WO2012056359A1

WO2012056359A1 - Mould for manufacturing slabs of agglomerate material

Info

Publication number: WO2012056359A1
Application number: PCT/IB2011/054564
Authority: WO
Inventors: Luca Toncelli
Original assignee: Luca Toncelli
Priority date: 2010-10-25
Filing date: 2011-10-14
Publication date: 2012-05-03
Also published as: ITTV20100141A1

Abstract

In the manufacture of slabs of agglomerate material moulds comprising two fabric- reinforced elastomer sheets (20, 100) are used to enclose the mixture (12). The sheets have a structure consisting of elastomer layers (24, 28) between which fabric reinforcing layers (26) are arranged. The surface of the sheet (20) directed towards the outside preferably consists of a similar layer of fabric (22), while the surface of the sheet directed towards the inside and therefore intended to come into contact with the mixture consists of a layer of fabric impregnated with silicone rubber (30).

Description

"Mould for manufacturing slabs of agglomerate material"

DESCRIPTION

The present invention relates to the production of moulds for manufacturing agglomerate products in the form of slabs, composed of granules or fine particles of stone material bonded with a hardening resin, and more specifically relates to an improvement to the structure of moulds used in the associated production line.

These slabs are manufactured using a method where a mixture consisting of granules of selected size and hardening resin is distributed in a metered amount on a support or tray made of an elastomeric, preferably fabric-reinforced, material. The mixture is then covered with a sheet or layer of protective material made of the same material as the support. The tray with the top closing sheet thus forms a mould for the mixture. The mixture thus enclosed is conveyed to a compacting station where it undergoes a vacuum compression action with simultaneous application of a vibratory movement of predefined frequency. Then the compacted mixture is transferred to a station for performing hardening of the resin, preferably by means of heating.

The elastomer sheets used to manufacture the mould must have a number of essential characteristics which must be present in order to ensure optimum results.

To summarise, the elastomer sheet must have the following characteristics:

(a) it must be able to withstand the operating temperatures which during hardening of the resin are higher than 100°C and normally in the region of 150°C;

(b) it must be able to maintain substantially the same properties unchanged over time;

(c) it must have excellent mechanical properties in order to contain the mixture without undergoing excessive deformation and prevent the formation of irregularities on the surface of the final product.

As regards the nature of the elastomer forming the sheet, rubbers which are particularly resistant to mechanical stresses and which have a vulcanization temperature in the region of 160°C and higher are normally used, avoiding sulphur-based rubbers, since at the operating temperatures the sulphur bonds break, and giving preference instead to the peroxide-containing rubbers which have stronger bonds.

Among the latter synthetic rubbers known as EPM (ethylene and propylene copolymers) and rubbers of the EPDM type (ethylene and propylene copolymers with diene monomer) can be effectively used.

Italian patent application No. TV97A000148 filed on 27 October 1997 describes a particular structure of the compacting support. This structure is designed such that the rubber sheet contains an intermediate cloth or fabric layer consisting of substantially inextensible material (such as Kevlar, nylon or polyester) which is thus enclosed between two rubber layers.

Preferably this cloth or fabric undergoes a preliminary pre-tensioning treatment in order to avoid subsequent hysteresis.

However, this sheet, although it is able to satisfy the first two abovementioned requisites, namely resistance to high operating temperatures and maintaining unchanged properties over time, is unable to satisfy the third requisite.

In fact, even if in this way the sheet manages to contain the mixture being formed without undergoing excessive deformation, owing to shrinkage of the material during catalysis and owing to the - albeit minimal - residual elasticity of the mixture, the final product has surface undulations.

Italian utility model application TV99U000055 filed on 6.12.1999 describes a rubber sheet structure similar to that described in Italian application No. TV97A000148 in which the bottom rubber sheet is lined with a cloth or fabric layer consisting of substantially inextensible material.

In this way the resistance to peak loads of the moulding lining increases, preventing the appearance of undulations on the surface of the product.

However, there still remain unresolved problems.

After the hardening step it is in fact necessary to remove firstly the top sheet and then separate the hardened slab from the bottom sheet or tray. In order to facilitate the separation of both the top sheet and the bottom sheet from the hardened slab a separating material in the form of a thin film is applied beforehand onto the surfaces of the two sheets intended to come into contact with the mixture.

However, this separating film often tears and does not always ensure perfect separation of the sheets from the slab; in particular, in the case where particularly adhesive resins are used, it has been found that on certain occasions said separation is difficult to achieve. Moreover, hardened mixture, which is difficult to remove, may remain encrusted on the rubber sheets in the region of the film tearing zones.

