MXPA98008483A - Strings with memory of shape for pneumatic reinforcing tires, fabricated tires and pneumatic tires including those cuer - Google Patents

Abstract

The present invention relates to a pneumatic tire for vehicle wheels comprising a plurality of reinforcing cords, each formed by metal wires wound spirally around each other, at least one of which is formed of a material with memory of In a manner having recovery capabilities in a previously memorized form, each shape memory wire is formed in the memorized form wherein the recovery capabilities are essentially active in a first heat cycle and degrade to at least a significant predetermined extent after of the first cycle of lime

Description

STRINGS WITH MEMORY OF FORM FOR PNEUMATIC REINFORCING TIRES, FABRICATED TIRES AND PNEUMATIC TIRES INCLUDING THOSE STRINGS The present invention relates to articles made of elastomeric material, particularly pneumatic tires reinforced with rubberized fabrics comprising cords with at least one wire of shape; and also to the corresponding fabrics and ropes.

The invention also relates to a process for the manufacture of these rubberized fabrics.

Many articles made of elastomeric materials, including pneumatic tires for vehicle wheels, conveyor belts, flexible hoses for the transport of fluids and the like, comprise at least one rubberized fabric formed of a plurality of reinforcing cords, usually textile or metal, placed parallel to one another and incorporated in an elastomeric material.

In the next part of the description, the phrasing "elastomeric material" is intended to denote the composition of the incorporating material as a whole, in other words the rubber, including the polymer base, the reinforcing fillers and the various protective agents, accelerators, anti-aging and others, all according to the recipes well known to those experts in the art.

It is also known that metal cords are. formed from a plurality of single metal wires wound spirally with respect to one another, with predetermined intervals according to a plurality of configurations which are well known to those skilled in the art.

In general, the articles cited require ropes that have particular characteristics of mechanical strength when exposed to various stresses including stresses and compressive stresses, and that have a resistance to corrosion. Corrosion can be initiated on the metal wires of the rope by the presence of moisture in the residual air inside the cords incorporated in the rubber, or by direct contact with the water when the break of the rubber layer exposes the rope to the external environment.

Once started, corrosion can propagate along the wires in the absence of an adequate protective coating of the wires.

To meet the corrosion resistance requirements, it is desirable that the space between the metal wires of the rope be completely filled with rubber to avoid the presence of air incorporated between the wires and the subsequent formation of moisture with consequent development and the propagation of the phenomenon of corrosion.

Additionally, in order to withstand mechanical stress, the string wires must be closely associated with one another in order to ensure correct operation behavior, as graphically presented, in n Cartesian stress-strain diagram, by a characteristic essentially linear.

In fact, due to the distance between the wires, a rope is subjected to mechanical hysteresis and a risk of wire failure, even under a lower compressive load that could be supported by a rope in which the distance between the constituent wires It is minimal or zero.

The requirements of good penetration of the rubber between the wires and the superior operation of the cords in the operation are particularly important in pneumatic tires; these are normally made by assembling a plurality of different semi-finished components, some of which consist of strips of various sizes formed from the aforementioned rubberized fabrics.

The manufacture of the rubberized fabrics for the pneumatic tires is carried out by incorporating the bare strings into an elastomeric material, preferably by means of known counterbalancing devices such as extruders and calenders, supplied from supply reels of the bare wires placed before said devices. It is during this phase of incorporation that the penetration of the elastomeric material into the strings has been achieved.

There are several solutions designed to ensure a good penetration of the rubber inside the rope, all are characterized because the strings which are easily penetrable by the rubber do not have an optimal behavior in the pneumatic rim during its use.

In a suitable solution for the cords in threads, the cord comprises a first pair of wires placed in a plane and a second pair of wires placed in an additional plane that rotate with respect to the first along the longitudinal development of the cord, so that in each cross section the surfaces of the wires have a maximum exposure and consequently a maximum coating with the elastomeric material. This solution involves a non-uniformity in the arrangement of the wires along the development of the rope with an unsatisfactory operation in use.

A different solution specifies strings in which the wires are kept loose (open strings) so that a small distance is left between them. In the passage through the gating device, the distance placed between the wires allows a good penetration of the rubber inside the rope. This solution can cause the compaction of the wires against one another due to the tension to which they are subjected even before they reach the device, thus making it impossible or very difficult for the rubber to penetrate inside the cord; when this does not happen, the rope is hooked in an optimal way but maintains a behavior which is hysterical, and therefore unsatisfactory in use.

An additional solution specifies the arrangement in the rope of a wire having a non-linear (zig-zag) configuration so that a space is provided between each of the various wires and the next one, and the penetration of the rubber into the center of the wire. the rope is promoted. This solution involves a lower resistance to fatigue of the non-linear wire and therefore of the complete cord.

If we now examine the multiple layer type cords, they comprise a central core covered with a plurality of concentric layers of wires, as in the case of the known cord having a configuration of 3 + 9 + 15m in other words a core of three wires twisted together, around which is wound a first layer of nine wires on which a second layer of fifteen wires is wound. These ropes are used, in particular, in layers of tire tires for trucks.

In this rope, very little rubber penetrates inside the inner layer and practically none penetrates inside the core, due to the physical barrier created by the radially outer layers of wires. In these types of rope, in order to achieve a sufficient rubber penetration, the solution based on the use of wires of different diameters is convenient.

Even though on the other hand this solution improves the penetration of the rubber, on the other hand it is unsatisfactory with respect to the operation of the rope in use.

To improve the performance characteristics of the pneumatic tire in use, the metal cords in which at least one of the component wires is made of an alloy of a shape memory material have recently been used.

The materials with shape memory are described for example on pages 3 to 20 of the publication "Aspects of Engineering of Alloys with Memory of Form", by Butterworth-Heinemann, published in 1990.

The shape memory wire, as will be described in greater detail subsequently, has the properties of (1) having a precise memorized shape which is imparted to it by a heat treatment carried out at a specific temperature which imparts to the wire a predetermined critical point, (2) of losing this form as a result of the mechanical stresses imparted at a temperature below the critical point, and (3) of returning to the memorized form whenever its temperature exceeds the critical point.

For use in pneumatic tires, this type of wire, which has been heat treated so that it has, for example, an undulating shape, is subjected to. stretching which imparts another configuration, for example, linear, at room temperature before it is twisted with the other wires to form a rope.

When the temperature in the pneumatic tire increases, for example as a result of high speed, to a point higher than the critical point of the memory wire, the wire tends to return to its originally memorized undulating shape.

However, given the shape memory wire is twisted with other wires and the whole string is fixed to the elastomeric matrix, and the entire structure is subjected to tension, this wire is unable to contract to assume its own undulating configuration of a shorter length Consequently there is an increase in the tensile stress in the shape memory wire (the wire acts as a stretched spring), the effect of which is to increase the stiffness of the structure in position to the effect of the centrifugal force.

In particular, U.S. Patent No. 5,242,002 discloses a radial rim whose band assembly comprises three bolts, the first two having strings inclined symmetrically with respect to the equatorial plane and the third having circumferentially placed cords.

The cords are formed of a plurality of wires wound spirally with respect to each other and each cord of the inner bands comprises a plurality of metal wires, at least one of which is made of an alloy of a material with shape memory .

