Patent Publication Number: US-10766217-B2

Title: Process and plant for building tyres for vehicle wheels

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. application Ser. No. 13/993,156, filed Jun. 11, 2013, which is a National Phase application based on PCT/IB2011/055272, filed Nov. 24, 2011, which claims the priority of Italian Patent Application No. MI2010A002377, filed Dec. 23, 2010, and the benefit of U.S. Provisional Application No. 61/429,304, filed Jan. 3, 2011, all of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a process and a plant for building tyres for vehicle wheels. More specifically, the invention is particularly addressed to manufacture of crown structures, in particular in production contexts in which building of the tyre takes place by assembling elementary semifinished products such as rubberised textile or metallic cords, strip-like elements formed starting from a continuous ribbon-like element cut to size and comprising a plurality of textile or metallic cords disposes parallel and adjacent to each other, and/or continuous elongated elements of elastomeric material circumferentially wound into a plurality of mutually adjacent turns. 
     Description of the Related Art 
     A tyre for vehicle wheels generally comprises a carcass structure including at least one carcass ply having respectively opposite end flaps in engagement with respective annular anchoring structures, integrated into the regions usually identified as “beads”, defining the radially internal circumferential tyre edges. 
     Associated with the carcass structure is a belt structure comprising one or more belt layers, placed in radially superposed relationship relative to each other and to the carcass ply, provided with textile or metallic reinforcing cords having crossed orientation and/or substantially parallel to the circumferential extension direction of the tyre. Applied at a radially external position to the belt layers is a tread band, made of elastomeric material too, like other semifinished products constituting the tyre. 
     In addition, respective sidewalls of elastomeric material are applied at an axially external position to the side surfaces of the carcass structure, each extending from one of the side edges of the tread band until close to the respective annular anchoring structure to the beads. In tyres of the “tubeless” type, an airtight coating layer, usually referred to as “liner” covers the inner surfaces of the tyre. 
     To the aims of the present specification and the following claims, by “crown structure” of a tyre it is intended at least one belt structure having at least one belt layer or strip. More preferably, the crown structure comprises a belt structure having at least one belt layer or strip and a tread band. 
     In the specification and in the following claims the term “component” is understood as indicating any part of the tyre that is suitable to perform a function, or a portion thereof. Therefore, defined as components are for example the liner, underliner, abrasion-proof element, bead core, bead filler, carcass ply, belt strip, belt under-layer, tread under-layer, sidewall inserts, sidewalls, tread band, reinforcing inserts. 
     In the present specification and in the following claims the term “strip-like element” is understood as indicating an elongated element of elastomeric material of flattened shape and cut to size, including at least one, preferably at least two textile or metallic reinforcing cords that are parallel to each other and to the longitudinal axis of the elongated element itself. 
     SUMMARY OF THE INVENTION 
     The Applicant has observed that it is possible to provide a forming drum comprising a plurality of supporting elements having stiff surfaces for the tyre components and disposed along the drum circumference, in which the support elements, considered in a diametrical section plane containing the geometric axis of the drum, comprise central supporting portions and lateral supporting portions fastened thereto. The central supporting portions are movable by means of first actuating devices between a first position at which the respective supporting elements form a supporting surface parallel to the geometric axis of the drum, and at least one second position at which the supporting elements form a convex surface. The first actuating devices are connected to the central portions of the supporting elements for at least keeping them parallel to the geometric axis at least in the second position. 
     The Applicant has also observed that on a forming drum externally having a substantially cylindrical deposition surface, a plurality of strip-like elements can be applied, which are disposed in mutually approached relationship so as to form at least one first annular reinforcing layer on the forming drum itself set to a first work diameter in which each of the applied strip-like elements on the deposition surface subtends an arc of a circumference the width of which is equal to a submultiple integer of the overall circumferential extension of the deposition surface. Adjusting devices operating on the forming drum will subsequently expand it to a second work diameter greater than the first work diameter, while maintaining the deposition surface thereof substantially cylindrical. The Applicant has also observed that the forming drum may comprise consecutive circumferential sectors radially movable upon command of the adjusting devices. Each of the circumferential sectors has comb-shaped end portions that are each operatively engaged in a comb-shaped end portion complementary thereto carried by a circumferentially adjacent circumferential sector. 
     The Applicant has noticed that basically each tyre size requires a specific forming drum and in particular a specific auxiliary drum for forming one or more belt layers or a crown structure. 
     In fact, it is the Applicant&#39;s opinion that it is desirable for the belt layers and/or other components of the crown structure to be made according to a transverse outline which is as much as possible close to or coincident with the outline that the components must have in the finished tyre. 
     While having verified that it is possible to use the same type of forming drum for two or more tyre sizes, the Applicant has however noticed that a process and apparatus as above described would require management of many forming drums for which a specific storehouse is necessary. 
