An improved process for the reconstruction of tyres

Abstract

Process for the retreading of tyres (1), in particular of tyres having the corresponding tread (2) which is worn following their use, and wherein said process comprises: - a step of high pressure waterjet application on the external surface (2') of the worn tread (2) of the tyre (1) to be retreaded to thus generate an underlying adhesion surface (6) which is devulcanized, - a step of applying a new layer (4) of a rubber-based compound on the devulcanized adhesion surface (6), - a vulcanization step of the tyre, with the new layer already applied (4).

Description

[0001] AN IMPROVED PROCESS FOR THE RECONSTRUCTION OF TYRES

[0002] TECHNICAL FIELD

[0003] The present invention relates to an improved process for the retreading of tyres.

[0004] STATE OF THE ART

[0005] The tyre sector is certainly in continuous development, especially in countries like Italy, where road freight transport covers about 90% of total transport. It is therefore clear that in parallel with a large production of tyres, there is also the problem of their disposal. It is estimated that of the approximately 400,000 tons of used tyres that are generated annually in Italy, 50% are used as fuel, 25% are ground and reused as raw material for a series of applications and 25% are dispersed in illegal landfills.

[0006] Therefore, for several decades now, processes have been found to give new life to already worn tyres, that is, tyres which - due to the wear caused by their use - have a residual tread height that is substantially less than 15% of the initial height.

[0007] In other words, the tyre can be retreaded by replacing, in the used tyre (which thus retains its structural characteristics), the worn tread with new material with characteristics completely similar to the original, restoring the tread height. Conveniently, such a retreading is possible because the innermost structure of a tyre (the so-called "carcass") has a much longer useful life than the tread.

[0008] A conventional retreading process involves an initial selection step (cf. fig. 1a) of the retreadable tyre carcasses, which must be intact and have passed all quality controls. An expert operator carefully inspects tyre 1 , both outside and inside, using specific tools. The operator's control is integrated with instrumental control using various technologies such as shearography.

[0009] Subsequently, in a second step (cf. fig. 1 b), through a scraping action, the worn tread 2 and the underlayer / undertread 8 (cf. fig. 5b) are completely removed. This operation is carried out by using specific machinery that usually uses a lathe and metal blades.

[0010] Once the scraping is complete, a third step begins, wherein the carcass is further inspected to identify and remove any defects. Specifically, an operator manually removes the craters that the lathe was unable to eliminate during the scraping step. In this third step, which is long and laborious, the operator removes the rubber inside the cavities using a small manual cutter.

[0011] Therefore, at the end of the second and / or third step, all the rubber 37 of the tread 2 and of the underlayer / undertread 8 is removed until substantially reaching the layers 11 containing the steel belts provided above the carcass 9 of the tyre (cf. fig. l c).

[0012] In a fourth step, called the solution step, a layer of liquid rubber is applied which prepares the surface for the application of the new material. During this step, various solvents are used which are potentially toxic to the operator's health and harmful to the environment, such as benzene, methanol, etc.

[0013] Subsequently, a fifth step is carried out to realise a new tread by applying a layer of rubber-based compound 4 with a thickness substantially corresponding to that of the tread to be retreaded (cf. fig. 1 d). In particular, the applied rubber layer 4 has a thickness substantially corresponding to that of the tread of the unworn tyre (i.e. just produced and before its use). This step may involve the application of a pre-printed tread with an appropriate pattern (which is defined by a series of grooves / grooves 10) and already vulcanised in the shape of a closed band with lateral fins (cold technique) or the application of a band of new smooth rubber without tread (hot technique, cf. fig. l d).

[0014] In the sixth step, the tyre is mounted on a special machine for the application of the so-called “envelopes” and is placed under vacuum in order to extract the residual air between the envelopes and the tyre prepared with the pre-printed tread. The tyre then enters an autoclave to be vulcanized at a temperature of approximately 110 °C for approximately 3 hours. In the case of the hot technique, the tyre prepared with a smooth profile enters a vulcanization press equipped with a mould with the pattern that will be imprinted on the tyre (cf. fig. 1 e). The press is equipped with devices to regulate time, temperature and internal pressure. The vulcanization process according to the hot technique takes place at a temperature between 150 °C and 160 °C at a pressure of approximately 14-16 atmospheres and lasts approximately 6 hours.

[0015] Thus, at the end of the fifth and / or sixth step, a retreaded tyre T is obtained (cf. fig. 1e) having a tread 20 which is provided with an appropriate pattern and which has a thickness substantially corresponding to that of the tread of the unworn tyre (i.e. just produced and before its use).

[0016] Finally, appropriately, in a seventh step, the retreaded tyre T is subjected to a final internal and external control through specific verification systems in order to evaluate whether the tyre complies with the sector regulations.

[0017] However, companies involved in the production process of retreaded tyres are currently in full crisis, mainly due to the increase in the cost of raw materials and high energy costs that make the final cost of the retreaded tyre uncompetitive compared to a new tyre. Furthermore, the tyre retreading process involves the use of substances that are potentially harmful to the environment and to the health of the operators.

[0018] IT201900005780 describes a process for the retreading of tyres having the corresponding tread which is worn and which presents a series of grooves on the surface defining a corresponding pattern. In particular, the known process according to IT201900005780 includes the following steps:

[0019] - an initial step of water scraping carried out on the external surface of the tread of the tyre to be retreaded to thus generate a devulcanized adhesion surface underneath,

[0020] - a subsequent step of applying a new rubber layer on the devulcanized adhesion surface that has been prepared / obtained by the previous scraping step,

[0021] - a heating step of the tyre to thus bond the new rubber layer to said adhesion surface of the starting tyre to be retreaded,

[0022] - a step of definition of the pattern on the rubber layer applied in the previous step, by using a milling cutter or by using a heated mould which reproduces in negative the shape of the pattern to be defined, thus obtaining a retreaded tyre.

[0023] Other known processes for the retreading of tyres are described for example in 1020210023489 and BR9405160.

[0024] OBJECTS OF THE INVENTION

[0025] The object of the present invention is to propose a process for the retreading of tyres which allows to overcome, at least in part, the drawbacks of traditional solutions.

[0026] Another object is to propose a more efficient and functional process for the retreading of tyres.

[0027] Another object of the invention is to propose a process for the retreading of tyres which requires lower energy consumption.

[0028] Another object of the invention is to propose a process for the retreading of tyres that is highly eco-sustainable.

[0029] Another object of the invention is to propose a process for the retreading of tyres which reduces the quantity of rubber removed from the worn tyre and to be disposed of.

[0030] Another object of the invention is to propose a process for the retreading of tyres that allows to reduce the quantity of new rubber to be applied.

[0031] Another object of the invention is to propose a process that allows for obtaining a high quality tyre retreading. Another object of the invention is to propose a process for the retreading of tyres that is suitable for being inserted and / or implemented on an industrial level and in a highly automated manner.

[0032] Another object of the invention is to propose a process for the retreading of tyres that is an improvement and / or is alternative to traditional solutions.

