Process and apparatus for manufacturing tyres

Abstract

A process for manufacturing tyres, comprising: depositing a first layer (21) made of elastomeric material on an outer surface of a building support (11); pre-vulcanising said first layer (21); depositing a plurality of tyre components around said first layer (21) carried by the building support (11), in order to form a green tyre (2); vulcanising the green tyre (2), in order to obtain a moulded and vulcanised tyre (2); wherein pre-vulcanising said first layer (21) comprises heating said first layer (21) carried by the building support (11), by an electromagnetic radiation irradiated from the exterior of the building support (11) towards an outer surface of said first layer (21).

Description

[0001] PROCESS AND APPARATUS FOR MANUFACTURING TYRES

[0002] The present invention relates to a process for manufacturing tyres for vehicle wheels. The invention also relates to an apparatus for manufacturing said tyres.

[0003] In the tyre production cycle, provision is made that - following a building process in which the various components of the tyre itself are made and assembled - a moulding and vulcanisation process is actuated, aimed to establish the structure of the tyre according to a desired geometric shape, normally characterised by a particular tread design.

[0004] For such purpose, the tyre is introduced in a vulcanisation mould normally comprising a pair of axially approachable sidewall plates, arranged for operating on the bead and on the sidewalls of the tyre, and at least one crown of sectors that are circumferentially distributed and radially approachable in order to operate at the tread band of the tyre. More particularly, the sidewall plates and the sectors are mutually movable between an open condition, in which they are spaced in order to allow the operation of loading the tyres being processed, and a closed condition in which they define a moulding cavity shaped according to the geometric configuration of the outer surfaces of the tyre to be obtained.

[0005] For the purpose of the description, by "geometric rotation axis" (not visible in the drawings) it is intended the axis of a building drum, corresponding to the rotation axis of the tyre in operating conditions. The terms "radial" and "axial" and the expressions "radially inner / outer" and "axially inner / outer" are used with reference to the radial direction of the tyre or of the building drum (i.e. to a direction perpendicular to the geometric rotation axis of the tyre or of the building drum) and to the axial direction of the tyre or of the building drum (i.e. to a direction parallel to the geometric rotation axis of the tyre or of the building drum).

[0006] In one of the most widespread moulding methods, provision is made such that within the green tyre closed in the moulding cavity, a vulcanisation membrane is inserted that is made of rubber inflated with water vapour and / or another fluid heated at high pressure. In this manner, the tyre is suitably pressed against the inner walls moulding cavity and consolidated in the geometric shape imposed thereto, following the crosslinking process that the elastomeric material constituting the tyre itself encounters. The crosslinking is attained due to the supply of heat transmitted by the vapour through the chamber, as well as by the walls of the mould.

[0007] Since the vulcanisation membrane is an element that is deformable by its nature, its use involves various drawbacks such as, for example, geometric imperfections of the tyre due to possible distortions sustained by the chamber itself, formation of burrs, particularly at the beads, due to undesired leaks of part of the elastomeric material in the initial instants of the vulcanisation process. The thermal inertia of the material itself, that constitutes the vulcanisation membrane, also represents an obstacle to transferring heat to the tyre by the fluid introduced in the chamber itself.

[0008] Also known are methods for vulcanisation in which the water vapour or another pressurised heating fluid is placed directly in contact with the inner surface of the tyre closed in the moulding cavity, in the absence of any vulcanisation membrane. For example, in the document WO 2004 / 045838, a green tyre arranged on the forming drum is subjected to a pressing against a heated toroidal support, in order to determine a partial vulcanisation of the innermost layer and of the beads of the tyre, before the same is pressed against the inner walls of the mould by introduction of the operating fluid in a diffusion interspace, created between the outer surface of the toroidal support and the inner surface of the tyre.

[0009] EP 0 976 534 A2 proposes a process in which the outer surface of a preheated toroidal support is sprinkled with a primer in aqueous solution. The heat transmitted by the heated drum determines the evaporation of the solvents and a prevulcanisation of the primer. A liner is subsequently applied on the pre-vulcanised primer, and then other structural components are applied thereon in order to form a green tyre. The tyre is then introduced in a vulcanisation mould together with the toroidal support.

