Process and apparatus for manufacturing tyres for vehicle wheels

Abstract

A carcass ply is built on a forming drum by application of a plurality of strip-like elements by the steps of: setting a width of these strip-like elements, setting a width of the overlapped part between two adjacent strip-like elements, setting a fitting diameter of the forming drum by calculating a corresponding extension of a radially external laying surface, and calculating a whole number of strip-like elements to be applied. The whole number of drip-like elements is applied by rotating the forming drum around a geometric rotation axis thereof, and applying pairs of strip-like elements by means of a first laying unit and a second laying unit located close to opposite portions of the forming drum relative to the geometric rotation axis. When the calculated whole number of strip-like elements is an odd number, before at least one application step, the first laying unit is shifted along an adjustment path orthogonal to the geometric rotation axis and substantially tangent to the radially external laying surface of the forming drum.

Claims

1. An apparatus for manufacturing tyres for vehicle wheels, each tyre comprising a carcass structure including at least one carcass ply, a tread band at a radially external position to said carcass structure and a belt structure interposed between said carcass structure and tread band, the tyres being manufactured including tyres comprising carcass plies made by laying down an even whole number of strip-like elements and tyres comprising carcass plies made by laying down an odd whole number of strip-like elements, comprising: a forming drum having at least one radially external laying surface; devices for building at least one carcass ply around said radially external surface, said at least one carcass ply having axially opposite end flaps; wherein the devices for building at least one carcass ply around said radially external surface comprise: devices for setting the forming drum in rotation around a geometric rotation axis thereof; a first laying unit and a second laying unit mounted at mutually opposite portions of the forming drum and adapted to apply a plurality of strip-like elements along the circumferential extension of the forming drum; an adjustment device for shifting the first laying unit along an arced adjustment path which lies in a plane orthogonal to the geometric rotation axis, the arced adjustment path being an arc of a circumference coaxial with the geometric rotation axis for applying a single strip-like element; a bearing structure adapted to carry the forming drum; a first frame installed on the bearing structure above the forming drum and carrying the first laying unit; and a second frame installed on the bearing structure under the forming drum and carrying the second laying unit, wherein the adjustment device is mounted between the bearing structure and the first frame to shift the first laying unit along said adjustment path and wherein the adjustment device comprises a supporting plate hinged on the bearing structure around a hinge axis coincident with the geometric rotation axis and at least one actuator disposed between the supporting plate and the bearing structure, the first frame being installed on said supporting plate.

2. The apparatus as claimed in claim 1, wherein said first laying unit and second laying unit are adapted to apply pairs of strip-like elements.

3. The apparatus as claimed in claim 1, comprising a first auxiliary adjustment device and a second auxiliary adjustment device to shift each of said first and second laying units around respective correction axes that are substantially radial to the geometric rotation axis.

4. The apparatus as claimed in claim 1, wherein the supporting plate has a C-shaped conformation delimiting a housing region adapted to receive the forming drum.

5. The apparatus as claimed in claim 1, comprising a first auxiliary adjustment device and a second auxiliary adjustment device to shift each of said first and second laying units around respective correction axes that are substantially radial to the geometric rotation axis, wherein the second auxiliary adjustment device comprises: arched guides mounted on the bearing structure and coaxial with a correction axis that is substantially radial to the geometric rotation axis, the second frame being mounted on said arched guides; and at least one actuator to move the second frame on said arched guides.

6. The apparatus as claimed in claim 1, comprising a first auxiliary adjustment device and a second auxiliary adjustment device to shift each of said first and second laying units around respective correction axes that are substantially radial to the geometric rotation axis, wherein the first auxiliary adjustment device comprises: arched guides mounted on the supporting plate and coaxial with a correction axis that is substantially radial to the geometric rotation axis, the first frame being mounted on said arched guides; and at least one actuator to move the first frame on said arched guides.

7. The apparatus as claimed in claim 1, comprising successive work stations; a transport line extending between said successive work stations; a picking-up device to shift the forming drum between the transport line and a work region of the bearing structure positioned between the first and second laying units.

8. The apparatus as claimed in claim 7, wherein the picking-up device comprises a vertically movable lifter and a horizontally movable conveyor.

