Apparatus for holding tubular SiO2 blanks in external deposition and method for manufacturing tubular SiO2 blanks

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 manufacturing tubular SiO2 blanks in an external deposition method, A substrate having a longitudinal axis of the substrate, a length of the substrate, a first end face of the substrate, a second end face of the substrate, an outer surface of the substrate, an inner surface of the substrate, an outer diameter of the substrate, an inner diameter of the substrate, a wall thickness of the substrate, and a through-opening that extends coaxially with the longitudinal axis of the substrate and is continuous, A substrate pipe holder, including a clamping device, is designed to support the substrate pipe and to rotate the substrate pipe around a rotation axis that extends coaxially or parallel to the longitudinal axis of the substrate pipe. Regarding devices including...

[0002] Furthermore, the present invention relates to a method for manufacturing tubular SiO2 blanks in an external deposition method, (a) A step of preparing a substrate pipe having a longitudinal axis of the substrate pipe, a length of the substrate pipe, a first end face of the substrate pipe, a second end face of the substrate pipe, an outer surface of the substrate pipe, an inner surface of the substrate pipe, an outer diameter of the substrate pipe, and a through-opening that extends coaxially with the longitudinal axis of the substrate pipe and is continuous, (b) A step of supporting the substrate pipe with a substrate pipe holder including a clamping device, (c) A step of rotating the substrate pipe around a rotation axis that extends coaxially or parallel to the longitudinal axis of the substrate pipe, (d) A step of forming the tubular SiO2 blank by depositing SiO2 particles on the outer surface of the substrate tube with at least one deposit burner. This also relates to methods that include this.

[0003] Components made from 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 manufactured by thermal formation and / or mechanical processing from tubular blanks made of synthetic silicon dioxide. With increasing productivity, there is a growing demand for larger dimensions, particularly greater wall thickness and inner diameter, for these components.

[0004] To manufacture tubular blanks from synthetically produced silicon dioxide, the CVD (Chemical Vapor Deposition) method is known, in which SiO2 particles are deposited onto a substrate from the gas phase. CVD, known as "OVD" (Outside Vapor Deposition), is generally suitable for the production of large-volume blanks. In this method, silicon-containing raw materials are converted into SiO2 particles by flame hydrolysis or thermal decomposition in a reaction region, and these particles are deposited as layers on the outer jacket of a cylindrical substrate rotating around its longitudinal axis. The reaction region is generated by a heat source, and the substrate's longitudinal axis and the heat source move back and forth relative to each other. The substrate can be tubular and will be referred to here and below as a "substrate tube." The substrate tube is made of, for example, SiC, SiSiC (reaction-sintered silicon carbide), Al2O3, or another ceramic material or graphite, and is held by a lathe-like device, also referred to here as a "substrate tube holder," and rotates around its longitudinal axis.

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

[0006] To produce SiO2 bodies from synthetic silicon dioxide with large inner diameters using the external deposition method, it is necessary to use substrate tubes with appropriate outer diameters and substrate tube holders that are compatible with them. The fundamental challenge here is to compensate as much as possible for the difference in the linear thermal expansion coefficients (hereinafter also referred to as thermal expansion or CTE (Coefficient of Thermal Expansion)) of the SiO2 bodies, substrate tubes, and substrate tube holder materials.

[0007] For example, a horizontal lathe for manufacturing a preform known from EP3584023A1 from porous silicon dioxide by the OVD method has a mechanism to compensate for axial thermal expansion. This mechanism includes a clamping device having a first chuck that is rotatable around the axis of rotation and grips one end of the substrate tube, and a second chuck that grips the other end of the substrate tube and is movable back and forth in the direction of the axis of rotation. This back and forth movement is made possible, for example, by a roller bearing of the second chuck to which a spring preload is added to counteract axial stretching due to thermal expansion.

[0008] KR10-2452282B1 describes an OVD (External Oxidation Deposition) method and apparatus for manufacturing quartz glass tubes. A stepped substrate tube is proposed, consisting of a cylindrical deposition section with a larger outer diameter, to which clamping sections with a smaller outer diameter are connected, and which are fitted into the clamping jaws of a horizontal glass lathe. The deposition section and the clamping sections on both sides can be realized as a single component, or the deposition section is connected to the clamping sections on both sides. Screw, pin, and latch connections are mentioned as means of connection, or there are embodiments in which the support or deposition section has threads and is connected by a screw method. In the OVD deposition method, an SiO2 soot body is formed on the cylindrical surface of the deposition section while this soot body is rotated around a rotation axis by the clamping sections on both sides. Technical challenges

[0009] In OVD (External Optical Deposition), the outside of the substrate tube heats more than the inside. The resulting mechanical stress accumulates along the wall thickness, which can lead to failure. For example, with small substrate tube diameters less than 80 mm and short substrate tube lengths less than 2,000 mm, the CTE difference is not very serious and affects mostly only the axial direction (along the longitudinal axis of the substrate tube). However, for large, thick-walled substrate tubes, for example, with an inner diameter greater than 200 mm and a wall thickness greater than 25 mm, radial thermal expansion can no longer be ignored. These substrate tubes are also heavier, increasing the requirements for stability and power of the substrate tube holder.

[0010] The reaction region where the deposition process occurs is typically shorter in the axial direction compared to the substrate length. A substrate clamped at both ends is heated only in the narrow length section of the deposition region, while the end region held by the substrate holder is not heated as intensely. Thermal stress between the colder end region and the hotter center of the tube can also cause cracking in the substrate.

[0011] For equipment and correspondingly large equipment components used to manufacture large volume tubular blanks from synthetic silicon dioxide by OVD (External Deposition Modeling), the manufacturing process becomes even more difficult due to weight, local temperature differences within the component, and differences in CTE (Critical Temperature Exhaust) between different components connected to each other.

[0012] Therefore, the object of the present invention is to avoid at least some of the above-mentioned disadvantages and to provide an apparatus particularly suitable for reliably and reproducibly holding large-volume tubular SiO2 blanks by external deposition methods, especially OVD external deposition methods.

[0013] In particular, the object of the present invention is to provide an apparatus for holding a large-walled tubular blank with a large inner diameter, for example, an outer diameter greater than 200 mm, and a wall thickness greater than 25 mm, in an external deposition method, which is suitable for avoiding or compensating for mechanical stress caused by dimensional deviations of apparatus components and errors in calibration, alignment and adjustment, as well as by CTE differences of axial and radial components.

[0014] Furthermore, an object of the present invention is to provide a method for producing a tubular blank with a large inner diameter and a large wall thickness, particularly a tubular blank having a tube inner diameter greater than 200 mm and a tube wall thickness greater than 25 mm, by an external deposition method, particularly from synthetic silicon dioxide, which avoids the above disadvantages and particularly reduces the risk of defective products. Summary of the Invention

[0015] With respect to this apparatus, starting from the apparatus as described above, the substrate tube holder includes a clamping mechanism comprising 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 at least one force element configured to generate an axial contact pressure by a force component acting in the direction of the longitudinal axis of the substrate tube, and the substrate tube is clamped between the first pressure unit and the second pressure unit by said force component, whereby this object is achieved by the present invention.

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

[0017] The substrate tube has, for example, a maximum length of 4 m, and has a cylindrical, conical or stepped shape over the entire length or a part of the length. The inner contour is constant or varies along the length of the substrate tube.

