EP1855874A1

EP1855874A1 - Method and apparatus for manufacturing pneumatic tyres for vehicule wheels

Info

Publication number: EP1855874A1
Application number: EP05719021A
Authority: EP
Inventors: Giovanni c/o Pirelli Tyre S.p.A. POZZATI; Claudio c/o Pirelli Tyre S.p.A. LACAGNINA
Original assignee: Pirelli SpA; Pirelli Tyre SpA
Current assignee: Pirelli and C SpA; Pirelli Tyre SpA
Priority date: 2005-02-28
Filing date: 2005-02-28
Publication date: 2007-11-21
Also published as: WO2006090418A1

Abstract

A carcass structure (3) is manufactured on a building drum (17) and subsequently transferred to a primary drum (15). Simultaneously, a belt structure (4) comprising a resistant insert (11) of the 'zero-degree' type is made on an auxiliary drum (19). An annular transfer device (23) provided with magnetic inserts (27) integrated into grip sectors (25) or into an expandable bladder (26) picks the belt structure (4) up to transfer it onto the primary drum (15) carrying the carcass structure (3). The magnetic inserts (27) perform stabilisation of the belt structure (4) avoiding structural deformations being produced thereon also in the absence of a tread band (5) or of additional resistant layers having crossed cords. The tread band (5) can be then made through spiralling of a continuous elongated element (12) directly on the belt structure (4) already associated with the carcass structure (3).

Description

- i -

METHOD AND APPARATUS FOR MANUFACTURING PNEUMATIC TYRES FOR VEHICLE WHEELS

D e s c r i p t i o n

The present invention relates to a method of manufacturing pneumatic tyres for vehicle wheels.

The invention also relates to an apparatus' for manufacturing pneumatic tyres in accordance with the above mentioned method.

Manufacture of a tyre for vehicle wheels generally involves preparation of a carcass structure comprising at least one carcass ply that is formed by circumferentially winding on a so-called "building drum", at least one semi-finished product comprising textile or metallic reinforcing cords oriented transversely of the longitudinal extension of the article of manufacture itself.

When winding has been completed, the respectively opposite end flaps of the carcass ply are looped back around annular anchoring structures, each usually formed of a substantially, circumferential annular insert to which at least one ^' filling insert is applied, at a radially external position.

Simultaneously, on a second or auxiliary drum an outer sleeve is formed which _. comprises a belt structure with which a tread band applied at a radially external position, is 'coupled.

Referring particularly to production of pneumatic tyres for motorcycles to which the^' present invention particularly applies, in document EP 718 122 in the name of the same Applicant, it is provided for the belt structure to comprise a single reinforcing layer of the so-called "zero degree" type, obtained with the aid of at least one continuous elongated element comprising one or more generally metallic parallel cords, that is wound up on the auxiliary drum to form circumferential coils that are suitably distributed in an axial direction. The conformation of the auxiliary drum is of such a nature that the belt layer is given an arched profile with a marked curvature, typical of tyres for motorcycles. A correct maintenance of the geometric features of this profile is a decisive factor as regards functionality of the whole tyre.

Associated with the belt structure formed on the auxiliary drum is the tread band, currently obtained by cutting out a section of suitable length from a semifinished product of elastomeric material previously made in the form of a continuous strip. The strip section constituting the tread band is first wound up at a radially external position on the belt structure supported by the auxiliary drum; then, with the aid of expandable bladders and/or by a rolling operation, the side edges of said section are knocked down radially inwards so that the tread band is shaped according to the curvature profile of the belt structure and correctly adheres to the whole surface extension thereof.

The outer sleeve (that after radial knocking down of the edges has taken the shape of a semitorus) made up of the tread band coupled with the belt structure can therefore be picked up from the auxiliary drum by means of an annular transfer device, to be coupled with the carcass sleeve.

To this aim, the outer sleeve is disposed in coaxial relatioship around the carcass sleeve and afterwards the carcass ply is given a toroidal configuration by mutual axial approaching of the tyre beads and simultaneous admission of fluid under pressure to the inside of the carcass sleeve, so as to cause application of the outer sleeve to the tyre carcass structure, at a radially external position. Assembling of the carcass sleeve with the outer sleeve can be carried out on the same drum as used for manufacturing the carcass sleeve, in which case reference is made to "a unistage building process". A building process of this type is described in document US 3,990,931, for example .

