CRITCHLEY, Keith, William (18 Easington Road, NutgroveSt Helens, Merseyside WA9 5LW, GB)
KIRBY, Graham (9 Fieldview, Hall GreenUp-Holland, Lancashire WN8 0BG, GB)
CRITCHLEY, Keith, William (18 Easington Road, NutgroveSt Helens, Merseyside WA9 5LW, GB)
| CLAIMS 1. A method of applying a solution comprising a stain inhibitor to a glass surface comprising the steps: (a) arranging a manifold comprising an array of at least two outlet pipes above the glass surface; (b) supplying the manifold with the solution; (c) increasing the flow rate of the solution to the manifold to overcome the back pressure thereof, such that the solution flows from each outlet pipe and (d) depositing the solution onto the glass surface. 2. A method according to claim 1, wherein the outlet pipes are positioned above an absorbent strip such that solution that flows from the outlet pipes is absorbed by the absorbent strip to wet the strip, and liquid is deposited onto the glass surface by transferring solution from the wet absorbent strip to the glass surface. 3. A method according to claim 2, wherein a portion of the absorbent strip is in contact with the glass surface. 4. A method according to any preceding claim, wherein the volume of solution that is deposited on the glass surface is between ImI per square meter and 50ml per square meter, preferably between 5ml per square meter and 10ml per square meter. 5. A method according to claim 4 when appendant upon claim 3, wherein the liquid is uniformly deposited on the glass surface. 6. A method according to any preceding claim, wherein the flow rate from each outlet pipe is between ImI and 20ml per minute per outlet pipe, preferably between 4ml and 10ml per minute per outlet pipe. 7. A method according to any preceding claim, wherein the flow rate of solution from each outlet pipe is substantially the same. 8. A method according to any preceding claim, wherein the liquid flows into each outlet pipe in an opposite direction to the flow of liquid out of the respective outlet pipe. 9. A method according to any of the preceding claims, wherein the glass surface is a surface of a float glass sheet or ribbon, preferably the upper surface. 10. A method according to any preceding claim, wherein the glass surface has a coating thereon. 11. A method according to any preceding claim, wherein the solution drips from each outlet pipe such that each droplet has a volume between 0.01ml and 10ml, preferably about 0.05ml. 12. Apparatus for depositing a solution comprising a stain inhibitor onto a surface of a float glass ribbon, preferably the upper surface of a float glass ribbon, the apparatus comprising a reservoir for containing the liquid, the reservoir being in fluid communication with a manifold, the manifold comprising an array of at least two outlet pipes, each outlet pipe having an inlet for introducing solution into the outlet pipe, and an outlet orifice through which solution can flow, and wherein each outlet pipe provides a sufficient back pressure such that flow of solution from the outlet pipe is restricted, the outlet pipes being arranged such that for a sufficient input flow of solution to the manifold, solution flows from each outlet pipe. 13. Apparatus according to claim 12, wherein the manifold is configured such that there is a target flow rate for each outlet pipe, preferably the same target flow rate for each outlet pipe. 14. Apparatus according to claim 13, wherein in use, the flow rate from each outlet pipe is within +25% of the target flow rate for the respective outlet pipe. 15. Apparatus according to any of the claims 12 to 14, wherein each outlet pipe is configured such that the inlet faces in an opposite direction to the outlet orifice. 16. An assembly for use in applying a solution comprising a stain inhibitor to a surface of a float glass ribbon, in particular the upper surface of the float glass ribbon, the assembly comprising an apparatus according to the any of the claims 12 to 15 and a transfer device, preferably an absorbent strip, located below the outlet pipes, such that in use, the solution flows from the outlet pipes onto the transfer device to wet the transfer device, and the solution is transferable from the wet transfer device to the surface of the float glass ribbon. |
The present invention relates to an apparatus for use in applying a solution comprising a stain inhibitor to a glass surface and to a method of applying a solution comprising a stain inhibitor to a glass surface. Such an apparatus and method find particular use in applying an aqueous solution comprising a stain inhibitor to the surface of a moving sheet of glass produced by a float process.
It is well known to one skilled in the art that glass can corrode when exposed to water or humid conditions. The problem of glass corrosion is particularly evident when glass sheets are stored in a pack, for example a pack of soda- lime-silica glass sheets produced by a float process.
