Segmented mold for a tire and related molding method

A mold for a tire is disclosed herein. The mold includes first and second shells mold-able to lateral sidewalls of the tire, and a plurality of sectors that are distributed in the circumferential direction and are mold-able to the tread of said tire. The sectors are radially movable between an open position and a closed position of the mold. The mold also comprises at least one spacing interposed between each sector and each shell in order to keep said sector and the shells spaced apart in the radial direction in the closed position of the mold, such that the shells and the sectors are in contact in the radial direction only by way of the spacing. The spacing is also able to limit the heat transfer between the shells and the sectors in said closed position.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a 371 national phase entry of PCT/EP2014/075888, filed 28 Nov. 2014, which claims the benefit of French Patent Application No. 1362060, filed 4 Dec. 2013, the contents of which are incorporated herein by reference for all purposes.

BACKGROUND

The aspects disclosed herein relate to the field of molds for curing or vulcanizing vehicle tires, and more particularly molds of the sectored type.

This type of mold mainly includes two shells that each mold one of the lateral sidewalls of the tire, a plurality of sectors that mold the tread of said tire and are radially movable between an open position and a closed position of the mold, and at least one clamping ring for allowing the sectors to move radially.

The shells and the sectors define an inner space that is intended to be brought into contact with the unvulcanized green form of tire. For more details concerning such a type of sectored mold, reference may be made for example to the documents DE 1 808 811, U.S. Pat. No. 3,797,979, EP-A2-0 701 894 and EP-B1-2 040 911.

The manufacturing of the tire, and more particularly the vulcanization phase, requires that a pressure is applied to the green tire in order to press it against the internal faces of the mold and that heat is supplied to the mold. It is also known practice to heat the mold by electrical induction and/or by magnetic induction. It is also known practice to heat the mold by means of a heat-transfer fluid such as pressurized water vapour.

In order to optimize the curing of the tire, one solution consists in heating the two shells of the mold to and keeping them at a temperature different from that to which the sectors are heated.

However, in the closed position of the mold, each shell is generally provided to bear directly against the sectors in the radial direction. Such instances of contact promote heat transfer by conduction inside the mold, between the sectors and the shells. This can be incompatible with optimal curing of the tire.

Also known, from the Patent EP-B1-0 522 374, is a sectored mold that also comprises two lateral rings that are fastened to the sectors and bear radially against the shells in the closed position. Such rings aim to avoid the occurrence of molding burrs on the manufactured tires and are made of steel, like the sectors and the shells, such that only steel parts come into contact when the mold is closed.

This solution also promotes heat transfer by conduction between the sectors and the shells and also a uniform distribution of the temperature in the mold.

SUMMARY

The aspects disclosed herein aim to remedy these drawbacks.

More particularly, the present disclosure aims to provide a sectored mold that makes it possible to be able to stably keep the shells and the sectors at different temperature levels during the curing phase of the tire.

In one embodiment, the mold is intended for a tire of the type comprising a tread and two lateral sidewalls. The mold comprises first and second shells that are intended to mold the lateral sidewalls of the tire, and a plurality of sectors that are distributed in the circumferential direction and are intended to mold the tread of said tire. The sectors are radially movable between an open position and a closed position of the mold. The mold also comprises at least one spacing means interposed between each sector and each shell in order to keep said sector and the shells spaced apart in the radial direction in the closed position of the mold, such that the shells and the sectors are in contact in the radial direction only by way of the spacing means. Said spacing means are able to limit the heat transfer between the shells and the sectors in the closed position of the mold.

The mounting of at least one such spacing means, which is interposed between each sector and each shell, makes it possible to limit heat transfer by conduction between these parts of the mold during the curing of the tire. It is thus possible to keep the shells and the sectors at different temperatures so as to maintain a non-uniform temperature distribution inside the mold. This makes it possible to be able to optimize the curing of the tire. The spacing means are separate from the shells and the sectors.

In one embodiment, each spacing means is made at least in part of thermally insulating material having a thermal conductivity lower than that of the materials of the sectors and of the shells.

Advantageously, each spacing means comprises a spacing part made in the form of a section of a ring and the spacing means are disposed such that the spacing parts form at least one ring between the sectors and each shell.

