Prior art Existing systems for the production of covering sheets, in particular in clay mixes or similar to protect foundations or the ground adjacent to a building (for example from contamination by pollutants), are either of the type with flat head, which extrude in the final width and thickness, or with cylindrical head, which extrude a tube of the final thickness and circumference corresponding to the final width: after having made a cut parallel to the direction of extrusion, the tube is opened and laid on a flat support.

The aforesaid system are well suited to the production of layers of limited widths, but have limits for the production of sheets of considerable width: in fact, with a flat extrusion head of a width in excess of one metre, it is increasingly difficult to obtain an even extrusion pressure, which tends to decrease in relation to the distance from the axis of the extruder, and the dimensioning of the latter increases excessively in relation to the increase in the rate of extruded material.

With a cylindrical extrusion head, the thinner the sheet is the more easily it is damaged, as it is not joined to any support upon delivery from the extrusion head; moreover, if two metres of circumference are exceeded the dimensions of the extruder become increasingly technically complicated and costly.

Lastly, with both flat and cylindrical extrusion heads, in order to vary the thickness of the laminate it is necessary to replace extrusion outlets of considerable dimensions.

An underlying problem of the present invention is to provide a simple device and a method for the production of coverings in sheets of large dimensions and which are relatively thin.

This problem, according to an aspect of the present invention is solved with a method with the features as claimed in claim 1 and with a system with the features

as claimed in claim 14.

The material with which the sheets are produced with the devices and methods according to the present invention can be of different types, such as sheets of clay mixes covered by plastic films or sheets of material of various types, both organic and inorganic, incorporated in a polymeric matrix.

In addition to overcoming the disadvantages of prior art mentioned above, another advantage attainable with the present invention is the fact that it is possible to produce, with an extrusion system with smaller dimensions operating with relatively low extrusion pressures, coverings in sheets which are larger and thinner than those obtainable with known methods and machines; the thickness of the sheets is more even and may be easily varied, by replacing a flat extrusion nozzle of small dimensions. The design of the system is simple and therefore costs are relatively low. According to a preferred embodiment, it is possible to obtain thinner sheets with larger dimensions than in the past, composed of a clay mix, such as bentonite, covered on both larger sides by two supporting films, for example in plastic.

Brief description of the drawings Further advantages attainable with the present invention shall become more evident to those skilled in the art from the following detailed description of a non- limiting example of specific embodiment, with reference to the accompanying figures, in which: Figure 1 schematically shows a plan view of a preferred example of embodiment of a device according to the present invention; Figure 2 schematically shows an elevation of the device in Figure 1.

Figure 3 schematically shows the section of a covering in sheets obtained with the device in Figure 1.

Figure 4 schematically shows the sectional side view of a suction inlet on the wall of the revolving drum of the device in Figure 1.

Detailed description of the invention Figures 1 and 2 respectively show the plan view and elevation view of a device for producing insulating linings or coverings in sheets according to a preferred embodiment of the present invention, suitable to produce coverings in sheets of

clay materials, such as bentonite, different clays, smectites, illites, zeolites, used for insulation and protection of building foundations controlling the degree of permeability or impermeability, or for example to protect the ground around a plant from which there may be leakages of pollutants; without departing from the scope of the present invention, similar devices may be applied to the production of coverings in sheets of large dimensions in polymeric material, with a polymeric matrix or in other extrusible compounds.

Reference number 1 indicates the storage silo for powders which, mixed with water and appropriate additives, form the mix to be extruded in the extrusion unit 2.

According to a procedure per se known, and therefore not further described, the powders are taken from the silo 1 by means of a feed auger 3 and sent from the pneumatic conveyor system 3 through the pneumatic transport pipes 4 to the mixing device 5, in this specific case-although not necessarily-composed of two mixers 60 and 70. Each mixer is composed essentially of two shafts bearing a series of double-bladed screws, which mix and feed the powders; the mixer 60 further upstream mixes the powders with water, while appropriate additives are added in the mixer 70 according to the type of mix.

Again according to the type of mix, there can be only one or several mixers, or there may be a plasticization screw.

The mix from the mixer 70 further downstream is fed into the extruder 2.

According to an aspect of the present invention, the extruder 2 is provided with an extrusion nozzle suitable to extrude a strip 6 of mix or other extrusible material and this strip is deposited on a revolving drum 7 on its longitudinal axis, and the speed at which the extrusion head 2 of the material of the strip 6 translates parallel to the axis of rotation of the revolving drum 7, the rate and direction of extrusion of the extruded strip 6 and the rotation speed of the drum 7 on its longitudinal axis, are determined so that the extruded strip 6 deposited on the drum 7 is helically wound on the revolving drum 7, and moreover the helically wound strip 6 is cut according to a line transverse to the turns of the helix ; in a device according to another aspect of the present invention the extrusion head 2 can run at least parallel to the axis of rotation of the revolving drum 7 and the strip 6 of helically wound extrusible

material is cut with cutting means 14.

