Process and plant for building tyres for vehicle wheels

Abstract

In a shaping station (13), a toroidal forming drum (23) is positioned within a carcass sleeve (12) comprising at least one carcass ply (3) associated with a pair of beads (6) in radially inner position. The carcass sleeve (12) is toroidally shaped by radial expansion of the forming drum (23). The forming drum (23) carrying the shaped carcass sleeve (12) is removed from the shaping station (13). Tyre components (7, 8, 9) are applied externally on the shaped carcass sleeve (12), carried by the forming drum (23). At the end of the shaping and during the application of the tyre components (7, 8, 9), axially inner sides of said beads (6) are arranged axially against respective circumferential axially outer portions (S1) of an abutment surface (S) carried by the expanded forming drum (23), having shape corresponding to an inner shape of the shaped carcass sleeve (12).

Claims

1. A process for building tyres comprising: positioning, in a shaping station, a toroidal forming drum within a carcass sleeve comprising at least one carcass ply associated with a pair of beads; wherein after positioning in the shaping station, the carcass sleeve is engaged by one or more gripping elements operating axially and/or radially inside the beads; shaping the carcass sleeve toroidally by radial expansion of the forming drum from a first, radially contracted, operating condition, up to a second, radially expanded, operating condition forming an expanded forming drum, the expanded forming drum having a toroidal shape corresponding to an inner shape of the shaped carcass sleeve; wherein during shaping by radial expansion of the forming drum, the one or more gripping elements disengage the beads after a radially outer portion of the forming drum has abutted against the carcass sleeve; imposing a controlled tension to the carcass sleeve by the expanded forming drum at the second, radially expanded, operating condition after the end of the shaping and causing the beads, due to the controlled tension, to act in axial thrust relation against respective axially outer circumferential portions of an abutment surface carried by the expanded forming drum; removing the forming drum carrying the shaped carcass sleeve from the shaping station; and applying sidewall portions externally on the shaped carcass sleeve carried by the expanded forming drum; wherein the sidewall portions are applied by wrapping at least one elongated continuous element made of elastomeric material according to circumferential turns against axially opposite lateral portions of the carcass sleeve in proximity to the beads, while the forming drum rotates and moves to distribute the circumferential turns according to a predefined scheme; wherein wrapping of the elongated continuous element takes place with the aid of an applicator roller exerting a thrust action on the carcass sleeve; further comprising maintaining the controlled tension to the carcass sleeve by the expanded forming drum at the second, radially expanded, operating condition after the end of the shaping and causing the beads, due to the controlled tension, to maintain their axial thrust action against the expanded forming drum after the end of shaping, wherein during the application of said sidewall portions, entire axially inner surfaces of said beads are in axial thrust relation against the respective axially outer circumferential portions of the abutment surface, while the beads oppose the thrust action exerted by the applicator roller in proximity to radially inner edges of the forming drum.

2. The process according to claim 1, wherein shaping takes place due to a radial thrust action exerted by the radial extension of the forming drum directly against the carcass sleeve.

3. The process according to claim 2, wherein shaping takes place absent internal pressurization of the carcass sleeve.

4. The process according to claim 3, wherein during shaping, radially inner parts of the carcass sleeve are in fluid communication with an external environment.

5. The process according to claim 4, further comprising engaging the carcass sleeve prior to the shaping by radially expanding the one or more gripping elements, wherein each is axially inside one of said beads.

6. The process according to claim 5, wherein before the shaping of the carcass sleeve is completed, the one or more gripping elements disengage the beads during the radial expansion of the forming drum.

7. The process according to claim 6, wherein during shaping, the one or more gripping elements are disengaged from the beads after said abutment surface has abutted against the carcass sleeve.

8. The process according to claim 7, wherein before being placed within the carcass sleeve, the forming drum is arranged in the first, radially contracted, operating condition.

9. The process according to claim 8, wherein during the shaping of the carcass sleeve, translating circumferentially consecutive sectors of said forming drum radially between the first, radially contracted, operating condition wherein said sectors are approached with respect to a geometric rotation axis of the forming drum, and the second, radially expanded, operating condition wherein the sectors are radially distanced from said geometric rotation axis to define said abutment surface.

10. The process according to claim 9, wherein shaping takes place by the radial moving away of the sectors of the forming drum up to said second operating condition.

