WO2007049149A2

WO2007049149A2 - Continuous method and system for manufacturing of polycrystalline glass-ceramic compositions

Info

Publication number: WO2007049149A2
Application number: PCT/IB2006/003350
Authority: WO
Inventors: Tsvi Kaufman; Evgeny Meyerovich
Original assignee: Hyattville Company Ltd.
Priority date: 2005-10-28
Filing date: 2006-10-30
Publication date: 2007-05-03
Also published as: WO2007049149A3

Abstract

The present invention discloses a method for the preparation of a polycrystalline glass-ceramic comprising mixing raw materials capable of crystallization, heating the mixture of raw materials to form a molten glass and subjecting the molten glass to a heating and cooling temperature regime to bring about crystallization and form a polycrystalline glass-ceramic, characterized in that, prior to crystallization, pigment is added to the molten glass in a coloring unit comprising a changeable chamber for receiving the molten glass and pigment and/or the molten glass is subjected to a rolling and forming process comprising the use of horizontally (5,6) as well as orthogonally (16,17) positioned rollers, relative to the glass ribbon (18) . The present invention further discloses a coloring unit for coloring a molten glass in a device for manufacturing a poly-crystalline glass-ceramic comprising a separate changeable chamber for receiving the molten glass and pigment. The present invention finally discloses a rolling and forming unit for rolling and shaping the molten glass comprising at least one pair of horizontal (5,6) as well as orthogonal (16,17) rollers.

Description

CONTINUOUS METHOD AND SYSTEM FOR MANUFACTURING OF POLYCRYSTALLINE COMPOSITIONS

The present invention relates to the manufacturing of polycrystalline compositions, especially glass-ceramics .

Glass ceramics are produced through the crystallization of glass - where the glass component is converted into a fine-grained polycrystalline ceramic by a controlled nucleation and crystal growth heat treatment schedule. Methods for manufacturing polycrystalline glass- ceramics typically comprises the steps of mixing raw materials capable of crystallization, heating the mixture of raw materials to form a molten glass, rolling the molten glass to form a glass ribbon and subjecting the glass ribbon to a controlled heating and cooling temperature regime to bring about crystallization so that the final product is a polycrystalline glass-ceramic. Pigments typically are part of the starting raw materials. Such methods are described in e.g. US 3,841,856, US 4,055,436 and US 2005/0016214.

US 4,055,436 and US 2005/0016214 further disclose the importance of controlling the viscosity of the molten glass during processing. US 4,055,436 discloses that the viscosity of molten glass can be increased by including K₂O in an amount of 4 to 7% by weight in the composition. US 2005/0016214 describes that the molten glass passes a viscosity-adjusting unit disposed downstream of the melting furnace and upstream of a roller unit.

Methods for the manufacturing of glass-ceramic products further have been developed as a potential solution for disposal of industrial residues like coal fly ash. However, the high iron content of the coal ash provides the glass-ceramic products with a dark color, which limits their possible applications.

US 6,825,139 discloses a method for the preparation. of a polycrystalline composition using coal ash as starting material, whereby differences in starting materials and in heating and cooling conditions were shown to influence the color and texture of the end products.

There is a need for a method that preferably can be performed in a continuous way and that enables as much as possible freedom with regard to the choice of process conditions that influence the properties, e.g. color, texture and/or shape, of the final product.

According to one aspect of this invention, there is provided a method for manufacturing a polycrystalline glass-ceramic composition advantageously allowing such freedom of process adjustment.

In one embodiment of the invention, pigments are applied to the process separately from the crystal-forming raw materials at a stage prior to crystallization, but after melting of the crystal-forming raw materials using a coloring unit comprising a changeable chamber for receiving molten glass and pigment and a stationary pendent arch positioned above the changeable chamber. This advantageously allows adjustment of the type of pigment (s) and concentration thereof separately from the composition of the crystal-forming raw materials.

In another embodiment of the invention, the molten raw materials, also called molten glass, is subjected to a particular rolling and shape forming process. This advantageously allows forming the glass material to a desired shape prior to crystallization.

Thus, there is provided a method for manufacturing a polycrystalline glass-ceramic comprising mixing raw materials capable of crystallization, heating the mixture of raw materials to form a molten glass and subjecting the molten glass to a heating and cooling temperature regime to bring about crystallization and form a polycrystalline glass-ceramic, characterized in that, prior to crystallization, pigment is added to the molten glass in a coloring unit comprising a changeable chamber for receiving the molten glass and pigment, and/or the molten glass in the form of a ribbon is subjected to a rolling and ^"forming process, wherein rollers are used that are positioned horizontally as well as orthogonally relative to the glass ribbon.