9. The apparatus as claimed in claim 1, wherein the forming drum has a substantially cylindrical side surface.

10. The apparatus as claimed in claim 1, comprising at least one calculation unit to calculate a whole number of strip-like elements to be laid down.

11. The apparatus as claimed in claim 10, wherein said calculation unit is interfaced with a control unit for command of said adjustment device when an odd number of strip-like elements is to be laid down.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages will become more apparent from the detailed description of a preferred but not exclusive embodiment of a process 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:

(2) FIG. 1 diagrammatically shows a top view of an apparatus for manufacturing tyres for vehicle wheels made in accordance with the present invention;

(3) FIG. 2 is a perspective view of a station of the apparatus seen in FIG. 1, in which a carcass ply is laid down on a forming drum;

(4) FIG. 3 is a side view of the station shown in FIG. 2;

(5) FIGS. 4a and 4b show diagrammatic side views of the forming drum housed in the station in FIG. 2 during respective steps of the process according to the-invention;

(6) FIG. 5 is a diagrammatic front view of the forming drum seen in FIG. 3 provided with a carcass ply;

(7) FIG. 6 diagrammatically shows a laying unit for strip-like elements;

(8) FIG. 7 is a fragmentary diametrical section view of a tyre that can be manufactured with the process and apparatus in question.

DETAILED DESCRIPTION OF THE INVENTION

(9) With reference to the drawings, an apparatus for manufacturing tyres for vehicle wheels designed to put into practice a process according to the present invention has been generally identified with reference numeral 1.

(10) Apparatus 1 is designed to manufacture tyres 2 (FIG. 7) essentially comprising a carcass structure 2a having at least one carcass ply 3. A layer of airtight elastomeric material, or so-called liner 4, can be applied internally of the carcass ply/plies 3. Two annular anchoring structures 5 each comprising a so-called bead core 5a carrying an elastomeric filler 5b at a radially external position, are in engagement with respective end flaps 3a of the carcass ply/plies 3. The annular anchoring structures 5 are integrated close to regions usually identified with the name of beads 6, at which usually engagement between tyre 2 and a respective mounting rim occurs.

(11) A belt structure 7 comprising one or more belt layers 7a. 7b is circumferentially applied around the carcass ply/plies 3 and a tread band 8 is circumferentially superposed on the belt structure 7.

(12) So-called underbelt inserts can be associated with the belt structure 7; they are each located between the carcass ply/plies 3 and one of the axially opposite end edges of the belt structure 7. In addition, or as an alternative to the underbelt inserts 9, annular inserts (not shown) of elastomeric material and/or comprising textile or metallic cords substantially parallel to the circumferential extension direction of the tyre (0-degree belt layer) or other reinforcing elements can be radially superposed at least on the axially opposite end edge of the belt layers 7a, 7b and/or interposed between the belt layers 7a, 7b themselves at least at said end edges.

(13) Two sidewalls 10 each extending from the corresponding bead 6 to a corresponding side edge of the tread band 8, are applied at laterally opposite positions to the carcass ply/plies 3.

(14) Apparatus 1 comprises a forming drum 11 on which at least part of the components designed to form the carcass structure 2a of tyre 2 is built and/or assembled. The forming drum 11 can consist either of a first stage building drum if apparatus 1 is designed to carry out a building process of the so-called two-stage type, or of a building drum of the type usually referred to as unistage if a unistage building process is wished to be carried out.

(15) In more detail, the forming drum 11 lends itself to first receive the possible liner 4 and subsequently the carcass ply or plies 3, so as to form a cylindrical carcass sleeve.

(16) Devices not shown coaxially engage one of the annular anchoring structures 5 around each of the end flaps 3a by positioning an outer sleeve comprising the belt structure 7 and tread band 8 to a coaxially centred position around the cylindrical carcass sleeve and shaping the carcass sleeve into a toroidal configuration through radial expansion of the carcass ply, so as to cause application thereof against a radially internal surface of the outer sleeve.

(17) Tyre 2 thus built lends itself to be submitted to a vulcanisation treatment and/or other working operations provided in the work cycle.

(18) According to the present invention, it is provided that during building of tyre 2, said at least one carcass ply 3 be made by means of building devices 12 designed to apply a plurality of strip-like elements 13 in mutual circumferential contact relationship onto the forming drum 11, so as to form at least one ply layer having a continuous circumferential extension around the geometric axis X-X of said forming drum 11. The forming drum 11 has a radially external laying surface 14 that is substantially cylindrical.

