Method and apparatus for manufacture of float glass
United States Patent Lawrenson et al.  
 1451 *Apr. 8, 1975 METHOD AND APPARATUS FOR MANUFACTURE OF FLOAT GLASS Assignee:  
 Pilkington Brothers Limited,  
 Liverpool, Lancashire. England Notice:  
 The portion of the term of this patent subsequent to Apr. 25, 1989. has been disclaimed.  
 Filed:  
 Feb. 6, 1974 Appl. No.: 439.851  
 Related US. Application Data Continuation of Ser. No. 218.120. Jan. 17. 1972. abandoned. which is a continuation-in-part of Ser. No. 810.248. March 25. 1969. Pat. No. 3.658.501.  
 Foreign Application Priority Data Apr. 9. 1968 United Kingdom 17077/68 US. Cl 65/30; 65/99 A; 65/182 R;  
  204/196 Int. Cl. C03C 21/00 Field of Search... 65/99 A. 182 R. 101, 30;  
 [56] References Cited UNITED STATES PATENTS 3.108.939 10/1963 Sabins 204/196 3.445.373 5/1969 Schuckeret a1. 204/225 X 3.515.659 6/1970 Proat et a1 204/224 M 3.607.175 9/1971 Robinson 65/99 A X 3.632.322 1/1972 Loulges et a1. 65/99 A X 3.658.501 4/1972 Lawrenson et a1 65/182 R X 3.684.680 8/1972 Heuze 204/196 Primary Examiner-S. Leon Bashore Assistant Examiner-Kenneth M. Schor Attorney. Agent. or FirmBurns, Doane. Swecker &amp; Mathis [57] ABSTRACT Float glass in manufactured with predetermined characteristics imparted to the glass by a body of molten material which clings to an electrode bar extending across the path of travel of a ribbon of float glass and which contacts the upper surface of the glass ribbon. The lower face of at least the downstream edge of the bar is formed of material sufficiently resistant to wear by the molten body to maintain constant the length of the body of molten material. in the direction of relative movement between the glass and the body. in any section through the body in that direction.  
 22 Claims, 9 Drawing Figures PATENTEDAPR 81975 SHIT 1 [IF 4 METHOD AND APPARATUS FOR MANUFACTURE OF FLOAT GLASS BACKGROUND or THE INVENTION This is a continuation of application Ser. .No. 218,120, filed Jan. 17, 1972, and now abandoned.  
  Application Ser. No. 218120 is a continuation-inpart application of copending application, Ser. No. 810,248, filed Mar. 25, 1969 and now Pat. No. 3,658,501, and entitled Manufacture of Glass.  
  This invention relates to the manufacture of float glass, and more especially the invention concerns processes and apparatus for producing float glass in which predetermined characteristics are imparted to the glass by migration of an element or elements into the glass from a body of molten material which is held in contact with the surface of the glass.  
  In such processes the body of molten material .may be a molten metal or molten alloy which clings to a locating member positioned adjacent te glass; surface. Relative movement is effected between the glass and the locating member, and the molten body is maintained in position by clinging to the locating member. The migration of the element or elements into the glass from the body is controlled, for example, by regulating the oxidizing conditions at the interface between the glass and the body, as described and claimed in copending application, Ser. No. 765,428, filed Oct. 7, 1968 and now US. Pat. No. 3632322. Alternatively, an electrolytic method may be used, in which the locating member acts as an electrode and current is passed through the glass (which is electrically conductive at the elevated temperatures of treatment) from the molten body to effect controlled migration of an element or elements from the molten body into the glass.  
  As the process proceeds, material from the locating member is under certain conditions dissolved by the molten body, resulting in an appearance of wear of the lower part of the locating member.  
  It is a main object of the present invention to maintain a desired uniformity of characteristic in the treated glass by maintaining constant the intensity of treatment of each part of the glass throughout a manufacturing run of the process.  
