GB2124201A - Process for the reconstitution of slates - Google Patents

Abstract

A process for reconstituting slate is described in which the slate is ground so as to produce seven portions each with a different grain size. The ground slate is then mixed with a settable synthetic resin e.g. a methacrylic resin and stirred for up to 20 minutes before being poured into a mould which is vibrated during the setting of the reconstituted slate with the resin.

Description

SPECIFICATION Process for the reconstitution of rocks particularly slates The present invention has for its object a process for the reconstitution of rocks and more particularly for the reconstitution of schists or slates from tailings of said rocks, particularly slates.

Ever since the remote past natural stone has been used for the construction of buildings and public works, for purposes of support or lining, decoration and roofing. In areas which do not possess the appropriate quarries it is necessary to import the rocks to be used, such as marble, granite, slate, etc., which makes their use enormously dearer, because of the cost of transport, while large quantities of tailings of said rocks are produced at the quarry, as "sound" blocks only are marketable, all of which makes the use of the stone in building even dearer.

On the other hand, the use of blocks or sheets of natural stone increases considerably the weight of the construction, the foundations and structures of which have to be designed and carried out in such a way that they are able to bear this additional weight brought about by the blocks of stone applied as wall facings, or by the slabs of stone used as roof coverings.

Many attempts have already been made at obviating these difficulties consequent upon the weight of the natural stone, the scarcity of sound blocks and the need to meet the demand for building materials of impressive appearance in areas which are naturally lacking in them, by means of the employment of "artificial" stone which, generally, are based on sections of varying size of natural stone and a hydraulic agglutinant or, in more modern terms, a synthetic agglutinant.

However, such artificial stone with hydraulic agglutinant cannot be used in all cases and the mechanical properties of the stone are not always comparable with those of the original natural stone; also, its weight could be substantially the same as that of said natural stone, as a result of which no advantage is obtained, especially when the artificial stone is to be used for covering purposes without increasing substantially the weight of the construction.

On the other hand, artificial stone with synthetic agglutinant is difficult to see on building sites which have to remain exposed to the weather as, normally, this stone suffers more or less pronounced weathering damage due to the atmospheric agents such as light, ultra-violet radiation, rain, etc.; also, it frequently suffers damage by friction for which reason it cannot be used either for flooring in buildings.

It has also been attempted to make artificially slabs of reconstituted stone having the appearance of natural slate, for roof covering, based on asbestos, cement and pigments, on a small semiskilled scale, that is to say by making the slate tiles one by one artificially. This process is associated with considerable ecological danger due to the use of asbestos, the employment of which is being questioned in developed countries, even forbidden, as asbestos is regarded as an undoubted source of industrial diseases very serious for those who are exposed to the action of said product.

The present invention has for its object to provide an industrial process for the reconstitution of stones, particularly slate, which solves the drawbacks described hereinabove.

With the process of the present invention it is possible to make use of residues of stones of any size, as a result of which the exploitation of quarries may be considered to be integral.

The process of the invention permits making building materials to enhance the appearance of buildings without substantially increasing their weight and, therefore, without making more costly the construction of the structures so as to support excessive weight.

The building materials made according to the process of the present invention are weatherresistant, and thus perfectly utilizable on the external parts of buildings, such as roofs, terraces, stairs, fascias, general equipment, etc.

In the following sections of the present specification special reference will be made to a process for the reconstitution of slates, though this description should not be regarded as limitative in any way, as the process claimed in applicable also to any other type of natural stone.

In accordance with the process of the present invention the starting material is tailings or residues of the stone under consideration, in the present case concretely slate, as was stated in the foregoing paragraph, or slaty material exhibiting some drawbacks for the making of natural slates; said slate tailings are ground, initially with a cone grinder, and then with a rod grinder, the ground product being finally sorted with a cyclone type sieve, in the dry state.

