Device for holding tubular SiO2 blank during external deposition process and method for producing tubular SiO2 blank

Abstract

Known apparatus for producing tubular SiO2 blanks in an external deposition process has a substrate tube and a substrate tube holder comprising clamping means, the substrate tube holder being designed to support the substrate tube and to rotate the substrate tube about an axis of rotation. On this basis, in order to provide a reproducible and operationally reliable holder for large-volume tubular SiO2 blanks in an external deposition process, it is proposed that the base tube holder comprises a clamping mechanism, the clamping mechanism has a first pressure unit which adjoins a first base tube end face, a second pressure unit which adjoins a second base 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 base tube.

Description

Background Art

[0001] The invention relates to a device for producing tubular SiO2 blanks in an external deposition process, the device comprising:

[0002] a substrate tube having a substrate tube longitudinal axis, a substrate tube length, a first substrate tube end face, a second substrate tube end face, a substrate tube outer surface, a substrate tube inner surface, a substrate tube outer diameter, a substrate tube inner diameter, a substrate tube wall thickness, and a continuous opening extending coaxially with the substrate tube longitudinal axis,

[0003] and a substrate tube holder comprising a clamping device and designed to support the substrate tube and to rotate the substrate tube about a rotation axis running coaxially or parallel to the longitudinal axis of the substrate tube.

[0004] The invention also relates to a method for producing a tubular SiO2 blank in an external deposition process, the method comprising the following method steps:

[0005] (a) providing a substrate tube having a substrate tube longitudinal axis, a substrate tube length, a first substrate tube end face, a second substrate tube end face, a substrate tube outer side surface, a substrate tube inner side surface, a substrate tube outer diameter, and a continuous opening extending coaxially with the substrate tube longitudinal axis,

[0006] (b) supporting the substrate tube in a substrate tube holder including a clamping device,

[0007] (c) rotating the substrate tube about an axis of rotation extending coaxially or parallel to the longitudinal axis of the substrate tube, and

[0008] (d) depositing SiO 2 particles on the outer surface of the substrate tube by at least one deposition burner, thereby forming the tubular SiO 2 blank.

[0009] 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 in the manufacture of optical fibers. Such components are usually produced from tubular blanks made of synthetic silica by hot forming and / or mechanical treatment. In the course of increasing productivity, there is an increasing demand for such components to have larger dimensions, in particular larger wall thicknesses and inner diameters.

[0010] In order to produce tubular blanks from synthetically produced silicon dioxide, a CVD process (chemical vapor deposition) is known, in which SiO particles are deposited on a substrate from the gas phase. The CVD external deposition process, abbreviated as "OVD" (external vapor deposition), is generally suitable for producing large-volume blanks. In this process, the silicon-containing starting material is converted into SiO particles by flame hydrolysis or pyrolysis in a reaction zone, and these particles are deposited in layers on the outer jacket of a cylindrical substrate rotating around its longitudinal axis. The reaction zone is generated by a heat source, in which the substrate longitudinal axis and the heating source move back and forth relative to each other. The substrate can be tubular, and is also referred to as "substrate tube" here and below. The substrate tube is, for example, composed of SiC, SiSiC (reaction bonded silicon carbide), AlO or another ceramic material or composed of graphite, and is fixed and rotated around its longitudinal axis by a lathe-shaped device (also referred to as "substrate tube holder" here).

[0011] The result of this deposition process is a substantially cylindrical, tubular SiO2 blank which, depending on the temperature during the deposition process, is a porous SiO2 body (hereinafter also referred to as "soot body") or a body made of more or less transparent quartz glass. In the case of a porous soot body, this body is sintered in a separate method step to form a more or less transparent quartz glass body (this sintering process is also referred to as "vitrification"). From this more or less transparent quartz glass body, by mechanical, chemical and / or thermal aftertreatment, synthetic quartz glass components such as solid cylinders, hollow cylinders or parts of these components are obtained, which themselves can also be used as semi-finished products for the production of other components.

[0012] Prior art

[0013] In order to produce SiO2 bodies from synthetic silicon dioxide with a large inner tube diameter using an external deposition process, substrate tubes with a suitable outer diameter and substrate tube holders adapted thereto must be used. The fundamental problem that arises here is to compensate as far as possible for differences in the linear coefficients of thermal expansion (hereinafter also referred to as thermal expansion or CTE (coefficient of thermal expansion)) of the materials of the SiO2 body, substrate tube and substrate tube holder.

[0014] For example, a horizontal lathe for producing preforms from porous silicon dioxide using the OVD method, known from EP 3 584 023 A1, has a mechanism for compensating thermal expansion in the axial direction. The mechanism comprises a clamping device having a first chuck which can be rotated about an axis of rotation and which clamps one of the ends of the substrate tube, and a second chuck which clamps the other end of the substrate tube and can be moved back and forth in the direction of the axis of rotation. This back and forth movement is achieved, for example, by means of a roller bearing of the second chuck, which is advantageously supplemented by a spring preload, which counteracts the axial elongation caused by thermal expansion.

[0015] KR 10-2452282B1 describes an OVD external deposition process for manufacturing a quartz glass tube, and a device for this purpose. A stepped substrate tube is proposed, which is formed by a cylindrical deposition piece with a large outer diameter, to which clamping pieces extending outward on both sides and having a smaller outer diameter are connected, and these clamping pieces fit into the jaws of a horizontal glass lathe. The deposition piece and the clamping pieces on both sides can be realized in one piece, or the deposition piece is connected to the clamping pieces on both sides. Screw, pin and latch connections are mentioned as connection methods, and alternatively, are mentioned as embodiments in which the support piece or the deposition piece is provided with a thread and connected by a screw method. In the OVD deposition process, a SiO2 soot body is produced on the cylindrical side surface of the deposition piece, while the soot body is rotated around the rotation axis by the clamping pieces on both sides.

[0016] Technical issues

[0017] During the OVD external separation process, the substrate tube heats up more on the outside than on the inside. The resulting mechanical stresses accumulate over the wall thickness and can lead to fractures. For example, in the case of small substrate tube diameters of less than 80 mm and small substrate tube lengths of less than 2,000 mm, the CTE differences are not so severe and have an effect almost only in the axial direction (in the direction of the longitudinal axis of the substrate tube). However, in the case of large and thick-walled substrate tubes, for example with an inner diameter of more than 200 mm and a wall thickness of more than 25 mm, the radial thermal expansion is no longer negligible. These substrate tubes also have a high weight, which increases the requirements on the stability and dynamics of the substrate tube holder.

[0018] The reaction zone in which the deposition process takes place usually has a shorter axial dimension compared to the length of the substrate tube. A substrate tube clamped at both ends is heated only in a narrow length section of the deposition zone, but not as intensely in the end regions held in the substrate tube holder. Thermal stresses between the cooler end regions and the hotter middle of the tube can also lead to cracks in the substrate tube.

[0019] In devices for producing large-volume tubular blanks from synthetic silica using an OVD outside deposition process and correspondingly large device components, weight, local temperature differences within the component and CTE differences between different components connected to each other increasingly make the manufacturing process more difficult.

[0020] The object of the present invention is therefore to provide a device which avoids at least some of the above-mentioned disadvantages and which is particularly suitable for reproducibly and reliably holding large-volume tubular SiO2 blanks by an external deposition process, in particular an OVD external deposition process.

[0021] In particular, the object of the present invention is to provide a device for holding thick-walled tubular blanks with a large inner diameter (for example with an outer diameter greater than 200 mm and a large wall thickness greater than 25 mm) during an external deposition process, which device is suitable for avoiding or compensating for mechanical stresses caused by dimensional deviations and calibration, alignment and adjustment errors in the components of the device and due to CTE differences in the components in the axial direction and in the radial direction.

[0022] Furthermore, the object of the present invention is to propose a method for producing tubular blanks with a large inner diameter and a large wall thickness, in particular with an inner tube diameter of more than 200 mm and with a tube wall thickness of more than 25 mm, according to an external deposition process, in particular from synthetic silicon dioxide, which method avoids the above-mentioned disadvantages and in which in particular the risk of producing rejects is reduced. DETAILED DESCRIPTION

[0023] With regard to the device, this object is achieved according to the invention starting from a device of the type mentioned at the outset, wherein the substrate tube holder comprises a clamping mechanism having a first pressure unit adjoining a first substrate tube end face, a second pressure unit adjoining a second substrate tube end face, and at least one force element which is designed to generate an axial contact pressure having a force component acting in the direction of the longitudinal axis of the substrate tube, which causes the substrate tube to be clamped between the first pressure unit and the second pressure unit.