(19) The building devices 12 are placed in a laying station 15, shown in FIGS. 1, 2 and 3, which in the preferred embodiment comprises a bearing structure 16 consisting of a lattice of tubes.

(20) The bearing structure 16 delimits a seat in which the forming drum 11 is positioned and supported in a rotatable manner around its geometric axis X-X. Devices 17, in the form of a mandrel driven by a motor for example, serve to set the forming drum 11 in rotation around said geometric axis X-X.

(21) A first laying unit 18 and a second laying unit 19 are mounted on the bearing structure 16 close to mutually opposite portions of the forming drum 11 and are adapted to apply the strip-like elements 13 onto said forming drum 11 during rotation of the latter.

(22) Preferably, the forming drum 11 is rotated by steps and after each rotation step, the laying units 18, 19 each simultaneously apply a strip-like element 13.

(23) Apparatus 1 further comprises two feeding units 20, each designed to supply the strip-like elements 13 of predetermined length, preferably one by one, to the respective laying unit 18, 19. For the sake of simplicity, FIG. 6 only shows the feeding unit 20 interlocked with the first laying unit 18.

(24) The strip-like elements 13 are obtained by cutting operations sequentially carried out on at least one continuous strip element 21 coming from an extrusion and/or calendering device, or from a feed reel and therefore all have the same width W. Preferably, this width W is included between about 20 mm and about 40 mm.

(25) The continuous strip element 21, and consequently the strip-like elements 13 obtained therefrom, each have a plurality of cords or similar thread elements of metallic or textile material, extending parallel to each other along the longitudinal extension of the continuous strip element and the strip-like element itself, and at least partly coated with a layer of elastomeric material applied by an extrusion and/or calendering operation.

(26) The laying units 18, 19 and feeding units 20 are of the type for example described in the International Patent Application WO2006IB002070 in the name of the same Applicant.

(27) In particular, each feeding unit 20 comprises at least one cutting member 22 designed to cut the continuous strip element 21 perpendicularly or according to a predetermined inclination relative to the longitudinal extension of same, to obtain the individual strip-like elements 13.

(28) Combined with the cutting member 22 is at least one grip member 23 movable between a first work position at which it is adapted to engage a final end of the continuous strip element 21 close to the cutting member 22, and a second work position at which it is spaced apart from the cutting member 22 itself.

(29) Following translation from the first to the second work positions, the grip member 23 drags along the continuous strip element 21 so as to stretch it out beyond the cutting member 22 and preferably at a position radially close to the forming drum 11, according to a segment of a length corresponding to that of the strip-like element 13 to be obtained following subsequent operation of the cutting member 22. In the accompanying figures, a pair of guide rollers operating on the continuous strip element 21 at a region immediately upstream of the cutting member 22 is identified with 24.

(30) Each of the laying units 18, 19 lends itself to sequentially engage each of the strip-like elements 13 prepared in the previously described manner, to determine application of same onto the radially external laying surface 14 exhibited by the forming drum 11.

(31) In this regard, it should be pointed out that said radially external surface 14 can be either the radially external surface belonging to the forming drum 14 or, preferably, the radially external surface belonging to components of tyre 2 already laid on said forming drum 11, such as liner 4 for example.

(32) Each of the laying units 18, 19 comprises at least one presser element 25 movable along the strip-like element 13, in a contrast relationship against the radially external surface 14 of the forming drum 11.

(33) In more detail, in a preferred embodiment, use of at least two presser elements 25 is provided, each of them being carried by a support element 26 movable along a guide structure 27 upon the action of transverse-movement devices, of the worm screw type for example, not shown as they can be made in any manner convenient for a person skilled in the art.

(34) Also preferably in engagement with each support element 26 is at least one auxiliary retaining element 28 adapted to co-operate with the respective presser element 25 to retain the strip-like element 13 at the instants elapsing between cutting of said strip-like element upon the action of the cutting unit 22 and application of same onto the forming drum 11.

(35) In more detail, each auxiliary retaining element 28 can consist of a small plate (or other similar mechanical element) projecting from the respective support element 26 so as to offer a supporting seat for the continuous strip element 21 dragged along by the grip member 23 and for the cut strip-like element 13.

