Method of making green tyre

Abstract: A method of making a green tyre comprises: winding a carcass ply of rubberised cords around a building drum (1) into a substantially cylindrical body (A); pressing the cylindrical body (A) against the building drum (1) through the entire circumference so as not to allow the carcass cords to move axially and circumferentially of the drum; constricting edge portions of the substantially cylindrical body (A) so that the outer diameter thereof is decreased; setting a bead core (C) around each of the constricted edge portions; folding back the edge portions around the bead cores (C); releasing the cylindrical body (A) from the pressing against the building drum (1) after the edge portions are constricted at the earliest; and swelling a main portion of the cylindrical body between the bead cores (C) while decreasing the width between the bead cores (C).

Description: The present invention relates to a method of making a green tyre being capable of improving tyre uniformity by decreasing variation of the carcass cord lengths. In general, in the manufacture of pneumatic tyres, in order to make a green tyre, an inner liner of gas-impermeable rubber, one or more strips or plies of rubberised cords for a carcass ply, reinforcing layer, etc. are wound on a building drum. The elastomers used in such rubber material and rubberised materials are not vulcanised when wound around the building drum. Therefore, their own adhesiveness is utilised to fix these materials onto the drum. As to the unvulcanised carcass ply material, it is first wound into a substantially cylindrical shape, and then the shape is gradually changed to the finished shape or a toroidal shape. US Patent Number 2313035 describes a method of manufacturing a green tyre comprising the steps of: winding a carcass ply of rubberized cords around a building drum into a substantially cylindrical body, pressing the cylindrical body against the building drum through the entire circumference, constricting edge portions of the substantially cylindrical body so that the outer diameter thereof is decreased, setting a bead core around each of the constricted edge portions, folding back the edge portions around the bead cores and swelling a main portion of the cylindrical body between the bead cores while decreasing the width between the bead cores. In this known method, during the above mentioned step of constricting the edge portions of the cylindrical body, the main portion of the cylindrical body is no longer pressed against the building drum, with the consequence that a disarrangement of the carcass cords may arise and the cord lengths between the bead cores in the finished tyre may vary because the carcass cords' paths are varied. Even if the variation is small, under high-speed running conditions in particular, deterioration in tyre uniformity such a radial run-out becomes not ignorable. In addition, since the presser springs (400) of the apparatus described in US Patent Number 2313035 are moved in opposite directions when pressing the cylindrical body against the building drum, the carcass cords are bent off their original direction, in particular, if the carcass cords are inclined as regards the moving direction of the presser springs, leading also to a disarrangement of the carcass cords. It is therefore, an object of the present invention to provide a method of making a green tyre, in which disarrangement of the carcass cords is prevented so that the carcass cords' paths are constant and thereby the deterioration in the tyre uniformity due to cord path variation is avoided. This object is achieved by the features of claim 1. Preferred embodiments of the invention are defined in the dependent claims. According to the present invention, a method of making a green tyre is disclosed which comprises the following steps: winding a carcass ply of rubberised cords around a building drum into a substantially cylindrical body, pressing the cylindrical body against the building drum through the entire circumference, constricting edge portions of the substantially cylindrical body so that the outer diameter thereof is decreased, setting a bead core around each of the constricted edge portions, folding back the edge portions around the bead cores and swelling a main portion of the cylindrical body between the bead cores (C) while decreasing the width between the bead cores, wherein the step of pressing the cylindrical body against the building drum is carried out in a way as not to allow the carcass cords to move axially and circumferentially of the drum and the step of releasing the cylindrical body from the pressing against the building drum is carried out after the edge portions are constricted at the earliest. An embodiment of the present invention will now be described in detail in conjunction with the accompanying drawings, in which: Figs. 1A, 1B, 1C, 1D, 1E and 1F are diagrams for explaining an example of the method of making a green tyre according to the present invention; Fig.2 is a diagram showing an example of the building drum; Fig.3 is a diagram for explaining an example of the holding apparatus for the cylindrical body; Fig. 4 is a schematic perspective view of an example of the constrictor for the edge portions of the cylindrical body; Figs.5A, 5B and 5C are diagrams for explaining a problem in constricting the edge portions of the cylindrical body; and Fig.6 shows a resultant disarray causing variation of the carcass cord paths. According to the present invention, a building drum 1 is used to make a green tyre. The building drum 1 has an outer surface 1S on which unvulcanised sheet-like tyre components are wound. The sheet-like tyre components (a) include at least one carcass ply and usually an inner liner rubber and optionally a reinforcing layer. The outer surface 1S is a cylindrically curved circumferential surface. Thus, in a cross section including the axis of the drum, the surface 