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] Document US4057089 discloses a pneumatic tyre comprising a tread band. The tread band has a plurality of blocks. Each block extends in a curved manner to one side of the tread band towards the centre of this tread band. More particularly, the blocks are curved along structural curvature of a parabola of the second order.

[03] Document 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 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 the groove thus moulded. [04] It is an object of the present invention to propose a mould for moulding curved blocks with cover 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 "moulding surface" of a moulding element means the surface of the mould that is intended to mould the surface of the tyre tread.

[12] A "rib" of a moulding element means a protrusion projecting from the moulding surface. The width of the rib is 2 mm or more. [13] A "lamella" of a moulding element means a protrusion projecting from the moulding surface. The width of the lamella is less than 2 mm. [14] A "rib with a rounded end" means that the end of the rib is domed.

[15] An "acute angle" means an angle smaller than 90°. SUMMARY OF THE INVENTION

[16] The invention relates to a moulding element comprising a main lamella and two ribs positioned on either side of the main lamella at a certain distance from this main lamella. The ribs are intended to mould grooves in the tread, this ribs comprising rounded ends. The main lamella comprises cutting edge, this cutting edge making an acute angle. The ribs are curved in their length with a curvature C and in that the lamella is curved with the same curvature C.

[17] Thus, it is possible to mould curved blocks with cover layer in an easy manner.

[18] In a variant, the moulding element comprises a plurality of secondary lamellas. Each of these secondary lamellas comprises a cutting edge and in that the secondary lamellas extend globally perpendicularly to the main lamella.

[19] We make easier the positioning of the cover layer on the walls of the groove moulded by the rib. Indeed, we avoid the presence of a part of the cover layer over the surface contact of the block, since the cover layer is well adapting with the curved form of the block. [20] In a variant, the pitch between the plurality of secondary lamellas is globally equal along the main lamella .

[21] We improve the cutting of the cover layer. BRIEF DESCRIPTION OF THE DRAWINGS

[22] 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;

- Figure 2 illustrates a second embodiment of the moulding element of the Figure 1.

[23] In the description that follows, elements that are substantially identical or similar will be denoted by identical references.

[24] Figure 1 depicts a moulding element 1 according to the invention. The moulding element 1 comprises one main lamella 7 and two ribs 3 positioned on either side of the main lamella 7 at a certain distance from this main lamella 7. The main lamella 7 comprises cutting edge making an acute angle. The cutting edge is able to cut a cover layer 11 that covers a green tyre 13. 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°. Each rib 3 comprises a rounded end. This rib will mould a groove in the tread and at the same time guide part of the cover layer into this groove thus moulded.

[25] More particularly, each rib 3 is curved in its length with a curvature C and the main lamella 7 is curved with the same curvature C. [26] Figure 2 illustrates a second embodiment in which the moulding element 1 comprises a plurality of secondary lamellas. This secondary lamellas extend globally perpendicularly to the main lamella 7. Each of these secondary lamellas comprises a cutting edge for cutting the cover layer. Indeed, the pitch between the plurality of secondary lamellas is globally equal along the main lamella 7.

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