CA1101164A - Method and apparatus for producing fibers for optical transmission - Google Patents
Method and apparatus for producing fibers for optical transmissionInfo
- Publication number
- CA1101164A CA1101164A CA302,178A CA302178A CA1101164A CA 1101164 A CA1101164 A CA 1101164A CA 302178 A CA302178 A CA 302178A CA 1101164 A CA1101164 A CA 1101164A
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- CA
- Canada
- Prior art keywords
- fiber
- carbon
- furnace
- oven
- graphite
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
- C03B37/01—Manufacture of glass fibres or filaments
- C03B37/02—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor
- C03B37/025—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor from reheated softened tubes, rods, fibres or filaments, e.g. drawing fibres from preforms
- C03B37/029—Furnaces therefor
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2205/00—Fibre drawing or extruding details
- C03B2205/60—Optical fibre draw furnaces
- C03B2205/62—Heating means for drawing
- C03B2205/64—Induction furnaces, i.e. HF/RF coil, e.g. of the graphite or zirconia susceptor type
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P40/00—Technologies relating to the processing of minerals
- Y02P40/50—Glass production, e.g. reusing waste heat during processing or shaping
- Y02P40/57—Improving the yield, e-g- reduction of reject rates
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Surface Treatment Of Glass Fibres Or Filaments (AREA)
- Manufacture, Treatment Of Glass Fibers (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Fibers especially suitable for use in optical communi-cations are manufactured according to a spinning process.
Contamination of the fiber material by the carbon or graphite heating element is prevented by utilizing a glassy carbon or pyrolitic graphite containing little or no detached carbon as the heating element. The quality of drawn optical fibers is enhanced by utilizing an oven having an interior surface free of discontinuous or stepped portions.
Fibers especially suitable for use in optical communi-cations are manufactured according to a spinning process.
Contamination of the fiber material by the carbon or graphite heating element is prevented by utilizing a glassy carbon or pyrolitic graphite containing little or no detached carbon as the heating element. The quality of drawn optical fibers is enhanced by utilizing an oven having an interior surface free of discontinuous or stepped portions.
Description
116~
1 B~CK~ROUND O~ T~E INVENTION
, .. .. . .
This invention relates to a method and apparatus for manufacturing fibers for use in optical communication.
Methods for manufacturing fibers for use in optical communication (the fibers of this type will be referred to simply as optical fibers or fibers, hereinafter) from a preformed or raw material are classified into two typesj i.e., a preforming method and a double-crucible method. The present invention is associated with the former preforming method, according to which -a preformed or raw material for fibers is delivered at a given speed into a furnace to heat and soften the same, and then a fiber is drawn therefrom. This method is referred to as a fiber drawing methodO ~ne of the requirements in this method is the uniformity in high mechanical stength and outer diameter of obtained fibers along its length. The strength of fibers is essential to sustain subse~uent cabling processes, and cable installation processes. Particulalrly, the uniformity in outer diame~er of fibers is extremely important so improve character-istics for fiber splicing and connecting.
In putting an optical fiber cable to practical use, the most important point is the uniformity of the outer diameter of the fiber along its length and the reproducibility thereof, since the variation of the outer diameter of the fiber causes the variation of the core diameter, ~hich in turn causes conversion of the transmission mode and deterioration of transmission characteristics. Further, in this field, fiber splicing and connecting should be paid careful attention~ In order to obtain substantiall~r a perfect fiber splicing or connection, light is usually pro~ected into a fiber from one end thereof and is received at- the other end of the other fiber. The relative , 1101~64 1 positions of the fi~ers are adjusted until a maximum level of light is received~ However, such work takes considerable time, particularly in installing the optical fiber cable at a manhole or underground passage. According to recent fiber connecting methods, a melt bonding connection or V-shaped groove is used to fix the fibers relative to each other, standardizing the outer diameter o~ the optical fibers. In this case, it is necessary to prepare fibers having substantially the same outer diameter.
This invention will now be described by way of examples with reference to the accompanying drawings in which:
Fig. 1 is a schematic view showing the essential elements in a fiber drawing operation;
Fig. 2 is a graph showing the relationship bet~een the draw-forming temperature and the axial position in the furnace with the zero point being defined only as the axial position within the furnace at which the temperature is at a maximum;
Fig. 3 is a cross-sectional view of a high frequency induction heating apparatus according to a first embodiment of the present invention;
Fig~ ~ is a graph showing the relationship between the temperature wit~in the furnace and the outer diameter of the fiber;
Fig. 5 is a cross-sectional view of a high frequency induction heating apparatus according to a second embodiment of the present invention;
Fig. 6 is a cross-sectional view of a high frequency induction heati~g apparatus according to a third embodiment of the present invention;
Fig. 7 is a cross-sectional view of a high frequency induction heating apparatus according to a fourth embodiment of the present invention;
B
1 Fig. 8 is a cross-sectional view o~ a resistance heating apparatus according to a fifth embodiment of the present invention;
Fig. 9 is a cross-sectional view of a resistance heating apparatus according to a sixth em~odiment of the present invention;
Fig. 10 is a graph showing the variation of the outer diameter of a fiber formed by an apparatus according to the present invention;
Fig. 11 is a graph showing the relationship between applied wave length and the transmission loss of a plastic cladding fiber according to the present invention;
Fig. 12 is a second graph showing the relationship between the applied wave length and the transmission loss of a plastic cladding fiber according to the present invention;
Fig. 13 is a graph showing the fiber strength of a conventional fiber; and Fig. 14 is a graph sho~ing the fiber strength of a f iber according to the present invention.
Fig. 1 shows an essential part of a drawing furnace.
20 Shown at 1 is a preformed material having an outer diameter D
and supplied into a furnace at a speed V. Shown at 2 is a draw-forming furnace, at 3 a neck-down region of the fiber, at 4 a fiber drawn at a speed v, and at 5 a fiber-diameter measuring system. Assume that there is no variation in specific gravity due to the evaporation of raw material at the time of heating and due to the drawing of the fiber,then the following equation may be established among ~, V, d, v in the normal condition:
D2V = d2V ........................ (1) wherein d is an outer diameter of the fiber. --.
