Method for making a quartz glass plate large in size and high in purity

Abstract: A quartz glass plate large in size, high in purity, smooth at surface, and excellent in planeness and a method and a device for making said plate by cutting and unfolding a quartz glass tube, which is characterized in that, as shown in Figs. 1 and 2, a quartz glass tube (1) slotted along the axial direction thereof and preferably having a band-like slot part (1a) is turned into a plate through a process in which the glass tube (1) is stretched, beginning at a specified band-like part, in the direction roughly tangential to the circumference thereof while subjected to heating and softening at one band-like part after another each extending across the entire width of the tube in the axial direction and arranged in the circumferential direction of the tube starting at said specified part.

Description: Field of the invention The present invention relates to a manufacturing method for a large quartz glass plate of high transparency and purity. Background of the invention A large, flat quartz glass plate of high purity and transparency has typically been used as material for manufacturing square tanks for washing high-purity elements, such as wafers, large diameter quartz glass observation ports and lamp covers, where the adhesion of impurities must be avoided. Compared to other glass materials, the quartz glass used for these applications retains high viscosity even at high temperatures, which makes it difficult to form and cast it when it is melted and, therefore, difficult to form it into plate. Generally, there are two existing methods by which such quartz glass plate is produced. One is by cutting a block of quartz glass into thin sheets. The other is a process in which a quartz glass tube is opened to form a quartz glass plate. The prior art applied in the former method employs a technology in which a plate is formed from pulverized powder by refining natural crystal or quartzite and then heating the powder electrically or with a gas burner to melt and fuse it into a block of quartz glass, which is then cut into plate using a diamond cutter or the like. However, as this method involves cutting blocks of quartz glass with a diamond cutter or the like, the surface of the plate thus obtained is rough, necessitating a surface smoothing treatment, such as a special separate polishing operation to make the surface transparent. Quartz glass is a material with superior transparency and light transmission, and particularly in applications such as observation ports, lamp covers and the like, the material is usually required to have excellent optical transparency. Therefore, it is necessary to perform transparency finishing with some type of surface treatment, for example, surface fusing with fire or specular glossing with a granular abrasive after the coarse polishing on the plate material, which leaves a rough surface and reduced transparency as described in the previous paragraph. This transparency finishing treatment is extremely labor intensive and time consuming. Moreover, during the polishing with the granular abrasive, the material can be easily contaminated by impurities and metal elements which will have detrimental effects on semiconductors. In the surface fusing treatment using fire, thermal distortion tends to cause cracking, so this method is highly disadvantageous from an industrial point of view. Also, because the aforementioned block forms are manufactured by melting and fusing a pulverized powder of natural crystal or quartzite in a special die, impurities or reactive gasses originating in the die body, as well as residual gasses within the melted substance tend to be retained in the form of bubbles in the melted, high viscosity quartz glass. Since this tendency becomes more pronounced as the size of the block body increases, inevitably there are foreign substances and bubbles in a large plate cut from such blocks. This makes it difficult to use such plate for products that require a high degree of transparency such as quartz glass observation ports and lamp covers. Also, because of the poor mechanical strength and heat resistance of the die used for melting and fusing the quartz powder, the prior art has substantial restrictions on the size of the block body that can be obtained. Furthermore, if large plate material is to be obtained from such large blocks, the thickness of the diamond cutter needs to be increased, resulting in a great deal of expensive quartz glass lost to the cutting margin. Thus, not only is it extremely disadvantageous from an industrial point of view, the resulting plate material is uneconomical. In summary, this method for the production of large quartz glass plate has a number of serious drawbacks. Moreover, the size of square washing tank that can be manufactured from such quartz glass plate is restricted to the limited size of the plate itself and it is becoming more and more difficult to keep up with the demand for ever larger-diameter semiconductor wafers and the like, and the tanks required for washing them. Meanwhile, in the latter mentioned prior art (tube opening), as illustrated in Figure 5, for example, a quartz glass tube 100 is slit open in the