VULCANIZING MOLD FOR A TIRE WITH MEANS FOR CUTTING A RUBBER MOLD SEAM

Description

[0001] The invention relates to the field of tire manufacturing and more particularly relates to a tire baking mold comprising means for cutting out a rubber burr.

[0002] The manufacture of a tire includes a curing step during which a tire blank is molded and vulcanized to give the tire its characteristics and final appearance. The curing of a tire is carried out in a curing mold. The mold comprises several molding elements which form, in the closed position of the mold, an internal molding surface corresponding in negative to the external surface of the tire. In particular, the mold comprises several sectors distributed circumferentially to the axis of the mold which are intended to mold the tread of the tire, and two shells arranged axially which are intended to mold the sidewalls of the tire.

[0003] During curing, a rubber-based tire blank is pressed against the internal molding surface. At the same time, the molding elements are kept in contact with each other by closing means in order to prevent the mold from opening under the effect of the pressure exerted by the tire blank against the internal molding surface. Thus, during curing, the mold remains closed and the rubber under pressure does not insinuate itself between the molding elements. However, it may happen that certain molding elements are separated by a very narrow space resulting, for example, from wear of the contact surfaces between said molding elements, or from a design choice relating to the need to evacuate the air trapped between the tire blank and the mold.The rubber under pressure is then able to insinuate itself into said space so as to form a burr on the tire which may harm its characteristics and its final appearance. Documents WO2017 / 221283, EP2813354, JPH03279006 and DE102018213083 describe a tire mold comprising a molding insert provided with means for cutting a molded part during demolding.

[0004] Application US2007284783A1 describes a mold in which each sector comprises, on its circumferential edges, a contact surface bearing on the contact surface of the adjacent sector, and a slightly circumferentially recessed surface called a "non-contact" surface arranged radially towards the inside of the mold and having a roughness of between 50 and 200 µm. During curing, the non-contact surfaces of two adjacent sectors move closer together under the effect of their thermal expansion so as to bear against each other. Thus, the mold does not allow the rubber under pressure to insinuate itself between the sectors, while allowing the evacuation of air thanks to the roughness of the non-contact surfaces.

[0005] However, wear of the contact surfaces between the sectors results in the non-contact surfaces moving closer together and an increase in the contact pressure between the non-contact surfaces when they come into contact due to the thermal expansion of the sectors, said pressure being able to cause premature deterioration of the roughness of the non-contact surfaces by matting. Conversely, when the mold is no longer capable of compensating for the contact surfaces between the sectors moving closer together due to their wear, a gap is observed to form between the contact and non-contact surfaces, said gap being able to cause the creation of a burr.

[0006] An objective of the invention is to remedy the drawbacks of the state of the art and to provide an original solution in order to improve the characteristics and final appearance of the tires, while avoiding premature deterioration of the molding elements.

[0007] This objective is achieved by the invention which proposes, according to a first object, a curing mold for a tire comprising at least two molding elements according to claim 1, said molding elements being separated, in the closed position of the mold, by a space creating a flash during the curing of a tire, characterized in that said molding elements comprise cutting means capable of cutting said flash when opening the mold.

[0008] In other words, it is better to maintain a very narrow gap between certain casting elements, even taking into account their thermal expansion, in order to avoid deterioration of said casting elements.

[0009] Furthermore, when the mold is opened, said molding elements move away from the tire along given trajectories. The cutting means of said molding elements then cut the flash created between the two molding elements. The flash is cut, torn, or cracked so as to allow its elimination during rolling of the tire, which then quickly regains satisfactory characteristics and appearance.

[0010] Advantageously, each of said molding elements comprises an edge partially delimiting the space which separates them in the closed position, the cutting means being arranged on the edge of at least one of said molding elements in such a way that the cutting means cut said burr when they are removed from the tire, each of said molding elements being movable for withdrawal when the mold is opened. Such an arrangement of the cutting means is simple and makes it possible to obtain effective cutting of the burr.

[0011] Preferably, the cutting means are arranged on said edge of each of said molding elements, the cutting means of each of said molding elements taking complementary shapes. Such shapes make it possible to improve the efficiency of cutting the flash.

[0012] Advantageously, the cutting means are integral with the edge of at least one of said molding elements. Such a design is simple and saves time during the manufacture of the molding elements.

[0013] Preferably, the cutting means take a recessed and / or protruding shape. Such a non-rectilinear shape makes it possible to extend the parts of the cutting means in contact with the burr and, consequently, to increase the efficiency of cutting the burr.

[0014] It has been illustrated at the figure 2said space 36 which, advantageously, has a length L of between 0.2 and 20 mm and, more preferably, of between 0.5 and 5 mm. Preferably, said space 36 has a thickness E of between 0.1 and 3 mm, more preferably, of between 0.2 and 2 mm, and even more preferably, of between 0.3 and 1 mm.

[0015] Such a space with restricted dimensions requires having molding elements of equally restricted dimensions and, consequently, fragile. Such sizing of the molding elements makes the implementation of the invention particularly advantageous.