Also known are building processes of the so-called "two-stage" type, in which as described in document EP 0 613 757 for example, assembling between the carcass structure and belt structure is carried out on a so- called shaping drum to which the carcass sleeve picked up from the building drum, as well as, subsequently, the outer sleeve picked up from the auxiliary drum are transferred.

The Applicant has realised that knocking down of the opposite side edges of the tread band to give the latter the same conformation as the curved profile of the belt structure, can give rise to further structural defects in the finished product. In fact, the side portions of the tread band, first disposed according to a diameter corresponding to the maximum diameter measurable along the equatorial plane of the tyre, must be brought to adhere to .the portions of the belt structure that, by effect of the curved profile typical of tyres for two-wheeled vehicles, have a remarkably reduced diameter. The corresponding reduction in the circumferential extension ^' imposed on the side portions of the tread band can give rise to severe unevennesses in thickness.

The Applicant has further found that handling of the semifinished product in the form of a strip designed to constitute the tread band can .involve several problems, such as undesirable structural deformations of the article of manufacture due to unavoidable stresses induced on the latter during the operations of cutting and winding the strip on the belt structure, or also merely due to collapsing of the material by effect of its weight. These structural deformations that can be hardly controlled can easily induce geometric unevennesses in the finished product.

The Applicant has however found that both the problems linked to deformation of the semifinished product that will constitute the tread band and those linked to the above described structural faults can be advantageously overcome if, instead of manufacturing the tread band starting from a semifinished product in the form of a strip, said tread band is obtained by laying a continuous elongated element according to a' predetermined path, for example in the form of coils suitably disposed in side by side relationship at a radially external position to- the -belt structure. Manufacture of the tread band in the above described manner however, ..involves longer times than those usually required when said tread band is made starting from a semifinished product in the form of a strip. This circumstance would lead to an unbalance in the times for performing the working operations carried out on the building drum, the auxiliary drum and possibly the shaping drum, respectively.

The Applicant has also perceived that the times for completing a work cycle on the different parts of a tyre manufacturing apparatus can be optimised if manufacture of the tread band on the belt structure is executed after the belt structure has been associated with the carcass structure. However, it has been ascertained that at the present state of the art it is impossible to carry out transfer of the belt structure in the absence of the tread band, when the belt structure is by itself very weak, which usually happens when tyres for motorcycles, are to be manufacture. In fact, a belt structure comprising only one "zero degree" resistant layer, formed of one or more continuous elements wound up into coils disposed in side by side relationship in the absence of further resistant inserts having a crossed orientation relative to the coils, would tend to collapse as soon as it is removed from the auxiliary drum, since the strengthening effect usually performed by the tread band applied thereto in known processes is lacking.

In dealing with the above described problems, the Applicant has however become aware of the fact that by a suitable structural stabilisation of the belt structure during transfer of same from the auxiliary drum to the carcass structure, also belt structures of weak structural consistency can be handled in an easy and efficient manner, without running the risk of their geometric features being impaired, even in the absence of a tread band and/or further inserts or belt layers formed of crossed cords. In more detail, in accordance with the present invention, the Applicant has found that ^'a satisfactory- structural stabilisation can be advantageously achieved by submitting the belt structure to forces oriented in a radially external direction against the annular transfer device, during engagement of the belt structure by the transfer device itself.

In a first aspect, the present invention relates to a method of manufacturing tyres, comprising the steps of: applying a carcass structure onto a primary drum; preparing a belt structure on an auxiliary drum; engaging the belt structure with a transfer device; submitting the belt structure to forces oriented in a radially external direction towards an abutment surface belonging to the transfer device; disengaging from the auxiliary drum, the belt structure engaged by the transfer device; associating the belt structure with the carcass structure; manufacturing a tread band at a radially external position to said belt structure.

In a preferential embodiment, said forces are each oriented in a direction passing through a point of tangency between the abutment surface and the tangent plane thereof, at right angles to said tangent plane. By so doing, each portion of the belt structure is perpendicularly pushed against the abutment surface, so that components of forces that can induce relative displacements between the different parts of the belt structure itself are avoided. Thus, all risks of anomalous 'deformations of the belt structure are eliminated, even when said belt structure comprises one resistant layer alone formed of at least one continuous elongated element wound up into coils disposed in side by side relationship, in the absence of further inserts with cords having a crossed orientation relative to the coils.

According to a preferred embodiment mode, said forces are generated through magnetic attraction of the belt structure against said abutment surface, advantageously giving an efficient structural stabilisation to the shape of the belt structure.

According to a further preferred embodiment, said forces are generated through suction of the belt structure against said abutment surface.