direction of the axis or the quartz glass tube is cut into two and a quartz glass dowel is welded, centered onto its edge, to form an operating handle 101. While holding the handle 101, the opened quartz glass tube 100 is heated and softened all over. Next, the whole quartz glass tube is opened into a curved plate, then while heating and softening part of it, the softened section 100a is pressed and flattened on a carbon plate 103 with a carbon press 104 or the like. After that, the operation is repeated while the welded position of the handle 101 is relocated to flatten other areas sequentially in stages to create the quartz glass plate. Another method of the prior art is that in which the quartz glass tube 100, already opened in the form of a curved plate as described above, is then sandwiched between carbon slabs while being heated and softened to make it into a flat plate. However, this entire operation must be carried out manually. Therefore, the plate thickness and size are necessarily restricted. Generally speaking, the maximum size that can be produced in this way is approximately 300 X 300mm. Moreover, this operation is very time consuming and requires a great deal of experience. Also, as the aforementioned flattening methods involve the use of a carbon press or carbon slabs pressing against the curved plate, scoring will occur, caused by contact with the carbon press or slab. Irregularities on the surface of the carbon tends to become imprinted on the surface of the plate, making it rough. Furthermore, surface undulations resulting from uneven flattening processes also occurs. Thus, smoothing and flattening results in these methods are erratic. There is also the fact that, as the carbon press, carbon slabs or carbon plate comes in contact with the upper surface of the quartz glass under pressure, the quartz glass also comes in contact with impurities and they tend to remain in the glass. This makes it even more difficult to manufacture high-purity flat plate. These residual impurities not only poison the semiconductors, they also accelerate the crystallization of the quartz glass itself so that it becomes opaque (devitrified). This is due to microcracking, which results from local crystallization and which creates even more problems in applications that require a high degree of transparency. In a prior use by Westdeutsche Quarzschmeize GmbH & Co KG, Geesthacht, Germany, flat quartz glass plates were produced by lengthwise cutting an opening into a quartz glass tube, gripping the tube with clamps and rotating it across heating means while pulling and straightening it (WQS Speciality Catalogue, May, 1989). SUMMARY OF THE INVENTION The objective of the present invention is to address these problems of the prior art and to provide a manufacturing method for a large quartz glass plate with no bubbles. This object is solved by the method of claim 1. The subclaims relate to preferred embodiments of the invention. Brief description of the drawings Figure 1 is a basic structural diagram of the manufacturing system. Figure 2 is a series of operation diagrams showing the manufacturing process. Figure 3 is a front view of the overall structure of the equipment. Figure 4 is a perspective view of the structure of key parts. Figure 5 shows the prior art process in which a quartz glass tube is flattened into a plate. As illustrated in Figures 1 and 2, a quartz glass tube 1 is provided with a band-like opening 1a running over a specific width in the direction of the tube shaft, the opening being preferably long and narrow. Then, while heating and softening a band-like area of the glass tube 1 over the entire width in the direction of the tube shaft, starting from a specific position along the direction of the tube circumference and working sequentially, the quartz glass tube is stretched in a line approximately tangential to the circumference of the glass tube from the aforementioned specific position to make the glass tube 1 into a flat plate. The position of the heating bodies 3A and 3B is fixed in the vicinity of the leading edge 1b of the opening in the quartz glass tube 1, and rotate the tube opening along the external circumference of glass tube 1 in the direction of the circumference, and along with that rotation, the means of pulling 2 pull linearly in an approximately tangential direction from the opening leading edge 1b to make the glass tube 1 into a flat plate. Also, the peripheral speed of the quartz glass tube 1 and the pulling speed of the means of pulling 2 are not necessarily the same. By setting these speeds appropriately, it is possible to adjust the thickness of the formed flat plate thicker or thinner in relation to the thickness of the glass tube 1. For example, by setting the pulling speed higher than the peripheral speed of the quartz glass tube 1, large, flat glass plate thinner than the tube material can be produced. Conversely, by setting the pulling speed slower than the peripheral speed of the quartz glass tube 1, large, flat glass plate thicker than the tube material can be produced. If the means of pulling 2 directly grip the leading edge 1b of the opening in the quartz glass tube 1, it would be difficult to form a high-purity quartz glass plate