JP4375493B2 - Method for producing porous glass base material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a glass preform capable of reducing a tapered portion formed at the end part of a glass particle deposit without increasing the number of burners. <P>SOLUTION: The method of manufacturing the glass preform comprises continuously depositing glass particles on the surface of a starting rod by: disposing a plurality of burners for synthesizing the glass particles so as to face the rotating starting rod; reciprocating relatively the starting rod and the burners; moving a returning position of the reciprocal movement in a certain direction; and repeating an operation of reversely moving the returning position when the returning position is moved to a predetermined position, wherein a moving distance for one reciprocating is less than two times a distance between the burners. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a method for producing a porous glass base material (glass particulate deposit) in which glass particulates are deposited in a radial direction on a starting rod while relatively moving (reciprocating) a starting rod and a glass particulate synthesis burner. In particular, the present invention relates to a method for manufacturing a porous glass base material from which a porous glass base material with few tapered portions formed at both ends is obtained.

As a method for producing a large porous glass base material at high speed, as shown in FIG. 7, a plurality of glass fine particle synthesis burners 7 are arranged at regular intervals so as to face a starting rod 1 in a container 4 and start rotating. The rod 1 and the row of the burners 7 are reciprocally moved relative to each other (in the figure, the starting rod 1 is reciprocated up and down), and glass fine particles are deposited in layers on the surface of the starting rod 1 to be porous. There is a method (multi-layering method) for obtaining a glass base material (glass fine particle deposit) 6.
In such a method for producing a porous glass base material, it is possible to reduce fluctuations in the outer diameter over the longitudinal direction of the porous glass base material from the viewpoint of quality improvement, and at the end of the porous glass base material from the viewpoint of productivity. Making the length of the formed tapered portion (ineffective portion) as short as possible is a major problem, and various methods for solving these problems have been proposed.

  For example, the one-way travel distance of the reciprocating movement is set to the burner interval, the start position of the reciprocating movement is moved every reciprocating movement, and after moving to a predetermined position, the reciprocating movement is started in the reverse direction to start the first reciprocating movement. The end of the reciprocating movement, which has substantially increased the deposition time by returning to the position, is dispersed throughout the glass particulate deposit, and the glass particulate deposition time of the entire glass particulate deposit and the deposition of glass particulates such as burner flames. A method has been proposed in which the amount of deposition of glass fine particles is made equal in the longitudinal direction by making the fluctuations in contact with the body equal to each other, thereby reducing fluctuations in the outer diameter (see Patent Document 1).

Similarly, as a method of reducing the outer diameter fluctuation, based on the method described in Patent Document 1, the outer diameter fluctuation of the entire glass fine particle deposit is measured using a CCD camera and a central information processing device that can monitor the entire area of the glass fine particle deposit. Further, there has been proposed a method of reducing fluctuations in the outer diameter by supplementing the deposition of glass particles in a portion where the amount of accumulated glass particles is small by an auxiliary burner capable of traversing the entire glass particle deposit body alone (see Patent Document 2). .
In addition, when depositing glass particles while moving the traverse start position, clean air is supplied vertically to the entire glass particle deposit to reduce the temperature gradient during deposition in the longitudinal direction of the glass particle deposit. There is a method to do so (see Patent Document 3).

  Further, as a method for smoothly moving the turn-back position of the reciprocating movement, the burner row is installed on the first moving shaft and moved back and forth, and the first moving shaft is installed on the second moving shaft, A method has been proposed in which the reciprocating movement of the moving shaft is changed to a simple reciprocating movement at a constant interval, and the reciprocating distance of each moving shaft, the reciprocating moving speed, or both the distance and speed are made different to move the folding position ( According to this method, the folding position of the reciprocating movement of the burner row can be moved only by a simple mechanical method.

JP-A-3-228845 Japanese Patent Laid-Open No. 10-158025 JP-A-4-260618 Japanese Patent Laid-Open No. 2001-19441 JP 2001-31431 A

In the case of the method for moving the folding position of the traverse as shown in Patent Document 1, FIG. 8 shows an example of the relative position of the starting rod and the burner and the number of deposited layers, as shown in FIG. The deposition shape of the glass fine particles deposited by the burner located in the position is tapered (the number of deposited layers decreases toward the end).
FIG. 8 shows the outermost burner 2 and the second burner 3 on the outermost side of the burner row (the same situation applies to the outer and inner burners on the opposite side). The number of deposited layers of glass particles formed on the starting rod 1 during a series of reciprocating movements (one set of reciprocating movements) until the folding position returns to the initial position is shown. The example of FIG. 8 is an example in which 10 reciprocations are performed during one set of reciprocating movements, and the maximum number of deposited layers is 20. In the portion below the 20th layer in the figure, since there is deposition by the third and subsequent burners, there are 20 constant layers except for the lower end. In principle, the number of deposited layers is reduced only in the portion where the glass fine particles are deposited by the burner at the end, but the glass by the burner located second from the end because the glass fine particles are deposited in a tapered shape at the end of the glass fine particle deposit. The fine particles also flow to the outside, so that most of the glass fine particles accumulate in a tapered shape, resulting in an increase in the tapered portion that is an ineffective portion. The taper portion having the same shape is also formed by the methods of Patent Document 2 and Patent Document 3 that employ the same reciprocating movement method.