     The Applicant has felt the necessity to optimise management of the forming drums without being obliged to provide a specific storehouse of big sizes for forming drums having shapes and/or sizes different from each other, while at the same time ensuring the availability of a forming drum of appropriate sizes and shape for each type of tyre to be produced. 
     The Applicant has found that by providing a forming drum in which the curvature outline and therefore the deposition surface thereof can be configured in shape and sizes as a function of the size of the tyre to be produced, the warehouse for the forming drums can be eliminated or greatly reduced. 
     More particularly, in accordance with a first aspect, the invention relates to a process for building tyres for vehicle wheels, comprising:
         making carcass structures;   making crown structures;   associating each carcass structure with each crown structure;       

     wherein making said crown structures comprises:
         providing at least one first forming drum having a deposition surface and comprising sectors radially movable relative to a geometric rotation axis, and circumferentially distributed one after the other;   setting the deposition surface in a first deposition configuration;   depositing strip-like elements in circumferential side by side relationship on the deposition surface set in the first deposition configuration, so as to form at least one component of at least one first crown structure;       

     wherein the action of setting said deposition surface comprises:
         radially moving said sectors to give the deposition surface a predetermined diameter;   carrying out a relative movement between a central portion and axially external end portions of each sector, to shape the deposition surface into a predetermined curvature outline.       

     The Applicant thinks that each component of the crown structure formed on the deposition surface already set to the desired deposition configuration, can advantageously have geometric features substantially coincident with those required in the finished tyre. The Applicant has further ascertained that the components of the crown structure as obtained will not necessarily have to be submitted to important deformation actions for adapting the shape thereof to the design parameters during the work steps following their manufacture. Thus important qualitative improvements can be obtained in the final product. In addition, as the Applicant ascertained, a greater production flexibility can be advantageously achieved, since a wide variety of sizes and curvature outlines obtained using the same forming drum is made available, while at the same time being limited the space not directly concerned with production, like that for storing the forming drums, and being reduced the manufacturing and management costs for a great number of forming drums. 
     In accordance with a second aspect, the invention relates to a plant for building tyres for vehicle wheels, comprising:
         a carcass-structure building line;   a crown-structure building line;   an assembling station for coupling each carcass structure to each crown structure;       

     wherein the crown-structure building line comprises:
         at least one first forming drum including sectors that are radially movable relative to a geometric rotation axis, each of them having at least one central portion and axially external end portions that are radially movable relative to the central portion, wherein said sectors are circumferentially distributed one after the other so as to define a deposition surface;   devices for setting the deposition surface in at least one deposition configuration;   devices for depositing strip-like elements in circumferential side by side relationship on the deposition surface set in said deposition configuration, so as to form at least one component of at least one crown structure;       

     wherein said devices for setting the deposition surface comprise:
         radial-movement devices for moving the sectors so as to give the deposition surface a predetermined diameter;   relative-movement devices for movement between the end portions and central portion of each sector relative to the geometric rotation axis, in order to shape the deposition surface into a predetermined curvature outline.       

     This plant helps in making available a wide variety of curvature outlines and diametrical sizes of the deposition surface on the same forming drum. 
     The present invention, in accordance with one of said aspects, can have one or more of the preferred features hereinafter described. 
     In accordance with a possible embodiment, provision is made for: coupling said at least one first forming drum 
     with a handling device adapted to be activated for setting the deposition surface to the first deposition configuration; decoupling said at least one first forming drum from the handling device before completing formation of the first crown structure. 
     Also preferably provided is the action of coupling said at least one first forming drum again to the handling device, for setting the deposition surface to a second deposition configuration. 
     Decoupling of the forming drum makes the handling device available for other operations. 
     For instance, the handling device decoupled from said at least one first forming drum can be coupled to at least one second forming drum. Coupling of the handling device to said at least one second forming drum can for example enable setting of the deposition surface and/or execution of other processing operations on the second forming drum itself. 
     Preferably, coupling of the handling device to said at least one second forming drum is carried out before coupling said at least one first forming drum again to the handling device. 
     Meanwhile, the decoupled forming drum can be submitted to other processing operations provided in the building cycle of the crown structure. 
     For instance, at least one additional component of the crown structure can be made on said at least one first forming drum decoupled from the handling device. 
     Also provided can be at least transfer of said at least one first forming drum from a first work location to at least one second work location. 
     At least one additional component of the crown structure can be made on said at least one first forming drum transferred to the second work location. 
     Provision is also preferably made for locking the deposition surface to the respective deposition configuration during transfer of said at least one first forming drum. 
     In particular flowing of different forming drums along the work locations can be such managed that the simultaneous processing of different crown structures can be carried out. 
     Transfer of said at least one first forming drum from the first work location to said at least one second work location is carried out by said handling device. 
     A structural simplification of the plants and a reduction in the processing times can be thus achieved. 