if the grip was made of a metal, since impurities would enter from the grip due to the heat during the heating and softening process. Therefore, it is ideal to pull without grips directly gripping the leading edge 1b of the opening but rather by gripping a connecting piece of quartz glass material 4. Also, the heating of the aforementioned glass tube 1 may be performed from one side. However, if there is a difference in temperature between the front and rear sides, consistent and even pulling becomes difficult. Therefore, preferably, heating should be done from both the front and rear of the quartz glass tube 1 over the entire width in the direction of the tube shaft. It is advisable to move heating bodies 3A and 3B in a reciprocating motion in the heating area relative to the quartz glass tube 1 in the direction of the tube shaft in order to eliminate inconsistency of heat supply in the direction of the shaft of the quartz glass tube 1. It will be even more preferable to soften the glass tube 1 over the entire width in a band-like area while moving the heating bodies 3A and 3B in a reciprocating motion. Since the heat source may be placed inside the quartz glass tube 1 which is the base material in the present invention, it is not feasible to use a tube with an extremely small diameter. In practice, it is desirable to use a transparent quartz glass tube with a diameter ranging from 100 to 500mm and a thickness of 2 to 20mm. Inter alia the manufacturing method can be implemented by providing a quartz glass tube 1 which has an opening 1a over a specific width in the direction of the tube shaft, preferably in the form of a band, means 5 to rotate the aforementioned glass tube 1 with its tube shaft as the center of the rotation and means 2 for pulling the glass tube 1 in a line approximately tangential to the leading edge 1b of the opening in the glass tube 1 while the glass tube 1 is heated and softened in a band-like area over the entire width of the tube, in the direction of the tube shaft. It is difficult to rotate the quartz glass tube 1 around the tube shaft center with a high degree of precision because the inside of the glass tube 1 is hollow. Therefore means 6 for supporting the quartz glass tube 1 by the circumferential surface is provided and either the axis of the means 5 of rotation and the axis of the quartz glass tube 1 are made to align and coincide or the means 6 of support and means 5 of rotation are structured so that they can move freely in the plane of cross section of the glass tube. In order for the glass tube 1 to be pulled in the direction of a line tangential to the leading edge 1b of the opening, it is required that the trailing edge 1c of the opening that faces the leading edge 1b of the opening, be positioned at a location that does not intersect the line tangential to the leading edge 1b. Therefore, it is desirable to set the initial support position of the means of support for the quartz glass tube 1 at a location that makes the leading edge 1b of the opening further out, horizontally, from a vertical line through the tube axis, than the trailing edge 1c of the opening. At the same time, it is difficult to form a high-purity quartz glass plate if the means 5 of rotation is structured so that it directly grips the leading edge 1b of the opening in the quartz glass tube 1 by using a clamping member or the like, because impurities are likely to be transferred from the clamping member at the time of heating and softening. Therefore, the structure of the means 5 of rotation should be a rotating plate or arm member that can rotate around the rotating shaft as the center of rotation without the clamping member directly gripping the leading edge 1b of the opening. It is preferable to use some quartz glass material 8 or the like to the trailing edge 1c of the opening of the glass tube 1, that is clamped by the arm member, thus making it possible to rotate the quartz glass tube 1 in conformance with the rotation of the arm part. A flat plate which is manufactured thus from such a quartz glass tube 1 will be a flat, high-purity, high transparency quartz glass plate with its long side at least 300mm with a thickness of 2 ∼ 20mm. Also, as the aforementioned quartz glass tube 1 is formed from a relatively small quartz glass ingot, it has almost no bubbles or impurities present, as is likely in a large block Therefore, a quartz glass plate formed from this ingot will have a high degree of purity and transparency, ideal for observation ports and square tanks. Also, since factors that could introduce impurities during manufacturing are minimized, it is possible to form a transparent quartz glass plate in which the total content of the following elements; Na, Li, Fe, Al, Cu, Ca, Ni, B, Mg, Y, Ti, and Cr is 100 ppm (weight) or less. Furthermore, the content of elements such as Na, K and Cu and especially Ca, which contaminates particularly easily, can be held down to 0.5 ppm or less. The resulting transparent quartz glass plate will be ideal for observation ports, single-crystal, pull-up devices and square wash tanks for wafers. Furthermore, by using a synthetic quartz glass for the aforementioned quartz glass tube 1, it is possible to keep the total content of