deformation.

[0010] In this case, it is preferable that the concave grooves have a width of 0.3 mm to 3.5 mm, a depth of 0.3 mm to 3.0 mm, and a pitch of 3 mm to 20 mm, and are a plurality of grooves concentric with the mold rotation axis.

[0011] By forming such grooves on the inner surface of the first curved portion of the mold, the silica powder can be more suitably caught in the grooves on the inner surface of the mold, improving the adhesion of the silica powder, and as a result, the silica powder can be more effectively prevented from slipping off the inner surface of the mold.

[0012] Also, in this case, the range in which the first curved portion has the multiple concentric grooves can be at least the range from point A at which a straight line extended from the center of the virtual circle intersects with the mold when extended horizontally, when a virtual circle tangent to the inner surface of the first curved portion is defined based on the radius of curvature r of the first curved portion, to point B at which a straight line extended from the center of the virtual circle intersects with the mold when rotated 45° from the horizontal direction toward the center of the bottom of the mold.

[0013] By providing a mold having grooves in at least this range, it is possible to ensure sufficient adhesion of the raw material silica powder to the first curved portion.

[0014] The mold is preferably made of stainless steel or carbon.

[0015] By using such a mold material, the mold can be made more suitable for manufacturing quartz crucibles.

[0016] The present invention also provides a method for manufacturing a quartz crucible, which includes a step of rotating any of the above-mentioned molds while spraying quartz powder onto the inner surface of the rotating mold to mold a quartz powder molded body of a predetermined shape made of quartz powder, and a step of melting the molded quartz powder molded body to produce a quartz crucible.

[0017] As described above, in the mold of the present invention, the raw quartz powder can be supplied to the inner surface of the mold so that the shape defects caused by the wavy deformation during melting can be efficiently improved. Therefore, the manufacturing method of the quartz crucible using this mold can efficiently improve the shape defects caused by the wavy deformation in the manufactured quartz crucible. Effect of the Invention

[0018] In the mold of the present invention, the grooves in the first curved portion improve the adhesion of the quartz powder in the first curved portion, making it less likely to slip. This also prevents slippage of the molten portion corresponding to the small R portion of the quartz crucible. Furthermore, by smoothing at least the portion of the second curved portion continuing from the first curved portion, the raw material powder supplied to the second curved portion is subjected to a centrifugal force in the direction of the first curved portion, preventing slippage of the molten portion corresponding to the small R portion of the quartz crucible. Due to these effects, the mold of the present invention can efficiently improve the shape defects caused by the wavy deformation of the quartz crucible to be manufactured. This improves the yield in the manufacture of quartz crucibles. [Brief description of the drawings]

[0019] [Figure 1] 1A and 1B are diagrams showing an example of a mold according to the present invention, in which (a) is a schematic cross-sectional view and (b) is a schematic top view. [Diagram 2] 3 is a schematic cross-sectional view for explaining a portion of a mold according to the present invention. FIG. [Diagram 3] 4 is a schematic cross-sectional view for explaining the upper and lower ranges of a first curved portion of a mold according to the present invention. FIG. [Figure 4] 4 is a schematic cross-sectional view for explaining a groove shape in a mold according to the present invention. FIG. [Diagram 5] FIG. 1 is a schematic cross-sectional view for explaining the occurrence of wavy deformation in a quartz crucible manufactured using a conventional mold. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] As described above, when manufacturing a quartz crucible by heating, melting and vitrifying quartz powder, there was a problem that the molten part corresponding to the straight body part of the quartz crucible could not withstand its own weight (load), resulting in defective shape due to wavy deformation.