     Preferably, carrying out of said relative movement comprises: locking the central portion of each sector relative to the geometric rotation axis; moving the end portions of each sector relative to the geometric rotation axis. 
     Preferably, during said relative movement, the end portions of each sector are moved towards the geometric rotation axis. 
     Thus a convex curvature outline can be given to the deposition surface. 
     Radial movement of the sectors is preferably carried out through respective sliders carried by the end portions of each sector. 
     It is also preferably provided that the radial movement of the sectors be carried out by driving at least one spiral-shaped cam in rotation around said geometric rotation axis. 
     Thus a symmetric and timed movement of the end portions of each sector can be obtained. 
     In a preferred example of the invention the following actions are in addition carried out: removing said at least one component of at least one first crown structure from said at least one first forming drum; setting the deposition surface to a second deposition configuration; forming at least one component of at least one second crown structure on the deposition surface. 
     Preferably, said at least one component of said at least one first crown structure formed through deposition of strip-like elements in circumferential side by side relationship is a belt layer. 
     Preferably, at least one component of said at least one first crown structure is made on said at least one first forming drum decoupled from the handling device. 
     According to a preferred embodiment, at least one component of the crown structure is made on said at least one first forming drum transferred to said at least one second work location. 
     Preferably provided are central-portion locking devices, operating on the central portion of each sector so as to lock it to a predetermined work position selected from a plurality of positions included between a maximum-contraction position and a maximum-expansion position. 
     Also provided can be end-portion locking devices, operating on the end portions of each sector for locking them to a predetermined work position selected from a plurality of positions included between a maximum-contraction position and a minimum-contraction position relative to the corresponding central portion. 
     Said relative-movement devices can be preferably activated concurrently with activation of the central-portion locking devices. 
     Said radial-movement devices can be preferably activated concurrently with activation of the end-portion locking devices. 
     The devices for setting the deposition surface preferably comprise at least one handling device capable of being coupled in a removable manner to said at least one first forming drum. 
     More particularly, said handling device can be preferably operatively coupled to said radial-movement devices for determining activation thereof. 
     Said handling device can be operatively coupled to said relative-movement devices for determining activation thereof. 
     Preferably, said handling device can be operatively coupled to said central-portion locking devices for operating deactivation thereof. 
     Preferably, the handling device is movable between a first work location and at least one second work location for transfer of the forming drum between said first work location and said at least one second work location. 
     Preferably, the handling device comprises a robotized arm, preferably an anthropomorphous robotized arm. 
     In each sector, the end portions are preferably hinged on respective opposite ends of the central portion. 
     Each sector can further comprise intermediate portions each secured between one of the end portions and the central portion. 
     The radial-movement devices preferably comprise at least one spiral-shaped cam operatively engaging said sectors and drivable in rotation around the geometric axis to determine radial movement of the sectors. 
     Said spiral-shaped cam can be operatively in engagement with sliders, each carried by one of the end portions of one of said sectors. 
     Preferably the end portions of each sector are mutually interconnected by a bridge structure. 
     Preferably, said bridge structure carries the end-portion locking devices. 
     The central-portion locking devices preferably comprise first brakes drivable for unlocking the radial movement of the central portions. 
     More particular, each of said first brakes preferably operates between a rod radial to the respective sector and a first runner slidably guided relative to the rod. 
     The end-portion locking devices can comprise second brakes drivable for unlocking the radial movement of the end portions relative to the central portions. 
     More particularly, each of said second brakes operates between a rod radial to the respective sector and a second runner slidably guided relative to said rod. 
     Also preferably provided are devices for selecting the deposition configuration to be given to the deposition surface as a function of the type of tyre being processed. 
     The crown-structure building line preferably comprises a setting location provided for receiving said at least one first forming drum. 
     Said setting location comprises control devices that can be operatively coupled to said end-portion locking devices, and can be activated for unlocking the radial movement of the end portions relative to the central portions. 
     Further features and advantages will become more apparent from the detailed description of a preferred but not exclusive embodiment of a process and a plant for building tyres, in accordance with the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       This description will be set out hereinafter with reference to the accompanying drawings, given by way of non-limiting example, in which: 
         FIG. 1  diagrammatically shows a top view of a plant for building tyres produced in accordance with the present invention; 
         FIG. 2  shows a diametrical half-section of the forming drum; 
         FIG. 3  shows a section of a construction detail taken at one of the circumferential sectors of the forming drum; 
         FIG. 4  shows the detail seen in  FIG. 3  in a perspective view; 
         FIG. 5  shows a portion of the forming drum set to a diametrical maximum-contraction condition with some parts removed for better emphasising others; 
         FIG. 6  shows the drum of  FIG. 5  set to a possible deposition configuration; 
         FIG. 7  is a fragmentary diametrical section of a tyre that can be manufactured by the process and plant in reference. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the drawings, a plant for building tyres for vehicle wheels, provided for carrying into practice a process according to the invention has been generally identified by reference numeral  1 . 
