Abstract:
The invention relates to the process and apparatus coating of a substrate, particularly a glass ribbon, with a pulverulent product. The invention proposes the implementation of a distribution nozzle (10, 24) that sprays the pulverulent product in suspension in a gas, and a suction device (14) for evacuating the resultant waste of the decomposition of the pulverulent product from a coating zone (Z). The invention concerns the formation of at least one to extend the residence time of the pulverulent product in the coating zone to facilitate its deposit on the substrate. The invention also concerns the production of substrates, particularly glazings, coated with metal oxides.

Description:
DESCRIPTION 
     1. Technical Field 
     The invention is in a process, and apparatus, for coating a glass which may be a glass ribbon with a pulverulent product. The pulverulent product comprising the coating is entrained in and mixed with a gas current (carrier) to be directed over the glass at an angle of incidence. The coating operation is carried out by a nozzle having a slotted end. The carrier and pulverulent product sweep the surface of the glass before the surface is suctioned by a slotted device located at a distance from and parallel to the nozzle. 
     2. Background of the Invention 
     According to the prior art, processes have been developed to provide a glass ribbon with a coating. The coating may be in the form of a layer of metal oxide to impart to the glass ribbon precise qualities of reflection or transmission. These processes may be carried out directly along the production line of the glass ribbon, shortly after its production, while the glass ribbon is at an elevated temperature. Halogenated compounds in a powder state, such as those described in German published application DE No. 3,010,077 and its U.S. Equivalent, U.S. Pat. No. 4,707,383, for example, are used to obtain a layer of tin oxide doped with fluorine reflecting infrared. 
     It has been found that only a minor portion of the powder suspended in the gas current remains attached to the surface of the glass ribbon. As such, only a minor portion of the powder is destroyed by pyrolysis to form the desired oxide film under the effect of the high temperature of the glass ribbon. The major portion of the powder remains entrained in and is carried away by the gas current to be suctioned by a slotted device, for example. 
     SUMMARY OF THE INVENTION 
     The invention improves upon the prior art by markedly increasing the efficiency of the deposition process. To this end, the process of the invention and the apparatus for carrying out the process functions in a manner whereby an amount of powder greater than the minor portion of powder heretofore being capable of deposit is deposited on the surface of the glass which may be a glass ribbon. Thus, the process and the apparatus for carrying out the process provides for the production of desired layers with reduced amounts of powder. The improved operation is attained by creating and maintaining at least one eddy of gas charged with powders in the space in a coating deposition chamber between the nozzle and suction device. 
     Each eddy provides a rotary circulation, and within the heart of the eddy particles of powder entrained in the gas current rotate approximately like a solid body. The particles of powder rather than being removed rapidly from the zone of deposition by the suction device along a straight line path of movement are drawn into a path of circular movement so that the average time of residence of the particles of powder in the zone of deposition within the depositing chamber is lengthened. Generally, the eddy causes the particles of powder to sweep the surface of the glass several times to increase the probability of greater amounts of powder depositing on the surface. The greatly increased efficiency of the process leads to a very significant savings in pulverulent product. 
     The size of the eddy, referring to the diameter of the eddy, and its speed of rotation may be adjusted by a modification of the volume of gas sprayed by the nozzle and/or volume of gas to be suctioned by the suction device. These modifications have a direct effect on the residence time of the particles of powder in the depositing chamber so that the particles of powder sweep the surface of the glass for as along a period as possible. 
     The invention envisions the formation and maintenance of a second eddy in the space between the nozzle and suction device which rotates in a direction opposite of the direction of rotation of the first eddy. The eddies are formed by a gas current directed parallel to the surface of the glass against the suspension, that is, the gas charged with powders sprayed by the nozzle, and onto the surface of the glass outside the suction current. The formation and maintenance of additional eddies further improves the desired effect. 
     Other developments and advantages of the process according to the invention, and the apparatus for carrying out the process, will be detailed as the description to be read in conjunction with reference to the accompanying drawing continues. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 illustrates an installation for coating a glass in the form of a float glass strip with a pulverulent product according to an embodiment of the invention; 
     FIG. 2 illustrates the coating installation including a depositing device, a nozzle and a zone of eddies; and 
     FIG. 3 illustrates an installation similar to that of FIG. 2 and structure providing conditions of the process wherein two eddies rotating in opposite directions are formed on each side of a nozzle. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The invention in the process and the apparatus for carrying out the process has a particular application of use for coating float glass directly after the production of the continuous glass strip. Similarly, the invention may be used to coat cast glass under circumstances that the glass ribbon is produced by a rolling device and, thereafter, moved directly to a cooling furnace. The drawing Figures illustrate the float glass process. 
     Referring to the drawing, a glass ribbon 1 (hereafter &#34;glass&#34;) is illustrated supported on a metal bath 2 of molten tin within a chamber 3. The glass is formed under reduced atmosphere conditions within the chamber, and raised above the level of the metal bath in the chamber to exit the chamber along rollers of a roller conveyor. Movement of the glass, in the direction of arrow F may be imparted by rollers 4 which direct the glass to and through a cooling furnace 5. The glass may be at a temperature of about 600° C. at the exit of chamber 3 and is cooled in the cooling furnace to about ambient temperature. 