[0024] The substrate tube is designed to support a tubular SiO2 body (especially made of synthetic silicon dioxide) with a large inner diameter on its outer surface based on an external deposition process. The tubular SiO2 body is, for example, a SiO2 soot body or a body made of partially or completely densely sintered quartz glass.

[0025] For example, the substrate tube has a substrate tube length of at most 4 m and is cylindrical, conical or stepped over its entire length or over part of its length. The inner profile can be constant over the length of the substrate tube or it can vary.

[0026] After the deposition process has been completed, the substrate tube can remain in the composite of substrate tube and SiO2 blank, or it can be removed from the substrate tube-blank composite. The substrate tube remaining in the substrate tube-SiO2 bulk composite can become part of the SiO2 blank; it is made of, for example, quartz glass. The substrate tube remaining in the substrate tube-SiO2 bulk 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 the case may be.

[0027] The substrate tube removed from the substrate tube-SiO2 bulk composite after the deposition process or at a later stage of the process is preferably made of SiC, SiSiC, Al2O3 or another ceramic material or of graphite. It preferably has an outer diameter of at least 250 mm. Its wall thickness is optionally preferably in the range of 5 mm to 30 mm.

[0028] The wall thickness of the substrate tube is therefore small relative to its outer diameter and is preferably less than 20% of the outer diameter of the substrate tube. Thus, on the one hand, the substrate tube has a low weight, which reduces the dynamics of the rotational movement and facilitates handling and alignment, and on the other hand, the substrate tube has a low thermal mass, which keeps the heat dissipation and the formation of thermal stresses in the wall at a low level.

[0029] On the other hand, the wall thickness of the substrate tube is large enough to support a large volume of SiO2 body. Therefore, the wall thickness of the substrate tube is preferably at least 1% of the outer diameter of the substrate tube.

[0030] Wall thickness "W S "(in mm) may also depend on the length of the substrate tube. Advantageously, the wall thickness also increases with increasing length of the substrate tube. Thus, W S Alternatively, it may depend on the outer diameter D of the substrate tube S (in mm), and also taking into account the length of the substrate tube "L S ” (in mm), as follows: W S <0.2*(L S / 2,000mm)*D S .

[0031] A substrate tube holder for supporting and rotating a substrate tube comprises a clamping device and a clamping mechanism with two pressure units, one of which bears against each end face of the substrate tube. The clamping mechanism causes the substrate tube to be clamped by applying an axial clamping force to its end faces on both sides. For this axial clamping, the 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 adjoining the end faces are sufficient. The elimination of the usual positive fit or material connection between the substrate tube and the clamping device provides an additional degree of freedom for the movement of the substrate tube in the radial direction, in which respect a certain mechanical decoupling of the substrate tube from the clamping device is achieved even if the pressure units are fixedly connected to the clamping device. Thus, thermally induced changes in the diameter of the substrate tube occurring during the deposition process can be compensated or these diameter changes can be permitted without mechanical stresses forming between the clamping device and the substrate tube.

[0032] The clamping mechanism may also help to compensate for thermal expansion in the direction of the longitudinal axis of the substrate tube.

[0033] The first pressure unit and the second pressure unit preferably each comprise a contact pressure surface which abuts the corresponding substrate tube end face and is composed of a graphite-containing material. The graphite-containing material is relatively soft and can absorb shocks and pulses. This will be explained in more detail below.

[0034] The pressure units on both sides transmit both a rotational movement of the clamping device and a component of the contact pressure generated by at least one force element and acting in the direction of the longitudinal axis of the substrate tube to the substrate tube end face. In the simplest case, a rotational movement of the substrate tube can also be achieved solely by an axial non-positive connection (static friction) between the substrate tube and the contact pressure unit adjoining the end face of the substrate tube. For this purpose, only a sufficiently high contact pressure is required. For this purpose, a drive element can be arranged on the end face of the substrate tube and / or on one or both of the pressure units adjoining thereto, which drive element produces a positive fit for the rotational movement and does not eliminate the above-mentioned additional degree of freedom for the movement of the substrate tube in the radial direction.

[0035] The pressure unit itself consists of one or more components on each side. In the preferred case, they are identical in design. The components directly adjoining the end face of the substrate tube are, for example, plate-shaped or ring-shaped, or form spherical or elliptical segments. In the simplest case, the surfaces adjoining the end face of the substrate tube are flat; they can also be designed to be curved or stepped.

[0036] The first pressure unit and the second pressure unit are pressed against each other due to the action of at least one force element, so that the pressure units exert an axial contact pressure on the substrate tube, which is sufficient for supporting and rotating the substrate tube. It is sufficient if the at least one force element acts on only one of the two pressure units, so that this pressure unit transmits the contact pressure to the corresponding substrate tube end face. If necessary, the other pressure unit, which is positioned opposite in the direction of the longitudinal axis of the substrate tube, forms a passive abutment without the need for an additional force element.

[0037] In a preferred embodiment of the device, the clamping device comprises a first spindle rotatable about a rotation axis and a second spindle positioned axially opposite the first spindle in the direction of the longitudinal axis of the substrate tube and rotatable about the rotation axis, wherein the first spindle is mounted on or connected to a first pressure unit in a rotationally fixed but pivotable manner and transmits an axial contact pressure to the first pressure unit, and wherein the second spindle is mounted on or connected to the second pressure unit so as to be rotationally fixed but movable relative to each other and transmits an axial contact pressure to the second pressure unit.

[0038] 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 a mechanical guide element for their respective pressure unit; they transmit the rotational movement and the axial contact pressure of the clamping device to their respective pressure unit. The spindles are designed in one piece or consist of several parts; in the simplest case, for example, they are designed as a tube, a solid rod or a cone. Each of the two spindles is connected to its corresponding pressure unit for force transmission. The connection is rotationally fixed but allows at least a pivoting movement.

[0039] For example, it is designed as a joint, such as a hinge, a ball joint, a universal joint or a cardan joint, or as a fixed or floating bearing, such as a ball bearing, a tapered bearing, a roller bearing or a universal joint bearing or a mounting. This pivot connection between the pressure unit and the spindle leads to an additional decoupling between the clamping device and the substrate tube, which helps to compensate for alignment, positioning or dimensional deviations. For example, in this way, end faces that are not exactly perpendicular to the longitudinal axis of the substrate tube can be compensated, and rocking movements caused by the substrate tube not being centered absolutely exactly can be compensated.

[0040] In the simplest and particularly preferred case, the first spindle has a free distal end on which the first pressure unit is pivotably mounted, and the second spindle also has a free distal end on which the second pressure unit is pivotably mounted.

[0041] The two spindles thus transmit contact pressure and rotational movement to the substrate tube on the one hand and support pressure units on the other hand. These units are arranged on the respective distal spindle ends.

[0042] In the region of the distal ends of the first and second spindles, at least one support element is arranged in each case, on which the respective spindle can roll. The at least one support element serves to support the spindles, especially when the weight of the substrate tube and the SiO2 body is heavy.

[0043] Particularly preferably, the pivot connection between the spindle and the pressure unit is designed as a floating bearing and preferably comprises a universal ball-conical seat. Here, the seat on the spindle side is conical in shape and the pressure unit movably mounted thereon has a spherical or radius section that interacts with the seat, or vice versa: the seat on the spindle side has a convexly curved spherical or radius section that corresponds to the concavely curved pressure unit movably mounted thereon.

[0044] In particular, in the case of very long substrate tubes having a length of more than 2 m, an additional stabilization of the rotation axis may be helpful. In this regard, the substrate tube holder comprises a centering unit comprising at least one tubular or rod-shaped centering support which extends through the through opening of the substrate tube and is located between the first pressure unit and the second pressure unit.

[0045] The centering support is preferably loosely mounted in the region of the respective pressure unit and is mechanically decoupled from the spindle on both sides in such a way that it does not hinder an axial displacement of the spindle for compensating for a change in length.

[0046] For example, a connecting rod can be used for this purpose, which extends through a through-opening in the base tube from one spindle to the opposite spindle. The connecting rod consists, for example, of one or more rods, which are each uniformly distributed around the axis of rotation and are connected to the spindles on both sides directly or indirectly (via correspondingly mounted intermediate elements).

[0047] Alternatively or additionally, in a particularly preferred embodiment, it is provided that the first spindle is designed as a hollow spindle having a first inner hole, and the second spindle is designed as a hollow spindle having a second inner hole, and the centering support extends the first end into the first inner hole and extends the second end into the second inner hole.