  In addition, the time when the glass fine particle deposition step is completed is optimal at the moment when the number of deposited layers in the steady portion becomes uniform. However, if the turn-back positions are dispersed densely, the number of deposited layers increases until the number of deposited layers becomes uniform, and it becomes difficult to adjust the amount of deposited glass particles. Therefore, Patent Document 1 discloses that when the deposition amount approaches the target weight, the folding position dispersion interval is increased to adjust the glass particle deposition amount. This will reduce the effect of stabilizing the outer diameter.

  In the methods of Patent Documents 4 and 5, which are different from the methods of Patent Documents 1 to 3, in which the deposition form of the glass fine particles is different, the burner is moved by two moving axes, so that the control system becomes complicated. In addition, the number of deposited layers in the stationary part varies depending on the difference between the moving distance and the moving speed of the two moving axes, but the number of deposited layers is not uniform, and the parts with different deposited layers appear alternately. In addition, a portion with a different number of deposited layers appears. In this method, for example, if the moving distance of the first and second moving axes is an integral multiple of the burner interval, the portions with different numbers of deposited layers appear alternately, and if the alternately appearing interval is fine, the outer diameter Stabilization is possible. However, even in this method, as in the method of Patent Document 1, ineffective portions having a length that is an integral multiple of the burner interval are formed at both ends.

As one method for solving the problem of an increase in the tapered portion, it is conceivable to narrow the burner interval and increase the number of burners accordingly. By doing so, the deposition interval of the glass particles by the outer burner and the second burner is reduced, and the taper portion can be reduced. However, if the burner interval is reduced, it is necessary to increase the number of burners in order to produce a glass particulate deposit having an effective portion of the same length. Therefore, the gas supply system is increased, and the equipment cost is increased.
In addition, if the burner flames interfere with each other, the deposition efficiency of each burner becomes unstable and the outer diameter fluctuates, so there is a limit to shortening the burner interval, and a dramatic taper reduction effect can be expected. Absent.

  The present invention solves such problems in the prior art and provides a method for producing a porous glass base material that can reduce the taper portion formed at the end of the glass particulate deposit without increasing the number of burners. For the purpose.

The present invention employs the following configurations (1) to (10) as means for solving the above-described problems.
(1) A plurality of glass particle synthesizing burners are arranged at equal intervals so as to face the rotating starting rod, and the starting rod and the glass particle synthesizing burner are relatively parallel to each other in the initial position of the return path from the return path. Reciprocating so as not to exceed the position, moving the return position of the return path from the forward path of the reciprocating movement in a certain direction, and moving the return position of the return path from the forward path to a predetermined position to move in the reverse direction, In a method of manufacturing a porous glass base material by setting the operation until each burner returns to the initial position as one set and sequentially repeating this operation to deposit glass fine particles synthesized by the burner sequentially on the surface of the starting rod. The average reciprocating distance of one set is less than twice the burner interval, and when each burner in the set returns to the initial position, the number of deposited layers in the stationary part is long. And setting to be uniform in direction, a manufacturing method of a porous glass preform.

(2) The method for producing a porous glass base material according to the above (1), wherein the distance traveled each time from the forward path of the reciprocating motion to the return position of the return path is equal.
(3) When the return position of the return path from the forward path of the reciprocating movement has moved to a predetermined position, the operation of returning each burner to the initial position by the next movement is set as one set. Method for producing a glass base material.
(4) In the first movement, each burner is moved to a predetermined position and turned back. Thereafter, the return position of the return path is moved from the return path to the initial position of each burner. The method for producing a porous glass base material according to (1) above, wherein the operation until returning to the position is set as one set.
(5) The method for producing a porous glass base material according to (1), wherein the moving distance of the return position of the return path from the forward path of the reciprocating motion is changed in one set.

(6) The porous glass mother according to (1) or (2) above, wherein the range of movement from the reciprocating forward path to the return path folding position is n times the burner interval (n is an integer of 1 to 3). A method of manufacturing the material.
(7) The moving range of the return position from the forward path to the return path of the reciprocating motion is shorter than the burner interval by n times (n is an integer of 1 to 3) by the minimum moving distance of the return position in one set. The method for producing a porous glass base material according to any one of (1) and (3) to (5).
(8) The above-described (1), wherein the average moving distance of one turn from the forward path of the reciprocating motion to the return path in one set is a length of (m + 1) times the burner interval (m is a natural number). )-(7) The manufacturing method of any one porous glass base material.

(9) The average moving distance of one time of the return position of the reciprocating movement from the reciprocating movement in the one set is Amm, the average reciprocating movement distance of one set is Dmm, and A is in the range of 5 to 60 mm, and , D is in the range of 4 × A ≦ D ≦ 240. (8) The method for producing a porous glass base material according to (8) above.
(10) From the relationship between the speed of the reciprocating motion and the weight of the glass fine particles deposited until the end of the glass fine particle deposition, the reciprocating speed capable of achieving the target glass fine particle deposition amount at the end of the glass fine particle deposition is determined The porous glass according to any one of (1) to (9), wherein the target deposition amount can be achieved at the completion time of the glass particulate deposition by depositing the glass particulates at that speed. A manufacturing method of a base material.

In order to shorten the length of the tapered portion as much as possible, the present inventors have made various studies on the reciprocating method, and set the average reciprocating distance of one set to less than twice the burner interval, and preferably the reciprocating position of the reciprocating movement. By setting A to be in the range of 5 to 60 mm and D being in the range of 4 × A ≦ D ≦ 240, where Amm is the moving distance of Amm and the average reciprocating distance of one set is Dmm, It has been found that a porous glass base material having a small taper portion can be produced efficiently.
Here, one set of average reciprocation distance is an average reciprocation distance obtained by dividing one set of total movement distances by the number of reciprocations of one set.
The return position of the reciprocating movement is a position where the return path (the burner moves relatively in the direction of the initial position) from the forward path (the burner moves relatively in the direction away from the initial position).
In the method of the present invention, the average reciprocating distance of one set is less than twice the burner interval, and the folding position is moved for each reciprocating movement. In this case, the travel distance of the forward path and the return path does not become an integral multiple of the burner interval.

