Patent Publication Number: US-2009229738-A1

Title: Method and apparatus for manufacturing layered articles made of elastomeric material

Description:
The present invention relates to a method of manufacturing layered articles of elastomeric material. 
     The invention also relates to an apparatus for manufacturing layered articles of elastomeric material, following the above mentioned method. 
     During the present description the invention will be set out making specific reference to the manufacture of tyres for vehicle wheels. This does not exclude the possibility of manufacturing other different articles such as vulcanisation bladders used in tyre manufacturing processes, expandable bags used in tyre manufacturing apparatus, or still others. 
     A tyre for vehicle wheels generally comprises a carcass structure including at least one carcass ply made up of reinforcing cords incorporated in an elastomer matrix. The carcass ply has end flaps respectively engaged with annular reinforcing structures located in the regions usually identified as “beads” and each normally formed of a substantially circumferential annular insert onto which at least one filling insert is applied, at a radially external position. 
     Associated with the carcass ply at a radially external position is a belt structure comprising one or more belt layers disposed in radial superposed relationship with each other and having textile or metallic reinforcing cords with a crossed orientation and/or substantially parallel to the circumferential extension direction of the tyre. A tread band also made of elastomer material as other structural elements constituting the tyre, is applied to the belt structure, at a radially external position. 
     A so-called “under-layer” can be interposed between the tread band and the belt structure, said under-layer being made of elastomeric material having properties adapted to ensure a steady union of the tread band. 
     It is to be pointed out that to the aims of the present description with the term “elastomeric material” it is intended a composition comprising at least one elastomeric polymer and at least one reinforcing filler. Preferably, this composition further comprises additives such as a cross-linking agent and/or a plasticizer. Due to the presence of the cross-linking agent, this material can be cross-linked through heating so as to form the final article. 
     Respective sidewalls of elastomeric material are also applied 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 the carcass ply is fully coated with a layer of a preferably butyl-based elastomeric material usually referred to as “liner” having optimal airtightness features and extending from one of the beads to the other. 
     In tyres of the run flat type or for other particular uses, the carcass structure can further be provided with auxiliary support inserts of elastomeric material, located at an axially internal position to each of the sidewalls. These auxiliary support inserts usually called “sidewall inserts”, lend themselves to support the loads transmitted to the wheel in case of accidental deflation of the tyre, to enable the vehicle to go on running under safety conditions. 
     In many known processes for manufacturing a tyre the carcass structure and belt structure, as well as the tread band, sidewalls and any other structural element of elastomeric material, are made separately from each other in respective work stations, and then stowed in storage stations or magazines from which they are subsequently picked up for mutual-assembly purposes along a tyre manufacturing line. 
     Also recently developed have been production processes in which, as described in WO 01/36185 in the name of the same Applicant for example, the structural elements of the tyre are built on a suitably shaped forming support, by sequentially laying on the latter, a plurality of elementary components consisting of single rubberised cords or cords grouped together in parallel side by side relationship to form narrow strips for example, that are particularly used in the manufacture of the carcass and belt structures, and of continuous elongated elements of elastomeric material, particularly used for manufacturing other structural elements of the tyre such as tread band, sidewalls, liner, fillers, auxiliary support inserts. More specifically, a robotized arm bears a toroidal support on which each of the structural elements of a tyre under production is directly made. The robotized arm gives the toroidal support a circumferential-distribution motion around the geometric axis thereof, simultaneously with controlled displacements of transverse distribution in front of a delivery member supplying a continuous elongated element of elastomeric material. The continuous elongated element therefore forms a plurality of coils the orientation and mutual-superposition parameters of which are treated so as to control the thickness variations to be given to a structural element of a tyre being manufactured, based on a predetermined laying-down scheme pre-set in an electronic computer. 
     GB 1,048,241 teaches how to directly wind up on a tyre being manufactured, a continuous elongated element directly coming from an extruder so as to form coils disposed in axial side by side and/or radial superposition relationship in order to obtain the tread band. The tread band is directly made on the carcass sleeve of a cylindrical shape disposed on the building drum before the sleeve itself is shaped into a toroidal conformation. 
