EP3019453A1 - Method for producing a large quartz-glass pipe - Google Patents

Method for producing a large quartz-glass pipe

Info

Publication number
EP3019453A1
EP3019453A1 EP14736800.5A EP14736800A EP3019453A1 EP 3019453 A1 EP3019453 A1 EP 3019453A1 EP 14736800 A EP14736800 A EP 14736800A EP 3019453 A1 EP3019453 A1 EP 3019453A1
Authority
EP
European Patent Office
Prior art keywords
quartz glass
cylinder
ppm
less
intermediate cylinder
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.)
Withdrawn
Application number
EP14736800.5A
Other languages
German (de)
French (fr)
Inventor
Boris Gromann
Burkhard Oberle
Christian Schenk
Gero Fischer
Pèlagie DECLERCK
Bernhard Franz
Ulrich Lein
Alexander LAAZ
Achim Hofmann
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Heraeus Quarzglas GmbH and Co KG
Original Assignee
Heraeus Quarzglas GmbH and Co KG
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Heraeus Quarzglas GmbH and Co KG filed Critical Heraeus Quarzglas GmbH and Co KG
Publication of EP3019453A1 publication Critical patent/EP3019453A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C3/00—Glass compositions
    • C03C3/04—Glass compositions containing silica
    • C03C3/06—Glass compositions containing silica with more than 90% silica by weight, e.g. quartz
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B23/00—Re-forming shaped glass
    • C03B23/04—Re-forming tubes or rods
    • C03B23/053—Re-forming tubes or rods by centrifuging
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B19/00—Other methods of shaping glass
    • C03B19/14—Other methods of shaping glass by gas- or vapour- phase reaction processes
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B23/00—Re-forming shaped glass
    • C03B23/04—Re-forming tubes or rods
    • C03B23/043—Heating devices specially adapted for re-forming tubes or rods in general, e.g. burners
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B23/00—Re-forming shaped glass
    • C03B23/04—Re-forming tubes or rods
    • C03B23/045—Tools or apparatus specially adapted for re-forming tubes or rods in general, e.g. glass lathes, chucks
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B23/00—Re-forming shaped glass
    • C03B23/04—Re-forming tubes or rods
    • C03B23/07—Re-forming tubes or rods by blowing, e.g. for making electric bulbs
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B23/00—Re-forming shaped glass
    • C03B23/04—Re-forming tubes or rods
    • C03B23/08—Re-forming tubes or rods to exact dimensions, e.g. calibrating
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2201/00—Type of glass produced
    • C03B2201/02—Pure silica glass, e.g. pure fused quartz
    • C03B2201/03—Impurity concentration specified
    • C03B2201/04—Hydroxyl ion (OH)
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2203/00—Production processes
    • C03C2203/40—Gas-phase processes
    • C03C2203/42—Gas-phase processes using silicon halides as starting materials
    • C03C2203/44—Gas-phase processes using silicon halides as starting materials chlorine containing

Definitions

  • the invention relates to a method for producing a quartz glass tube by multi-stage molding, wherein in a first molding step using a mold, an intermediate cylinder made of quartz glass with an intermediate cylinder wall thickness and an intermediate cylinder outer diameter is formed and then cooled, and in a At least one longitudinal section of the cooled intermediate cylinder of a heating zone is fed to the second forming step, heated zone by zone to a softening temperature, and converted around its longitudinal axis to form the quartz glass tube with an end wall thickness and an end outside diameter.
  • a quartz glass hollow cylinder By forming a quartz glass hollow cylinder in two or more forming stages, an increase in the tube outer diameter or a change in its cross-sectional profile is effected.
  • the forming in several stages facilitates compliance with the specified radial dimensions such as outer diameter, inner diameter or wall thickness of the withdrawn pipe string.
  • a generic two-stage forming process is known from DE 10 2007 061 609 A1.
  • a first forming step which is referred to as "upsetting”
  • an output cylinder of quartz glass rotating around its longitudinal axis is partially softened in a front heating zone produced by electrical heating, while being compressed by a mandrel fixed in the cylinder longitudinal axis and at the same time with its cylinder outer casing pressed against a molded part, which is arranged at a predetermined distance from the mandrel, thereby forming a hollow, cylindrical intermediate product of softened quartz glass generates, the inner diameter of the mandrel and its outer diameter determines the molding.
  • the gap between mandrel and molded part defines the desired wall thickness of the hollow intermediate product.
  • the intermediate product As soon as the intermediate product has reached a certain degree of dimensional stability, it is subjected to the second forming step, referred to as "inflation", in which the hollow intermediate product is continuously fed to a rear heating zone, also produced by electric heating, softened therein, and by applying a From there, a thin-walled quartz glass tube with an outer diameter of 305 mm in the direction of the tube longitudinal axis is withdrawn, whereby the "peeling" in an axial stabilization of the quartz glass tube can be exhausted without that the Quartz glass tube further elongating tensile force is applied to the quartz glass tube.
  • inflation in which the hollow intermediate product is continuously fed to a rear heating zone, also produced by electric heating, softened therein, and by applying a From there, a thin-walled quartz glass tube with an outer diameter of 305 mm in the direction of the tube longitudinal axis is withdrawn, whereby the "peeling" in an axial stabilization of the quartz glass tube can be exhausted without that the Quartz glass tube
  • a discontinuous two-stage forming process in order to produce a quartz glass tube made of synthetic quartz glass, a quartz glass is produced in a first forming stage. Glass block converted into a thick-walled hollow cylinder. The hollow cylinder is inflated in a second forming stage to a thin-walled quartz glass tube. In this case, the thick-walled hollow cylinder is clamped in a horizontal orientation in a glass lathe and softened zone by zone by means of a narrow induction-heated graphite heating element which is moved continuously along the hollow cylinder longitudinal axis.
  • the softened area is elongated and at the same time inflated by applying a gas internal pressure without contact to a mold to a thin-walled quartz glass tube having a large outer diameter.
  • a gas internal pressure without contact to a mold to a thin-walled quartz glass tube having a large outer diameter.
  • the non-contact inflation of the hollow cylinder in the last forming step avoids drawing strips and similar defects, as they occur when using molds.
  • compliance with a given dimensional accuracy of the withdrawn quartz glass tube proves to be problematic in this procedure.
  • a solution to this problem is provided by a method variant known from JP 2004 149325 A, in which the last forming stage is repeated several times, so that the final diameter of the quartz glass tube is obtained by gradual enlargement. The diameter increase takes place by rotating the zonewise softened starting tube under the effect of centrifugal force.
  • each enlargement step offers the possibility of taking into account and correcting existing deviations in the respective output tube.
  • this procedure requires a lot of time and energy, but this is justifiable in the case of large quartz glass tubes and very high dimensional stability requirements.
  • Geometry fluctuations increase exponentially with the outer diameter of the tailpipe.
  • the larger the tailpipe diameter the more difficult it is to produce a dimensionally stable large pipe. It is therefore an object of the invention to provide a method that allows the production of quartz glass tubes at economically justifiable expense, which have a high dimensional accuracy, even with a large outer diameter of more than 500 mm.
  • a molding tool is used in the first molding step, so that an intermediate cylinder having a defined outside diameter is obtained.
  • the mold is, for example, mold baking, as described above, or a drawing die, as used in drawing quartz glass tubes from a crucible. In the latter case, a viscous quartz glass mass is formed by means of the die in a quartz glass strand.
  • the problem with the second forming step is to achieve an economically acceptable degree of deformation - that is, to increase the outer diameter of the intermediate cylinder - while maintaining a predetermined dimensional accuracy.
  • the second forming step may also be divided into several sub-forming steps with a lower degree of deformation, as is known from the above-mentioned prior art.
  • the hydroxyl group content of the silica glass and its axial distribution over the length of the intermediate cylinder are crucial parameters.
  • the hydroxyl group content of quartz glass has an effect on its viscosity. Accordingly, gradients in hydroxyl group concentration upon softening of the silica glass cause local viscosity differences in the intercylinder wall which can lead to undesirable and unpredictable deformations. This effect is further enhanced by the fact that the hydroxyl group content of the quartz glass also has an effect on the absorption of infrared radiation. A higher hydroxyl group content leads to an increased absorption and a higher radiation in the infrared wavelength range. Such quartz glass gets hotter faster and it cools faster than quartz glass with a lower hydroxyl group content. Variations in the hydroxyl group content therefore affect viscosity in several respects and lead to undesirable and barely controllable deformations in the forming process.
  • quartz glass of naturally occurring raw material which generally has a low hydroxyl group content, should prove less sensitive to undesirable deformations.
  • this is not confirmed in this unambiguity in practice.
  • the transformation of quartz glass from natural raw material to large-scale to scale true is problematic. This can be attributed to other impurities present in the natural quartz raw material.
  • Synthetically produced quartz glass usually shows a high purity, but often contains large amounts of hydroxyl groups due to the production, which can lead to unpredictable and undefined deformations at high degrees of deformation, as explained above.
  • the invention now provides a method which, in compliance with narrow framework conditions, an economical processing of synthetic produced quartz glass to dimensionally large pipes allowed, even if this high degrees of deformation are required.
  • the synthetic quartz glass of the intermediate cylinder has a low average hydroxyl group content of 10 ppm by weight or less, preferably 2 ppm by weight or less, and that the hydroxyl group content is longer than the inter-cylinder length is distributed so homogeneously, which differ in subdivision of the intermediate cylinder into lengths with a length of 1 cm, adjacent lengths in their average hydroxyl group content by less than 2 ppm by weight, preferably less than 1 ppm by weight, from each other.
  • the production of synthetic quartz glass with such a low hydroxyl group content generally proceeds via a porous semifinished product of SiO 2 particles, which requires a drying treatment to eliminate it contained hydroxyl groups allows.
  • the drying treatment of the porous SiO 2 body can be carried out purely thermally - assisted by negative pressure - or by chemical reaction with a drying reagent - such as chlorine.
  • the setting of an average hydroxyl group content of less than 10 ppm by weight is less problematic than the generation of a uniform over the volume of the porous SiO 2 body concentration profile.
  • DE 10 152 328 A1 describes a procedure for solving this problem, which already begins in an early phase of the production of the quartz glass tube.
  • the synthetically produced quartz glass has a high average hydroxyl group content above 10 ppm by weight, it proves to be increasingly difficult to ensure the required dimensional stability of the large pile as a whole. If the axial concentration profile shows fluctuations of more than 2 ppm by weight / mm over a length of 1 cm, the second forming process will easily lead to local deviations in the wall thickness of the large pipe.
  • the content of hydroxyl groups of the quartz glass is determined by measuring the IR absorption by the method of D.M. Dodd and D.B. Fräser, Optical determination of OH in fused silica, Journal of Applied Physics, Vol. 37 (1966), p. 391 1.