[0048] The first spindle and the second spindle are designed here as hollow spindles with an inner bore. The inner bore is designed as a through hole, or the hollow spindle is closed on its proximal end side (facing the clamping device). In the simplest case, the inner bore has a circular cross section; however, they can also have a cross section that deviates from a circular shape, such as an elliptical or polygonal cross section. The inner cross section of the first hollow spindle and the second hollow spindle is identical or different to one another. The inner cross section of the hollow spindle is preferably adapted to the corresponding outer cross section of the centering support in the sense of a clearance fit.

[0049] The centering support as part of the centering unit has a centering support longitudinal axis and is, for example, rod-shaped or tubular. It extends completely through the through-opening of the substrate tube, but preferably ends on both sides in the inner bore of the hollow spindle. In the corresponding inner bore, the centering support is mounted according to the telescopic principle so as to be axially displaceable with a small 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 and preferably in the range of a few tenths of a millimeter, for example 0.2 mm to 0.5 mm. Thus, the centering support is supported on the inner walls of the inner bores of the two hollow spindles and simultaneously centers them relative to each other in the axial direction in the sense of the coaxiality of the longitudinal axes of the centering support and the hollow spindle. On the one hand, the clearance fit prevents an overdetermination of the substrate tube bearing and, on the other hand, an axial guidance is achieved which counteracts mutual tilting or twisting of the hollow spindle and the longitudinal axis of the substrate tube.

[0050] In a preferred embodiment of the centering support, the support is freely rotatable on both sides within the inner bore of the hollow spindle and also does not execute a rotational movement of the hollow spindle, or only partially executes a rotational movement of the hollow spindle. In another embodiment of the centering support, the centering support is mounted on both sides in a rotationally fixed manner within the inner bore of the hollow spindle inner bore, so that the centering support rotates together with the hollow spindle. The rotationally fixed mounting can be achieved, for example, by a non-circular inner geometry of at least one of the hollow spindles, for example by a polygonal or elliptical inner geometry, and an outer contour of the centering support adapted thereto in the sense of a key-lock combination.

[0051] In a preferred development of the embodiment with the centering support element, the centering support element is freely movable in the axial direction in the first inner bore and in the second inner bore.

[0052] Here, the centering support ends in a corresponding inner bore and can move freely therein in the axial direction (except for friction). Due to the axial mobility of the centering support, thermal expansion differences between the centering support and the hollow spindle can be compensated and thus thermally induced stresses in the substrate tube holder can be avoided.

[0053] The free distance "a" between the hollow spindles positioned opposite each other is usually constant. The length "L of the centering support Z " is greater than the free distance "a". In some cases, if the movement play of the centering support in the axial direction is large enough for this, the centering support can still completely slide out of one of the hollow spindle inner holes. This sliding out can be achieved, for example, by the length "L Z " to prevent, the length includes the free distance "a" plus an additional length (La+Lb), which takes into account the axial movement clearance on both sides of the first inner hole and the second inner hole.

[0054] In particular, with regard to the function of the centering support as an axial guide on both sides of the hollow spindle, it is advantageous if the centering support extends in both hollow spindles over a certain extension length La or Lb. The length La or Lb is preferably at least twice as large as the inner diameter of the respective hollow spindle. The inner diameter of the hollow spindle is preferably in the range of 40 mm to 100 mm.

[0055] On the other hand, for reasons of stability and in particular in order to guide the hollow spindle as effectively as possible on both sides by the centering support, it can also be advantageous to limit the entire axial displacement range "B" of the centering support to a predetermined value. Z ”(B a +B b) is limited on both sides of the interior of the hollow main shaft, and the "B Z " is designed to be as large as necessary but as small as possible. In this regard, it has been shown that if B Z It is useful if the following conditions are met: B Z <20mm, and preferably 5mm Z <15mm.

[0056] The total axial movement clearance of the centering support in the axial direction inside the hollow spindle is limited to a few millimeters. This is usually sufficient to compensate for the CTE difference between the hollow spindle and the centering support in the axial direction. This limitation can be achieved, for example, by a stop element extending into the inner bore of the hollow spindle, or by shrinking or closing the inner bore of the hollow spindle.

[0057] In a particularly preferred development of an embodiment of the device with a centering support, it is provided that the centering unit comprises centering elements which are placed on the centering support in a through-hole in the substrate tube and wherein a first centering element is arranged in the region of a first substrate tube end face and a second centering element is arranged in the region of a second substrate tube end face.

[0058] The centering elements are inserted into the substrate tube through-hole in the region of the two ends. They serve to guide the substrate tube and act as a "collapse protection" to prevent slipping out. Therefore, they have an outer contour that is adapted to the inner contour of the substrate tube through-hole. They are designed, for example, as a circular ring, a polygonal ring or a star shape with support arms pointing outward. The diameter of the enveloping circle around the centering elements is smaller than the inner diameter of the substrate tube through-hole. The inner contour of the centering elements is preferably adapted to the outer contour of the centering support in such a way that they are placed on the centering support with a clearance fit in a sliding manner. For example, in the case of a circular configuration, the inner diameter of the centering elements is 0.5 mm to 2 mm larger than the outer diameter of the centering support.

[0059] The centering element facilitates the mounting of the substrate tube holder and reduces the risk of the substrate tube slipping out of the axial clamping when used for the deposition process. In order to reduce the deflection of the substrate tube, at least one further centering element can be arranged in the region between the end centering elements. The centering element preferably consists of graphite or of another graphite-containing material.

[0060] The SiO2 blank to be produced usually consists of synthetic silicon dioxide, which has a low CTE. It varies depending on the composition and the production method and is about 0.5 μm / m / K (0.5×10 -6 ​ / K). Metals are preferably selected as the material of 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 impulses during deposition. Particular preference is given to metals with high chemical resistance, such as stainless steels (with a CTE in the range of 10 μm / m / K to 17 μm / m / K, depending on the alloy), and / or metals with a thermal expansion coefficient comparable to that of silicon dioxide, such as the iron-nickel alloys known under the collective name "INVAR", whose CTE is typically in the range of 1.2 μm / m / K or lower.

[0061] The at least one deposition burner generates a burner flame, the hottest point of which is usually located spatially before or on the surface of the SiO2 body to be deposited. The area around the hottest point is also referred to as the "reaction zone".

[0062] In this regard, in a preferred embodiment of the device, the maximum dimension of the spindle in the radial direction, such as 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, it is at least 100 mm smaller. This ensures that the spindle is located outside the "reaction zone" of the one or more deposition burners.

[0063] The device has a first side (eg, left side) and a second side (eg, right side). When the following explanation only relates to the first side of the two sides, the second side is designed to be substantially the same or equivalent to the first side, unless otherwise explicitly stated.

[0064] It has proven successful if the first pressure unit has a first pressure transmission element and a first damping element which is connected thereto in a rotationally fixed manner and preferably consists of a graphite-containing material, wherein the pressure transmission element is mounted on or connected to the first main shaft in a rotationally fixed but pivotable manner, and wherein the first damping element is arranged between the pressure transmission element and the substrate tube and adjoins the first substrate tube end face.

[0065] The first pressure transmission element is part of the first extrusion unit. It is designed to transmit the axial contact pressure generated by the at least one force element to the first substrate tube end face or to act as an abutment of the first substrate tube end face if the axial contact pressure generated by the force element also acts on or only acts on the second substrate tube end face. The pressure transmission element interacts directly or indirectly (i.e. via an intermediate element) with the first spindle, to which it is mounted or connected in a rotationally fixed but pivotable manner. 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 preferably consists of metal, for example of stainless steel.

[0066] A buffer element is arranged between the pressure transmission element and the first substrate tube end face. It serves on the one hand to improve the clamping effect and on the other hand to absorb impulses in the axial or azimuthal direction which might otherwise act on the relatively impact-sensitive end face. The buffer element is designed, for example, in the form of a ring or star. It preferably has a low hardness and allows a relatively high contact pressure to be applied without damaging the substrate tube end face, and it generates sufficiently high friction to transmit the rotational movement. A suitable material is, for example, graphite which, due to its lubricating properties, allows radial sliding of the tube end face on the graphite and thus radial thermal expansion of the substrate tube, but always has sufficient friction to transmit impulses and forces during azimuthal acceleration.

[0067] The force flow of the contact pressure is here: force element (eg spring-loaded chuck)→first displacement unit with first spindle→joint / pivotable bearing→first pressure transmission element→first damping element→first substrate tube end face.

