Curing mould for a tyre

Abstract

Disclosed is a tyre curing mould (10) comprising moulding parts (11), wherein the mould comprises heating elements disposed in at least one of said moulding parts (11) and wherein the mould comprises several insulating elements (40, 41a, 41b, 43, 44, 45) and every insulating element is made of at least one thermally insulating material, said insulating elements being disposed on the outer faces of the moulding parts so as to thermally insulate them substantially completely from the other parts of the mould.

Description

COOKING MOLD FOR TIRES

[0001] The invention relates to the manufacture of tires and in particular to baking or vulcanization molds for tires and more particularly to sector-type molds.

[0002] The manufacture of a tire comprises a curing step during which a raw tire blank is molded and vulcanized in order to obtain a tire having desired mechanical characteristics, geometry and appearance. Curing is carried out in a tire curing mold comprising an upper and a lower molding assembly, axially movable relative to each other, as well as a ring of radially movable sectors. More precisely, a tire curing mold mainly comprises two molding shells for the tire sidewalls and two molding rings for the tire beads which are located axially on either side of a ring comprising several circumferential molding sectors for the tire tread. The interior space defined by these parts in the closed position of the mold forms a molding cavity for the tire blank.Such a curing mold is arranged within a curing press comprising, among other things, mechanisms for opening and closing the curing mold on a tire blank and for opening it in order to extract the vulcanized tire and introduce a new blank.

[0003] The curing of a tire blank is done, in a known manner, with a heat input inside and outside the blank. Thus, a flexible curing membrane is deployed inside the blank using pressurized steam to press the tire blank against the walls of the molding cavity. The outside of the mold is often placed in a steam environment which ensures the heat input to the outside of the tire blank. Working satisfactorily, it has however been noted that the heat transfer efficiency with this type of conventional curing is very low, it is approximately 3% to 7%, because it is necessary to heat the entire mold, in particular the molding parts and the resistant parts in order to transmit the heat to the tire blank. We generally understand by resistant parts the parts which do not do not participate in the molding of the tire, but which support the molding parts, when they are fixed, or even cause them to move, in the case where the molding parts are required to move between the open and closed positions of the mold.

[0004] Document JP 2004-34652 proposes a solution to this problem. This document describes a vulcanization mold comprising an upper ring, a lower ring and a plurality of radially movable sectors. The radially outer surface of the sectors is inclined to cooperate with the inclined radially inner surface of an axially movable clamping ring. The radial displacement of the sectors is thus ensured during the axial displacement of the clamping ring. More particularly according to this document, the supply of heat from the outside of the blank is achieved by providing each sector with heating elements arranged so as to be close to the tire blank and by isolating the heating elements radially on the outside within each sector.While this certainly allows for a reduction in heat loss to the outside of the sectors, it is noted that, due to the fact that many metal parts are in contact during cooking at the level of the molding cavity, including at the level of the sectors, the heat still escapes to the outside of it, towards the resistant parts of the mold.

[0005] However, the need to improve the thermal efficiency of a tire vulcanization mold remains present.

[0006] An objective of the invention is to remedy the aforementioned drawbacks and to propose a vulcanization mold for tires capable of achieving efficient curing of a tire blank, while reducing the risk of overcuring in areas comprising thin walls of the tire.

[0007] This objective is achieved by the invention which provides a tire curing mold comprising molding parts formed by - an upper molding shell of an upper tire sidewall, - a lower molding shell of a lower tire sidewall, - an upper ring for molding an upper tire bead; - a lower ring for molding a lower tire bead; - a crown of radially movable circumferential sectors for molding a tire tread, where each sector comprises a molding lining of a tire tread portion, characterized in that the mold comprises heating elements arranged in at least one of said molding portions and in that the mold comprises several insulating elements where each insulating element is made of at least one thermally insulating material, said insulating elements being arranged on the external faces of said molding portions so as to thermally insulate them substantially completely from the other parts of the mold.

[0008] A curing mold comprises molding parts that cooperate with resisting parts capable of supporting or driving the molding parts in movement. According to the invention, at least one of the molding parts comprises a heating element and all the molding parts are substantially completely thermally insulated from the resisting parts. More particularly, elements made of a thermally insulating material are arranged on the external surface of all the molding parts. By external surface of a molding part is meant the surface that does not participate in the molding. Thus, the molding parts that come directly into contact with the tire can be heated to the desired curing temperature, without heat loss to the tire blank due to thermal inertia, and without heat loss to the resisting parts.Indeed, the parts of a tire curing mold are made of metallic materials for reasons of mechanical resistance to pressure and temperature. Such parts are brought into contact during curing and easily conduct heat by thermal contact. However, with the solution of the invention, by interposing thermal insulating elements on the external faces of all the molding parts, it is possible to thermally decouple the molding parts by avoiding metal / metal contact (for example steel / steel or aluminum / steel contact) between the molding parts and the resistant parts of the mold. According to the invention, the ratio between the external surface not thermally insulated and that thermally insulated of all the molding parts can be less than 1%. The percentage of 1% can be due to the fixing of the insulators with metal screws.