  • the average content of hydroxyl groups of the quartz glass is determined by measuring through the pipe wall in the direction of the longitudinal axis of the intermediate tube.
  • the average value of the hydroxyl group content in length sections of 1 cm is considered to be the measured value which, when measured in the geometric center of the respective length section, is obtained through the wall of the intermediate tube and perpendicular to its longitudinal axis.
  • quartz glass halide starting materials are frequently used - for example SiCl 4 or halogen-containing drying reagents - for example chlorine- or halogen-containing dopants - for example fluorine. Because of this, large quantities of halogens can be contained in the synthetic quartz glass. However, it has been shown that, in addition to the hydroxyl group content, the halogen content in the second forming step old - and especially the chlorine content - can make the dimensional accuracy of the final quartz glass tube and on the bubble content noticeable.
  • quartz glass is preferably used, the average chlorine concentration of less than 3000 ppm by weight.
  • the chlorine concentration is determined as the mean value of test samples taken at three points uniformly distributed over the inter-cylinder length (start, middle, end) by dissolving the test samples in aqueous HF solution and the resulting solutions after addition of AgNO 3 be subjected to nephelometric analysis.
  • a method variant has proven to be advantageous in which the quartz glass tube is not elongated in the second forming step, wherein the diameter increase based on centrifugal force or blowing pressure.
  • holders are welded to the quartz glass cylinder to be formed on the front side, and these are clamped in the chuck of a glass lathe and rotated synchronously.
  • a heating source is moved in zones along the quartz glass cylinder.
  • a defined internal pressure can be adjusted in the inner bore of the quartz glass cylinder.
  • the quartz glass tube is compressed in the second forming step in the direction of its longitudinal axis, so that its wall thickness after upsetting is between 70% and at most 100% of its wall thickness before upsetting.
  • the aim of the second forming step is a diameter increase of the quartz glass tube while largely maintaining its wall thickness. This is achieved by shortening the initial length of the quartz glass tube in the forming step, so the output tube is compressed.
  • the upsetting lies the wall thickness preferably between 70% and at most 100% of the initial value.
  • the homogeneity of the temperature field and the composition of the atmosphere in the region of the heating zone have as important parameters for a reproducible forming process little control needed.
  • the heating zone is formed by a plurality of annularly distributed around the circumference of the intermediate cylinder heat sources, which are selected from the group: plasma torch, gas burner, laser.
  • the heating energy compared to a furnace can be set locally defined and metered faster and more accurate and thus set or corrected even a predetermined temperature field, even if it is not rotationally symmetrical.
  • the heat sources are able to provide a high level of energy at specific points. At least five such heat sources are evenly distributed in a circular ring around the intermediate cylinder to be softened. Compared to an oven, the diameter of the circular ring shape can be more easily adapted to the diameter of the quartz glass cylinder to be softened, for example, even if the second forming step is divided into sub-forming steps each having a smaller degree of deformation, wherein the outer diameter of the quartz glass cylinder to be formed is gradually increased. With a view to avoiding the entry of hydroxyl groups, hydrogen-free plasma torches or CO 2 lasers are preferred.
  • metal oxide impurities In addition to hydroxyl groups and halogens, metal oxide impurities also have an effect on the viscosity of the synthetic quartz glass, aluminum oxide in particular being mentioned here. Possible concentration fluctuations This contamination is the more pronounced and effective, the higher their average concentration.
  • quartz glass is preferably used which has a concentration of aluminum (Al) of less than 1 ppm by weight and a total content of other metallic impurities of less than 4 ppm by weight.
  • the quartz glass has a concentration of alkali and alkaline earth metal impurities of less than 0.3 ppm by weight.
  • Alkali and alkaline earth ions already have a noticeable effect on the viscosity of quartz glass in a small amount and they promote its crystallization tendency.
  • an initial hollow cylinder made of quartz glass is fed to an electrically heated furnace, softened in zones and continuously and rotating about its longitudinal axis with its cylinder outer shell against the mold and continuously formed by the mold to the intermediate cylinder.
  • This procedure allows the production of thick-walled and yet accurate intermediate cylinders.
  • An electrically heated oven generally causes higher energy costs than burner heating.
  • the electric heating facilitates the maintenance of a predetermined temperature field and a low-hydrogen and hydrogen-poor atmosphere.
  • an electrically heated furnace is used for the forming of the output cylinder to the intermediate cylinder.
  • the dimensions of the furnace seen in the direction of the cylinder longitudinal axis are at least 500 mm and the distance between the outer wall of the intermediate cylinder and an inner wall of the furnace less than 100 mm.
  • the intermediate cylinder obtained after the first forming process can be subsequently processed.
  • FIG. 1 shows a device for carrying out a first forming process for the production of an intermediate tube made of synthetically produced quartz glass in a side view
  • FIG. 2 shows a device for carrying out a second forming process for the purpose of producing a large pipe from the intermediate pipe in a side view.
  • a hollow cylinder 1 made of synthetically produced quartz glass is provided, which satisfies high demands on its purity and on the homogeneity of the viscosity-influencing components.
  • the preparation comprises the flame hydrolysis of SiCl 4 , in which SiO 2 particles are formed and deposited in layers on the cylinder jacket surface of a support rotating about its longitudinal axis to form a soot body.
  • the method known from DE 10 152 328 A is used to produce a specific radial density profile within the soot body wall, that is, in the deposition of the first soot layers, a comparatively high surface temperature and thus a soot area with a comparatively high density generated by about 30%.
  • the soot density then continues to gradually increase until it reaches about 32% in a "transitional area.”
  • the surface temperature of the forming soot body is lowered continuously and thus the soot density reduced.
  • a soot tube having a specific radial density profile is obtained.
  • the soot tube is subjected to a dehydration treatment and treated in a vertical orientation in a dehydration oven initially at a temperature of about 900 ° C. in a chlorine-containing atmosphere.
  • the treatment takes about eight hours. This sets a low hydroxyl group content.
  • the process-related different effectiveness of the penetrating over the mantle surfaces in the soot body chlorine is compensated by the previously generated density profile, so that sets over the thickness of the wall, a substantially homogeneous, radial concentration profile for the hydroxyl groups.
  • soot tube is placed in a vertically oriented vitrification furnace and treated therein with oxygen at a temperature around 1000 ° C to remove chlorine and to saturate any oxygen deficiency defects. Subsequently, the soot tube is sintered at a temperature around 1300 ° C by being fed to an annular heating zone and heated therein in zones.
  • the hollow cylinder 1 thus produced (see FIG. 1) has a length of 300 cm, an outer diameter of 200 mm and an inner diameter of 40 mm. It consists of synthetic quartz glass with a low content of metal oxide impurities whose concentrations (in ppm by weight) are given in Table 1:
  • the quartz glass has an average hydroxyl group content of 8.3 ppm by weight (measured over the tube longitudinal axis) and a mean chlorine concentration of 1710 ppm by weight. Viewed along the length of the thick-walled hollow cylinder, the hydroxyl group content determined at 29 measuring points at a distance of 10 cm varies by +/- 0.9 ppm by weight (standard deviation).
  • the first forming step takes place by means of the method described in DE 10 2007 051 898 A1.
  • FIG. 1 shows diagrammatically the device by means of which the thick-walled quartz glass hollow cylinder 1 is formed into a thin-walled intermediate cylinder 2 with an outer diameter of 320 mm, a wall thickness of 15 mm and a length of 6.20 m.
  • the hollow cylinder 1 is pushed with a feed device continuously and under rotation about its longitudinal axis 3 at a feed rate of 4 cm / min in a resistance furnace 4, which surrounds the hollow cylinder 1 annular with an inner diameter of 400 mm and in zonewise to a temperature around 2100 ° C heated up.
  • a (not shown in the figure) pulling device is used, which rotates the intermediate cylinder 2 about its longitudinal axis 3 rotating at a peel rate of about 12 cm / min in the direction of the longitudinal axis 3.
  • the quartz glass hollow cylinder 1 is closed at its free end face with a gas-tight rotary feedthrough.
  • a mold that has two water-cooled mold jaws 5, which are occupied with graphite fits (in Figure 1 only schematically indicated).
  • a gas flow is introduced into the rotating quartz glass hollow cylinder 1, so that a controllable internal overpressure of about 10 mbar is established.
  • the hollow cylinder 1 is thereby inflated against the mold jaws 5 to the target diameter of 340 mm, with a peripheral bead 6 forms in front of the mold jaws 5.
  • the intermediate cylinder 2 can then be released from the mold jaws 5, so that the actually adjusting outer diameter may differ slightly from the distance of the mold jaws.
  • a measuring and control device 13 For measuring and controlling the outer diameter, a measuring and control device 13 is shown schematically provided, the two high-resolution CCD cameras 7; 8 for detecting the longitudinal edges 10; 1 1 of the hollow cylinder 1 and 12 monitors that indicate the relative axial position of the optically detected longitudinal edges 10, 1 1.
  • the control device 13 For further details of the operation of the control device 13, reference is made to DE 10 2007 051 898 A1.
  • the thus obtained intermediate cylinder 2 is characterized by a defined outer diameter and overall high dimensional accuracy.
  • the quality of the quartz glass corresponds unchanged to that of the hollow cylinder 1, as explained above. It is suitable as a defined starting material for the production of a large pipe.
  • Second forming step for producing the large pipe Figure 2 shows schematically the apparatus for forming the intermediate cylinder 2 to the desired large pipe 22 with an outer diameter of 960 mm.
  • a burner carriage 21 drives the intermediate cylinder 2 from right to left, as indicated by the directional arrow 23.
  • a burner ring is mounted, which serves to heat and soften the intermediate cylinder 2.
  • the burner ring 25 is formed from five gas burners which are circular and evenly distributed around the cylinder longitudinal axis 3.
  • the intermediate cylinder 2 is continuously rotated under its longitudinal axis 3 at a speed of 60 rpm (corresponding to the axis of rotation) under the action of the torch ring and thus becomes high temperature 2,100 ° C heated.
  • the inner bore 20 can be flushed with a gas and a defined and regulated internal pressure can be adjusted to about 100 mbar in the inner bore 20.
  • the quartz glass tube (22) thus obtained serves as an intermediate cylinder 2 for further forming on the basis of the method shown in FIG.
  • the intermediate cylinder 2 is gradually expanded to the quartz glass tube 22, wherein each deformation step makes a diameter widening of 65 mm or less.
  • the outer diameter of the burner ring 25 can be easily adapted to the respective outer diameter of the deformation stage.
  • the inflated large tube 22 has approximately the same wall thickness (100%) as the initially inserted intermediate tube 2 and is compressed to a final length of 2.976 m.
  • a large tube 22 made of synthetic quartz glass with overall high dimensional accuracy is economically obtained with only two forming steps but in compliance with the above-mentioned boundary conditions with respect to the chemical composition of the quartz glass and its homogeneity.