     Plant  1  is intended for manufacturing tyres  2  ( FIG. 7 ) essentially comprising a carcass structure  2   a  having at least one carcass ply  3 . A layer of airtight elastomeric material or a so-called liner  4  can be applied to the inside of the carcass ply/plies  3 . Two annular anchoring structures  5  each comprising a so called bead core  5   a  carrying an elastomeric filler  5   b  at a radially external position, are in engagement with respective end flaps  3   a  of the carcass ply or plies  3 . The annular anchoring structures  5  are integrated in the vicinity of regions usually identified as “beads”  6 , at which engagement between tyre  2  and a respective mounting rim usually takes place. 
     A crown structure  7  is circumferentially applied around the carcass ply/plies  3 . The crown structure comprises a belt structure  8  having one or more belt layers  8   a ,  8   b  and preferably a tread band  9  circumferentially superposed on the belt structure  8 . 
     So called “under-belt inserts”  8   c  can be associated with the belt structure  8  and they are each placed between the carcass ply/plies  3  and one of the axially opposite end edges of the belt structure  8 . Alternatively or in addition to the under-belt inserts  8   c , annular inserts of elastomeric material and/or comprising cords or other reinforcing elements can be radially superposed at least on the axially opposite end edges of the belt structure  8 , and/or interposed between the belt layers  8   a ,  8   b , at least at said end edges. 
     Two sidewalls  10  each extending from the corresponding bead  6  to a corresponding side edge of the tread band  9 , are applied to the carcass ply/plies  3  at laterally opposite positions. 
     Plant  1  essentially comprises a carcass-structure building line  11 , wherein the carcass structures  2   a  of the tyres under production are formed. The crown structures  7  are produced in a crown-structure building line, generally denoted at  12  in  FIG. 1 . 
     In an assembling station  100 , operatively interposed between the carcass-structure building line  11  and the crown-structure building line  12  or operatively integrated into one of them, coupling of each carcass structure  2   a  to a respective crown structure  7  is carried out. 
     The carcass-structure building line  11  comprises a primary building drum  14 , on which the carcass structure  2   a  of tyre  2  is preferably built and/or assembled. The primary drum  14  preferably is a building drum having a substantially cylindrical shape. 
     The primary drum  14  can be operatively supported by a mandrel  15 , a robotized arm, or another device enabling it to be, if necessary, driven in rotation and/or suitably handled during application of the components of the carcass structure  2   a  at the building station  11 . 
     More particularly, the primary drum  14  is adapted to first receive liner  4 , if any, and subsequently the carcass ply or plies  3 , so as to form a cylindrical sleeve on the opposite end flaps of which the annular anchoring structures  5  are afterwards fitted. Turning-up of the end flaps  3   a  of the carcass ply/plies  3  can be then carried out around the annular anchoring structures  5 . Also provided may be application of at least one sidewall portion  10  onto the primary drum  14 , as well as at least one abrasion-proof element, depending on the construction process. 
     In the example shown, the primary drum  14  and the carcass structure  2   a  supported thereby, made in the form of a cylindrical sleeve, are picked up by a first transfer member, diagrammatically shown in  FIG. 1  and denoted by arrow “T”, which member carries out transfer of them to the assembling station  100  for engaging the primary drum  14  on shaping devices herein not shown as they can be made according to the disclosure of document WO 2010/064077 in the name of the same Applicant, for example. 
     The crown-structure building line  12  is equipped with at least one forming drum  18  usually also referred to as “auxiliary drum” that is adapted to be sequentially transferred between two or more work locations  19 ,  20 ,  21  dedicated to manufacture of the crown structure. 
     In greater detail, in a possible embodiment at least one first work location  19  is dedicated to formation of the belt layer or layers  8   a ,  8   b , and/or to assembly of other components of the belt structure  8 , according to a predetermined sequence. At least one second work location  20  can be designed for formation of the tread band  9  on the belt structure  8 , at a radially external position. A third work location  21  can be provided for applying additional annular inserts, such as the under-belt inserts  8   c  and/or at least one portion of the sidewalls  10  in the continuation of the axially opposite edges of the tread band  9 . 
     A possible second transfer member  22  movable from and to the main drum  14  associated with the aforesaid shaping devices, carries out transfer of the crown structure  8  from the forming drum  18  brought to the assembling station  100  too, to the carcass structure  2   a , at a radially external position thereto ( FIG. 1 ). In known manner, when the crown structure  8  is in a centred position relative to the carcass structure  2   a , the latter is shaped in a toroidal configuration. The consequent radial expansion of the carcass ply/plies  3  leads the same to adhere against the inner surface of the crown structure  8 , retained by the second transfer member  22 . 