[0018] After the deposition process is complete, the substrate tubes may remain in the substrate tube-SiO2 blank composite or be removed from the substrate tube-blank composite. Substrate tubes remaining in the substrate tube-SiO2 composite can become part of the SiO2 blank, which is made of, for example, quartz glass. Substrate tubes remaining in the substrate tube-SiO2 composite and becoming part of the SiO2 blank preferably have an inner diameter of at least 250 mm. Their wall thickness is preferably in the range of 4 mm to 10 mm.

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

[0020] Therefore, the wall thickness of the substrate pipe is small relative to its outer diameter, preferably less than 20% of the outer diameter of the substrate pipe. Consequently, the substrate pipe has low weight, which reduces the driving force for rotational motion and makes handling and alignment easier, and low thermal mass, which allows for continued heat dissipation and keeps the formation of thermal stress within 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. Therefore, it is preferable that the wall thickness of the substrate tube be at least 1% of the outer diameter of the substrate tube.

[0022] Wall thickness “W” S The length (in mm) can also depend on the substrate length. It is beneficial to increase the wall thickness as the substrate length increases. Therefore, W S Instead, the outer diameter of the substrate pipe is D S (in mm) Substrate pipe length "L S Taking further consideration (in mm), it can be set as follows: W S <0.2 × (LS (2,000mm) × D S .

[0023] A substrate tube holder for supporting and rotating a substrate tube includes a clamping device and a clamping mechanism having two pressure units, each pressure unit adjacent to each end face of the substrate tube. The substrate tube is clamped by the clamping mechanism applying axial clamping forces to both end faces. 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. As a result of eliminating the usually common positive fit or material connection between the substrate tube and the clamping device, a degree of freedom of radial movement of the substrate tube is added, in which case some mechanical decoupling of the substrate tube from the clamping device occurs even though the pressure units are fixedly connected to the clamping device. As a result, thermal changes in the diameter of the substrate tube that occur during the deposition process can be mitigated, or these diameter changes can be made without the accumulation of mechanical stress between the clamping device and the substrate tube.

[0024] The clamping mechanism can also contribute to mitigating thermal expansion in the longitudinal direction of the substrate pipe.

[0025] The first and second pressure units are preferably adjacent to the corresponding substrate end faces and include contact pressure surfaces made of graphite-containing material. Graphite-containing material is relatively soft and can absorb shocks and impacts. This will be explained in more detail below.

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

[0027] The pressure units on both sides each consist of one or more parts. In a preferred example, they are of the same structure. The parts directly adjacent to the substrate end face are, for example, plate-shaped, ring-shaped, or form a spherical or ellipsoidal segment. In the simplest case, the surfaces adjacent to the substrate end face are flat, but they 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, thereby exerting sufficient axial contact pressure on the substrate pipe for support and rotational motion of the substrate pipe. To achieve this, it is sufficient that at least one force element acts on only one of the two pressure units so that the pressure unit transmits the contact pressure to each end face of the substrate pipe. If necessary, the other pressure unit located opposite in the direction of the longitudinal axis of the substrate pipe forms a stationary adjacent part without the need for further force elements.

[0029] In a preferred embodiment of the apparatus, the clamping device includes a first spindle rotatable around the rotation axis and a second spindle rotatable around the rotation axis, the first spindle being fixed in the rotational direction but pivotable and mounted or coupled to the first pressure unit to transmit the axial contact pressure to the first pressure unit, the second spindle being fixed in the rotational direction but movable relative to the second pressure unit to transmit the axial contact pressure to the second pressure unit.

[0030] The first spindle (e.g., the left one) and the second spindle (e.g., the right one) are each assigned to a pressure unit. They form mechanical guide elements for each pressure unit, transmitting the rotational motion and axial contact pressure of the clamping device to each pressure unit. The spindle is designed as a single unit or consists of multiple parts. In the simplest case, for example, the spindle is designed as a tube, a non-hollow rod, or a cone. Each of the two spindles is connected to the corresponding pressure unit for force transmission. The connection is fixed in the rotational direction but allows at least swirling motion.

[0031] For example, it can be designed as a joint such as a hinge, ball joint, universal joint, or cardan joint, or as a fixed or floating bearing such as a ball bearing, conical bearing, roller bearing, cardan bearing, or holder. The swivel connection between this pressure unit and the spindle provides further decoupling between the clamping device and the substrate pipe, which contributes to compensating for alignment, position, or dimensional deviations. For example, this can compensate for end faces that are not precisely perpendicular to the longitudinal axis of the substrate pipe, and can compensate for wobbling caused by the substrate pipe not being perfectly centered.

[0032] In its simplest and most preferred case, the first spindle has a free distal end to which the first pressure unit is mounted so as to be rotatable, and the second spindle also has a free distal end to which the second pressure unit is mounted so as to be rotatable.

[0033] Therefore, the two spindles transmit contact pressure and rotational motion to the substrate tube on one side, and support the pressure unit on the other. These are located on the corresponding distal spindle ends.

[0034] It is beneficial to position at least one support element in the distal end region of the first and second spindles, on which the corresponding spindle can roll. At least one support element is used to support the spindle, especially when the weight of the substrate tube and SiO2 body is high.

[0035] Particularly preferably, the swivel connection between the spindle and the pressure unit is designed as a floating bearing and preferably includes a cardan cardboard conical sheet, where the sheet on the spindle side is formed conically and a pressure unit movably mounted thereon has a sphere or radial section that interacts with the sheet, or conversely, the sheet on the spindle side has a convex sphere or radial section that corresponds to a concave pressure unit movably mounted thereon.

[0036] In particular, for very long substrate pipes exceeding 2m in length, further stabilization of the rotation axis is useful. In this regard, the substrate pipe holder includes a centering unit comprising at least one tubular or rod-shaped centering support extending between the first and second pressure units through a through-opening in the substrate pipe.

[0037] The centering support is preferably loosely mounted in the region of each pressure unit and mechanically decoupled from the spindle on both sides so as not to interfere with the axial movement of the spindle to compensate for changes in length.

[0038] For example, for this purpose, a link can be used that extends through a through-opening in a substrate tube from one spindle to the opposite spindle. The link consists of one or more rods, for example, that are evenly distributed around the axis of rotation and connected directly or indirectly (via corresponding intermediate elements attached) to the spindles on both sides.

[0039] Alternatively, or in addition, in a particularly preferred embodiment, 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, with the centering support being designed to protrude into the first internal bore at the first end and into the second internal bore at the second end.

[0040] The first and second spindles are designed here as hollow spindles having internal bores. The internal bores are designed as through bores, or the hollow spindles are closed on one side at the proximal end (facing the clamping device). In the simplest case, the internal bores have a circular cross-section, but they may also have a non-circular cross-section, such as an elliptical or polygonal cross-section. The internal cross-sections of the first and second hollow spindles are the same or different from each other. The internal cross-sections of the hollow spindles are preferably matched to the external cross-sections of their respective centering supports in the sense of clearance fitting.