 SUMMARY According to the invention there is provided a method of producing glass in which predetermined characteristics are imparted to the glass from a body of molten material which contacts a surface of the glass and which clings to a locating member positioned adjacent said glass surface, and in which relative movement is effected between the glass and the locating member, characterized by maintaining constant the length of the body of molten material in the direction of relative movement in any section through the body in that direction.  
  It has been found that parts of the locating member to which the molten body clings are more susceptible to wear than the rest of the locating member. Wear has been found at the front and rear faces of the lower part of the locating member. In a preferred embodiment of the invention this wear is obviated by providing that at least one edge portion of the locating member, to which an edge of the molten body extending transversely of the direction of relative movement clings, is formed of a material which is more resistant to wear by the material of the molten body than the remainder of the locating member. The wear resistant material is preferablu located adjacent the downstream edge of the locating member, i.e., the edge from which the treated glass emerges.  
  In apparatus according to the invention for effecting an electrolytic treatment of the glass, the locating member and the molten material are electrically conductive and electrical connections are made to the 10- cating member and to the glass support means for passing electric current through the molten body and the glass to assist the migration of an element into the glass from the body of molten material.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a diagrammatic, partly cut-away, perspective view of an apparatus for treating glass in sheet form to which the present invention is applicable; and  
  FIGS. 2 to 9 are diagrammatic, cross-sectional views. each illustrating a different example of an insertreinforced locating member for use in apparatus according to the invention.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS Soda-Iime-silica glass, for example, is fed on to the bath 3 at a controlled rate, either as preformed ribbon of glass or as molten glass which is poured on to the bath at one end thereof and permitted to flow laterally unhindered to the limit of its free flow under the influence of surface tension and gravitational forces to form a flat ribbon 4 of glass which is advanced along the surface of the bath in the direction of arrow A.  
  The temperature of the glass ribbon 4 is regulated as theribbon is advanced along the bath by means of controlled heaters (not shown) immersed in the bath 3 and located in the said headspace over the bath 3.  
  A both 5 of molten material for modifying the upper surface of the glass is maintained in contact with the upper face of the ribbon 4, the body 5 extending across the ribbon transversely of the direction of advance A thereof at a fixed station in the tank structure. The molten body 5, which does not wet the surface of the glass, is maintained in position by an elongated locating member 6 extending transversely across the ribbon 4 and parallel to the upper face thereof, so that a gap of uniform depth (for example, about 3 to 4 mm) is maintained between the lower surface of the member 6 and the upper face of the ribbon 4.  
  The molten material of the body 5 wets the lower surface of &#39;the locating member 6 and clings thereto, so that as the ribbon4 passes continuously beneath the body 5, the latter is confined by the member 6 to the gap between the member 6 and the ribbon 4.  
  The molten material of the body 5 may comprise a metal, an alloy or a salt. For example, the material may be tin, lead, bismuth, antimony, indium, zinc, or thallium. Examples of suitable molten alloys are alloys of tin or lead or bismuth as a solvent metal with lithium, sodium, potassium, zinc, magnesium, copper, or silver as a solute metal. Sodium chloride is an example of a molten salt which may be used.  
  The locating member 6 may be of an unreactive metal, for example, one of the platinum group metals. Alternatively, the member 6 may comprise a base of, for example, copper, silver, brass, steel, alloys, containing copper or silver, or a refractory material having a coating of an unreactive metal such as, for example. ruthenium.  
  As the glass ribbon 4 passes beneath the molten body, its surface is modified by migration of.one or more elements from the body 5 into the glass surface.  
  In a preferred electrolytic process, the migration is controlled by passing a regulated electric current through the body 5 and the ribbon 4 to cause transfer of ions from the body 5 into the glass. For this purpose. the locating member 6 is electrically conductive and is connected to the positive terminal of a direct current supply source 7 so that the molten body 5 acts as an anode and the bath 3 as a cathode of an electrolytic circuit, the glass of the ribbon 4 being the electrolyte. A negative electrode 8 connected to the negative terminal of the source 7 is immersed in the molten metal bath 3 on one side of the ribbon 4.  
  The surface modification of the glass ribbon 4 may alternatively be regulated by controlling oxidizing conditions in the body 5 so as to regulate the migration of an element or elements from the body 5 into the glass.  