     Tyre  2  thus built can be removed from the primary drum  14  to be submitted to a vulcanisation treatment and/or other processing operations provided in the work cycle. 
     The forming drum  18  externally has a substantially cylindrical deposition surface, formed with a plurality of sectors  24  circumferentially distributed one after the other around a geometric rotation axis X of the forming drum. 
     To the aims of the present invention by “substantially cylindrical” deposition surface  23  it is intended a deposition surface the shape of which corresponds to a solid of revolution defined by a generatrix having rectilinear development or arched development, as can be viewed from the accompanying drawings. 
     In other words, along the development of each sector  24 , in a radial-section plane relative to the geometric rotation axis X, it is possible to detect a curvature outline of the deposition surface  23 . Preferably, this curvature outline is such that the difference between a maximum diameter Dmax measurable at a symmetry plane orthogonal to the geometric rotation axis X of the forming drum  18 , and a minimum diameter Dmin findable at the axially opposite edges of the drum itself, is included between about 0 (cylindrical surface—straight curvature outline) and about 30% of the axial size E measurable between said axially opposite edges ( FIG. 3 ). 
     In other words, the following relation is valid:
 
0=&lt;(Dmax−Dmin)=&gt;0.3* E.  
 
     Associated with each forming drum  18  are setting devices  25  that can be preferably activated before starting manufacture of the first belt layer  8   a  on the forming drum  18 , to set the deposition surface  23  in at least one predetermined deposition configuration. 
     In greater detail, the deposition surface  23  can be preferably set in several deposition configurations, each of which can be selected each time in accordance with the geometric and/or dimensional features of the tyre under production. 
     Each sector  24  to this aim comprises at least one central portion  26  and at least two end portions  27  axially external relative to the central portion  26  and extending in axially opposite directions relative to the latter. The end portions  27  are preferably hinged on the central portion  26 , by hinging pins  28  for example that are in engagement with the respectively opposite ends of the central portion so as to be radially movable relative thereto. 
     In a possible variant not shown, each sector  24  can further comprise intermediate portions each secured between one of the end portions  27  and the central portion  26  so as to make sectors  24 , if necessary, more adaptable to the required different curvature outlines. 
     The setting devices  25  essentially comprise radial-movement devices  29  to move sectors  24  so as to give the deposition surface  23  a predetermined diameter, which cooperate with relative-movement devices  30  for movement between the end portions and central portion of each sector relative to the geometric rotation axis, in order to shape the deposition surface into a predetermined curvature outline. 
     More particularly, the radial-movement devices  29  are adapted to simultaneously cause translation of sectors  24  in a direction radial to the geometric rotation axis X, so as to determine a variation in the diametrical sizes of the forming drum  18 , starting from a maximum-contraction and minimum-curvature condition of the deposition surface  23 , in which sectors  24  can act in mutual abutment by means of respective circumferential shoulders  24   a  so as to give the deposition surface  23  a continuous course. 
     The circumferential shoulders  24   a  of each sector  24  are preferably defined at respective comb-shaped end portions  31  each of which operatively engages a comb-shaped end portion  31  geometrically complementary thereto, carried by a circumferentially adjacent sector  24 . In this manner, the deposition surface  23  advantageously keeps its substantially cylindrical conformation and a substantially continuous extension, i.e. without important discontinuities even following strong expansion of the forming drum  18 . Thus the forming drum  18  can be easily adapted to processing of tyres with geometric and diametrical measures even greatly different from each other. 
     Each sector  24  is carried by at least one or, as shown, one pair of radial arms  32  preferably placed in the vicinity of respective axially opposite sides of the forming drum  18  and each operatively in engagement with one of the end portions  27  of the respective sector  24 . In a preferred solution, rotatably secured to each radial arm  32  is an end of at least one connecting rod  33  the opposite end of which is hinged on the corresponding end portion  27  of sector  24 . Preferably, a bridge portion  34  extends between the radial arms  32  and is rigidly engaged relative to the same, so as to mutually interconnect the end portions  27  of each sector  24 . 
     At least one or, as shown, one pair of spiral-shaped cams  35  operatively engage sectors  24  at respective sliders  35  each carried by the respective end portion of each sector  27 . More particularly, each slider  36  is preferably in engagement with one of said radial arms  32 . 
     Each spiral-shaped cam  35  is fastened to a grip shank  37  coaxial with the geometric rotation axis X, and it engages the sliders  36  of the radial arms  32  disposes on the same side of the forming drum  18 . 
     At least one or, as shown, one pair of guide flanges  38  support sectors  24  radially guiding them relative to the geometric rotation axis X by means of guide seats  39  slidably passed through by the respective radial arms  32 . The guide flanges  38  are rotatably supported by the grip shank  37  by rolling bearings  40 , and at least one of them can carry stop devices  41  to selectively enable and disable freedom of rotation of the guide flanges relative to the grip shank  37 . Said stop devices  41  are not described in detail as they can be made following the description in document WO2008/152453 in the name of the same Applicant, for example. 