the following elements: Na, Li, Fe, Al, Cu, Ca, Ni, B, Mg, Y, Ti and Cr at a maximum of 200 ppb. The manufacturing of a quartz glass plate with such high degree of purity and transparency can only be achieved by keeping the quartz glass tube 1 out of contact with any jig other than one made of quartz glass during the manufacturing process. Preferred embodiments of the present invention Figure 3 shows an overall structural view of the flat plate manufacturing system, which includes a support mechanism 50 that supports a quartz glass tube 1 which has a band-like opening running in the direction of the tube shaft which is supported with two pairs of support rollers 57, 58, one each at the top and bottom, a support delivery device 70 consisting of a delivery mechanism 60 that transports the support mechanism 50 to a specific position in front of the flat plate forming device 10, means 5 of rotation that rotates the quartz glass tube 1 around the tube shaft center, means 3 of heating to heat and soften the glass tube 1 in a band-shaped area over- the entire width in the direction of the tube shaft. The flat plate forming device 10 consisting of a means 2 of pulling that pulls the heated and softened glass tube 1 in a line approximately tangential to the leading edge 1b of the opening. Next, each device is explained in detail. The delivery mechanism 60 consists of a screw shaft 61 that is provided on the base body 80 and runs horizontally, extending towards the flat plate forming device 10, a horizontal table 64 that advances toward, and withdraws from the flat plate forming device 10 by means of forward and reverse rotation of the drive motor 63 via the nut section 62 that is threaded on to the said screw shaft 61 and the vertical tower 65 that is erected vertically on the horizontal table 64. On the front of the vertical tower 65, a vertical guide rail 66 is provided and inside the tower 65, a vertical screw shaft 67 is provided that extends vertically, parallel with the guide rail 66. A drive motor 68 that rotates the said vertical screw shaft 67 in both forward and reverse directions is also provided in the tower. The vertical stay section 51 is securely mounted in a bracket frame 52, which is fitted to the guide rail 66 so that the bracket frame can be freely elevated and lowered, being linked to the vertical screw shaft 67 via the nut section 52a. As a result, the support mechanism 50 is elevated and lowered via the bracket frame 52 along the guide rail 66 by rotating the vertical screw shaft 67 in the forward and reverse directions, driven by the drive motor 68. The support mechanism 50 consisting of the drive motor 53 and the vertical stay 51, in which a rotating screw shaft 54 rotates in the forward and reverse directions, driven by the drive motor 53, is vertically mounted, extending almost the entire length of the stay. A pair of support stays 56A and 56B are elevated and lowered, traveling toward and away from each other through the reverse and forward rotation of the rotating screw shaft 54 on to which the nut section 55 is threaded. The support stays 56A and 56B extend horizontally from the vertical stay 51 where the aforementioned nut section 55 is mounted, to support the pairs of support rollers 57 and 58 at their shafts which are located one pair each on the upper and lower surfaces that face each other. Between the support rollers 57 and 58, it is possible to clamp and secure the quartz glass tube 1. After mounting the quartz glass tube 1 on the pair of support rollers 57 on support stay 56A, the quartz glass tube 1 can be clamped as the two support stays 56A and 56B approach each other by rotating the screw shaft 54 in the forward direction through the drive motor 53. Next, the structure of the flat plate forming device 10 is explained using Figure 4. First, the means 5 of rotation includes support bases 21 and 22, located on either side in the direction of the shaft and a space between them for placing the quartz glass tube 1. On one of the bases 22, a drive motor 23 is provided with an attached rotating plate 24. On the base 21, which is on the opposite side, across the space provided for the glass tube 1, a driven rotating mechanism 6B is provided, aligned with the extended line of the shaft of the drive motor 23. The circular rotating plate 24 is mounted facing opposite the quartz glass tube 1 on the rotating shaft 23a of the drive motor 23. On the rotating plate 24, a clamping member 11A is provided to clamp the band-like glass plate 8, one edge of which is fused to the trailing edge 1c of the opening in the quartz glass tube 1. The distance between the center of the rotating plate 24 and the clamping position of the clamping member 11A (radius) must match the radius of the quartz glass tube 1. Meanwhile, on the other base 21, the driven rotating mechanism 6B includes a pair of shaft bearings 26A and 26B that are mounted on a sliding table 26 which can move along the two parallel rails 25 which extend across the base 21 in the direction of the shaft. The large diameter shaft 28, the axis of which is aligned with the axis of rotating shaft 23a of the drive motor 23, can rotate within shaft bearings 26A and 26B. A rotating arm 29 that extends from the tip