MXPA98002597A - Process and apparatus for modifying and homogenizing glass melts - Google Patents

Abstract

A method of modifying a base glass composition so as to change its properties in which molten glass is caused to flow in a stream unidirectionally through a substantially horizontal channel with the modifying material then being added thereto. The horizontal and vertical distribution of the modifying material in the glass stream are effected separately. The molten glass with the modifying material homogeneously distributed therein is then delivered to a forming facility.

Description

PROCESS AND APPARATUS TO MODIFY AND HOMOGENIZE GLASS MASSES The present invention relates to the manufacture of glass and more particularly to the modification of base glass to change its properties, for example to impart a desired color. The concept of adding a colorant to the molten glass base is well known, but it is believed that it has to be practically applied in the field of the glass container (sometimes referred to as "coloration prior to the crucible") more than in the field of flat glass. This is mainly due to the fact that the quality and, especially, the bubble and homogeneity requirements for flat glass are higher than those for the container glass and for floating glass that continuously become more resistant. In particular, apart from special products of the "artistic" type, the coloring of flat glass and especially of floating glass needs to have a uniform inking throughout the area and therefore, the coloring material must be added distributing it very evenly in the glass. In addition, the addition and distribution must be done in a manner that produces unacceptable bubbles. However, proposals have been made to add the coloring material to the composite of the molten glass base to produce a colored flat glass. It will be understood that, if this can be done successfully, it will greatly reduce the changeover time to make clear flat glass and colored flat glass, or to effect a change in dye from one color to another, which is required when a Different composition has to be melted in the tank or basic melting furnace. EP 0 599 403A presents an arrangement for making containers for colored glass, EP 0 556 576A presents a coloration arrangement of glass or window glass compositions for vessels and EP 0 275 534A presents an arrangement for making colored floating glass. All arrangements have some form of action to mix the coloring additive material in the molten glass. EO 0 599 403A has a bubble pusher, while EP 0 556 576a, which is particularly concerned to avoid bubbles, has an arrangement of mechanical stirrers. EP 0 275 534A also has an arrangement of mechanical agitators. It will be understood that each of the agitators in these arrangements imparts the same type of stirring action to the glass. This type of stirring action does not achieve the uniformity required for the distribution of the coloring material within the glass.

According to the present invention, a method is provided for modifying a base glass by changing its properties, which comprises flowing the molten glass base in virtually one direction in a stream or flow along a substantially horizontal channel, adding the modifier material to the molten glass base that flows horizontally and vertically distribute the modifier material in the molten glass, separately distribute the modifier material, horizontally in the molten glass with a transverse component in the direction of travel or displacement of the flow, and deliver or distribute the flow of molten glass with the modifier material substantially homogeneously distributed therein to the training facility. When a vertical and horizontal distribution of the modifier material in the molten glass is carried out separately, a more even dispersion can be achieved and in this way, bubbles that are not well accepted are avoided. The modifier material can be added to the molten glass base and then, formed separately, it is distributed vertically in the molten glass. This vertical distribution can be effected by stirring the molten glass base which flows horizontally carrying the modifying material so as to cause a relative vertical movement within the glass.

The vertical agitation can be carried out by rotating substantially vertical axes in which a blades are placed in the form of impeller blades, at least partially in the molten glass. These mechanical stirrers can be made of refractory material, and preferably of refractory metal such as platinum. The modifier material can be horizontally distributed in the molten glass by stirring the molten glass base that flows horizontally, carrying the modifying material in such a way as to cause horizontal relative movement within the molten glass with a component transverse to the direction of travel or displacement of the flow. The horizontal flow is preferably carried out by rotating the substantially vertical axes, in which the blades are placed at least partially immersed in the molten glass. Preferably, the agitation to produce a relative vertical movement is carried out before the separate agitation to cause a relative horizontal movement. In other words, the vertical agitation is effected upstream of the horizontal agitation with respect to the flow displacement of the molten glass.