11. The process according to claim 10, wherein said axially outer circumferential portions are on circumferentially consecutive sectors of the forming drum.

12. The process according to claim 11, wherein each of said sectors has, in radially outer position, a cross section profile extending according to said abutment surface from one to the other of said axially outer circumferential portions.

13. The process according to claim 12, further comprising axially moving away the beads one with respect to the other, before said abutment surface abuts against the carcass sleeve.

14. The process according to claim 13, wherein the abutment surface is at least partly defined by a stratiform coating applied on the forming drum.

15. The process according to claim 14, wherein said stratiform coating comprises an elastic membrane.

16. The process according to claim 15, wherein during the radial expansion of the forming drum, said stratiform coating expands in sliding contact relation against the sectors.

17. The process according to claim 16, wherein during the radial expansion of the forming drum, said stratiform coating expands in substantially static contact relation against the radially inner surface of the carcass sleeve.

18. The process according to claim 17, wherein during the radial expansion of the forming drum, said stratiform coating expands in substantial absence of sliding with respect to the radially inner surface of the carcass sleeve.

19. The process according to claim 18, wherein during the radial expansion of the forming drum, the abutment surface abuts against the carcass sleeve progressively towards the beads.

20. The process according to claim 19, wherein during the radial expansion of the forming drum, a progressive axial approach of the beads towards the abutment surface is carried out as a result of tensions transmitted through the carcass sleeve.

21. The process according claim 20, wherein prior to the shaping, the carcass sleeve is axially centered with respect to the forming drum.

22. The process according claim 21, wherein prior to the shaping by the axial movement of the one or more gripping elements, the carcass sleeve is axially centered with respect to the forming drum.

23. The process according claim 22, wherein before positioning, the carcass sleeve is made in at least one building location and subsequently transferred to said shaping station.

24. The process according to claim 23, wherein during positioning, the carcass sleeve is arranged around the forming drum arranged in the shaping station by a relative axial translation between the carcass sleeve and the forming drum.

25. The process according to claim 24, wherein before applying, the expanded forming drum is transferred to deposition devices to build, externally on the carcass sleeve, the sidewall portions.

26. The process according to claim 25, wherein the one or more tyre components is made by wrapping at least one elongated continuous element according to circumferential turns axially side by side around a radially outer surface of the carcass sleeve coupled to the expanded forming drum.

27. The process according to claim 26, wherein the one or more tyre components comprises at least one sidewall portion with a radially inner apex joining with one of said beads.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Such description will be set forth hereinbelow with reference to the enclosed drawings, provided only as a non-limiting example, in which:

(2) FIG. 1 schematically shows a top view of a plant for building tyres in accordance with the present invention;

(3) FIG. 2 schematically shows a side view in partial section of the loading of a carcass sleeve on a shaping station;

(4) FIG. 3 schematically shows a side view in partial section of the action of centring the carcass sleeve with respect to a expandable forming drum engaged within the carcass sleeve itself;

(5) FIG. 4 schematically shows a side view of the carcass sleeve immediately after an initial shaping step;

(6) FIG. 5 schematically shows a side view of the carcass sleeve engaged with the forming drum at the end of the shaping;

(7) FIG. 6 shows a perspective view of several sectors of a forming drum in a first operating condition, radially contracted;

(8) FIG. 7 shows the sectors of FIG. 6 in a second operating condition, radially expanded;

(9) FIGS. 8 and 9 show a single sector of the forming drum seen in perspective view from respectively opposite angles;

(10) FIG. 10 shows the application of a belt layer on the shaped carcass sleeve that is coupled to a forming drum;

(11) FIG. 11 shows the application of a sidewall on the shaped carcass sleeve that is coupled to a forming drum;

(12) FIG. 12 schematically shows a radial half-section of a tyre attainable in accordance with the present invention.

(13) With reference to the abovementioned figures, reference number 1 overall indicates a plant for building tyres for vehicle wheels, arranged to actuate a process according to the present invention.

(14) The plant 1 is set to make tyres 2 (FIG. 12) essentially comprising at least one carcass ply 3 preferably internally covered by a layer of impermeable elastomeric material or so-called liner 4. Two anchoring annular structures 5, each comprising a so-called bead core 5a, are engaged with respective end flaps 3a of the carcass ply/plies 3. Each bead core 5a preferably carries an elastomeric filler 5b in radially outer position. The anchoring annular structures 5 are integrated in proximity to zones normally identified with the name beads 6, at which the engagement between the tyre 2 and a respective mounting rim (not depicted) normally takes place.