1S is substantially straight and parallel with the axis. An example of the building drum 1 is schematically shown in Fig.2, and it comprises a plurality of circumferentially divided sectors 4 which are arranged around the axis of the drum 1. The sectors 4 collectively form the above-mentioned cylindrical outer surface 1S at their radially outer positions. In order to be ab!e to contract the drum, the sectors 4 can move from the above-mentioned outer positions to inner positions. The building drum 1 is supported rotatably around the axis by a shaft 3. In the normal or expanded state of the drum in which the sectors 4 are at the radially outer positions, the tyre components (a) are wound into a cylindrical body (A) on the outer surface 1S, while rotating the building drum 1 relatively to feeders for the components. The winding can be done by (i) applying the components one on the outside of the other, or (ii) first making a laminated sheet of the components and then applying the laminated sheet on the drum, or (iii) a combination of (i) and (ii). For example, in case (i), firstly the inner liner rubber is wound on to the drum, and then the carcass ply is wound on the inner liner. In case (ii), firstly the inner liner rubber and the carcass ply thereon are laminated into a sheet, and then the laminated sheet is wound on to the drum. In case (iii), of course at least three sheet-like components are used, for example, an inner liner and a carcass ply which are laminated into a sheet, and another carcass ply or a reinforcing layer wound on the laminated sheet. The cylindrical body (A) is wider than the outer surface 1S, and as a result, it has a main portion A1 on the outer surface 1S and edge portions A2 which protrude from the respective edges of the outer surface 1S. Fig.1A shows such cylindrical body (A) formed on the building drum 1. with protruding the edge portions A2 protruding. Next, as shown in Fig.1B, the cylindrical body (A) is secured by a holding apparatus 2 so as not to allow the carcass cords therein to move axially or circumferentially of the drum. The holding apparatus 2 presses the main portion A1 against the outer surface 1S of the building drum 1 around the entire circumference in order to prevent the carcass cords from being moved. An example of the holding apparatus 2 is schematically shown in Fig.3, wherein a plurality of profiled presser plates 6 are arranged around the building drum 1. The presser plates 6 can be moved towards the axis of the building drum 1 to press the main portion A1 against the drum. Preferably, the presser plates 6 are staggered about a circumferential line for example the centre line of the main portion A1 so as to be able to overlap each other in the pressing state thus not to form a circumferential gap between them. To ensure the prevention of the carcass cord movement in the main portion A1, the pressing or holding width W2 by the holding apparatus 2 is preferably set in a range of not less than 0.3 times the width W1 of the main portion A1. For the pressing position in the axial direction of the drum, in the case of a single position as shown in Fig.1B, the centre of the main portion A1 is preferred. In the case of two positions (not shown), near the edges of the main portion A1 are preferred. Of course, three or more positions are also possible. Next, in order to set a bead core C around each of the edge portions A2, the outside diameter of the edge portions A2 is decreased by a constrictor F because the outside diameter is otherwise more than the inside diameter of the bead core C. In the normal or expanded state of the building drum 1, the outside diameter thereof is more than the inside diameter of the bead core C, and accordingly, the outside diameter of the cylindrical body (A) wound on the drum is also more than the inside diameter of the bead core C. An example of the constrictor F is shown in Fig.4, which comprises a plurality of narrow width flat springs (f) one end of which is pivoted movably from a radial state to a parallel state. In the radial state, as depicted with an imaginary line, the longitudinal directions of the flat springs (f) are radial about the drum's axis. In the parallel state, as depicted with a solid line, the longitudinal directions are parallel to the drum's axis. As shown in Fig. 1C, the constrictor F in the radial state is disposed on each side of the drum coaxially therewith, and then the flat springs (f) are gradually moved towards the parallel state. Therefore, the outer surface of the edge portions A2 is compressed by the flat springs (f), and the outside diameter of the edge portions A2 becomes less than the inside diameter of the bead core C. Next, as shown in Fig.1D, the bead cores C are moved to their respective positions on the edge portions A2 from the side so that the bead cores C are located adjacently to the axial edges of the main portion A1. In this example, each bead core C and an unvulcanised bead apex rubber having a triangular sectional shape are assembled in advance by adhering the apex rubber onto the outer circumferential surface of the bead core C. After the bead cores are set, as shown in Fig. 1E, each of the edge portions A2 is folded back around the bead core C and bead apex, using a folding apparatus 5. Further, as shown in Fig.1F, the main portion A1 is swelled while decreasing the width between the bead cores C, and then tread components T including a tread reinforcing belt T1, a tread rubber T2, etc. are applied to the crown portion of the expanded main portion A1. Also, rubber layers for tyre sidewall, bead and the like are applied at appropriate times. Thus, a green tyre is formed, and it is put in a mould and vulcanised into the finished shape. As to the time sequence of the folding back of the edge portions and the applying of the tread components, they can be done almost simultaneously as well as in a sequence of the above order. As an example of the folding