The glass base can be substantially transparent glass or inked glass and the modifying material can be dye material to thereby produce inked glass or modify the dye of the colored glass base. It will be appreciated that the uniform distribution of the modifier material will produce a uniform inking. Preferably, the modifying material is in molten form as it is added to the molten glass base. This can slide on the upper surface of the substantially horizontal flow of the molten glass base. Alternatively, it can be added below the surface of the molten glass base, for example, by inserting it from a member whose feed end is immersed in the molten glass and can be added so that it is distributed vertically in the glass melted as it is added. The training facility can be a flat glass factory (and especially float glass) and the method can comprise the formation of molten glass with the modifier material distributed substantially homogeneously in the flat glass (and especially in the float glass). In addition, the invention provides flat glass (and especially float glass) produced by means of this process.

Another aspect of the invention is to provide an apparatus (suitable for use in the method according to the invention, but not exclusive) to add the modifying material during the displacement of the substantially horizontal flow of the molten glass base comprising a member of feed having a lower portion for immersion in the molten glass and with an outlet for the modifying material, and mechanisms for feeding or providing the modifying material in the feed member so that it exits through its outlet into the flow of molten glass, below its surface, where the outlet is extended by means of a vertical component such that it distributes the modifying material, at least, over most of the depth of the flow. The outlet may be on one side of the feeding member which, in use, faces towards the direction of travel or displacement of the flow and preferably comprises a series of holes that may be arranged, for example in a substantially vertical line. Preferably, the modifier material emerges from the melt outlet and the apparatus may comprise a melter to melt the modifier material and provide it in a molten state in the feed member. Preferably, the melter includes a filter device to prevent unwanted material that can be introduced into the feed member. Conveniently, the feeding member is a tube. Next the forms will be described. of embodiment according to the invention, by means of the examples and in relation to the accompanying drawings, wherein: Figure 1 is a plan, schematic view of the furnace or tank for melting the glass. Figure 2 is a vertical section, schematic, through the feeder for the modifying material. Figure 3 is a vertical section, schematic through an alternative form of the feeder for the modifying material. Figure 4 is a vertical section, schematic of another form of the feeder for the modifying material. Figure 5 is a schematic, planar view of the furnace or tank for melting the glass, and Figure 6 is a schematic, planar view of the entrance to an installation for the formation of floating glass or a glass bath. The furnace or tank for melting the glass shown schematically in Figure 1 comprises an upstream part 1 having a melting zone or area 2 and a refining zone or area 3 connected by means of its central part 4. at one end of work 5. Channel 6 leads from work end 5 towards outlet 7 at the entrance to the training facility. The material the batch is fed into the melting zone 2 in the well-known manner and melted there to form the molten glass which is then refined, ie the bubbles are removed, in the refining zone 3. The molten glass passes through the central part 4 towards the working end 5 and then travels along the channel 6 towards the outlet 7, the conditioning of the glass it is carried out at the working end 5 and the channel 6. Those skilled in the art will understand that, generally, fixed connections are not required between the melting, refining and conditioning zones. The central part 4, the working end 5 and the channel 6 form a substantially horizontal channel through which the molten and refined glass base, in part 1 of the tank, moves in a substantially unidirectional flow, ie water down to exit 7 without any upstream travel. Preferably, the flow of molten glass is also displaced unidirectionally in the downstream part of the refining zone 3, for example by a distance upstream of the central part 4 approximately the same as the width of the flow. The feeders 8 placed in the. central part 4 add the modifying material, for example dye, to the molten glass base which flows horizontally and the modifying material is distributed vertically in the molten glass by means of the stirrers in the form of helices. 9 placed towards the end upstream of the working end 5. The agitators 9 comprise vertical shafts that carry blades in the form of helices at least partially immersed in the molten glass so that in this way the shafts produce a stirring of the glass base A horizontally flowing cast that carries the modifying material to cause a relatively vertical movement within the molten glass that distributes the modifying material vertically. In addition, downstream of the agitators 9 and towards the upstream end of the channel 6, are the agitators 10 which are designed to distribute the modifier material horizontally in the molten glass with a component transverse to the direction of flow travel, is say laterally or transversely. This horizontal distribution is carried out separately from the vertical distribution that is effected by means of the agitators in the form of helices 9. The agitators 10 comprise vertical axes carrying blades of substantially vertical blades, at least partially immersed in the molten glass , so that the rotation of the shafts produces an agitation of the molten glass base horizontally, carrying the modifying material so as to cause a relative horizontal movement inside the molten glass with a component