Method for controlling the thickness of a continuous elongated element made of elastomeric material in a process for building tyres

Abstract

A method for controlling the thickness of a continuous elongated element made of elastomeric material, applied according to coils wound on a forming support, includes: advancing a head end of the continuous elongated element toward the forming support; subjecting, during the advancement, the continuous elongated element to a first stretching with a first stretch coefficient before applying on the forming support; and subjecting, during the advancement, the continuous elongated element to a second stretching with a second stretch coefficient during the application on the forming support. During the first stretching, a span of the continuous elongated element adjacent to the head end is stretched with a supplementary stretch coefficient greater than the first stretch coefficient, in a manner so as to confer, also to the span adjacent to the head end, a stretch and a section similar or substantially equivalent to those of the rest of the continuous elongated element.

Claims

1. A method for controlling a thickness of a continuous elongated element made of elastomeric material applied according to coils wound on a forming support, comprising: advancing a head end of the continuous elongated element toward the forming support; subjecting, during the advancement, the continuous elongated element to a first stretching with a first stretch coefficient before application on the forming support; and subjecting, during the advancement, the continuous elongated element to a second stretching with a second stretch coefficient during application on the forming support, wherein, during the first stretching, a span of the continuous elongated element adjacent to the head end is stretched with a supplementary stretch coefficient greater than the first stretch coefficient, wherein advancing the head end of the continuous elongated element toward the forming support is performed by advancing the head end in a linear direction in between a pair of opposing conveyor belts interposed between an exit opening of an extruder through which the continuous elongated element is delivered and a forming surface of the forming support on which the continuous elongated element is applied, the conveyor belts each being wound around a respective pulley arranged adjacent the extruder and a respective roller arranged adjacent the forming support, and wherein the span stretched with the supplementary stretch coefficient extends from the head end of the continuous elongated element for a length that is equal to a difference between (i) a second distance measured parallel to the conveyor belts and extending from a center of the respective roller furthest from the forming support to a point on the forming surface at which the continuous elongated element is applied, and (ii) a first distance measured parallel to the conveyor belts and extending from the exit opening of the extruder to a point of contact between the conveyor belts situated on a line joining axes of rotation of the respective pulleys.

2. The method according to claim 1, wherein the supplementary stretch coefficient is equal to a product of the first stretch coefficient and the second stretch coefficient.

3. The method according to claim 1, wherein the supplementary stretch coefficient is less than a product of the first stretch coefficient and the second stretch coefficient.

4. The method according to claim 1, wherein the first stretch coefficient is between about 1 and about 1.5.

5. The method according to claim 1, wherein the second stretch coefficient is between about 1 and about 3.

6. The method according to claim 1, wherein the supplementary stretch coefficient is between about 1 and about 2.

7. The method according to claim 1, wherein the first stretching is performed by controlling a linear speed of the opposing conveyor belts using a control unit such that an operating linear speed of the opposing conveyor belts is greater than an exit speed at which the continuous elongated element is extruded through the exit opening of the extruder.

8. The method according to claim 7, wherein the second stretching is performed by controlling a peripheral speed of the forming support using the control unit such that the peripheral speed of the forming support is greater than the operating linear speed of the opposing conveyor belts.

9. The method of claim 8, wherein the span of the continuous elongated element adjacent to the head end is stretched with the supplementary stretch coefficient greater than the first stretch coefficient by controlling the linear speed of the opposing conveyor belts during an initial transient time period to be greater than the operating linear speed of the opposing conveyor belts.

10. The method of claim 9, wherein the initial transient time period is measured starting from when the head end of the continuous elongated element is engaged between the opposing conveyor belts.

11. The method of claim 10, wherein the linear speed of the opposing conveyor belts during the initial transient time period is equal to the peripheral speed of the forming support.

12. The method of claim 10, wherein the linear speed of the opposing conveyor belts during the initial transient time period is greater than the operating linear speed and less than the peripheral speed of the forming support.

13. The method of claim 7, wherein the control unit is configured to maintain ratios between the exit speed of the continuous elongated element from the extruder, the linear speed of the opposing conveyor belts, and a peripheral speed of the forming support constant during an entire work cycle during which the continuous elongated element is applied on the forming support.

14. The method of claim 1, wherein a peripheral speed of the forming support is controlled using a control unit to be greater than an exit speed at which the continuous elongated element is extruded through the exit opening of the extruder.