(36) Associated with each of the laying units 18, 19 are radial-movement devices designed to move the presser elements 25 radially close to the radially external surface 14 of the forming drum 11. These radial-movement devices are not shown or described in detail as they can be made in any manner convenient for a person skilled in the art, and can operate on the guide structure 27 for example, and/or directly on the presser elements 25, in order to bring the strip-like element 13 in contact relationship on the radially external surface 14.

(37) Also provided are transverse-movement devices, not shown too, as they can be made in any convenient manner, and operating between the guide structure 27 and the support elements 26 for example, to move the presser elements 25 between a first operating condition at which they are disposed mutually close and a second operating condition at which they are spaced apart relative to a transverse symmetry plane of the forming drum 11.

(38) In the embodiment shown, the first and second laying units 18, 19 are installed on respective first and second frames 29, 30, mounted on the bearing structure 16. In more detail, the guide structure 27 of each of the laying units 18, 19 is connected to and supported by the respective frame 29, 30, which has a lattice structure surrounding the laying unit 18, 19 itself. When the bearing structure 16 is correctly installed with its base 31 resting on the ground, the first and second frames 29, 30 lie one upon the other substantially aligned along a vertical direction.

(39) The seat in which the forming drum 11 is housed remains interposed between the first and second laying units 18, 19, and said two laying units 18, 19 face up towards the portions of the forming drum 11 lying on substantially opposite sides relative to the geometric axis X-X.

(40) According to a preferred embodiment, the first laying unit 18 is located over the forming drum 11 and the second laying unit 19 is located under the forming drum 11.

(41) The bearing structure 16 therefore defines a sort of cage inside which the laying units 18, 19 and forming drum 11 are housed.

(42) Apparatus 1 further comprises an adjustment device 32 entrusted with the task of shifting one of the laying units 18, 19 along an adjustment path C-C lying in a plane orthogonal to the geometric rotation axis X-X of the forming drum 11 and being substantially arced about the radially external laying surface 14 exhibited by the forming drum 11. Preferably, path C-C is an arc of a circumference coaxial with said geometric rotation axis X-X (FIGS. 4a and 4b).

(43) In the non-limiting embodiment shown, the adjustment device 32 is mounted between the bearing structure 16 and the first frame 29 and therefore allows adjustment of the position of the first laying unit 18 along said path C-C, so as to lay down the strip-like elements 13 in an even or odd number, as shown in the following.

(44) In detail, the first frame 29 is installed on a supporting plate 33 which in turn is movable on the bearing structure 16 around an axis coincident with the geometric rotation axis X-X of the forming drum 11.

(45) In the embodiment shown, the supporting plate 33 is hinged around said geometric rotation axis X-X and an actuator 34 spaced apart from this axis X-X causes rotational movement of same.

(46) The supporting plate 33 further has an opening defining a housing region in which the forming drum 11 is accommodated, so that the first laying unit 18 can operate on the radially external surface 14 from the top.

(47) Preferably, said housing region, as shown, is delimited by a C-shaped outline of the supporting plate 33 which is open towards a picking up device 35 that, as illustrated in the following, enables the forming drum 11 to be easily put down into the seat or removed therefrom.

(48) The second frame 30 is mounted on the base 31 of the bearing structure 16 and the second laying unit 19 operates on the radially external surface 14 of the forming drum 11 from below.

(49) Apparatus 1 further comprises a first auxiliary adjustment device 36 and a second auxiliary adjustment device 37 capable of shifting each of said first and second laying units 18, 19 around respective correction axes Y-Y, Y-Y that are substantially radial to the geometric rotation axis X-X.

(50) The auxiliary adjustment devices 36, 37 have the function of laying the strip-like elements 13 on the forming drum 11 with any angle relative to the circumferential extension of same, so as to make carcass plies in which the cords being part thereof have a ply angle different from 90 (FIG. 5) relative to a longitudinal extension direction of the ply, i.e. relative to a circumferential direction of the tyre to be made.

