JP4455490B2 - Method and apparatus for producing quartz glass tube - Google Patents

Description

  In an optical communication system, for the purpose of further increasing the speed and capacity of optical communication, an increase in wavelength multiplicity, a higher bit rate, an expansion of a use wavelength region, and the like are being promoted. Along with these demands, there has been a demand for higher precision optical fibers. Usually, an optical fiber is manufactured by drawing an optical fiber preform called a preform and reducing the diameter to a predetermined size. Therefore, the quality of the optical fiber basically depends on the quality of the preform, and extremely high quality is required for manufacturing the preform.

  Preforms are mainly manufactured by MCVD (Modified Chemical Vapor Deposition Method), VAD (Vapor Phase Axial Deposition Method), OVD (Outside Vapor Phase Deposition Method), etc. It is common to be done.

  For example, in the case of the MCVD method, first, a quartz glass tube called a substrate tube is used, and a portion corresponding to the core of the optical fiber is internally attached by the MCVD method. It is inserted into a quartz glass tube called, and the preform is manufactured by integrating the core rod and jacket tube by heating. The technology for integrating the core rod and the jacket tube is not limited to the MCVD method, and it is also possible to manufacture a preform by integrating the core rod manufactured by the VAD method or the OVD method with the jacket tube.

  Since the above-mentioned substrate tube is used for the production of a core rod, it is easy to influence the characteristics of the optical fiber, and a tube having an extremely excellent thickness deviation rate and non-circularity is required. Also, in the jacket tube, if the thickness deviation ratio is large, the center axis of the outer diameter is shifted from the center axis of the inner diameter, and if the variation of the inner diameter is large, a gap is generated between the core rod. In either case, it becomes a factor of deteriorating the characteristics of the optical fiber. Accordingly, extremely high dimensional accuracy is required for the quartz glass tube used in manufacturing the preform.

  In Patent Document 1, the tip of the quartz glass rod is heated and softened while rotating the cylindrical quartz glass rod about its long axis, and the tip of the drilling plug is sharpened at the center of the tip surface of the quartz glass rod. A method of manufacturing a quartz glass tube is disclosed which engages the ends and rotates with respect to the drilling plug.

  In Patent Document 2, when a quartz glass material is heated and softened by a heating means and a plug is penetrated relatively in the axial direction from the end of the quartz glass material, its penetration pressure is detected, and this detection signal is detected. A method for manufacturing a glass pipe for optical fiber is disclosed in which the heating means is controlled so that the penetration pressure becomes constant by feeding back the above.

Patent No. 2798465 JP 2003-221247 A

  In the production method described in Patent Document 1, depending on the concentration of OH groups, Cl groups, and the like of the quartz glass rod and the distribution state thereof, the variation in the softening point (that is, the viscosity) in each part of the quartz glass rod increases. It becomes difficult to perforate the entire quartz glass rod while keeping the viscosity constant. For this reason, the dimensional accuracy of the quartz glass tube manufactured by this method is not good.

  The manufacturing method described in Patent Document 2 is superior in dimensional accuracy of the quartz glass tube to the manufacturing method described in Patent Document 1 in that variation in viscosity of the silica glass rod is taken into consideration. However, the temperature of the quartz glass material is highest at the center position in the heater longitudinal direction, but the plug is disposed downstream of the position. What can be grasped by the penetration pressure is the heating state in contact with the plug of the quartz glass rod. Even if the heater temperature is adjusted according to the heating state at this time, a control delay occurs and the penetration pressure is kept constant. It is not easy to hold on.

  The present invention has been made to solve such a problem. Before the press-fitting by the plug is started, that is, before the press-fitting load is detected, the viscosity of the quartz glass is grasped and press-fitted. It is an object of the present invention to provide a method and apparatus for manufacturing a quartz glass tube that can reduce the variation in load and manufacture the quartz glass tube with higher dimensional accuracy.

  The present inventors conducted the following experiment in order to solve the above problems.

