CN113784937A

CN113784937A - Method for producing a bending mould for ceramics for glass sheets

Info

Publication number: CN113784937A
Application number: CN202180001226.1A
Authority: CN
Inventors: A·帕尔芒捷; A·蔡希纳; M·N·阿尔廷; P·席林斯; C·希斯; F·维莱莫
Original assignee: Saint Gobain Glass France SAS
Current assignee: Saint Gobain Glass France SAS; Compagnie de Saint Gobain SA
Priority date: 2020-04-06
Filing date: 2021-03-03
Publication date: 2021-12-10
Also published as: WO2021204468A1

Abstract

The invention relates to a method for producing a ceramic bending mould (K) for glass sheets, comprising the following method steps: (A) determining the contact surface (F-K) of the bending die (K); (B) -making a mould (1) with a mould surface (F-1) corresponding to the contact surface (F-K); (C) providing the mould surface (F-1) with a mat (3) of ceramic or glass fibers, which is impregnated with a ceramic suspension, wherein the mat (3) is arranged on the separating layer (2) and dried, thereby producing a ceramic hollow mould (4) with a contact surface (F-K); (D) removing the ceramic hollow mould (4) from the mould (1); (E) the ceramic hollow mould (4) is provided with a ceramic or metal stable bracket (5); (F) the ceramic hollow mould (4) with the stabilizing support (5) is burnt, whereby a ceramic bending mould (K) is produced.

Description

Method for producing a bending mould for ceramics for glass sheets

Technical Field

The invention relates to a method for producing a ceramic bending tool for glass sheets, a correspondingly produced ceramic bending tool and the use thereof.

Background

Especially in the automotive field, glass pieces often have bends. Different methods for producing such bends are known. In so-called gravity bending (also gravity bending) or sag bending), a glass sheet which is flat in the initial state is arranged on a supporting surface of a bending mould and heated to at least its softening temperature, so that the glass sheet rests at the supporting surface under the influence of gravity. In the so-called press bending method, the sheet material is arranged between two complementary tools (bending dies) which jointly apply a pressing action to the sheet material in order to produce the bend. Apparatuses and methods for bending glass sheets are well known to those skilled in the art from a large number of publications. Reference is made, by way of example only, to EP1358131a1, EP2463247a1, WO2017178733a1, DE10314267B3, WO2007125973a1, EP0677488a2 and WO9707066a 1.

Conventional bending moulds are made of metal, wherein the contact surfaces are optionally coated with a steel fabric in order to protect the glass surface. Metallic bending dies are stable and subject to testing for use in industrial mass manufacturing. But its manufacture is rather costly and costly.

The bending mould is manufactured specifically for each model of the glass sheet, wherein the contact surfaces of the bending mould determine the three-dimensional geometry of the bend, i.e. the glass sheet. Before a particular model of glass sheet is put into mass production, it is often necessary or desirable to make a prototype where, for example, tests can be performed or the prototype can be presented to potential customers. It has hitherto been customary to also produce one or more metal bending moulds for the production of prototypes. Thus, the prototype is long lasting and costly to manufacture.

Disclosure of Invention

There is therefore a need for a bending mould for bending glass sheets, in particular for prototyping, which can be manufactured quickly and cost-effectively. The bending die must be temperature stable enough to withstand the high temperatures when the glass is bent. The invention is based on the object of providing a method for producing such a bending tool.

The object of the invention is achieved according to the invention by a method according to independent claim 1. Preferred embodiments follow from the dependent claims.

The method according to the invention is used for manufacturing a bending mould for ceramic of glass sheets, more precisely for bending ceramic of glass sheets. The method according to the invention comprises at least the following method steps:

(A) determining a contact surface of a bending die;

(B) making a mold with a mold surface, the mold surface corresponding to the contact surface;

(C) optionally: a separating layer is arranged on the model surface;

(D) providing the mould surface with a mat of ceramic fibers, which is impregnated with a suspension of the ceramic, wherein the mat is arranged on a separating layer and dried, thereby producing a ceramic hollow mould with a contact surface;

(E) removing the hollow mould of ceramic from the mould;

(F) providing a ceramic or metallic stabilizing support to the ceramic hollow mould;

(G) the ceramic hollow mould with the stabilizing support is burned, thereby producing a ceramic bending mould.