(15) A belt structure 7 is circumferentially applied around the carcass ply/plies 3, and a tread band 8 is circumferentially superimposed on the belt structure 7. Two sidewalls 9, each extending from the corresponding bead 6 to a corresponding lateral edge of the tread band 8, are applied in laterally opposite positions on the carcass ply/plies 3. Each sidewall 9 can have a radially inner apex 9a joining with one of said beads 6, and a radially outer apex 9b joining with an axially outer edge of the tread band 8.

(16) The plant 1 comprises a carcass building line 10 having one or more building locations 11 where the making of a carcass sleeve having substantially cylindrical shape is executed, for example according to known modes. The carcass sleeve 12 comprises said at least one carcass ply 3, preferably internally covered by the liner 4, and having the respective end flaps 3a engaged, e.g. by means of turning up, with the respective anchoring annular structures 5. If necessary, the carcass sleeve 12 made on the carcass building line 10 can also comprise the sidewalls 9 or portions thereof, each extending starting from a respective bead 6.

(17) The carcass building line 10 refers to a shaping station 13 comprising engagement devices 14 for the carcass sleeve 12 and shaping devices 15, upon action whereof the carcass sleeve 12 is shaped according to a toroidal configuration.

(18) The engagement devices 14 comprise for example a first gripping element 16a and a second gripping element 16b preferably annular, coaxially facing each other and having respective circumferential engagement seats 17a, 17b, radially expandable, by means of which they are operatively engageable, each at one of the beads 6 respectively carried by the axially opposite ends of the carcass sleeve 12.

(19) The engagement devices 14 can also comprise axial movement members 18 for the gripping elements 16a, 16b. More in detail, provision can be made such that at least one of the gripping elements 16a, 16b, for example the first gripping element 16a, is carried by a movable carriage 19 along one or more linear guides 20, parallel to a geometric axis of mutual alignment between the gripping elements 16a, 16b and preferably integral with respect to a fixed base 21, carrying the second gripping element 16b. The movement of the carriage 19 along the linear guides 20 determines the communication of the shaping station 13 between a condition of loading/unloading and a working condition. In the loading/unloading condition (FIG. 2), the first gripping element 16a is spaced from the second gripping element 16b according to an extent that is greaterexplanatorily at least doublethan an axial dimension of the non-shaped carcass sleeve 12, coming from the carcass building line 10. In the working condition, the gripping elements 16a, 16b, and more precisely the respective circumferential engagement seats 17a, 17b thereof, are mutually spaced according to an extent substantially corresponding to the axial dimension of the carcass sleeve 12.

(20) The shaping devices 15 can for example comprise a toroidal forming drum 23, rigid and expandable, which is arranged within the carcass sleeve 12 in the shaping station 13.

(21) The forming drum 23 is expandable between a first operating condition, radially contracted (FIGS. 2, 3 and 6), and a second radially expanded operating condition (FIGS. 5, 7, 10 and 11). For such purpose, provision can for example be made such that the forming drum 23 comprises a plurality of sectors 24 circumferentially distributed around a central shaft 25.

(22) The sectors 24 are movable, preferably simultaneously with respect to each other, from the aforesaid first operating condition in which they are approached to the central shaft 25, to the second operating condition in which said sectors 24 are moved away from the central shaft 25. For such purpose, provision can be made such that the sectors 24 are carried by respective telescopically extensible guide members 26, radially extending from the central shaft 25.

(23) The movement of the sectors 24 can be attained by transmission mechanisms 27, for example comprising driving levers 28 hinged, each at the respectively opposite ends thereof, to one of said sectors 24 and to at least one driving collar 29 slidably fit along the central shaft 25. More particularly a pair of driving collars 29 situated along the central shaft 25 are preferably provided in axially opposite position with respect to the sectors 24, each engaging respective driving levers 28.

(24) Each driving collar 29 is operatively connected to a threaded bar 30, rotatably engaged coaxially within the central shaft 25. The threaded bar 30 extends along the central shaft 25, nearly for the entirely length thereof or beyond, and carries two axially opposite threads 30a, 30b, respectively clockwise and anticlockwise. On the threads 30a, 30b, respective nut screws 31 are operatively engaged, axially movable inside the central shaft 25, each connected to one of the driving collars 29, e.g. by means of at least one block 32 radially traversing the central shaft 25 at a longitudinal slit thereof 33.

