D e s c r i p t i o n

The present invention relates to a semi-worked piece based on a so-called "metallic mesh" (or more generally a structure of the "textile" type formed with metal elements consisting of suitably combined weft and warp wires), as well as to the method of manufacturing it.

It is known that working of woven objects based on metal materials involves some technological expedients, exactly in connection with the particular nature of the material that is submitted to these working operations; as a compensation for the difficulty in working some metal materials, the resultant "woven" products have mechanical and/or operating capabilities that can be hardly repeated using other types of materials.

On the other hand, textile semi-worked products of (threadlike) metal materials have a wide application in a great number of technical fields; for instance, these metallic meshes are used for reinforcing otherwise yielding structures, or as individual-protection elements such as garments or shoes (and so on) .

As a particular example of what hereabove generally stated, reference can be made to the machinery for working polymeric materials, where mesh-like filtering elements can be often found; usually, these filtering elements consist of woven materials made of annealed low-carbon steel. These filtering elements are impinged on by the flow of plastic material that is worked by the machinery and therefore must bear important stresses and pressures, or at all events must tackle with very particular work conditions, due to the nature and/or aggregation state of the polymeric material itself (in a granular, powdery, fluid or multi-phase condition) .

The filtering elements of known type are generally characterised by some important drawbacks and mainly suffer for a limited operating life, high tendency to geometric and mechanical decay, inconstancy of the filtering power over time and necessity of frequent interventions for replacement and servicing.

Therefore, the metallic-mesh semi-worked products of known type cannot be always planned and (above all) made in such a manner as to satisfy particular design requirements, since certain interknitting typologies of the semi-worked piece (and in particular for some mesh densities) associated with predetermined strength features of the metal wires are actually incompatible.

In other words, use of metal wires with high mechanical performance makes manufacture of particularly close metal meshes/wire cloths very difficult and almost impossible, since the high metal strength of the wires makes ^• them of difficult interweaving.

In the light of the known art discussed above, it is an aim of the present invention to make a metallic-mesh semi-worked piece as well as to provide a method of producing this semi-worked piece that are capable of obviating the above mentioned drawbacks. In particular, the present invention aims at conceiving a metallic-mesh semi-worked piece that simultaneously can have satisfactory mechanical-geometric strength and coherence and can be woven following particular weft and yarn patterns.

At the same time, the present invention aims at conceiving a metallic-mesh semi-worked piece that can be used as a filtering element in machinery for processing plastic materials and can therein offer high operating performance both in terms of filtering capability and constant yield as well as useful operating life.

In addition, the present invention aims at making available a metallic-mesh semi-worked piece (and the related production method) enabling the production costs to be greatly reduced and the environmental impact to be improved where possible, while at the same time being exploitable in a wide range of variants.

The foregoing and further aims are achieved by a metallic-mesh semi-worked piece and a method of obtaining this semi-worked piece, in accordance with the present invention, having the features illustrated in the appended claims and described hereinafter in an embodiment thereof given by way of non-limiting example and with reference to the accompanying drawings, in which: - Fig. 1 is a diagrammatic view of the semi-worked piece according to the invention;

- Fig. 2 is an enlarged view of part of the semi-worked piece seen in Fig. 1; and

- Figs. 3 and 4 show two possible alternative embodiments of the semi-worked piece according to the invention .

With reference to the drawings, the metallic-mesh semi- worked piece according to the invention is generally denoted by reference numeral 1 and it can be conveniently used as the filtering element in machines for filtering of the molten mass in recycling of polymeric/plastic materials (extruders, feeding hoppers, moulds and others, for example) .

From a structural point of view, the semi-worked piece 1 comprises a weft 2, defined by a multiplicity of primary threadlike elements 2a made of metal material, and a warp 3 interlaced with the weft 2 and in turn defined by a multiplicity of secondary threadlike elements 3a; advantageously, and unlike the filtering elements of known type, at least one of the primary and/or secondary threadlike elements 2a and/or 3a consists of high-carbon steel.

Within the scope of the present invention, it is therefore possible that part of the warp and/or weft wires will be made of the above mentioned particular material (high-carbon steel) , which has a very high tensile strength and therefore gives the semi-worked product particular behavioural features.