The raw materials that are used may be any raw materials that are capable of crystallization and suitable to form a polycrystalline glass-ceramic. The concentration of each individual component of the raw materials may be adjusted depending on the desired properties of the end product. Preferably, the raw materials comprise industrial waste such as coal fly ash, salt cake oxides, metallurgical slag, etc., in a weight percentage of 50%-95%.

The raw materials typically may comprise at least Al₂O₃, CaO and SiO₂, in ranges of e.g. 10-20%, 25-45% and 22-50%, respectively.

Mixing of the raw materials may occur in any suitable mixing device for powders known to the person skilled in the art.

After mixing, the mixture of raw materials may optionally be charged into a heating unit, for instance a rotary kiln, to remove volatile components. This step is also commonly known as burning. Heating may occur for 1-1.5 hours at a temperature of 650-750⁰C.

The mixture of raw materials, optionally burnt, is transferred to a melting unit, wherein the mixture is heated to form a molten glass. The melting unit may be any melting furnace known to the skilled person. Melting may occur for a few hours at a temperature varying from 1400⁰C - 1600⁰C. Exact temperature and duration of the melting step may depend on the nature and amount of material to be subjected to melting.

In one embodiment of the invention, the molten glass then is transferred to a coloring unit comprising a changeable chamber for receiving the molten glass and pigment. A pendent arch of the coloring unit positioned above the changeable chamber forms the stationary part when changing the changeable coloring chamber for another equivalent changeable chamber.

The transfer to the coloring unit may conveniently be done through a confluent chute with a temperature of 1250⁰C - 1400⁰C.

The coloring unit thus comprises a changeable chamber for receiving the molten glass as well as the pigment (s). A changeable chamber means that the chamber is changeable for another equivalent chamber. A changeable chamber for receiving the molten glass and pigment advantageously provides freedom to add to the process any type of pigment or mixture thereof in any concentration, independently from the raw materials capable of crystallization. It further advantageously allows a replacement of one pigment (mixture) for another without the need to interrupt the process. The latter would be necessary if pigments are added simultaneously with other raw materials at the onset of the process. Thus, the use of a coloring unit comprising a changeable coloring chamber advantageously allows the process to be performed in a continuous fashion. The volume of the molten glass in the changeable chamber preferably is 0.5%-5% of the volume of the molten glass in the glass melting furnace.

The changeable chamber comprises (from up- to downstream direction) a reaction zone for adding pigment to the molten glass and stirring and homogenizing the molten glass, a settling zone, a downward baffle, a cooling zone and a tap hole for discharging the molten glass for further processing. The dimensions of the changeable chamber advantageously allow proper control of the viscosity- characteristics of the molten glass. For instance, the pool depth of the molten glass in the reaction zone of the changeable chamber is less than the pool depth of the molten glass in the settling and cooling zone. In addition, the volume of the molten glass in the settling zone is smaller than the volume of the glass in the cooling zone.

The changeable coloring chamber preferably is a chamber as described in a further aspect of this invention. Next to the changeable chamber, the coloring unit comprises a pigment feeder, a mixing device, a heating device and/or a cooling device and a pendent arch positioned above the changeable chamber.

The pigment feeder comprises a metal or ceramic pipe connected to automatic pigment stock silos. The pigment feeder is standard equipment for material supply.

The mixing device ensures material homogeneity in the chamber and may be a mechanic, an electric, a pneumatic, a magnetic and/or a hydraulic mixing device. Preferably, a mechanic mixing device with electric motor is used.

The heating and/or cooling device will keep the glass in the chamber at a suitable temperature during coloring, to ensure molten glass homogeneity and to maintain a proper viscosity for further processing of the molten glass.

Through the pendent arch, pigment supply, stirring and heating and/or cooling can be effectuated in the changeable chamber.

The pigment may be added to the molten glass as a powder and/or as a melt.

