WO2003072517A1

WO2003072517A1 - Production of cladding glass for fibre optic cable

Info

Publication number: WO2003072517A1
Application number: PCT/DE2002/000720
Authority: WO
Inventors: Manfred Wittmann
Original assignee: S & S Technologie- Und Investitionsgesellschaft Gmbh
Priority date: 2002-02-27
Filing date: 2002-02-27
Publication date: 2003-09-04
Also published as: AU2002249087A1; DE10296573D2

Abstract

The invention relates to a device and method for producing highly pure quartz glass using silicon dioxide with a particle size of 40 nanometers, in order to deposit the cladding glass that surrounds the core preform onto the substrate recipient, by means of an external coating method achieved by radial epitaxy and a high blowing speed. The silicon dioxide is supplied to an oxygen stream via a powder balance comprising weighing cells and by means of a feed pump, screw conveyer and cellular wheel sluice, said stream conveying the silicon dioxide into the coating facility, in which hydrogen and oxygen are supplied and the core preform body is heated so that the supplied silicon dioxide particles can precipitate onto the preform body, whereby the required temperature is guaranteed by two pyrometers. The invention also uses a red-light scanner detector system for supplying the individual gases required, in addition to the silicon dioxide and for monitoring the operation until the final diameter has been attained.

Description

description

Manufacture of cladding glass for optical fibers

The present invention relates to a method and the system for the exact metering of silicon dioxide for the production of high-purity quartz glass in the field of optical waveguide production using silicon dioxide powder (SiO), which is applied from the outside in order to manufacture the enveloping glass surrounding the core area. by metering the SiO ₂ particles, which have a diameter of about 40 nanometers, into a propellant gas stream and are heated by a burner and blown onto a substrate template and growing radially onto a cylinder in one or both directions by constant movement of a burner. With the CVD, OVD and VAD processes, both the light-guiding core glass and the enveloping cladding glass can be constructed. The core area of the light-conducting glass (core preform) is manufactured using the CVD process. The disadvantage here is the high environmental impact at the site of the preform production, because silicon tetrachloride (SiCl) is used as the starting material for the production of high-purity quartz glass. This is a corrosive liquid that spontaneously develops hydrochloric acid (HO) with moisture and can only be processed in closed systems without moisture. The reaction with oxygen at high temperatures also produces chlorine gas, which must be collected as a reactive and corrosive gas and disposed of in a gas scrubber. The chlorine-containing, gaseous compound from chlorine gas (Cl ₂ ) or as hydrochloric acid (HC1) is converted to sodium chloride in a gas scrubber with sodium hydroxide solution (NaOH). In this way, the chlorine gas becomes a salt load (NaCl) in the exhaust gas scrubber and represents an environmental pollution that must be disposed of specifically. The production of one million fiber kilometers consumes around 160 t of SiCl ₄ , which in turn produces 140 t of chlorine gas or hydrochloric acid as a waste product contaminated with silicon dioxide (SiO). In the chlorine gas scrubber, about 240 l of sodium chloride (NaCl) are created as the brine to be disposed of. The patent specification DE 29 52 038 C2 describes the detailed structure of a special burner for free-flowing particles, the division of the individual areas of the burner into the driving zone, heating zone and conveying zone being mentioned in particular. In the process, free-flowing quartz glass particles in the size range from 0.01 to 2.5 mm fed to the burner via an inlet funnel with an outlet hole and accelerated via the propellant and heating gases so that the melted particles melt immediately into a transparent body. The burner is located in the axial direction and allows the material to grow on the face of a cylinder. The patent DE 196 28 958 C2 describes a process for the production of quartz glass bodies by multi-burners in parallel operation, silicon tetrachloride (SiCl ₄ ) being reacted with a burner and the silicon dioxide thus formed being deposited on the surface.

Also in the process named in the patent specification DE 195 27 451 C2, the silicon dioxide is only formed in the flame of the burner by the starting product silicon tetrachloride (SiCl ₄ ).