From the selection made in the cyclone, in the dry state, at least five fractions are formed with different grain size margins, the ranges of which are comprised between 0 and 30, particularly 0 and 16 mm.

At a later stage storage is effected in five different silos, at least, in each one of which a fraction of the ground product is stored within a concrete grain size range, taking into account that the minimum range of said grain size must be comprised between 0 and 0.25 mm and that the maximum range must be comprised between 6 and 30, preferably between 8 and 1 6 mm.

In separate steel or polyethylene tanks the agglutinant is placed. This agglutinant may be a methacrylic synthetic resin off MAMMA type, of brand DEGAMENT 1 370 EGUSSA which contains a cobalt polymerization accelerator, for example, having the following characteristics: In the liquid state Viscosity below 10 mP Density at 20do: 0.950 g/cm3 Refraction index nD 20"C, value = 1.415 APHA Colouring below 50 Acidity index below 1 pH In the solid state Apparent density 1.2 g/cm3 Bending strength above 1 50 N/mm2 Compressive strength above 30 N/min2 Tensile strength above 60 N/mm2 Elasticity greater than 60 N/mm2 Final conductivity 0'2 W-mk Heat stability above 80"C.

Heat linear coefficient 8.10-5 Water absorption-0' 1 %.

Separately, in another container, one places a catalyst for the polymerization of synthetic resin, of organic peroxide type, such as benzoyl peroxide, in phlegmatized form.

Once the selection of the grain size ranges of the ground slate has been effected, and the containers have been charged with resin, plus accelerator and catalyst, the despatch is effected, by means of an automatic mixer, and through individual ducts, of the necessary amounts of ground material, resin, accelerator and catalyst, towards an initial mixing zone, the time required to perfect this mixing depending both upon the actual nature of the components and upon the temperature of same and the ambient temperature.

Thus, for example, at ambient temperature, mixing time is generally comprised between 10 and 20 minutes, and full hardening is obtained in the mould at the end of a miximum of about one hour. The polymerization of the resin ends at the time when the maximum temperature of about 70"C is reached and the product thus prepared may be left to "mature" for some days, taking into account that the relative moisture of the ambient air must not exceed 2% after moulding.

According to the process of the present invention it is a fundamental requirement to maintain a relation between the thickness of the manufactured item and the amount of resin used; Thus, for example, further to the work carried out in connection with the present invention, the following ratios have been found: Thickness in mm Percentage of resin 10 4-10 7 6-11 2.5 8-14 1 10-16 After the above-mentioned mix has been prepared it is placed in moulds which must be completely clean and dry, and, if necessary, provided with a film of demoulding agent such as a silicone, for example.

These moulds are made, preferably, in polyethylene or steel and, if necessary, they are suitably reinforced. In the process of the present invention it must be taken into account that the moulds must not lose their shape at a temperature below, or equal to, approximately 80'C; moreover, said moulds must be resonance-free to prevent a dissociation of the components occurring during the operation of compaction of the mix, and a distorsion of the moulded parts.

After the moulds have been charged with the composition prepared at the initial phase of the process, they are moved, by any known means, whether automatic, manual, mechanical or pneumatic, to a vibratory installation, to the exclusion of any rsonance, there being effected in said installation the vibration of said moulds loaded with the composition, for example on vibrating metal plates, with a vibration range comprised between 100 and 150 Hz/sec., depending upon the thickness of the mass in the mould.

According to the process of the present invention, the compositions made up of slate grains, synthetic resins, catalyst and accelerator, may, in specific cases, be subjected before and/or during and/or after the vibrating of the moulds to a colouring stage with natural and/or synthetic pigments compatible with the resin and other products used. i.e. said colouring may be effected within the mass, or on the surface, or in combined form, if judged appropriate.

Generally, the product is coloured in the mass with synthetic pigments, such as Beyer Green, and surface colouring with natural pigments such as lamp black and carbon black, though this is not limitative.