[0041] The centering support, which is part of the centering unit, has a longitudinal axis and is, for example, rod-shaped or tubular. The centering support extends entirely through the through-opening of the substrate tube, but preferably has ends in the internal holes of the hollow spindles on both sides. Within each internal hole, the centering support is mounted according to the principle of a telescope so that it is 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 in the range of a few tenths of a millimeter, for example, 0.2 to 0.5 mm. The centering support is thus supported by the inner walls of the internal holes of both hollow spindles, and at the same time axially centering them with respect to each other in terms of coaxiality of the longitudinal axes of the centering support and the hollow spindles. On the one hand, the clearance fit prevents over-determination of the substrate tube bearing, and on the other hand, an axial guide is obtained that cancels out the relative tilt or twist of the hollow spindles from the longitudinal axis of the substrate tube.

[0042] In a preferred embodiment of the centering support, the support is freely rotatable within the hollow spindle internal bores on both sides and does not perform, or performs only partially, the rotational motion of the hollow spindle. In another embodiment of the centering support, it is mounted to be fixed in the rotational direction within the internal bores of the hollow spindle internal bores on both sides so as to rotate together with the hollow spindle. The rotationally fixed mounting can be achieved in a key-locking sense by, for example, a non-circular internal shape of at least one of the hollow spindles, such as a polygonal or elliptical internal shape, and the outer contour of the centering support adapted thereto.

[0043] In a preferred development of an embodiment with a centering support, it can be freely moved axially within the first and second internal bores.

[0044] Here, the centering support has ends within each internal bore, where it can move freely in the axial direction (excluding friction). The axial movability of the centering support enables compensation for the difference in thermal expansion between the centering support and the hollow spindle, thereby avoiding thermal stress in the substrate tube holder.

[0045] The free distance "a between oppositely arranged hollow spindles is normally constant. The length "L of the centering support Z " is greater than said free distance "a". Under certain conditions, if the play for axial movement of the centering support is sufficiently large for this purpose, the centering support may nevertheless completely slip out of one of the internal bores of the hollow spindle. This slipping out can be prevented, for example, by the length "L Z " including the free distance "a" and an additional length (La+Lb) that accounts for the axial movement allowance 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 hollow spindles on both sides, it is advantageous that the centering support extends 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 spindle 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 spindles on both sides as effectively as possible by means of the centering support, it may also be advantageous to limit the overall axial movable range "B Z " (B a +B b ) of the centering support on both sides within the hollow spindles, and to design "B Z " to be as large as necessary and as small as possible. In this regard, it has been found to be useful if the following applies to B Z : B Z < 20 mm, preferably 5 mm < B Z < 15 mm.

[0048] The total axial movement range of the centering support within the hollow spindle is limited to a few millimeters. This 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 having a stop element protrude into the hollow spindle's internal bore, or by narrowing or blocking the hollow spindle's internal bore.

[0049] In a particularly preferred development of an embodiment of a device having a centering support, the centering unit includes a plurality of centering elements placed on a centering support within a through-hole of a substrate pipe, the first centering element being positioned in the region of a first end face of the substrate pipe, and the second centering element being positioned in the region of a second end face of the substrate pipe.

[0050] The centering element is inserted into the substrate pipe through-hole at both ends. It serves to guide the substrate pipe and acts as "collapse protection" against pull-out. Therefore, it has an outer contour that conforms to the inner contour of the substrate pipe through-hole. For example, it may be designed as a circular ring, a polygonal ring, or a star shape with outward-facing support arms. The diameter of the circle surrounding the centering element is smaller than the inner diameter of the substrate pipe through-hole. The inner contour of the centering element is preferably conformed to the outer contour of the centering support so that it sits on the centering support in a slidable clearance fit. For example, in the case of a circular structure, the inner diameter of the centering element is 0.5 to 2 mm larger than the outer diameter of the centering support.

[0051] Centering elements facilitate the installation of the substrate pipe holder and reduce the risk of the substrate pipe coming loose from the axial clamp when used in the deposition process. To reduce the warping of the substrate pipe, at least one additional centering element may be placed in the region between the end centering elements. The centering elements are preferably made of graphite or another graphite-containing material.

[0052] The manufactured SiO2 blanks typically consist of synthetic silicon dioxide with a low CTE. Depending on the composition and manufacturing method, the CTE is approximately 0.5 μm / m / °K (0.5 × 10⁻⁶). -6 The temperature is (CTE) / °K. Metals are preferred as the spindle material. Metals are generally characterized by their ability to absorb mechanical energy during plastic deformation (toughness), and thus can compensate for mechanical stress during the deposition process. Particularly preferred are metals with high chemical resistance, such as stainless steel (CTE ranges from 10 μm / m / °K to 17 μm / m / °K depending on the alloy), and / or metals such as iron-nickel alloys, collectively known as "INVAR," which have a coefficient of thermal expansion equivalent to silicon dioxide and a CTE of usually 1.2 μm / m / °K or less.

[0053] At least one deposit burner generates a burner flame where the hottest spot is typically located spatially in front of or on the surface of the SiO2 material being 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 maximum radial dimension of the spindle, for example, the outer diameter in the case of a circular spindle cross-section, is significantly smaller than the outer diameter of the substrate tube, for example, by at least 100 mm. This ensures that the spindle is outside the "reaction area" of one or more deposit burners.

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

[0056] The first pressure unit includes a first pressure transmission element and a first buffer element, preferably made of a graphite-containing material, connected to it so as to be fixed in the rotational direction, wherein the pressure transmission element is fixed in the rotational direction but is mounted or coupled to a first spindle so as to be rotatable, and the first buffer element is preferably 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 axial contact pressure generated by at least one force element to the first end face of the substrate pipe, or, if the axial contact pressure generated by the force element acts on or only on the second end face of the substrate pipe, to function as an adjacent part to the first end face of the substrate pipe. The pressure transmission element acts directly or indirectly (i.e., via an intermediate element) with a first spindle that is fixed to it in the rotational direction but is mounted or coupled to it in a swivelable manner. For example, the pressure transmission element has a central opening with a circumferential opening edge that rests on the first spindle. The pressure transmission element is preferably made of metal, such as stainless steel.

[0058] The buffer element is positioned between the pressure transmission element and the first end face of the substrate pipe. On the one hand, it improves the clamping effect, and on the other hand, it absorbs axial or azimuthal stimuli that may act on the relatively shock-sensitive end face. The buffer element is designed, for example, in an annular or star shape. Preferably, it has low hardness, allowing relatively high contact pressure to be applied without damaging the substrate pipe end face, and generating sufficient friction to transmit rotational motion. A suitable material is, for example, graphite, whose lubricating properties allow the pipe end face to slide radially on the graphite, thereby allowing radial thermal expansion of the substrate pipe, while always having sufficient friction to transmit stimuli and forces during azimuthal acceleration.

[0059] The force flow of the contact pressure here is as follows: force element (e.g., spring-loaded chuck) → first pressure unit with first spindle → joint / swivel bearing → first pressure transmission element → first buffer element → first end face of substrate pipe.

[0060] The first buffer element can be designed as a stepped annular disc having a hollow cylindrical section with an outwardly projecting flange, the flange adjacent to the first end face of the substrate pipe, and the hollow cylindrical section protruding into the substrate pipe through-hole. The stepped disc buffer element engages with the inner wall of the substrate pipe with almost no play and simultaneously functions as a centering element. This is one way to ensure the position of the first centering element in the area of ​​the first end face of the substrate pipe, where necessary or convenient. In this embodiment, the centering element and the buffer element are designed as a single component.