In one embodiment, said spacing part internally delimits at least one cavity. Preferably, said cavity is delimited in the radial direction by an inner wall and an outer wall of the spacing part, said walls being mounted in contact with the associated shell and with the associated sector.

The presence of at least one cavity in the spacing part makes it possible to limit the flow cross sections of a heat flux over the spacing means. Thus, the propagation of the heat through the spacing means is limited further. The air present in the cavity or cavities increases the insulating properties of the spacing means.

Alternatively or in combination, the mold can also comprise means for supplying cooling fluid to the cavity and means for the outlet of said fluid so as to obtain a flow of the cooling fluid along said cavity.

A flow of cooling fluid in the cavity of each spacing means can also be provided so as to limit the heat transfer between the sectors and the shells inside the mold during the curing of the tire.

In one embodiment, each spacing means comprises at least one fastening part extending substantially radially from the spacing part inside a hole formed in the associated sector or in the associated shell. The mold can comprise a fastening means that is mounted in said hole and extends inside said fastening part.

Preferably, each spacing means is radially in contact on one side with the associated shell and radially in contact on the other side with the associated sector. Each spacing means can comprise a contact face for contact with the tire in the closed position of the mold.

Advantageously, each spacing means is made of a non-metal material, notably of a composite material. Alternatively, each spacing means can be made of a metal material, notably of titanium.

In one embodiment, each sector comprises a support and a mold fitting fastened to said support. The spacing means can be fastened to the sectors and retain the mold fittings on the supports.

The mold can also comprise at least one clamping ring that cooperates with outer faces of the sectors.

The invention also relates to a method for molding a tire with the aid of a mold as defined above, wherein the two shells are heated to a temperature different from that to which the sectors of the mold are heated.

DETAILED DESCRIPTION

FIG. 1shows an exemplary embodiment of a sectored mold, bearing the overall reference10, provided for the curing or vulcanization of an annular tire that comprises a cylindrical tread extended by first and second opposite lateral sidewalls. The tire is for a motor vehicle which can be for example a passenger car, a utility vehicle or a vehicle of the heavy goods type. InFIG. 1, the mold10is illustrated in a position assumed to be vertical. The mold10has an axis X-X′ of symmetry which is coincident with the axis of revolution of the tire.

The mold10comprises lower and upper plates12,14, a lower and an upper annular shell16,18mounted so as to bear against the plates, axially facing the latter, and a ring of sectors20that are disposed axially between the plates12,14and radially surround the shells16,18. The shells16,18and the sectors20are centred on the axis X-X′. The sectors20are distributed circumferentially around said axis. In the exemplary embodiment illustrated, the sectors20are identical to one another and there are nine thereof. The sectors20are radially movable between a moved-together position with respect to the shells16,18, as illustrated inFIG. 1, corresponding to a closed position of the mold10, and a spaced-apart, open position of said mold. In the closed position, the shells16,18and the plurality of sectors20jointly delimit an impression22of the tire. The closed position of the mold10corresponds to the molding position of the tire.

The mold10also comprises a clamping ring24that is secured to the upper plate14and comprises an inner face24awith a frustoconical shape that bears radially against a complementary outer face20aof each sector. In a manner known per se, each sector20is connected to the clamping ring24by way of a slide (not shown) such that an axial movement of said ring causes the radial movement of the sectors20between the closed position and the open position of the mold, or vice versa.

Each shell16,18comprises an internal annular face16a,18afor molding the lateral sidewalls of the tire. The internal face16aaxially faces the opposite internal face18a. The internal faces16a,18aare mutually symmetrical with respect to a radial median plane of the mold10. A radial external face16b,18bof each shell is mounted so as to bear axially against a radial internal face of the associated plate12,14. The external face16b,18bof each shell is axially on the opposite side from the internal face16a,18a. Each plate12,14forms a support plate for the associated shell16or18. Each plate12,14is situated axially on the opposite side from the impression22delimited by the shells16,18and the sectors20. Each sector20also comprises an inner face20b, radially on the opposite side from the frustoconical outer face20a, in order to mold the tread of the tire. In the description, the terms “internal” and “external” are used to define an orientation in the radial direction, while the terms “inner” and “outer” are used to define an orientation in the axial direction.

The mold10also comprises a lower and an upper annular bead ring (not shown) that are mounted so as to bear against the shells16,18in order to mold the lateral beads of the tire. The bead rings can be attached parts that are fastened to the shells16,18or be produced in one piece with said shells.