15. The method of claim 14, wherein the peripheral speed of the forming support is controlled using the control unit to be greater than the exit speed at which the continuous elongated element is extruded through the exit opening of the extruder during the entire time the continuous elongated element is applied to the forming support.

16. The method of claim 14, wherein a ratio between the peripheral speed of the forming support and the exit speed of the continuous elongated element from the extruder is a total stretch coefficient that is between from about 1 to about 4.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

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

(3) FIG. 2 shows in detail an apparatus of the plant of FIG. 1;

(4) FIGS. 3a, 3b and 3c show respective continuous elongated elements obtained with the apparatus of FIG. 2;

(5) FIG. 4 schematically shows, in diameter section, a tyre for vehicle wheels obtained with the plant of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

(6) With reference to the abovementioned figures, with 1 a plant is indicated in its entirety for the building of tyres 2 in accordance with the present invention.

(7) The plant 1 is set to obtain tyres 2 (FIG. 4) essentially comprising at least one carcass ply 3 preferably internally coated with a layer of impermeable elastomeric material or so-called liner 4, two so-called “beads” 5 integrating respective annular anchoring structures 6 comprising respective bead cores 6a possibly associated with elastomeric fillers 6b and engaged with the circumferential edges of the carcass ply 3, a belt structure 7 applied in radially outer position to the carcass ply 3, a tread band 8 applied in radially outer position to the belt structure 7, in a so-called crown area of the tyre 2, and two sidewalls 9 applied in laterally opposite positions on the carcass ply 3, each at a lateral area of the tyre 2, being extended from the corresponding bead 5 to the corresponding lateral edge of the tread band 8.

(8) The plant 1 comprises a plurality of work stations, each for example arranged to form a component of the tyre 2 being processed directly on a forming support 11, 16 preferably with cylindrical or toroidal conformation. As an alternative, it can be provided that one or more components of the tyre 2 being processed, rather than be directly obtained on the forming support, are obtained as semifinished products from preceding processing steps and assembled with other components on said forming support.

(9) By way of example, the plant 1 preferably comprises a line 10 for building carcass structures, in which a carcass structure, comprising at least one of the carcass plies 3 and the annular anchoring structures 6, is formed on a forming support defined by a building drum 11. The line 10 for building carcass structures comprises a device 12 for building carcass sleeves on the building drums 11. The building device 12 comprises a plurality of work stations 13. For example, a first work station 13 achieves the liner 4, in at least one second work station 13 of the building device 12 the obtainment of one or more carcass plies 3 can be actuated. The line 10 for building carcass structures also comprises a further work station 14 dedicated to the integration of the annular anchoring structures 6 in said at least one carcass ply 3, through application of the same annular anchoring structures 6 in axially outer position to the flaps of said at least one carcass ply 3 turned down in the direction of the rotation axis of said building drum 11, flaps which are subsequently turned up around the annular anchoring structures 6. Downstream of the work station 14 for the integration of the annular anchoring structures 6, further work stations 13 can be present, for example for obtaining at least one portion of an anti-abrasive element or of the sidewalls 9.

(10) The plant 1 also comprises a line 15 for building crown structures, in which a crown structure, comprising at least the belt structure 7 and preferably also the tread band 8, is formed on a forming support defined by a forming drum 16. In FIG. 1 a plurality of work stations 17 are indicated that belong to the aforesaid line 15 for building crown structures, each dedicated to forming at least one portion of a component of the crown structure itself of the tyre 2 on the forming drum 16. The forming drum 16 is sequentially transferred from one work station to the next work station by means of suitable devices, not illustrated. At least one work station 17 can be dedicated to the obtainment of the belt structure 7. By way of example, a work station 17 is preferably arranged for obtaining the tread band 8 and/or the sidewalls 9. The plant 1 is also provided with an assembly and shaping station 18 operatively associated with the line 10 for building the carcass structures and with the line 15 for building crown structures. In the assembly and shaping station 18, the carcass structure is toroidally shaped and associated with the crown structure, in a manner so as to obtain a green tyre. The green tyres built by the plant 1 are sequentially transferred to a vulcanization line 19, from which the moulded and vulcanized tyres 2 are obtained.