[0061] On the other hand, the buffer element is subjected to strong forces and can wear out relatively quickly. It is also advantageous that the centering element and the buffer element can be thermally decoupled, for example, by a gap. As a wearable part, it is preferable that the buffer element is easy and inexpensive to replace. With this in mind, it was found to be advantageous that the first centering element be detachably and non-rotatably connected to the first buffer element.

[0062] This is a further means of ensuring the position of the first centering element in the region of the first end face of the substrate pipe, where necessary or convenient. The removable connection described above is performed, for example, using screws. The buffer element can thus be easily replaced, for example, if it becomes worn. Torsional strength is also ensured by a loose connection only between the buffer element and the centering element, which allows for mechanical play on the one hand and leaves a gap between the buffer element and the centering element for thermal decoupling on the other hand. In this case, for example, screws are provided that guide play in the holes of the buffer element and the centering element so as not to interfere with the articulated connection between each spindle and the pressure unit. The screws can function as a driving element for the rotational motion of the substrate pipe by providing a positive fit connection for rotational motion.

[0063] Furthermore, it was found that if the device includes a first buffer element, it is advantageous for the buffer element to protrude radially beyond the pressure transmission element and the substrate pipe.

[0064] During the OVD (External Oxidation Deposition) method, the flame of at least one deposition burner strikes the surface of the substrate tube or the SiO2 body being formed, and can then be deflected laterally so as to spread tangentially to the surface of the material towards the end region of the SiO2 body. As a result of the buffer element radially protruding relative to the pressure transfer element, the latter is largely protected from thermal and corrosive loads by being in the shadow of the flame, while the buffer element is exposed to them. The height of the radial protrusion is preferably in the range of 1 cm to 3 cm.

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

[0066] Regarding a method for manufacturing an SiO2 blank, based on the method described above, the substrate tube holder is used to generate axial contact pressure on the first and second end faces by 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 problems.

[0067] The above method includes a step of producing a tubular SiO2 blank, particularly one made of synthetic silicon dioxide, based on an external deposition method. Depending on the temperature during the deposition process, a porous SiO2 soot or a generally transparent glassy SiO2 body is formed on the surface of the substrate tube. In the case of a porous SiO2 soot, the porous SiO2 soot can be dehydrated in an inert gas, a chlorine-containing gas, or under vacuum to reduce the hydroxyl group content of the quartz glass before sintering to form a generally transparent glassy 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] Substrate tubes, for example, have a maximum substrate length of 4m and have cylindrical, conical, or stepped shapes over their entire length or in part of their length. Substrate tubes are designed to produce tubular SiO2 bodies, particularly synthetic silicon dioxide, with large inner diameters on their outer surface based on the OVD (External Oxide Deposition) method. The dimensions of the SiO2 blanks obtained after this process are, for example, as follows: inner diameter in the range of 250mm to 650mm, wall thickness in the range of 25mm to 150mm, and length in the range of 800mm to 3,800mm. From there, synthetic quartz glass components, such as quartz glass tubes or quartz glass rings, are obtained by mechanical, chemical, and / or thermal treatment.

[0069] Therefore, this method makes it possible to manufacture large-volume quartz glass tubes, particularly those with an inner diameter of at least 250 mm and a wall thickness of at least 25 mm.

[0070] Preferably, the substrate tube holder of the apparatus according to the present invention is used to support the substrate tube according to process (b). This will be explained in more detail below.

[0071] After the deposition process is complete, the substrate tubes may remain in the substrate tube-SiO2 composite or be removed from the substrate tube-SiO2 composite. Substrate tubes remaining in the substrate tube-SiO2 composite can become part of the SiO2 blank, which may be made of, for example, quartz glass. Substrate tubes remaining in the substrate tube-SiO2 composite and becoming part of the SiO2 blank preferably have an inner diameter of at least 250 mm. Their wall thickness is preferably in the range of 4 to 10 mm. Substrate tubes removed from the substrate tube-SiO2 composite after the deposition process or at a later stage of the process preferably consist of SiC, SiSiC, Al2O3, or another ceramic material or graphite. Their outer diameter is preferably at least 250 mm. Their wall thickness is preferably in the range of 5 to 30 mm.

[0072] Therefore, the wall thickness of a substrate tube is small relative to its outer diameter, usually less than 20% of the outer diameter. Consequently, substrate tubes have low weight, which reduces the driving force for rotational motion and makes them easier to handle and align, and low heat capacity, which allows for continuous heat dissipation and keeps the formation of thermal stress within the walls low.

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

[0074] A substrate pipe holder is used for supporting and rotating a substrate pipe. The substrate pipe holder includes a clamping device and a clamping mechanism having two pressure units, each pressure unit adjacent to one end face of the substrate pipe. The substrate pipe is clamped by the clamping mechanism applying axial clamping force to both end faces.

[0075] Rotational support and rotation are 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 axial contact pressure on the first and second end faces by a force component acting in the direction of the longitudinal axis of the substrate tube. The axial contact pressure acts on the first and / or second pressure units with a force component acting in the direction of the longitudinal axis of the substrate tube. This contact pressure is transmitted by the pressure units to the end faces of the substrate tube, thereby clamping and holding the substrate tube so as to be fixed in the rotational direction between the pressure units on both sides. 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. As a result of eliminating the typically common positive fit or material connection between the substrate tube and the clamping device, a degree of freedom of radial movement of the substrate tube is added, and in this respect, some degree of mechanical decoupling of the substrate tube from the clamping device occurs even if the pressure unit is fixedly connected to the clamping device. As a result, thermal changes in diameter that occur during the deposition process can be compensated for, or these changes in diameter can be made without the accumulation of mechanical stress between the clamping device and the substrate tube.

[0076] The clamping mechanism can also contribute to mitigating thermal expansion in the longitudinal direction of the substrate pipe.

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

[0078] The pressure units on both sides each consist of one or more parts. In a preferred example, they are of the same structure. The parts directly adjacent to the substrate end face are, for example, plate-shaped, ring-shaped, or form a spherical or ellipsoidal segment. In the simplest case, the surfaces adjacent to the substrate end face are flat, but they 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, thereby exerting sufficient axial contact pressure on the substrate pipe for support and rotational motion of the substrate pipe. To achieve this, it is sufficient that at least one force element acts on only one of the two pressure units so that the pressure unit transmits the contact pressure to each end face of the substrate pipe. If necessary, the other pressure unit located opposite in the direction of the longitudinal axis of the substrate pipe forms a stationary adjacent part without the need for further force elements.

[0080] In a preferred procedure, an axial contact pressure to a first pressure unit is generated by a first spindle connected to a clamping device and rotatable around a rotation axis, and an axial contact pressure to a second pressure unit is generated by a second spindle connected to a clamping device and rotatable around a rotation axis, the first spindle being fixed in the rotational direction but swiveling, and the second spindle being fixed in the rotational direction but movable relative to each other, and mounted 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 rotational motion and axial contact pressure of the clamping device to their respective pressure units. The spindles are designed as a single unit or consist of multiple parts. In the simplest case, for example, the spindle is designed as a tube, a non-hollow rod, or a cone. Each of the two spindles is connected to the corresponding pressure unit for force transmission. The connection is fixed in the rotational direction but allows at least swirling motion.