  A supply duct (not shown) is provided in the headspace adjacent the member 6 for replenishing the body 5 of molten material with the element (or elements) which migrates into the glass ribbon 4 in operation of the apparatus.  
  In order to ensure uniform surface treatment of the glass ribbon across its width, it is important to ensure that there is no variation in the size of the gap between the lower surface of the locating member 6 and the upper surface of the ribbon 4 along the width of the ribbon. With this object in view, the locating member 6 is supported from a rigid beam structure 10 extending transversely over the bath 3.  
  The beam structure 10 is shown partially broken away in FIG. 1 for the sake of clarity. The beam struc ture 10 comprises two parallel, juxtaposed, boxsection, hollow beams 10a, 10b, through which a coolant fluid, conveniently water. is circulated so as to maintain the beam structure 10 at a temperature which is considerably lower than the temperature of the molten body 5 and locating member 6, which temperature is typically of the order of 700C.  
  The locating member 6 comprises an elongated strip having a flat lower face, parallel to the surface of the ribbon 4 to which the molten body 5 clings. Along its upper surface the member 6 is provided with an elongated key 11 which fits into a keyway 12 provided in an elongated holder 13. In this way, the member 6 is free to undergo thermal expansion relative to the holder 13 without restraint, and therefore without the occurrence of any deformation.  
  The holder 13 is suspended from the beam structure 10 by a plurality (four in the illustrated example) of support members 14, each of which has an enlarged T- shaped head which is located in longitudinally extending slots 15 provided in the upper surface of the holder 13. The spacing of the support members 14 along the holder 13 is so chosen that the natural bending of the holder and locating member 6 between adjacent support members 14 is less than an acceptable maximum. To compensate for the tendency of the supported holder 13 and locating member 6 to flex under gravity between the outer ends of the beam structure 10, at least the center ones of the support members 14 are made adjustable in length. For example, the support members 14 may comprise respective screw-jack devices. A linkage is preferably provided for permitting adjustment of the support members 14 from positions externally of the tank structure.  
  By suitably adjusting the support members 14 and end supports (not shown) for the beam structure 10, the height of the gap between the locating member 6 and the ribbon 4 can be maintained uniform within acceptable limits over the length of the member 6.  
  It will be appreciated that the molten material in the body 5 is not static in operation of the apparatus, even though the body 5 as a whole is held in the same position by clinging to the locating member. Since the lower face of the molten body 5 is in contact with the upper surface of the advancing glass ribbon 4, material in the body 5 close to the ribbon 4 is carried along with the glass. A return flow in the opposite direction takes place in the molten material close to the lower face of the locating member 6 resulting in some wear of the locating member which in some instances is due to dissolving of the material of the locating member 6 into the molten body 5, for example when the molten body 5 is a copper-lead alloy and the locating member 6 is a copper bar. Any such wear of the bottom of the locating member is usually uneven.  
 In the course of time, erosion of the trailing edge of the locating member 6 may locally increase the gap be tween the lower face of the member 6 and the upper face of the ribbon 4, to an extent such that the molten material can no longer remain in that part of the gap by surface tension. As a result, the molten body 5 may recede unevenly from the eroded edge of the locating member 6.  
  The present invention avoids any such difficulty by ensuring that the length of the molten body 5 in any section therethrough in the direction of glass advance is maintained substantially constant, so that the method can be used with reliable results with high rates of glass movement and with high currents.  
  At least the trailing edge portion of the locating member 6 is constituted by a face of wear-resistant material to which the molten material of the body clings, and as shown in FIGS. 2 to 9, the locating member 6 is provided with an elongate insert 16 comprising a material which is more resistant to erosion than the main body of the locating member 6. For example, where the locating member 6 is of copper and the molten body 5 is copper-lead alloy, the insert 16 may comprise iron, mild steel, ruthenium, nickel, or cobalt, each of which has a low solubility in the molten material of the body 5 which wets on to the insert.  