It is the object of this invention to present an apparatus for metering silicon dioxide powder for producing high-purity quartz glass by means of SiO ₂ powder, which applies the injected silicon dioxide powder to the sintered body by constant movement of the burner. These silicon dioxide particles are blown onto the body and thus form the quartz sintered body by continuous spinning. The size of the silicon dioxide particles used is approximately 40 nanometers. This also introduces a new process for the production of high-purity quartz glass using silicon dioxide powder (SiO ₂ ) in order to manufacture the enveloping glass surrounding the core area by external coating by means of radial growth and high inflation speed onto the substrate template, by using the silicon dioxide Particles are warmed up and then grown on the substrate body (outside powder deposition). The advantage of the new process is that the environmentally harmful waste products no longer arise.

In order to accomplish the first task, an apparatus is brought in for registration, with which it is possible, depending on the diameter of the quartz glass produced, to supply the necessary silicon dioxide by means of transport by means of oxygen (O ₂ ) and the separate supply of further oxygen and hydrogen , each separately, in the burner chamber. Another object of this invention is to ensure and control the inflow of SiO ₂ and the other gases hydrogen and oxygen with increasing size of the quartz glass body by means of a or two pyrometers (s) connected to the mass flow controller for hydrogen in the coating installation, the temperature of the cylinder is kept constant according to its diameter at a value between 1000 ° C. and 1250 ° C., preferably 1200 ° C. In FIG the entire process technology for the supply of silicon dioxide

Powder shown;

FIG. 1b shows the process technology with the possibility of the separate inlet of silicon dioxide of different particle size, this being done by separating the storage container into two chambers. FIG. 1c shows the separation of silicon dioxide / oxygen flow for supplying several burners.

Figure 2a shows the burner tube with the individual feed lines for oxygen, hydrogen and the silicon dioxide-oxygen mixture in cross section. Figure 2b illustrates the burner in a side view. In Figure 3, the lathe as such and the necessary system components for the outer coating are shown.

As can be seen from FIG. 1, the entire plant for process engineering consists of individual modules and a general oxygen supply 4 for the fluidization of the silicon dioxide powder. One such module is the storage container 6 for the silicon dioxide powder, which is supplied via a filling station 1 with the supply of oxygen (O ₂ ) 3 using a gate valve 2 and a feed pump 15 via a feed line 5 The capacity of the storage container 6 is approximately 2 m. The storage tank 6 has level switches 8a, 8b in order to avoid overfilling 8a or underfilling 8b with silicon dioxide powder. Furthermore, there is a filter system 9 on the storage tank in order to retain the silicon dioxide particles of the outflowing gas during filling. The storage container 6 can also be separated internally in accordance with FIG. 1b. This enables the supply of silicon dioxide particles of different sizes to be fed to the system and thus also to the burner 27. The storage tank shown in FIG. 1b has feed lines 9a, 9b which lead to a filter system 9. By actuating the gate valve 10 in FIG. ₁ a, the silicon dioxide powder is filled in fluidized form by supplying oxygen (O ₂ ) via a feed line 7 into the reservoir of a differential balance 11. This also has a level switch to avoid overfilling 13. When the upper fill level is reached, the gate valve 10 to the reservoir is closed. The differential balance 11 now conveys the silicon dioxide into a downpipe tube with fluidizing device 18 by means of an integrated conveyor screw 17 with a slow pulsating supply of oxygen (O ₂ ) via the feed line 12. A constant material flow is ensured by the conveyor screw 17 because this is at a constant speed conveyed an equal amount of fluidized silica powder. The material metering is ensured with the aid of the load cells 14 in the differential balance 11 by the predetermined material flow (g / min) being discharged from the container 11 via a constant speed control of the screw conveyor 17. A controlled increase in the material flow with increasing process time is also possible. The silicon dioxide fluid transported in this way is now conveyed into a downpipe with fluidization device 18. This fluidization takes place in turn by the supply of oxygen (O ₂ ). The downpipe is interspersed with tubes and is located in a gas-tight cladding tube, so that oxygen (O ₂ ) can flow through the pores and fluidize the particles. The silicon dioxide fluid is metered through a pressure-tight rotary valve 19 at a constant speed into a regulated, closed oxygen stream 20.