[0021] As a result of the inventor's research, it was found that when the above-mentioned wavy deformation occurs, the outer surface of the fusion part corresponding to the small R part of the quartz crucible, i.e., the raw material quartz powder molded on the inner surface side of the mold, also slides in conjunction with the deformation. Based on this knowledge, the inventor has completed the present invention. That is, the present invention is a mold for manufacturing a quartz crucible by a rotational mold method, the mold being a bottomed cylindrical mold having a straight body portion, a first curved portion that is continuous with the lower end of the straight body portion and has a radius of curvature r of 50 mm to 300 mm, and a second curved portion that is continuous with the first curved portion and has a radius of curvature R of 350 mm to 2000 mm, the inner surface of the first curved portion has a concave groove, the groove being a non-through groove that does not penetrate the mold, the inner surface of the second curved portion does not have the concave groove within a range of at least 35 mm in the direction from the position tangent to the first curved portion along the curved shape toward the center of the bottom, and the inner surface within that range has a smoothness with an arithmetic surface roughness Ra of 20 μm or less.

[0022] The present invention will now be described in more detail with reference to the drawings.

[0023] FIG. 1 shows an example of a mold according to the present invention. FIG. 1(a) is a schematic cross-sectional view of the mold, and FIG. 1(b) is a top view of the mold. FIG. 2 shows a schematic cross-sectional view for explaining the parts of the mold. With reference to FIGS. 1 and 2, the mold 11 will be described. The mold 11 is a mold for manufacturing a quartz crucible by a rotational molding method. The mold 11 is a bottomed cylindrical mold having a straight body portion 22, a first curved portion 24, and a bottom portion having a second curved portion 26. The first curved portion 24 is continuous with the lower end of the straight body portion 22, and has a radius of curvature r of 50 mm to 300 mm. The second curved portion 26 is continuous with the first curved portion 24, and has a radius of curvature R of 350 mm to 2000 mm. Furthermore, among the inner surface 12 of the mold 11, the inner surface of the first curved portion 24 has a concave groove 13, and the groove 13 is a non-penetrating groove that does not penetrate the mold 11. Among the second curved portion 26, the inner surface does not have a concave groove within a range of at least 35 mm in the direction from the position tangent to the first curved portion 24 along the curved shape toward the bottom center 27, and the inner surface within that range has smoothness with an arithmetic surface roughness Ra of 20 μm or less.

[0024] 2 shows an inscribed circle (virtual circle) 25 for the cross section of the first curved portion 24. This virtual circle 25 has a radius r (i.e., the radius of curvature r of the first curved portion 24). As shown in FIG. 2, the part having a shape inscribed in the virtual circle 25 is the first curved portion 24, and a second curved portion 26 having a larger radius of curvature R (R is not shown) is formed away from the virtual circle 25. Note that, although an example in which the entire bottom of the mold 11 is constituted by the second curved portion 26 is shown in FIG. 1 and FIG. 2, the second curved portion 26 may be only a portion continuing from the first curved portion 24, and may have a larger radius of curvature near the bottom center 27.

[0025] In the mold 11 of the present invention, the grooves in the first curved portion 24 form a shape that allows the raw quartz powder to be caught on the inner surface of the mold 11. This improves the adhesion of the quartz powder and makes it less likely to slip. This also prevents slippage of the molten part corresponding to the small R part of the quartz crucible. Furthermore, by smoothing at least the part of the second curved portion 26 that is continuous with the first curved portion 24, the raw material powder supplied to the second curved portion 26 is subjected to centrifugal force in the direction of the first curved portion 24, preventing slippage of the molten part corresponding to the small R part of the quartz crucible. These effects make it possible to efficiently improve the shape defects caused by wavy deformation of the manufactured quartz crucible.

[0026] It is essential that grooves 13 are formed in first curved portion 24, and that grooves are not formed in the above-mentioned predetermined range of second curved portion 26, but grooves may be present in other locations. For example, grooves 13 may be formed in at least a part of straight body portion 22. If grooves 13 are also formed in the straight body portion, the adhesive force of the raw material powder can be improved, as described in Patent Document 2.

[0027] Further, the groove 13 may be present in a part of the first curved portion 24, but the groove 13 may be present over the entire first curved portion 24.