(25) The rotation of the threaded bar 30 in the central shaft 25, actuatable by means of a rotary driver 34 or actuator devices of another type operating in the shaping station 13, determines an axial movement of the nut screws 31 and of the driving collars 29, corresponding with a radial movement of the sectors 24, towards the first or the second operating condition depending on the rotation direction of the threaded bar 30.

(26) Preferably the forming drum also comprises at least one elastic membrane 35 or other stratiform coating, e.g. made of viscous material, engaged in sliding contact relation on the sectors 24. In the illustrated example, the membrane 35 is fit in a condition of suitable elastic dilation outside the sectors 24 when the forming drum is in the first operating condition. The membrane 35, preferably made of elastomeric material with low friction coefficient, such as EPDM or silicone, has a radially inner surface engaged in sliding contact relation on the sectors 24, and is further expanded during the expansion of the forming drum 23 towards the second operating condition.

(27) The expanded forming drum 23 in the second operating condition has a toroidal shape corresponding to an inner shape of the shaped carcass sleeve 12. More particularly, the set of the sectors 24 and/or the possible elastic membrane 35 or other stratiform coating applied around the same define along the circumferential extension of the forming drum, in radially outer position, a toroidal abutment surface S shaped according to the internal configuration that the carcass sleeve 12 must assume upon completed shaping. The abutment surface S is delimited between respective circumferential axially outer portions S1, arranged at radially inner circumferential edges S2 of the same abutment surface S.

(28) Advantageously, provision can be made such that the forming drum 23 in the second operating condition has a curvature ratio comprised between about 0.15 and about 0.45, typically suitable for making tyres for motorcycles or other two-wheel vehicles. If necessary, curvature ratios with values smaller than those indicated above can nevertheless be employed, e.g. suitable for the production of tyres for cars or trucks.

(29) As illustrated in FIGS. 8 and 9, each of the sectors 24 has a first coupling portion 36a and a second coupling portion 36b which are circumferentially opposite, preferably interconnected by means of an intermediate portion 36c which has, at least on the abutment surface S, a main extension direction parallel to a radial plane of the forming drum 23. Each of the coupling portions 36a, 36b has a plurality of elongated protrusions 37 extended in circumferential direction from the intermediate portion 36c, alternated with respective circumferentially elongated cavities 39.

(30) In a same sector 24, the protrusions 37 belonging to one of the coupling portions, for example the first coupling portion 36a, are offset with respect to the protrusions 37 of the other coupling portion 36b.

(31) At least some of the protrusions 37 can have substantially plate-like structure, and lie according to surfaces parallel to a circumferential extension direction of the abutment surface S. Such protrusions 37 therefore have side walls 38 extending according to planes orthogonal to the geometric rotation axis X-X of the drum.

(32) At least some of the cavities 39 are axially delimited, each between the side walls 38 of two axially consecutive protrusions 37. As better illustrated in FIGS. 6 and 7, the protrusions 37 of each sector 24 are slidably engaged in the respective cavities 39 of the circumferentially adjacent sectors 24, and are adapted to slide in the cavities themselves in order to support the expansion and contraction movements of the forming drum 23.

(33) The side walls 38 of the protrusions 37, respectively mating, belonging to circumferentially contiguous sectors 24, mutually guide the sectors themselves during the expansion and contraction movement, and facilitate the maintenance of a satisfactory structural solidity of the forming drum 23 in its entirety, both in the first operating condition and in the second operating condition.

(34) In the first operating condition (FIG. 6), the protrusions 37 of each sector 24 penetrate into the respective cavities 39, approaching until touching (or nearly touching) the intermediate portion 36c of the adjacent sector 24. For example, in the first operating condition, the protrusions 37 can be inserted in the respective cavities 39 according to an extent at least equal to 80% of their length.

(35) In the second operating condition (FIG. 7), the protrusions 37 are extracted from the cavities 39, for example according to an extent at least equal to 80% of their length.