For a soda-lime-silica glass, it is thought that corrosion of a glass surface in the presence of water involves sodium ions being leached out of the glass surface and into the water. As the level of sodium in the water increases, the pH of the solution in contact with the glass surface increases, accelerating the corrosion process and causing the glass surface to be etched. The resulting alkaline solution can cause the silicate structure of the glass to dissolve, which can then react with calcium oxide in the glass to precipitate insoluble deposits of calcium silicate on the glass surface. The combined effect of the etching process and the accumulation of insoluble deposits on the surface is to create a hazy glass surface. This haziness is usually referred to as "stain".
In order to improve the stain resistance of soda lime silica glass such as float glass, the surface of the annealed float glass that has not been in contact with the tin bath is normally covered with a protective layer. The protective layer is designed to prevent alkaline attack that results when sodium is leached from the glass and dissolves in the water in contact with the glass surface. Whilst sheets of paper may be used as the protective layer, usually the protective layer comprises a weak acid, such as adipic acid, to neutralise the alkaline solution that is formed on the glass surface due to sodium leaching. Adipic acid has been used for many years in the glass industry as a stain inhibitor.
It is possible to apply a weak acid stain inhibitor in liquid form, for example an aqueous solution. A typical "stain inhibitor" solution contains less than 5% by weight adipic acid dissolved in deionised water. Often a low level i.e. less than 0.5% by weight, of a suitable surfactant is also present to aid dispersion of the solution on the glass surface. Known methods of applying the solution comprising the weak acid stain inhibitor to the surface of a glass sheet are spraying, dip coating, meniscus coating, flood coating, rollers and brushes. In all these particular cases, the solution is deposited on the glass surface. As the solution dries, the stain inhibitor is left on the glass surface, thereby giving the surface increased protection against stain. In the glass industry, a stain inhibitor adheres to the glass surface to protect the glass but must be able to be washed off with water to expose the glass surface.
It is desirable to coat the glass surface with the lowest amount of stain inhibitor to provide the glass surface with adequate protection against stain. To obtain adequate protection uniformly across the glass surface, it is desirable that the coating of stain inhibitor uniformly covers the glass surface.
Clearly to give the surface uniform protection against stain, it is possible to coat the glass surface with a level of stain inhibitor well above the minimum required to provide adequate protection, so that non-uniformity of the application becomes less important. However this is not a cost effective option. Additionally, if the stain inhibitor is applied in liquid form, by applying excess liquid to the surface, suitable drainage and collection of liquid that flows from the surface is required, or the additional liquid may be evaporated. This is particularly important for glass produced by a float process. It is preferred that the continuous glass ribbon that is produced in a float process is sufficiently dry before being cut into sheets. If the glass surface is not sufficiently dry, excess liquid may interfere with the action of cutting oil, which is generally used to obtain a clean score and snap for glass cutting. Clearly, the more liquid that is applied, the more difficult it becomes to ensure sufficient evaporation before cutting.
When the glass surface is the surface of a moving ribbon of glass, for example a glass ribbon that has been produced using a float process, in order to uniformly coat the glass surface with solution, solution may be uniformly applied to the surface, either directly thereto, or indirectly via a transfer device comprising an absorbent strip or a roller.
One method of directly applying a uniform coating of stain inhibitor to a glass surface is atomise the liquid to a fine spray and to then spray the liquid onto the glass surface to deposit liquid thereon. This has environmental issues because the resulting aerosol or mist may be hazardous to health and the fine nozzles that produce the spray may become blocked over time due to crystallisation of the stain inhibitor from the solution. A method of indirectly applying a uniform coating of stain inhibitor to a glass surface is to use an absorbent strip of material to act as a transfer medium. By firstly applying the solution to the absorbent strip, the wet strip can then be contacted with the glass surface, thereby transferring solution from the wet strip to deposit the solution onto the glass surface. By moving the glass surface relative to the wet strip, the entire glass surface may be coated with the solution.
Indirect application as mentioned above does not suffer from the problems of directly spraying onto the glass surface. However if the above method of indirectly applying liquid to the glass surface is used to apply a stain inhibitor solution to a moving float glass ribbon, it is difficult to apply only sufficient solution to provide adequate surface protection. Given that a typical float glass ribbon is around 3m wide, and moves at speeds between 5m per minute and 20m per minute, to obtain uniform application of stain inhibitor solution to the absorbent strip such that a suitable volume of stain inhibitor solution is deposited on the glass surface is difficult.
