GB2023664A - Apparatus for applying metal coating to continuously fed band of glass - Google Patents

Abstract

An apparatus for applying a metal coating to a continuously fed band of glass 9 comprises a water- cooled horseshoe electromagnet 12 having poles extending transversely of the glass band and spaced apart in the feed direction, a pipe 8 with perforations 10 for depositing molten metal 11 onto the glass band between the poles, a pipe 14 for supplying oxidizing atmosphere, and electrical contacts 13 carried at the ends of the electromagnet 12 for passing an electric current through the layer of molten metal. Electrical contacts 15 carried by the electromagnet sense the depth of the metal layer 11 on the glass and control the valve 16 in duct 6 to keep the depth constant. The vessel 1 includes heaters 3, thermocouple 4 and level indicator 5. The oxidizing gas oxidises the surface of the melt in the strip, the oxidised material adhering to the substrate during rotation of the melt. <IMAGE>

Description

SPECIFICATION Apparatus for applying metal coating to continuously fed band of glass The present invention relates to sheet glass treatment techniques and, more particularly, to a device for applying a metal coating to a continuously fed band of glass.

Such devices are used to apply a metal coating to a glass band, while carrying out what is known as "two-stage moulding" or "float" processes. Devices of this type can be used to best advantage in the production of building and finishing materials and articles, as well as in construction, where metal-coated glass can be used in guard rails, door partitions, etc., and in interior decoration. The invention is also applicable to the manufacture of furniture, where metal-coated glass can be used to make mirrors.

According to the invention, there is provided an apparatus for applying a metal coating to a continuously fed band of glass, comprising an electromagnet positioned above the feed path of the band of glass, the poles of the electromagnet extending transversely to the glass band feed direction and being spaced apart in said direction, means located between the poles of the electromagnet for depositing molten metal on the surface of the glass band and for supplying oxidising gas, respectively, and electrical contacts carried by the electromagnet at the ends thereof for contacting a layer of molten metal deposited on the band of glass to pass an electric current through the layer of molten metal.

In a preferred form of apparatus means for supplying molten metal to the depositing means comprises a vessel having a charging opening, a discharge opening, and a duct for the supply of reducing atmosphere to the vessel to force molten metal out through the discharge opening. The electromagnet is a water-cooled horseshoe magnet and accomodated between the poles of the electromagnet are pipes for the supply of molten metal communicating with the discharge opening of the vessel and having perforations in its wall facing the glass band.

The duct for supplying reducing atmosphere to the vessel is provided with a flow control valve having an electric control circuit which includes electrical contacts attached to that wall of the electromagnet which faces the direction from which the glass band is fed for sensing the depth of the layer of molten metal on the glass band between the poles of the electromagnet.

Heating elements are provided in the walls of the vessel, and are controlled by a thermocouple arranged in the vessel to sense the temperature of the molten metal.

An upper part of the vessel accommodates a level indicator for indicating the level of molten metal in the vessel, which level indicator is a float having one of its ends immersed in the melt.

In operation of the apparatus, metal intended to produce a coating on the surface of a continuously fed band of glass, is charged into the vessel, where it is melted and heated to a desired temperature. Upon reaching this temperature, the thermocouple switches off the heaters. The impurities and oxides contained in the metal rise to the surface. The lever meter indicates the level of molten metal in the vessel. The reducing atmosphere supplied to the vessel prevents oxidation of the melt and at the same time exerts pressure upon the melt, forcing it through the discharge opening into the pipe arranged between the poles of the electromagnet.

Through the perforations in the lower wall of the pipe, the melt is applied onto the glass band, forming an elongated layer thereon.

Direct current is passed through the layer of molten metal via the busbars secured at the end faces of the electromagnet. The magnet's field interacts with the current according to the left-hand rule, preventing the molten meatl from being drawn away by the moving glass band. Upon the accumulation of a certain volume of molten metal in the layer, the metal is brought in contact with the electrical contacts attached to that wall of the electromagnet which faces the direction wherefrom the glass band is fed. The contacts are closed.