Japanese patent application JP 4362401 relates to a radial rim having a band structure whose outer layer comprises a two-way shape memory expansion element, preferably a spring-type element made of a Ni-Ti alloy , wound in the circumferential direction (at 0o) on the underlying band layers.

The shape memory element tends to contract in the circumferential direction when the rim is subjected to heating in a high speed travel.

However, since this contraction is impeded by the underlying band structure, the element develops a tension force which makes the band assembly more rigid, thereby controlling the phenomenon of high-speed tire expansion.

At low speeds or under normal conditions of use, the shape memory element maintains the initial shape or returns to the initial shape as a result of inflation pressure. The Applicant has perceived that failure to achieve optimum performance as described above may depend on the particular behavior of said cords with shape memory wires which, together with their advantages, place a considerable problem.

What happens in practice is that, during vulcanization of the tire, which is how it is known carried out at a temperature of the order of 150 ° C and sometimes above it, in its initial phase, when the compound of Rubber has low viscosity, the shrinkage of the shape memory wire causes the opening of the rope, in other words spacing and separating the component wires.

The rubber is then vulcanized, losing its plasticity, but the rope is unable to close, being prevented from doing so by the shrinkage of the shape memory wire, and is therefore consolidated in the vulcanized rim in this swollen configuration, with all the cited disadvantages of unstable behavior and low compressive strength, resulting in particularly poor resistance to bending and compression stresses.

The aforementioned patents of the United States of North American No. 5,242,002 and Japanese No. 4362401 fail to deal with this aspect, and therefore the problem of improving the penetration of the elastomeric material between wires of a rope while obtaining a good functioning of the rope, and consistently of the rim in the use, remains essentially unresolved so far.

The Applicant has realized that it is possible to simultaneously improve the characteristics of penetration of the rubber between the wires of a rope and the operation of the rope in the tire in use, by making use of cords which contain at least one shape memory wire with recovery characteristics of a previously memorized shape, and which are mainly active in a first heat cycle, the wire also being provided with programmed significant characteristics of memory degradation after the first heat cycle.

The following preliminary observations and definitions relating to shape memory materials will help to provide a clearer understanding of the nature of the applicant's invention.

The shape memory is the capacity, possessed by some metal alloys, to eliminate deformations of a seemingly plastic nature through an adequate heating of the material.

It is known ("Alloys with Memory of Form" - Edition H. Funakubo - Gordon and Breach Science Publisher - 1987) that the properties of shape memory are imparted by a phase transformation of solid-solid (from martensite to austenite when they pass from a low to high temperature, and vice versa), called "thermoelastic martensitic transformation". This transformation is known as "direct" in the case of cooling and "reverse" in the case of heating. The direct transformation which corresponds to the formation of the martensitic structure begins at a temperature Ms and ends at a lower temperature Mf. The inverse transformation, which corresponds to the formation of an austenitic structure, begins at an As temperature and ends at a higher temperature Af.

Since, in general Ms? Mf? So? Af, the said martensitic transformation is hysteritic. In particular, if Mf < : Ms < As < Af, the martensitic transformation is said to be of type 1; yes Mf < As < Ms < Af, the martensitic transformation is said to be type 2.

The martensite phase has a typical microstructure consisting of domes (called martensitic variants) which can be oriented differently under the action of still limited voltage states (for example 50 MPa). A shape memory material acquires a predetermined shape by heat treatment for a specific time and at a specific temperature. This treatment is carried out on the wire of a specific material of a particular composition in order to obtain a predetermined transformation temperature. When the material cools the transformation of the austenite phase to the martensite phase takes place, and if the material is subjected to a state of tension capable of producing the process of orientation of the variants, the deformation e * associated with this phenomenon is makes permanent, for temperatures of less than As, after the removal of force (pseudo-plastic deformation). However, during the subsequent heating to temperatures of more than As, the deformation e * was removed by an inverse martensitic transformation, and consequently the original shape was recovered (the shape memory effect). The elimination of the deformation e * is total if e * < / = e-jax where emax is the maximum deformation eliminated by the shape memory effect and is characteristic of the material with specific shape memory and the specific heat treatment to impart the memory. If the elimination of e * is impeded, partially or completely, by conditions of mechanical restriction in the passage of the temperature As in the passage of the upper temperature Af during heating, the material develops a tensile force called the reconversion force.

In conclusion, the heat treatment is used to impart the four characteristic temperatures of a shape memory alloy, indicated above as Ms? Mf? So? Af.

The ability of a complete elimination of the deformation e * in the face or subsequent cycles suffered by the material is generally the object for a degradation, represented by the decrease in the number of subsequent heat cycles in which this elimination can be obtained , this degradation increasing when approaching e * a emax. This decrease in the value of the e * portion of the residual disposable pseudoplastic deformation, also known as the "shape memory degradation" is defined as a continuous change of the shape memory characteristics of a material, determined by the number of heat cycles suffered, and represents the useful life of a shape memory material.

For a more precise definition of the shape memory degradation of a material, reference should now be made to the description on pages 256 to 259 of the publication "Aspects of Engineering of Alloys with Memory of Form" by Butterworth-Heinemann, published in 1990. In this publication it is indicated that the life of such material is expressed as the recovery of a given previously memorized form. When the material is no longer able to recover the memorized form, it is considered to end its useful life.

For example, for a NiTi alloy in which emax, the number of subsequent heat cycles for which a deformation e * can be repeatedly and completely eliminated varies as a function of the value of e *, as shown in the following table ( of J. Cederstrom and J. Van Humbeeck, Journal of Physics IV C2, 1995, pages 335-341). 6 * Heat Cycles 8% (= emax) 1 4% 100 2% 10000 1% 100000 It will be seen from the table that if an elongation e * (of pseudoplastic formation) of 8% is imparted to the material, particularly to the metal wire, it will be completely removable during the first heat cycle, but it will no longer be removable in the heat cycles. Subsequent, during which only a progressively decreasing fraction of this elongation can be eliminated. Conversely, if the pseudoplastic elongation imparted e * is only equal to 2%, it will be completely eliminated through 10,000 subsequent heat cycles before the onset of degradation. For the purposes of the present invention, each heat cycle comprises both the heating phase and the subsequent cooling phase of the material.

If a pseudoplastic deformation etot of more than emax is imparted to said material, this deformation consists of a removable part e * and a non-removable part e .: (plastic deformation). Therefore etot = e * + epl.

In this case, in subsequent heat cycles e * always coincides with emax, even though here the emax value changes continuously and each specific cycle depends on the number of heat cycles previously suffered.

In other words, if the same etot deformation is always produced at the end of each heat cycle, the composition of etot varies from one cycle to the next, with the progressive decrease in the eliminable part of e * and a simultaneous increase in the part of plastic deformation epl.

The Applicant has realized that considerable advantages can be obtained in the operation of the cords by using, for at least one wire, shape memory materials with suitable characteristics of memory degradation produced in the wire by a heat treatment. specific carried out on the wire before it is twisted with other wires.

The Applicant has realized that it is possible to make an advantageous use of the shape memory effect of the wire, in other words the ability to eliminate an elongation imposed by the recovery of a predetermined initial shape, by limiting this effect to the phase of incorporation of the ropes in an elastomeric material, in order to obtain an optimal penetration of the rubber inside the rope, this phase being simultaneous with the first heat cycle to which the rope, and with this the shape memory wire, submit Preferably, this incorporation phase is carried out at a temperature TA which is greater than the temperature As of the transformation range [As-Af] assigned to the wire and, even more preferably, also greater than the maximum temperature Af of the said range .