(51) As illustrated, the first auxiliary adjustment device 36 comprises two arched guides 38 mounted on an upper face of the supporting plate 33 and coaxial with the respective correction axis Y-Y. The first frame 29 is mounted by means of runners 39 on these arched guides 38 and an actuator, not shown, enables said first frame 29 to be moved on said arched guides 38 around the respective correction axis Y-Y. Likewise, the second auxiliary adjustment device 37 comprises two arched guides 40 mounted on the base 31 of the bearing structure 16 and coaxial with the respective correction axis Y1-Y1. The second frame 30 is mounted by means of runners 41 on said arched guides 40 and an actuator, not shown, enables said second frame 30 to be moved on said arched guides 40 around the respective correction axis Y-Y.

(52) Each of the auxiliary adjustment devices 36, 37 allows a rotation of the laying units 18, 19 around the respective correction axes Y-Y, - according to a rotation angle of about 60, i.e. of about +/30 relative to a direction parallel to the geometric rotation axis X-X.

(53) Preferably, apparatus 1 according to the invention comprises a plurality of work stations WS (diagrammatically shown in FIG. 1); among which the laying station 15, at each of which one or more of the above mentioned operations for manufacturing tyre 2 are carried out. For instance,in a station placed before the laying station 15, liner 4 is applied onto the forming drum 11. In a station placed after the laying station 15, the annular anchoring structures 5 are associated with the carcass ply 3.

(54) A transport line 42 extends between said work stations WS and is used to shift the forming drum 11 between one station WS and the subsequent one.

(55) The above mentioned picking up device 35 is used to pick up the forming drum 11 from the transport line 42 and position it into the seat of the bearing structure 16 where it is engaged by the mandrel and, once the strip-like elements 13 have been applied, to bring the drum 11 back on the transport line 42. In the embodiment shown, the picking up device 35 comprises a lifter 43 moved by motors not shown along a vertical guide 44. Lifter 43 comprises a pair of arms 45 having grip ends 46 adapted to engage pins 47 of the forming drum 11 coaxial with the geometric rotation axis X-X. Arms 45 are movable between a lower position and a raised position in which they substantially lie at the same height as the mandrel of the bearing structure 16.

(56) The picking up device 35 further comprises a conveyor 48 moved by motors not shown along a horizontal guide 49. Conveyor 48 comprises a pair of arms 50 substantially placed at the same height as the mandrel of the bearing structure 16 and having catching clamps 51 adapted to engage the pins 47 of the forming drum 11. Arms 50 are movable between a first position at which they lie spaced apart from the bearing structure 16 and substantially over the transport line 42, and a second position at which they lie close to the mandrel in the bearing structure 16.

(57) Lifter 43 carries drum 1 in the raised position where conveyor 48 picks it up and brings it as far as into the seat of the bearing structure 16. Once the forming drum 11 is positioned in the seat of the bearing structure 16 and associated with the mandrel, the position of the supporting plate 33 is adjusted in such a manner as to shift, if necessary, the first laying unit 18 along the arc of a circumference C-C and apply the strip-like elements 13 in the correct manner around drum 11.

(58) In particular, shifting of the first laying unit 18 along the arc of a circumference C-C subtends a predetermined angle measured relative to a diametrical vertical direction d passing through the second laying unit 19, the value of said predetermined angle being calculated starting from the tyre fitting, the width W of the strip-like elements 13, the ply angle and the possible width of the overlapped part S between adjacent strip-like elements 13.

(59) The width W of the strip-like elements 13, measured transversely of the longitudinal extension of the strip-like element 13, is preferably included between about 20 mm and about 40 mm, more preferably between about 25 mm and about 35 mm.

(60) In fact, according to an embodiment of the process, the strip-like elements 13 are mutually approached along the circumferential extension of drum 11.

(61) According to a preferred variant of the process, the strip-like elements 13 on the contrary partly overlap each other. Under this situation, it is defined as the width of the overlapped part S the extension of the overlapped-part region between two adjacent strip-like elements 13 measured along the circumferential extension of the forming drum 11.

(62) This width of the overlapped part S is preferably included between about 1 mm and 2.5 mm, more preferably included between about 1.5 mm and 2 mm.

(63) In more detail, the circumferential extension of drum 11 and the circumferential extension of the radially external surface 14 corresponding to the extension of the carcass ply 3 are calculated from the fitting diameter and from the thickness of liner 4, if any, or of possible other components to be previously laid on the forming drum 11.