  • the wall thickness variation of the quartz glass bulk product 22 produced in this way is less than 0.42 mm per pipe length meter.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Manufacturing & Machinery (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Chemical & Material Sciences (AREA)
  • Geochemistry & Mineralogy (AREA)
  • Re-Forming, After-Treatment, Cutting And Transporting Of Glass Products (AREA)
  • Glass Melting And Manufacturing (AREA)

Abstract

Multi-step shaping methods for producing a large quartz-glass pipe are known, in which in a first forming step an intermediate cylinder made of quartz glass and having an intermediate-cylinder wall thickness and an intermediate-cylinder outside diameter is formed by using a forming tool and is then cooled, and in a second shaping step at least one length segment of the cooled intermediate cylinder is fed to a heating zone, is heated to a softening temperature zone by zone therein, and, while rotating about the longitudinal axis of the intermediate cylinder, is shaped into the large quartz-glass pipe having a final wall thickness and a final outside diameter. Geometry fluctuations increase exponentially with the outside diameter of the final pipe. In order to specify a method on the basis thereof which permits quartz-glass pipes having high dimensional accuracy even for large outside diameters greater than 500 mm to be produced at economically justifiable expense, the quartz glass according to the invention is synthetically produced and has an average hydroxyl group content of 10 ppm by weight or less, with the additional stipulation that, if the intermediate cylinder is divided into length segments having a length of 1 cm, adjacent length segments have a difference of less than 2 ppm by weight in the average hydroxyl group content thereof.

Description

Verfahren zur Herstellung eines Quarzglas-Großrohres  Method for producing a quartz glass large tube
Beschreibung description
Technisches Gebiet Die Erfindung betrifft ein Verfahren zur Herstellung eines Quarzglas-Großrohres durch mehrstufiges Formen, wobei in einem ersten Formschritt unter Einsatz eines Formwerkzeugs ein Zwischenzylinder aus Quarzglas mit einer Zwischenzylinder-Wandstärke und einem Zwischenzylinder-Außendurchmesser geformt und anschließend abgekühlt wird, und indem in einem zweiten Umformschritt mindes- tens ein Längenabschnitt des abgekühlten Zwischenzylinders einer Heizzone zugeführt, darin zonenweise auf eine Erweichungstemperatur erhitzt und um seine Längsachse rotierend zu dem Quarzglas-Großrohr mit einer End-Wandstärke und einem End-Außendurchmesser umgeformt wird. TECHNICAL FIELD The invention relates to a method for producing a quartz glass tube by multi-stage molding, wherein in a first molding step using a mold, an intermediate cylinder made of quartz glass with an intermediate cylinder wall thickness and an intermediate cylinder outer diameter is formed and then cooled, and in a At least one longitudinal section of the cooled intermediate cylinder of a heating zone is fed to the second forming step, heated zone by zone to a softening temperature, and converted around its longitudinal axis to form the quartz glass tube with an end wall thickness and an end outside diameter.
Durch Formen eines Quarzglas-Hohlzylinders in zwei oder mehr Umformstufen wird eine Vergrößerung des Rohr-Außendurchmessers oder eine Veränderung von dessen Querschnittsprofil bewirkt. Das Umformen in mehreren Stufen erleichtert die Einhaltung der vorgegebenen radialen Abmessungen wie Außendurchmesser, Innendurchmessers oder Wandstärke des abgezogenen Rohrstrangs. By forming a quartz glass hollow cylinder in two or more forming stages, an increase in the tube outer diameter or a change in its cross-sectional profile is effected. The forming in several stages facilitates compliance with the specified radial dimensions such as outer diameter, inner diameter or wall thickness of the withdrawn pipe string.
Stand der Technik Ein gattungsgemäßes zweistufiges Umformverfahren ist aus der DE 10 2007 061 609 A1 bekannt. In einem ersten Umformschritt, der als„Stauchen" bezeichnet wird, wird ein um seine Längsachse rotierender Ausgangszylinder aus Quarzglas bereichsweise in einer vorderen, durch elektrisches Beheizen erzeugten Heizzone erweicht, dabei über einen in der Zylinder-Längsachse feststehenden Dorn gestaucht und gleichzeitig mit seinem Zylinderaußenmantel gegen ein Formteil gedrückt, das in einem vorgegebenen Abstand zum Dorn angeordnet ist. Dabei wird ein hohles, zylinderförmiges Zwischenprodukt aus erweichtem Quarzglas erzeugt, dessen Innendurchmesser der Dorn und dessen Außendurchmesser das Formteil festlegt. Der Spalt zwischen Dorn und Formteil definiert die Soll- Wandstärke des hohlen Zwischenproduktes. PRIOR ART A generic two-stage forming process is known from DE 10 2007 061 609 A1. In a first forming step, which is referred to as "upsetting", an output cylinder of quartz glass rotating around its longitudinal axis is partially softened in a front heating zone produced by electrical heating, while being compressed by a mandrel fixed in the cylinder longitudinal axis and at the same time with its cylinder outer casing pressed against a molded part, which is arranged at a predetermined distance from the mandrel, thereby forming a hollow, cylindrical intermediate product of softened quartz glass generates, the inner diameter of the mandrel and its outer diameter determines the molding. The gap between mandrel and molded part defines the desired wall thickness of the hollow intermediate product.
Sobald das Zwischenprodukt eine gewisse Formstabilität erreicht hat, wird es im selben Arbeitsgang dem zweiten Umformschritt unterzogen, der als„Aufblasen" bezeichnet wird. Dabei wird das hohle Zwischenprodukt kontinuierlich einer hinteren, ebenfalls durch elektrisches Beheizen erzeugten Heizzone zugeführt, darin erweicht und durch Anlegen eines Innendrucks im Hohlraum gegen ein zweites Formteil geblasen. Von dort wird ein dünnwandiges Quarzglasrohr mit einem Au- ßendurchmesser von 305 mm in Richtung der Rohr-Längsachse abgezogen, wobei sich das„Abziehen" in einer axialen Stabilisierung des Quarzglasrohres erschöpfen kann, ohne dass eine das Quarzglasrohr weiter elongierende Zugkraft an dem Quarzglasrohr anliegt. As soon as the intermediate product has reached a certain degree of dimensional stability, it is subjected to the second forming step, referred to as "inflation", in which the hollow intermediate product is continuously fed to a rear heating zone, also produced by electric heating, softened therein, and by applying a From there, a thin-walled quartz glass tube with an outer diameter of 305 mm in the direction of the tube longitudinal axis is withdrawn, whereby the "peeling" in an axial stabilization of the quartz glass tube can be exhausted without that the Quartz glass tube further elongating tensile force is applied to the quartz glass tube.
Der Außendurchmesser des Quarzglasrohres wird durch den radialen Abstand des Formwerkzeugs von der Längsachse (=Ziehachse) bestimmt, und die Wandstärke durch das Verhältnis der Zufuhrgeschwindigkeit des Ausgangszylinders und der Abzugsgeschwindigkeit des Quarzglasrohres. The outer diameter of the quartz glass tube is determined by the radial distance of the mold from the longitudinal axis (= drawing axis), and the wall thickness by the ratio of the feed rate of the output cylinder and the withdrawal speed of the quartz glass tube.
Da Stauchen und Aufblasen in einem Arbeitsgang erfolgen, ergibt sich eine beträchtliche Zeit- und Energieeinsparung. Die Innenwandung des so erhaltenen Quarzglasrohres ist werkzeugfrei geformt. Der Außenmantel kommt jedoch in Kontakt mit dem Formwerkzeug, so dass sich bei hohem Druck auf das weiche Quarzglas Ziehstreifen oder andere Defekte ausbilden können. Zudem kann es nach dem Ablösen des Quarzglasrohr-Strangs vom letzten Formwerkzeug noch zu Durchmesseränderungen kommen. Im Zuge steigender Anforderungen an die Defektfreiheit und Maßhaltigkeit der Bauteile erweist sich diese Verfahrensweise als unzureichend. Since upsetting and inflation occur in one operation, there is a considerable time and energy savings. The inner wall of the quartz glass tube thus obtained is formed without tools. However, the outer sheath comes into contact with the mold, so that at high pressure on the soft quartz glass drawing strips or other defects can form. In addition, after the detachment of the quartz glass tube strand from the last forming tool, there may still be changes in the diameter. In the course of increasing demands on the defect-free and dimensional accuracy of the components, this procedure proves to be inadequate.
Diese Nachteile vermeidet ein diskontinuierliches zweistufiges Umformverfahren, wie es aus der JP H04-26522 A bekannt ist. Zur Herstellung eines Quarzglasrohres aus synthetischem Quarzglas wird in einer ersten Umformstufe ein Quarz- glasblock zu einem dickwandigen Hohlzylinder umgeformt. Der Hohlzylinder wird in einer zweiten Umformstufe zu einem dünnwandigen Quarzglasrohr aufgeblasen. Dabei wird der dickwandige Hohlzylinder in horizontaler Orientierung in einer Glasdrehbank eingespannt und mittels eines schmalen induktionsbeheizten Gra- fit-Heizelements, das kontinuierlich entlang der Hohlzylinder-Längsachse bewegt wird, zonenweise erweicht. Der erweichte Bereich wird elongiert und gleichzeitig durch Anlegen eines Gas-Innenüberdrucks ohne Kontakt zu einem Formwerkzeug zu einem dünnwandigen Quarzglasrohr mit großem Außendurchmesser aufgeblasen. Das kontaktfreie Aufblasen des Hohlzylinders im letzten Umformschritt vermeidet zwar Ziehstreifen und ähnliche Defekte, wie sie bei Einsatz von Formwerkzeugen auftreten. Andererseits erweist sich bei dieser Verfahrensweise die Einhaltung einer vorgegebenen Maßhaltigkeit des abgezogenen Quarzglasrohres als problematisch. Eine Lösung für dieses Problem bietet eine aus der JP 2004 149325 A bekannte Verfahrensvariante, bei der die letzte Umformstufe mehrfach wiederholt wird, so dass sich der endgültige Durchmesser des Quarzglas-Rohres durch allmähliche Vergrößerung ergibt. Die Durchmesser-Vergrößerung erfolgt dabei durch Rotieren des zonenweise erweichten Ausgangsrohres unter Wirkung der Zentrifugal- kraft. These disadvantages are avoided by a discontinuous two-stage forming process, as known from JP H04-26522 A. In order to produce a quartz glass tube made of synthetic quartz glass, a quartz glass is produced in a first forming stage. Glass block converted into a thick-walled hollow cylinder. The hollow cylinder is inflated in a second forming stage to a thin-walled quartz glass tube. In this case, the thick-walled hollow cylinder is clamped in a horizontal orientation in a glass lathe and softened zone by zone by means of a narrow induction-heated graphite heating element which is moved continuously along the hollow cylinder longitudinal axis. The softened area is elongated and at the same time inflated by applying a gas internal pressure without contact to a mold to a thin-walled quartz glass tube having a large outer diameter. Although the non-contact inflation of the hollow cylinder in the last forming step avoids drawing strips and similar defects, as they occur when using molds. On the other hand, compliance with a given dimensional accuracy of the withdrawn quartz glass tube proves to be problematic in this procedure. A solution to this problem is provided by a method variant known from JP 2004 149325 A, in which the last forming stage is repeated several times, so that the final diameter of the quartz glass tube is obtained by gradual enlargement. The diameter increase takes place by rotating the zonewise softened starting tube under the effect of centrifugal force.