. ' ' ' ': :
11~1164 According to the draw-forming step of the preforming method, no jig such as a die for the neck-down step of the fiber is used, as shown in Fig. 1. The outer diameter d of a fiber derived is yoverned by the following equationO
d = D ~ ............ ~....... ~.. t2) ~I v '-, wherein D represents the outer diameter of a preformed material, V represents the feeding speed of a preformed material, and v represents a drawing speed of the fiber.
A further important factor to be considered in fiber formation is the disadvantageous variation in diameter of a fiber along its length due to variations in t~e viscosity of the fiber in the neck-do~n region and also in the temperature for heating and softening the preformed material.
Variations in the diameter of fibers may be classified into two categories, i.e., a short periodic-variation and a long periodic-variation. The short periodic-variation has a period in a range of about several centimeters to one meter, while the long periodic-variation has a period of ovex one meter. The long periodic-variation may be correctea with relative ease by adopting an automatic control system for controlling the fiber diameter. However, in the drawing process, a variation in the diameter of a fiber is detected after a dead time during which .
the variation in diameter has taken place. Such an unwanted lapse of time is apparently caused by the position of the fiber-diameter-measuring s~stem 5 as shown in Fig~ 1. In the control system with such a dead time there exists a minimum possi~le period which may theoretically be controlled. Accordingly, a ` variation for a relatively short period fails to be improved by -~
the automatic control system for fiber diameter, and therefore it is necessary to eliminate the factor which causes these dis-' 11~1164 1 advantageous relatively small periodic variations.
An additional concern in the fiber drawing operationis the material of the heating means which affects the outer diameter of the fibers and the mechanical stren~th thereof.
Carbon serving as a heat generating ele~ent is t~picall~
manufactured by molding a material consisting of petroleum cokes, pitch cokes and carbon black, followed by baking at a temperature of 1000 to 1300C. On the other hand, graphite is made of the same raw material as that for carbon by being molded into a desired ~hape, followed by baking at a temperature of 1000- 1300C, and then further heating at a temperature of 2500 - 3000C for graphitization.
If carbon and graphite are used for heat generating elements in the draw-forming furnace, a binder contained therein is evaporated due to the heating encountered during its service, so that car~on powder forming the carbon or graphite heating element becomes exposed. Under this condition, the carbon powder floats or flies within the furnace, thus impairing the atmosphere in the furnace. The adverse influences exerted by the carbon powder are enumerated as below:
First, carbon powder is brought into contact with the - heated preformed material for reaction with constituents contained therein. For instance, carbon powder reacts with SiO2 in the preformed material, as follows:
Si2 + C - > SiC + 2 In this m~tter, part of the surface of the preformed material is formed of silicon carbide~ As a result, a foreign material is formed so that the strength of such a portion of the fiber is lowered, accompanied by a variation in diameter of the fiber in _ 5 _ '~ .
11~1164 1 such a portion. If a quartz rod with carbon powders adhering to the surface thexeof is drawn at a temperature of about 2000C, the obtained fiber becomes extremely fragile or brittle, so that such fiber will not survive in actual use.
Second, if carbon powder clings to such a portion of the fiber, there results a wider variation in the apparent outer diameter of the fiber when the tempe~ature is lowered.
This exerts an adverse influence on the automatic control of the diameter of the fiber. Further, plastics cladding fiber, one example of a fiber ~or optical communication, is produced b~ setting a pure quartz or optical glass rod into the draw-forming furnace to o~tain a core having a predetermined core diameter, and immediately thereafter a plastic material having a lo~er refractive index than that of the core is coated thereon to form a cladding. If the atmosphere-in the drawing furnace is contaminated, the core surface will be polluted, so that the characteristic of the fiher is degraded. Particularly, transmission loss is increased. In case pure quartz or quartz ~ -glass is used, the dra~-forming temperature should be extremely high, about 2000~C as shown in Fig. 2, so that such a high temperature would affect the atmosphere within the furnace. For example, carbon powders floating in the furnace are easily reacted with a silica as mentioned above in the quartz or optical glass to produce silicon carbide at the core surface under the high temperature of 2000C.
The mechanical strength of the optical fiber is also important in order to avoid snapping of the fiber in the manu-facturing process to enhance yieldability. Further it is advantageous in designing and producing t~e optical cable, if ; 30 the high mechanical stength of the fiber is maintained. Further-l~Q1164 1 more, the obtained optical fiber cable will be compact because there will be no need for reinforcing the fiber, which enhances communication capacity per unit area of the fiber cable. There-fore, a fiber having high mechanical strength has been badl~
needed.
SUMMARY OF THE INVENTION
-It is, therefore, an object of the present invention to overcome the above-mentioned drawbacks and disadvantages and to provide an improved method and apparatus for producing optical glass fibers. More specifically, the present invention is directed to improvements in uniformity in strength and in outer ; diameter of fi~ers formed in a draw-forming step according to the preforming method. It is an ob~ect of the present invention ; to provide a furnace free of turbulence ~hich is filled with a clean atmosphere free of carbon dust stemming from a carbon or graphite heating element.
Briefly and in accordance with the present invention, the innermost wall surface of the draw-forming furnace is cylindrical with no stepped, or discontinuous, portion to thereby ellminate turbulence of the inert gas stream within the furnace.
The material to be applied to the innermost wall of the draw-forming furnace is a special type carbon which prevents the :
carbon powders from separating therefrom and floating within the ~ furnace. In this way, the chemical reaction of the carbon with ; the silica can be prevented.
DET~ILED DESC~IPTION OF THE INVENTION
Included in the heat sources for use in draw-forming a fiber are high freguency induction heating, resistance heating, oxyhydrogen flame, C02 laser and plasma flame.
':
',' ~ - ., . ' .
11~1164 1 Accoxding to the present invention, however, high frequency induction heating and resistance heating using carbon or graphite heating elements are employed.
A carbon is generally used as a heat generating element for use in a fi~er-drawing furnace. For this reason, the furnace is filled with an inert gas such as Ar, or N~ for preventing oxidation, and hence consumption, of carbon in the furnace, maintaining the internal pressure in the furnace at a positive pressure level. The inventor's various experiments have shown that if there is a discontinuous portion or stepped portion in the inner wall of the furnace, it is impossible to xeduce a short periodic-variation wit~in + 3 ~um. On the other -hand, the experiments show that if the furnace is constructe~
having an inner wall free of discontinuities but generall~
cylindrical as shown in the first e~bodiment illustrated in Fig. 3, the variation period may ~e reduced to + 0.5 ,um. ~lthcugh Fig. 3 shows a high frequency induction heating furnace according to a first embodiment of the present invention, the same results ; may be attained by means of a resistance furnace.
