Method of stretching a glass parent material and stretching device

Abstract

Provided is an extension method for extending a glass parent material, which has a dummy hanging rod made of a glass rod fused to an end face of a transparent tapered portion at an upper end, by heating the glass parent material while moving it downward inside an extension device. The extension method includes a start stage in which heating of the glass parent material from the lower end side is started to extend the glass parent material by maintaining the glass parent material at a range above a predetermined extension processing temperature inside the extension device, and an end stage in which the operation of extending the glass parent material is ended after the tapered portion enters a range and before the end face enters a range.

Description

Technical Field

[0001] The invention relates to a glass mother material extending method and an extending device. Background Art

[0002] Patent Document 1 describes the following: "A method, characterized in that: a glass base material having a large diameter is extended to produce a glass rod having a smaller diameter. When a glass base material having a transparent glass tapered portion at one end of a straight body portion and a glass tapered portion including an opaque glass portion at the other end is extended, a dummy hanging rod is fused to the front end of the transparent glass tapered portion before the extension. The dummy hanging rod is connected to a conveying mechanism and inserted into a heating furnace from the bottom of the glass base material for extension, thereby aligning the axis of the straight body portion of the glass base material with the axis of the dummy hanging rod" (paragraph 0021).

[0003] [Background Art Literature]

[0004] [Patent Document]

[0005] [Patent Document 1] Japanese Patent No. 5766157 Summary of the Invention

[0006] The object of the present invention is to provide a method and apparatus for extending a glass mother material.

[0007] To achieve the above object, the present invention includes the following technical solutions:

[0008] A stretching method is provided in which a glass mother material is stretched by heating the glass mother material while moving it downward within a stretching device, wherein a suspended dummy rod composed of a glass rod is fused to the end face of a transparent tapered portion located at the upper end of the glass mother material. The stretching method comprises: a starting stage in which the glass mother material is stretched by heating it from the lower end side by maintaining it within the stretching device at a temperature above a predetermined stretching processing temperature; and an ending stage in which the stretching operation of the glass mother material is terminated after the tapered portion enters the range and before the end face enters the range.

[0009] A stretching device is provided for stretching a glass mother material by heating the glass mother material while moving it downwardly within a container. The glass mother material has a suspended dummy rod formed of a glass rod fused to the end face of a transparent tapered portion located at the upper end. The glass mother material is maintained within a temperature range above a predetermined stretching processing temperature within the container. Heating is initiated from the lower end of the glass mother material to stretch the glass mother material. The stretching operation is terminated after the tapered portion enters the range and before the end face enters the range. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic longitudinal sectional view showing an example of the stretching device 100 .

[0011] Figure 2 This is a schematic diagram showing the relationship between the position of the first tapered portion 16 at the upper end of the glass base material 12 and the temperature when the glass base material 12 has reached the elongation end position. DETAILED DESCRIPTION

[0012] The present invention will be described below by way of embodiments of the invention, but the following embodiments do not limit the invention described in the claims. Furthermore, not all combinations of features described in the embodiments are essential to the solution provided by the invention.

[0013] Figure 1 This is a schematic longitudinal cross-sectional view showing an example of an elongation apparatus 100. The elongation apparatus 100 heats and elongates a glass base material 12 while moving it downward therein. By elongating the glass base material 12, the elongation apparatus 100 produces a glass rod having a diameter thinner than that of the glass base material 12. The elongation apparatus 100 in this embodiment includes a heater 1, a heat insulator 2, a water-cooled chamber 3, a top chamber 4, a suspension shaft 5, a connecting jig 6, a conveying mechanism 7, a lower gas seal 8, a guide roller 9, an upper pulling roller 10, and a lower pulling roller 11.

[0014] The glass base material 12 is made of, for example, silica glass. The glass base material 12 made of silica glass is elongated by the elongation device 100 to become, for example, a silica glass rod such as an optical fiber preform. The elongation temperature of the glass base material 12 made of silica glass is, for example, 1900°C.

[0015] The glass mother material 12 has a columnar shape, for example, a substantially cylindrical shape. In the following description, the glass mother material 12 is sometimes assumed to be already disposed within the elongation apparatus 100. One end of the glass mother material 12 located above the elongation apparatus 100 is sometimes referred to as the upper end, and the other end of the glass mother material 12 located below the elongation apparatus 100 is sometimes referred to as the lower end.