The present invention aims to address the above mentioned problems of applying a low volume of liquid to a large surface area.
Accordingly the present invention provides from a first aspect a method of applying a solution comprising a stain inhibitor to a glass surface comprising the steps: (a) arranging a manifold comprising an array of at least two outlet pipes above the glass surface; (b) supplying the manifold with the solution; (c) increasing the flow rate of the solution to the manifold to overcome the back pressure thereof, such that the solution flows from each outlet pipe, and (d) depositing the solution onto the glass surface.
Within the context of the present invention, a stain inhibitor improves the stain resistance of a glass surface and can be removed from the glass surface by washing with water. Preferably the stain inhibitor is soluble in water.
Preferably the outlet pipes are positioned above an absorbent strip such that solution that flows from the outlet pipes is absorbed by the absorbent strip to wet the strip, and solution is deposited onto the glass surface by transferring solution from the wet absorbent strip to the glass surface.
Preferably a portion of the absorbent strip is in contact with the glass surface.
Preferably the volume of liquid that is deposited on the glass surface is between ImI per square meter and 50ml per square meter, preferably between 5ml per square meter and 10ml per square meter. Suitably the surface has an area of more than one square meter, and the liquid is uniformly deposited on the surface.
When the liquid is deposited onto the glass surface by being transferred from a wet absorbent strip, it is preferred that the solution is uniformly deposited onto the glass surface. This means that the variation of the volume of liquid applied to the glass surface in two adjacent areas, each area having the same dimensions, is less than 30%, preferably less than 20%, more preferably less than 10%.
In other embodiments, preferably the flow rate from each outlet pipe is between ImI and 20ml per minute per outlet pipe, preferably between 4ml and 10ml per minute per outlet pipe.
Preferably the flow rate of solution from each outlet pipe is substantially the same.
Preferably the solution flows into each outlet pipe in an opposite direction to the flow of solution out of the respective outlet pipe. This provides the advantage of providing the manifold with an increased back pressure, thereby allowing a greater degree of control over the flow rate of the solution that flows from each outlet pipe.
Preferably the liquid is a solution comprising a stain inhibitor.
Preferably the glass surface is a surface of a float glass sheet or ribbon. The surface of the float glass sheet or ribbon is preferably the upper surface of the float glass sheet or ribbon, i.e. that glass surface that has not been in contact with molten tin when the float glass was formed on the float bath. By float glass, it is meant any glass composition that has been formed by a float process i.e. has been formed on a molten pool of tin. Typical float glass compositions include soda- lime-silica glass compositions, borosilicate glass compositions or alumino- silicate glass compositions. The surface of the float glass sheet or ribbon may have a coating thereon, in which case the glass surface may have a different chemical composition to the bulk glass composition. The coating may have been applied using an atmospheric chemical vapour deposition process. For surface of a glass sheet i.e. a pane of glass that has been cut from a float glass ribbon, the coating may have been applied by a sputtering process under vacuum, or a similar process known to one skilled in the art. The stain inhibitor may be applied to the coated glass surface.
Suitably the array spans between Im and 4m, preferably about 3m.
Preferably the manifold comprises between 10 and 100 outlet pipes, more preferably between 30 and 50 outlet pipes. Preferably the solution drips from each outlet pipe such that each droplet has a volume between 0.01ml and 10ml, preferably about 0.05ml.
In preferable embodiments of the first aspect of the present invention, the flow rate of liquid to the manifold is between 100ml per minute and 500ml litre per minute.
In certain embodiments of the first aspect of the present invention, the liquid is pumped and/or flows under gravity to the manifold.
Depending upon the width of the float glass ribbon or sheet, the number of outlet pipes, the droplet size from each outlet pipe and the flow rate to the manifold may be varied to ensure a sufficient flow of liquid from the outlet pipes to the glass surface. From a second aspect the present invention provides an apparatus for depositing a solution comprising a stain inhibitor onto a surface of a float glass ribbon, the apparatus comprising a reservoir for containing the solution, the reservoir being in fluid communication with a manifold, the manifold comprising an array of at least two outlet pipes, each outlet pipe having an inlet for introducing solution into the outlet pipe, and an outlet orifice through which solution can flow, and wherein each outlet pipe provides a sufficient back pressure such that flow of liquid from the outlet pipe is restricted, the outlet pipes being arranged such that for a sufficient input flow of solution to the manifold, solution flows from each outlet pipe. The surface is preferably the upper surface of the float glass ribbon.