[0033] Another object of the invention is to propose a process for the retreading of tyres that can be implemented simply, quickly and at low costs.

[0034] Another object of the invention is to propose a process with an alternative characterization, both in functional and implementation terms, compared to traditional ones.

[0035] SUMMARY OF THE INVENTION

[0036] All the objects mentioned herein, considered either individually or in any combination thereof, and others which will result from the following description are achieved, according to the invention, with a process according to one or more of the claims appended hereto.

[0037] In particular, the present invention relates to an improved process for the retreading of tyres, in particular of tyres having the corresponding tread which is worn following their use, said tread presenting on the surface a series of grooves defining a corresponding pattern, said process being characterised in that it comprises in sequence the following steps:

[0038] - a step of high pressure water jet application (so-called “water jet”) on the external surface of the worn tread of the tyre to be retreaded in order to remove an external layer of said worn tread and thus generate an underlying adhesion surface which is devulcanized,

[0039] - a step of applying a new layer of a rubber-based compound on the devulcanized adhesion surface,

[0040] - a vulcanization step of the tyre, with the new layer already applied, inside a mould that includes a negative pattern, with reliefs and cavities, which reproduces in negative the shape of the pattern to be defined.

[0041] In particular, the present invention relates to an improved process for the retreading of tyres, in particular of tyres having the corresponding tread which is worn following their use, said tread presenting on the surface a series of grooves defining a corresponding pattern, said process being characterised in that it comprises in sequence the following steps:

[0042] - a step of high pressure water jet application (so-called “water jet”) on the external surface of the worn tread of the tyre to be retreaded in order to remove an external layer of said worn tread and thus generate an underlying adhesion surface which is devulcanized,

[0043] - a step of injecting a rubber-based compound into a mould, wherein the tyre having said underlying devulcanized adhesion surface has been previously positioned, to thus define on the devulcanized adhesion surface a new layer with said rubberbased compound, and wherein said mould comprises a negative pattern, with reliefs and cavities, which reproduces in negative the shape of the pattern to be defined on the new layer,

[0044] - a vulcanization step of the tyre with the new layer, preferably by heating inside said mould.

[0045] Conveniently, the tyre is inserted into the mould before said injection step.

[0046] In particular, the present invention relates to an improved process for the retreading of tyres, in particular of tyres having the corresponding tread which is worn following their use, said tread presenting on the surface a series of grooves defining a corresponding pattern, said process being characterised in that it comprises the following steps:

[0047] - a high pressure water jet (so-called “water jet”) is applied to the external surface of the worn tread to remove an outer layer of said worn tread and thus generate an underlying adhesion surface which is devulcanized,

[0048] - on the devulcanized adhesion surface it is defined a new layer with a rubber-based compound that contains and is obtained using rubber-based powder which, in turn, has been obtained by applying a high-pressure water jet to the rubber layer of the tread and / or sidewall of at least one tyre,

[0049] - the tyre with the new layer is vulcanized, and in particular is heated.

[0050] Preferably, the process according to the invention also comprises a preliminary step of engraving at least one existing groove and / or at least one new / additional groove on said tread of the worn tyre to be retreaded.

[0051] Preferably, this engraving step is carried out by applying a high-pressure water jet and / or by milling or other equivalent processing.

[0052] Preferably, said step of engraving at least one existing groove and / or at least one new / additional groove is carried out before said step of high pressure water jet application to the external surface of the worn tread of the tyre to be retreaded in order to thus remove an external layer of said worn tread and thus generate an underlying adhesion surface which is devulcanized.

[0053] Preferably, said step of engraving at least one existing groove and / or at least one new / additional groove is carried out simultaneously with said step of high pressure waterjet application to the external surface of the worn tread of the tyre to be retreaded in order to thus remove an external layer of said worn tread and thus generate an underlying adhesion surface which is devulcanized.

[0054] Preferably, this step of engraving at least one groove, already existing in the pattern of the worn tyre to be retreaded or new (i.e. not present in the pattern of the worn tyre to be retreaded), is carried out by means of a high-pressure water jet (particularly in the case of truck tyres) or by milling (particularly in the case of OTR tyres) or equivalent processing (for example by cutting with a hot knife).

[0055] Ideally, in a possible embodiment, said step of engraving at least one existing groove and / or at least one new / additional groove on said tread is carried out by means of a high-pressure water jet and, in particular, is carried out by the same machine and substantially simultaneously with said step wherein, by means of the high-pressure waterjet (so-called “waterjet”), an external layer of said worn tread is removed and the underlying devulcanized adhesion surface is generated.

[0056] Preferably, this engraving step is configured to excavate and / or widen an existing groove on the tread of the worn tyre to be retreaded.

[0057] Preferably, said engraving step is configured to obtain on said tread of the worn tyre to be retreaded at least one new groove that is not provided on the tread of the worn tyre to be retreaded.

[0058] Conveniently, said at least one existing and / or new groove is engraved based on the negative pattern of the mold.

[0059] Preferably, the step of high pressure waterjet application (so-called “waterjet”) to the outer surface of the worn tread, which may have been previously engraved, of the tyre to be retreaded substantially comprises a water-scraping of the outer surface of the worn tread of the tyre.

[0060] Preferably, said step of applying a new layer involves applying a new layer of height substantially greater than the height / depth of said existing and / or new grooves that have been engraved.

[0061] Preferably, said new layer is applied / defined so as to completely fill said existing and / or new grooves that have been engraved.

[0062] Preferably, said new layer may be applied to the underlying devulcanized adhesion surface using an adhesive.

[0063] Preferably, the vulcanization step is carried out - at least in part - inside a mould that is heated.

[0064] Preferably, the reliefs of the negative pattern of said mould are configured to penetrate into said grooves, already existing and / or new, which have been engraved on said tread, causing the rubber-based compound to escape from said grooves, already existing and / or new, to enter and thus fill the cavities of the negative pattern of said mould (cf. fig. 8a).

[0065] Preferably, the process according to the invention may also involve to:

[0066] - perform and / or obtain a 2D or 3D scan of the tread of the worn tyre to be retreaded,

[0067] - compare the scan thus obtained with a pre-stored model of the mould pattern,

[0068] - determine, on the basis of this comparison, the quantity of rubber compound to be used to apply / define the new layer.

[0069] Advantageously, the quantity of rubber compound to be used for the new layer is determined by considering the depth of the grooves, already existing or new, and also considering the height of the reliefs of the mould pattern.

[0070] Preferably, the new layer of rubber-based compound, to be applied / defined on the devulcanized adhesion surface, contains and is obtained using rubber-based powder which, in turn, has been obtained by applying a high-pressure water jet to the rubber layer of the tread and / or sidewall of at least one tyre, and / or to the rubber layer of the tread and / or sidewall of the same worn tyre to be retreaded.

