DK154338B - PROCEDURE AND PLANT FOR THE MANUFACTURE OF PLANGLAS - Google Patents

Description

DK 154338B

The present invention relates to a process for the production of flat glass and is of the kind specified in the preamble of claim 1.

In the flow process for making flat glass, molten glass is fed at one controlled rate to one end, the hot end, of a molten metal bath contained in an elongated container structure. Usually, the molten metal is bath of molten tin or of a molten tin alloy in which tin is overweight. The finished glass band is withdrawn from the bath by means of pulling means, usually driven pull rollers disposed outside the outlet end of the bath, which pull means exert a pulling force to move the tape forward along the bath.

In some methods of carrying out the flow process, the control of the applied tensile effect is carried out together with the regulation of the thermal conditions to which the forward-moving glass band is exposed, so as to thin the band to a desired width and thickness.

When operating under high load conditions, e.g. at a feed rate of the molten glass to the bath of 2000 tons per day. a week or more is a high departure rate for the finished glass strip from the bath, e.g. greater than 10 meters per per minute, necessary for thinning the glass to thicknesses below 3 mm. As the forward migrating glass band is accelerated with thinning to a uniformly high exit velocity from the bath, it includes a significant amount of the molten metal in the bath along the bath's surface towards the bath's end, which produces an opposite return stream of colder molten metal from the bath's outlet end along the bottom. of the bath to the zone of bath where the glass band is thinned. In this zone, the glass has a viscosity such that it is particularly sensitive to temperature variations across the surface of the molten metal bath and it has been found that distortion introduced into the lower surface of the glass band in this thinning zone is present in the final band. .

Temperature variations across the surface of the bath may result from a temperature gradient through the depth of the bath, and it is desirable to minimize such temperature gradients, especially in the thinning zone. However, although a relatively small temperature gradient can be obtained at a relatively small bath depth at low band speeds, a high band speed over a small bath depth produces turbulence in the molten metal from which distortion in the band may result. A greater bathing depth will reduce turbulence at high belt speeds, but will necessarily provide a greater temperature gradient through the bathing depth, which may introduce distortion into the belt.

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It has previously been proposed in British Patent No. 1,452,625 to fight the introduction of such distortion into the glass band in the thinning zone by using a first barrier at a first location in the region around the end of the thinning zone in the direction of flow to force the flow of the melt metal at this location for forward flow of molten metal carried under the binder, and opposite flow of molten metal along the sides of the strip from a position seen in flow direction after that location, and using another barrier at another location located seen in flow direction above the first location and in the range of maximum acceleration of the glass to force the flow of molten metal at this second location to forward flow of molten metal entrained under the accelerating glass and opposite flow of molten metal along the sides of the strip from a position seen in flow direction below the second site, establishing lateral adga ng to the region of the bath which supports the band between the first and second locations of said opposite molten metal flow at the first location to ensure replenishment of the molten metal in the bath in the thinning zone between the first and second locations. Such an arrangement reduces the temperature difference between the molten metal above the surface and the molten metal below the surface in the thinning zone, thereby reducing temperature variations in this zone which tend to introduce distortion in the band.

The object of the present invention is to provide such a temperature equalization and flow rate in the thinning zone that the said distortion is avoided or reduced.

According to the invention, the object is achieved by practicing the method mentioned in the introduction as set forth in the characterizing part of claim 1.

Preferably, the region of greater bath depth extends over a length in the direction of movement of the belt sufficient to ensure mixing of the molten metal in said return stream with molten metal contained in the region of greater bath depth.

The method according to the invention may comprise placing the molten metal bath in a container structure having a bottom formed of adjacent blocks of refractory material, the upper side of which determines the level of the bottom of the molten metal bath, and defining said area of greater bath depth. blocks whose upper sides are lower than the upper sides 3

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of the blocks which 'determine the bath depth in the vicinity of said area.

The method of the invention may further comprise limiting said return stream of colder molten metal to a lesser depth than the depth of said area of greater bath depth, thereby reducing the rate of return stream as the return stream enters said area of greater bath depth. the return flow of the molten metal in said region is increased.

The invention may also comprise limiting the flow of molten metal entrained by the glass band at a location immediately above said area of greater bath depth to a surface area of the metal bath and streams drawn from the area of larger bath depth taking the form of streams along the glass band. side edges from said area to the area of the metal bath which supports the glass band above the area of greater bath depth.

In addition, according to the invention, the applied traction can be adjusted to thin the strip to a desired width and thickness in a thinning zone where the glass is accelerated along the bath, and said demarcation of the molten metal flow can occur at a location in the downstream region of the thinning zone.

The countercurrents along the sides of the band can be selectively heated.

Furthermore, according to the invention, a method is provided. manufacture of floating glass having a thickness in the range of 1.5 mm to 3 mm, where edge forces are applied to the accelerating glass at a series of mutually spaced positions along the bath to control the bandwidth and thickness reduction, by which method said boundary of the molten metal flow is made at a location in the region of the lower end of the thinning zone seen in the direction of movement of the belt and a distance below the lower position where edge forces are applied to the belt.

