DEVICE FOR HOLDING TUBULAR SiO2 BLANK IN EXTERNAL DEPOSITION PROCESS AND METHOD FOR MANUFACTURING TUBULAR SiO2 BLANK

Abstract

To provide a device and method for manufacturing large-volume tubular SiO2 blanks.SOLUTION: A device for manufacturing a tubular SiO2 blank in an external deposition process has a substrate tube and a substrate tube holder comprising a clamping device, which is designed to support the substrate tube and to rotate the substrate tube about an axis of rotation. In order to provide, on this basis, a reproducible and operationally reliable holder for a large-volume, tubular SiO2 blank in an external deposition process, it is proposed that the substrate tube holder comprises a clamping mechanism which has a first pressure unit abutting the first substrate tube end face, a second pressure unit abutting the second substrate tube end face, and at least one force element which is designed to generate an axial contact pressure with a force component acting in the direction of the longitudinal axis of the substrate tube.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an apparatus for producing tubular SiO2 blanks in an external deposition process, comprising: a sub-straight tube having a sub-straight tube longitudinal axis, a sub-straight tube length, a sub-straight tube first end face, a sub-straight tube second end face, a sub-straight tube outer surface, a sub-straight tube inner surface, a sub-straight tube outer diameter, a sub-straight tube inner diameter, a sub-straight tube wall thickness, and a through opening extending coaxially with and continuous with the sub-straight tube longitudinal axis; a substrate tube holder including a clamping device and designed to support the substrate tube and rotate the substrate tube about an axis of rotation extending coaxially or parallel to a longitudinal axis of the substrate tube; The present invention relates to an apparatus comprising:

[0002] The present invention also relates to a method for producing a tubular SiO2 blank in an external deposition process, comprising the steps of: (a) providing a sub-straight tube having a sub-straight tube longitudinal axis, a sub-straight tube length, a sub-straight tube first end face, a sub-straight tube second end face, a sub-straight tube outer surface, a sub-straight tube inner surface, a sub-straight tube outer diameter, and a through opening extending coaxially with and continuous with the sub-straight tube longitudinal axis; (b) supporting the substrate tube with a substrate tube holder including a clamping device; (c) rotating the substrate tube about a rotation axis extending coaxially or parallel to a longitudinal axis of the substrate tube; (d) depositing SiO2 particles on the outer surface of the substrate tube with at least one deposition burner to form the tubular SiO2 blank; The present invention also relates to a method comprising the steps of:

[0003] Components made of synthetic quartz glass in the form of preforms, tubes, rods, flanges, plates, rings, reactors, crucibles, etc., are used in semiconductor production and optical fiber manufacturing. Such components are often fabricated by thermal forming and / or mechanical machining from tubular blanks made of synthetic silicon dioxide. With increasing productivity, there is an increasing demand for such components with larger dimensions, especially larger wall thicknesses and inner diameters.

[0004] For the production of tubular blanks from synthetically produced silicon dioxide, the CVD method (Chemical Vapor Deposition) is known, in which SiO2 particles are deposited from the gas phase onto a substrate. The CVD outside deposition method, known by the abbreviation "OVD" (Outside Vapor Deposition), is generally suitable for the production of large volume blanks. In this method, a silicon-containing raw material is converted into SiO2 particles by flame hydrolysis or pyrolysis in a reaction zone, which are deposited as a layer on the outer jacket of a cylindrical substrate rotating about its longitudinal axis. The reaction zone is generated by a heat source, which moves back and forth relative to the substrate longitudinal axis and the heat source. The substrate can be tubular and is here and below also referred to as "substrate tube". The substrate tube consists, for example, of SiC, SiSiC (reaction bonded silicon carbide), Al2O3 or another ceramic material or graphite, and is held and rotated about its longitudinal axis by a lathe-like device, which is here also referred to as "substrate tube holder".

[0005] The result of this deposition process is a substantially cylindrical tubular SiO2 blank, which, depending on the temperature during the deposition process, is either a porous SiO2 body (hereinafter also called "soot body") or an object made of mostly transparent quartz glass. In the case of a porous soot body, this soot body is sintered in a separate step to form an object made of mostly transparent quartz glass (the sintering process is also called "vitrification"). From the object made of mostly transparent quartz glass, components of synthetic quartz glass, for example solid cylinders, hollow cylinders or parts of these components, which can themselves also serve as semi-finished products for the manufacture of other components, can be obtained by mechanical, chemical and / or thermal post-treatment. [Background technology]

[0006] To produce SiO2 bodies from synthetic silicon dioxide with large tube inner diameters by external deposition, it is necessary to use substrate tubes with suitable outer diameters and substrate tube holders that are matched to them. The fundamental problem that arises here is to compensate as much as possible for the differences in the linear thermal expansion coefficients (hereinafter also called Coefficient of Thermal Expansion or CTE) of the materials of the SiO2 body, the substrate tube and the substrate tube holder.

[0007] For example, a horizontal lathe for producing preforms from porous silicon dioxide by the OVD method known from EP 3584023 A1 has a mechanism for compensating for thermal axial expansion. This mechanism comprises a clamping device having a first chuck rotatable about an axis of rotation and gripping one end of the substrate tube, and a second chuck gripping the other end of the substrate tube and movable back and forth in the direction of the axis of rotation. This back and forth mobility is possible for example by roller bearings of the second chuck, which are preferably supplemented with a spring preload to counteract the axial stretch due to thermal expansion.

[0008] KR10-2452282B1 describes an OVD external deposition method for producing quartz glass tubes and a device therefor. A stepped substrate tube is proposed consisting of a cylindrical deposition section with a larger outer diameter, which protrudes outward on both sides and is connected to clamping sections with a smaller outer diameter that fit into the clamping jaws of a horizontal glass lathe. The deposition section and the clamping sections on both sides can be realized as one part, or the deposition section is connected to the clamping sections on both sides. Screws, pins and latch connections are mentioned as connection means, or there are embodiments in which the support section or the deposition section is provided with a thread and connected in a screw manner. In the OVD deposition method, a SiO2 soot body is produced on the cylindrical surface of the deposition section while the soot body is rotated around a rotation axis by the clamping sections on both sides. Technical problem

[0009] In OVD external deposition, the substrate tube heats up more on the outside than on the inside. The resulting mechanical stresses build up across the wall thickness and can lead to failure. For small substrate tube diameters, e.g. less than 80 mm, and for small substrate tube lengths, e.g. less than 2,000 mm, the CTE difference is not very significant and affects almost only axially (in the direction of the substrate tube longitudinal axis). However, for large and thick-walled substrate tubes, e.g. with inner diameters greater than 200 mm and wall thicknesses greater than 25 mm, the radial thermal expansion can no longer be neglected. These substrate tubes are also heavy, which increases the demands on the stability and dynamics of the substrate tube holder.

[0010] The reaction zone where the deposition process occurs is usually small in axial dimension compared to the substrate tube length. A substrate tube that is clamped at both ends heats only in a small length section of the deposition zone, but not as strongly in the end regions that are held by the substrate tube holders. Thermal stresses between the cooler end regions and the hotter center of the tube can also cause the substrate tube to crack.

[0011] For equipment for producing large volume tubular blanks from synthetic silicon dioxide by OVD external deposition and correspondingly large equipment components, the manufacturing process is made even more difficult by the weight, local temperature differences within the components and differences in the CTE of different components connected to each other.

[0012] It is therefore an object of the present invention to avoid at least some of the abovementioned disadvantages and to provide an apparatus that is particularly suitable for reproducibly and reliably holding large volume tubular SiO2 blanks by external deposition methods, in particular by OVD external deposition methods.

[0013] In particular, the object of the present invention is to provide an apparatus for holding thick-walled tubular blanks with a large inner diameter, for example with an outer diameter greater than 200 mm and a thick wall thickness greater than 25 mm, in an external deposition process, which is suitable for avoiding or compensating for mechanical stresses due to dimensional deviations and calibration, alignment and adjustment errors of the parts of the apparatus, and due to CTE differences of the parts in the axial and radial directions.

[0014] Furthermore, it is an object of the present invention to provide a method for producing tubular blanks with large inner diameters and large wall thicknesses, in particular from synthetic silicon dioxide, by the external deposition method, in which the above-mentioned disadvantages are avoided and in particular the risk of rejects is reduced. Summary of the Invention

[0015] With regard to this device, the present invention solves this problem by starting with an apparatus as described above, wherein the substrate tube holder comprises a first pressure unit adjacent to a first end face of the substrate tube, a second pressure unit adjacent to a second end face of the substrate tube, and a clamping mechanism including at least one force element designed to generate an axial contact pressure by a force component acting in the direction of the substrate tube longitudinal axis, whereby the substrate tube is clamped between the first pressure unit and the second pressure unit by means of said force component.