     In document WO 2004-041522, also in the name of the same Applicant, the carcass structure and belt structure of a tyre being manufactured are made through assembling of semi-finished structural elements on a building drum and an auxiliary drum respectively, while some other structural elements of elastomeric material, in particular the tread band, under-layer and/or sidewalls, are made through spiralling of a continuous elongated element produced by an extruder, directly onto the carcass and/or belt structures. 
     The applicant has encountered difficulties in obtaining under-layers or other structural elements of limited thickness through spiralling of a continuous elongated element directly coming from an extruder. Actually, to enable the continuous elongated element to have a sufficient structural consistency for subsequent handling and to be extruded with the necessary regularity, the thickness of said element is required not to be under given values. Extrusion of a continuous elongated element of a small thickness in addition would impose important restrictions to the exit speed of the element itself from the extrusion die, with possible productivity drops. 
     The applicant has also perceived that if the under-layer and tread band are made in two distinct work stations by means of said continuous elongated element, it is not possible to fully exploit the production capacities of the installation designed for tyre manufacture. 
     In spite of the above listed problems relating to said restrictions in the exit speed of the continuous elongated element from the extrusion die, the Applicant has however ascertained that manufacture of the under-layer is tendentially completed in greatly shorter times than those required for manufacturing the tread band having a much greater thickness than that of the under-layer. Consequently, the work station dedicated to manufacture of the under-layer is necessarily submitted to important stand-by times between working of two tyres in succession, to enable the work station dedicated to manufacture of the tread band to complete working. 
     In accordance with the present invention, the Applicant has perceived that if the material designed to form the under-layer (or other relatively thin structural element) is coupled with at least part of the material designed to form the tread band (or other structural element to be manufactured adjacent to the thin element) before carrying out spiralling, a continuous elongated element of a suitable structural consistency can be obtained which is adapted to, for example, give a very thin under-layer simultaneously with part of the tread band. 
     The Applicant has therefore found that by preparing a continuous elongated element through co-extrusion of a first and a second elastomeric materials, and spiralling said element so as to obtain a layered component on the forming support, the productivity can also be increased in the manufacture of very thin structural elements and, in case of need, a better distribution can be obtained as regards the working time required from different work stations co-operating in producing the tyre. 
     In the present specification and in the following claims, by “layered component” it is intended a structural tyre element or a portion thereof. 
     Within the present definition, by “structural element” of the tyre it is intended any part made of elastomeric material such as the tread band, sidewalls, auxiliary support inserts, fillers, liner and/or under-liner, or a portion thereof, or also the assembly formed of two or more of said parts or portions. 
     In the present specification and in the following claims, by “layered element” it is intended an article of manufacture different from a tyre or from a structural element thereof, such as a vulcanisation bladder, an expandable bag and the like, or a portion of same. 
     In more detail, the invention relates to a method of manufacturing a tyre for vehicle wheels, comprising the steps of: forming a carcass structure comprising elongated reinforcing elements incorporated in an elastomer matrix; associating structural elements of elastomeric material with said carcass structure; wherein the step of associating structural elements of elastomeric material with the carcass structure comprises preparation of at least one layered component through the steps of: conveying a first and a second elastomeric materials to an extrusion die; coupling the first and second elastomeric materials through said extrusion die, to deliver a first continuous elongated element defined by a first longitudinal portion and a second longitudinal portion disposed side by side and respectively made up of said first and second elastomeric materials; laying said continuous elongated element on a forming support by means of coils wound up according to a predetermined path so as to form said layered component consisting of a first layer and a second layer made by said first and second elastomeric materials, respectively; curing the tyre. 
     In accordance with a further aspect, it is an object of the invention to provide an apparatus for manufacturing tyres of vehicle wheels comprising: devices designed to form a carcass structure comprising elongated reinforcing elements incorporated in an elastomer matrix, devices for associating structural elements of elastomeric material with said carcass structure; devices for curing said tyre, wherein the devices for associating the structural elements of elastomeric material with the carcass structure comprise at least one unit for manufacturing layered components, comprising: first devices for feeding a first elastomeric material; second devices for feeding a second elastomeric material; an extrusion die communicating with said first and second feeding devices to deliver a first continuous elongated element defined by a first longitudinal portion and a second longitudinal portion disposed close to each other and made up of said first and second elastomeric materials, respectively; members for laying said continuous elongated element on a forming support in the form of coils wound up following a predetermined path, so as to obtain a layered component having a first layer and a second layer consisting of said first and second elastomeric materials, respectively. 