[0010] WO 2005 / 042237 proposes building at least one carcass structure on a toroidal support and subjecting it to a first vulcanisation step, exerting pressure on the same carcass structure from the exterior towards the interior, while heat is generated at least on the surface of the toroidal support, obtaining a partially vulcanised carcass structure that is geometrically stable and suitable for completing the building of the tyre. Subsequently, a second vulcanisation step is executed, accompanied by the moulding of the tread band and of the sidewalls, in order to obtain a finished tyre. The first vulcanisation step is actuated by administering heat to the toroidal support, which transfers it via conduction to the inner surface of the tyre being processed, in contact with the same toroidal support.

[0011] EP 1645404 Al proposes heating a forming drum in order to obtain the activation of an adhesive arranged on the outer surface of the liner, before assembling the other structural components of the tyre and subjecting the latter to vulcanisation.

[0012] According to the Applicant, the use of the known methods makes it difficult to obtain a precise control of the level of prevulcanisation induced to the liner and / or other parts of the tyre. The Applicant has in fact observed that the heated forming drum, with its own thermal inertia, tends to prolong the transfer of the heat, even beyond the time strictly necessary for obtaining the desired pre-crosslinking level, during the process steps actuated for the purpose of assembly of the various components.

[0013] This circumstance can lead to undesired production discards, due to the phenomena of excessive crosslinking of the materials and, above all, to a difficult control of the process variables, for example in the case of sudden stops along the production line.

[0014] In addition, with the use of the known methods, the need to heat the forming drum involves undesired energy dispersions, with consequent increases in the production costs and negative effects for the environment.

[0015] The Applicant has perceived that by limiting the energy exchange to only the elastomeric materials that one wishes to pre-vulcanise, to the extent strictly indispensable for obtaining the desired crosslinking level, it is possible to attain greater control over the process variables. More precisely, the Applicant has found that by heating a first layer made of elastomeric material carried by a building support, by an electromagnetic radiation irradiated from the exterior of the building support directly towards an outer surface of said first layer, it is possible to concentrate the energy exchange only on the first layer, minimising the transfer of heat to the building support. A reduction of the masses, and hence in the corresponding thermal inertias, affected by the heat exchanges is therefore achieved, attaining an improved control of the energy supplies and of the heat administration times.

[0016] More particularly, the invention relates to a process for manufacturing tyres.

[0017] Preferably, provision is made for depositing a first layer made of elastomeric material on an outer surface of a building support. Preferably, provision is made for pre-vulcanising said first layer. Preferably, provision is made for depositing a plurality of tyre components around said first layer carried by the building support, in order to form a green tyre.

[0018] Preferably, provision is made for vulcanising the green tyre, in order to obtain a moulded and vulcanised tyre.

[0019] Preferably, pre-vulcanising said first layer comprises heating said first layer carried by the building support, by an electromagnetic radiation irradiated from the exterior of the building support towards an outer surface of said first layer.

[0020] In a further aspect, the invention relates to an apparatus for manufacturing tyres.

[0021] Preferably, provision is made for a building support.

[0022] Preferably, provision is made for an applicator configured for depositing a first layer made of elastomeric material on a forming surface shown externally on the building support.

[0023] Preferably, provision is made for a pre-vulcanisation area comprising at least one radiant group configured for heating the first layer carried by the building support, by an electromagnetic radiation irradiated from the exterior of the building support towards an outer surface of the first layer, so as to pre-vulcanise said first layer.

[0024] Preferably, provision is made for one or more application units configured for depositing a plurality of tyre components around said first layer carried by the building support, in order to form a green tyre.

[0025] Preferably, provision is made for a vulcanisation group configured for vulcanising the green tyre, so as to obtain a moulded and vulcanised tyre.

[0026] The Applicant deems that the use of a radiation irradiated directly against the first layer from the outside is the best way to attain an effective crosslinking, minimising the transfer of heat to the building support and / or other parts of the apparatus in contact with the first layer itself. The consequent reduction of the heat storage and of the process variants facilitates a sudden interruption of the molecular crosslinking process upon reaching the desired level, to the benefit of an efficient and precise prevulcanisation of said first layer.

[0027] In at least one convenient embodiment, the invention also comprises one or more following preferred characteristics.

[0028] Preferably, the pre-vulcanisation is actuated in a pressurised treatment chamber.