[0068] The first damping element can be designed as a stepped annular disk having a hollow cylindrical section with an outwardly projecting flange, wherein the flange abuts the first substrate tube end face and the hollow cylindrical section projects into the through hole of the substrate tube. The stepped disk damping element engages with little play below the inner wall of the substrate tube and simultaneously serves as a centering element. This is one way of ensuring the position of the first centering element in the region of the first substrate tube end face, if this appears to be necessary or advantageous. In this embodiment, the centering element and the damping element are designed in one piece.

[0069] On the other hand, the damping element is exposed to higher forces and can wear relatively quickly. It is also advantageous if the centering element and the damping element can be thermally decoupled, for example by a gap. As a wear part, the damping element is preferably easy and inexpensive to replace. With this in mind, it has proven to be advantageous if the first centering element is connected to the first damping element in a detachable and non-rotatable manner.

[0070] If this appears necessary or advantageous, this is a further possibility for ensuring the positioning of the first centering element in the region of the first substrate tube end face. The detachable connection is produced, for example, using screws. Thus, for example in the event of wear, the buffer element can be easily replaced. Torsional strength is also ensured by a connection between the buffer element and the centering element that is only loose, which connection 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, screws are provided, which are guided with play in holes in the buffer element and the centering element, so that the articulated connection between the respective spindle and the pressure unit is not hindered. The screws produce a positive-fit connection for the rotational movement and can therefore serve as a drive element for the rotational movement of the substrate tube.

[0071] When the device is equipped with a first damping element, it has also proven to be advantageous if the damping element projects beyond the pressure transmission element and the substrate tube in the radial direction.

[0072] During the OVD external deposition process, the flame of at least one deposition burner strikes the side surface of the substrate tube or the SiO2 body being formed and can then be deflected laterally so that it spreads tangentially to the body side surface in the direction of the end region of the SiO2 body. Due to the radial protrusion of the buffer element relative to the pressure transmission element, the pressure transmission element is located in the flame shadow and is thereby largely protected from thermal and corrosion stresses to which the buffer element is exposed on the other hand. The height of the radial protrusion is preferably in the range of 1 cm to 3 cm.

[0073] In a preferred embodiment of the device according to the invention, the substrate tube holder comprises a compensation mechanism for compensating thermal expansion in the direction of the longitudinal axis of the substrate tube. The compensation mechanism and the clamping mechanism can have common components. For example, the compensation mechanism usually comprises a spring element, wherein preferably the force element of the clamping mechanism also comprises a spring element, which is simultaneously a component of the compensation mechanism. The spring element is therefore both a component of the compensation mechanism and a component of the clamping mechanism of the substrate tube holder. The spring element is designed, for example, as a chuck that is spring-mounted on one or both sides.

[0074] With regard to the method for producing a SiO2 blank, the above technical object is achieved according to the invention based on a method of the type mentioned at the outset, wherein an axial contact pressure is generated on a first end face and a second end face using a substrate tube holder, the axial contact pressure having a force component acting in the direction of the longitudinal axis of the substrate tube, which causes the substrate tube to be clamped between a first pressure unit adjoining the first end face and a second pressure unit adjoining the second end face.

[0075] The method comprises a method step in which a tubular SiO2 blank, in particular synthetic silicon dioxide, is produced based on an external deposition process. Depending on the temperature during the deposition process, a porous SiO2 soot body or a more or less transparent vitreous SiO2 body is produced on the side surface of the substrate tube. In the case of a porous SiO2 soot body, the body can be subjected to a dehydration treatment in an inert gas, a chlorine-containing gas or under vacuum to reduce the hydroxyl group content of the quartz glass and then sintered to form a more or less transparent vitreous SiO2 body. Sintering (or vitrification) takes place, for example, under vacuum or in an atmosphere containing helium and / or hydrogen and / or nitrogen.

[0076] For example, the substrate tube has a substrate tube length of up to 4 m and is cylindrical, conical or stepped over its entire length or over part of its length. It is designed to produce a tubular SiO2 body (in particular made of synthetic silicon dioxide) with a large inner diameter on its outer surface based on an OVD external deposition process. The SiO2 blank obtained after this process step has, for example, the following dimensions: inner diameter in the range of 250 mm to 650 mm, wall thickness in the range of 25 mm to 150 mm and length in the range of 800 mm to 3,800 mm. By mechanical, chemical and / or thermal treatment, a component of synthetic quartz glass, for example a quartz glass tube or a quartz glass ring, is obtained therefrom.

[0077] The method therefore makes it possible in particular to produce large-volume quartz glass tubes having an inner diameter of at least 250 mm and a wall thickness of at least 25 mm.

[0078] Preferably, the substrate tube holder of the device according to the invention is used to support the substrate tube according to method step (b). This will be explained in more detail below:

[0079] After the deposition process is complete, the substrate tube can remain in the composite of substrate tube and SiO2 body or be removed from the substrate tube-SiO2 body composite. The substrate tube remaining in the substrate tube-SiO2 body composite can become part of the SiO2 blank; it is 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 optionally preferably in the range of 4 mm to 10 mm. After the deposition process or at a later stage of the process, the substrate tube removed from the substrate tube-SiO2 body composite is preferably made of SiC, SiSiC, Al2O3 or another ceramic material or of graphite. It preferably has an outer diameter of at least 250 mm. Its wall thickness is optionally preferably in the range of 5 mm to 30 mm.

[0080] The wall thickness of the substrate tube is therefore small relative to its outer diameter and is typically less than 20% of the outer diameter of the substrate tube. Thus, on the one hand, the substrate tube has a low weight, which reduces the dynamics of the rotational movement and facilitates handling and alignment, and on the other hand, the substrate tube has a low thermal mass, which keeps the heat dissipation and the formation of thermal stresses in the wall at a low level.

[0081] On the other hand, the wall thickness of the substrate tube is large enough to support a large volume of SiO2 body. Therefore, the wall thickness of the substrate tube is preferably at least 1% of the outer diameter of the substrate tube. Preferably, the wall thickness "W S "(in mm) may also depend on the length of the substrate tube. Advantageously, the wall thickness also increases with increasing length of the substrate tube. Thus, W S Alternatively, it may depend on the outer diameter D of the substrate tubeS (in mm), and also taking into account the length of the substrate tube "L S ” (in mm), as follows: W S <0.2*(L S / 2,000mm)*D S .

[0082] The substrate tube holder is used to support and rotate the substrate tube. It includes a clamping device and a clamping mechanism with two pressure units, one of which is against each end face of the substrate tube. The clamping mechanism clamps the substrate tube by applying axial clamping force to its end faces on both sides.

[0083] The rotationally fixed mounting 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. To this end, the substrate tube holder is designed to generate an axial contact pressure on the first end face and the second end face, which axial contact pressure has a force component acting in the direction of the longitudinal axis of the substrate tube. The axial contact pressure acts on the first pressure unit and / or the second pressure unit with a force component acting in the direction of the longitudinal axis of the substrate tube. This contact pressure is transmitted to the end faces of the substrate tube by the pressure units, so that the substrate tube is clamped on both sides and held in a rotationally fixed manner between the pressure units. For the axial clamping, the applied axial clamping force and, in the simplest case, a non-positive connection based only on friction between the substrate tube and the pressure unit adjacent to the end face are sufficient. Even if the pressure unit is fixedly connected to the clamping device, the elimination of the usual positive fit or material connection between the substrate tube and the clamping device leads to an additional degree of freedom of movement of the substrate tube in the radial direction and, in this regard, a certain mechanical decoupling of the substrate tube from the clamping device. Thus, thermally induced changes in diameter occurring during the deposition process can be compensated for or these changes in diameter can be permitted without mechanical stresses forming between the clamping device and the substrate tube.

[0084] The clamping mechanism may also help to compensate for thermal expansion in the direction of the longitudinal axis of the substrate tube.

[0085] The pressure units on both sides transmit both a rotational movement of the clamping device and a component of the contact pressure generated by at least one force element and acting in the direction of the longitudinal axis of the substrate tube to the substrate tube end face. In the simplest case, a rotational movement of the substrate tube can also be achieved solely by an axial non-positive connection (static friction) between the substrate tube and the contact pressure unit adjoining the end face of the substrate tube. For this purpose, only a sufficiently high contact pressure is required. For this purpose, a drive element can be arranged on the end face of the substrate tube and / or on one or both of the pressure units adjoining thereto, which drive element produces a positive fit for the rotational movement and does not eliminate the above-mentioned additional degree of freedom for the movement of the substrate tube in the radial direction.