     Further features and advantages will become more apparent from the de-ailed description of a preferred but not exclusive embodiment of a method and an apparatus for manufacturing tyres for vehicle wheels or other articles of elastomeric material, in accordance with the present invention. 
    
    
     
       This description will be set out hereinafter with reference to the accompanying drawings, given by way of non-limiting example, in which: 
         FIG. 1  is a diagrammatic top view of an apparatus for manufacturing tyres in accordance with the present invention; 
         FIG. 2  is an elevation view of a portion of the apparatus shown in  FIG. 1 ; 
         FIG. 3  shows a detail of an extrusion die, sectioned along a diametral plane identified with III-III in  FIGS. 6 and 7 ; 
         FIG. 4  is a fragmentary perspective view in a cross section plane of a continuous elongated element emerging from the extrusion die; 
         FIG. 5  is a fragmentary perspective view in a cross section plane of a further example of a continuous elongated element obtainable in accordance with the invention; 
         FIG. 6  shows a section taken along line VI-VI in  FIG. 3 , during extrusion of a continuous elongated element as seen in  FIG. 4 ; 
         FIG. 7  shows a section taken along line VII-VII in  FIG. 3 , during extrusion of a continuous elongated element as seen in  FIG. 5 ; 
         FIG. 8  is a laying-down scheme given by way of example, of the continuous elongated element seen in  FIG. 4 , in the form of coils disposed close to each other, in order to obtain a layered component; 
         FIG. 9  is a fragmentary diagrammatic cross-section view of a tyre obtainable in accordance with the present invention. 
     
    
    
     Referring particularly to  FIGS. 1 and 2 , an apparatus for manufacturing tyres for vehicle wheels designed to put into practice a manufacturing method in accordance with the present invention has been generally identified with reference numeral  100 . 
     In the embodiment shown, apparatus  100  is set for manufacturing tyres of the type shown by way of example in  FIG. 9  and generally denoted at  1 . Tyre  1  essentially comprises a carcass structure  2  of substantially toroidal conformation comprising cords or other elongated reinforcing elements incorporated in an elastomer matrix, and structural elements of elastomeric material  5 ,  8 ,  9 ,  10 ,  11  associated with the carcass structure  2 , as better described in the following. 
     In more detail, the carcass structure  2  may for example comprises a pair of annular anchoring structures  3  integrated into the regions usually identified as “beads”; each consisting of at least one substantially circumferential annular insert  4 , usually called “bead core”, formed of one or more rubberised cords or equivalent elongated reinforcing elements incorporated in an elastomer matrix. An elastomeric filling  5  can be applied to the bead ring  4  at a radially external position. In engagement with each of the annular anchoring structures  3  are the end flaps  6   a  of at least one carcass ply  6  comprising textile or metallic rubberised cords, or equivalent elongated reinforcing elements incorporated in an elastomer matrix and extending transversely of the circumferential extension of tyre  2 , possibly with a predetermined inclination, from one of the annular anchoring structures  3  to the other. 
     In tyres of the tubeless type, i.e. without an air tube, the carcass structure  2  at a radially internal position is provided with a layer of a substantially airtight elastomeric material generally referred to as “liner” and not shown. 
     Usually associated with the carcass structure  2  is also one or more belt layers  7   a ,  7   b  comprising metallic or textile rubberised cords or equivalent elongated reinforcing elements incorporated in an elastomer matrix, suitably inclined relative to the circumferential extension of the tyre according to preferably crossed orientations between one belt layer and the other, as well as a possible outer belting layer (not shown) comprising one or more cords circumferentially wound into coils disposed axially in side by side relationship around the belt layers  7   a ,  7   b . The assembly consisting of the belt layers  7   a ,  7   b  and the possible outer belting layer defines a so-called belt structure generally denoted at  7 , of a substantially cylindrical annular conformation, applied at a radially external position around the carcass structure  2 . To the aims of the present specification and the following claims, the belt structure  7 , while described as a distinct component, is considered (when not otherwise expressly stated) to be an integral part of the carcass structure  2 . 
