AU784337B2 - Method for producing a glass product from recycled glass, and glass product - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): MR DOUGLAS TWEED Invention Title: METHOD FOR PRODUCING A GLASS PRODUCT FROM RECYCLED GLASS, AND GLASS PRODUCT The following statement is a full description of this invention, including the best method of performing it known to me/us: r.

r 2 METHOD FOR PRODUCING A GLASS PRODUCT FROM RECYCLED GLASS, AND GLASS PRODUCT This invention relates to a method of producing a glass product from recycled glass, and to a glass product.

The recycling of glass to form new glass products is known.

Generally, the current technique for recycling glass comprises crushing or breaking the glass into pieces, called cullets. The cullet is then combined with raw product from which glass is conventionally made, and the combination of the cullets and raw product is heated to a temperature of about 13000. The application of heat reduces the cullets to its constituent materials and also 15 burns out any colouring in the glass. The constituents then mix with the new raw material and glass products can be formed in the same manner as if only raw material was used to produce the glass 20 The present invention may be said to reside in a method of forming a glass product comprising; providing recycled glass in the form of glass cullet; supplying the cullet to a surface and preventing 25 the transfer of heat to the surface to prevent a temperature gradient occurring between an internal portion of the product and an external surface of the product which will induce thermal stress and cracking of the product; heating the glass cullet to a temperature in the range 850 0 C to 1050°C so as to cause the cullet to become semi-molten and to fuse together; and allowing the fused cullet to cool.

The step of heating the glass to the temperature in the range of 850 0 C to 1050 0 C has a result that the cullet is made to become semi-molten rather than completely reduced to its constituent components. Thus, the cullet, that is H:\Luisal\Keep\Speci\Tweed D P09259 Complete.doc 9/01/06 3 the glass pieces, to some extent, retain their integrity and merely fuse with other glass pieces because of their molten state so as to form the glass product. The temperature is not sufficient to burn out any colour in the recycled glass and therefore the product can retain the colour and characteristics of the recycled glass from which the product is formed.

Furthermore, because the cullets becomes molten rather than reduced to its constituent materials, the integrity of the glass pieces is maintained so that when they fuse together they fuse together as a collection of discrete pieces which gives the formed product a marble like appearance particularly if the recycled glass used in the process does have some original colour.

The glass product made according to the invention can be used as a building product and can be used as a substitute 2 for marble. The product has some advantages over marble product because the glass product is stain resistant, is not porous and has great strength. The glass product formed according to the invention may have application in the formation of both floor and wall tiles, table-tops, bench tops, shelving and many other uses.

In the preferred embodiment of the invention the temperature range is preferably in the range 900 0 C to 1000 0 C, more preferably 930 0 C to 990 0 C and most preferably 945 0 C to 985 0 C. The most preferred temperature for most applications of the invention is about 970 0

C.

Preferably the method includes supplying the cullets to a mould so as to shape the formed glass product.

The mould may take any particular shape but is preferably in the form of a square or rectangle for the formation of tiles.

H:\Luisal\Keep\Speci\Tweed D PQ9259 Complete.doc 9/01/06 4 However, in other embodiments the mould can be formed from two surfaces which are spaced apart to form a cavity and the cullet is supplied to the cavity so as to form a glass product which has the shape of the cavity. This form of moulding may be suitable for forming other articles such as containers or articles other than of a generally flat nature.

Preferably the step of preventing heat transfer comprises using as the surface, an insulating sheet, or locating an insulating sheet on the surface.

Preferably the step of heating the cullet is preformed in a 15 kiln and most preferably the interior of the kiln has a substantially homogenous heat distribution during the heating process.

The invention may also be said to reside in a glass product 20 formed according to the abovementioned method.

*oo *oo *o *ooo *iii oo H:\Luisal\Keep\Speci\T.eed D P09259 Completedoc 9/01/06 5 Preferred embodiments of the invention will be described, by way of example, with reference to the accompanying drawings in which; Figure 1 is a plan view of a glass product in the form of tile made according to the preferred embodiment of the invention; Figure 2 is a side view illustrating the method according to the preferred embodiment of the invention; Figure 3 is a plan view of Figure 2; and Figure 4 is a view of an alternative mould with which the invention can be used.