(36) The presence of the protrusions 37, of the cavities 39 and their mutual relation ensure that, in proximity to the abutment surface, circumferential rows of solid portions 40, defined by the protrusions 37, interposed between empty portions 41 defined by the cavities 39, can be identified at least in the second operating condition. The solid portions 40 and the empty portions 41 belonging to each circumferential row are circumferentially offset with respect to the solid portions 40 and, respectively, to the empty portions 41 of axially adjacent circumferential rows.

(37) In order to ensure that the surface discontinuities induced by the alternation of solid portions 40 and empty portions 41 do not compromise a correct execution of the building, it is preferable that at least in proximity to an axial middle line plane E of the forming drum 23, still more preferably on all the protrusions 37 except those situated in proximity to the circumferential axially outer portions S1 of the abutment surface S, each protrusion 37 has axial dimension approximately comprised between about 4 mm and about 15 mm, preferably equal to about 8 mm. Each cavity 39 preferably has axial dimension equal to that of the protrusions 37 circumferentially aligned therewith.

(38) It is also preferably provided that the empty portions 41 in the second operating condition have circumferential size comprised between about 30 mm and about 60 mm, preferably equal to about 40 mm.

(39) In radially outer position, the protrusions 37 and the cavities 39 are shaped such that each of the sectors 24 overall has a cross section profile extending so as to substantially describe the entire transverse extension of the abutment surface S, from one to the other of said circumferential axially outer portions S1.

(40) At the circumferential axially outer portions S1 of the abutment surface S, the axial size of the protrusions 37 and cavities 39 indicated above may prove unsuitable for a correct working.

(41) Indeed it has been observed that due to the curvature presented by the cross section profile of the abutment surface S, the transverse dimension of the solid portions 40 and empty portions 41 is not equal to the axial dimension of the corresponding protrusions 37 and cavities 39 to which they belong. In particular, in the forming drums dedicated to making tyres for two-wheel vehicles, where the curvature ratio is relatively accentuated, the transverse dimension of the solid portions 40 and of the empty portions 41 at the circumferential axially outer portions S1 can be many times greater than that found in proximity to the axial middle line plane E.

(42) Consequently, axially opposite terminal portions of the carcass sleeve 12, situated at the beads 6, might not be suitably supported and might be too free to move for the purpose of adequate opposition to the stresses.

(43) In order for the carcass sleeve 12 to be efficiently supported by the forming drum 23, it is therefore provided that in the second operating condition the radially inner circumferential edges S2 of the abutment surface S have a diameter D1 not greater than a radially inner diameter D2 of the beads 6. More particularly, in the illustrated example, the diameter D1 of the radially inner circumferential edges S2 is preferably equal to or smaller than the radially inner diameter of the beads 6. In this manner, at the end of the shaping of the carcass sleeve 12, axially inner sides of said beads 6 are arranged in axial abutment relation against the respective circumferential axially outer portions S1 of the abutment surface S, defined on the circumferentially consecutive sectors 24.

(44) Preferably, the forming drum 23 is positioned in the shaping station 13 before the respective carcass sleeve 12, e.g. still being worked along the carcass building line 10, reaches the shaping station 13 itself.

(45) More particularly, it is preferably provided that the forming drum 23 be projectingly supported in the shaping station 13. For example, a first end 25a of the central shaft 25 of the forming drum 23 can for such purpose be retained by a mandrel 42 coaxially housed in the first gripping element 16a and carrying the rotary driver 34 couplable with the threaded bar 30 in order to drive it in rotation.

(46) The forming drum 23 can therefore be arranged in the first operating condition by said rotary driver 34, if it is not already in such condition upon reaching the shaping station 13.

(47) By means of carcass loading devices 43, the carcass sleeve 12 coming from the carcass building line 10 is then transferred into the shaping station 13 in order to be coaxially arranged in radially outer position around the forming drum 23 arranged in the first operating condition, radially contracted.

(48) The carcass loading devices 43 can for example comprise a carcass handler 44 preferably operating on an outer surface of the carcass sleeve 12. With a radial translation movement (with respect to the forming drum 23), the carcass sleeve 12 is first inserted, in axial alignment relation with the forming drum 23, between the gripping elements 16a, 16b arranged in the loading/unloading condition (FIG. 2). The carcass sleeve 12 is subsequently arranged around the forming drum 23, preferably following a movement of relative axial translation with respect to the forming drum itself. In the illustrated example, the forming drum 23 is coaxially inserted in the carcass sleeve 12 by a movement of the carriage 19 along the linear guides 20. Preferably, the translation of the carriage 19 and of the forming drum 23 terminates with the engagement of a second end 25b of the central shaft 25 with a tailstock 45, situated within the second gripping element 16b (hatched line in FIG. 2).

