Method and unit for stitching multilayer products of green elastomeric material

Abstract: A method and unit (1) for stitching multilayer products (2) of green elastomeric material, whereby an annular multilayer product (2) of green elastomeric material, particularly a product forming at least part of a tire (2), is placed inside a hollow annular body designed to house the multilayer product (2) and forming a stitching mold (5) having a concave inner surface (5a) contacting a first convex surface (34a) of the multilayer product (2) and negatively reproducing the final shape to be imparted on the multilayer product (2); a stitching device (24) being brought into contact, at a given pressure, with a second concave surface (34) of the multilayer product (2); and relative motion being produced between the stitching device (24) and the multilayer product (2), so as to cause the stitching device (24) to stitch the multilayer product (2) in contact with the inner surface (5a) of the stitching mold (5).

Description: The present invention relates to a method of stitching multilayer products of green elastomeric material. The present invention may be employed to advantage, among other things, for producing road vehicle tires and/or tire parts to which the following description refers purely by way of example. Road vehicle tires are usually made by superimposing a number of layers of elastomeric material defining two multilayer annular products respectively consisting of an inner carcass and an outer tread belt. The outer tread belt comprises an outer tread surrounding a reinforcing belt comprising at least one tread ply, while the inner carcass usually presents a substantially U-shaped section, and comprises an annular layer defined by a body ply and by an innerliner covering part of the inner surface of the body ply, the remaining inner surface of which is covered by two abrasion strips and two sidewalls on opposite sides of the innerliner. The carcass also comprises two beads, each housed inside a respective lateral wall of the carcass formed by turning a respective lateral end of the annular layer up about the bead. For achieving maximum uniformity of the tire, the above two multilayer products and, especially, those produced by combining the same, i.e. the finished green tires, are compacted by means of a stitching operation. The following description deals solely, though without departing from the wider scope of the present invention, with the stitching of said two multilayer products for producing a finished green tire, no mention being made of any intermediate stitching for compacting each of said two multilayer products, to which the same considerations also apply. For producing a green tire, the outer tread belt is normally stitched to the inner carcass from the outside, to withstand which the green tire must be connected in fluidtight manner to an inner support and inflated. Moreover, to enable it to be stitched from the outside, the outer surface of the green tire must be freely accessible. External stitching is usually performed by rotating the green tire in contact with a stationary stitching device by which a given, usually radial, pressure is applied on the tire. A major drawback of external stitching is that, due to the freedom of the outer surface of the green tire, any distortion of the tire caused by the radial pressure applied by the stationary stitching device is totally uncontrollable, and may easily result in displacement of the cords in the body plies and/or tread plies, thus seriously impairing the uniformity of the tire. Moreover, when applied externally, said radial pressure may result in failure of the joints on the innerliner of the carcass. JP-B-45028499 provides a method according to which a tread belt is arranged inside a rigid ring, and a relevant multilayer carcass is arranged inside the tread belt, is inflated to radially expand into contact with an inner surface of the tread belt, and is stitched from the inside against the tread belt to form a green tire by means of an internal stitcher rotating about an axis of the tire itself. The above method does not overcome the drawback referred to above since, also in this case, the external surface of the green tire is substantially free, and any distortion of the green tire caused by expanding the carcass under pressure into contact with the tread belt is completely uncontrolled. It is an object of the present invention to provide a stitching method designed to overcome the aforementioned drawbacks. According to the present invention, there is provided a method of stitching multilayer products of green elastomeric material, particularly those forming at least part of a green tire, wherein an annular multilayer product of elastomeric material having a first external convex surface is arranged inside a hollow annular body, and is stitched from the inside against a concave inner surface of the annular body, characterised by the fact that the annular body defines a stitching mold in which said concave inner surface extends, during stitching, over, and in contact with, the whole said first surface of said multilayer product; said inner