[0009] The energy efficiency of a baking mold of the invention is between 70 and 75%, which is significantly higher than that of molds of the state of the art.

[0010] According to advantageous and non-limiting characteristics, taken alone or in combination when technically possible: the mold may comprise first insulating elements which may be made of a first thermally insulating material so as to ensure the transmission of mechanical forces to the molding parts which they thermally insulate; said first thermally insulating material may be a composite material comprising glass fibers in an epoxy resin matrix; the thermal conductivity of said first thermally insulating material of the first insulating elements may be between 0.2 and 0.4 W / mK; the mold may comprise second insulating elements which may be made of a second thermally insulating material which may have a thermal conductivity of less than 0.03 W / mK;the surface area occupied by the first insulating elements may be at most 30% of the surface area of ​​the molding parts with which they come into contact and the second insulating elements may occupy the remainder of the external surface area of ​​said molding parts; thus, the surface area occupied by the first insulating elements is limited as much as possible and to just what is necessary so that they can take up the forces undergone during operation, the remainder of the external surface area of ​​the molding parts being covered by the second insulating elements having better thermal insulation properties in order to obtain optimized thermal insulation of the molding parts relative to the resistant parts of the mold; the mold may comprise electric heating elements which have the advantage of being able to provide better energy efficiency, compared to molds whose heating elements include a circulation of water vapor;each molding part may comprise at least one electric heating element, which makes it possible to achieve differentiated heating of the molding parts with respect to each other; by differentiated heating it is understood that the molding parts are heated to different temperatures relative to each other; each molding part may comprise at least one temperature sensor, which makes it possible to adapt the temperature of the heating element to the area of ​​the tire blank; the temperature sensors may be connected to a control unit capable of controlling said electric heating elements.

[0011] According to an advantageous aspect, the mold of the invention may comprise means for actuating the sectors in a radial movement, said means comprising a hooping ring whose internal surface is inclined to cooperate with the inclined external surface of the sectors and where, for each sector, the hooping ring can transmit the clamping force to prismatic shims or to insulating strips which can bear directly on the lining of the sector.

[0012] According to another advantageous aspect, the mold may comprise central portions for actuating a cooking membrane and the mold may comprise thermally insulating elements arranged axially outside said central portions.

[0013] The invention also relates to a method for molding a tire blank using a curing mold comprising molding parts according to one of the preceding claims, characterized in that at least one of said molding parts is heated by at least one heating element and in that all the molding parts are thermally insulated substantially completely from the other parts of the mold.

[0014] The heating elements can be electric heating elements with temperature sensors attached.

[0015] Each heating element can be controlled at a pre-set cooking temperature, at least two heating elements can be controlled at different temperatures from each other

[0016] The invention will be better understood from the rest of the description, which is based on the following figures: Figure 1 is an axial sectional view of a cooking mold according to a first embodiment of the invention; Figure 2 is a radial sectional view of the mold of Figure 1; Figure 3 is an enlarged scale view of a portion of the mold shown in Figure 2; Figure 4 is an axial sectional view of a circumferential sector of the mold of Figure 1; Figure 5 is an exploded view of the sector of Figure 4; Figure 6 is an axial sectional view of a baking mold according to a second embodiment of the invention; Figure 7 is a perspective view of a circumferential sector of the mold of Figure 6; Figure 8 is a perspective view of the back of the lining of the sector of Figure 7; Figure 9 is a schematic top view of an upper flat ring which is part of the mold of Figure 1.

[0017] In the various figures, identical or similar elements bear the same reference. Their description is therefore not systematically repeated.

[0018] Figure 1 illustrates a curing mold 10 of a tire blank according to a first embodiment of the invention, a mold intended for curing a tire for a passenger vehicle. The curing mold 10 is intended to be inserted between the upper 2 and lower 4 plates of a curing press 1. A curing press comprises a frame forming a base, assumed to be stationary and fixed to the ground. The press also comprises, in a known manner, means for guiding and actuating (for example hydraulic cylinders) the drive mechanisms in a movement of opening and closing the mold, as well as an installation making it possible to provide the mold with the curing conditions (in terms of pressure and temperature of the heat transfer fluid) necessary for vulcanizing the tire.