of the shaft 28 perpendicular to the axis, includes the clamping member 11B attached at the tip of the arm 29, for the band-like glass plate 8, one edge of which is fused to the trailing edge 1c of the opening in the quartz glass tube 1. Also, as with the aforementioned rotating plate 24, the distance between the center of the aforementioned large diameter shaft 28 and the clamping position of the clamping member 11B (radius) must be the same as the radius of the quartz glass tube 1. At the same time, on support base 22 a hydraulic cylinder 31 is mounted parallel with the axis that connects the drive motor 23 and the large diameter shaft 28. On the other base 21, a guide rail 32 is provided along the same axis. These two rails are bridged by a support body 33, which is provided with a pair of heating bodies 3A and 3B mounted on to it. One end of the support body 33 is secured on to the shaft section of the hydraulic cylinder 31 and the other end is secured on to the perpendicular bracket 34 which is fitted onto the guide rail 32 in such a way that back and forth movement of the structure is possible along the axis by advancing and retracting the hydraulic cylinder 31. A sub support body 33B that is bent to form an L shape is provided at the half way position through the range of movement along the axis so that it is opposite support body 33, facing it across the leading edge 1b of the opening in the quartz glass tube 1. Heating bodies 3A and 3B, which are more or less flat bars in shape, and are each integrated body consisting of a great number of burner nozzles, are provided on the two support bodies 33 and 33B. The length of the stroke of the hydraulic cylinder 31 and the guide rail 32 must be set at a length which makes it possible to keep the sub support body 33B from coming into contact with the quartz glass tube 1. Also, the heating bodies 3A and 3B are structured by providing a great number of burner nozzles in rows so that the jets are aimed toward the quartz glass tube 1. They are structured in such a way that jets of flame from propane or oxyhydrogen fuel can be provided along their length, which should be slightly greater than the length of the shaft of the quartz glass tube. As shown in Figure 3, the means of pulling 2 includes a vertical guide rail 41 mounted on the front side of the vertical table 40 that is erected vertically on the base 80, a vertical screw shaft 42 that extends vertically and parallel with the guide rail 41 inside the vertical table 40, and a drive motor 43 that rotates the vertical screw shaft 42 in the forward and reverse directions. In the vertical table 40, the pulling table 45 connected with the vertical screw shaft 42 via the nut section 46 is fitted on the guide rail 41 so that it can be elevated and lowered freely. On the front of the pulling table, clamping members 44 are provided to clamp the band-like glass plate 4. The pulling table 45, as shown in Figure 4, has arm sections on both sides extending toward the quartz glass tube 1 with the clamping members 44 for the band-like glass plate 4, one end of which are bonded to the leading edge of the opening 1b in the quartz glass tube 1 and the other end of which extends vertically down to the clamping members 44 attached to the end of the arm sections. In addition, the drive motor 23 must have an internal speed changer so that its rotating speed can be freely adjusted. Next, the actual method of manufacturing a flat plate based on this embodiment is explained. A high-purity, high transparency quartz glass tube 1 with an external diameter of 240mm and a thickness of 4mm is cut to a length of 500mm . Then a band-like opening is created in the tube to a width of : approximately 10 ∼ 15° (approximately 30mm) to create an opened quartz glass tube 1. The impurity contents of the glass tube 1 is 200ppb or less in total content of Na, Li, Fe, Al, Cu, Ca, Ni, B, Mg, Y, Ti and Cr. Next, place the quartz glass tube 1 on the pairs of support rollers 57 and 58 on the support stays 56A, 56B at the lower part of the delivery mechanism 60 so that the leading edge 1b of the opening is set on the horizontal line and the trailing edge is of the opening is vertically displaced from the leading edge 1b toward the inside by a distance h as shown in Figure 2 (A). It should be noted that the aforementioned distance h can be any distance as long as there is no hindrance to the band-like glass plate 4, a more detailed explanation of which will be given later, which is fused to the leading edge 1b of the opening for pulling the glass tube 1. Likewise, the opening angle  can be set arbitrarily within the range of 10 ∼ 15° according to the distance required. After the quartz glass tube 1 is set in the specific position, it is positioned with the lower and upper support stays 56A and 56B which approach each other by rotating the drive motor 53 within the vertical stay 51 and then the quartz glass tube 1 is held within the upper and lower pairs of support rollers 57 and 58. Then the support mechanism 50 that is now holding the quartz glass tube 1 first elevates the quartz glass tube 1 via the drive motor in the vertical tower 65, to a height that matches the axis of the means 5 of rotation on the flat plate