[0071] DETAILED DESCRIPTION OF THE FIGURES

[0072] The present invention is further clarified below in a preferred practical embodiment, reported for purely exemplifying and non-limiting purposes with reference to the attached drawings, wherein:

[0073] Figures 1 a - 1 e schematically show the sequence of steps involved in the retreading procedure according to the state of the art,

[0074] Figure 2a shows schematically the components of a tyre according to a radial section,

[0075] Figure 2b shows an enlarged detail of Fig. 2a,

[0076] Figure 3 shows an unworn tyre according to a radial section,

[0077] Figure 3a shows an enlarged detail of Fig. 3,

[0078] Figure 4 shows the worn tyre according to a radial section,

[0079] Figure 4a shows an enlarged detail of Fig. 4,

[0080] Figure 5a schematically shows a first step of the retreading process according to the invention wherein the grooves already present in the original pattern of the worn tyre to be retreaded are engraved,

[0081] Figure 5b schematically shows a variant of the first step of the retreading process according to the invention wherein additional / new grooves are engraved that were not present in the original pattern of the worn tyre to be retreaded, Figure 6 shows schematically the tyre of Fig. 5a or 5b after the step of high pressure waterjet application to generate the underlying vulcanised adhesion surface,

[0082] Figure 7 shows schematically the tyre of Fig. 6 after the application of a new layer of rubber-based compound,

[0083] Figure 8 shows schematically the tyre of Fig. 7 inside the heated mould,

[0084] Figure 8a shows an enlarged detail of the tyre in Fig. 8 at the insertion of the reliefs of the negative pattern of the mould inside the grooves of the tyre so as to cause the rubber to come out of said grooves, which thus fills the cavities, placed between the reliefs, of the negative pattern of the mould defining the corresponding blocks of the retreaded tyre.

[0085] DETAILED DESCRIPTION OF THE INVENTION AND OF SOME PREFERRED EMBODIMENTS

[0086] Preliminarily, as shown in figures 2a and 2b, it is specified that hereinafter by tread block 3 it is intended that portion of tread 2 defined between the grooves 10, and which protrudes towards the outside of the tyre 1 , and which, substantially, is the portion which grips the ground.

[0087] Furthermore, as shown in fig. 5b, the undertread or underlayer 8 is defined as the portion of the tyre 1 defined between the bottom 13 of the grooves 10 and the underlying layers 11 containing the metal (steel) cloths / belts provided above the carcass 9 of the tyre. Furthermore, the depth / height 7 of the grooves 10 is conveniently defined by the distance between the outermost surface 15 of the tread (i.e. the surface of the blocks 3) and the internal bottom 13 of said grooves 10.

[0088] Conveniently, in a worn tyre (cf. Fig. 4 and 4a), the tread 2 is worn and has a lower height than that of a non-worn tyre (cf. 3 and 3a); in particular, the depth / height 7 of the grooves 10 (i.e. the distance between the outermost surface of the tread and the bottom 13 of the grooves) is lower in a worn tyre (cf. Fig. 4 and 4a) than in a nonworn tyre (cf. 3 and 3a).

[0089] Conveniently, the tyre 1 to be retreaded can be, for example, a car tyre, a truck tyre or an OTR type.

[0090] As shown in the figures, the present invention relates to an improved process for the retreading of tyres 1 , in particular of tyres having the corresponding tread 2 which is worn following their use, and wherein said tread 2 has a series of grooves 10 on its surface defining a corresponding pattern. Said process comprises the following steps in sequence: - a step of high pressure water jet application (so-called “water jet”) on the external surface 2' of the worn tread 2, which may have been previously engraved, of the tyre 1 to be retreaded in order to thus remove an external layer of said worn tread 2 and thus generate an underlying adhesion surface 6 which is devulcanized (cf. Fig. 6),

[0091] - a step of applying a new layer 4 of a rubber-based compound on the devulcanized adhesion surface 6 (cf. Fig. 7),

[0092] - a vulcanization step of the tyre, with the new layer 4 already applied, inside a mould 16 which includes a negative pattern, with reliefs 17 and cavities 19, which reproduces in negative the shape of the pattern to be defined (cf. Fig. 8).

[0093] Preferably, the process may also comprise a preliminary step of engraving at least one existing groove 10 (cf. Fig. 5a) and / or engraving at least one new / additional groove 10' (cf. Fig. 5b) on said tread 2 of the worn tyre to be retreaded.

[0094] In a possible embodiment, the process according to the invention may not envisage the step of engraving the already existing 10 and / or new 10' grooves on the tread 2 of the worn tyre to be retreaded. In particular, the step of engraving the grooves is not envisaged / necessary in the case of extremely worn tyres that substantially no longer have the pattern (i.e. they are substantially smooth) or in the case of a carcass with a diameter smaller than that of the mould; more specifically, in the latter case the old pattern of the worn tyre to be retreaded is completely covered / submerged by the new layer 4 of rubber-based compound and the new pattern to be defined is completely above it (i.e. the bottom of the groove of the new pattern is radially more external than the external diameter of the carcass).

[0095] Preferably, the reliefs 17 of the negative pattern of said mould are configured to penetrate said already existing 10 and / or new 10' grooves, which have been engraved on said tread 2, causing the rubber-based compound to escape from said existing and / or new grooves to enter and thus fill the cavities of the negative pattern of said mould (cf. Fig. 8a).

[0096] In a possible embodiment, the present invention relates to an improved process for the retreading of tyres 1 , in particular of tyres having the corresponding tread 2 which is worn following their use, said tread 2 presenting on its surface a series of grooves 10 defining a corresponding pattern, said process being characterised in that it comprises the following steps in sequence:

[0097] - a step of high pressure water jet application (so-called “water jet”) on the external surface 2' of the previously engraved worn tread 2 of the tyre 1 to be retreaded to thus remove an external layer of said worn tread 2 and thus generate an underlying adhesion surface 6 which is devulcanized,

[0098] - the thus treated tyre is positioned inside a mould 16,

[0099] - a step of injecting a rubber-based compound into said mould 16, wherein the tyre having said underlying devulcanized adhesion surface 6 has been previously positioned, to thus define on the devulcanized adhesion surface 6 a new layer 4 with said rubber-based compound, and wherein said mould 16 comprises a negative pattern, with reliefs and cavities, which reproduces in negative the shape of the pattern to be defined on the new layer 4,

[0100] - a vulcanization step, in particular by heating, inside said mould 16 of the tyre with the new layer 4.

[0101] In a possible embodiment, the present invention relates to an improved process for the retreading of tyres 1 , in particular of tyres having the corresponding tread 2 which is worn following their use, said tread 2 presenting on its surface a series of grooves 10 defining a corresponding pattern, said process being characterised in that it comprises the following steps:

[0102] - a high pressure water jet (so-called “water jet”) is applied to the external surface 2' of the worn tread 2 to thus remove an external layer of said worn tread 2 and thus generate an underlying adhesion surface 6 which is devulcanized,

[0103] - it is defined on the devulcanized adhesion surface 6 a new layer 4 with a rubberbased compound which contains and is obtained using rubber-based powder which, in turn, has been obtained by applying a high-pressure water jet to the rubber layer of the tread and / or sidewall of at least one tyre,

[0104] - the tyre with the new layer 4 is vulcanized, and in particular is heated.