[0086] The pressure unit itself consists of one or more components on each side. In the preferred case, they are identical in design. The components directly adjoining the end face of the substrate tube are, for example, plate-shaped or ring-shaped, or form spherical or elliptical segments. In the simplest case, the surfaces adjoining the end face of the substrate tube are flat; they can also be designed to be curved or stepped.

[0087] The first pressure unit and the second pressure unit are pressed against each other due to the action of at least one force element, so that the pressure units exert an axial contact pressure on the substrate tube, which is sufficient for supporting and rotating the substrate tube. It is sufficient if the at least one force element acts on only one of the two pressure units, so that this pressure unit transmits the contact pressure to the corresponding substrate tube end face. If necessary, the other pressure unit, which is positioned opposite in the direction of the longitudinal axis of the substrate tube, forms a passive abutment without the need for an additional force element.

[0088] 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 capable of rotating about a rotation axis, and the axial contact pressure on the second pressure unit is generated by a second spindle connected to the clamping device and capable of rotating about a rotation axis, wherein the first spindle is mounted on or connected to the first pressure unit in a rotationally fixed but pivotable manner, and wherein the second spindle is mounted on or connected to the second pressure unit so as to be rotationally fixed but movable relative to each other.

[0089] The first and second spindles form the mechanical guide elements and are each assigned to a pressure unit. They transmit the rotational movement and the axial contact pressure of the clamping device to their respective pressure unit. The spindles are designed in one piece or consist of several parts; in the simplest case, for example, they are designed as tubes, solid bars or cones. Each of the two spindles is connected to its corresponding pressure unit for force transmission. The connection is rotationally fixed but allows at least a pivoting movement.

[0090] For example, it is designed as a joint, such as a hinge, a ball joint, a universal joint or a cardan joint, or as a fixed or floating bearing, such as a ball bearing, a tapered bearing, a roller bearing or a universal joint bearing or a mounting. This pivot connection between the pressure unit and the spindle leads to an additional decoupling between the clamping device and the substrate tube, which helps to compensate for alignment, positioning or dimensional deviations. For example, in this way, end faces that are not exactly perpendicular to the longitudinal axis of the substrate tube can be compensated, and rocking movements caused by the substrate tube not being centered absolutely exactly can be compensated.

[0091] In the simplest and particularly preferred case, the first spindle has a free distal end on which the first pressure unit is pivotably mounted, and the second spindle also has a free distal end on which the second pressure unit is pivotably mounted.

[0092] The two spindles thus transmit contact pressure and rotational movement to the substrate tube on the one hand and support pressure units on the other hand. These units are arranged on the respective distal spindle ends.

[0093] In the region of the distal ends of the first and second spindles, at least one support element is arranged in each case, on which the respective spindle can roll. The at least one support element serves to support the spindles, especially when the weight of the substrate tube and the SiO2 body is heavy.

[0094] Particularly preferably, the pivot connection between the spindle and the pressure unit is designed as a floating bearing and preferably comprises a universal ball-conical seat. Here, the seat on the spindle side is conical and the pressure unit movably mounted thereon has a spherical or radius section that interacts with the seat, or vice versa: the seat on the spindle side has a spherical or radius section that corresponds to the concavely curved pressure unit movably mounted thereon.

[0095] In particular in the case of very long substrate pipes with a length of more than 2 m, an additional stabilization of the axis of rotation may be helpful.

[0096] In this regard, a substrate tube holder is advantageously used which comprises a centering unit comprising at least one tubular or rod-shaped centering support which extends through the through opening of the substrate tube and is located between the first pressure unit and the second pressure unit.

[0097] The centering support is preferably loosely mounted in the region of the respective pressure unit and is mechanically decoupled from the spindle on both sides in such a way that it does not hinder an axial displacement of the spindle for compensating for a change in length.

[0098] For example, a connecting rod can be used for this purpose, which extends through a through-opening in the base tube from one spindle to the opposite spindle. The connecting rod consists, for example, of two or more rods, which are each distributed uniformly around the axis of rotation and are connected on both sides directly or indirectly (via correspondingly mounted intermediate elements) to the spindle.

[0099] Alternatively or additionally, in a particularly preferred procedure, it is provided that the first spindle is designed as a hollow spindle having a first inner hole, and the second spindle is designed as a hollow spindle having a second inner hole, and the centering support extends from the first end into the first inner hole and from the second end into the second inner hole.

[0100] The first spindle and the second spindle are designed here as hollow spindles with an inner bore. The inner bore is designed as a through hole, or the hollow spindle is closed on its proximal end side (facing the clamping device). In the simplest case, the inner bore has a circular cross section; however, they can also have a cross section that deviates from a circular shape, such as an elliptical or polygonal cross section. The inner cross section of the first hollow spindle and the second hollow spindle is identical or different to one another. The inner cross section of the hollow spindle is preferably adapted to the corresponding outer cross section of the centering support in the sense of a clearance fit.

[0101] The centering support as part of the centering unit has a centering support longitudinal axis and is, for example, rod-shaped or tubular. It extends completely through the through-opening of the substrate tube, but preferably ends on both sides in the inner bore of the hollow spindle. In the corresponding inner bore, the centering support is mounted according to the telescopic principle so as to be axially displaceable with a small 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 and preferably in the range of a few tenths of a millimeter, for example 0.2 mm to 0.5 mm. Thus, the centering support is supported on the inner walls of the inner bores of the two hollow spindles and simultaneously centers them relative to each other in the axial direction in the sense of the coaxiality of the longitudinal axes of the centering support and the hollow spindle. On the one hand, the clearance fit prevents an overdetermination of the substrate tube bearing and, on the other hand, an axial guidance is achieved which counteracts mutual tilting or twisting of the hollow spindle and the longitudinal axis of the substrate tube.

[0102] In a preferred arrangement, the centering support is freely rotatable on both sides within the inner bore of the hollow spindle and also does not execute a rotational movement of the hollow spindle, or only partially executes a rotational movement of the hollow spindle. In another arrangement, the centering support is mounted on both sides in a rotationally fixed manner within the inner bore of the hollow spindle, so that the centering support rotates together with the hollow spindle. The rotationally fixed mounting can be achieved, for example, by a non-circular inner geometry of at least one of the hollow spindles, for example by a polygonal or elliptical inner geometry, and an outer contour of the centering support adapted thereto in the sense of a key-lock combination.

[0103] In a preferred development of the procedure using a centering support, the support is freely movable in the first inner bore and in the second inner bore in the axial direction.

[0104] Here, the centering support ends in a corresponding inner bore and can move freely therein in the axial direction (except for friction). Due to the axial mobility of the centering support, thermal expansion differences between the centering support and the hollow spindle can be compensated and thus thermally induced stresses in the substrate tube holder can be avoided.

[0105] The free distance "a" between the hollow spindles positioned opposite each other is usually constant. The length "L of the centering supportZ " is greater than the free distance "a". In some cases, if the movement play of the centering support in the axial direction is large enough for this, the centering support can still completely slide out of one of the hollow spindle inner holes. This sliding out can be achieved, for example, by the length "L Z " to prevent, the length includes the free distance "a" plus an additional length (La+Lb), which takes into account the axial movement clearance on both sides of the first inner hole and the second inner hole.

[0106] In particular, with regard to the function of the centering support as an axial guide on both sides of the hollow spindle, it is advantageous if the centering support extends in both hollow spindles over a certain extension length La or Lb. The lengths La and Lb are preferably at least twice as large as the inner diameter of the respective hollow spindle. The inner diameter of the hollow spindle is preferably in the range of 40 mm to 100 mm.

[0107] On the other hand, for reasons of stability and in particular in order to guide the hollow spindle as effectively as possible on both sides by the centering support, it can also be advantageous to limit the entire axial displacement range "B" of the centering support to a predetermined value. Z ” is limited on both sides of the hollow spindle, and the “B Z " is designed to be as large as necessary but as small as possible. In this regard, it has been shown that if B Z It is useful if the following conditions are met: B Z <20mm, and preferably 5mm Z <15mm.

[0108] The total axial movement clearance of the centering support in the axial direction inside the hollow spindle is limited to a few millimeters. This is usually sufficient to compensate for the CTE difference between the hollow spindle and the centering support in the axial direction. This limitation can be achieved, for example, by a stop element extending into the inner bore of the hollow spindle, or by shrinking or closing the inner bore of the hollow spindle.