[0082] For example, it can be designed as a joint such as a hinge, ball joint, universal joint, or cardan joint, or as a fixed or floating bearing such as a ball bearing, conical bearing, roller bearing, cardan bearing, or holder. The swivel connection between this pressure unit and the spindle provides further decoupling between the clamping device and the substrate pipe, which contributes to compensating for misalignment, positional, or dimensional deviations. For example, this allows for adjustment of end faces that are not precisely perpendicular to the longitudinal axis of the substrate pipe, and can compensate for wobbling caused by the substrate pipe not being perfectly centered.

[0083] In its simplest and most preferred case, the first spindle has a free distal end to which the first pressure unit is mounted so as to be rotatable, and the second spindle also has a free distal end to which the second pressure unit is mounted so as to be rotatable.

[0084] Therefore, the two spindles transmit contact pressure and rotational motion to the substrate tube on one side, and support the pressure unit on the other. These are located on the corresponding distal spindle ends.

[0085] It is beneficial to position at least one support element in the distal end region of the first and second spindles, on which the corresponding spindle can roll. At least one support element is used to support the spindle, especially when the weight of the substrate tube and SiO2 body is high.

[0086] Particularly preferably, the swivel connection between the spindle and the pressure unit is designed as a floating bearing and preferably includes a cardan cardboard conical sheet, where the sheet on the spindle side is formed conically and a pressure unit movably mounted thereon has a sphere or radial section that interacts with the sheet, or conversely, the sheet on the spindle side has a sphere or radial section corresponding to a concavely curved pressure unit movably mounted thereon.

[0087] In particular, for very long substrates exceeding 2 meters in length, further stabilization of the rotation axis is useful.

[0088] In this regard, it is beneficial to use a substrate pipe holder that includes a centering unit comprising at least one tubular or rod-shaped centering support extending between the first and second pressure units through a through-opening in the substrate pipe.

[0089] The centering support is preferably loosely mounted in the region of each pressure unit and mechanically decoupled from the spindle on both sides so as not to interfere with the axial movement of the spindle to compensate for changes in length.

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

[0091] Alternatively, or in addition, in a particularly preferred procedure, 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, with the centering support designed to protrude into the first internal bore at the first end and into the second internal bore at the second end.

[0092] The first and second spindles are designed here as hollow spindles having internal bores. The internal bores are designed as through bores, or the hollow spindles are closed on one side at the proximal end (facing the clamping device). In the simplest case, the internal bores have a circular cross-section, but they may also have a non-circular cross-section, such as an elliptical or polygonal cross-section. The internal cross-sections of the first and second hollow spindles are the same or different from each other. The internal cross-sections of the hollow spindles are preferably matched to the external cross-sections of their respective centering supports in the sense of clearance fitting.

[0093] The centering support, which is part of the centering unit, has a longitudinal axis and is, for example, rod-shaped or tubular. The centering support extends entirely through the through-opening of the substrate tube, but preferably has ends in the internal holes of the hollow spindles on both sides. Within each internal hole, the centering support is mounted according to the principle of a telescope so that it is 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 in the range of a few tenths of a millimeter, for example, 0.2 to 0.5 mm. The centering support is thus supported by the inner walls of the internal holes of both hollow spindles, and at the same time axially centering them with respect to each other in terms of coaxiality of the longitudinal axes of the centering support and the hollow spindles. On the one hand, the clearance fit prevents over-determination of the substrate tube bearing, and on the other hand, an axial guide is obtained that cancels out the relative tilt or twist of the hollow spindles from the longitudinal axis of the substrate tube.

[0094] In a preferred procedure, the centering support is freely rotatable within the hollow spindle internal bores on both sides, and does not perform any, or only partially, rotational motion of the hollow spindle. In another procedure, the centering support is mounted so as to be fixed in the rotational direction within the hollow spindle internal bores on both sides, so as to rotate together with the hollow spindle. The rotationally fixed mounting can be achieved in the sense of a key-lock coupling by, for example, a non-circular inner shape of at least one of the hollow spindles, such as a polygonal or elliptical inner shape, and the outer contour of the centering support adapted thereto.

[0095] In a preferred development of the procedure using a centering support, it can be freely moved axially within the first and second internal bores.

[0096] Here, the centering support has an end within each internal hole, where it can move freely in the axial direction (except for friction). The axial mobility of the centering support can mitigate the difference in thermal expansion between the centering support and the hollow spindle, thereby avoiding thermal stress on the substrate tube holder.

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

[0098] In particular, regarding the effect of the centering support as an axial guide for both hollow spindles, it is beneficial for the centering support to extend into both hollow spindles over a certain 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 stability reasons, and especially to guide the hollow spindles on both sides as effectively as possible by the centering supports, the axial range of motion of the centering supports on both sides within the hollow spindle is "B Z Restrict the entire "B" Z It can also be beneficial to design the "as large as necessary and as small as possible." In this regard, B Z It was found to be useful when the following applies: B Z <20mm, preferably 5mm Z <15mm.

[0100] ​The total axial movement range of the centering support within the hollow spindle is limited to a few millimeters. This 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 having a stop element protrude into the hollow spindle's internal bore, or by narrowing or blocking the hollow spindle's internal bore.

[0101] In a particularly preferred development of the procedure using a centering support, the centering unit includes a plurality of centering elements placed on a centering support within a through-hole of the substrate pipe, the first centering element being positioned in the region of the first end face of the substrate pipe, and the second centering element being positioned in the region of the second end face of the substrate pipe.

[0102] The centering element is inserted into the substrate pipe through-hole at both ends. It serves to guide the substrate pipe and acts as "collapse protection" against pull-out. Therefore, it has an outer contour that conforms to the inner contour of the substrate pipe through-hole. For example, it may be designed as a circular ring, a polygonal ring, or a star shape with outward-facing support arms. The diameter of the circle surrounding the centering element is smaller than the inner diameter of the substrate pipe through-hole.

[0103] The inner contour of the centering element is preferably fitted to the outer contour of the centering support so that it is placed on the centering support in a slidable gap fit. For example, in the case of a circular structure, the inner diameter of the centering element is 0.5 to 2 mm larger than the outer diameter of the centering support.

[0104] Centering elements facilitate the installation of the substrate pipe holder and reduce the risk of the substrate pipe coming loose from the axial clamp when used in the deposition process. To reduce the warping of the substrate pipe, at least one additional centering element may be placed in the region between the end centering elements. The centering elements are preferably made of graphite or another graphite-containing material.

[0105] The manufactured SiO2 blank consists of synthetic silicon dioxide with a low CTE. Depending on the composition and manufacturing method, the CTE is approximately 0.5 μm / m / °K (0.5 × 10⁻⁶). -6 The temperature is (CTE) / °K. Metals are preferred as the spindle material. Metals are generally characterized by their ability to absorb mechanical energy during plastic deformation (toughness), and thus can compensate for mechanical stress during the deposition process. Particularly preferred are metals with high chemical resistance, such as stainless steel (CTE ranges from 10 μm / m / °K to 17 μm / m / °K depending on the alloy), and / or metals such as iron-nickel alloys, collectively known as "INVAR," which have a coefficient of thermal expansion equivalent to silicon dioxide and a CTE of usually 1.2 μm / m / °K or less.