In a further aspect, the invention relates to an apparatus for manufacturing tyres, comprising: devices for applying a carcass structure onto a primary drum; devices for preparing a belt structure on an auxiliary drum; a transfer device set to remove the belt structure from the auxiliary drum to position it in coaxial relationship around the carcass structure; stabilisation devices for transmitting forces to the belt structure, which forces are oriented in a radially external direction towards at least one abutment surface belonging to the transfer device; devices for associating the carcass structure with the belt structure carried by the transfer device; devices for manufacturing a tread band at a radially external position to the belt structure.

Further features and advantages will become more apparent from the detailed description of a preferred but not exclusive embodiment of a method and an apparatus for manufacturing tyres, 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 a first embodiment of the invention;

- Fig. 2 is a diagrammatic top view of a manufacturing apparatus according to a possible alternative embodiment of the invention; - Fig. 3 is a fragmentary diametrical section view showing a device for manufacturing a belt structure being part of the apparatus referred to in Figs. 1 and 2;

- Fig. 4 shows the device seen in Fig. 3 during formation of a resistant belt layer;

- Fig. 5 is a fragmentary diametrical section view showing an annular transfer device in accordance with a first manufacturing example;

- Fig. 6 is a fragmentary diametrical section view of a transfer device in accordance with a second manufacturing example;

- Fig. 7 diagrammatically shows an operating step in which a tread band is made on the belt structure coupled with a carcass of a tyre being worked.

Referring particularly to Figs. 1 and 2, an apparatus for manufacturing tyres for vehicle wheels, set to put into practice a manufacturing method in accordance with the present invention has been generally identified by reference numeral 1.

In the embodiments described in the following, the invention is particularly conceived for manufacturing tyres for two-wheeled vehicles, of the type generally denoted at 2 in Fig. 7. As compared with tyres for four-wheeled vehicles, tyres for two-wheeled vehicles are distinguishable for their marked transverse curvature. This transverse curvature is usually defined by the particular value of a so- called curvature ratio "R" between the distance "D" existing between the radially external point of the tread band and the line passing through the opposite lateral extremities of the tread band itself measured on the equatorial plane of the tyre, and the distance "L" measured along the tyre chord between said extremities. In tyres for two-wheeled vehicles, the curvature ratio value is generally at least as high as 0.15 and it is usually in the order of about 0.3 as regards rear tyres and even higher, until about 0.45, in the case of front tyres.

It is however to be pointed out that the innovative aspects of the invention can also be adopted, in case of need, in manufacturing tyres for motor vehicles, in which the curvature ratio is usually smaller than 0.05.

Likewise, in the case of any building drum in a substantially toroidal configuration, defined as curvature ratio "Rt" is the ratio between the distance "Dt" existing between a radially external point of the toroidal surface of the drum and the line passing through the laterally opposite extremities of the drum itself measured on the equatorial plane of the drum

(that is substantially coincident with the equatorial plane of the tyre manufactured with use of the same drum) , and the distance "Lt" measured along the chord of the drum between said extremities. In drums designed to manufacture tyres for two-wheeled vehicles, the curvature ratio value Rt is, as a result of what discussed above, included between about 0.15 and about 0 . 45 .

As viewed from Fig. 7, tyre 2 comprises a carcass structure 3 of substantially toroidal conformation, a belt structure 4 circumferentially extending around the carcass structure 3, a tread band 5 applied to the belt structure 4 at a circumferentially external position, and a pair of sidewalls 6 laterally applied to the carcass structure 3 on opposite sides, and each extending from a side edge of the tread band 5 until a region close to a radially internal edge of the carcass structure 3 itself. Each of the sidewalls 6 and the tread band 5 essentially comprises at least one layer of elastoineric material of suitable thickness.

It is to be pointed out, to the aims of the present description, that by 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 cross-linking agents and/or plasticizers . Due to the presence of the cross-linking agents, this material can be cross-linked through heating, so as to form the final article of manufacture.

The carcass structure 3 comprises a pair of annular anchoring structures 7, integrated into regions usually identified as "beads", each made up of a substantially circumferential annular insert 8 for example, that is usually called "bead core", which insert carries an elastomeric filler 9 at a radially external position. The end flaps 10a of one or more carcass plies 10 are turned up around each of the annular anchoring structures, which end flaps 10 comprise textile or metallic cords extending transversely of the circumferential extension of tyre 2, possibly according to a predetermined inclination, from one of the annular anchoring structures 7 to the other.