In the above-described prior art, the average reciprocating distance is basically twice the burner interval. Compared to these prior arts, the method of the present invention has the following advantages.
First, the total number of layers deposited on the stationary part by one set of swinging reciprocating movements in which the turning points are dispersed at the same interval over the entire length of the base material is always smaller in the present invention (the accuracy of achieving the target weight is improved). In addition, the length of the ineffective portion formed at both ends of the base material is always shorter in the present invention (deposition efficiency can be improved). Further, in the prior art, the ineffective portions at both ends of the base metal are lengthened in proportion to the burner interval, but in the optimal embodiment of the present invention, the ineffective portion length can be minimized without depending on the distance of the burner interval. Yes (even if the burner interval is increased and the base material is enlarged, the ineffective portion length can be minimized).

  The basic methods of reciprocation in the method of the present invention include the following movement modes 1 to 4. The first movement mode is a system in which the movement distance for each turn of the return position of the reciprocating movement is approximately equal. The second movement mode is a system in which a set of operations for returning each burner to the initial position by the next movement when the return position of the reciprocation moves to a predetermined position by repeating the reciprocation. In the third movement mode, on the contrary, each burner is moved to a predetermined position by the first movement and turned back. Thereafter, the turn-back position of the reciprocating movement is moved in the direction of the initial position of each burner. This is a system in which the operation until each burner returns to the initial position is set as one set. The fourth movement mode is a method in which the movement distance of the return position of the reciprocating movement is changed in one set.

In the first movement mode, the number of deposited layers in the stationary part is approximately in the length direction at two points when the folding position moves to a predetermined position in one set and when each burner returns to the initial position. It becomes uniform.
In this first movement mode, the optimum embodiment is that the reciprocating movement is the forward path 2 × A, the return path is A, the return position movement is repeated in the same direction, and the reciprocating movement forward path is 2 × when the burner interval folding position is moved. A is set to 3xA for the return path only, and the return position is moved in the opposite direction and the reciprocating movement until returning to the very first position is set as one set, and this is repeated to deposit the glass particles. Yes (average distance 2 × A for one-way reciprocating movement, moving distance for one turn-back position is Amm). In this way, the length of the portion where the number of deposited layers is insufficient is only 2 × A at both ends of the porous glass base material, and the taper is the shortest. This theoretically shortest taper length is called the principle taper length. In this case, the principle taper length is 2 × A. However, in reality, since the glass particles flow along the taper shape, the taper shape is larger than 2 × A. When the forward path 3 × A, the backward path 2 × A, and the burner interval turn-back position movement, the forward path 3 × A and the backward path 4 × A (average distance 3 × A of the reciprocating one-way movement) are used. Both ends of the glass base material are 3 × A (principle taper length 3 × A). However, when the principle taper length is about 120 mm or less, glass particles flow along the inclination of the taper, and the influence of the deterioration of the deposition efficiency is more dominant. The actual taper length is the same as when the principle taper length is 2A. Almost no change at 3A.

  However, if the average distance of the reciprocating one-way is increased to 4 × A, 5 × A,..., The principle taper length also increases to 4 × A, 5 × A,. When the length of the part where the number of deposited layers is actually increased, the taper length starts to increase beyond the influence of the flow of glass particles along the taper when the taper length becomes longer to some extent. The taper length increases if (B + 1) × A = Cmm (B = 1, 2, 3...) Is defined when the moving distance of the position is Amm and the coefficient indicating the average distance of the reciprocating one-way is B. It is considered that there is C that starts to become noticeable.

  This C is considered to change somewhat depending on the shape of the burner, etc., but if it is within at least about 120 mm, it is possible to prevent the taper length from becoming significantly long. Therefore, a desirable range is 5 mm ≦ A ≦ 60 mm in order to suppress the outer diameter fluctuation at the turn-back position, and a range of 2 × A ≦ (B + 1) × A ≦ 120 is considered optimal. Here, the lower limit 2 × A is a theoretical lower limit. Further, A more suitable for suppressing fluctuations in the outer diameter is 5 ≦ A ≦ 40. Since the average distance D of the reciprocating movement is D = 2 × (B + 1) × Amm (B = 1, 2,...), It is (B + 1) × A = D ÷ 2, and the above desired range 2 × A ≦ (B + 1) ) × A ≦ 120 and substituting this inequality into the average distance of reciprocating movement results in 4 × A ≦ D ≦ 240.

In the second movement form, the optimum form is that the reciprocating movement is the forward path 2 × A, the return path is A, the movement of the folding position is repeated in the same direction, and when the folding position moves to a position that is A mm farther than the burner interval, the return path of the reciprocating movement Is a set of reciprocating movements until the first position is returned to the first position as burner interval + A, and this is repeated to deposit glass particles (average distance 2 × A of reciprocating one-way, Amm over burner interval) Until the folding position moves to a far position, the distance of one movement of the folding position is Amm).
In the third movement form, the optimum form is to move to a position that is Amm farther than the burner interval in the first movement, and thereafter reciprocate with 2xA for the return path, A for the forward path, and Amm as the single movement distance at the return position. This is a form in which the reciprocating movement until the first position is repeatedly returned is set as one set, and the glass particles are deposited while repeating this (average distance 2 × A of the one-way reciprocating movement).
Further, in the fourth movement mode, the optimum embodiment is that the forward path is 2 × A, the return path is A, the one-time movement distance of the folding position is Amm, and the folding position is moved to a position shorter by A mm than the burner interval. Based on a reciprocating movement where the forward path is A, the return path is 2 × A, and the one-time movement distance of the folding position is Amm, including movement in which one movement distance of the folding position is larger than A in one set. It is a form (average distance 2 * A of a one-way reciprocation).