[0028] Also, as shown in FIG. 3, the groove 13 can be at least present on the upper side 24a of the first curved portion 24. In this case, in the mold 11 of the present invention, the range in which the first curved portion 24 has a plurality of concentric grooves 13 can be at least the range from point A where a straight line extending from the center of the imaginary circle 25 intersects with the mold 11 when extended horizontally, when a virtual circle 25 based on the radius of curvature r of the first curved portion 24 that is tangent to the inner surface of the first curved portion 24 is defined, to point B where a straight line extending from the center of the virtual circle 25 intersects with the mold 11 when rotated 45° from the horizontal direction toward the bottom center 27 of the mold 11. This range is the upper side 24a of the first curved portion 24 shown in FIG. 3. By making the mold have grooves at least in such a range, the adhesion of the raw material quartz powder to the first curved portion can be sufficiently ensured. Of course, the first curved portion may also have grooves 13 formed on the lower side 24b. FIG. 3 also shows a contact point C between the first curved portion 24 and the second curved portion 26.

[0029] In the present invention, the concave grooves 13 on the inner surface 12 of the mold 11 preferably have a width of 0.3 mm to 3.5 mm, a depth of 0.3 mm to 3.0 mm, and a pitch of 3 mm to 20 mm, and are preferably a plurality of grooves concentric with the mold rotation axis 15. Note that FIG. 4 illustrates the groove width, groove depth, groove angle, and groove pitch. By forming such grooves 13 at the above-mentioned predetermined positions on the inner surface 12 of the mold 11, the quartz powder can be more suitably caught in the grooves on the inner surface of the mold, and the adhesion of the quartz powder can be improved. As a result, the slipping off of the quartz powder on the inner surface of the mold can be more effectively suppressed. In addition, the lower limit of the width of each groove is more preferably 0.5 mm or more, and the upper limit is more preferably 2.0 mm or less.

[0030] In addition, if the depth of the groove is 3.0 mm or less, the shape of the outer surface of the crucible when manufactured using the mold can be within a range that does not cause any problems when used as a crucible. The range of the depth of the groove can be determined according to conditions such as the material of the mold. For example, when the material of the mold is stainless steel, the upper limit of the groove depth can be set to 2.5 mm. This is because, in the case of a stainless steel mold, the manufacturing cost increases as the mold thickness increases. Therefore, in the case of a stainless steel mold, when the original thickness of the mold is 6 mm, the depth is preferably set to 2.5 mm. In addition, for example, when the material of the mold is carbon, the thickness of the mold itself may be thick, so that the upper limit of the groove depth is preferably set to 3.0 mm as described above. In order to ensure the effect of the groove, the depth of the groove should be 0.3 mm or more.

[0031] Moreover, it is more preferable that the upper limit of the pitch of each groove is 15 mm or less. The lower limit of the pitch of each groove is preferably 3 mm or more as described above, as long as the grooves can be stably formed. Of course, the groove pitch must be larger than the groove width.

[0032] The cross-sectional shape of each groove of the grooves 13 is not particularly limited, and may be, for example, a V-groove, a round groove, or a square groove. From the viewpoint of ease of processing, a V-groove is preferable.

[0033] The silica powder used as the raw material usually has a particle size of 50 μm or more and 300 μm or less. The silica powder having such a particle size is easily caught by the grooves 13 having the width, depth, and pitch described above. The mold of the present invention can also be applied to silica powder having a particle size outside this range.

[0034] In the mold 11 of the present invention, the mold material is preferably stainless steel or carbon. By using such a mold material, the mold can be made more suitable for manufacturing quartz crucibles. When a carbon mold is used, it can be used under reduced pressure by suction from the outside. Even in this case, in the mold of the present invention, the groove 13 needs to be formed as a non-through groove.

[0035] When using a carbon mold to manufacture a quartz crucible by the reduced pressure method, the molten part is inherently less slippery even if the entire inner surface of the mold is smooth, and the rate of shape defects due to wavy deformation is better than that of a stainless steel mold. However, when the grooves of the present invention are formed, shape defects due to wavy deformation are even less likely to occur than with a carbon mold whose entire surface is smooth.