[0106] At least one deposit burner generates a burner flame where the hottest spot is typically located spatially in front of or on the surface of the SiO2 material being 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, for example, the outer diameter in the case of a circular spindle cross-section, is significantly smaller than the outer diameter of the substrate tube, for example, by at least 100 mm. This ensures that the spindle is outside the “reaction area” of the at least one of the deposition burners.

[0108] The apparatus for performing 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 referred to, the second side is designed to be essentially identical or equivalent to the first side unless otherwise specified.

[0109] The first pressure unit includes a first pressure transmission element and a first buffer element, preferably made of a graphite-containing material, connected to it so as to be fixed in the rotational direction, wherein the pressure transmission element is fixed in the rotational direction but is mounted or coupled to a first spindle so as to be rotatable, and the first buffer element is preferably 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 axial contact pressure generated by at least one force element to the first end face of the substrate pipe, or, if the axial contact pressure generated by the force element acts on or only on the second end face of the substrate pipe, to function as an adjacent part to the first end face of the substrate pipe. The pressure transmission element acts directly or indirectly (i.e., via an intermediate element) with a first spindle that is fixed to it in the rotational direction but is mounted or coupled to it in a swivelable manner. For example, the pressure transmission element has a central opening with a circumferential opening edge that rests on the first spindle. The pressure transmission element is preferably made of metal, such as stainless steel.

[0111] The buffer element is positioned between the pressure transmission element and the first end face of the substrate pipe. On the one hand, it improves the clamping effect, and on the other hand, it absorbs axial or azimuthal stimuli that may act on the relatively shock-sensitive end face. The buffer element is designed, for example, in an annular or star shape. Preferably, it has low hardness, allowing relatively high contact pressure to be applied without damaging the substrate pipe end face, and generating sufficient friction to transmit rotational motion. A suitable material is, for example, graphite, whose lubricating properties allow the pipe end face to slide radially on the graphite, thereby allowing radial thermal expansion of the substrate pipe, while always having sufficient friction to transmit stimuli and forces during azimuthal acceleration.

[0112] The force flow of the contact pressure here is as follows: force element (e.g., spring-loaded chuck) → first pressure unit with first spindle → joint / swivel bearing → first pressure transmission element → first buffer element → first end face of substrate pipe.

[0113] The first buffer element can be designed as a stepped annular disc having a hollow cylindrical section with an outwardly projecting flange, the flange adjacent to the first end face of the substrate pipe, and the hollow cylindrical section protruding into the substrate pipe through-hole. The stepped disc buffer element engages with the inner wall of the substrate pipe with almost no play and simultaneously functions as a centering element. This is one way to ensure the position of the first centering element in the area of ​​the first end face of the substrate pipe, where necessary or convenient. In this embodiment, the centering element and the buffer element are designed as a single component.

[0114] On the other hand, the buffer element is subjected to strong forces and can wear out relatively quickly. It is also advantageous that the centering element and the buffer element can be thermally decoupled, for example, by a gap. As a wearable part, it is preferable that the buffer element is easy and inexpensive to replace. With this in mind, it was found to be advantageous that the first centering element be detachably and non-rotatably connected to the first buffer element.

[0115] This is a further means of ensuring the position of the first centering element in the region of the first end face of the substrate pipe, where necessary or convenient. The removable connection described above is performed, for example, using screws. The buffer element can thus be easily replaced, for example, if it becomes worn. Torsional strength is also ensured by a loose connection only between the buffer element and the centering element, which allows for mechanical play on the one hand and leaves a gap between the buffer element and the centering element for thermal decoupling on the other hand. In this case, for example, screws are provided that guide play in the holes of the buffer element and the centering element so as not to interfere with the articulated connection between each spindle and the pressure unit. The screws can function as a driving element for the rotational motion of the substrate pipe by providing a positive fit connection for rotational motion.

[0116] Furthermore, in the procedure using the first buffer element, it was found to be advantageous for the buffer element to protrude radially beyond the pressure transmission element and the substrate pipe.

[0117] During the OVD (External Oxidation Deposition) method, the flame of at least one deposition burner strikes the surface of the substrate tube or the SiO2 body being formed, and can then be deflected laterally so as to spread tangentially to the surface of the material towards the end region of the SiO2 body. As a result of the buffer element radially protruding relative to the pressure transfer element, the latter is largely protected from thermal and corrosive loads by being in the shadow of the flame, while the buffer element is exposed to them. The height of the radial protrusion is preferably in the range of 1 cm to 3 cm.

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

[0119] [Definitions and Measurement Methods] The terms used in the above description are further defined below. These definitions are part of the description of the present invention. For terms and measuring means not specifically defined in the specification, the interpretation of the International Telecommunication Union (ITU) applies. In the event of any conflict 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 an object made of synthetic silicon dioxide. Depending on the temperature during the deposition process, the object made of synthetic silicon dioxide may be a porous "soot body" or an object made of generally transparent quartz glass, which we will refer to here as the "SiO2 body". The SiO2 body may be the sole component of the tubular SiO2 blank, or the substrate tube may be a further component of the SiO2 blank, limiting its internal pores. Substrate tubes made of materials other than quartz glass are not part of the SiO2 blank.

[0121] [Component 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, machining, milling, grinding, and polishing of the internal and external contours. Further thermal treatments include heat drying, sintering, vitrification, melting, molding, 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 and quartz glass rings.

[0122] [Quartz glass / Synthetic quartz glass / Synthetic silicon dioxide] Here, quartz glass and synthetic silicon dioxide refer to glass having an SiO2 content of at least 87% by weight. This is doped not present (SiO2 content = 100%) or contains dopants such as fluorine, chlorine, nitrogen, carbon, or oxides of boron, germanium, rare earth metals, aluminum, or titanium.

[0123] Quartz glass consists of, for example, a molten form of naturally occurring SiO2 raw material (natural quartz glass), a synthesized form (synthetic quartz glass), or a mixture of these types of quartz glass. Synthetic transparent quartz glass can be obtained, for example, by flame hydrolysis or oxidation of a synthesized silicon compound, by polycondensation of organosilicon compounds using the so-called sol-gel method, or by hydrolysis and precipitation of an inorganic silicon compound in liquid.

[0124] [Sintering / Vitrification] "Sintering" or "vitrification" here refers to the process of treating porous silicon dioxide (SiO2) at high temperatures 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] [Outer diameter of substrate pipe / Inner diameter of substrate pipe] The cross-section of a substrate pipe has a circular outer contour or a non-circular outer contour. If the outer contour is non-circular, the local "outer diameter value" is given by the (minimum) circumference diameter.

[0126] The cross-section of a substrate pipe has either a circular or non-circular inner contour. If the inner contour is non-circular, the local "inner diameter value" is given by the diameter of the (maximum) inscribed circle.