     Further associated with the carcass structure  2  is a tread band  8  circumferentially applied to the belt structure  7  at a radially external position, after possible interposition of a so-called “under-layer”  9  formed of a thin layer of elastomeric material having suitable composition and physico-chemical features and acting as an interface between the true tread band and the underlying belt structure  7 . A pair of sidewalls  10  is laterally applied to the carcass structure  2  at respectively opposite sides. 
     In run flat tyres or tyres intended for particular uses, auxiliary support inserts  11  may be also provided, of the type usually referred to as “sidewall inserts” for example, that are applied to the region close to the sidewalls  10  internally of the carcass ply  6 , as shown by way of example in  FIG. 1 , or between two paired carcass plies or also at a position radially external to the carcass structure  2 . 
     Tyre  1  lends itself to be obtained using a manufacturing apparatus  100  essentially comprising devices designed to form the carcass structure  2  and devices for carrying out association of the carcass structure  2  with the tread band  8 , sidewalls  10 , possible auxiliary support inserts  11 , said liner and/or other structural elements of elastomeric material co-operating in forming tyre  1 . 
     The individual components of the carcass structure  2  and the belt structure  7  such as in particular the annular anchoring structures  3 , carcass ply or plies  6 , belt layers  7   a ,  7   b  and further possible reinforcements designed to constitute the outer belting layer, can be supplied to apparatus  100  in the form of semi-finished products, made in preceding working steps, to be suitably assembled with each other. 
     In this case, the devices for making the carcass structure  2  can usually comprise a manufacturing line  101 , not described in detail as obtainable in any convenient manner, having a building drum  102  on which the carcass ply or plies  6  coming from a feeding unit  103  are first wound up so as to form a so-called “carcass sleeve” that is substantially cylindrical. Fitted on the end flaps  6   a  of the carcass ply/plies  6  are the annular anchoring structures  3 , so that afterwards turning up of the end flaps themselves is carried out to cause engagement of the anchoring structures in the loops thus formed by the turned-up ply/plies  6 . If required, the manufacturing line  101  may comprise devices for associating auxiliary support inserts with the carcass ply or plies  6 , which auxiliary inserts are applied during preliminary steps or steps alternated with the steps of laying the ply or plies  6  and/or other components of the carcass structure  2 . In particular, application of said auxiliary support inserts  11  or “sidewall inserts” can be provided directly on the building drum  102  before application of the carcass ply or plies  6 , or on one of the carcass plies before application of an additional carcass ply  6 . 
     When assembling of the components has been completed, transfer devices not shown pick up the carcass structure  2  from the building drum  102  to transfer it onto a primary drum  104 , of the type usually referred to as “shaping drum” for example, to produce the tyre following a manufacturing process of the so-called “two-stage” type. 
     Alternatively, assembling of the components of the carcass structure  2  can be directly carried out on the primary drum  104 , to produce the tyre following a manufacturing process of the so-called “unistage” type. 
     Simultaneously with assembling of the carcass structure  2  on the building drum  102  or directly on the primary drum  104 , the belt structure  7  is made on an auxiliary drum  105 . More particularly, to this aim the auxiliary drum  105  is provided to interact with devices  106  for application of the belt structure  7  that can for example comprise at least one feeding unit  107  along which semifinished products in the form of a continuous strip are moved forward, to be then cut into sections of a length corresponding to the extension of the auxiliary drum  105 , concurrently with formation of the corresponding belt layers  7   a ,  7   b  thereon. Combined with the unit for feeding the belt layers  107  can be a feeding unit for supplying one or more additional reinforcing inserts such as continuous cords (not shown in the drawings) to be applied to the belt layers  7   a ,  7   b  so as to form the outer belting layer in the form of axially contiguous circumferential coils. 