The belt structure 4 can in turn comprise at least one resistant belt layer 11 preferably formed of at least one continuous elongated element 12 comprising one or more cords 13 made up of filament-like elements of textile or metallic material, incorporated into an elastomeric matrix. In a preferential embodiment, the continuous elongated element 12 comprises two cords 13. The continuous elongated element 12 is wound around the geometric rotation axis of tyre 2 into circumferential coils 12a axially distributed so as to define the resistant belt layer 11. In more detail, coils 12a can be disposed axially close to each other and/or axially distributed to a suitable mutual distance. This distance can be constant or variable, with a decreasing rate on moving close to the opposite side edges of the belt structure 4 or in other manner according to need.

The resistant belt layer 11 can be applied at a radially external position, to at least one elastomeric base layer 14, possibly filled with fibres or other reinforcing inserts as disclosed in document EP 0718122 for example, in the name of the same Applicant. Preferably, in a tyre for two-wheeled vehicles the above_ described resistant belt layer 11 is applied to the elastomeric base layer 14 in the absence of further layers comprising cords having a crossed orientation relative to the circumferential coils 12a, which further layers are instead usually provided in the belt structure of tyres for motor vehicles. The . individual components of the carcass structure 3, such as in particular the annular anchoring structures 1, carcass plies 10, elastomeric base layer 14 of the belt ^'structure 4, and/or possible auxiliary belt layers, can be supplied to apparatus 1 in the form of semi-finished products manufactured in prior working steps, to be suitably assembled with each other.

Apparatus 1 is equipped with devices for applying the carcass structure 3 on a primary drum 15. These applying devices preferably comprise a manufacturing station 16, not described in detail because it can be

- made in any convenient manner, which has a building drum 17 on which the carcass ply or plies 10 are first wound up, which carcass ply/plies come from a feeding line 16a along which they are cut into sections of suitable length correlated with the circumferential extension of the building drum 17, before being applied thereto to form a so-called "carcass sleeve" of substantially cylindrical shape; Fitted on the end flaps 10a of plies 10 are the annular anchoring structures 7 so that turning up of the end flaps can be then carried out, to cause engagement of the anchoring structures in the loops consequently formed by the turned-up plies 10. -If required, the manufacturing station 16 can comprise devices for associating the sidewalls 6 with the carcass ply or plies 10.

When assembling of the components has been completed, transfer devices not shown pick up the carcass structure 3 from the building drum 17 to transfer it onto the primary drum 15, of the type usually referred to as "shaping drum" for example, which is conveniently set to continue building of the tyre according to a manufacturing process of the so-called "two-stage" type in a respective assembling station 18.

Alternatively, assembling of the components of the carcass structure 3 can be directly carried out on the primary drum 15 following a building process of the so-called "unistage type".

Simultaneously with preparation of the carcass structure 3 on the building drum 17 or directly on the primary drum 15, the belt structure 4 is prepared on an auxiliary drum 19 located in a respective auxiliary work station 20.

To this aim, it is provided for the auxiliary drum 19 to interact with devices for preparing the belt structure 4 which may comprise at least one second feeding line 21 for example, or feeding members of other type terminating at a so-called comb drum 22 designed to contain the auxiliary drum 19 when the latter is in a radially contracted position, as shown in Fig. 3. A semifinished product of elastomeric material in the form of a continuous strip is fed along the second feeding line 21, which semifinished product is then cut into sections of suitable length, concurrently with winding of same on the comb drum 22 to make the elastomeric base layer 14 initially having a cylindrical conformation as seen in Fig. 3.

The auxiliary drum 19, usually formed of radially movable sectors, is then brought to a radial-expansion condition so that said sectors radially project through respective passages arranged in the comb drum 22, to expand the base layer 14 and give it a conformation according to a cross-section profile of suitable curvature. To this aim, the radial sectors of the auxiliary drum 19 in the radially expanded condition define, at a radially external position, a forming surface having an arched profile with a curvature ratio Rt included between about 0.15 and about 0.45, in accordance with the transverse curvature of the tyre 2 that is wished to be obtained.

Once engagement of the elastomeric base layer 14 has occurred as above described, the auxiliary drum 19 is disengaged from the comb drum 22 through an axial movement as shown in Fig. 4, to co-operate with winding members for the continuous elongated element 12 designed to make the resistant belt layer 11. These winding members, not shown as feasible in a manner known by itself, can for example comprise an axially and/or radially movable delivery member to lay the continuous elongated element 12 on the forming surface 19a defined by the sectors of the auxiliary drum 19, while the latter is driven in rotation around its geometric axis.