Electric current is passed through the contacts to actuate the flow control valve which discontinues the supply of reducing atmosphere to the vessel. The pressure in the vessel drops so that the supply of molten metal to the surface of the glass band is also discontinued. The volume of molten metal in the layer is reduced to a point when there is no longer any contact between the metal and the electrical contacts. As a result, the electric circuit, comprising the electrical contacts, the flow control valve, a current source and leads, is broken.

The flow control valve opens to continue the supply of reducing atmosphere to the vessel. Upon entering the vessel, the reducing atmosphere forces the melt into the pipe, wherefrom it is applied onto the glass band.

Thus the volume of the layer of molten metal on the band is kept constant. Through the second pipe arranged between the poles of the electromagnet, oxidizing atmosphere Is supplied to the surface of the molten metal layer. The oxidizing atmosphere contains an oxidizer (oxygen and sulphur) and an inert gas. The degree of oxidation of the molten metal is controlled by varying the oxidizer content in the oxidizing atmosphere. As a result, an oxide film is produced on the surface of the molten metal layer. Due to the rotation of the melt, the film is transferred to the glass-melt boundary and adheres to the glass. The layer of molten metal is rotated by the force caused by the interaction between the magnet's field and the current passed from the busbars through the layer of molten metal, and by the force of friction between the glass band and the layer of molten metal.Part of the molten metal is drawn away in the film adhered to the glass band.

By changing the current passed through the winding of the electromagnet and the current passed through the layer of molten metal, one can vary the magnitude of force which keeps molten metal on the band's surface; hence, one can control the amount of metal carried away by the moving band and, consequently, the thickness of the metal coating applied to the band.

To take care of problems which may arise in the mirror manufacture, it must be emphasized that under certain conditions the oxide film is extremely thin so that it in no way impairs the reflectivity of the metal coating.

The electromagnet's winding is produced from copper tube 8 mm in diameter. The magnet is cooled by passing water through the tube. The magnetic force lines of the magnet are curved so that the molten metal is acted upon by forces of variable vectors. At the edges of the molten metal layer, the forces are directed towards the center of the layer, whereas in the layer's center the forces are directed upwards at a perpendicular to the layer's surface, whereby the pressure of the molten metal layer upon the glass is reduced.

The device of this invention features a high efficiency which is only limited by the speed of the band's motion. The device is small in size and can be easily incorporated into a conventional line for the production of polished sheet glass with the use of the "twostage molding" or "float" techniques.

A better understanding of the present invention will be had from a consideration of the following detailed description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings, wherein: Figure 1 is a schematic view of a device in accordance with the invention; Figure 2 is a section taken on line ll-ll of Fig. 1.

Referring to the attached drawings, the device (Fig. 1) according to the invention comprises a vessel 1 intended for melting metal placed therein through a charging opening 2.

Built into the walls of the vessel 1 are heaters 3 intended to heat the metal contained in the vessel 1 to a prescribed temperature. The vessel 1 also accommodates a thermocouple 4 for measuring the fusing temperature of the metal contained in the vessel 1. The level of molten metal in the vessel 1 is measured with the aid of a level meter 5 which is a float having one of its ends immersed in the melt.

Communicating with the vessel 1 is a duct 6 intended to supply reducing atmosphere under pressure to the vessel 1. The pressure of the reducing atmosphere forces the molten metal out through a discharge opening 7 into a pipe 8 communicating with the opening 7.

The wall of the pipe 8, facing a glass band 9, has perforations 10 through which molten metal is forced onto the band 9 to form an elongated layer 11 on the surface of the band 9. The layer 11 of molten metal is formed and kept on the surface of the band due to the interaction between the magnetic field produced by a water-cooled horseshoe electromagnet 1 2 and current passed through busbars 1 3 mounted on the end faces of the electromagnet 1 2. The latter is arranged above the glass band 9, at a perpendicular to the plane of its motion. Accommodated in the spacing between the poles of the electromagnet 12 are pipes 8 and 14 (Fig. 2) for the supply of molten metal and oxidizing atmosphere, respectively, to the surface of the glass band 9.The volume of the molten metal layer 11 on the surface of the glass band 9 is controlled by a system comprising a current source (not shown), two electrical contacts 1 5 attached to that wall of the electromagnetl 2 which faces the direction wherefrom the glass band 9 is fed, and a flow control valve 1 6 installed in the duct 6 and connected by a wire to the contact 1 5.