In Fig. 3, 6 is a top lid for the furnace, 7 a lower lid, 8 a fixing or clamping metal piece, 9 an O-ring, 10 a quartz tube, 11 a heat insulating material, 12 a carbon heat-generating element, 13 an induction coil, and 14 an inlet for an inert gas.
The innermost peripheral wall of the furnace, namel~
the heat-generating element 12 is linear in cross section, i.e., it is cylindrical with no surface discontinuities or stepped portions. The reason for the reduction of small periodic-variations by forming the inner wall of the furnace with no stepped portion is as follo~s:
- ~8 .
, 1 Despi~e the fact that an ordinar~ thermal phenomenon requ'~res a considerably long time constant, a ~uick response may be achieved in the draw-forming process because the thermal transmission mechanism is radiation and the thermal capacity of the neck-down region is extremely small. This is well substantiated ~y tests is which the temperature of the furnace is varied quickl~ or sharply (for instance, the output of a high frequency oscillator is varied), and a response in the diameter of fibers results instantaneously, i.e., the diameter of the fibers is increased very quickly as shown in Fig. 4.
As is apparent from the foregoing, according to the present invention there is no discontinuous or stepped portion in the inner wall of the furnace and, thus, there is no danger of inert gas streams causing a turbulence. Since the draw-formation is carried out by using a heat-generating element which is free of a discontinuous portion, variations in temperature which would otherwise have been caused due to turbulence of th~
gas streams is minimized. As a result, ~ariations in the diameters of fibers derived according to the process of the present inven-tion ma~ be reduced to below + 0.5 Sum.
A second embodiment according to the present invention is shown in Fig. 5, wherein a high frequency induction heating apparatus is illustrated. A heater 15 made of carbon or graphite has a large wall-thickness at an intermediate portion thereof in order to reduce its impedence. Shown at 16 is a heat-insulating material, at 17 a spacer, at 18 an entrance for inert gas, at 19 furnace pipe made of quartz, and at 20 an induction coil.
According to this embodiment, an ordinar~ type carbon or graphite is used as a raw material for the heater 15, but 1 a coating 15a of pyrolitic carbon made by Nippon Carbon K.K., under the product name PYROLYTIC GRAPHITE, or made by Tokai Carbon K.K. under the product name TOPCOA~, is coated over a par~
or the entire inner peripheral surface of the heater 15. This pyrolitic graphite is laminated on t~e surface of the raw material according to a CVD ~Chemical Vapor Decomposition) method well known in the art, and the layers thus prepared exhibit a high density and high purity.
In manufacturing glassy carbons, a Furan resin raw material is placed in a mold and gradually h~at~d in an oven until it decomposes. Since the carbonization rate of the material reaches 60 - 70~, the material contracts significantly so that a homogeneous high-density carbon results. Thus, glassy carbon will give off much less carbon dust than conventional carbon or graphite which has a relatively porous structure.
Pyrolitic graphite is formed by introducing a hydrocarbon such as propane as an additional raw material into the heated base material. The gas is thermally decomposed according to a known Chemical Vapor Decomposition (CVD) process and a laminated high-density layer is formed on the base material~
The oxidation of these special carbons merely produces CO and C02 gases, with little or no production of detached carbon powder as is experienced with conventional carbon heating elements.
As a result, the atmosphere in the furnace îs improved to a large extent. Of course, the variation of the diameter of fibers due to the turbulence of inert gas streams is prevented by forming a cylindrical inner peripheral surface having no dis-continuities.
A third embodîment in accordance with the present invention is shown in Fig. 6, wherein a refractory tube 22 made *Trade Mark ~10~`
11~1164 1 of carbon or graphite is coated on its inner surface with pyrolitic carbon having a thickness less than 4 mm. In this embodiment, the interior of the furnace is covered with the p~rolitic carbon and is substantially cylindrical avoiding stepped wall portions and, therefore, pure and clean atmosphere results and a fiber having a uniform outer diameter along its length is obtained. Of course, the ~all thickness of the central portion of the heater is large as in the second embodiment, the principal difference being that the tube is now heated indirectly by the heating means rather than comprising an integral part of the heater as in Fig. 5.
A fourth embodiment in accordance with the present invention is shown in Fig~ 7 wherein reference numeral 29 designates a refractory tube made of glassy carbon. The remain-ing structure is similar to the device of Fig. 5. With this structure, since the refractory tube 29 is made of glassy carbonr and since the glassy carbon itself does not create carbon particles due to its wearing, clean atmosphere in the furnace results. Furthermore, disadvantageous carbon powders generated from the heater 15 are blocked by the refractory tube 29, and therefore r carbon powders do not float within the tube 29. Of course, the inner wall of the drawing furnace is cylindrical having no discontinuous or stepped portions, so that a stable flow of the inert yas is provided, which in turn reduces the above-mentioned short period-variation of the fiber.
;~ A fifth embodiment according to the present invention is shown in Fig. 8, wherein a resistance heating furnace is shown as opposed to the first through fourth embodiments wherein high frequency induction heaters are shown. The fifth embodiment is substantially similar to the embodiment illustrated in Fig. 5, .`11-. . ,~ .
.
.
11C~11~i4 1 except that heat is applied b~ an electrical resistant heater 35 made of carbon or graphite connected to electrodes 38, 38.
Reference numeral 36 designates a refractory tube made of carbon, 37 a heat insulator, 39 spacer to support the heater 35, 40 an inert gas inlet for preventing the heater 35 and the refractory tube from wearing due to oxidation, and 41 the outer wall of the furnace. Water ma~ be introduced into the wall 41 for cooling purposes. In this embodiment, the refractory tube 36 made of carbon and graphite is coated with a pyrolitic carbon coating 36a having a thickness of less than 4 mm on part or all of the inner peripheral surface thereof. The same effect and function is obtained in this embodiment as obtained from the foregoing embodiments. However, it should be noted that in order to avoid a short circuit between the electrical resistance heater 35 and the refractory tube and the coating, a clearance is required therebet~een and preferably,the specific carbon should be insulated from the other elements.
A sixth embodiment according to the present invention is shown in Fig. ~, wherein a resistance heating furnace is shown~
In this embodiment, the carbon tube 42 is made of glassy carbon.