[0109] In a particularly preferred development of the procedure using a centering support, it is provided that the centering unit comprises centering elements which are placed on a centering support in a through-hole in the substrate tube and wherein a first centering element is arranged in the region of a first substrate tube end face and a second centering element is arranged in the region of a second substrate tube end face.

[0110] ​The centering elements are inserted into the substrate tube through-hole in the region of the two ends. They serve to guide the substrate tube and act as a "collapse protection" to prevent slipping out. They therefore have an outer contour adapted to the inner contour of the substrate tube through-hole. They are designed, for example, as a circular ring, a polygonal ring or a star shape with outwardly pointing support arms. The diameter of the enveloping circle around the centering element is smaller than the inner diameter of the substrate tube through-hole.

[0111] The inner contour of the centering element is preferably adapted to the outer contour of the centering support in such a way that they rest on the centering support with a clearance fit in a sliding manner. For example, in the case of a circular configuration, the inner diameter of the centering element is 0.5 mm to 2 mm larger than the outer diameter of the centering support.

[0112] The centering element facilitates the mounting of the substrate tube holder and reduces the risk of the substrate tube slipping out of the axial clamping when used for the deposition process. In order to reduce the deflection of the substrate tube, at least one further centering element can be arranged in the region between the end centering elements. The centering element preferably consists of graphite or of another graphite-containing material.

[0113] The SiO2 blank to be produced consists of synthetic silicon dioxide, which has a low CTE. It varies depending on the composition and the production method and is about 0.5 μm / m / K (0.5×10 -6 / K). Metals are preferably selected as the material of 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 impulses during deposition. Particular preference is given to metals with high chemical resistance, such as stainless steels (with a CTE in the range of 10 μm / m / K to 17 μm / m / K, depending on the alloy), and / or metals with a thermal expansion coefficient comparable to that of silicon dioxide, such as the iron-nickel alloys known under the collective name "INVAR", whose CTE is typically in the range of 1.2 μm / m / K or lower.

[0114] The at least one deposition burner generates a burner flame, the hottest point of which is usually located spatially before or on the surface of the SiO2 body to be deposited. The area around the hottest point is also referred to as the "reaction zone".

[0115] In this regard, in a preferred procedure, the maximum dimension of the spindle in the radial direction, such as the outer diameter in the case of a circular spindle cross section, is significantly smaller than the substrate tube outer diameter; for example, it is at least 100 mm smaller. This ensures that the spindle is located outside the "reaction zone" of at least one deposition burner.

[0116] The device for implementing the method has a first side (e.g., left side) and a second side (e.g., right side). When the following explanation only relates to the first side of the two sides, the second side is designed to be substantially the same or equivalent to the first side, unless otherwise explicitly stated.

[0117] It has proven successful if the first pressure unit has a first pressure transmission element and a first damping element which is connected thereto in a rotationally fixed manner and preferably consists of a graphite-containing material, wherein the pressure transmission element is mounted on or connected to the first main shaft in a rotationally fixed but pivotable manner, and wherein the first damping element is arranged between the pressure transmission element and the substrate tube and adjoins the first substrate tube end face.

[0118] The first pressure transmission element is part of the first extrusion unit. It is designed to transmit the axial contact pressure generated by the at least one force element to the first substrate tube end face or to act as an abutment of the first substrate tube end face if the axial contact pressure generated by the force element also acts on or only acts on the second substrate tube end face. The pressure transmission element interacts directly or indirectly (i.e. via an intermediate element) with the first spindle, to which it is mounted or connected in a rotationally fixed but pivotable manner. 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 preferably consists of metal, for example of stainless steel.

[0119] A buffer element is arranged between the pressure transmission element and the first substrate tube end face. It serves on the one hand to improve the clamping effect and on the other hand to absorb impulses in the axial or azimuthal direction which would otherwise act on the relatively impact-sensitive end face. The buffer element is designed, for example, in the form of a ring or star. It preferably has a low hardness and allows a relatively high contact pressure to be applied without damaging the substrate tube end face, and it generates sufficiently high friction to transmit the rotational movement. A suitable material is, for example, graphite which, due to its lubricating properties, allows radial sliding of the tube end face on the graphite and thus radial thermal expansion of the substrate tube, but always has sufficient friction to transmit impulses and forces during azimuthal acceleration.

[0120] The force flow of the contact pressure is here: force element (eg spring-loaded chuck)→first displacement unit with first spindle→joint / pivotable bearing→first pressure transmission element→first damping element→first substrate tube end face.

[0121] The first damping element can be designed as a stepped annular disk having a hollow cylindrical section with an outwardly projecting flange, wherein the flange abuts the first substrate tube end face and the hollow cylindrical section projects into the through hole of the substrate tube. The stepped disk damping element engages with little play below the inner wall of the substrate tube and simultaneously serves as a centering element. This is one way of ensuring the position of the first centering element in the region of the first substrate tube end face, if this appears to be necessary or advantageous. In this embodiment, the centering element and the damping element are designed in one piece.

[0122] On the other hand, the damping element is exposed to higher forces and can wear relatively quickly. It is also advantageous if the centering element and the damping element can be thermally decoupled, for example by a gap. As a wear part, the damping element is preferably easy and inexpensive to replace. With this in mind, it has proven to be advantageous if the first centering element is connected to the first damping element in a detachable and non-rotatable manner.

[0123] If this appears necessary or advantageous, this is a further possibility for ensuring the positioning of the first centering element in the region of the first substrate tube end face. The detachable connection is produced, for example, using screws. Thus, for example in the event of wear, the buffer element can be easily replaced. Torsional strength is also ensured by a connection between the buffer element and the centering element that is only loose, which connection 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, screws are provided, which are guided with play in holes in the buffer element and the centering element, so that the articulated connection between the respective spindle and the pressure unit is not hindered. The screws produce a positive-fit connection for the rotational movement and can therefore serve as a drive element for the rotational movement of the substrate tube.

[0124] In the case of the use of a first damping element, it has proven to be advantageous if this damping element projects beyond the pressure transmission element and the substrate tube in the radial direction.

[0125] During the OVD external deposition process, the flame of at least one deposition burner strikes the side surface of the substrate tube or the SiO2 body being formed and can then be deflected laterally so that it spreads tangentially to the body side surface in the direction of the end region of the SiO2 body. Due to the radial protrusion of the buffer element relative to the pressure transmission element, the pressure transmission element is located in the flame shadow and is thereby largely protected from thermal and corrosion stresses to which the buffer element is exposed on the other hand. The height of the radial protrusion is preferably in the range of 1 cm to 3 cm.

[0126] The substrate tube holder preferably has a compensation mechanism for compensating thermal expansion in the direction of the longitudinal axis of the substrate tube. The compensation mechanism and the clamping mechanism can have common components. For example, the compensation mechanism usually comprises a spring element, wherein in a preferred procedure, the force element of the clamping mechanism also comprises a spring element, which is simultaneously a component of the compensation mechanism. The spring element is therefore both a component of the compensation mechanism and a component of the clamping mechanism of the substrate tube holder. The spring element is designed, for example, as a chuck that is spring-mounted on one or both sides.

[0127] Definition and measurement methods

[0128] The various terms described above are further defined below. These definitions are part of the specification of the present invention. For terms and measurement methods that are not specifically defined in the specification, the interpretation according to the International Telecommunication Union (ITU) is relevant. In the event that one of the following definitions is inconsistent with the rest of the specification, the statement in this specification shall prevail.

[0129] Tubular SiO2 blank

[0130] The result of the deposition process is a tubular composite body made of a substrate tube and a synthetic silica body. Depending on the temperature during the deposition process, the synthetic silica body is a porous "soot body" or a more or less transparent quartz glass body. Here, it is referred to as a "SiO2 body". The SiO2 body is the only component of the tubular SiO2 blank, or the substrate tube is another component of the SiO2 blank and can limit its inner pores. A substrate tube made of a material other than quartz glass is not part of the SiO2 blank.

[0131] Components made of synthetic quartz glass

[0132] Components made of synthetic quartz glass are obtained by mechanical, thermal or chemical treatment of tubular SiO2 blanks. Further mechanical treatment includes sawing, cutting, milling, grinding, and polishing of inner and outer contours. Thermal further treatment includes thermal drying, sintering, vitrification, melting, forming, and tempering. Chemical further treatment includes chemical or thermal or vacuum drying (dehydration treatment), doping and etching. The component is a ready-to-use quartz glass product or a semi-finished product thereof, such as a quartz glass tube or a quartz glass ring.