The pigment may be any pigment suitable for providing color to a polycrystalline glass-ceramic. It may be a metal oxide and/or a spinel and/or another coloring agent. Preferably, the pigment is selected from the group consisting of NiO, which is green, Cu₂O, which is red, MnO₂, which is black, CoO, which is black, Fe₂O₃, which is brown, and Cr₂Oa, which is green, spinel of Zn-Cr-Ni-Al oxide having grey color, spinel of Sn-Si-Ca-Cr-Zn oxide having pink color, zircon of Zr-Si-Pr oxide having yellow color, zircon of Zr-Si-V-Pr oxide having green color, zircon of Zr-Si-V oxide having blue color, spinel of Al-Co- Cr-Zn oxide having blue color, spinel of Al-Zn-Fe-Cr oxide having brown color, spinel of Fe-Cr-Zn-Al oxide having gold color, spinel of Fe-Cr-Zn oxide having brown color, spinel of Fe-Cr-Ni-Mn oxide having black color, silver-containing mordant-staining material and/or gold-containing mordant- staining material.

The melting furnace and the changeable chamber of the coloring unit are provided with a tap hole for discharging the molten glass for further processing.

In a preferred embodiment, a cooling frame is inserted into the tap hole for discharging the molten glass for further processing, in such a way that the glass is transferred through the cooling frame before further processing occurs. The presence of a cooling frame has several advantages. For instance, the presence of a cooling frame allows control of the flow, velocity and volume of the glass. In addition, the surface of the glass is slightly cooled by the cooling frame, providing a proper plasticity of the glass. Furthermore, the dimensions of the opening of the cooling frame determine the cross-sectional dimensions of the final polycrystalline product, providing for a simple adjustment of the dimensions of the opening of the cooling frame depending on the desired cross-sectional dimensions of the final product. Further processing for instance may be into a unit for rolling the molten glass. The cooling frame preferably is water cooled. After coloring, the colored molten glass may be transferred to either a commonly known rolling unit or to a particular rolling and forming unit according to the present invention.

In another embodiment of the invention, the molten glass, whether or not subjected to a previous coloring process, is subjected to a particular rolling and shape forming process, comprising the use of pairs of horizontally as well as orthogonally positioned rollers relative to the glass ribbon.

When the molten glass is not subjected to a coloring process, care should be taken to include measures for appropriate control of the temperature of the molten glass prior to rolling and forming, which control otherwise would have occurred in the coloring unit. For instance, a unit corresponding to the coloring unit may be used, but without the addition of any pigment. Alternatively, additional heating and/or cooling devices may be installed prior to rolling and forming. Thus, the (colored) molten glass continues to flow from a preceding unit, e.g. the melting furnace or the coloring unit, onto a rolling and forming unit.

The rolling and forming may occur in one unit, i.e. using one engine, one cooling system, and the like, or may occur in different units. In the latter case, the shape forming is done directly after and close to the rolling so as to maintain a proper viscosity of the glass.

Rolling comprises transfer of the molten glass over at least one pair of horizontal rollers, allowing the formation of a ribbon of molten glass, as is commonly known to the person skilled in the art.

The length of the horizontal rollers may relate to the width of the tap hole of the melting furnace or changeable chamber of the coloring unit.

Throughout this invention, the term "horizontal" or "horizontally positioned" roller is used for a roller that extends substantially horizontally to define the top and under side of the glass ribbon. To keep the molten glass in a suitable condition for rolling, forming and proper crystallization, and to allow production of straight (plates) and shaped materials on an industrial scale, the temperature (influencing viscosity) and/or velocity of the molten glass being transferred over the horizontal rollers and being subjected to shape forming should be controlled at specific optimal values that do not tolerate large deviations. For instance, measures are taken to enable maintenance of the temperature within an optimal range that does not tolerate a Δ- temperature larger than about 20-50⁰C. This is in sharp contrast to the processing of molten glass for amorphous glass manufacturing, tolerating a much larger Δ- temperature of >150°C. A first temperature control measure is provided by the cooling frame inserted into the tap hole of the preceding unit.

Additional temperature control is provided by allowing the distance (in vertical and horizontal direction) between the tap hole of the preceding unit and the horizontal rollers of the rolling and forming unit to be varied.

In addition, the horizontal rollers are cooled by water and/or steam and/or air, whereby the extent of cooling may advantageously be precisely adjusted.

In addition, a pair of horizontal rollers preferably comprises two rollers of different diameters, with the bottom roller having the larger diameter. More preferably, the diameter of the top roller is 10%-95% of the diameter of the bottom roller.