(11) In accordance with the present invention, at least one of the components made of elastomeric material of the tyre 2, such as the liner 4, fillers 6b and/or other parts made of elastomeric material of sidewalls 9, tread band 8, under-belt layer, underlayer of the tread band, anti-abrasives and/or other, is obtained by an apparatus indicated in its entirety with 20 (FIG. 2), through winding of a continuous elongated element 21 made of elastomeric material preferably according to coils mutually adjacent or partially superimposed and distributed along a forming surface 11a, 16a of the forming support 11, 16 preferably with cylindrical or toroidal conformation.

(12) The apparatus 20 comprises an extruder 22 equipped with a cylinder 23 in which elastomeric material is introduced. The cylinder 23, heated to a controlled temperature, approximately comprised between about 40° C. and about 120° C., operatively houses a rotary screw 24; upon actuating such screw, elastomeric material is thrust along the cylinder 23 itself, towards an exit opening 25 of the extruder 22. The elastomeric material is conveyed through a gear pump 26, operatively interposed between the rotary screw 24 and the exit opening 25, in order to ensure greater flow rate uniformity through the latter. More in detail, a flange 22a is mounted on the extruder 22 and carries an output opening 22b delimiting exit duct 22c terminating with said exit opening 25. The exit opening 25 is close to the gear pump 26. In particular, the distance between the abovementioned gear pump 26 and the exit opening 25, i.e. the length of the delimited duct 22c of the output opening 22b, is less than about 100 mm, preferably comprised between about 60 mm and about 80 mm, in a manner so as to limit the sliding of the elastomeric material on the walls of the duct 22c and therewith the generation of damaging local cross-linking of the elastomeric material itself. Preferably, also the flange 22a and the output opening 22b are thermoregulated, i.e. heated to a controlled temperature. Also the screw 24 and the gear pump 26 can be heated to a controlled temperature, approximately comprised between about 40° C. and about 120° C. The output opening 22b has a tapered profile with external walls that converge towards the exit opening 25. Through the exit opening 25, the continuous elongated element 21 made of green elastomeric material is consequently delivered, such element having a profile of substantially circular or ellipsoidal cross section. In both of the aforesaid cases, the area of the cross section of the exit opening 25 is preferably comprised between about 10 mm.sup.2 and about 40 mm.sup.2.

(13) The apparatus 20 comprises a conveyor 27, interposed between the extruder 22 and the forming support 11, 16 and adapted to carry the continuous elongated element 21 up to the forming support 11, 16, a laying member 28 for pressing the continuous elongated element 21 against said forming support 11, 16 while the latter revolves, moved by devices 29 in order to make it rotate on its axis “X-X”.

(14) The conveyor 27 comprises two conveyor belts: a first conveyor belt 30 (upper belt in the FIG. 2) and a second conveyor belt 31 (lower belt in the FIG. 2).

(15) The first conveyor belt 30 is wound on a first pulley 32 arranged at the extruder 22 and on a first roller 33 arranged at the laying member 28. The first roller 33 is smaller than the first pulley 32 and, preferably, the diameter “D1” of the first pulley 32 is about four times the diameter “D2” of the first roller 33. In the embodiment illustrated in FIG. 2, the roller 33 can for example have a diameter “D2” comprised between about 25 mm and about 30 mm, while the pulley 32 can have a diameter “D1” of about 100 mm. The first pulley 32 and the first roller 33 are rotatably mounted on a first support frame 34. The first conveyor belt 30 is extended along a preferably triangular path (and has a first rectilinear conveyor branch 30a adapted to come into contact with the continuous elongated element 21 to be conveyed. In the illustrated embodiment, such first conveyor branch 30a has its face intended to come into contact with the continuous elongated element 21 turned downward.

(16) The second conveyor belt 31 is wound on a second pulley 35 arranged at the extruder 22 and on a second roller 36 arranged at the laying member 28. Analogous to that described for the first conveyor belt 30, the second roller 36 is smaller than the second pulley 35 and, preferably, the diameter “D3” of the second pulley 35 is about four times the diameter “D4” of the second roller 36. The diameter “D3” of the second pulley 35 is preferably equal to that of the first pulley 32. The diameter “D4” of the second roller 36 is therefore preferably equal to that of the first roller 33. The second pulley 35 and the second roller 36 are rotatably mounted on a second support frame 37. Also the second conveyor belt 31 is extended along a substantially triangular path and has a rectilinear second conveyor branch 31a adapted to come into contact with the continuous elongated element 21 to be conveyed. In the illustrated embodiment, such second conveyor branch 31a has its face intended to come into contact with the continuous elongated element 21 turned upward.