[0016] The glass base material 12 includes a transparent first tapered portion 16 located at the upper end, a second tapered portion 17 located at the lower end, and a straight portion 18 located between the first tapered portion 16 and the second tapered portion 17 .

[0017] First tapered portion 16 has a shape that tapers toward the upper end of glass base material 12. First tapered portion 16 has end face 19, a cut surface formed by cutting the base material, on the tapered side. A dummy hanging rod 13, made of a glass rod, is pre-fused to end face 19 of first tapered portion 16.

[0018] The second tapered portion 17 has a shape that tapers toward the lower end of the glass base material 12. The second tapered portion 17 has a cut surface formed by cutting the base material on the tapered side. For example, the glass base material 12 is manufactured from a porous glass base material. Therefore, the opaque portion 15 is located on the cut surface side of the second tapered portion 17. For example, the straight body portion 18 has a substantially uniform outer diameter from the portion connecting to the first tapered portion 16 to the portion connecting to the second tapered portion 17.

[0019] Furthermore, the opaque portion 15 may be intentionally left to prevent excessive elongation of the second tapered portion 17 during the process of forming the glass base material 12 by sintering the porous glass base material to achieve transparent vitrification. More specifically, in this process, sintering is performed from below with the second tapered portion 17 positioned upward and the porous glass base material suspended vertically. Therefore, if complete transparent vitrification is attempted up to the tapered tip of the second tapered portion 17, the entire weight of the already vitrified ingot will be applied to this tip, causing the second tapered portion 17 to excessively elongate. To prevent this, the front end of the second tapered portion 17 may be intentionally incompletely vitrified, allowing the opaque portion 15 to remain in the second tapered portion 17.

[0020] In the following description, regarding the various components of the stretching apparatus 100, the heater 1, heat insulating material 2, water-cooling chamber 3, top chamber 4, and lower gas seal 8 may be collectively referred to as a heating furnace. Furthermore, the suspension shaft 5, connecting jig 6, and conveying mechanism 7 may be collectively referred to as a conveying section. Furthermore, the guide roller 9, upper pulling roller 10, and lower pulling roller 11 may be collectively referred to as a pulling section.

[0021] Heater 1 heats the interior of elongation apparatus 100, heating at least the area surrounding heater 1 to a temperature above a predetermined elongation temperature, for example, above 1900°C, the elongation temperature of quartz glass. Heat insulation material 2 is disposed so as to enclose heater 1. A water-cooled chamber 3 is formed so as to enclose heat insulation material 2, with cooling water flowing therein. A top chamber 4 is connected to the upper portion of water-cooled chamber 3 and, together with heater 1, heat insulation material 2, and water-cooled chamber 3, forms the housing of elongation apparatus 100. A lower gas seal 8 is an openable and closeable seal installed at the lower portion of water-cooled chamber 3.

[0022] A conveyor mechanism 7 is disposed above the heating furnace and is capable of vertically moving a suspension shaft 5 suspended from the conveyor mechanism 7. The suspension shaft 5 can be inserted and removed into the top chamber 4. The upper side of a connecting fixture 6 is fixed to the front end of the suspension shaft 5 within the top chamber 4. Components such as a dummy rod 13 can be mechanically connected to the lower side of the connecting fixture 6.

[0023] The guide rollers 9, upper traction rollers 10, and lower traction rollers 11 are multiple rollers located below the heating furnace, capable of clamping and releasing components positioned between them. The guide rollers 9 are made of heat-resistant materials such as carbon and are used to guide the clamped components along the axis of the stretching device 100. The upper traction rollers 10 and lower traction rollers 11 are driven by motors and pull the clamped components downward, stretching them.