[0029] Preferably, during the pre-vulcanisation the treatment chamber is pressurised at an operating pressure greater than an atmospheric pressure.

[0030] Preferably, during the pre-vulcanisation, the treatment chamber is pressurised at an operating pressure equal to or greater than 150 KPa.

[0031] Preferably, said operating pressure is equally diffused outside and inside the building support.

[0032] Preferably, the operating pressure is applied by a pressurisation fluid introduced in a treatment chamber that contains the building support carrying said first layer.

[0033] Preferably, heating said first layer is attained by first radiant elements distributed around a geometric rotation axis of the building support.

[0034] Preferably, heating said first layer is attained by second radiant elements in side-by-side relationship with the building support in axially opposite positions.

[0035] Preferably, the first layer is heated to a temperature comprised between 170 °C and 260 °C.

[0036] Preferably, during the action of heating said first layer, the building support reaches a temperature comprised between 50 °C and 75 °C.

[0037] Preferably, during the action of heating said first layer, the building support rotates around said geometric rotation axis.

[0038] Preferably, the building support has a forming surface having toroidal shape.

[0039] Preferably, said forming surface is counter-shaped with respect to an inner surface of the green tyre.

[0040] Preferably, the pre-vulcanisation is interrupted before depositing said plurality of tyre components.

[0041] Preferably, the pre-vulcanisation is interrupted when said first layer has reached a crosslinking level comprised between 50% and 100%.

[0042] Preferably, the pre-vulcanisation is interrupted by cooling of said first layer and of the building support.

[0043] Preferably, the pre-vulcanisation is interrupted by adiabatic expansion of the pressurisation fluid.

[0044] Preferably, provision is also made for applying a coupling interface in radially outer position with respect to said first layer, before applying said tyre components.

[0045] Preferably, the coupling interface is applied after the pre- vulcanisation of said first layer.

[0046] Preferably, the pre-vulcanisation area also comprises a treatment chamber configured for containing the building support carrying the first layer.

[0047] Preferably, the pre-vulcanisation area also comprises pressurisation devices for introducing a pressurisation fluid in the treatment chamber.

[0048] Preferably, the pressurisation devices comprise a duct for feeding a pressurisation fluid.

[0049] Preferably, the pressurisation devices also comprise a discharge valve for evacuating the pressurisation fluid from the treatment chamber. The evacuation occurs in an extremely quick manner, so as to obtain an adiabatic expansion with consequent cooling of the treatment chamber, of the first layer and of the building support.

[0050] Preferably, said at least one radiant group comprises first radiant elements distributed around a geometric rotation axis of the building support, in a position radially distant from the forming surface. Preferably, the first radiant elements comprise one or more infrared ray lamps.

[0051] Preferably, the first radiant elements lie distant from the geometric rotation axis according to a measure greater than a maximum radius of the building support around the same geometric rotation axis.

[0052] Preferably, the first radiant elements are distributed according to a curved extension around the geometric rotation axis.

[0053] Preferably, said curved extension subtends an angle comprised between 45° and 90° around the geometric rotation axis.

[0054] Preferably, said at least one radiant group comprises second radiant elements in side-by-side relationship with the building support in axially opposite positions.

[0055] More preferably, said second radiant elements are movable at a variable distance from the surface to be irradiated.

[0056] Preferably, the second radiant elements comprise one or more infrared ray lamps.

[0057] Preferably, the second radiant elements are distributed according to a curved extension around the rotation axis.

[0058] More preferably, the second radiant elements can vary their distance from the building support as a function of the size of the building support, so as to maintain constant the radiant power per unit of surface area.

[0059] Preferably, the pre-vulcanisation area also comprises a motor configured for actuating the toroidal support in rotation around said rotation axis.

[0060] Preferably, the building support has a toroidal shape countershaped with respect to an inner surface of the tyre.

[0061] Preferably, provision is also made for a transfer line of the building support from the pre-vulcanisation area to said one or more application units.

[0062] Preferably, provision is also made for at least one additional applicator configured for applying a coupling interface to the exterior of the first layer.

[0063] Preferably, the additional applicator operates immediately downstream of the pre-vulcanisation area, and upstream of said one or more application units.