(17) The first and the second conveyor branch 30a, 31a are arranged face to face. When the continuous elongated element 21 is not present between them, said two conveyor branches 30a, 31a are in mutual contact. For such purpose, the first support frame 34 and the second support frame 37 are installed on a support structure, not illustrated.

(18) The first and the second pulley 32, 35 lie in mutual contact (only separated by the conveyor belts 30, 31 which partly wrap around them) and the second conveyor branch 31a is longer than the first conveyor branch 30a, i.e. the second roller 36 is moved more towards the laying member 28 with respect to the first roller 33. Therefore, a terminal span 38 of the second conveyor branch 31a close to the second roller 36 remains free, i.e. not facing the first conveyor branch 30a. The aforesaid embodiment allows leaving more maneuvering space for the movement of the laying member 28.

(19) The second pulley 35 is operatively connected, for example by means of a belt 39, to a motor 40 which moves it in rotation around its rotation axis “Y-Y”. The second (motorized) pulley 35 transmits motion to the second conveyor belt 31 (e.g. through a toothing) and to the second roller 36. Due to the friction between the conveyor branches 30a, 31a in direct contact or between the conveyor branches and the continuous elongated element 21 interposed between them, the second pulley 35 drives the first conveyor belt 30 and rotates the first pulley 32 around its rotation axis “Z-Z” and the first roller 33. This allows driving the continuous elongated element 21 between the aforesaid opposite conveyor belts without relative movements or sliding respect thereto. In practice, the speed of the conveyor belts coincides with the advancement speed of the continuous elongated element 21.

(20) The first support frame 34 can be vertically moved, with a limited travel, with respect to the support structure on which it is mounted by means of suitable guides, not illustrated.

(21) An actuator 41, e.g. a hydraulic or pneumatic piston, is mounted on the support structure and is connected to the first support frame 34. In the illustrated embodiment, the actuator 41 has a body 42 constrained to the support structure and a stem 43 constrained to the first support frame 34 and preferably perpendicular to the conveyor branches 30a, 31a. A movement sensor 44 positioned at the first conveyor belt 30 is capable of detecting each vertical movement of the first conveyor branch 30a.

(22) The laying member 28 comprises a roller 45 operating in thrust relation towards the forming support 11, 16 due to the action, for example, of a second actuator 46. In the illustrated exemplifying embodiment, the roller 45 is idly mounted on an end of a stem 47 of the second actuator 46, obtained for example by a pneumatic piston. A lateral cylindrical surface of the idle roller 45 abuts and pushes against the continuous elongated element 21 applied to the forming support 11, 16.

(23) The first pulley 32 and the second pulley 35 identify a mutual area of maximum proximity 48 situated on the line that joins the axes of rotation “Z-Z”, “y-Y” of said two pulleys 32, 35. Such area of maximum proximity 48 is the first contact area between the two opposite conveyor belts 30, 31 and the continuous elongated element 21 which exits from the extruder 22.

(24) The first pulley 32 identifies a first input portion 49 of the respective first conveyor belt 30 which is arranged in contact with the respective first pulley 32; such pulley describes an arc of a circle and is facing from the top to the output opening 22b of the extruder 22. Analogously, the second pulley 35 identifies a second input portion 50 of the respective second conveyor belt 31 which is arranged in contact with the respective second pulley 35; such pulley describes an arc of a circle and is facing from the bottom to the output opening 22b of the extruder 22. The first input portion 49 and the second input portion 50 converge towards each other and towards the area of maximum proximity 48, delimiting between them a wedge-shaped space or housing.

(25) The output opening 22b of the extruder 22 is positioned in said wedge-shaped housing and the exit opening 25 is turned towards the area of maximum proximity 48 and situated at a first distance “d1” less than about 10 mm and preferably comprised between about 1 mm and about 5 mm from said area of maximum proximity 48. An end 51 of the conveyor 27 opposite the area of maximum proximity 48, which in the illustrated embodiment is the terminal end of the first conveyor branch 30a arranged at the first roller 33, is situated at a second distance “d2” from the laying member 28, more particularly, from the point of contact between the idle roller 45 and the forming support 11, 16 (in the absence of the continuous elongated element 21) or between the idle roller 45 and a first contact area 52 of the continuous elongated element 21 with the forming support 11, 16.