[0036] The present invention also provides a method for producing a quartz crucible, which includes a step of spraying quartz powder onto the inner surface 12 of the rotating mold 11 while rotating the mold 11 according to the present invention to mold a quartz powder molded body of a predetermined shape made of quartz powder, and a step of melting the molded quartz powder molded body to produce a quartz crucible. EXAMPLES

[0037] The present invention will be explained in more detail below with reference to examples and comparative examples. However, the present invention is not limited to these examples, and various modifications are possible without departing from the technical concept of the present invention.

[0038] Example 1 The mold had a thickness of 5 mm, an inner diameter of 24 inches (620 mm), a radius of curvature r of the first curved portion 24 of 140 mm, and a radius of curvature R of the second curved portion 26 of 610 mm (the entire bottom is the second curved portion 26. In the second curved portion 26, the length from the contact point C with the first curved portion 24 to the bottom center 27 is 225 mm when the entire surface is smooth.) The groove processing of the present invention was performed on the inner surface of the mold. In this case, the groove 13 was concentric, with a groove width of 1.0 mm, a groove angle of 60°, a groove depth of 0.9 mm, and a groove pitch of 10 mm. The names of the groove parameters are as shown in FIG. 4. The groove processing was performed on the entire surface of the first curved portion 24 of the mold 11 as well as the entire surface of the straight body portion 22. In addition, the second curved portion 26 was left as a smooth surface (Ra of 20 μm or less) over the entire range.

[0039] A quartz crucible was manufactured using such a mold (stainless steel mold) 11. First, natural quartz powder was supplied into the rotating mold 11 with an inner diameter of 620 mm, and a molded body consisting of a powder layer with a thickness of 25 mm was molded as an outer layer. Next, the molded body was heated and melted from the inside by arc discharge, and at the same time, synthetic quartz powder was supplied into the high-temperature atmosphere at a rate of 100 to 500 g / min to form a synthetic glass layer with a thickness of 1 to 5 mm over the entire inner surface area. After melting was completed, it was cooled to obtain a quartz crucible with a diameter of 600 to 610 mm. The upper end of this quartz crucible was cut so that the height H (the height from the center point of the outer surface of the bottom to the upper end of the straight body) was 400 mm, and a quartz crucible was manufactured. The rate of shape defects due to wavy deformation of the manufactured quartz crucible was investigated. The results are shown in Table 1.

[0040] The shape defect due to wavy deformation was defined as unevenness of 1 mm or more and 10 mm or more in length in the quartz crucible. The wavy deformation was measured by placing a ruler on the outer surface of the crucible and measuring the unevenness with a taper gauge.

[0041] The evaluation of shape defects due to wavy deformation is defined as follows. ◎ Particularly good 〇···Good △... Slight improvement, but mass production is impossible due to yield ×...Bad

[0042] Example 2 A quartz crucible was manufactured using the same mold 11 as in Example 1, except that no grooves were formed in the body portion 22, and the incidence of shape defects due to wavy deformation was investigated.

[0043] Example 3 Quartz crucibles were manufactured using a mold 11 similar to that of Example 1, except that the range of the smooth surface (Ra of 20 μm or less) of the second curved portion 26 was set to 50 mm from the contact point (point C) with the first curved portion 24, and grooves were machined on the surfaces other than the smooth surface, and the occurrence rate of shape defects due to wavy deformation was investigated.

[0044] Example 4 A quartz crucible was manufactured using the same mold 11 as in Example 1, except that the groove processing in the first curved portion 24 was performed only on the upper side 24a of the first curved portion 24, and the incidence of shape defects due to wavy deformation was investigated. The upper side 24a and the lower side 24b of the first curved portion 24 are defined as above (see FIG. 3).

[0045] Example 5 A quartz crucible was manufactured using a mold 11 similar to that of Example 1, except that groove processing in the first curved portion 24 was limited to the lower side 24b of the first curved portion 24, and the incidence of shape defects due to wavy deformation was investigated.

[0046] Comparative Example 1 A quartz crucible was manufactured without any groove machining being performed on the inner surface of the stainless steel mold prepared in Example 1 before groove machining, and the incidence of shape defects due to wavy deformation was investigated.