[0064] Preferably, provision is also made for at least one transfer unit configured for picking up the building support together with the green tyre from said one or more application units and loading it into a mould constituting part of the vulcanisation group.

[0065] Further characteristics and advantages will be clearer from the detailed description of preferred but not exclusive embodiments of a process and an apparatus for manufacturing tyres for vehicle wheels, in accordance with the present invention. Such description will be set forth hereinbelow with reference to the enclosed drawings, provided merely as a non-limiting example, in which:

[0066] - figure 1 schematically shows a lay-out of an apparatus for manufacturing tyres, in accordance with the present invention;

[0067] - figure 2 schematically shows the deposition of a first layer on a building support, executed in a pre-vulcanisation area of the apparatus of figure 1;

[0068] - figure 3 schematically shows the first layer during the execution of a pre-vulcanisation treatment in the pre- vulcanisation area of figure 1;

[0069] - figure 4 schematically shows the deposition of a second layer, executed in an intermediate area of the apparatus of figure 1; - figure 5 shows a graph obtainable from a laboratory test aimed to detect the crosslinking level of a test piece;

[0070] - figure 6 shows, in partial diameter section, a tyre obtainable according to the present invention.

[0071] With reference to the enclosed figures, reference number 1 overall indicates an apparatus for manufacturing tyres, in accordance with the present invention.

[0072] The present invention is aimed for manufacturing tyres for vehicle wheels, of the type better represented in figure 6 and overall indicated with 2.

[0073] The tyre 2 has a carcass structure 3 comprising at least one carcass ply 4 at whose interior a so-called impermeable liner 5 is placed. The carcass ply / plies 4 have respective end flaps 4a fixed at so-called beads 6 defined along radially inner edges of the tyre 2, at which the engagement between the tyre itself and a respective mounting rim (not depicted) usually occurs.

[0074] Around the carcass structure 3, a crown structure 7 is placed, comprising one or more belt layers 8, and a tread band 9 radially superimposed on the belt layer(s) 8.

[0075] The tyre 2 also comprises a pair of sidewalls 10, applied in laterally opposite positions on the carcass ply / plies 4 and extended in substantially radial direction, each from the corresponding bead 6 towards a corresponding axial edge of the tread band 9.

[0076] The building of the tyre 2 typically provides for the attainment of the carcass structure 3 by assembly of its tyre components (liner, beads 6, carcass ply / plies 4, etc.) on a building support In the illustrated example, the building support 11 is made in rigid and modular toroidal drum form, externally having a forming surface FS with toroidal shape, substantially coinciding with that of an inner surface IS of the tyre 2 being processed. More precisely, the forming surface FS is counter-shaped with respect to inner surface IS of the tyre 2 at the green state that is about to be built, before this is moulded and vulcanised.

[0077] During the building of the tyre 2, the building support 11 is adapted to be moved, e.g. by transfer units 12, each in the form of a robotic arm or another type, between a plurality of work areas 13, 14, 15, 16, in each of which one or more of the operations provided in the building cycle of the tyre itself are executed.

[0078] In figure 1 the following are illustrated: a pre-vulcanisation area or station 13, an intermediate area 14, a first building area 15 and a second building area 16, arranged in succession along a transfer line 17. The presence of two building areas 15, 16 is merely exemplifying, since their quantity can vary depending on the needs. Each building area 15, 16 can be equipped with one or more application units 18, configured for the application of the respective tyre components on the toroidal support and / or on the carcass structure 3 being processed. For example, the first building area 15 can be arranged in order to form the carcass structure 3 by application of the carcass ply / plies 4 and possible other tyre components.

[0079] The second building area 16 can in turn be configured for applying the crown structure 7 around the carcass structure 3, for example directly forming the respective tyre components (belt layers 8, tread band 9 etc.) directly on the carcass structure 3.

[0080] In a different non-illustrated embodiment, a building support can be employed in drum form, substantially cylindrical. The crown structure 7 can be made separately on an auxiliary drum in order to then be transferred to the carcass structure 3 and coupled therewith following a processing step in which the carcass structure 3, initially in cylindrical sleeve form, is toroidally shaped by axial approaching of the beads 6 and simultaneous introduction of fluid at its interior.

