FIELD OF THE INVENTION

[01] The present invention relates to the field of moulds for moulding and vulcanizing a tyre tread. More specifically, the invention relates to the moulds used for moulding in the tread grooves which are partially or completely covered by an additional cover layer.

PRIOR ART

[02] WO2012087826 discloses a moulding element of a mould for moulding and vulcanizing a tyre tread. The moulding element comprises a moulding surface intended to mould part of the tyre tread surface and a rib intended to mould a groove in the tread. In addition, the moulding element comprises two lamellas positioned on either side of the rib at a certain distance from this rib, each lamella comprising a cutting edge, this cutting edge making an acute angle. The cutting edge is able to cut a cover layer that covers a green tyre. The rib itself will mould a groove in the tread and at the same time guide part of the cover layer into the groove thus moulded.

[03] Document WO03089257 discloses a pneumatic tyre which has fine grooves formed in a tread surface for improve brake and drive performance on ice-bound roads in early periods of wear, and which prevents snow clogging in the fine grooves, thereby enabling a further enhancement of the effect of improving the brake and drive performance.

[04] There is a need to improve the conception of the mould for moulding fine groove on the tread surface of the tire and in the same time incorporating a covering layer . DEFINITIONS

[05] A "tyre" means all types of elastic tyre whether or not subjected to an internal pressure.

[06] A "green tyre" or "green form" of a tyre means a superposition of a plurality of semi-finished rubber products present in the form of strips or sheets, with or without reinforcement. The green tyre is intended to be vulcanized in a mould in order to obtain the tyre.

[07] The "tread" of a tyre means a quantity of rubber material bounded by lateral surfaces and by two main surfaces one of which is intended to come into contact with a road surface when the tyre is running.

[08] A "tread surface" means the surface formed by those points on the tyre tread that come into contact with the road surface when the tyre is running.

[09] A "mould" means a collection of separate moulding elements which, when brought closer towards one another, delimit a toroidal moulding space.

[10] A "moulding element" of a mould means part of a mould. A moulding element is, for example, a mould segment . [11] A "rib" of a moulding element means a protrusion projecting from the moulding surface. A rib is intended to mould a groove in the tyre tread. The width of the groove is 2 mm or more. [12] A "lamella" of a moulding element means a protrusion projecting from the moulding surface. A lamella is intended to mould a sipe in the tyre tread The width of the lamella is less than 2 mm. [13] A "rib with a rounded end" means that the end of the rib is domed. [14] An "acute angle" means an angle smaller than 90°.

SUMMARY OF THE INVENTION

[15] The invention relates to a moulding element of a mould for moulding and vulcanizing a tyre tread. The moulding element comprises a rib intend to mould a groove in the tyre tread, this rib comprising a rounded end. Indeed, the moulding element comprises two cutting means positioned on either side of the rib at a certain distance from this rib, each cutting means comprises a cutting edge, this cutting edge making an acute angle. The moulding element comprises a plurality of lamellas positioned between the rib and the cutting means, the lamellas being shallower than the ribs. The rib having a direction of extension X and each lamella having a direction of extension Y, the direction of extension Y of the lamella makes an angle a with the direction of extension X of the rib, this angle a being less than 20° .

[16] The cutting means are able to cut a cover layer that covers a green tyre. The rib itself will mould a groove in the tread and at the same time guide part of the cover layer into this groove thus moulded. In the same time, the lamellas mould a plurality of sipes on the tread surface of the tyre. Indeed, with the angle a we limit more unexpected trapping of the covering material .

[17] In a variant, there is a minimum distance D between the rib and the nearest lamella, this distance is at least 1 mm. Thanks to this minimum distance, we limit unexpected trapping of the covering material by the lamella. [18] In a preferred embodiment, the angle a is less than or equal to 10°.

BRIEF DESCRIPTION OF THE DRAWINGS [19] Other features and advantages of the invention will emerge from the following description, given by way of nonlimiting example, with reference to the attached drawings in which:

Figure 1 schematically depicts a moulding element according to the invention at a first step;

Figure 2 schematically depicts the moulding element of the figure 1 at a second step;

Figure 3 illustrates the moulding element of figure 1 in another view..

[20] In the description that follows, elements that are substantially identical or similar will be denoted by identical references. [21] Figure 1 depicts a moulding element 1 according to the invention at a first step. The moulding element 1 comprises a rib 5 and two cutting means 7 positioned on either side of the rib 5 at a certain distance from this rib. The cutting means 7 are able to cut a cover layer 11 that covers a green tyre 13. The rib 5 itself will mould a groove in the tread and at the same time guide part of the cover layer into this groove thus moulded .

[22] More particularly, the rib 5 comprises a rounded end. The cutting means 7 comprises a cutting edge 8, the cutting edge making an acute angle. In a preferred embodiment, the acute angle is lower than or equal to 60°. In a variant, the acute angle is lower than or equal to 35°. In other variant, the acute angle is lower than or equal to 20°. Indeed, the moulding element 1 comprises a plurality of lamellas 9 positioned between the rib 5 and the cutting means 7, the lamellas being shallower than the rib. More particularly, the lamella have a height between 0,1 and 0,8 mm, a width between 0,1 and 0,8 mm and the pitch of the lamellas being between 0,5 and 3,0 mm. [23] Figure 2 depicts the moulding element 1 of the invention at a second step. A this step, the moulding element 1 and the green tyre 9 move closer to one another. This movement is, for example, initiated by a membrane not depicted) in the mould. Under the action of a quantity of pressurized steam, this membrane swells and pushes the green tyre towards the moulding element 1. At the step of Figure 2, the cutting means 7 have cut the cover layer 11. The rib 5 is moulding a groove in the tread and at the same time guide part of the cover layer into this groove. The invention proposes to maintain a minimum distance D between the rib 5 and the nearest lamella 9. Thanks to this minimum distance, we limit unexpected trapping of the covering material by the lamella. More particularly, the distance D is at least 1 mm.

[24] Figure 3 illustrates the moulding element 1 of figure 1 in another view. In this view, the rib 5 has a direction of extension X and each lamella has a direction of extension Y. The direction of extension Y of the lamella makes an angle a with the direction of extension X of the rib, this angle a being less than 20°. In a preferred embodiment, the angle a is less than or equal to 10°.

[25] The invention is not restricted to the examples described and depicted and various modifications can be made thereto without departing from its scope.