     Upon the action of suitable transfer devices  108 , the belt structure  7  disposed on the auxiliary drum  105  lends itself to be picked up from the latter and transferred onto the carcass structure  2  shaped as a cylindrical sleeve and disposed on the primary, drum  104 . The transfer devices  108  may comprise a transfer member of substantially annular conformation that is moved until it is disposed around the auxiliary drum  105  to pick up the belt structure  7  therefrom. In a manner known by itself, the auxiliary drum  105  releases the belt structure  7  that is then moved by the transfer member  108  to be placed to a radially external position relative to the primary drum  104  carrying the carcass structure  2  and coaxially centred thereon. 
     The primary drum  104  can be provided to be picked up from the manufacturing line  101  and transferred to a position suitable for interaction with the transfer member  108  by a suitable laying-down member such as a robotized arm  109 . The robotized arm  109  preferably comprises a base  110  rotatable on a fixed platform  111  around a first vertical axis, a first section  112  linked to base  110  in an oscillating manner around a second preferably horizontal axis, a second section  113  linked to the first section  112  in an oscillating manner along a third axis, also preferably horizontal, and a third section  114  rotatably supported by the second section  113  along an axis orthogonal to the third oscillation axis. Linked to the end of the third section  114  of the robotized arm  109  with possibility of oscillation around a fifth and a sixth oscillation axes orthogonal to each other, is a head  115  carrying a motor  116  for rotational driving of the primary drum  104 , susceptible of engagement with the head itself in cantilevered fashion. 
     The robotized arm  109  therefore is adapted to support and control movement of the primary drum  104  or other forming support during the whole production cycle, conveniently positioning it for interaction with the manufacturing line  101  and, subsequently, with the transfer member  108  for the belt structure  7 . 
     The carcass structure  2  coaxially positioned within the belt structure  7  retained by the transfer member  108  is shaped in a toroidal configuration through mutual axial approaching of the annular anchoring structures  3  and simultaneous admission of fluid under pressure into said carcass structure until the carcass ply or plies  6  are brought into contact with the inner surface of the belt structure  7 . 
     Alternatively, the primary drum  104  can consist of a rigid forming support conforming in shape to the inner surface of tyre  1  under production. In this case, manufacture of the carcass structure  2  and the respective belt structure  7  can be directly carried out on the primary drum  104  while the latter is sequentially brought, through the robotized arm  109  or other suitable devices, to interact with one or more work stations located along the manufacturing line  101 , to directly form the carcass ply  6 , annular anchoring structures  3 , belt layers  7   a ,  7   b  and/or other constituent elements of tyre  1  through laying of elementary components such as narrow strips of rubberised cords, and/or continuous elongated elements of elastomeric material, as described for example in document U.S. Pat. No. 6,457,504 in the name of the same Applicant. 
     The structural elements of elastomeric material of tyre  1 , such as the tread band  8 , under-layer  9 , sidewalls  10 , auxiliary support inserts  11 , said liner, or at least one of them, can be in turn made by winding at least one continuous elongated element  117  of elastomeric material into contiguous circumferential coils, around a forming support that, in the embodiment shown, is represented by the carcass structure  2  in engagement with the primary drum  104  and carrying the respective belt structure  7 . 
     Alternatively, the forming support can consist of the primary drum  104  itself. Said primary drum can be made in the form of a rigid drum conforming in shape to the inner surface extension of tyre  1 . 
     In more detail, the sidewalls  10  can be made directly against the side surfaces of the carcass ply  6 . The tread band  8  can be in turn manufactured at a radially external position to the carcass structure  2  and more specifically on the belt structure  7 , before or after assembling of the belt structure to the carcass structure  2 . Other structural elements such as the liner, possible auxiliary support inserts  11  and/or other structural elements disposed at the inner surfaces of tyre  1 , or to be applied to the carcass structure  2  at a second time, can be directly made on the primary drum  104  or other forming support in the form of a rigid drum. 
     In a preferential embodiment the devices set to associate the structural elements of elastomeric material  8 ,  9 ,  10 ,  11  with the carcass structure  2  comprise at least one unit for manufacturing layered components  118  that, in the embodiment shown, is specifically dedicated to the manufacture of the tread band  8  and the related under-layer  9 . 
