Molding element including cutting means for molding and vulcanizing at least one tire tread

Abstract

A mold element for molding and vulcanizing a tire tread having a plurality of raised elements, each raised element having a contact face intended to come into contact with a road surface and lateral faces connected thereto. The mold element comprises cutting blades able to cut a cover layer already applied to a green form of the tire. Each cutting blade comprises a body, at least one of the cutting blades comprises a protrusion projecting from this body, able to drive a cut part of the cover layer into the depth of the green tire to cover all or part of a lateral face of a raised element. The cutting blade comprises, at one end of the body, a cutting edge forming an acute angle for cutting the cover layer.

Claims

1. A mold element for molding and vulcanizing a tire tread, the tread comprising a plurality of raised elements, each raised element comprising a contact face adapted to come into contact with a road surface and lateral faces connected to this contact face, wherein the mold element comprises: cutting blades adapted to cut a cover layer already applied to a green form of a tire, wherein each cutting blade comprises a body, wherein at least one of the cutting blades comprises a protrusion projecting from the body, wherein the protrusion is adapted to drive a cut part of the cover layer into the depth of the green tire to cover all or part of a lateral face of a raised element, wherein the cutting blade comprises, at one end of the body thereof, a cutting edge forming an acute angle for cutting the cover layer, and wherein the protrusion comprises a driving pad, the driving pad being defined as a second protrusion rectangular-shaped and situated on a surface of the protrusion that comes in contact with the cover layer first.

2. The mold element according to claim 1, wherein the protrusion is discontinuous along the length (L) of the cutting blade.

3. The mold element according to claim 1, wherein, viewed in cross section, the protrusion has a triangular profile.

4. The mold element according to claim 1, wherein the cutting blade comprises two protrusions arranged one on each side of the body of the blade.

5. A mold for molding and vulcanizing a tire tread, the mold comprising a plurality of mold elements according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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:

(2) FIG. 1 schematically depicts a part of a tire tread;

(3) FIG. 2 schematically depicts a mold element according to an embodiment of the invention which is able to mold part of the tread of FIG. 1;

(4) FIG. 3 illustrates a first step of molding using the mold element of FIG. 2,

(5) FIG. 4 illustrates a second step of molding using the mold element of FIG. 2;

(6) FIG. 5 illustrates a third step of molding using the mold element of FIG. 2;

(7) FIG. 6 schematically depicts part of the tread of a tire obtained following the molding steps of FIGS. 3-5;

(8) FIG. 7 schematically depicts a second alternative form of the cutting sipe blade of FIG. 2;

(9) FIG. 8 schematically depicts a third alternative form of the cutting sipe blade of FIG. 2;

(10) FIG. 9 schematically depicts a fourth alternative form of the cutting sipe blade of FIG. 2;

(11) FIG. 10 schematically depicts a fifth alternative form of the cutting sipe blade of FIG. 2.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

(12) In the description that follows, elements that are substantially identical or similar will be denoted by identical references.

(13) FIG. 1 depicts part of a tread 1 of a tire. This tread comprises a plurality of raised tread blocks 2 organized to form the tread pattern of this tread. The tread blocks 2 are delimited by grooves 4 which may run in an axial direction Y parallel to the axis of rotation of the tire, in a circumferential direction X perpendicular to the axial direction Y, or in an oblique direction that has both a non-zero circumferential component and a non-zero axial component. Each tread block 2 here is divided into a plurality of rubber strips 7 separated by sipes 3.

(14) FIG. 2 depicts a mold element 9 able to mold part of the tread of FIG. 1. This mold element comprises a molding surface 11 able to mold part of a tread surface of a tread and cutting sipe blades 13 projecting from the molding surface 11. Each cutting sipe blade 13 comprises a body 15, cutting means 17 situated at one end of this body 15, and a protrusion 19 projecting from the body 15. The cutting means 17 here take the form of a cutting edge having an acute angle less than or equal to 60. In one preferred embodiment, the angle is less than or equal to 35. In another preferred embodiment, the angle is less than or equal to 20.

(15) FIG. 3 illustrates a first step of molding in which the cutting means 17 of the cutting sipe blades 13 are in contact with a cover layer 21 covering the green form 23 of a tire.