The angle α between the plane connecting the axes of the horizontal bottom and top roller and the horizontal plane may further be varied, preferably the angle is 30°- 180 °C. Variation of this angle α advantageously allows adjustment of the extent of exposure of the glass ribbon to the surface of the cooled horizontal bottom roller.

Upstream of the horizontal rollers, orthogonal protecting rollers may be placed at each edge of the glass ribbon to roughly provide the glass ribbon with a preliminary direction and shape. Preferably, at least one pair of orthogonal protecting rollers is placed, the rollers of a pair at each edge of the glass ribbon. Up to five pairs conveniently may be placed. Throughout this invention, the term "orthogonal" or orthogonally positioned" roller is used for a roller that extends substantially orthogonally relative to the glass ribbon to define the edges of the glass ribbon. Conveniently, a deviation of ± 10 degrees to this orthogonality is allowed.

Forming allows the formation of shapes in the glass. Forming according to the invention comprises the use of orthogonal forming rollers placed at each edge of the glass ribbon, downstream of the horizontal rollers.

Preferably, one to five pairs of forming rollers may be used, the rollers of a pair at each edge of the glass ribbon. Preferably, the orthogonal forming rollers are placed as close as possible to the horizontal rollers, whereby the rollers of the first pair of forming rollers may be in contact with a horizontal roller. The shape of the forming rollers may preferably be adapted to accommodate the desired form of the final polycrystalline product, e.g. may be adapted to ensure uprising and/or bending and/or ends forming and/or other shape forming of the glass ribbon.

The horizontal bottom and top rollers and/or the orthogonal forming rollers may have a polished surface and/or a surface with a pattern, to create a suitable finished product surface by means of "printing".

The rollers may be metal rollers or metal rollers with ceramic covering, cooled by water and/or steam and/or air, preferably by water. Preferably, a rolling and forming unit as provided in a further aspect of this invention is used for rolling and forming the molten glass.

After rolling and shape forming, the (colored) glass is transferred to a heating and cooling unit (crystallization unit) for annealing and crystallization.

Annealing and crystallization may be done in one combined unit or in two separate, disconnected units. The transfer may be done on rolls of any material, e.g. metal rolls and/or ceramic rolls, or preferably on a movable table. Annealing is done to eliminate stress created in the glass ribbon during processing. The crystallization unit preferably is a crystallization tunnel, more preferably a lehr conveyer. For annealing and crystallization, the glass composition, preferably in the form of ribbon(s), is exposed to a controlled temperature regime comprising temperature changes between 700 °C - 1200⁰C during 1-5 hours. See for instance US 2005/0016214. The controlled heating and cooling creates the desired mechanical characteristics, color shades and surface texture of the resulting polycrystalline glass-ceramic.

In a preferred embodiment, the method according to the invention comprises the coloring and the rolling and forming steps as specified above. In particular, the method according to the invention comprises the steps of: (a) mixing raw materials capable of crystallization; (b) optionally charging the mixture of raw materials to a heating unit and heating the mixture to remove volatile compounds; (c) transferring the mixture of raw materials to a melting unit and heating the mixture to form a molten glass; (d) transferring the molten glass to a coloring unit comprising a changeable coloring chamber to color the molten glass with a suitable pigment; (e) transferring the colored molten glass to a rolling and forming unit to roll and form the glass; (f) transferring the formed glass to an annealing and crystallization unit to subject the formed glass to a heating and cooling temperature regime to form a polycrystalline glass-ceramic. The invention advantageously allows performance of the method of the invention in a continuous fashion, without a need for interruption when a change of e.g. color and/or shape is desired. In a further aspect, the present invention relates to a polycrystalline glass-ceramic obtainable by the method of the first aspect.

In still a further aspect, the present invention relates to devices for use in manufacturing the polycrystalline glass-ceramic according to the method of the first aspect.

Schematic drawings of the devices are provided in the Figures 1-7. Figure 1 shows a coloring unit comprising a changeable chamber.

Figure 2 shows the relative dimensions of the coloring chamber.

Figure 3 shows an upper view of the coloring chamber and the first horizontal rollers, showing the width of the tap hole and the length of the horizontal roller.

Figure 4 shows a side view of the coloring chamber and the rolling and forming unit.

Figure 5 shows an upper view of the coloring chamber and the rolling and forming unit with a horizontal roller pair and orthogonally positioned protecting and shape forming rollers.

Figure 6 shows a side view of a horizontal roller pair and orthogonally positioned protecting and shape forming rollers.