In the second to fourth optimum movement modes, the length of the portion where the number of deposited layers is insufficient is only A at each end of the porous glass base material (principle taper length A), and the taper length is the most. Can be shortened. However, in reality, the taper shape is larger than A. Similar to the first movement mode, when the principle taper length is as short as 2A or 3A, the actual taper length hardly changes.
Further, when the coefficient indicating the average moving distance of the one-way reciprocating movement is defined as B, if (B + 1) × A = Cmm (B = 1, 2, 3,...) Is defined, an increase in taper length starts to become remarkable. C exists.
As in the first movement mode, C is preferably within about 120 mm. If 5 ≦ A ≦ 60 mm for stabilizing the outer diameter is taken into consideration, the desirable range of the average distance D for reciprocation is the same as in the first pattern. And 4 × A ≦ D ≦ 240.

  In the inventions of Patent Document 1 and subsequent documents, the reciprocating distance (one way) has a substantially lower burner interval as the lower limit. This indicates that the multi-layering method is based on the idea that a glass layer must be formed over the entire range of the effective length for each reciprocation. However, in the present invention, the idea is changed that it is only necessary to make uniform before the difference in deposition thickness becomes significant without forming a glass layer in the entire range of the effective part length by one reciprocating movement. In addition, a glass fine particle deposition layer having a uniform thickness is formed at least once or more in one set for moving the folding position. The effect due to the difference in the concept makes it possible to significantly reduce the ineffective portion (tapered portion), which is considered difficult to reduce and has not been disclosed.

  In the method of the present invention, the return position of the reciprocating movement is moved stepwise for each reciprocating movement from the position closest to the initial burner position to the position farthest (predetermined position). In order to smooth the stationary portion (effective portion), a predetermined distance (a distance between the folding position closest to the initial burner position and the farthest folding position) for moving the folding position is set as the first distance. In the movement mode, approximately n times the burner interval (n is an integer of 1 to 3), and in the second to fourth movement modes, approximately n times the burner interval (n is an integer of 1 to 3). Also, it is preferable to shorten the distance by the minimum moving distance in one set. Particularly, when n is 1, the length of the ineffective portion can be shortened most, and the deposition efficiency is preferable. When the burner includes a pattern in which the burner moves between the initial position and the farthest position in one operation as in the second or third movement mode, one burner is used at the folded position. After being heated, the time until it is heated by the adjacent burner is shortened, and the temperature of the portion may be increased and the bulk density may be increased. However, n is 2 or 3 as compared with the case where n is 1. In this case, the influence is alleviated and the smoothness is improved.

As in the prior art, when n is increased, the smoothness of the effective portion is improved, but the length of the ineffective portion is increased and the deposition efficiency is lowered. However, in the present invention, even if the same integer multiple as in the prior art is selected and the smoothness is maintained at the same level as that in the prior art, the length of the ineffective portion is shortened by about the burner interval compared to the prior art, and the deposition efficiency There is little decline.
In the conventional technique in which the average reciprocating distance is twice the burner interval, when the predetermined distance for moving the folding position is n times the burner interval, the length of the ineffective portion is n times the burner interval. In the case of the present invention in which the reciprocating distance is less than twice the burner interval, the length of the ineffective portion is smaller than the burner interval when n = 1, and is approximately equal to the burner interval when n = 2 or 3, respectively. It is only slightly larger than twice the burner interval and is shorter than n times the prior art burner interval. n is preferably 2 or less, and when n = 2, while maintaining the same smoothness as twice that of the prior art, the length of the ineffective portion is about the burner interval. Further, when n is 1, the ineffective portion length is less than the burner interval that could not be realized by the prior art, and the ineffective portion can be shortened to the shortest, which is most preferable.

  FIG. 1 shows an example of a situation of a change with time of the relative position between the starting rod and the burner in the first movement form. FIG. 1 shows an example in which the inside of the burner interval is divided into five sections so that the comparison with FIG. 8 showing the prior art example is easy, and the outer burner 2 on the outermost side and the second burner 3 on the outermost side of the burner row are shown. (The same situation applies to the outer and inner burners on the opposite side.) The value on the right is a series of reciprocating movements (one set of reciprocating movements) until the return position returns to the starting position. The number of deposited layers of glass fine particles formed on the starting rod 1 in the meantime is shown.

In the example of FIG. 1, in the first half of one set of reciprocating movements, it moves by two sections in one direction and returns one section, and in the second half, the movement in one direction remains as two sections and returns by three sections. It returns to the initial relative position. In this case, the number of deposited layers is 2, 6, 8, 8, 8... As shown on the right side of the figure, and the portion smaller than the number of deposited layers in the effective portion is the burner interval at the end of the base material. There are only 2 sections.
In the case of this folding method, even if the number of divisions within the burner interval is increased in order to further enhance the dispersion effect, there are only two sections located at the end of the base material where the number of deposited layers is small. That is, when the number of divisions is increased, the length of the portion having a small number of deposited layers is further shortened.

