Curing mold for tires including a device for cutting off rubber molding flash

Abstract

A curing mould (10) for a tyre, comprising: a plurality of circumferentially distributed sectors (18) intended to mould the tread band of the tyre; at least one sipe blade (40) for moulding a recess in the tread band, said sipe blade extending over two adjacent sectors (18) so that said sipe blade comprises a portion (40a, 40b) in each of the two sectors, the two portions of the sipe blade being separated when the mould is in the closed position by a space (26) where flash is generated during curing of the tyre, said portion of the sipe blade comprising a cutting device (38) capable of cutting off the flash when the mould is opened.

Description

Technical Field

[0001] The present invention relates to the field of tire manufacturing, and more particularly to a mold for curing tires having a device for cutting off rubber flash. Background Art

[0002] The manufacture of the tire comprises a curing step during which the green tire is molded and vulcanized to give the tire its characteristics and its final appearance. The tire is cured in a curing mold. The mold comprises a plurality of molding elements which, in the closed position of the mold, form an inner molding surface which corresponds to the negative of the outer surface of the tire. In particular, the mold comprises a plurality of sectors distributed circumferentially with respect to the axis of the mold and intended to mold the tread of the tire, and two shells arranged axially and intended to mold the sidewalls of the tire.

[0003] During curing, the rubber-based green tire is pressed against the inner molding surface. At the same time, the molding elements are kept in contact with each other by closing means to prevent the mold from opening under the effect of the pressure exerted by the green tire on the inner molding surface. Therefore, during curing, the mold remains closed and the rubber subjected to pressure does not creep between the molding elements. However, it is possible that some molding elements are separated by very narrow spaces, for example due to wear of the contact surfaces between the molding elements or design choices related to the need to evacuate the air trapped between the green tire and the mold. The rubber subjected to pressure can then creep into said space and form flash on the tire that can have a negative impact on its properties and its final appearance.

[0004] Application US2007284783A1 describes a mould in which each sector has, at its circumferential edge, a contact surface resting against the contact surface of an adjacent sector and a surface slightly set back in the circumferential direction and referred to as a “non-contact” surface, which is arranged radially towards the inside of the mould and has a roughness between 50 and 200 μm. During curing, the non-contact surfaces of two adjacent sectors move towards each other under the effect of their thermal expansion, thus coming to bear against each other. Thus, the mould does not allow the rubber, which is subjected to pressure, to creep between the sectors, while allowing the air to escape by virtue of the roughness of the non-contact surfaces.

[0005] However, the wear of the contact surfaces between the sectors causes the non-contact surfaces to come closer together, and when the non-contact surfaces come into contact under the effect of the thermal expansion of the sectors, the contact pressure between the non-contact surfaces increases, which can lead to a premature degradation of the roughness of the non-contact surfaces due to grinding. Conversely, when the mold can no longer compensate for the increasing proximity of the contact surfaces between the sectors due to the wear of the sectors, it is observed that a space is formed between the contact surface and the non-contact surface, which space can lead to the generation of flash. Summary of the invention

[0006] The object of the present invention is to overcome the drawbacks of the prior art and to provide an inventive solution to improve the characteristics and the final appearance of the tyre while avoiding premature degradation of the moulding elements.

[0007] This object has been achieved by the invention which, according to a first subject, proposes a mould for curing tyres, said mould comprising at least two moulding elements which, in the closed position of the mould, are separated by a space in which flash is produced during the curing of the tyre, characterised in that said moulding elements comprise cutting means capable of cutting off said flash during the opening of the mould.

[0008] In other words, even if thermal expansion of the molding elements is taken into account, it is still preferable to maintain a very narrow space between some molding elements to avoid degradation of the molding elements.

[0009] In addition, during the opening of the mold, the molding element moves away from the tire along a given trajectory. Then, the cutting device of the molding element cuts off the flash generated between the two molding elements. The flash is cut, torn or broken so that it is eliminated during the operation of the tire, so this quickly achieves satisfactory characteristics and appearance.

