Patent Application
20160121569
The present disclosure relates to the field of molds for molding and vulcanizing a tire tread. More specifically, an embodiment of the invention relates to the molds used for molding in the tread grooves which are partially or completely covered by an additional cover layer.
It is known practice to design tires 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.
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 tire 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 molded by these ribs.
This method of manufacture has its limits, particularly as far as obtaining precision molding 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 tire are then reduced.
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.
There is therefore a need to improve the incorporation of a cover layer on the walls of grooves of a tire tread.
A “tire” means all types of elastic tire whether or not subjected to an internal pressure.
A “green tire” or “green form” of a tire 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 tire is intended to be vulcanized in a mould in order to obtain the tire.
The “tread” of a tire 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 tire is running.
A “tread surface” means the surface formed by those points on the tire tread that come into contact with the road surface when the tire is running.
A “mould” means a collection of separate molding elements which, when brought closer towards one another, delimit a toroidal molding space.
A “molding element” of a mould means part of a mould. A molding element is, for example, a mould segment.
A “molding surface” of a molding element means the surface of the mould that is intended to mould the surface of the tire tread.
A “blade” of a molding element means a protrusion projecting from the molding 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 tire tread, which means cuts which at least partially close up when they fall within the contact patch where the tire 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 tire makes contact with the ground.
A “blade with a rounded end” means that the end of the blade is domed.
The “height of the blade means the distance between the molding surface of the mould and the end of the blade.
An “acute angle” means an angle less than or equal to 90°.
The embodiment of the invention relates to a molding element of a mould for molding and vulcanizing a tire tread. This tread comprises a tread surface intended to come into contact with the ground when the said tire is rolling. This molding element comprises a molding surface intended to mould part of the tire 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 comprises a rounded end extending along the length L of the blade in a direction of extension X. The molding element comprises two cutting means able to cut a cover layer already applied to a green form of the tire and positioned on either side of the blade at a certain distance from this blade. Each cutting means comprises a cutting edge extending in the direction of extension, this cutting edge making an acute angle α in a sectional drawing perpendicular to this direction of extension X able to cut the cover layer, the distance between this cutting means and the molding surface being lower than the height H of the blade.
The cutting means are able to cut a cover layer that covers a green tire. 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 molded.
The embodiment of the invention proposes that the cover layer is cut and some parts of this layer are positioned within the depth of the green tire during one and the same movement of the molding element with respect to the green tire. Indeed, the blade can strain the cover layer when it comes into contact with it, before the cutting means. Thus, having a cover layer strained by the blade improves the cutting operation made by the cutting means.
In an alternative form of the embodiment, the angle of the cutting edge is less than or equal to 60°. The cutting ability of the cutting means is thus improved.
In a preferred form of embodiment, the angle of the cutting edge is less than or equal to 35°.
The cutting ability of the cutting means is thus improved even further.
In another preferred form of embodiment, the angle of the cutting edge is less than or equal to 20°.
The cutting ability of the cutting means is thus improved even more.
Another subject of the embodiment of the invention is a method of manufacturing a tire tread. This tread comprises a plurality of raised elements, each raised element comprising a contact face intended to come into contact with a ground when the tire is rolling along and lateral faces connected to this contact face. The method of manufacturing comprises a step of preparing a green form of the tire, a step of laying a cover layer over all or part of an external surface of the green tire, a step of laying the green tire in a mould, with the mould comprising a blade, a step of using this blade to mould a lateral face of a raised element, a step of vulcanizing the green tire in order to obtain the tire. The method of manufacturing further comprises a step of straining the cover layer by the blade, a step of cutting the cover layer using cutting means belonging to the mould, a step whereby the blade drives a cut part of the cover layer into the green tire so that the lateral face of the raised element is partially or fully covered by this cut part.
In an alternative form of the embodiment, the cover layer is extendable and the coefficient of extension of this cover layer is comprised between 10% and 80%.
With the mold, the distance between the blade and respectively each cutting means can be lower than the height H of this blade. In this case, the lateral faces of the raised element molded by the blade are partially covered by the cover layer. By using an extendable cover layer, it is possible to enlarge this cover layer during the step where the cover layer is strained by the blade. Thus, the lateral faces of the raised element are more covered or totally covered by the cover layer. Consequently, the performances of the tire are increased.
In an alternative form of the embodiment, the cover layer comprises an elastomeric material and a collection of woven or nonwoven fibers, these fibers being impregnated with this elastomeric material.
By using fibers in the cover layer, the mechanical integrity of this layer is enhanced, making it easier to cut. Further, the presence of a collection of fibers in the cover layer makes it possible, because of the intrinsic rigidity of these fibers, to limit the extensibility of the cover layer as it is being cut, making it easier to apply to the green tire. Finally, impregnating the fibers with the elastomeric material provides the whole with excellent cohesion. The cover layer thus behaves as an entity when it is being cut and applied to the green tire. The fibers may be impregnated by hot calendering, molding in a press or injection molding under pressure.
Another subject of the embodiment of the invention is a mould for molding and vulcanizing a tire tread, this mould comprising a plurality of molding elements as described hereinabove.
Other features and advantages of an embodiment of the invention will emerge from the following description, given by way of non-limiting example, with reference to the attached drawings in which:
In the description that follows, elements that are substantially identical or similar will be denoted by identical references.
More specifically, the molding element 1 comprises a molding surface 3 intended to mould part of the tread surface of a tire. The molding element 1 also comprises blades 5 of which just one is depicted here to make the embodiment of the invention easier to understand. The blade in this instance is a rib 5 intended to mould a groove in the tire 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 molding surface 3 with an height H. The rib 5 also extends lengthwise in a direction of extension X. In the mould, this direction may be a circumferential direction following the circumference of the mould. As an alternative, the direction of extension is a transverse direction perpendicular to the circumferential direction of the mould. In another alternative form, this direction of extension is an oblique direction making a non-zero angle with the circumferential direction and with the transverse direction of the mould.
The molding element 1 of
Each cutting means 7 comprises a cutting edge 8 extending in the direction of extension X. This cutting edge makes an acute angle α in a sectional drawing perpendicular to the direction of extension X. The distance D between this cutting edge and the molding surface 3 is lower than the height H of the rib 5. The cutting edge has, in the plane of
The method of manufacturing further comprises the following steps:
The embodiment of the invention is not restricted to the examples described and depicted and various modifications can be made thereto without departing from its scope.
| Number | Date | Country | Kind |
|---|---|---|---|
| 13172034.4 | Jun 2013 | EP | regional |
This application is a 371 national phase entry of PCT/EP2014/061798, filed 6 Jun. 2014, which claims benefit of European Patent Application No. 13172034.4, filed 14 Jun. 2013, the contents of which are incorporated herein by reference for all purposes.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/061798 | 6/6/2014 | WO | 00 |