     A coating zone Z is located between chamber 3 and cooling furnace 5. It is within the zone Z that the glass 1 is coated with pulverulent product forming by pryolitic transformation of a partially reflective metal oxide layer 8. Heating devices (not shown) may be located within zone Z above and/or below the glass to adjust the temperature conditions. 
     The pulverulent product, for example, may comprise a very finely divided powder of dibutyltin difluoride under circumstances of producing a layer of tin oxide doped with fluorine. A nozzle 10 having a slotted end of a length to extend throughout the width of glass 1 may be used in the uniform distribution of the pulverulent product. A nozzle of this type is described in European application 125,153 and its U.S. Equivalents U.S. Pat. Nos. 4,562,095 and 4,533,571. 
     The nozzle 10 is located slightly above the glass 1, and the pulverulent coating material is blown onto the glass in the form of a suspension of particles of powder in a gas current. In FIG. 1, the nozzle is located at an angle of less than 90° relative to the surface of the glass moving through zone Z. The suspension is identified by the numeral 12. The gas current and entrained powder is directed over the glass ribbon along a length S before penetrating through suction opening 14. The suction opening is located in closed box 15 and suctioned by pipe 16. Suction opening 14 includes a slotted end like the slotted end of nozzle 10. As such, the slotted end of the suction opening also extends throughout the width of glass 1. The slotted end of the suction opening is also located slightly above the glass and formed partially by a wall 18 that extends toward the path of movement of the glass and substantially into contact with its surface. The wall, thus, delimits the coating zone Z at the downstream end and prevents the gas current charged with powder from leaving the zone except through the suction opening. The other side of the suction opening is formed by a wall which is arcuate in outline from the opening to the nozzle 10 near the nozzle opening. 
     The geometric ratios between the size of the chamber formed by nozzle 10, suction opening 14, closed box 15, and wall 18, and the suspension 12 of powder in a gas current as sprayed by nozzle 10 and suctioned through the suction opening 14 are determined and controlled to form a stable gas eddy in the chamber of coating zone Z. The eddy and particularly the rotating current surrounding the eddy prevents the suspension of powder in the gas current sprayed by nozzle 10 from being suctioned directly from the chamber by the slotted end of the suction opening 14 after only one sweep of glass ribbon 1. Rather, it is a consequence of eddy 20 to envelope or entrain a more or less large portion of the suspension so that the suspension sweeps the glass surface several times before being suctioned from the chamber. 
     Referring to FIG. 2, the chamber of coating zone Z is illustrated between the chamber 3 of the flotation furnace and cooling furnace 5. A distribution nozzle 24 is arranged so that a current 25 of gas and entrained powder is directed vertically toward glass 1. The current 25 will divide into two substantially equal subcurrents 25&#39; and 25&#34; each of which circulate in opposite directions. Particularly, the subpart 25&#34; circulates in a counterclockwise direction and subpart 25&#39; circulates in the opposite direction. 
     The coating chamber is closed by a pair of spaced vertical walls located upstream and downstream the distribution nozzle 24. The vertical walls each define a subchamber 26 which otherwise is open. Hot gas under a pressure higher than ambient pressure conditions is introduced by pipes 27 to each subchamber. The walls like the wall 18 extend toward the glass to provide a slot 29 below the suction opening 14. The hot gas is evacuated from the subchambers 26 to enter into the coating chamber S as a partial current 28. 
     Suction openings 14 are located parallel to chambers 26 and each suction opening communicates with a suction chamber. The suction chambers are formed by a helical pipe 30 and the gas is suctioned through pipe 31. 
     Nozzle 24, more particularly, the nozzle body, supports a number of blowing nozzles 33 each located to provide an outlet opening along the lower walls 34 of nozzle 24. The nozzles 33 provide a source of an auxiliary hot gas current which is communicated from pipes 35 and dividing boxes 36 into the coating chamber. The gas current is directed from each nozzle 33 along a length of nozzle 24 and assures that distribution nozzle 24 is heated. The gas current also assures the heating of the gaseous mixture in the coating chamber. 
     Two walls 38, each extending from the suction opening of a suction nozzle to the outlet opening of nozzle 33, limit the height of the coating chamber. The walls each have a cylindrical shape to prevent the formation of dead zones for the circulation of the gases. 
     The arrangement on each side of the distribution nozzle 24 provides or forms a stable eddy 20 from the gas-powder mixture. The eddies 20, as previously discussed, rotate in opposite directions. The currents, illustrated as gas currents 22, with fluid flows outside the eddies supply the eddies with powder so that each eddy undergoes a rotary circulation and approaches the glass surface several times before being evacuated. Accordingly, the likelihood of powder being deposited on the glass surface is considerably increased. 
     The device of FIG. 3 for implementing the process corresponds in most essential characteristics to the device of FIG. 2. According to FIG. 3, however, it will be possible to obtain two additional eddies including eddies 40, 42 on each side of distribution nozzle 24. Each pair of eddies, both upstream and downstream in the direction of movement of glass 1, rotate in opposite directions. The eddies may be formed by increasing the volume of current through pipes 27 which circulates in chambers 26, by simultaneously increasing the suctioned gas volume, and, if necessary, by modifying the gas current charged with powder sprayed by the distribution nozzle. It should be noted, also, that the gas volume suctioned through pipes 30 and 31 plays a role in the formation of the double eddies. 
     All gas volumes are determined and controlled so that the eddies of rotating gas currents 40, 42 are stable to attain a lengthening of the residence time the gas powder mixture in the coating chamber.