The shape memory wire is previously subjected to an elongation of a predetermined value e * while it is at a temperature T0 lower than As (eg, room temperature), and then twisted together with the other wires, by known methods and means to form a rope.

In the phase of the incorporation of the cord which contains said memory-shaped wire, carried at high temperature, the elimination of the deformation takes place in association with a contraction of the wire which, in a condition of friction with the other wires of the rope develops a force of contraction therefore causing a disarrangement of the wires, in other words a swelling of the rope.

In practice, the rope is made to open with a good penetration of the rubber inside it.

Subsequently, the tension exerted on the cords after the incorporation phase, during the collection of the fabric and its cooling of the temperature of incorporation to values decreases progressively at room temperature, advantageously causes the recovery of the state of deformation of the wire of with memory of form with a return to the value of e *, possibly by means of the limited forces required by the processes of orientation of the martensite with the consequent return of the wires towards each other in the rope, until their compaction, in other words the closing of the rope is obtained.

This compact configuration remains practically unchanged in subsequent heat cycles due to the shape memory degradation characteristics imparted to the shape memory wires which makes possible a substantial recovery of a portion of e * In this way the maintenance of a closed configuration of the ropes in the subsequent vulcanizations of the heating cycle is obtained, despite the high temperature of the cycle, so that the rope is incorporated in the vulcanized rim in a substantially closed configuration.

Consequently, the articles, and in particular the pneumatic tires, constructed with rubberized fabrics prepared as indicated above, show an optimal functioning of the cords.

In a first aspect, the invention therefore relates to a metal rope for reinforcing articles made of elastomeric material, comprising a plurality of metal wires wound spirally around each other, at least one of which is formed of a material with shape memory, which is able to recover a previously memorized shape and deforms from said memorized form, the cord being characterized in that said cord with cord memory has the recovery capabilities essentially active in a first heat cycle and degrades to at least one significant predetermined extension after the first heat cycle.

In another aspect, the invention relates to a metal rope for reinforcing articles made of elastomeric material, such as pneumatic tires, conveyor belts, flexible hoses and the like, comprising a plurality of metal wires wound spirally about others, at least one of said wires being formed with a shape memory material, the cord being characterized in that the shape memory wire at room temperature has: - the memory in a different way, with a length 10 which is less than the length lx of the wire at room temperature, stored at a temperature As which is greater than the ambient temperature T0; - an emax / c pseudoplastic elongation removable by the shape memory effect, and having a value between 0.2% and 8% of the length of the memorized form; - an etot elongation having a value of at least 85% of said emax / c value; - a decrease in the pseudoelastic elongation removable e * after the first heat cycle carried out at a temperature of Tx > Thus, this decrease being at least 40% of the value of the emaxc pseudoplastic elongation.

In a second aspect, the invention relates to a rubberized fabric for use in articles made of elastomeric material reinforced with the cords according to the invention as defined above: alternatively, the invention relates to a rubberized cloth for use in articles made of an elastomeric material comprising a plurality of reinforcing cords incorporated in the elastomeric material of said fabric and positioned so that these are coplanar with, parallel to and adjacent to each other in the same direction, each cord being formed of a plurality of wires of metal spirally wound together, at least one of the constituent wires of at least one of said cords being formed of a shape memory material, the fabric being characterized in that said wire made with a shape memory material has the following characteristics at room temperature: - the memory in a different way, with a length 10 which is less than the length l of the wire at room temperature, stored at a temperature As which is greater than the ambient temperature T0; - an emax / t pseudoplastic elongation removable by the shape memory effect, and having a value between 0.01% and 8% of the length 10 of said memorized form; - a pseudoplastic lengthening etot having a value of at least twice that value eraax t; a decrease in the removable pseudoplastic elongation e * N + 1 for each subsequent heat cycle, carried out at a temperature of x > Thus, this decrease being at least 40% of the value of the pseudoplastic lengthening emax / N of the preceding cycle.

In the fabric according to the invention, the perfect rubbering of the metal wires of the ropes was obtained during the cloth heating cycle by means of separating actions exerted on the adjacent metal wires by the memory wire so that it tends to recover the predetermined memorized shape of a smaller length, with a consequent renewed swelling of the cord and a penetration of the rubber between the wires of the open cord: conversely, the good performances of the cords of said fabrics on the rim in use are obtained by the configuration of the cords that remain essentially closed in the heat cycles developed during the use of the rim due to the decrease in the value of the residual pseudoplastic elongation e * removable by the shape memory effect, this decrease occurs as a result of the heat cycles of the rubberized fabric and the vulcanization of the rim.

In a third aspect, the invention relates to an article made of an elastomeric material, and more particularly to a pneumatic tire for vehicle wheels, reinforced with cords according to the invention, and more preferably with the rubberized fabrics according to the invention. invention, as described above; In a preferred aspect, the invention relates to a pneumatic tire for vehicle wheels, comprising a toroidal tire having a crown part and two axes axially opposite, ending in a pair of beads to fix the rim to a corresponding mounting eyebrow, a tread surface band positioned on the crown of said tire and a band structure interposed between said tire and said tread surface band, the rim structure comprising a plurality of reinforcing cords, each formed of rolled metal wires spirally with respect to each other, at least one of which is a wire made of a shape memory material, characterized in that said wire made of a shape memory material has the following characteristics at room temperature: - the memory in a different way, with a length 10 which is smaller than the length 11 of the wire at room temperature, stored at a temperature As which is greater than the ambient temperature T0; - an emax / c pseudoplastic elongation removable by the shape memory effect, with a value between 0.05% and 8% of the length 10 of said memorized form; - a pseudoplastic elongation having a value of at least six times said emaxp value; - a decrease in the value of the residual removable pseudoelastic elongation e * N + 1 for each heat cycle after the vulcanization of the rim, carried out at a temperature of Tx > Ag / this decrease being at least 40% of the value of the pseudoplastic lengthening emaxN of the preceding cycle.

Preferably, the rim is of a radial type and the roped fabrics comprising at least one shape memory wire are used in the bands and / or in the cover layers.

In a further aspect, the invention also relates to the process of assembling said pneumatic tire, characterized by the use of the cords as described above.

In still another different aspect, the invention relates to a process for the manufacture of a rubberized reinforcing fabric for articles made of elastomeric material, such as pneumatic tires, conveyor belts, hoses and the like, comprising a plurality of parallel oriented reinforcing cords. each other in one direction and incorporated in an elastomeric material of said fabric.

In these fabrics, each cord comprises metal wires wound spirally around each other, and in at least one of said cords, at least one of said component wires is formed of a shape memory material which has memorized, by means of a suitable heat treatment, a predetermined shape with a length less than that of the wire at room temperature which deforms by elongation at room temperature by a predetermined percentage amount etot.