The mixers 60 and 70, and the extruder 2 are arranged on a platform 8 that can run on tracks 9 in a direction parallel to the axis of the revolving drum 7, and both the revolving drum 7 and the platform 8 are operated for example with electric gear motors controlled by inverters. The two heads of the revolving drum 7 are preferably resting on a pair of motor-driven wheels operated by the aforesaid gear motors.

Advantageously, the revolving drum (7) has a circular cross-section.

Advantageously, the extruded strip 6 has a flat and thin transverse section.

The strip of extruded mix 6 is taken to the revolving drum 7 supported by a first supporting strip 15A which preferably runs above a first conveyor belt 10, which in turn runs with a speed equal to the extrusion rate of the extruded strip 6. The first supporting strip 15A can be conveyed and supported from the point of extrusion towards the point of winding on the drum 7 with a range of other devices, such as alternatively using a roller table-motor-driven or idle, according to the mechanical resistance of the strip 15A-or a chute.

The first supporting strip 15A is preferably although not necessarily wound on the first conveyor belt 10, and under the strip 6 of extruded mix, by a first unwinding device 21-hereinafter also called first unreeling device 21-at a speed equal to the extrusion speed of the strip 6.

The strip of extruded material 6 winds to continuously cover the surface of the revolving drum 7 forming a helix, in which the edges of adjacent turns are partly overlapped and in any case in contact with one another. The edges of two adjacent turns of the helix are preferably joined together by pressing them, for example with a thickness limiting device 11, carried out for example with a roller positioned at a fixed distance from the surface of the drum 7, so as to obtain a clay covering with a constant thickness. The thickness limiting roller 11 may for example be provided with a sensor to control its distance from the surface of the drum 7.

When the extrusion unit comes near to an end, or head, of the revolving drum, and the surface of the latter is almost completely covered by the helix of extruded mix, extrusion of the strip 6 is halted and a second conveyor belt 12 or, more generally,

a supporting bed 12-such as a roller table or even a simple table-, running on tracks 13 perpendicular to the axis of the drum 7 is made to move and positioned under the latter ; on the carriage which supports the second conveyor device 12 a cutting device 14 is arranged, such as a knife with a revolving blade which slides along a guide fitted on the aforesaid carriage and parallel to the longitudinal axis of the revolving drum 7; by running the second conveyor belt 12 under the revolving drum 7-the dashed rectangle 23 in Figure 1 indicates the position of the bed 12 completely inserted under the drum 7-, the cutting unit is set beside the drum 7; drum rotation is halted and, in a method according to an aspect of the present invention, the helix of extruded material is cut along a line transverse to the turns of the helix, for example with the blade 14 sliding longitudinally-revolving-blade, knife-blade or similar.

The line of cut is preferably a line parallel to the axis of the drum.

Advantageously, the revolving drum 7 is internally hollow, and on its surface has a plurality of suction inlets 18 connected to a vacuum circuit: in this way, owing to the difference in pressure between the faces of the strip 6 internal and external to the winding helix, it is possible to maintain the extruded strip 6 adhering to the surface-or surfaces-of the drum on the drum 7 as extrusion proceeds.

The suction inlets 18 may be replaced equivalently with other devices capable of producing adherence of the extruded strip against the wall of the revolving drum 7, such as other vacuum devices such as suction cups-driven for example with cam or electromechanical remote controls-, mechanical grasping or support devices- such as mobile supports positioned beside the revolving drum during the phase to release the cut helix-, magnetic devices, etc..

Advantageously, the suction inlets 18 are arranged along a line parallel to the longitudinal axis of rotation of the drum 7.

When the helical winding is over, the drum 7 is halted in a position such that the line of suction inlets 18 is positioned immediately above the cutting line. After cutting with the longitudinal cutting blade 14, vacuum pressure of the vacuum circuit applied to the helix of extruded strip 6 during or at the end of the helical winding operation, holds a first flap of the layer 19-composed of the cut helix of extruded material-adhering to the wall of the drum 7; the revolving drum 7 is then

rotated and the conveyor belt 12 is made to run appropriately under the drum 7, in order to gradually deposit, through controlled dropping, the layer 19 formed of the cut helix of extruded material on the second conveyor belt 12-or supporting bed 12-, opening it and extending it on top, starting from the second flap of the layer 19 released and not held by vacuum pressure adhering to the wall of the drum; lastly, the suction inlets 18 cease to suck and the first flap of the layer is also released and deposited on the second conveyor belt 12 which, during these unloading operations, is halted and does not run in the direction of its length.