(49) In order for the axial movement of the forming drum 23 with respect to the carcass sleeve 12 to be able to take place in the absence of mutual mechanical interferences, it is preferably provided that, in the first operating condition, the forming drum 23 has a maximum outer diameter smaller than the radially inner diameter D2 of the beads 6, which typically represents the minimum inner diameter detectable in the carcass sleeve 12.

(50) At the end of the axial movement, each of the anchoring annular structures 5 integrated in the beads 6 is situated in axially inner position with respect to the circumferential engagement seat 17a, 17b of the respective first and second gripping element 16a, 16b.

(51) Upon action of the axial movement members 18 and/or other suitable devices, the gripping elements 16a, 16b are moved axially close to each other, translating the respective engagement seats 17a, 17b in mutual approaching in order insert them axially in the carcass sleeve 12. More particularly, the engagement seats 17a, 17b axially translate, each from the exterior towards the interior of the respective anchoring annular structure 5, until they are stopped substantially in a radial alignment relation within the latter.

(52) The carcass handler 44 can be moved away from the shaping station 13 after having disengaged the carcass sleeve 12, which remains suspended with the anchoring annular structures 5 thereof in abutment against the engagement seats 17a, 17b.

(53) Expansion members associated with each of said gripping elements 16a, 16b and not depicted since attainable in any convenient manner, determine an expansion of the circumferential engagement seats 17a, 17b. Following such radial expansion, the gripping elements 16a, 16b are induced to act, by means of the respective circumferential engagement seats 17a, 17b, each in radial thrust relation from the interior towards the exterior against one of the anchoring annular structures 5. The carcass sleeve 12 is thus stably constrained to the gripping elements 16a, 16b.

(54) In conjunction with the radial expansion of the engagement seats 17a, 17b, i.e. immediately before, immediately after or during at least one part of such radial expansion, an axial movement of mutual moving away of the gripping elements 16a, 16b can be driven upon action of the axial movement members 18 and/or other suitable devices. In this situation, the gripping seats 17a, 17b act in axial thrust relation from the interior towards the exterior against the axially inner sides of the respective anchoring annular structures 5, determining a mutual axial moving away thereof with consequent axial extension of the carcass sleeve 12. If necessary, the axial movement of the gripping elements 16a, 16b is also exploited so that the carcass sleeve 12 is axially centred with respect to the forming drum 23. By means of rotation of the threaded bar 30 upon action of the rotary driver 34, the radial expansion of the forming drum 23 can be driven in order to start the shaping of the carcass sleeve 12.

(55) Preferably, the shaping of the carcass sleeve 12 takes place only by radial expansion of the forming drum 23, in the absence of internal pressurisation actions of the carcass sleeve 12 itself. In other words, during the shaping of the carcass sleeve 12, the radially inner parts of the latter can be conveniently maintained in fluid communication with the external environment, hence at atmospheric pressure.

(56) As schematised in FIG. 4, during the expansion of the forming drum 23, immediately after a radially outer portion of the latter has abutted against the carcass sleeve 12, e.g. coming into direct contact with the latter in proximity to the axial middle line plane E, the gripping seats 17a, 17b can be radially contracted and possibly moved away from each other, so that the gripping elements 16a, 16b disengage the anchoring annular structures 5 and remain disengaged therefrom for the remaining part of the expansion of the forming drum 23.

(57) When the gripping elements 16a, 16b disengage the carcass sleeve 12, the beads 6 remain projectingly suspended from the forming drum 23 itself, while the contact between the radially outer part of the forming drum 23 and the carcass sleeve 12 stabilises the positioning of the latter with respect to the forming drum itself.

(58) With the progression of the radial expansion, the carcass sleeve 12 is toroidally shaped due to a radial thrust action exerted by the sectors 24 of the forming drum 23 directly against the carcass sleeve 12 itself.