The process, comprising the known steps of incorporating the ropes into a layer of elastomeric material to form the reinforcing fabric, and then cooling and collecting the fabric, and based on innovative phases of: a) using a shape memory wire with characteristics of degradation of the shape memory effect so that the emax pseudoplastic elongation removable by the shape memory effect, after the heat cycle of the fabric laminate, lies between a value from zero and a value equal to a maximum of 40% of the initial value eraax, with a decrease in emax in each subsequent heat cycle preferably having the same percentage value as in the preceding cycle; b) incorporating the strings in the elastomeric material at a temperature T1 greater than the temperature at the beginning of the transformation phase As; c) in the phase of incorporation of the cords in the elastomeric material, use the recovery of the predetermined shape memorized by the wire to transmit to the surrounding wires the restoring force originated during said recovery, with effects of spacing the wires outwards. of others and the penetration of the rubber inside the rope in an essentially open configuration; d) pull the strings during cooling and the collection of the fabrics to restore the original length of the strings.

In either case the present invention will now be clearly understood with the help of the following description and the accompanying drawings, provided only by way of example and not for the purpose of restriction, in which: Figure 1 is a perspective amplification of a metal rope according to the invention, - Figure 2 is a schematic partial perspective view of a rubberized fabric incorporating a plurality of cords according to the invention; Figure 3 shows in a diagram provided by way of example a top view of a fabric tufting device for incorporating the cords into the elastomeric material; Figure 4 shows in a diagram provided by way of example a side view of the cloth tamping device consisting of a calendering; Figure 5 shows, in a partial perspective view with parts removed, a pneumatic tire according to the invention, - Figure 6 shows, in a qualitative diagram, the variation of the characteristics of the part of the pseudoplastic elongation by the memory shape effect in the corresponding metal wire, for the bare rope, by the rope in the rubberized fabric before the vulcanization, and the vulcanized llanca respectively.

The invention is initially described with reference to a metal rope 1 (figure) designed to form a reinforcing element for an article made of the elastomeric material.

For simplicity of representation, the illustration shows a cord of the type comprising a rectilinear wire 3 in a central position, forming the core of the cord, surrounded by a layer of six wires 4 wound spirally around the central wire, forming the cover. However, it is specified that the rope can have any known configuration, either of the twisted type or of the type with a central core and one more concentric layers, in which both the rope and the layer can be formed of single wires or wires twisted or of any combination of these.

Examples of known ropes, particularly those used to reinforce pneumatic tires for vehicle tires are those usually identified as 1x4, 3x7, 1 + 6, 2 + 2, 1x3 + 6 + 15.

In the cords according to the invention, at least one wire, for example the wire 3 of 1 + 6 cited above, is made of a material with shape memory with the characteristics specified below, while the other wires (4) they are of the conventional type made of steel, preferably of the HT type, in other words steel with a high carbon content, such as of > 0.9% In pneumatic tire technology, the diameter of said wires is preferably between 0.12 mm and 0.38 mm.

The shape memory material of the wire 3 is preferably made of alloys selected from the group comprising Fe-Mn-Si, Cu-Zn-Al, Cu-Al-Ni, Cu-Al-Be, Fe-Ni-Co-Ti , and Ni-Ti.

Before being twisted with the other wires to form the bare cord wire 3 has undergone a heat treatment which has imparted to it a predetermined memory shape, a specific range of transformation temperatures (Ms Mf As Af) and a gradient particular decrease in shape memory for subsequent heating cycles.

After the heat treatment, it has undergone a stretch at a temperature T < Thus, it has been imparted to a pseudoplastic etot deformation and to a length 11.

Consequently, in the rope according to the invention the wire with shape memory, at the ambient temperature T0 which conventionally assumed to be 25 ° C, has the following characteristics: - the memory of a different shape with a length 10 which is less than the length l of the wire at room temperature, is stored in the temperature range A. - Af, where As is greater than the ambient temperature T0; - a pseudoplastic lengthening eraax / c removable by the shape memory effect, with a value between 0.2% and 8% of the length 10 of the memorized form; - an etot elongation, imparted by stretching the wire at room temperature, having a value of at least 85% of said value wasax / c; a decrease in residual residual pseudoplastic elongation e *, after a first heat cycle carried out at a temperature Tx > Thus, this decrease being at least 40% of the value of the pseudoplastic elongation emax / c.

Preferably, the elongation etot has a value of not less than said value emaxc.

In particular, for the previously mentioned materials, the emaxc elongation value as defined above varies with the material being, for example, 0.2% for a Fe-Si-Mn alloy and 8% for a Ni-Ti alloy.

The maximum conversion force * exerted by said alloys is 400 MPa (megapscales) for a Fe-Si-Mn alloy and 600 MPa for a Ni-Ti alloy.

Preferably, the decrease, after a first heat cycle carried out at a temperature Tx > Thus, of the elongation on the residual removable plastic e * (also referred to in the present description as the degradation of the shape memory material) is also maintained in the subsequent heat cycles which the rope suffers during the assembly and use of the product.

More precisely, if e * indicates the amount of deformation that can be eliminated by the memory effect in the first heat cycle, the degradation of the wire can be defined as the value of the residual amount of deformation at the end of the subsequent heat cycle.

According to the invention, this value is not more than 40% of e * and preferably not greater than 35% of e *.

Preferably, the elongate pseudoelastic elongations in heat cycles after the first are determined by the following law: where N is the progressive heat cycle number after the first and Q% is the percentage of the deformation that can be eliminated by the shape memory effect which the material can be available in the subsequent heat cycle as a result of the phenomenon of degradation.

Preferably the Q% value is selected to not be more than 40% e * N, preferably not more than 35% and even more preferably not greater than 25% e * N.

According to the characteristics specified above, the shape memory wire, in the rope according to the invention, develops its maximum contraction during the first heat cycle to which it is subjected, normally that of the rubbering of the fabric, at the end of the which its contraction capacity is essentially reduced or practically zero.

To summarize, the rope is capable of opening during the fabric tufting phase, when a high possibility of penetration of the rubber inside the rope is required, while remaining essentially compact during the vulcanization of the tire.

The degradation of the shape memory has always been seen as a negative element in the materials, and consequently its use according to the invention constitutes a novelty in the art, since these materials are generally used precisely because of their ability to recover the shape stored in memory in a way which is practically constant over time.

It is pointed out that the effect of the spacing of the wires which is useful for the opening of the rope can be advantageously improved by the use of a wire 3 treated with a suitable heat treatment in such a way that it memorizes the shapes which are more useful than the linear form for the specified purposes, such as a wavy shape, preferably in the form of a spiral, like a spring.

In this case also, the wire 3 is previously stretched in a linear fashion at a temperature T < As, and then twist with the other wires to produce the desired string.

In the gumming phase of fabric, the wire 3 recovers the undulating form and transmits the sling forces towards the surrounding wires by means of the previously mentioned contraction force and by the forces developed by the undulations; in this way a greater opening of the rope and consequently a better incorporation of the rubber in? e this one is obtained.

In a particular embodiment of the invention, use was made of a shape memory wire made of a Fe-Mn-Si alloy, characterized by a removable pseudoplastic deformation emax = 2%, capable of developing a reconversion force of 400 MPa , with a percentage of eliminable deformation (degradation coefficient Q%) equal to 25%, The invention also relates to the rubberized fabric (Figure 2) provided with said cords.

A rubberized fabric essentially consists of a strip 2 of elastomeric material whose length is undefined (or in other words is greater than the width), comprising a plurality of strings 1 arranged so that these are on one side and coplanar with one another, oriented in the longitudinal direction of the strip and incorporated in the elastomeric material.

