In the process of tyre production a carcass assembly is inflated and shaped on a tyre building drum, so that partial bonding with a belt-tread assembly, prepared in advance, is achieved. Subsequently, the tyre building drum is rotated so that also the belt-tread assembly is rotated together with the inflated carcass.
Final joining of the belt-tread assembly with the inflated carcass assembly is usually performed using compressive force exerted by an elastic cylinder on stitching rollers in radial direction.
Methods of joining a belt-tread assembly with an inflated carcass assembly, known so far, make use of a compressive force exerted in radial direction by an elastic pneumatic cylinder, on which divided stitching rollers are disposed. The divided stitching rollers, differing in diameter, have a profile usually designed so as to press the surface of the tyre tread along its entire length.
A further method of joining a belt-tread with an inflated carcass, makes use of a compressive force exerted in radial direction by an elastic pneumatic cylinder, on which a pair of stitching rollers is located. The pair of stitching rollers gradually symmetrically moves by an axial movement in parallel with the tyre axis from the centre to the belt-tread edges.
There may be various design solutions for the stitching devices. Such devices may be designed, for example, as dynamic that is each of the rollers rotates during stitching around its own axis which is parallel to the rotation axis of the tyre being produced and, simultaneously, the rollers move mutually symmetrically in the direction from the central part of the outer peripheral surface of the tyre being produced to its shoulders, i. e. the stitching rollers are moved in parallel with the rotation axis of the tyre; such design solution can be found, for example, in the patent EP 0 770 475 B1, where a system of two stitching rollers disposed on pneumatic cylinders attached to a fixed support is used, wherein the movement of the support in radial direction and the movement of stitching rollers disposed on pneumatic cylinders in axial direction is ensured by means of threaded rods connected with electric motors. A device according to the above patent comprises also means for deflecting the rotation axis of the stitching rollers from a position parallel to the rotation axis of the tyre building drum.
A further type of stitching devices is constituted by static stitching devices in which, when used, rollers are moved only around their own axes without relative movement of the rollers used. A combination of static and dynamic rollers is possible as well. It is described e.g. in the patent EP 0 627 302 B1, where the subject-matter of the invention is a device for radial tyre production, a part of the device consisting of a pressure unit provided with at least one roller. Specifically, there are three rollers, wherein one of them being static presses down the central part of the outer peripheral surface of the tyre and two dynamic rollers are disposed so as to press down the belt-tread edges. These rollers are moved by the action of a pneumatic cylinder into openings of a transfer unit, which is adapted specifically for this purpose and transfers the belt and tread from a winding drum to the tyre building drum.
Static stitching rollers may be designed also as divided, having different diameters, and their profile allows to press down the tyre tread surface along its entire width. However, also when using divided stitching rollers, it is possible to make use also of the movement of the stitching unit with rollers in a direction parallel to the building drum axis, as described, for example, in the patent SU 1305056 A1, where each single part of the divided stitching roller comprises a spring, so that its position is not fixed, but can vary depending on the varying surface during axial movement of the divided roller relative to the building drum axis.
By using the above devices it is possible to accomplish a method of pressing down—stitching a belt-tread assembly to a carcass assembly, wherein in this case elastic elements acting in opposite directions come into contact, namely the inflated belt-tread assembly and the pneumatic cylinder with stitching rollers. If common surface non-uniformities of the rotating belt-tread occur, mutual interaction of stitching rollers and belt-tread arises. This interaction has an adverse effect on the uniformity of the produced tyres.
Disadvantages of the above methods consist in lower uniformity of the produced tyres, deformation of carcass fibres, possibility of presence of air pockets in the tyre shoulders and complicated adjusting of the stitching roller profile during dimension change of the produced tyres.
Now it has been surprisingly found that the above interaction between two elastic elements, which consist of a pneumatic cylinder constituting a part of the stitching unit containing at least one stitching roller and of an inflated carcass assembly, can be reduced in such a way that no elastic element, but instead a rigid inelastic element is used in the design of the stitching unit. Utilising the method and device according to the present invention higher uniformity of the produced tyres is achieved.
A method of green tyre production usually includes the following operations:                production of an integrated carcass assembly in the form of a cylinder jacket, consisting usually of inner rubber, sidewalls and carcass plies, and subsequent mounting of bead wires,        production of the belt-tread assembly in the form of a cylinder jacket, usually consisting of several belt plies and a tread,        transferring the belt-tread assembly to a given position over the carcass assembly,        shaping the carcass assembly into a toroidal shape by inflating the assembly with simultaneous approaching the bead wires, turn-up the carcass plies and sidewalls around the bead wires, pressing the sidewalls of the tyre being produced against the carcass assembly, wherein during the drum rotation the inflated carcass assembly is partially joined with the belt-tread assembly which rotates on the building drum together with the inflated carcass assembly in the form of a toroid,        complete joining the belt-tread assembly with the carcass assembly in the form of a toroid by stitching during rotation of the building drum.        