Dadurch ergibt sich bei jedem einzelnen Vergrößerungsschritt ein vergleichsweise geringer Verformungsgrad, was mit einer geringeren Abweichung von der Soll- Abmessung bei der jeweils erhaltenen Zwischengröße einhergeht. Außerdem bietet jeder Vergrößerungsschritt die Möglichkeit, im jeweiligen Ausgangsrohr vor- handene Maßabweichungen zu berücksichtigen und zu korrigieren. Andererseits liegt es aber auf der Hand, dass diese Verfahrensweise einen hohen Zeit- und Energieaufwand erfordert, der aber bei großen Quarzglasrohren und sehr hohen Anforderungen an die Maßhaltigkeit zu rechtfertigen ist. Technische Aufgabe This results in each individual enlargement step, a comparatively low degree of deformation, which is associated with a smaller deviation from the nominal dimension in each case obtained intermediate size. In addition, each enlargement step offers the possibility of taking into account and correcting existing deviations in the respective output tube. On the other hand, it is obvious that this procedure requires a lot of time and energy, but this is justifiable in the case of large quartz glass tubes and very high dimensional stability requirements. Technical task
Geometrieschwankungen nehmen mit dem Außendurchmesser des Endrohres exponentiell zu. Je größer der Endrohr-Durchmesser ist, umso schwieriger wird die Herstellung eines maßhaltigen Großrohres. Es ist daher Aufgabe der Erfindung, ein Verfahren anzugeben, das bei wirtschaftlich vertretbarem Aufwand die Herstellung von Quarzglasrohren erlaubt, die auch bei großem Außendurchmesser von mehr als 500 mm eine hohe Maßhaltigkeit haben. Geometry fluctuations increase exponentially with the outer diameter of the tailpipe. The larger the tailpipe diameter, the more difficult it is to produce a dimensionally stable large pipe. It is therefore an object of the invention to provide a method that allows the production of quartz glass tubes at economically justifiable expense, which have a high dimensional accuracy, even with a large outer diameter of more than 500 mm.
Allgemeine Beschreibung der Erfindung Diese Aufgabe wird ausgehend von einem Verfahren der eingangs genannten Gattung erfindungsgemäß dadurch gelöst, dass das Quarzglas synthetisch erzeugt ist und einen mittleren Hydroxylgruppengehalt von 10 Gew.-ppm oder weniger hat, mit der zusätzlichen Maßgabe, dass bei Unterteilung des Zwischenzylinders in Längenabschnitte mit einer Länge von 1 cm, benachbarte Längenab- schnitte in ihrem mittleren Hydroxylgruppengehalt einen Unterschied von weniger als 2 Gew.-ppm aufweisen. General description of the invention This object is achieved on the basis of a method of the type mentioned above in that the quartz glass is synthetically produced and has an average hydroxyl group content of 10 ppm by weight or less, with the additional proviso that when subdividing the intermediate cylinder in Length sections with a length of 1 cm, adjacent length sections in their average hydroxyl group content have a difference of less than 2 ppm by weight.
Beim erfindungsgemäßen Verfahren wird im ersten Formschritt ein Formwerkzeug eingesetzt, so dass ein Zwischenzylinder mit definiertem Außendurchmesser erhalten wird. Bei dem Formwerkzeug handelt es sich beispielsweise um Formbacken, wie oben beschrieben, oder um eine Ziehdüse, wie sie beim Ziehen von Quarzglasrohren aus einem Schmelztiegel eingesetzt wird. Im letztgenannten Fall wird eine zähflüssige Quarzglasmasse mittels der Ziehdüse in einen Quarzglasstrang umgeformt. Problematisch beim zweiten Umformschritt ist, einen in wirtschaftlicher Hinsicht akzeptablen Grad an Umformung - das heißt an Vergrößerung des Außendurchmessers des Zwischenzylinders - bei gleichzeitiger Einhaltung einer vorgegebenen Maßhaltigkeit zu erreichen. Der zweite Umformschritt kann auch in mehrere Sub-Umformschritte mit geringerem Verformungsgrad unterteilt sein, wie dies aus dem oben genannten Stand der Technik bekannt ist. In the method according to the invention, a molding tool is used in the first molding step, so that an intermediate cylinder having a defined outside diameter is obtained. The mold is, for example, mold baking, as described above, or a drawing die, as used in drawing quartz glass tubes from a crucible. In the latter case, a viscous quartz glass mass is formed by means of the die in a quartz glass strand. The problem with the second forming step is to achieve an economically acceptable degree of deformation - that is, to increase the outer diameter of the intermediate cylinder - while maintaining a predetermined dimensional accuracy. The second forming step may also be divided into several sub-forming steps with a lower degree of deformation, as is known from the above-mentioned prior art.
Es hat sich gezeigt, dass in dieser Hinsicht der Hydroxylgruppengehalt des Quarzglases und dessen axiale Verteilung über die Länge des Zwischenzylinders entscheidende Parameter sind. Der Hydroxylgruppengehalt von Quarzglas hat Auswirkungen auf dessen Viskosität. Demgemäß verursachen Gradienten in der Hydroxylgruppen-Konzentration beim Erweichen des Quarzglases lokale Viskositätsunterschiede in der Zwischenzylinder-Wandung, die zu unerwünschten und nicht vorhersehbaren Verformungen führen können. Dieser Effekt wird noch dadurch verstärkt, dass der Hydroxylgruppengehalt des Quarzglases auch Auswirkungen auf die Absorption von Infrarotstrahlung hat. Ein höherer Hydroxylgruppengehalt führt zu einer verstärkten Absorption und einer höheren Abstrahlung im infraroten Wellenlängenbereich. Solches Quarzglas wird schneller heiß und es kühlt schneller ab als Quarzglas mit geringerem Hydro- xylgruppengehalt. Schwankungen im Hydroxylgruppengehalt wirken sich daher in mehrfacher Hinsicht auf Viskosität aus und führen zu unerwünschten und kaum beherrschbaren Verformungen beim Umformprozess. It has been found that in this regard, the hydroxyl group content of the silica glass and its axial distribution over the length of the intermediate cylinder are crucial parameters. The hydroxyl group content of quartz glass has an effect on its viscosity. Accordingly, gradients in hydroxyl group concentration upon softening of the silica glass cause local viscosity differences in the intercylinder wall which can lead to undesirable and unpredictable deformations. This effect is further enhanced by the fact that the hydroxyl group content of the quartz glass also has an effect on the absorption of infrared radiation. A higher hydroxyl group content leads to an increased absorption and a higher radiation in the infrared wavelength range. Such quartz glass gets hotter faster and it cools faster than quartz glass with a lower hydroxyl group content. Variations in the hydroxyl group content therefore affect viscosity in several respects and lead to undesirable and barely controllable deformations in the forming process.
Im Hinblick darauf sollte sich Quarzglas aus natürlich vorkommendem Rohstoff, das in der Regel einen niedrigen Hydroxylgruppengehalt hat, gegen unerwünsch- te Verformungen als weniger empfindlich erweisen. Dies bestätigt sich jedoch in dieser Eindeutigkeit in der Praxis nicht. Im Gegenteil, das Umformen von Quarzglas aus natürlichem Rohstoff zu maßstabsgenauen Großrohren erweist sich als problematisch. Dies kann auf andere im natürlichen Quarzrohstoff vorhandene Verunreinigungen zurückgeführt werden. Synthetisch erzeugtes Quarzglas zeigt zwar in der Regel eine hohe Reinheit, enthält jedoch herstellungsbedingt häufig große Mengen an Hydroxylgruppen, die bei großen Umformgraden zu unvorhersehbaren und Undefinierten Verformungen führen können, wie oben erläutert. In view of this, quartz glass of naturally occurring raw material, which generally has a low hydroxyl group content, should prove less sensitive to undesirable deformations. However, this is not confirmed in this unambiguity in practice. On the contrary, the transformation of quartz glass from natural raw material to large-scale to scale true is problematic. This can be attributed to other impurities present in the natural quartz raw material. Synthetically produced quartz glass usually shows a high purity, but often contains large amounts of hydroxyl groups due to the production, which can lead to unpredictable and undefined deformations at high degrees of deformation, as explained above.
Die Erfindung stellt nun eine Methode zur Verfügung, die bei Einhaltung enger Rahmenbedingungen eine wirtschaftliche Verarbeitung von synthetisch erzeugtem Quarzglas zu maßhaltigen Großrohren erlaubt, auch wenn dafür hohe Unformgrade erforderlich sind. The invention now provides a method which, in compliance with narrow framework conditions, an economical processing of synthetic produced quartz glass to dimensionally large pipes allowed, even if this high degrees of deformation are required.
Die wichtigsten Rahmenbedingungen sind: The most important basic conditions are:
(a) der Einsatz eines mindestens zweistufigen Umformprozesses, wobei in der ersten Umformstufe zur möglichst genauen Einhaltung eines vorgegebenen(A) the use of an at least two-stage forming process, wherein in the first forming stage for the most accurate compliance with a predetermined
Außendurchmessers des dabei erzeugten Umform Produktes ein Formwerkzeug eingesetzt wird. Das Umformprodukt dieser Umformstufe dient als Ausgangszylinder im zweiten Umformschritt, der sich unmittelbar anschließen kann. (b) Dabei hat es sich als wichtig erwiesen, dass das synthetische Quarzglas des Zwischenzylinders einen geringen mittleren Hydroxylgruppengehalt von 10 Gew.-ppm oder weniger, vorzugsweise von 2 Gew.-ppm oder weniger hat, und dass der Hydroxylgruppengehalt über die Zwischenzylinder-Länge so homogen verteilt ist, das sich bei Unterteilung des Zwischenzylinders in Längenabschnitte mit einer Länge von 1 cm, benachbarte Längenabschnitte in ihrem mittleren Hydroxylgruppengehalt um weniger als 2 Gew.-ppm, vorzugsweise weniger als 1 Gew.-ppm, voneinander unterscheiden. Outer diameter of the resulting forming product a mold is used. The forming product of this forming stage serves as a starting cylinder in the second forming step, which can connect directly. (b) It has been found to be important that the synthetic quartz glass of the intermediate cylinder has a low average hydroxyl group content of 10 ppm by weight or less, preferably 2 ppm by weight or less, and that the hydroxyl group content is longer than the inter-cylinder length is distributed so homogeneously, which differ in subdivision of the intermediate cylinder into lengths with a length of 1 cm, adjacent lengths in their average hydroxyl group content by less than 2 ppm by weight, preferably less than 1 ppm by weight, from each other.