  The insert 16 may be keyed into the locating member 6, as shown in FIGS. 2, 3, and 5 to 9, or secured thereto by means of bolts, as in FIG. 4. It is apparent that the lower face of the insert is fixed in relation to the lower face of the upstream portions of the locating member. To assist the initial wetting of the insert 16 by the molten body 5, the insert 16 may be provided with a thin coating of copper, for example, by plating.  
  An insert 16 of porous refractory or porous graphite can conveniently be used when the molten body 5 is of molten lead or a lead alloy. The porosity of graphite causes lead to be absorbed, giving a wetting effect.  
  It has been found that the face of the locating member 6 may wear at its leading edge 16a at a greater rate than over its main wetted surface, although the rate of wear is not as great as that which occurs at the trailing edge. To avoid wear of the leading edge, it is also desirable to provide a further wear-resistant insert. similar to the insert 16 shownin FIGS. 2 to 9. along the leading edge 16a of the wetted face of the locating member 6. The arrangement of FIG. 9 is particularly suitable where the insert 16 is made. of porous graphite. a thin lip 17 of the material of the locating member 6 (e.g.. copper) extends initially along the trailing edge face of the member 6. This lip 17 after. a short period of operation is dissolved away to the limit shown in broken lines. This assists the initial wetting of the trailing edge of the graphite insert 16. Thereafter, the trailing edge of the molten body 5 clings to the trailing edge of the insert 16, as shown in broken lines.  
  Instead of an insert of wear-resistant material, the edges of the locating member 6 may be plated so as to provide a wear-resistant face. For example, acopper bar may have its edges plated withruthenium.  
  The invention is described thereinabove with particular reference to the treatment of glass in sheet or ribbon form, and&#39;i&#39;s equally applicable to the treatment of glass articles, e. g., curved glass, pressed ware, or rolled glass sections.  
  The shape of the wetted surface of the locating member 6 and consequently of the body 5 clinging thereto may be modified to suit particular requirements. For example, the locating member 6 may have a width in the direction of relative movement A of the glass which varies in a predetermined manner across the glass ribbon when it is desired to produce a glass having shaded characteristicstransversely of the glass.  
  What is claimed is: 1. In a process of imparting surface characteristics to a ribbon of float glass during manufacture thereof with improved maintenance of the intensity of treatment and uniformity of the imparted eharacteristics to a run of glass, the steps of:  
 advancing the ribbon of float glass along a molten metal bath provided in an elongated tank structure;  
 causing a molten metal body to wet onto and cling to the lower face of a locating member extending across the upper surface of said ribbon to locate said molten metal body on the upper surface of said advancing ribbon of glass such that relative movement occurs between said molten metal of said body and said lower face during glass advancement in a manner tending to wear a downstream edge portion of said lower face at a greater rate than upstream portions thereof;  
 enforcing migration of an element from said molten metal body into said glass surface to impart surface characteristics to said glass ribbon;  
 providing said locating member in the form of a loeating member, the material of which is soluble in said molten metal body; and  
 stabilizing the location of the downstream edge portion of said molten metal body by providing a downstream edge portion of said lower face of said locating member in the form of an edge portion of a material onto which said molten body wets and clings, which last-named material has a greater resistance to wear resulting from the moving molten metal of said body than upstream portions of said lower face of said locating member, therby to improve maintenance of the intensity of treatment and uniformity of the imparted characteristics to a run of glass.  
 3. The method according to claim 1 including the step of causing the lower face of said downstream edge portion to be fixed in relation to the lower face of said upstream portions. I  
 4. The method according to claim 1, wherein: said molten metal body is formed from a metal alloy; said locating member being formed of one of the constituent metals of the alloy, and  
  the downstream edge of the locating member being formed of a material which has a low solubility the alloy. 5. The method according to claim 4, wherein the molten metal body is a copper/lead alloy and the locating member is formed of copper.  
  6. The method according to claim 5, wherein said material having a low solubility in the alloy is iron.  
  7. The method according to claim 5, wherein said material having a low solubility in the alloy is ruthenium.  
  8. The method according to claim 5, wherein said material having a low solubility in the alloy is graphite. 9. The method according to claim 5, wherein said material having a low solubility in the alloy is nickel.  