Figure 7 shows examples of shape forming rollers.

In one embodiment, the present invention provides a coloring unit for coloring a molten glass in a device for manufacturing a poly-crystalline glass-ceramic comprising a changeable chamber for receiving molten glass and pigment.

The coloring unit (see Figure 1) further comprises a pigment feeder 13 for pigment loading into the chamber, a mixing device 12 for stirring and homogenizing the molten glass in the chamber, a heating device 10 and/or a cooling device 14 for controlling the temperature and viscosity of the molten glass in the changeable chamber and a pendent arch 11 positioned above the changeable chamber. The pendent arch of the coloring unit forms the stationary part when changing the changeable coloring chamber for another equivalent changeable chamber.

In particular, the present invention provides a changeable chamber for receiving molten glass and pigment. The changeable chamber typically comprises (see Figure 2) : a reaction zone 1 for loading pigment into the molten glass and stirring and homogenizing the molten glass, a settling zone 2 for completing all reactions, a downward baffle 3, a cooling zone 4 downstream of the downward baffle and a tap hole 7 (see Figure 3) for discharging the molten glass for further processing, e.g. into a rolling unit.

The heating device and/or cooling device (s) may be equipped with an optical or thermocouple temperature sensor for controlling the temperature of the molten glass in the chamber so as to adjust the molten glass to have a predetermined viscosity. Preferably, the heating device is located in the first part of the chamber upstream of the downward baffle above the molten glass discharge from the glass melting furnace and the cooling device is located in the second part of the chamber downstream of the downward baffle.

Preferably, the downward baffle is cooled by water and/or a steam and/or air.

The changeable chamber preferably has relative dimensions as set out below, each independently or any combination thereof (see Figure 2) . The length b2 of the settling zone is 30-70% of the sum of the lengths bl and b2, respectively, of the reaction zone and the settling zone.

The length b3 of the cooling zone is 80-120% of the sum of the lengths bl and b2 of the reaction zone and the settling zone, respectively.

When being filled with molten glass, the distance h3 between the downward baffle bottom line and the chamber bottom line is 10%-40% of the pool depth hi of the molten glass in the settling zone.

The pool depth h2 of the molten glass in the reaction zone is 20-40% of the pool depth hi of the molten glass in the settling zone.

In one embodiment of the invention, a cooling frame 15 is inserted into the tap hole of the changeable chamber for discharging the molten glass for further processing (see Figures 4 and 5) . Preferably, the internal height of the cooling frame is 5-50 mm and the length of the cooling frame is similar to the width al of the tap hole of the chamber.

The cooling frame may further have dimensions depending on configuration of a common rolling unit or the rolling and forming unit of the invention as described below. In another embodiment, the present invention provides a rolling and forming unit for forming a molten glass ribbon in a device for manufacturing a poly- crystalline glass-ceramic, wherein the rollers present in the unit comprise pairs of horizontal as well as orthogonal rollers, in one combined unit or in separate units.

The rolling and forming unit comprises at least one pair of horizontal rollers 5 and 6 of different diameters, with the bottom roller 5 having the larger diameter (see Figure 2). Preferably, the diameter Dl of the top roller 6 is 10%-95% of the diameter D2 of the bottom roller 5. The angle α between the plane connecting both roller axes and the horizontal plane is 30°-180°. The length of the horizontal rollers may relate to the width of the tap hole of the preceding unit, e.g. the melting furnace or the changeable chamber of the coloring unit.

Preferably, the width al of the tap hole for discharging the molten glass for further processing into the rolling (and forming) unit is smaller than the length a2 of the horizontal bottom roller of the rolling (and forming) unit (see Figure 3) . More preferably, the length a2 of the ^~horizontal bottom roller is 140%-170% of the width al of the tap hole of the preceding unit (e.g. changeable chamber of the coloring unit or the melting furnace) .

Also preferably, the distance between the cooling frame inserted in the tap hole of the preceding unit and the vertical plane through the axis of the bottom horizontal roller is 10-250% of the height of the cooling frame. Also preferably, the distance between the bottom of the cooling frame and the contact line between the horizontal bottom roller and the glass ribbon 18 is 200- 1000 mm.