This oxygen stream 20 is provided with a gas quantity regulator 22 which can be set in a range from 10 to 100 liters per minute and can convey a powder quantity from 10 to 100 grams per minute. This silicon dioxide fluid is then conveyed into the powder coating installation (FIG. 2) 27 via a movable tube 21, usually a hose. Furthermore, the additional supply of oxygen (O ₂ ) via a separate movable line 23 is required for the powder separation process. This supply can be controlled by a further gas quantity regulator / mass flow regulator 24 in accordance with the diameter of the substrate charge, which is formed by separation in the burner chamber , The powder separation technology requires the supply of hydrogen (H ₂ ), which is supplied in a corresponding amount to the powder coating system 27 via a separate movable tube 25, also via a hose. The quantity control takes place via a gas quantity regulator / mass flow regulator 26 in order to ensure a hydrogen supply corresponding to the size of the substrate charge 35. To avoid temperature fluctuations on the surface of the substrate body, there are two pyrometers 38, 39 (FIG. 3) in the powder coating system. This burner 27, FIGS. 2a, 2b, consists of several centric ring segments with embedded nozzles. In the centrally located ring segment 28 with an inner diameter of 4-10 millimeters, preferably 8 millimeters, the powder flow is fed centrally to the burner 27, the oxygen gas flow 21 conveying the powder being varied in time or regulated by a gas quantity regulator / mass flow regulator 22. In the outer cladding tubes of the burner 31, hydrogen H _{2 is conducted} with embedded, oxygen-carrying nozzles 32 in order to be burned as a pre-mixed gas before it leaves the burner head 33. The flame cone of the burner can be adjusted in a length of 4 to 10 centimeters by means of the gas quantity regulator / mass flow regulator 22, 26 via the burned gas quantity and the mixing ratio of oxygen O ₂ to hydrogen H ₂ .

The pyrmometers 38 9 are attached to the support 45 of the burner 27 at one end at a distance of 500 mm from the substrate body 35 within the powder coating system. When moving from left to right, the hot zone is dragged a few millimeters to the left of the center of the burner depending on the feed speed. The pyrometer 38 has a measuring point of approximately 5 millimeters in diameter and is adjusted to the maximum of the hot zone outside the center of the burner on the left. At the turning point of the burner, the hot zone shifts from the left side to the right side of the burner. The pyrometer 39 takes over the temperature measurement on the right side of the burner 5 millimeters behind the turning point. The pyrometer 39 is adjusted so that the 5 mm measuring point lies in the maximum of the hot zone, which is shifted to the right by a few millimeters outside the center of the burner. A regulator 40 is connected to the pyrometers 38, 39, which in turn controls the gas quantity regulator 26. If the surface temperature of the substrate body 35 decreases or increases, the regulator 40 adjusts the gas quantity regulator 26 in such a way that the supply of hydrogen changes according to the temperature to be achieved of 1200 ° C. The powder coating system 27 shown in Figure 3 consists of a 3 meter wide lathe 41, in which a 1.3 meter long substrate template 35, on which 42 and 43 43 left 0.6 meter long welding rods 42, 43 are welded as holding rods, in the Jaw chucks 44 is clamped. The substrate template 35 has a diameter of 18-20 millimeters and consists of a core preform, which is manufactured according to the CVD process. has been set and rotates at 10-60 revolutions per minute, in one embodiment at 30 revolutions per minute in the lathe. A coating burner system (FIGS. 2a and 2b) is attached to the support 45 on the movable lathe bed. The burner 27 is to be positioned in accordance with FIG. 3 in relation to the substrate tube 35 in such a way that the flame tip of the burner 27 reaches the surface of the substrate 35 and a maximum energy transfer takes place between the flame and the substrate. The burner 27 travels at a deposition speed of 15 to 40 centimeters per minute, preferably 25 centimeters per minute, in a horizontal direction between the end positions on a support 34. It can be in one direction, that is to say in each case forward or backward, or in both directions be moved one after the other. The rotating substrate body 35 can now accommodate the silicon dioxide particles, the size of which is approximately 40 nanometers, which is metered in at high speed. The heated SiO ₂ particles thus adhere to the surface of the rotating substrate body 35 and form the enveloping glass surrounding the core body with increasing thickness. Two auxiliary burners 36a, 36b heat the transition zone between substrate rod 35 and sintered material to about 1000 ° C. at the respective Umkelrrpunkt to minimize the surface tensions occurring in this zone by cooling and heating at a constant temperature. In order to be able to maintain the optimum distance of the burner 27 from the substrate template 35, it is positioned on a displacement device 37 and can be displaced backwards by up to 100 millimeters with increasing diameter of the substrate template 35. The outer diameter of the cylinder is monitored with a red light scanner detector system 38 and the coating process is terminated after the outer diameter has been reached, ie the supply of silicon dioxide and oxygen and hydrogen is stopped. Powder that does not adhere to the surface of the substrate template 35 is extracted with an exhaust air stream from the closed housing and a filter device 39.