  For example, moving the folding position by 40 mm with respect to the burner interval of 200 mm corresponds to the division number of 5 sections (200 mm ÷ 40 mm = 5 sections) in FIG. In this case, the length of the portion where the number of deposited layers is insufficient is 40 mm × 2 sections = 80 mm. However, if the folding positions are dispersed at intervals of 20 mm in order to further improve the dispersion effect, the length within the 200 mm burner interval. Is divided into 10 sections (200 mm ÷ 20 mm = 10 sections), and the length of the portion where the number of deposited layers is insufficient is 20 mm × 2 sections = 40 mm. In the conventional technique in which the movement distance in one direction at each time is almost the burner interval, the number of deposited layers is insufficient at the entire interval of 200 mm, but according to this method, the length of the portion where the number of deposited layers is insufficient. The height is only 40 mm. The effect of reducing the length of the portion where the number of deposited layers is insufficient becomes larger as the burner interval becomes longer.

Furthermore, according to the first movement mode, there is an effect that the number of deposited layers required for one set of a series of reciprocating movements for dispersing the return position of the reciprocating movements over the entire length of the base material is small. That is, in the prior art of FIG. 8, 20 glass particles are deposited with the number of effective portions in one set, whereas in the method of the present invention of FIG. 1, only 8 layers are deposited.
In the method of FIG. 1, the number of deposited layers in the effective portion in one set is always 8 layers. On the other hand, in the conventional manufacturing method, if the moving distance of the folding position is shortened or the burner interval is lengthened in order to enhance the dispersion effect, the number of deposited layers of effective portions required for one set increases. For example, it increases to 20 layers in the case of 5 sections, 24 layers in the case of 6 sections, and 28 layers in the case of 7 sections.
In the conventional technique in which the average reciprocation distance is twice the burner interval and this first movement mode, there are times when the dispersion of the folding position and the number of deposited layers of the effective portion become uniform every half set. It is preferable to end the fine particle deposition step. In this case, the difference in the number of deposited layers (≈deposited glass weight) compared to the prior art (number of deposited layers in the first moving form ÷ number of deposited layers in the prior art) is 2/5 and 6 compartments in the case of 5 compartments. In the case of 1/3, it becomes 2/7 in the case of 7 sections, and in the first moving form, the amount of deposited glass fine particles can be finely adjusted even if the number of dispersion at the folding position is increased in order to stabilize the outer diameter. .

  Next, FIG. 2 shows an example of the change over time of the relative position between the starting rod and the burner in the second movement mode. 2 shows an example in which the burner interval is divided into five sections so that the comparison with FIG. 8 showing the prior art example is easy. (The same situation applies to the outer and inner burners on the opposite side.) The value on the right is a series of reciprocating movements (one set of reciprocating movements) until the return position returns to the starting position. The number of deposited layers of glass fine particles formed on the starting rod 1 in the meantime is shown.

In the example of FIG. 2, in the first half of one set of reciprocating movements, they move in two directions in one direction and return one section, and the return position of the reciprocating movement moves to a position one section farther than the burner interval, and then the next movement To return to the initial relative position. The turn-back position of the reciprocating movement moves by one section to a predetermined position that is one section away from the burner interval. The number of deposited layers in this case is 2, 4, 4, 4, 4... As shown on the right side of the figure, and the portion less than the number of deposited layers in the effective portion is the burner interval at the end of the base material. There is only one section.
In this folding method as well, even if the number of divisions within the burner interval is increased in order to further increase the dispersion effect, as in the first moving mode, the portion where the number of deposited layers is small is one section located at the end of the base material. Only exists. That is, when the number of divisions is increased, the length of the portion having a small number of deposited layers is further shortened.

For example, shifting the folding position by 40 mm with respect to the burner interval of 200 mm corresponds to the division number of 5 sections (200 mm ÷ 40 mm = 5 sections) in FIG. 2. In this case, the length of the portion where the number of deposited layers is insufficient is 40 mm × 1 section = 40 mm. However, if the folding positions are dispersed at intervals of 20 mm in order to further improve the dispersion effect, the length within the 200 mm burner interval. Is divided into 10 sections (200 mm ÷ 20 mm = 10 sections), and the length of the portion where the number of deposited layers is insufficient is 20 mm × 1 section = 20 mm.
Further, in the second movement form shown in FIG. 2, as in the first movement form, the number of effective layers deposited in one set does not increase even if the number of dispersions at the folding position is increased, and always 4. It is a layer, and it is possible to finely adjust the glass particle deposition amount as in the first movement mode.

  Next, FIG. 3 shows an example of the change with time of the relative position between the starting rod and the burner in the third movement mode. FIG. 3 shows an example in which the inside of the burner interval is divided into five sections so that the comparison with FIG. 8 showing an example of the prior art is easy. The outermost burner 2 and the second burner 3 on the outermost side of the burner row are shown. (The same situation applies to the outer and inner burners on the opposite side.) The value on the right is a series of reciprocating movements (one set of reciprocating movements) until the return position returns to the starting position. The number of deposited layers of glass fine particles formed on the starting rod 1 in the meantime is shown.