[0024] In the elongation method performed using the elongation apparatus 100 of this embodiment, before elongating the glass base material 12, the upper end of a dummy hanging rod 13, which is fused to the end surface 19 of the first tapered portion 16, is mechanically connected to a connecting jig 6. This connects the glass base material 12 to the conveyor mechanism 7 via the suspension shaft 5, enabling vertical movement within the elongation apparatus 100. Furthermore, the conveyor mechanism 7 moves the glass base material 12 so that the cut surface of the second tapered portion 17 is positioned near the heater 1. Furthermore, a dummy pulling rod 14 is aligned with the axis of the elongation apparatus 100 by the guide rollers 9 and the upper pulling rollers 10 and inserted into the elongation apparatus 100 from below. With the upper end of the dummy pulling rod 14 in contact with the cut surface of the second tapered portion 17, the contacting portion is fused by heat from the heater 1.

[0025] exist Figure 1 1 shows an example of a state after the above pretreatment, that is, a state before starting to elongate the glass base material 12. In the elongation method performed using the elongation apparatus 100 of this embodiment, the glass base material 12 is maintained at a temperature within the elongation apparatus 100 that is above a predetermined elongation temperature, and then heating is started from the lower end side of the glass base material 12 to elongate it.

[0026] Specifically, according to the extension method, Figure 1 In a state where the lower side of the second tapered portion 17 is located near the heater 1, the temperature around the heater 1 is raised to 1900°C or higher. It is preferred to raise the temperature of the heater 1 in this manner while the dummy rod 14 is not located near the heater 1. In response to the fact that the temperature around the heater 1 has reached 1900°C or higher, the dummy rod 13 is fed out by the conveying mechanism 7 while the dummy rod 14 is pulled downward at a speed faster than the feeding speed of the conveying mechanism 7 through at least one of the upper pulling roller 10 and the lower pulling roller 11. Thus, the dummy rod 14 begins to extend from the lower end side of the glass base material 12. In addition, the range refers to a range where the temperature around the heater 1 is maintained at 1900°C or higher, for example.

[0027] Furthermore, in the elongation method performed by the elongation apparatus 100 of this embodiment, the elongation of the glass base material 12 is completed after the first tapered portion 16 of the glass base material 12 enters the range and before the end surface 19 of the first tapered portion 16 enters the range.

[0028] When the end of the characteristic effective portion of the glass mother material 12, that is, the portion corresponding to the end of the range of the glass rod generated from the glass mother material 12 used as a product, is too close to the end face 19 of the first tapered portion 16, if the glass mother material 12 is to be extended to the effective portion end, there is a concern that the hanging dummy rod 13 or the vicinity of the end face 19 of the first tapered portion 16 may be deformed due to heat before the effective portion end.

[0029] The portion of the end face 19 of the first tapered portion 16 where the dummy hanging rod 13 is fused often contains small bubbles, making it more susceptible to deformation than the surrounding area. Furthermore, to reduce costs, the dummy hanging rod 13 is often made of a glass rod with an outer diameter smaller than that of the end face 19 of the first tapered portion 16. For these reasons, the area near the end face 19 of the first tapered portion 16 is heated to a temperature exceeding 1900°C, the processing temperature for quartz glass, while being subjected to a load within the stretching apparatus, potentially causing the aforementioned deformation. Consequently, the dummy hanging rod 13 or the area near the end face 19 of the first tapered portion 16 may break, causing the glass base material 12 to fall within the stretching apparatus. Furthermore, thermal deformation near the end face 19 of the first tapered portion 16 may result in a glass rod with significant bending and a significant outer diameter fluctuation.

[0030] In contrast, according to the elongation method performed using the elongation apparatus 100 of the present embodiment, the operation of elongating the glass preform 12 is completed after the first tapered portion 16 of the glass preform 12 enters the aforementioned range and before the end surface 19 of the first tapered portion 16 enters the aforementioned range. For example, the elongation apparatus 100 is controlled so that the aforementioned range is located vertically below the end surface 19 of the first tapered portion 16 at the time when the glass preform 12 is transported into the interior by the conveying mechanism 7 or the like.

[0031] This stretching method can suppress thermal deformation near the end surface 19 of the hanging dummy rod 13 or the first tapered portion 16. Consequently, this stretching method can prevent the hanging dummy rod 13 or the first tapered portion 16 from breaking near the end surface 19, which could cause the glass base material 12 to fall within the stretching apparatus 100. Furthermore, by suppressing thermal deformation near the end surface 19 of the first tapered portion 16, this stretching method can produce a glass rod with minimal bending and minimal outer diameter variation. Furthermore, this stretching method prevents the glass base material 12 from falling, improving the rate of producing glass rods whose bending or outer diameter variation is within the allowable range required for the product. This improves the yield of the glass rods, thereby reducing manufacturing costs.