[0047] Comparative Example 2 Quartz crucibles were manufactured using a mold similar to that of Example 1, except that grooves were machined on the entire inner surface of the mold (i.e., grooves were machined on the entire surface of the second curved portion 26), and the incidence of shape defects due to wavy deformation was investigated.

[0048] Comparative Example 3 A quartz crucible was manufactured using a mold similar to that of Example 1, except that the smooth surface (Ra of 20 μm or less) of the second curved portion 26 was extended to 20 mm from the contact point (point C) with the first curved portion 24, and grooves were formed on the surfaces other than the smooth surface, and the occurrence rate of shape defects due to wavy deformation was investigated.

[0049] Comparative Example 4 A quartz crucible was manufactured using a mold similar to that of Example 1, except that grooves were formed in the straight body portion 22 and the second curved portion 26, while no grooves were formed in the first curved portion 24, and the incidence of shape defects due to wavy deformation was investigated.

[0050] Comparative Example 5 A quartz crucible was manufactured using the same mold as in Example 1, except that grooves were formed in the straight body portion 22, but not in the first curved portion 24. The smooth surface (Ra of 20 μm or less) of the second curved portion 26 was limited to a distance of 50 mm from the contact point (point C) with the first curved portion 24, and grooves were formed on surfaces other than the smooth surface. The incidence of shape defects due to wavy deformation was investigated.

[0051] Example 6 A quartz crucible was manufactured using the same mold 11 as in Example 1, except that the groove angle of the grooves 13 was 90° and the groove depth was 0.5 mm, and the incidence of shape defects due to wavy deformation was investigated.

[0052] Example 7 A quartz crucible was manufactured using the same mold 11 as in Example 1, except that the groove width and depth of the grooves 13 were 0.3 mm and 0.3 mm, respectively, and the incidence of shape defects due to wavy deformation was investigated.

[0053] Example 8 A quartz crucible was manufactured using the same mold 11 as in Example 1, except that the groove width of the groove 13 was 3.5 mm and the groove depth was 3.0 mm, and the incidence of shape defects due to wavy deformation was investigated.

[0054] Example 9 A quartz crucible was manufactured using the same mold 11 as in Example 1, except that the groove pitch of the grooves 13 was set to 3 mm, and the incidence of shape defects due to wavy deformation was investigated.

[0055] Example 10 A quartz crucible was manufactured using the same mold 11 as in Example 1, except that the groove pitch of the grooves 13 was set to 20 mm, and the incidence of shape defects due to wavy deformation was investigated.

[0056] Example 11 A quartz crucible was manufactured using the same mold 11 as in Example 1, except that the groove width and depth of the grooves 13 were 0.1 mm and 0.1 mm, respectively, and the incidence of shape defects due to wavy deformation was investigated.

[0057] Example 12 A quartz crucible was manufactured using the same mold 11 as in Example 1, except that the groove width of the groove 13 was 4.6 mm and the groove depth was 4.0 mm, and the incidence of shape defects due to wavy deformation was investigated.

[0058] (Example 13) A quartz crucible was manufactured using the same mold 11 as in Example 1, except that the groove pitch of the grooves 13 was set to 30 mm, and the incidence of shape defects due to wavy deformation was investigated.

[0059] Example 14 Quartz crucibles were manufactured using a mold 11 similar to that of Example 1, except that the range of the smooth surface (Ra of 20 μm or less) of the second curved portion 26 was set to 35 mm from the contact point (point C) with the first curved portion 24, and the incidence of shape defects due to wavy deformation was investigated.

[0060] Example 15 A conventional carbon mold was prepared as a mold before groove processing. This carbon mold had a mold thickness of 100 mm, an inner diameter of 24 inches (620 mm), a radius of curvature r of the first curved portion 24 of 140 mm, and a radius of curvature R of the second curved portion 26 (the entire bottom portion is the second curved portion 26) of 610 mm. Groove processing was performed on this carbon mold in the same manner as in Example 1.