For this operation, advantageously the revolving drum 7 is fitted horizontally.

Advantageously, the suction inlets 18 are positioned at a distance from one another, along the longitudinal direction of the drum 7, equal to the pitch of the winding helix of the flat strip of extruded mix 6.

When the layer 19 composed of the cut helix of extruded material has been completely laid on the second conveyor belt 12, the latter is removed from under the revolving drum 7 by making it run on tracks 13 and taking it to a position external to the drum 7.

Preferably to provide extremely thin sheets of clay mixes, such as bentonite, with sufficient mechanical resistance, and in general according to the nature of the material to extrude the layer 19 formed of the cut helix is coated on one or on both faces by a layer-respectively by two layers-or supporting strip 15,15A, such as one-or two-plastic films, strips in mesh, gauze, fabric, felt, film, of appropriate materials. In the preferred example in Figures 1 and 2, upon delivery from the extrusion nozzle the mix 6 is laid on a first supporting strip 15A, in the particular example a plastic film, which advances at the same speed as the extruded strip 6 and is wound on the revolving drum 7 together with the flat extruded strip.

Preferably, although not essentially, the first supporting strip 15A is made to advance by the first conveyor belt 10 or a motor-driven roller table.

The layer 19 formed of the cut helix of extruded material is preferably deposited on a second film 15 which a second unreeling device 16-also called second unwinding device 16-has previously extended on top of a second conveyor belt 12 or supporting bed 12; the second unreeling device may be an automatic unwinding device which runs on guides along the supporting bed 12 or even an

operator who manually lays the second film 15. The second conveyor belt 12 is then started up and made to run, the layer 19 with the two films 15,15A is made to pass through a series of pressure rollers (not shown) to compact together the layer 19 of clay or bentonite 6 and the two bottom 15 and top 15A coating films, and then wound in a roll by a winding device 17-or reeling device 17- ; in this way it was possible to obtain for example coverings in sheets with indicative dimensions of 25 x 4 metres and even only a few millimetres thick, using an extrusion nozzle with a width of 0.5 m.

In the example in Figures 1-2, a third unreeling device 22, near the outlet of the second conveyor belt 12, covers the entire top face of the layer 19 formed of the cut helix with a third film 24, the presence of which depends simply on the particular specification of the covering in sheets to be produced, and which could easily be excluded in other types of coverings in sheets. The third unreeling device 22 applies the third film 24 as the layer 19 formed of the cut helix runs underneath it, wound by the winding device 17.

Advantageously the suction inlets 18 are closed by a suitable diaphragm support 180-Figure 4, reference 182 indicates the wall of the revolving drum, reference 183 the pipe for connection to the vacuum circuit-permeable to air flow, such as an open cell synthetic foam buffer, a diaphragm in non-woven fabric fitted on a grid 181 or similar : during suction the first supporting strip 15A with the extended strip 6 is pressed against the diaphragm support 180 without being sucked into the inlet or excessively deformed. A man skilled in the art will be responsible for choosing the materials of the diaphragm support so that this produces pressure drops, on the suction air flow, that are not excessive even if unavoidable.

The example of preferred embodiment described above may undergo various modifications without departing from the scope of the present invention: for example, the second conveyor belt 12 may be replaced with a roller table, a chute or simple a supporting table in the case of a less automated process; the revolving drum 7 may have a cross section that is not necessarily circular, but for example polygonal or oval ; the suction inlets 18 of the drum may be arranged over the entire surface of the revolving drum rather than only in a single longitudinal line, and may be connectable/disconnectable to the vacuum pump according to sectors

longitudinal and/or transverse to the drum 7 separate from one another, for example to facilitate adherence of the extruded strip 6 during winding on the drum 7, each of which has separate vacuum control from the other sectors.

The first supporting strip 15A + the extruded strip 6 may be drawn by only the drum 7 running on idle rollers or on a fixed chute rather than being moved by the first conveyor belt 10.

The strip of extruded material 6 may be deposited and held directly on the revolving drum 7 without a supporting film 15A, or extruded by taking the extrusion nozzle directly over the surface of the drum 7, eliminating the first conveyor belt 10.

The first and/or second supporting strip 15A, 15 may be produced comprising, separately or in a combination, plastic films, a non-woven fabric, a normal fabric, gauze, a layer of felt, all materials appropriate for the purpose.

Between the supporting bed 12 and the reeling device 17 a machine may be interposed for a further operation of mechanical connection of the supporting strips 15A, 15 and 24-when present-, for example by stitching, quilting, riveting, needle- punching or equivalent methods.