The invention also relates to a flat glass manufacturing plant according to the method, which comprises an elongated container structure with end walls, side walls and a base for accommodating a molten metal bath, glass supply means for the bath at a controlled rate and conveying the ribbon glass along the bath, and means for applying a pulling force to the final ribbon to accelerate the glass to a final withdrawal rate.

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What is peculiar to the plant is that in the area of the container structure where the tape achieves its final withdrawal rate, the bottom of the container structure is made deeper to form a reserve zone for receiving the return flow of colder molten metal which is forced in a direction opposite to that of the tape. direction of movement above the bottom by the inclusion of warmer molten metal of the forward-moving glass band, which is located at a distance from the end wall of the container structure at the place of removal of the glass band.

A preferred embodiment of the plant comprises a transverse barrier at the bottom of the container structure at a location immediately above (seen relative to the direction of movement of the belt) the deepened container bottom, which barrier extends beyond the position of the edges of the belt, the top of the barrier being located piece below the level of the bath surface, which is capable of forcing the molten metal stream at that location substantially for forward flow of molten metal included under the belt and to a countercurrent of molten metal along the sides of the belt.

The reserve zone, which forms at the bottom of the container structure immediately below the barrier, may have greater depth than the bath above the barrier.

The depth of the reserve zone can be approximately twice the depth of the bath near the zone.

Preferably, the reserve zone extends over the full width of the bottom of the container structure.

In a preferred embodiment, the container structure is enclosed in a metal sheath, and the bottom of the container structure comprises adjacent blocks of refractory material attached to the metal sheath, and the reserve zone with greater bath depth is delimited by blocks whose upper sides lie in a lower level than the upper sides of the adjacent blocks.

The upper sides of the blocks above and below the reserve zone may be at the same level. Preferably the blocks are refractory aluminum-silicate material.

In one embodiment, the bottom of the container structure below the barrier is constructed such that, seen in the direction of movement of the belt, it defines the reserve zone with greater depth than the bath depth above the barrier, an area of less depth than the reserve zone, and a further area of greater depth than the bath depth above the barrier. which additional area extends to the outlet end

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5 of the container structure.

A steep step can be provided where the bottom determines a change in bath depth.

In the preferred embodiment, the elongated container structure has a shoulder region connecting an upper portion with greater bath depth to a below portion with a smaller bath depth, wherein the greater bath depth zone is located at said shoulder area and the barrier is located immediately above the shoulder area.

Top rollers may be arranged so that they engage with the top surface of the strip edges at a series of opposite positions along the bath to control the reduction in width and thickness of the strip, the pair of top rollers located furthest in the direction of movement of the strip being at a position above the barrier.

Heaters may be mounted near the container side walls above the barrier to provide local heating to molten metal countercurrents.

The invention will now be explained in more detail with reference to the drawing, in which fig. 1 is a plan view of an elongated container structure containing a molten metal bath for use in the float process to produce thin flat glass in the process of the invention; FIG. 2 is a longitudinal section at the bottom of the container structure of FIG. 1, FIG. 3 is an enlarged view of a portion of FIG. 2, which image further shows a glass band; 6

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FIG. 4 is an enlarged view of a portion of FIG. 1, FIG. 5 is a view similar to FIG. 4 and showing a modification of the system of FIG. 1-4, FIG. 6 is a view similar to FIG. 5 and showing another modification of the system of FIG. -1-4, fig. 7 is a view similar to FIG. 5 and showing further modifications of the system of FIG. 1-4, and FIG. 8 is a longitudinal sectional view of a portion of the bottom of the container structure showing a different construction method of the bottom.

In the drawing, FIG. 1 is a plan view of an elongated container structure for the manufacture of flat glass in the flow process. The container structure comprises an end wall 1 at its entrance end and an end wall 2 at its exit end and parallel side walls 3 extending from the entrance end to a shoulder region formed by inwardly sloping side wall portions 4 connecting the side walls 3 with additional parallel side walls 5 extending to the exit end. The container structure contains a molten metal bath which is usually molten tin. The design of the container structure is such that between the side walls 3 in its wide portion above the shoulder area, it will allow for the maximum required glass layer on the bath surface and between the side walls 5 of the narrow portion below the shoulder area the maximum required bandwidth.

Melted soda-lime quartz glass is introduced into the bath at the inlet end of the container structure by pouring from a spout 6 extending over the inlet end wall 1. A regulating voice wall 7 controls the flow rate of molten glass over the spout onto the bath surface 8.

In a well-known manner within the flow process, temperature controllers are arranged in a roof structure not shown, which is arranged above the container structure and defines a space above the bath, in which a protective atmosphere is maintained. The temperature conditions at the entrance end of the bath are such that the molten glass 9 which arrives on the bath is allowed to flow freely and unobstructed to the sides during the first portion of its passage along the bath. The temperature of the glass is 99o ° C when the maximum spread is reached and the glass thickness is of the order of 7 mm. The layer of molten glass is advanced in band form and initially the strip is formed of low viscosity glass, e.g. at a 4 8 viscosity of lo 'poises. This glass is gradually cooled during its initial movement forward along the bath, and its viscosity slowly increases.

