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] It is known practice to design tyres the tread of which comprises various rubber compounds. Document WO 03089257 discloses such treads. More specifically, document WO 03089257 discloses a tread comprising grooves the walls of which are covered with a cover layer. The material of which this cover layer is made differs from the rubber compound of which the tread is made. This material notably has much better wet grip than the wet grip of the rubber compound. This allows a very significant improvement in cornering performance on wet ground.

[03] One way of manufacturing this tread is notably disclosed in document WO 2006069912. According to this method of manufacture, in a first step, provision is made for the material intended to constitute a cover layer to be injected in the form of one or more inserts into the green tyre using an injection nozzle. The insert or inserts is or are then shaped, in a second step, by ribs of a vulcanizing mould so that they cover all or part of the walls of the grooves moulded by these ribs. [04] This method of manufacture has its limits, particularly as far as obtaining precision mouldings is concerned. Specifically, during the shaping thereof, the insert experiences a significant shear force from the rib in order to convert this insert into a layer of lesser thickness. This shear force may cause cracking within the insert, making it more difficult to control the movements of the material of which this insert is made. The shape and the thickness of the cover layer thus formed may therefore be somewhat haphazard. The advantages afforded by the additional layer to the performance of the tyre are then reduced.

[05] In addition, in this method of manufacture, it is necessary to make the inserts align with the ribs. This makes manufacture of the tread more complicated.

[06] There is therefore a need to improve the incorporation of a cover layer on the walls of grooves of a tyre tread.

DEFINITIONS

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

[08] 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.

[09] 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. [10] 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. [11] A "mould" means a collection of separate moulding elements which, when brought closer towards one another, delimit a toroidal moulding space.

[12] A "moulding element" of a mould means part of a mould. A moulding element is, for example, a mould segment .

[13] A "moulding surface" of a moulding element means the surface of the mould that is intended to mould the surface of the tyre tread.

[14] A "blade" of a moulding element means a protrusion projecting from the moulding surface. In the blades category, a distinction is made between sipe blades which are less than 2 mm wide and ribs which have a width of 2 mm or more. Sipe blades are intended to mould sipes in the tyre tread, which means cuts which at least partially close up when they fall within the contact patch where the tyre makes contact with the ground. The ribs are intended to mould grooves in the tread, which means cuts which do not close up when they fall within the contact patch in which the tyre makes contact with the ground.

SUMMARY OF THE INVENTION

[17] The invention relates to a moulding element of a mould for moulding and vulcanizing a tyre tread. This tread comprises a tread surface intended to come into contact with the ground when the tyre is rolling. The moulding element comprises a moulding surface intended to mould part of the tyre tread surface and a blade of length L and of height H intended to mould a sipe or a groove in the tread. The blade extends along the length L of the blade in a first direction of extension Y. Indeed, the moulding element comprises two cutting means positioned on either side of the blade at a certain distance from this blade. Indeed, the moulding element comprises a third cutting means of height He extending in a second direction of extension X, this second direction of extension X making an angle a with the first direction Y which is comprised between 45° and 135°. The height He of the third cutting means is greater than the height H of the blade.

[18] The cutting means are able to cut a cover layer that covers a green tyre. The blade itself will mould a groove in the tread and at the same time guide part of the cover layer into the groove thus moulded.

[19] The invention thus proposes that the cover layer is cut at different time. Firstly, the third cutting means cut the layer along the second direction of extension X. Then, the layer is cut along the first direction Y by the two cutting means and in the same time, this layer is guided by the blade into the groove. Thus, the cover layer has not at the same time two directional cutting tensions (direction X and Y) . As a result, the guidance of the cover layer by the blade into the groove is improved and the walls of the groove are better covered by this cover layer.

[20] In a variant, the difference between the height He of the third cutting means and the height H of the blade is comprised between 0,1 mm and 1 mm.

[21] In another variant, the difference between the height He of the third cutting means and the height H of the blade is equal to 0,5 mm.

BRIEF DESCRIPTION OF THE DRAWINGS [22] Other features and advantages of the invention will emerge from the following description, given by way of non-limiting example, with reference to the attached drawings in which:

Figure 1 shows a perspective view of a part of a moulding element according to the invention ;

Figure 2 is a sectional view taken along A-A line in 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 perspective view of a part of a moulding element according to the invention. The moulding element comprises blade 5 intended to mould a sipe or a groove in the tread, and two cutting means 7 positioned on either side of the blade at a certain distance from this blade. This two cutting means 7 extend in a direction of extension Y with a length L, parallel to the direction of extension of the blade 5.

[25] The moulding element comprises also a third cutting means extending in a second direction of extension X. This second direction of extension X making angle a with the first direction Y. This angle a is comprised between 45° and 135°.

[26] In the example of Figure 1, the direction X is the circumferential direction following the circumference of the mould and the direction Y is a transverse direction perpendicular to the circumferential direction of the mould.

[27] Figure 2 is a sectional view taken along A-A line in Figure 1. The moulding element 1 comprises a moulding surface 3 intended to mould part of the tread surface of a tyre. As explained above, the moulding element 1 comprises blades 5 of which just one is depicted here to make the invention easier to understand. The blade in this instance is a rib 5 comprising a rounded end and intended to mould a groove in the tyre tread. A "groove" in a tread means a cut in this tread of a width, i.e. the distance separating two lateral walls of this groove, greater than 2 mm. The rib 5 extends heightwise and projects from this moulding surface 3 with an height H.

[28] The third cutting means 11 have an height He which is here greater than the height H of the blade 5.

[27] In one preferred embodiment, the difference between the height He of the third cutting means and the height H of the blade 5 is comprised between 0,1 mm and 1 mm. Preferentially, this difference is equal to 0 , 5 mm .

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

[29] The cutting means 7, 11 comprise, here, at one hand an alternation of peaks and throughs . In another embodiment, this cutting means have a cutting edge extending continuously and having an acute angle, equal to or less than 90°, in order to cut the cover layer.