surface negatively matching the shape to be imparted on said multilayer product; and the stitching from inside being carried out by bringing stitching means into direct contact, at a given pressure, with a second internal concave surface of said multilayer product opposite to said first surface; and by creating a relative motion between said stitching means and said multilayer product, so as to cause said stitching means to stitch said multilayer product in contact with said inner surface of said stitching mold. The present invention also relates to a unit implementing the above method. According to the present invention, there is provided a unit for stitching multilayer products of green elastomeric material, particularly those forming at least part of a green tire, the unit comprising an hollow annular body having a concave inner surface and adapted to accommodate an annular multilayer product of elastomeric material having a first external convex surface, and stitching means to stitch the multilayer product from the inside against said concave inner surface of the annular body, characterised by the fact that the annular body defines a stitching mold in which said concave inner surface extends, in use, over, and in contact with, the whole said first surface of said multilayer product; said inner surface negatively matching the shape to be imparted on said multilayer product; the stitching means being movable to and from an operating position directly contacting a second internal concave surface of said multilayer product; and actuating means being provided for producing relative motion of said stitching means and said multilayer product, so as to cause said stitching means to stitch said multilayer product in contact with said inner surface of said stitching mold. The invention will now be described by way of examples with reference to the accompanying drawings, in which: Fig.1 shows a schematic axial cross section of a first preferred embodiment of a stitching unit in accordance with the present invention; Fig.2 shows a larger-scale view of a detail in Fig.1; Fig.s 3 and 4 show sections along line III-III in Fig.1, with parts removed for simplicity, of the Fig.1 unit in two different operating positions; Fig.s 5, 6, 7 and 8 show larger-scale, partially sectioned views of respective details in Fig.s 3 and 4; Fig.9 shows a section along line IX-IX in Fig.8; Fig.10 shows a larger-scale section of a further detail in Fig.s 3 and 4; Fig.11 shows a section along line XI-XI in Fig.10; Fig.12 shows a plan view of a further detail in Fig.s 3 and 4; Fig.s 13 and 14 show larger-scale views of respective details in Fig.12 at different operating stages; Fig.15 shows a schematic axial cross section of a second preferred embodiment of a stitching unit in accordance with the present invention. Number 1 in Fig.1 indicates a unit for internally stitching a green tire 2. Unit 1 comprises a tubular outer body 3 coaxial with axis 4 of tire 2 and fitted, on its inner surface, with a toroidal building mold 5 open along its inner edge and designed to house tire 2. In shape, the inner surface of mold 5 is substantially a negative reproduction of a finished smooth-tread tire obtainable by curing green tire 2. Unit 1 also comprises an inner drum 6 in turn comprising a central hollow shaft 7 coaxial with axis 4 and fitted with a coupling 8; and a tubular body 9 coaxial with shaft 7 and fitted to the outside of coupling 8. Tubular body 9 is defined by two coaxial tubular elements 10 and 11 preferably, but not necessarily, angularly integral with each other (as explained in detail later on). Elements 10 and 11 are arranged facing a respective bead portion 12 of tire 2, and define an annular opening 13 located centrally, in use, between bead portions 12 of tire 2 housed inside mold 5. Tubular body 9 of unit 1 in Fig.1 is supported for rotation on coupling 8 by means of a frame 14 comprising a number of radial brackets 15 (only two of which are shown in Fig.1), each having one end connected integral with the inner surface of tubular body 9, and the opposite end integral with the outer surface of a collar 16, the inner surface of which is connected for rotation to the outer surface of coupling 8. One of brackets 15 supports a motor 17, the output shaft of which is connected to coupling 8 by means of a pinion-ring gear joint 18. As shown in Fig.1, tubular body 3 is supported for rotation on drum 6 by means of a frame 19 comprising a number of radial brackets 20, each having one end connected integral with the inner surface of tubular body 3, and the opposite end integral with the outer surface of a collar 21, the inner surface of which is connected for rotation to the outer surface of tubular body 9. One of brackets 20 supports a motor 22, the output shaft of which is connected to tubular body 9 by means of a pinion-ring gear joint 23. As shown in Fig.s 3 and 4, the outer surface of coupling 8 is fitted with a stitching device 24 comprising, in the example shown, three arms 25, 26 and 27, each hinged at one end, by means of hinge 28, to a respective fork 29 integral with the inner surface of drum 6 and extending towards coupling 