FI86166C - FOERFARANDE FOER FORMNING AV GLAS. - Google Patents

Description

1 86166

Method for forming glass

The present invention relates to a floating process for the manufacture of flat glass, in which molten glass is introduced into a molten metal pond (comprising mainly molten tin), on which the molten glass floats to a uniform surface and thinned to the desired thickness. The invention is particularly directed to improvements in the feeding of molten glass from a melting and cleaning apparatus to a floatation chamber.

In the context of the buoyancy formation process, it has been found that the arrangement by which the molten glass is initially deposited on the surface of the molten metal pond is critical to achieving the desired optical quality for the flat glass. Thoroughly cleaned and homogenized glass becomes slightly soiled, at least in its base, as it passes through a channel or 20 other ducts connecting the melting and cleaning device to the forming chamber when it comes into contact with the ceramic refractory materials from which the feed structure is made. This soiling is known to cause distortions in glass sheets made from such glass. In previous * floating processes, such as those described in: U.S. Patent No. 3,220,816 (Pilkington), molten 1 glass was passed over molten tin by a chute which: causes a molten glass to fall into a free-falling strip, a portion of which flows backwards and then outwards. initial contact with the molten metal.

30 This flow pattern has acted as a molten stream of molten glass. . to direct the known bottom surface portion to the edge portions of the glass strip which is then formed in the floating chamber. These edge portions could be cut off and discarded: 'away, leaving the center of the strip relatively free of distortion caused by the resilient material.

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A different approach to this problem is described in U.S. Patent 3,843,346 (Edge et al.). In this solution, only the surface part of the molten glass is drawn from the melting furnace into the forming chamber, thus avoiding contamination caused by the refractory material in all parts of the glass strip to be manufactured. However, even in this arrangement, there is inevitably little contact with the refractory material contained in the sill member over which the glass flows immediately prior to contact with the molten metal. Although said sill member can be made of a relatively clean and uncontaminated refractory material, its gradual wear can cause some distortion effects in the glass and must be periodically replaced to maintain the desired quality level of the manufactured glass. It would thus be desirable to minimize contact of the molten glass with the refractory material when feeding the molten glass into the forming chamber.

U.S. Patent No. 3,843,344 (Galey) discloses an arrangement in which a threshold is set upstream of an upper glass flow control member, referred to as a "barrier plate". Such an arrangement can reduce shear forces at the threshold and thus wear the threshold, but still cause some glass wear. contact with the refractory material at the sill and barrier plate A similar arrangement is disclosed in U.S. Patent No. 4,395,272 to Kunkle et al.

U.S. Patent Nos. 3,468,649 (Delajarte et al.) And 3,765,857 (Lecourt) each disclose a cylindrical passage through which molten glass is fed into a buoyancy chamber. Neither patent discloses a material from which such ducts could be made, nor any details of the structure or purpose of such ducts. Since both of these patents deal primarily with other features, it is apparent that the ducts 35 shown in each of them are merely shown as an abstract schematic example of 3 86166 from a glass transfer device to a flotation chamber.

U.S. Patent Nos. 3,318,671 (Brichard et al.); 3,488,175 (Montgomery) and 3,679,389 (Kanai) each describe the formation of a glass plate 5 which is led mainly vertically to a molten metal bath. In order to make the glass strip self-supporting in such an arrangement, the viscosity of the glass must be relatively high, and thus the glass strip in the molten metal bath cannot be significantly smoothed or thinned unless the glass is significantly reheated while on the molten metal. Reheating, on the other hand, reduces the energy efficiency of the process. In U.S. Pat. No. 4,203,750 (Shay), a seemingly less viscous glass strip is directed into a molten metal bath, on the surface of which it is thinned by means of edge rollers. However, the viscosity of the glass would have to be relatively high to form the strip before it is fed into the bath, and the preforming of the strip requires considerable contact with the refractory material, which can be detrimental to glass fouling and optical distortion.

In U.S. Patent No. 4,162,907 (Anderson), discrete lumps of molten glass are extruded into a small bath of molten tin. Since such a * 25 arrangement is discontinuous, the velocity of the substance passing through it is limited and the supply of the molten glass to the molten metal is then disadvantageously dependent on a complex mechanism with several moving parts.