Within the scope of the present invention, it is also possible to notice that the expression "part of the warp and/or weft wires" can mean either that the semi- worked piece comprises "individual" high-carbon wires disposed randomly, or that the semi-worked piece comprises high-carbon wires disposed in a predetermined "sequence" (i.e. a high-carbon wire every N wires made of another material) ; at all events, the mesh density of the present semi-worked piece can be typically included within the values detailed in the following.

In ^' particular, use of threadlike elements made of high- carbon steel allows creation of a filtering element which can be mounted on machines for plastic material and/or polymeric material processing, and offers a high filtering power (or more generally, offers the possibility of suitably varying the filtering power by an ^' appropriate pre-selection of the mesh density) and at the same time enables a high planar character to be maintained, as well as a mechanical strength and a prolonged filtering constancy even when said filtering element is submitted to plastic/polymeric material flows that are particularly intense or have a high viscosity.

To the aims of the present invention, and in particular for making semi-worked products having mechanical properties that are widely differentiated from each other depending on the final uses, it is conveniently possible that only part of a single wire or a fraction of the overall wires used will be made of high-carbon steel (for instance, high carbon steel can be only used on the semi-worked piece edges, while far from the edges, wires of different material can form the weft and warp wires, such as low-carbon steel for example) .

It is also to be noted that within the scope of the present invention a metallic-mesh semi-worked piece is wished to be made which combines a particular material selection with a particular "mesh density", i.e. a ratio between the number of wires and a dimensional coordinate (a linear or surface co-ordinate) that is significantly higher than that of similar metallic-mesh semi-worked pieces already known in the art; in this regard it will be recognised that the known art is not substantially able to obtain metallic meshes in which meshes are very close or have a high density, using high-carbon steel wires, due to the difficulties in working this material.

To complete the description, the expression "high- carbon steel" referred to in this specification (and also repeated in the following claims) is used to indicate a steel family in which there is such a carbon percentage that particular values of modulus of elasticity and breaking stress are determined, as shown in the following table by way of example:

More particularly, for the material concerned with the present invention, an overall range of modulus of elasticity included between 2000 and 335 N/iran ² can be identified.

At the same time, the sizes of the wires that can be used in the present invention, and the related "obtainable mesh densities" (both in the weft and in the warp direction) can be summarised in the following table of examples:

In one of the possible embodiments of the invention, all primary threadlike elements 2a and/or all secondary threadlike elements 3a (or also part of them, such as one wire every "n" wires, n" varying between 2 and 10, for example) are made up of high-carbon steel.

To enable the desired combinations between high mesh density and appropriate mechanical performance to be obtained, the average diameter of the primary threadlike elements 2a can be included between 0.10 mm and 0.60 mm (and it may be included between 0.25 mm and 0.55 mm for example, or also between 0.30 mm and 0.45 mm) .

At the same time, the average diameter of the secondary threadlike elements 3a can be included between 0.10 mm and 0.50 mm (and may be included between 0.15 mm and 0.26 mm or also between 0.16 mm and 0.20 mm, for example) .

On the contrary, as to the mesh densities obtainable with the present invention, it is possible to state just as an indication that the primary threadlike elements 2a define an average mesh density "in the weft direction" included between 4 wires/cm and 12 wires/cm, while the secondary threadlike elements 3a define an average mesh density "in the warp direction" included between 16 wires/cm and 120 wires/cm.

From a structural point of view, the weft and warp wires can be of any type, provided they are adapted to ensure the necessary dimensional coherence and the required compactness (for instance, in order to obtain an optimal compromise between high filtering capability and maintenance of the planar character and sturdiness, should the semi-worked piece in accordance with the invention act as a filtering element in machines for processing plastic and/or polymeric materials) ; for instance, the ends of the weft wires can be "open"

(i.e. cut, so that the weft is defined by a series of segmented wires parallel to each other but discontinuous from the topologic point of view) or "closed" (therefore giving rise to a weft formed of a single wire having a serpentine-like course) .

Conveniently, the choice of providing a weft with "open" or "closed" ends is based on current requirements, such as taking into account the different types of finish to be given to the edges of the semi- worked piece, for example.

The semi-worked piece of the invention can take different conformations in space, a planar conformation or not, depending on current requirements; in a particularly simple embodiment thereof, a polygonal

(typically rectangular) flat figure is defined or, more generally, a figure having a middle axis 4 (in the same direction as the weft 2 or as warp 3) .