Therefore, after removing the hardened slab, often it is required to perform the difficult operations of removal of the encrustations from the two rubber sheets.

Moreover, in the case of adhesion of the rubber sheets to the mixture, it is required to apply a strong pulling force in order to separate them from the hardened slab. This vigorous action consequently reduces the working life of the rubber moulds with a not insignificant increase in the costs.

The object of the invention is therefore to facilitate separation of the mould from the hardened slab, even in the case of tearing of the separating film, by exerting a limited pulling force so that no material remains encrusted on the two sheets, thus increasing also the working life of the moulds with a consequent reduction in costs. It has now been found that all these objects are achieved in a satisfactory manner with a mould for manufacturing stone products in the form of slabs, suitable for containing a mixture of agglomerate material with resin and having walls realized at least partially with at least one reinforced rubber layer, characterized in that said reinforced rubber layer is at least partially lined on the inside of the mould with a layer of fabric which is impregnated superficially with silicone rubber on the surface intended to come into contact with said mixture of agglomerate material.

In this way, owing to the high- temperature resistance and non- adhesive characteristics of the silicone rubber, it is sufficient to exert a light pulling force in order to separate the sheets from the hardened slab even in the case of tearing of the separating film, preventing at the same time the presence of encrustations on the sheets. At the same time separation of the non-adhesive layer from the reinforced rubber layer of the mould is prevented.

The particular features and advantages of the present invention will emerge more clearly from the description which follows of a preferred example of embodiment of the principles of the invention, with reference to the drawings in which:

- Figure 1 is a cross-sectional view of a mould formed by a shaped bottom sheet or tray and by a flat top sheet, provided in accordance with the present invention;

- Figure 2 is a view, on a larger scale, of the detail indicated by A in Fig. 1 ;

- Figure 3 is a view, on a larger scale, of the detail indicated by B in Fig. 1.

With reference to the figures, Figure 1 shows a tray-like mould 10 for manufacturing stone products in the form of slabs, according to a known method, for example vacuum vibrocompression. This mould is able to contain a mixture 12 of agglomerate material with resin which, after suitable hardening, forms the product. The method used will not be shown or described here in detail, since it is well-known to the person skilled in the art.

In particular, the mould 10 of the embodiment shown here comprises a bottom sheet or tray 100, formed with a bottom having a perimetral border or lateral lips 102 for defining a volume intended to contain the mixture, and a removable sheet 20 for closing this volume at the top, so as to cover the mixture itself.

The bottom sheet 100 has a perimetral border 102, the inner side of which may have a predetermined inclination for easier extraction of the hardened mixture.

As can be seen more clearly in Figures 2 and 3, the mould 10 comprises walls which are formed at least partially with at least one reinforced rubber layer.

Here the term "walls" is understood as meaning the inner walls of the mould which define, even only partially, the mixture receiving zone, whether they be on the sides or on the top or bottom.

For example, in Figure 2 it can be seen that the top sheet 20, which has a thickness of a few millimetres, may comprise a reinforced rubber layer consisting of a first and second rubber layer 24 and 28 between which a layer of substantially inextensible cloth or fabric 26 is arranged.

The rubber of the layers 24 and 28 is preferably an EPM or EPDM rubber vulcanized by means of a peroxide in a manner known per se resistant to 150°C.

The cloth or fabric of the layer 26 is preferably of the type comprising a polyamide (in particular nylon) weft and a polyester warp, or of the type comprising both a polyester weft and polyester warp, pre-tensioned in both directions (namely weft and warp).

A second cloth or fabric layer 22 having the same characteristics as the layer 26 is advantageously added to the reinforced rubber layer on one side and precisely onto the first rubber layer 24.

The reinforced rubber layer (or layers) is at least partially lined on the inside of the mould with a fabric layer 34 impregnated superficially with silicone rubber 32 on the surface of the mould which is intended to come into contact with said mixture of agglomerate material. The fabric layer 34 may be advantageously a cotton fabric.

A silicone rubber lining layer 30 is thus formed.

It should be noted that it would not be possible to apply directly the silicone rubber onto the reinforced rubber layer owing to its known non-adhesive properties. It is therefore necessary to insert the fabric layer 34 which thus acts as a layer for joining together the two rubbers of a different nature. Although various systems may be used to fix this fabric layer to the reinforced rubber, it has been found to be particularly advantageous for the fabric to be impregnated by the rubber of the layer 28, 128 on the opposite side to that with the silicone rubber. This may be performed directly during formation of the rubber layer for construction of the mould.