Preferably the apparatus is configured such that for i outlet pipes, there is a target flow rate, Fi, for each of the outlet pipes. Preferably the target flow rate for each outlet pipe is the same.
The apparatus is configured such that in use, preferably the flow rate from each outlet pipe is the within +25% of the target flow rate Fi for the respective outlet pipe, more preferably within +10% of the target flow rate Fi for the respective outlet pipe, even more preferably within + 5% of the target flow rate Fi for the respective outlet pipe.
In a most preferred embodiment, in use, the flow rate from each outlet pipe is substantially the same. Preferably the apparatus is configured such that liquid flows from each outlet pipe as a series of droplets.
Preferably the outlet pipe is configured such that in use, each droplet that is emitted from each outlet pipe has a volume between 0.01ml and 10ml, preferably about 0.05ml. Preferably the manifold comprises between 10 and 100 outlet pipes, more preferably between 30 and 50 outlet pipes. Preferably the apparatus is configured such that for an input flow to the manifold of between 100ml per minute and 500ml per minute, the output flow from each outlet tube is between ImI and 20 ml per minute per outlet pipe, more preferably between 4ml and 10ml per minute per outlet pipe.
Preferably the spacing of adjacent outlet pipes is between 50mm and 100mm.
Preferably the outlet pipes are uniformly spaced.
Preferably the array of outlet pipes spans the width of the float glass ribbon. Preferably the array spans between Im and 4m, more preferably about 3m. The array may span up to 6m or more.
Preferably the apparatus comprises a pump to pump liquid from the reservoir to the manifold.
In use, the reservoir may be located higher than the manifold so that the liquid flows to the manifold under the action of gravity. Preferably the outlet pipes comprise a curved portion.
Preferably the flow rate from each outlet pipe is between ImI per minute and 20ml per minute, more preferably between 4 ml per minute and 10ml per minute.
Preferably the array is a linear array.
Preferably each outlet pipe is configured such that the inlet faces in an opposite direction to the outlet orifice. This means that in use, the liquid flows into the inlet in an opposite direction to the direction of the liquid that flows from the outlet orifice. This provides the advantage of providing the manifold with an increased back pressure, thereby allowing a greater degree of control over the flow rate of the liquid that flows from each outlet pipe. Preferably at least one outlet pipe has a bore diameter of between 0.5mm and 2mm, preferably about lmm.
The invention provides from a third aspect an assembly for use in applying a solution comprising a stain inhibitor to a surface of a float glass ribbon, in particular the upper surface of the float glass ribbon, the assembly comprising an apparatus according to the second aspect of the invention and a transfer device located below the outlet pipes, configured such that in use, the solution flows from the outlet pipes onto the transfer device to wet the transfer device, and the solution is transferable from the wet transfer device to the surface of the float glass ribbon. Preferably the transfer device comprises a roller.
Preferably the transfer device comprises an absorbent strip. Preferably the absorbent strip comprises a felt. Preferably the absorbent strip comprises an outer layer that is harder wearing than the absorbent strip but is able to allow the solution to permeate therethrough. When the transfer device is an absorbent strip, preferably the assembly is configured such that solution that flows from the outlet pipes onto the absorbent strip spreads laterally thereon. Preferably the lateral spread of solution on the absorbent strip is at least half the distance between a pair of adjacent outlet pipes. This provides the advantage that the absorbent strip may be completely wetted beneath the array of outlet pipes. For a given size of absorbent strip, the number of pipes may be varied depending upon the volume of solution that flows from each outlet pipe.
The invention will be described by way of example with reference to the accompanying figures (not to scale), in which: Figure 1 shows a side view of a liquid applicator for use in an apparatus in accordance with the second aspect of the present invention.
Figure 2 shows a front view of the liquid applicator shown in figure 1.
Figure 3 shows a plan view of part of a manifold comprising two liquid applicators of the type shown in figure 1.
Figure 4 shows a plan view of an apparatus for supplying liquid directly to the upper surface of a moving glass sheet.
Figure 5 shows a plan view of an apparatus for supplying liquid indirectly to the upper surface of a moving glass sheet. Figure 6 shows a side view of figure 5.
With reference to figures 1 and 2, the liquid applicator 1 comprises a length of stainless steel tubing 3 about 6cm long with an internal diameter of about 5mm and a wall diameter of about 0.5mm.