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temperature state to which the forward-moving glass is subjected, which state keeps the glass in a deformable state over a longitudinal region of the band and in which the glass progressively thins as its velocity increases under the influence of traction exerted on the final glass band 1, by means of driven rollers 11 located outside the outlet end wall 2 of the container structure. As the velocity of the glass increases, the influence of the longitudinal tensile force resulting from the rollers 11 will also grow and stretch the glass band. Gradual and progressive reduction in the width and thickness of the glass is regulated by the use of upper rollers which engage with the upper surfaces of the edges of the glass.

Initially, while the glass has a low viscosity, the edges of the tape are gripped by a pair of inclined upper rollers 12 arranged at opposite positions on shafts 13 extending through the side walls 3 of the container and driven by motors 14. The upper rollers 12 are ribbed or toothed rolls of graphite, stainless steel or soft steel which are water cooled inside. The axes of the rollers are inclined at an angle with a line perpendicular to the direction of advance of the glass strip along the bath. Outwardly and longitudinally directed forces are thereby applied to the edges of the belt which is being formed, the outward force components providing an obstacle to an excessive loss in width. Slight thinning of the tape begins to occur in this area.

Further similar pairs of upper rollers 15,16,17,18 and 19 are spaced apart along the container structure, mounted on respective shafts 20, 21, 22, 23 and 24 and driven by motors 25,26,27,28 and 29, the upper rollers of each pair being at opposite positions. With such pairs of upper rollers at a number of spaced positions along the bath, adjustment of the progressive decrease in the width and thickness of the belt is achieved. As the glass passes past the last pair of upper rollers 19, its temperature is cooled below 88 ° C corresponding to a viscosity of lO 'poises.

After the glass leaves the lower pair of upper rollers 19 in the direction of movement of the belt, its width and thickness continue to be reduced to a position at or near the shoulder region of the container structure where its viscosity under the printed temperature conditions is so high that the belt assumes its final width and thickness and obtains its final withdrawal speed, which is the effective surface velocity of the rollers 11.

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soda-lime silica glass has a viscosity of lo poises corresponding to a temperature of 75 ° C and is in a state in which further dimensional change cannot take place under the influence of the applied traction. The band is further cooled during its migration between the side walls 5 to the outlet end of the bath.

The glass is accelerated and the belt is thinned in a zone above the shoulder area of the container structure. The lower end of this thinning zone seen in the direction of movement of the belt is located substantially at or near the shoulder region, and the position of maximum acceleration of the glass is substantially above the last pair of upper rollers 19. When the belt is accelerated in the thinning zone, a ever-increasing inclusion of molten metal in the bath in a forward surface flow which migrates towards the outlet end of the bath. This forward surface flow overlies an opposite return stream of colder molten metal from the outlet end of the bath, and molten metal is continuously drawn under the belt to compensate for what is included. It is the generalized return flow of colder molten metal along the bottom of the bath, which produces temperature gradients from top to bottom through the depth of the bath, which has been found to be particularly troublesome in the area of the bath where the rapidly accelerating band is thinning, and especially in the bath. the area between the last pair of upper rollers 19 and the shoulder area. To combat this effect, the return flow of colder molten metal is received in an area of greater bath depth than the bath depth in the vicinity of this deeper area.

FIG. 2 shows the profile of the bottom FL of the container structure which provides different bath depths at different areas along the length of the bath. At the entrance end of the bath, the bottom forms an initial region 3o of greater depth than the flatter area 31, which follows in the flow direction, the latter region 31 providing most of the length of the bath above the shoulders and in fact lying throughout the thinning zone. The initial region 3o may have a depth of approx. 1½ times the depth of the subsequent area 31. For example, the area 3o may have a depth of 83 mm and the area 31 a depth of 58 mm.

The area 31 extends downward to a position near the shoulder area, e.g. to a position one or two meters above a line connecting them seen in relation to the upper direction of the flow direction of the side walls of the shoulders 4.

At this position, an area with greater bath depth than the bath depth near that area begins. The deepened bottom of the container structure forming the pocket region 32 is formed as a

9 DK 154338B

Tea pocket area 32 includes the shoulder area and extends a bit downwards in the flow direction of about 3 meters past a line connecting the lower ends of the shoulders sidewalls 4. The pocket area 32, for example, extends longitudinally of the bath over a total distance of 7.5 meters. and providing a reserve zone for receiving colder molten metal flow which is forced in an upward flow direction over the bottom by the inclusion of warmer molten metal by the advancing glass band. The depth of the area 32 is approx. twice the bath depth in the adjoining area 31. When, for example, the depth of the area 31 is 58 mm, the bath depth in the reserve zone 32 can be lo8 mm.

Below the recess 32, the bottom rises again, for example over a length of 3 meters, to provide an area 33 in the vicinity of the reserve zone with the same bathing depth as the depth of the area 31 above the reserve zone. From the area 33 to the outlet end of the bath, the bottom level is such that an area 34 of the same bath depth is provided as at the entrance end area 30 of the bath, i.e. less than the depth of the reserve zone.