[0105] Conveniently, the adhesion surface 6 belongs to and is defined by the material of the original (starting) tyre 1 , a tyre that is worn and needs to be retreaded.

[0106] Conveniently, the quantity of the applied new layer 4 of rubber-based compound is such that the assembly defined by the worn tyre 1 , after the high pressure water application step, and by said new layer 4, has a thickness substantially corresponding to or greater than that of the unworn tyre, i.e. just produced and before any use thereof.

[0107] Conveniently, the mould 16 comprises a negative pattern with reliefs 17 and cavities 19; the quantity of the applied new layer 4 of rubber-based compound is such as to fill the cavities of the negative pattern of the mould when the reliefs of said negative pattern of the same mould come into contact with the bottom 13 of the grooves, or in any case when they are inserted entirely or mostly into the grooves that have been engraved on the tread of the worn tyre to be retreaded.

[0108] Advantageously, according to the invention, the new rubber compound layer 4 that is applied corresponds to approximately 5 - 30%, preferably approximately 5-20%, of the weight of the unworn tyre and this differs from the state of the art processes wherein the retreading with the new layer 4 of rubber-based compound replaces approximately 30-35% of the weight of the tyre.

[0109] According to the invention, the step of high pressure water jet application involves acting on the external surface 2' of the worn tread in such a way as to remove from the latter a layer lower than the bottom 13 of the grooves 10 defining the pattern of said tread 2.

[0110] Advantageously, in the process according to the invention, the step of high pressure water jet application involves removing - preferably uniformly, over the entire external surface of the tyre 1 to be retreaded - a layer of the worn tread 2 that is below the thickness / height of the grooves 10 of the worn tread 2, without ever damaging the underlayer / undertread 8 of the tyre 1. In more detail, in essence, in the process according to the invention, one acts only on the residual thickness / height of the blocks 3 of the worn tread 2, without acting on the part of the underlayer / undertread 8.

[0111] Preferably, the step of high pressure water jet application involves acting on the external surface 2' of the worn tread 2 in such a way as to remove from the latter a layer of rubber 5 that has a height equal to or less than 5 mm so that an underlying layer remains which belongs to the tyre 1 to be retreaded. Preferably, the step of high pressure water jet application involves the removal of a layer of rubber 5 of the worn tread 2 that can vary from approximately 0.01 to approximately 5 mm, more preferably approximately 0.5 - 5 mm.

[0112] Preferably, the step of high-pressure water jet application may involve the removal of a rubber layer 5 of the worn tread 2 which is approximately 1 - 2 mm.

[0113] Conveniently, as mentioned, the step of high pressure water jet application is configured to generate an underlying adhesion surface 6 which is devulcanized and on which it is then possible to adhere a new layer 4 of rubber-based compound, thus defining a retreading layer.

[0114] Conveniently, the step of high pressure water jet application causes a devulcanization process , that is, the breaking of the hydrogen bonds present between the sulphur atoms and the hydrogen atoms comprised in the polymers, or of the carbon bonds between sulphur and carbon, all of which are elements present in the tyre compound. In particular, the step of high pressure water jet application (in addition to devulcanizing the removed layer 5) causes the devulcanization of the adhesion surface 6, thus preparing it to be bonded with a new layer of rubber-based compound 4 which is deposited / applied over it.

[0115] In particular, appropriately, the devulcanization affects the adhesion surface 6 on which the new layer 4 of rubber-based compound is then intended to be applied. In more detail, this allows for better interpenetration between the new layer 4 and the adhesion surface 6 prepared by applying a high-pressure water jet. In particular, once the new layer 4 has been applied to the adhesion surface 6, a subsequent vulcanization process is carried out, thus obtaining perfect homogenization of the layer 4 on the surface 6 of the starting tyre 1 , and therefore high mechanical properties, since the tyre thus retreaded is substantially identical at a molecular level to an original tyre.

[0116] Preferably, as mentioned, the devulcanization process is carried out by applying a high-pressure water jet, i.e. by spraying a high-pressure water jet onto the worn tread 2 of the tyre to be retreaded 1 .

[0117] Preferably, in a possible embodiment, the process and apparatus necessary to implement said step are for example those described in patent IT2015000013614, which is intended to be incorporated herein by reference in its entirety.

[0118] This process is preferably carried out by means of a lance terminating in a nozzle, and configured to spray liquids under pressure, for example at a pressure between 1500 bar and 3000 bar, and preferably of about 2200 bar. Conveniently, the nozzle may have a diameter between 0.25 mm and 0.80 mm, and a jet aperture between 30° and 60°. Conveniently, the nozzle may be kept at a distance between about 10 mm and 50 mm from the tyre to be treated.

[0119] Conveniently, following the step of high pressure waterjet application, a drying step can be provided, in order to remove the water remaining at the adhesion surface 6 of the tyre 1. Advantageously, this drying can be carried out by heating by radiation; conveniently, in this way, the black colour of the tyre is exploited, and therefore its predisposition to absorb a large part of the visible light spectrum.

[0120] Conveniently, the devulcanization process carried out by applying a high- pressure waterjet avoids the use of chemical substances that are usually polluting and harmful to workers and / or the environment, as well as requiring specific disposal, with a consequent increase in costs. Furthermore, the devulcanization process carried out by applying a high-pressure water jet is faster than the devulcanization carried out by using chemical substances because, in the latter case, the process is kinetically slow, and furthermore the substance must be able to penetrate inside the rubber, soaking it, with a consequent further increase in times.

[0121] Conveniently, the step of high pressure water jet application may allow the removal of a particularly thin layer (about 0.1 mm - 5 mm, preferably about 1 - 2 mm) of the worn tread 2 and is lower than the bottom 13 of the grooves 10 defining the pattern. Advantageously, this allows the entire original underlayer / undertread 8 of the tyre to be maintained, thus obtaining a high quality of the retreaded tyre 1' and at the same time a great saving of materials and costs. Advantageously, in essence, in the process according to the invention, the original underlayer / undertread 8 of the tyre 1 is never affected / removed and this allows the resistance characteristics of the carcass 9 to be left unchanged, which does not happen in the traditional process where the removal of the underlayer / undertread 8 causes a weakening of the carcass and the new layer of added rubber does not help to restore the initial mechanical resistance characteristics of the tyre because it is substantially a non-continuous added body.

[0122] Furthermore, in the process according to the invention, the rubber removed from the tyre 1 is reduced, thus making the process more economical and also reducing the quantity of rubber to be disposed of, with a consequent lower environmental impact. Furthermore, in this way, the initial removal step has a shorter duration, thus allowing the retreading process to be speeded up and a further reduction in costs to be achieved.