(26) More generally, the second distance “d2” is defined as the distance comprised between the point proximal to the forming support 11, 16 at which the first conveyor branch 30a and the second conveyor branch 31a are not facing each other and the point of contact between the idle roller 45 and the forming support 11, 16 (or between the idle roller 45 and a first contact area 52 of the continuous elongated element 21 with the forming support 11, 16).

(27) In particular, when for structural reasons, the conveyor branches 30a and 31a do not coincide for their entire length (as in FIG. 2), the distance “d2” is substantially calculated starting from the projection of the centre of the roller furthest from the forming support on the corresponding conveyor branch; when the branches 30a and 31a coincide, such distance is calculated starting from the projection of the centre of any one of the two rollers on the corresponding conveyor branch.

(28) Such second distance “d2” is less than about 100 mm and preferably comprised between about 10 mm and about 50 mm. The first distance “d1” and the second distance “d2” are measured parallel to the conveyor branches 30a, 31a. The apparatus 20 also comprises at least one control unit 53 operatively connected to the motor 40, to the devices 29 for moving the forming support 11, 16, to the extruder 22, to the actuator 41, to the laying member 28 and to the movement sensor 44.

(29) During use and in accordance with the method and the process of the present invention, the continuous elongated element 21 produced by the extruder 22 commanded by the control unit 53 exits from the exit opening 25. At the start of the production, a head end 54 of the continuous elongated element 21 just exited from the abovementioned exit opening 25 is engaged between the first and the second pulley 32, 35, which are already in rotation, at the area of maximum proximity 48. The continuous elongated element 21 is advanced between the two branches 30a, 31a of the two conveyor belts 30, 31 up to the end 51. Given the proximity from the exit opening 25 to the area of maximum proximity 48, the head end 54 is only slightly bent downward, without however compromising the direct and correct insertion between the conveyor belts 30, 31. At the instant of insertion, due to the thickness of the continuous elongated element 21, the first support frame 34 together with the first conveyor belt 30 are slightly lifted upward on the abovementioned guides and such movement “ΔS” is detected by the movement sensor 44 which sends a signal “s” to the control unit 53. The control unit 53 controls the start of the rotation of the forming support 11, 16 on the basis of the received signal, when the continuous elongated element 21 is about to reach the end 51. In order to ensure that the continuous elongated element 21 advances together with the belts 30, 31 without sliding and without being excessively crushed, the actuator 41, possibly commanded by the control unit 53, compresses the first conveyor belt 30 against the continuous elongated element 21 (the action of the actuator 41 is summed with the weight of the first conveyor belt 30 and the first support frame 34) or it tends to lift the first conveyor belt 30 in a manner so as to partly unload the weight of the first conveyor belt 30 and the first support frame 34da from the continuous elongated element 21. Once it reaches the second roller 36, the head end 54 is laid on the forming surface 11a, 16a of the forming support 11, 16 already in rotation and is driven to below the roller 45 of the laying member 28 which presses it and fixes it against said forming surface 11a, 16a. The rotation of the forming support 11, 16 causes the winding of the continuous elongated element 21 continuously delivered from the extruder 22 on the forming support 11, 16 itself.

(30) The control unit 53 is capable of adjusting the power of the rotary screw 24 and/or of the gear pump 26, of the motor 40 and of the devices 29 for moving the forming support 11, 16. In this manner, the control unit 53 controls and adjusts the exit speed “Ve” of the continuous elongated element 21 from the output opening 22b, the linear speed “Vt” of the conveyor belts 30, 31 and of the span of continuous elongated element 21 interposed between them and the peripheral speed “Vs” of the forming support 11, 16 and of the span of the continuous elongated element 21 adhering to the forming surface 11a, 16a.

(31) The peripheral speed “Vs” of the forming support 11, 16 is maintained, both at the start and during operation, greater than the exit speed “Ve”, in a manner so as to extrude the continuous elongated element 21 with a specific section (such to not lead to extrusion problems), stretch it and deposit it on the forming support 11, 16 with a desired design section (less than the extrusion section). By total stretch coefficient “K.sub.tot” it is intended the ratio between the peripheral speed “Vs” and the exit speed “Ve”. The stretching involves an elongation and a decrease of the section of the continuous elongated element 21. The total stretch coefficient “K.sub.tot” is for example equal to about 1.4.