Where there is a change in the bottom level which provides a change in the bath depth, the step in the bottom may be obliquely cut as shown in FIG. 2 or a steep step as shown in FIG. 8th

The provision of a deepened reserve zone only such as the recessed pocket 32 in the region of the bath where the final withdrawal velocity of the tape is obtained has been found to be advantageous as the pocket receives the return flow of colder molten metal created in relation to the direction of movement of the tape. and mixing this colder molten metal with molten metal held in the reserve zone so that the colder molten metal is heated, and there is minimal risk of introducing thermal inhomogeneities under the accelerating glass due to molten metal currents being drawn upwards relative to the direction of movement of the belt from the reserve zone to replace the molten metal included by the accelerating belt.

The effect of the reserve zone is increased in the illustrated embodiments by providing at a location immediately above the area 32 with greater band depth of a transverse barrier 35 extending upwardly from the bottom. The barrier 35 is a carbon bar with upward rectangular cross section and has a dovetail base 36, see FIG. 3, which is wedged into a corresponding dovetail case 37 formed transversely in the container structure at the bottom thereof at the lower end of the flow direction 31, i.e. in the area around the lower end of the thinning zone.

The flat top of the bar is approx. 5o mm long in the band

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10, surface 8 which is sufficient to force molten metal at this location into forward flow 39 which is included under the belt and countercurrent 40 along the sides of the belt from the greater bath depth 32. The barrier 35 ensures that the lower layers of entrained molten metal in the forward flow are directed downwards and then back opposite to the direction of movement of the belt, as indicated by arrow 38 in FIG. 3. Usually, the top surface of the barrier 35 is from 6 mm to 15 mm below the level of the bath surface, the optimum distance being dependent on the speed and acceleration of the tape. In principle, the top of the barrier 35 may be at a depth below the level of the bath surface 8, which is exactly such that all of the included molten metal in the forward flow 39 moves over the barrier, but a return stream of molten metal cannot pass over the. In practice, however, such an accurate adjustment is difficult to achieve, and the barrier height is therefore preferably set as described above to guide the lower layers of the entrained molten metal in the forward flow, as indicated at 38.

The molten metal streams 38 are directed outward and have a favorable effect on the temperature of the molten metal along the sides of the strip by mixing with colder counterflows from the reserve zone, as described below.

In the illustrated embodiments, the barrier 35 extends across the bath past the positions of the band edges, but stops abruptly before the sidewalls 3. Thus, the ends of the barrier 35 are spaced from the sidewalls 3 to form molten metal countercurrent channels indicated by arrows 4o. in FIG. 4, from the reserve zone 32 below the barrier around its ends and into the area above the barrier.

The barrier 35 prevents direct return of molten metal along the bottom of the bath into the area above the barrier location, but allows countercurrent around the ends of the barrier from the greater bath depth area to thereby provide lateral access to the area of the bath which supports the band as it is thinned by acceleration of the bath. the glass above the barrier position.

The transverse barrier 35 is located at a location immediately above the upper end of the bath, relative to the direction of movement of the belt. For example, the barrier 35 may lie 15o mm from the upper end of the pocket area 32. Return flow indicated by arrows 41 in FIG. 3 and 4 of colder molten metal moving along the bottom of the bath in an opposite direction to the direction of movement of the belt towards the barrier site is received in the pocket area 32 with greater depth immediately below the barrier 35. This reduces the velocity of the 11

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leaflets return flow thereby allowing time for mixing of the molten metal in the molten metal return stream contained in the greater bath depth region so that there is time for heating of the molten metal in the return stream. pocket area 32 thus acts as a buffer.

Replacement of molten metal supporting the accelerating glass is effected by means of molten metal countercurrent 40 from pocket region 32 around the ends of barrier 35 and into the region above it, the lateral access provided allowing these countercurrents to move under the belt. .

The provision of the larger bath depth region 32, in which the cold molten metal return current is received, ensures that the molten metal countercurrent 4o along the sides of the band around the ends of the barrier 35 has a relatively small temperature difference between the molten metal at the surface and the molten metal below. surface. Such a small temperature difference between the top and bottom of the molten metal reduces the risk of local temperature variations in the molten metal upon which the glass band is supported while accelerating, thereby minimizing distortion in the lower surface of the band.

Examples of measured temperatures of the molten metal above and below at positions immediately along the edge of the belt are given below, the temperatures being measured by thermocouples at a position A near the lower end of the pocket 32, i.e. 6 meters below the barrier 35, a position B about the middle of the pocket 32 3 meters below the barrier 35, a position C immediately below the barrier 35, ie. at the upper end of the pocket 32, a position D immediately above the barrier 35, a position E 3 meters above the barrier 35 and a position F 6 meters above the barrier 35, i. 2 meters below the last upper rollers 19.