(c) Bei Einhaltung der Bedingungen (a) und (b) ergibt sich in der zweiten Umformstufe zum Quarzglas-Großrohr ein reproduzierbares Umformverhalten mit geringem Korrektur- und Nachsteuerungsbedarf. Dadurch kann auch bei hohem Umformgrad im besten Fall auf ein Formwerkzeug verzichtet werden. Wird dabei ein Formwerkzeug eingesetzt, genügt eine geringfügige Einwirkung auf die Außenwandung des Großrohres, so dass als Umformprodukt dieses Umformschritts ein Quarzglas-Großrohr mit der gewünschten Maß- haltigkeit, glatter und qualitativ hochwertiger Innenwandung und trotzdem weitgehend defektfreier und streifenfreier Oberfläche erhalten wird. (c) If the conditions (a) and (b) are adhered to, a reproducible forming behavior results in the second forming step for the quartz glass large tube with little need for correction and readjustment. As a result, even with a high degree of deformation, a mold can be dispensed with in the best case. If a mold is used in this case, a slight effect on the outer wall of the large pipe is sufficient, so that a large-diameter quartz glass tube having the desired dimensional stability, smooth and high-quality inner wall and nevertheless largely defect-free and streak-free surface is obtained as the formed product of this forming step.
Die Herstellung von synthetischem Quarzglas mit derartig niedrigem Hydroxylgruppengehalt geht in der Regel über ein poröses Halbzeug aus SiO2- Teilchen, das eine Trocknungsbehandlung zur Beseitigung herstellungsbedingt enthaltener Hydroxylgruppen ermöglicht. Die Trocknungsbehandlung des porösen SiO2-Körpers kann dabei rein thermisch - unterstützt durch Unterdruck - oder durch chemische Reaktion mit einem Trocknungsreagenz - wie etwa Chlor - erfolgen. Die Einstellung eines mittleren Hydroxylgruppengehalts von weniger als 10 Gew.-ppm ist dabei weniger problematisch als die Erzeugung eines über das Volumen des porösen SiO2-Körpers gleichmäßigen Konzentrationsprofils. Die DE 10 152 328 A1 beschreibt eine Verfahrensweise zur Lösung dieses Problems, das bereits in einer frühen Phase der Herstellung des Quarzglasrohres ansetzt. The production of synthetic quartz glass with such a low hydroxyl group content generally proceeds via a porous semifinished product of SiO 2 particles, which requires a drying treatment to eliminate it contained hydroxyl groups allows. The drying treatment of the porous SiO 2 body can be carried out purely thermally - assisted by negative pressure - or by chemical reaction with a drying reagent - such as chlorine. The setting of an average hydroxyl group content of less than 10 ppm by weight is less problematic than the generation of a uniform over the volume of the porous SiO 2 body concentration profile. DE 10 152 328 A1 describes a procedure for solving this problem, which already begins in an early phase of the production of the quartz glass tube.
Hat das synthetisch erzeugte Quarzglas einen hohen mittleren Hydroxylgruppen- gehalt oberhalb von 10 Gew.-ppm, erweist es sich als zunehmend schwierig die geforderte Maßhaltigkeit des Großrohes insgesamt zu gewährleisten. Zeigt der axiale Konzentrationsverlauf Schwankungen von mehr als 2 Gew.-ppm/mm über eine Länge von 1 cm betrachtet, kommt es beim zweiten Umformprozess leicht zu lokalen Abweichungen der Wandstärke des Großrohres. Der Gehalt an Hydroxylgruppen des Quarzglases ergibt sich durch Messung der IR-Absorption nach der Methode von D.M. Dodd and D.B. Fräser, Optical deter- mination of OH in fused silica, Journal of Applied Physics, Vol. 37(1966), p. 391 1 . If the synthetically produced quartz glass has a high average hydroxyl group content above 10 ppm by weight, it proves to be increasingly difficult to ensure the required dimensional stability of the large pile as a whole. If the axial concentration profile shows fluctuations of more than 2 ppm by weight / mm over a length of 1 cm, the second forming process will easily lead to local deviations in the wall thickness of the large pipe. The content of hydroxyl groups of the quartz glass is determined by measuring the IR absorption by the method of D.M. Dodd and D.B. Fräser, Optical determination of OH in fused silica, Journal of Applied Physics, Vol. 37 (1966), p. 391 1.
Dabei wird der mittlere Gehalt an Hydroxylgruppen des Quarzglases durch eine Messung durch die Rohrwandung in Richtung der Längsachse des Zwischenroh- res ermittelt. Als Mittelwert des Hydroxylgruppengehalts in Längenabschnitten von 1 cm wird derjenige Messwert betrachtet, der bei einer Messung in der geometrischen Mitte des jeweiligen Längenabschnitts durch die Wandung des Zwischenrohres und senkrecht zu seiner Längsachse erhalten wird. The average content of hydroxyl groups of the quartz glass is determined by measuring through the pipe wall in the direction of the longitudinal axis of the intermediate tube. The average value of the hydroxyl group content in length sections of 1 cm is considered to be the measured value which, when measured in the geometric center of the respective length section, is obtained through the wall of the intermediate tube and perpendicular to its longitudinal axis.
Zur Herstellung von synthetisch erzeugtem Quarzglas werden häufig halogenhal- tige Ausgangssubstanzen - beispielsweise SiCI4 - oder halogenhaltige Trocknungsreagenzien - beispielsweise Chlor - oder halogenhaltige Dotierstoffe - beispielsweise Fluor - eingesetzt. Deswegen können große Mengen an Halogenen im synthetischen Quarzglas enthalten sein. Es hat sich aber gezeigt, dass sich im zweiten Umformschritt neben dem Hydroxylgruppengehalt auch der Halogengeh- alt - und dabei insbesondere der Chlorgehalt - auf die Maßhaltigkeit des endgültigen Quarzglasrohres und auf den Blasengehalt bemerkbar machen kann. For the production of synthetically produced quartz glass halide starting materials are frequently used - for example SiCl 4 or halogen-containing drying reagents - for example chlorine- or halogen-containing dopants - for example fluorine. Because of this, large quantities of halogens can be contained in the synthetic quartz glass. However, it has been shown that, in addition to the hydroxyl group content, the halogen content in the second forming step old - and especially the chlorine content - can make the dimensional accuracy of the final quartz glass tube and on the bubble content noticeable.
Daher wird bevorzugt Quarzglas eingesetzt, das mittlere Chlor-Konzentration von weniger als 3000 Gew.-ppm aufweist. Die Chlor-Konzentration wird als Mittelwert von Messproben ermittelt, die an drei gleichmäßig über die Zwischenzylinderlänge verteilten Stellen (Anfang, Mitte, Ende) genommen werden, indem die Messproben in wässriger HF-Lösung aufgelöst und die so erhaltene Lösungen nach Zusatz von AgNO3 einer nephelometrischen Analyse unterzogen werden. Im Hinblick auf eine maßgenaue Einstellung des Außendurchmessers des Großrohres hat sich eine Verfahrensvariante als vorteilhaft erwiesen, bei der das Quarzglas-Großrohr im zweiten Umformschritt nicht elongiert wird, wobei die Durchmesservergrößerung auf Zentrifugalkraft oder Blasdruck beruht. Therefore, quartz glass is preferably used, the average chlorine concentration of less than 3000 ppm by weight. The chlorine concentration is determined as the mean value of test samples taken at three points uniformly distributed over the inter-cylinder length (start, middle, end) by dissolving the test samples in aqueous HF solution and the resulting solutions after addition of AgNO 3 be subjected to nephelometric analysis. With regard to a dimensionally accurate adjustment of the outer diameter of the large tube, a method variant has proven to be advantageous in which the quartz glass tube is not elongated in the second forming step, wherein the diameter increase based on centrifugal force or blowing pressure.
Dabei werden an den umzuformenden Quarzglaszylinder stirnseitig Halter ge- schweißt und diese in Spannfutter einer Glasdrehbank eingespannt und synchron rotiert. Ein Heizquelle wird zonenweise entlang des Quarzglaszylinders bewegt. In der Innenbohrung des Quarzglaszylinders kann ein definierter Innendruck eingestellt werden. Infolge der Rotation und getrieben durch die Zentrifugalkraft und den Innendruck erweitert sich die Innenbohrung, ohne dass hierzu die Spannfut- ter auseinanderbewegt werden müssen. In this case, holders are welded to the quartz glass cylinder to be formed on the front side, and these are clamped in the chuck of a glass lathe and rotated synchronously. A heating source is moved in zones along the quartz glass cylinder. In the inner bore of the quartz glass cylinder, a defined internal pressure can be adjusted. As a result of the rotation and driven by the centrifugal force and the internal pressure, the inner bore widens without the chucks having to be moved apart.
Es hat sich sogar als besonders vorteilhaft erwiesen, wenn das Quarzglas- Großrohr im zweiten Umformschritt in Richtung seiner Längsachse gestaucht wird, derart dass seine Wandstärke nach dem Stauchen zwischen 70 % und maximal 100 % seiner Wandstärke vor dem Stauchen beträgt. Ziel des zweiten Umformschritts ist dabei eine Durchmesser-Vergrößerung des Quarzglasrohres bei weitgehender Beibehaltung seiner Wandstärke. Dies gelingt, indem die Ausgangslänge des Quarzglasrohres beim Umformschritt verkürzt, das Ausgangsrohr also gestaucht wird. Nach dem Stauchen liegt die Wandstärke bevorzugt zwischen 70 % und maximal 100 % des Ausgangswertes. Ein Stauch- prozess, der zu einer Vergrößerung der Wandstärke führt (> 100 %) ist zwar auch möglich, führt allerdings zu unerwünschten Verformungen. It has even proven to be particularly advantageous if the quartz glass tube is compressed in the second forming step in the direction of its longitudinal axis, so that its wall thickness after upsetting is between 70% and at most 100% of its wall thickness before upsetting. The aim of the second forming step is a diameter increase of the quartz glass tube while largely maintaining its wall thickness. This is achieved by shortening the initial length of the quartz glass tube in the forming step, so the output tube is compressed. After the upsetting lies the wall thickness preferably between 70% and at most 100% of the initial value. An upsetting process that leads to an increase in wall thickness (> 100%) is also possible, but leads to undesirable deformations.