Synchronisation of delivery of the continuous elongated element 12 and axial and/or radial movement of the delivery member, concurrently with rotation of the auxiliary drum 19, pauses laying of the coils 12a forming the resistant belt layer 11, following the arched profile of the forming surface 19a.

In contrast to what usually provided in making tyres for motor-vehicles, in the manufacture of belt structures intended for tyres for two-wheeled vehicles the above described laying of the continuous elongated element 12 is provided to take place directly on the elastomeric base layer 14 previously formed on the auxiliary drum 19, in the absence of further layers comprising cords 13 with a crossed orientation relative to the circumferential coils 12a.

The thus obtained belt structure 4 is adapted to be engaged by an annular transfer device 23 designed to remove the belt structure 4 from the auxiliary drum 19, for engagement of same with the carcass structure 3 set on the primary drum 15.

To this aim, the primary drum 15 and auxiliary drum 19 are provided to be respectively aligned along a guide structure 24 on which translation of the annular transfer device 23 can occur. The annular transfer device 23 is laid in coaxial relationship around the auxiliary drum 19 carrying the belt structure 4-, to engage the latter by means of grip devices comprising a plurality of shaped grip sectors 25 for example, that are circumferentially distributed and radially movable between a rest condition at which they are radially spaced apart from a geometric axis of the annular transfer device, and a work position at which they are moved radially close thereto to engage the belt structure 4. In more detail, the grip sectors 25 lend themselves ' to act on the belt structure 4 by at least one abutment surface 25a the shape of which matches that of the belt structure 4 itself, according to the transverse curvature profile of the latter.

In accordance with a possible alternative embodiment, the grip devices comprise a circumferential bladder 26 in engagement with the annular transfer device 23 at a radially internal position. Following admission of air or other fluid under pressure, bladder 26 lends itself to be radially expanded from the outside to the inside, between a rest position at which it has an inner diameter greater than the outer diameter of the belt structure 4 formed on the auxiliary drum 19 so as to enable axial insertion and release of the annular transfer device 23 relative to the auxiliary drum 19 carrying the belt structure 4, and a work condition at which., as shown in Fig. 6, it defines an abutment surface conforming in shape to the belt structure 4 and operating against the latter to cause engagement of the same by the annular transfer device 23 itself.

In a preferential embodiment, said circumferential bladder 26 is anchored to the radially movable grip sectors 25 so as to increase travel in the radial direction and improve the engagement/disengagement operations.

When engagement has occurred, the sectors of the auxiliary drum 19 are translated to a radially contracted position, to enable the belt structure 4 to be removed from the auxiliary drum 19 following axial movement of the annular transfer device 23.

Concurrently with engagement by the annular transfer device 23, the belt structure 4 is advantageously submitted to the action of stabilisation devices 27 that transmit forces directed radially outwardly to said belt, structure 4 and push it against the abutment surface 25a, 26a carried by the annular transfer device 23. Due to the action of these forces the conformation of the belt structure 4 is stabilised, even if the • latter should have a very reduced structural consistency.

In a preferential embodiment, the stabilisation devices 27 comprise magnetic inserts integrated into the grip sectors 25 or the circumferential bladder 26 at the abutment surface and for example formed with plate-like elements of elastomeric material containing charges consisting of a neodymium-iron-boron dispersion.

Alternatively or in addition to the above, the stabilisation forces can be generated through suction of the belt structure 4 against the abutment surface 25a, 26a. To this aim, the stabilisation devices 27 may comprise a suction circuit (not shown) terminating at apertures suitably distributed on the abutment surface 25a, 26a.

Both the above described embodiments allow stabilisation forces oriented at right angles to the abutment surface 26a, 26a to be obtained, as shown by arrows F in Figs. 5 and 6. More particularly, each of the stabilisation forces F is oriented in a direction passing through a tangency P between the abutment surface 25a, 26a and a tangent plane "t" thereof, at right angles to said plane. In other words, as clearly shown in Figs. 5 and 6, each stabilisation force F is oriented perpendicular to the abutment surface 25a,

26a, i.e. to the plane "t" tangent to the surface itself, at the point passed across by the direction of the stabilisation force.

In this way, the stabilisation forces F act on each of coils 12a always in a direction perpendicular to the abutment surface 25a, 26a. This condition ensures an excellent stability of the belt structure 4 even after disengagement of said belt structure 4 from the auxiliary drum 19. In fact, coils 12a are pushed against the abutment surface 25a, 26a in the absence of tangential components that could cause undesirable mutual displacements of said coils.