[0061] A quartz crucible was manufactured using such a mold (carbon mold) 11. First, natural quartz powder was supplied into the rotating mold 11 with an inner diameter of 620 mm, and a molded body consisting of a powder layer with a thickness of 25 mm was molded as an outer layer. Then, synthetic quartz powder was supplied into the mold 11 on the inner surface of the natural quartz powder molded body, and a molded body consisting of a powder layer with a thickness of 5 mm was molded as an inner layer. Next, a quartz crucible was manufactured by heating and melting the molded body while reducing the pressure inside the molded body by arc discharge. After melting was completed, the quartz crucible was cooled to obtain a quartz crucible with a diameter of 600 to 610 mm. The upper end of this quartz crucible was cut so that the height H (the height from the center point of the outer surface of the bottom to the upper end of the straight body) was 400 mm, and a quartz crucible was manufactured. The rate of shape defects due to wavy deformation of the manufactured quartz crucible was investigated. The results are shown in Table 1.

[0062] Comparative Example 6 A quartz crucible was manufactured without performing any groove machining on the inner surface of the conventional carbon mold prepared in Example 15 before groove machining, and the incidence of shape defects due to wavy deformation was investigated.

[0063] [Table 1]

[0064] <Comparison between Examples and Comparative Examples> [Groove of the first curved section and smooth surface of the second curved section] All of Examples 1 to 15 fulfilled the requirements of the present invention, and had concave grooves 13 on the inner surface of the first curved portion 24, while having no groove at least in a predetermined portion of the second curved portion 26. All of these were rated as "particularly good" to "good" in the evaluation of shape defects due to wavy deformation of the quartz crucible.

[0065] [Whether or not there is a groove in the straight body] There was no significant difference in the rate of shape defects due to wavy deformation between Example 1, which had grooves 13 in the straight body portion 22, and Example 2, which did not have groove processing in the straight body portion 22. However, from the viewpoint of improving powder adhesion described in Patent Document 2, it is preferable that the straight body portion 22 also has grooves 13.

[0066] [Smooth surface area at second curved section] The embodiment and the comparative example are compared in which the shape defect rate due to wavy deformation was investigated under the conditions of a groove width of 1.0 mm, a groove angle of 60°, a groove depth of 0.9 mm, a groove pitch of 10 mm, and straight groove processing.

[0067] Compared to a mold with no grooves on the inner surface and the entire surface being smooth (Comparative Example 1), the mold with grooves on the entire inner surface (Comparative Example 2) showed a slight improvement in the rate of shape defects due to wavy deformation; however, the rate of shape defects due to wavy deformation was still high and not suitable for mass production.

[0068] In the mold in which the entire surface (Example 1), the area from the contact point (point C) with the first curved portion 24 to 50 mm (Example 3), and the area from the contact point (point C) with the first curved portion 24 to 35 mm (Example 14) were smoothed in the second curved portion 26, the shape defect rate due to wavy deformation was improved. In the mold in which the area from the contact point (point C) with the first curved portion 24 to 20 mm was smoothed in the second curved portion 26 (Comparative Example 3), the shape defect rate due to wavy deformation was slightly improved compared to the mold in which the entire surface was smoothed without groove processing (Comparative Example 1), but the shape defect rate due to wavy deformation was still high and not suitable for mass production. In the second curved portion 26, if groove processing is performed in the area from the contact point (point C) with the first curved portion 24 to 35 mm, the groove processing acts as a stopper and centrifugal force does not work sufficiently, so that the weight of the molten part corresponding to the straight body part to the small R part of the quartz crucible cannot be supported, and shape defects due to wavy deformation are likely to occur. From this, it was found that in the second curved portion 26, in the direction from the position (point C) where it contacts the first curved portion 24 along the curved shape toward the bottom center 27, at least a range of 35 mm in the inner surface does not have concave grooves 13, and the inner surface in this range must have a smoothness with an arithmetic surface roughness Ra of 20 μm or less. In this way, the centrifugal force supports the weight of the molten part corresponding to the straight body part to the small R part of the quartz crucible, and shape defects due to wavy deformation can be improved.