Abgesehen von oben beschriebenen Anforderungen an die Zusammensetzung des synthetisch erzeugten Quarzglas, insbesondere hinsichtlich der zulässigen Menge an Hydroxylgruppen und deren örtlicher Verteilung, haben sich die Homogenität des Temperaturfeldes und die Zusammensetzung der Atmosphäre im Bereich der Heizzone als wichtige Parameter für einen reproduzierbaren Umform- prozess mit wenig Steuerungsbedarf erwiesen. Insbesondere auch aus diesem Grund hat sich bewährt, wenn die Heizzone von mehreren, ringförmig um den Umfang des Zwischenzylinders gleichmäßig verteilten Heizquellen gebildet wird, die ausgewählt sind aus der Gruppe: Plasmabrenner, Gasbrenner, Laser. Apart from the above-described requirements on the composition of the synthetically produced quartz glass, in particular with regard to the permissible amount of hydroxyl groups and their local distribution, the homogeneity of the temperature field and the composition of the atmosphere in the region of the heating zone have as important parameters for a reproducible forming process little control needed. In particular, for this reason, it has proven useful if the heating zone is formed by a plurality of annularly distributed around the circumference of the intermediate cylinder heat sources, which are selected from the group: plasma torch, gas burner, laser.
Mit derartigen Heizquellen kann die Heizenergie im Vergleich zu einem Ofen ört- lieh definierter eingestellt und schneller und genauer dosiert und damit auch ein vorgegebenes Temperaturfeld eingestellt oder korrigiert werden, auch wenn es nicht rotationssymmetrisch ist. Die Heizquellen sind in der Lage, punktuell eine hohe Energie bereitzustellen. Mindestens fünf derartiger Heizquellen sind in einer Kreisringform um den zu erweichenden Zwischenzylinder gleichmäßig verteilt. Im Vergleich zu einem Ofen kann der Durchmesser der Kreisringform einfacher an den Durchmesser des zu erweichenden Quarzglaszylinders angepasst werden, beispielsweise auch dann, wenn der zweite Umformschritt in Sub-Umformschritte mit jeweils kleinerem Umformgrad unterteilt ist, wobei der Außendurchmesser des umzuformenden Quarzglaszylinders stufenweise größer wird. Im Hinblick auf die Vermeidung des Eintrags on Hydroxylgruppen werden wasserstofffreie Plasmabrenner oder CO2-Laser bevorzugt. With such heat sources, the heating energy compared to a furnace can be set locally defined and metered faster and more accurate and thus set or corrected even a predetermined temperature field, even if it is not rotationally symmetrical. The heat sources are able to provide a high level of energy at specific points. At least five such heat sources are evenly distributed in a circular ring around the intermediate cylinder to be softened. Compared to an oven, the diameter of the circular ring shape can be more easily adapted to the diameter of the quartz glass cylinder to be softened, for example, even if the second forming step is divided into sub-forming steps each having a smaller degree of deformation, wherein the outer diameter of the quartz glass cylinder to be formed is gradually increased. With a view to avoiding the entry of hydroxyl groups, hydrogen-free plasma torches or CO 2 lasers are preferred.
Neben Hydroxylgruppen und Halogenen wirken sich auch metalloxidische Verunreinigungen auf die Viskosität des synthetischen Quarzglases aus, wobei insbesondere Aluminiumoxid zu nennen ist. Mögliche Konzentrationsschwankungen dieser Verunreinigung sind umso ausgeprägter und wirksamer, je höher ihre mittlere Konzentration ist. In addition to hydroxyl groups and halogens, metal oxide impurities also have an effect on the viscosity of the synthetic quartz glass, aluminum oxide in particular being mentioned here. Possible concentration fluctuations This contamination is the more pronounced and effective, the higher their average concentration.
Aus diesem Grund wird vorzugsweise Quarzglas eigesetzt, das eine Konzentration an Aluminium (AI) von weniger als 1 Gew.-ppm und einen Gesamtgehalt ande- rer metallischer Verunreinigungen von weniger als 4 Gew.-ppm aufweist. For this reason, quartz glass is preferably used which has a concentration of aluminum (Al) of less than 1 ppm by weight and a total content of other metallic impurities of less than 4 ppm by weight.
Außerdem hat es sich als vorteilhaft erwiesen, wenn das Quarzglas eine Konzentration an Alkali- und Erdalkalimetall-Verunreinigungen von weniger als 0,3 Gew.- ppm aufweist. In addition, it has proved to be advantageous if the quartz glass has a concentration of alkali and alkaline earth metal impurities of less than 0.3 ppm by weight.
Alkali- und Erdalkali -Ionen wirken sich bereits in geringer Menge merklich auf die Viskosität von Quarzglas aus und sie fördern dessen Kristallisationsneigung. Alkali and alkaline earth ions already have a noticeable effect on the viscosity of quartz glass in a small amount and they promote its crystallization tendency.
Aluminium sowie Alkali- und Erdalkali-Verunreinigungen liegen im Quarzglas zwar in oxidischer Form vor; alle oben genannten Gewichtsangaben beziehen sich aber auf die metallische Form. Although aluminum and alkali and alkaline earth impurities are present in the quartz glass in oxide form; All weights mentioned above refer to the metallic form.
Bei einer besonders bevorzugten Verfahrensvariante wird im ersten Umformschritt ein Ausgangs-Hohlzylinder aus Quarzglas einem elektrisch beheizten Ofen zugeführt, darin zonenweise erweicht und kontinuierlich und um seine Längsachse rotierend mit seinem Zylinder-Außenmantel gegen das Formwerkzeug gedrückt und vom Formwerkzeug kontinuierlich zu dem Zwischenzylinder umgeformt. In a particularly preferred variant of the method an initial hollow cylinder made of quartz glass is fed to an electrically heated furnace, softened in zones and continuously and rotating about its longitudinal axis with its cylinder outer shell against the mold and continuously formed by the mold to the intermediate cylinder.
Diese Verfahrensweise erlaubt die Herstellung dickwandiger und dennoch maß- genauer Zwischenzylinder. This procedure allows the production of thick-walled and yet accurate intermediate cylinders.
Ein elektrisch beheizter Ofen verursacht im Allgemeinen höhere Energiekosten als die Beheizung mittels Brennern. Andererseits erleichtert die elektrische Beheizung das Einhalten eines vorgegebenen Temperaturfeldes und einer wasser- und wasserstoffarmen Atmosphäre. Im Hinblick darauf wird für das Umformen des Ausgangszylinders zum Zwischenzylinder vorzugsweise ein elektrisch beheizter Ofen eingesetzt. Dabei betragen die Abmessungen des Ofens in Richtung der Zylinder-Längsachse gesehen mindestens 500 mm und der Abstand zwischen der Außenwandung des Zwischenzylinders und einer Innenwandung des Ofens weniger als 100 mm. Der nach dem ersten Umformprozess erhaltene Zwischenzylinder kann nachträglich bearbeitet werden. An electrically heated oven generally causes higher energy costs than burner heating. On the other hand, the electric heating facilitates the maintenance of a predetermined temperature field and a low-hydrogen and hydrogen-poor atmosphere. In view of this, preferably an electrically heated furnace is used for the forming of the output cylinder to the intermediate cylinder. In this case, the dimensions of the furnace seen in the direction of the cylinder longitudinal axis are at least 500 mm and the distance between the outer wall of the intermediate cylinder and an inner wall of the furnace less than 100 mm. The intermediate cylinder obtained after the first forming process can be subsequently processed.
Ausführungsbeispiel embodiment
Nachfolgend wird die Erfindung anhand eines Ausführungsbeispiels und einer Zeichnung näher erläutert. Im Einzelnen zeigt in schematischer Darstellung The invention will be explained in more detail with reference to an embodiment and a drawing. In detail shows in a schematic representation
Figur 1 eine Vorrichtung zur Durchführung eines ersten Umformprozesses zwecks Herstellung eines Zwischenrohres aus synthetisch erzeugtem Quarzglas in einer Seitenansicht, und 1 shows a device for carrying out a first forming process for the production of an intermediate tube made of synthetically produced quartz glass in a side view, and
Figur 2 eine Vorrichtung zur Durchführung eines zweiten Umform prozesses zwecks Herstellung eines Großrohres aus dem Zwischenrohr in einer Seitenansicht. 2 shows a device for carrying out a second forming process for the purpose of producing a large pipe from the intermediate pipe in a side view.
Herstellung eines Hohlzylinders aus synthetischem Quarzglas Production of a hollow cylinder made of synthetic quartz glass
Es wird ein Hohlzylinder 1 aus synthetisch erzeugtem Quarzglas bereitgestellt, der hohen Anforderungen an seine Reinheit und an die Homogenität der viskosi- täts-beeinflussenden Komponenten genügt. A hollow cylinder 1 made of synthetically produced quartz glass is provided, which satisfies high demands on its purity and on the homogeneity of the viscosity-influencing components.
Die Herstellung umfasst die Flammenhydrolyse von SiCI4, bei der SiO2-Partikel gebildet und auf der Zylindermantelfläche eines um seine Längsachse rotierenden Trägers unter Bildung eines Sootkorpers schichtweise abgeschieden werden. Zur Erzeugung eines spezifischen radialen Dichteverlaufs innerhalb der Sootkör- per-Wandung wird die aus der DE 10 152 328 A bekannte Methode verwendet, das heißt, bei der Abscheidung der ersten Soot-Lagen wird eine vergleichsweise hohe Oberflächentemperatur und damit ein Sootbereich mit vergleichsweise hoher Dichte von etwa 30 % erzeugt. Die Soot-Dichte wird daraufhin noch weiter allmählich bis sie in einem„Übergangsbereich" etwa 32 % erreicht. Bei der Ab- Scheidung der nachfolgenden Soot-Lagen wird die Oberflächentemperatur des sich bildenden Sootkorpers kontinuierlich abgesenkt und damit die Sootdichte verringert. Nach Beendigung des Abscheideverfahrens und Entfernen des Trägerstabs wird ein Sootrohr mit einem spezifischen radialen Dichte-Profil erhalten. The preparation comprises the flame hydrolysis of SiCl 4 , in which SiO 2 particles are formed and deposited in layers on the cylinder jacket surface of a support rotating about its longitudinal axis to form a soot body. The method known from DE 10 152 328 A is used to produce a specific radial density profile within the soot body wall, that is, in the deposition of the first soot layers, a comparatively high surface temperature and thus a soot area with a comparatively high density generated by about 30%. The soot density then continues to gradually increase until it reaches about 32% in a "transitional area." In the deposition of the subsequent soot layers, the surface temperature of the forming soot body is lowered continuously and thus the soot density reduced. Upon completion of the deposition process and removal of the carrier rod, a soot tube having a specific radial density profile is obtained.