8. Stitching device 24 also comprises three pairs of conical rollers 30, 31 and 32 connected for rotation to the free end of respective arms 25, 26 and 27; and a control device 33 (Fig.s 10 and 11) for rotating arms 25, 26 and 27, in relation to drum 6 and about respective hinges 28, between a withdrawn idle position (Fig.3) wherein pairs of rollers 30, 31 and 32 are located inside tubular body 9 at a distance from axis 4 of less than the inside radius of tire 2, and an extracted operating position as shown in Fig.4. In the extracted operating position, arms 25, 26 and 27 extend outwards of tubular body 9 through opening 13, and pairs of rollers 30, 31 and 32 engage the inner surface 34 (Fig.2) of tire 2, which presents a convex outer surface 34a contacting the concave inner surface 5a of mold 5, and is mounted with bead portions 12 facing the outer surface of respective tubular elements 10 and 11. As shown in Fig.s 3 and 4, and particularly in Fig.7, rollers 30 are located coaxially on opposite sides of an end portion 35 of arm 25, with their wider ends facing. For reasons explained later on, rollers 30 can be maintained with their common axis parallel to axis 4 throughout displacement of arm 25 between said idle and operating positions, whereas rollers 31 and 32 must be rotated approximately 90° about the axes of respective arms 26 and 27 as these move between said idle and operating positions. As shown in Fig.s 3 and 4, arm 25 is formed in one substantially rectangular-section piece, the larger lateral surfaces of which are flat, and the smaller lateral surfaces of which are rounded. Each of arms 26 and 27, on the other hand, comprises a tubular element 36 hinged to respective fork 29; and a rod 37 of substantially the same shape as arm 25. As shown in Fig.8, on the end facing respective tubular element 36, each rod 37 is fitted integral with a pin 38 engaged for rotation inside an axial hole on tubular element 36. On the ends opposite those fitted with respective pins 38, rods 37 of arms 26 and 27 are also fitted with respective forks 39 and 40. As shown in Fig.s 8 and 9, each pin 38 presents an intermediate circumferential groove 41 extending over an arc of 90° about pin 38 and engaged in sliding manner by an end portion of a radial pin 42 extending through tubular element 36. As they move from the idle to the extracted operating position, pairs of rollers 30, 31 and 32 project from tubular body 9 through respective openings 43, 44 and 45 (Fig.s 12 to 14) formed through a cylindrical annular element 46 supported by tubular elements 10 and 11, not necessarily secured angularly to each other, so as to close groove 13. Opening 43, enabling the passage of conical rollers 30, is substantially T-shaped, and comprises a wide portion 47, the width of which, measured parallel to axis 4, is at least equal to the total length of rollers 30; and a narrow portion 48, the width of which is substantially equal to the distance between the two larger faces of arm 25, and which provides for laterally supporting arm 25 in the extracted operating position. At openings 44 and 45, annular element 46 is fitted with two plates 49 and 50 defining, at openings 44 and 45, respective cam openings 51 and 52, each comprising, as shown particularly in Fig.s 13 and 14, a wide inlet portion 53 at least as wide as the distance between the two smaller rounded faces of respective rod 37, and a narrow end portion 54 substantially equal in width to the distance between the larger lateral faces of respective rod 37. Said two portions 53 and 54 are blended on one side by an inclined cam surface 55 which, as respective rod 37 moves from the idle to the extracted operating position, and after respective pairs of rollers 31 and 32, originally perpendicular to axis 4 (Fig.3), have moved through respective openings 44 and 45, engages a smaller lateral surface of respective rod 37, which travels along wide portion 53 of respective opening 51,52, transversely in relation to its larger lateral surfaces. On engaging respective inclined surface 55, each rod 37 rotates 90° about its axis in relation to respective tubular element 36, and against the action of a torsion spring 56 between each tubular element 36 and respective pin 38, so as to engage narrow portion 54 of respective opening 51, 52. As shown in Fig.5, fork 39 comprises two arms 57 parallel to rod 37 and each fitted with a respective pin 57a supporting for rotation a respective roller 31 extending outwards of fork 39, perpendicular to respective arm 57, and having its larger side adjacent to arm 57. As shown in Fig.6, fork 40 comprises two arms 58 diverging in relation to each other and to the axis of respective rod 37, and each fitted with a respective pin 58a supporting for rotation a respective roller 32 extending outwards of fork 40, perpendicular to respective arm 58, and having is larger side adjacent to arm 58. Rollers 31 and 32 are defined respectively by a number of plates 59 and 60 connected together in axially-fixed manner and so as to rotate in relation to one other about respective pins 57a and 58a. As shown in Fig.2, when arms 25, 26 and 27 are in the extracted operating