Mold with sectors for a tire including insulating supporting plates, and associated molding method

A mold for a tire comprises first and second shells that are intended to mold lateral sidewalk of the tire, a plurality of sectors that are distributed in the circumferential direction and are intended to mold a tread of said tire, a first and a second support plate that each comprise a bearing face with which the associated shell is mounted axially in contact, and a plurality of first and second heating means for heating at least the first and the second shell, respectively.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a 371 national phase entry of PCT/EP2014/077015 filed 9 Dec. 2014 which claims the benefit of French Patent Application No 1162344 filed 10 Dec. 2013, the contents of which are incorporated herein by reference for all purposes.

BACKGROUND

The present disclosure relates to the field of molds for curing or vulcanizing vehicle tire, and more particularly molds of the sectored type.

This type of mold mainly comprises 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. For example, it is known practice to heat the mold by means of a heat-transfer fluid such as pressurized water vapour, as is described in the Patent Application EP-A1-2 072 235.

It is also known practice to heat the mold electrically or else by magnetic induction, as is illustrated in the document JP-A-2012-25126. In that document, first heating means are mounted on the shells radially on the inner side of the mold and second heating means are mounted both on the shells and on the sectors.

The heat is thus produced directly in the mold, thereby making it possible to obtain satisfactory energy efficiency. Moreover, such mounting of the magnetic induction heating means promotes the obtaining of a uniform temperature in the mold.

However, in order to optimize the curing of the tire, it is necessary to heat the two shells of the mold to and keep them at a temperature different from that to which the sectors are heated. Moreover, it may also be necessary, for each of the shells, for separate regions to be heated to and kept at different temperatures.

SUMMARY

The present disclosure aims to meet these requirements.

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

The present disclosure aims to provide a sectored mold that makes it possible to be able to heat separate regions of each shell to and keep them at different temperatures.

In one embodiment, the mold is intended for a tire of the type comprising a tread and two lateral sidewalk. The mold comprises first and second shells that are intended to mold the lateral sidewalk of the tire, a plurality of sectors that are distributed in the circumferential direction and are intended to mold the tread of said tire, and a first and a second support plate that each comprise a bearing face with which the associated shell is mounted axially in contact.

The mold also comprises a plurality of first heating means for heating at least the first shell and a plurality of second heating means for heating at least the second shell. Each support plate comprises at least one body that is made of a thermally insulating material and delimits the bearing face of said plate. At least one recess is formed in said bearing face, the first or second associated heating means being accommodated in said recess.

Providing the body of each support plate in a thermally insulating material combined with the mounting of the associated heating means inside at least one recess provided in the bearing face of said body makes it possible to obtain a mold with satisfactory energy efficiency. Moreover, it is possible to keep the shells and the sectors at different temperatures. The production of each plate from a thermally insulating material makes it possible to limit heat exchanges within the plates and to be able to maintain a non-uniform temperature distribution inside the mold. This makes it possible to be able to optimize the curing of the tire.

In a preferred embodiment, a plurality of spaced-apart recesses are formed in the bearing face of each support plate, one of the first or second heating means being accommodated inside each of said recesses. Advantageously, each heating means is able to generate heat independently of the activation of the other heating means. Preferably, the recess(es) in each support plate are oriented axially towards the inside of said mold. The recess(es) in each support plate can also be made in the form of annular and concentric grooves.

In one embodiment, the first and second heating means each comprise at least one first group of heating means disposed axially facing the associated shell. The first and second heating means can each comprise at least one second group of heating means disposed axially facing the sectors.

Preferably, the sectors are mounted axially in contact with the bearing faces of the support plates in the closed position of said mold.

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

Advantageously, the body of each support plate is made of a thermally insulating material that has a thermal conductivity lower than that of the materials of the sectors and of the shells. The body of each support plate can be made of a non-metal material, notably of a composite material.

In one embodiment, the body of each support plate has an axial thickness of between 35 mm and 60 mm.

Preferably, the first and second heating means are electric.