Zur Reinigung und zum Entfernen der herstellungsbedingt eingebrachten Hydroxylgruppen wird das Sootrohr einer Dehydratationsbehandlung unterzogen und dabei in vertikaler Ausrichtung in einen Dehydratationsofen zunächst bei einer Temperatur um 900 °C in einer chlorhaltigen Atmosphäre behandelt. Die Behandlungsdauer beträgt etwa acht Stunden. Dadurch wird ein geringer Hydroxylgruppengehalt eingestellt. For cleaning and removal of the hydroxyl group caused by the preparation, the soot tube is subjected to a dehydration treatment and treated in a vertical orientation in a dehydration oven initially at a temperature of about 900 ° C. in a chlorine-containing atmosphere. The treatment takes about eight hours. This sets a low hydroxyl group content.
Dabei wird die prozessbedingt unterschiedliche Effektivität des über die Mantel- flächen in den Sootkörper eindringenden Chlors durch das vorab erzeugte Dichteprofil kompensiert, so dass sich über die Dicke der Wandung ein weitgehend homogenes, radiales Konzentrationsprofil für die Hydroxylgruppen einstellt. In this case, the process-related different effectiveness of the penetrating over the mantle surfaces in the soot body chlorine is compensated by the previously generated density profile, so that sets over the thickness of the wall, a substantially homogeneous, radial concentration profile for the hydroxyl groups.
Danach wird das Sootrohr in einen vertikal orientierten Verglasungsofen eingebracht und darin bei einer Temperatur um 1000 °C zwecks Entfernens von Chlor und zur Absättigung etwaiger Sauerstoffmangeldefekte mit Sauerstoff behandelt. Anschließend wird das Sootrohr bei einer Temperatur um 1300 °C gesintert, indem es einer ringförmigen Heizzone zugeführt und darin zonenweise erhitzt wird. Thereafter, the soot tube is placed in a vertically oriented vitrification furnace and treated therein with oxygen at a temperature around 1000 ° C to remove chlorine and to saturate any oxygen deficiency defects. Subsequently, the soot tube is sintered at a temperature around 1300 ° C by being fed to an annular heating zone and heated therein in zones.
Der so hergestellte Hohlzylinder 1 (siehe Figur 1 ) hat eine Länge von 300 cm, einen Außendurchmesser von 200 mm und einen Innendurchmesser von 40 mm. Er besteht aus synthetischem Quarzglas, mit geringem Gehalt an metall- oxidischen Verunreinigungen, deren Konzentrationen (in Gew.-ppm) in Tabelle 1 angegeben sind: The hollow cylinder 1 thus produced (see FIG. 1) has a length of 300 cm, an outer diameter of 200 mm and an inner diameter of 40 mm. It consists of synthetic quartz glass with a low content of metal oxide impurities whose concentrations (in ppm by weight) are given in Table 1:
Tabelle 1 Table 1
Alle Angaben in Gew.-ppm Das Quarzglas hat einen mittleren Hydroxylgruppengehalt von 8,3 Gew.-ppm (gemessen über die Rohr-Längsachse) und eine mittlere Chlor-Konzentration von 1710 Gew.-ppm. Über die Länge des dickwandigen Hohlzylinders gesehen variiert der an 29 Messpunkten im Abstand von 10 cm ermittelte Hydroxylgruppenge- halt um +/- 0,9 Gew.-ppm (Standardabweichung). All data in ppm by weight The quartz glass has an average hydroxyl group content of 8.3 ppm by weight (measured over the tube longitudinal axis) and a mean chlorine concentration of 1710 ppm by weight. Viewed along the length of the thick-walled hollow cylinder, the hydroxyl group content determined at 29 measuring points at a distance of 10 cm varies by +/- 0.9 ppm by weight (standard deviation).
Erster Umformschritt zur Erzeugung eines Zwischenzylinders First forming step for producing an intermediate cylinder
Der erste Umformschritt erfolgt anhand der in DE 10 2007 051 898 A1 beschriebenen Methode. The first forming step takes place by means of the method described in DE 10 2007 051 898 A1.
Figur 1 zeigt schematisch die Vorrichtung, mittels der der dickwandige Quarz- glas-Hohlzylinders 1 zu einem dünnwandigeren Zwischenzylinder 2 mit einem Außendurchmesser von 320 mm, einer Wandstärke von 15 mm und einer Länge von 6,20 m umgeformt wird. FIG. 1 shows diagrammatically the device by means of which the thick-walled quartz glass hollow cylinder 1 is formed into a thin-walled intermediate cylinder 2 with an outer diameter of 320 mm, a wall thickness of 15 mm and a length of 6.20 m.
Der Hohlzylinder 1 wird mit einer Vorschubeinrichtung kontinuierlich und unter Rotation um seine Längsachse 3 mit einer Zufuhrgeschwindigkeit von 4 cm/min in einen Widerstandsofen 4 geschoben, der den Hohlzylinder 1 ringförmig mit einem Innendurchmesser von 400 mm umgibt und darin zonenweise auf eine Temperatur um 2100 °C aufgeheizt. Zum Ausziehen wird eine (in der Figur nicht gezeigte) Zieheinrichtung verwendet, die den Zwischenzylinder 2 um seine Längsachse 3 drehend mit einer Abziehgeschwindigkeit von etwa 12 cm/min in Richtung der Längsachse 3 abzieht. The hollow cylinder 1 is pushed with a feed device continuously and under rotation about its longitudinal axis 3 at a feed rate of 4 cm / min in a resistance furnace 4, which surrounds the hollow cylinder 1 annular with an inner diameter of 400 mm and in zonewise to a temperature around 2100 ° C heated up. To pull out a (not shown in the figure) pulling device is used, which rotates the intermediate cylinder 2 about its longitudinal axis 3 rotating at a peel rate of about 12 cm / min in the direction of the longitudinal axis 3.
Der Quarzglas-Hohlzylinder 1 ist an seiner freien Stirnseite mit einer gasdichten Drehdurchführung verschlossen. In den Ofen 4 ragt ein Formwerkzeug, das zwei wassergekühlte Formbacken 5 aufweist, die mit Graphitzungen belegt sind (in Figur 1 nur schematisch angedeutet). Durch die Drehdurchführung wird in den rotierenden Quarzglas-Hohlzylinder 1 ein Gasstrom eingeleitet, so dass sich ein regelbarer Innen-Überdruck von etwa 10 mbar eingestellt. Der Hohlzylinder 1 wird dadurch gegen die Formbacken 5 auf den Soll-Durchmesser von 340 mm aufgeblasen, wobei sich vor den Formbacken 5 ein Umfangswulst 6 bildet. Der Zwischenzylinder 2 kann sich danach von den Formbacken 5 lösen, so dass der sich tatsächlich einstellende Außendurchmesser vom Abstand der Formbacken geringfügig abweichen kann. Zur Messung und Regelung des Außendurchmessers ist eine schematisch dargestellte Mess- und Regeleinrichtung 13 vorge- sehen, die zwei hochauflösende CCD-Kameras 7; 8 zur Erfassung der Längskanten 10; 1 1 des Hohlzylinders 1 und Monitore 12 umfasst, die die relative axiale Lage der optisch erfassten Längskanten 10, 1 1 anzeigen. Zu weiteren Details der Funktionsweise der Regeleinrichtung 13 wird auf die DE 10 2007 051 898 A1 verwiesen. Der so erhaltene Zwischenzylinder 2 zeichnet sich durch einen definierten Außendurchmesser und insgesamt hohe Maßhaltigkeit aus. Die Qualität des Quarzglases entspricht unverändert der des Hohlzylinders 1 , wie oben erläutert. Er ist als definiertes Ausgangsprodukt zur Herstellung eines Großrohres geeignet. The quartz glass hollow cylinder 1 is closed at its free end face with a gas-tight rotary feedthrough. In the oven 4 projects a mold that has two water-cooled mold jaws 5, which are occupied with graphite fits (in Figure 1 only schematically indicated). Through the rotary feedthrough, a gas flow is introduced into the rotating quartz glass hollow cylinder 1, so that a controllable internal overpressure of about 10 mbar is established. The hollow cylinder 1 is thereby inflated against the mold jaws 5 to the target diameter of 340 mm, with a peripheral bead 6 forms in front of the mold jaws 5. The intermediate cylinder 2 can then be released from the mold jaws 5, so that the actually adjusting outer diameter may differ slightly from the distance of the mold jaws. For measuring and controlling the outer diameter, a measuring and control device 13 is shown schematically provided, the two high-resolution CCD cameras 7; 8 for detecting the longitudinal edges 10; 1 1 of the hollow cylinder 1 and 12 monitors that indicate the relative axial position of the optically detected longitudinal edges 10, 1 1. For further details of the operation of the control device 13, reference is made to DE 10 2007 051 898 A1. The thus obtained intermediate cylinder 2 is characterized by a defined outer diameter and overall high dimensional accuracy. The quality of the quartz glass corresponds unchanged to that of the hollow cylinder 1, as explained above. It is suitable as a defined starting material for the production of a large pipe.
Zweiter Umformschritt zur Erzeugung des Großrohres Figur 2 zeigt schematisch die Vorrichtung zum Umformen des Zwischenzylinders 2 zu dem gewünschten Großrohr 22 mit einem Außendurchmesser von 960 mm. Second forming step for producing the large pipe Figure 2 shows schematically the apparatus for forming the intermediate cylinder 2 to the desired large pipe 22 with an outer diameter of 960 mm.
An den Zwischenzylinder 2 sind links und rechts Halterohre angeschweißt (in der Figur nicht gezeigt), die in die beiden Spannfutter einer Glasdrehbank eingespannt sind und die synchron rotieren. Ein Brennerwagen 21 fährt den Zwischenzylinder 2 von rechts nach links ab, wie vom Richtungspfeil 23 angezeigt. Auf dem Brennerwagen 21 ist ein Brennerring montiert, der zur Erwärmung und Erweichung des Zwischenzylinders 2 dient. Der Brennerring 25 wird aus fünf Gasbrenner gebildet welche kreisringförmig und gleichmäßig um die Zylinder-Längsachse 3 verteilt sind. Durch Vorschub des Brennerwagens 21 mit einer Geschwindigkeit von 4 cm/min wird der Zwischenzylinder 2 unter Rotation um seine Längsachse 3 mit einer Geschwindigkeit von 60 U/min (die der Rotationsachse entspricht) kontinuierlich unter die Einwirkung des Brennerrings und wird so auf hohe Temperatur um 2.100 °C erhitzt. Dabei kann die Innenbohrung 20 mit einem Gas gespült werden und ein definierter und geregelter Innendruck bis etwa 100 mbar in der Innenbohrung 20 eingestellt werden. To the intermediate cylinder 2 left and right holding tubes are welded (not shown in the figure), which are clamped in the two chucks of a glass lathe and rotate synchronously. A burner carriage 21 drives the intermediate cylinder 2 from right to left, as indicated by the directional arrow 23. On the burner carriage 21, a burner ring is mounted, which serves to heat and soften the intermediate cylinder 2. The burner ring 25 is formed from five gas burners which are circular and evenly distributed around the cylinder longitudinal axis 3. By advancing the torch carriage 21 at a speed of 4 cm / min., The intermediate cylinder 2 is continuously rotated under its longitudinal axis 3 at a speed of 60 rpm (corresponding to the axis of rotation) under the action of the torch ring and thus becomes high temperature 2,100 ° C heated. In this case, the inner bore 20 can be flushed with a gas and a defined and regulated internal pressure can be adjusted to about 100 mbar in the inner bore 20.