     The spiral-shaped cams  35  lend themselves to rotate together with the grip shank  37  relative to the guide flanges  38  and the circumferential sectors  24 . Thus it is possible to determine a simultaneous radial movement of the circumferential sectors  24  and place them to a plurality of positions included between a maximum-contraction position and a maximum-expansion position. 
     Central-portion locking devices  42  operate on the central portion  26  of each sector  24  so as to lock it to a predetermined work position that can be selected as a function of the geometrical and/or dimensional features of the tyre being processed. 
     More particularly, the central-portion locking devices  42  preferably comprise first brakes  42   a  each operating between a rod  43  radial to the respective sector  24  and a first runner  44  slidably guided relative to rod  43 . In a preferred embodiment the first runner  44  is fastened to the guide flanges  38  and is slidably passed through by rod  43  rigidly connected to the central portion  26  of the respective sector  24 . In greater detail, formed on a radially external end portion of rod  43  is a pair of extensions  45 , rigidly connected to the central portion  26  of the respective sector  24 . 
     Each of the first brakes  42   a , not shown in detail as they can be made in known manner, is operatively integrated into one of the first runners  44  and, under rest conditions, is pushed against the rod  43  by one or more spring members, to rigidly retain the central portion  26  of the respective sector  24 . The first brakes  42   a  are further adapted to be simultaneously deactivated, pneumatically for example, by overcoming the action of the respective spring members, to free movement of rods  43  relative to the first runners  44 , so as to enable radial movement of the central portions of sectors  24 . 
     To this aim, the first brakes  42   a  can be connected to at least one first pneumatic-connection terminal  46  placed in the vicinity of the stop devices  40  for example, and laterally appearing from the forming drum  18 . 
     Also provided are end-portion locking devices  47  operating on the end portions  27  of each sector  24  to lock them to a predetermined work position, selected from a plurality of positions included between a maximum-contraction position and a minimum-contraction position relative to the corresponding central portion  26 . 
     In greater detail, to this aim second brakes  47   a  can be provided, each of which operates between one of rods  43  and a second runner  48  slidably guided relative to the rod itself. More particularly, in a preferred embodiment, a pair of second brakes  47   a  is provided for each sector  24 , which brakes are each associated with one of the end portions  27  and preferably integrated into at least one respective second runner  48 . Each second runner  48  is preferably fastened to the bridge structure  34  of the respective sector  24  and is slidably passed through by said extensions  45 , radial to the respective sector  24 . 
     Spring members push the second brakes  47   a  of each sector  24  against the respective extensions  45 , so as to lock the bridge structure  34  and rigidly retain the end portions  27  of the respective sector  24 . The second brakes  47   a  are further adapted to be simultaneously deactivated, pneumatically for example, by overcoming the action of the respective spring members, to make movement of the second runners  48  free along the extensions  45  so as to enable radial movement of the end portions  27  of sectors  24  relative to the central portions  26 . 
     To this aim, the second brakes  47   a  can be connected to at least one second pneumatic-connection terminal  49  located at an end of the grip shank  37  for example, which is therefore provided with at least one inner pipeline  50 . 
     Operating in the crown-structure building line  12  is at least one handling device  51  preferably comprising a preferably anthropomorphic robotized arm, of the type provided with six or more movement axes, movable between the first and second work locations  19 ,  20  and/or other locations provided in the crown-structure building line  12 . The handling device  51  can be removably coupled to the forming drum  18  to transfer it between the work locations  19 ,  20 ,  21  provided in the crown-structure building line  12 , and it forms an integral part of the setting devices  25  being operatively coupled to the radial-movement devices  29  and/or the relative-movement devices  30 . 
     More particularly, the handling device  51  engages the forming drum  18  at an end of the grip shank  37 , preferably opposite to the second pneumatic-connection terminal and can operate on the latter to drive along in rotation the spiral-shaped cams  35  relative to the guide flanges  38 . The handling device  51  can further be operatively coupled with the central-portion locking devices  42 , by at least one first quick-fit pneumatic connection  52  for example, that can be operatively coupled with the first pneumatic-connection terminal  46 , through which introduction of compressed air to the brakes  42   a  can be caused to determine deactivation thereof. 
     Control devices  53  that can be operatively coupled to the end-portion locking devices  47  can be provided in a setting location  54  operating along the crown-structure building line  12  to receive each forming drum  18  for carrying out setting of the deposition surface  23  according to the desired deposition configuration. 
     These control devices  53  may for example comprise at least one second quick-fit pneumatic connection to be operatively coupled with the second pneumatic-connection terminal  49  through which introduction of compressed air to the second brakes  47   a  can be caused to determine deactivation of the latter. 