With reference to Figure i, a glass product embodying the invention is shown which is in the form of a tile which can be used as a wall or floor tile or, if made in a larger size could form a bench-top, shelf or any other building product. The glass product could also be used for non building purposes such as an ornamental piece which has no more than aesthetic value.

The glass product according to Figure 1 has a generally "marble like appearance and is formed from recycled bottle glass by breaking the bottle glass into pieces and supplying the broken pieces to a mould. The pieces are then heated so that the pieces become semi-molten and fuse together. The heating of the pieces to make them semimolten maintains the general integrity of each of the broken pieces but does soften them so that they do merge together at their peripheral portions and generally flatten out. The result of this is that the discrete pieces of broken glass from which the product is formed can be seen in the formed product thereby giving the product a generally marble like appearance. That is, according to the preferred embodiment of the invention the actual discrete nature of the broken pieces of glass is not completely destroyed during the heating process so that the \\melbfiles\hoeS\L.isa\Ieep\Speci\Tweed D P09259 Coa1ete.doc 1/08/01 6 pieces would otherwise convert to their constituent components or simply become a generally liquid mass.

Rather the discrete nature of the pieces is maintained and the pieces are fused into one another so as to form the completed product.

The preferred form of the product therefore can be used as a substitute for marble in building and has the advantage that the product is stain resistant, non porous and very strong.

Figures 2 and 3 show one form of a moulding technique according to the preferred form of the invention. With reference to Figures 2 and 3 a mould 10 in the form of a grid having compartments 12 is supported on an insulating layer 30 of a shelf 40 of a kiln 50. Broken glass pieces 70 are provided to each of the compartments 12 and may be smoothed out or flattened out within the compartments 12.

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The kiln 50 is then controlled so as to raise the temperature of the interior of the kiln to a temperature in the range 8500 to 1050 0 C so as to cause the glass pieces to become semi-molten so that the glass pieces merge together and become fused whilst at the same time maintaining the general discrete integral nature of each of the glass pieces within the fused and formed product. This fusing process of the discrete pieces together gives the product the marble like appearance because the appearance of each of the pieces can be seen in the final product as best shown in Figure 1.

The insulating layer 30 which supports the mould prevents heat transfer to or from the surface of the product as it is being heated and as it is cooling to prevent the formation of a substantial temperature gradient from an internal portion of the product to the external surface of the product thereby preventing thermal stressing \\melbfile\homeS\Luia\Keep\Speci\Teed D PQ9259 Coaolete.doc 1/08/01 7 and cracking at the surface of the product.

Figure 4 shows another preferred form of the invention in which a mould 15 is in the form of a container having an outer mould wall 16 and an inner mould wall 17 which define a cavity 18. The glass pieces 70 are supplied to the cavity 18 and the glass pieces heated so as to form a product having the shape of the mould in the same manner as previously described.

Thus, in this embodiment of the invention the layer forms the base portion of the mould 10 on which the glass pieces 70 sit within the compartments 12.

In this embodiment of the invention an insulating layer need not be used because the outer wall 16 will act as an insulating layer to prevent the formation of thermal gradiance within the product 70 as it is heated and as it cools.

In other embodiments, the mould may take the form of a bowl or dish shape into which the cullet can be located.

Alternatively, the cullet can be supported on a flat sheet which, during the heating process becomes softened and conforms to a bowl shaped mould arranged below the flat sheet so as to cause the cullet to take up the shape of the mould to form a bowl like article.

The interior of the kiln 50 should be remain at substantially homogenous temperature throughout during the heating and cooling process.

The surface of the formed glass product may be finished by a polishing or griding step by polishing or grinding the surface. Alternatively, the surface may be left in its natural formed state depending on the use to which the product is to be put.

\\melbf i1es\homeS\lui88\Keep\Speci\Twed D PQ9259 Com1ete.dc 1/08/01 8 Furthermore, the colour of the product may be provided or modified if the glass cullet is already coloured, by the addition of oxide to the glass cullet when the glass cullet is supplied to the mould 10. Alternatively, the colouring oxide may be applied to the surface of the formed product and the product again fired to cause the oxide to fuse to the product to colour the surface of the product.

The glass cullet may be provided by any conventional process which crushes bottles. The cullet may be graded into particular sizes for use in particular applications or in particular products. Furtherstill, the formed product may be cut in any conventional glass cutting technique and this step may include lineshing where cut.

