Spreading head particularly for spreading one or more adhesives or mixtures of adhesives

A spreading head particularly for spreading one or more adhesives or mixtures of adhesives, of the hot-melt or cold type, comprising a body which has two or more ducts, which are all separate or of which two or more converge, each duct being connected to one or more feed channels for conveying the one or more adhesives or mixtures of adhesives to one or more extrusion chambers formed on the upper surface of the body; an abutment element for the one or more adhesives or mixtures of adhesives which exit from the one or more mixing chambers is associable in an upper region with the body.

The present invention relates to a spreading head particularly for spreading one or more adhesives or mixtures of adhesives, both of the hot-melt type and of the cold type.

BACKGROUND OF THE INVENTION

Currently it is known to use, for the application of adhesives to substrates made of various materials, such as for example fabrics or ribbons made of plastic material, spreading devices which comprise one or more spreading heads provided with a duct for feeding the adhesive, the delivery end of which faces, during use, a substrate which is made to advance in close contact therewith in the form of a ribbon.

The adhesive is introduced in the duct in the liquid state, typically by means of appropriately provided gear pumps, and can be applied either continuously or intermittently, by throttling the flow thereof by means of appropriately provided valves of a known type which are arranged in the spreading head.

Such valves further allow to vary the width of the region of application of the adhesive and to perform throttlings of the adhesive, with a preset pitch, transversely to the ribbon of substrate.

As an alternative to the valves, the variation of the width of the region of application of the adhesive can also be achieved by means of one or more inserts of a known type, which can be arranged automatically or manually within the duct so as to partially obstruct its cross-section, so as to adapt its width to the width of the ribbon.

It is also known to insert, transversely to the duct, appropriately provided contoured laminas, which are adapted to obstruct the duct partially so as to be able to obtain a selected distribution of the adhesive transversely to the substrate; it is thus possible to achieve, for example, a distribution of the adhesive which affects uniformly the entire substrate or also a distribution of the so-called “multiline” type, which is constituted by a plurality of longitudinal layers of adhesive which are mutually parallel and spaced.

These known types of spreading head, however, have drawbacks: first of all, they do not allow to obtain layers of different adhesives arranged side-by-side or laterally adjacent layers of a same adhesive with different grammages.

Moreover, the use of these known types of head entails a waste of adhesive if an adhesive of higher value and/or grammage (therefore also having a structural function) is required only in some regions of the substrate while in other regions an adhesive of lower value and/or grammage is sufficient, since it forces to use the higher-value and/or higher-grammage adhesive for all the regions of the substrate.

Moreover, said known types of head allow to obtain only a uniform film of adhesive in contact with both surfaces of the materials to be coupled; this entails the need to use a high-value adhesive even if its use is required only by one of the two surfaces to be coupled, with an additional waste of material.

Further, if the substrate is porous, the use of known types of head entails an additional waste of high-value adhesive, since said adhesive also acts as a filler for the pores of the substrate.

There are also applications in which such known types of head are used to provide membranes which in some regions must have breathability characteristics, and therefore require low grammages of applied adhesive, and in other regions must instead provide a vapor barrier effect and therefore require high adhesive grammages; to achieve this embodiment, known types of head require a double passage over the substrate, which is performed either with different heads or with a same head which is modified at a later time, and this increases the production times, and therefore the production costs, of producing said membranes.

Moreover, since many thermoplastic adhesives have a residual stickiness after their spreading, it is not possible to apply them with a double pass.

In the case of cold adhesives, spreading heads are known which allow to apply multiple superimposed layers; however, such heads do not allow to perform combined applications, i.e., multilayer products in certain regions and single-layer products in other regions, and also do not allow intermittent and/or combined applications of the so-called “multiline” type.

SUMMARY OF THE INVENTION

The aim of the present invention is to solve the above mentioned problems, eliminating the drawbacks of the cited background art, by providing a spreading head which allows to spread one or more adhesives onto a substrate, so as to obtain, in selected regions thereof, layers of the chosen type of chosen adhesive and/or of the chosen grammage.

Within this aim, an object of the invention is to provide a spreading head which allows to obtain, even in a single pass, the spreading onto a substrate of two or more superimposed layers of one or more adhesives.

Another object is to provide a spreading head which allows to achieve the spreading of one or more adhesives in multiple layers which are arranged side-by-side and optionally mutually spaced, in which each layer has the selected characteristics of width and/or composition and/or grammage and/or number of superimposed layers that compose it.