     The unit for manufacturing layered components  118  comprises at least one extrusion die  119  communicating with a first extruder  120  and a second extruder  121  or other suitable feeding devices, set to send a first and a second elastomeric materials having different compositions from each other to the extrusion die itself. In the embodiment described, the first elastomeric material is designed and formulated for manufacturing the under-layer  9 , whereas the second elastomeric material has a formulation suitable for manufacturing the tread band  8 . 
     As better shown in  FIG. 3 , die  119  communicates with the first and second extruders  120 ,  121  through a first and a second inlet channels  122 ,  123  respectively, that convey the first and second elastomeric materials towards an outflow port  124  arranged in the die itself. The first and second materials flowing through the extrusion die  119  are mutually coupled ( FIGS. 4 and 5 ) so that through the outflow port  124  a first continuous elongated element  117  is delivered that is defined by a first longitudinal portion  125  and a second longitudinal portion  126  disposed close to each other and made up of the first and second elastomeric materials, respectively. In more detail, the outflow port  124  preferably has a perimetral profile of a substantially flattened conformation, the size of greater width of which corresponds to at least 1.5 times the size of smaller width. Correspondingly, the continuous elongated element  117  extruded through the outflow port  124  will have a substantially flattened cross-section profile with a width L at least equal to 1.5 times the thickness H size. As shown in  FIGS. 4 and 5 , the width L and thickness H of the continuous elongated element  117  correspond to the size of greater width and the size of smaller width respectively of the outflow port  124 . 
     As can be viewed from  FIG. 3 , the first and second inlet channels  122 ,  123  converge towards the outflow port  124  at positions that are substantially aligned with each other and parallel to the size of greater width L. Consequently, according to the conformation of the continuous elongated element  117  extruded from the outflow port  124 , the first and second longitudinal portions  125 ,  126  are respectively aligned along a main extension axis Z of the cross-section profile of the elongated element, as shown in  FIGS. 4 and 5 . 
     It is also preferably provided that the first and second inlet channels  122 ,  123  be separated from each other, at the die  119 , by means of a partition  127  at a distal position relative to said outflow port  124 . Preferably, the partition  127  is substantially disposed in a plane that is inclined to the size of greater width L of the outflow port  124 , so that in the continuous elongated element  117  obtained, the first and second longitudinal portions  125 ,  126  are delimited by an interface line  117   a  correspondingly inclined to the main extension axis Z, just as an indication according to an angle preferably included between about 15° and about 90°, and more preferably included between about 40° and about 50°. 
     Alternatively, the first and second longitudinal portions  125 ,  126  can be provided to be superposed in a direction perpendicular to the main extension axis Z and preferably delimited by an interface line  117   a  substantially parallel to the main extension axis Z. 
     The continuous elongated element  117  coming out of the extrusion die  119  is laid on the carcass structure  2  or other forming support  104  in the form of coils wound up following a predetermined path. 
     To this aim, through the robotized arm  109 , the carcass structure  2  carried by the primary drum  103  or other forming support, is positioned in front of the outflow port  124  of the extrusion nozzle  119  and submitted to a circumferential-distribution rotatory motion around a geometric rotation axis X thereof, upon the action of motor  116  or other suitable rotational-driving devices. By effect of this circumferential-distribution rotatory motion the continuous elongated element delivered from the outflow port  124  is suitably distributed, to form the circumferential coils  128  on the forming support  2 ,  104 . 
     Simultaneously, the different movable sections  112 ,  113 ,  114  and/or the head  115  associated with the robotized arm  109 , and/or other suitable translational-driving devices, move the forming support  2 ,  104  in front of the extrusion die  119  through controlled relative displacements of transverse distribution, so that the coils  128  made up of the continuous elongated element  117  are distributed according to a desired path to cause formation of at least one layered component  129  having a first layer  130  and a second layer  131  consisting of the first and second elastomeric materials, respectively. 