In the example of FIG. 3, the first movement of one set is moved to a position one block farther than the burner interval, then it is folded and moved by two blocks, and after that, the operation of moving one block and then returning two blocks is repeated to initialize It returns to the relative position. In the first movement, each burner moves to a predetermined position and turns back. Thereafter, the turn-back position of the reciprocating movement moves by one section in the direction of the initial position of each burner. The number of deposited layers in this case is 2, 4, 4, 4, 4... As shown on the right side of the figure, and the portion less than the number of deposited layers in the effective portion is the burner interval at the end of the base material. There is only one section.
Even in this folding method, even if the number of divisions in the burner interval is increased in order to further increase the dispersion effect as in the first and second movement modes, the portion with a small number of deposited layers is positioned at the end of the base material. There is only one section. That is, when the number of divisions is increased, the length of the portion having a small number of deposited layers is further shortened.
As in the first and second movement forms, the third movement form shown in FIG. 3 does not always increase the number of deposited layers of the effective portion deposited in one set even if the number of dispersions at the folding position is increased. There are four layers, and it is possible to finely adjust the amount of deposited glass fine particles as in the first and second moving modes.

  Next, FIGS. 4A and 4B show an example of the change over time of the relative position between the starting rod and the burner in the fourth movement mode. 4 shows an example in which the inside of the burner interval is divided into five sections so that the comparison with FIG. 8 showing an example of the prior art is easy, and the outer burner 2 and the second burner 3 on the outermost side of the burner row are shown. (The same situation applies to the outer and inner burners on the opposite side.) The value on the right is a series of reciprocating movements (one set of reciprocating movements) until the return position returns to the starting position. The number of deposited layers of glass fine particles formed on the starting rod 1 in the meantime is shown.

In the example of FIG. 4 (a), in the first half of one set of reciprocating movements, the operation of moving two sections in one direction and returning one section is repeated twice, then moving four sections and the return position of the reciprocating movement is the burner. Move to a position one section farther than the interval, and in the second half, repeat the reciprocating movement of two sections on the return path and one section on the outbound path, and then return to the initial relative position by returning four sections on the next movement. ing. The moving distance of the turn-back position of the reciprocating movement changes as 1 section, 3 sections, 1 section, and 3 sections during one set. The number of deposited layers in this case is 2, 4, 4, 4, 4... As shown on the right side of the figure, and the portion less than the number of deposited layers in the effective portion is the burner interval at the end of the base material. There is only one section. In the example of FIG. 4B, the formation state of the deposited layer is the same except that the pattern for changing the moving distance of the folding position is different.
Even in this folding method, even if the number of divisions in the burner interval is increased in order to further increase the dispersion effect as in the first to third movement modes, the portion with a small number of deposited layers is located at the end of the base material. There is only one section. That is, when the number of divisions is increased, the length of the portion having a small number of deposited layers is further shortened.
In the fourth movement form shown in FIG. 4, as in the first to third movement forms, the number of effective layers deposited in one set does not increase even if the dispersion number of the folding position is increased. It is a layer, and it is possible to finely adjust the glass particle deposition amount as in the first to third moving modes.

In the method of the present invention, it is preferable that the average moving distance of one turn of the reciprocating position of the reciprocating movement in one set is approximately 1 / (m + 1) (m is a natural number) of the burner interval. By doing so, one set of reciprocation can be terminated at the initial reciprocation start position, and the length of the tapered portion can be minimized. It is not preferable that the moving distance for each time greatly deviates from the length of about (m + 1) (m is a natural number) of the burner interval, because the number of deposited layers changes at the overlapping portion with the adjacent burner. Here, approximately one (m + 1) of the burner interval (m is a natural number) means one (m + 1) (m is a natural number) of “burner interval ± burner thickness”.
In addition, it is preferable that the movement interval of the turn-back position of the reciprocating movement is in the range of 5 to 60 mm, and more preferably in the range of 5 to 40 mm. If the movement interval of the folding position of the burner is less than 5 mm, the outer diameter fluctuates before the folding effect of the folding position appears, and if it exceeds 60 mm, the dispersion effect of the folding position becomes small.

  Furthermore, in order to reduce the fluctuation of the outer diameter, the glass fine particle deposition step is performed when the number of effective layer deposition layers present in one set considered to have the most dispersion effect and the dispersion density at the turn-back position are uniform. It is desirable to terminate. This optimum point in time for the end of deposition exists twice in one set in the conventional technique and the first movement form, and once in the second to fourth movement forms. That is, it is desirable that the glass fine particle deposition end timing is the time when the number of effective layers deposited twice in one set and the distribution of the folding positions are uniform in the first movement mode. It is desirable to set at the time when the reciprocating movement is finished with the integer set. Even with this setting, in the method of the present invention, from the time when the number of deposited layers of the effective portion and the distribution of the folding positions becomes uniform, the time from when the distribution of the number of the deposited layers of the next effective portion and the folding positions becomes uniform. Since the number of glass fine particles deposited in between is smaller than that of the conventional method, it is possible to finely control the amount of glass fine particles deposited.

  On the other hand, in the conventional manufacturing method, if the moving distance of the folding position is shortened in order to enhance the dispersion effect, the number of deposited layers of glass particles required for dispersion over the entire length of the base material increases. In the moving system in which the turning points of the reciprocating movement are uniformly dispersed, the timing for ending the deposition of the glass fine particles is the time when the number of the fine particle deposited layers in the effective portion existing in one set and the dispersion density of the turning positions are uniform. Is the best. Assuming that the weight of the glass fine particles deposited from the optimal time for the end to the next optimal optimal time is Mkg, the weight of the glass fine particle deposit at the time when the deposition of the glass fine particles is completed can be adjusted only in increments of Mkg. In the conventional manufacturing method, it becomes more difficult to reduce M as the number of deposited layers increases during the optimal time point of completion, so that it is difficult to obtain a glass particle deposit having a desired weight. In the present invention, M can be reduced, and a glass particulate deposit with a desired weight can be obtained.