forming device 10. Then it moves the glass tube 1 horizontally to a position that is aligned with the axis of the means 5 of rotation on the flat plate forming device 10 by sliding the horizontal table 64. The piston shaft 31a of the hydraulic cylinder 31 must be extended so that the glass tube 1 will not contact the sub-support body 33B of the heating mechanism 3A.3B at this time. Then, as shown in Figure 2(B), band-like quartz glass plates 8 made of high-purity synthetic quartz glass are fused horizontally in the direction of the shaft on to each end of the tube aligned with the trailing edge 1 c of the opening. Then, each of them is clamped by clamping member 11a of the rotating plate 24, or the clamping member at the end of the rotating arm 29. Next, in a similar manner, band-like quartz glass plates 4 are fused on to the end surface of the leading edge 1b of the opening at both the right and left sides in such a way that they will extend vertically downwards along a line tangential to the quartz glass tube 1 and their lower ends are clamped by the clamping members 44 of the pulling table 45. When thus secured, the drive motor 53 inside the vertical stay 51 is rotated in the reverse direction to increase the distance between the lower and upper support stays 56A and 56B which have been positioning and supporting the quartz glass tube 1. Then, the delivery mechanism 60 is retracted from the supporting position and returned to its original position. Then the hydraulic cylinder 31 is retracted so that the sub-support body 33 of the heating mechanism 30 can enter the quartz glass tube 1. Overall, it should be structured so that heating bodies 3A and 3B can face each other across the leading edge 1b of the opening at this time. Now we are ready to start the actual flattening operation. First, as shown in Figure 2(C), fuel gas is ejected from the heating bodies 3A and 3B from the inside and the outside of the tube in a horizontal direction so that the gas will be supplied over the entire width of the tube shaft. At this time, if the heating bodies 3A and 3B have rows of nozzle burners, the line of heating tends to be uneven because of the intervals between the burners. If that is the case, consistent even heating can be achieved by moving the heating bodies back and forth by using the hydraulic cylinder 31 with strokes that are slightly longer than the distance between the burners. When the leading edge 1b of the opening has been heated and softened over the entire line of heating, the rotation of the quartz glass tube 1 by the drive motor 23 and the lowering of the leading edge 1b of the opening by means 2 of pulling are begun together. At this time, if the pulling speed is made to perfectly match the rotation speed throughout the entire period, then the thickness of the resulting flat plate will be exactly the same as that of the quartz glass tube. If the pulling speed is set slightly higher, a flat plate that is slightly thinner will result. Conversely, by making the pulling speed slower, a flat plate that is slightly thicker than the quartz glass tube 1 will result. In the manner described above, plate forming is performed to the position indicated in Figure 2(D). Immediately before the trailing edge 1c of the opening of the quartz glass tube 1 reaches the position of the heating bodies 3A and 3B, the three operations; heating by the heating bodies 3A and 3B, rotation by means 5 of rotation and pulling by means 2 of pulling, are all stopped simultaneously. After the band-like quartz glass plates which have been fused as described earlier, are severed and the quartz glass plate which has been flattened as described above is removed from the forming device 10, the section at the trailing edge 1c of the opening which has not been flattened is cut off to form a completed flat plate. Then, when specified finishing treatments, such as washing, annealing or the like have been performed, the plate is ready to be shipped as a product. We have examined the purity of plate thus manufactured and in every case we have found that it is desirable to combine a transaction guide mechanism in the lower section. The quartz glass plate thus stretched into a flat plate in this manner is then cooled and formed into a large, high transparency quartz glass plate. The plate prepared in this manner does not have any waviness on the surface and the impurity content is 200ppb or less in Na, Li, Fe, Al, Cu, Ca, Ni, B, Mg, Y, Ti and Cr, showing hardly any change from the impurity content before processing. Then, in order to investigate changes in thickness, a similar transparent quartz glass tube 1 with an external diameter of 240mm, a thickness of 4mm, a length of 500mm and an opening width of approximately 30mm was used to produce a quartz glass plate by following a procedure similar to that described above with a rotating speed of 60mm/min. In this case, the pulling speed was changed to: 50mm/minute, 60mm/minute, 65mm/minute and 70mm/minute. The resulting plate had differing thicknesses of 4.8mm, 4.0mm, 3.7mm and 3.4mm respectively. Thus, we succeeded in changing the thickness of the product. The flat plate formed in this way did not have any surface waviness and were otherwise good quality plate.

