Tire forming method

Abstract: A method of forming a tire (1) inside a forming mold (2) having an inner surface negatively reproducing the outer surface of the finished tire (1), which method provides for forming a second stage tread assembly (13) of the tire (1) in an annular housing (3b) defined by an annular body (3) constituting an outer portion of the forming mold (2), and by two auxiliary outer rings (47) fitted in releasable manner to the opposite axial ends of the annular body (3); the two auxiliary rings (47) subsequently being removed for fitting the annular body (3), in place of the auxiliary rings (47), with two annular lateral plates (6) defining respective lateral portions of the forming mold (2).

Description: The present invention relates to a tire forming method. In particular, the present invention relates to a method substantially of the type disclosed in GB-A-2 133 357, that is a method of forming a tire inside a forming mold having an inner surface negatively reproducing the outer surface of the finished tire, said tire comprising an inner carcass and a tread assembly in turn comprising a tread cap, a tread base located inside said tread cap, and a tread belt arranged inside said tread base; and said method comprising stages of forming the tread assembly inside an annular housing comprising an annular body, and two auxiliary rings connected in a releasable manner to the opposite axial ends of said annular body, which constitutes an outer portion of said forming mold, and presents an inner surface negatively reproducing the pattern of the tread cap of the finished tire; feeding said carcass inside said tread assembly; forming said carcass against said tread assembly and said annular body; and fitting said annular body with two annular plates, each constituting a lateral portion of said forming mold. All the known methods of the type set forth above suffer from the drawback that the extraction of the finished tires from the forming mold is always very complicated, and that the use of a segmented forming mold is in any case requested. It is an object of the present invention to improve the method set forth above so as to enable not only straightforward, low-cost forming of a tire inside a forming mold of the aforementioned type, but also correct removal of the formed tire in a manner not requiring the use of a mold of excessively complex mechanical design. According to the present invention, there is provided a method of forming a tire inside a forming mold having an inner surface negatively reproducing the outer surface of the finished tire, said tire comprising an inner carcass and a tread assembly in turn comprising a tread cap, a tread base located inside said tread cap and having two lateral tabs projecting from opposite sides of said tread cap, and a tread belt arranged inside said tread base; and said method comprising stages of forming the tread assembly inside an annular housing comprising an annular body, and two auxiliary rings connected in a releasable manner to the opposite axial ends of said annular body, which constitutes an outer portion of said forming mold, and presents an inner surface negatively reproducing the pattern of the tread cap of the finished tire; removing said two auxiliary rings; feeding said carcass inside said tread assembly; forming said carcass against said tread assembly and said annular body; and fitting said annular body with two annular plates, each constituting a lateral portion of said forming mold; each said auxiliary ring being fitted in releasable manner inside a respective one of two seats formed on the opposite axial ends of said annular body; said annular plates being fitted into said seats after removal of the auxiliary rings; and each said auxiliary ring having an inner surface negatively reproducing the outer shape of a respective said tab. In the above method, the inner surface of the annular body is limited solely to the tread cap, so that the shoulder portions of the tread are obviously formed against the inner surface of the auxiliary rings. Also, as the annular plates of the forming mold are fitted to the annular body in the same seats as the auxiliary rings, once the tire is formed and the annular plates removed, the shoulder portions of the tire are obviously exposed, with relatively little interference between the formed tire and the annular body, and such as to enable the tire to be safely removed axially from the annular body, which may thus be a continuous, non-segmented body. The invention will now be described by way of example with reference to the accompanying drawings, in which: Fig.s 1 to 6 show schematic axial half sections of successive stages in the method according to the present invention. Number 1 in Fig.6 indicates a green tire formed inside a substantially toroidal forming mold 2 comprising an outer annular body 3; two inner annular supports 4, each fitted to a respective bead portion 5 of tire 1; and two annular plates 6, each connecting a respective annular support 4 to a respective axial end of outer annular body 3, and having an outer peripheral portion connected