This embodiment is substantially similar to the embodiment of Fig. 6 with the exception of the resistance heater, and the same function and effect is obtained as in the foregoing embodiments.
Fig. 10 shows the variation of the outer diameter of the fiber obtained by the apparatus shown in Fig. 9. In Fig.
10, owing~to the automatic control system for fiber diameter, long periodic-variation is completely eliminated and, furthermore~
the amplitude of the short periodic-variation is reduced to ~ 0.3 ~m.
In Figs. 11 and 12, the transmission loss characteristics ~12~
11~1164 1 of the plastic cladding fibers is shown, in which quartz and silicone resin are used as the core material and clad material, respectively, and the dra~ing furnace according to Fig. 6 is employed.
The core diameter is 150 ~m and the clad diameter is 350 ~m, the cladding having a refractive index 4.0~ lower than that of the core. In the test piece used in connection with Fig. 11, a quartz rod made by Komatsu Denshi Kinzoku K.K., under the product name Silanox-WF* is used as the core and a silicone resin made by Shinetsu Kagaku K.K., under the product name KE-103RTV* is used as a cladding material. In the test piece used in connection ~ith Fig. 12, a synthetic quartz rod obtained by using high frequency plasma heating is used as a core, and the same material as above is used as cladding material.
According to Fig. 11, at the wave length of 0.83 ~m, a low transmission loss of 3.7 dB/km is obtained, and according to Fig. 12, at the wave length of 1.05 lum a low transmission loss of 2.4 dB/km is obtained~
These values can be considered a minor transmission loss due largely to the intrinsic loss of the quartz glass core and the intxinsic loss of the clad material. The above tests and considerations prove that the atmosphere in draw forming furnace according to the present invention is extremely clean.
Fig. 13 shows Weibull probability plots of the strength of the fiber obtained by the conventional fiber drawing furnace.
The conventional furnace was obtained by removing the glassy carbon-refractory tube from the embodiment'shown in Fig. 7 and, therefore, the atmosphere in the conventional furnace is extremely contaminated. The plastic coated fiber is obtained by the'method de~crlbed in Japanese Prel'iminary Publication *Trade Mark ' - 13 -l~U11~;4 1 No. 51-100734 (1976),published September 6, 1976, in which the primary coating is effected immedia~ely after fiber-draw formation, and thereafter a polyethylene is coated thereon.
Fig. 14 shows Wei~ull probability plots for fiber strength obtained ~y the instant furnace as shown in Fig. 6, and the optical fiber is obtained by the method as above. The fiber thus obtained has an outer fiber diameter of 150 ~m, an outer diameter of the polyethylene coating of 0.9 mm, and the tensile strength test was made by using such a fiber having a length of lm and a tensile rate set at 5 mm/min~
As is clear from the two graphs, the optical fiber obtained by the instant furnace exhibits remarkably high tensile strength up to 7 kg, and no sample exhibits fracture a~ less than 7 kg according to tensile strength test.
In view of the foregoing, the outer diameter variation of the fiber produced by using the draw forming furnace according to the present invention is reduced to less than ~ 0.5 pm, and an optical fiber having high tensile strength of 7 kg is obtaina~le. Further, the furnace of this invention can provide a remarkably clear atmosphere, since the transmission loss of the plastic cladding fiber is in the range of 2.4 - 3.7 dB/km and this value is almost equal to the intrinsic transmissiQn 10s9 of the quartr.
1 B~CK~ROUND O~ T~E INVENTION
, .. .. . .
This invention relates to a method and apparatus for manufacturing fibers for use in optical communication.
Methods for manufacturing fibers for use in optical communication (the fibers of this type will be referred to simply as optical fibers or fibers, hereinafter) from a preformed or raw material are classified into two typesj i.e., a preforming method and a double-crucible method. The present invention is associated with the former preforming method, according to which -a preformed or raw material for fibers is delivered at a given speed into a furnace to heat and soften the same, and then a fiber is drawn therefrom. This method is referred to as a fiber drawing methodO ~ne of the requirements in this method is the uniformity in high mechanical stength and outer diameter of obtained fibers along its length. The strength of fibers is essential to sustain subse~uent cabling processes, and cable installation processes. Particulalrly, the uniformity in outer diame~er of fibers is extremely important so improve character-istics for fiber splicing and connecting.
In putting an optical fiber cable to practical use, the most important point is the uniformity of the outer diameter of the fiber along its length and the reproducibility thereof, since the variation of the outer diameter of the fiber causes the variation of the core diameter, ~hich in turn causes conversion of the transmission mode and deterioration of transmission characteristics. Further, in this field, fiber splicing and connecting should be paid careful attention~ In order to obtain substantiall~r a perfect fiber splicing or connection, light is usually pro~ected into a fiber from one end thereof and is received at- the other end of the other fiber. The relative , 1101~64 1 positions of the fi~ers are adjusted until a maximum level of light is received~ However, such work takes considerable time, particularly in installing the optical fiber cable at a manhole or underground passage. According to recent fiber connecting methods, a melt bonding connection or V-shaped groove is used to fix the fibers relative to each other, standardizing the outer diameter o~ the optical fibers. In this case, it is necessary to prepare fibers having substantially the same outer diameter.
This invention will now be described by way of examples with reference to the accompanying drawings in which:
Fig. 1 is a schematic view showing the essential elements in a fiber drawing operation;
Fig. 2 is a graph showing the relationship bet~een the draw-forming temperature and the axial position in the furnace with the zero point being defined only as the axial position within the furnace at which the temperature is at a maximum;
Fig. 3 is a cross-sectional view of a high frequency induction heating apparatus according to a first embodiment of the present invention;
Fig~ ~ is a graph showing the relationship between the temperature wit~in the furnace and the outer diameter of the fiber;
Fig. 5 is a cross-sectional view of a high frequency induction heating apparatus according to a second embodiment of the present invention;
Fig. 6 is a cross-sectional view of a high frequency induction heati~g apparatus according to a third embodiment of the present invention;
Fig. 7 is a cross-sectional view of a high frequency induction heating apparatus according to a fourth embodiment of the present invention;
B
1 Fig. 8 is a cross-sectional view o~ a resistance heating apparatus according to a fifth embodiment of the present invention;
Fig. 9 is a cross-sectional view of a resistance heating apparatus according to a sixth em~odiment of the present invention;
Fig. 10 is a graph showing the variation of the outer diameter of a fiber formed by an apparatus according to the present invention;
Fig. 11 is a graph showing the relationship between applied wave length and the transmission loss of a plastic cladding fiber according to the present invention;
Fig. 12 is a second graph showing the relationship between the applied wave length and the transmission loss of a plastic cladding fiber according to the present invention;
Fig. 13 is a graph showing the fiber strength of a conventional fiber; and Fig. 14 is a graph sho~ing the fiber strength of a f iber according to the present invention.