Another object is to provide a spreading head which allows the spreading in rapid succession of adhesives having different chemical properties and/or colorings, which may even be mutually incompatible.

Another object of the invention is to reduce the time and cost for producing membranes which have breathable regions and regions which are impermeable to vapor.

Another object of the invention is to reduce the waste of high-value adhesive in the process for spreading it onto a substrate, even a porous one.

Another object of the invention is to achieve a reduction in the costs for spreading one or more adhesives onto a substrate.

Another object is to provide a spreading head which is structurally simple and has low manufacturing costs.

This aim and these and other objects, as well as others which will become apparent hereinafter, are achieved by a spreading head particularly for spreading one or more adhesives or mixtures of adhesives, of the hot-melt or cold type, characterized in that it comprises a body which has two or more ducts, which are all separate or of which two or more converge, each duct being connected to one or more feed channels for conveying said one or more adhesives or mixtures of adhesives to one or more extrusion chambers formed on the upper surface of said body, an abutment element for said one or more adhesives or mixtures of adhesives which exit from said one or more mixing chambers being associable in an upper region with said body.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the exemplary embodiments that follow, individual characteristics, given in relation to specific examples, may actually be interchanged with other different characteristics that exist in other exemplary embodiments.

Moreover, it is noted that anything found to be already known during the patenting process is understood not to be claimed and to be the subject of a disclaimer.

With reference to the figures, the reference numeral1generally designates a spreading head, particularly for spreading one or more adhesives or mixtures of adhesives, of the hot-melt or cold type, on an appropriately provided substrate60constituted for example by a ribbon made of fabric or plastic material.

The spreading head1is constituted by a body2which is advantageously but not necessarily shaped approximately like a parallelepiped with a transverse cross-section which is approximately shaped like a right-angled trapezoid.

Two or more ducts are formed within the body2; all of said ducts are separate, or two or more of them converge.

With reference toFIGS. 1 and 2, the body2has a first duct and a second duct, designated respectively by the reference numerals4and5, which are approximately mutually parallel and affect longitudinally the body2, preferably along most of its width; advantageously, the first and second ducts4and5respectively have one or more first and second accesses, designated respectively by the reference numerals4′ and5′, from which it is possible to introduce, for example by means of appropriately provided rotary pumps, not shown in the accompanying figures, one or more adhesives or mixtures of adhesives or catalysts for adhesives.

Advantageously, the first and second ducts4and5mutually converge inside the body2; the first and second ducts4and5are connected respectively to first and second output ducts, designated respectively by the reference numerals6and7, which converge in pairs, preferably with the interposition of appropriately provided first and second valves of a known type, designated respectively by the reference numerals8and9, within appropriately provided mixing channels10.

Advantageously, the first and second output ducts6and7are formed along axes which are substantially perpendicular to the first and second ducts4and5; the first and second output ducts6and7are present in a chosen number and are distributed, in a preferably equidistant arrangement, respectively along the first and second ducts4and5.

A first feed channel11for conveying said one or more adhesives or mixtures of adhesives to one or more appropriately provided first extrusion chambers41formed on an upper surface37of the body2protrudes from each of the mixing channels10.

Advantageously but not necessarily, the one or more first extrusion chambers41are laterally adjacent and aligned along a same longitudinal axis with respect to the body2.

With reference toFIGS. 1 and 2, the body2has a third duct12, which is approximately parallel to the first duct4and the second duct5and again affects longitudinally the body2preferably along most of its width.

The third duct12has one or more third accesses13for an adhesive or a mixture of adhesives or catalyst for adhesives.

One or more second feed channels14exit from the third duct12and are designed to convey said one or more adhesives or mixtures of adhesives again to the first extrusion chambers41formed in the upper surface37of the body2; as shown schematically inFIG. 6(in which, for the sake of clarity in description, the second duct5, the first and second output ducts, and the mixing chamber10have not been shown), each of the first extrusion chambers41receives therefore one or more feed channels11and one or more second feed channels14.

Advantageously, the second feed channels14are connected to the third duct12through appropriately provided third valves15of a known type.

Advantageously, the second feed channels14are formed along axes which are substantially perpendicular to the longitudinal axis of the third duct12; the second feed channels14are provided in a selected number and are distributed, preferably in an equidistant configuration, along the third duct12.