[0081] Downstream of the building areas 15, 16, the built green tyre 2 is adapted to be picked up by one of the transfer units 12, and transferred into a vulcanisation group 19 configured for vulcanising the green tyre 2, so as to obtain a moulded and vulcanised tyre 2.

[0082] In the pre-vulcanisation area 13, or in a possible auxiliary building area (not illustrated) upstream of the same, at least one applicator 20 operates which is configured for depositing a first layer 21 made of elastomeric material on an outer surface of the building support 11.

[0083] As is better schematised in figure 2, the first layer 21 can for example be formed by a continuous elongated element, attained with an elastomeric composition suitably for forming the liner of the tyre 2. For example, a compound with butyl base and / or containing talc can be used. Such continuous elongated element, approximately with width comprised between 5mm and 20mm and thickness between 0.5mm and 1.5mm, can be dispensed by the applicator 20 on the forming surface FS while the building support 11, e.g. supported by the respective transfer unit 12 in robotic arm form, is rotated around a geometric rotation axis thereof (not illustrated and parallel to a reference direction indicated with X in figures 2, 3 and 4) and suitably moved with respect to the applicator 20, such that the same continuous elongated element forms a plurality of consecutively approached turns, possibly at least partially superimposed, to cover the forming surface FS.

[0084] Alternatively, the first layer 21 can be obtained by circumferentially winding a strip of elastomeric material of suitable width around the geometric rotation axis of the building support in substantially cylindrical drum form. At the end of the winding, the opposite ends of the strip, cut to size, are mutually joined by a head-head joint.

[0085] Further preferred embodiments can provide for the dispensing of the first layer 21 in the form of liquid or semi-liquid solution, suitably distributed on the forming surface FS by a brush applicator 20, roller applicator, by spraying or by immersion of the forming surface FS in the liquid solution.

[0086] Once the application of the first layer 21 has terminated, the building support 11 is subjected to the action of at least one radiant group 22 operating in the pre-vulcanisation area 13 for heating the first layer 21 carried by the building support 11. As is better illustrated in figure 3, the radiant group 22 can comprise first radiant elements 23 distributed according to a curved extension around the geometric rotation axis of the building support 11, at a distance L from the same geometric axis greater than a maximum radius R. of the building support 11. Second radiant elements 24 can also be provided for, in side-by-side relationship with the building support 11 in axially opposite positions and, preferably, these too distributed according to a curved extension around the geometric rotation axis. The first radiant elements 23 and the possible second radiant elements 24, for example made in the form of infrared ray lamps, microwave radiators or radiators of another type, are therefore situated at a certain distance L from the forming surface FS, so as to administer energy to the first layer 21 by an electromagnetic radiation irradiated from the exterior of the building support 11 towards an outer surface of the first layer 21 itself. The energy supply transmitted by the radiant elements can therefore directly reach the first layer 21 without requiring conduction through the building support 11. The first layer 21 can thus be easily brought to a desired pre-vulcanisation temperature, e.g. comprised between 170°C and 260°C, minimising the heating of the building support 11. This circumstance allows limiting energy consumptions and the cycle time, preferably less than 5 min. An improved result repeatability is also attained due to the better control of the temperatures reached by the building support 11, preferably limited to values comprised between 50°C and 75°C.

[0087] The first radiant elements 23 and / or the possible second radiant elements 24 can be distributed around the entire circumferential extension of the building support 11, in a manner such to simultaneously irradiate the entire circumferential extension of the first layer 21. Nevertheless, in a preferred embodiment, provision is made such that the first radiant elements 23 and / or the second radiant elements 24 are distributed according to a curved extension, which for example subtends an angle comprised between 45° and 90° around the geometric rotation axis. This solution allows reducing the bulk and the manufacturing costs, and facilitates the insertion and the removal of the building support 11 in the pre-vulcanisation area 13.

[0088] During the activation of the radiant elements 23, 24 and the consequent heating of the first layer 21, a motor M operating in the pre-vulcanisation area 13 rotates the building support 11 around its geometric rotation axis, approximately at an angular speed comprised between 0.2 rad / s and 1 rad / s, such that the radiations emitted by the radiant group 22 are uniformly distributed according to the entire circumferential extension of the forming surface FS.