[0069] [Grooving on the upper and lower sides of the first curved section] In a mold (Example 4) in which grooves were applied only to the upper side 24a of the first curved portion 24 and the entire surfaces of the lower side 24b of the first curved portion 24 and the second curved portion 26 were smooth, shape defects due to wavy deformation were improved. In a mold (Example 5) in which grooves were applied only to the lower side 24b of the first curved portion 24 and the entire surfaces of the upper side 24a of the first curved portion 24 and the second curved portion 26 were smooth, shape defects due to wavy deformation in the second curved portion 26 were improved, but new shape defects due to wavy deformation occurred in the upper side 24a of the first curved portion 24 where there are no grooves. However, the rate of shape defects due to wavy deformation was improved, and mass production is possible.

[0070] When the first curved portion 24 was entirely smooth, neither the mold in which the entire surface of the second curved portion 26 was grooved (Comparative Example 4) nor the mold in which the range from the contact point (point C) of the first curved portion 24 to 50 mm away (Comparative Example 5) was smooth did not improve the shape defect caused by the wavy deformation.

[0071] When at least the upper side 24a of the first curved portion 24 is grooved, the presence of the grooves 13 can effectively prevent "slippage" due to the weight of the molten portion corresponding to the straight body portion to the small R portion of the quartz crucible. If only the lower side 24b of the first curved portion 24 is grooved, new shape defects due to wavy deformation will occur on the upper side 24a of the first curved portion 24, so it is preferable to groove at least the upper side 24a of the first curved portion 24.

[0072] [Consideration of groove conditions] The following example is an example in which the optimum conditions for the grooves were investigated based on the conditions of Example 1, in which the rate of shape defects due to wavy deformation was improved.

[0073] (groove angle) There was no significant difference in the rate of shape defects due to wavy deformation between the molds with different groove angles (Example 1 and Example 6).

[0074] (groove width, groove depth (60°)) The shape defect rate due to wavy deformation was improved when the groove width was 0.3 mm and the groove depth was 0.3 mm (Example 7) and when the groove width was 3.5 mm and the groove depth was 3.0 mm (Example 8).

[0075] With a groove width of 0.1 mm and a groove depth of 0.1 mm (Example 11), the shape defect rate due to wavy deformation was improved, but the degree of improvement was lower than in Examples 1, 7, and 8. However, the shape defect rate due to wavy deformation was improved, making it suitable for mass production.

[0076] In the case of a groove width of 4.6 mm and a groove depth of 4.0 mm (Example 12), no shape defects due to wavy deformation occurred, but streaks occurred on the outer surface of the crucible, resulting in poor appearance. However, the rate of shape defects due to wavy deformation was improved, making it suitable for mass production.

[0077] For these reasons, it is preferable that the groove width is 0.3 mm or more and 3.5 mm or less, and the groove depth is 0.3 mm or more and 3.0 mm or less.

[0078] [pitch] When the groove pitch was 3 mm or more and 20 mm or less (Examples 9 and 10), the rate of shape defects due to wavy deformation was improved.

[0079] With a groove pitch of 30 mm (Example 13), the rate of shape defects due to wavy deformation was improved, but the degree of improvement was lower than in Examples 1, 9, and 10. However, the rate of shape defects due to wavy deformation was improved, making it suitable for mass production.

[0080] For these reasons, it is more preferable that the upper limit of the pitch of each groove is 20 mm or less. The lower limit of the pitch of each groove is preferably 3 mm or more, so long as the grooves can be stably formed. Note that the groove pitch must, of course, be larger than the groove width.

[0081] [Carbon mold (reduced pressure method)] As shown in Comparative Example 6, even if the entire inner surface of the carbon mold is smooth, the quartz powder is sucked from the outside using a reduced pressure method, making the molten part less slippery than in the normal pressure method using a stainless steel mold, and the rate of shape defects due to wavy deformation is originally good. However, in Example 15, in which groove processing was performed, the rate of shape defects due to wavy deformation was further improved, and the effects of the present invention were obtained.