The disclosure also relates to a method for molding a tire with the aid of a mold as defined above, wherein the operation of the first and second heating means is controlled such that they heat the two shells to a temperature different from that to which the sectors of the mold are heated.

DETAILED DESCRIPTION

The present disclosure will be understood better from reading the detailed description of an embodiment considered by way of entirely non-limiting example and illustrated by the appended FIGURE, which is a half view in cross section of a sectored mold for a tire according to one exemplary embodiment of the disclosure in a closed position of said mold.

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. In the FIGURE 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 lower sectors20and upper sectors22that are disposed axially between the plates12,14and radially surround the shells16,18. The shells16,18and the sectors20,22are centred on the axis X-X′. The sectors20,22are distributed circumferentially around said axis. The lower sectors20bear axially against the upper sectors22. The sectors20are identical to one another and symmetrical with respect to the sectors22, with respect to a radial median plane of the mold10.

The sectors20,22are radially movable jointly between a moved-together position with respect to the shells16,18, as illustrated in the FIGURE, 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 sectors20,22jointly delimit an impression24of the tire. The closed position of the mold10corresponds to the molding position of the tire.

The mold10also comprises a lower clamping ring26that is secured to the lower plate12and comprises an inner face26awith a frustoconical shape that bears radially against a complementary outer face20aof each lower sector20. The mold10also comprises an upper clamping ring28that is secured to the upper plate14and comprises an inner face28awith a frustoconical shape that bears radially against a complementary outer face22aof each upper sector20. The clamping rings26,28axially face one another and leave a slight axial clearance between one another. In a manner known per se, each sector20,22is connected to the associated clamping ring26,28by way of a slide (not shown) such that an axial movement of said ring causes the radial movement of the associated sectors20,22between the closed position and the open position of the mold, or vice versa.

Each shell16,18comprises an internal annular face16a,18afor molding the lateral sidewalk of the tire. The internal face16aaxially faces the opposite internal face18a. The internal faces16a,18aare mutually symmetrical with respect to the radial median plane of the mold10. A radial external face16b,18bof each shell is mounted so as to bear axially against a radial internal face12a,14aof 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 shell16,18. Each shell16,18is fastened to the associated support plate12,14. Each plate12,14is situated axially on the opposite side from the impression24delimited by the shells16,18and the sectors20,22.

Each sector20,22also comprises an inner face20b,22b, radially on the opposite side from the frustoconical outer face20a,22a, in order to mold the tread of the tire. In the description, the terms “internal” and “external” are used to define an orientation of the faces in the radial direction, while the terms “inner” and “outer” are used to define an orientation of the faces in the axial direction.

The mold10also comprises a lower and an upper annular bead ring30,32that are mounted so as to bear against the shells16,18in order to mold the lateral beads of the tire. In the exemplary embodiment illustrated, the bead rings are attached parts that are fastened to the shells16,18. Alternatively, the bead rings30,32can be produced in one piece with said shells.

In the exemplary embodiment illustrated, each sector20,22comprises a support34,36that delimits the outer face20a,22ain contact with the clamping ring26,28, and a mold fitting38,40that is fastened to the support and delimits the inner face20b,22bbearing the impression of the tread of the tire. The mold fitting38,40is situated radially on the inner side of the associated support34,36. The support34,36can be made of a metal material, notably of steel, and the mold fitting38,40of aluminium. The shells16,18and the bead rings30,32can be made of a metal material, notably of steel.

In the closed position of the mold10, the lower sectors20and upper sectors22, respectively, are radially in contact with the shell16and the shell18, respectively. The shells16,18and the sectors20,22are in contact in the radial direction by way of the mold fittings38,40. The inner face20b,22bof each sector20,22locally extends the internal face16a,18aof the associated shell.

The mold10also comprises a plurality of lower and upper heating means42,44that are mounted respectively on the lower and upper support plates12,14. Each heating means42,44is electric and advantageously produced in the form of an electrical heating resistor. Each electrical heating means42,44is able to generate heat independently of the operation of the other heating means. The heating means42,44are identical to one another.