After the vibrating of the moulds has been effected and the composition has set, it is possible to fix, in specific cases, a coating of a natural insulator, such as glass fibre, on the unseen layer of the moulded product and, subsequently, it is possible to extract the finished products which may have, depending on requirements, sizes ranging from 1 cm X 1 mm to 50 cm x 50 cm X 1 cm, or above, these indications being for the sake of example and in no way limitative.

Also, the moulded pieces may exhibit different reliefs and/or shapes, or, in specific cases, they may have metal inserts for anchoring, with a view to eliminate preparatory work for application, said inserts and/or auxiliary elements being inserted before the vibrating and setting of the composition of resin and slate granules.

The demoulded parts must be stored in a level, well ventilated area until full cooling down is reached; the parts are able subsequently to undergo the mechanical and chemical stresses actually occurring in natural stone.

The slate plates obtained according to the process of the present invention are applicable also to the construction of electrical appliances, as insulators, on account of their good electric resistance and smaller weight than natural slate.

Below, some examples of embodiment of the process of the present invention are given purely for the sake of illustration and in no way limitatively.

EXAMPLE 1 Slate tailings were ground in a cone grinder and subsequently in a bar grinder. The ground product was sieved in such a way that batches were formed with the following grain size ranges: 1)from8 to16mm 2) from 4 to 8 mm 3) from 2 to 4 mm 4) from 1 to 2 mm 5) from 0.5 to 1 mm 6) from 0.25 to 0.5 mm 7) from 0 to 0.25 mm At a second stage the simultaneous combination was effected of the following parts by weight (pbw) of the portions indicated hereinafter: 26 pbw of batch 4); 1 9 pbw of batch 5); 8 pbw of batch 6) with 2 pbw of the catalytic composition and 14 pbw of the resin containing the polymerization accelerator at ambient temperature for a period of 10 minutes approximately and, subsequently, they were placed in polyethylene moulds shaped as tiles of 1 5 cm X 1 5 cm x 1 cm approximately, the bottom of which simulated the texture of natural slate, and which has been previously treated by spraying with a demoulding silicone oil. The moulds thus charged were moved to a vibrating plant where vibrating was carried out at between 100 and 1 50 Hz/second, with polymerization of the resin for a period of 1 to 5 mins. approx. until an appropriate temperature of 70"C was reached.After about 2 to 3 hours there was placed on the face of the moulded mass, visible in the mould, a coating of a natural insulator such as glass fibre and, subsequently, when the insulator was secured, the parts thus produced were demoulded, showing an excellent appearance of natural state; they were stored on a level, ventilated area for a period of several days.

Said moulded pieces were coloured either in the mass or superficially in the earlier-indicated manner.

EXAMPLES 2 to 4 The process of Example 1 was repeated, but modifying the pbw amounts of the various batches of the product made from ground slate and the resins used according to the following table: TABLE BATCH EXAMPLE 2 (pbw) EXAMPLE 3 (pbw) EXAMPLE 4 (pbw) 1 0 0 26 2 0 26 20 3 26 19 33 4 19 13 10 5 12 9 7 6 10 6 4 7 33 27 20 Catalyst 2 2 2 Resin and catalyst 11 9 6 Products were obtained similar to those of Example 1.

Given below are the mechanical properties of the products obtained according to the process of the present invention, based on formulations made from Tannus quartzite with rounded-off edges. Unless otherwise specified, the values indicated are applicable to a normal climate according to 23/50 DIN 50 014 (23"C + 2'C and 50 + 5% relative humidity of the air).The values shown first relate to formulations with low resin contents, and the values shown second relate to formulations with high resin contents: Compressive strength 150-115 N/mm2 Bending strength 29-34 N/mm2 Bending strength at - 20"C 35-40 N/mm2 Modulus of elasticity 30,000-21,000 N/mm2 Dimensional stability to heat 110-1 00'C Heat conductivity 2-1.5 Kcal/m:h.'K Earth resistance 1015 ohm . cm.

