JP7464429B2 - Glass base material manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a glass base material.

Patent Document 1 discloses a method of heating a rotating glass preform (optical fiber preform) with a burner and gripping and correcting the bent portion of the glass preform. The burner is configured to be movable along the longitudinal direction of the glass preform, so that the bend can be corrected along the entire length of the glass preform.

Japanese Patent Application Laid-Open No. 4-331735

Patent Document 1 does not mention moving the burner in the longitudinal direction while emitting a flame. In other words, it is considered that the burner is fixed to the glass base material while the glass base material is being heated. After extensive research, the inventors of the present application found that if the glass base material is heated with the burner fixed, the surface temperature of the glass base material increases for a long period of time, causing the surface of the glass base material to be chipped.

The present invention was made in consideration of these circumstances, and aims to suppress chipping of the surface of the glass base material when correcting bending of the glass base material.

In order to solve the above problem, a method for manufacturing a glass base material according to one aspect of the present invention places a burner at a position away from the starting point of the bending of the glass base material in the longitudinal direction, emits a flame from the burner toward the rotating glass base material, and moves the burner toward the starting point while the contact portion of a correction unit is in contact with the glass base material.

According to the above aspect of the present invention, it is possible to suppress chipping of the surface of the glass base material when correcting the bending of the glass base material.

1A to 1C are diagrams illustrating how a bend in a glass base material is corrected using the correction device according to the present embodiment. FIG. 2 is a diagram illustrating a process following FIG. 1 . 1 is a diagram showing the outer diameter of the glass base material after the bending of the glass base material is corrected under the conditions of Comparative Example 1. FIG. FIG. 13 is a diagram showing the outer diameter of the glass base material after the bending of the glass base material is corrected under the conditions of Example 1.

Hereinafter, the method for producing a glass base material according to the present embodiment will be described with reference to the drawings.
In this embodiment, the "glass preform" includes a starting material and an optical fiber preform.
The starting member is a glass rod that will be the center of the optical fiber preform. For example, in soot methods such as the Vapor-phase Axial Deposition (VAD) method and the Outside Vapor Deposition (OVD) method, a soot of glass particles is deposited around the starting preform to obtain an optical fiber preform. In addition, the optical fiber preform is subjected to a sintering process, a dehydration process, and the like, and then the optical fiber preform is drawn to obtain an optical fiber.

To stabilize the quality of the optical fiber, it is preferable that the optical fiber preform has as little bending as possible. Also, to minimize bending of the optical fiber preform, it is preferable that the starting member has as little bending as possible. In other words, to stabilize the quality of the optical fiber, it is required that the starting preform or optical fiber preform has as little bending as possible and that there is also little variation in the outer diameter in the longitudinal direction. Therefore, in this embodiment, a method is provided for correcting bending of the starting member or optical fiber preform while suppressing the variation in the outer diameter. Hereinafter, the starting preform and optical fiber preform are collectively referred to as "glass preform M."

As shown in FIG. 1, in this embodiment, a correction device 1 is used to correct bending of a glass base material M. The correction device 1 includes a rotating chuck 2, a burner 3, a rail 4, a correction unit 5, and a control unit 6.

(Direction definition)
In this embodiment, the longitudinal direction of the glass base material M is simply referred to as the longitudinal direction, and is represented by the X-axis in Fig. 1. The side of the rotating chuck 2 on the X-axis is referred to as the -X side, and the opposite side is referred to as the +X side. The burner 3 is located on the +X side of the rotating chuck 2, and the correction unit 5 is located on the +X side of the burner 3.
The longitudinal direction (X-axis) may be horizontal or vertical, or may be inclined with respect to the horizontal and vertical directions.

The rotating chuck 2 is configured to be able to grip an end of the glass base material M and rotate it.
The burner 3 emits a flame toward the glass base material M and is configured to be movable in the longitudinal direction relative to the glass base material M. The number of burners 3 may be one or two or more. When two or more burners 3 are used, it is preferable that the burners 3 are arranged at the same positions in the longitudinal direction and heat the same portion of the glass base material M in the longitudinal direction.