[0133] Quartz glass / Synthetic quartz glass / Synthetic silicon dioxide

[0134] Quartz glass and synthetic silicon dioxide are understood here to mean glass with a SiO2 content of at least 87% by weight. Quartz glass is doped (SiO2 content = 100%) or contains dopants such as fluorine, chlorine, nitrogen, carbon, or oxides of boron, germanium, rare earth metals, aluminum, or titanium.

[0135] Quartz glass is, for example, a fusion product from a naturally occurring SiO2 raw material (natural quartz glass), or it is produced synthetically (synthetic quartz glass), or consists of a mixture of these quartz glass types. Synthetic transparent quartz glass is obtained, for example, by flame hydrolysis or oxidation of synthetically produced silicon compounds, by polycondensation of organic silicon compounds according to the so-called sol-gel process, or by hydrolysis and precipitation of inorganic silicon compounds in a liquid.

[0136] Sintering / vitrification

[0137] "Sintering" or "vitrification" here means a process step in which a SiO2 body of porous silicon dioxide is treated in an oven at high temperature. Sintering / vitrification takes place in an inert gas, in an atmosphere containing hydrogen and / or helium or in a vacuum. Vacuum refers to an absolute gas pressure of less than 2 mbar. The result of vitrification / sintering is a "tubular blank made of synthetic silicon dioxide".

[0138] Base tube outer diameter / base tube inner diameter

[0139] The substrate tube cross section has a circular outer contour or an outer contour that deviates from a circular shape. If the outer contour deviates from a circular shape, the local "outer diameter value" is given by the diameter of the (smallest) circumference.

[0140] The substrate tube cross section has a circular inner contour or an inner contour that deviates from a circular shape. If the inner contour deviates from a circular shape, the local "inner diameter value" is given by the diameter of the (largest) inscribed circle.

[0141] In a longitudinal section of the substrate tube, the local value of the outer diameter may be constant or not constant over the entire length of the substrate tube. In the case of a constant outer diameter value, the substrate tube has a cylindrical shape when viewed from the outside. Non-constant outer diameter values ​​may vary over the entire length or over a portion of the length. The outer contour may vary, for example, continuously or gradually. In this case, the outer diameter results from the local outer diameter values ​​averaged over the entire length.

[0142] In a longitudinal section of the substrate tube, the local value of the outer diameter may be constant or not constant over the entire length of the substrate tube. In the case of a constant inner diameter value, the through-opening of the substrate tube is cylindrical. Non-constant inner diameter values ​​may vary over the entire length or over a portion of the length. The inner contour may vary, for example, continuously or gradually. In this case, the inner diameter results from the local inner diameter values ​​averaged over the entire length.

[0143] Clearance fit

[0144] The clearance fit is determined, for example, on the basis of tolerance tables according to DIN EN ISO 286-Part 2. In order to ensure a certain amount of axial mobility between the respective bore and spindle, the tolerance zones must be matched to one another so 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 are, for example, g, f and e.

[0145] Exemplary embodiments

[0146] The present invention is explained in more detail below with reference to exemplary embodiments and the accompanying drawings. In detail, in the schematic diagram,

[0147] Figure 1shows a longitudinal section through a device for producing tubular SiO2 blanks in a first embodiment of a substrate tube holder,

[0148] Figure 2 shows a longitudinal section through a device for producing tubular SiO2 blanks from synthetic silicon dioxide in a second embodiment of a substrate tube holder, partly in detail, and

[0149] Figure 3 yes Figure 2 An enlarged view of a portion of the substrate tube holder.

[0150] exist Figure 1 The apparatus schematically shown in FIG. 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 side surface 1c, an inner side surface 1d, a horizontally oriented longitudinal axis 1e, and a cylindrical through hole 1f. The substrate tube 1 has a length of 2m, an outer diameter of 280mm, and a wall thickness of 20mm. Therefore, the inner diameter is 240mm.

[0151] The glass lathe 2 is represented by two oppositely positioned chucks 2a, 2b, wherein the chuck 2a is spring loaded as indicated by the compression spring 2c. The compression spring 2c generates a pressure F which presses the two chucks 2a, 2b against each other as indicated by the directional arrow 2d.

[0152] A hollow spindle 3a, 3b made of stainless steel is clamped in each of these chucks at the proximal end of the chucks 2a, 2b. Ideally, the axis of rotation 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.

[0153] The distal ends of the hollow spindles 3a, 3b are pivotably connected to annular pressure plates 4a, 4b made of stainless steel. To this end, the distal ends of the hollow spindles 3a, 3b taper conically and are pressed against the corresponding pressure plates 4a, 4b due to the force of the spring 2c. Here, the conical ends protrude into the central holes of the corresponding annular pressure plates 4a, 4b and abut against the inner edges of the central holes.

[0154] The pressure plates 4a, 4b are each adjoined by a buffer disk 5a, 5b made of graphite, which in turn adjoin the substrate tube end faces 1a and 1b, respectively. The buffer disks 5a, 5b have a central hole, the diameter of which corresponds to the diameter of the pressure plates and extends coaxially therewith. The outer diameter of the pressure plates 4a, 4b is 10 mm smaller than the outer diameter of the substrate tube. The outer diameter of the buffer disks 5a, 5b extends beyond the outer diameter of the substrate tube 1 by 40 mm.

[0155] The total length of the SiSiC is L ZA tubular centering support 6 having an outer diameter of 80 mm extends through the base tube through hole 1f and through the central holes of the pressure plates 4a, 4b and the buffer plates 5a, 5b. One end 6a of the centering support 6 is at least 500 mm long. a The hollow spindle 3a extends into the hollow spindle 3a and ends inside the hollow spindle, leaving a variable movement gap B of about 6 mm. a The other end 6b has a length L of 600 mm. b The axially extending portion of the hollow spindle 3b protrudes into the hollow spindle 3b and ends inside the hollow spindle, leaving a variable movement gap B of also about 6 mm. b Therefore, the total movement clearance B0 of the centering support 6 in the hollow spindle 3a, 3b is B a +B b The outer diameter of the centering support 6 is constant over its length and is adapted to the inner diameter of the hollow spindles 3a, 3b in a clearance fit and can be displaced telescopically therein.

[0156] Three centering rings 7a, 7b, 7c made of graphite are placed on the centering support 6. The centering ring 7a is located in the area of ​​the left substrate tube end face 1a, the centering ring 7b is located in the area of ​​the right substrate tube end face 1b, and the centering ring 7c is located approximately in the middle of the substrate tube through hole 1f. All centering rings 7a, 7b, 7c have an outer diameter that matches the inner diameter of the substrate tube in a clearance fit, and they have an inner diameter that matches the outer diameter of the centering support in a clearance fit.

[0157] The end centering ring 7a, the buffer disk 5a and the pressure disk 4a are loosely connected to each other by means of screws 4c. The screws 4c have threads that are adjacent to the cylindrical part 4d. The threads are in each case engaged in the internal threads in the pressure disk 4a, so that the cylindrical part 4d rests firmly against the pressure disk 4a in the tightened state. The length of the cylindrical part 4d is greater than the total thickness of the component stack of the centering ring 7a and the buffer disk 5a, so that the head of the screw 4c does not rest against the centering ring 7a, but there is a gap between the centering ring 7a and the screw head. In addition, the through hole in the buffer disk 5a and the centering ring 7a through which the cylindrical part 4d passes is greater than the diameter of the cylindrical part 4d, so that the screw 4c can also be slightly tilted in the through hole and thus does not hinder the possible pivoting movement of the joint. Therefore, this loose connection is suitable both for allowing thermally induced length changes between the components of the substrate tube holder and for compensating for deviations in the target size, positioning and alignment of the components. Furthermore, the screw 4c provides a certain 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 serves as a driving element for this rotational movement. The same applies to the connection of the centering ring 7b, the buffer disk 5b and the pressure disk 4b; for the purpose of thermal decoupling, a gap (not visible in the figure) is provided between the centering ring 7a, 7b and the buffer disk 5a, 5b.

[0158] Several deposition burners 8 for generating SiO2 particles are mounted on a common slide 8a, by means of which they can be moved reversibly and laterally along the outer surface 1c of the substrate tube 1 or along the formed SiO2 soot body 9, and can be moved perpendicularly to this outer surface, as indicated by the direction arrow 8b.

[0159] In the following, reference is made to Figure 1 An example of the production of a component made of quartz glass is explained.

[0160] Oxygen and hydrogen are supplied as burner gases to a deposition burner 8, and a gas stream containing SiCl4 or another silicon-containing starting material is used as feed material for forming SiO2 particles. These components are converted into SiO2 particles in the associated burner flame, and these SiO2 particles are deposited on the substrate tube 1 rotating about the longitudinal axis 1e, thereby forming a soot body 9 from porous SiO2 soot.