Parts of the rubberized fabric, conveniently cut at suitable angles, form the basic semi-finished products for the assembly of various articles made of elastomeric material such as pneumatic tires, conveyor belts, flexible hoses for transporting fluids, transmission belts and other similar items; said parts of the fabric allow reinforcement elements consisting of the strings to be placed in the structure of the articles in the desired position, in the desired manner and with the desired orientation.

A process for the assembly of the fabric consists essentially of the phase of incorporation of the cords in the sheet of elastomeric material by means of a gumming device, as shown schematically in FIG. 3, which conveniently consists of a calender with a plurality of cylinders or an extrusion head supplied from an extruder. A plurality of strings 1 is taken to the rubberizing device 5, the rubberized fabric 2 emerges from the calender or the extruder die and consists of the sheet of elastomeric material (Figure 3) incorporating said plurality of strings 1, oriented in the forward direction of the sheet, which is taken under tension, in the form of a continuous strip, by means of a suitable collection which is not illustrated since it is of any known type. For ease of understanding and simplicity of the description, the following text will not only refer to the glued web worn by a calender.

The calender comprises, as shown in FIG. 4, two opposed cylinders 5 and 6, which rotate in opposite directions to one another, placed at a distance from one another equal to the thickness required for the fabric: for example, for use on tires pneumatic, this distance is preferably from 0.6 to 4 millimeters.

Outside the two cylinders 5 and 6 are placed at least two other cylinders 7 and 8 designed to process, heat and guide the elastomeric buffer material towards the space between the rolling cylinders 5 and 6, with the directions of rotation and flow of the cylinder. material equaling one another, as shown in figure 4.

A plurality of rolls 9 each comprising a rope wound in a coil over a stretch of several thousand meters, is placed in front of the calender.

The various rolls or reels are provided with suitable braking means for regulating the unwinding pole on the cords provided by the aforementioned collection device located after the calender: it will be evident that the gating position (the separation between the cylinders 5 and 6) forms a braking point for advancing the ropes, so that different rods can be applied to the fabrics or in front of and after the calender, preferably with the greater pole applied later.

A distributor 9 'is positioned between the plurality of reels and the gating device for positioning the cords so that they are parallel to and coplanar with each other in a single horizontal plane before they reach the calender.

According to the invention, each reel is loaded with a cord comprising at least one wire with shape memory provided with the characteristics previously mentioned: in particular, it has stored a linear shape of the length L0 at a temperature range As -Af of from 60 to 120 ° C, and more preferably from 90 to 100 ° C, where As is lower than the temperature of the calender, in other words the temperature of the rope.

The strings, unrolled with a predetermined pull of the corresponding reels, pass through the distributor and are then taken between the calendering cylinders where they reach the calender temperature, preferably 70 ° C and 100 ° C, and they incorporate between two sheets of elastomeric material which are supplied from the upper and lower cylinder respectively.

The temperature of the wire 3 of each string reaching the calender changes from the ambient temperature T0 to the typical As temperature of the selected shape memory material, which corresponds to the beginning of the transformation of the martensitic to austenitic wire structure, with the termination of said transformation at a temperature below the maximum temperature of incorporation of the strings which is of the order of 100 ° C.

During the transformation, as previously stated and as known in the art of shape memory materials, the contractile forces arise and are used for the recovery of the previously memorized form by the wire 3. The recovery force corresponds to the incorporation temperature, which is maximum if Af < the said temperature is transmitted by friction to the surrounding wires, causing a disarrangement of their reciprocal arrangement, preferably with a shortening of the inclination of the cord, and an elimination of the pseudoplastic deformation e * removable by the shape memory effect .

In practice, the rope, due to the recovery of the length 10 initially stored by the wire 3, and due to the fact that the elastomeric material in the plastic state allows this, it swells, with the consequent good penetration of the rubber between the wires of which it consists.

Upon leaving the calender, the newly formed fabric is taken to the collection device, by the pull applied to the fabric and therefore to the ropes, and is simultaneously cooled from the temperature of the loosening to temperatures that progressively decrease to the ambient temperature T0.

During this cooling, the wire 3 reaches a temperature, typical of the selected shape memory material, at which the transformation of the austenite phase to the martensite phase begins, followed by the complete formation of a martensitic structure at a still temperature. lower additional.

During this transformation, in which, as a martensitic structure is known to be deformable to a considerable extent by limited forces, the pull to which the wire 3 is subjected is sufficient to restore the pseudoplastic elongation which the wire itself originally had , with the consequent stretching and recompaction of all the wires of the rope.

In practice, the rope is closed again, but at the same time the complete rubbering of each wire is retained.

The advantage of the fabric according to the invention is represented by the fact that the smoothing heat cycle has practically exhausted the elimination capacity of the pseudoelastic elongation e *, due to the degradation value imparted to the cords.

According to this invention, preferably, in the rubberized fabric according to the invention, at room temperature, the wire with shape memory of the strings incorporated in the fabric has the memory of a different shape, with a length 10 which is less than l? of the wire at room temperature, stored at a temperature As, which is greater than the ambient temperature T0, an elongation pseudoelastic eraax / t removable by the effect of shape memory and having a value of between 0.1% and 8% of the length 10 of said memorized form, a pseudoelastic elongation etot with a value of at least equal to twice that value emax / t and a decrease in residual pseudoelastic elongation e * N +? for each subsequent heat cycle brought to a temperature Tx > Thus, this decrease being at least 40% of the value of the pseudoplastic elongation of the e - ^ / j, of the preceding cycle. Figure 5 illustrates a pneumatic rim of the radial type 10 made with rubberized fabrics provided with reinforcing cords according to the invention.

The pneumatic tire 10, to which the inventrefers, preferably comprises a radial cover 20, internally lined and with a rubber sheet 28 which is impermeable to air, a tread surface band 11 placed on the crown of said cover , of the shoulders 12, of the side walls 13, the beads 14 reinforced with the cores 15 and the corresponding counting fillers 16, the reinforcing tapes 19 and a band structure 21 interposed between said cover and said surface band of rolling.

The cover 20 comprises one or more cover layers folded from the inside to the outside around the cores 15. The cover layer or layers are formed by parts of the rubberized fabric reinforced with the ropes 22 embedded in the rubber of the fabric. , represented schematically.

The band structure 21 comprises two inner bands 23 and 24, one being radially superimposed on the other, and a third band in a radially outer posit The bands 23 and 24 are formed by parts of the rubberized fabric incorporating the metal cords inclined with respect to the equatorial plane of the rim 10 in such a way that the cords are parallel to each other in each band and transverse to each other in the superimposed bands, while band 25 is provided with the cords oriented circumferentially, in other words at zero degrees c-with respect to said equatorial plane.