[0123] Conveniently, the devulcanization of the adhesion surface 6 obtained by applying a high-pressure water jet may allow to avoid the use of glue, since - as mentioned - the subsequent vulcanization process allows the creation of molecular bonds between the polymers that make up the new layer 4 of rubber-based compound and the polymers already present within the adhesion surface 6 of the tyre 1 to be retreaded. In essence, in this way it is possible to obtain a substantial continuity of the material that makes up the retreaded tyre 1 ', guaranteeing perfect resistance even in the absence of mastic or other glues.

[0124] As mentioned, the process according to the invention comprises a step wherein, by means of moulding, a pattern comprising grooves 10' corresponding to those of the pattern of the original tyre or even totally / partially different is obtained / defined on the applied new layer 4 of rubber-based compound.

[0125] Advantageously, before and / or during said pattern moulding step, the tyre to be retreaded 1 is heated to a temperature above 100°C, and preferably around 150°C, or in any case to a temperature suitable to allow the vulcanisation of the new layer 4 of rubber-based compound which has been applied to the adhesion layer 6 of the tyre to be retreaded 1 . Conveniently, the moulding procedure involves the use of a mould 16 that can be placed inside a press and / or the use of a rotating roller mould placed in a lathe. Conveniently, the mould 16 reproduces in negative the shape of the pattern to be defined on the applied new layer 4 of rubber-based compound. In particular, the mould 16 has internally a plurality of reliefs 17 and / or cavities 19 configured (i.e. sized and arranged) so as to define the negative of the pattern to be obtained on the new rubber layer 4 applied on the adhesion surface 6 prepared on the tyre 1 to be retreaded. In more detail, conveniently, the reliefs 17 of the mould 16 push the rubber of the new layer 4 to fill the cavities 19 present in the same mould 16.

[0126] Advantageously, during the step of high pressure waterjet application, a layer of the original and worn tread 2 of the tyre to be retreaded 1 is removed so that, when the tyre 1 thus treated is inserted inside the closed mould 16, the reliefs 17 of said mould substantially come into contact with the adhesion surface 6 obtained at the end of the step of high pressure water jet application.

[0127] Advantageously, by means of the engraving step, grooves 10 are dug and / or obtained on the original and worn tread 2 of the tyre to be retreaded 1 so that, when the tyre 1 thus treated is inserted inside the closed mould 16, the reliefs 17 of said mould penetrate inside the grooves 10, possibly coming into contact with or reaching the proximity of the bottom 13 of said grooves 10.

[0128] Conveniently, the mould 16 may be complete / whole and therefore comprises a plurality of modules that cover the entire external surface of the tyre 1 to be retreaded and, in particular, the entire surface of the applied new layer 4 of rubber-based compound.

[0129] Alternatively, the mould 16 may comprise a single module which is configured to transfer the pattern only onto a portion (sector) of the new rubber compound layer 4 of the tyre 1 , which is rotated, so that the module can act successively on different portions (sectors) of the tyre 1 and thus transfer the corresponding pattern onto the entire layer 4 of rubber-based compound; or the mould may consist of a rotoid configured to transfer the pattern onto the applied new layer 4 of the tyre 1 which is rotated synchronously with said rotoid-shaped mould which thus transfers the pattern onto the entire layer 4.

[0130] Advantageously, the moulding procedure can be carried out at high heat, that is, the mould 16 is heated (preferably to a temperature above 100°C, and even more preferably about 150°C) in order to vulcanize the new layer 4 of rubber-based compound during the moulding procedure. In essence, the rubber is vulcanized by heating the tyre 1 with the applied new layer 4 of rubber-based compound during the moulding of the latter.

[0131] Conveniently, in a possible embodiment, following the moulding step, a pattern finishing step may be provided by milling, or equivalent mechanical processing (for example by means of a lathe). Preferably, the milling finishing step may be implemented by using a milling cutter, which is preferably moved automatically. Conveniently, the milling cutter may be installed on an industrial robotic arm, which allows it to be moved along and / or in contact with the new layer of rubber-based compound 4 exiting the mould 16.

[0132] Conveniently, the fact that - following the devulcanization process (carried out during the step of high pressure water jet application) - a vulcanisation process is carried out allows for continuity of the intermolecular bonds to be obtained between the polymers of the adhesion surface 6 of the original tyre 1 to be retreaded and the polymers that make up the new rubber layer 4 that is applied.

[0133] In this way, therefore, the retreaded tyre 1' according to the invention has a new tread with the desired pattern and with perfect adhesion between the new retreaded layer 4 and the underlying adhesion surface 6 of the original (starting) tyre.

[0134] Conveniently, the retreaded tyre 1' according to the invention has a new tread thickness / height that may substantially correspond (or even be slightly greater) to that of the original, unworn tyre 1 (i.e. corresponding to that of the tyre just produced and before its use).

[0135] A possible embodiment

[0136] Advantageously, in a possible embodiment, the procedure comprises the following steps:

[0137] - the residual tread 2 of the worn tyre 1 to be rebuilt is subjected to an engraving step to carve grooves into the tread itself corresponding to a pattern that is the same or completely different from that present on the original and worn tread 2,

[0138] - a step of high pressure water jet application on the external surface 2' of the tread 2 of the worn tyre 1 to be retreaded to thus generate an underlying adhesion surface 6; conveniently, in this way, the adhesion surface 6 is also devulcanized,

[0139] - a step of applying a new layer 4 of a rubber-based compound on the devulcanized adhesion surface 6 obtained / prepared by the previous step,

[0140] - a pattern definition step on the layer 4 of rubber-based compound, which was applied in the previous step, by hot moulding in order to vulcanize the applied new layer 4 of rubber-based compound; conveniently, the mould 16 is configured to imprint the desired pattern on the applied layer 4 of rubber-based compound. Preferably, during the aforementioned engraving step, the grooves 10 of the residual tread 2 are appropriately excavated or repatterned, for example by machining with a milling cutter, preferably a robotic milling cutter. Advantageously, this engraving step is necessary to allow - during the pattern definition step - an adequate insertion and coupling of the tyre 1 within the mould 16.

[0141] Conveniently, as mentioned, the engraving step involves obtaining on the residual tread 2 grooves 10 of a pattern (which is defined by a specific arrangement, shape and / or depth of a plurality of grooves 10) which is equal to that of the tread of the original and worn tyre 1 (cf. Fig. 5a). Alternatively, the pattern to be obtained on the residual tread 2 may be different from that of the original and worn tyre 1 (cf. Fig. 5b) and this, advantageously, allows a tyre to be rebuilt by modifying its intended use, such as for example the terrain or the type of vehicle for which it is intended.

[0142] Conveniently, the application of a high-pressure waterjet (so-called “waterjet”) on the external surface 2' of the worn tread 2, in particular causes the devulcanization of the adhesion surface 6 and, in particular, the rubber of said surface (and belonging to the tread of the original tyre) is prepared to be bonded to a new layer 4 of rubberbased compound. Preferably, the application of a high-pressure water jet (so-called “water jet”) on the external surface 2' of the worn tread 2, comprises a water scraping that acts on the external surface 2' in such a way as to remove a minimal part of the residual tread 2 (preferably a maximum of 2 mm), thus maintaining - in addition to the underlayer / undertread 8 of the original tyre 1 - also a layer of the tread 2 of said original tyre. Conveniently, the new layer 4 of rubber-based compound may be deposited / applied locally around the grooves 10 present on the adhesion surface 6 obtained at the end of the step of high-pressure water jet application.