In one operating example, molten glass was added to the bath at a rate of 3,326 tonnes per day. per week to produce a final strip thickness of 2.5 mm with a total width of 3.74 meters, the strip moving at a rate of 865 meters per square meter. hour. The pairs of upper rollers 12 and 15-19 were distributed along the bath at intervals of 3 meters, the last upper rollers 19 being located 8.2 meters above the barrier 35 and positioned with their axes at angles of rotation with respect to an axis perpendicular to the strip direction of movement and was driven at peripheral speeds as given below: 12

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Top rollers Angle of rotation Speed 12 2 ° 165 m / hour 15 5 ° 181 m / hour 16 7 ° 2ol m / hour 17 9 ° 232 m / hour 18 9 ° 291 m / hour 19 9 ° 34o m / hour

The upper and lower defrost temperatures at the above positions immediately along the edge of the belt were measured as follows:

Position Top Tint Temperature Bottom Tent _ (° C) _ Perature (° C) A 797 784 B 807 797 C 818 812 D 836 836 E 826 822 F 841 826

It will be seen that immediately above the barrier 35 at position D, the difference between the bath temperature at the top and bottom zero was less than 5 ° C at a position 3 meters further up at position E.

It has been found that uniformity of temperature can be further improved, i.e. the temperature difference from top to bottom of the molten metal can be reduced further above the barrier if the longitudinal flows of molten metal near the sidewalls of the bath are blocked at a position above the barrier site. To achieve this, a pair of carbon screens or plates 42 can be mounted in the vicinity of the side walls 3 at opposite positions located slightly above the barrier 35 as shown in FIG. 5. The screens or plates 42 have a greater height than the depth of the charge and are mounted on the bottom and adjacent to the side walls, thus completely blocking longitudinal flows of molten metal in the vicinity of the side walls. It is believed that this blockage of longitudinal lateral flows improves the mixing of outward currents indicated by red arrows 43 of relatively hot molten surface metal from the area under the breath with countercurrents 4o of colder molten metal coming from slightly deeper bathing area below the barrier as this mixing occurs along the

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The screens or plates 42 are believed to prevent countercurrents 40 from moving along the side walls of the bath and then under the belt at a supine position without interfering with currents 43.

In one operating example, screens or plates 42 were mounted near the side walls 3 at opposite positions 3 meters above the barrier site, the plates extending inwards from the side wall at a distance of 46o mm. Melted glass was added to the bath at a rate of 3.4oo tons per day. per week to produce a final strip with a thickness of 2.5 mm and a total width of 3.62 meters and with a movement speed of 865 meters per second. hour. The positions of the upper rollers were the same as in the example described above, but the angles of rotation of the last three pairs were changed and the velocities were quite different as indicated below: Upper rollers Angle of rotation Speed 12 2 ° 165 m / hour 15 5 ° 182 m / hour 16 7 ° 202 m / hour 17 7 ° 234 m / hour 18 8 ° 292 m / hour 19 8 ° 338 m / hour

With this arrangement, the temperatures of the bath above and below were measured at positions immediately along the band edges above the barrier, the actual positions being in this case position G 3 meters above the barrier and 1 meter below the carbon plate or shield 42, position H 2.1 meters above the carbon plate or shield 42 and position I approximately at the position of the last upper roller 19. The measured temperatures were:

Position Top tint temperature Bottom tint temperature _ (° C) _ temperature (° C) G 840 842 H 837 828 I 851 839

It will be seen that at position G immediately below the carbon plate or screen 42, the temperature difference from top to bottom was only 2 ° C, the bottom of the bath being warmer than the top, and at position

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14 in comparison with the difference of 15 ° at substantially the same position F in the previous example. Even at position I of the last Upper Roll, the temperature difference between the top and bottom of the bath was only 12 ° C.

Longitudinal streams of molten metal near the side walls of the bath can be obstructed at more than one position above the barrier site. For example, as shown in FIG. 6, a further pair of carbon plates or shields 44 are mounted adjacent the side walls 3 at opposite positions and a distance below the shields or plates 42 such that they are located near or slightly above the barrier site. The gaps between the end of the barrier 35 and the inner ends of the plates or screens 44 are sufficient to allow molten metal counterflows 40 through. The dimensions of the screens or plates 42 and 44, ie. the piece which extends inwardly from the side walls 3 of the bath is selected in accordance with the particular operating requirements, and as seen in relation to the direction of movement of the belt upper screens or plates 42 may extend inwardly different from the portion which the screens or plates 44 below extend inwardly. The effect of the additional pair of screens or plates 44, as shown in FIG. 6, is similar to that obtained by the first pair 42, in that it is thought to effect outwardly flowing hot melt metal 43 from the area under the belt to better blend with countercurrents 40 at a position along the sides of the belt and to preventing countercurrents 40 from moving along the side wall of the bath and then under the belt at an above-lying position without mixing.

FIG. 6 also shows a further pair of top rollers 45 mounted on shafts 46 driven by motors 47 at opposite positions located below the top rollers 19. This additional pair of top rollers 45 is useful in making glass thinner than in the previous examples.