30 It would be desirable to provide an arrangement for continuously feeding molten glass into a molten metal pond for making flat glass. by means of a snow process which avoids the disadvantages of the previously known solutions:: 35. The goal is to form successive belts in the forming chamber. · * ·. utilization of shells to produce thinned glass.

4 86166

The invention thus relates to a method for forming glass into a flat strip, in which the flow of molten glass is fed over a molten metal pond in the forming chamber, characterized in that the flow to the first zone of the molten glass forming chamber is collected as a relatively narrow and deep glass mass in contact with this glass mass is dispensed from the first zone of the forming chamber to its second zone where 10 glass is allowed to spread over a wider width in contact with the sidewalls and the depth of the glass mass is reduced, and the glass is passed to the third zone of the forming chamber.

In the context of the present invention, the molten glass is fed into the flat glass forming chamber as a vertically falling substantially cylindrical stream. This current passes through the roof of the forming chamber and no structure is required inside the forming chamber to direct or shape this current as it enters the chamber. The molten glass is first received in the chamber as a relatively deep layer into a container from which the glass flows and spreads, forming a relatively thin strip on the surface of the molten metal pond.

• ** 25 The molten glass in the container also preferably rests on a layer of molten metal which insulates a considerable surface area of the glass from dirty contact with the refractory material. The molten metal may extend continuously from the tank to the rest of the forming chamber.

. The container into which the molten glass is initially received in the forming chamber is preferably relatively deep. and narrow. In preferred embodiments, the spreading of the molten glass is achieved approximately as desired. to a width in the intermediate zone where the glass is allowed to flow in contact with the relatively far apart side walls, thereby significantly reducing the thickness of the glass layer. The glass is then drawn downstream of an even wider forming chamber, where the glass is placed at a distance from the side walls and pulled by means of a pull-5 device to achieve the final desired thickness of the glass strip.

Vertical feeding, collecting the glass in the tank and applying the glass to said intermediate zone require glass temperatures higher than those used in connection with a conventional flotation chamber. Since the glass in these stages is required to flow freely, its viscosity must be relatively low. Thus, for soda lime silicon glass having a conventional composition, the temperature of the glass in the receiving tank is preferably at least 2100 ° F (1150 ° C) and most preferably about 2400 ° F (1310 ° C). The temperature of the glass is allowed to drop as the glass passes through the interlayer step, and as the strip separates from the sidewalls, its temperature is normally about 1800 ° F (980 ° C) to 2100 ° F (1150 ° F).

Allowing the glass to flow mainly to the final strip width at high temperatures is advantageous because, in the case of low viscosities, the wave-type surface defects disappear quite quickly, thus enabling the production of glass with improved optical quality.

'1 25 The free flow of low-viscosity glass and thus: the rapid attainment of strip width allow the use of relatively short and economically advantageous forming chambers. Feeding glass into the forming chamber at the high temperatures associated with such a process would cause rapid wear of conventional glass feeders. Such wear first of all dirt. : adversely affects glass and also requires expensive replacement of refractory materials in the supply area.

Thus, a vertical feeding system is preferred for feeding a high temperature glass in connection with this type of forming process.

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Since the glass stream entering the forming chamber does not have to be shaped by means of flow guides and since it falls freely, it is not necessary in this system to use a channel structure or the like to transfer the molten glass 5 from the melting device to the forming chamber. In this way, not only is the source of possible contamination of the glass avoided, but also greater freedom is given for the choice of materials at the outlet end of the melter. In particular, the outlet of the melting device and the valve assembly can be made of platinum, which is not normally possible with the use of the inlet structure of the forming chamber due to the reducing atmosphere maintained in the forming chamber, usually for storing molten metal. Although platinum has excellent corrosion resistance upon contact with molten glass, it does not withstand reducing conditions. A valve assembly at the outlet end of the melter can be used to control the flow of molten glass to the tank portion of the forming chamber. The barrier plate can be used to control the flow of molten glass from the container to the intermediate chamber, however, the barrier plate and its contact with the refractory material can be eliminated by using a valve at the outlet end of the melter to control the glass flow rate.