Fig. 1 shows an essential part of a drawing furnace.
20 Shown at 1 is a preformed material having an outer diameter D
and supplied into a furnace at a speed V. Shown at 2 is a draw-forming furnace, at 3 a neck-down region of the fiber, at 4 a fiber drawn at a speed v, and at 5 a fiber-diameter measuring system. Assume that there is no variation in specific gravity due to the evaporation of raw material at the time of heating and due to the drawing of the fiber,then the following equation may be established among ~, V, d, v in the normal condition:
D2V = d2V ........................ (1) wherein d is an outer diameter of the fiber. --.
. ' ' ' ': :
11~1164 According to the draw-forming step of the preforming method, no jig such as a die for the neck-down step of the fiber is used, as shown in Fig. 1. The outer diameter d of a fiber derived is yoverned by the following equationO
d = D ~ ............ ~....... ~.. t2) ~I v '-, wherein D represents the outer diameter of a preformed material, V represents the feeding speed of a preformed material, and v represents a drawing speed of the fiber.
A further important factor to be considered in fiber formation is the disadvantageous variation in diameter of a fiber along its length due to variations in t~e viscosity of the fiber in the neck-do~n region and also in the temperature for heating and softening the preformed material.
Variations in the diameter of fibers may be classified into two categories, i.e., a short periodic-variation and a long periodic-variation. The short periodic-variation has a period in a range of about several centimeters to one meter, while the long periodic-variation has a period of ovex one meter. The long periodic-variation may be correctea with relative ease by adopting an automatic control system for controlling the fiber diameter. However, in the drawing process, a variation in the diameter of a fiber is detected after a dead time during which .
the variation in diameter has taken place. Such an unwanted lapse of time is apparently caused by the position of the fiber-diameter-measuring s~stem 5 as shown in Fig~ 1. In the control system with such a dead time there exists a minimum possi~le period which may theoretically be controlled. Accordingly, a ` variation for a relatively short period fails to be improved by -~
the automatic control system for fiber diameter, and therefore it is necessary to eliminate the factor which causes these dis-' 11~1164 1 advantageous relatively small periodic variations.
An additional concern in the fiber drawing operationis the material of the heating means which affects the outer diameter of the fibers and the mechanical stren~th thereof.
Carbon serving as a heat generating ele~ent is t~picall~
manufactured by molding a material consisting of petroleum cokes, pitch cokes and carbon black, followed by baking at a temperature of 1000 to 1300C. On the other hand, graphite is made of the same raw material as that for carbon by being molded into a desired ~hape, followed by baking at a temperature of 1000- 1300C, and then further heating at a temperature of 2500 - 3000C for graphitization.
If carbon and graphite are used for heat generating elements in the draw-forming furnace, a binder contained therein is evaporated due to the heating encountered during its service, so that car~on powder forming the carbon or graphite heating element becomes exposed. Under this condition, the carbon powder floats or flies within the furnace, thus impairing the atmosphere in the furnace. The adverse influences exerted by the carbon powder are enumerated as below:
First, carbon powder is brought into contact with the - heated preformed material for reaction with constituents contained therein. For instance, carbon powder reacts with SiO2 in the preformed material, as follows:
Si2 + C - > SiC + 2 In this m~tter, part of the surface of the preformed material is formed of silicon carbide~ As a result, a foreign material is formed so that the strength of such a portion of the fiber is lowered, accompanied by a variation in diameter of the fiber in _ 5 _ '~ .
11~1164 1 such a portion. If a quartz rod with carbon powders adhering to the surface thexeof is drawn at a temperature of about 2000C, the obtained fiber becomes extremely fragile or brittle, so that such fiber will not survive in actual use.
Second, if carbon powder clings to such a portion of the fiber, there results a wider variation in the apparent outer diameter of the fiber when the tempe~ature is lowered.
This exerts an adverse influence on the automatic control of the diameter of the fiber. Further, plastics cladding fiber, one example of a fiber ~or optical communication, is produced b~ setting a pure quartz or optical glass rod into the draw-forming furnace to o~tain a core having a predetermined core diameter, and immediately thereafter a plastic material having a lo~er refractive index than that of the core is coated thereon to form a cladding. If the atmosphere-in the drawing furnace is contaminated, the core surface will be polluted, so that the characteristic of the fiher is degraded. Particularly, transmission loss is increased. In case pure quartz or quartz ~ -glass is used, the dra~-forming temperature should be extremely high, about 2000~C as shown in Fig. 2, so that such a high temperature would affect the atmosphere within the furnace. For example, carbon powders floating in the furnace are easily reacted with a silica as mentioned above in the quartz or optical glass to produce silicon carbide at the core surface under the high temperature of 2000C.
The mechanical strength of the optical fiber is also important in order to avoid snapping of the fiber in the manu-facturing process to enhance yieldability. Further it is advantageous in designing and producing t~e optical cable, if ; 30 the high mechanical stength of the fiber is maintained. Further-l~Q1164 1 more, the obtained optical fiber cable will be compact because there will be no need for reinforcing the fiber, which enhances communication capacity per unit area of the fiber cable. There-fore, a fiber having high mechanical strength has been badl~
needed.
SUMMARY OF THE INVENTION
-It is, therefore, an object of the present invention to overcome the above-mentioned drawbacks and disadvantages and to provide an improved method and apparatus for producing optical glass fibers. More specifically, the present invention is directed to improvements in uniformity in strength and in outer ; diameter of fi~ers formed in a draw-forming step according to the preforming method. It is an ob~ect of the present invention ; to provide a furnace free of turbulence ~hich is filled with a clean atmosphere free of carbon dust stemming from a carbon or graphite heating element.
Briefly and in accordance with the present invention, the innermost wall surface of the draw-forming furnace is cylindrical with no stepped, or discontinuous, portion to thereby ellminate turbulence of the inert gas stream within the furnace.