[0016] The substrate tube is designed to support on its outer surface, according to the external deposition method, a tubular SiO2 body with a large inner diameter, in particular made of synthetic silicon dioxide, for example a SiO2 soot body or a body made of partially or completely dense sintered quartz glass.

[0017] The substrate tube may be, for example, up to 4m long, and may be cylindrical, conical or stepped over the entire length or over part of the length. The inner profile may be constant or may vary over the substrate tube length.

[0018] After completion of the deposition process, the substrate tube may remain in the composite of the substrate tube and the SiO2 blank or may be removed from the substrate tube-blank composite. The substrate tube remaining in the substrate tube-SiO2 body composite can become part of the SiO2 blank and may be made of, for example, quartz glass. The substrate tube remaining in the substrate tube-SiO2 body composite and becoming part of the SiO2 blank preferably has an inner diameter of at least 250 mm. Its wall thickness is preferably in the range of 4 mm to 10 mm, as appropriate.

[0019] The substrate tube, which is removed from the substrate tube-SiO2 body composite after the deposition process or at a later stage in the process, is preferably made of SiC, SiSiC, Al2O3 or another ceramic material or graphite. Its outer diameter is preferably at least 250 mm. Its wall thickness is suitably in the range 5-30 mm.

[0020] The wall thickness of the substrate tube is therefore small in relation to its outer diameter, preferably less than 20% of the outer diameter of the substrate tube, so that the substrate tube on the one hand has a low weight, which reduces the driving forces of the rotational movements making it easier to handle and align, and on the other hand has a low thermal mass, which keeps the heat dissipation and the formation of thermal stresses in the wall low.

[0021] On the other hand, the wall thickness of the substrate tube is large enough to support a large volume of SiO2 body, and therefore, the wall thickness of the substrate tube is preferably at least 1% of the substrate tube outer diameter.

[0022] Wall thickness “W” S (in mm) can also depend on the substrate tube length. It is beneficial to increase the wall thickness as the substrate tube length increases. Thus, W S Instead, the outer diameter of the substrate tube D S By (mm) substrate tube length "L S Taking into account the additional factor (in mm), it can be set as follows: W S <0.2×(LS / 2,000mm)×D S .

[0023] The substrate tube holder for supporting and rotating the substrate tube includes a clamping device and a clamping mechanism having two pressure units, one adjacent to each end face of the substrate tube. The substrate tube is clamped by applying an axial clamping force to both end faces by the clamping mechanism. For this axial clamping, a non-positive connection based only on the applied axial clamping force and, in the simplest case, friction between the substrate tube and the pressure units adjacent to the end faces is sufficient. The elimination of the normally common positive fit or material connection between the substrate tube and the clamping device results in an additional degree of radial movement of the substrate tube, in which there is a degree of mechanical decoupling of the substrate tube from the clamping device, even if the pressure units are fixedly connected to the clamping device. As a result, thermally induced changes in the diameter of the substrate tube occurring during the deposition process can be mitigated or these diameter changes are possible without the accumulation of mechanical stress between the clamping device and the substrate tube.

[0024] The clamping mechanism can also help to mitigate thermal expansion in the direction of the substrate tube longitudinal axis.

[0025] The first pressure unit and the second pressure unit each preferably include a contact pressure surface adjacent a corresponding end surface of the substrate tube, the contact pressure surface being made of a graphite-containing material, which is relatively soft and capable of absorbing shocks and stimuli, as will be described in more detail below.

[0026] The pressure units on both sides transmit both the rotational movement of the clamping device and the component of the contact pressure generated by at least one force element and acting on the substrate tube end face in the direction of the substrate tube longitudinal axis. In the simplest case, the rotational movement of the substrate tube can also be obtained only by a non-positive axial connection (static friction) between the substrate tube and the substrate tube end face and the adjacent contact pressure unit. For this, only a sufficiently high contact pressure is required. As a support, the substrate tube end face and / or one or both of the adjacent pressure units can be provided with a drive element, which provides a positive fit with respect to the rotational movement and does not exclude an additional degree of freedom of movement of the substrate tube in the radial direction mentioned above.

[0027] The pressure units on both sides themselves consist of one or more parts each. In a preferred embodiment, they are of the same structure. The part directly adjacent to the substrate tube end face is, for example, plate-shaped or ring-shaped or forms a sphere or ellipsoid segment. In the simplest case, the surface adjacent to the substrate tube end face is flat, but it can also be designed to be curved or stepped.

[0028] The first and second pressure units are pressed against each other by the action of at least one force element, whereby the pressure units exert an axial contact pressure on the substrate tube sufficient for supporting and rotating the substrate tube. For this purpose, it is sufficient for at least one force element to act on only one of the two pressure units, so that it transmits a contact pressure to the respective substrate tube end face. If necessary, the other pressure unit, located opposite in the direction of the substrate tube longitudinal axis, forms a stationary abutment without the need for further force elements.

[0029] In a preferred embodiment of the device, the clamping device includes a first spindle rotatable about the rotation axis and a second spindle located axially opposite the first spindle in the direction of the substrate tube longitudinal axis and rotatable about the rotation axis, the first spindle being rotationally fixed but rotatably attached or coupled to the first pressure unit and transmitting the axial contact pressure to the first pressure unit, and the second spindle being rotationally fixed but rotatably attached or coupled to the second pressure unit and transmitting the axial contact pressure to the second pressure unit.

[0030] A first spindle (e.g. on the left) and a second spindle (e.g. on the right) are each assigned to a pressure unit. They form mechanical guide elements for the respective pressure unit and transmit the rotary movement and the axial contact pressure of the clamping device to the respective pressure unit. The spindles are designed as one piece or consist of several parts. In the simplest case, for example, the spindles are designed as a tube, a solid rod or a cone. Each of the two spindles is connected to a corresponding pressure unit for force transmission. The connection is fixed in the direction of rotation but allows at least a swiveling movement.

[0031] For example, joints such as hinges, ball joints, universal joints, cardan joints, etc. or fixed or floating bearings such as ball bearings, conical bearings, roller bearings, cardan bearings or holders are designed. This swivellable connection between the pressure unit and the spindle provides an additional decoupling between the clamping device and the substrate tube, which helps to compensate for alignment, position or dimensional deviations. For example, this makes it possible to compensate for end faces that are not exactly perpendicular to the substrate tube longitudinal axis, or to compensate for wobbling that occurs due to the substrate tube not being perfectly centered.

[0032] In the simplest and particularly preferred case, the first spindle has a free distal end to which the first pressure unit is pivotally mounted and the second spindle also has a free distal end to which the second pressure unit is pivotally mounted.

[0033] Thus, the two spindles transmit, on the one hand, the contact pressure and the rotational movement to the substrate tube and, on the other hand, support the pressure units, which are placed on the corresponding distal spindle ends.

[0034] Advantageously, at least one support element is arranged in the region of the distal ends of the first and second spindles, on which the respective corresponding spindle can roll, which is used to support the spindles, especially if the weight of the substrate tube and the SiO2 body is high.

[0035] Particularly preferably, the swivellable connection between the spindle and the pressure unit is designed as a floating bearing and preferably comprises a cardboard-conical seat, where the spindle-side seat is formed conically and the pressure unit movably mounted thereon has a spherical or radial section which interacts with the seat, or vice versa, the spindle-side seat has a convexly curved spherical or radial section corresponding to the concavely curved pressure unit movably mounted thereon.

[0036] In particular for very long substrate tubes, the length of which exceeds 2 m, further stabilization of the rotation axis is useful, in this respect the substrate tube holder comprises a centering unit which comprises at least one tubular or rod-shaped centering support which extends between the first and second pressure units through the through opening in the substrate tube.

[0037] The centering supports are preferably loosely mounted in the area of ​​the respective pressure unit and are mechanically decoupled from the spindle on both sides so as not to impede the axial movement of the spindle to compensate for changes in length.

[0038] For example, for this purpose, a link can be used which runs from one spindle to the opposite spindle through a through opening in the substrate tube, the link consisting, for example, of a rod or rods which are each uniformly distributed around the axis of rotation and which are connected directly or indirectly (through corresponding attached intermediate elements) to the spindles on both sides.

[0039] Alternatively or additionally, in a particularly preferred embodiment, the first spindle is designed as a hollow spindle with a first internal bore and the second spindle is designed as a hollow spindle with a second internal bore, the centering support being designed to protrude with a first end into the first internal bore and with a second end into the second internal bore.