Thus, the belt structure 4 can be disengaged from the auxiliary drum 19 and translated to the assembling station 18 without the risk of impairing the geometric and structural features thereof that would give rise to repercussions on the functional features of tyre 2.

By axial movement of the annular transfer device 23, the belt structure 4 is positioned in coaxial relationship around the primary drum 15 to be associated with the carcass structure 3 set thereon.

To this aim, the carcass structure 3 is shaped into a toroidal configuration through axial mutual approaching of the annular anchoring structures 7 and simultaneous admission of fluid under pressure to the inside of said carcass structure 3 until bringing the carcass ply or plies 10 into contact with the inner surface of the belt structure 4 retained by the annular transfer device 23.

When engagement has occurred, the grip sectors 25 or the circumferential bladder 26 are brought back to the rest position, to enable removal of the annular transfer device 23 from the belt structure 4 applied to the carcass structure 3.

A rolling step, to be performed in any convenient manner, can be carried out on the belt structure - 4 after the step of shaping the carcass structure 3 or concurrently with said step, to obtain a better adhesion against the carcass ply or plies 10.

In the assembling station 18 a tread band 5 is subsequently made, at a radially external position to the belt structure 4 already associated with the carcass structure 3.

In accordance with the present invention, manufacture of the tread band 5 is preferably carried out through spiralling of at least one continuous thread element 29 of elastomeric material. To this aim, the devices for manufacturing the tread band 5 comprise at least one extruder, an applicator roller or other delivery member 28 that, through an outlet nozzle operating adjacent to the primary drum 15, lends itself to deliver the continuous thread element 29 directly against the belt structure 4, simultaneously with winding of the continuous thread element itself into coils 29a distributed following a predetermined path against the •radially external surface of the belt structure 4.

To this aim, a transverse-movement unit 30 determines a relative transverse motion between the delivery member

28 and the primary drum 15 to cause a predetermined axial distribution of the coils 29a formed of the continuous thread element 29, while the primary drum 15 is driven in rotation around its geometric axis. The continuous thread element 29 fed from the delivery member 28 can advantageously have a flattened section so that it can modulate the thickness of the elastomeric layer being formed by varying the overlapping amount of the contiguous coils 29a and/or orientation of the surface of tyre 2 being worked relative to the cross-section^' profile of the thread element coming from the delivery member 28 itself.

In the embodiment in Fig. 1 the transverse-movement unit 30 comprises a carriage 30a carrying the primary drum 15 and movable along said guide structure 24, in the vicinity of the delivery member 28. The delivery member 28 in turn can be movable in translation along an auxiliary guide extending at right angles to the guide structure 24, to enable the delivery member 28 to move close to and away from the primary drum 15. During working, the delivery member 28 preferably keeps a fixed positioning, while the primary drum 15 is being driven in rotation and suitably moved in a transverse direction by the movement unit 30, so as to cause distribution of the continuous elongated element 12 in such a manner as to form a tread layer of suitable shape and thickness on the belt structure 4.

In the embodiment in Fig. 2, on the contrary, it is the primary drum 15 driven in rotation that keeps a fixed axial positioning, while the movement unit 30 carries out translation of the delivery member 28 in a transverse and radial direction relative to the circumferential extension of the belt structure 4, to cause transverse distribution of the coils formed by the continuous thread element 29. To this aim, the movement unit 30 comprises a pair of orthogonal guides 30b carrying the delivery member 28, so as to enable movement of the latter both in a radial direction close to and away from the primary drum 15, and in a direction parallel to the rotation axis of said primary drum 15.

If required, also manufacture of the sidewalls 6 can be carried out in the same manner as described in relation to accomplishment of the tread band 5, using the same delivery member 28 for example, or other specifically dedicated delivery devices. According to a further alternative embodiment, the tread band 5 can be obtained by cutting a section of suitable length from a semifinished product in the form of a continuous strip coming from a respective feed line.

When manufacture of the tread band 5 and sidewalls 6 has been completed, the assembled tyre 2 can be removed from the primary drum 15 to be submitted to a subsequent vulcanisation step and/or a step involving other working operations.

The present invention enables transfer of the belt structure 4 devoid of the tread band 5 without the risk that, due to the absence of the structural consolidation and stabilisation effect usually carried out by the tread band itself, structural deformations or damages to the belt structure 4 may occur. This risk can also be found when the building features of the belt structure 4 are of such a nature as to make said belt structure very weak or in any case not very resistant, which often occurs in manufacturing tyres for motorcycles wherein the presence of a single resistant layer of the so-called "zero degree" type is -required, i.e. a layer having cords 13 wound up into circumferential coils 12a possibly spaced apart in an axial direction.