The method according to the invention for producing a ceramic bending tool enables rapid and cost-effective production, in particular in comparison with metallic bending tools, and is therefore particularly suitable for producing prototypes. Furthermore, the method can be carried out relatively simply, so that the ceramic bending mould can be produced on site by the glass manufacturer itself with a suitable stock of the required materials and without having to place an order. Thereby, a simple batch of different bending moulds for a model of a glass sheet can also be manufactured in order to compare the quality of the products manufactured thereby. Ceramic bending moulds are temperature-resistant to a large extent, so that they can be used in glass bending processes. The ceramic bending mould is a reinforced hollow mould and has a low weight per se. This is a great advantage of the present invention.

The bending mould for ceramics manufactured according to the invention is arranged for bending glass sheets, in particular for bending glass sheets which are heated to their softening temperature. Upon heating, the glass sheet is capable of plastic deformation. In this method, the glass sheets are generally heated to a temperature of more than 500 ℃, in particular to a temperature of 500 to 700 ℃, whereby the glass sheets soften and can be deformed and can be shaped by the contact surfaces of the bending mould. Typical temperatures when bending a sheet of soda-lime glass are at least 600 ℃, for example about 650 ℃.

The bending die has a contact surface. The contact surface is the surface of the bending mould which is provided as specified for directly or indirectly contacting the glass sheet in order to deform the glass sheet and thereby bend the glass sheet. In a preferred embodiment, the bending tool is a so-called solid tool with a full-surface contact surface, which is provided for contacting a large part of the glass sheet surface. In principle, however, bending tools with frame-like contact surfaces can also be produced by means of the method according to the invention. Such a bending mould can also be referred to as a ring (bending ring) or a frame (frame mould). The frame-like contact surface is provided for contacting only the circumferential edge region of the glass sheet, while the majority of the glass sheet surface is not in contact with the bending mould.

The bending mould according to the invention is not limited with regard to the type of glass bending for which the bending mould can be used. The bending mould (which can also be referred to as bending tool) can be an upper bending mould or a lower bending mould. A lower bending tool in the sense of the present invention is understood to be a tool which touches or is associated with a lower, ground-facing surface of the glass sheet and acts on this lower surface. An upper bending tool is understood to mean a tool which touches or is associated with the upper surface of the glass sheet facing away from the ground and acts on this upper surface. In the upper bending mould the contact surface points downwards and faces the ground, and in the lower bending mould the contact surface points upwards and faces away from the ground. The bending die can be a gravity bending die, an extrusion bending die or a suction bending die. The gravity bending mould is a lower bending mould onto which the glass sheet is placed and after heating is deformed under the influence of gravity and adapted to the shape of the contact surface. In press bending in a relatively compact manner, the glass sheet is pressed and thereby deformed between two bending dies, typically between an upper bending die and a lower bending die. In other words, such a method is also referred to as press bending, in which the glass sheets are pressed against ("blown onto") the upper bending tool by an upwardly directed air flow. Two variants of press bending are generally combined: the glass sheet is pressed by an upwardly directed air flow against the upper bending mould and is then pressed between the upper bending mould and the complementary lower bending mould. During the suction bending, the glass sheet is sucked onto the contact surface, wherein holes are usually introduced into the contact surface in the solid mold for transmitting the suction effect. In particular, a combination of press bending and suction bending is often used, wherein, for example, in addition to the pressing action, the glass sheet is also sucked to the upper bending tool.

It is preferred to produce an upper press and/or suction bending die with a full-area contact surface, a lower press bending die with a frame-like contact surface and a lower gravity bending die with a frame-like or full-area contact surface. These bending moulds have proved to be particularly suitable for the manufacture of visually high-value glass sheets. In a particularly preferred embodiment, the bending tool according to the invention is a press and/or suction bending tool with an upper part of the full-surface contact area. Such bending moulds are often used for a large number of sheet patterns in the field of vehicles and allow, with good takt time and quality, a large bandwidth of the sheet geometry.

In a particularly advantageous embodiment, the bending tool according to the invention is provided for producing prototypes or small series. The bending tool according to the invention is particularly suitable for producing prototypes or small series because of its rapid, simple and cost-effective production. When the bending mould is only arranged for the production of one or some small number of prototypes or small number of glass sheets in a small batch range, the bending mould does not have to have the long-term stability of a conventional metallic bending mould.