The correction unit 5 is configured to be movable in the longitudinal direction relative to the glass base material M. The correction unit 5 has a contact portion 5a, a biasing member 5b, a support portion 5c, and a load meter 5d. The support portion 5c supports the biasing member 5b and the contact portion 5a. The biasing member 5b is located between the contact portion 5a and the support portion 5c, and biases the contact portion 5a toward the glass base material M. A coil spring or the like can be used as the biasing member 5b. The contact portion 5a abuts against the glass base material M while being biased by the biasing member 5b.

The load meter 5d is configured to measure the magnitude of the biasing force of the biasing member 5b toward the glass base material M of the contact portion 5a. For example, a load cell or the like can be used as the load meter 5d. The load meter 5d may be sandwiched between the biasing member 5b and the support portion 5c as shown in FIG. 1, or may be sandwiched between the contact portion 5a and the biasing member 5b. Note that the specific configuration and arrangement of the load meter 5d may be changed as appropriate as long as it can measure the biasing force.

If the glass base material M is bent, when the correction unit 5 is moved in the longitudinal direction relative to the glass base material M while the contact portion 5a is in contact with the glass base material M, the measurement result by the load meter 5d changes according to the magnitude of the bend. Therefore, by referring to the position of the correction unit 5 in the longitudinal direction and the measurement result by the load meter 5d, the position and magnitude of the bend in the glass base material M can be ascertained.

The rail 4 extends along the longitudinal direction and guides the burner 3 when the burner 3 moves longitudinally relative to the glass base material M. The rail 4 may also guide the correction unit 5 when the correction unit 5 moves longitudinally relative to the glass base material M. Alternatively, the correction unit 5 may be guided by a member other than the rail 4.

The control unit 6 is electrically connected to the correction unit 5 and is configured to collect the measurement results of the biasing force by the load meter 5d in correspondence with the position of the correction unit 5 in the longitudinal direction. The control unit 6 may also control the positions of the correction unit 5 and the burner 3 in the longitudinal direction. The control unit 6 may be, for example, an integrated circuit such as a microcontroller, an IC (Integrated Circuit), an LSI (Large-scale Integrated Circuit), or an ASIC (Application Specific Integrated Circuit).

Next, we will explain a method for correcting a bend in glass base material M using correction device 1, and a manufacturing method for glass base material M that includes this correction method.

First, a curved glass base material M is prepared (preparation step).
Next, the position and magnitude of the bend of the glass base material M are measured (measurement step). Specifically, the glass base material M is attached to the rotating chuck 2, rotated, and the correction unit 5 is moved in the longitudinal direction while the contact portion 5a is brought into contact with the glass base material M. The control unit 6 calculates the magnitude of the bend and the position of the starting point of the bend based on the measurement result of the biasing force associated with the position of the correction unit 5 in the longitudinal direction. In FIG. 1, the symbol Xa indicates the position of the starting point of the bend on the -X side of the glass base material M in the longitudinal direction. Hereinafter, the starting point of the bend on the -X side is simply referred to as "starting point Xa". A single glass base material M may have multiple bends (i.e., multiple starting points Xa).

In the measurement step, the glass base material M may be rotated by the rotating chuck 2 to measure the runout of the glass base material M.
In the measurement process, in order to measure the bending of the glass base material M before it is heated and softened, the burner 3 is turned off or ignited with a weak flame, and the glass base material M is not actively heated.

Next, the burner 3 and the correction unit 5 are arranged in the longitudinal direction with the starting point Xa between them (arrangement process). In FIG. 1, the burner 3 is positioned at point Xb on the -X side of the starting point Xa, and the correction unit 5 is positioned on the +X side of the starting point Xa. Hereinafter, the position in the longitudinal direction where the burner 3 is arranged in the arrangement process is referred to as the starting point Xb.

