DE102004052514B4 - Method and mold for casting glass blocks - Google Patents

Abstract

A method for casting glass blocks having a mass of at least 500 kg in the batch process, wherein a molten glass is poured into a metal mold (12) by means of a glass jet flowing from a feeder at a rate of at least 50 kg / min Metal mold (26) releasable ceramic insulation (30) is lined, whose thermal conductivity in the range between 800 and 1400 ° C between 0.2 and 2.0 W · K ^-1 · m ^-1 .

Description

The The invention relates to a method for casting glass blocks with a mass of at least 500 kg in the batch process.

The The invention further relates to a mold suitable for casting such large glass blocks and can be used in mass production.

In Bach, Hans (Editor): "Low Thermal Expansion Glass Ceramics", Springer Verlag Berlin, Heidelberg, New York, 1995, ISBN: 3-540-58598-2, is on pages 107-214 the technology of making the glass ceramic Zerodur ^® described which is manufactured by the applicant and sold In Zerodur is a lithium aluminosilicate glass-ceramics with very low thermal expansion and high stability, which is used as a base material for a variety of precision applications use, for example for the production of mirrors. for large-scale telescopes, but which is also used to make precision components on a small scale, such as for the fabrication of microlithographic stages.

at The production of such a glass ceramic is in several stages proceed. First is used for this purpose lithium aluminosilicate glass in a melted, refined and homogenized.

to Production of large Components, the melting process is discontinuous. From the melting tank the glass melt according to the above mentioned Book issued in a preheated form. For the production of large parts The mold is filled with a flow rate of about 200 kg / min.

To the casting process will the shape first down to a temperature nearby the transformation temperature (675 ° C) cooled relatively quickly, then with a sufficiently slow cooling rate to room temperature cooled. This is followed by an optical inspection for inhomogeneities, cracks and the like, before the glass block of a thermal treatment is subjected to transfer the glass block into a glass ceramic what is referred to as ceramization, before the Kerami tion is the Glass block usually mechanically pretreated, for example sawed or ground to achieve a close to net shaping. To Completion of ceramization, depending on the size of the glass block up to several Months to complete the completion of the produced glass ceramic block, for example, from this one Mirror for to make a telescope.

It understands that for the production of a glass block or a glass ceramic block greater Dimension that for precision applications is suitable, all Manufacturing steps must be coordinated and considerable effort is required, for example, a glass block with several meters diameter in high homogeneity and precision to be able to.

One These problems exist in casting a homogeneous glass block with a large volume.

this includes is intended in the context of this application a glass block with a mass of at least 500 kg.

at the production of Zerodur glass ceramics as well as in the production of optical glasses for large volume Optical components, such as lenses, are known in the art usually forms of refractory material used, depending on the while casting used temperature, the type of glass, the size of the glass block and is suitably adapted and selected on the basis of further parameters. Such forms of refractory material may u. a. made from raw materials containing silica, magnesia, mullite, alumina and other raw materials can. The production of suitable refractory shapes is the most diverse in the glass industry Applications basically known.

One Disadvantage of using refractory shapes is that forms usually in each case when making a single casting become useless. This refractory forms are basically about for the production of very large volumes Glass components suitable, such as for telescope mirror, since this If necessary, the high costs can be accepted.

For a serial production of large volume Glass components, however, the use of refractory shapes is very Time and cost intensive and therefore not very suitable.

Another problem when casting large-volume glass components is especially when the glass components are to be produced with a shape approximated to a cube or a sphere. If, for example, a cylindrical block of glass is produced, the influence of the shape on the quality of the glass block during the production in the casting process can be described with a form factor R = h / d, where h corresponds to the height of the glass block and d to the diameter. While in the production of large-volume glass components such as lenses or telescope mirrors the form factors are usually below 0.1, are Recently, large-volume glass components are required, whose form factors are above 0.1, for example in the range between 0.1 and 0.3. Such large-volume glass components are required for example in larger quantities for the production of prisms.

at so big Form factors, however, result in further problems due to the casting process itself. the formation of inhomogeneities, in particular inclusion from larger and larger lead to smaller bubbles, for streaking and the like more. This problem will arise fluidic effects of the glass jet entering the mold is returned at large form factors, since the Form during the casting process cooled considerably faster in peripheral areas than in the area, in which the liquid Glass jet enters the mold. This problem is caused by the low thermal conductivity considerably strengthened by glass. Especially in the production of large-volume glass components in one Mass of at least 500 kg and with form factors greater than 0.1, it is extremely difficult to obtain homogeneous castings.