[0040] The first and second spindles are designed here as hollow spindles with an internal bore. The internal bore is designed as a through bore or the hollow spindle is closed on one side at the proximal end (facing the clamping device). In the simplest case, the internal bore has a circular cross section, but it can also have a cross section different from circular, such as an elliptical or polygonal cross section. The inner cross sections of the first and second hollow spindles are the same or different from each other. The inner cross section of the hollow spindle is adapted to the outer cross section of the respective centering support, preferably in the sense of a clearance fit.

[0041] The centering supports, which are part of the centering unit, have a centering support longitudinal axis and are, for example, rod-shaped or tubular. The centering supports extend completely through the through openings of the substrate tubes, but preferably end in the internal bores of the hollow spindles on both sides. In each internal bore, the centering supports are mounted according to the telescopic principle so that they are axially movable with little radial play. The gap between the inner wall of the hollow spindle and the outer wall of the centering support is as small as possible, preferably a few tenths of a millimeter, for example in the range of 0.2-0.5 mm. The centering supports are thus supported on the inner walls of the internal bores of both hollow spindles and at the same time axially center them relative to each other in the sense of the coaxiality of the longitudinal axes of the centering supports and the hollow spindles. On the one hand, the clearance fit prevents overdetermination of the substrate tube bearings, and on the other hand, an axial guide is obtained which counteracts the mutual tilt or twist of the hollow spindles from the substrate tube longitudinal axis.

[0042] In a preferred embodiment of the centering support, this support is freely rotatable in the internal bores of the hollow spindles on both sides and does not or only partially execute a hollow spindle rotational movement. In another embodiment of the centering support, it is mounted in a rotationally fixed manner in the internal bores of the hollow spindles on both sides so as to rotate together with the hollow spindles. A rotationally fixed installation can be obtained, for example, in the sense of a key-lock connection, by a non-circular, for example polygonal or elliptical, internal shape of at least one of the hollow spindles and an outer contour of the centering support adapted thereto.

[0043] In a preferred development of one embodiment of the centering support, it is free to move axially within the first internal bore and within the second internal bore.

[0044] Here, the centering supports have ends in each internal bore where they are free to move axially (except for friction). The axial mobility of the centering supports allows compensation for differential thermal expansion between the centering supports and the hollow spindle, thereby avoiding thermal stresses in the substrate tube holder.

[0045] The free distance "a" between the oppositely positioned hollow spindles is usually constant. The length of the centering support "L Z " is greater than this free distance "a". Under certain conditions, the centering support may still completely slip out of one of the hollow spindle inner bores, if the axial movement play of the centering support is large enough for this. This slipout can occur, for example, when the length "L Z This can be prevented by including the free distance "a" and an additional length (La+Lb) to allow for room for axial movement on both sides within the first and second internal bores.

[0046] In particular, with regard to the effect of the centering support as an axial guide for the two hollow spindles, it is advantageous for the centering support to extend into both hollow spindles over a constant extension length La or Lb. The lengths La and Lb are preferably at least twice the inner diameter of each hollow spindle. The inner diameter of the hollow spindles is preferably in the range of 40 mm to 100 mm.

[0047] On the other hand, for reasons of stability and in particular in order to guide the hollow spindle on both sides by the centering supports as effectively as possible, the axial movement range of the centering supports on both sides in the hollow spindle, “B Z " (B a +B b ) as a whole, and "B Z It may be beneficial to design " as large as necessary and as small as possible. Z It has been found useful to apply the following to: Z <20mm, preferably 5mm Z <15mm. ​

[0048] The total axial movement free space of the centering support in the axial hollow spindle is limited to a few millimeters, which is usually sufficient to compensate for the axial CTE difference between the hollow spindle and the centering support. This limitation can be achieved, for example, by stop elements protruding into the hollow spindle inner bore or by the hollow spindle inner bore being narrowed or blocked.

[0049] In a particularly preferred development of the embodiment of the device with a centering support, the centering unit comprises a number of centering elements placed on the centering support in the through-hole of the substrate tube, of which a first centering element is arranged in the region of a first end face of the substrate tube and a second centering element is designed to be arranged in the region of a second end face of the substrate tube.

[0050] The centering element is inserted into the substrate tube through-hole in the region of both ends. It serves to guide the substrate tube and acts as a "collapse protection" against slipping out. It therefore has an outer contour adapted to the inner contour of the substrate tube through-hole. It is designed, for example, as a circular ring, a polygonal ring or a star with outwardly pointing support arms. The diameter of the circle surrounding the centering element is smaller than the inner diameter of the substrate tube through-hole. The inner contour of the centering element is preferably adapted to the outer contour of the centering support so that it rests on the centering support with a slidable clearance fit. For example, in the case of a circular construction, the inner diameter of the centering element is 0.5-2 mm larger than the outer diameter of the centering support.

[0051] The centering elements facilitate installation of the substrate tube holder and reduce the risk of the substrate tube coming out of the axial clamp when used in a deposition process. At least one further centering element can be disposed in the area between the end centering elements to reduce bowing of the substrate tube. The centering elements are preferably made of graphite or another graphite-containing material.

[0052] The SiO2 blanks produced are usually made of synthetic silicon dioxide with a low CTE. Depending on the composition and production method, it has a CTE of approximately 0.5 μm / m / °K (0.5×10 -6 / °K). Metals are the preferred choice of material for the spindle. Metals are generally characterized by their ability to absorb mechanical energy during plastic deformation (toughness) and are therefore able to compensate for mechanical stimuli during the deposition process. Particularly preferred are metals with high chemical resistance, such as stainless steels (with a CTE ranging from 10 μm / m / °K to 17 μm / m / °K depending on the alloy) and / or iron-nickel alloys, known collectively as "INVAR", with a thermal expansion coefficient similar to that of silicon dioxide, with a CTE usually in the range of 1.2 μm / m / °K or less.

[0053] At least one deposition burner generates a burner flame whose hottest spot is usually spatially located in front of or on the surface of the SiO2 body to be deposited. The area around this hottest spot is also called the "reaction zone".

[0054] In this regard, in a preferred embodiment of the apparatus, the largest radial dimension of the spindle, e.g. the outer diameter in the case of a circular spindle cross section, is significantly smaller than the outer diameter of the substrate tube, e.g. at least 100 mm smaller, thereby ensuring that the spindle is outside the "reaction zone" of the deposition burner(s).

[0055] The device has a first side (e.g., left side) and a second side (e.g., right side). In the following description, when only the first of these two sides is mentioned, the second side is designed to be essentially the same or equivalent to the first side, unless otherwise specified.

[0056] It has been found that the first pressure unit includes a first pressure transmission element and a first buffer element, preferably made of a graphite-containing material, connected thereto in a rotationally fixed manner, the pressure transmission element being mounted or coupled to the first spindle in a rotationally fixed but rotatable manner, and the first buffer element being positioned between the pressure transmission element and the substrate tube and adjacent to the first end face of the substrate tube.

[0057] The first pressure transmission element is part of the first pressure unit. It is designed to transmit the axial contact pressure generated by at least one force element to the substrate tube first end face, or to act as an abutment of the substrate tube first end face if the axial contact pressure generated by the force element also or only acts on the substrate tube second end face. The pressure transmission element interacts directly or indirectly (i.e. via an intermediate element) with the first spindle which is rotationally fixed to it but pivotably mounted or coupled thereto. For example, the pressure transmission element has a central opening with a circumferential opening edge which rests on the first spindle. The pressure transmission element is preferably made of metal, for example stainless steel.

[0058] The buffer element is arranged between the pressure transmission element and the first end face of the substrate tube. On the one hand, it serves to improve the clamping effect and, on the other hand, to absorb axial or azimuthal stimuli which may act on the relatively shock-sensitive end face. The buffer element is designed, for example, in the form of an annular or star shape. It preferably has a low hardness, which allows a relatively high contact pressure to be applied without damaging the substrate tube end face, and which generates a friction that is high enough to transmit the rotational movement. A suitable material is, for example, graphite, which, due to its lubricating properties, allows the tube end face to slide radially on the graphite, thus allowing for radial thermal expansion of the substrate tube, but always with sufficient friction to transmit stimuli and forces during azimuthal acceleration.

[0059] The force flow of the contact pressure is now: force element (e.g. spring-loaded chuck) → first pressure unit with first spindle → joint / swivellable bearing → first pressure transmission element → first buffer element → first end face of the substrate tube.

[0060] The first buffer element can be designed as a stepped annular disk having a hollow cylindrical section with an outwardly protruding flange, the flange abutting the substrate tube first end face and the hollow cylindrical section protruding into the substrate tube through-hole. The stepped disk buffer element engages under the inner wall of the substrate tube with little play and at the same time functions as a centering element. This is one way to ensure the position of the first centering element in the region of the substrate tube first end face, if this is deemed necessary or expedient. In this embodiment, the centering element and the buffer element are designed as one part.