The device operates as follows.

Electric current is applied to the winding of the horseshoe electromagnet 1 2. Metal is charged into the vessel 1 through the charging opening 2, whereupon the opening 2 is hermetically sealed by a lid. The heaters 3 melt the metal in the vessel 1. Upon reaching a prescribed temperature, the thermocouple 4 automatically switches off the heaters 3. The level meter 5 indicates the level of molten metal in the vessel 1. Reducing atmosphere is fed under pressure through the duct 6 and forces the molten metal through the opening 7 into the pipe 8. Through the perforations 10 provided in the wall of the pipe 8, facing the glass band 9, the molten metal flows onto the band 9, forming the layer 11 of molten metal extending transversely of the glass band 9. According to Fig. 1, the band 9 moves towards the viewer. Electric current is passed via the busbars 1 3 through the layer 11 of molten metal. Interacting with the electric current passed through the layer 11 of molten metal, the field of the electromagnet 1 2 prevents the layer 11 from being drawn away by the moving band 9. As the volume of molten metal in the layer 11 reaches a certain level, the layer 11 comes as high as the contacts 1 5 and closes them. As a result, the flow control valve 1 6 is actuated and discontinues the supply of reducing atmosphere to the vessel 1. The pressure of the reducing atmosphere in the vessel 1 drops, and the feeding of molten metal into the pipe 8 is also discontinued.As the volume of molten metal in the layer 11 decreases, the electric circuit is broken, and reducing atmosphere is again supplied to the vessel 1. In order to produce an oxide film on the surface of molten metal, oxidizing atmosphere is fed through the pipe 1 4 to the layer 11 of molten metal. The oxide film is forced to the glass-molten metal boundary and adheres to the glass, producing a coating. The thickness of the coating is controlled by varying the intensity of the current passed through the layer 11 of molten metal, or by varying the intensity of the magnetic field produced by the electromagnet 1 2. The thickness of the metal coating may vary from 50 to 500 mu.

The invention provides for complete automation of the process of applying a metal coating to a continuously fed band of glass and makes it possible to considerably reduce the coat of manufacturing metal-coated glass.

For example, a mirror coating produced with the use of the device according to the invention is 10 times cheaper than a similar coating produced by means of vacuum evaporation.

Claims (8)

1. An apparatus for applying a metal coating to a continuously fed band of glass, comprising an electromagnet positioned above the feed path of the band of glass, the poles of the electromagnet extending transversely to the glass band feed direction and being spaced apart in said direction, means located between the poles of the electromagnet for depositing molten metal on the surface of the glass band and for supplying oxidising gas, respectively, and electrical contacts carried by the electromagnet at the ends thereof for contacting a layer of molten metal deposited on the band of glass to pass an electric current through the layer of molten metal.

2. An apparatus according to claim 1, wherein means for supplying molten metal to the depositing means includes a vessel having a discharge opening connected to the depositing means, and means for supplying nonoxidising gas to the vessel to force molten metal contained in the vessel out through the discharge opening.

3. An apparatus according to claim 2, wherein the means for supplying gas to the vessel includes a control valve, the valve being controlled by an electric circuit including a pair of contacts carried by the electromagnet for sensing the depth of the layer of molten metal on the glass band between the poles of the electromagnet.

4. An apparatus according to claim 2, or 3, wherein heating elements are provided in the walls of the vessel, and a thermocouple is accommodated in the vessel for sensing the temperature of the molten metal.

5. An apparatus according to any one of claims 2 to 4, wherein the vessel accommodates a level indicator for indicating the level of molten metal in the vessel.

An apparatus according to claim 5, wherein the indicator comprises a float.

7. An apparatus according to any one of claims 1 to 6 wherein the depositing means comprises a pipe with perforations directed towards the band of glass.

8. An apparatus for applying a metal coating to a continuously fed band of glass, substantially as herein described with reference to the accompanying drawing.