In an operating example with an arrangement as shown in FIG. 6, molten glass was added to the bath at a rate of 3.38o tons per day. per week to produce a final band of 2.3 mm thickness and a total width of 3.65 meters and a moving speed of 94o meters per second. hour. The carbon plates or screens 42 extended 61o mm inward from the side walls 3 and the carbon plates or screens 44 extended 46o mm inwards from the side walls 3. The positions of the top rollers 12 and 15-19 were as described in the previous examples, and the further upper rollers 45 were located at a position 3 meters below the top rollers 19, ie. 5.2 meters above the barrier 35 and 2.2 meters above the plates or screens 42. The angles of rotation and periphery __3 ^ iT λ ρ · + * λ ττ * 5ΐ βΛν trr> v PAm an / τί ττδΊ- * ϊ Α δ + · ΊΤΟ · η -

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4β: Top rollers Angle of rotation Speed 12 2 ° 164 m / hour 15 3 ° 182 m / hour 16 5 ° 202 m / hour 17 7 ° 234 m / hour 18 8 ° 292 m / hour 19 8 ° 338 m / hour 45 8 ° 400 m / h

The bath temperatures at the top and bottom were measured immediately along the band edge at a position J 3 meters below the barrier 35, ie. in the pocket 32, position K immediately below the barrier .35 at the upper end of the pocket 32, position L immediately above the barrier 35 and the screen 4M, position M approximately at the position of the upper roller 45 <and at position N approximately at the position of the Upper roller 71¾. The measured temperatures were as follows:

Position Top tint temperature Bottom tint temperature _ (° C) _ temperature (° C) J 811 799 K 813 797 L 842 842 M 854 837 N 865 856

It will be seen that the temperature difference between the top and bottom immediately above the barrier 35 at position L was again zero as at position D in the example described above with reference to FIG. 4. The temperature difference between top and bottom at the position of the top roller 19, position N, was only 9 ° C. However, at the position of the last pair of upper rollers 45, the temperature difference between the top and bottom of the bath was somewhat higher, being 17 ° C at position M.

The screens or plates 42 and 44 were then changed to increase their length by 15o mm, so that the screens or plates 42 extended 76o mm inward from the side walls 3 and the screens or plates 44 extended 61o mm inwards. The innermost ends of the screens or plates 42 were then only 155 mm from the edges of the tape.

In an operating example with this modified screen or plate 16

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3.37o tons per per week to produce a final tape of 2.3 mm thickness with a total width of 3.58 meters and a moving speed of 94o meters per second. hour. The positions of the top rollers 45 were shifted 61o mm upwards so as to be approx. 2.45 meters from the top rollers 19. The angles and speeds of the top rollers were as follows: Top rollers Rotation angle Speed 12 2 ° 162 m / hour 15 3 ° 18o m / hour 16 5 ° 201 m / hour 17 6 ° 232 m / hour 18 7 ° 284 m / hour 19 7 ° 330 m / hour 45 7 ° 493 m / hour

With this arrangement, the temperature difference between the top and bottom of the bath was at the position of the last upper rollers 45, i.e. position M in FIG. 6, reduced to 12 ° C.

In another operating example with an arrangement as shown in FIG. 6, a strip of thinner glass was produced at a significantly increased final band speed. Melted glass was added to the bath at a rate of 3.41 ounces per hour. per week to produce a final strip with a thickness of 1.8 mm, a total width of 3.37 meters and a movement speed of 1.252 meters per square meter. hour. The screens or plates 42 and 44 were positioned as in the previous two examples, but the screens 42 extended 51o mm inwards and the screens 44 extended 61o mm inwards. Thus, in this example, as seen in the direction of movement of the belt, lower screens 44 were slightly louder than upper screens 42. The upper rollers were located as in the above-described example and had the following angles of rotation and velocities: Upper rollers Rotation angle Speed 12 2 ° 163 m / hour 15 3 ° 180 m / hour 16 5 ° 201 m / hour 17 6 ° 232 m / hour 18 10 ° 284 m / hour 19 10 ° 324 m / hour 45 11 ° 402 m / hour

Temateraturn lines at ton οσ bottom of bath 7-mm part bare lanrrs 17

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the band of the tape was performed at the previously described positions J, K, L, M and N as well as at further positions below, namely at position 0 immediately below the lower end of the pocket 32 and a position P in the pocket 32 immediately above its lower end. The measured temperatures were as follows:.

Position Top tine temperature Bottom tine temperature (° C) temperature (° C) 0 748 729 P 774 754 J 783 772 K 775 765 L 831 830 M 837 818 N 844 830

It will be seen that the temperature differences from top to bottom are 14 ° C at position M at the last upper rollers 45, increase 19 ° C at position N at the penultimate upper rollers 19. Even at this high belt speed which is 45% faster however, than the first two examples described above and 33% faster than in the other examples, it will be seen that the temperature difference from top to bottom of the bath immediately above the barrier at position L was only 1 ° C. Furthermore, the effectiveness of the relatively deep pocket area 32 is particularly evident in this example, since the temperature difference from top to bottom of the bath at the lower end of pocket 32, positions 0 and P, was 20 ° C, but was reduced to 100 ° C at top end of pocket, positions J and K.

It was also found that the arrangement with the pocket 32 and the barrier 35 had an advantageous effect by reducing lateral temperature variations across the bath and temperature variations in the band from the edges towards the center.