  Furthermore, from the relationship between the speed of the reciprocating movement and the weight of the glass fine particles deposited before the end of the glass fine particle deposition, the reciprocating speed at which the target glass fine particle deposition amount can be achieved at the end of the glass fine particle deposition is determined, By depositing the glass particulates at that speed, the target deposition amount can be achieved at the end of the glass particulate deposition, and the glass particulate deposition amount can be controlled more effectively.

The present invention is not limited to the above embodiment. In the description of the embodiment, the forward path is the movement from the top to the bottom, but it may be the reverse direction.
The glass fine particle synthesizing burner does not necessarily mean a glass raw material gas that generates glass fine particles using a chemical reaction in a flame. It is used as a general term for mechanisms having the function of supplying glass particles to the starting rod and depositing and bonding them.

(Example)
Hereinafter, the method of the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto.
(Comparative Example 1)
Using a vertical glass fine particle deposition apparatus in which four burners were arranged in a row at 200 mm intervals so as to face the starting rod, glass fine particles were deposited by reciprocating the starting rod up and down. A starting rod with a diameter of 36 mm is used, and the reciprocating movement is the pattern shown in FIG. 8. The starting rod 1 is moved 200 mm downward, then moved upward 180 mm, and the return position of the reciprocating movement is moved downward by 20 mm. I made it. After the folding position has moved down by the burner interval, the downward movement distance remains 200 mm, the upward movement distance is 220 mm, and the folding position is moved upward by 20 mm to the initial position. The set until returning was one set, and 40 sets were repeated to deposit glass particles.

  The obtained glass fine particle deposit (porous glass base material) has a total length of 1100 mm, an outer diameter of 240 mm, an effective portion (a portion having a constant outer diameter) is 500 mm, and has tapered portions formed at both ends. Each length was 300 mm. In principle, the length of the tapered portion that can be formed at both ends is 200 mm. However, since the glass particles actually flow along the taper to the outside, the inside of the portion (600 mm) that should be the effective portion (in this case) Can be seen to be tapered (50 mm at both ends).

Example 1
The same starting rod and glass fine particle volume device as those used in Comparative Example 1 were used, and the reciprocating movement was the pattern shown in FIG. 1. The starting rod 1 was moved 40 mm downward, then moved 20 mm upward, and the return position of the reciprocating movement was reached. Moved downward by 20 mm. After the folding position has moved down by the burner interval, the downward moving distance remains 40 mm, the upward moving distance is set to 60 mm, and the folding position is moved upward by 20 mm to the initial position. One set was set until the return, and 200 sets were repeated. The other conditions were the same as those in Comparative Example 1, and glass fine particles were deposited. The obtained glass fine particle deposit (porous glass base material) had a total length of 900 mm, an outer diameter of 240 mm, an effective portion length of 500 mm, and a tapered portion formed at both ends, each having a length of 200 mm. The length of the effective portion is not changed as compared with Comparative Example 1, but the length of the ineffective portion (tapered portion) can be shortened by 100 mm.

(Example 2)
Glass particulates were deposited with a burner spacing of 260 mm under the same conditions as in Example 1 so that a glass particulate deposit having substantially the same length as Comparative Example 1 was obtained. In the same manner as in Example 1, the starting rod 1 was moved downward by 40 mm and then moved upward by 20 mm so that the return position of the reciprocating movement was moved downward by 20 mm. After the folding position has moved down by the burner interval, the downward moving distance remains 40 mm, the upward moving distance is set to 60 mm, and the folding position is moved upward by 20 mm to the initial position. The set until returning was one set, and 200 sets were repeated. The obtained glass fine particle deposit had a total length of 1140 mm, the lengths of the taper portions at both ends were 200 mm as in Example 1, and the length of the effective portion was 740 mm. It can be seen that the length of the effective portion can be increased by the method of the present invention by adjusting the burner interval so that the same number of burners and the same length of glass fine particle deposits can be obtained.

(Example 3)
The travel distance of the return position is Amm, and the reciprocation of the forward path (B + 1) × A and the return path B × A is repeated. After the return position moves by the burner interval, the forward path (B + 1) × A and the return path (B + 2) × A are obtained. The folding position is moved in the opposite direction, and a series of reciprocating movements until the folding position returns to the first position is set as one set, and the glass particles are deposited while repeating this. The average round-trip distance D at this time is D = 2 × (B + 1) × A mm (B = 1, 2, 3,...). A = 20 mm, other conditions (burner spacing, starting rod diameter, etc.) are the same as in Example 1, and a porous glass base material having a base material outer diameter of 240 mm is prepared. The relationship between the change in B and the length of the ineffective portion at this time is as follows. That is, when B = 1, 2, 3, 4, 5, 6, 7, 8, 9, the average reciprocating distance is D = 80, 120, 160, 200, 240, 280, 320, 360, 400 mm. In this case, the lengths of the ineffective portions are 200, 202, 207, 205, 210, 238, 262, 278, and 300 mm. This situation is shown in FIG.
Here, B = 9 and D = 400 indicate the same case as in the prior art, and are the points where the ineffective portion length becomes the shortest in the prior art. In any of the ranges B = 1 to 8 smaller than B = 9, a shorter ineffective portion than the shortest ineffective portion length of the prior art is realized, and in a more preferable range, it converges to about 200 mm (at this time D ≦ 240).