The container provides a suitable location for agitating the molten glass 25 after it has been fed into the forming chamber to mitigate the optical distortion effects caused by the inhomogeneous locations of the glass. Glass passing through »m: [| cleaned and fed into the forming chamber without significant contamination by the duct made of refractory material, it is not necessary to homogenize. For glass intended for use other than. : as a transparent glass, lower requirements can be set for its optical integrity and thus there may be no need for confusion. Although the feeding of molten glass into the forming chamber in accordance with the present invention greatly reduces the potential for fouling by the refractory material, it may be observed that there are inhomogeneous spots in the glass before it enters the feed zone. Since in the feeding arrangement according to the present invention, no more soiled parts of the glass are directed to the edge parts of the glass strip, the use of agitation is recommended in the context of the present invention when making a transparent flat glass.

Other features of the invention will become apparent from the drawings and the following description of specific embodiments. In the drawings: Fig. 1 shows a schematic plan view of a forming chamber according to the present invention, the upper part of which is cut away; Fig. 2 shows a schematic cross-sectional side view of the forming chamber of Fig. 1; Fig. 3 is an enlarged cross-sectional side view of a portion of the feed chamber 20 of Figs. 1 and 2, showing an embodiment of the present invention for vertically feeding molten glass into the forming chamber; Fig. 4 is an enlarged cross-sectional side view of the feed chamber and feed section of the forming chamber shown in Figs. 1 and 2, showing: a preferred embodiment of the present invention for vertical feeding of molten glass into the forming chamber as well as an arrangement for agitating the glass; Fig. 5 shows an enlarged cross-sectional side view of the feed section of the forming chamber shown in Figs. 1 and 2, showing an alternative embodiment of the present invention.

Referring to Figures 1 and 2, there is shown a general structure of a forming chamber 10 according to an embodiment of the present invention. The forming chamber is connected to a source 11 of molten glass, which may be any type of melting furnace known in the art. In more detail, the molten glass fed to the forming chamber has in most cases been subjected to a post-melting cleaning process and in some cases also to a heat treatment step. It should thus be understood that the source of the molten glass 11 could be a cleaning or treatment vessel, hereinafter referred to as a "melting device" for simplicity. The vertically falling glass stream 12 flows from the melting device 11 through an opening in the roof of the forming chamber 10 and is received in the first zone 13 of the forming chamber. Figure 2 shows a preferred arrangement in which the molten metal layer 22 extends over the entire area of the forming chamber, including the first chamber 13. The molten metal 20 is preferably tin, which may contain smaller amounts of other elements such as iron or copper. In the first zone 13, it is preferable to use molten metal to form an uncontaminated contact surface against the bottom of the glass container 14. Some features of the present invention do not require the presence of molten metal in the zone::: 13.

The intermediate zone 20 is wider than the first zone 13 and the molten glass in the intermediate zone is sufficiently lower in viscosity so that the glass mass 30 spreads in contact with the side walls. The width obtained by the glass mass in the intermediate zone 20 is preferably approximately the same as that of the final glass strip to be produced. As the adjusted amount of .1 ·· 1 glass flows under the barrier plate 15, spreading a gap to the zone 20, its thickness decreases to a uniform thickness of 35 or becomes equal to the thickness of the intermediate zone at the end of the intermediate zone. Alternatively, the barrier plate 23 shown in broken lines in Figures 1 and 2 may be used at the end of the intermediate zone 20 to pressurize the gas on the glass 21 in the intermediate zone to a value above atmospheric pressure, whereby the thickness of the glass mass can be reduced below the equilibrium thickness in the intermediate zone. This alternative technique is in accordance with U.S. Patent 4,395,272 to Kunkle et al.

With further reference to Figures 1 and 2, the third zone of the forming chamber 10 resembles a conventional floating forming chamber. The side walls of the third zone 25 are spaced a greater distance apart than the side walls of the intermediate zone 20 so that the edges of the glass strip 26 are spaced apart therefrom. Edge gripping devices, such as ta-15 conventional toothed wheels 27, may be attached to opposite side edge portions of the strip 26 in a third zone to control the width of the strip. In those embodiments where the glass enters the third zone at or slightly above the equilibrium thickness, the edge gripping devices maintain the strip width or reduce the strip width loss when the strip is stretched longitudinally to form thicknesses below the equilibrium thickness. In embodiments where the thickness of the glass is reduced below the equilibrium value in the intermediate zone, the edge gripping device maintains the strip width and thus the reduced thickness of the glass. The number and setting of edge grippers can: vary considerably according to specific production requirements.