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

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

[0129] [Gap fitting] Clearance fitting is performed based on tolerance tables, for example, DIN EN ISO 286 - Part 2. To ensure some degree of axial mobility between each hole and spindle, the tolerance zones must be matched such that the maximum dimension of the spindle is always smaller than the minimum dimension of the hole. Appropriate tolerance zones for the hole are, for example, H, G, F, and E, and for the spindle, for example, g, f, and e. Exemplary Embodiments

[0130] The present invention will be described in more detail below with reference to an example of an embodiment and the figures. The individual figures are schematic diagrams shown below. [Brief explanation of the drawing]

[0131] [Figure 1] A longitudinal cross-section of an apparatus for manufacturing tubular SiO2 blanks in a first embodiment of a substrate tube holder is shown. [Figure 2] This is a partial detail view showing a longitudinal section of an apparatus for manufacturing a tubular SiO2 blank from synthetic silicon dioxide in a second embodiment of a substrate tube holder. [Figure 3] Figure 2 is a magnified view of a portion of the substrate pipe holder.

[0132] The apparatus schematically shown in Figure 1 includes a glass lathe 2 for holding and rotating a SiSiC substrate tube 1. 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 hole 1f. The substrate tube 1 has a length of 2 m, an outer diameter of 280 mm, and a wall thickness of 20 mm. Therefore, its inner diameter is 240 mm.

[0133] The glass lathe 2 is represented by two opposing chucks 2a and 2b, of which chuck 2a is spring-loaded as indicated by a compression spring 2c. The compression spring 2c generates a pressure F that pushes the two chucks 2a and 2b against each other, as indicated by the directional arrow 2d.

[0134] Hollow spindles 3a and 3b, made of stainless steel, are clamped at their proximal ends to chucks 2a and 2b, respectively. In the ideal case, the rotational axes of the hollow spindles 3a and 3b extend coaxially with the longitudinal axis 1e of the substrate tube. The hollow spindles 3a and 3b have an outer diameter of 90 mm and an inner diameter of 82 mm.

[0135] The distal ends of the hollow spindles 3a and 3b are connected to annular pressure plates 4a and 4b made of stainless steel so as to be rotatable. For this purpose, the distal ends of the hollow spindles 3a and 3b are tapered into a conical shape and, as a result of the force of the spring 2c, press against each pressure plate 4a and 4b. Here, the conical ends protrude into the central holes of each annular pressure plate 4a and 4b and are adjacent to the inner edges of the central holes.

[0136] The pressure plates 4a and 4b are adjacent to buffer discs 5a and 5b, respectively, which are made of graphite, and these buffer discs are further adjacent to the substrate pipe end faces 1a and 1b, respectively. The buffer discs 5a and 5b have a central hole that extends coaxially with the pressure plates and whose diameter corresponds to the diameter of the pressure plates. The pressure plates 4a and 4b have an outer diameter that is 10 mm smaller than the outer diameter of the substrate pipe. The buffer discs 5a and 5b have an outer diameter that extends more than 40 mm beyond the outer diameter of the substrate pipe 1.

[0137] Made of SiSiC, with a total length of L Z The tubular centering support 6, having an outer diameter of 80 mm, extends through the substrate pipe through hole 1f and also through the central holes of the pressure plates 4a, 4b and buffer discs 5a, 5b. One end 6a of the centering support 6 has a length L of at least 500 mm. a It protrudes into the hollow spindle 3a over a certain distance, with its end located within it, and has a variable range of movement B of approximately 6 mm. a This remains. The other end 6b has a length L of 600 mm. b It protrudes into the hollow spindle 3b over a certain distance, with its end inside, and also has a variable range of movement B of approximately 6 mm. b The remaining amount is B0 = B. The total range of motion within the hollow spindles 3a and 3b of the centering support 6. a +B b Therefore, it is 12 mm. The outer diameter of the centering support 6 is constant over its length and fits into the inner diameters of the hollow spindles 3a and 3b by clearance fitting, allowing them to move in a nested manner within it.

[0138] Three centering rings 7a, 7b, and 7c made of graphite are placed on the centering support 6. Centering ring 7a is located in the area of ​​the left substrate pipe end face 1a, centering ring 7b is located in the area of ​​the right substrate pipe end face 1b, and centering ring 7c is located approximately in the center of the substrate pipe through hole 1f. All centering rings 7a, 7b, and 7c have outer diameters that fit the inner diameter of the substrate pipe by clearance, and inner diameters that fit the outer diameter of the centering support by clearance.

[0139] The end centering ring 7a, buffer disc 5a, and pressure disc 4a are loosely connected to each other by screws 4c. The screws 4c have threads adjacent to the cylindrical portion 4d. Each thread engages with an inner thread within the pressure disc 4a, and when tightened, the cylindrical portion 4d makes firm contact with the pressure disc 4a. The length of the cylindrical portion 4d is greater than the overall thickness of the component stack of the centering ring 7a and buffer disc 5a, so the head of the screw 4c does not touch the centering ring 7a, leaving a gap between the centering ring 7a and the screw head. Furthermore, the through holes in the buffer disc 5a and centering ring 7a for passing through the cylindrical portion 4d are larger than the diameter of the cylindrical portion 4d, allowing the screw 4c to be slightly tilted within the through hole, thereby not hindering any possible rotational movement of the joint. Therefore, this loose connection is suitable for allowing changes in length between the components of the substrate tube holder due to heat, and for compensating for deviations of the components from their target dimensions, positioning, and alignment. Furthermore, the thread 4c provides some torsional strength between the buffer disc 5a and the pressure disc 4a during the rotational motion of the substrate tube 1, and in this respect, functions as a driving element for this rotational motion. The same applies to the connection of the centering ring 7b, buffer disc 5b, and pressure disc 4b. For thermal decoupling, a gap (not visible in the diagram) is provided between the centering rings 7a, 7b and the buffer discs 5a, 5b.

[0140] Multiple deposition burners 8 for generating 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 SiO2 soot body 9 being formed, as indicated by the directional arrow 8b, and also perpendicular to it.

[0141] The following describes an example of manufacturing a component made of quartz glass, with reference to Figure 1.

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

[0143] To rotate the substrate tube 1, the glass lathe 2 has a hollow spindle 3a, 3b Torque is transmitted to the spindles. Simultaneously, an axial pressure F is generated by the compression spring 2c, which pushes the two hollow spindles 3a and 3b against each other, ranging from 0.5kN to 10kN depending on the spring's rest length. The initially set pressure F, for example, 1kN, is also applied to the pressure plates 4a and 4b, the buffer discs 5a and 5b, and thereby to the substrate tube end faces 1a and 1b. This pressure F forms a frictional bond between the buffer discs 5a and 5b, which is sufficient to support the weight of the substrate tube 1 and the weight of the soot body 9. The centering rings 7a, 7b, and 7c are used solely to prevent unexpected slippage or deflection of the substrate tube 1. A certain degree of axial guidance is provided by the interaction between the hollow spindles 3a and 3b and the centering support 6, which, due to the existing mechanical play, compensates for any radial offset or angular difference between the rotation axes of the hollow spindles 3a and 3b and avoids mechanical stress.

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

[0145] Substrate tube 1 is removed, and the soot body 9 is dehydrated. The subsequent vitrification of the soot body is carried out in a zone sintering furnace under vacuum or in an atmosphere of gas that diffuses rapidly within the quartz glass without generating bubbles, such as helium or hydrogen. The resulting quartz glass tube has a length of 1,750 mm, an inner diameter of 280 mm, and a wall thickness of 45 mm.