[0061] On the one hand, the buffer element is exposed to strong forces and can wear out relatively quickly. It is also advantageous if the centering element and the buffer element can be thermally decoupled, for example by a gap. As a wearing part, the buffer element is preferably easy and cheap to replace. With this in mind, it has been found to be advantageous if the first centering element is removably and non-rotatably connected to the first buffer element.

[0062] This is a further measure for ensuring the position of the first centering element in the region of the first end face of the substrate tube, if this is deemed necessary or expedient. The above-mentioned detachable connection is carried out, for example, by means of a screw. The buffer element can thus be easily replaced, for example if it becomes worn. The torsional strength is also ensured by an only loose connection between the buffer element and the centering element, which on the one hand allows mechanical play and on the other hand leaves a gap between the buffer element and the centering element for thermal decoupling. In this case, for example, a screw guided with play in the bores of the buffer element and the centering element is provided so that the articulation connection between the respective spindle and the pressure unit is not hindered. The screw can serve as a drive element for the rotational movement of the substrate tube by providing a positive-fit connection for the rotational movement.

[0063] It has also proven to be advantageous if the device comprises a first buffer element, said buffer element protruding radially beyond the pressure transmission element and the substrate tube.

[0064] During the OVD external deposition process, the flame of at least one deposition burner impinges on the surface of the substrate tube or on the forming SiO2 body and can then be deflected laterally so as to spread tangentially to the object surface in the direction of the end region of the SiO2 body. As a result of the buffer elements projecting radially relative to the pressure transfer elements, the latter are largely protected from thermal and corrosive loads by being located in the shadow of the flame, while the buffer elements are exposed to them. The height of the radial projection is preferably in the range of 1 cm to 3 cm.

[0065] In a preferred embodiment of the device according to the invention, the substrate tube holder comprises a compensation mechanism for compensating for the thermal expansion in the direction of the substrate tube longitudinal axis. The compensation mechanism and the clamping mechanism can have common parts. For example, the compensation mechanism usually comprises a spring element, preferably also the force element of the clamping mechanism comprises a spring element, which spring element is simultaneously part of the compensation mechanism. The spring element is thus both part of the compensation mechanism and part of the clamping mechanism of the substrate tube holder. The spring element is for example designed as a chuck with a spring on one or both sides.

[0066] Regarding a method for manufacturing a SiO2 blank, based on the above-mentioned method, the substrate tube holder is used to generate an axial contact pressure on the first end face and the second end face with a force component acting in the direction of the longitudinal axis of the substrate tube, and the substrate tube is clamped between a first pressure unit adjacent to the first end face and a second pressure unit adjacent to the second end face, thereby solving the above-mentioned technical problem by the present invention.

[0067] The method includes the step of producing a tubular SiO2 blank, in particular made of synthetic silicon dioxide, based on an external deposition method. Depending on the temperature during the deposition process, a porous SiO2 soot body or a substantially transparent vitreous SiO2 body is generated on the surface of the substrate tube. In the case of a porous SiO2 soot body, the porous SiO2 soot body can be subjected to a dehydration treatment in an inert gas, a chlorine-containing gas or in vacuum in order to reduce the hydroxyl content of the quartz glass before sintering to form a substantially transparent vitreous SiO2 body. Sintering (or vitrification) is carried out, for example, under vacuum or in an atmosphere containing helium and / or hydrogen and / or nitrogen.

[0068] The substrate tubes are, for example, up to 4 m long and have a cylindrical, conical or stepped shape over the entire length or over part of the length. The substrate tubes are designed to produce tubular SiO2 bodies with large inner diameters, in particular consisting of synthetic silicon dioxide, on their outer surface based on the OVD external deposition method. The dimensions of the SiO2 blanks obtained after this process are, for example, as follows: inner diameter in the range of 250 mm to 650 mm, wall thickness in the range of 25 mm to 150 mm, length in the range of 800 mm to 3,800 mm. By mechanical, chemical and / or thermal treatments, parts of synthetic quartz glass, for example quartz glass tubes or quartz glass rings, are obtained therefrom.

[0069] This method therefore makes it possible to produce large-volume quartz glass tubes, in particular with an inside diameter of at least 250 mm and a wall thickness of at least 25 mm.

[0070] Preferably, a substrate tube holder of the apparatus according to the invention is used to support the substrate tube in accordance with step (b), as will be described in more detail below.

[0071] After completion of the deposition process, the substrate tube may remain in the composite of the substrate tube and the SiO2 body or may be removed from the substrate tube-SiO2 body composite. The substrate tube remaining in the substrate tube-SiO2 body composite may become part of the SiO2 blank, e.g. made of quartz glass. The substrate tube remaining in the substrate tube-SiO2 body composite and becoming part of the SiO2 blank preferably has an inner diameter of at least 250 mm. Its wall thickness is suitably in the range 4-10 mm. The substrate tube removed from the substrate tube-SiO2 body composite after the deposition process or at a later stage in the process preferably consists of SiC, SiSiC, Al2O3 or another ceramic material or graphite. Its outer diameter is preferably at least 250 mm. Its wall thickness is suitably in the range 5-30 mm.

[0072] The wall thickness of the substrate tube is therefore small relative to its outer diameter, typically less than 20% of the outer diameter of the substrate tube, so that the substrate tube on the one hand has a low weight, which reduces the driving forces of the rotational movements and makes it easier to handle and align, and on the other hand has a low heat capacity, which keeps the heat dissipation and keeps the formation of thermal stresses in the wall low.

[0073] On the other hand, the wall thickness of the substrate tube is large enough to support a large volume of SiO2 body. Therefore, it is preferable that the wall thickness of the substrate tube is at least 1% of the outer diameter of the substrate tube. S (in mm) can also depend on the substrate tube length. It is beneficial to increase the wall thickness as the substrate tube length increases. Thus, W S Instead, the outer diameter of the substrate tube D S By (mm) substrate tube length "L S Taking into account the additional factor (in mm), it can be set as follows: W S <0.2×(L S / 2,000mm)×D S .

[0074] The substrate tube holder is used for supporting and rotating the substrate tube. The substrate tube holder includes a clamping device and a clamping mechanism having two pressure units, one adjacent to each end face of the substrate tube. The clamping mechanism applies an axial clamping force to both end faces to clamp the substrate tube.

[0075] The rotationally fixed support and rotation is achieved by clamping the substrate tube between a first pressure unit adjacent to the first end face and a second pressure unit adjacent to the second end face. For this purpose, the substrate tube holder is designed to generate an axial contact pressure on the first and second end faces with a force component acting in the direction of the substrate tube longitudinal axis. The axial contact pressure acts on the first and / or second pressure unit with a force component acting in the direction of the substrate tube longitudinal axis. This contact pressure is transmitted by the pressure units to the end faces of the substrate tube, whereby the substrate tube is clamped and held in a rotationally fixed manner between the pressure units on both sides. For this axial clamping, an applied axial clamping force and, in the simplest case, a non-positive connection based only on friction between the substrate tube and the pressure units adjacent to the end faces is sufficient. The elimination of the normally common positive fit or material connection between the substrate tube and the clamping device results in an additional degree of radial movement of the substrate tube, in that there is a degree of mechanical decoupling of the substrate tube from the clamping device even though the pressure unit is fixedly connected to the clamping device, so that thermally induced diameter changes that occur during the deposition process can be compensated for or are possible without the build-up of mechanical stress between the clamping device and the substrate tube.

[0076] The clamping mechanism can also help to mitigate thermal expansion in the direction of the substrate tube longitudinal axis.

[0077] The pressure units on both sides transmit both the rotational movement of the clamping device and the component of the contact pressure generated by at least one force element and acting on the substrate tube end face in the direction of the substrate tube longitudinal axis. In the simplest case, the rotational movement of the substrate tube can also be obtained only by a non-positive axial connection (static friction) between the substrate tube and the substrate tube end face and the adjacent contact pressure unit. For this, only a sufficiently high contact pressure is required. As a support, the substrate tube end face and / or one or both of the adjacent pressure units can be provided with a drive element, which provides a positive fit with respect to the rotational movement and does not exclude an additional degree of freedom of movement of the substrate tube in the radial direction mentioned above.

[0078] The pressure units on both sides themselves consist of one or more parts each. In a preferred embodiment, they are of the same structure. The part directly adjacent to the substrate tube end face is, for example, plate-shaped or ring-shaped or forms a sphere or ellipsoid segment. In the simplest case, the surface adjacent to the substrate tube end face is flat, but it can also be designed to be curved or stepped.