to outer annular body 3 at a respective annular seat 3a formed on a respective axial end of outer annular body 3. Tire 1 comprises a first stage carcass 7 in turn comprising two metal beads 8, each having a respective substantially triangular-section filler 9, and each located at a respective bead portion 5. Carcass 7 also comprises a reinforced body ply 10 about beads 8; an innerliner 11 on the inner surface portion of ply 10 between beads 8; and two abrasion strips 12, each covering a respective portion of ply 10 about respective bead 8. As shown in Fig.6, in addition to carcass 7, tire 1 also comprises a second stage assembly 13 defined, in the example shown, by an annular tread cap 14 having an inner cushion (not shown) and housed inside an outer groove of a tread base 15 having two substantially triangular-section tabs 16 projecting laterally in relation to cap 14. In addition to a cover ply 17, base 15 also houses a reinforced tread belt 18 defined, in the example shown, by two reinforced tread plies 19 and 20, the first outside the second. Tire 1 in the example shown also comprises two annular sidewalls 21, each outside body ply 10 and having an inner peripheral portion covering part of a respective abrasion strip 12, and an outer peripheral portion covering a respective tab 16. As shown in Fig.6, outer annular body 3 is defined by a cylindrical ring 22 having two outer annular end ribs 23, and defined internally by a cylindrical surface 24. From a central portion of surface 24, there projects radially inwards an annular rib 25, the axial ends of which are defined by respective flat annular shoulders 26 perpendicular to and blending with surface 24 via respective inward-tapering, truncated-cone-shaped surfaces 27. Surfaces 24, 26 and 27 combine to define the inner surface of a respective annular seat 3a. Surface 24 presents two circumferential grooves 28, each outwards of a respective surface 27; and rib 25 is defined internally by an annular substantially barrel-shaped surface 29 negatively reproducing the pattern of finished tread cap 14. As shown in Fig.6, each annular support 4 comprises an annular plate 30, the outer cylindrical surface 31 of which, on the side facing the other annular support 4, presents a substantially triangular-section annular rib 32 defined, on the side facing the other annular support 4, by a concave annular surface 33 so shaped as to mate with a respective abrasion strip 12. On the outward side, each annular rib 32 is defined by a truncated-cone-shaped surface 34 tapering outwards and connected to surface 31 by an annular shoulder 35. Annular surface 31 also presents an annular groove 36 outwards of annular shoulder 35. As shown in Fig.6, each annular plate 6 presents a cylindrical inner surface 37 and a cylindrical outer surface 38 positioned facing and substantially contacting cylindrical surface 31 of respective annular support 4 and inner surface 24 of ring 22 respectively. On the side facing the other plate 6, each plate 6 is defined by an annular shoulder 39 adjacent to surface 37 and positionable facing and substantially contacting annular shoulder 35 of respective annular support 4; by a first truncated-cone-shaped surface 40 adjacent to shoulder 39 and positioned contacting truncated-cone-shaped surface 34 of respective annular support 4; by a second truncated-cone-shaped surface 41 adjacent to surface 38 and contacting respective truncated-cone-shaped surface 27; by a flat annular surface 42 adjacent to surface 41 and contacting respective shoulder 26 of annular body 3; and by a concave annular surface 43 connecting surfaces 40 and 42. Each plate 6 presents a first number of spherical locking devices 44 evenly spaced along surface 37 and engaging groove 36 of respective annular support 4; and a second number of spherical locking devices 45 evenly spaced along surface 38 and engaging respective groove 28. When engaged inside respective grooves 36 and 28, devices 44 and 45 lock respective plates 6 in an operating assembly position wherein surfaces 43 connect surfaces 29 and 33 in such a manner as to define the inner surface of annular forming mold 2. As shown in Fig.1, in actual use, outer annular body 3 is first used alone for forming tread cap 14 as described and claimed in co-pending European Patent Application n. 0545080, to which full reference is made herein in the interest of full disclosure. When completed, tread cap 14 is defined laterally by two annular surfaces 46 coplanar with shoulders 26. As shown in Fig.2, annular body 3 is then fitted, in seats 3a, with two auxiliary rings 47 defining, together with annular body 3, an annular housing 3b for forming second stage tread assembly 13. Each auxiliary ring 47 presents a cylindrical outer surface 48 facing and substantially contacting inner surface 24 of ring 22. On the side facing the other ring 47, each ring 47 is defined by a truncated-cone-shaped surface 49 adjacent to surface 48 and contacting respective truncated-cone-shaped surface 27; by a flat annular surface 50 adjacent to surface 49 and contacting respective shoulder 26 of annular body 3; by