(59) Simultaneously, the elastic membrane 35, having respective radially inner circumferential flaps 35a constrained to the sectors 24 at the radially inner circumferential edges S2 of the abutment surface S, expands in sliding contact relation against the sectors 24, while it maintains a substantially static abutment relation, i.e. in the absence of significant sliding and preferably by direct contact, with respect to the inner surface of the carcass sleeve 12. The presence of the elastic membrane 35 or other stratiform coating eliminates the risk of damage of the carcass sleeve 12 as a result of the undesired sliding against the abutment surface S. With the progress of the radial expansion of the forming drum 23, also the carcass sleeve 12 is radially expanded according to a toroidal configuration, adhering against the abutment surface S progressively moving away from the axial middle line plane E, towards the beads 6. More particularly, the tensions transmitted through the carcass sleeve 12 during the progressive radial moving away of the sectors 24 determine a corresponding progressive axial approach of the beads 6 to the abutment surface S. The substantial inextensibility of the cords that normally constitute the carcass ply or plies 3 facilitates said tension.

(60) When the forming drum 23 reaches the second operating condition, the beads 6 abut against the respective circumferential axially outer portions S1 of the abutment surface S, situated at the radially inner circumferential edges S2, completing the shaping of the carcass sleeve 12.

(61) In order to facilitate a suitable support for the beads 6, the diameter D1 of the radially inner circumferential edges S2 of the abutment surface S is preferably smaller than a radially outer diameter Dmax of said annular gripping elements 16a,16b. Advantageously, the disengagement and moving away of the gripping elements 16a, 16b from the beads 6 in the initial phase of the shaping simplifies the elimination of possible mechanical interferences between the gripping elements themselves and the forming drum 23.

(62) It can be provided that with the attainment of the second operating condition, the radial moving away of the sectors 24 at the end of the shaping also imposes a controlled tension at the carcass sleeve 12, which can be maintained up to the removal of the forming drum 23 from the built tyre 2. Such controlled tension can facilitate the maintenance of the beads 6 in axial thrust relation against the circumferential axially outer portions S1 of the abutment surface S.

(63) Carcass sleeve 12 and forming drum 23 in mutual coupling relation are adapted to be removed from the shaping station 13 and subjected to the action of deposition devices 46, configured for forming further components of the tyre 2 being worked outside the shaped carcass sleeve 12, e.g. by means of application of one or more elementary semi-finished products 54 in radially outer position with respect to the abutment surface S. The deposition devices 46 can for example comprise at least one device 47 for building at least one belt layer in radially outer position with respect to the shaped carcass sleeve 12. Such device 47 is preferably installed in an application station 48 that is remote with respect to said shaping station 13.

(64) In order to allow the transfer thereof to the application station 48, it is provided that the forming drum 23 carrying the carcass sleeve 12 be supported by the mandrel 42 operating at the first end 25a of the central shaft 25, while the tailstock 45 is disengaged from the second end 25b of the central shaft 25 itself. With a retreating of the carriage 19 carrying the first gripping element 16a, the shaping station 13 is brought back into the loading/unloading condition, freeing the access to suitable transfer devices, configured for transferring the forming drum 23 carrying the carcass sleeve 12 from the shaping station to the deposition devices 46. The transfer devices can for example comprise a first anthropomorphic robotic arm 49, preferably with at least six axes, which provides for engaging the forming drum 23 at the second end 25b of the central shaft 25.

(65) In the illustrated example, the first robotic arm 49 transfers the forming drum 23 from the shaping station 13 to the application station 48. The first robotic arm 49 also provides for suitably moving the forming drum 23 in front of the building device 47 of the belt layer, which can for example comprise a dispenser which feeds at least one first elementary semi-finished product 47a, e.g. one or more rubber-covered cords or other elongated continuous reinforcement element made of textile and/or metallic material covered with elastomeric material, to a first applicator roller 50. The first applicator roller 50 provides for depositing the first elementary semi-finished product 47a on the carcass sleeve 12, according to circumferential turns C axially side by side each other, so as to make the belt layer 7a around the radially outer surface of the carcass sleeve 12 coupled to the toroidal expanded forming drum 23, while the latter is rotated and suitably moved by the first robotic arm 49.