[0010] Advantageously, each of the molding elements comprises an edge partially defining the space separating the molding elements in the closed position, and a cutting device is provided at the edge of at least one of the molding elements so that the cutting device cuts off the flash during removal from the tire, each molding element being able to be removed during opening of the mold. This arrangement of the cutting device is simple and allows efficient cutting of the flash.

[0011] Preferably, the cutting device is arranged on the edge of each molding element, and the cutting device of each molding element has a complementary shape, which can improve the cutting efficiency of the flash.

[0012] Advantageously, the cutting means are integral with the edge of at least one of the moulding elements.Such a design is simple and enables time to be saved during the manufacture of the moulding element.

[0013] Preferably, the cutting device has a concave and / or convex shape. Such a non-linear shape can extend the portion of the cutting device in contact with the flash, thereby improving the cutting efficiency of the flash.

[0014] Figure 2 Said space 26 is shown, advantageously having a length L between 0.2 and 20 mm, more preferably between 0.5 and 5 mm. Preferably, said space 26 has a thickness E between 0.1 and 3 mm, more preferably between 0.2 and 2 mm, even more preferably between 0.3 and 1 mm.

[0015] This space of limited dimensions means that the moulding element also has limited dimensions, so that the moulding element is delicate. Such dimensions of the moulding element make the implementation of the invention particularly advantageous.

[0016] Preferably, the mold comprises:

[0017] - a plurality of circumferentially distributed sectors intended to mould the tread of said tyre,

[0018] - at least one sipe blade intended to mould a void in the tread, the sipe blade extending over two adjacent sectors so that the sipe blade comprises a portion on each of the two sectors, the moulding element taking the shape of each portion of the sipe blade. The sipe blade has a thickness between 0.2 and 20 mm, more preferably between 0.5 and 5 mm. In the same way, this arrangement and this size of the moulding element make the implementation of the invention particularly advantageous.

[0019] Preferably, the cutting device has a triangular or sawtooth shape. Such a shape can improve the cutting efficiency of the flash.

[0020] Advantageously, the cutting device is obtained by a selective melt consolidation process. The use of such a process makes it possible to reduce the manufacturing costs and duration of the cutting device, as well as the manufacture of the moulding element provided with the cutting device.

[0021] A second subject of the invention is a method for manufacturing a tyre comprising a step of curing the tyre in a curing mould according to the first subject of the invention.

[0022] Finally, a third subject of the invention is a tyre intended to be mounted on a wheel rim, said tyre being obtained by the manufacturing method according to the second subject of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be better understood through the rest of the application document based on the following drawings:

[0024] - Figure 1 is a schematic diagram of a curing mold according to the prior art;

[0025] - Figure 2 for Figure 1 A schematic diagram of certain elements of the die, as described above;

[0026] - Figure 3 Schematic diagram of certain elements of a curing mold according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0027] In the various drawings, the same or similar elements are provided with the same reference numerals, and therefore, a systematic repetitive description is not required.

[0028] Figure 1 A schematic diagram of a curing mold 10 for molding and curing a green tire to obtain a tire with desired characteristics and desired appearance is shown. The mold defines a cavity 11 that is generally rotationally symmetrical around a central axis 12. The mold comprises a frame, a molding element, a curing device, and a device for opening and closing the mold. The opening and closing device enables the molding element to be arranged to move between an open position and a closed position. The open position corresponds to the step of removing the molded and cured tire, and to the step of introducing a new green tire. The closed position ( Figure 1 ) corresponds to the step of molding and curing the green tire. In the closed position of the mold, the molding elements form an inner molding surface 14 that is negative of the desired outer surface of the tire. The curing device can provide the heat energy and / or pressure required to cure and / or press the green tire against the inner molding surface 14, respectively. For example, the heat energy and pressure are provided by pressurized steam circulating around the mold inside the green tire in a stretchable membrane.

