Tire of Which the Tread Comprises Wavy Grooves

Abstract

Mould for moulding a tread of a tire, this tread having a thickness of material to be worn away and a tread surface intended to come into contact with the road surface when the tire is running, this mould having a moulding surface intended to mould the tread surface of the tread, and having a moulding element formed of a blade and a bar, the blade being attached to the moulding surface to mould a sipe in the tread, the bar, borne by the blade to form an enlarged part of maximum width D, being intended to mould a channel in the tread, this channel itself being intended to form a new groove when the tread becomes part worn. Each blade is delimited by two lateral faces forming between them a mean angle of between 6 degrees and 18. The blade width decreasing from the mould surface when new, as far as the connection with the bar, the blade width meets the bar being at least equal to between 0.2 and 0.4 times the maximum width D.

Claims

1. A mould for moulding a tread of a tire, the tread having a thickness of material to be worn away and a tread surface intended to come into contact with the road surface when the tire is running, said mould comprising: a moulding surface intended to mould the tread surface of the tread, said moulding surface comprising at least one moulding element formed of a blade and a bar, the blade being borne by the moulding surface of the mould so as to mould a sipe in the tread, the bar, borne by the blade forming an enlarged part of maximum width D, being intended to mould a channel in the tread, said channel itself being intended to form a new groove when the tread becomes part worn, this moulding element being such that each blade is delimited by two lateral faces forming between them a mean angle at least equal to 6 degrees and at most to 18 degrees, the blade having a maximum width LM at the moulding surface of the mould or close to the moulding surface of the mould, this width gradually decreasing to be equal to Lm at the connection with the bar, the minimum width Lm of the blade at the connection with the bar being at least equal to 0.2 times and at most equal to 0.4 times the maximum width D of the bar.

2. The mould according to claim 1, wherein the plane that bisects the angle formed by the lateral faces of the blade makes an angle different from zero and at most equal to 6 degrees with a plane perpendicular to the moulding surface of the mould.

3. The mould according to claim 1, wherein the moulding element is formed of at least a first portion and a second portion, the plane that bisects the angle formed by the lateral faces delimiting the blade in the first portion being inclined to one side with respect to a plane perpendicular to the surface of the mould, and to another side with respect to that same perpendicular plane in a second portion of moulding element.

4. The mould according to claim 3, wherein there is formed, between a first portion and a second portion, a transition portion ensuring the continuity of the moulding element.

5. The mould according to claim 1, wherein cylindrical surfaces, of which the radius is at least equal to 0.6 times and at most equal to 2 times the maximum width D of the bar, are formed where the blade meets the bar.

6. A tread having been moulded in a mould according to claim 1, and intended to equip a heavy-duty vehicle tire.

7. A tread having been moulded in a mould according to claim 1 and intended for retreading a heavy-duty vehicle tire.

8. The mould according to claim 2, the moulding element is formed of at least a first portion and a second portion, the plane that bisects the angle formed by the lateral faces delimiting the blade in the first portion being inclined to one side with respect to a plane perpendicular to the surface of the mould, and to another side with respect to that same perpendicular plane in a second portion of moulding element.

9. The mould according to claim 2, wherein cylindrical surfaces, of which the radius is at least equal to 0.6 times and at most equal to 2 times the maximum width D of the bar, are formed where the blade meets the bar.

10. The mould according to claim 8, wherein cylindrical surfaces, of which the radius is at least equal to 0.6 times and at most equal to 2 times the maximum width D of the bar, are formed where the blade meets the bar.

11. The mould according to claim 4, wherein cylindrical surfaces, of which the radius is at least equal to 0.6 times and at most equal to 2 times the maximum width D of the bar, are formed where the blade meets the bar.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0033] FIG. 1 shows a partial view of a mould according to the invention for moulding a tread for a heavy-duty vehicle tire comprising hidden grooves extended towards the tread surface by sipes;

[0034] FIG. 2 shows a view in cross section of the mould of FIG. 1;

[0035] FIGS. 3 and 4 show the same alternative form of a tread mould according to the invention.

DESCRIPTION OF THE FIGURES

[0036] In order to make the figures easier to understand, identical reference signs have been used to describe alternative forms of the invention where these reference signs refer to elements of the same kind, whether structurally or functionally.

[0037] FIG. 1 shows a part of a mould 1 used for moulding a tread for a tire intended to be fitted to a heavy-duty vehicle.

[0038] This mould 1 comprises a moulding surface 10 for moulding a tread surface of the tread, this tread surface being intended to come into contact with a roadway during running.

[0039] On this moulding surface 10, there can be seen a rib 2 that is continuous in the circumferential direction, this rib 2 having a total height H corresponding to the depth of the groove which it is intended to mould in a tread (this height H is here equal to 17 mm). The width of this rib 2 gradually decreases, starting from a maximum width LM at the level of the moulding surface 10 and moving away from said surface to reach a minimum thickness Lm. In the present case, these thicknesses are respectively 2 mm and 0.6 mm.

[0040] Also depicted is a moulding element 3 for moulding a hidden channel inside a tread, this channel being extended towards the tread surface of the tread when new by a sipe. The height of this relief element, measured with respect to the moulding surface 10, is identical to the height H of the continuous rib 2.

