RELATED APPLICATIONS

This application is a 35 U.S.C. 371 national stage filing from International Application No. PCT/IB2015/055709, filed Jul. 29, 2015, which claims priority to Italian Application No. TV2014A000115, filed Jul. 30, 2014, the teachings of which are incorporated herein by reference.

The present invention relates to an improvement to the method for manufacturing conglomerate stone slabs using the Bretonstone technology and more specifically to an improvement to the temporary substrate for supporting the mixture, used in this technology.

The expression “Bretonstone technology” is understood as referring to a method and plant for manufacturing conglomerate stone slabs.

In general terms this technology envisages a first stage for preparation of a mixture consisting mainly of granules of stone material (for example marble or granite or quartz) with a predefined grain size and a binder which may be organic or inorganic. In case of inorganic binder it consists of a cement binder which has the same hardening characteristics as cement articles, while in the first case (organic binder) it consists here of a resin, preferably a styrene polyester resin, hardening of which is normally performed under hot conditions with the aid of a catalyst.

During a second stage the mixture is poured in the form of a layer with a predefined thickness onto a support which may be temporary and on which the mixture undergoes vacuum vibrocompression.

The third and final stage (irrespective of the subsequent stages involving specific machining and finishing of the resultant rough-formed slabs) consists in the aforementioned hardening operation.

It is known to produce Bretonstone slabs using the following supports for the mixture to be compacted:(a) a bottom paper sheet onto which the mixture is poured and a top paper sheet for covering the mixture (cf. U.S. Pat. No. 4,204,820 corresponding to Italian patent application No. 85564°/77 filed on Apr. 22, 1977 and entitled: “Improvements to the method with combined vibrating and pressing action in an airless environment for forming resin-bonded granite slabs”);(b) a bottom rubber sheet, preferably in the form of a tray and a top rubber sheet (cf. Italian patent No. 1288566 and European patent No. EP 1027205).

The first process is performed by means of a less expensive plant but has not insignificant drawbacks, especially in the case of resin-based binders.

It should be remembered in fact that the catalysis step is performed in suitable ovens consisting of several heating surfaces, where the slab is enclosed between two surfaces.

The temperature reached is usually about 80-140° C. so that fluidization of the resin occurs and organic vapours (in particular styrene vapours if a polyester resin is used) are generated.

Paper, since it is porous, does not form a barrier to the vapours of solvents or other chemical compounds and to migration of the resin, so that these agents pass easily through the sheet of paper and are deposited on the surfaces of the catalysis oven.

These chemical agents cause various problems:since the styrene, when it polymerizes, becomes polystyrol, the slab adheres to the surfaces of the oven, with the result that extraction of the slab, usually performed by means of a mechanical thruster, is hindered;entry of a new slab inside the oven, again performed by means of a mechanical thruster, is hindered;a layer of insulating material is formed and prevents the uniform transmission of heat from the heating surfaces to the slab.

The surfaces of the oven must therefore be frequently cleaned.

This operation results in the need to interrupt operation of the plant, thus increasing the production costs. Moreover, the cleaning operation is not easy at all since the resin adheres stubbornly to the oven shelves.

In order to limit partly this problem, the idea has occurred to line the surfaces of the oven with removable plates so that cleaning of the plates may be performed outside the oven, thus avoiding in particular prolonged stoppage of the plant.

However, even with this measure, the aforementioned problems are only partly overcome, but not eliminated.

Moreover, whereas when using rubber trays the compacted and hardened slab is extracted from the tray before being sized and smoothed, in the case where paper is used, the slab, lined with paper on both sides, enters instead directly into the sizing and smoothing lines where the sizing and smoothing tools, with the aid of the cooling water, grind and reduce to a mash the sheets of paper which cover the slabs.

These operations produce a waste mixture composed principally not only of the components of the catalysed starting mixture and cooling water used to cool the tools of the sizing and smoothing machines, but also the ground paper, and therefore the mixture is substantially composed of water, powder stone material (e.g. marble or granite or quartz), bonding resin and paper.

These waste products (in the form of sludges) are decanted, filter-pressed and finally disposed of in suitable waste collection and disposal centres.

For further information regarding the possibilities for disposal of machining sludges, reference may be made to the following patent documents:Patent Application No. PCT/EP08/61112, which relates to a method and a plant for treating and recycling machining sludges by means of drying and incineration;Patent Application No. PCT/IB2010/50961, which relates to a method and a plant for treating the aforementioned machining sludges, in which it is envisaged adding an inorganic binder to the sludges so as to convert them into inert granules to be used in the building sector.

From the above considerations it therefore emerges that the main unresolved problems are those relating to the plants and processes based on paper elements for containing the starting mixture; the main object of the invention is therefore to provide a containment element for the mixture to be used in Bretonstone technology and therefore in the methods and the plants hitherto designed to use the top and bottom paper sheets, while eliminating however the abovementioned drawbacks and therefore preventing the aforementioned chemical agents from coming into contact with the oven shelves, so as to eliminate the need for cleaning thereof and consequent stoppage of the plant.