The body2further has a fourth duct and a fifth duct, designated respectively by the reference numerals16and17, which are approximately parallel to the first, second and third ducts and affect longitudinally the body2preferably along most of its width; the fourth and fifth ducts16and17respectively have fourth and fifth accesses, designated respectively by the reference numerals18and19, for an adhesive or a mixture of adhesives or catalysts for adhesives.

Respectively one or more third feed channels20and one or more fourth feed channels21exit from the fourth and fifth ducts16and17to convey said one or more adhesives or mixtures of adhesives respectively to one or more second extrusion chambers42and to one or more third extrusion chambers43formed on the upper surface37of the body2.

The third feed channels20and the fourth feed channels21are connected to the respective fourth and fifth ducts respectively by means of appropriately provided fourth and fifth valves of a known type, designated respectively by the reference numerals22and23.

Advantageously, the third and fourth feed channels20and21are formed along axes which are substantially perpendicular respectively to the longitudinal axes of the fourth and fifth ducts16and17; the third and fourth feed channels20and21are provided in a selected number and are distributed, preferably equidistantly, respectively along the fourth and fifth ducts16and17.

Advantageously, the second extrusion chambers42and the third extrusion chambers43are aligned respectively along two axes which are arranged longitudinally to the body2and are substantially parallel and spaced with respect to each other and to the axis along which the first extrusion chambers41are aligned.

Advantageously, a plurality of sets of three extrusion chambers are formed on the upper surface37of the body2; said sets are mutually laterally adjacent and each set is constituted by a first extrusion chamber41, a second extrusion chamber42and a third extrusion chamber43, which are arranged parallel to each other and to the longitudinal axis of the body2.

The shape, and therefore the size, of the first, second and third extrusion chambers that compose each of said sets are substantially the same.

The longitudinal extension of the first, second and third extrusion chambers of each of said sets of three extrusion chambers is therefore identical, while the longitudinal extension of two of said sets arranged mutually side by side can be different; this allows to obtain in output layers of adhesive which are laterally side by side and have different widths.

In the example shown inFIG. 3, some of said sets of three extrusion chambers are shown; in each of said sets, the first extrusion chamber41lies furthest from the lamination plane, while the third chamber43lies closest to said lamination plane.

Advantageously, in each of the sets of three extrusion chambers, the outlet of the third extrusion chamber43, which lies closest to the lamination plane, is, with respect to said lamination plane, at a lower height than the outlet of the adjacent second extrusion chamber42, and the latter in turn is at a lower height than the adjacent first extrusion chamber41which lies furthest from the lamination plane; this allows to achieve the extrusion of two or three superimposed layers of adhesive which, after exiting from the respective first, second and third extrusion chamber; remain one on top of the other due to their different relative densities.

As an alternative, with reference toFIG. 4, the third feed channels20and/or the fourth feed channels21can be connected to one or more fourth extrusion chambers44, which have different shapes and arrangements with respect to the first, second and third extrusion chambers described earlier; the fourth extrusion chambers44are arranged along an axis which is perpendicular to the axis of the first, second and third extrusion chambers, and are interposed between each pair of the sets of three extrusion chambers.

The fourth extrusion chambers44start from the perimetric edge37aof the upper surface37of the body2which is directed toward the substrate60during use; as described in greater detail hereinafter, this configuration of the extrusion chambers allows to obtain in output laterally adjacent layers of adhesive spaced by microlayers of reduced width.

Advantageously, on the upper surface37of the body2there is a slit30, provided preferably by removing material and so as to affect the outlet of at least the third extrusion chambers43which lie closer to the lamination plane: said slit arranges on a lower plane the outlet of the third extrusion chambers43with respect to the plane of arrangement of the second extrusion chamber42and the first extrusion chamber41.

The slit30guides the outflow of the layer or layers of adhesive from the body2onto the substrate60.

In another embodiment, shown inFIG. 5, one or more of the first extrusion chambers41and/or of the second extrusion chambers42and/or of the third extrusion chambers43and/or of the fourth extrusion chambers44may have, along an axis which lies longitudinally with respect to the body2, reduced lengths so as to constitute microchannels, which are designated by the reference numerals50aand50b.