The barrier 35 need not stop some distance from the sidewalls of the container structure as in the embodiments shown, but can extend all the way to the sidewalls 3 with cut-outs in the top of the barrier along the sides of the strip to provide channels for the molten metal counterframes arriving. from the elaborate area 32.

The area 33 of smaller bath depth immediately: below the area 32 has the same depth as the area 31 above the barrier 35. Area 33 separates the deepened area 32 from the outlet area 34, which has a smaller bathing depth than the bathing depth in the deepened area 32, but greater bathing depth. 18

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{Relief for cold molten metal return flow along the very bottom of the bath in outlet region 34, thereby reducing the rate of return flow as the return stream enters the region 32 with greater bath depth, and mixing of the return stream with the molten metal in the region 32 is increased. The area 33 also provides an area of relatively low bath depth where linear motors mounted over the bath can be used particularly effectively to control molten metal flows.

However, the depth of the bath may be constant from the lower end of the pocket area 32 to the outlet end of the bath. The provision of an increased bath depth along the outlet area 34 relative to the bath depth in the area 31 above the barrier 35 enables the effective placement of refrigerators at the outlet end of the bath.

If desired, linear induction motors can be used to increase or regulate molten metal flows in the region of barrier 35. FIG. 7 shows a pair of such motors 48 mounted above the surface of the bath above the barrier 35 in relation to the direction of movement of the belt to induce electromagnetic paths by flowing molten metal currents from countercurrents 40 to enter below the accelerating band. Alternatively, the motors 48 may induce molten metal flow in an outward direction to increase outward currents 38 and / or 43 and assist in mixing these outward currents with countercurrents 40. Linear induction motors can also be positioned as indicated by dotted at 49 in FIG. 7 to promote the movement of molten metal in the pocket 32 into the counterflows 4o. Additional linear induction motors may be arranged as indicated at 5o and 51 to direct the countercurrents.

Submerged or partially submerged heaters adapted to cause selective local heating of molten metal flowing under the heaters may also be used to heat the countercurrents. For example, a pair of such heaters 52 may be disposed near each end of the barrier 35 to heat the countercurrents 40.

If necessary, small extension pieces 53 can be found at each end of the barrier to ensure that all of the molten metal flow past this end of the barrier is conducted under the respective heater 52. Heaters may also be used in conjunction with or in place of the linear induction motors at the positions 5o and 51.

As shown in FIG. 8, the bottom FL of the container structure may be formed by abutting blocks 54 of refractory material, preferably refractory aluminum silica material, which is attached in known manner to a metal sheath or metal housing 55 surrounding the container structure. The tops of the blocks form the bottom of the molten metal.

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smaller height dimension than the blocks in the adjacent areas 31 and 33, so that the upper sides of the blocks in the zone 32 are at a lower level than the upper sides of the adjacent blocks.

As shown in FIG. 2 and 3, however, where the vertical dimension is greatly exaggerated relative to the horizontal dimension, the blocks may be arranged to provide a stepped bottom of the container structure such that the upper sides of blocks of the same height dimension at the entrance end of the container structure lie at different levels so that provide different bath depths in areas 30 and 31, and in the area around the outlet end of the bath, the upper surfaces of blocks of different height dimensions are at the same level to provide the same bath depth in area 34.

The method and plant of the present invention are particularly advantageous for the manufacture of float glass having a thickness in the range of 1.5 mm to 3 mm. The invention can advantageously be used in the manufacture of larger-thickness floating glass, when the charge and band speed is such that there is an adverse movement of the molten metal, e.g. for glass with a thickness up to 5 mm or more. The method and plant according to the invention can be used in the manufacture of glass of even greater thickness.

Although the invention has been specifically described above in connection with a bath with a shoulder area, it can also be used in a parallel-walled container structure having a constant spacing from the inlet end to the outlet end or container structure.

If desired, one or more additional barriers may be placed on the bottom of the container structure to extend upwardly in the bath at one or more positions located above the barrier 35, for example, as described in the aforementioned British patent specification.

Furthermore, the barrier 35, although conveniently designed and mounted on the bottom ridge as described above, may have a different shape, e.g. as described in the aforementioned patent, and in particular it may be cylindrical. One or more additional barriers may also take any of the forms described in the aforementioned patent, and may, if desired, be movable between different positions along the bath as described therein.

Claims (20)