[0089] The power of the radiation and the stay time of the building support 11 under the action of the radiant group 22 can be modulated as a function of the needs. By way of example, provision is made such that the action of heating and the consequent pre-vulcanisation of the first layer 21 are interrupted when the first layer 21 has reached a crosslinking level comprised between 50% and 100%.

[0090] Figure 5 is a graph obtainable from a typical laboratory test in which the curve K represents the elastic reaction F set forth by a test sample over time t. As can be observed, in an initial step A of the test, the elastic reaction F undergoes a slight reduction, due to the reduced viscosity of the material following heating, up to reaching a minimum value Fmin that is conventionally considered as a reference which represents a crosslinking level equal to zero. In a step B following the initial step A, the elastic reaction F progressively increases up to reaching a maximum value Fmax, to which a crosslinking level percentage equal to 100% is conventionally assigned.

[0091] At each point Pl, P2 of the length of the curve K that subtends step B, the percentage value of the crosslinking level reached by the material in the corresponding instant tl, t2 is respectively expressed by:

[0092] 100 x (Fl-Fmin) / (Fmax-Fmin)

[0093] 100 X (F2-Fmin) / (Fmax-Fmin), in which Fl or F2 represents the value of elastic reaction of the sample at instant tl or t2.

[0094] As is better seen in figure 3, the area of pre-vulcanisation 13 can conveniently comprise a treatment chamber 25 configured for containing the building support 11 carrying the first layer 21, together with the radiant group 22 and with the motor M for the rotational actuation of the building support 11 itself. The treatment chamber 25, preferably hermetically closeable, is equipped with pressurisation devices 26, for example comprising at least one feed duct of air or another pressurisation fluid in the treatment chamber 25. The pressurisation devices 26 are adapted to be activated before or simultaneously with the activation of the radiant group 22, in order to create a pressurised environment in the treatment chamber 25 which contains the building support 11 carrying the first layer 21. More particularly, the treatment chamber 25 is preferably pressurised at an operating pressure greater than an atmospheric pressure and preferably equal to or greater than 150 KPa.

[0095] The consequent execution of the pre-vulcanisation in a pressurised environment allows minimising undesired developments of gas bubbles in the elastomeric material that constitutes the first elastomeric layer 21 subjected to heating. In addition, a close contact is facilitated between the first layer 21 and the forming surface FS of the building support 11, facilitating the attainment of high temperatures in the first layer 21 without risk of damaging it.

[0096] Preferably, the operating pressure is equally diffused outside and inside the building support 11, such that the pre-vulcanisation of the first layer 21 occurs in hydrostatic condition. It is thus possible to increase the operating pressure within the treatment chamber 25, without risking that the elastomeric material that constitutes the first layer 21 can infiltrate into the joints between different components of the building support 11 when the latter is of modular type, causing undesired structural defects.

[0097] The pressurisation devices 26 can be paired with at least one discharge valve 27 , selectively activatable in order to determine a sudden outflow of the pressurisation fluid from the treatment chamber 25.

[0098] The pre-vulcanisation is interrupted when the first layer 21 has reached the desired crosslinking level, suitable for conferring it sufficient impermeability to vapour or another pressurised operating fluid that will be employed during the subsequent treatment of moulding and vulcanisation of the tyre 2.

[0099] In order to interrupt the pre-vulcanisation, the deactivation of the radiant group 22 and the opening of the discharge valve 27 are determined, with a consequent lowering of the operating pressure and restoration of the ambient pressure. The pre- vulcanisation is therefore interrupted with an adiabatic expansion of the pressurisation fluid and consequent sudden cooling of the first layer 21 and of the building support 11, thus facilitating a better control of the crosslinking level reached by the first layer 21. Indeed, the lowering of the temperature in the first layer 21 and in the building support 11 determines a nearly instantaneous interruption of the crosslinking process, also avoiding uncontrolled crosslinking triggering in the elastomeric components subsequently applied on the first layer 21.

[0100] At the end of the pre-vulcanisation, the building support 11 can be extracted from the treatment chamber 25 and preferably subjected to the application of a coupling interface 28 at the exterior of the first pre-vulcanised layer 21, before applying the other tyre components.