apparatus 5, a bladder 5A can be used. A bladder 5A is disposed on each side of the building drum 1 in its deflated sate such that a part thereof is put in the open end of the cylindrical body. By inflation of the bladder 5A, the edge portion is contacted by the inflating bladder and folded. Incidentally, to detach the tyre materials wound on the building drum 1 therefrom, the drum 1 has to contract such that its outside diameter becomes less than the smallest inside diameters of the wound materials which occurs under the bead cores. The releasing of the main portion A1 from the pressing force by the holding apparatus 2 must be done after the constriction of the edge portions A2 by the constrictor F is finished. Preferably, the releasing is done after the bead cores are set at the earliest. Also it is possible to release the main portion A1 after the edge portions A2 are folded. If the main portion A1 (or the carcass cords therein) is not secured to the drum 1, there is a possibility that some of the carcass cords are pulled in a direction as shown by arrows in Figs.5A, 5B and 5C when the constricting starts earlier on one side than the other side (Fig.5A), the constriction is stronger on one side than the other side (Fig.5B), and the gap (g) between the drum and constrictor is narrower on one side than the other side (Fig.5C). At the worst, such cord pulling occurs on both sides alternately in the circumferential direction, and the carcass cords are disarranged as shown in Fig.6. According to the present invention, such disarrangement can be effectively prevented. Comparison Tests Radial tyres of size 195/65R15 for passenger cars were made experimentally according to the present invention. And the length of the carcass cord path between the bead cores was measured at eight different circumferentially spaced positions. The mean deviation and standard deviation were calculated from the data. Further, the radial force variation was measured according to JASO C607 (Test method for automobile tyre uniformity) to obtain the mean value and standard deviation of ten sample tyres. The test results are shown in the following Table 1. Tyre Ref. Ex. Carcass cord path Mean deviation (mm) 2 1 Standard deviation (mm) 1.5 0.5 RFV Mean value (N) 63.7 48 Standard deviation (N) 17.6 7.8 From the test results, it was confirmed that the tyres made according to the present invention were effectively improved in uniformity.

Claims: A method of making a green tyre comprising winding a carcass ply of rubberised cords around a building drum (1) into a substantially cylindrical body (A), pressing the cylindrical body (A) against the building drum (1) through the entire circumference, constricting edge portions of the substantially cylindrical body so that the outer diameter thereof is decreased, setting a bead core (C) around each of the constricted edge portions, folding back the edge portions around the bead cores (C) and swelling a main portion of the cylindrical body between the bead cores (C) while decreasing the width between the bead cores, characterized in that the pressing of the cylindrical body (A) against the building drum (1) is carried out in a way so as not to allow the carcass cords to move axially and circumferentially of the drum, and that the step of releasing the cylindrical body from the pressing against the building drum (1) is carried out after the edge portions are constricted at the earliest. A method according to claim 1, characterised in that the carcass ply is wound directly or indirectly on a substantially cylindrical outer surface (1S) of the building drum (1) and the substantially cylindrical outer surface (1S) is narrower in axial width than the substantially cylindrical body (A) and the edge portions to be constricted protrude from the axial edges of the substantially cylindrical outer surface of the drum. A method according to claim 1 or 2, characterised in that the pressing of the cylindrical body (A) against the building drum is done by an apparatus which comprises presser plates (6) arranged around the building drum (1) movably towards the axis of the drum to press the substantially cylindrical body (A). A method according to claim 3, characterised in that the presser plates (6) are staggered about a circumferential line so that the presser plates (6) overlap each other when pressing the cylindrical body (A). A method according to any of claims 1 to 4, characterised in that the constricting of the edge portions is done by a device (F) which comprises a plurality of narrow width flat springs (f) one end of which is pivoted movably from a radial state to a parallel state, in the radial state, the longitudinal directions of the flat springs (f) are radial about the drum's axis, in the parallel state, the longitudinal directions are parallel to the drum's axis, and by the motion of the flat springs (f) from the radial state to the parallel state, the edge portion is constricted. A method according to any of claims 1 to 5, characterised in that the folding back of each of the edge portions is done by inflation of a bladder (5A) disposed on each side of the building drum (1). A method according to any of claims 1 to 6, characterised in that the releasing of the cylindrical body (A) from the pressing against the building drum (1) is done after the bead cores (C) are set. A method according to any of claims 1 to 7, characterised in that the releasing of the cylindrical body (A) from the pressing against the building drum (1) is done after the edge portions are bolded back. A method according to any of claims 1 to 8, characterised in that after the main portion of the cylindrical body is expanded to a certain diameter by the swelling, a tread rubber is disposed around a crown portion thereof.

Inventors: OMOKAWA TOSHIHIKO, OMOKAWA, TOSHIHIKO
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LIMITED
Application year: 2001
Main classification: B29D30
IPC codes: B29D30, G01M1