The free-flowing nature of the molten glass in the first and second zones of the forming process of the present invention is indicated by the buoyancy. : lower viscosity and higher than normal viscosity normally associated with refining processes. The glass temperatures in the first: V 35 zone 13 and at least in the upstream part of the intermediate zone 20 • 1 «« 1 a 10 6 61 6 6 are at least 2100 ° F (1150 ° C). As the glass exits the intermediate zone 20, its temperature may have dropped to as high as 1800 ° F (980 ° C). Because the glass cools as it passes through the forming chamber, significantly higher temperatures occur in the upstream portions of the forming chamber. For example, the glass mass formed by the container 14 is preferably at a temperature of at least 2200 ° F (1200 ° C). Such temperatures are especially recommended if the glass is to be agitated in the first zone. The glass stream 12 entering the Muo-10 dosing chamber may be at correspondingly higher temperatures, generally in the range of about 2300 ° F (1260 ° C) to 2400 ° F (1315 eC). There is no substantially accurate upper limit for the temperature of the glass entering the first zone, but in practice it is most likely that the temperature of the glass would be slightly below the temperature during the melting and cleaning process upstream of the glass, which is usually not higher than 2800 eF (1500 eC ). In practice, allowing the glass to cool considerably before entering the forming chamber would in some cases be advisable to increase the service life of various elements, such as valve devices and the refractory side walls of the forming chamber. At these relatively high temperatures, a significant advantage is provided by the molten metal layer 22 in the first and second zones of the chamber forming the glass, which insulates the molten glass from contact with ceramic refractories. which would have a significant contaminating effect on the molten glass at these temperatures. It is equally important 30 that the high temperature glass stream 12 need not come into contact with ceramic refractory materials. with structural elements made of.

# ·; ·. The temperatures given below relate to the conventional floating mixture used in the commercial use of soda-lime silicon. For other compositions, these * · · »·

P

m · 11 8 61 6 6 temperatures vary according to the temperature / viscosity ratio of the glass mixture. In order to extrapolate the temperatures reported in this context to other glass mixtures, the relationship between the temperature and the viscosity of the snow-5 mixture of the sodium lime silicon in question is given below:

Viscosity (Off Temperature 100 2630 ° F (1443 ° C) 1000 2164 ° F (1184 ° C) 10 10000 1876 ° F (1024 eC) 100000 1663 ° F (906 ° C))

Figure 3 shows details for an example of a valve arrangement for conducting a stream of molten glass 15 from a melting or cleaning device 11 to a forming chamber. In this example, a tube 30 made of a refractory metal, such as platinum, passes through the bottom of the refractory vessel 11, limiting the outlet through which the glass stream 12 passes. The vertically adjustable plunger 31, which may also be made of or coated with a refractory material such as platinum, controls the flow of molten glass through the tube 30. This arrangement of submersible piston and outlet pipe is common in some sectors of the glass industry, such as in the manufacture of bottles, and these component parts are readily commercially available, but the use of such an arrangement in the flat glass forming process is novel. The molten glass: source 11 shown in Figure 3 represents the end portion of a horizontal tank-type melting furnace 30 commonly used in the glass industry. The end portion of such an oven may comprise a pre-furnace in which the glass: can be heat treated and homogenized.

In order to prevent excessive oxidation of the molten metal in the buoyancy chamber, a generally non-oxidizing atmosphere is maintained in the formation chamber, which usually comprises a noble gas such as nitrogen and small amounts of a reducing gas such as hydrogen. In the context of the present invention, where the molten glass 14 completely covers the molten metal 22 in the first zone 13 and the barrier plate 5 insulates the atmosphere of the first chamber from the rest of the forming chamber, it may be unnecessary to form a reducing atmosphere in the first zone. In this case, the tube 30 of Fig. 3 may extend to the first zone 13 of the forming chamber because platinum, as its main material, is not susceptible to the corrosive effects of the reducing atmosphere. Extending the tube 30 a short distance above the surface of the glass container 14 is recommended to prevent the formation of air pockets and inclusions as the flow 12 enters the container. It would also be advantageous if this tube extended below the surface of the glass 14. It is clear that platinum in this context refers to various alloys of platinum, in particular the alloy of platinum and rhodium, which are generally used in glass contact applications.

Figure 4 shows a preferred embodiment of the present invention including a plurality of agitators 40 for agitating a glass container 14 in the first zone 13 of the forming chamber 13.