(32) According to one embodiment, the linear speed “Vt” of the two branches 30a, 31a of the conveyor belts 30, 31 is greater than the exit speed “Ve” in a manner so as to subject the continuous elongated element 21 to two stretchings, one between the extruder 22 and the conveyor 27 and one between the conveyor 27 and the laying member 28.

(33) By first stretch coefficient “K.sub.1” it is intended the ratio between the linear speed “Vt” and the exit speed “Ve”. By second stretch coefficient “K.sub.2” it is intended the ratio between the peripheral speed “Vs” and the linear speed “Vt”. The total stretch coefficient “K.sub.tot” is equal to the product (K.sub.1*K.sub.2) of the first stretch coefficient “K.sub.1” and the second stretch coefficient “K.sub.2”. The first stretch coefficient “K.sub.1” is for example comprised between about 1 and about 1.5. The second stretch coefficient “K.sub.2” is for example comprised between about 1 and about 3.

(34) According to one embodiment, the ratios between the exit speed “Ve”, the linear speed “Vt” and the peripheral speed “Vs” are maintained constant during the entire work cycle. The head end 54 of the continuous elongated element 21 with length “11” equal to the first distance “d1” (11=d1) is not subjected to any stretching. A span 55 of the continuous elongated element 21 immediately adjacent to the head end 54 and with length “12” equal to the difference between the second distance “d2” and the first distance “d1” (12=d2−d1) is subjected to a single stretching with the first stretch coefficient “K.sub.1” and the rest of the continuous elongated element 21 is subjected both to the first stretching and to a second stretching with the second stretch coefficient “K.sub.2”. The rest of the continuous elongated element 21 is subjected to a total stretching with the total stretch coefficient “K.sub.tot” equal to the product of the first stretch coefficient “K.sub.1” and the second stretch coefficient “K.sub.2”. It follows that, as illustrated in FIG. 3a, the head end 54 has a first thickness “t1” greater than a second thickness “t2” of the span 55 adjacent to the head end 54 which is in turn greater than a third thickness “t3” of the rest of the continuous elongated element 21. Analogously, the continuous elongated element 21 in the head end 54, in the span 55 adjacent to the head end 54 and in all of the remaining part thereof has different, progressively decreasing widths (not illustrated in the figures).

(35) According to one embodiment, during an initial transient “Δt”, measured starting from when the head end 54 is engaged between the conveyor belts 30, 31, the linear speed “V′t” is greater than the operating linear speed “Vt”. Said initial transient “Δt” is such that the continuous elongated element 21 travels the length “12” of the span 55 of the continuous elongated element 21 immediately adjacent to the head end 54, i.e. it is equal to the ratio between the difference between the second distance “d2” and the first distance “d1” divided by the linear speed “V′t” during the transient “Δt” (Δt=(d2−d1)/V′t).

(36) If the linear speed “V′t” during the transient “Δt” is equal to the peripheral speed “Vs”, said span 55 is stretched with a supplementary stretch coefficient “K′±” equal to the total stretch coefficient “Kt0r” and has a second thickness “t2” equal to the third thickness “t3” of the rest of the continuous elongated element 21 (FIG. 3b).

(37) If the linear speed “V′t” during the transient “Δt” is less than the peripheral speed “Vs” (but still greater than the operating linear speed “Vt”), said span 55 is stretched with a supplementary stretch coefficient “K′.sub.1” less than the total stretch coefficient “K.sub.tot” (but still greater than the first stretch coefficient “K.sub.1”) and has a second thickness “t2” greater than the third thickness “t3” (FIG. 3c) but less than the thickness that it would have if during the transient “Δt” the linear speed was the operating linear speed “Vt” (FIG. 3a).

(38) Upon termination of the delivery, the control unit 53 stops the extruder 22, allowing the conveyor belts 30, 31 to revolve until the residue continuous elongated element 21 is removed. If, between one production cycle and the next, a small amount of elastomeric material exits from the opening 22b of the extruder 22 due to the pressure, this is deposited at the area of maximum proximity 48 and can be removed by moving the conveyor belts 30, 31.