[0032] As a specific example, in this stretching method, when the length of the range in the vertical direction of the stretching device 100 is set to X [mm], the length from the center position of the range in the vertical direction to the end face 19 is set to Y [mm], and the length of the first tapered portion 16 in the vertical direction is set to Z [mm], the operation of stretching the glass base material 12 can also be completed in a manner that satisfies (X / 2)<Y<{(X / 2)+Z}.

[0033] According to an example of the stretching method, it can also be said that when the glass mother material 12 is fed into the heating furnace of the stretching device 100 that has been heated to the specified stretching processing temperature, and the glass rods that have been stretched to the specified diameter are pulled sequentially from the lower part of the stretching device 100, the stretching is continued during the period when the longitudinal length Y (mm) of the device from the center of the heater 1 to the connection end of the glass mother material 12 to the hanging dummy rod 13 is not lower than 1 / 2 of the longitudinal length X (mm) of the device that maintains the specified stretching processing temperature at the temperature in the heating furnace, and the stretching is terminated under the condition that X / 2 is shorter than Y (mm).

[0034] Figure 2 This is a schematic diagram showing the relationship between the position of the first tapered portion 16 at the upper end of the glass base material 12 and the temperature when the glass base material 12 has reached the elongation end position. Figure 2 In the graph on the right, the vertical axis represents the vertical distance (mm) from the center of heater 1, with the center position of heater 1 being 0, and the horizontal axis represents the furnace temperature (°C), that is, the temperature (°C) inside the stretching apparatus 100. In the figure, the solid line curve represents the furnace temperature distribution in which the center position of heater 1 is the highest temperature.

[0035] Figure 2 In the figure, it can be seen that the longitudinal length Y (mm) of the device from the center of the heater 1 to the connection end between the first tapered portion 16 of the glass base material 12 and the hanging dummy rod 13 is longer than 1 / 2 of the longitudinal length X (mm) of the device at which the temperature in the heating furnace is maintained at the processing temperature of quartz glass, that is, above 1900°C.

[0036] Thus, during the elongation process, the first tapered portion 16 of the glass base material 12 and the connection end of the hanging dummy rod 13 are always in a temperature range lower than the processing temperature of quartz glass, that is, 1900° C., thereby preventing undesirable deformation near the connection end of the hanging dummy rod 13 and the resulting large diameter change or falling of the product portion, thereby safely obtaining a glass rod with a good shape.

[0037] In the above embodiment, as an example, the outer diameter of the straight body portion 18 of the glass preform 12 is preferably larger than the outer diameter of a typical optical fiber preform, which is 80 mm. By using a glass preform 12 having a straight body portion 18 with an outer diameter greater than 80 mm, the elongation apparatus 100 can improve equipment availability compared to conventional optical fiber preform elongation apparatuses.

[0038] Here, as a comparative example of the elongation device 100, a glass lathe, which uses a burner as a heat source, is considered. For example, when a glass base material 12 having a straight body portion 18 with an outer diameter of approximately 150 mm is used on the glass lathe, it is difficult to correct the curvature of the glass rod formed from the glass base material 12. This is because the heating performed by the burner in the glass lathe is performed in the open air. Therefore, cooling occurs simultaneously with heating due to radiation. The larger the outer diameter, the greater the cooling effect due to radiation, making it difficult to fully increase the temperature. Furthermore, it is difficult to remove residual strain at the curvature correction location.

[0039] In contrast, as described above, the elongation apparatus 100 fuses the suspended dummy rod 13 to the cut surface, i.e., the end surface 19, of the transparent first tapered portion 16, and then elongates the glass base material 12. This aligns the axis of the glass base material 12 with the center of the elongation apparatus 100. The elongation apparatus 100 then executes the elongation method. Consequently, even when using a glass base material 12 having an outer diameter of the straight portion 18 of approximately 150 mm, the elongation apparatus 100 can produce a glass rod with a small amount of curvature, for example, a glass rod with a curvature of 2 mm / m or less, or close to 2 mm / m.