position, and pairs of rollers 30, 31 and 32 are arranged contacting inner surface 34 of tire 2, each of rollers 31 rolls in contact with an annular strip of surface 34 located between an annular rolling strip of respective roller 30 and an annular rolling strip of respective roller 32. As shown also in Fig.2, each of said three rolling strips overlaps the adjacent strip so as to define a continuous annular rolling or stitching surface extending over the entire central portion of inner surface 34. As shown in Fig.s 10 and 11, control device 33 comprises three equally spaced radial appendixes 61 connected integral with the outer surface of coupling 8 and each having a circumferential groove 62 closed by an annular body 63 (Fig.11) facing groove 62, so as to define, with an end portion of appendix 61, a radial opening 64 enabling external communication of groove 62. Each groove 62 defines a slideway for a respective slide 65 forming a first portion of a circular-sector-shaped element 66 also forming part of device 33 and comprising a second portion 67 extending radially outwards of appendix 61 through opening 64 and having peripheral outer teeth 68. Teeth 68 mesh with teeth 69 of respective gears 70, each located inside respective fork 29 (Fig.9) and fitted on to a respective arm 25, 26, 27. As shown in Fig.10, when arms 25, 26 and 27 are in the withdrawn idle position, each element 66 is held against a circumferential end surface 71 of opening 64 by a spring 72 housed inside groove 62 and having one end connected to element 66, and the opposite end connected to the end of a threaded pin 73 fitted in axially-adjustable manner through radial wall 74 of appendix 61. Commencing with arms 25, 26 and 27 in the withdrawn idle position, when motor 17 is activated, coupling 8 rotates anticlockwise, thus rotating arms 25, 26 and 27 clockwise about respective hinges 28, so as to move rollers 30, 31 and 32 outwards of drum 6 through respective openings 43, 44 and 45. At this point, by rotating coupling 8 further, rollers 30 continue moving towards inner surface 34 of tire 2, still rotating solely about respective hinge 28, and arm 25 engages portion 48 of opening 43. In addition to rotating about respective hinges 28, rollers 31 and 32 are rotated 90° anticlockwise about the axis of respective arms 26 and 27, subsequent to rods 37 contacting respective cam surfaces 55 of plates 49 and 50, and against the action of respective torsion springs 56. Further rotation of coupling 8 engages rods 37 with respective portions 54 of openings 51 and 52, and presses rollers 30, 31 and 32 on to surface 34 of tire 2, the contact pressure of which is adjustable by regulating the preload on respective springs 72 by axially adjusting respective threaded pins 73. Once the required contact pressure is achieved, and subsequent to further rotation of coupling 8, arms 25, 26 and 27 remain in a substantially fixed angular position in relation to drum 6, by virtue of elements 66 sliding inside respective circumferential groove 62 against the action of springs 72. At this point, with arms 25, 26 and 27 maintained in a fixed angular position in relation to drum 6, operation of motor 22 rotates drum 6 and, consequently, arms 25, 26 and 27 in relation to both tubular body 3 and tire 2. As arms 25, 26 and 27 rotate about axis 4 of tire 2, rollers 30, 31 and 32 provide for stitching the inside of tire 2 with substantially no slippage between rollers 30, 31, 32 and tire 2. In fact, plates 59 and 60 of respective rollers 31 and 32 rotate about their axes at different surface speeds, in particular, at surface speeds equal to that of tire 2 at the point of contact with respective plate 59, 60. At the end of the stitching operation, coupling 8 is rotated clockwise, and arms 25, 26 and 27 restored to the withdrawn idle position in the same way as described above, only in reverse. In particular, rods 37 of arms 26 and 27 and, consequently, pairs of rollers 31 and 32 are returned to the starting position by means of torsion springs 56. Unit 1 as described above therefore provides for stitching tire 2 from the inside, which not only provides for forming tire 2 against a perfectly circular surface 34, the mold 5 of which is a perfect negative reproduction of the final shape of tire 2, capable of withstanding stitching pressure with substantially no distortion, but also enables any faulty splicing of the component layers of tire 2 to be smoothed out from the inside. The Fig.15 embodiment relates to a stitching unit 75 similar to unit 1, except that, instead of being movable, drum 6 is angularly fixed; and tubular body 3 is connected for rotation to drum 6 by means of frame 19, and driven by motor 22 supported on tubular body 9 and having its output shaft connected to tubular body 3 via a pinion-ring gear joint 76. In use, displacement of arms 25, 26 and 27 from the withdrawn idle to the extracted operating positions and vice versa is the same as for unit 1 in Fig.1. In this case, however, operation of motor 22 rotates body 3 in relation to drum 6 and, consequently, tire 2 about axis 4, while arms 25, 26 and 27 remain stationary together with drum 6.