First, the contact surface is determined, which the bending tool according to the invention should have. The shape of the contact surface is determined by the shape of the glass sheet to be bent with the contact surface. The required contact surface is determined by means of CAD methods (computer-aided design ) which are preferably customary in the technical field. However, other methods are also known, which are to be dealt with without CAD calculation. The desired contact surface can thus also be approximated iteratively by a manual or machine-supported machining of the initial shape. The shape of the contact surface does not usually correspond exactly to the shape of the glass sheet, but the compensated shape of the contact surface corresponds to the shape of the glass sheet, which takes into account the sagging of the glass sheet under its weight after the action of the bending mould. In the simulation for determining the compensated contact surface, the bending furnace to be used and the bending method to be used are based. In addition to the desired sheet shape, for example, the bending temperature and the dwell time in the bending furnace and the type of bending tool used are also critical here. The compensated shape of the contact surface corresponds to the shape of the glass sheet immediately after the action of the bending tool during this time, which contact surface is calculated in such a way that the desired final shape of the glass sheet is obtained, taking into account the later deformation of the glass sheet, in particular due to sagging under the influence of gravity.

After the contact surface has been determined, a model mold is manufactured according to the invention. The mold die has a die surface, which corresponds to the contact surface. This means that the molding surface is a projection of the contact surface, wherein this projection can be positive or negative. In the case of a negative mapping, the curved model surface extends to some extent opposite to the calculated contact surface. The mold die is to some extent a shaped body or a shaped tool of a bending die for manufacturing ceramics.

In one embodiment of the invention, the mold tool is a positive tool for a bending tool. The model surface is here a direct copy of the contact surface, i.e. it is a male part (positive mapping) having the same direction of curvature as the contact surface. If the contact surface is concave, the model surface is also concave and if the contact surface is convex, the model surface is also convex. The geometry of the mould surface corresponds exactly to the geometry of the contact surface, with the same geometric distribution of radii and directions of curvature occurring as in the contact surface.

In an alternative embodiment of the invention, the mold tool is a negative mold for the bending tool. The model surface is here a complementary copy of the contact surface, i.e. a female part (negative mapping) which has a curvature direction opposite to the contact surface. If the contact surface is concave, the model surface is convex, and if the contact surface is convex, the model surface is also concave. The geometry of the mould surface is thus complementary to the geometry of the contact surface, the same geometric distribution of the radii of curvature occurs as in the contact surface, but with respectively opposite directions of curvature.

The mould tools are preferably made of a suitable and easily processable material. Wood, plastic and resin, especially synthetic resin, are preferable as materials for the mold of the model. The pattern tool made of wood can be constructed as a solid, one-piece wood block or as a plurality of individual parts, for example from composite wood panels, such as medium-density wood fiber boards (MDF-panels), which are stacked on top of one another and are connected to one another, in particular adhesively bonded. As synthetic resin, for example, "460 resin" can be used, as is customary in gauge engineering. Resin-based wood-plastic mixtures can also be used, as is also known from gauge engineering. The mold die is preferably produced by a subtractive production method, wherein the mold die is machined from a larger workpiece by material removal. In particular, cutting-type production methods are used, such as milling, grinding, planing, filing, scraping or chiseling, in particular milling or grinding. The production is preferably carried out automatically by means of CAD processing, wherein a processing machine (CNC machine, computer numerical control) is provided with CAD data of the model tool and the processing machine processes the model tool from the initial workpiece by means of the CAD data. Machining from suitable materials is less time-consuming and less costly and is therefore particularly suitable. In principle, however, it is also possible to produce the model tool from plastic by means of injection molding or by means of generative or additive production methods, for example 3D printing.

The mould surface is optionally provided with a separating layer in order to be able to easily separate the part of the bending mould which is manufactured with the mould from the mould. The separating layer can be, for example, a cover, a paper layer or a film. The separating layer is as thin as possible so that it does not give rise to errors in the shape of the contact surfaces. The separating layer is made of a material which is able to release well from the mold tool on the one hand and from the ceramic hollow mold on the other hand and which has sufficient mechanical and chemical stability. In a particularly preferred embodiment, membranes based on plastics, in particular Polyethylene (PE), polypropylene (PP) or Polyvinyl Chloride (PCV), or coatings based on boron nitride, graphite, oil or grease or anti-adhesion sprays customary on the market are considered as separating layers. The separating layer formed as a paper layer can be formed, for example, from kraft paper or blotter paper. The thickness of the separation layer in the case of a cover is preferably 10nm to 500 μm, in the case of a plastic film and a paper layer preferably 1 μm to 1mm, particularly preferably 5 μm to 50 μm. If the mould is made of an inert plastic, no separating layer is required.