Das Quarzglas erhält durch das Aufheizen im Brennerring 25 eine so geringe Vis- kosität, so dass es sich leicht verformt, so dass sich die Rohr-Außenwandung unter Einwirkung von Zentrifugalkraft und Innendruck gegen ein Formteil 27 aus Grafit mit einer Wandstärke von 7,5 mm anlegt. Ein zusätzliches Elongieren findet dabei nicht statt, im Gegenteil, das Quarzglasrohr wird gestaucht, wie von den Blockpfeilen 24 angedeutet, derart, dass das aufgeblasene Großrohr 22 etwa die- selbe Wandstärke hat, wie das Zwischenrohr 2. The quartz glass obtained by the heating in the burner ring 25 so low viscosity, so that it deforms slightly, so that the tube outer wall under the action of centrifugal force and internal pressure against a molding 27 made of graphite with a wall thickness of 7.5 mm invests. An additional elongation does not take place, on the contrary, the quartz glass tube is compressed, as indicated by the block arrows 24, such that the inflated large tube 22 has approximately the same wall thickness, as the intermediate tube. 2
Das so erhaltene Quarzglasrohr (22) dient als Zwischenzylinder 2 für ein weiteres Umformen anhand des in Figur 2 gezeigten Verfahrens. Auf diese Weise wird der Zwischenzylinder 2 stufenweise zu dem Quarzglas-Großrohr 22 aufgeweitet, wobei jede Verformungsstufe eine Durchmesser-Aufweitung von 65 mm oder weni- ger ausmacht. Der Außendurchmesser des Brennerrings 25 kann dabei einfach an den jeweiligen Außendurchmesser der Verformungsstufe angepasst werden. The quartz glass tube (22) thus obtained serves as an intermediate cylinder 2 for further forming on the basis of the method shown in FIG. In this way, the intermediate cylinder 2 is gradually expanded to the quartz glass tube 22, wherein each deformation step makes a diameter widening of 65 mm or less. The outer diameter of the burner ring 25 can be easily adapted to the respective outer diameter of the deformation stage.
Das aufgeblasene Großrohr 22 hat etwa dieselbe Wandstärke (100 %) wie das anfänglich eingesetzte Zwischenrohr 2 und ist auf eine Endlänge von 2,976 m gestaucht. Anhand dieses Verfahrens wird auf wirtschaftliche Weise mit nur zwei Umformschritten aber unter Einhaltung der oben erläuterten Randbedingungen bezüglich der chemischen Zusammensetzung des Quarzglases und seiner Homogenität ein Großrohr 22 aus synthetischem Quarzglas mit insgesamt hoher Maßhaltigkeit erhalten. Die Wanddickenschwankung des so erzeugten Quarzglas-Großrohes 22 beträgt weniger als 0,42 mm pro Rohrlängenmeter. The inflated large tube 22 has approximately the same wall thickness (100%) as the initially inserted intermediate tube 2 and is compressed to a final length of 2.976 m. By means of this method, a large tube 22 made of synthetic quartz glass with overall high dimensional accuracy is economically obtained with only two forming steps but in compliance with the above-mentioned boundary conditions with respect to the chemical composition of the quartz glass and its homogeneity. The wall thickness variation of the quartz glass bulk product 22 produced in this way is less than 0.42 mm per pipe length meter.

Claims

Patentansprüche  claims
Verfahren zur Herstellung eines Quarzglas-Großrohres (22) durch mehrstufiges Formen, wobei in einem ersten Formschritt unter Einsatz eines Formwerkzeugs (5) ein Zwischenzylinder (2) aus Quarzglas mit einer Zwischenzylinder-Wandstärke und einem Zwischenzylinder-Außendurchmesser geformt und anschließend abgekühlt wird, und indem in einem zweiten Umformschritt mindestens ein Längenabschnitt des abgekühlten Zwischenzylinders (2) einer Heizzone (25) zugeführt, darin zonenweise auf eine Erweichungstemperatur erhitzt und um seine Längsachse (3) rotierend zu dem Quarzglas- Großrohr (22) mit einer End-Wandstärke und einem End-Außendurchmesser umgeformt wird, dadurch gekennzeichnet, dass das Quarzglas synthetisch erzeugt ist und einen mittleren Hydroxylgruppengehalt von 10 Gew.-ppm oder weniger hat, mit der zusätzlichen Maßgabe, dass bei Unterteilung des Zwischenzylinders in Längenabschnitte mit einer Länge von 1 cm, benachbarte Längenabschnitte in ihrem mittleren Hydroxylgruppengehalt einen Unterschied von weniger als 2 Gew.-ppm aufweisen. A method for producing a quartz glass tube (22) by multi-stage molding, wherein in a first molding step using a mold (5) an intermediate cylinder (2) made of quartz glass with an intermediate cylinder wall thickness and an intermediate cylinder outer diameter is formed and then cooled, and in a second forming step, at least one length section of the cooled intermediate cylinder (2) is fed to a heating zone (25), heated zone by zone to a softening temperature and rotating about its longitudinal axis (3) to the quartz glass tube (22) with an end wall thickness and a End-outer diameter is formed, characterized in that the quartz glass is synthetically produced and has an average hydroxyl group content of 10 ppm by weight or less, with the additional proviso that when subdividing the intermediate cylinder into lengths with a length of 1 cm, adjacent lengths in their middle hydroxyl group have a difference of less than 2 ppm by weight.
Verfahren nach Anspruch 1 , dadurch gekennzeichnet, dass das Quarzglas einen mittleren Hydroxylgruppengehalt von 2 Gew.-ppm oder weniger hat, und dass benachbarte Längenabschnitte des Zwischenzylinders in ihrem mittleren Hydroxylgruppengehalt einen Unterschied von weniger als A method according to claim 1, characterized in that the quartz glass has an average hydroxyl group content of 2 ppm by weight or less, and that adjacent lengths of the intermediate cylinder have a difference in their mean hydroxyl group content of less than
1 Gew.-ppm aufweisen. 1 ppm by weight.
Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass das Quarzglas eine mittlere Chlor-Konzentration von weniger als 3000 Gew.- ppm hat. A method according to claim 1 or 2, characterized in that the quartz glass has a mean chlorine concentration of less than 3000 ppm by weight.
Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass das Quarzglas-Großrohr (22) im zweiten Umformschritt nicht elongiert wird und dass seine Durchmesservergrößerung auf Zentrifugalkraft oder Blasdruck beruht. Method according to one of the preceding claims, characterized in that the quartz glass tube (22) is not elongated in the second forming step and that its increase in diameter based on centrifugal force or blowing pressure.
5. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass das Quarzglas-Großrohr (22) im zweiten Umformschritt in Richtung seiner Längsachse (3) gestaucht wird, derart dass seine Wandstärke nach dem Stauchen zwischen 70 % und maximal 100 % seiner Wandstärke vor dem Stauchen beträgt. 5. The method according to any one of the preceding claims, characterized in that the quartz glass tube (22) is compressed in the second forming step in the direction of its longitudinal axis (3), such that its wall thickness after upsetting between 70% and at most 100% of its wall thickness before the upsetting is.
6. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Heizzone von mehreren, ringförmig um den Umfang des Zwischenzylinders (2) gleichmäßig verteilten Heizquellen (25) gebildet wird, die ausgewählt sind aus der Gruppe: Plasmabrenner, Gasbrenner, Laser. 7. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass das Quarzglas eine Konzentration an Aluminium (AI) von weniger als 1 Gew.-ppm und einen Gesamtgehalt anderer metallischer Verunreinigungen von weniger als 4 Gew.-ppm aufweist. 6. The method according to any one of the preceding claims, characterized in that the heating zone of a plurality of annularly around the circumference of the intermediate cylinder (2) evenly distributed heating sources (25) is formed, which are selected from the group: plasma torch, gas burner, laser. 7. The method according to any one of the preceding claims, characterized in that the quartz glass has a concentration of aluminum (AI) of less than 1 ppm by weight and a total content of other metallic impurities of less than 4 ppm by weight.
8. Verfahren nach Anspruch 7, dadurch gekennzeichnet, dass das Quarzglas eine Konzentration an Alkali- und Erdalkalimetall-Verunreinigungen von weniger als 0,3 Gew.-ppm aufweist. 8. The method according to claim 7, characterized in that the quartz glass has a concentration of alkali and alkaline earth metal impurities of less than 0.3 ppm by weight.
9. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass im ersten Formschritt ein Ausgangs-Hohlzylinder (1 ) aus Quarzglas einem elektrisch beheizten Ofen (4) zugeführt, darin zonenweise erweicht und kontinuierlich und um seine Längsachse (3) rotierend mit seinem Zylinder-Außenmantel gegen das Formwerkzeug (5) gedrückt und vom Formwerkzeug (5) kontinuierlich zu dem Zwischenzylinder (2) umgeformt wird. 9. The method according to any one of the preceding claims, characterized in that in the first forming step, an output hollow cylinder (1) made of quartz glass an electrically heated oven (4) fed, softened in zones and continuously and about its longitudinal axis (3) rotating with its cylinder -Outer jacket against the mold (5) pressed and the mold (5) is continuously formed to the intermediate cylinder (2).
10. Verfahren nach Anspruch 9, dadurch gekennzeichnet, dass die Abmessung des elektrisch beheizten Ofens (4) in Richtung der Zylinder-Längsachse (3) gesehen mindestens 500 mm und der Abstand zwischen der Außenwandung des Zwischenzylinders (2) und einer Innenwandung des Ofens (4) weniger als 100 mm betragen. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass ein Großrohr (22) mit einer Wanddickenschwankung von weniger als 0,5 mm pro Rohrlängenmeter erhalten wird. 10. The method according to claim 9, characterized in that the dimension of the electrically heated furnace (4) in the direction of the cylinder longitudinal axis (3) seen at least 500 mm and the distance between the outer wall of the intermediate cylinder (2) and an inner wall of the furnace ( 4) less than 100 mm. Method according to one of the preceding claims, characterized in that a large pipe (22) is obtained with a wall thickness variation of less than 0.5 mm per pipe length meter.
EP14736800.5A 2013-07-12 2014-07-08 Method for producing a large quartz-glass pipe Withdrawn EP3019453A1 (en)

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DE102013107435B4 (en) 2015-01-29
TWI565666B (en) 2017-01-11
JP6478990B2 (en) 2019-03-06
US20160168005A1 (en) 2016-06-16
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TW201504166A (en) 2015-02-01
SG11201600207TA (en) 2016-02-26

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