The rolling and forming unit further preferably comprises orthogonal protective rollers 17 (see Figures 4, 5 and 6), upstream of the horizontal rollers. Preferably, at least one pair of orthogonal protective rollers is placed, in such a way that the rollers of a pair are placed at each edge of the glass ribbon 18. Up to five pairs conveniently may be placed. Preferably, the angle between the axis of an orthogonal protecting roller 17 and the vertical line is 0°-45°.

The rolling and forming unit further comprises orthogonal forming rollers 16 (see Figures 4, 5, 6 and 7) downstream of the horizontal rollers. Preferably, one to five pairs of orthogonal forming rollers may be used, in such a way that the rollers of a pair are placed at each edge of the glass ribbon. Preferably, the forming rollers are placed as close as possible to the horizontal rollers, whereby the first pair of forming rollers may be in contact with a horizontal roller.

The shape of the forming rollers may preferably be adapted to accommodate the desired form of the final polycrystalline product, e.g. may be adapted to ensure uprising and/or bending and/or ends forming and/or other shape forming of the glass ribbon. See Figure 7 for a few examples of shape forming rollers.

The rollers may have polished surfaces and/or surfaces with a pattern, to create a suitable finished product surface by means of "printing".

The rollers may be metal rollers or metal rollers with a ceramic covering, and comprise means to allow cooling by water and/or steam and/or air, preferably by water.

In a preferred embodiment, the dimensions of the rolling and forming unit are adapted relative to the dimensions of the coloring unit or the melting furnace.

In particular, the length a2 of the horizontal bottom roller is 140%-170% of the width al of the tap hole of the changeable chamber of the coloring unit (see Figure 3) or the tap hole of the melting furnace. In one embodiment, a device is provided that is suitable to perform the overall process. The device comprises: (a) a mixer for mixing the raw materials, (b) optionally a rotary kiln for volatile compounds removal and production of a burnt composition, disposed downstream of the mixer, (c) a glass melting furnace for melting the, optionally burnt, composition to form a molten glass, disposed downstream of the glass melting furnace or, optionally, the rotary kiln; (d) a coloring unit for coloring the molten glass comprising a changeable chamber for receiving molten glass and pigment, (e) a rolling unit for receiving the colored molten glass from the coloring unit, (f) an annealing and crystallization unit for receiving the molten glass from the rolling unit, permitting crystallization of the glass and formation of a polycrystalline glass-ceramic.

Preferably, the rolling unit is the rolling and forming unit of the present invention as described herein above . The present invention envisages the establishment of two or more separate production lines running in parallel, for instance to increase capacity or to enable simultaneous production of two or more polycrystalline glass-ceramic products with different colors and/or shapes. Separate production lines may for instance be established by providing the melting furnace with two or more tap holes, which allows connection to corresponding quantities of either a coloring unit or a rolling and shape forming unit, or corresponding quantities of a coloring unit as well as a rolling and shape forming unit, and further connection to similar quantities of crystallization tunnels .

Claims

1. A method for manufacturing a polycrystalline glass- ceramic comprising mixing raw materials capable of crystallization, heating the mixture of raw materials to form a molten glass and subjecting the molten glass to a heating and cooling temperature regime to bring about crystallization and to form a polycrystalline glass- ceramic, characterized in that, prior to crystallization, pigment is added to the molten glass in a coloring unit comprising a changeable chamber for receiving the molten glass and pigment.

2. The method according to claim 1, wherein the changeable chamber comprises, from up- to downstream direction, a reaction zone for adding pigment to the molten glass and stirring and homogenizing the molten glass, a settling zone, a downward baffle, a cooling zone and a tap hole for discharging the molten glass for further processing.

3. The method according to claim 1 or 2 further comprising treating the mixture of raw materials to remove volatile compounds prior to heating the mixture of raw materials to form a molten glass.

4. The method according to any one of the claims 1-3, wherein the molten glass is passed through a cooling frame that is inserted into a tap hole of the changeable chamber for discharging the molten glass for further processing.

5. A changeable chamber for use in a coloring unit for coloring a molten glass in a device for manufacturing a polycrystalline glass-ceramic, wherein the chamber comprises a reaction zone (1) for adding pigment to the molten glass and stirring and homogenizing the molten glass, a settling zone (2) , a downward baffle (3) , a cooling zone (4) downstream of the downward baffle and a tap hole (7) for discharging the molten glass for further processing.

6. The chamber of claim 5, wherein the length (b2) of the settling zone is 30-70% of the sum of the lengths (bl) and

(b2) of the reaction zone and the settling zone, respectively.