[0082] This specification includes the following inventions. [1]: A mold for manufacturing a quartz crucible by a rotational mold method, the mold being a cylindrical mold with a bottom having a straight body portion, a first curved portion that is continuous with the lower end of the straight body portion and has a radius of curvature r of 50 mm to 300 mm, and a second curved portion that is continuous with the first curved portion and has a radius of curvature R of 350 mm to 2000 mm, the mold being characterized in that the inner surface of the first curved portion has a concave groove, the groove being a non-through groove that does not penetrate the mold, the second curved portion has an inner surface that does not have the concave groove within a range of at least 35 mm in the direction from the position that contacts the first curved portion along the curved shape toward the center of the bottom, and the inner surface within that range has a smoothness with an arithmetic surface roughness Ra of 20 μm or less. [2]: The mold of [1] above, wherein the concave grooves have a width of 0.3 mm or more and 3.5 mm or less, a depth of 0.3 mm or more and 3.0 mm or less, and a pitch of 3 mm or more and 20 mm or less, and are multiple grooves concentric with the mold rotation axis. [3]: The mold of [2] above, wherein the range in which the first curved portion has the plurality of concentric grooves is at least the range from point A where a straight line extended from the center of the imaginary circle intersects with the mold when extended horizontally, when a virtual circle tangent to the inner surface of the first curved portion is defined based on the radius of curvature r of the first curved portion, to point B where a straight line extended from the center of the imaginary circle intersects with the mold when rotated 45° from the horizontal direction toward the center of the bottom of the mold. [4]: The mold according to any one of [1] to [3] above, wherein the mold is made of stainless steel or carbon. [5]: A method for manufacturing a quartz crucible, comprising the steps of: rotating a mold according to any one of [1] to [4] above while spraying quartz powder onto the inner surface of the rotating mold to mold a quartz powder molded body of a predetermined shape made of quartz powder; and melting the molded quartz powder molded body to produce a quartz crucible.

[0083] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention. [Explanation of symbols]

[0084] 11... mold; 12... inner surface; 13... groove; 15... mold rotation axis; 22...straight body part, 24…first curved portion, 24a...upper side of the first curved portion, 24b…the lower side of the first curved portion; 25...An inscribed circle (imaginary circle) for the cross section of the first curved portion, 26...second curved portion, 27…Bottom center.

Claims

1. A mold for manufacturing a quartz crucible by a rotational mold method, comprising: The mold is A straight body portion; A first curved portion that is continuous with the lower end of the straight body portion and has a curvature radius r of 50 mm to 300 mm; a bottom portion having a second curved portion continuous with the first curved portion and having a radius of curvature R of 350 mm to 2000 mm; A bottomed cylindrical mold having a concave groove is provided on an inner surface of the first curved portion, the concave groove being a non-penetrating groove that does not penetrate the mold; A mold characterized in that, of the second curved portion, an inner surface within a range of at least 35 mm in a direction from a position tangent to the first curved portion along the curved shape toward the center of the bottom does not have the concave groove, and the inner surface within that range has a smoothness with an arithmetic surface roughness Ra of 20 μm or less.

2. The mold according to claim 1, characterized in that the concave grooves have a width of 0.3 mm or more and 3.5 mm or less, a depth of 0.3 mm or more and 3.0 mm or less, and a pitch of 3 mm or more and 20 mm or less, and are multiple grooves concentric with the mold rotation axis.

3. The range in which the first curved portion has the plurality of concentric grooves is at least When a virtual circle tangent to the inner surface of the first curved portion is defined based on a curvature radius r of the first curved portion, From point A where a straight line extending from the center of the imaginary circle intersects with the mold when extended horizontally, The mold according to claim 2, characterized in that the range is from a point B where a straight line extended from the center of the imaginary circle intersects with the mold when rotated 45° from the horizontal direction toward the center of the bottom of the mold.

4. 2. The mold according to claim 1, wherein the mold is made of stainless steel or carbon.

5. A step of spraying quartz powder onto an inner surface of the rotating mold according to any one of claims 1 to 4 to mold a quartz powder molded body having a predetermined shape made of quartz powder; A step of melting the molded quartz powder body to prepare a quartz crucible; A method for manufacturing a quartz crucible having the above structure.

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