A ceramic hollow mould is then produced by means of a mould model, which is provided as part of a ceramic bending mould and which has a contact surface which is then used for bending the glass sheets. The so-called prepreg technique is used for the production of hollow moulds (prepreg fibres ). The mold surface of the mold tool is provided with a mat of ceramic or glass fibers, which is impregnated with a ceramic suspension. The mat is placed on a separating layer and dried. Drying does not mean final firing of the ceramic, but rather predrying, so that the fiber mat forms a dimensionally stable workpiece which can be removed from the mold tool and further processed. During the pre-drying, the water in the cavity, in particular the mechanical entrapment, is removed. The predrying can be effected at room temperature or by heating. A ceramic hollow mould is produced, which has a contact surface. If the mould surface is the male part of the contact surface, the surface of the hollow mould that is opposite to the mould forms the contact surface. If the mould surface is a female part of the contact surface, the surface of the hollow mould facing the mould forms the contact surface.

The entire mould surface is provided with a pre-impregnated felt, in particular in layers, so that the hollow mould has a sufficient thickness to form a stable curved mould. Typical fiber mats have a thickness of 0.1mm to 5mm, especially 0.3mm to 2 mm. The hollow mould preferably has a thickness of 1mm to 30mm, particularly preferably 2mm to 10 mm.

The thickness of the hollow mould is as uniform as possible. The hollow mould therefore preferably has a constant, position-independent thickness. This is particularly important when the mould face is the male part of the contact face and the contact face is thus configured by the surface of the hollow mould facing away from the mould tool in order to transfer the shape of the mould face onto the contact face. When the mould surface is a female part of the contact surface and the contact surface is thus configured by the surface of the hollow mould facing the mould, then the constant thickness is less important, since no errors in the shape of the contact surface occur by the non-constant thickness. For this reason, a matrix mold with a lower mold surface, which is the female part of the contact surface, can be preferred.

If ceramic fibers are used for the felt, in a preferred embodiment oxide ceramics or silicate ceramics are used, which are particularly suitable for producing bending molds because of their hardness, wear resistance and heat resistance. Suitable oxide ceramics are based, for example, on aluminum oxide (Al)₂O₃) Zirconium oxide (ZrO)₂) Titanium (IV) oxide (TiO)₂) Magnesium oxide (MgO), zinc oxide (ZnO), aluminum titanate (Al)₂O₃+TiO₂) Barium titanate (BaO + TiO)₂) And (5) constructing. Preferred silicate ceramics are based on mullite constructions. Particularly preferred materials for the ceramic are mullite or alumina (Al)₂O₃). However, other ceramics, such as other oxide or silicate ceramics or non-oxide ceramics (in particular based on silicon carbide (SiC), Boron Nitride (BN), boron carbide (B)₄C) Silicon nitride, aluminum nitride, molybdenum disilicide, or tungsten carbide).

If glass fibers are used for the mat, the mat preferably has a silica-content (SiO) of at least 80 weight percent, preferably at least 90 weight percent₂)。

Preferred materials for the ceramic suspension correspond to the materials listed above for the ceramic fibers of the felt, i.e. in particular oxide ceramics, such as alumina ceramics or silicate ceramics, such as mullite ceramics. In a particularly preferred embodiment, a ceramic material based on a silicon aluminum oxide (silicon aluminum ceramic) is used, which has a particularly high density and thus stability, wherein Al is present₂O₃And SiO₂The sum of the portions of (a) is in particular at least 95% by weight.

The material of the fibres and the material of the suspension can be freely chosen by the person skilled in the art independently of each other.

After pre-drying, which is performed, for example, at a temperature of 30 to 80 ℃, the hollow mould is removed from the mould.