In the exemplary embodiment illustrated, each sector20comprises a support26that delimits the outer face20ain contact with the clamping ring24, and a mold fitting28that is fastened to the support and delimits the inner face20bbearing the impression of the tread of the tire. The mold fitting28is situated radially on the inner side of the support26. The support26can be made of a metal material, notably of steel, and the mold fitting28of aluminium. The shells16,18can be made of a metal material, notably of steel.

The mold10also comprises a plurality of spacing means30interposed between the sectors20and the shells16,18in order to keep them spaced apart in the radial direction in the closed position of said mold. Each sector20supports two spacing means30. Each spacing means30is fastened to one lateral end of the associated sector20and bears radially against the associated shell16,18in the closed position of the mold10. The spacing means30are disposed relative to one another so as to form an upper and a lower ring that are interposed radially between the sectors20and the shells16,18. The spacing means30are identical to one another.

In order to limit heat transfer by conduction between the sectors20and the shells16,18in the closed position of the mold, each spacing means30is made of a thermally insulating material which has a thermal conductivity lower than the thermal conductivity of each of the materials of the sectors20and lower than the thermal conductivity of the material of the shells16,18. Advantageously, the spacing means30are made of a metal material such as titanium, or of a composite material. The spacing means30fulfil a double function, namely that of maintaining a spacing in the radial direction between the sectors20and the shells16,18and that of limiting heat transfer by conduction between these elements in the closed position of the mold10.

Each spacing means30comprises a spacing part32interposed radially between the associated sector20and the shell16or18, and fastening parts34extending radially towards the outside, each inside a hole36made in the thickness of said sector. Each spacing part32has a curved or bent shape and is made in the form of a section of a ring that extends circumferentially (FIGS. 3 and 4). In the closed position of the mold10, each spacing part32is radially in contact on one side with the associated sector20and radially in contact on the other side with the shell16or18.

As illustrated more clearly inFIG. 2, each spacing part32comprises an axial inner wall32athat comes radially into contact with an axial outer end face16c, or18c, of the associated shell in the closed position of the mold. The end face16c, or18c, of the shell radially delimits, on the outer side, the internal and external faces16aand16b, or18aand18b.

Each spacing part32also comprises an outer wall32bwhich is radially on the opposite side from the inner wall32aand mounted so as to bear radially against an inner end face of the associated sector20. The inner end face radially faces the outer end face16c, or18c, of each shell, remaining at a distance from the latter. The outer wall32bis mounted so as to bear radially against an axial inner end face26aof the support26and against a frustoconical inner end face28aof the mold fitting28. The end faces26a,28aform the inner end face of the sector.

Each spacing part32also comprises an internal wall32cconnecting the inner wall32aand outer wall32b, and delimiting a contact face32dprovided to bear against the tire in the closed position of the mold10. The contact face32dfocally extends the inner face20bof the associated sector and the associated internal face16a, or18a, of the shells.

Each spacing part32internally delimits an empty cavity38with a curved shape that extends along the entire length of said part. The cavity38is delimited in the radial direction by the inner wall32aand outer wall32b. The cavity38is formed in the radial thickness of the spacing part32. The spacing part32has a curved hollow overall shape.

As illustrated more clearly inFIGS. 3 and 4, each spacing part32is delimited in the circumferential direction by two opposite end walls (not referenced). The end walls delimit the cavity38in the circumferential direction. In the closed position of the mold10, each end wall of a spacing part32is mounted so as to bear against one of the end walls of the immediately adjacent spacing part32. In this position, the spacing means30are positioned end-to-end in the circumferential direction and the spacing parts32delimit the lower and upper rings interposed between the sectors20and the shells16,18. In the closed position of the mold10, there is a slight circumferential clearance between two adjacent supports26and the mold fittings28bear against one another in the circumferential direction.

Each fastening part34extends substantially radially towards the outside from the associated spacing part32. Each fastening part34has a tubular shape with a circular section and opens into the cavity38in the spacing part32. In the exemplary embodiment illustrated, each spacing means30comprises three fastening parts34. One of the fastening parts34is situated substantially in the middle of the spacing part32and the two other fastening parts34are each situated in the vicinity of one of the end walls of said spacing part. Each fastening part34is accommodated inside one of the through-holes36provided in the associated sector20. Each bole36extends substantially radially from the outer face20aof the associated sector and opens onto the inner end face26aof the support. The holes36of each sector are identical.