[0016] Preferably, the mold comprises: several sectors distributed circumferentially, intended to mold the tread of said tire, at least one sipe intended to mold a notch in said tread, said sipe extending over two adjacent sectors in such a way that said sipe comprises a part on each of the two sectors, said molding elements taking the shape of each part of the sipe. The sipe has a thickness of between 0.2 and 20 mm and, more preferably, of between 0.5 and 5 mm. In the same way, such an arrangement and such a dimensioning of the molding elements make the implementation of the invention particularly advantageous.

[0017] Preferably, the cutting means take the form of triangular or serrated teeth. Such a shape makes it possible to improve the efficiency of cutting the burr.

[0018] Advantageously, the cutting means are obtained using a selective melt consolidation process. The use of such a process, also employed in the manufacture of the molding elements on which the cutting means are arranged, makes it possible to reduce the cost and manufacturing time of the cutting means.

[0019] The second subject of the invention is a method of manufacturing a tire comprising a step of baking a tire in a baking mold according to the first subject of the invention.

[0020] The invention will be better understood from the rest of the description, which is based on the following figures: there figure 1 is a schematic representation of a cooking mold according to the state of the art; the figure 2 , already described, is a schematic representation of certain elements of the mold of the figure 1 ; there figure 3is a schematic representation of certain elements of a baking mold according to a preferred embodiment of the invention;

[0021] In the various figures, identical or similar elements bear the same reference. Their description is therefore not systematically repeated.

[0022] It has been illustrated at the figure 1a schematic representation of a curing mold 10 used to mold and cure a tire blank, with a view to obtaining a tire with desired characteristics and appearance. The mold delimits a cavity 11 generally symmetrical by revolution of central axis 12. The mold comprises a frame, molding elements, curing means, and means for opening and closing the mold. The opening and closing means are capable of moving the molding elements between an open position and a closed position. The open position corresponds to the step of extracting a molded and vulcanized tire, as well as to the step of introducing a new tire blank. The closed position ( figure 1) corresponds to the step of molding and curing the tire blank. In the closed position of the mold, the molding elements form an internal molding surface 14 corresponding in negative to the desired external surface of the tire. The curing means are capable of providing the thermal energy and / or pressure necessary, respectively, for curing and / or pressing the tire blank against the internal molding surface 14. By way of example, the supply of thermal energy and pressure is ensured by pressurized water vapor circulating around the mold, and inside the tire blank in an extensible membrane.

[0023] Throughout the following and unless otherwise indicated, an axial direction designates a direction parallel to the central axis 12, a radial direction 16 designates a direction perpendicular to the central axis 12 and which intercepts it, and a circumferential direction designates a direction perpendicular to a radial direction 16 and to the central axis 12.

[0024] The mold 10 more particularly comprises several sectors 18 intended to mold the tread of the tire, two shells 20 intended to mold the sidewalls of the tire, and two rings 22 intended to mold the beads of the tire. In the closed position of the mold, the sectors 18 are distributed circumferentially to the central axis 12 of the mold so as to form a ring, and are movable with radial withdrawal relative to the tire when the mold is opened.

[0025] It has been illustrated at the figure 2certain elements of the mold 10 which comprises at least two adjacent molding elements 24, said molding elements being separated, in the closed position of the mold, by a space 26 creating a flash (not shown) during the curing of a tire. For example, the two molding elements 26 may be two sectors 18, a sector 18 and a shell 20, or two elements entering into the composition of one or more sectors such as lining elements 28, blades 30 intended to mold grooves in the tread of the tire, or sipes intended to mold notches in said tread. Each of said molding elements 24 comprises a plurality of faces with varied functionalities.In particular, a molding element comprises a molding surface 32 contributing to the internal molding surface 14 of the mold, several contact surfaces 34 or interfaces with adjacent molding elements and at least one edge 36 partially delimiting the space 26 creating the flash. For example, the presence of said space 26 is the result of a design choice aimed at avoiding impacts between fragile parts of the two molding elements 24, said molding elements coming into hard contact by their contact surfaces 34 during the closing of the mold.

[0026] There figure 3illustrates said molding elements 24 which comprise, according to the invention, cutting means 38 capable of cutting said flash when the mold is opened. When the mold is opened, said molding elements move away from the tire along given trajectories. The cutting means of said molding elements then cut the flash created between the two molding elements. The cutting means are arranged on the edge 36 of at least one of said molding elements 24 in such a way that said flash slides along the cutting means when they are removed.

[0027] The cutting means take the form of a hollow and / or a protrusion. The hollows and protrusions of the cutting means make it possible to lengthen the sliding path of the burr along the cutting means during their removal. For example, the cutting means take the form of scissors, blades, points or any shape suitable for cutting, tearing or forming a break point in the burr.

[0028] Preferably, the cutting means are arranged on the edge 36 of each of said molding elements 24, the cutting means of each of said molding elements taking complementary shapes. Thus, the efficiency of the cutting of the flash by the cutting means is improved. The cutting means 38 are integral with the edge 36 of at least one of said molding elements 24. By way of example, the cutting means can also be fixed on the edges 36 of the molding elements 24 by any other suitable means.