The ceramic hollow mould is then provided with a stabilizing support. The stabilizing brackets on the one hand achieve mechanical stabilization of the hollow mould so that it does not deform during the bending of the glass and on the other hand serve to connect the ceramic bending mould with the bending device. The stabilizing support is arranged opposite the contact surface at the hollow mould, so that the contact surface faces away from the stabilizing support and is exposed as intended. The stabilizing brace is then fixed to the concave surface of the hollow mould with a convex contact surface and to the convex surface of the hollow mould with a concave contact surface.

The stabilizer is preferably likewise made of ceramic (ceramic stabilizer), but can also be made of metal (metallic stabilizer), for example of steel, for example temperature-resistant stainless steel. Ceramics are preferred, since thereby a thermal expansion coefficient of the hollow mould and of the stabilizing support which is as similar as possible can be achieved. The stabilizing support is preferably formed by a (ceramic or metallic) tube or rod. In the case of ceramic tubes or rods, the latter preferably already have finished burning, but it is likewise possible to stabilize them solely by predrying. The stabilizing support can likewise be made of a fibrous ceramic or of a conventional ceramic, for example an oxide ceramic or a silicate ceramic. Preferably, the same ceramic material as used for the hollow mould is used. The connection between the hollow mould and the stabilizer bar (and, if appropriate, the tube or rod between the stabilizer bars) is effected, for example, by gluing, nailing, riveting, screwing or plugging.

The ceramic hollow mould with the (preferably ceramic) stabilizing support is then subjected to a temperature treatment, in which the ceramic is burned or sintered. In this case, the bound water is removed in a physicochemical and chemical manner, the other volatile constituents are driven off and a transformation of the mineral and crystal structure can take place. The combustion is usually carried out at temperatures of 600 to 1500 ℃, in particular 850 to 1300 ℃. The duration of combustion is typically 1 to 3 hours. A ceramic bending die is produced by burning ceramic.

A ceramic bending mould is provided for being mounted in a bending apparatus (glass bending apparatus). The bending device has a bending station in which the required bending moulds (below which at least one ceramic bending mould according to the invention is located) are arranged and in which the shaping of the glass sheets takes place by means of the bending moulds. Furthermore, the bending device has means for heating the glass sheets to a softening temperature. In one embodiment, the bending station is arranged in a heated section (bending chamber) of the bending device ("hot bending"). The heating means are arranged here either in the bending chamber itself (combined heating and bending chamber) or in a separate heating chamber, for example in the form of a tunnel furnace through which the glass sheets are passed before entering the bending chamber. In a further embodiment, the bending station is arranged in a section of the bending device that is not heated ("cold bending"). The glass sheet then passes through a heating chamber and is then bent without further heating, wherein the glass sheet cannot of course yet be cooled below its softening temperature. In addition, typical bending apparatuses include means for moving the glass sheets through the heating chamber and the bending station. The movement means can be configured, for example, as rollers or a moving belt conveyor system, wherein the glass sheets rest either directly on the rollers or the moving belt conveyor system or on a transport mold, in particular a transport frame, which is moved by the rollers or the moving belt conveyor system.

Preferably, a metallic attachment unit for placing a ceramic bending mould in the bending station is placed at the stabilizing cradle and/or at the hollow mould. The attachment unit provides, to a certain extent, an interface for mounting in a bending station, in particular an interface corresponding to a conventional metal bending mould. The attachment unit is made of metal, in particular of steel, for example temperature-resistant stainless steel. The attachment unit is preferably placed after the hollow mould and the stabilizing bracket are connected to the bending mould. The type of attachment unit depends on the bending station used. The placement of the attachment unit at the bending die is preferably done by screwing, riveting or suspending/pushing into a receptacle provided for it (for example in the manner of a drawer). The attachment unit can be disposed at the bending die where the combustion is completed. It is also possible, however, to place the attachment unit before the combustion of the ceramic, in particular the hollow mould, and then to carry out the combustion in the bending furnace itself. This saves one method step by carrying out the combustion in the own furnace and is therefore advantageous. In suitable ceramics, combustion can be achieved at a bend temperature, which is typically 600 ℃ to 700 ℃. If higher temperatures are required for the combustion of the ceramic, the bending furnace must be adapted to produce this temperature.

In a particularly advantageous embodiment, the section of the stabilizing support furthest from the hollow mould opens a flat surface for connection to the attachment unit. The attachment unit can then have a flat plate at which the stabilizing brackets of differently designed bending dies can be placed. Differently designed bending moulds can then be placed at the same attachment unit and it is not necessary to provide each bending mould with its own attachment unit.