Next, with the burner 3 positioned at the starting point Xb, active heating of the glass base material M is started (heating start process). Specifically, if the burner 3 was turned off in the measurement process, the burner 3 is ignited. Alternatively, if the heat of the burner 3 was weakened in the measurement process, the heat is increased so as to actively heat the glass base material M. As the burner 3 heats the glass base material M at the starting point Xb, the temperature of the glass base material M at the starting point Xa gradually increases due to thermal conduction inside the glass base material M. After the heating start process, the movement of the burner 3 may not be started immediately, and the glass base material M may be heated at the starting point Xb for a predetermined time (preheating process).

Next, the glass base material M is heated, and while the contact portion 5a is in contact with the glass base material M and the glass base material M is rotating, the burner 3 is moved from the starting point Xb to the starting point Xa (correction process). While the burner 3 heats the glass base material M between the starting point Xb and the starting point Xa, the temperature of the glass base material M at the starting point Xa increases due to thermal conduction. The glass base material M softens at the starting point Xa due to the increase in temperature, so the glass base material M biased by the contact portion 5a deforms around the starting point Xa. This deformation is in the direction of returning the shape of the glass base material M to a straight line. Therefore, the bending of the glass base material M is corrected.

If the glass base material M has multiple bends, the above-mentioned correction process is performed for each bend. It is preferable to move the burner 3 only toward one side in the longitudinal direction while one correction process (a process for correcting one bend) is being performed. For example, in FIG. 1 and FIG. 2, the burner 3 is moved only toward the +X side from the starting point Xb while the burner 3 is heating the glass base material M. In other words, after the burner 3 reaches the starting point Xa, the burner 3 is not moved toward the -X side while the glass base material M is still heated. In this way, by not moving the burner 3 back and forth while heating the glass base material M, it is possible to prevent the surface temperature of the glass base material M from rising excessively.

After the curvature of the glass base material M has been corrected, an inspection of the outer diameter and linearity may be performed as necessary. This inspection may be performed using the correction device 1, as in the measurement process described above. Alternatively, inspection after the curvature of the glass base material M has been corrected may be performed by measurement using a three-dimensional measuring machine, measurement using a laser outer diameter measuring device, measurement using an image, etc.

As described above, in the manufacturing method of the glass base material M of this embodiment, the burner 3 is placed at a position (starting point Xb) away from the starting point Xa of the bending of the glass base material M in the longitudinal direction, a flame is emitted from the burner 3 toward the rotating glass base material M, and the burner 3 is moved toward the starting point Xa while the abutting portion 5a of the correction unit 5 is abutted against the glass base material M. In this way, heating of the glass base material M is started from a position away from the starting point Xa in the longitudinal direction, and the temperature of the starting point Xa is increased by thermal conduction. As a result, compared to the case where only the starting point Xa of the bending of the glass base material M is heated, it is possible to suppress chipping of the glass base material M due to an excessive rise in the surface temperature of the glass base material M at the starting point Xa.

The manufacturing method of this embodiment also includes a measurement process in which the contact portion 5a is moved along the longitudinal direction while measuring the force that biases the contact portion 5a toward the glass base material M. This makes it possible to use the correction device 1 to grasp the position of the starting point Xa of the bending of the glass base material M and the magnitude of the bending.

In addition, while correcting one bend in the glass base material M, it is preferable to move the burner 3 only toward one side in the longitudinal direction. This makes it possible to further suppress the rise in the surface temperature of the glass base material M compared to, for example, the case in which the burner 3 is moved back and forth in the longitudinal direction while the glass base material M is heated.

The above embodiment will be explained below using specific examples. Note that the present invention is not limited to the following examples.

Two glass preforms M with similar curvatures were prepared, and the curvatures were corrected under the conditions of Comparative Example 1 and Example 1 shown in Table 1 below. Each glass preform M had an outer diameter of 80 mm and had four bends spaced apart in the longitudinal direction.

In Comparative Example 1, the glass base material M was heated for 8 minutes at each of the four bend starting points Xa with the burner 3 fixed. In addition, the bends were corrected by abutting the contact portion 5a of the correction unit 5 at a position away from the starting points Xa.