[0040] In the above embodiment, when the outer diameter of the end face 19 is set to D1 [mm] and the outer diameter of the dummy rod 13 on the side of the end face 19 is set to D2 [mm], it is preferable that D2 ≤ D1 < 140. Specifically, the outer diameter of the cut surface of the glass base material 12, that is, the outer diameter of the end face 19, is set to be greater than the outer diameter on the side of the dummy rod 13 on the end face 19. Furthermore, the outer diameter of the end face 19 of the glass base material 12 is preferably set to be 140 mm or less. If the outer diameter of the end face 19 of the glass base material 12 is greater than 140 mm, there is a possibility that heating near the fusion point of the dummy rod 13 on the end face 19 of the first tapered portion 16 may become insufficient, and strain may remain in this area. There is a concern that cracks may form in the area where strain remains. If cracks form in the glass rod produced by stretching the glass base material 12 using the stretching device 100, the burden on the operator when removing the glass rod from the stretching device 100 increases.

[0041] Furthermore, in the above embodiment, the outer diameter of the dummy hanging rod 13 on the end surface 19 side is preferably between 30 mm and 60 mm. If the outer diameter of the dummy hanging rod 13 is smaller than 30 mm, cracks may form from fine scratches due to the load during extension or ambient heat, or the product may not be fully supported during installation before extension or removal after extension, resulting in instability. On the other hand, if the outer diameter of the dummy hanging rod 13 is larger than 60 mm, the unit price of the dummy hanging rod 13 itself increases, resulting in cost issues, which is not desirable.

[0042] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[0043] [Example]

[0044] A glass matrix with a straight body length of 2200mm, a tapered portion length of 500mm at both ends, and an outer diameter of 190mm at the straight body was used, and the extension target diameter was set to 150mm for extension. The glass matrix is ​​manufactured by sintering a porous glass matrix obtained by depositing glass particles on a target using the OVD (Outside Vapour Deposition) method. The target has dummy rods connected to both ends of a core component whose refractive index is adjusted for use in a single-mode optical fiber. The glass matrix has a transparent glass tapered portion at one end and a tapered portion including an opaque glass portion at the other end. The tapered portion including the opaque glass portion is cut at a position 170mm toward the dummy rod side at the junction line between the core rod of the glass matrix and the dummy rod. The transparent glass tapered portion side is cut at a position where the outer diameter of the front end is 110mm, and a hanging dummy rod with an outer diameter of 40mm is welded to the cut surface using a glass lathe.

[0045] Extension device use Figure 1 The elongation apparatus shown uses a quartz glass chamber as its top chamber 4. The glass base material is positioned with the transparent glass tapered portion facing upward and the opaque glass tapered portion facing downward, with the lower end of the glass base material aligned with the center of the heater. The temperature is raised from room temperature to 2100°C at a rate of 40°C / min, and then a dummy rod is fused and pulled before elongation.

[0046] In the elongation apparatus, an OMEGA (registered trademark) ultrahigh-temperature thermocouple probe was used to measure the temperature distribution within the furnace by increasing the temperature when no preform was present. The results showed that the longitudinal length X of the apparatus, which maintained the temperature above 1900°C within the furnace, was 340 mm. The distance Y between the fusion end of the suspended dummy rod and the center of the heater at the end of the glass preform elongation was varied, and elongation was performed in the following Comparative Examples 1 to 3 and Examples 1 to 3. The detailed conditions are described below.

[0047] [Comparative Example 1] The glass base material is extended under the condition that the longitudinal length of the device is X / 2=170mm while maintaining the temperature above 1900°C in the furnace. When the distance Y between the welding end position of the hanging dummy rod and the center position of the heater becomes Y=150mm, the extension is ended.

[0048] [Comparative Example 2] The glass mother material is extended under the condition that the longitudinal length of the device is X / 2=170mm while maintaining the temperature above 1900°C in the furnace. When the distance Y between the welding end position of the hanging dummy rod and the center position of the heater becomes Y=160mm, the extension is ended.

[0049] [Comparative Example 3] The glass mother material is extended under the condition that the longitudinal length of the device is X / 2=170mm while maintaining the temperature above 1900°C in the furnace. When the distance Y between the welding end position of the hanging dummy rod and the center position of the heater becomes Y=170mm, the extension is ended.