In an advantageous embodiment, the contact surface is finished, in particular by polishing and/or coating. The refining can be, for example:

-after the manufacture of the hollow mould and before its connection with the stabilizer bracket;

-after the hollow mould is connected to the stabilizing support and before the ceramic is burnt;

-after the ceramic has been burnt.

It is also possible to carry out a plurality of refining steps at different points in time. It is preferred to polish the contact surfaces before the ceramic burns, since the contact surfaces can then also be processed more easily. The coating is preferably a ceramic coating, particularly preferably based on boron nitride or oxide ceramics or silicate ceramics, for example based on mullite, Al₂O₃Or a coating of silicon aluminum oxide. The coating imparts a high surface quality to the contact surface and achieves a high resistance to damage and scratch resistance, which is particularly advantageous when the contact surface is to be coated with a steel fabric for bending.

If the contact surface of the hollow mould is to have deviations from the set geometry (for example due to a non-optimal model surface or a non-optimal transfer of the mould surface onto the contact surface by means of a prepreg technology), the deviations can be corrected by means of a cutting process, in particular grinding. The contact surface is then machined before or after combustion in order to produce the calculated contact surface of the bending die. In a preferred embodiment, the cutting process is again carried out automatically by means of a CAD process, wherein the machine (CNC machine, computer numerical control) is provided with CAD data of the contact surface and the machine processes the contact surface by means of the CAD data.

Alternatively, the hollow mould can be provided with a through-going guide (hole), for example for screwing or riveting with a stabilizing bracket or an attachment unit. The leadthrough is then arranged in particular in the edge region of the hollow mould. Alternatively, the feed-through can also be used to exert a suction effect on the glass sheets during bending of the glass in order to suck the glass sheets at the contact faces, when the bending furnace is designed for this purpose. In this case, the leadthrough is distributed, in particular uniformly distributed, over the contact surface. These holes are preferably introduced before the ceramic is burnt, particularly preferably before the hollow mould is connected to the stabilizing support. Alternatively, a small tube or a small rod can also be used as a receptacle during the production of the hollow mould, which is removed later in order to form the passage.

The ceramic bending mould is preferably inserted into a bending device, in particular into a bending furnace, via a metallic attachment unit and is used there for bending one or more glass sheets. For this purpose, in an advantageous embodiment, the contact surface is coated with a steel fabric, as is also customary in conventional bending tools. The steel fabric prevents direct contact between the contact face and the glass sheet, thereby advantageously configuring the surface quality and visual quality of the bent glass sheet.

The invention also comprises a ceramic bending mould which is produced or can be produced by means of the method according to the invention.

The invention also comprises the use of a bending mould for ceramics according to the invention for bending, in particular hot bending, glass sheets, in particular for producing prototypes or small series with at most 1000 glass sheets. The glass sheet is preferably a window sheet for rail vehicles or motor vehicles, in particular a windshield sheet, rear window sheet, side window sheet or roof sheet for passenger cars.

The glass sheets to be bent comprise preferably soda-lime glass, as is customary for window sheets, but can also comprise other glass types, such as borosilicate glass, aluminosilicate glass or quartz glass. The thickness of the glass sheets is generally from 0.5mm to 10mm, preferably from 1mm to 5 mm. Typical temperatures for bending glass sheets are between 500 ℃ and 700 ℃, especially around 650 ℃ when bending sheets composed of soda lime glass.

Drawings

The invention is explained in detail below with the aid of figures and examples. The figures are schematic and not to scale. The drawings in no way limit the invention.

In the drawings:

figure 1 shows a cross-section during a first phase of an embodiment of a method for manufacturing a ceramic bending mould according to the invention,

fig. 2 shows a cross-section during a second stage of an embodiment of the method according to the invention, which follows the first stage in fig. 1,

figure 3 shows a cross-section of one design of a ceramic bending mould according to the invention during bending of a glass sheet,

figure 4 shows a cross-section during a method step of another embodiment of the method according to the invention,

FIG. 5 shows an alternative design of a bending die according to the invention, and

fig. 6 shows a flow chart of an embodiment of the method according to the invention.