Similarly, other rim component elements can be formed from pieces of rubberized fabric with the reinforcing cords suitably inclined with respect to the axial, radial or circumferential direct of the rim: for example, the reinforcing belt cited 19 has the inclined cords at an angle between 30 ° and 60 ° with respect to the radial direct All the reinforcing cords are made of any suitable material, particularly of a textile or metal material, according to the functl characteristics required in the rim: the inventis preferably referred to metallic materials and refers to cords consisting of a plurality of metal wires twisted together, at least one of which is made of a shape memory material according to the invent A first example of the use of the wire according to the inventrelates to the band structure of a pneumatic tire for trucks in which the strings of the crossover strips are metal cords in an arrangement HT LL of 3x0.22 + 6x0 .38, in other words the Lang Lay (LL = Lapg Lay) strings consist of a core of three steel wires, with a wire diameter of 0 = 0.22 mm, surrounded by a layer of six steel wires, with a diameter of wire of 0 = 0.38 mm, where the wires are made of steel with a high carbon content (HT - High Tens and have a breaking load of at least about 30 to 50 MPa.

The rope comprises at least one shape memory wire made of an Fe16Mn9Cr? Si4Ni alloy with a breaking load of at least 750 MPa. The wire has a maximum recoverable pseudo-elastic deformatfor the memory effect eraax = 2% and can exert a maximum conversforce of 400 MPa. In one case, the shape memory wire is part of the core where the wires are wound with an inclinatof 11 millimeters, while the layer wires are wound with an 18 millimeter inclinat both groups of wires are wound spirally with a winding directof type "S".

In another case, the shape memory wire is part of the layer, the core and the layer have the same inclinat and winding direct as those cited above.

Preferably, the shape memory wire, both in this and in other embodiments which will be described, have the same diameter as the steel wire which they replace.

A further example of an incorporation is provided with a strip structure with cloth strips comprising strings of an HT arrangement of 3x0.15 + 6x0.27 with a steel wire breaking load equal to 2750 MPa: the roll inclinations they are 9.5 mm and 12.5 mm, with the winding directions "S" and "Z" respectively. The shape memory wire can equally well replace one or more wires of the core and / or the layer.

The cores according to the invention have also been used as reinforcement elements in the cover layers of pneumatic tires for road transport.

In a first example of a modality, the roof ropes have a CC (Compact Rope) arrangement of 1x0.22 + 6x0.20 + 12x0.20 with a breaking load of steel wires of at least 2750 MPa. The winding slope is 14 mm, with the "S" direction, in both layers.

In a further example of an incorporation, the strings with a CC arrangement 1x0.25 + 6x0.23 + 12x0.23 were used, again with a breaking load of the steel wires of at least 2750 MPa, with a roll tilt of 16 mm, and an "S" direction, in both layers.

The shape memory wire replaced one or more of the core steel wires and / or the six-wire layer and / or the twelve-wire layer.

These ropes have characteristics capable of allowing a complete penetration of the rubber between the wires in the smoothing phase, while they have an excellent functioning in use; in fact, the analysis of the prototype rims after vulcanization, has revealed that in these structures the band and the roof ropes showed a complete rubbering of the wires, even those of the core, confirming their high penetrability by the rubber.

The unprocessed tire, complete in all its parts, was placed in a vulcanization press where this phase of the process was carried out at a temperature of the order of 140 ° C, using steam at a high temperature and pressure brought into the interior of the tire. the rim by means of a vulcanization chamber which presses the internal toroidal surface of the rim against the walls of the press: in this phase, the tread surface band is printed with a suitable tread pattern.

During the vulcanization phase, the wires 3 of each string are no longer capable of recovering a pseudo-elastic elongation equal to the elongation e * recovered in the first heat cycle, since its ability to recover the memorized form has been adequately degraded to a value The residual pseudoplastic elongation of e * uj which is preferably not more than 25% e *.

Consequently, the force transmitted by friction from the wires 3 to the surrounding wires is much lower than that previously developed: in addition, the wires 3 are able to open the corresponding rope in a very small extension, thus allowing an additional penetration of the compound inside. of the rope as a result of the high initial fluidity of the compound due to high temperature in the first phase of the vulcanization process. Preferably the degradation value of the residual pseudoelastic elongation e *. { 1) is appropriately selected to maximize this result.

The closing of the cords of the cover layers and of the bands with circumferentially oriented cords is then ensured by the pressure of the vulcanization fluid which inflates the rim, exerts a thrust against the inner surface of the press and puts the cover and the tension band assembly: preferably this thrust with swelling is further maintained during the gradual cooling of the rim, with the known means and methods of the subsequent swelling.

In use, the tire undergoes several cycles of caler which as a result of the conditions of use (load and inflation pressure) and / or the driving behavior and / or the effects of the ambient temperature, cause the heating of the tire. the rim and the constituent materials, including the ropes, at a temperature value which is higher than the aforementioned threshold value A3.

However, under these conditions, due to the degradation of the memory recovery capacity already suffered, and also due to the fact that it is embedded in a vulcanized compound, the cord remains practically closed and, in addition, the memory wires of Form 3 of each rope can develop a small counter-force which is quickly and progressively eliminated: the degradation of the memory recovery capacity imparted to the wires 3 of each rope can be considered to be such that the capacity for recovery is practically of zero after a number of 30-50 heat cycles from the beginning of the use of the tire, which is generally characterized by approximately 30-50 thousand heat cycles during its life.

The rims according to the invention are therefore provided with ropes comprising at least one wire with shape memory, whose behavior, in the use of the rim, after a number of initial heating cycles, becomes similar to that of the surrounding wires made of a conventional material.

The qualitative diagram of Figure 6 shows the variation of the characteristics of that part of the pseudoplastic elongation e * removable by the shape memory effect, in the corresponding metal wire, for (1) the bare rope, (2) the rope in the rubberized fabric before vulcanization, and (3) in the vulcanized rim respectively.

The length of a part of the wire made of shape memory material is indicated by 117 and consists of a part "a" with a length 10 corresponding to the length of the shape memorized in the wire, and a pseudoplastic deformation etot (imparted by the lengthening of the martensitic structure) which in turn consists of a part "b" corresponding to the proportion e * removable by the shape memory effect and the part "c" corresponds to the ePL ratio plastically deformed in a In a non-recoverable way, the symbol e in this case indicates absolute values rather than elongation percentages.

The degradation characteristics imparted to the memory wire according to the invention determine the movement of the separation line between e * and ePL due to the heating cycles suffered by the wire.

In the rope itself, the wire has undergone an etot elongation of at least 85% emax / c but preferably at least equal to, and more preferably greater than, emax / c, to impose the condition that the degradation of the memory starts with the second subsequent heating cycle: in other words, in the second heating cycle the recoverable proportion of the elongation is made to be considerably smaller than the rate recovered during the first heating cycle. In this way, in each subsequent heating cycle the recoverable proportion of the elongation e * always coincides with the emax / N value in relation to this cycle and consequently is not capable of repetition in the next cycle.

The diagram in figure 6, according to a preferred value of degradation of the order of 50% according to the invention shows that the value of the recoverable proportion of elongation e * is about half that of the naked cord in the rubberized fabric and about a quarter of said value on the vulcanized rim.

The features of the invention described previously in relation to the opening of the cords in the incorporation phase in the elastomeric material makes it possible to use string arrangements each of which consists of a plurality of layers of metal wire, without the risk of a poor penetration of the rubber inside the wires of the inner layers.

In addition, due to full penetration of the rubber between the rope wires, it is possible to use any new arrangements of metal ropes with a greater number of layers of metal wires than those used in the current art, in particular for the ropes. of reinforcement of the fabrics that cause the rubbering for the motor vehicle tires.