     In more detail, each of the coils  128  formed following laying of the continuous elongated element  117  identifies therealong, a corresponding stretch of the first longitudinal portion  125  coupled with a corresponding stretch of the second longitudinal portion  126 . Laying is carried out in such a manner that the consecutive stretches of the first longitudinal portion  125  belonging each to one of the coils  128 , are disposed against each other to form the first layer  130  preferably having a thickness included between about 0.2 mm and about 10 mm and more preferably between about 2 mm and about 6 mm. The consecutive stretches of the second longitudinal portion  126 , in turn, belonging each to one of the coils  128 , are disposed against each other, to form the second layer  131  overlapping the first layer  130 . 
     If the first and second longitudinal portions  125 ,  126  of the continuous elongated element  117  are superposed at right angles relative to the main extension axis Z, the above described formation of layers  130 ,  131  can be obtained by disposing the longitudinal element itself in such a manner that, during formation of each coil  128 , the main extension axis Z is substantially parallel to a plane tangent to the surface of the forming support  2 ,  104 , at the laying point of the elongated element itself. 
     If, on the contrary, as in the example shown in  FIGS. 4 and 5 , the first and second longitudinal portions  125 ,  126  of the continuous elongated element  117  are aligned in parallel relationship with the main axis Z, each of the coils  128  is provided to partly overlap the previously formed coil, except for laying of the first coil, so that the second longitudinal portion  126  of the elongated element, in the stretch belonging to each coil  128 , is superposed relative to the first longitudinal portion  125 . The first longitudinal portion  125  in turn will be at least partly interposed between the forming support  2 ,  104  and the second longitudinal portion  126  of the continuous elongated element  117 . 
     Therefore it is advantageously possible to manufacture, in a single operation, a first structural element represented by the first layer  130 , together with at least one portion of a second structural element represented by the second layer  131 . In the described example and with reference to the accompanying drawings, the first and second structural elements are represented by the under-layer  9  and tread band  8  respectively, that are directly made at a radially external position to the carcass structure  2  and more specifically on the belt structure  7 , before or after associating said belt structure with the remaining parts of the carcass structure  2 . 
     If required, the first layer  130  can advantageously have a very reduced thickness, even smaller than 0.5 mm, without involving complications in the correct laying of the continuous elongated element  117 . In fact, even if the first longitudinal portion  125  designed to form the first layer  130  has small sizes, the presence of the second longitudinal portion  126  coupled therewith enables a continuous and uniform dragging along of the first longitudinal portion emerging from die  119  and ensures a structural consistency to the continuous elongated element as a whole, which is suitable for correct laying on the forming support. 
     If required, the first and/or second extruders  120 ,  121  can be equipped with control devices, not further described or illustrated as they can be made in any convenient manner, which for example enable the operation speed of the extruders themselves to be modified and/or the amount of the elastomeric material sent into the die  119  to be partly reduced so as to suitably modulate delivery of the first and/or second elastomeric material at the exit. Thus it is possible to obtain thickness variations in the first and/or second layers  130 ,  131  during delivery, or to keep the thickness of the obtained layered components to a predetermined constant value, or also to make structural elements of variable thickness. 
     In case of need, the control devices can also disable delivery of the first and/or second material thereby allowing delivery of a continuous elongated element  117  made of a single material. This also enables manufacture of layered components  129  in which the first and/or second layer  130 ,  131  have an interrupted and/or alternated extension. 
     If required, at least one covering layer  132  of elastomeric material can be applied to the layered component  129 , said covering layer preferably having the same composition as the second layer  131  of the layered component that will be interposed between the first layer  130  and the covering layer itself. 
     This solution is particularly advantageous when the second layer  131  of the layered component  129  must only constitute part of the structural element coupled with the first layer  130 . 
     In the embodiment shown, the covering layer  132  is formed by a first auxiliary unit  133  comprising a third extruder  134  or equivalent devices designed to deliver a second continuous elongated element (not shown) onto the layered component  129  previously formed on the carcass structure  2 , or other forming support that, through the robotized arm  109 , is brought in front of the auxiliary unit itself and suitably driven in rotation and moved in front of the latter so that the second continuous elongated element is distributed into coils wound up according to a predetermined path. Thus the covering layer  132  is obtained, which layer in the embodiment herein shown, together with the second layer  131  of the layered component  129  forms the tread band  8 . 