The mentioned at the beginning publication while basically revealing that certain molds can be used which are provided with a mold release agent to a dissolution of the glass block to allow out of shape.

however lacks any information regarding the design of the molds, which address the above-described manufacturing problems greater glass blocks avoid it.

From the DE 666 990 A discloses a method and an apparatus for producing large castings of glass, the glass melt being filled into a mobile mold covered by a heatable hood consisting of a refractory, highly heat-insulating ceramic material held together by a metal outer mold , For pouring, the molten glass is taken from a storage container and introduced by means of ladles or the like into the oven, in which the mold is received, so as to feel the shape.

With Although such a method can in principle produce large glass blocks, However, due to the filling by means of ladles arise considerable inhomogeneities and impurities of the manufactured glass blocks.

According to the WO 03/038361 A1 For example, there is known a method of vitrifying contaminated waste material which involves providing a container with a ceramic liner, placing the waste within the lined container, heating the material by direct electrical heating to melt the material, and so after cooling solidified, glazed mass to produce.

One Such method is obviously not suitable to large glass blocks with a good homogeneity manufacture.

In front In this background, the invention is based on the object Method of pouring glass blocks with a mass of at least 500 kg in the batch process specify with which the problems in particular with the production of components with large Form factors are reduced, so as to produce even large-volume glass blocks with big Form factors with good homogeneity to enable. Furthermore, the method should as possible for one Series production should be suitable, finally, a suitable form be specified for uses such a casting process can be.

This object is achieved by a method for casting glass blocks having a mass of at least 500 kg in the batch process, in which a glass melt is poured by means of a feeder-flowing glass jet at a rate of at least 50 kg / min in a metal mold with is lined with a detachable from the metal mold ceramic insulation whose thermal conductivity in the range between 800 and 1400 ° C between 0.2 and 2.0 W · K ^-1 · m ^-1 .

The object is further achieved by a mold for the discontinuous casting of large glass blocks having a mass of at least 500 kg, the mold having a metal mold consisting of a high-temperature steel and lined with a ceramic insulation detachable from the bottom and the side wall of the mold, whose thermal conductivity lies in the range between 800 and 1400 ° C, between 0.2 and 2.0 W · K ^-1 · m ^-1 .

The The object of the invention is completely solved in this way.

In accordance with the present invention, reusable metal molds can now be used to cast large blocks of glass lined by suitable ceramic insulation which are releasable from the metal mold. Due to the specially set thermal conductivity of the ceramic insulation used, the problem of the formation of inhomogeneities in the casting of großvolumi conditions glass blocks with large form factors of 0.1 and greater significantly reduced. In addition, by the use of reusable metal molds now a cost-effective manufacturing process for a series production possible.

The Ceramic insulation acts as a release agent, causing a loosening of Glass block ensured by the metal mold after manufacture is. At the same time protects the ceramic insulation prevents the metal mold from being damaged or softened too high a thermal load.

In Advantageous development of the method according to the invention is the inside the metal mold is lined with a solid layer of fused silica, on which a quartz sand layer is applied.

According to one alternative version The invention is the metal mold with a fiber layer of high temperature resistant Lined fibers.

hereby let yourself achieve a particularly advantageous manufacturing process, since the Fiber layer of prefabricated mats in easier and less expensive Be used for lining the inner surface of the mold can, while maintaining the strength the fiber layer can be suitably adjusted.

For this can used in an advantageous embodiment of this embodiment fiber layers made of zirconium oxide fibers, fused silica fibers, silicon carbide fibers, Aluminum silicate fibers or mixtures thereof.

such Fibers have a sufficiently high temperature resistance on the metal molds used, for example steel molds, before the high casting temperatures to protect.

The Strength The fiber layer is in this case preferably between about 5 and 100 mm, preferably set between 10 and 50 mm.

On This way, the necessary thermal insulation in particular dependent on from the mass and the shape factor of the glass block to be cast in appropriate Be customized.