[0041] The moulding element 3 comprises a bar 31 or enlarged part of substantially circular section in the present instance, having a maximum width D which is here equal to 6 mm; this enlarged part 31 is extended towards the surface of the mould 10 by a blade 32 of variable width, this width decreasing progressively from the surface of the mould 10 towards the bar 31. This blade 32 has a minimum width Lm equal to 1.9 mm at its connection with the enlarged part 31 and a maximum width LM equal to 3.5 mm at the level of the surface of the mould 10.

[0042] The blade 32 is, in the present instance, limited by two lateral flat faces 321, 322 originating on the surface of the mould 10 and forming between them an angle A equal to 13 degrees.

[0043] In the case presented and as can be seen in FIG. 2, which shows the same mould 1 seen in section on a plane identified by the line II-II in FIG. 1, the blade 32 comprises one planar lateral face 321 which is perpendicular to the surface of the mould 10 and another planar lateral face 322 inclined at an angle equal to 84 degrees relative to the moulding surface 10 so as to make an angle A of 13 degrees with the other lateral face 321.

[0044] FIGS. 3 to 5 show an alternative form of a tread mould according to the invention.

[0045] FIG. 3 shows a partial view of a mould 1 comprising on its moulding surface 10, a moulding element 3 comprising a first portion 301 and a second portion 302, the second portion 302 being placed in the extension of the first portion 301 via a transition portion 303. Each portion of the element comprises a blade of variable thickness fixed on the moulding surface 10 of the mould, this blade carrying an enlarged part forming a continuous bar.

[0046] The first portion 301 is depicted in section in FIG. 3; this first portion 301 comprises a bar 31 of maximum width D (equal in this instance to 6 mm) kept at a distance from the moulding surface 10 of the mould by a blade 32 having a maximum thickness LM (equal to 3.5 mm) at the level of the surface of the mould 10, this blade 32 being delimited by two lateral faces, a first lateral face 321 inclined by an angle A of 2 degrees relative to a plane perpendicular to the moulding surface 10 and a second lateral face 322 inclined by an angle B of 6 degrees relative to this same plane. The two lateral faces 321, 322 form an angle of 8 degrees between them. The blade 32 has a minimum thickness Lm (equal to 1.9 mm) where it meets the bar 31.

[0047] The plane that bisects the angle formed between the two lateral faces 321, 322 of the blade 32 is represented by its trace B1 in the plane of FIG. 3; this bisector plane B1 makes an angle of 2 degrees with respect to the plane perpendicular to the surface of the mould 10 and is oriented to the right with respect to this perpendicular plane B1 in this plane of section.

[0048] A second portion 302 of the same relief element 3 is shown in section in FIG. 5; this second portion 302 comprises a bar 31 in the continuity of the bar 31 of the first portion 301 which is kept at a distance from the moulding surface 10 of the mould by a blade 32 having a maximum thickness at the level of the moulding surface 10. This blade 32 is delimited by two lateral faces, a first lateral face 321 inclined by an angle A of 6 degrees relative to a plane perpendicular to the moulding surface 10 and a second lateral face 322 inclined by an angle B of 2 degrees with respect to this same plane. The two lateral faces form an angle of 8 degrees between them.

[0049] Unlike the case with the first portion 301, for the second portion 302 the plane that bisects the angle between the lateral faces 321 and 322 of this second portion, represented by its trace B1 in the plane of FIG. 4, makes an angle of 2 degrees with respect to the perpendicular plane and is oriented to the left with respect to this perpendicular plane in the plane of FIG. 4.

[0050] Thanks to this alternating arrangement of bisector planes B1 and B1 between the first portion 301 and the second portion 302 of the one same moulding element 3, it is possible to significantly reduce the overall forces to be provided in order to achieve demoulding. The quality of the moulding of the treads is thereby improved.

[0051] In addition, between each lateral face of the blades 32 and 32 and the enlarged part 31 of the relief element 3 there is formed a connecting region which, seen in the plane of section of FIGS. 4 and 5, corresponds to a circular arc tangential both to the bar and to the lateral face of the blade with which it connects. The radii R1, R2, R1, R2 of these circular arcs are all equal to 3.6 mm R1 corresponds to the radius of the circular arc tangential to both the bar and the lateral face 321, while R2 corresponds to the radius of the circular arc tangential to both the bar and the lateral face 322. The radii R1 and R2 are the equivalents of these radii R1 and R2 for the blade 32.

[0052] If for aesthetic purposes in particular the part of the sipe opening onto the tread surface is provided with a chamfer on each of its lateral faces, the maximum width LM of the sipe is considered at the last point of the sipe that is lacking this chamfer.

[0053] The invention also relates to a tread moulded in a mould as described above and intended to equip a tire for a heavy-duty vehicle.

[0054] Of course, the invention is not limited to the examples described and depicted and various modifications can be made thereto without departing from the scope as defined by the claims. In particular, the faces of the blade may be non-planar; in such a case, a mean angle is considered for the angle of each lateral face.