In the exemplary embodiment shown inFIG. 5, the microchannels50aand50bare arranged at right angles to the first, second and third extrusion chambers, are mutually parallel and are interposed between two pairs of said sets of three extrusion chambers.

The configuration of the microchannels50aand50bwith respect to the upper surface37of the body2is preferably comb-like, with teeth which advantageously have two different lengths and are arranged preferably alternately.

Advantageously, an abutment element31for the one or more adhesives or mixtures of adhesives that exit from the first, second, third or fourth mixing chambers formed in the upper surface37is fixed to the upper surface37of the body2; the abutment element31, which is preferably approximately shaped like a parallelepiped with a transverse cross-section shaped like a right-angled trapezoid, guides the one or more adhesives or mixtures of adhesives so that they exit from the slits30.

Operation is therefore as follows. With reference to the accompanying figures, it is possible to introduce, for example by means of appropriately provided rotary pumps, not shown in the accompanying figures, one or more adhesives or mixtures of adhesives in the liquid state, or optionally one or more appropriately provided catalysts, in one or more among the first duct4, the second duct5, the third duct12, the fourth duct16and the fifth duct17.

By adjusting appropriately the open or closed state of the first, second, third, fourth and fifth valves, it is possible to feed into the first and/or second and/or third and/or fourth extrusion chambers the chosen adhesive or mixture of adhesives so as to obtain in output a chosen configuration of the spread layer or layers of adhesive.

For example, with reference toFIGS. 7 to 11, it is possible to feed just the first duct4and the third duct12with two separate adhesives or alternately with the same adhesive having a different grammage, or also with an adhesive and an appropriately provided catalyst.

As shown inFIG. 10, by opening one or both of the first valve8and third valve15which are interposed respectively between the first duct4, the third duct12and a same first extrusion chamber41, it is possible to allow the access to the first extrusion chamber41of just one or both of the adhesives or mixture of adhesives or adhesive and catalyst that are present respectively in the first duct4and in the third duct12.

If, as shown inFIG. 10, both the first valve8and the third valve15are open, in the first extrusion chamber41mixing occurs between the two adhesives or between the adhesive and the catalyst, contained respectively in the first and third ducts; from the first extrusion chamber41, the mixture of adhesives or the adhesive mixed with the catalyst is then extruded through the slit30.

As an alternative, if only one of the first and third valves respectively of the first feed channel11and of the second feed channel14that lead into a same first extrusion chamber41is open, only one of the two adhesives flows into the chamber and therefore exits directly through the slit30.

In this manner it is therefore possible to obtain a plurality of layers of adhesive which are laterally mutually adjacent and have the chosen composition; the embodiment shown inFIG. 9, for example, obtains a first layer32aof a first adhesive, a second layer32bof a second adhesive and a third layer32c, which is interposed laterally between the preceding ones and is constituted by a mixture thereof.

This distribution of the layers of adhesive in output can also be achieved with a simplified configuration of the spreading head1in which the body2has only the first duct4and the third duct12, from which a corresponding number of first and second feed channels11and14exit respectively through one or more first valves8and third valves15.

In this simplified configuration, on the upper surface37of the body2there are only the first extrusion chambers41, each of which is connected in input to the first feed channel11and to the second feed channel14; as shown inFIG. 11, the various first extrusion chambers41in this case are mutually laterally adjacent.

With reference toFIGS. 12 to 16, it is further possible to feed only the third duct12and the fourth duct16with two separate adhesives or as an alternative with a same adhesive having a different grammage.

As shown inFIG. 15, by appropriately adjusting the opening of the third valves15and fourth valves22it is possible to make the two adhesives converge within the microchannels50aand50balone.

If, as shown inFIGS. 13,15and16, in the upper surface37of the body2there are only the microchannels50aand50b, it is possible to spread an alternation of microlayers, generally designated by the reference numeral33, of the two adhesives.

With reference toFIGS. 13,15and16, said distribution of the adhesive layers in output can also be achieved with a simplified configuration of the spreading head1, in which the body2has only the third duct12and the fourth duct16, from which a corresponding number of second and third feed channels14and20protrude respectively through one or more third valves15and fourth valves22and are connected respectively to one or more microchannels50aand50b, which are arranged in a comb-like configuration and are mutually alternated.