     As an alternative to the above description, the covering layer  132  can be prepared as a semifinished product in the form of a continuous strip of a length corresponding to the circumferential extension of the layered component  129 . In this case, the auxiliary unit  133  will be provided with devices for winding the strip of elastomeric material on the layered component  129  and for mutually joining the opposite ends of the strip wound up on said layered component  129 , in a manner known by itself. 
     It is to be pointed out that the auxiliary unit  133  utilised for manufacturing the covering layer  132  will require a lower productivity than that usually needed in the known art for the units dedicated to the manufacture of the whole tread band  8 . 
     In addition to, or in place of the first auxiliary unit  133 , a second auxiliary unit (not shown) can be provided, said unit being designed to apply at least one base layer of elastomeric material to the carcass structure  2  or other forming support, said base layer being interposed between the forming support itself and the first layer  130  of the layered component  129 , subsequently formed on the base layer. In the same manner as described with reference to the first auxiliary unit  133 , this second auxiliary unit too may comprise a respective extruder or similar devices, to deliver a third continuous elongated element disposed in a manner adapted to form coils wound up in a predetermined path on the carcass structure  2  or other forming support positioned and suitably moved in front of the auxiliary unit itself by means of the robotized arm  109  or other handling devices. 
     Alternatively, the second auxiliary unit may comprise devices designed to arrange a semifinished product of elastomeric material in the form of a strip of a length corresponding to the circumferential extension of the carcass structure  2  or other forming support, then winding this strip on the forming support and subsequently joining the opposite ends of the strip wound up on said forming support. 
     The base layer can be made of the same material as, or a material compatible with, the material forming the first layer  130  that will be interposed between the base layer itself and the second layer  131  of the layered component  129 . In case of need, this enables the obtainable thickness of the first layer  130  in the layered component  129  to be increased and/or the layered component  129  to be coupled with any different structural element constituting the base layer. 
     In addition to, or in place of formation of the tread band  8  and respective under-layer  9 , the above described unit  118  for manufacturing layered components can be designed for manufacturing the sidewalls  10 , possible auxiliary support inserts  11 , said liner and/or any other structural element of elastomeric material of the tyre  1  under working. 
     In more detail, operation of the robotized arm  109  and of unit  118  for manufacturing layered components, or a similar unit combined with apparatus  1 , may be provided to be co-ordinated so as to cause formation of the continuous elongated element  117  laterally against the carcass structure  2 , the obtained layered component  129  thereby constituting at least part of the sidewall  10  of tyre  1 . Thus, sidewalls  10  made up of two or more portions consisting of different elastomeric materials can be manufactured. 
     In addition or as an alternative to the above, operation of unit  118  for manufacturing layered components and of the robotized arm  109  can be co-ordinated so as to carry out laying of the continuous elongated element  117  at an axially external position to the forming support, before or after application of the carcass structure  2 , to manufacture possible auxiliary support inserts  11  that, after the carcass structure  2  is disposed on the forming support, will appear to be laterally applied, at the inside or outside of the carcass ply  6 . 
     Likewise, a unit  118  for manufacturing layered components can be used to make a liner in combination with a so-called under-liner and/or at least part of the possible auxiliary support inserts  11  or other structural elements of tyre  1 , to be set internally of the carcass structure  2 . 
     When manufacture of the tread band  8  and sidewalls  10  has been completed, the robotized arm  109  carries out a new translation of the primary drum  104  to position it in front of devices that, if required, disengage the assembled tyre  1  from said primary drum  140  and transfer it into a mould or other devices used for carrying out a moulding and curing step on the tyre itself. 
     It will be recognised that the invention can be also advantageously utilised, with the aid of the unit for forming layered components of the above described type, for making manufactured articles different from tyres for motor-vehicles. In particular, the invention can be for example used for making layered elements such as expandable bladders of the type currently used in vulcanisation apparatus and/or inflatable bags used in apparatus for manufacturing the tyres themselves.