In Example 1, starting points Xb were set at positions 91 mm away from the starting points Xa of the four bends in the longitudinal direction. In other words, four starting points Xb were set. At the starting points Xb, the burner 3 was ignited while remaining stationary and preheated for three minutes, after which the burner 3 was moved toward the starting point Xa corresponding to the starting point Xb while the contact portion 5a of the correction unit 5 was brought into contact with the starting point Xa to correct the bend. The moving speed of the burner 3 was 13 mm/min, and the moving time was 7 minutes. In other words, the total heating time was 10 minutes. The same procedure was carried out for the four bends.

The outer diameter of the glass base material M after the bending was corrected is shown in FIG. 3 (Comparative Example 1) and FIG. 4 (Example 1).
3, in Comparative Example 1, chipping occurred on the surface of the glass base material M, centered around four points Xa1, Xa2, Xa3, and Xa4 in the longitudinal direction. Each of the points Xa1 to Xa4 is the position of the starting point of each of the four bends, and is the position heated by the burner 3. The amount of chipping of the glass base material M at these four points was within the range of 0.3 to 0.5 mm.
4, in Example 1, the amount of chipping of the glass base material M could be significantly reduced compared to Comparative Example 1. The amount of chipping was 0.05 mm or less in all four locations.

Let us consider the difference between Comparative Example 1 and Example 1. In Comparative Example 1, the burner 3 is fixed, so in order to heat the inside of the glass base material M to a temperature at which the bending can be corrected, it is necessary to continue heating the same point on the surface of the glass base material M. This causes the surface temperature of the glass base material M to remain high, resulting in a large amount of chipping. In contrast, in Example 1, heating begins when the burner 3 is away from the starting point Xa, and the inside of the glass base material M at the starting point Xa is heated by thermal conduction while the burner 3 is moved. This prevents the surface temperature of the glass base material M at the starting point Xa from remaining high, making it possible to reduce the amount of chipping.

The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

For example, in the above embodiment, the position of the bending start point Xa of the glass base material M and the magnitude of the bending are determined by a measurement process using the correction device 1. However, it is possible to determine the position of the bending start point Xa of the glass base material M and the magnitude of the bending by, for example, performing measurements in advance using a coordinate measuring machine, a laser outer diameter measuring device, or an image measurement. For this reason, the measurement process using the correction device 1 is not essential in the manufacturing method of the above embodiment.

In addition, in the above embodiment, in the placement process, the burner 3 and the correction unit 5 are placed in the longitudinal direction so as to sandwich the starting point Xa of the glass base material M between them. However, for example, in FIG. 1, the burner 3 may be placed on the +X side of the starting point Xa, and in the correction process, the burner 3 may be moved toward the -X side. In other words, the starting point Xa, the starting point Xb, and the correction unit 5 may be arranged in this order in the longitudinal direction. In this case, the same effect as in the above embodiment can be obtained.

In addition, in the above embodiment, while correcting one bend in the glass base material M, the burner 3 is moved only toward one side in the longitudinal direction. However, for example, the burner 3 may be moved back and forth in the longitudinal direction centered on the starting point Xa. In this case, too, it is possible to suppress the increase in the surface temperature of the glass base material M and reduce chipping, compared to a configuration in which the burner 3 is heated without moving from the starting point Xa.

In addition, the components in the above-described embodiments may be replaced with well-known components as appropriate without departing from the spirit of the present invention, and the above-described embodiments and variations may be combined as appropriate.

1...Correction device 3...Burner 5...Correction unit 5a...Contact part M...Glass base material

Claims (2)

The burner is disposed at a position away from the starting point of the bending of the glass base material in the longitudinal direction;
A method for manufacturing a glass base material, comprising: emitting a flame from the burner toward the rotating glass base material to heat the glass base material; and moving the burner toward the starting point at a temperature at which the glass base material softens while a contact portion of a correction unit is in contact with the glass base material,
A method for manufacturing a glass base material, comprising: a step of moving the contact portion along the longitudinal direction while measuring a biasing force that biases the contact portion toward the glass base material. The method for manufacturing a glass base material according to claim 1, wherein the burner is moved only toward one side in the longitudinal direction while correcting one bend in the glass base material.

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