Detailed Description

Fig. 1 schematically shows different method steps in a first stage of an embodiment of a method according to the invention for producing a ceramic bending mould.

First a mould 1 is manufactured (fig. 1 a). The model tool 1 is made of wood, for example, and is produced from larger wood pieces by means of milling and grinding. The model mold 1 has a mold face F-1 which is to some extent a positive copy (in a size ratio of 1: 1) of the contact face of the curved mold to be produced. The molding surface F-1 has the same geometric distribution of the radii of curvature as the contact surface. The same applies to the curvature direction: the contact surface is also convexly configured like the model surface F-1. The required shape of the contact surface is calculated beforehand using CAD methods common in the art (in particular as a compensated contact surface, which is calculated taking into account the sag after bending in order to achieve the desired final sheet geometry). The processing of the wood pieces for making the model mould 1 is automatically carried out on the basis of the CAD data.

The mould surface F-1 is then provided with a separating layer 2 (FIG. 1 b). The separation layer 2 is, for example, a plastic film made of PE and having a thickness of 10 μm.

The mat 3 of ceramic fibers is then arranged in layers on the separating layer (fig. 1c), so that the entire mould face F-1 is provided with the mat 3 and the entire layer built up by the mat 3 has a thickness of, for example, 10 mm. The felt 3 is impregnated with a ceramic suspension (presoaking-technique). The ceramic material of the fibers is, for example, an oxide material, such as alumina (Al)₂O₃) And the ceramic material of the suspension is a silicon aluminum oxide. The felt 3 is dried, thereby constructing a hollow mould 4 (fig. 1 d). Since the mould face F-1 is the male part of the desired contact face, said contact face F-K is formed by the surface of the hollow mould 4 facing away from the mould tool 4. In order to transfer the shape of the mould surface F-1 as accurately as possible to the contact surface F-K, the hollow mould 4 has a thickness which is as uniform as possible. The hollow mould 4 is removed from the mould part 1 after drying (fig. 1e), which can be achieved without difficulty due to the separating layer 2.

The hollow mould can now optionally be provided with a feedthrough, for example for subsequently fixing a stabilization bracket or through which a suction effect can be applied to the glass sheet later on bending of the glass. Likewise, the contact surface F-K can optionally be ground or coated in order to improve its surface quality.

Fig. 2 schematically shows the different method steps in a second phase following fig. 1 of an embodiment of the method according to the invention, in which a bending tool K according to the invention is produced from the hollow tool 4 (fig. 2a) produced according to fig. 1. For this purpose, a ceramic stabilizing support 5 is arranged at the surface of the hollow mould 4 facing away from the contact surface F-K (fig. 2 b). The hollow mould 4 and the stabilizing bracket 5 form a ceramic bending mould K according to the invention, the manufacture of which can now be finished by burning ceramic.

The stabilizer brackets 5 are constructed, for example, from ceramic rods which are screwed to one another and to the hollow mould 4. The ceramic material of the stabilizer 5 is, for example, likewise aluminum oxide (Al)₂O₃)。

Glass bending devices usually have standardized receptacles for exchangeable bending moulds. In order to be able to load the ceramic bending mould K into the glass bending device, the glass bending device is equipped with a metallic attachment unit 6, for example an attachment unit composed of stainless steel (fig. 2 c). The attachment unit 6 has, for example, a flat plate, at which the stabilization bracket 5 is arranged (for example, screwed) and, opposite the plate, has a section which is complementary to the receptacle of the glass bending device and can be inserted into the receptacle.

Fig. 3 schematically shows a ceramic bending mould K with an attachment unit 6, produced according to fig. 1 and 2, in use as intended. The bending die K is installed in a bending furnace, not shown, and is used for bending the glass sheet I. The contact surface F-K is coated with a not shown steel fabric for protecting the glass sheet I and is applied to the heated and softened glass sheet I, whereby the glass sheet I is bent according to the shape of the contact surface F-K. This effect can be achieved, for example, by blowing the glass sheet I by means of an upwardly directed air flow at the contact face F-K or by pressing the glass sheet I between the bending die K and a complementary lower bending die, not shown.

The glass sheet I is made of soda lime glass, for example, has a thickness of 3.5mm, and is provided as a rear window glass of a passenger car.