[0146] In Figures 2 and 3, when the same reference numerals are used as in Figure 1, they indicate the same or equivalent parts or components of a device.

[0147] The apparatus schematically shown in Figure 2 is essentially different from that in Figure 1 in terms of the type and properties of the substrate tube holder and, in this case, the substrate tube 21 made of quartz glass. The substrate tube 21 has a length of 1.5 m, an outer diameter of 280 mm, and a wall thickness of 5 mm. Therefore, its inner diameter is 270 mm.

[0148] The hollow spindles 23a and 23b, each clamped to a clamp chuck at its proximal end, are made of stainless steel. In the ideal case, the rotational axes of the hollow spindles 23a and 23b extend coaxially with the longitudinal axis 1e of the substrate tube. The hollow spindles 23a and 23b have an outer diameter of 100 mm. Circumferential extension arm 23c These are welded to the distal end regions of the hollow spindles 23a and 23b, respectively.

[0149] Hollow spindles 23a, 23b and corresponding pressure plate 24a, 24b The swivel connection between the two is designed here as a floating bearing and preferably includes a cardan cardboard conical sheet. Here, the distal ends of the hollow spindles 23a and 23b each form a convexly curved seat having a spherical or radial portion. A pressure plate 24a or pressure plate 24b is movably mounted on this portion, with a concavely curved spherical or radial portion complementing the convexly curved seat.

[0150] Figure 3 is an enlarged view of the swivelable connection between the hollow spindles 23a, 23b and the respective pressure plates 24a, 24b. The end centering ring 7a, buffer disc 5a, and pressure disc 24a form a stack of parts loosely connected to each other by a screw 24c, each engaging with the threads of the extension arm 23c. The length of the cylindrical portion 24d is greater than the overall thickness of the parts stack consisting of the centering ring 7a, buffer disc 5a, and pressure disc 24a. Also, the width of the hole in the parts stack for receiving the screw 24c is significantly larger than the diameter of the cylindrical portion 24d. As a result, several gaps 25 exist between the screw head 24e and the centering ring 7a and the pressure plate, even when the screw 24c is fixedly tightened. 24a The gap 25 remains between the extension arm 23c and along the cylindrical portion 24d. The gap 25 ensures that the connection between the hollow spindles 23a, 23b and the corresponding pressure plates 24a, 24b remains rotatable. At the same time, the screw 24c functions as a driving element for the rotational motion of the substrate pipe 1.

Claims

1. In the external deposition method, tubular SiO ２ A device for manufacturing blanks, - A substrate having a longitudinal axis of the substrate, a substrate length, a first end face of the substrate, a second end face of the substrate, an outer surface of the substrate, an inner surface of the substrate, an outer diameter of the substrate, an inner diameter of the substrate, a wall thickness of the substrate, and a through-opening that extends coaxially with the longitudinal axis of the substrate and is continuous, A substrate pipe holder, including a clamping device, is designed to support the substrate pipe and to rotate the substrate pipe around a rotation axis that extends coaxially or parallel to the longitudinal axis of the substrate pipe. Includes, The substrate pipe holder includes a clamping mechanism comprising a first pressure unit adjacent to the first end face of the substrate pipe, a second pressure unit adjacent to the second end face of the substrate pipe, and at least one force element designed to generate axial contact pressure by a force component acting in the direction of the longitudinal axis of the substrate pipe, wherein the substrate pipe is clamped between the first and second pressure units by the force component. The clamping device includes a first spindle rotatable around the rotation axis and a second spindle positioned axially opposite the first spindle in the direction of the longitudinal axis of the substrate pipe and rotatable around the rotation axis, wherein the first spindle is fixed in the rotational direction but is mounted or coupled to the first pressure unit so as to be swiveling and transmits the axial contact pressure to the first pressure unit, and the second spindle is fixed in the rotational direction but is mounted or coupled to the second pressure unit so as to be movable relative to each other and transmits the axial contact pressure to the second pressure unit.

2. The apparatus according to claim 1, characterized in that the first spindle has a free distal end to which the first pressure unit is mounted so as to be rotatable, and the second spindle has a free distal end to which the second pressure unit is mounted so as to be rotatable.

3. The apparatus according to claim 2, wherein the substrate pipe holder includes a centering unit which includes 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 pipe.

4. The apparatus according to claim 3, wherein the first spindle is designed as a hollow spindle having a first internal bore, the second spindle is designed as a hollow spindle having a second internal bore, and the centering support protrudes into the first internal bore at its first end and into the second internal bore at its second end.

5. The apparatus according to claim 4, wherein the centering unit includes a plurality of centering elements placed on the centering support within the through-hole of the substrate pipe, the first centering element being positioned in the region of the first end face of the substrate pipe, and the second centering element being positioned in the region of the second end face of the substrate pipe.

6. The apparatus according to claim 1, wherein the first pressure unit includes a first pressure transmission element and a first buffer element connected thereto to be fixed in the rotational direction, the pressure transmission element being fixed in the rotational direction but rotatably mounted or coupled to the first spindle, and the first buffer element being positioned between the pressure transmission element and the substrate pipe and adjacent to the first end face of the substrate pipe.

7. The apparatus according to claim 6, characterized in that the first buffer element protrudes radially beyond the pressure transmission element and the substrate pipe.

8. The apparatus according to claim 1, characterized in that the first pressure unit includes a pressure surface made of a graphite-containing material adjacent to the first end face of the substrate pipe.

9. The apparatus according to claim 1, characterized in that the wall thickness of the substrate pipe is less than 20% of the outer diameter of the substrate pipe.

10. The apparatus according to claim 1, characterized in that the substrate pipe holder includes a compensation mechanism for compensating for thermal expansion in the direction of the longitudinal axis of the substrate pipe.

11. The apparatus according to claim 2, characterized in that at least one support element is positioned in the distal end region of the first spindle and / or the second spindle, and the corresponding spindle can rotate over the support element.

12. In the external deposition method, tubular SiO ２ A method for manufacturing a blank, (a) A step of preparing a substrate pipe having a substrate pipe longitudinal axis, substrate pipe length, substrate pipe first end face, substrate pipe second end face, substrate pipe outer surface, substrate pipe inner surface, substrate pipe outer diameter, and a through opening that extends coaxially with the substrate pipe longitudinal axis and is continuous, (b) A step of supporting the substrate pipe with a substrate pipe holder including a clamping device, (c) A step of rotating the substrate pipe around a rotation axis that extends coaxially or parallel to the longitudinal axis of the substrate pipe, (d) Deposition of SiO2 on the outer surface of the substrate tube by at least one deposition burner ２ By depositing particles, the tubular SiO ２ The process of forming a blank and Includes, The substrate pipe holder is used to generate axial contact pressure on the first and second end faces by a force component acting in the direction of the longitudinal axis of the substrate pipe, and the substrate pipe is clamped between a first pressure unit adjacent to the first end face and a second pressure unit adjacent to the second end face. A method characterized by using a substrate tube made of SiC, SiSiC, Al₂O₃, or another ceramic material or graphite, with an outer diameter of at least 250 mm, or a substrate tube made of quartz glass, with an inner diameter of at least 250 mm.

13. The method according to claim 12, characterized in that the substrate tube holder of the apparatus according to claim 1 is used to support the substrate tube in accordance with step (b).

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