Transfer of the belt structure 4 in the absence of the tread band 5 advantageously makes it possible to produce the tread band 5 itself through spiralling of a continuous thread element 29, subsequently to coupling of the belt structure 4 with the carcass structure 3, so that the times for carrying out the working cycle on the auxiliary drum 19 are not overloaded.

The required time for manufacturing the tread band 5 through spiralling of the continuous thread element 29 on the primary drum 15 is compensated for by elimination or simplification of the rolling operations usually required in the known art in order to try to level the thickness of the tread band 5 obtained from a semifinished product in the form of a continuous strip.

Manufacture of the tread band 5 through spiralling also enables elimination of all drawbacks in terms of workability and production quality connected with working of the semifinished products in the form of a continuous strip and application of the tread bands 5 obtained therefrom following the teachings of the known art. In particular, the geometric features of the tread band 5 can be advantageously controlled in a more precise manner so that, for instance, a controlled and constant thickness can be obtained both close to the equatorial plane and close to the shoulders of tyre 2, even during working of particularly soft blends.

Claims

C L A I M S

1. A method of manufacturing tyres, comprising the steps of: - applying a carcass structure (3) onto a primary drum (15);

- preparing a belt structure (4) on an auxiliary drum

(19);

- bringing the belt structure (4) in engagement with a transfer device (23) ;

- submitting the belt structure (4) to forces (F) oriented in a radially external direction, towards an abutment surface (25a, 26a) belonging to the transfer device (23) ; - disengaging from the auxiliary drum (19) , the belt structure (4) engaged by the transfer device (23);

- associating the belt structure (4) with the carcass structure (3) ;

- manufacturing a tread band (5) at a radially external position to said belt structure (4) .

2. A method as claimed in claim 1, wherein the step of submitting the belt structure (4) to said forces (F), starts before disengagement of the belt structure (4) from the auxiliary drum (19) , and is completed after association of the belt structure (4) with the carcass structure (3) .

3. A method as claimed in claim 1 or 2, wherein said forces (F) are each oriented in a direction passing through a tangency point (P) between the abutment surface (25a, 26a) and a tangent plane (t) thereof, at right angles to said tangent plane (t) .

4. A method as claimed in one or more of the preceding claims, wherein said forces (F) are generated through magnetic attraction of the belt structure (4) against said abutment surface (25a, 26a) .

5. Α method as claimed in one or more of the preceding claims, wherein said forces (F) are generated through suction of the belt structure (4) against said abutment surface (25a, 26a) .

6. A method as claimed in one or more of the preceding claims, wherein preparation of the belt structure (4) comprises the steps of winding up, on the auxiliary drum (19) , at least one continuous elongated element

(12) in the form of circumferential coils (12a) that are axially distributed to obtain a resistant belt layer (11) .

7. A method as claimed in claim 6, wherein said forces (F) act on each of said coils (12a) in a direction perpendicular to the abutment surface (25a, 26a) .

8. A method as claimed in claim 6, wherein said continuous elongated element (12) comprises at least one cord (13) incorporated into an elastomeric matrix.

9. A method as claimed in claim 8, wherein said cord

(13) comprises filament-like elements of metal material.

10. A method as claimed in claim 6, wherein the continuous elongated element (12) is wound on an elastomeric base layer (14) previously laid on the auxiliary drum (19) .

11. A method as claimed in claim 6, wherein said resistant belt layer (11) is formed in the absence of further layers comprising cords having a crossed orientation relative to the circumferential coils (12a) .

12. A method as claimed in one or more of the preceding claims, wherein the belt structure (4) is formed according to an arched profile having a curvature ratio included between about 0.15 and about 0.45.

13. A method as claimed in one or more of the preceding claims, wherein association of the belt structure (4) with the carcass structure (3) comprises the steps of:

- disposing the belt structure (4) in coaxial relationship around the carcass structure (3) ;

- radially expanding the carcass structure (3) for associating it with the belt structure (4) .

14. A method as claimed in one or more of the preceding claims, wherein application of the carcass structure

(3) comprises the step of assembling the carcass structure (3) on a building drum (17) and transferring the carcass structure (3) from the building drum (17) to the primary drum (15) , association of the belt structure (4) with the carcass structure (3) being carried out on the primary drum (15) .