  In other words, high-purity SiCl4 is hydrolyzed in an oxyhydrogen flame, and the porous body on which silica fine particles are deposited and grown is sintered and transparentized to form a quartz glass ingot. This synthetic quartz glass ingot is used as a starting material. A quartz glass rod having an outer diameter of 150 mm and a length of 1000 mm was produced. Using this quartz glass rod, the quartz glass material 2 is press-fitted into the space formed by the die 5 and the plug 6 using a quartz glass tube manufacturing apparatus 1-1 shown in FIG. A quartz glass tube 8 having an inner diameter of 92 mm was produced.

  In this experiment, the heating temperature is 2300 ° C., the rotational speed of the inlet side chuck 4-1 is 5 rpm, the rotational speed of the outlet side chuck 4-2 is 20 rpm, the feeding speed of the quartz glass material 2 is 17.15 mm / min, The drawing speed of the quartz glass tube 8 after the press-fitting was set to 22.52 mm / min.

  At this time, the press-fitting load of the plug and the torque behavior of the quartz glass material were measured, and the results were plotted in FIG. The torque of the quartz glass material was calculated from the amount of electric power in the rotary motor 7-2 of the exit side chuck 4-2.

  As shown in FIG. 3, the press-fitting load (solid line in the figure) of the plug rises rapidly immediately after the quartz glass material is press-fitted, and then decreases once, but constantly fluctuates, and the total amount of the quartz glass material is changed. Viscosity varies irregularly in the region. On the other hand, the torque (broken line in the figure) is detected from the start of twisting and becomes a curve having a tendency similar to that at an earlier stage than the press-fitting load (solid line in the figure) of the plug.

  In other words, since this experiment was conducted under the condition of a constant heating temperature, both the torque and the plug press-fit load increase as the viscosity increases due to material variations. This is an earlier stage than the position where the load increases or decreases.

  Thus, the present inventors have found that if the torque of the quartz glass material is detected, the press-fitting load of the plug can be predicted at an early stage, and the present invention has been completed.

  The gist of the present invention is a quartz glass tube manufacturing method shown in the following (1) and a quartz glass tube manufacturing apparatus shown in (2).

  (1) In a method of manufacturing a quartz glass tube by heating a quartz glass material and press-fitting it into a space formed between a die and a plug in a state where the leading end and the trailing end are rotated at different rotational speeds. The quartz glass is characterized by detecting the torque generated by rotating the front and rear ends of the quartz glass material at different rotational speeds and controlling the heating temperature of the quartz glass material so that the detected torque becomes constant. Method for manufacturing a tube.

  In addition, in the manufacturing method of the quartz glass tube as described in said (1), it is desirable that the rotational speed difference of the front-end | tip of a quartz glass raw material and a rear end is 5 rpm or more. When a hollow quartz glass material is used as the quartz glass material, it is desirable to depressurize the hollow quartz glass material tube before press-fitting the plug. Furthermore, it is also desirable to depressurize the quartz glass tube after the plug is press-fitted.

  (2) A heater for heating the quartz glass material, a pair of chucks that can be moved at different speeds while giving different rotation speeds to the quartz glass material on the side to be fed to the heating area by the heater and the drawing side, and the outer diameter of the quartz glass tube A die for forming a plug, a plug for forming a through-hole in the central portion of the quartz glass material in the axial direction, torque detecting means for detecting torque generated in the quartz glass material, and the detected torque to be constant And a heating control means for controlling a heating temperature of the heater.

  In the quartz glass tube manufacturing apparatus described in (2) above, the torque detecting means has a mechanism for detecting the power consumption of the rotating motor of the chuck and calculating the torque from the detected power consumption value. Is desirable. Further, it is desirable to provide a material decompressing means for decompressing the inside of the hollow quartz glass material tube before press-fitting the plug and / or a tube decompressing means for decompressing the inside of the quartz glass tube after the plug is press-fitted.

  According to the present invention, since the quartz glass material can be pressed into the space formed between the die and the plug under the condition that the viscosity of the quartz glass material is constant, a quartz glass tube having high dimensional accuracy can be manufactured.

  FIG. 1 is a schematic view illustrating a quartz glass tube manufacturing apparatus according to the present invention.