(16) This cover layer 21 here has an elastic modulus higher than the elastic modulus of the rubber material of which the tread 1 is made. Such a material is, for example, an elastomeric material of which the dynamic shear modulus G*, when subjected to a maximum alternating stress of 0.7 MPa, at a frequency of 10 Hz and a temperature of 10 C., is higher than 200 MPa and preferably higher than 300 MPa. In this document, the terms elastic modulus G and viscous modulus G denote dynamic properties well known to those skilled in the art. These properties are measured on a Metravib VA4000 viscoanalyser on test specimens molded from uncured compositions. Test specimens such as those described in the standard ASTM D 599296 (the version published in September 2006, initially approved in 1996), in Figure X2.1 (circular procedure) are used. The diameter of the test specimen is 10 mm (and it therefore has a circular cross section of 78.5 mm.sup.2), the thickness of each of the portions of rubber composition is 2 mm, giving a diameter-to-thickness ratio of 5 (contrary to standard ISO 2856, mentioned in the ASTM standard at paragraph X2.4, and which recommends a d/L value of 2). The response of a test specimen of vulcanized rubber composition subjected to a simple alternating sinusoidal shear stress at a frequency of 10 Hz is recorded. The test specimen is loaded under sinusoidal stressing at 10 Hz, with the stress (0.7 MPa) applied symmetrically about its equilibrium position. The measurements are taken during an increasing temperature gradient of 1.5 C. per minute, from a temperature Tmin below the glass transition temperature (Tg) of the material, up to a temperature Tmax which may correspond to the rubber plateau of the material. Before commencing the sweep, the test specimen is stabilized at the temperature Tmin for 20 minutes in order to obtain a uniform temperature throughout the test specimen. The result used is the dynamic shear elastic modulus (G) and the viscous shear modulus (G) at the chosen temperatures (in this instance 0, 5 and 20 C.). The complex modulus G* is defined as the absolute value of the complex sum of the elastic modulus G and viscous modulus G values: G*={square root over ((G.sup.2+G.sup.2))}.

(17) In one alternative form of embodiment, the elastomeric material of the cover layer contains a composition based on at least one diene elastomer with a very high sulphur content, such as ebonite.

(18) In another alternative form of embodiment, the cover layer comprises a collection of fibers, for example a three dimensional collection of fibers forming felt. The fibers in this felt may be selected from the group consisting of textile fibers, mineral fibers and mixtures thereof. It will also be noted that the fibers in this felt may be chosen from textile fibers of natural origin, for example from the group of silk, cotton, bamboo, cellulose, wool fibers and mixtures thereof.

(19) In another alternative form of the embodiment, the elastomeric material of the cover layer contains a composition based on at least one thermoplastic polymer, such as polyethylene terephthalate (PET). Such a polymer may have a Young's modulus higher than 1 GPa.

(20) FIG. 4 illustrates a second molding step in which the cutting sipe blades 13 have cut the cover layer 21 and the protrusion 19 comes into contact with part of this cut cover layer 21.

(21) FIG. 5 illustrates a third molding step in which the cutting sipe blade 13 is positioned wholly in the green tire 23. The cut part of the cover layer 21 has been driven into the depths of the green tire 23 by the protrusion 19.

(22) In molding steps that have not been depicted, the green tire is then vulcanized to obtain a pneumatic tire and the cutting sipe blade 13 is extracted from this tire with the opening of the mold. FIG. 6 depicts part of the tread of this tire. More specifically, FIG. 6 depicts the tread of FIG. 1 in section on A-A. In this sectional view, the strips of rubber 7 delimited by the sipes 3 comprise depressions 25 which have been molded by the protrusions 19. These depressions are delimited by the cover layer 21.

(23) FIG. 7 depicts a second alternative form of the cutting sipe blade 13 in which the protrusion 19 is discontinuous along the length L of this sipe blade 13.

(24) FIG. 8 depicts a third alternative form, in which the protrusion 19 comprises at least one driving pad. This pad is intended to improve the ability of the protrusion 19 to catch the cover layer and drive it into the depth of the green tire.

(25) FIG. 9 depicts a fourth alternative form in which the protrusion 19 has a triangular profile to make it easier to extract from the tire once the latter has been vulcanized.

(26) FIG. 10 depicts a fifth alternative form in which the cutting sipe blade 13 comprises two protrusions 10 positioned one on each side of the body 15 of the sipe blade 13. These protrusions in this instance are offset in the heightwise direction of the sipe blade 13. As an alternative, these protrusions could be positioned opposite each other.

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