20 DK 154338 B Patent claims. A method of producing flat glass, wherein a glass band is moved forward along a molten metal bath, and traction is applied to the final glass band to accelerate the glass to a final withdrawal rate and, as the glass is accelerated, causes the ever-increasing inclusion of the molten metal of the bath over a return stream of colder molten metal from the outlet end of the bath, characterized in that in the region of the bath where the final withdrawal rate of the strip is obtained, the return stream of colder molten metal is absorbed in an area of greater bath depth than the bath depth in the adjacent areas, from which region with greater bath depth, molten metal flows are drawn in the direction opposite to the direction of motion of the belt to replace the molten metal included by the accelerating belt. Method according to claim 1, characterized in that the area of greater bath depth extends over a length in the direction of movement of the strip sufficient to ensure mixing of the molten metal in the return stream with molten metal contained in the area of greater bath depth. Method according to claim 1 or 2, characterized in that the molten metal bath is accommodated in the container structure with a bottom formed of adjacent blocks of refractory material, the upper side of which determines the level of the bottom of the molten metal bath and bathing depth is formed by blocks whose upper sides are located at a lower level than the tops of the blocks which determine the bathing depth in the vicinity of this area. Method according to any one of claims 1-3, characterized in that the return flow of colder molten metal is limited to a depth less than the depth of said area of greater bath depth, whereby the speed of the return flow decreases as the return flow enters. into said area of greater bath depth and mixing of the return stream with the molten metal in that area is increased. Process according to any one of claims 1-4, characterized in that the stream of molten metal entrained by the glass band is defined at a location immediately above said area of greater bath depth to a surface area of the metal bath and the streams drawn from it. In the area of greater bath depth, the currents take the form of currents along the side edges of the glass band from said area to the area of the metal bath which supports the glass band above the area of greater bath depth. Method according to claim 5, characterized in that the applied traction force is regulated to thin the strip to a desired width and thickness in a thinning zone, whereby the glass is accelerated along the bath and said delimitation of the flow of molten metal occurs in the downstream region of depletion zone. A method according to claim 5 or 6, characterized in that the countercurrents along the sides of the belt are selectively heated. The method of claim 6 for the manufacture of float glass having a thickness in the range of 1.5 mm to 3 mm, wherein: edge forces are applied to the accelerating glass in a series of opposite positions distributed along the bath to control bandwidth reduction and - thickness, characterized in that said demarcation of the flow of molten metal is made at a location in the region about the lower end of the thinning zone as seen in the direction of movement of the belt and a distance below the lower position at which edge forces are exerted on the belt. A flat glass manufacturing plant according to the method of claim 1, comprising an elongated container structure with end walls, side walls and a base for accommodating a molten metal bath, means for supplying glass to the bath at a controlled rate and conveying the glass in ribbon form along the bath, and means for applying a pulling force to the final glass ribbon to accelerate the glass to a final withdrawal rate, characterized in that in the region (32) of the container structure where the ribbon achieves its final withdrawal velocity is bottom of the receptacle the construction made deeper to form a reserve zone for receiving the return flow of colder molten metal which is forced in a direction opposite to the direction of movement of the belt over the bottom at it. forward-moving glass ribbon inclusion of warmer molten metal, which is spaced apart from the container end wall of the structure at the glass rib's point of removal. Installation according to claim 9, characterized by a transverse barrier (35) on the bottom (FL) of the container structure at a location immediately above the deeper container bottom (32), which barrier (35) extends beyond the position of the edges of the railing DK 154338 B, the upper part of the barrier being located below the level of the bath surface at a distance effective for forcing molten metal flow at this location substantially for forward flow of molten metal included under the belt and for a countercurrent of molten metal along the sides of the ribbon. Installation according to claim 10, characterized in that the reserve zone (32) formed at the bottom of the container structure immediately below the barrier (35) has a greater depth than the bathing depth above the barrier. Installation according to any one of claims 9-11, characterized in that the depth of the reserve zone (32) is approximately twice the bathing depth in the vicinity of said zone. Installation according to any one of claims 9-12, characterized in that the reserve zone (32) extends over the full width of the bottom of the container structure. Installation according to any one of claims 9-13, characterized in that the container structure is enclosed in a metal sheath (55), the bottom (FL) of the container structure comprising adjacent blocks (54) of refractory material. which is attached to the metal sheath and that the reserve zone (32) of greater bath depth is formed by blocks (54) whose upper sides are at a lower level than the upper sides of the adjacent blocks. Plant according to claim 14, characterized in that the upper sides of the blocks (54) above and below the reserve zone (32) are at the same level. Installation according to claim 11, characterized in that the bottom (FL) of the container structure below the barrier (35) is constructed such that, seen in the direction of movement of the belt, it forms the said reserve zone (32) with greater depth than the bathing depth above the barrier (35), a region (33) of less depth than the reserve zone (32) and a further region (34) of greater depth than the bath depth above the barrier (35), which further region (34) extends to the outlet end (2) of the container structure. Installation according to any one of claims 9-16, characterized in that a steep step is provided, whereby the bottom determines a change in bath depth. Installation according to claim 10 or 11, characterized in that the elongated container structure has a shoulder area (4) which connects an upper portion with a larger bath depth DK 154338 B with a portion below a smaller bath depth and that the reserve zone (32). ) with greater bath depth is located at said shoulder area, and the barrier (35) is located immediately above the shoulder area. A system according to claim 10 or 11, characterized by upper rollers <12,15,16,17,18,19,45) adapted to engage with the upper surface of the stripe edges at a series of opposite positions along the bath to control the reduction in width and thickness of the belt, wherein the pair of upper rollers (19), which are furthest forward in the direction of movement of the belt, are located at a position slightly above the barrier (35). System according to claim 10 or 11, characterized by heaters <S2) mounted near the side walls (3) of the container above the barrier (35) seen in relation to the direction of movement of the belt to provide local heating to the countercurrent of molten metal.