[0029] Said space 26 has a length L of between 0.2 and 20 mm and, more preferably, of between 0.5 and 5 mm. The length of said space designates, in a circumferential plane, the longest distance along which the two molding elements are edge to edge. Thus, it is particularly relevant to provide a space 26 and cutting means 38 on the edges of molding elements 24 whose contact surface is small and, consequently, more fragile.

[0030] Said space has a thickness E of between 0.1 and 3 mm, more preferably between 0.2 and 2 mm, and even more preferably between 0.3 and 1 mm. The thickness of said space designates, in a circumferential plane, the shortest distance separating the two molding elements. It is necessary for the molding elements to be sufficiently distant to prevent any risk of impact between them and sufficiently close to minimize the thickness of the flash, and thus facilitate its cutting.

[0031] According to a preferred embodiment, the mold comprises at least one strip 40 extending over two adjacent sectors 18 in such a way that said strip comprises a part on each of the two sectors. In other words, said strip comprises two parts 40a, 40b, said molding elements 24 taking the shape of each part of the strip and, possibly, of the sector 18 on which a part of the strip is assembled. It is particularly relevant to provide a space 26 and cutting means 38 on the particularly fragile edges of a “sectorized” strip. The strip has a thickness of between 0.2 and 20 mm and, more preferably, of between 0.5 and 5 mm.

[0032] Preferably, the cutting means take the form of triangular or serrated teeth. Such a shape is particularly easy to arrange on the edge 36 of a strip 40.

[0033] The various molding elements 24 and the cutting means 38 forming part of the mold 10 are made from steel alloys, aluminum, polymer resin or other rigid material suitable for such use.

[0034] The various molding elements 24 and the cutting means 38 are obtained using a process chosen from the following group of processes: foundry, stamping, laser cutting, laser trimming, electroerosion or consolidation by selective melting.

[0035] By "selective consolidation by fusion" is meant an additive manufacturing process aimed at progressively and selectively aggregating or agglomerating a supply of incoming work material so as to obtain an outgoing work material. The incoming work material takes the form of and / or is part of the composition of a powder, a wire or a solution / bath. The incoming work material is generally supplied by depositing a powder on a support so as to form a layer. The support takes the form of a plate or a previously agglomerated layer. Agglomeration is generally obtained by solidifying the incoming work material which has undergone total or partial fusion (sintering) by a localized or generalized input of energy, then cooled. The energy input is generally carried out by a laser or an electron beam, although it can be carried out by induction or infrared radiation.In the case of laser and electron beam, the localization of the energy input is achieved by means of orienting the energy input such as, respectively, optical or electromagnetic means. The process gives the incoming work material a predetermined shape and mechanical characteristics. Said shape and said characteristics are functions of the material of the incoming work material and of process parameters. Said shape is generally a single-piece solid, although it can be made up of several single-piece solids.

[0036] Other variations and embodiments of the invention may be envisaged without departing from the scope of these claims.

Claims

1. Mould (10) for curing a tyre, comprising: - a plurality of circumferentially distributed sectors (18) that are intended to mould the tread of said tyre, - at least one sipe blade (40) intended to mould a void in said tread, said sipe blade extending over two adjacent sectors (18) such that said sipe blade comprises a part (40a, 40b) in each of the two sectors, the two parts of the sipe blade being separated, in the closed position of the mould, by a space (26) made in such a way as to cause the creation of a flash during the curing of a tyre, said parts of the sipe blade comprising cutting means (38) that are able to cut off said flash during the opening of the mould.

2. Mould according to the preceding claim, wherein each of said parts of the sipe blade (24) comprises an edge (36) partially delimiting said space (26), the cutting means (38) being arranged on the edge of at least one of said parts of the sipe blade such that the cutting means (38) cut off said flash during their withdrawal from the tyre, each of said parts of the sipe blade (24) being able to be withdrawn during the opening of the mould.

3. Mould according to the preceding claim, wherein the cutting means (38) are arranged on the edge (36) of each of said parts of the sipe blade, the cutting means of each of said parts of the sipe blade (24) having complementary shapes.

4. Mould according to either of Claims 2 and 3, wherein the cutting means (38) are integral with the edge (36) of at least one of said parts of the sipe blade (24).

5. Mould according to one of the preceding claims, wherein the cutting means (38) have a recessed and / or protruding shape.

6. Mould according to one of the preceding claims, wherein said space (26) has a length (L) of between 0.2 and 20 mm, and more preferably between 0.5 and 5 mm.

7. Mould according to one of the preceding claims, wherein said space (26) has a thickness (E) of between 0.1 and 3 mm, more preferably between 0.2 and 2 mm, and even more preferably between 0.3 and 1 mm.

8. Mould according to one of the preceding claims, wherein the sipe blade (40) has a thickness of between 0.2 and 20 mm, and more preferably between 0.5 and 5 mm.

9. Mould according to one of the preceding claims, wherein the cutting means (38) have the shape of a triangular or crenellated toothing.

10. Mould according to one of the preceding claims, wherein the cutting means (38) are obtained by way of a process of consolidation by selective melting.

11. Method for manufacturing a tyre, comprising a step of curing a tyre in a mould (10) according to one of Claims 1 to 10.