With reference toFIGS. 17 to 21, it is further possible to feed only the third duct12and the fourth duct16with two separate adhesives or, as an alternative, with a same adhesive having a different grammage; as shown inFIG. 17, by means of the third valves15and the fourth valves22it is possible to make one of the two adhesives converge into the first extrusion chambers41and make the other adhesive converge into the fourth extrusion chambers44which are interposed between the first extrusion chambers41which are arranged laterally side-by-side.

It is therefore possible to obtain in output from an extrusion tool3a series of layers of adhesive32which are laterally adjacent and are spaced by microlayers33of a different adhesive.

For example, with reference to the embodiment shown inFIG. 19, six layers32of a first adhesive, each enclosed between two microlayers33of a second adhesive, have been obtained.

With reference toFIGS. 18 and 21, this distribution of the layers of adhesive in output can also be achieved with a simplified configuration of the spreading head1, in which the body2has only the third duct12and the fourth duct16, from which a corresponding number of second and third feed channels14and20exit respectively through one or more third valves15and fourth valves22; said feed channels are connected respectively to one or more first extrusion chambers41and to one or more fourth extrusion chambers44.

With reference toFIGS. 22 to 26, it is further possible to feed only the third duct12and the fourth duct16with two separate adhesives or, as an alternative, with a same adhesive having a different grammage; the third duct12and the fourth duct16are connected respectively to the first extrusion chambers41and to the second extrusion chambers42which are contiguous to these last.

By acting on the open condition of the third valves15and the fourth valves22it is possible to make one or the other of the adhesives flow respectively to said first or second extrusion chambers; in this manner, it is possible to obtain in output from the extrusion tool3a series of layers of adhesive which are laterally mutually adjacent and have the chosen composition.

In the embodiment shown inFIG. 24, for example, two first layers32aof a first adhesive and two second layers, designated by the reference numeral32b, of a second adhesive, arranged alternately with respect to each other, have been obtained.

By opening both the third valve15and the fourth valve22, which control the input respectively into the first extrusion chamber41and into the second extrusion chamber42arranged below the latter, it is possible to make both adhesives exit simultaneously from said first and second extrusion chambers, so as to achieve the spreading of a double layer.

With reference toFIGS. 23 and 26, this distribution of the layers of adhesive in output can also be achieved with a simplified configuration of the spreading head1, in which the body2has only the third duct12and the fourth duct16, from which a corresponding number of second and third feed channels14and20exit respectively through one or more third valves15and fourth valves22and are connected respectively to one or more first extrusion chambers41and to one or more second extrusion chambers42.

With reference toFIGS. 27 to 30, it is possible to feed the first duct4and the second duct5with two separate adhesives or with an adhesive and an appropriate catalyst and then the fifth duct17with an additional adhesive.

By opening the first and second valves8and9, the adhesive or adhesives and the catalyst contained respectively in the first and second ducts enter the mixing channel10, from which they exit, after being mixed, by means of the first extrusion channels11, entering the first extrusion chambers41.

By opening the fifth valves23, the adhesive contained in the fifth duct17enters the fourth feed channels21and then exits from the third extrusion chambers43.

As shown inFIG. 30, the adhesive that exits from the first extrusion chambers41and the adhesive that exits from the underlying second extrusion chambers43are extruded simultaneously; such adhesives remain one on top of the other due to their different relative densities, thus forming a double layer, designated inFIG. 30by the reference numeral34, which is composed of a lower layer34aof the first adhesive (which arrives from the fourth feed channels21) and an upper layer34bof the second adhesive (which arrives from the first feed channels11).

By closing the first and second valves which enter a given mixing channel10, or one of the fifth valves23, it is also possible to achieve the extrusion of a single layer of adhesive or mixture of adhesives, respectively from one of the third extrusion chambers43or of the first extrusion chambers41; it is thus possible to obtain in output a selected distribution of adhesives, not shown in the accompanying figures, which is constituted by a series of laterally adjacent layers, one or more of which is constituted by a single layer of one adhesive or the other, and one or more of which is constituted by a double layer which is similar to the one designated by the reference numeral34inFIG. 30.

With reference toFIGS. 28,29and30, this distribution of the adhesive layers in output can also be achieved with a simplified configuration of the spreading head1, in which the body2has only the first duct4and the second duct5, which mutually converge in a suitable mixing channel10with the interposition of the first and second valves; the body2further has the fifth duct17which is connected, by means of the fifth valves23, to the fourth feed channels21.