[0029] Hereinafter, unless otherwise stated, the axial direction refers to a direction parallel to the central axis 12 , the radial direction 16 refers to a direction perpendicular to and intersecting the central axis 12 , and the circumferential direction refers to a direction perpendicular to the radial direction 16 and the central axis 12 .

[0030] More specifically, the mold 10 comprises a plurality of 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 relative to the central axis 12 of the mold so as to form a ring, and can be removed radially relative to the tire during opening of the mold.

[0031] Figure 2Some elements of the mold 10 are shown, which include at least two adjacent molding elements 24, which are separated by a space 26 that generates flash (not shown) during tire curing in the closed position of the mold. For example, the two molding elements 24 can be two sectors 18, a sector 18 and a shell 20, or two elements used in a combination of one or more sectors, such as a lining element 28, a sipe blade 30 intended to mold a groove in the tread of the tire, or a sipe blade intended to mold a void in the tread. Each of the molding elements 24 includes a plurality of faces with various functions. In particular, the molding elements include a molding surface 32 constituting the inner molding surface 14 of the mold, a plurality of contact surfaces 34 or interfaces of adjacent molding elements, and at least one edge 36 that partially defines the space 26 that generates flash. For example, the presence of the space 26 results from a design choice intended to avoid impacts between delicate parts of the two molding elements 24, which are in close contact via their contact surfaces 34 during the closing of the mold.

[0032] Figure 3 The molding element 24 is shown, which, according to the invention, comprises a cutting device 38 capable of cutting off the flash during the opening of the mold. During the opening of the mold, the molding element moves away from the tire along a given trajectory. The cutting device of the molding element then cuts off the flash generated between two molding elements. The cutting device is arranged at an edge 36 of at least one of the molding elements 24, so that the flash slides along the cutting device when the cutting device is removed.

[0033] The cutting device has a concave and / or convex shape. When the cutting device is removed, the concave and convex of the cutting device can make the flash edge lengthen along the sliding path of the cutting device. For example, the cutting device is in the form of scissors, blades, points or any other suitable shape for cutting, tearing or forming an incipient rupture in the flash edge.

[0034] Preferably, the cutting device is arranged at the edge 36 of each molding element 24, and the cutting device of each molding element has a complementary shape. Therefore, the efficiency of cutting off the flash by the cutting device is improved. The cutting device 38 is integrated with the edge 36 of at least one molding element 24. For example, the cutting device can also be fixed to the edge 36 of the molding element 24 by any other suitable means.

[0035] The length L of the space 26 is between 0.2 and 20 mm, more preferably between 0.5 and 5 mm. The length of the space represents the longest distance along which two molding elements are edge to edge in a circumferential plane. It is therefore particularly suitable to arrange the space 26 and the cutting device 38 at the edge of a molding element 24, the contact surface of which has a shorter extension, thereby making the molding element 24 more delicate.

[0036] The thickness E of the space is between 0.1 and 3 mm, more preferably between 0.2 and 2 mm, even more preferably between 0.3 and 1 mm. The thickness of the space represents the shortest distance separating two molding elements in a circumferential plane. The molding elements need to be sufficiently far apart to avoid any risk of impact between them, and the molding elements need to be sufficiently close to minimize the thickness of the flash, making it easier to cut off.

[0037] According to a preferred embodiment, the mould comprises at least one slot blade 40 extending over two adjacent sectors 18, so that the slot blade comprises a portion in each of the two sectors. In other words, the slot blade comprises two portions 40a, 40b, the moulding element 24 being in the form of each portion of the slot blade and, optionally, in the form of the sector 18 to which the slot blade is connected. This is particularly suitable for providing the space 26 and the cutting means 38 at a particularly delicate edge of a "sector" slot blade. The thickness of the slot blade is between 0.2 and 20 mm, more preferably between 0.5 and 5 mm.

[0038] Preferably, the cutting means has a triangular or sawtooth shape. Such a shape is particularly easy to arrange on the edge 36 of the slit blade 40.