     In accordance with a building process according to the invention, for manufacture of the crown structures  7 , the forming drum  18  for instance picked up from the assembling station  100  by the handling device  51  at the end of building of a tyre, is provided to be engaged in the setting location  54  at which connection of the second brakes  47   a  to a compressed-air feeding line is enabled, following coupling of the second quick-fit pneumatic connection  53  with the second pneumatic-connection terminal  49 . 
     Selection devices not shown, comprising a programmable governing unit supervising operation of the crown-structure building line  12  and possibly of other parts of plant  1 , carries out selection of a first deposition configuration to be given to the deposition surface  23  selected as a function of the previously stored type of tyre being processed. 
     The forming drum  18  at least partly contracted due to removal of the previously formed crown structure  7 , can be, if necessary, submitted to a preliminary operation for initialising the position of sectors  24 , implementing the maximum-contraction and minimum-curvature condition of the deposition surface  23 . To this aim, the handling device  51  acts on the grip shank  37  to drive the spiral-shaped cams  15  in rotation so as to bring back the end portions  27 , if necessary, to the minimum-contraction position relative to the central portions  26 . This action is carried out after deactivation of the second brakes  47   a  by introduction of compressed air through the second pneumatic-connection terminal  49 , while the first brakes  42   a  remain active on the respective rods  43  to retain the central portions  26  during actuation of the spiral-shaped cams  35 . 
     When the end portions  27  have reached to minimum-contraction position, deactivation of the first brakes  42   a  through the first pneumatic-connection terminal  46  is produced, concurrently with activation of the second brakes  47   a . The handling device  51  then rotates the grip shank  37 , if necessary, in the opposite direction relative to the preceding action, to bring the central portions  26  of sectors  24  back to the maximum-contraction position. The end portions  27 , locked upon the action of the second brakes  47   a , follow the central portions  26  in their motion of approaching the geometric rotation axis X. 
     When the above described possible initialising operation has been completed, the forming drum  18  is submitted to setting of the deposition surface  23  to the first deposition configuration. 
     To this aim, while the first brakes  42   a  are maintained inactive and the second brakes  47   a  are maintained active, the handling device  51  acts on the grip shank  37  to determine radial expansion of the deposition surface  23 , until sectors  24  reach a work position corresponding to a predetermined diameter of the deposition surface  23 . 
     If the minimum-contraction position maintained by the end portions  27  were not already in accordance with the desired curvature outline to be given to the deposition surface  23 , the spiral-shaped cams  35  can be driven in rotation in the opposite way relative to the preceding action, concurrently with deactivation of the second brakes  47   a  or re-activation of the first brakes  42   a  for locking the central portions  26  relative to the geometric rotation axis X. Thus a relative movement between the central portion  26  and the axially external end portions  27  of each sector  24  is carried out to shape the deposition surface  23  according to a predetermined curvature outline. More particularly, the end portions  27  move towards the geometric rotation axis X rotating around the respective hinging pins  28 , so as to progressively increase the curvature outline of the deposition surface  23  until the desired value is reached. 
     Therefore the forming drum  18  has a diameter and a curvature outline that can be modulated in a manner independent of each other, to prepare the deposition surface  23  to process tyres geometrically different from each other. 
     When the desired deposition configuration has been reached, the handling device  51  can remove the forming drum  18  from the setting location  54  for proceeding with building of the crown structure  7 . 
     The action of the first and second brakes  42   a ,  47   a  ensures that the desired deposition configuration is maintained during the processing operations and the transfer actions of the forming drum  18  between the work locations  19 ,  20 ,  21 , until the end of the process. Possible modifications of the forming drum diameter during the process for manufacturing the crown structure  7 , if required, can be at all events carried out through actuation of the radial-movement devices  29  upon command of the handling device  51 , after deactivation of the first brakes  42   a.    
     In greater detail, the handling device  51  is adapted to retain the grip shank  37  to transfer the forming drum  18  to the first work location  19 , at which at least one belt layer  8   a ,  8   b  or other component of the crown structure  7  is produced by means of applicator devices  55  preferably provided for depositing a plurality of strip-like elements B in circumferential side by side relationship on the forming drum  18 . 
     Said applicator devices  55 , not described in detail for clearness of exposition, can be accomplished following the description of patent U.S. Pat. No. 6,702,913 in the name of the same Applicant, for example. 
     The handling device  51  carries out appropriate positioning of the forming drum  18  at the applicator devices  55  and drives it in rotation, for example in a step-by-step movement, in timed relationship with deposition of the individual strip-like elements B on the deposition surface  23 , so that said strip-like elements are applied in succession one adjacent to the other, each according to an orientation parallel to or suitably inclined relative to the geometric rotation axis X, until they cover the whole circumferential extension of the deposition surface  23 . 