Suitably connected to the lower end of tube 3 is a T-piece 5, also made of stainless steel. The tube 3 connects to the upper limb of T-piece 5 via a suitable connection assembly 6. The T-piece has two inlets 7, 9 through which liquid such as a solution comprising a stain inhibitor may be input i.e. in the direction of arrows 11 and 13 respectively. Liquid flows out of the T-piece through outlet 15 so that liquid can flow along tube 3 in the direction of arrow 17. Suitably connected to the upper end of tube 3 is another stainless steel tube 19 having a bore diameter of about 3mm and a wall thickness of about 0.5mm. Tube 19 connects to tube 3 via a suitable connection assembly 21.
Connected to the upper end of tube 19 is an outlet pipe 23. Outlet pipe 23 has an inlet portion 24, a curved portion 25 and an outlet orifice 27. Liquid may flow from outlet orifice 27 as a series of droplets that fall in the direction of arrow 29. Outlet pipe 23 connects to tube 19 via a suitable connection assembly 31. The lower end of outlet pipe 23 has a frustoconical portion 33 attached thereto to form a water tight seal to the upper portion of tube 19. The frustoconical portion surrounds the outlet pipe inlet. The outlet pipe 23 is made of stainless steel and has an inner bore diameter of about lmm and a wall thickness of about 0.5mm.
By arranging the liquid applicator such that liquid flows into the applicator in the opposite direction to the direction of liquid flow out of the applicator, the liquid applicator is able to provide a sufficient back pressure to restrict the flow of liquid out of the outlet pipe. That is, the direction of arrow 17 is in the opposite direction to arrow 29.
The back pressure of the apparatus is a function of at least (i) the bore diameter of the tubes that make up the liquid applicator, (ii) the material used for the tubing and (iii) the viscosity of the liquid that flows through the applicator.
Figure 3 shows a plan view of part of an apparatus for applying a solution comprising a stain inhibitor to onto a surface of a float glass ribbon. The apparatus 51 comprises a pair of liquid applicators 53, 55 of the type shown in figures 1 and 2. Liquid applicator 53 comprises a T-piece 57 and an outlet pipe 61. Liquid applicator 55 comprises a T-piece 59 and an outlet pipe 63. The T-pieces 57, 59 are suitably connected via a stainless steel tube 65, such that liquid applicator 53 is in fluid communication with liquid applicator 55. The limb of T-piece 57 that is opposite the limb connected to tube 65 is connected to a stainless steel tube 67. Liquid can flow into T-piece 57 via tube 67 in the direction of arrow 71. The limb of T-piece 59 that is opposite the limb connected to tube 65 is connected to a stainless steel tube 69. Liquid can flow into T-piece 59 via tube 69 in the direction of arrow 73. The assembly of liquid applicators 53, 55 and connecting tubes
65, 67 and 69 are part of the manifold of the apparatus.
Each outlet pipe 61, 63 has an outlet orifice through which liquid can flow, preferably as a series of droplets. For clarity, only the connection assemblies 6, 21, 31 for the liquid applicator 53 have been indicated.
The spacing 70 between the two adjacent liquid applicators shown in figure 3 is preferably between 50mm and 100mm. Suitably the spacing is 75mm. The spacing refers to the spacing between the outlet orifice in each respective outlet pipe. Figure 4 shows a plan view of part of an apparatus for directly applying a liquid to a surface of a glass sheet. The apparatus comprises a manifold 91 shown having eight liquid applicators 93, 95, 97, 99, 101, 103, 105 and 107 of the type shown in figure 1 and figure 2. Each liquid applicator 93, 95, 97, 99, 101, 103, 105, 107 comprises a respective outlet pipe 109, 111, 113, 115, 117, 119, 121, 123. Adjacent T-piece portions are connection via a stainless steel tube, as described with reference to figure 3. The liquid applicators are shown connected as a linear array. The liquid applicators may have a staggered arrangement.