The material to be applied to the innermost wall of the draw-forming furnace is a special type carbon which prevents the :
carbon powders from separating therefrom and floating within the ~ furnace. In this way, the chemical reaction of the carbon with ; the silica can be prevented.
DET~ILED DESC~IPTION OF THE INVENTION
Included in the heat sources for use in draw-forming a fiber are high freguency induction heating, resistance heating, oxyhydrogen flame, C02 laser and plasma flame.
':
',' ~ - ., . ' .
11~1164 1 Accoxding to the present invention, however, high frequency induction heating and resistance heating using carbon or graphite heating elements are employed.
A carbon is generally used as a heat generating element for use in a fi~er-drawing furnace. For this reason, the furnace is filled with an inert gas such as Ar, or N~ for preventing oxidation, and hence consumption, of carbon in the furnace, maintaining the internal pressure in the furnace at a positive pressure level. The inventor's various experiments have shown that if there is a discontinuous portion or stepped portion in the inner wall of the furnace, it is impossible to xeduce a short periodic-variation wit~in + 3 ~um. On the other -hand, the experiments show that if the furnace is constructe~
having an inner wall free of discontinuities but generall~
cylindrical as shown in the first e~bodiment illustrated in Fig. 3, the variation period may ~e reduced to + 0.5 ,um. ~lthcugh Fig. 3 shows a high frequency induction heating furnace according to a first embodiment of the present invention, the same results ; may be attained by means of a resistance furnace.
In Fig. 3, 6 is a top lid for the furnace, 7 a lower lid, 8 a fixing or clamping metal piece, 9 an O-ring, 10 a quartz tube, 11 a heat insulating material, 12 a carbon heat-generating element, 13 an induction coil, and 14 an inlet for an inert gas.
The innermost peripheral wall of the furnace, namel~
the heat-generating element 12 is linear in cross section, i.e., it is cylindrical with no surface discontinuities or stepped portions. The reason for the reduction of small periodic-variations by forming the inner wall of the furnace with no stepped portion is as follo~s:
- ~8 .
, 1 Despi~e the fact that an ordinar~ thermal phenomenon requ'~res a considerably long time constant, a ~uick response may be achieved in the draw-forming process because the thermal transmission mechanism is radiation and the thermal capacity of the neck-down region is extremely small. This is well substantiated ~y tests is which the temperature of the furnace is varied quickl~ or sharply (for instance, the output of a high frequency oscillator is varied), and a response in the diameter of fibers results instantaneously, i.e., the diameter of the fibers is increased very quickly as shown in Fig. 4.
As is apparent from the foregoing, according to the present invention there is no discontinuous or stepped portion in the inner wall of the furnace and, thus, there is no danger of inert gas streams causing a turbulence. Since the draw-formation is carried out by using a heat-generating element which is free of a discontinuous portion, variations in temperature which would otherwise have been caused due to turbulence of th~
gas streams is minimized. As a result, ~ariations in the diameters of fibers derived according to the process of the present inven-tion ma~ be reduced to below + 0.5 Sum.
A second embodiment according to the present invention is shown in Fig. 5, wherein a high frequency induction heating apparatus is illustrated. A heater 15 made of carbon or graphite has a large wall-thickness at an intermediate portion thereof in order to reduce its impedence. Shown at 16 is a heat-insulating material, at 17 a spacer, at 18 an entrance for inert gas, at 19 furnace pipe made of quartz, and at 20 an induction coil.
According to this embodiment, an ordinar~ type carbon or graphite is used as a raw material for the heater 15, but 1 a coating 15a of pyrolitic carbon made by Nippon Carbon K.K., under the product name PYROLYTIC GRAPHITE, or made by Tokai Carbon K.K. under the product name TOPCOA~, is coated over a par~
or the entire inner peripheral surface of the heater 15. This pyrolitic graphite is laminated on t~e surface of the raw material according to a CVD ~Chemical Vapor Decomposition) method well known in the art, and the layers thus prepared exhibit a high density and high purity.
In manufacturing glassy carbons, a Furan resin raw material is placed in a mold and gradually h~at~d in an oven until it decomposes. Since the carbonization rate of the material reaches 60 - 70~, the material contracts significantly so that a homogeneous high-density carbon results. Thus, glassy carbon will give off much less carbon dust than conventional carbon or graphite which has a relatively porous structure.
Pyrolitic graphite is formed by introducing a hydrocarbon such as propane as an additional raw material into the heated base material. The gas is thermally decomposed according to a known Chemical Vapor Decomposition (CVD) process and a laminated high-density layer is formed on the base material~
The oxidation of these special carbons merely produces CO and C02 gases, with little or no production of detached carbon powder as is experienced with conventional carbon heating elements.
As a result, the atmosphere in the furnace îs improved to a large extent. Of course, the variation of the diameter of fibers due to the turbulence of inert gas streams is prevented by forming a cylindrical inner peripheral surface having no dis-continuities.
A third embodîment in accordance with the present invention is shown in Fig. 6, wherein a refractory tube 22 made *Trade Mark ~10~`
11~1164 1 of carbon or graphite is coated on its inner surface with pyrolitic carbon having a thickness less than 4 mm. In this embodiment, the interior of the furnace is covered with the p~rolitic carbon and is substantially cylindrical avoiding stepped wall portions and, therefore, pure and clean atmosphere results and a fiber having a uniform outer diameter along its length is obtained. Of course, the ~all thickness of the central portion of the heater is large as in the second embodiment, the principal difference being that the tube is now heated indirectly by the heating means rather than comprising an integral part of the heater as in Fig. 5.
A fourth embodiment in accordance with the present invention is shown in Fig~ 7 wherein reference numeral 29 designates a refractory tube made of glassy carbon. The remain-ing structure is similar to the device of Fig. 5. With this structure, since the refractory tube 29 is made of glassy carbonr and since the glassy carbon itself does not create carbon particles due to its wearing, clean atmosphere in the furnace results. Furthermore, disadvantageous carbon powders generated from the heater 15 are blocked by the refractory tube 29, and therefore r carbon powders do not float within the tube 29. Of course, the inner wall of the drawing furnace is cylindrical having no discontinuous or stepped portions, so that a stable flow of the inert yas is provided, which in turn reduces the above-mentioned short period-variation of the fiber.