With the sheet structure according to the present invention, which has a considerable mechanical strength at high temperatures and a low- adhesion surface, the desired results are achieved.

The bottom sheet or tray 100, as shown in Figure 3, has a structure similar to that of the top sheet 20, so that similar layers are indicated by a reference number which is the same as that of the corresponding layer of the top sheet, increased by 100.

In particular, the bottom layer has a reinforced rubber layer advantageously consisting of two rubber layers 124,128 with, in between, an intermediate cloth or fabric layer 126. Again advantageously, a second outer cloth or fabric layer 122 is applied on one side, while, on the other side, i.e. the side suitable for making contact with the mixture, the silicone rubber lining layer 130, as described above, composed of a fabric layer 134 impregnated on the outer side with a silicone rubber layer 132, is formed.

In particular, both the bottom sheet or tray 100 and the top sheet 20 conveniently have a similar structure and thickness so as to ensure during catalysis a homogeneous exchange of heat with the mixture contained in the "lining" defined by the two - top and bottom - rubber sheets.

The rigid silicone rubber layer has preferably a Shore hardness of 70-80. This value has been found to be particularly advantageous for preventing the mould from adhering to the mixture, in particular in the case of particularly adhesive resins such as bioresins.

At this point it is clear how the predefined objects have been achieved.

Owing to the mould according to the invention separation of the two sheets forming the mould from the hardened slab is performed by exerting a very light pulling force so that not only is there is no risk of the sheets being damaged, but also separation of parts of the hardened sheet, which could also adhere to the sheet, is very unlikely.

Moreover, the moulds do not have to be regularly cleaned, it being recommended to carry out cleaning only when they have been used a large number of times.

Owing to the fact that the fabric layer 34, 134 is impregnated on both sides with two different rubbers, there is no possibility that the silicone layer may become detached, even only partially, during normal operating conditions, not even as a result of the continuous flexing and bending which may affect both the bottom sheet and the top sheet.

Obviously, the above description of an embodiment applying the innovative principles of the present invention is provided by way of example of these innovative principles and must therefore not be regarded as limiting the scope of the rights claimed herein.

It is evident that variants or modifications which are functionally or conceptually equivalent fall within the scope of protection of the present invention.

For example, it is possible to envisage a rigid silicone rubber layer consisting therefore of a fabric layer impregnated superficially with silicone rubber also for lining the inner surface of the perimetral border of the bottom sheet. The various layers may be formed and joined together during vulcanization of the rubbers or glued together using known methods.

Claims

1. Mould for manufacturing stone products in the form of slabs, suitable for containing a mixture of agglomerate material with resin (12) and having walls at least partially realized with at least one reinforced rubber layer (24,26,28; 124,126,128), characterized in that said reinforced rubber layer is at least partially lined on the inside of the mould with a layer of fabric (34, 134) which is impregnated superficially with silicone rubber (32, 132) on the surface intended to come into contact with said mixture of agglomerate material.

2. Mould according to claim 1, characterized in that said reinforced rubber layer comprises a cloth or fabric layer (26) consisting of substantially inextensible material enclosed between two rubber layers (24,28).

3. Mould according to claim 1, characterized in that a substantially inextensible cloth or fabric layer (22) is applied onto said reinforced rubber layer on the opposite side to the that lined with said fabric layer superficially impregnated with silicone rubber (30).

4. Mould according to any one of the preceding claims, characterized in that said rubber (24,28) is an EPM or EPDM rubber vulcanized with peroxides.

5. Mould according to claim 2 or 3, characterized in that said cloth or fabrics (22,26) is formed by a polyester warp and a polyamide weft.

6. Mould according to claim 2 or 3, characterized in that said cloth or fabric (22,26) is formed by a polyester warp and a polyester weft.

7. Mould according to any one of the preceding claims, characterized in that said walls are formed by a tray, having a bottom with lateral lips so as to define a volume intended to contain the mixture, and by a removable sheet for closing said volume at the top.

8. Mould according to claim 7, characterized in that said bottom and said removable sheet comprise the said at least one reinforced rubber layer lined with the impregnated fabric layer.

9. Mould according to claim 1, characterized in that the said impregnated fabric layer is formed by a cotton fabric.

10. Mould according to claim 1, characterized in that the fabric layer, which is impregnated superficially with silicone rubber (30) on the surface intended to come into contact with said mixture of agglomerate material, has the opposite surface which is impregnated by the rubber of the reinforced layer that it lines.