In order to allow the mounting of the heating means42and44, each plate12,14comprises a plurality of grooves12b,14bthat are formed on the internal face12a,14awhich forms a bearing face with which the associated shell16,18is mounted axially in direct contact. In the closed position of the mold10, the external faces of the sectors20,22are in axial contact with the internal face12a,14aof the associated plate. In this closed position, an axial clearance exists between each clamping ring26,28and the internal face12a,14aof the axially facing plate.

The grooves12b,14bin each plate extend axially in the direction of a radial external face12c,14cof said plate which is axially on the opposite side from the internal face12a,14aand is intended to bear axially against the associated vulcanizing press (not shown). The grooves12b,14bextend axially towards the outside through the thickness of the plate12,14starting from the internal face12a,14a. The bottom of each groove12b,14bis axially offset towards the outside with respect to the internal face12a,14aof the plate. Each groove12b,14bis open and oriented axially towards the inside of the mold, i.e. axially on the side of the shells16,18, the sectors20,22and the clamping rings26,28. Each groove12b,14bthat forms a recess opens out onto the internal face12a,14a. In the exemplary embodiment illustrated, the grooves12b,14bare annular and concentric, of axis X-X′.

The grooves12b,14bin a plate are identical to one another and disposed on the internal face12a,14aof said plate with a regular radial spacing. The grooves12bin the lower plate are symmetrical with respect to the grooves14bin the upper plate, with regard to the radial median plane of the mold10. In the exemplary embodiment illustrated, the grooves12b,14bhave a cross section with a U-shaped profile. Alternatively, the grooves could have some other profile, for example a stepped profile, or a square or rectangular profile.

In the exemplary embodiment illustrated, the grooves12b,14bform three groups on each plate. For each support plate12,14, the grooves of the first group radially surround the shell16,18, the grooves of the second group radially surround the sectors20,22, and the grooves of the third group radially surround the clamping ring26,28. The groups of grooves12b,14bin each plate are disposed radially at the periphery of the shell16,18, of the sectors20,22and the clamping ring26,28, respectively. The first, second and third groups of grooves12b,14bin each plate axially face the external faces of the shell16,18, of the sectors20,22and of the ring26,28, respectively.

Each lower heating means42is accommodated inside one of the grooves12bin the lower plate. The heating means42are offset axially towards the outside with respect to the shell16, to the sectors20and to the clamping ring26. The heating means42are situated axially between the external faces of the shell16, of the sectors20and of the ring26, and the bottom of the grooves12b.

In a similar manner, each upper heating means44is housed inside one of the grooves14bin the upper plate and is offset axially towards the outside with respect to the shell18, to the sectors22and to the clamping ring28. The heating means44are situated axially between the external faces of the shell18, of the sectors22and of the ring28, and the bottom of the grooves14b.

For each support plate12,14, the associated heating means42,44are distributed among three groups. The heating means42,44of the first group are mounted inside the first group of grooves12b,14band axially face the shell16,18. The heating means42,44of the second group and of the third group, respectively, are mounted inside the second group and third group, respectively, of grooves12b,14band axially face the sectors20,22and the clamping ring26,28, respectively. The heating means42,44are oriented axially towards the inside in the direction of the shell16,18, or of the sectors20,22or of the clamping ring26,28. No means is interposed axially between these elements of the mold10and the heating means42,44.

As indicated above, in the closed position of the mold10, the internal face12a,14aof each plate comes axially into contact with the shell16,18and with the sectors20,22. In the exemplary embodiment illustrated, the heating means42,44are axially flush with the internal face12a,14aof the associated plate. Thus, the heating means42,44carried by the plates12,14are also axially in contact with the shells16,18and the sectors20,22.

Such contacts between the heating means42,44and the shells16,18and sectors20,22promote heat transfer by conduction inside the mold10. Alternatively, the heating means42,44can be slightly spaced apart axially with respect to the shells and/or sectors. In this case, the heat transfer takes place mainly by radiation.