(66) The rigidity of the forming drum 23 ensures a stable positioning of the single circumferential turns C formed directly on the shaped carcass sleeve 12, without undesired deformations of the carcass sleeve 12 being verified due to the stresses transmitted on the outer surface thereof during application, e.g. due to the first applicator roller 50. The stickiness of the green elastomeric material that constitutes the carcass ply or plies 3 prevents undesired spontaneous and/or non-controlled movements of the single circumferential turns C, without it being necessary for such purpose to arrange additional intermediate layers between the belt layer 7a being made and the underlying application surface. In other words, a precise positioning is facilitated for the single circumferential turns C of the belt layer 7a, directly formed according to the desired final profile of the carcass sleeve 12 upon completed shaping, even when such profile has an accentuated transverse curvature as for example can be typically found in the tyres intended for motorcycles or other two-wheel vehicles.

(67) The application station 48 can if necessary comprise devices 51 for building one or more auxiliary layers 7b, to be applied on the shaped carcass sleeve 12 before or after the application of said at least one belt layer 7a. In particular, such auxiliary layers 7b can comprise textile or metallic parallel cords, arranged according to an orientation that is tilted with respect to the circumferential extension direction of the carcass sleeve 12, respectively cross between auxiliary layers 7b that are adjacent to each other.

(68) By means of the first robotic arm 49, or by means of a second anthropomorphic robotic arm or manipulator of another type, the forming drum 23 is then transferred from the application station 48 to a sidewalls application station 52, preferably being part of the deposition devices 46 integrating the same application station 48.

(69) In the sidewalls application station 52, a coiling unit 53 can for example operate. Such coiling unit 53 is configured for wrapping at least one second elementary semi-finished product 54 in the form of an elongated continuous element made of elastomeric material according to circumferential turns C1 axially side by side and/or at least partially superimposed against axially opposite lateral portions of the carcass sleeve 12 in proximity to the beads 6, while the forming drum 23 is driven to rotate and suitably moved, for example by the same first robotic arm 49, in order to distribute the circumferential turns C1 according to a predefined scheme. The application of the second elementary semi-finished product 54 in the form of an elongated continuous element preferably takes place with the aid of a respective second applicator roller 55.

(70) The plant 1 can also comprise devices for making tread bands 56 that can operate in an analogous manner to the coiling unit, in order to make the tread band 8 around the belt structure 7 up to in proximity to the sidewalls 9, before or after the making thereof.

(71) The geometric and size parameters of the protrusions 37 and cavities 39 arranged in the forming drum 23 allow suitably supporting the carcass sleeve 12 without the same having to sustain excessive localised stresses or twisting under the effect of the thrust exerted by the applicator rollers 50 and 55. Indeed, at each of the cavities 39, the carcass sleeve 12 is supported as a bridge between two axially contiguous protrusions 37.

(72) In addition, at each of the cavities 39 situated along the radially inner circumferential edges S1, each bead core 5a is adapted to act as a kind of bridge-like beam supported between two abutments, suitably opposing the thrust action exerted by the second applicator roller 55, even if the latter is localised in an action area, measurable against the abutment surface S in a radial plane of the forming drum 23, having transverse dimension smaller than the transverse dimension of the empty portions 41, as exemplified in FIG. 11. Such FIG. 11 illustrates the application of the second elementary semi-finished product 54 for the purpose of attaining a radially inner portion of one of the sidewalls 9, in proximity to the respective radially inner apex 9a. Due to the abutment of the bead cores 5a against the solid portions 40 of circumferentially contiguous sectors 24 at the circumferential axially outer portions S1 of the abutment surface S, the beads 6 are able to effectively oppose the thrust action exerted by the second applicator roller 55 even in proximity to the zones proximal to the radially inner edges S2 and axially opposite edges of the forming drum 23, where the orientation of the abutment surface itself is substantially radial with respect to the geometric rotation axis X-X or in any case quite tilted with respect to the latter.

(73) It is therefore possible to effectively apply the radially inner apices 9a of the sidewalls 9 and/or other components at the beads 6, without inducing significant deformations of the carcass sleeve 12 under the thrust action exerted by the second applicator roller 55.

(74) The controlled tension conferred to the carcass sleeve 12 at the end of the shaping ensures a constant thrust of the beads 6 against the drum, facilitating the stability of the latter. In particular, it is possible to eliminate undesired vibratory oscillations of the beads 6 which could negatively affect a correct application of the components, particularly in proximity to the beads 6 themselves.

(75) The built green tyre 2 is subsequently adapted to be removed from the forming drum 23 in order to be moulded and vulcanised in a vulcanisation unit 57.