The mold10also comprises a plurality of fastening screws40that are each mounted inside one of the holes36of the sectors and inside the associated fastening part34of the spacing means. Each fastening part34internally comprises a thread for immobilizing the spacing means30on the sectors20via the screws40. Three screws40are provided for fastening each spacing means30to the associated sector20. For each sector20, the two spacing means30keep the mold fitting28on and fasten it to the support26of said sector.

In the closed position of the mold10, the sectors20are kept spaced apart from the shells16,18in the radial direction by way of the spacing means30. The shells16,18and the sectors20are in contact in the radial direction only by way of the spacing means30. In this molding position of the tire, no direct radial contact exists between the shells16,18and the mold fitting28and the support26of each sector. For each sector20, each of the two associated spacing means30is interposed between one of the two shells16,18, for the one part, and the mold fitting28and the support26of said sector, for the other part.

The production of the spacing means30from a thermally insulating material which has a thermal conductivity lower than the thermal conductivities of the materials of the shells16and18, of the mold fitting28and of the support26makes it possible to reduce the heat transfer by conduction that exists between the shells16,18and the sectors20of the mold during the curing of the tire.

During curing, the two shells16,18of the mold can be heated to a temperature different from that to which the sectors20are heated. In the closed position of the mold10, the spacing means30make it possible to reduce heat exchanges inside the mold so as to keep the thermal difference provided between the shells16,18and the sectors20substantially constant in this way, the curing of the tire is optimized.

In this embodiment, the spacing means30are made entirely of a material having a thermal conductivity lower than that of the materials of the sectors and of the shells. In one variant embodiment, it may be conceivable to produce each spacing means from several materials, for example from a first thermally insulating material as defined above for the spacing part, and from a second material that can be metal for the fastening parts.

In the exemplary embodiment described, the spacing parts32of the spacing means30are hollow so as to further limit heat exchanges between the shells16,18and the sectors20of the mold by the presence of air. Alternatively, it may, however, be possible to provide spacing parts with a solid section.

The exemplary embodiment illustrated inFIG. 5, in which identical elements bear the same references, differs in that each spacing means30is fastened to the associated sector20by way of a single fastening screw40. The screw40is situated in the middle of the associated spacing means30. For each spacing means30, the two fastening parts34that are left free are attached to supply and outlet ducts (not shown) of the mold10so as to obtain the flow of a cooling fluid inside and along the cavity38of said spacing means. Each of the supply and outlet ducts is mounted inside the associated fastening part34of the spacing means and of the corresponding hole36of the sector20. The flow of the cooling fluid inside each sector20and inside each associated spacing means30is illustrated schematically by the arrows referenced42to46.

With a flow of the cooling fluid inside each spacing means30, heat transfers that can occur between the shells16,18and the sectors20of the mold during the curing of the tire are limited. In this variant embodiment, each spacing means30can be made of a thermally conductive material, notably of steel, of aluminium, etc. In order to further limit the heat transfers between the shells16,18and the sectors20of the mold in the closed position, each spacing means30can be made of a thermally insulating material as defined in the first exemplary embodiment.

In one variant embodiment, it is possible to provide fluidic communication between the spacing means30so as to provide a single fluid supply duct and a single outlet duct mounted on the mold10. To this end, it may be possible to mount these two ducts on two successive spacing means30that each comprise a single end wall mounted so as to bear against the end wall of the other spacing means, and not to provide end walls for the other spacing means30so as to form a single circular cavity common to all of the spacing means.

In the exemplary embodiments described, the spacing means30are fastened to the sectors20of the mold. This disposition is advantageous in as much as it makes it possible to fasten the mold fittings28to the supports26of the sectors by way of the spacing means30. Alternatively, it may, however, be possible to provide for the spacing means30to be fastened to the shells16,18of the mold.

The present invention has been illustrated on the basis of a mold comprising a single set of sectors for molding the tread of the tire. It is also possible, without departing from the scope of the invention, to provide a mold comprising a set of lower sectors and a set of upper sectors for molding the tread of the tire, wherein the movement of each set of sectors is controlled by a specific clamping ring.