     At least one second belt layer  8   b  can be formed at a position radially external to the first belt layer  8   a , in the same manner as previously described but with the strip-like elements B preferably extending in a crossed orientation relative to those of the first belt layer  8   a . During manufacture of the second belt layer  8   b , the deposition surface  23  of the forming drum  18  will be represented by the previously formed first belt layer  8   a.    
     Before and/or after manufacture of the belt layer/s  8   a ,  8   b , at least one annular insert of elastomeric material can be formed around the deposition surface  23 . 
     Said at least one annular insert may consist for example of part of the tread band  9 , applied at a radially external position to the first and/or second belt layer  8   a ,  8   b , and/or at least part of the sidewalls  10 , each extending on the deposition surface  23 , axially beyond the edges of said first and/or second belt layer  8   a ,  8   b . One or more annular inserts of elastomeric material can also form the under-belt inserts  8   c , applied onto the deposition surface  23  at a position radially internal to the axially opposite edges of the belt layers  8   a ,  8   b.    
     Each annular insert can be advantageously made by spiraling at least one continuous elongated element of elastomeric material, i.e. by winding said continuous elongated element into substantially circumferential turns that are disposed in mutual side by side relationship around the deposition surface  23 . 
     To this aim, the second and/or third work location  20 ,  21  can comprise at least one delivery device  56 , such as an extrusion die for example, distributing the continuous elongated element on the forming drum  18 , while the latter is being driven in rotation around its geometric rotation axis X through the handling device  51 , and conveniently moved by the latter to determine distribution of the turns in a manner adapted to give a desired final conformation to the under-belt inserts  8   c , the tread band  9 , and/or the sidewalls  10  being produced. 
     At least formation of the under-belt inserts  8   c  should have to be preferably carried out before setting of the deposition surface  23  to the desired deposition configuration, i.e. with the deposition surface in the maximum-contraction and minimum-curvature condition to which mutual contact of sectors  24  in surface continuity relationship corresponds. Thus it is possible to eliminate the risk that the continuous elongated element applied directly in contact with the forming drum  18 , may break during winding by effect of anomalous stresses caused by undesirable surface discontinuities of the forming drum  18 . 
     To this aim, the handling device  51  can carry out transfer of the forming drum  18  from the setting position  54  to the second and/or third work location  20 ,  21  after the initialising operation. 
     When application of the under-belt inserts  8   c  and/or possible other elements radially internal to the belt layers  8   a ,  8   b  has been completed, the forming drum  18  can be transferred again to the setting location  54  to be set to the desired deposition configuration. When setting is over, the handling device  51  transfers the forming drum  18  from the setting location  54  to the first work location  19  to form the belt layer or layers  8   a ,  8   b . Subsequently the handling device  51  can carry out transfer of the forming drum  18  from the first work location  19  to the second and/or third work location  20 ,  21 , to determine formation of the tread band  9  and of at least one portion of the sidewalls  10 . 
     When manufacture of the crown structure  7  has been completed, the handling device  51  can transfer the forming drum to the assembling station  100 , to enable engagement of the crown structure  7  by the second transfer member  22 . Following radial contraction of sectors  24  of the forming drum  18 , after unlocking of the first brakes  42   a , the forming drum  18  can be axially slipped off and disengaged from the crown structure  7  and be transferred again to the crown-structure building line  12  for starting manufacture of a new crown structure  7 . 
     If required, the forming drum  18  can be engaged again in the setting location  54 , before starting formation of a new crown structure  7  for setting the deposition surface  23  to a second deposition configuration or bringing back the deposition surface  23  to the maximum-contraction and minimum-curvature condition before forming the under-belt inserts  8   c  designed to build a new crown structure  7 . Alternatively, the forming drum  18  can be directly transferred to one of the first, second or third work location  19 ,  20 ,  21 , in particular if the geometrical and dimensional features of the new crown structure  7  do not require modifications in the shape of the deposition surface  23 . 
     The crown-structure building line  12  can be advantageously equipped with several forming drums, at least one first and one second forming drums  18   a ,  18   b , for example, to enable simultaneous processing of several crown structures  7 . 
     Each of the forming drums  18 , the first forming drum  18   a  for example, can be advantageously decoupled from the handling device  51  before formation of the crown structure  7  on the first forming drum  18  itself has been completed, to enable it to be conveniently engaged, supported and moved in the first, second and/or third work location  19 ,  20 ,  21 , by a second robotized arm or device of other type (not shown), for example, so as to form one or more of the corresponding components of the crown structure  7 . Thus the handling device  51  decoupled from the first forming drum  18   a  will be available for engaging the second forming drum  18   a  so as to start formation of a new crown structure  7 . 
     The handling device  51  itself will be in a position to be coupled with the first forming drum  18   a  again, to start a new work cycle and possibly set the deposition surface  23  of the first forming drum itself to a new deposition configuration.