The additional characteristic of the closure of the rope in the cooling phase of the fabric, after calendering, by means of a pull on the regulated cords in such a way that the wires of each rope are made to approach the center, favorably allows the recovery of the group of wires essentially as they were before they were moved outward from each other in the calendering phase.

This is due, in the aforementioned cooling phase, to the fact that the shape memory wire subjected to heat regains its initial length, so that all the wires of each string are recompacted together according to the pull applied to them, on the upper part of the rubber that has penetrated inside the rope, to restore the original length.

The next vulcanization heat cycle is only able to re-open the rope at a very small extent, while the subsequent heat cycles, up to a rather small number, occurring during the use of the tire can only develop forces of reconversion, which becomes weaker as the number of cycles increases.

It has been seen, then, that the basic feature of the invention, such as a shape memory recovery which is greatly degraded according to the predetermined values at the start, allows the rope to remain closed when in use.

If, for example, it is presumed that the pseudoelastic deformation e * recoverable by the memory effect in the first heat cycle is 2% and the use is made of a shape memory wire with degradation of the memory effect so that if Q% is 25% there will be a recoverable deformation e * (N) in the following N heat cycles (N = l, 2,3) of 0.5%, 0.125%, 0.03% respectively, and more.

Considering the values quoted, it will be evident that shape memory recovery can already be considered minimal in the heat cycle immediately after that of the vulcanization of the tire, and can be considered as zero in the thousands of subsequent cycles of heat to which the tire is subjected when in use.

Consequently, due to the good penetration of the rubber between the wires and the closing of the rope with the recompaction of the wires in the initial configuration, the rope has both a good resistance to corrosion and high-grade performance when the rope is in use.

The maintenance of the closure of each rope through the thousands of heat cycles to which a tire is subjected is manifested, in practice, in the fact that the wire with shape memory or the wires contained in the rope behave in the same way as the other steel wires of the conventional type present in the same rope.

This is because the wire which was originally introduced into the rope precisely because of its ability to recover in a certain way loses the ability to recover subsequently so that, when exposed to the thermal and mechanical stresses to the which the string is subjected to, this will behave in the same way as the other wires, particularly with respect to its modulus of elasticity in tension and its elongation to breaking.

The behavior of the shape memory wire of the rope according to the invention is therefore completely different from that described and used in the prior art, in which the recoverability of the memorized form is always present and if it is essentially unchanged through a large part of the life of the tire.

It has also been pointed out that the penetration of the rubber between the wires of a rope can increase with considerable advantage by increasing the number of wires with shape memory.

For example, in a rope structure with a plurality of layers, it is possible to place three shape memory wires with an angular range of 120o between these or four wires with an angular range of 90o between these or other convenient arrangements to obtain a maximum effect of the disarrangement between the wires in the phase of the incorporation of the strings inside the elastomeric material.

It is also possible to increase the opening of the rope by requiring the wire manufacturer to provide, by means of the heat treatment, a higher recovery force of the memory in the fabric tufting phase.

In this case, both the choice of materials and the heat treatment makes it possible to obtain temperature values at the beginning of the austenitic phase and at the end of the austenitic phase, corresponding to the recovery force having the desired value.

Therefore, the shape memorized by the linear and / or undulating wire, of the material which consists, the type of heat treatment, and the number of shape memory wires inserted inside the rope advantageously provide different solutions which can be combined with each other in various ways to obtain a desired opening of the rope with a consistent high penetration of the rubber inside it.

A further advantage of the invention lies in the fact that new materials are used in the rope without changing the conventional pneumatic tire manufacturing cycle It is also emphasized that the present solution to the technical problem that has arisen in relation to the use of shape memory degradation is not a simple or obvious choice.

Indeed, it is only in the applicant's perception that the degradation of shape memory, which has never been used in the prior art and certainly has not been suggested in publications relating to this subject, since it constitutes a worsening of the behavior of shape memory materials, has become a basic characteristic for the solution of a previously unresolved technical problem.

Claims (26)

R E I V I N D I C A C I O N S

1. A metal rope for reinforcing articulos made of elastomeric material, comprising a plurality of metal wires wound spirally around each other, at least one of which is formed of a material with shape memory, has capabilities of recovering a previously memorized shape, and deforming from the memorized form, said cord being characterized in that the shape memory wire has said recovery capabilities essentially active in a first heat cycle and degrades to at least a significant predetermined extension after the first heat cycle.

2. A metal rope as claimed in clause 1, characterized in that said wire with shape memory at room temperature has: memory in a different way, with a length 10 which is less than the length lx of the wire at room temperature, stored at a temperature As which is greater than the ambient temperature T0; an emax / c pseudoplastic elongation removable by the shape memory effect, and having a value between 0.2% and 8% of the length of said memorized form; an etot elongation having a value of at least 85% of said amax / c value; a decrease in residual residual pseudoplastic elongation e * after a first heat cycle carried out at a temperature Tx > Thus, this decrease being at least 40% of the value of said pseudoplastic elongation '-max / c •

3. A metal rope as claimed in clause 1, characterized in that said wire with metal shape memory has a linear shape memorized.

4. A metal rope as claimed in clause 1, characterized in that said wire with metal shape memory has an undulating shape memorized.

5. A metal rope as claimed in clause 1, characterized in that said metal shape memory wire, in the recovery phase of the memorized form, during said first recovery heat cycle exerts a reconversion force of between 50 and 800 MPa.

6. A metal rope as claimed in clause 1, of the multi-layered type with a central core, characterized in that said metal shape memory wire is part of said core.

7. A metal rope as claimed in clause 1, of the multi-layer type with a central core, characterized in that said metal sheath memory wire is part of one of said layers.

8. A metal rope as claimed in clause 1, of the twisted type, characterized in that said metal shape memory wire forms one of the elements of the twisted.

9. A metal rope as claimed in clause 1, characterized in that the material of said shape memory wire comprises an alloy chosen from the group consisting of Ni-Ti, Ni-Ti-Co-Fe, Fe-Si- Mn, Cu-Zn, Al, Cu-Al -Ni, Cu-Al-Be.

10. A pneumatic tire for vehicle wheels, comprising a plurality of reinforcing cords, each formed with metal wires wound spirally around each other, at least one of which is formed of a shape memory material, has the capacity of recovering a previously memorized shape, and deforming the memorized shape, the rim being characterized in that the shape memory wire has said recovery capabilities substantially active in a first heat cycle and degraded. to at least one significant predetermined extension after the first heat cycle.

11. An air tire as claimed in clause 10, characterized in that it comprises a toroidal shaped cover having a crown part and two axially opposite ladcs ending in a pair of beads to fix the rim to a corresponding mounting eyebrow, a strip of running surface placed on the crown of said cover and a band structure interposed between said cover and the tread surface strip, said rim comprises a plurality of reinforcing elements made of rubberized fabric provided with reinforcing cords placed at one side and parallel to each other, each being formed of metal wires wound spirally around each other, said rim being characterized in that each of the metal cords comprises at least one of said memory-shaped wires.