Liquid may flow into either or both inlets 125, 127 so that liquid flows in the direction of respective arrow 129, 131. Liquid may be ejected from each outlet orifice in each outlet pipe directly onto the upper surface of the glass sheet 133. The glass sheet may be a float glass ribbon moving at speeds between 5m per minute and 20m per minute in the direction of arrow 135. The manifold 91 may not be perpendicular to the direction of the moving glass indicated by arrow 135. As described with reference to figures 1 and 2, outlet tubes 109, 111, 113, 115, 117, 119, 121 and 123 have a curved portion. Each liquid applicator is substantially the same. The upper part of the curved portion of each outlet tube is at substantially the same distance from the upper surface of the glass sheet 133. The outlet orifice of each outlet pipe is at substantially the same distance from the upper surface of the glass sheet 133. For a sufficient input flow to either or both inlets 125, 127, liquid flows from the outlet orifice in the respective outlet pipe of each liquid applicator at substantially the same rate.
The apparatus is configured such that for a given number i of outlet pipes, there is a target flow rate per minute per outlet pipe of Fi for each of the outlet pipes. Preferably the target flow rate for each outlet pipe is the same, for example 5ml per minute per outlet pipe. If it is desired to supply a total volume V per minute to a surface using a method or an apparatus according to the present invention, and the manifold comprises i outlet pipes, the volume flow per minute per outlet pipe may be VIi.
Preferably the apparatus is configured such that the actual flow rate from each outlet pipe (Fp) is at least within +25% of the target flow rate for the respective outlet pipe, more preferably within +10% of the target flow rate for the respective outlet pipe, even more preferably within + 5% of the target flow rate for the respective outlet pipe.
In a most preferred embodiment, the flow rate per outlet pipe is the same, or substantially the same. Preferably the liquid flows from the outlet orifice in each outlet pipe as a series of droplets.
Figure 5 shows a plan view of part of an assembly for indirectly applying a liquid to the upper surface of a glass sheet. The assembly comprises an apparatus of the same construction as described with reference to figure 4. The manifold 91 is arranged such that the outlet pipe, and consequently the outlet orifice, of each liquid applicator is above a strip of absorbent material 141. The absorbent strip is preferably a felt. Suitably the absorbent strip comprises an outer layer, preferably an outer layer of nylon. Preferably the outer layer is woven from a single monofilament. The absorbent strip is hung from a support 143 such that a portion of the strip contacts the upper surface of the glass sheet 133 and a portion of the strip is suspended above the upper surface of the glass sheet.
Liquid may flow into either or both of inlets 125, 127 of the manifold 91 such that liquid flows in the manifold in the direction of arrows 129, 131. For a sufficient input flow rate to the manifold, liquid may be ejected from each outlet orifice at substantially the same rate, preferably as a series of droplets. The preferred rate of liquid flow from each outlet orifice is between 1 and 20 ml per minute per outlet pipe, preferably between
4 and 10ml per minute per outlet pipe.
By using the absorbent strip, the liquid may be uniformly applied to the upper surface of the glass sheet 133. Preferably the glass sheet is a float glass ribbon moving in the direction of arrow 135 at speeds between 5m per minute and 20m per minute.
Typically the glass sheet 133 has a width of about 3m i.e. 3.3m. Liquid may be uniformly applied to the upper surface of the glass sheet between the dotted lines 130, 132.
Alternatively, the liquid may be uniformly applied to the entire width of the glass sheet or ribbon having a suitable size of absorbent strip.
The liquid applied to the absorbent strip is a solution comprising a stain inhibitor.
The absorbent strip provides a means of depositing a low volume of the solution over a large surface area uniformly. When the solution on the glass surface is dried, the stain inhibitor is uniformly spread over the glass surface such that the resistance to stain of the glass surface is improved over all, or substantially all the treated glass surface.
Although the assembly shown in figure 5 may be used to uniformly deposit low amounts of stain inhibitor to the glass surface, such that acceptable stain resistance is provided to the glass surface, the assembly may be used to deposit high amounts of stain inhibitor to the glass surface to modify the properties thereof. When the stain inhibitor is adipic acid, a low amount of stain inhibitor applied to the glass surface is in the region of O.lg per m 2 , whereas a high amount of stain inhibitor applied to the glass surface is in the region of Ig per m 2 . The assembly shown in figure 5 may be used to uniformly deposit low and high levels of adipic acid to the upper surface of a float glass ribbon. The upper surface of the float glass ribbon may have a coating thereon such that the solution is applied to the coating.