In Advantageous development of this embodiment is the strength of Insulating layer along the inner surface of the metal mold locally changed.

in this connection is preferably the strength the insulating layer in the middle region of the soil less than executed in the border areas.

On In this way, an improved homogeneity of the cooling behavior is achieved because the casting mold during the casting process cools much faster in the edge areas than in the central area, in which the glass melt enters. Thus, by a lesser Strength the insulating layer in the central region of the soil and by a higher strength of the Insulating layer in the edge areas a more uniform temperature distribution causes, resulting in improved homogeneity of the glass block produced supports and counteracts the adverse effects of large form factors.

In preferred development of the invention, the casting takes place with a filling speed between 50 and 300 kg / min, in particular with 60 to 200 kg / min.

at the use of such filling speeds can be very in connection with the designed forms according to the invention homogeneous large volume Glass components also with large form factors which are between 0.1 and 0.3 up to a maximum of about 0.5 can.

in this connection the form factor R = h / d is defined as the ratio of height h to transverse extent d, wherein the transverse dimension d in the case of a cylindrical shape thereof Diameter is and in the case of a cuboid shape whose diagonal is.

In preferred embodiment of the invention consists of the metal mold a heat-resistant steel.

On this way you can the molds in conjunction with appropriate ceramic linings, after every watering Completely to be released from the mold, for many Castings in one Series production can be used.

According to one Another advantageous embodiment of the invention is a form used, which has in its center a flow opening through which those from above Glass melt before beginning the filling process first comes down. After setting a sufficient glass quality is the Metal mold with a closure arranged below the metal mold (lower pair of scissors) closed. The metal mold is lowered and the shutter is raised so that the molten glass supplied from above while the casting process maintains a defined distance to the bottom of the metal mold.

With such a procedure can be a glass block with excellent homogeneity (physical properties of the glass such. Refractive index, thermal expansion, absorption, bubble and streaking quality etc.).

In order to ensure a homogeneous temperature distribution on the ground during the casting process, the lower scissors is also previously with Kera mikisolierung covered whose thermal conductivity and strength is substantially identical to the ceramic insulation used in the adjacent area of the mold.

In additional Development of the invention, the glass feed before the end of casting process caught by a closure (upper scissors) above the metal mold and remove the metal mold from the area of the closure.

Further The mold is preferably before and during the casting process means A top heating system specifically heated locally and the shape in the area of Soil and its sidewall cooled specifically to one for the casting process to achieve optimal temperature distribution.

Also This counteracts the generation of inhomogeneities at the end of the casting process.

It it is understood that the above and the following yet to be explained features of the invention not only in the respective specified combination, but also usable in other combinations, without the To leave frame of the invention.

Further Features and advantages of the invention will become apparent from the following Description of a preferred embodiment with reference on the drawing.

The single figure shows a highly simplified, schematic representation a casting mold according to the invention associated upper and lower scissors and above arranged melting tank.

In the figure, an apparatus which can be used for the method according to the invention is shown very schematically and in total with the numeral 10 designated.

The device 10 has a melting tank 12 with standard refractory lining, in which a glass melt 14 is produced. At the bottom of the melting tank 12 is a closure or feeder 16 arranged, from the open state down a liquid glass jet 22 can exit down.

Below the melting tank 12 is a total with the numeral 24 designated form arranged. Form 24 has a cylindrical metal shape 26 made of heat-resistant steel, whose inner surface is completely covered with a ceramic insulation 30 is lined in the form of a layer of a ceramic fiber material of high temperature resistant fibers. In the middle of the bottom of the metal mold 26 is a circular opening 28 provided, the size of which is measured such that, with appropriate positioning of the metal mold 26 below the melting tank 12 the emerging liquid glass jet 22 first through the opening 28 can pass down. This opening 28 can by a so-called lower scissors 20 be closed, the means of a punch up against the metal mold 26 can be moved to the opening 28 to close.

Between the feeder 16 the melting tank 12 and the shape 24 is an upper pair of scissors 18 arranged with two movable segments, through which the glass jet 22 can be collected and interrupted at the end of the casting process.

The upper pair of scissors 18 is in a section 34 an upper heating 32 movably recorded. The upper heating 32 has a plurality of individually controllable heating zones, by means of which a targeted locally and temporally controllable temperature distribution during the casting process can be adjusted.