[0143] Conveniently, the pattern definition step involves inserting the tyre 1 (in which the new layer 4 of rubber-based compound has been applied to the underlying adhesion layer 6) into a mould 16 which is placed in a heated press and which reproduces in negative the shape of the pattern to be defined on the applied new layer 4 of rubberbased compound.

[0144] Conveniently, the mould 16 can have a plurality of reliefs 17 configured (i.e. sized and arranged) in such a way as to define the negative of the pattern that was obtained, at least in part, on the residual tread 2 during the initial engraving step.

[0145] In particular, the mould 16 used during the pattern definition step has internal reliefs 17 intended to fit into the grooves 10' drawn during the initial engraving step.

[0146] Conveniently, when positioning and inserting the tyre 1 into the mould 16, it is necessary that the reliefs 17 of the internal surface of the mould are aligned with the grooves 10' of the adhesion surface 6 of the tyre 1 so that, when the mould 16 closes, the reliefs 17 of the latter do not come into contact with the blocks 3 of said adhesion surface. Advantageously, this alignment can be obtained by accurate manual positioning of the tyre 1 into the mould 16, or by means of automatic positioning systems, for example by laser marking.

[0147] Advantageously, this second form of implementation of the process according to the invention allows for the use of a smaller quantity of rubber (approximately 25- 50% less than traditional solutions) in the step of applying the new layer of rubberbased compound 4.

[0148] Preferably, after moulding, the pattern definition step may also include a finishing operation during which, for example, the grooves 10' of the pattern are further refined using a milling cutter, a lathe or equivalent machines.

[0149] Powder

[0150] Conveniently, by applying a high-pressure water jet to the vulcanized rubber layer of a tyre tread and / or tyre sidewall, a rubber-based powder is obtained.

[0151] Advantageously, the process according to the invention provides for reusing for the retreading of the tyre the powder that is obtained from the step of high pressure water jet application on the layer of vulcanized rubber that constitutes the tread of a tyre and / or the sidewall of a tyre.

[0152] Preferably, the powder obtained by applying a high-pressure water jet to the rubber layer of the tyre comprises a plurality of granules of irregular shape. Advantageously, this allows to increase the contact and bonding surface with the other components within a rubber-based compound. Conveniently, the granules of the powder do not have a spherical shape.

[0153] Preferably, the powder obtained by applying a high-pressure water jet to the rubber layer of the tyre comprises fragmented granules of various irregular shapes.

[0154] Preferably, the powder obtained by applying a high-pressure water jet to the rubber layer of the tyre comprises granules that are pedunculated and, in particular, that have on their surface a plurality of peduncles (i.e. protuberances or projections of elongated shape). Conveniently, the powder granules do not have a smooth surface.

[0155] Preferably, the powder obtained by applying a high-pressure water jet to the rubber layer of the tyre comprises granules and is devulcanized.

[0156] Preferably, the powder obtained by applying a high-pressure water jet to the rubber layer of the tyre comprises granules that are not obtained and treated by a micronization process or other equivalent mechanical grinding or abrasion treatments. Preferably, the powder obtained by applying a high-pressure water jet to the rubber layer of the tyre comprises granules with a devulcanized surface greater than 80%. More preferably, the powder comprises granules with a devulcanized surface greater than 95%. Ideally, the powder comprises granules with a completely devulcanized surface.

[0157] Preferably, the powder obtained by applying a high-pressure water jet to the rubber layer of the tyre comprises granules having dimensions less than about 1 mm. Preferably, the rubber-based powder comprises granules having dimensions predominantly of about 0.01 - 0.6 mm, more preferably of about 0.1 - 0.6 mm.

[0158] Preferably, the powder obtained by applying a high-pressure water jet to the rubber layer of the tyre comprises granules that are porous and / or spongy.

[0159] Preferably, the powder obtained by applying a high-pressure water jet to the rubber layer of the tyre comprises granules that are soft to the touch.

[0160] Preferably, the powder obtained by applying a high-pressure water jet to the rubber layer of the tyre comprises granules of amorphous structure.

[0161] Rubber-based compound

[0162] The rubber-based compound which is applied or injected to define the new layer 4 on the devulcanized adhesion surface 6 contains said powder, as described above in its essential characteristics and possibly in one or more optional and preferential characteristics.

[0163] The rubber-based compound which is applied or injected to define the new layer 4 on the devulcanized adhesion surface 6 contains said powder, as described above in its essential characteristics and possibly in one or more optional and preferential characteristics, in an amount of approximately 1-60%, more preferably approximately 5-30% of the total weight of the compound.

[0164] Ideally, in one possible embodiment, the rubber-based compound of / for the new layer 4 contains said powder in an amount of approximately 10 - 20% of the total weight of the compound.

[0165] Appropriately, the rubber-based compound of / for the new layer 4 also includes components / ingredients that are intended for the production of a conventional tyre. In particular, the rubber-based compound of the new layer 4 includes, in addition to said powder, also natural rubber, synthetic elastomers (such as SBR or BR), reinforcing agents (such as carbon black and / or silica), vulcanizing agents (e.g. sulphur) and other additives or secondary ingredients (e.g. stabilizers, antioxidants, plasticizing oils and other ingredients that may be added to improve specific properties of the tyre). Preferably, within the rubber-based compound of the new layer 4, the powder is mixed together with the other components / ingredients.

[0166] The rubber-based compound of / forthe new layer 4 is particularly advantageous as it has mechanical characteristics - for example in terms of hardness, elasticity (“rebound”), resistance to tear propagation, density, abrasion, tensile strength, elongation at break, 100% modulus and 300% modulus - which are substantially corresponding to those of the rubber-based compound without said powder.

[0167] Process for obtaining the powder for the rubber-based compound for the new layer 4

[0168] Preferably, the rubber-based compound powder of / for the new layer 4 is obtained by removing the vulcanized rubber of the tread and / or sidewall of a tyre, preferably out of commission, by means of a high-pressure waterjet (i.e. the so-called “water jet”). More in detail, the process involves sending at least one high-pressure water jet against the rubber layer of a tyre, preferably an out of commission tyre.

[0169] Advantageously, the high pressure jet allows the rubber layer to be crushed / removed from the steel plies of the tyres (also cleaning said plies), thus obtaining the powder granules, and also causes the devulcanization of said granules.

[0170] Preferably, the water jet is delivered at a pressure of approximately 1500 - 3500 bar, more preferably approximately 1800 - 2800 bar.

[0171] The water jet emerges from a delivery section of a head that rotates on itself and, preferably, rotates around the exit axis of the high-pressure waterjet.