transverse to the direction of the displacement of the flow that it distributes in modifier material horizontally across the width of the flow. The agitators in the form of helices 9 and the paddle agitators 10 each have a shape known per se and are made of a suitable refractory material and preferably of a refractory metal such as platinum. The propeller-shaped agitators 9 are shown as a pair rotating in the same direction (indicated by arrows in the counter-clockwise direction) while the paddle agitators 10 are shown as a torque rotating in directions opposite (indicated by the arrows) in the way it has to drive the molten glass between them. However, it will be appreciated that the number of agitators (along the flow) and their direction of rotation may be selected according to the particular requirements, but must be sufficiently effective to cover the total width of the flow of molten glass in the locations of the agitators. Also it will be appreciated, that in. the practice of purely vertical or horizontal relative movement within the molten glass can be difficult, if not impossible, to be achieved by means of respectively different agitators and references to horizontal or vertical movement have the intention of indicating predominantly horizontal and vertical movement respectively. further, the connoisseurs of the technique, will appreciate that when making a vertical movement (predominant) and a horizontal movement (predominant) separately by means of respectively different agitation actions, produced by the agitators 9 and 10, a relatively simple total arrangement can be used, if it is compared, favorably, with various much more complicated arrangements of agitators, which are sometimes used in the manufacture of glass containers. In Figure 1 of the embodiment, the temperature of the glass in place of the agitators 9 can vary from 1200 ° C to 1450 ° C, for example about 1300 BC. In the place of the agitators 10 the temperature of the molten glass can vary in a range from 1150 ° C to 1400 ° C, for example about 1280 ° C. The longitudinal distance between the location of the agitators 9 and that of the agitators 10 is sufficient to avoid a clash of the mixture and, from this point of view, an amplitude of the flow of molten glass, which optically can be several between 1 mm, is preferable. up to 4 mm. However, it may be desirable to make this distance greater to avoid adverse interaction between operations that can, in particular, generate bubbles. Thus, the preferable distance is greater than twice the width of the flow of molten glass, ie, of the working end 5m and typically can be in the range from 2m to 8m, for example about 4m. The depth of the molten glass flow is such that it is consistent with the unidirectional flow and typically can vary between 200 mm to 800 mm, for example about 500 mm with a long channel (for example 50 m in length) or approximately 250 mm with a shorter channel (for example 10 m in length) at the location of the agitators. The location of the agitators 9 is not particularly critical but may, for example, be a distance downstream from the feeders 8 which is approximately equal to the width of the flow of molten glass, i.e. from the working end 5. Figure 1, shows schematically three feeders 8 spaced in the direction of the width of the central part 4, wherein the temperature of the molten glass can typically be from 1200 ° C to 1480 ° C, for example about 1320 ° C. It will be understood that any suitable number of feeders can be provided and that the feeders can take any desired shape. Preferably, this number is such that the material that is added is molten as it is added to the molten glass base. In Figure 2, a simple form of feeder is shown schematically. This comprises a vertical tube 11 having a funnel 12 in the upper part or end. The tube is placed in the refractory ceiling 13 in the central part 4 (whose base is shown in Figure 2) and the lower part of the tube 11 enters the molten glass so that its end 14 is below the surface S of the glass. There is a clearance between the ceiling 13 and the surface S of the molten glass through which the tube 11 passes and this provides a sufficiently hot environment for melting the addition material in the tube. In use, the additive material of a suitable form, for example tablets, is fed into the funnel 12 in any desired and convenient manner, and melts as it travels or moves, thanks to gravity, towards the tube 11. It emerges from the lower end 14 of the tube (as indicated by the arrow) below the surface S, and therefore in the flowing body of the molten glass base that flows (as indicated by the arrow) ) towards the agitators) (Figure 1). Figure 3 indicates, schematically, an alternative form of feeder that is a modified version of that shown in Figure 2 and has the same reference numbers indicating the same parts. The version of Figure 3 differs from Figure 2 in the lower part of the tube 11. In Figure 3 the tube ends in a conical portion 15 with a central hole leading to a vertical tube 16 having an associated guide 17 that has a slight shape to guide the addition material from a vertical path to a horizontal path. The lower end 18 the tube 16 is separated a small distance above the level of the surface S of the molten glass to give it a fall height preferably three times smaller than the diameter of the tube orifice, whose orifice diameter can be, for example, approximately 10 mm. The lower end 19 of the guide 17 is flush with the surface S of the molten glass. The molten additive material travels by gravity towards the lower part of the tube 1 and passes through the central hole in the conical portion 15 in the tube 16 to emerge from its lower part 18 from where it falls on the guide 17. Then, the molten additive material it slides smoothly on the surface S of the molten glass base from the end 19 of the guide 17. It will be appreciated that by causing the molten additive to enter below the surface of the glass as seen in Figure 2 or to slide towards the