(64) The width W of the strip-like elements 13 and the ply angle being known, and given the width of the overlapped part S, a theoretical pitch of the strip-like elements 13 is calculated along the extension of drum 11. The theoretical pitch is equal to the difference between the width W of the strip-like elements 13 and the width of the overlapped part S divided by the sine of the ply angle .

(65) Calculated from the theoretical pitch is the number of strip-like elements 13 necessary to have that theoretical pitch, as the ratio of the circumferential extension of ply 3, liner 4 being taken into account, to the theoretical pitch, and this number is approximated to the closest integer or whole number

(66) In particular, if the difference between the calculated number and its whole part is smaller than or equal to 0.5, approximation to the lower integer n is done. If the difference between the calculated number and its whole part is greater than or equal to 0.51 approximation to the higher integer n is done.

(67) The whole number of strip-like elements 13 being known, the true pitch P.sub.e of the strip-like elements 13 is calculated and, since the width W of the strip-like elements 13 is fixed, the true width of the overlapped part S.sub.e. The true pitch P.sub.e is equal to the ratio between the circumferential extension of the ply and the whole number n. The true width of the overlapped part S.sub.e is equal to the difference between the width W of the strip-like elements 13 and the true pitch P.sub.e multiplied by the sine of the ply angle .

(68) Being the number of the strip-like elements 13 known, it is further calculated the advancing angle that the forming drum 11 must cover at each rotation step, as the ratio between the round angle and the whole number n.

(69) If the whole number n of strip-like elements 13 to be laid down is an even number, the first laying unit 18 is positioned exactly on the vertical diametrical direction d passing through the second laying unit 19, i.e. exactly facing the second laying unit 19. Under this situation the predetermined angle as above defined is equal to zero.

(70) The first laying unit 18 being thus positioned, the forming drum 11 is moved forward by steps and at each step the two laying units 18, 19 apply two strip-like elements 13.

(71) The two units 18, 19 apply the same number of strip-like elements 13 corresponding to half the whole number n and each unit 18, 19 applies the strip-like elements on an arc of 180.

(72) In addition, during laying of the strip-like elements 13 a relative angular rotation is carried out between the strip-like elements 13 and the forming drum 11 by rotation of the first and second frames 29, 30 around the respective correction axes Y-Y, Y-Y, preferably in a progressive manner during laying of the strip-like elements 13 themselves, so as to obtain the ply angle .

(73) If the whole number n of strip-like elements 13 to be laid down is an odd number, the first laying unit 18 is positioned in such a manner that the predetermined angle is equal to about half the advancing angle (FIGS. 4a and 4b).

(74) This predetermined angle is preferably included between about 2 and about 10 and more preferably between about 4 and about 8.

(75) The first laying unit 18 being thus positioned, the forming drum 11 is moved forward by steps and at each of the first rotation steps the two laying units 18, 19 apply a pair of strip-like elements 13 each time.

(76) Due to the mutual position of the two laying units 18, 19, the two strip-like elements13 of the pair are mutually offset relative to a diametrical direction passing through the geometric rotation axis.

(77) Therefore an empty portion remains where a single strip-like element 13 is to be ^ applied in register with a last rotation step, which strip-like element is applied by one alone of the laying units 18, 19 while the other is idle (FIG. 4b).

(78) In accordance with an embodiment of the process shown in FIGS. 4a and 4b, the first laying unit 18 is shifted along the path C-C in a direction consistent with a rotation direction V of the forming drum 11.

(79) Under this situation, the single strip-like element 13 is laid last by the first laying unit 18.

(80) In accordance with an alternative embodiment of the process, the first laying unit 18 is shifted along the path C-C in an opposite direction relative to the rotation direction V of the forming drum 11.

(81) Under this situation, the single strip-like element 13 is laid last by the second laying unit 19.

(82) Preferably, apparatus 1 further comprises a control unit, not shown, which is interfaced with a calculation unit capable of carrying out the above mentioned calculations based on the input data (fitting diameter of drum 11, radial thickness of the components laid on the drum prior to the carcass ply/plies 3, width W of the strip-like elements 13, ply angle and width of the overlapped part S) entered by an operator, and by means of devices capable of automatically operating at least the adjustment device 32 to shift the first laying unit 18 based on the calculated data.