[0079] The first and second pressure units are pressed against each other by the action of at least one force element, whereby the pressure units exert an axial contact pressure on the substrate tube sufficient for supporting and rotating the substrate tube. For this purpose, it is sufficient for at least one force element to act on only one of the two pressure units, so that it transmits a contact pressure to the respective substrate tube end face. If necessary, the other pressure unit, located opposite in the direction of the substrate tube longitudinal axis, forms a stationary abutment without the need for further force elements.

[0080] In a preferred procedure, the axial contact pressure on the first pressure unit is generated by a first spindle connected to the clamping device and rotatable about an axis of rotation, and the axial contact pressure on the second pressure unit is generated by a second spindle connected to the clamping device and rotatable about an axis of rotation, the first spindle being rotationally fixed but pivotably attached or coupled to the first pressure unit and the second spindle being rotationally fixed but pivotably attached or coupled to the second pressure unit.

[0081] The first and second spindles form mechanical guide elements and are each assigned to a pressure unit. They transmit the rotary movement and the axial contact pressure of the clamping device to the respective pressure unit. The spindles are designed as one piece or consist of several parts. In the simplest case, for example, the spindles are designed as a tube, a solid rod or a cone. Each of the two spindles is connected to a corresponding pressure unit for force transmission. The connection is fixed in the direction of rotation but allows at least a swivel movement.

[0082] For example, joints such as hinges, ball joints, universal joints, cardan joints, etc. or fixed or floating bearings such as ball bearings, conical bearings, roller bearings, cardan bearings or holders are designed. This swivellable connection between the pressure unit and the spindle provides an additional decoupling between the clamping device and the substrate tube, which helps to compensate for alignment, position or dimensional deviations. For example, this makes it possible to adjust end faces that are not exactly perpendicular to the substrate tube longitudinal axis and to adjust for wobbling that occurs due to the substrate tube not being perfectly centered.

[0083] In the simplest and particularly preferred case, the first spindle has a free distal end to which the first pressure unit is pivotally mounted and the second spindle also has a free distal end to which the second pressure unit is pivotally mounted.

[0084] Thus, the two spindles transmit, on the one hand, the contact pressure and the rotational movement to the substrate tube and, on the other hand, support the pressure units, which are placed on the corresponding distal spindle ends.

[0085] Advantageously, at least one support element is arranged in the region of the distal ends of the first and second spindles, on which the respective corresponding spindle can roll, which is used to support the spindles, especially if the weight of the substrate tube and the SiO2 body is high.

[0086] Particularly preferably, the swivellable connection between the spindle and the pressure unit is designed as a floating bearing and preferably comprises a cardboard-conical seat, where the spindle-side seat is formed conically and the pressure unit movably mounted thereon has a sphere or radius section which interacts with the seat, or vice versa, the spindle-side seat has a corresponding sphere or radius section with a concavely curved pressure unit movably mounted thereon.

[0087] Especially for very long substrate tubes, over 2m in length, further stabilization of the rotation axis is useful.

[0088] In this regard, it is advantageous to use a substrate tube holder which includes a centering unit including at least one tubular or rod-shaped centering support extending between the first pressure unit and the second pressure unit through the through opening of the substrate tube.

[0089] The centering supports are preferably loosely mounted in the area of ​​the respective pressure units and are mechanically decoupled from the spindle on both sides so as not to impede the axial movement of the spindle to compensate for changes in length.

[0090] For example, for this purpose, a link can be used which runs from one spindle to the opposite spindle through a through opening in the substrate tube, the link consisting, for example, of two or more rods each evenly distributed around the axis of rotation and connected directly or indirectly (through corresponding attached intermediate elements) to the spindles on both sides.

[0091] Alternatively or additionally, in a particularly preferred procedure, the first spindle is designed as a hollow spindle with a first internal bore and the second spindle is designed as a hollow spindle with a second internal bore, the centering support being designed to protrude with a first end into the first internal bore and with a second end into the second internal bore.

[0092] The first and second spindles are designed here as hollow spindles with an internal bore. The internal bore is designed as a through bore or the hollow spindle is closed on one side at the proximal end (facing the clamping device). In the simplest case, the internal bore has a circular cross section, but it can also have a cross section different from circular, such as an elliptical or polygonal cross section. The inner cross sections of the first and second hollow spindles are the same or different from each other. The inner cross section of the hollow spindle is adapted to the outer cross section of the respective centering support, preferably in the sense of a clearance fit.

[0093] The centering supports, which are part of the centering unit, have a centering support longitudinal axis and are, for example, rod-shaped or tubular. The centering supports extend completely through the through openings of the substrate tubes, but preferably end in the internal bores of the hollow spindles on both sides. In each internal bore, the centering supports are mounted according to the telescopic principle so that they are axially movable with little radial play. The gap between the inner wall of the hollow spindle and the outer wall of the centering support is as small as possible, preferably a few tenths of a millimeter, for example in the range of 0.2-0.5 mm. The centering supports are thus supported on the inner walls of the internal bores of both hollow spindles and at the same time axially center them relative to each other in the sense of the coaxiality of the longitudinal axes of the centering supports and the hollow spindles. On the one hand, the clearance fit prevents overdetermination of the substrate tube bearings, and on the other hand, an axial guide is obtained which counteracts the mutual tilt or twist of the hollow spindles from the substrate tube longitudinal axis.

[0094] In a preferred procedure, the centering supports are freely rotatable in the internal bores of the hollow spindles on both sides and do not or only partially perform a hollow spindle rotational movement. In another procedure, the centering supports are mounted rotationally fixed in the internal bores of the hollow spindles on both sides so as to rotate together with the hollow spindles. A rotationally fixed installation can be obtained, for example, in the sense of a key-lock connection, by a non-circular, for example polygonal or elliptical, internal shape of at least one of the hollow spindles and an outer contour of the centering support adapted thereto.

[0095] In a preferred development of the procedure with a centering support, it is free to move axially within the first internal bore and within the second internal bore.

[0096] Here, the centering supports have ends within each of the internal bores where they are free to move axially (except for friction). The axial mobility of the centering supports allows for differential thermal expansion between the centering supports and the hollow spindle, thereby avoiding thermal stresses in the substrate tube holder.

[0097] The free distance "a" between the oppositely positioned hollow spindles is usually constant. The length of the centering support "L Z " is greater than this free distance "a". Under certain conditions, the centering support may still completely slip out of one of the hollow spindle inner bores, if the axial movement play of the centering support is large enough for this. This slipout can occur, for example, when the length "L Z This can be prevented by including the free distance "a" and an additional length (La+Lb) to allow for room for axial movement on both sides within the first and second internal bores.

[0098] In particular, with regard to the effect of the centering support as an axial guide for the two hollow spindles, it is advantageous for the centering support to extend into both hollow spindles over a constant extension length La or Lb. The lengths La and Lb are preferably at least twice the inner diameter of each hollow spindle. The inner diameter of the hollow spindles is preferably in the range of 40 mm to 100 mm.

[0099] On the other hand, for reasons of stability and in particular in order to guide the hollow spindle on both sides by the centering supports as effectively as possible, the axial movement range of the centering supports on both sides in the hollow spindle, “B Z " and limit the whole "B Z It may be beneficial to design " as large as necessary and as small as possible. Z It has been found useful to apply the following to: Z <20mm, preferably 5mm Z <15mm.

[0100] ​The total axial movement free space of the centering support in the axial hollow spindle is limited to a few millimeters, which is usually sufficient to compensate for the axial CTE difference between the hollow spindle and the centering support. This limitation can be achieved, for example, by stop elements protruding into the hollow spindle inner bore or by the hollow spindle inner bore being narrowed or blocked.

[0101] In a particularly preferred development of the procedure using a centering support, the centering unit is designed to include a number of centering elements placed on the centering support in the through-hole of the substrate tube, of which a first centering element is arranged in the region of a first end face of the substrate tube and a second centering element is arranged in the region of a second end face of the substrate tube.

[0102] The centering element is inserted into the substrate tube through-hole in the region of both ends. It serves to guide the substrate tube and acts as a "collapse protection" against slipping out. It therefore has an outer contour adapted to the inner contour of the substrate tube through-hole. It is designed, for example, as a circular ring, a polygonal ring or a star with outwardly pointing support arms. The diameter of the circle surrounding the centering element is smaller than the inner diameter of the substrate tube through-hole.

[0103] The inner contour of the centering element is preferably adapted to the outer contour of the centering support so that it rests on the centering support with a slidable clearance fit, e.g., in the case of a circular construction, the inner diameter of the centering element is 0.5-2 mm larger than the outer diameter of the centering support.

[0104] The centering elements facilitate installation of the substrate tube holder and reduce the risk of the substrate tube coming out of the axial clamp when used in a deposition process. At least one further centering element can be disposed in the area between the end centering elements to reduce bowing of the substrate tube. The centering elements are preferably made of graphite or another graphite-containing material.