surface of the glass as indicated in Figure 3, bubbles are avoided or minimized, which would otherwise occur (for example if the additive material were allowed to fall directly into the glass). Figure 4 shows, schematically, a further form of feeder that introduces the additive material below the base surface of molten glass. This comprises a vertical feeding member in the form of a tube 20 having a lower end portion 21, which enters below the surface of the glass. The lower end 22 of the tube is closed and the immersed end portion 21 has on one side an outlet that extends in a vertical direction formed by a series of small holes 23 arranged in a vertical line and facing the flow direction of travel of molten glass (as indicated by the arrow). The additive material in the molten state in the tube 20 emerges through the holes 23 (which may be, for example, about 1 mm in diameter) in the molten glass base. Since the orifices are distributed vertically along the immersed end portion 21 of the tube, the additive material is distributed vertically in the molten glass by a larger portion and preferably in the total depth of the flow as it is added. The upper part of the tube 20 carries a portion of the head with a larger diameter 24 above which is the hollow melting device having an inclined part 25 and a horizontal part 26 located in a hot environment. The hollowed-out melting device can be heated directly by electricity, although alternative methods of heating can be used. A pair of superposed baffles 27 and 28 are arranged in the horizontal part 26 just upstream of the outlet pipe 29 in its lower part which feeds the portion of the head 24 of the pipe 20. The inclined part 25 of the melting device has an inlet 30. in which, with use, the tablets of additive material are supplied for their fusion. The molten additive material passes along the horizontal part 26 of the deflectors 27 and 28 which can only pass through the flow below the upper deflector 27 and then over the lower deflector 28. By means of this arrangement, with the edge lower of the upper baffle 27 at a lower level than the upper edge of the lower baffle 28, the baffles form a filter device against debris or any other undesirable material, allowing only the clean, molten additive material to pass between them. Then, this material flows through the outlet tube 29 to the head portion 24 of the tube 20 and down into this tube to emerge through the holes 23 in its lowermost portion 21, which was described above. Since with this embodiment the feeder of the molten additive material is distributed vertically in the molten glass base as it is added to it, it may be unnecessary to provide an additional vertical distribution, for example by means of the propeller-shaped stirrers. as described above. Thus, Figure 4 shows, schematically, a pair of agitators with vanes having a vertical axis 31 carrying the vertical vanes projecting 32 at their lower lower end. The axes 31 rotate (as indicated by the arrow) and the immersed paddles 32 agitate, horizontally, the molten glass base that flows carrying the modifying material so as to cause a horizontal movement within the molten glass with a component transverse to the direction of flow displacement. This distributes the modifier material horizontally in the molten glass. The feed tube 20 and the agitator shaft 31 are suitably mounted to pass through the roof 33 above the substantially horizontal channel along which the flow of molten glass is displaced and whose base is indicated by the number 34 in Figure 4. An upper portion of the tube 20, which passes through the refractory structure of the roof 33, is directly heated by electricity in order to ensure that the temperature is maintained at the point that the flow of liquid additive will continue to flow. Figure 4 further shows electric heaters 35 mounted in the free separation between the roof 33 and the molten glass surface S which also heats the tube 20 to ensure the flow of liquid additive. A number of tubes 20 and a number of paddle agitators can be separated through and / or along the glass flow. Preferably, the paddle agitators are placed at a relatively small distance downstream from the tubes 20 so as to present the molten glass carrying the modifier material thereto and avoid any substantially vertical displacement, ie sinking of the modifying material. It will be appreciated that the vertical line that was described 23 in the lower end portion 21 of the tube 20 is presented by way of example and other output arrangements may be employed. The output that is required does not necessarily give to the direction of travel of the flow and, as another example, may be a series of holes arranged around the circumference of the tube which, if desired, could be rotated. In addition, the tube that is required is not necessarily vertical but can be tilted in whole or in part so that the outlet extends with a vertical component. In particular, the immersed end portion 21 could be at an angle along the direction of flow displacement so that the lower end 22 is lower than the upper end thereof. Similarly, the non-immersed portion of the tube 20 could be inclined if a straight tube is used or it could be vertical with a fold in the region of the glass surface S to provide a lower inclined portion 21. Other possibilities are possible different arrangements for particular geometry required. Also, the modifying material that is required does not necessarily have to be melted separately as described with reference to Figure 4, but it could be melted in a tube 11 as described with reference to Figure 3. A shorter tube 20 of the Figure 4 can be connected to the lower end of tube 11 in Figure 3 instead of tube 16 and guide 17. If desired, vacuum or reduced pressure can be applied to tube 11 so as to have a degassing effect on the material containing to reduce the risk of bubbles. Figure 5 is a schematic view similar to that of Figure 1 and uses the same reference numbers to indicate the same parts. The arrangement