[0050] [Example 1] The glass base material is extended under the condition that the longitudinal length of the device is X / 2=170mm while maintaining the temperature above 1900°C in the furnace. When the distance Y between the welding end position of the hanging dummy rod and the center position of the heater becomes Y=180mm, the extension is completed.

[0051] [Example 2] The glass mother material is extended under the condition that the longitudinal length of the device is X / 2=170mm while maintaining the temperature above 1900°C in the furnace. When the distance Y between the welding end position of the hanging dummy rod and the center position of the heater becomes Y=190mm, the extension is ended.

[0052] [Example 3] The glass mother material is extended under the condition that the longitudinal length of the device is X / 2=170mm while maintaining the temperature above 1900°C in the furnace. When the distance Y between the welding end position of the hanging dummy rod and the center position of the heater becomes Y=200mm, the extension is ended.

[0053] In Comparative Examples 1-3 and Examples 1-3, three glass base materials were stretched in each case. The fluctuation in the outer diameter of the stretched product and the stability of the product after removal were evaluated. The results are shown in Table 1. In Table 1, ∘ indicates good, and x indicates a problem.

[0054] [Table 1]

[0055]

[0056] In the case of Comparative Examples 1 to 3, at the end of extension, the welded end of the suspended dummy rod is heated and produces an undesirable large deformation. The outer diameter variation of the product part is larger than the target extension diameter, ranging from -1.9mm to +2.7mm, and the bending amount is also large, ranging from 2.7mm / m to 3.8mm / m.

[0057] In the cases of Examples 1 to 3, at the end of extension, the welded end of the suspended dummy rod did not deform, and the outer diameter variation of the product part was also smaller than the target extension diameter, at -0.2mm to +0.7mm, and the bending amount was also suppressed to a small level, at 0.4mm / m to 1.3mm / m.

[0058] Therefore, if the vertical length X of the device maintaining a temperature of 1900°C or above within the furnace is divided by two to obtain the value X / 2, which is 170 mm, then the distance Y between the welded end of the suspended dummy rod and the center of the heater at the end of the extension should be set to Y = 180 mm or greater. In other words, X / 2 < Y should be set.

[0059] Next, the outer diameter of the cut surface of the transparent glass tapered portion of the glass base material where the dummy rod is fused, and the outer diameter of the dummy rod fused to the cut surface were variously changed, and the following Examples 4 to 14 were further extended.

[0060] The glass base material was manufactured in the same manner as the glass base materials provided in the comparative examples and embodiments above, and had a straight body length of 2200 mm, a tapered portion length of 500 mm at both ends, and an outer diameter of the straight body of 190 mm. The extension was performed with the extension target diameter set to 150 mm.

[0061] The glass base material was positioned with the transparent glass tapered portion facing upward and the bottom end of the glass base material aligned with the center of the heater. The temperature was then raised from room temperature to 2100°C at a rate of 40°C / min. A dummy rod was then fused and drawn, followed by elongation. The tapered portion, including the opaque glass portion, was cut 170 mm toward the dummy rod at the junction line between the core rod and the dummy rod in the glass base material.

[0062] Using an OMEGA (registered trademark) ultra-high temperature thermocouple probe, the temperature distribution in the elongation device furnace was measured by increasing the temperature when no preform rod was present. The result showed that the longitudinal length of the device in the furnace that maintained above 1900°C was X = 340 mm (X / 2 = 170 mm).

[0063] In Examples 4 to 14 below, stretching was terminated when the distance Y between the welded end of the suspended dummy rod and the center of the heater reached Y = 180 mm. Detailed conditions are shown below.

[0064] [Example 4] The transparent glass conical portion of the glass mother material is cut at a position where the outer diameter of the front end is 95 mm, and a hanging dummy rod with an outer diameter of 40 mm is welded to the cut surface using a glass lathe. The glass mother material formed in this way is set in an elongation device for elongation.

[0065] [Example 5] The transparent glass conical portion of the glass mother material is cut at a position where the outer diameter of the front end is 110 mm, and a hanging dummy rod with an outer diameter of 40 mm is welded to the cut surface using a glass lathe. The glass mother material formed in this way is set in an elongation device for elongation.