a cylindrical inner surface 51; and by a further truncated-cone-shaped surface 52 tapered oppositely to surface 49 and connecting surfaces 50 and 51. Each ring 47 presents a number of spherical locking devices 53 equally spaced along surface 48 and engaging respective groove 28 for locking ring 47 to annular body 3. As shown in Fig.2, each surface 50 projects inside the inner edge of respective shoulder 26, and is positioned facing the part of respective surface 46 left exposed by respective tab 16 of base 15; while each truncated-cone-shaped surface 52 constitutes the outer forming surface of a respective tab 16, which is preferably formed against respective surface 52 via internal stitching by rollers 54 shown by the dotted line in Fig.2. Second stage tread assembly 13 is then completed by fitting belt 18 inside base 15 in known manner (not shown). At this point, auxiliary rings 47 are removed, and, as shown in Fig.3, tabs 16, no longer supported by auxiliary rings 47, are flexed outwards of the original forming position, to enable carcass 7 to be inserted inside and subsequently formed against tread assembly 13 (Fig.s 4 and 5). Outward flexing of tabs 16 may be achieved either by rolling, using the same rollers 54, or centrifugally by rotating annular body 3 about its axis. Once carcass 7 has been formed against tread assembly 13, tabs 16 are restored to their former position, and annular plates 6 assembled. Plates 6 provide not only for locking annular supports 4 in relation to annular body 3 to complete forming mold 2, but also for fitting carcass 7 with sidewalls 21 fitted beforehand to the inner surface of respective annular plates 6. In other words, auxiliary rings 47 not only provide, as already stated, for greatly simplifying the design of annular body 3 by minimising interference between annular body 3 and tire 1, but also for accurately forming inner portions of tire 1, such as tabs 16, and greatly simplifying application of sidewalls 21 on tabs 16.

Claims: A method of forming a tire (1) inside a forming mold (2) having an inner surface negatively reproducing the outer surface of the finished tire (1), said tire (1) comprising an inner carcass (7) and a tread assembly (13) in turn comprising a tread cap (14), a tread base (15) located inside said tread cap (14) and having two lateral tabs (16) projecting from opposite sides of said tread cap (14), and a tread belt (18) arranged inside said tread base (15); and said method comprising stages of forming the tread assembly (13) inside an annular housing (3b) comprising an annular body (3), and two auxiliary rings (47) connected in a releasable manner to the opposite axial ends of said annular body (3), which constitutes an outer portion of said forming mold (2), and presents an inner surface (29) negatively reproducing the pattern of the tread cap (14) of the finished tire (1); removing said two auxiliary rings (47); feeding said carcass (7) inside said tread assembly (13); forming said carcass (7) against said tread assembly (13) and said annular body (3); and fitting said annular body (3) with two annular plates (6), each constituting a lateral portion of said forming mold (2); each said auxiliary ring (47) being fitted in releasable manner inside a respective one of two seats (3a) formed on the opposite axial ends of said annular body (3); said annular plates being fitted into said seats (3a) after removal of the auxiliary rings (47); and each said auxiliary ring (47) having an inner surface (52) negatively reproducing the outer shape of a respective said tab (16). A method as claimed in Claim 1, characterised by the fact that each said tab (16) is stitched against said inner surface (52) of a respective said auxiliary ring (47). A method as claimed in Claim 2, characterised by the fact that, following removal of said two auxiliary rings (47), said two tabs (16) of said tread base (15) are flexed outwards of their original forming position against said inner surface (52) of said respective auxiliary rings (47), for enabling insertion of said carcass (7) inside said second stage tread assembly (13). A method as claimed in Claim 3, characterised by the fact that said tabs (16) are flexed outwards via rolling. A method as claimed in Claim 3, characterised by the fact that said tabs (16) are spun outwards. A method as claimed in any one of the foregoing Claims from 3 to 5, for producing a tire (1) comprising two annular sidewalls (21) applied externally to said carcass (7); characterised by the fact that it comprises stages consisting in fitting each said annular sidewall (21) to the inner surface of a respective said annular plate (6); and fitting said sidewalls (21) to said carcass (7) when said annular plates (6) are fitted to said annular body (3). A method as claimed in Claim 6, characterised by the fact that said tabs (16) are restored to their original forming position prior to assembly of said annular plates (6).

Inventors: SIEGENTHALER KARL J, SIEGENTHALER, KARL J.
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1992
Main classification: B29D30
IPC codes: B29D30, B29K21, B29C33, B29L30