Examples of forming glass products according to the method of the invention will now be described; Example 1; this example relates to the formation of a glass tile of size 100mm x 100mm and thickness of 6mm. The tile is formed in a mould of the type described with reference to Figures 2 and 3 and a plurality of the tiles can be •formed in a grid like mould at one time.

The cullet formed from the glass pieces 70 is applied to the mould which may be supported on the insulating surface and the surface 30 and mould are then located in a kiln.

The kiln is fired up to a temperature of 6750 without any ramp and the temperature of 6750 is held for twenty minutes. The temperature is then increased to 9700 without any ramp and the temperature held at 9700 for thirty minutes. The temperature is then decreased to 5450 without any ramp and held for ninety minutes. The temperature of the product is then allowed to cool to ambient temperature over a period which may be as long as two days.

Example 2; this example relates to the formation of a glass \\melb.f iles\homS\LuiSa\Kee\SpeCi\Tweed D PQ9259 Coffpete.doc 1/08/01 9 tile of the same size as example 1 except that it is intended that a smoother surface finish be provided during formation of the product.

In the example the cullet and mould are located in a kiln in the same manner as example 1 and then the temperature is ramped at 300 0 C to 650 0 C and held for thirty minutes. The ramping causes a controlled increase up to the temperature of 650 0 C at a rate of 300 0 C per hour until the temperature of 650 0 C is reached. After the thirty minute period the temperature is increased to 970 0 C without any ramp and held for thirty minutes at that temperature. After the thirty minute period the temperature is reduced to 545 0 C without any ramp and held for ninety minutes. The product is then allowed to cool to ambient temperature. The controlled ramping of the temperature referred to above has been found to give a different finish to the product and in particular a smoother finish.

20 Example 3; this example relates to formation of a glass tile of size 100mm x 100mm and thickness in the range of to The method employed is the same as example 1 except that after the temperature has been reduced to 545 0 C and held for ninety minutes there is a further controlled cooling step which comprises ramping the temperature at 30 0 C down to a temperature of 3000 and then allowing the product to o" cool to ambient temperature. This controlled last stage of cooling assists in formation of a thicker product because it controls the temperature decreases down to 300 0 C thereby not enabling the outer surface to cool too quickly relative to the thicker interior which may induce stresses and cracking of the product.

\\me b-f i es\homeS\Luis&\Keep\Speci \weed D P09259 Completedoc 1/08/01 10 Since modifications within the spirit and scope of the invention may readily be effected by persons skilled within the art, it is to be understood that this invention is not limited to the particular embodiment described by way of example hereinabove.

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Claims (9)

1. A method of forming a glass product comprising; providing recycled glass in the form of glass cullet; supplying the cullet to a surface and preventing the transfer of heat to the surface to prevent a temperature gradient occurring between an internal portion of the product and an external surface of the product which will induce thermal stress and cracking of the product; heating the glass cullet to a temperature in the range 850 0 C to 1050 0 C so as to cause the cullet to become semi-molten and to fuse together; and allowing the fused cullet to cool.

2. The method of claim 1 wherein the temperature range is in the range 900 0 C to 1000 0 C.

3. The method of claim 1 wherein the temperature 20 range is in the range 930 0 C to 990 0 C.

4. The method of claim 1 wherein the temperature range is 945 0 C to 985 0 C. 25

5. The method of claim 1 wherein the temperature is about 970 0 C.

6. The method of any one of claims 1 to 5 including supplying the cullets to a mould so as to shape the formed glass product.

7. The method of claim 1 wherein the step of preventing heat transfer comprises using as the surface, an insulating sheet, or locating an insulating sheet on the surface. H:\Luisal\Keep\Speci\Tweed D P09259 Complete.doc 9/01/06 12

8. The method of any one of claims 1 to 7 wherein the step of heating the cullet is preformed in a kiln and most preferably the interior of the kiln has a substantially homogenous heat distribution during the heating process.

9. A glass product formed according to the method of any one of the preceding claims. Dated this 9th day of January 2006 DOUGLAS TWEED By their Patent Attorneys GRIFFITH HACK 15 Fellows Institute of Patent and Trade Mark Attorneys of Australia S** S** S** H:\Luisal\Keep\Speci\Tweed D P09259 Complete.doc 9/01/06