  10. The method according to claim 5, wherein said material having a low solubility in the alloy is cobalt.  
  11. In a process of imparting surface characteristics to a ribbon of float glass during manufacture thereof with improved maintenance of the intensity of treatment and uniformity of the imparted characteristics to a run of glass, the steps of:  
 advancing the ribbon of float glass along a molten metal bath provided in an elongated tank structure;  
 causing a molten body of glass-modifying material to cling to the lower face of a locating member extending across the upper surface of said ribbon to locate said molten body on the upper surface of said advancing ribbon of glass such that relative movement occurs between said molten material of said body and said lower face during glass advancement in a manner tending to wear a downstream edge portion of said lower face at a greater rate than upstream portions thereof;  
 enforcing migration of an element from said molten body into said glass surface to impart surface characteristics to said glass ribbon; and  
 stabilizing the location of the downstream edge portion of said molten body by providing a downstream edge portion of said lower face of said locating member in the form of an edge portion of a material onto which said molten body wets and clings, which last-named material. has a greater resistance to wear resulting from the moving molten metal of said body than upstream portions of said lower face of said locating member, thereby to improve maintenance of the intensity of treatment and uniformity of the imparted characteristics to a run of glass.  
  12. Apparatus for imparting surface characteristics to a ribbon of float glass during manufacture thereof with improved maintenance of the intensity of treatment and uniformity of the imparted characteristics to a run of glass, comprising:  
  an elongated tank structure containing a bath of molten metal;  
 means for advancing the ribbon of glass along the bath;  
 a locating member extending across said tank structure just above the surface of said bath and having a lower face to locate a body of molten glassmodifying material on the upper surface of said advancing ribbon of glass such that relative movement occurs between said molten material of said body and said lower face during glass advancement in a manner tending to wear a downstream edge portion of said lower face at a greater rate than upstream portions thereof; and  
 said lower face of said locating member including a downstream edge portion formed from a material onto which said molten body wets and clings; said last-named material having a greater resistance to wear resulting from the moving molten material of said glass-modifying body than upstream portions of said lower face of said locating member, thereby to improve maintenance of the intensity of treatment and uniformity of the imparted characteristics to a run of glass.  
  13. Apparatus for imparting surface characteristics to a ribbon of float glass during manufacture thereof with improved maintenance of the intensity of treatment and uniformity of the imparted characteristics to a run of glass, comprising:  
 an elongated tank structure containing a bath of molten metal;  
 means for advancing the ribbon of glass along the bath;  
 a locating member extending across said tank structure just above the surface of said bath and having a lower face to locate a body of molten glassmodifying metal on the upper surface of said advancing ribbon of glass such that relative movement occurs between said molten metal of said body and said lower face during glass advancement in a manner tending to&#39;wear a downstream edge portion of said lower face at a greater rate than upstream portions thereof;  
 said lower face of said locating member being formed of a material which is soluble in said molten metal body; and  
 said lower face of said locating member including a downstream edge portion formed from a material onto which said molten body wets and clings; said lastnamed material having a greater resistance to wear resulting from the moving molten metal of said body than upstream portions of said lower face of said locating member, thereby to improve maintenance of the intensity of treatment and uniformity of the imparted characteristics to a run of glass.  
  14. Apparatus according to claim 13, wherein said downstream edge portion comprises an elongate member which is attached to an upstream portion of the 10- cating member.  
  15. Apparatus according to claim 14, wherein said elongate member is keyed into an elongated channel formed in the locating member.  
  .16. Apparatus according to claim 14, wherein said elongate member is formed of iron.  
 17. Apparatus according to claim 14, wherein said elongate member is formed of mild steel.  
  18. Apparatus according to claim 14, wherein said elongate member is formed of ruthenium.  
 19. Apparatus according to claim 14, wherein said elongate member is formed of graphite.  
 relation to the lower face of said upstream portions.