[0105] The SiO2 blanks produced consist of synthetic silicon dioxide with a low CTE. Depending on the composition and production method, it has a CTE of approximately 0.5 μm / m / °K (0.5×10 -6 / °K). Metals are the preferred choice of material for the spindle. Metals are generally characterized by their ability to absorb mechanical energy during plastic deformation (toughness) and are therefore able to compensate for mechanical stimuli during the deposition process. Particularly preferred are metals with high chemical resistance, such as stainless steels (with a CTE ranging from 10 μm / m / °K to 17 μm / m / °K depending on the alloy) and / or iron-nickel alloys, known collectively as "INVAR", with a thermal expansion coefficient similar to that of silicon dioxide, with a CTE usually in the range of 1.2 μm / m / °K or less.

[0106] At least one deposition burner generates a burner flame whose hottest spot is usually spatially located in front of or on the surface of the SiO2 body to be deposited. The area around this hottest spot is also called the "reaction zone".

[0107] In this regard, in a preferred procedure, the maximum radial dimension of the spindle, e.g. the outer diameter in the case of a circular spindle cross section, is significantly smaller than the outer diameter of the substrate tube, e.g. at least 100 mm smaller, thereby ensuring that the spindle is outside the "reaction zone" of the at least one deposition burner.

[0108] An apparatus for carrying out the above method has a first side (e.g., left side) and a second side (e.g., right side). In the following description, when only the first of these two sides is mentioned, the second side is designed essentially the same or equivalent to the first side, unless otherwise specified.

[0109] It has been found that the first pressure unit includes a first pressure transmission element and a first buffer element, preferably made of a graphite-containing material, connected thereto in a rotationally fixed manner, the pressure transmission element being mounted or coupled to the first spindle in a rotationally fixed but rotatable manner, and the first buffer element being positioned between the pressure transmission element and the substrate tube and adjacent to the first end face of the substrate tube.

[0110] The first pressure transmission element is part of the first pressure unit. It is designed to transmit the axial contact pressure generated by at least one force element to the substrate tube first end face, or to act as an abutment of the substrate tube first end face if the axial contact pressure generated by the force element also or only acts on the substrate tube second end face. The pressure transmission element interacts directly or indirectly (i.e. via an intermediate element) with the first spindle which is rotationally fixed to it but pivotably mounted or coupled thereto. For example, the pressure transmission element has a central opening with a circumferential opening edge which rests on the first spindle. The pressure transmission element is preferably made of metal, for example stainless steel.

[0111] The buffer element is arranged between the pressure transmission element and the first end face of the substrate tube. On the one hand, it serves to improve the clamping effect and, on the other hand, to absorb axial or azimuthal stimuli which may act on the relatively shock-sensitive end face. The buffer element is designed, for example, in the form of an annular or star shape. It preferably has a low hardness, which allows a relatively high contact pressure to be applied without damaging the substrate tube end face, and which generates a friction that is high enough to transmit the rotational movement. A suitable material is, for example, graphite, which, due to its lubricating properties, allows the tube end face to slide radially on the graphite, thus allowing for radial thermal expansion of the substrate tube, but always with sufficient friction to transmit stimuli and forces during azimuthal acceleration.

[0112] The force flow of the contact pressure is now: force element (e.g. spring-loaded chuck) → first pressure unit with first spindle → joint / swivellable bearing → first pressure transmission element → first buffer element → first end face of the substrate tube.

[0113] The first buffer element can be designed as a stepped annular disk having a hollow cylindrical section with an outwardly protruding flange, the flange abutting the substrate tube first end face and the hollow cylindrical section protruding into the substrate tube through-hole. The stepped disk buffer element engages under the inner wall of the substrate tube with little play and at the same time functions as a centering element. This is one way to ensure the position of the first centering element in the region of the substrate tube first end face, if this is deemed necessary or expedient. In this embodiment, the centering element and the buffer element are designed as one part.

[0114] On the one hand, the buffer element is exposed to strong forces and can wear out relatively quickly. It is also advantageous if the centering element and the buffer element can be thermally decoupled, for example by a gap. As a wearing part, the buffer element is preferably easy and cheap to replace. With this in mind, it has been found to be advantageous if the first centering element is removably and non-rotatably connected to the first buffer element.

[0115] This is a further measure for ensuring the position of the first centering element in the region of the first end face of the substrate tube, if this is deemed necessary or expedient. The above-mentioned detachable connection is carried out, for example, by means of a screw. The buffer element can thus be easily replaced, for example if it becomes worn. The torsional strength is also ensured by an only loose connection between the buffer element and the centering element, which on the one hand allows mechanical play and on the other hand leaves a gap between the buffer element and the centering element for thermal decoupling. In this case, for example, a screw guided with play in the bores of the buffer element and the centering element is provided so that the articulation connection between the respective spindle and the pressure unit is not hindered. The screw can serve as a drive element for the rotational movement of the substrate tube by providing a positive-fit connection for the rotational movement.

[0116] It has also proven to be advantageous in procedures using a first buffer element if the buffer element protrudes radially beyond the pressure transmission element and the substrate tube.

[0117] During the OVD external deposition process, the flame of at least one deposition burner impinges on the surface of the substrate tube or on the forming SiO2 body and can then be deflected laterally so as to spread tangentially to the object surface in the direction of the end region of the SiO2 body. As a result of the buffer elements projecting radially relative to the pressure transfer elements, the latter are largely protected from thermal and corrosive loads by being located in the shadow of the flame, while the buffer elements are exposed to them. The height of the radial projection is preferably in the range of 1 cm to 3 cm.

[0118] The substrate tube holder preferably comprises a compensation mechanism for compensating for thermal expansion in the direction of the substrate tube longitudinal axis. The compensation mechanism and the clamping mechanism can have common parts. For example, the compensation mechanism usually comprises a spring element, and in a preferred procedure the force element of the clamping mechanism also comprises a spring element, which spring element is simultaneously part of the compensation mechanism. The spring element is thus both part of the compensation mechanism and part of the clamping mechanism of the substrate tube holder. The spring element is for example designed as a chuck with a spring on one or both sides.

[0119] [Definition and measurement methods] The individual terms in the above description are further defined below. The definitions are part of the description of the present invention. For terms and measurement means not specifically defined in the specification, the interpretation given by the International Telecommunication Union (ITU) applies. In case of any discrepancy between the definitions below and the remainder of the specification, the description in the specification shall prevail.

[0120] [Tubular SiO2 blank] The result of the deposition process is a tubular composite consisting of a substrate tube and a body made of synthetic silicon dioxide. Depending on the temperature during the deposition process, the body made of synthetic silicon dioxide is either a porous "soot body" or a body made of mostly transparent quartz glass, referred to herein as the "SiO2 body". The SiO2 body may be the only part of the tubular SiO2 blank or the substrate tube may be a further part of the SiO2 blank, limiting its internal porosity. Substrate tubes made of materials other than quartz glass are not part of the SiO2 blank.

[0121] [Parts made of synthetic quartz glass] Components made of synthetic quartz glass are obtained by mechanical, thermal or chemical treatment of tubular SiO2 blanks. Further mechanical treatments include cutting, cutting, milling, grinding and polishing of the internal and external contours. Further thermal treatments include thermal drying, sintering, vitrification, melting, shaping and tempering. Further chemical treatments include chemical, thermal or vacuum drying (dehydration), doping and etching. The components are ready-to-use quartz glass products or semi-finished products therefor, such as quartz glass tubes or quartz glass rings.

[0122] [Quartz glass / Synthetic quartz glass / Synthetic silicon dioxide] Quartz glass and synthetic silicon dioxide are understood here to mean glasses with a SiO2 content of at least 87% by weight, which are doped (SiO2 content = 100%) or contain dopants such as oxides of fluorine, chlorine, nitrogen, carbon or boron, germanium, rare earth metals, aluminum or titanium.

[0123] Quartz glass can be, for example, a melt of naturally occurring SiO2 raw materials (natural quartz glass), can be synthesized (synthetic quartz glass), or can consist of a mixture of these quartz glass types. Synthetic transparent quartz glass can be obtained, for example, by flame hydrolysis or oxidation of synthesized silicon compounds, by polycondensation of organic silicon compounds by the so-called sol-gel process, or by hydrolysis and precipitation in liquid of inorganic silicon compounds.

[0124] [Sintering / vitrification] "Sintering" or "vitrification" refers here to a process in which a porous silicon dioxide SiO2 body is treated at high temperature in a furnace. Sintering / vitrification is carried out in an inert gas, hydrogen and / or helium containing atmosphere or under vacuum. Vacuum means an absolute gas pressure of less than 2 mbar. The result of vitrification / sintering is a "tubular blank made of synthetic silicon dioxide".