. These agitators are preferably arranged in series with a plurality of agitators arranged in each of a plurality of rows. The exact number of agitators required depends on the degree of homogenization desired and the agitating power of the particular agitator selected. The agitators shown in Figure 4 are of the helical type, but any type of glass agitator known in the art may be used. When agitation is used, it is recommended to add dyes or other additives to the glass upstream of the agitators in the first zone 13. For this purpose, a screw feeder 41, 35 can be used which penetrates the chamber through the side wall.

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The source 42 of molten glass in the embodiment shown in Figure 4 may be of a type similar to the sources described in connection with other embodiments or a less commonly used type of melting or cleaning device. For example, the vertical cleaning apparatus described in U.S. Patent No. 4,610,711 (Matesa et al.) Can be used to feed molten glass to the forming process of the present invention. The fused glass source 42 is provided with an outlet pipe 43, which is preferably made of an inlet of a refractory metal such as platinum. In this embodiment, the molten glass flow control arrangement is located outside the source of the molten glass 42. This valve assembly is in accordance with U.S. Patent 4,600,426 (Schwenninger) including a spherical member 44 supported by a lateral arm 45, this arm 45 being in turn supported for vertical adjustment. To prevent rotation of the glass and the formation of air inclusions therein, the elongate rear portion 46 may extend downwardly from the spherical member 42 into the forming chamber in the first chamber 20 of the glass mass 14 slightly above or preferably below or below that level. The elements of this valve assembly are preferably made of a refractory metal such as platinum or molybdenum.

Referring to Figure 5, there is shown an embodiment incorporating several of the above-mentioned preferred features, while representing a novel arrangement for feeding molten glass to a flat glass forming process within the broadest scope of the present invention. The variations shown in Figure 5 may be used together as described or separately in connection with the other embodiments shown. Fig. 5 shows a conventional melting or cleaning device 50, from which the side flow 51 is fed through the end part instead of the outlet at the bottom. In the example shown, the glass is fed:. 35 through a narrow trough 52 provided with a vertically adjustable gate 53 for varying the flow rate. The width of the trough 52 is most suitably minimized to minimize the surface area of contact with the refractory material, whereby the trough 5 may, however, be approximately rectangular in cross-section.

However, the vertically falling flow of the glass 51 tends to assume a cylindrical shape due to the relatively large distance due to the surface tension and the free fall. If desired, the trough 52 may be clad in platinum or other non-soiled material. The first zone 55 of the forming chamber includes a glass container 56, but is not provided with a layer, preferably formed of molten metal, between the glass and the refractory base. One of the glass contact surfaces in zone 55 or 15 may all be coated with platinum or other refractory material. The container 56 is relatively deep and narrow as in previous embodiments. The glass flow from the first zone 55 to the second zone 57 becomes regulated between the vertically adjustable barrier plate 20 and the sill member 59, which is preferably made of an unpolluted refractory material such as fused quartz. The glass in the intermediate zone 57 is allowed to flow over a wider width of the molten metal. above the previous embodiments.

The present invention has been described by way of specific examples, but it will be apparent to those skilled in the art that other changes and modifications may be made therein without departing from the scope of the invention as defined in the appended claims.

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Claims (6)

15 861 66 A method of forming glass into a flat strip, the method comprising feeding a flow of molten glass onto a molten metal pond in a forming chamber, characterized in that the flow into the first zone (13) of the molten glass forming chamber is collected as a relatively narrow and deep glass mass in lateral contact that this glass mass is dispensed from the first zone (13) of the forming chamber to its second zone (20), where the glass is allowed to spread over a wider width in contact with the side walls and where the depth of the glass mass is reduced, and that the glass is fed to the third zone 15 (25) of the forming chamber. separated from the side walls and thinned to the desired thickness to form a glass strip (26). Method according to Claim 1, characterized in that the glass mass is supported on the molten metal (22) in a third zone (25). Method according to Claim 1 or 2, characterized in that the glass mass is supported on the molten metal (22) in a second zone (20). Method according to one of the preceding claims, characterized in that the glass mass is supported on the molten metal (22) in the first zone: · (13). Method according to one of the preceding claims, characterized in that the glass in the first zone (13) is at a temperature of at least 1150 ° C (2100 ° F). Method according to one of the preceding claims, characterized in that the pressure exceeding the atmospheric pressure is maintained in the second zone (20) in order to reduce the thickness of the glass. : V 35 ie 86166