The metal mold 26 has a bottom, which in a manner not shown with the side wall of the metal mold 26 is detachably connected. In addition, the side wall of the metal mold 26 in segments, eg. B. two half-shells, divided, which are releasably connected together in a manner not shown.

example

It is a glass of the following composition in the melting tank 12 melted (in% by weight on an oxide basis): SiO ₂ 55.5 Al ₂ O ₃ 25.3 P ₂ O ₅ 7.9 Li ₂ O 3.7 Na ₂ O 0.5 MgO 1.0 ZnO 1.4 TiO ₂ 2.3 ZrO ₂ 1.9 As ₂ O ₃ 0.5.

This starting glass, which can be used for the production of the lithium-aluminosilicate glass ceramic Zerodur ^® is, for example, melted in a melting tank with 28 m ³ for a period of several days, wherein the temperature is maintained at about 1600 ° C. The decomposition of As ₂ O ₃ produces refining gases, which take small gaseous inclusions and homogenize the melt. During the refining phase as well as during a subsequent cooling phase, the glass melt is further homogenized. During a subsequent cooling phase, which may also take several days, the temperature of the molten glass is reduced to about 1400 ° C.

As a casting mold 24 becomes a metal mold 26 made of high-temperature steel with a diameter d of 2.5 m and a filling height h of 50 cm, so that the form factor R = h / d is about 0.2. The used metal mold 26 may for example have a wall thickness of about 3 cm and lined with a lining of zirconia fibers in mat form with a density of about 70 kg / m ³ . While the cylindrical surface is lined, for example, with zirconium oxide fiber mats a total thickness of 25 mm and also the bottom of the metal mold between the maximum diameter and a diameter of about 1.5 m is lined with this thickness, the central region of the bottom is up to a diameter of 1.5 m only lined with a wall thickness of about 10 mm, whereby naturally the central opening 28 is omitted for the passage of the glass beam. Alternatively, a continuous or quasi-continuous reduction in the strength of the insulation from the edge region to the opening 28 possible.

The lower pair of scissors 20 comes with a removable ceramic insulation 30 covered, their thermal conductivity and layer thickness of the ceramic insulation used in the adjacent area of the soil 30 equivalent.

At the beginning of the casting process, the metal mold is preheated by means of an upper heating to about 800 ° C, wherein the ceramic insulation 30 is cleaned of organic components or impurities. Then the feeder 16 the melting tank 12 opened, leaving a glass jar 22 first through the opening 28 at the bottom of the metal mold 26 comes down and on the underlying lower scissors 20 which is thus cleaned of impurities. After a short while, the lower scissors will 20 lifted upwards, leaving the opening 28 the metal mold 26 is closed and the mold now with a filling rate of, for example, about 150 kg / min. is filled.

At the end of the casting process, the upper scissors 18 closed to the glass jar 22 to interrupt.

By raising the upper heating is now the molten glass in the form 24 rapidly to a temperature above the transfor mation temperature, in the present case, for example, to about 700 ° C, cooled.

Form 24 is then out of the area below the melting tank 12 moved away laterally and moved into a furnace for controlled cooling. To shrink the metal mold 26 to avoid the glass block during the cooling process, the metal mold is removed from the glass block after sufficient solidification thereof.

The controlled cooling to room temperature with sufficiently low cooling rate, to avoid tensions and the formation of cracks.

Of the thus produced glass block can after an optical inspection on Freedom from bubbles, cracks, etc., for example, a temperature treatment be subjected to ceramization.

It shows that very homogenous, crack-free glass blocks or Glass ceramic blocks which are largely free of inhomogeneities, such as Bubbles, streaks and the like are.

It it is understood that the above description of an embodiment is merely exemplary nature and that depending on the nature of used glass, the volume of the glass block to be cast, the casting temperature etc., other ceramic liners can be used, as in the beginning has been described.

Also It is understood that the thermal conductivity and the strength the ceramic lining used adapted in a suitable manner can be used to avoid rapid cooling in the edge area, However, in the middle of the glass block to ensure greater heat dissipation, so an overall even temperature distribution to obtain.

The Casting according to the invention is suitable for casting any glasses independent of the composition, provided that the casting temperature in a used for the Material of the metal mold and the ceramic lining used suitable Area is located.