[0172] Preferably, the rotation speed of said rotating head on itself is preferably between 300 revolutions per minute (hereinafter rpm) and 3000 rpm, for example approximately 800 rpm.

[0173] Preferably, the speed of advancement of the rotating head relative to the surface of the rubber layer to be devulcanized (or vice versa) is approximately 1 - 20 cm / second.

[0174] Preferably, the distance between the point of delivery of the water jet and the surface of the rubber layer to be devulcanized is approximately 10 - 40 mm.

[0175] Appropriately, the water jet / flow is substantially flared in shape (conical or truncated conical). Appropriately, the water jet / flow is substantially aligned to the normal N to the outermost surface of the rubber portion to be worked.

[0176] Preferably, the opening angle of the substantially flared shaped water jet is approximately 20 - 30°.

[0177] Advantageously, in this way, the water jet causes a scraping effect similar to that of a rotating excavation tip. Conveniently, in this way, the waterjet digs, in the rubber portion and at / under the impact zone, a groove with a substantially flared crater shape (i.e. substantially conical / pyramidal or truncated conical / truncated pyramidal).

[0178] In essence, when the water jet, which is applied with the process according to the invention and which comes out of the delivery section, impacts on the area of the rubber portion of the tyre, it removes from the latter (preferably disintegrates) a slice of rubber of a substantially conical / pyramidal shape (or truncated conical / truncated pyramidal), thus forming on the rubber portion of the same tyre a substantially flared crater-shaped groove.

[0179] Conveniently, the rubber-based compound of / for the new layer 4 contains powder which is obtained by removing with a high pressure water jet a layer of vulcanized rubber, comprising a compound with approximately 10 - 40% natural rubber, of a tyre.

[0180] According to a possible embodiment, the high-pressure water jet may contain ammonia, for example it may contain about 20 - 30% by weight of ammonia per 100 litres of water. Advantageously, this allows for a faster devulcanization.

[0181] According to a possible embodiment, the high pressure waterjet can be pulsed. More preferably, the water jet can be switched on / off (i.e. open / closed) and / or modulated with a frequency of about 1000 - 2000 cycles per minute. Advantageously, this increases the yield as it allows to obtain the powder faster, as well as allows to obtain more filamentous powder.

[0182] Preferably, before the said removal step by means of a high-pressure waterjet, no preliminary cleaning step is envisaged, and above all no rubbing step of the tyre is envisaged.

[0183] Preferably, the rubber compound powder applied or injected to define the new layer 4 is obtained by applying a high pressure water jet to a tyre.

[0184] Preferably, the powder thus obtained is dried, for example by means of a dryer. Preferably, the powder thus obtained is subjected to sieving.

[0185] Preferably, the powder obtained by applying a high-pressure waterjet to a tyre is first dried, for example by means of a dryer, and then mixed with other components / ingredients, thereby obtaining the rubber-based compound to be used for the new layer 4 to be applied / injected onto the devulcanized adhesion surface 6. More preferably, said other components / ingredients are components / ingredients intended for the production of a traditional tyre. In particular, said other components / ingredients comprise at least one of: natural rubber, synthetic elastomers (such as SBR or BR), reinforcing agents (such as carbon black and / or silica), vulcanizing agents (e.g. sulphur), other additives or secondary ingredients (e.g. stabilizers, antioxidants, plasticizing oils and other ingredients that may be added to improve specific properties of the tyre).

[0186] Preferably, the powder obtained by applying a high-pressure waterjet to a tyre is mixed in a mixer with said other components / ingredients, thus obtaining the rubberbased compound for the new layer 4.

[0187] Preferably, the new rubber compound layer 4 is applied to the devulcanized adhesion surface 6 of the worn tyre to be retreaded by means of an extruder.

[0188] Preferably, the new layer 4 of rubber-based compound us applied on the devulcanized adhesion surface 6 of the worn tyre to be retreaded by means of an extruder which is fluidically connected to a mixer so as to receive the rubber-based compound which is formed (at least for the most part) in said mixer; in particular, in said mixer the powder removed from the tyre by means of a high-pressure water jet is mixed with said other components / ingredients, to thus obtain the rubber-based compound for the new layer 4 to be applied.

[0189] Conveniently, the rubber-based compound powder that is applied or injected to define the new layer 4 can be obtained, by removal through the application of a high- pressure water jet, from the same worn tyre to be retreaded and / or from another tyre that is of the same type as the worn one to be retreaded and / or from another tyre that is of a different type than the worn one to be retreaded.

[0190] Advantageously, the rubber-based powder thus obtained is substantially ready to be used (i.e. it is “ready-to-use”) in order to obtain the rubber-based compound to be used to apply / define the new layer 4 and, in particular, does not require other mechanical processing processes, such as abrasion or micronization.

[0191] From what has been said it is clear that in all its implementations the process according to the invention is much more advantageous than traditional solutions because:

[0192] - it allows to reduce the quantity of removed rubber, thus reducing both the quantities of material to be disposed of and the quantity of waste produced,

[0193] - it allows to reduce the amount of new rubber to be applied,

[0194] - it allows for an optimal and more durable union of the new layer that is used and applied for the retreading,

[0195] - it allows for a significant reduction in energy consumption.

[0196] The present invention has been illustrated and described in a preferred embodiment, but it is understood that executive variations may be made to it in practice, without however departing from the scope of protection of the present patent for industrial invention.

Claims

C L A I M S1. Process for the retreading of tyres (1), in particular of tyres having the corresponding tread (2) which is worn following their use, said tread (2) presenting on the surface a series of grooves (10) defining a corresponding pattern, said process being characterised in that it comprises the following steps in sequence:- a step of high pressure waterjet application on the external surface (2') of the worn tread (2) of the tyre (1) to be retreaded in order to remove an external layer of said worn tread (2) and thus generate an underlying adhesion surface (6) which is devulcanized,- a step of applying a new layer (4) of a rubber-based compound on the devulcanized adhesion surface (6),- a vulcanization step of the tyre, with the new layer (4) already applied, inside a mould (16) which includes a negative pattern, and wherein said negative pattern of the mould (16) includes reliefs (17) and cavities (19), and reproduces in negative the shape of the pattern to be defined.

2. Process for the retreading of tyres (1), in particular of tyres having the corresponding tread (2) which is worn following their use, said tread (2) presenting on the surface a series of grooves (10) defining a corresponding pattern, said process being characterised in that it comprises the following steps in sequence:- a step of high pressure waterjet application on the external surface (2') of the worn tread (2) of the tyre (1) to be retreaded in order to remove an external layer of said worn tread (2) and thus generate an underlying adhesion surface (6) which is devulcanized,- a step of injection of a rubber-based compound into a mould (16), wherein the tyre having said underlying devulcanized adhesion surface (6) has been previously positioned, to thus define on the devulcanized adhesion surface (6) a new layer (4) with said rubber-based compound, and wherein said mould (16) comprises a negative pattern, and wherein said negative pattern of the mould (16) comprises reliefs and cavities, and reproduces in negative the shape of the pattern to be defined on the new layer (4),- a vulcanization step of the tyre with the new layer (4), preferably by heating inside said mould (16).