As indicated above, the heating means42,44of the third group of each support plate12,14axially face the clamping ring26,28. These heating means42,44are not used for heating the clamping rings26,28. Specific heating means (not shown) of the mold10are disposed to this end axially between the plates12,14and radially around the outer faces of said rings. Alternatively, each clamping ring26,28can have a circular cavity in which a heat transfer fluid flows. The third group of each of the heating means42,44is provided to obtain adaptability of the plates12,14of the mold10to tire models with greater diameters and so as to be able to heat the shells and the sectors associated with such tires. The same plates12,14can thus be used for heating shells and sectors having different dimensions. This is particularly useful when the plates12,14remain mounted on the vulcanizing press. In the exemplary embodiment illustrated, only the first and second groups of heating means42,44associated with the shells16,18and with the sectors20,22are active.

The plates12,14fulfil a double supporting function, namely that of supporting the shells16,18and of supporting the heating means42,44. Each plate12,14is made of a thermally insulating material that has a thermal conductivity lower than the thermal conductivity of the material of the shells16and18, lower than the thermal conductivity of each of the materials of the sectors20and22, and lower than the thermal conductivity of the material of the rings26,28. Advantageously, each plate12,14is made of a non-metal material, notably a composite material which can for example be based on cement and inorganic fibres. Alternatively, other types of thermally insulating materials can be provided. Each plate12,14can have an axial thickness of between 35 mm and 60 mm.

The production of each plate12,14from a thermally insulating material and the mounting of the heating means42,44inside the grooves12b,14bmake it possible to obtain good energy efficiency of the mold10. Specifically, the production of each plate12,14from a thermally insulating material promotes diffusion of the heat generated in the direction of the shells16,18and sectors20,22. Moreover, the heat is produced in the immediate vicinity of the external faces of these elements of the mold10. Furthermore, the disposition of the heating means42,44on the support plates12,14of the shells promotes axial compactness of the mold10.

The mold10also comprises a control unit (not shown) that is able to control the operation of the heating means42,44. The control unit makes it possible to control each heating means42,44independently of the operation of the other heating means such that one region of the mold can be heated to a temperature different from that to which another separate and adjacent region is heated.

For example, during curing, the two shells16,18of the mold can be heated by the heating means42,44of the first groups to a temperature different from that to which the sectors20,22are heated by the heating means42,44of the second groups. Each thermally insulating plate12,14makes it possible to limit heat exchanges inside said plate such that it is possible to keep the thermal difference provided between the shells16,18and the sectors20,22substantially constant. In this way, the curing of the tire is optimized. It is also possible to control, for each of the shells16and18, differential heating between a region of said shell and another separate region. Such thermal differentiation can also be controlled for the sectors20,22.

In the exemplary embodiment illustrated, each support plate12,14is made entirely of a thermally insulating material. Each plate12,14consists of a body made of thermally insulating material. In a variant embodiment, it may be conceivable to produce each support plate from several parts, said support plate being provided for example with a body that is made of thermally insulating material and comprises the grooves formed on the internal contact face, inside which groups the heating means are accommodated, and with a separate part that may for example be metal, axially covers the body on the opposite side from the grooves and is provided to come axially into contact with the vulcanizing press.

In the exemplary embodiment illustrated, each support plate comprises a plurality of grooves that form recesses and are each associated with a heating means. Alternatively, it may be possible to mount two heating means inside one single groove. In another alternative, it may also be possible to provide a single recess formed on the internal bearing face of each plate, to mount the heating means42or44inside said recess, and to provide thermally insulating partitions between two adjacent heating means. Such a solution is more complex to implement, however.

In the exemplary embodiment described, the heating means are produced in the form of electrical heating resistors. Alternatively, it is possible to provide other types of heating means, for example metal tubes through which a heat transfer fluid passes, notably water or pressurized steam at a temperature greater than 150° C., coming from a heat transfer fluid circuit that comprises means for controlling the circulation of fluid inside each tube independently.

The present disclosure has been illustrated on the basis of a mold comprising a set of lower sectors and a set of upper sectors for molding the tread of the tire. It is also possible, without departing from the scope of the disclosure, to provide a mold comprising a single set of sectors for molding this part of the tire. In this case, a single clamping ring is provided for the mold.