(Example 4)
The travel distance of the return position is Amm, and the reciprocation of the forward path (B + 1) × A and the return path B × A is repeated. After the return position moves to a position shorter than the burner interval by A, the burner is the first in the next movement A series of reciprocating movements returning to the position of (1) is taken as one set, and glass particles are deposited while repeating this. The average round-trip distance D at this time is D = 2 × (B + 1) × A mm (B = 1, 2, 3,...). A = 20 mm, other conditions (burner spacing, starting rod diameter, etc.) are the same as in Example 1, and a porous glass base material having a base material outer diameter of 240 mm is prepared. The relationship between the change in B and the length of the ineffective portion at this time is as follows. That is, when B = 1, 2, 3, 4, 5, 6, 7, 8, 9, the average reciprocating distance is D = 80, 120, 160, 200, 240, 280, 320, 360, 400 mm. The length of the ineffective portion at this time is 195, 199, 202, 206, 207, 223, 245, 260, 280 mm. This situation is shown in FIG.
The effect of reducing the ineffective portion is greater than that of Example 3 because the principle taper length is shorter by A mm for the same average moving distance. In a more preferable range, it converges to about 200 mm (D ≦ 240 at this time).

  According to the present invention, it is possible to reduce the taper portion formed at the end of the glass fine particle deposit without increasing the number of burners. In addition, the weight of the glass particulate deposit can be easily adjusted.

Explanatory drawing which shows an example of the condition of the relative movement of the starting rod and burner in the method of this invention. Explanatory drawing which shows another example of the condition of the relative movement of the starting rod and burner in the method of this invention. Explanatory drawing which shows another example of the condition of the relative movement of the starting rod and burner in the method of this invention. Explanatory drawing which shows another example of the condition of the relative movement of the starting rod and burner in the method of this invention. 10 is a graph showing the relationship between the average reciprocal movement distance and the ineffective portion length in Example 3. 10 is a graph showing the relationship between the average reciprocal movement distance and the ineffective portion length in Example 4. Explanatory drawing which shows the outline | summary of glass particulate deposit body manufacture by deposition of glass particulates. Explanatory drawing which shows one example of the condition of the relative movement of the starting rod and burner by the conventional method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Starting rod 2 Outer burner 3 Second burner 4 Container 5 Exhaust port 6 Glass particulate deposit 7 Burner

Claims (6)

  A plurality of glass particle synthesis burners are arranged at equal intervals so as to face the rotating starting rod, and the return position of the return path from the return path is set to the initial position relatively in parallel with the starting rod and the glass particle synthesis burner. The reciprocating movement is performed so as not to exceed, the return position of the return path from the forward path of the reciprocating movement is moved in a certain direction, and when the return position of the return path from the forward path is moved to a predetermined position, the burner is moved in the reverse direction. In the method of manufacturing a porous glass base material by setting the operations until returning to the initial position as one set and sequentially depositing the glass fine particles synthesized by the burner on the surface of the starting rod by sequentially repeating this operation. B + 1) × A, reciprocating movement of return path B × A is repeated (A: one-time movement distance of the folding position, B: natural number (1, 2, 3,...)), The folding. A series of reciprocating motions in which the position moves to the predetermined position and then returns to the first position in the next movement is one set, and one set of average reciprocating movement distance D = 2 × (B + 1) × A is the burner interval. Porous glass, wherein the number of deposited layers in the stationary part is set to be uniform in the length direction when each burner in one set returns to the initial position. A manufacturing method of a base material.   A plurality of glass particle synthesis burners are arranged at equal intervals so as to face the rotating starting rod, and the return position of the return path from the return path is set to the initial position relatively in parallel with the starting rod and the glass particle synthesis burner. The reciprocating movement is performed so as not to exceed, the return position of the return path from the forward path of the reciprocating movement is moved in a certain direction, and when the return position of the return path from the forward path is moved to a predetermined position, the burner is moved in the reverse direction. In the method for producing a porous glass base material by setting the operations until returning to the initial position as one set and sequentially depositing the glass fine particles synthesized by the burner on the surface of the starting rod by sequentially repeating this operation. It is moved to the predetermined position by the movement, and thereafter, the reciprocating motion of the return path (B + 1) × A and the forward path B × A is repeated (A: one movement distance of the folding position, B: Natural number (1, 2, 3,...), A series of reciprocating motions returning to the first position is one set, and one set of average reciprocating distance D = 2 × (B + 1) × A is burner. It is less than twice the interval, and when each burner in one set returns to the initial position, the number of deposited layers in the stationary part is set to be uniform in the length direction. Manufacturing method of glass base material.   The moving range of the return position of the return path from the forward path of the reciprocating movement is shorter than the burner interval by n times (n is an integer of 1 to 3) by the minimum movement distance of the return position in one set. A method for producing the porous glass preform according to 1 or 2.   4. The method according to claim 1, wherein a moving distance of one turn from the forward path of the reciprocating movement to the return path in one set is a length of (m + 1) times the burner interval (m is a natural number). A method for producing a porous glass base material according to claim 1.   The distance of one reciprocating movement from the return path of the reciprocating motion in the one set to the return path is Amm, the average reciprocating distance of one set is Dmm, A is in the range of 5 to 60 mm, and D is 4 It exists in the range of * A <= D <= 240, The manufacturing method of the porous glass base material of Claim 4 characterized by the above-mentioned.   Based on the relationship between the speed of reciprocating motion and the weight of glass particles deposited before the end of the deposition of glass particles, the reciprocating speed at which the target glass particle deposition amount can be achieved at the end of the glass particle deposition is determined. The porous glass base material according to any one of claims 1 to 5, wherein a target deposition amount can be achieved at the end of the glass particulate deposition by depositing glass particulates at Production method.

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