  As shown in FIG. 1, for example, a quartz glass tube manufacturing apparatus 1-1 of the present invention has a heater 3 for heating a quartz glass material 2, and different rotation speeds on the side fed to the heating area by the heater 3 and the drawing side. A pair of chucks 4-1 and 4-2 that can be moved at different speeds while being applied to the quartz glass material, a die 5 for forming the outer diameter of the quartz glass tube 8, and an axial center portion of the quartz glass material 2 A plug 6 for forming a through hole, and torque detecting means 8-1 and 8-2 for detecting electrical signals of chuck rotating motors 7-1 and 7-2 for detecting torque generated in the quartz glass material 2; The heating control means 9 controls the heating temperature of the heater 3 so that the detected torque is constant.

  In this manufacturing apparatus 1-1, a quartz glass material with a dummy material 10-1 connected in advance to one end is prepared in advance, and the connected dummy material 10-1 is gripped by an entrance side chuck 4-1. On the other hand, the dummy material 10-2 is held by the exit side chuck 4-2. In this state, the quartz glass material 2 is moved to the right in FIG. 1 while being rotated by the entrance side chuck 4-1, and is heated and softened by the heater 3, while the dummy material 10-2 is the exit side chuck. While being rotated by 4-2, it moves to the left in FIG.

  Then, in a state where the right end portion of the quartz glass material 2 and the left end portion of the dummy material 10-2 are sufficiently heated and softened, both end portions are brought close to each other and welded. Thereafter, the quartz glass material 2 is heated by the inlet side chuck 4-1 and the outlet side chuck 4-2 via the inlet side dummy material 10-1 and the outlet side dummy 10-2, while being heated. Is heated to a predetermined temperature and is press-fitted into a space formed by the die 5 and the plug 6.

  In the method for manufacturing a quartz glass tube of the present invention, the torque generated by rotating the front end and the rear end of the quartz glass material 2 at different rotational speeds is detected, and the quartz glass material 2 is set so that the detected torque becomes constant. The most important feature is to control the heating temperature. The reason will be described in detail below.

  In other words, there is a temperature distribution in the heating furnace, and the structure is generally such that the maximum temperature is reached near the longitudinal center of the furnace. And since the die is arranged near the exit side of the heating furnace and the plug is arranged in the portion where the inner diameter of the die is the smallest, the quartz glass material is formed between the die and the plug after passing through the region of the highest temperature. Will be press-fitted into the space.

  At this time, if the quartz glass material is twisted by rotating the tip and the rear end of the quartz glass material at different rotational speeds, the quartz glass material inevitably has the highest temperature position at which the viscosity decreases, that is, the quartz glass material It will be twisted at a position upstream from the press-fitting position. Therefore, the electric power value supplied to the rotary motors 7-1 and 7-2 of the entrance side chuck 4-1 and / or the exit side chuck 4-2 is detected and converted to torque. Can be used to grasp the viscosity at the position where the temperature reaches the maximum temperature.

  FIG. 2 is a schematic diagram showing a region for grasping the viscosity of the quartz glass tube. A in FIG. 2 is a region of viscosity that can be grasped by the method described in Patent Document 2 in which a press-fitting load when a quartz glass material is press-fitted into a plug is detected. That is, in the method described in Patent Document 2, the viscosity at the position where the quartz glass material and the plug are in contact with each other is grasped. However, since the viscosity of quartz glass material varies greatly depending on the concentration distribution state of OH groups, Cl groups, etc., it is difficult to perform press-fitting with a constant viscosity simply by controlling the press-fitting load. The dimensional accuracy is reduced.

  On the other hand, in the method of the present invention, the torque at the position B in FIG. 2, that is, the position where the quartz glass material is twisted can be detected, and the viscosity of the quartz glass material at that position can be grasped. It is. Thus, in the method of the present invention, the viscosity of the quartz glass material is grasped at an earlier stage than the detection of the press-fitting load of the plug, and if the heating temperature is controlled based on this, the problem of control delay is greatly improved. can do.

  That is, the torque of the quartz glass material 2 is detected by the torque detection means 8-1 and 8-2 from the electric power value of one or both of the rotary motors 7-1 and 7-2 of the entrance side chuck 4-1 and the exit side chuck 4-2. This is transmitted to the heating control means 9 and the heating temperature corresponding to the torque of the quartz glass material 2 is controlled, so that a quartz glass tube having high dimensional accuracy can be obtained.