3. Process for the retreading of tyres (1), in particular of tyres having the corresponding tread (2) which is worn following their use, said tread (2) presenting on the surface a series of grooves (10) defining a corresponding pattern, and wherein:- a high pressure water jet (so-called “water jet”) is applied to the external surface (2') of the worn tread (2) to thus remove an external layer of said worn tread (2) and thus generate an underlying adhesion surface (6) which is devulcanized,- it is defined on the devulcanized adhesion surface (6) a new layer (4) with a rubberbased compound which contains and is obtained using rubber-based powder which, in turn, has been obtained by applying a high-pressure water jet to the rubber layer of the tread and / or sidewall of at least one tyre,- the tyre with the new layer (4) is vulcanised, and preferably heated.

4. Process according to one of the preceding claims, comprising a preliminary step of engraving at least one existing groove (10) and / or at least one new / additional groove (10') on said tread (2) of the worn tyre (1) to be retreaded, said engraving step being carried out by applying a high pressure water jet and / or by milling or other equivalent processing.

5. Process according to the preceding claim, wherein said step of engraving at least one existing groove (10) and / or at least one new / additional groove (10') is carried out before and / or during said step of high pressure waterjet application on the external surface (2') of the worn tread (2) of the tyre (1) to be retreaded to thus remove an external layer of said worn tread (2) and thus generate an underlying adhesion surface (6) which is devulcanized.

6. Process according to one or more of the preceding claims, wherein before said step of high pressure water jet application, an incision step is carried out to obtain on the residual tread (2) grooves (10) of a pattern that is the same as that of the tread of the original and worn tyre (1).

7. Process according to one or more of the preceding claims, wherein before said step of high pressure water jet application, an incision step is carried out to obtain on the residual tread (2) grooves (10) of a pattern that is different from that of the tread of the original and worn tyre (1).

8. Process according to one or more of the preceding claims, wherein an engraving step is provided which is configured:- to dig and / or widen an existing groove (10) on the tread (2) of the worn tyre to be retreaded, and / or- to obtain on said tread (2) of the worn tyre to be retreaded at least one new / additional groove (10') which is not provided on the tread (2) of the worn tyre to be retreaded.

9. Process according to one or more of the preceding claims, wherein said at least one existing (10) and / or new (10') groove is engraved based on the negative pattern of the mould.

10. Process according to one or more of the preceding claims, wherein:- said application step of a new layer (4) involves applying a new layer (4) of a height substantially greater than the height / depth (7) of grooves (10, 10'), already existing and / or new, present in said underlying devulcanized adhesion surface (6),- said new layer (4) is applied / defined so as to completely fill said grooves (10, 10').

11. Process according to one or more of the preceding claims, wherein the vulcanization step is carried out, at least in part, inside a mould (16) which is heated.

12. Process according to one or more of the preceding claims, wherein the reliefs (17) of the negative pattern of said mould (16) are configured to penetrate into said grooves, already existing (10) and / or new (10'), which have been engraved on said tread (2), thus causing the rubber-based compound to escape from said grooves, already existing (10) and / or new (10'), to enter and thus fill the cavities (19) of the negative pattern of said mould (16).

13. Process according to one or more of the preceding claims, wherein said new layer (4) is applied to the underlying devulcanized adhesion surface (6) by means of an adhesive.

14. Process according to one or more of the preceding claims, characterised in that:- it is obtained a 2D or 3D scan of the tread of the worn tyre to be retreaded (1),- the scan thus performed is compared with a pre-stored model of the pattern of the mould (16),- it is determined, on the basis of this comparison, the quantity of rubber compound to be used to apply / define the new layer (4).

15. Process according to one or more of the preceding claims, wherein said quantity of rubber compound to be used to apply / define the new layer (4) is determined by considering the depth of the grooves (10, 10'), already existing or new, and also considering the height of the reliefs (17) of the negative pattern of the mould (16).

16. Process according to one or more of the preceding claims, wherein the new layer (4) of rubber-based compound, to be applied / defined on the devulcanized adhesion surface (6), contains and is obtained using rubber-based powder which has in turn been obtained by applying a high-pressure water jet to the rubber layer of the tread and / or sidewall of at least one tyre.

17. Process according to one or more of the preceding claims, wherein the new layer (4) of rubber-based compound, to be applied / defined on the devulcanized adhesionsurface (6), contains and is obtained using rubber-based powder which has in turn been obtained by applying a high-pressure water jet on the rubber layer of the tread and / or sidewall of the same worn tyre to be retreaded.

18. Process according to one or more of the preceding claims, wherein the new layer (4) of rubber-based compound, to be applied / defined on the devulcanized adhesion surface (6), has a weight of approximately 5 - 30%, preferably approximately 5 - 20%, with respect to the weight of the corresponding unworn tyre.

19. Process according to one or more of the preceding claims, wherein the step of high pressure water jet application involves acting on the external surface (2') of the worn tread so as to remove from the tread a layer lower than the bottom (13) of the grooves (10) defining the pattern of said tread (2).

20. Process according to one or more of the preceding claims, wherein the step of high pressure water jet application involves the removal of a rubber layer (5) of the worn tread (2) which is approximately 0.01 - 5 mm, preferably approximately 1 - 2 mm.

21. Process according to one or more of the preceding claims, wherein during the step of high-pressure water jet application, a layer of the original and worn tread (2) of the tyre to be retreaded (1 ) is removed so that, when the tyre (1) thus treated is then inserted inside the closed mould (16), the reliefs (17) of said mould substantially come into contact with the adhesion surface (6) obtained at the end of the application step of said high-pressure water jet.

22. Process according to one or more of the preceding claims, wherein, following the moulding step, a finishing step of the pattern by milling or an equivalent process is provided.

23. Process according to one or more of the preceding claims, wherein the retreaded tyre (1 ') has a tread depth that is equal to or even greater than that of the original, unworn tyre (1 ).

24. Process for the retreading of tyres (1), in particular of tyres having the corresponding tread (2) which is worn following their use, wherein a rubber-based compound is used comprising powder which is obtained by removing the vulcanised rubber from the tread and / or sidewall of a tyre, preferably out of commission, by means of a high-pressure water jet.

25. Process according to the preceding claim wherein a new layer (4) of said rubberbased compound is applied to a worn tyre or said rubber-based compound is injected into a mould (16) wherein said worn tyre has been positioned.

26. Process according to one or more of the preceding claims, wherein said rubberbased compound contains said powder in an amount of about 1 - 60 % of the totalweight of the compound, preferably in an amount of about 10 - 20 % of the total weight of the compound.

27. Process according to one or more of the preceding claims, wherein said powder obtained by means of a high-pressure water jet is directly used to obtain said rubber- based compound, i.e. it is substantially ready-to-use.

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