[0125] [Substraight pipe outer diameter / Substraight pipe inner diameter] The substrate tube cross-section may have a circular or out-of-round outer contour. If the outer contour deviates from a round shape, the local "outer diameter value" is given by the (smallest) circumferential diameter.

[0126] The substrate tube cross section may have a circular or out-of-round inner contour. If the inner contour deviates from round, the local "inner diameter value" is given by the diameter of the (largest) inscribed circle.

[0127] In a longitudinal section of the substrate tube, the local values ​​of the outer diameter may or may not be constant over the entire length of the substrate tube. If the outer diameter value is constant, the substrate tube is cylindrical when viewed from the outside. If the outer diameter value is not constant, the outer diameter value may vary over the entire length or over partial lengths. The outer contour may vary, for example, continuously or gradually. In this case, the outer diameter is the result of an average of the local outer diameter values ​​over the entire length.

[0128] In a longitudinal section of the substrate tube, the local value of the inner diameter may or may not be constant over the entire length of the substrate tube. If the inner diameter value is constant, the through opening of the substrate tube is cylindrical. If the inner diameter value is not constant, the inner diameter value may vary over the entire length or over a partial length. The inner contour may vary, for example, continuously or gradually. In this case, the inner diameter is the result of an average of the local inner diameter values ​​over the entire length.

[0129] [Gap fit] The clearance fit is carried out, for example, on the basis of the tolerance tables according to DIN EN ISO 286-Part 2. To ensure a certain degree of axial mobility between the respective bore and the spindle, the tolerance zones must match one another in such a way that the largest dimension of the spindle is always smaller than the smallest dimension of the bore. Suitable tolerance zones for the bore are, for example, H, G, F and E, and for the spindle, for example, g, f and e. Exemplary embodiment

[0130] The invention will now be explained in more detail with reference to an example embodiment and to the figures, the individual figures showing the following schematic diagrams: [Brief description of the drawings]

[0131] [Figure 1] 1 shows an apparatus for manufacturing a tubular SiO2 blank in a first embodiment of a substrate tube holder in longitudinal section. [Diagram 2] FIG. 2 is a partial detailed view in longitudinal section of an apparatus for producing tubular SiO2 blanks from synthetic silicon dioxide in a second embodiment of the substrate tube holder. [Diagram 3] FIG. 3 is an enlarged view of a portion of the substrate tube holder of FIG. 2.

[0132] The apparatus shown diagrammatically in Figure 1 includes a glass lathe 2 for holding and rotating a substrate tube 1 made of SiSiC. The substrate tube 1 has a left end face 1a, a right end face 1b, an outer surface 1c, an inner surface 1d, a horizontal longitudinal axis 1e, and a cylindrical through bore 1f. The substrate tube 1 is 2 m long, has an outer diameter of 280 mm, and a wall thickness of 20 mm. The inner diameter is therefore 240 mm.

[0133] The glass lathe 2 is represented by two oppositely situated chucks 2a, 2b, of which chuck 2a is sprung as shown by compression spring 2c. Compression spring 2c generates a pressure F which presses the two chucks 2a, 2b against each other as shown by directional arrow 2d.

[0134] A hollow spindle 3a, 3b made of stainless steel is clamped at its proximal end to each of the chucks 2a, 2b. In the ideal case, the rotation axis of the hollow spindle 3a, 3b extends coaxially with the substrate tube longitudinal axis 1e. The hollow spindle 3a, 3b has an outer diameter of 90 mm and an inner diameter of 82 mm.

[0135] The distal ends of the hollow spindles 3a, 3b are pivotally connected to annular pressure plates 4a, 4b made of stainless steel. For this purpose, the distal ends of the hollow spindles 3a, 3b are conically tapered and press against the respective pressure plates 4a, 4b as a result of the force of the springs 2c, whereby the conical ends protrude into the central bore of each annular pressure plate 4a, 4b and abut the inner edge of the central bore.

[0136] The pressure plates 4a, 4b are adjacent to respective buffer disks 5a, 5b made of graphite, which in turn are adjacent to the substrate tube end faces 1a and 1b, respectively. The buffer disks 5a, 5b have a central hole whose diameter corresponds to and extends coaxially with the diameter of the pressure plates. The pressure plates 4a, 4b have an outer diameter 10 mm smaller than the outer diameter of the substrate tube. The buffer disks 5a, 5b have an outer diameter extending 40 mm beyond the outer diameter of the substrate tube 1.

[0137] It is made of SiSiC and has a total length of L Z A tubular centering support 6 having an outer diameter of 80 mm at 100 mm extends through the substrate tube through hole 1f and through the central holes of the pressure plates 4a, 4b and the buffer disks 5a, 5b. One end 6a of the centering support 6 has a length L of at least 500 mm. a 3a and has an end in it, and has a variable movement room B of about 6 mm. a The other end 6b has a length L of 600 mm. b 3b and has an end in it, and also has a variable movement room B of about 6 mm. b The total space for movement within the hollow spindles 3a, 3b of the centering support 6 is B0=B a +B b is therefore 12 mm. The outside diameter of the centering support 6 is constant over its length and is adapted with a clearance fit to the inside diameter of the hollow spindles 3a, 3b so that it can be telescopically moved therein.

[0138] Three centering rings 7a, 7b, 7c made of graphite are placed on the centering support 6. Centering ring 7a is located in the area of ​​the left substrate tube end face 1a, centering ring 7b is located in the area of ​​the right substrate tube end face 1b, and centering ring 7c is located approximately in the center of the substrate tube through hole 1f. The outer diameter of all centering rings 7a, 7b, 7c is adapted with a clearance fit to the inner diameter of the substrate tube and the inner diameter is adapted with a clearance fit to the outer diameter of the centering support.

[0139] The end centering ring 7a, the buffer disk 5a and the pressure disk 4a are loosely connected to each other by a screw 4c. The screw 4c has a thread adjacent to the cylindrical part 4d. The threads respectively mesh into the inner threads in the pressure disk 4a, so that in the tightened state the cylindrical part 4d abuts tightly against the pressure disk 4a. The length of the cylindrical part 4d is greater than the total thickness of the part stack with the centering ring 7a and the buffer disk 5a, so that the head of the screw 4c does not abut against the centering ring 7a, and a gap remains between the centering ring 7a and the screw head. Furthermore, the through hole for passing the cylindrical part 4d of the buffer disk 5a and the centering ring 7a is larger than the diameter of the cylindrical part 4d, so that the screw 4c can also be slightly inclined in the through hole, which does not interfere with the possible pivoting movement of the joint. This loose connection is therefore suitable both to allow thermally induced length changes between the parts of the substrate tube holder and to compensate for deviations from the target dimensions, positioning and alignment of the parts. The screw 4c also provides a certain degree of torsional strength between the buffer disk 5a and the pressure disk 4a during the rotational movement of the substrate tube 1, and in this respect acts as a driving element for this rotational movement. The same is true for the connection of the centering ring 7b, the buffer disk 5b and the pressure disk 4b. For thermal decoupling, gaps (not visible in the figure) are provided between the centering rings 7a, 7b and the buffer disks 5a, 5b.

[0140] A number of deposition burners 8 for producing SiO2 particles are mounted on a common slide 8a which allows them to be moved reversibly laterally along the outer surface 1c of the substrate tube 1 or along the forming SiO2 soot body 9 as indicated by directional arrows 8b, or vertically thereto.

[0141] An example of the manufacture of a part made of quartz glass will be described below with reference to FIG.

[0142] Oxygen and hydrogen are supplied as burner gases to the deposition burners 8, and a gas stream containing SiCl4 or another silicon-containing raw material is supplied as a feed material for forming SiO2 particles. These components are converted in the respective burner flames into SiO2 particles, which are deposited on the substrate tube 1 rotating about its longitudinal axis 1e to form a soot body 9 from porous SiO2 soot.

[0143] To rotate the substrate tube 1, the glass lathe 2 transmits a torque to the hollow spindles 2a, 2b. At the same time, an axially acting pressure F is generated by the compression spring 2c, which presses the two hollow spindles 3a, 3b against each other and ranges between 0.5 kN and 10 kN depending on the deflection of the spring from its rest length. An initial pressure F of, for example, 1 kN is applied to the pressure plates 4a, 4b, the buffer disks 5a, 5b and thus also to the substrate tube end faces 1a, 1b. This pressure F forms a frictional bond between the buffer disks 5a, 5b, which is sufficient to support the weight of the substrate tube 1 itself and the weight of the soot body 9. The centering rings 7a, 7b, 7c are used only to prevent unexpected slippage and deflection of the substrate tube 1. A certain degree of axial guidance is provided by the interaction of the hollow spindles 3a, 3b with the centering support 6, which compensates for any radial offset or angular difference between the rotation axes of the hollow spindles 3a, 3b due to the existing mechanical play and avoids mechanical stresses.