  In FIG. 1, a case where hollow quartz glass (quartz glass tube) is used as the quartz glass material is illustrated, but a quartz glass rod can also be used as the quartz glass material. Accordingly, it is preferable to use a dummy rod when a quartz glass rod is used as the quartz glass material, and a dummy cylinder when a quartz glass tube is used as the dummy material on the quartz glass material 2 delivery side.

  The plug may be fixed and held at the tip of the mandrel, but may be held in a rotatable state independently from the mandrel from the viewpoint of preventing inner surface flaws of the quartz glass tube. In addition, the die may be fixedly held in the heating furnace, but from the viewpoint of preventing the outer surface flaw of the quartz glass tube or the like, it may be held in a state that can be rotated independently from the heating furnace. Good.

  The rotational speed difference between the entrance side chuck and the exit side chuck may be small, but is preferably 5 rpm or more in order to accurately detect the viscous state. Further, when setting the rotational speed difference, either the input side chuck may be faster or the output side chuck may be faster. The traveling speed ratio of the entrance side chuck 4-1 and the exit side chuck 4-2 is such that the cross-sectional area of the quartz glass material 2 and the breaking of the quartz glass tube 8 having a predetermined cross-sectional shape formed by the die 5 and the plug 6 are as follows. The reciprocal of the area ratio may be set.

  The torque may be detected based on one or both of the power value of the input side chuck rotation motor and the power value of the output side chuck rotation motor.

  When the quartz glass material is a quartz glass rod, the quartz glass tube can be manufactured with higher accuracy by reducing the pressure inside the quartz glass tube after being press-fitted. For the same reason, when the quartz glass material is a quartz glass tube, it is desirable to depressurize either the inside of the quartz glass material before press-fitting or the inside of the press-fitted quartz glass tube, and depressurize both of them. Is more desirable. In particular, when processing is performed for the purpose of enlarging the inner diameter of a quartz glass tube, which is a quartz glass material, the dimensional accuracy is further improved by reducing the pressure inside the quartz glass tube after being press-fitted.

  As shown in FIG. 1, in order to reduce the pressure of the hollow quartz glass material 2, for example, a holder 11-1 for blocking the entry of outside air is installed at the end of the dummy material 10-1, and the inside of the hollow quartz glass material is evacuated. Exhaust can be performed by pump 12-1. In addition, the quartz glass tube 8 after the press-fitting is reduced in pressure, for example, by providing a small hole (not shown) that can ground the holder 11-2 similar to the above at the end of the dummy material 10-2 and exhaust the side of the plug 6. The mandrel 13 holding the plug 6 can be made hollow and exhausted by the vacuum pump 12-2 through the mandrel 13.

  Thus, when evacuating from the small hole provided on the side surface of the plug, the opening corresponding to the inner diameter of the target quartz glass tube is press-fitted continuously along the outer surface of the plug in the axial direction. The quartz glass tube can be manufactured. However, the pressure reduction of the quartz glass tube 8 after press-fitting may be performed by providing a small hole in the middle of the mandrel and exhausting from the small hole, or by providing a small hole in the holder and exhausting from the small hole. May be.

  Since the above-described decompression in the quartz glass material 2 or the quartz glass tube 8 is effective even if it is performed even a little, the internal pressure may be 100000 Pa or less. However, the effect becomes remarkable when the internal pressure of the quartz glass material is 70000 Pa or less and the internal pressure of the quartz glass tube is 50000 Pa. On the other hand, if the internal pressure of the quartz glass material is excessively reduced to less than 30000 Pa, the quartz glass material may be closed.If the internal pressure of the quartz glass tube is reduced to less than 1000 Pa, the gap between the opening and the outer surface of the plug may be reduced. Contact may become intense, the load on the plug will increase, the plug may be damaged, and the inner surface of the quartz glass tube may be damaged. Accordingly, it is more desirable that the internal pressure of the quartz glass material is 30000-70000 Pa and the internal pressure of the quartz glass tube is 1000-50000 Pa.