In this simplified configuration, only the first and third extrusion chambers are formed on the upper surface37of the body2.

With reference toFIGS. 31 to 34, it is further possible to feed the third duct12, the fourth duct16and the fifth duct17with separate adhesives and/or with the same adhesive at different grammages.

By opening the third valves15, the fourth valves22and the fifth valves23, these adhesives enter respectively the second feed channels14, the third feed channels20and the fourth feed channels21and from there flow into the first, second and third extrusion chambers.

The three adhesives thus exit simultaneously respectively from the first, second and third extrusion chambers so as to be mutually superimposed, forming a triple layer, designated inFIG. 34by the reference numeral35, which is constituted by a lower layer35aof the first adhesive (which arrives from the fourth feed channels21), by an intermediate layer35bof the second adhesive (which arrives from the third feed channels20), and by an upper layer35cof the third adhesive, or optionally again of the first adhesive (which arrives from the second feed channels14).

By closing selectively the third, fourth and fifth valves, it is further possible to achieve the extrusion of a single layer of adhesive or also of a double layer; a distribution of adhesives, not shown in the accompanying figures, can thus be obtained in output, which is constituted by a series of laterally adjacent layers, of which one or more is constituted by a single layer of a chosen adhesive and optionally one or more is constituted by a double layer and one or more is constituted by a triple layer.

With reference toFIGS. 32,33and34, this distribution of the layers of adhesives in output can also be achieved with a simplified configuration of the spreading head1, in which the body2has only the third, fourth and fifth ducts and the respective third, fourth and fifth valves, through which said ducts are connected respectively to the second, third and fourth feed channels.

In this simplified configuration, on the upper surface37of the body2there are a plurality of sets of three extrusion chambers, each constituted by a first, second and third extrusion chamber, which are connected respectively to one or more second, third or fourth feed channels.

It has thus been found that the invention has achieved the intended aim and objects, a spreading head having been devised which allows to apply to selected areas of a substrate a chosen adhesive and/or different adhesives and/or a same adhesive with different grammages and/or a multiple layer of adhesives.

The spreading head according to the invention therefore allows to provide areas with differentiated grammage and also using differentiated adhesives, so as to be able to reduce (even by 70%, as has been found) the amount of (more expensive) structural adhesive that is required.

Further, the spreading head according to the invention allows to achieve the spreading on a substrate of a selected number of layers of adhesive arranged side-by-side and having a chosen width.

Moreover, the spreading head according to the invention allows to mix various adhesives or an adhesive and a suitable catalyst directly within the body.

By means of the spreading head according to the invention it is further possible to achieve, even in a single pass, the spreading of a multilayer film of adhesives, so as to be able to use products with a good grip on different substrates.

Thanks to the possibility to achieve the spreading of adhesives in multiple layers, the need is further avoided to use high-value adhesives even if their use is required only by one of the two surfaces to which they are to be applied.

Moreover, in cases in which the adhesive, in addition to having a structural function, also has the task of “filling” porous surfaces (for example in the lamination of recycled products or of products on chipwood panel substrates), the spreading head according to the invention allows to reduce the waste of “high-value” product, by making a low-cost resin perform the nonstructural function and making a thin layer of high-value resin perform the structural effect.

Further, the spreading head according to the invention allows to provide, even with a single pass, a membrane which has breathability characteristics in certain regions and a vapor barrier effect in others.

Moreover, the spreading head according to the invention is adapted for use for spreading thermoplastic adhesives and cold adhesives.

Moreover, the production costs of the spreading head according to the invention remain low, since it is made of components which are easy to manufacture and/or assemble.

The invention is of course susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.

Of course, the materials used, as well as the dimensions that constitute the individual components of the invention, may be more pertinent according to specific requirements.

The various means for performing certain different functions need not certainly coexist only in the illustrated embodiments but can be present per se in many embodiments, including ones that are not illustrated.

Of course, the selection of the feed to the extrusion tool of the chosen type of adhesive and/or mixtures of adhesives and/or catalysts can occur not only by activating or not activating the mentioned preset valves but also by way of equivalent means, such as for example the interposition of appropriately provided plates which are selectively perforated between the body and the extrusion tool.

The characteristics indicated as advantageous, convenient or the like may also be omitted or be replaced with equivalents.

The disclosures in Italian Patent Application No. TV2006A000123 from which this application claims priority are incorporated herein by reference.