15. A method as claimed in one or more of the preceding claims, wherein the step of manufacturing a tread band (5) is carried out through winding of at least one continuous thread element (29) of elastomeric material according to a predetermined path against a radially external surface of the belt structure (4) .

16. A method as claimed in claim 15, wherein manufacture of the tread band (5) is performed subsequently to association of the belt structure (4) with the carcass structure (3) .

17. An apparatus for manufacturing tyres, comprising:

- devices for applying a carcass structure (3) onto^' a primary drum (15) ;

- devices for preparing a belt structure (4) on an auxiliary drum (19) ; - a transfer device (23) set to remove the belt structure (4) from the auxiliary drum (19) to position it in coaxial relationship around the carcass structure (3);

- stabilisation devices (27) for transmitting forces (F) to the belt structure (4) , which forces (F) are oriented in a radially external direction towards at least one abutment surface (25a, 26a) belonging to the transfer device (23) ;

- devices for associating the carcass structure (3). with the belt structure (4) carried by the transfer device (23) ;

- devices for manufacturing a tread band (5) at a radially external position to the belt structure (4) .

18. An apparatus as claimed in claim 17,- wherein said stabilisation devices (27) comprise magnetic inserts operating at said abutment surface (25a, 26a) to generate said forces (F) through magnetic attraction of the belt structure (4) against the abutment surface (25a, 26a) .

19. An apparatus as claimed in claim 18, wherein said magnetic inserts (27) are carried by circumferentially- distributed grip sectors (25) that are radially movable relative to the transfer device (23) .

20. An apparatus as claimed in claim 18, wherein said magnetic inserts (27) are associated with at least one circumferential bladder (26) operatively carried by the transfer device (23) , said circumferential bladder (26) being expandable between a rest condition at which it has an inner diameter greater than the outer diameter of the belt structure (4) formed on the auxiliary drum (19), and a work condition at which it has a shape matching that of the belt structure (4) .

21. An apparatus as claimed in claim 18, wherein said magnetic inserts (27) are made of elastomeric material containing magnetic charges.

22. An apparatus as claimed in one or more of claims 17 to 21, wherein said stabilisation devices (27) comprise a suction circuit terminating at apertures distributed on said abutment surface (25a, 2βa) , to generate said forces (F) through suction of the belt structure (4) against the abutment surface (25a, 26a) .

23. An apparatus as claimed in one or more of claims 17 to 22, wherein the devices for preparing the belt structure (4) comprise members for winding up, on the auxiliary drum (19) , at least one continuous elongated element (12) in the form of circumferential coils (12a) that are axially distributed to obtain a resistant belt layer (11) .

24. An apparatus as claimed in claim 23, wherein said continuous elongated element (12) comprises at least one cord (23) incorporated into an elastomeric matrix.

25. An apparatus as claimed in claim 24, wherein said cord (23) comprises filament-like elements of metal material .

26. An apparatus as claimed in one or more of claims 23_. to 25, wherein the devices for preparing the belt structure (4) further comprise feed members to lay at least one elastomeric base layer (14) on the auxiliary drum (19), so as to carry out winding of the continuous elongated element (12) at a position radially external to said elastomeric base layer (14).

27. An apparatus as claimed in one or more of claims 23 to 26, wherein the devices ^' for preparing the belt structure (4) form said resistant belt layer (11) in the absence of further layers comprising cords with a crossed orientation relative to the circumferential coils (12a) .

28. An apparatus as claimed in one or more of claims 17 to 27, wherein the auxiliary drum (19) has a forming surface (19a) having an arched profile with a curvature ratio included between about 0.15 and about.0.45.

29. An apparatus as claimed in one or more of claims 17 to 28, wherein the devices for associating the carcass structure (3) with the belt structure (4) comprise a shaping drum (15) and a device (23) for transfer of the carcass structure (3) to the shaping drum (15) , said transfer device (23) being movable between the auxiliary drum (19) and shaping drum (15).

30. -An apparatus as claimed in one or more of claims 17 to 29, wherein said devices for manufacturing a tread band (5) carry out winding of at least one continuous thread element (29) of elastomeric material according to a predetermined path against a radially external surface of the belt structure (4) .

31. An apparatus as claimed in claim 30, wherein said devices for manufacturing the tread band (5) operate close to the devices carrying out association of the carcass structure (3) with the belt structure (4).

32. An apparatus as claimed in claim 20 , wherein the circumferential bladder (26) is radially anchored to said grip sectors (25) .