  The quartz glass material constituting the quartz glass material is not limited to synthetic quartz glass manufactured by the VAD method or the like, but can be applied to other quartz glass such as natural quartz glass using quartz powder as a raw material.

  As for the heating temperature of the quartz glass material, the softening point varies greatly depending on the OH group concentration and the Cl concentration of the quartz glass material. Therefore, an appropriate condition may be set according to the softening point. An example of the set temperature of the heating furnace is about 2000 to 2700 ° C. The heating atmosphere is not limited, but an inert atmosphere is desirable for preventing oxidation. Dies and plug materials that can be used in these temperature ranges include oxides of alumina oxide, metals such as tungsten and molybdenum, and graphite. Graphite is the most suitable in terms of strength and purity in the high temperature range. is there.

  High-purity SiCl4 is hydrolyzed in an oxyhydrogen flame to sinter and clarify the porous body on which silica fine particles are deposited and grown to form a quartz glass ingot. Using this synthetic quartz glass ingot as a starting material, quartz A quartz glass rod having an outer diameter of 150 mm and a length of 1000 mm as a glass material and a quartz glass tube having an outer diameter of 150 mm, an inner diameter of 66 mm and a length of 1200 mm were prepared. And the quartz glass tube was produced from these quartz glass materials by various methods.

(Comparative example)
Except for the point where the heating control means is not used and the point where the pressure is not reduced, the above-mentioned quartz glass rod is used in the same apparatus as the quartz glass tube manufacturing apparatus 1-1 shown in FIG. 1, using a die having an inner diameter of 160 mm and an outer diameter of 92 mm. A quartz glass tube 8 was manufactured by press-fitting into a space formed by a plug. In this experiment, the initial heating temperature is 2300 ° C, the rotation speed of both the inlet side chuck 4-1 and the outlet side chuck 4-2 is 5 rpm, the feeding speed of the quartz glass material 2 is 17.15 mm / min, and after press-fitting The extraction speed of the quartz glass tube 8 was set to 22.52 mm / min. At this time, the heating temperature was controlled in the range of 2220 to 2430 ° C. so as to keep the press-fitting load of the plug constant.

Example 1
Except that the quartz glass rod is not decompressed, an apparatus similar to the quartz glass tube manufacturing apparatus 1-1 shown in FIG. 1 is used to form a space formed by a die having an inner diameter of 160 mm and a plug having an outer diameter of 92 mm. The quartz glass tube 8 was manufactured by press-fitting. In this experiment, the initial heating temperature is 2300 ° C., the rotational speed of the inlet side chuck 4-1 is 5 rpm, the rotational speed of the outlet side chuck 4-2 is 20 rpm, and the feeding speed of the quartz glass material 2 is 17.15 mm / min, the drawing speed of the quartz glass tube 8 after press-fitting was set to 22.52 mm / min. At this time, the heating temperature was controlled in the range of 2230 to 2430 ° C. so as to keep the torque of the outlet chuck constant.

(Example 2)
The quartz glass tube 8 was manufactured by press-fitting the quartz glass tube into a space formed by a die having an inner diameter of 160 mm and a plug having an outer diameter of 92 mm using the quartz glass tube manufacturing apparatus 1-1 shown in FIG. . In this experiment, the initial heating temperature is 2300 ° C, the rotation speed of the inlet chuck 4-1 is 5 rpm, the rotation speed of the outlet chuck is 20 rpm, the feeding speed of the quartz glass material 2 is 21.26 mm / min, press-fitting The drawing speed of the later quartz glass tube 8 was set to 22.52 mm / min. In addition, the pressure inside the quartz glass tube after press-fitting was reduced to 2000 Pa so that the internal pressure of the quartz glass material was 50000 Pa. At this time, the heating temperature was controlled in the range of 2250 to 2450 ° C. so as to keep the torque of the outlet chuck constant.
(Note: Examples 2 and 4 were deleted.)