Fig. 4 schematically shows the manufacture of a hollow mould 4 during another embodiment of the method according to the invention. In distinction to fig. 1d, the mould surface F-1 of the mould 1 is a female part of the contact surface F-K. The mould surface F-1 has the same geometrical distribution of radii of curvature as the contact surface F-K, but with the opposite direction of curvature, i.e. the contact surface F-K is configured convexly, whereas the mould surface F-1 is configured concavely. The contact surface F-K is in this case formed by the surface of the hollow mould 4 facing the mould tool 4.

Fig. 5 shows an alternative embodiment of the bending tool K. The contact surface F-K is designed in a concave manner in this case. The stabilizing brackets 5 are thus placed at the opposite convex surfaces.

Fig. 6 shows an embodiment of the method according to the invention by means of a flow chart.

List of reference numerals

(K) Ceramic bending die

(1) Model die

(2) Separating layer

(3) Felt made of ceramic fibers

(4) Hollow mould of ceramic

(5) Stabilizing support

(6) Attachment unit for metal

(F-K) contact surface of ceramic bending die K

(F-1) mold surface of mold 1

(I) Glass sheet

Claims

1. Method for manufacturing a bending mould (K) for ceramics for glass sheets, comprising the following method steps:

(A) determining a contact surface (F-K) of the bending mould (K);

(B) -making a mould (1) with a mould surface (F-1) corresponding to said contact surface (F-K);

(C) -providing the mould surface (F-1) with a mat (3) of ceramic or glass fibers, which is impregnated with a suspension of ceramic, wherein the mat (3) is arranged on the separation layer (2) and dried, thereby producing a ceramic hollow mould (4) with the contact surface (F-K);

(D) removing the ceramic hollow mould (4) from the mould (1);

(E) providing the ceramic hollow mould (4) with a ceramic or metallic stabilizing support (5);

(F) -burning the ceramic hollow mould (4) with the stabilizing cradle (5), thereby producing a ceramic bending mould (K).

2. Method according to claim 1, wherein said molding surface (F-1) is a male or female part of said contact surface (F-K).

3. A method according to claim 1 or 2, wherein the mould (1) is manufactured by a cutting manufacturing method from a larger work piece, which is made of wood, plastic or resin.

4. Method according to any one of claims 1 to 3, wherein the mould face (F-1) is provided with a separating layer (2) before the mould face is provided with the felt (3), and wherein the separating layer (2) is constructed as a coating, a paper layer or as a film consisting of plastic.

5. Method according to any one of claims 1 to 4, wherein the fibres of the felt (3) are constructed of an oxide or silicate ceramic, in particular based on alumina (Al)₂O₃) Or mullite, or as glass fibers having a silica content of at least 80 percent by weight, and the suspension being composed of a silica-alumina oxide.

6. The method according to any one of claims 1 to 5, wherein the hollow mould (4) has a thickness of 1mm to 30 mm.

7. Method according to any one of claims 1 to 6, wherein the contact surface (F-K) of the hollow mould (4) is polished and/or coated, in particular with a coating based on an oxide ceramic or a silicate ceramic.

8. Method according to any one of claims 1 to 7, wherein the contact surface (F-K) is machined by grinding before or after combustion in order to correct deviations from the calculated contact surface (F-K).

9. Method according to any one of claims 1 to 8, wherein the hollow mould (4) is provided with a feedthrough.

10. Method according to any one of claims 1 to 9, wherein the stabilizing brackets (5) are formed by ceramic rods or tubes, preferably connected to each other and to the hollow mould (4) by gluing, nailing, riveting, screwing or plugging.

11. Method according to any one of claims 1 to 10, wherein a metallic attachment unit (6) is provided at the stabilizing cradle (5) and/or the hollow mould (4), said attachment unit being suitable for placing the bending mould (K) in a bending furnace.

12. Method according to any one of claims 1 to 11, wherein the combustion of the ceramic hollow mould (4) is carried out in a bending furnace.

13. Ceramic bending mould (K) manufactured according to the method according to any of claims 1 to 12.

14. Ceramic bending mould (K) according to claim 13, which is a press and/or suction bending mould with an upper part of the full area contact face (F-K).

15. Use of a ceramic bending mould (K) according to claim 13 or 14 for bending glass sheets (I), in particular for manufacturing prototypes or small batches with at most 1000 glass sheets (I).