;~ A fifth embodiment according to the present invention is shown in Fig. 8, wherein a resistance heating furnace is shown as opposed to the first through fourth embodiments wherein high frequency induction heaters are shown. The fifth embodiment is substantially similar to the embodiment illustrated in Fig. 5, .`11-. . ,~ .
.
.
11C~11~i4 1 except that heat is applied b~ an electrical resistant heater 35 made of carbon or graphite connected to electrodes 38, 38.
Reference numeral 36 designates a refractory tube made of carbon, 37 a heat insulator, 39 spacer to support the heater 35, 40 an inert gas inlet for preventing the heater 35 and the refractory tube from wearing due to oxidation, and 41 the outer wall of the furnace. Water ma~ be introduced into the wall 41 for cooling purposes. In this embodiment, the refractory tube 36 made of carbon and graphite is coated with a pyrolitic carbon coating 36a having a thickness of less than 4 mm on part or all of the inner peripheral surface thereof. The same effect and function is obtained in this embodiment as obtained from the foregoing embodiments. However, it should be noted that in order to avoid a short circuit between the electrical resistance heater 35 and the refractory tube and the coating, a clearance is required therebet~een and preferably,the specific carbon should be insulated from the other elements.
A sixth embodiment according to the present invention is shown in Fig. ~, wherein a resistance heating furnace is shown~
In this embodiment, the carbon tube 42 is made of glassy carbon.
This embodiment is substantially similar to the embodiment of Fig. 6 with the exception of the resistance heater, and the same function and effect is obtained as in the foregoing embodiments.
Fig. 10 shows the variation of the outer diameter of the fiber obtained by the apparatus shown in Fig. 9. In Fig.
10, owing~to the automatic control system for fiber diameter, long periodic-variation is completely eliminated and, furthermore~
the amplitude of the short periodic-variation is reduced to ~ 0.3 ~m.
In Figs. 11 and 12, the transmission loss characteristics ~12~
11~1164 1 of the plastic cladding fibers is shown, in which quartz and silicone resin are used as the core material and clad material, respectively, and the dra~ing furnace according to Fig. 6 is employed.
The core diameter is 150 ~m and the clad diameter is 350 ~m, the cladding having a refractive index 4.0~ lower than that of the core. In the test piece used in connection with Fig. 11, a quartz rod made by Komatsu Denshi Kinzoku K.K., under the product name Silanox-WF* is used as the core and a silicone resin made by Shinetsu Kagaku K.K., under the product name KE-103RTV* is used as a cladding material. In the test piece used in connection ~ith Fig. 12, a synthetic quartz rod obtained by using high frequency plasma heating is used as a core, and the same material as above is used as cladding material.
According to Fig. 11, at the wave length of 0.83 ~m, a low transmission loss of 3.7 dB/km is obtained, and according to Fig. 12, at the wave length of 1.05 lum a low transmission loss of 2.4 dB/km is obtained~
These values can be considered a minor transmission loss due largely to the intrinsic loss of the quartz glass core and the intxinsic loss of the clad material. The above tests and considerations prove that the atmosphere in draw forming furnace according to the present invention is extremely clean.
Fig. 13 shows Weibull probability plots of the strength of the fiber obtained by the conventional fiber drawing furnace.
The conventional furnace was obtained by removing the glassy carbon-refractory tube from the embodiment'shown in Fig. 7 and, therefore, the atmosphere in the conventional furnace is extremely contaminated. The plastic coated fiber is obtained by the'method de~crlbed in Japanese Prel'iminary Publication *Trade Mark ' - 13 -l~U11~;4 1 No. 51-100734 (1976),published September 6, 1976, in which the primary coating is effected immedia~ely after fiber-draw formation, and thereafter a polyethylene is coated thereon.
Fig. 14 shows Wei~ull probability plots for fiber strength obtained ~y the instant furnace as shown in Fig. 6, and the optical fiber is obtained by the method as above. The fiber thus obtained has an outer fiber diameter of 150 ~m, an outer diameter of the polyethylene coating of 0.9 mm, and the tensile strength test was made by using such a fiber having a length of lm and a tensile rate set at 5 mm/min~
As is clear from the two graphs, the optical fiber obtained by the instant furnace exhibits remarkably high tensile strength up to 7 kg, and no sample exhibits fracture a~ less than 7 kg according to tensile strength test.
In view of the foregoing, the outer diameter variation of the fiber produced by using the draw forming furnace according to the present invention is reduced to less than ~ 0.5 pm, and an optical fiber having high tensile strength of 7 kg is obtaina~le. Further, the furnace of this invention can provide a remarkably clear atmosphere, since the transmission loss of the plastic cladding fiber is in the range of 2.4 - 3.7 dB/km and this value is almost equal to the intrinsic transmissiQn 10s9 of the quartr.
Claims (4)
1. An apparatus for draw-forming optical fibers, said apparatus of the type having an oven containing an inert gas for receiving a preformed raw material and a heating means within said oven for heating said raw material to a temperature suitable for drawing, wherein the improvements comprise:
said oven having a substantially cylindrical interior surface having no stepped portions so that turbulence of said inert gas within said oven is minimized, thus minimizing fiber diameter variations due to temperature variations caused by said turbulence; and the surface of said heating means exposed to the interior of said oven comprising one of pyrolitic graphite and glassy carbon which releases little or no carbon powder when heated to said suitable temperature.
said oven having a substantially cylindrical interior surface having no stepped portions so that turbulence of said inert gas within said oven is minimized, thus minimizing fiber diameter variations due to temperature variations caused by said turbulence; and the surface of said heating means exposed to the interior of said oven comprising one of pyrolitic graphite and glassy carbon which releases little or no carbon powder when heated to said suitable temperature.
2. An apparatus according to claim 1, wherein the interior surface of said oven is a refractory tube comprising one of pyrolitic graphite and glassy carbon.
3. An apparatus according to claim 1, wherein said heating means comprises a carbon or graphite tube having on the interior surface thereof a coating comprising one of pyrolitic graphite and glassy carbon.