[0144] The deposition process is terminated as soon as the soot body 9 reaches a predefined outer diameter which, depending on the density of the soot layer, amounts to a predefined outer diameter of the hollow cylindrical quartz glass blank plus a predefined margin of, for example, 1 mm.

[0145] The substrate tube 1 is removed and the soot body 9 is subjected to a dehydration treatment. The subsequent vitrification of the soot body is carried out in a zone sintering furnace under vacuum or in an atmosphere of gases that diffuse quickly in the quartz glass and do not produce bubbles, such as helium or hydrogen. The quartz glass tube thus obtained has a length of 1,750 mm, an inner diameter of 280 mm and a wall thickness of 45 mm.

[0146] 2 and 3, when the same reference numbers are used as in FIG. 1, these indicate the same or equivalent parts or components of the apparatus.

[0147] The device shown diagrammatically in Figure 2 differs from that of Figure 1 essentially in the type and nature of the substrate tube holder and the substrate tube 21, here made of quartz glass. The substrate tube 21 is 1.5 m long, has an outer diameter of 280 mm and a wall thickness of 5 mm. The inner diameter is therefore 270 mm.

[0148] The hollow spindles 23a, 23b, each clamped at its proximal end in a clamping chuck, are made of stainless steel. In the ideal case, the rotation axes of the hollow spindles 23a, 23b extend coaxially with the substrate pipe longitudinal axis 1e. The hollow spindles 23a, 23b have an outside diameter of 100 mm. A circumferential extension arm 2c is welded to the hollow spindles 23a, 23b in the region of their respective distal ends.

[0149] The pivotable connection between the hollow spindle 23a, 23b and the corresponding pressure plate 24a, 24b is designed here as a floating bearing and preferably comprises a cardboard-conical seat, whereby the distal end of the hollow spindle 23a, 23b each forms a convexly curved seat and has a spherical or radial portion, on which the pressure plate 24a or 24b is movably mounted by means of a concavely curved spherical or radial portion which complements the convexly curved seat.

[0150] FIG. 3 shows an enlarged view of the pivotable connection between the hollow spindles 23a, 23b and the respective pressure plates 24a, 24b. The end centering rings 7a, the buffer disks 5a and the pressure disks 24a form a stack of parts loosely connected to each other by means of screws 24c, which engage with the threads of the extension arms 23c, respectively. The cylindrical part 24d has a length greater than the total thickness of the stack of parts consisting of the centering rings 7a, the buffer disks 5a and the pressure disks 24a. Also, the width of the hole in the stack of parts for receiving the screws 24c is significantly greater than the diameter of the cylindrical part 24d. Due to this, some gaps 25 remain between the screw heads 24e and the centering rings 7a, between the pressure plate 24 and the extension arms 23c, as well as along the cylindrical part 24d, even when the screws 24c are fixedly tightened. The gaps 25 ensure that the connection between the hollow spindles 23a, 23b and the corresponding pressure plates 24a, 24b remains pivotable. At the same time, the screw 24 c serves as a driving element for the rotational movement of the substrate tube 1 .

Claims

1. In the external deposition method, tubular SiO ２ 1. An apparatus for producing blanks, comprising: a sub-straight tube having a sub-straight tube longitudinal axis, a sub-straight tube length, a sub-straight tube first end face, a sub-straight tube second end face, a sub-straight tube outer surface, a sub-straight tube inner surface, a sub-straight tube outer diameter, a sub-straight tube inner diameter, a sub-straight tube wall thickness, and a through opening extending coaxially with and continuous with the sub-straight tube longitudinal axis; a substrate tube holder including a clamping device and designed to support the substrate tube and rotate the substrate tube about an axis of rotation extending coaxially or parallel to the substrate tube longitudinal axis; Including, The substrate tube holder includes a first pressure unit adjacent a first end face of the substrate tube, a second pressure unit adjacent a second end face of the substrate tube, and a clamping mechanism including at least one force element designed to generate an axial contact pressure with a force component acting in the direction of the substrate tube longitudinal axis, wherein the substrate tube is clamped between the first pressure unit and the second pressure unit by the force component.

2. The clamping device described in claim 1, characterized in that the clamping device includes a first spindle rotatable about the rotation axis and a second spindle located axially opposite the first spindle in the direction of the substrate pipe longitudinal axis and rotatable about the rotation axis, the first spindle being rotationally fixed but rotatably attached or coupled to the first pressure unit and transmitting the axial contact pressure to the first pressure unit, and the second spindle being rotationally fixed but movably attached or coupled to the second pressure unit and transmitting the axial contact pressure to the second pressure unit.

3. 3. The device according to claim 2, characterized in that the first spindle has a free distal end to which the first pressure unit is rotatably mounted and the second spindle has a free distal end to which the second pressure unit is rotatably mounted, the rotatable bearings being preferably designed as ball, conical, roller or plain bearings and preferably comprising cardboard conical seats.

4. 4. An apparatus as claimed in claim 2 or claim 3, characterized in that the substrate tube holder includes a centering unit including at least one tubular or rod-shaped centering support extending between the first pressure unit and the second pressure unit through the through opening of the substrate tube.

5. 5. The device according to claim 4, characterized in that the first spindle is designed as a hollow spindle having a first internal bore and the second spindle is designed as a hollow spindle having a second internal bore, and the centering support protrudes with a first end into the first internal bore and with a second end into the second internal bore.

6. 6. The apparatus according to claim 5, wherein the centering unit comprises a plurality of centering elements placed on the centering support in the through hole of the substrate tube, of which a first centering element is arranged in the region of a first end face of the substrate tube and a second centering element is arranged in the region of a second end face of the substrate tube.

7. 7. The apparatus according to claim 2, wherein the first pressure unit comprises a first pressure transmission element and a first buffer element, preferably made of a graphite-containing material, connected thereto in a rotationally fixed manner, the pressure transmission element being attached or coupled to the first spindle in a rotationally fixed but rotatable manner, the first buffer element being positioned between the pressure transmission element and the substrate tube and adjacent to the first end face of the substrate tube.

8. 8. The apparatus of claim 7, wherein the first buffer element protrudes radially beyond the pressure transfer element and the substrate tube.

9. 9. Apparatus according to one or more of the preceding claims, wherein the first pressure unit comprises a pressure surface made of a graphite-containing material adjacent the substrate tube first end face.

10. 10. Apparatus according to one or more of the preceding claims, characterized in that the substrate tube has a wall thickness which is less than 20% of the outer diameter of the substrate tube.

11. An apparatus according to one or more of claims 1 to 10, characterized in that the substrate tube holder comprises a compensation mechanism for compensating for thermal expansion in the direction of the substrate tube longitudinal axis, the force element of the clamping mechanism being preferably a spring element and at the same time part of the compensation mechanism.

12. 12. Apparatus according to any one of claims 2 to 11, characterized in that at least one support element is arranged in the region of the distal end of the first spindle and / or the second spindle, on which the corresponding spindle can rotate.

13. In the external deposition method, tubular SiO ２ 1. A method for producing a blank, comprising the steps of: (a) providing a sub-straight tube having a sub-straight tube longitudinal axis, a sub-straight tube length, a sub-straight tube first end face, a sub-straight tube second end face, a sub-straight tube outer surface, a sub-straight tube inner surface, a sub-straight tube outer diameter, and a through opening extending contiguous with and coaxial with the sub-straight tube longitudinal axis; (b) supporting the substrate tube with a substrate tube holder including a clamping device; (c) rotating the substrate tube about a rotation axis extending coaxially or parallel to a longitudinal axis of the substrate tube; (d) depositing SiO.sub.2 on the outer surface of the substrate tube by at least one deposition burner. ２ The tubular SiO ２ forming a blank; Including, The method, characterized in that the substrate tube holder is used to generate axial contact pressure against the first end face and the second end face with a force component acting in the direction of the substrate tube longitudinal axis, and the substrate tube is clamped between a first pressure unit adjacent to the first end face and a second pressure unit adjacent to the second end face.

14. 14. A method according to claim 13, characterized in that a substrate tube holder of an apparatus according to any one of claims 1 to 12 is used to support the substrate tube according to step (b).

15. SiC, SiSiC, Al ２ O ３ 15. The method according to claim 13 or 14, characterized in that a substrate tube made of another ceramic material or of graphite and having an outer diameter of at least 250 mm is used, or a substrate tube made of quartz glass and having an inner diameter of at least 250 mm is used.

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