Claims: A method of stitching multilayer products (2) of green elastomeric material, particularly those forming at least part of a green tire, wherein an annular multilayer product (2) of elastomeric material having a first external convex surface (34a) is arranged inside a hollow annular body (5), and is stitched from the inside against a concave inner surface (5a) of the annular body (5), characterised by the fact that the annular body (5) defines a stitching mold (5) in which said concave inner surface (5a) extends, during stitching, over, and in contact with, the whole said first surface (34a) of said multilayer product (2); said inner surface (5a) negatively matching the shape to be imparted on said multilayer product (2); and the stitching from inside being carried out by bringing stitching means (24) into direct contact, at a given pressure, with a second internal concave surface (34) of said multilayer product (2) opposite to said first surface (34a); and by creating a relative motion between said stitching means (24) and said multilayer product (2), so as to cause said stitching means (24) to stitch said multilayer product (2) in contact with said inner surface (5a) of said stitching mold (5). A method as claimed in Claim 1, characterised by the fact that said relative motion is achieved by maintaining said multilayer product (2) stationary, and by rotating said stitching means (24) about the axis (4) of said multilayer product (2). A method as claimed in Claim 1, characterised by the fact that said relative motion is achieved by maintaining said stitching means (24) stationary, and by rotating said multilayer product (2) about its axis (4). A method as claimed in any one of the foregoing Claims, characterised by the fact that said multilayer product (2) is stitched against said inner surface (5a) of said stitching mold (5) by means of a number of roller elements (30,31,32) forming part of said stitching means (24) and each traveling along at least a respective strip of said second surface (34). A method as claimed in Claim 4, characterised by the fact that each said strip overlaps each adjacent said strip. A method as claimed in any one of the foregoing Claims, characterised by the fact that said multilayer product (2) is a finished green tire (2); said second surface (34) being an inner surface of said tire (2); and said stitching means (24) being moved into an operating position contacting said inner surface (34) of said tire (2) commencing from an idle position wherein the distance between said stitching means (24) and said axis (4) of said tire (2) is less than the inside radius of said tire (2). A unit (1) for stitching multilayer products (2) of green elastomeric material, particularly those forming at least part of a green tire, the unit (1) comprising an hollow annular body (5) having a concave inner surface (5a) and adapted to accommodate an annular multilayer product (2) of elastomeric material having a first external convex surface (34a), and stitching means (24) to stitch the multilayer product (2) from the inside against said concave inner surface (5a) of the annular body (5), characterised by the fact that the annular body (5) defines a stitching mold (5) in which said concave inner surface (5a) extends, in use, over, and in contact with, the whole said first surface (34a) of said multilayer product (2); said inner surface (5a) negatively matching the shape to be imparted on said multilayer product (2); the stitching means (24) being movable to and from an operating position directly contacting a second internal concave surface (34) of said multilayer product (2); and actuating means (22) being provided for producing relative motion of said stitching means (24) and said multilayer product (2), so as to cause said stitching means (24) to stitch said multilayer product (2) in contact with said inner surface (5a) of said stitching mold (5). A unit as claimed in Claim 7, characterised by the fact that said stitching mold (5) is fixed, and said stitching means (24) are mounted so as to rotate, by virtue of said actuating means (22), in relation to said stitching mold (5) and about said axis (4) of said multilayer product (2). A unit as claimed in Claim 7, characterised by the fact that said stitching means (24) are fixed, and said stitching mold (5) is mounted so as to rotate, by virtue of said actuating means (22), about said stitching means (24) and about said axis (4) of said multilayer product (2). A unit as claimed in any one of the foregoing Claims from 7 to 9, characterised by the fact that said stitching means (24) comprise an internal control device (33), and a number of stitching elements (30,31,32) extending outwards from and connected to said control device (33), which comprises further actuating means (17) for moving said stitching elements (30,31,32) to and from said operating position. A unit as claimed in Claim 10, characterised by the fact that said control device (33) comprises a tubular body (9) extending coaxially through said stitching mold (5) and connected to the same via said actuating means (22). A unit as claimed in Claim 11, characterised by the fact that said tubular body (9) presents a circumferential opening (13); said stitching elements (30,31,32) being designed to move through said circumferential opening (13) between a first idle position, wherein said stitching elements (30,31,32) are housed inside said tubular body (9), and a second operating position wherein said stitching elements (30,31,32) extend through said opening (13).

Inventors: SIEGENTHALER KARL J, SIEGENTHALER, KARL J.
Applicants: BRIDGESTONE FIRESTONE INC, BRIDGESTONE/FIRESTONE, INC.
Application year: 1992
Main classification: B29D30
IPC codes: B29D30, B29C43