Surface resistance 10'3 ohm Water absorption 0.1 % Expansion coefficient 1-2'5 . 10-5 Linear contraction during polymerization O'1-0'1 5% These values of the mechanical and physical properties, as well as the chemical resistances specified hereinbelow were calculated as the average of 11 5 samples, taking into account that the formulation is made up of approximately 90% of mineral matter.

The products obtained with the process of the present invention also exhibited the following characteristics as regards the chemical agents, wherein a. means "chemically stable" b. means "swollen, resistant under certain conditions for a short action".

c. means "non-resistant".

Aqueous solutions Distilled water a Rainwater a Sodium cyanide solution a 20% sodium sulphate solution a 30% peroxide of hydrogen a Seawater a Sodium lye a Saturated sodium sulphate a 3% peroxide of hydrogen a Saturated sodium solution a Alkalis 10% potassium lye a 10% caustic soda lye a 50% potassium lye a 50% caustic soda lye a Acids 10% formic acid a Saturated citric acid solution a Concentrated acetic acid c 10% nitric acid a 10% hydrochloric acid a 10% sulphuric acid a 10% tartaric acid a 50% formic acid b 10% acetic acid a 10% lactic acid a Concentrated nitric acid c 20% hyrdrochloric acid a 50% sulphuric acid c 10% tartaric acid a Organic Solvents Acetone c 60% ethanol in water a Petrol (gasoline) a Butane c Chloroform c Glycerine b Methanol b Mineral oil a Pyridone c Super gasoline b Trichloro-ethylene c Ethanol b Ethyl acetate c Benzene c Butyl acetate c Gasoil a Isopropanol b Methylene chloride c Paraffin oil a Edible oil a Toluene c Xylene c An adequate description of the nature of the invention, as well as of the manner of carrying it out in practice having been given, it must be pointed out that the above-indicated provisions may suffer alterations of detail provided the fundamental principle is not affected.

Claims (5)

1. Process for the reconstitution of slates consisting in treating rock schists with synthetic resins, characterized in that it comprises, at a first stage, subjecting said slate to grinding in such a manner that seven aliquot parts are produced with the following grain sizes: from 8 to 16 mm; from 4 to 8 mm; from 2 to 4 mm; from 1 to 2 mm; from 0.5 to 1 mm; from 0.25 to 0.5 mm and from 0 to 0.25 mm, as a maximum; at a second stage the combination is effected simultaneously of a synthetic resin, which contains a suitable accelerator, with a polymerization catalyst and with the grond slate, according to the above-indicated grain sizes, while stirring at a temperature substantially equal to ambient temperature, said combination while stirring being continued for a period of about 20 minutes as a maximum, there being reached, as a maximum, in the reactor a temperature of about 70"C; at a third stage the product originating from the second stage is poured into a mould which is subjected to vibrating between about 100 and about 1 50 Hz/sec., and, subsequently, the vibrated mould is optionally subjected to compression comprised between 40 and 1 20 kg/cm2 or, possibly, two half moulds previously vibrated are pressed together; under said load, if desired, a layer of a natural and/or synthetic insulator is fixed onto the face of the moulded part, seen in the mould.

2. - Process according to Claim 1, characterized in that the resin is a methacrylic resin, with, incorporated into it, an accelerator, such as a cobalt accelerator, and in that it is combined with the ground slate in a proportion such that the final product contains, as a maximum, 20% by weight of said resin with the accelerator incorporated.

3. Process according to Claim 1, characterized in that the catalyst and the resin, with the accelerator incorporated, and the ground slate, are combined in a proportion such that the catalyst represents 10% by weight, as a maximum, of the finished product.

4. Process according to Claim 1, characterized in that a colouring in the mass is effected before the pouring from the moulds, or a surface colouring of the moulded product before, during or after the vibrating of the moulds.

5. Process for the reconstitution of slates, such as substantially described in the present specification.