[0066] [Example 6] The transparent glass conical portion of the glass mother material is cut at a position where the outer diameter of the front end is 125 mm, and a hanging dummy rod with an outer diameter of 40 mm is welded to the cut surface using a glass lathe. The glass mother material formed in this way is set in an elongation device for elongation.

[0067] [Example 7] The transparent glass conical portion of the glass mother material is cut at a position where the outer diameter of the front end is 140 mm, and a hanging dummy rod with an outer diameter of 40 mm is welded to the cut surface using a glass lathe. The glass mother material formed in this way is set in an elongation device for elongation.

[0068] [Example 8] The transparent glass conical portion of the glass mother material is cut at a position where the outer diameter of the front end is 150 mm, and a hanging dummy rod with an outer diameter of 40 mm is welded to the cut surface using a glass lathe. The glass mother material formed in this way is set in an elongation device for elongation.

[0069] [Example 9] The transparent glass conical portion of the glass mother material is cut at a position where the outer diameter of the front end is 110 mm, and a hanging dummy rod with an outer diameter of 20 mm is welded to the cut surface using a glass lathe. The glass mother material formed in this way is set in an elongation device for elongation.

[0070] [Example 10] The transparent glass conical portion of the glass mother material is cut at a position where the outer diameter of the front end is 110 mm, and a hanging dummy rod with an outer diameter of 30 mm is welded to the cut surface using a glass lathe. The glass mother material formed in this way is set in an elongation device for elongation.

[0071] [Example 11] The transparent glass conical portion of the glass mother material is cut at a position where the outer diameter of the front end is 110 mm, and a hanging dummy rod with an outer diameter of 40 mm is welded to the cut surface using a glass lathe. The glass mother material formed in this way is set in an elongation device for elongation.

[0072] [Example 12] The transparent glass conical portion of the glass mother material is cut at a position where the outer diameter of the front end is 110 mm, and a hanging dummy rod with an outer diameter of 50 mm is welded to the cut surface using a glass lathe. The glass mother material formed in this way is set in an elongation device for elongation.

[0073] [Example 13] The transparent glass conical portion of the glass mother material is cut at a position where the outer diameter of the front end is 110 mm, and a hanging dummy rod with an outer diameter of 60 mm is welded to the cut surface using a glass lathe. The glass mother material formed in this way is set in an elongation device for elongation.

[0074] [Example 14] The transparent glass conical portion of the glass mother material is cut at a position where the outer diameter of the front end is 110 mm, and a hanging dummy rod with an outer diameter of 70 mm is welded to the cut surface using a glass lathe. The glass mother material formed in this way is set in an elongation device for elongation.

[0075] In Examples 4 to 14, one glass base material was stretched, and the fluctuation in the outer diameter of the stretched product and the stability of the product after removal were evaluated. The results are shown in Table 2. In Table 2, ∘ indicates good, and Δ indicates that improvement is required.

[0076] [Table 2]

[0077]

[0078] In Examples 4 to 14, the outer diameter variation of the product portion is smaller than the target extension diameter, ranging from -0.3 mm to +0.6 mm, and the bending amount is also suppressed to a small level, ranging from 0.5 mm / m to 1.7 mm / m.

[0079] However, in Example 8, cracks formed near the welded portion of the hanging dummy rod in the tapered portion of the transparent glass during removal of the stretched product. This made product removal unstable and increased the burden on the operator. This is likely because the welded portion of the hanging dummy rod has a relatively large outer diameter of 150 mm. Therefore, insufficient heating near the connection by the glass lathe resulted in residual strain, which easily caused cracks. Therefore, the outer diameter of the cut surface of the tapered portion of the transparent glass should preferably be 140 mm or less.

[0080] Furthermore, in Example 9, cracks developed in the dummy hanging rod fused to the tapered portion of the transparent glass during removal of the stretched product. This made product removal unstable and increased the burden on the operator. This is likely due to the excessively thin 20 mm dummy hanging rod, which caused the cracks to form tiny scratches invisible to the naked eye due to the load during stretching and the surrounding heat.

