Process and apparatus for the production of flat glass by the float glass method
BACKGROUND OF THE INVENTION 
     By means of an already known process, transverse currents can be created in the metal bath by immersing coolers in it to create temperature gradients which then produce convection currents. The intensity of these convection currents is determined by the magnitude of the temperature gradient. Since the temperature gradient is in principle undesirable and can only be produced by means for continuous cooling, only relatively weak currents can be produced and maintained by this process. 
     By means of another known process, transverse currents can be produced in the metal bath by linear induction motors positioned near the side walls of, and immediately above, the metal bath. A disadvantage of this process is that it is very expensive to maintain electrical induction motors in working condition at approximately 1,000° C. 
     In the float method of producing flat glass, it is also conventional to use mechanically operating pumps in order to draw off the impurities that form on the surface of the metal bath. These pumps however are installed in a stationary manner outside of the actual tank and are connected to the bath through special pipes and/or bays. They are not used to create currents in the bath. 
     SUMMARY OF THE PRESENT INVENTION 
     The present invention provides an effective process that can be carried out with simple means and at minimal expense and by which the desired currents in the bath can be regulated within a wide range in both direction and strength. A particular advantage of the new process is that, on the one hand, the temperature of the metal bath is not disadvantageously affected and, on the other hand, the desired currents are produced by relatively simple means. 
     The process embodied in the present invention consists of mechanically or pneumatically producing the currents within the metal bath. For doing this, pumps are introduced into the tank from outside and placed in the desired location between the glass ribbon and the side wall of the tank. In construction, each pump includes a pump housing made of a material compatible with the molten metal. One or more inlets are provided on one side of the housing for drawing the metal in and one or more outlets on another side, preferably on the side lying opposite the inlets, for releasing the metal. A supporting device extending out of the float bath tank is connected to the pump housing. The pump can therefore be lowered into the metal bath and its position varied. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a horizontal sectional view along line I--I of FIG. 2 through a float glass apparatus constructed according to the invention; 
     FIG. 2 is a vertical cross-sectional view along line II--II of FIG. 1; 
     FIG. 3 is an enlarged plan view along line III--III of FIG. 4 of a pneumatically operating pump; 
     FIG. 4 is a vertical cross-sectional view along line IV--IV of FIG. 3; 
     FIG. 5 is a vertical sectional view through a vane pump with pneumatic drive; 
     FIG. 6 is a partial sectional view of a mechanically driven vane pump; and 
     FIG. 7 is a vertical sectional view through a mechanically driven screw pump. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The float glass installation in accordance with FIGS. 1 and 2 comprises a tank for a bath 1 of molten metal. Only the righthand portion of this tank is shown in the drawing. The tank has a bottom 2, side walls 3, and a cover 4. The glass ribbon 5 floats on bath 1. In space 6 above bath 1 and glass ribbon 5 there is a controlled atmosphere which prevents oxidation of the metal and/or gives rise to a slight reducing effect and produces a superatmospheric pressure inside the tank. A plurality of pumps 7, only one of which is shown in FIGS. 1 and 2, are installed in the space between glass ribbon 5 and side walls 3. The materials customarily used for devices that operate in a bath of molten metal such as, for example, graphite, are suitable for making the pump housing and other parts. 
     Pump 7, shown in FIGS. 1 and 2, is a pneumatic pump which works on the gas lift principle and is driven by the gases comprising the controlled atmosphere that fills space 6 above the glass ribbon and metal bath. The operation of this pump is shown in FIGS. 3 and 4. The pump consists of a housing 8 which rests on the bottom of the bath tank. This housing encloses a space 9 into which the liquified metal can penetrate through inlet 10. Near inlet 10, a pipe 12 introduces the pressurized gas comprising the controlled atmosphere through covering 11 into space 9. This gas escapes through openings 13 into space 6 above the glass ribbon and metal bath and carries the liquified metal along with it. The metal is raised into a collecting tank 14 and flows from it over the half-pipe gutters 15 back into the metal bath. 
     Gas supply 12 is designed to serve at the same time as a fixture for supporting the pump housing. It extends out of the bath tank through an opening 16 in its side wall 3. Opening 16 is large enough to allow introduction and withdrawal of the pump into and out of the bath. Opening 16 is sealed off around supply pipe 12 by means of a bellows type seal 16a. The direction of the transverse current in bath 1 can be changed by rotating pump 7 around the vertical axis of supply pipe 12. The conveying capacity of pump 7 which depends on the amount of gas going through openings 13 can easily be varied by changing the amount of gas supplied. By altering the height of intake 10 when required, the liquified metal can be drawn in from any desired level of the bath. 
     FIG. 5 shows a vane type pump designed for the generation of currents in the metal bath which is driven by the gas comprising the controlled atmosphere in the bath tank. The pump is contained in a housing 8 that rests on the bottom of the tank. Housing 8 has an inlet 10 and an outlet 17 for the liquified metal 1. Vane wheel 18 rotates freely on a shaft 19 securely fixed into the side walls of a cylindrical space 20. The vane wheel is driven by forcing compressed gas from the controlled atmosphere through pipe 12 and nozzle 21 onto the vanes of the wheel whereby it is made to revolve. The gas exits through opening 22 into space 6. The other end of gas pipe 12 extends back out of the tank through opening 16 in its side wall. 
     In order to change the direction of the transverse current in the bath 1, the pump can easily be rotated into the desired position at a threaded joint 23. The conveying capacity of this pump can also be varied by changing the amount of gas supplied through pipe 12. 
     FIG. 6 shows a vane type pump designed for the generation of a transverse current in metal bath 1. The conveying capacity of this pump is the same as that of the vane pump shown in FIG. 5. However, this pump is driven by a shaft 24 that drives vane wheel 18 by means of a bevel gear drive 25, 26. Shaft 24 extends out of the bath tank through an opening in one of the latter&#39;s side wall and is driven by a motor installed outside of the shallow tank. The direction of the suction opening as well as the conveying capacity can be varied in ways similar to those used for the vane pump in FIG. 5. 
     FIG. 7 shows a screw type pump for generating a transverse current in metal bath 1. Inside housing 8, a helix screw 34 is mounted inside a cylindrical borehole. A drive shaft 24 is connected to screw 34. Shaft 24 goes through shoulder 28, set collar 29, and borehole 30 in wall 27 which forms part of the housing. The screw is driven by shaft 24 in a manner similar to the vane wheel 18 of the vane pump in FIG. 6. Since the front and rear walls, 31 and 32 respectively, of the housing are open, the liquified metal has unimpeded access to the helix screw; and as a result of the screw&#39;s revolution, flows without hindrance through the pump housing and back into metal bath 1. The capacity of this pump can be varied by changing the speed of revolution of the screw, and the direction of its suction and discharge can be varied by rotating the pump as a whole.