4. An apparatus according to claim 3, wherein said coating is less than 4 mm thick.
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP50298/77 | 1977-04-30 | ||
| JP5029877A JPS53135648A (en) | 1977-04-30 | 1977-04-30 | Production of fibers for optical communication |
| JP50302/77 | 1977-04-30 | ||
| JP5030277A JPS53135649A (en) | 1977-04-30 | 1977-04-30 | Production of optical fibers |
| JP57253/77 | 1977-05-06 | ||
| JP5725377U JPS53154215U (en) | 1977-05-06 | 1977-05-06 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1101164A true CA1101164A (en) | 1981-05-19 |
Family
ID=27293915
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA302,178A Expired CA1101164A (en) | 1977-04-30 | 1978-04-27 | Method and apparatus for producing fibers for optical transmission |
Country Status (4)
| Country | Link |
|---|---|
| CA (1) | CA1101164A (en) |
| DE (1) | DE2818550C2 (en) |
| FR (1) | FR2401103A1 (en) |
| GB (1) | GB1575299A (en) |
Families Citing this family (18)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS605683B2 (en) * | 1979-08-21 | 1985-02-13 | 東邦レーヨン株式会社 | Graphite fiber manufacturing equipment |
| DE3369452D1 (en) * | 1982-05-28 | 1987-02-26 | Western Electric Co | Modified zirconia induction furnace |
| FR2532866B1 (en) * | 1982-09-13 | 1985-06-07 | Pont A Mousson | INDUCTION HEATED CASTING CHANNEL |
| US5236483A (en) * | 1985-07-16 | 1993-08-17 | Seiko Epson Corporation | Method of preparing silica glass |
| FR2587502B1 (en) * | 1985-09-19 | 1987-12-24 | Centre Nat Rech Scient | APPARATUS FOR FUSING AND DRAWING OPTICAL FIBERS, PARTICULARLY FOR MANUFACTURING COUPLERS |
| DE3855370T2 (en) * | 1987-02-16 | 1997-01-02 | Sumitomo Electric Industries | Oven for heating a glass preform for optical fiber and method for producing a glass preform |
| AU593724B2 (en) * | 1987-02-16 | 1990-02-15 | Sumitomo Electric Industries, Ltd. | Furnace for heating glass preform for optical fiber and method for producing glass preform |
| DE3735879C2 (en) * | 1987-10-23 | 1995-07-20 | Leybold Ag | Method and device for sintering ceramic blanks |
| JPH02196045A (en) * | 1989-01-23 | 1990-08-02 | Sumitomo Electric Ind Ltd | Heating furnace for manufacturing high purity quartz base material |
| JP2808857B2 (en) * | 1989-09-06 | 1998-10-08 | 住友電気工業株式会社 | Heating furnace and manufacturing method of glass preform for optical fiber |
| US5259856A (en) * | 1989-09-06 | 1993-11-09 | Sumitomo Electric Industrial, Ltd. | Method of producing glass preform in furnace for heating glass |
| CA2025880A1 (en) * | 1989-09-25 | 1991-03-26 | Ichiro Tsuchiya | Furnace for production of optical fiber preform |
| EP0867412B1 (en) | 1997-03-27 | 2001-03-07 | Alcatel | Thermal insulation of a furnace for drawing optical fibres |
| JP2001521871A (en) * | 1997-10-31 | 2001-11-13 | コーニング インコーポレイテッド | Apparatus and method for drawing waveguide fiber |
| DE19900375A1 (en) * | 1999-01-08 | 2000-07-13 | Alcatel Sa | Device for pulling a fiber |
| WO2000068157A1 (en) | 1999-05-10 | 2000-11-16 | Pirelli Cavi E Sistemi S.P.A. | Method and induction furnace for drawing large diameter preforms to optical fibres |
| CN113929462B (en) * | 2021-10-16 | 2022-08-09 | 上杭鑫昌龙实业有限公司 | Optical fiber annealing pipe and preparation process thereof |
| EP4197977A1 (en) * | 2021-12-08 | 2023-06-21 | Heraeus Quartz North America LLC | Inductive furnace with rotating susceptor for high precision waveguide glass draw |
Family Cites Families (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3549847A (en) * | 1967-04-18 | 1970-12-22 | Gen Electric | Graphite susceptor |
| FR2055893A5 (en) * | 1969-08-05 | 1971-05-14 | Lorraine Carbone | |
| JPS4946478B1 (en) * | 1970-07-27 | 1974-12-10 | ||
| DE2352613A1 (en) * | 1973-10-19 | 1975-05-15 | Nath Guenther | Fibre pulling furnace - has pulling weight suspended in viscous fluid and heating input control by pulling speed |
| DE2451969C2 (en) * | 1974-10-30 | 1976-11-08 | Aerospace Corp | PROCESS FOR GLAZING WORKPIECES MADE OF CERAMIC, CHARCOAL OR CARBON |
| FR2312004A1 (en) * | 1975-04-30 | 1976-12-17 | Gouronnec Alain | High temp. laboratory furnace - using graphite heating elements in separate refractory tubes under protective gas |
| US4101300A (en) * | 1975-11-27 | 1978-07-18 | Hitachi, Ltd. | Method and apparatus for drawing optical fiber |
| FR2339148A1 (en) * | 1976-01-22 | 1977-08-19 | Comp Generale Electricite | HIGH FREQUENCY ELECTRIC OVEN |
| FR2340519A1 (en) * | 1976-02-06 | 1977-09-02 | France Etat | OVEN FOR VERY HIGH TEMPERATURES |
| FR2342619A1 (en) * | 1976-02-25 | 1977-09-23 | Physique Appliquee Ind | Induction furnace for oxidation - uses radiation from steel rod to preheat zircon tube to temp. adequate for inductive coupling |
| US4030901A (en) * | 1976-07-19 | 1977-06-21 | Bell Telephone Laboratories, Incorporated | Method for drawing fibers |
| FR2368677A2 (en) * | 1976-10-19 | 1978-05-19 | France Etat | OVEN FOR VERY HIGH TEMPERATURES |
-
1978
- 1978-04-27 CA CA302,178A patent/CA1101164A/en not_active Expired
- 1978-04-27 DE DE2818550A patent/DE2818550C2/en not_active Expired - Lifetime
- 1978-04-28 FR FR7812700A patent/FR2401103A1/en active Granted
- 1978-05-02 GB GB17198/78A patent/GB1575299A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| FR2401103A1 (en) | 1979-03-23 |
| GB1575299A (en) | 1980-09-17 |
| DE2818550C2 (en) | 1990-03-29 |
| DE2818550A1 (en) | 1979-03-15 |
| FR2401103B1 (en) | 1982-12-17 |
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