Claims: A method for manufacturing a quartz glass plate, wherein a quartz glass tube (1) is provided with an opening (1a) which extends in the direction of the tube axis, and said tube is heated and softened in a band-like area which extends over the entire tube length in the direction of the tube axis and said band-like area of heating is moved relative to the tube along its circumference while said tube (1) is pulled in approximately tangential direction from said band-like area, to convert said tube into a flat plate, wherein: a position of heating said tube (1) is fixed at the initial position of the leading edge (1b) of said opening (1a) in said tube (1), and while said tube (1) is rotated towards said fixed heating position, it is pulled in approximately tangential direction from said leading edge (1b) of said opening (1a), to flatten said tube (1), and said quartz glass tube (1) is pulled while the leading edge (1b) of the opening (1a) of said glass tube (1) is linked to pulling means (2) by a quartz glass connecting piece (4). The method of claim 1, wherein said quartz glass tube (1) is pulled at a pulling speed approximately equal to the peripheral speed of said quartz glass tube (1). The method of claim 1, wherein said quartz glass tube (1) is pulled at a pulling speed which is faster than the peripheral speed of said quartz glass tube (1) to form a large quarts glass plate with reduced thickness. The method of claim 1, wherein said quartz glass tube (1) is pulled at a pulling speed which is slower than the peripheral speed of said quartz glass tube (1) to form a large quartz glass plate with increased thickness. The method of claim 1, wherein said quartz glass tube (1) is rotated and pulled in such a manner that it does not come in direct contact with either pulling means (2) or means (5) of rotating. The method of any of claims 1 to 5, wherein said quartz glass tube (1) is heated from both the inner and the outer sides in said band-like area. The method of any of claims 1 to 6, wherein said quartz glass tube (1) is evenly softened in said band-like area by heating means (3a, 3b) which are moved in relative reciprocal motion, in the direction of the tube axis. The method of any of the preceding claims, wherein said quartz glass tube (1) has a minimum diameter of 100 mm and a thickness of 2 to 20 mm. The method of any of the preceding claims, wherein said quartz glass tube (1) is made of transparent synthetic quartz glass.

Inventors: ASAJIMA KAZUO, ISE YOSIAKI, KIMURA HIROYUKI, OKOSI SHINICHI, ASAJIMA, KAZUO, ISE, YOSIAKI, KIMURA, HIROYUKI, OKOSI, SHINICHI, ASAJIMA, KAZUO, TAKEFU WORKS, SHIN-ETSU, ISE, YOSIAKI, TAKEFU WORKS, SHIN-ETSU, KIMURA, HIROYUKI, TAKEFU WORKS, SHIN-ETSU, OKOSI, SHINICHI, YAMAGATA SHIN-ETSU QUARTZ
Applicants: SHINETSU QUARTZ PROD, SHIN-ETSU QUARTZ PRODUCTS CO., LTD.
Application year: 1992
Main classification: C03B20
IPC codes: C03B23