Claims (21)

Method for casting glass blocks having a mass of at least 500 kg in the batch process, in which a molten glass is melted by means of a glass jet flowing from a feeder into a metal mold at a speed of at least 50 kg / min ( 12 ) cast with one of the metal molds ( 26 ) detachable ceramic insulation ( 30 ) whose thermal conductivity is in the range between 800 and 1400 ° C between 0.2 and 2.0 W · K ^-1 · m ^-1 . Method according to Claim 1, in which the inside of the metal mold ( 26 ) is lined with a solid layer of fused quartz, on which a quartz sand layer is applied. Method according to Claim 1 or 2, in which the metal mold ( 26 ) with a fibrous layer ( 30 ) is lined from high temperature resistant fibers. Method according to Claim 3, in which the metal mold ( 26 ) with a fiber layer consisting of zirconium oxide fibers, fused silica fibers, silicon carbide fibers, aluminum silicate fibers or mixtures thereof ( 30 ) is lined. Process according to Claim 3 or 4, in which the thickness of the fiber layer ( 30 ) is set between 5 and 100 mm, preferably between 10 and 50 mm. Method according to Claim 5, in which the thickness of the insulating layer ( 30 ) along the inner surface of the metal mold ( 26 ) is changed locally. Method according to Claim 6, in which the thickness of the insulating layer ( 30 ) is carried out in the middle region of the soil lower than in the edge regions. Method according to one of the preceding claims, in which the glass feed before closing of the casting process by a closure, the upper scissors ( 18 ), above the mold ( 24 ) and the shape ( 24 ) from the area of the closure ( 18 ) Will get removed. Method according to one of the preceding claims, in which a mold ( 24 ), which has a form factor (R) defined as the ratio of height (h) to transverse extent (d) with R = h / d of at most 0.5, preferably in the range between 0.1 and 0.3, the Transverse expansion (d) in the case of a cylindrical shape whose diameter is and in the case of a cuboid shape whose diagonal. Method according to one of the preceding claims, in which a metal mold ( 26 ) is used from a high temperature steel. Method according to one of the preceding claims, in which a mold ( 24 ), which at its center a flow opening ( 28 ), through which a glass jet ( 22 ) before the beginning of the filling process, first comes down and by a below the metal mold ( 26 ) arranged shutter, the lower scissors ( 20 ), with the lower scissors ( 20 ) after cleaning through the glass jet ( 22 ) is closed and raised to the flow opening ( 28 ) to close. Method according to claim 11, wherein the lower scissors ( 20 ) is covered with a detachable ceramic insulation whose thermal conductivity is identical to the ceramic insulation in the adjacent area of the mold ( 24 ). Method according to one of the preceding claims, in the ceramic insulation before the casting process by an upper heating is thermally cleaned. Method according to one of the preceding claims, in which the mold ( 24 ) is preheated before the casting process by means of an upper heater and adjusted to a defined temperature field. Method according to one of the preceding claims, in the shape at least in the area of its bottom and / or its edge while the casting process chilled becomes. Method according to one of the preceding claims, in which the mold ( 24 ) is filled at a rate between 50 and 300 kg / min, in particular at 60 to 200 kg / min. A mold for the discontinuous casting of large blocks of glass having a mass of at least 500 kg, the casting mold ( 24 ) a metal mold ( 26 ), which consists of a high-temperature steel and which is connected to one of the bottom and the wall of the metal mold ( 26 ) detachable ceramic insulation ( 30 ) whose thermal conductivity in the range between 800 and 1400 ° C is between 0.2 and 2.0 W · K ^-1 · m ^-1 . Mold according to Claim 17, in which the inner surface of the metal mold ( 26 ) is lined with a solid layer of fused quartz, which is provided with a quartz sand layer. Mold according to Claim 17, in which the inner surface of the metal mold ( 26 ) with a fiber layer consisting of zirconium oxide fibers, fused silica fibers, silicon carbide fibers, aluminum silicate fibers or mixtures thereof ( 30 ) is lined. Mold according to one of Claims 17 to 19, in which the metal mold ( 26 ) has a detachable from the bottom edge. The mold of claim 20, wherein the rim is segmented is split, the solvable connected to each other.