of Figure 5 has a pallet feeder and agitators as those described with reference to Figure 4, both located at the working end 5. For ease of illustration, Figure 5 shows a simple feeder 36 and a simple pair of paddle agitators 37, whereas, in practice, a variety of feeders could be used, for example two or three, and normally, there would be a respective pair of agitators associated with each feeder. With a variety of feeder tubes across the width of the molten glass flow, preferably there is a space therebetween which is a distance equal to or less than the spacing of the shafts of the blade agitator so that each feeder is clearly associated with a particular pair of blade agitators. The longitudinal distance of the agitators 37 from the feeders 36 is, preferably smaller than the spacing between the centers of the agitators which may be, typically, in the range from 300 mm to 1.3 m, for example 600 mm. The temperature of the molten glass at the location of the agitators 37 can be, typically, in the range from 1100 ° C to 1400 ° C, for example about 1180 ° C. Pallet stirrers in addition to the agitators 10 in Figure 1 can be retained in Figure 5 of the embodiment in the direction of the upstream end of the channel 6. If desired, additional paddle agitators 38 can be provided in the direction of the water end. down channel 6 both in Figure 1 and Figure 5 of the embodiments for effecting a further horizontal distribution of the additive modifier material. Generally, Figures 1 and 5 indicate an outlet 7. The flow of molten glass with the modifier material distributed substantially homogeneous therein is supplied from the outlet to the forming facility. Figure 6 indicates, schematically, an installation for forming floating glass comprising a flotation bath 39 in which the molten glass is delivered from the conduit 40 with an associated control wheel 41. For this installation the outlet 7 in Figures 1 and 5 are connected with a conduit 40 of Figure 6 and the molten glass supplied with the modifier material distributed substantially homogeneously therein is formed in a well-known float glass. The problems of the bubbles are avoided or minimized by first refining the molten glass and then adding and distributing the modifier material in the manner already described. The numerical values of the temperature and dimensions given by the above examples all relate to an oven or tank for melting glass for an installation or plant in which float glass is formed. Despite considering the high quality requirts of the flotation glass, the invention is particularly useful for flotation glass, other forms of flotation glass could be applied as for example rolled sheets or sheets. The invention can also be applied to other types of glass products such as television containers or tubes. In each case the outlet from the furnace or tank for molten glass is connected to an appropriate installation or plant. As indicated above, the modifying material can be coloring material. The base glass to which the dye is added can be transparent glass so that the dye gives a dye to a base glass can already be inked so that the dye changes the dye. In the latter case, the output of the modifier dye can be recirculated to the melting tank for the base dye. However, modifiers can be used for other properties besides color (for example, refractive index). It will be understood that with flat glass, which is usually seen through the thickness of the glass, a substantial change in the dye (or other property) in the glass area is easily observed while the change in thickness is generally less noticeable. Therefore, an even distribution of the modifier material in a glass area is more important than even distribution throughout the thickness and is referred to herein as a substantially homogeneous distribution in relation to the flat glass that is made in accordance with this. It will be appreciated that the accompanying drawings, especially Figures 1 and 5, are purely schematic and not to scale. The method of the invention can be used in a wide variety of furnaces or glass melting tanks and Figures 1 and 5 show, in diagram form, one of these as a lustration. Therefore, it will be understood that the substantially horizontal channel (provided with elts 4, 5 and 6 in Figures 1 and 5) can, but does not necessarily require, having changes in the width and / or depth along its length, preferably these changes are made gradually rather than step by step. In addition, the unidirectional displacement of the molten glass stream preferably begins upstream of the aggregate modifier material (e.g. in the refining zone or area 3 in Figures 1 and 5). Variations will be apparent to those skilled in the art from the embodiments especially described in the invention, which can be made without departing from the principles of the invention. For example, and although it will usually be preferable to carry out the vertical distribution of the modifier material in the molten glass prior to making the horizontal distribution, it can make circumstances in which the horizontal distribution before the vertical is usually effected. Also, the distribution of the modifier material in the molten glass can be done by other means than those described herein. Thus, in particular, the vertical distribution can be performed by the convection of currents produced by the heaters, such as electronic heaters, rather than by mechanical stirrers or there could be a combination of electrodes and stirrers. Further, while in the preferred embodiments of the furnace or molten glass tank it is described as a simple power unit, a tank can feed a variety of outputs connected with a variety of training facilities. If desired, the modifications to the glass can be carried out in the channel between the melting furnace or tank and the respective forming installation so that the different installations or lines can produce different products, for example as described in the Patent. of Invention of the United Kingdom No. 9616364.7