[0101] As schematised in figure 4, the coupling interface 28 can comprise a second elastomeric layer, e.g. a compound with butyl base and / or containing talc, possibly formulated in a manner such to offer a satisfactory level of impermeability to air or another fluid for inflating the finished tyre 2, in addition to a satisfactory molecular bond with the materials that constitute the first layer 21 and the tyre components (e.g. carcass ply / plies 4) applied radially to the outside of the second layer itself. In addition, the coupling interface 28 at the green state preferably has high plasticity, so as to be effectively adapted to possible surface irregularities present between the first layer 21 and the carcass ply / plies 4 or other tyre components applied in radially outer position.

[0102] The application of the coupling interface 28 can be carried out by an additional applicator 29, e.g. in dispenser form, for example operating in the intermediate area 14 immediately downstream of the pre-vulcanisation area 13 and upstream of the building areas 15, 16, in order to distribute the material of the second layer on the first layer 21 while the building support 11 rotates on its geometric rotation axis. Analogous to that stated with reference to the application of the first layer 21, the building support 11 can be suitably moved in front of the additional applicator 29 in order to determine a correct distribution of the coupling interface 28.

[0103] At the end of the application of the coupling interface 28, the building support 11 can be transferred to the first building area 15 in order to determine the application of the carcass ply / plies 4 and / or other tyre components. Each carcass ply 4 can be obtained by circumferentially winding around the building support in substantially cylindrical drum form, superimposed on the coupling interface 28, a semifinished product in strip form whose opposite ends are then joined by head-head joint. At least when a toroidal building support 11 is used, as in the example described herein, it is preferable to attain the carcass ply 4 by deposition of a plurality of strip-like elements (strips that are cut to size) each incorporating two or more cords incorporated in an elastomeric matrix. The strip-like elements, approximately with width comprised between 10 mm and 20 mm and thickness comprised between 1 mm and 2 mm, are each deposited according to an orientation that is parallel or suitably tilted with respect to the axial extension of the outer surface of the building support 11, and one after the other, possibly with mutual partial superimposition, along the circumferential extension of the building support 11 itself. The coupling interface 28 previously deposited on the first pre-vulcanised layer 21 offers a support surface that is suitable pliable and adaptable to possible discontinuities, for example in order to fill the empty spaces possibly created in the head-head joint or between the single strip-like elements of the carcass ply / plies 4 in order to minimise or eliminate undesired inclusions of air.

[0104] Following the formation of the carcass ply / plies 4, and possibly after the building of the beads 6, the application of the crown structure 7 in the second building area 16 can be executed, for example according to that previously described. In the second building area 16, the application of the sidewalls 10 and / or other tyre components can also be actuated.

[0105] Upon completed building, the green tyre 2 is transferred to the vulcanisation group 19, with or without the building support 11, for the execution of the moulding and vulcanisation treatment. The execution of this treatment provides for the introduction of vapour or another pressurised operating fluid within the tyre 2, previously closed within a moulding cavity of a mould 30. Due to the presence of the first pre-vulcanised layer 21, the pressurised operating fluid can be brought directly in contact with the inner surface IS of the tyre 2, without risking permeating into tyre components, even in the absence of a vulcanisation membrane normally required in the prior art.

[0106] The pressure exerted by the operating fluid determines the forming of the tyre 2 against the inner walls of the moulding cavity, while the transfer of heat through the mould 30 and / or the same operating fluid determines the vulcanisation and the consequent geometric and structural stabilisation of the finished tyre 2.

Claims

CLAIMS1. Process for manufacturing tyres, comprising: depositing a first layer (21) made of elastomeric material on an outer surface of a building support (11); pre-vulcanising said first layer (21); depositing a plurality of tyre components around said first layer (21) carried by the building support (11), in order to form a green tyre (2); vulcanising the green tyre (2), in order to obtain a moulded and vulcanised tyre (2); wherein pre-vulcanising said first layer (21) comprises heating said first layer (21) carried by the building support (11), by an electromagnetic radiation irradiated from the exterior of the building support (11) towards an outer surface of said first layer (21).

2. Process according to claim 1, wherein the prevulcanisation is actuated in a pressurised treatment chamber (25).

3. Process according to claim 2, wherein during the prevulcanisation the treatment chamber (25) is pressurised at an operating pressure greater than an atmospheric pressure, said operating pressure being equally diffused outside and inside the building support (11).