Conveniently, depending on the mechanical performance that is wished to be given to the semi-worked piece, at least one reinforcing side portion 5 can be present which extends parallel to said middle axis 4 and is located at and/or close to at least one edge 5a of the semi-worked piece.

Said reinforcing side portion 5 can be made in different ways: for instance, it can have a local mesh density (in the warp direction, for example) different from (e.g. slightly smaller than, but also equal to, depending on current requirements) that typical of the rest of the semi-worked piece; in order to maximise the performance of same (and at the same time minimise extension thereof) , the reinforcing side portion 5 can be made with high-carbon steel wires.

As an alternative to the presence of the reinforcing side portion 5 (but, if necessary, also in combination therewith) , at least one folded portion 6 which is disposed at and/or in the vicinity of at least one edge 5a can also be present; this folded portion 6 defines a folding line βa preferably parallel to the edge 5a, and use of same for instance takes place in those semi- worked products in which the weft wires have "open" ends; in these cases the folding line located close to edge 5a allows the ends of the weft wires to be brought inwards of the semi-worked piece, therefore eliminating possible risks of getting caught or even of loss of the interknitting structure.

To the aims of the present invention the presence of two or more reinforcing side portions 5 is also possible, as well as of two or more folded portions 6 that can be disposed close to/at the parallel sides of the semi-worked piece 1, for example.

As already mentioned at different points before, it is an aim of the present invention to conceive a particular application (or "use") of the semi-worked piece 1 herein described (and hereinafter claimed) ; in particular, it is an aim of the invention to provide a filtering element associable with machines for processing plastic and/or polymeric materials which comprises an active portion (adapted to carry out filtering on a flow of plastic and/or polymeric material) and a longitudinal hem delimiting this active portion.

Advantageously, at least the active portion of this filtering element can be made of at least one semi- worked piece 1 of metallic mesh as hereinbefore described and/or as claimed in the following.

Likewise, it is also an aim of the present invention to provide an innovative and original method of manufacturing a metallic-mesh semi-worked piece (which method can be for example put into practice for making a filtering element associable with processing machines for plastic and/or polymeric materials) .

This method comprises the following steps: - first of all, providing a multiplicity of primary threadlike elements 2a having an average diameter included between 0.10 mm and 0.60 mm (and preferably included between 0.30 mm and 0.45 mm);

- simultaneously providing a multiplicity of secondary threadlike elements 3a in turn having an average diameter included between 0.1 mm and 0.50 mm (and preferably included between 0.16 mm and 0.20 mm); and

- then ^• interweaving the primary threadlike elements 2a with the secondary threadlike elements 3a in order to obtain a textile structure consisting of a weft 2 and a warp 3.

Advantageously, the textile structure defined hereabove will have an "average" mesh density in the weft direction included between 4 wires/cm and 12 wires/cm, while it will have an "average" mesh density in the warp direction included between 16 wires/cm and 120 wires/cm; at the same time, at least one or preferably part of the primary threadlike elements 2a and/or of the secondary ones 3a will include high-carbon steel wires .

The invention allows achievement of important advantages .

First of all, it is to be pointed out that due to the particular construction architecture of the semi-worked piece 1 as well as the particular selection of the constituent materials thereof, an efficient mesh structure is obtained associated with ^' an efficient capability of withstanding mechanical stresses; this involves the possibility of using this semi-worked piece in heavy duty machinery (such as use as filtering element in machines for processing plastic materials) .

In addition, the possibility of introducing important structural variations ("closed" or "open" ends of the weft wires, presence of reinforcing portions in the vicinity of the edges, possible presence of structures having folded and/or layered portions and others) further increases the application flexibility of the present semi-worked piece, without at all events varying the inventive base concept.

Secondly, it is to be noted that due to the wide possibility of correlation between the material forming the wires and the mesh diameters and density, a wide variety of semi-worked products can be manufactured which therefore can be adjusted to different filtering conditions in as many different machines, or more generally can be such adjusted that they can satisfy different operating requirements in the most varied machines or environments .

It will be also appreciated that the possibility of using high-carbon steel wires through operations for waste recovery and/or recycling of other materials can constitute an efficient re-use of the materials themselves, which will advantageously reduce the environmental impact.

Finally, the present invention enables production of metallic-mesh semi-worked pieces offering high performance while at the same time allowing low production costs and consequently reduced sale prices.