[0039] The various molding elements 24 and the cutting device 38 used in the combination of the mold 10 are made of steel alloy, aluminum alloy, polymer resin or some other rigid material suitable for such use.

[0040] The different moulding elements 24 and the cutting device 38 are obtained using a process selected from the following processes: casting, pressing, laser cutting, laser machining, electrical discharge machining or selective melt consolidation.

[0041] "Selective melt consolidation" is understood to be an additive manufacturing process that aims to gradually and selectively aggregate or agglomerate the input processing material feed to obtain the output processing material. The input processing material is in the form of a powder, a wire or a solution / bath, and / or a combination of powders, wires or solutions / baths is used. Typically, the input processing material is introduced in the form of a powder deposited on a support to form a layer. The support is in the form of a plate or a pre-consolidated layer. Typically, agglomeration is achieved by solidification of the input processing material, which is completely melted or partially melted (sintered) by local or comprehensive energy input and then cooled. Although the energy input can be achieved by infrared radiation or infrared induction, it is usually achieved by laser or electron beam. In the case of laser and electron beam, the localization of energy input is achieved by a device for directing energy input (for example, by optical means or electromagnetic means, respectively). The process provides the input processing material with a preset shape and mechanical properties. The shape and the properties depend on the material of the input processing material and the process parameters. Although the shape can be composed of multiple integral solid objects, it is usually one integral solid object.

[0042] Other variants and embodiments of the invention can be envisaged without departing from the scope of the claims.

Claims

1. A mold (10) for curing a tire, comprising: - a plurality of circumferentially distributed sectors (18) intended to mould the tread of said tyre, - at least one sipe blade (40) intended to mould a void in the tread, said sipe blade extending over two adjacent sectors (18) such that said sipe blade comprises a portion (40a, 40b) in each of the two sectors, The two parts of the sipe blade are separated in the closed position of the mold by a space (26) which generates flash during tire curing. The portion of the slitting blade includes a cut-off device (38) capable of cutting off the flash during die opening.

2. A mould according to the preceding claim, wherein Each of the portions of the slitting blade (40) comprises an edge (36) which partially defines the space (26), and a cutting device (38) is arranged on the edge of at least one of the portions of the slitting blade so that the cutting device (38) cuts off the flash during removal from the tire, and each of the portions of the slitting blade (40) can be removed during opening of the mold.

3. A mould according to the preceding claim, wherein The cutting means (38) are provided at the edge (36) of each of the portions of the slot blade, the cutting means of each of the portions of the slot blade (40) having a complementary shape.

4. The mold according to any one of claims 2 and 3, wherein The severing means (38) is integral with the edge (36) of at least one of the portions of the slitting blade (40).

5. The mold according to claim 1, wherein: The cutting device (38) has a concave and / or convex shape.

6. The mold according to claim 1, wherein: The length (L) of the space (26) is between 0.2 and 20 mm.

7. The mold according to claim 1, wherein: The length (L) of the space (26) is between 0.5 and 5 mm.

8. The mold according to claim 1, wherein: The thickness (E) of the space (26) is between 0.1 and 3 mm.

9. The mold according to claim 1, wherein: The thickness (E) of the space (26) is between 0.2 and 2 mm.

10. The mold according to claim 1, wherein: The thickness (E) of the space (26) is between 0.3 and 1 mm.

11. The mold according to claim 1, wherein: The thickness of the sipe blade (40) is between 0.2 and 20 mm.

12. The mold according to claim 1, wherein: The thickness of the sipe blade (40) is between 0.5 and 5 mm.

13. The mold according to claim 1, wherein: The cutting device (38) has a triangular or sawtooth shape.

14. The mold according to claim 1, wherein The cutting device (38) is obtained by a selective melt consolidation process.

15. A method for manufacturing a tyre, comprising the step of curing the tyre in a mould (10) according to any one of claims 1 to 14.

Images