Claims (15)

1. A method for modifying a glass base to change its properties which comprises causing a molten glass base to flow substantially in one direction in a displacement along a substantially horizontal channel and to add the modifying material to the molten glass base that flows horizontally, characterized by the distribution of the modifier material vertically in the molten glass, the separate distribution of the modifier material horizontally in the molten glass with a distribution component transverse to the direction of flow displacement and the delivery of the glass stream fused with the modifier material that is distributed substantially homogeneously therein to the training facility.

2. The method according to claim 1, characterized in that the modifying material is added to the molten glass base and then distributed separately, vertically, in the molten glass.

The method according to claim 2 characterized in that the modifying material is vertically distributed in the molten glass by stirring the molten glass base which flows horizontally carrying the modifying material so as to cause a relatively vertical movement in the molten glass .

4. The method according to any of the preceding claims characterized in that. the modifier material distributes horizontally in the molten glass by stirring the molten glass base that flows horizontally carrying the modifier material so that a relatively horizontal movement is caused within the molten glass with a transverse component in the direction of travel or displacement of the flow .

The method according to claim 3 and 4, characterized in that the agitation causing a relatively vertical movement is carried out before the separation agitation to produce a relatively horizontal movement.

The method according to any of the preceding claims characterized in that the material that is added is in molten form as it is added to the molten glass base.

The method according to claim 6, characterized in that the molten material that is added slides on the surface of the molten glass base.

The method according to claim 6 characterized in that the additive melt material is added below the surface of the molten glass base.

9. The method according to claim 8 characterized in that the additive material is added in a form that is vertically distributed in the molten glass as it is added.

The method according to any of the preceding claims characterized in that the forming installation is for flat glass, optionally for float glass, and comprises the formation of molten glass with the modifier material distributed substantially homogeneously in the flat glass , optionally in the floating glass.

11. The flat glass, and optionally in float glass, which is produced by a process according to claim 10.

12. The apparatus for adding modifier material to a substantially horizontal flow of molten glass base which is characterized in that the member of The feed has a lower portion for immersion in the molten glass and with an outlet for the modifying material and the means for feeding the modifying material in the feed member so that it emerges through the outlet in the molten glass stream below. its surface or surfaces, in which the outlet extends with a vertical component so that it distributes the modifier material in at least the greater part of the depth of the flow.

13. The apparatus according to claim 12, characterized in that the outlet is on one side of the feed member which, in use, faces towards the direction of displacement of the flow or flows.

14. The apparatus according to claim 12 or 13 characterized in that the outputs comprise a series of holes.

15. The apparatus according to any of claims 12 to 14, characterized in that the melter melts the modifying material and supplies it in the molten state to the feeder member.