After the diameter of the substrate body of 120 millimeters has been reached, the entire process is terminated by the red light scanner detector system 38 in that the gas quantity regulators 22, 24, 26 receive an impulse and the production process is thus interrupted or ended.

Claims

Claims:

1. Process for the production of high-purity quartz glass in the field of optical waveguide production using silicon dioxide powder (SiO ₂ ), characterized in that the silicon dioxide particles transported with oxygen have a

Ring pipe are fed into the powder coating system at high speed and the core preform rotating at 15 to 60 revolutions per minute in the lathe through a burner located on a displacement device, the burner moving in one direction at a deposition speed of 15 to 40 cm / min, preferably 25 cm / min, moved in the horizontal direction, heated to a temperature of 1000-1250 ° C, preferably 1200 ° C, with the addition of oxygen and hydrogen, the burner flame can be designed variably via gas quantity regulator and the burner by the displacement device accordingly of the diameter of the enveloping body, the fed, warmed silicon dioxide particles swirl, on the heated

Remove the core preform body and thus form the enveloping glass enclosing the core area;

2. The method according to claim 1, characterized in that the burner moves horizontally in both directions within the powder coating system; 3. Plant for the exact dosing of silicon dioxide for the production of high-purity quartz glass in the field of optical waveguide production using silicon dioxide powder (SiO ₂ ), characterized in that the diameter of about 40 nanometers having SiO ₂ particles via a for fluidizing the Silicon dioxide-supplied storage tank with level switch and shut-off valve in a weighing system, which has a storage container, shut-off valve, an integrated screw conveyor and load cells, in order to ensure dosing with a silicon dioxide fluid, and then this fluid via a downpipe which penetrates with pores and is located in a gas-tight cladding tube to be transported into a rotary valve which continuously doses the silicon dioxide into an oxygen fuel gas stream which can be controlled via a gas quantity regulator / mass flow controller, this silicon dioxide propellant gas stream into the Powder coating system and the SiO _{2 is} blown onto a substrate template, the burner located on a displacement device through the separate supply of hydrogen H ₂ and oxygen O ₂ , each regulated by gas quantity controller / mass flow controller, are controlled and the outer diameter of the cylinder produced can be monitored by a Rotlich scanner detector system and the coating process can be interrupted once the outer diameter has been reached, and has pyrometer measurement technology, which ensures a constant temperature of 1200 ° C during the coating process, which is in direct coupling with a regulator connected to the gas quantity regulator for the hydrogen supply, so that the hydrogen required for the intensity of the burner flame can be supplied in an appropriate quantity; 4. Plant according to claim 3, characterized in that the storage container consists of two separate chambers with a common outlet and a filter system with two feed lines, each responsible for the corresponding chamber, so that two silicon dioxide powders of different particle sizes are processed in one process can be; 5. Plant according to claim 3 or claim 4, characterized in that a division of a fluidized silicon dioxide powder below the rotary valve by halving the space below the rotary valve in two separate outlets is provided for two separate gas flows, so that two separation burners supplied from a metering device can be.