  For the quartz glass tubes manufactured according to the above comparative example and Examples 1 and 2, 10 measurement positions are selected at approximately equal intervals in the length direction, and 4 positions are equally spaced in the circumferential direction at each measurement position. The outer diameter was measured, the average value of the four points was taken as the “outer diameter”, and the average value of 10 points of the “outer diameter” was taken as the “average outer diameter”. In addition, at the same measurement position where the outer diameter was measured, the thickness was measured at eight locations at equal intervals in the circumferential direction with an ultrasonic thickness meter, and the average value of the eight points was defined as “thickness”. The average of 10 points of “wall thickness” was defined as “average wall thickness”. The inner diameter was determined from the difference between the above “thickness” and “outer diameter”, and the average of the 10 points was defined as the “average inner diameter”.

  Further, the difference between the maximum value and the minimum value of 10 “outer diameters” was calculated, and this was divided by the total length of the quartz glass tube to determine the outer diameter fluctuation (mm / m). Similarly, the difference between the maximum value and the minimum value of the “inner diameter” at 10 locations was determined, and this was divided by the total length of the quartz glass tube to determine the inner diameter variation (mm / m).

  Table 1 shows the manufacturing conditions of the quartz glass tube in the comparative example and Examples 1 and 2, and Table 2 shows the measurement results.

  As shown in Table 2, in Examples 1 and 2 in which the heating temperature was controlled by torque, the dimensional accuracy of the quartz glass tube was greatly improved as compared with the comparative example in which the heating temperature was controlled by the press-fitting load of the plug.

  According to the present invention, since the quartz glass material can be pressed into the space formed between the die and the plug under the condition that the viscosity of the quartz glass material is constant, a quartz glass tube having high dimensional accuracy can be manufactured.

Schematic diagram illustrating a quartz glass tube manufacturing apparatus according to the present invention. Schematic diagram showing the area for grasping the viscosity of quartz glass tubes Diagram showing plug press-fit load and torque fluctuation

Explanation of symbols

1-1. 1. Quartz glass tube manufacturing equipment 2. Quartz glass material heater
4-1, 4-2. Chuck 5. Dice 6. plug
7-1, 7-2. Rotating motor
8-1, 8-2. Torque detection means 9. Heating control means
10-1, 10-2. Dummy material
11-1, 11-2. holder
12-1, 12-2. Vacuum pump
13. Mandrel bar

Claims (8)

  In a method of manufacturing a quartz glass tube by heating a quartz glass material and press-fitting it into a space formed between a die and a plug in a state where the front end and the rear end thereof are rotated at different rotational speeds. Production of a quartz glass tube characterized by detecting the torque generated by rotating the leading and trailing ends of the material at different rotational speeds and controlling the heating temperature of the quartz glass material so that the detected torque is constant Method.   The method for producing a quartz glass tube according to claim 1, wherein a difference in rotational speed between the front and rear ends of the quartz glass material is 5 rpm or more.   The method for producing a quartz glass tube according to claim 1 or 2, wherein a hollow quartz glass material is used as the quartz glass material, and the inside of the tube of the hollow quartz glass material before press-fitting the plug is decompressed.   The method for producing a quartz glass tube according to any one of claims 1 to 3, wherein the inside of the quartz glass tube after press-fitting the plug is decompressed.   A heater that heats the quartz glass material, a pair of chucks that can be moved at different speeds while giving different rotation speeds to the quartz glass material on the side of feeding to the heating area by the heater and the drawing side, and the outer diameter of the quartz glass tube are formed A die for forming a through hole in the axial center of the quartz glass material, a torque detecting means for detecting torque generated in the quartz glass material, and a heater so that the detected torque is constant. An apparatus for producing a quartz glass tube, comprising: a heating control means for controlling a heating temperature.   6. The quartz glass tube manufacturing apparatus according to claim 5, wherein the torque detecting means has a mechanism for detecting power consumption of a rotating motor of the chuck and calculating torque from the detected power consumption value.   7. The apparatus for producing a quartz glass tube according to claim 5, further comprising a material decompression means for decompressing the inside of the hollow quartz glass material tube before the plug is press-fitted. The apparatus for producing a quartz glass tube according to any one of claims 5 to 7, further comprising tube decompression means for decompressing the inside of the quartz glass tube after the plug is press-fitted.

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