[0081] Furthermore, in Example 14, while the product shape and stability during removal were not problematic, the outer diameter of the dummy hanging rod was 70 mm, which was relatively thick, thus posing a cost issue. The larger the outer diameter of the dummy hanging rod, the higher the unit price of the dummy hanging rod itself, thus increasing the preparation costs when used in large quantities. Therefore, dummy hanging rods with an outer diameter greater than 60 mm are not cost-effective.

[0082] According to the above embodiment, it can be said that the outer diameter of the portion where the dummy rod is fused to the cut surface of the tapered portion of the transparent glass is more preferably 30 mm or more and 60 mm or less.

[0083] While the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the embodiments. It will be apparent to those skilled in the art that various modifications or improvements may be made to the embodiments described. As will be clear from the claims, embodiments incorporating such modifications or improvements are also encompassed within the scope of protection of the present invention.

[0084] It should be noted that the order of execution of actions, sequences, steps, and stages, etc., in the apparatuses, systems, programs, and methods described in the claims, specifications, and drawings may be implemented in any order unless specifically indicated by "before," "prior to," etc., and as long as the output of a previous process is not used in a subsequent process. Regarding the action flow in the claims, specifications, and drawings, although the phrases "first," "next," etc., are used for convenience, this does not necessarily mean that the actions must be implemented in this order.

[0085] [Explanation of Reference Signs]

[0086] 1 heater

[0087] 2 Insulation materials

[0088] 3 Water-cooling chambers

[0089] 4 Top chamber

[0090] 5 suspension axles

[0091] 6. Connecting fixture

[0092] 7 Transmission mechanism

[0093] 8 Lower gas seal

[0094] 9 Guide rollers

[0095] 10 Upper traction roller

[0096] 11 Lower traction roller

[0097] 12 Glass mother material

[0098] 13 Hanging dummy stick

[0099] 14 Pulling dummy rod

[0100] 15 Opaque part

[0101] 16 1st tapered part

[0102] 17 Second tapered portion

[0103] 18 straight body part

[0104] 19 end face

[0105] 100 extension device

Claims

1. A method for elongating a glass base material by heating the glass base material while moving it downward within an elongation apparatus, wherein a dummy hanging rod composed of a glass rod is fused to the end surface of a transparent tapered portion located at the upper end of the glass base material, the method comprising: Starting stage: passing the glass mother material through the longitudinal length of the stretching device maintained at a predetermined stretching temperature or higher within the stretching device, and starting to heat the glass mother material from the lower end side to stretch it; and Ending stage: after the tapered portion enters the range and before the end surface enters the range, ending the operation of extending the glass base material; When the length of the range in the vertical direction of the stretching device is X mm, the length from the center position of the range in the vertical direction to the end surface is Y mm, and the length of the tapered portion in the vertical direction is Z mm, The end stage ends the operation of extending the glass base material so as to satisfy (X / 2)<Y<{(X / 2)+Z}.

2. The stretching method according to claim 1, wherein When the outer diameter of the end surface is set to D1 mm, and the outer diameter of the hanging dummy rod on the end surface side is set to D2 mm, D2≤D1<140 mm is satisfied.

3. The stretching method according to claim 1 or 2, wherein The outer diameter of the hanging dummy rod on the end surface side is not less than 30 mm and not more than 60 mm.

4. The stretching method according to claim 1 or 2, wherein The glass mother material includes quartz glass, and the stretching processing temperature is 1900°C.

5. An elongation device for elongating a glass base material by heating the glass base material while moving it downward inside the base material, wherein a dummy hanging rod composed of a glass rod is fused to the end face of a transparent tapered portion at the upper end of the glass base material. The glass base material is passed through the longitudinal length of the stretching device, the interior of which is maintained at a predetermined stretching temperature or higher, and is heated from the lower end side of the glass base material to be stretched, and After the tapered portion enters the range and before the end surface enters the range, the operation of extending the glass base material is terminated; When the length of the range in the vertical direction of the stretching device is X mm, the length from the center position of the range in the vertical direction to the end surface is Y mm, and the length of the tapered portion in the vertical direction is Z mm, The operation of stretching the glass base material is completed so that (X / 2)<Y<{(X / 2)+Z} is satisfied.

Images