[0161] In order to rotate the substrate tube 1, the glass lathe 2 transmits a torque to the hollow spindles 2a, 2b. At the same time, a pressure F acting in the axial direction is generated by the compression spring 2c, which presses the two hollow spindles 3a, 3b against each other and, depending on the deflection of the spring relative to the spring rest length, is in the range between 0.5 kN and 10 kN. For example, an initially set pressure F of 1 kN is applied to the pressure plates 4a, 4b, the buffer disks 5a, 5b and therefore also to the substrate tube end faces 1a, 1b. This pressure F creates a friction connection between the buffer disks 5a, 5b, which is sufficient to hold the inherent weight of the substrate tube 1 and the weight of the soot body 9. The centering rings 7a, 7b, 7c serve only to prevent the substrate tube 1 from accidentally sliding or bending. The interaction of the hollow spindles 3a, 3b and the centering support 6 provides a certain amount of axial guidance which compensates for any radial offset and angular differences between the axes of rotation of the hollow spindles 3a, 3b and avoids mechanical stresses due to the presence of mechanical play.

[0162] As soon as the soot body 9 reaches a predetermined outer diameter, which depends on the density of the soot layer, the deposition process is terminated, resulting in a predetermined outer diameter of the hollow cylindrical quartz glass blank plus a predetermined tolerance of, for example, 1 mm.

[0163] 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 zoned sintering furnace under vacuum or in an atmosphere of a gas that diffuses rapidly in quartz glass (such as helium and hydrogen), and therefore does not generate bubbles. The quartz glass tube obtained in this way has a length of 1,750 mm, an inner diameter of 280 mm, and a wall thickness of 45 mm.

[0164] When Figure 2 and Figure 3 Use with Figure 1 When the same reference numerals are used throughout the text, these reference numerals represent the same or equivalent components or parts of the device.

[0165] Figure 2 The device schematically shown in Figure 1 The devices of 1 and 2 differ primarily in the type and properties of the substrate tube holder and the substrate tube 21 (here 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. The inner diameter is therefore 270 mm.

[0166] The hollow spindles 23a, 23b are made of stainless steel and are each clamped with their proximal ends in a clamping chuck. Ideally, the axis of rotation of the hollow spindles 23a, 23b extends coaxially with the substrate tube longitudinal axis 1e. The hollow spindles 23a, 23b have an outer diameter of 100 mm. In the region of the distal ends of the hollow spindles 23a, 23b, a circumferential extension arm 2c is respectively welded.

[0167] The pivot connection between the hollow spindles 23a, 23b and the corresponding pressure plates 24a, 24 is designed here as a floating bearing and preferably comprises a universal ball-cone seat. Here, the distal ends of the hollow spindles 23a, 23b each form a convexly curved seat with a spherical or radius section, on which the pressure plate 24a or pressure plate 24b is movably mounted by having a concavely curved spherical or radius section that cooperates with the convexly curved seat.

[0168] Figure 3 2 is an enlarged view of the pivotal connection between the hollow spindle 23a, 23b and the corresponding pressure plate 24a, 24b. The end centering ring 7a, the buffer washer 5a and the pressure plate 24a form a stack of components, which are loosely connected to each other by threaded screws 24c, which are each engaged in the thread in the extension arm 23c. The length of the cylindrical portion 24d is greater than the total thickness of the component stack consisting of the centering ring 7a, the buffer plate 5a and the pressure plate 24a. In addition, the width of the hole for receiving the screw 24c in the component stack is significantly greater than the diameter of the cylindrical portion 24d. This results in a number of gaps 25 being retained between the screw head 24e and the centering ring 7a and between the pressure plate 24 and the extension arm 23c, even in the case of fixedly tightened threaded screws 24c, and along the cylindrical portion 24d. The gaps 25 ensure that the connection between the hollow spindle 23a, 23b and the corresponding pressure plate 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. A device for producing a tubular SiO2 blank in an external deposition process, the device comprising: a substrate tube having a substrate tube longitudinal axis, a substrate tube length, a first substrate tube end face, a second substrate tube end face, a substrate tube outer surface, a substrate tube inner surface, a substrate tube outer diameter, a substrate tube inner diameter, a substrate tube wall thickness, and a continuous opening extending coaxially with the substrate tube longitudinal axis, and a substrate tube holder, said substrate tube holder comprising a clamping device and being designed to support said substrate tube and to rotate said substrate tube about an axis of rotation running coaxially or parallel to said longitudinal axis of said substrate tube, The invention is characterized in that the substrate tube holder comprises a clamping mechanism, which comprises a first pressure unit abutting the first substrate tube end surface, a second pressure unit abutting the second substrate tube end surface, 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, which force component causes the substrate tube to be clamped between the first pressure unit and the second pressure unit.

2. The device according to claim 1, characterized in that The clamping device comprises a first spindle which is rotatable about the rotation axis and a second spindle which is positioned axially opposite the first spindle in the direction of the longitudinal axis of the substrate tube and is rotatable about the rotation axis, wherein the first spindle is mounted on or connected to the first pressure unit in a rotationally fixed but pivotable manner and transmits the axial contact pressure to the first pressure unit, and wherein the second spindle is mounted on or connected to the second pressure unit so as to be rotationally fixed but movable relative to each other and transmits the axial contact pressure to the second pressure unit.

3. The device according to claim 2, characterized in that The first spindle has a free distal end, the first pressure unit is pivotably mounted on the free distal end, and the second spindle has a free distal end, the second pressure unit is pivotably mounted on the free distal end, wherein the pivotable bearing is preferably designed as a ball bearing, a tapered bearing, a roller bearing or a plane bearing, and preferably comprises a universal ball and a tapered seat.

4. Device according to one or more of claims 2 or 3, characterized in that The substrate tube holder comprises a centering unit comprising at least one tubular or rod-shaped centering support extending through the through opening of the substrate tube and located between the first pressure unit and the second pressure unit.

5. The device according to claim 4, characterized in that The first spindle is designed as a hollow spindle including a first inner hole, and the second spindle is designed as a hollow spindle including a second inner hole, and the centering support protrudes from a first end into the first inner hole and from a second end into the second inner hole.

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

7. Device according to one or more of claims 2 to 6, characterized in that The first pressure unit comprises a first pressure transmission element and a first damping element which is connected thereto in a rotationally fixed manner and preferably consists of a graphite-containing material, wherein the pressure transmission element is mounted on or connected to the first main shaft in a rotationally fixed but pivotable manner, and wherein the first damping element is arranged between the pressure transmission element and the substrate tube and adjoins the first substrate tube end face.

8. The device according to claim 7, characterized in that The first damping element protrudes beyond the pressure transmission element and the substrate tube in the radial direction.

9. Device according to one or more of claims 1 to 8, characterized in that The first pressure unit includes a pressure surface adjacent to the first substrate tube end face and composed of a graphite-containing material.

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

11. Device according to one or more of the preceding claims, characterized in that The substrate tube holder comprises a compensation mechanism for compensating thermal expansions in the direction of the longitudinal axis of the substrate tube, and the force element of the clamping mechanism is preferably a spring element and at the same time a component of the compensation mechanism.

12. Device according to one of the preceding 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 respective spindle can roll.

13. A method for producing a tubular SiO2 blank in an external deposition process, the method comprising the following method steps: (a) providing a substrate tube having a substrate tube longitudinal axis, a substrate tube length, a first substrate tube end face, a second substrate tube end face, a substrate tube outer side surface, a substrate tube inner side surface, a substrate tube outer diameter, and a continuous opening extending coaxially with the substrate tube longitudinal axis, (b) supporting the substrate tube in a substrate tube holder including a clamping device, (c) rotating the base tube about a rotation axis running coaxially or parallel to the longitudinal axis of the base tube, (d) depositing SiO 2 particles on the outer surface of the substrate tube by at least one deposition burner, thereby forming the tubular SiO 2 blank, It is characterized in that An axial contact pressure is generated on the first and second end faces using the substrate tube holder, the axial contact pressure having a force component acting in the direction of the longitudinal axis of the substrate tube, the force component causing the substrate tube to be clamped between a first pressure unit adjoining the first end face and a second pressure unit adjoining the second end face.

14. The method according to claim 13, characterized in that The substrate tube holder of the device according to one of claims 1 to 12 is used for supporting the substrate tube according to method step (b).

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

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