12. An air tire as claimed in clause 11, characterized in that said wire made with a shape memory material has the following characteristics at room temperature: memory in a different way, with a length 10 which is less than the length lx of the wire at room temperature, stored at a temperature As which is greater than the ambient temperature T0; an emaxp pseudoplastic elongation removable by the shape memory effect, and having a value between 0.5% and 8% of the length 10 of the memorized form; a pseudoplastic elongation having a value of at least six times the value cxmaxp; a decrease in the value of the residual removable pseudoplastic elongation e * for each calender cycle after that of vulcanization of the rim carried out at a temperature Tx > Ag / this decrease being at least 40% of the value of the emax pseudoplastic elongation of the preceding cycle.

13. An air tire as claimed in clause 10, characterized in that said cords comprising at least one wire made with a shape memory material are formed according to at least one of the preceding clauses 3 to 9.

14. A pneumatic tire as claimed in clause 11, characterized in that said strip structure comprises at least one strip of rubberized cloth, in a radially outer position with the cords oriented in a circumferential direction, parallel to the equatorial plane of the rim , characterized in that the strings of said strip comprise at least one of said shape memory wires.

15. An air tire as claimed in clause 11, characterized in that said roof structure comprises at least one layer of rubberized fabric, provided with reinforcing cords, characterized in that said cords comprise at least one of the shape memory wires .

16. A rubberized fabric for reinforcing articulos made of elastomeric material, comprising a plurality of ropes incorporated in the elastomeric material of said fabric and placed so that these are coplanar with, parallel and adjacent to each other in the same direction, each cord being formed by a plurality of spirally wound metal wires together, at least one of which is formed of a shape memory material, has recovery capabilities of a previously memorized shape, and is deformed from said memorized form, the fabric being characterized in that the shape memory wire has the recovery capabilities essentially active in a first heat cycle and degrades to at least a significant predetermined extension after said first heat cycle.

17. A rubberized fabric as claimed in clause 16, characterized in that said wire made with a shape memory material has the following characteristics at room temperature: the memory of a different shape, with a length 10 which is smaller than the length lx of the wire at room temperature, stored at a temperature A3 which is greater than the ambient temperature T0; an emax / t pseudoplastic elongation removable by the shape memory effect, and having a value? e between 0.1% and 8% of the length 10 of said memorized form; a pseudoplastic elongation having a value of at least twice that value araax t; a decrease in residual residual pseudoplastic elongation e * for each subsequent heat cycle carried out at a temperature Tx > Thus, this decrease being at least 40% of the value of said pseudoplastic elongation eraax of the preceding cycle.

18. A process for the manufacture of a reinforcing rubberized fabric for articles made of elastomeric material, such as pneumatic tires, conveyor belts and conveyor, flexible tubes, and the like, comprising a plurality of strings oriented parallel to one another in the same direction and incorporated in said elastomeric material, characterized in that it comprises the steps of: a) preparing a plurality of metal cords to be sent to a gumming device of fabric, each rope comprises a plurality of single metal wires wound spirally around each other, at least one of said wires in at least one of the cords is formed of a shape memory material, with said shape recoverable by the action of a cycle with adequate heat, where said wire, at room temperature, has: the memory in a different way, with a length 10 which is less than the length lí of the wire at an ambient temperature, memorized at a temperature As which is greater than the ambient temperature T0; an emax pseudoplastic elongation removable by the shape memory effect, and having a value between 0.2% and 8% of the length of said memorized form; an etot elongation having a value of at least 85% of said amax value; a decrease in residual residual pseudoplastic elongation e * after a first heat cycle carried out at a temperature Tx > Thus, this decrease being at least 40% of the value of said pseudoplastic elongation b) feed said cords, coplanar with and parallel to each other, to the gating device for the incorporation of said cords in the layer of elastomeric material, c) carry out the incorporation at a temperature Tx > T0 so that the shape memorized in the wire is recovered, with the recovery of said emax recoverable pseudoplastic elongation in such a way that the reconversion of force produced by said shape memory wire during said recovery exerts on the surrounding wires spacing actions between each of said wires and the next, and the penetration of the elastomeric material into the cord which is in an essentially open configuration, d) removing the rubberized fabric from said gumming device, in the form of a continuous strip with a sufficient pull to restore the etot pseudoplastic elongation and the original configuration of said cords, the fabric being progressively cooled to room temperature.

19. A process as claimed in clause 18, characterized in that use is made of a shape memory wire which has a decrease in residual pseudoplastic elution a * for each heat cycle, followed by that of the rubberized of the fabric, carried out at a temperature Tt > Thus, this decrease being at least 40% of the value of the emax pseudoplastic elongation of the preceding cycle.

20. A process as claimed in clause 18, characterized in that use is made of a wire with shape memory in which said memorized form is an undulating form.

21. A process as claimed in clause 18, characterized in that the contraction of the wire with memory is used consistently on the recovery of said memorized form to cause, by friction, the spacing and separation of the surrounding wires with swelling of the rope and the penetration of the elastomeric material inside it.

22. A process as claimed in clause 17, characterized in that use is made of the recovery of the shape previously memorized in the shape memory wire to cause spacing of the surrounding wires separating them from each other with swelling of the cord and penetration of the elastomeric material within it.

23. A process as claimed in clause 17, characterized in that the incorporation temperature Tx is between 60 and 120oc.

24. A process as claimed in clause 23, characterized in that the incorporation temperature Tx is between 90 and 120 ° C.

25. A process for the manufacture of a pneumatic tire for vehicle wheels, the rim comprises a toroidal shaped tire having a crown part and two opposite side walls ending in a pair of beads to fix the rim to a corresponding mounting eyebrow, a a tread strip placed on the crown of said tire and a band structure interposed between said tire and the tread surface strip, said process comprises the phases of: preparing a raw cover comprising a plurality of reinforcing cords, each formed by metal wires wound spirally around each other, at least one of which is a wire made of a shape memory material, which has capabilities of recovering a previously memorized form, and deforming said memorized form; Y vulcanizing said unprocessed cover in a vulcanization press by means of a heat cycle defined by predetermined values of time, temperature and pressure, said process being characterized in that it uses ur. shape memory wire which has the recovery capabilities essentially active in a first heat cycle, and degrades to at least a predetermined significant extent after said first heat cycle, such that said recovery capacities are essentially eliminated in each heat cycle after the vulcanization cycle.

26. An article made of an elastomeric material provided with metal reinforcing cords, each comprising a plurality of metal wires wound spirally around each other, at least one of which is formed of a shape memory material, has recovering a previously memorized form, and deforming said memorized form, the article is characterized in that said shape memory wire has the recovery capabilities essentially active in a first heat cycle and degrades to at least a predetermined significant extent after said first cycle? heat. SUMMARY A process for the manufacture of a reinforcing fabric for articles made of rubber, such as pneumatic tires, conveyor belts, hoses and the like, comprising a plurality of metal cords oriented parallel to each other in a single direction in which each The rope comprises metal wires wound spirally around each other, wherein at least one of the wires of the rope consists of a material with shape memory. During the phase of incorporation of the strings inside the elastomeric material, the shape memory wire tends to recover the initially memorized shape and, by means of the force generated during this recovery, transmits by friction to the surrounding wires forces tending to cut the inclination of the rope with spacing of each wire of the next, resulting in a good penetration of the elastomeric material between the wires. The rope closure is maintained in subsequent heat cycles due to the memory degradation characteristics imparted to the wire. The invention is particularly suitable for fabrics forming web layers and cover layers in pneumatic tires.