4. Process according to one or more of the preceding claims, wherein heating said first layer (21) is attained by firstradiant elements (23) distributed around a geometric rotation axis of the building support (11).

5. Process according to one or more of the preceding claims, wherein heating said first layer (21) is attained by second radiant elements (24) in side-by-side relationship with the building support (11) in axially opposite positions.

6. Process according to one or more of the preceding claims, wherein the first layer (21) is heated to a temperature comprised between 170 °C and 260 °C.

7. Process according to one or more of the preceding claims, wherein during the action of heating said first layer (21), the building support (11) reaches a temperature comprised between 50 °C and 75 °C.

8. Process according to one or more of the preceding claims, wherein during the action of heating said first layer (21), the building support (11) rotates around a geometric rotation axis of the building support (11).

9. Process according to one or more of the preceding claims, wherein the building support (11) has a forming surface (FS) having toroidal shape.

10. Process according to one or more of the preceding claims, wherein said forming surface (FS) is counter-shaped with respect to an inner surface (IS) of the tyre (2).

11. Process according to one or more of the preceding claims, wherein the pre-vulcanisation is interrupted when said first layer (21) has reached a crosslinking level comprised between 50% and 100%.

12. Process according to one or more of the preceding claims, wherein the pre-vulcanisation is interrupted by adiabatic expansion of a pressurisation fluid.

13. Process according to one or more of the preceding claims, further comprising applying a coupling interface (28) in radially outer position with respect to said first layer (21), before applying said tyre components.

14. Apparatus for manufacturing tyres, comprising: a building support (11); an applicator (20) configured for depositing a first layer (21) made of elastomeric material on a forming surface (FS) shown externally on the building support (11); a pre-vulcanisation area (13) comprising at least one radiant group (22) configured for heating the first layer (21) carried by the building support (11), by an electromagnetic radiation irradiated from the exterior of the building support (11) towards an outer surface of the first layer (21), so as to prevulcanise said first layer (21); one or more application units (18) configured for depositing a plurality of tyre components around said first layer (21) carried by the building support (11), in order to form agreen tyre (2); a vulcanisation group (19) configured for vulcanising the green tyre (2), so as to obtain a moulded and vulcanised tyre (2).

15. Apparatus according to claim 14, wherein the prevulcanisation area (13) also comprises a treatment chamber (25) configured for containing the building support (11) carrying the first layer (21).

16. Apparatus according to claim 14 or 15, wherein the pre-vulcanisation area (13) also comprises pressurisation devices (26) for introducing a pressurisation fluid into the treatment chamber (25).

17. Apparatus according to claim 16, wherein the pressurisation devices (26) also comprise a discharge valve (27) for evacuating the pressurisation fluid from the treatment chamber (25).

18. Apparatus according to one or more of the claims 14 to 17, wherein said at least one radiant group (22) comprises first radiant elements (23) distributed around a geometric rotation axis of the building support (11), in a position radially distant from the forming surface (FS).

19. Apparatus according to claim 18, wherein the first radiant elements (23) lie distant from geometric rotation axis according to a measure greater than a maximum radius (R.) ofthe building support (11) around the same geometric rotation axis.

20. Apparatus according to claim 18 or 19, wherein the first radiant elements (23) are distributed according to a curved extension around the geometric rotation axis.

21. Apparatus according to one or more of the claims 14 to20, wherein said at least one radiant group (22) comprises second radiant elements (24) in side-by-side relationship with the building support (11) in axially opposite position.

22. Apparatus according to one or more of the claims 14 to21, wherein the building support (11) has a toroidal shape counter-shaped with respect to an inner surface (IS) of the tyre (2).

23. Apparatus according to one or more of the claims 14 to22, also comprising at least one additional applicator (29) configured for applying a coupling interface (28) to the exterior of the first layer (21).

24. Apparatus according to claim 23, wherein the additional applicator (29) operates immediately downstream of the pre-vulcanisation area (13), and upstream of said one or more application units (18).

25. Apparatus according to one or more of the claims 14 to 24, also comprising at least one transfer unit (12) configured forpicking up the building support (11) together with the green tyre (2) from said one or more application units (18) and loading it into a mould (30) constituting part of the vulcanisation group (19).

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