Figure 6 shows in slightly more detail a side view of the assembly shown in figure 5. The manifold 91 is connected by a pipe 161 to a flow regulator 163. The other end of the flow regulator is connected to a reservoir 165 via a pipe 161 and 167. The reservoir is in fluid communication with the manifold. Liquid may be pumped from the reservoir to the manifold via a suitable pump (not shown). Alternatively, the reservoir may be located higher than the manifold and the liquid may be fed by gravity thereto. The flow rate of liquid from the reservoir to the manifold may be controlled via the flow regulator 163.
When the manifold comprises forty liquid applicators of the type described with reference to figures 1 and 2, for a flow rate of 40ml/min to 300ml/min of solution to the manifold, preferably 175ml/min to 250ml/min, the flow rate from the outlet orifice in each outlet pipe is substantially the same, preferably between 1 and 20 ml per minute per outlet tube, more preferably between 4 and 10ml per minute per outlet tube. When there are forty liquid applicators, suitably between 4ml and 10ml of solution, preferably about 5ml to 7ml of solution, flows from the outlet orifice in each outlet pipe per minute.
The amount of solution comprising a stain inhibitor that is output from each liquid applicator may be varied depending upon the desired level of stain inhibitor that is to be deposited onto the glass surface.
Liquid applicator 107 is shown. This liquid applicator has a T-piece 108 and an outlet pipe 123 that has an outlet orifice 124.
The absorbent strip is suspended above the glass sheet 133 via a support 143. The support is shown connected to a linear actuator 145 so that the absorbent strip may be moved vertically in the direction of the arrow 151.
In use, a portion 147 of the absorbent strip is suspended above the upper surface of the glass sheet 133 and a portion 149 the absorbent strip lies on the upper surface of the glass sheet 133. By moving the glass sheet, which may be a float glass ribbon, in the direction of arrow 135, solution that has flowed onto the absorbent strip 141 may be deposited onto the upper surface of the glass sheet as a film 136. The film 136 may be suitably dried to leave stain inhibitor on the surface of the glass sheet 133. The upper surface of the glass sheet or ribbon may have a coating thereon, in which case the film 136 will be deposited onto the coating. In order to provide adequate stain resistance, it is desirable to apply O.lg of adipic acid per square metre to the surface of a float glass ribbon or sheet. Such a level of stain inhibitor may be considered a low level. For a typical stain inhibitor solution comprising 1.4% by weight adipic acid, the volume of liquid to be applied to one square metre of the glass surface is therefore about 7 ml. In order to provide uniform stain resistance over the entire one square metre of the glass surface, this volume of stain inhibitor solution must be uniformly applied to the glass surface. Given that a small drop from a burette is normally taken to be about 0.05ml, this means that about 140 drops of the stain inhibitor solution must be applied to one square metre of the glass surface. A small drop of water from a burette will only spread to a spot about 5-8mm in diameter (depending upon the surface tension), so the 140 drops will not cover the one square metre of the glass surface without additional spreading (the area of the 140 drops being about 0.007m 2 , i.e. only 0.7% of the required area to be covered).
Whilst it is possible to dilute the solution so that even more droplets are applied, this makes drying the solution that is on the glass surface more difficult because more solvent must be evaporated to leave the stain inhibitor on the glass surface. Another alternative is to atomise the solution, but as has been mentioned before, there are problems with using sprays, namely that the spray nozzles may become blocked, and that suitable extraction must be provided in order to reduce potential environmental effects. Using an absorbent strip i.e. a felt strip, the apparatus according to the present invention is able to supply the low volume (7ml) of liquid that is required to give a one square meter surface of float glass adequate stain resistance.
However, the apparatus may also be used with an absorbent strip i.e. a felt strip, to uniformly deposit high levels i.e. up to Ig per square meter, of adipic acid onto the surface of a float glass sheet or ribbon.
It is preferred that the solution drips at a substantially uniform rate from each outlet pipe in order to maintain a substantially uniform solution content of the absorbent strip. Using the apparatus and method according to the present invention, it is possible to supply a solution comprising a stain inhibitor to a manifold comprising at least two outlet pipes such that solution flows from each outlet pipe at a volume of about between 4ml and 10ml per minute, preferably as a series of droplets from each outlet pipe. The manifold may be in excess of 3m in length and may comprise at least 10 liquid applicators, preferably between 10 and 100 liquid applicators, more preferably between 30 and 50 liquid applicators.
Apparatus and methods according to the present invention are particularly useful when it is desirable that a small volume of liquid i.e. less than 20ml be deposited onto a large surface area, i.e. 1 square meter, particularly in a uniform manner.