7. The chamber of claim 5 or 6, wherein the length (b3) of the cooling zone is 80-120% of the sum of the lengths

(bl) and (b2) of the reaction zone and the settling zone, respectively.

8. The chamber of any one of claims 5 to 7, wherein, when being filled with molten glass, the pool depth (h2) of the molten glass in the reaction zone is 20-40% of the pool depth (hi) of the molten glass in the settling and cooling zone .

9. The chamber of any one of claims 5 to 8, wherein, when being filled with molten glass, the distance (h.3) between the downward baffle bottom line and the chamber bottom line is 10%-40% from the pool depth (hi) of the molten glass in the settling zone.

10. The chamber of any one of claims 5-9, wherein a cooling frame (15) is inserted into the tap hole.

11. The chamber of claim 10, wherein the height of the cooling frame is 5-50 mm and the length of the cooling frame is similar to the width al of the tap hole of the chamber.

12. A coloring unit for coloring a molten glass in a device for manufacturing a poly-crystalline glass-ceramic comprising the changeable chamber of any one of the claims 5-11 and a pendent arch (11) positioned above the changeable chamber, the pendent arch forming the stationary part when changing the changeable chamber for another equivalent changeable chamber and providing a pigment feeder (13), a mixing device (12) for stirring and homogenizing the molten glass in the chamber, a heating device (10) and/or a cooling device (14) for ensuring molten glass homogeneity and controlling the viscosity of the molten glass in the chamber.

13. The coloring unit of claim 12, wherein the heating device is located in the first part of the chamber upstream of the downward baffle and/or the cooling device is located in the second part of the chamber downstream of the downward baffle.

14. A method for manufacturing a polycrystalline glass- ceramic comprising mixing raw materials capable of crystallization, heating the mixture of raw materials to form a molten glass and subjecting the molten glass to a heating and cooling temperature regime to bring about crystallization and to form a polycrystalline glass- ceramic, characterized in that, prior to crystallization, the molten glass in the form of a ribbon is subjected to a rolling and forming process comprising the use of pairs of rollers, at least one pair positioned horizontally and at least one pair positioned orthogonally relative to the glass ribbon.

15. A rolling and forming unit for rolling and forming a molten glass in a device for manufacturing a poly- crystalline glass-ceramic, wherein the rollers present in the unit comprise -at least one pair of horizontal rollers comprising a bottom and top roller as well as at least one pair of orthogonal rollers.

16. The rolling and forming unit of claim 15 wherein the two horizontal rollers of a pair have a different diameter, the bottom roller having the larger diameter, preferably wherein diameter of the top roller is 10%-95% of the diameter of the bottom roller.

17. The rolling and forming unit of claim 15 or 16, wherein the angle α between the plane connecting the axes of the horizontal bottom and top rollers of a pair and the horizontal plane is 30°-180°.

18. The rolling and forming unit of any one of claims 15-

17, wherein at least one pair of orthogonal forming rollers (16) is placed downstream of the horizontal rollers.

19. The rolling and forming unit of any one of claims 15-

18, wherein at least one pair of orthogonal protecting rollers (17) is placed upstream of the horizontal rollers.

20. The rolling and forming unit of claim 19, wherein- the angle between the axis of the orthogonal protecting rollers 17 and a vertical line is 0°-45°.

21. A device for manufacturing a poly-crystalline glass- ceramic, comprising: (a) a mixer for mixing the raw materials; (b) optionally a rotary kiln for , volatile compounds removal and production of a burnt composition, disposed downstream of the mixer; (c) a glass melting furnace for melting the optionally burnt composition to form a molten glass, disposed downstream of the mixer or, optionally, the rotary kiln; (d) the coloring unit of claim 12 or 13 comprising the changeable chamber of any of the claim 5 to 11 for coloring the molten glass, disposed downstream of the glass melting furnace; (e) a rolling unit for receiving the colored molten glass from the coloring unit (f) an annealing and crystallization unit for receiving the molten glass from the rolling unit and permitting crystallization of the glass to obtain a poly- crystalline glass-ceramic.

22. The device of claim 21, wherein the changeable chamber has dimensions that are adapted to accept a volume of molten glass that is 0.5%-5% of the volume of the molten glass in the glass melting furnace.

23. The device of claim 21 or 22, wherein the rolling unit is the rolling and forming unit of any one of claims 15-20.

24. The device of any one of claims 21-23 comprising two or more separate production lines.