[0019] The curing mold 10 of a tire blank comprises an upper molding assembly and a lower molding assembly, each molding assembly comprising an upper shell 16a, respectively a lower shell 16b for molding a sidewall of the tire, and an upper ring 18a, respectively a lower ring 18b for molding a bead of the tire. A ring of circumferential sectors 20 for molding the tire tread completes the upper and lower molding assemblies and forms with them the molding parts 11 of the mold 10. In the closed position of the mold, the internal surfaces of the molding parts 11 together form a molding cavity intended to accommodate a tire blank.

[0020] In the example illustrated in Figures 1 to 5, the mold is of the “container” type, the upper shell 16a is caused to slide axially with the upper plate 2 of the press, to which it is rigidly fixed, the lower shell 16b being rigidly fixed to the lower plate 4 of the press which is itself fixed, and the circumferential sectors 20 are caused to perform movements in a radial direction when opening and closing the mold.

[0021] The baking mold 10 is substantially rotationally symmetrical with a central axis X-X'. The central axis extends vertically. In the remainder of the description, "axial" or "axially" refers to a direction or displacement parallel to the central axis, and "radial" or "radially" refers to a direction or displacement perpendicular to the central axis X-X'. A circumferential direction is a direction tangent to the radial direction and corresponds to the circumferential direction of the tire.

[0022] The circumferential sectors 20 of the sector ring are arranged side by side in the circumferential direction. Each sector comprises a lining 19 for molding the tread patterns of the tire, the lining being held by a sector support. Thus, the lining 19 of each sector extends from the interface with the upper shell 16a to the interface with the lower shell 16b.

[0023] The radially external surfaces 21 of the sector lining supports are conical, they all have the same inclination extending downwards and radially outwards.

[0024] The press further comprises a conical crown 14 whose radially inner surface 14a is inclined radially downwards and has the same inclination as the radially outer surfaces 21 of the sectors 20. The conical crown 14 is connected to a first actuator of the baking press, for example a hydraulic cylinder, which allows it to perform an axial movement upwards and downwards. When the mold is closed, the conical crown 14 descends, it is positioned on the crown of sectors 20, it brings the sectors radially inside the mold and applies a force to the sectors to keep the assembly closed during cooking when the temperature and pressure values ​​inside the molding cavity increase. The conical crown 14 comprises a plurality of rods 12 having a T-shaped cross section (figs. 2 and 3) each rigidly fixed to the conical crown, each rod 12 being intended to slide in a rail 17 of a corresponding sector 20 of the sector crown. Stops (not shown) located between one end of each rod 12 and a notch in the external surface 21 of each sector make it possible to limit the radial recoil travel of the sectors when the conical crown moves upwards to open the mold. In this exemplary embodiment, the conical crown 14, the rods 12 and their connecting elements to the mold sectors and to the upper plate of the press are of the type described in document WO 2014 / 044713.

[0025] The upper platen 2 of the press is connected to a second actuator, for example a hydraulic cylinder, which allows it to perform an axial movement upwards and downwards during the operations of closing and opening the mold, as will be explained later.

[0026] The conical crown 14, the upper 2 and lower 4 plates and the parts surrounding the molding cavity, but not comprising any part coming directly into contact with the tire blank, form the resistant parts of the mold, as opposed to the molding parts which, for their part, come directly into contact with the tire blank.

[0027] In the open position of the mold, the conical crown 14 as well as the molding parts located in the upper part of the mold: the upper shell 16a, the upper molding ring 18a and the sectors 20 are moved axially upwards together with the upper plate 2 of the press so as to clear the molding cavity (by molding cavity we understand the space formed inside all molding parts in the closed position of the mold) in order to be able to extract the cured tire and to introduce a new tire blank 3. Once the tire blank 3 is installed and centered on the molding components of the lower part of the mold, the upper plate 2 descends, under the effect of the first actuator of the press, bringing the molding parts towards the lower plate 4. Then, the conical crown 14 descends in turn, under the effect of the second actuator of the press, to close the cooking cavity by moving the sectors 20 radially inwards and thus the mold for a new cooking. The mold is opened by first raising the conical crown 14 followed by raising the upper plate 2.

[0028] The heat transfer fluid arrives inside the molding cavity from an internal baking device 25 located in the central part of the baking cavity, said device comprising a baking membrane which presses the tire blank onto the internal parts of the mold during baking, as well as means for placing the baking membrane in communication with a heat transfer fluid and for diffusing and increasing the pressure and temperature of the heat transfer fluid inside the baking membrane.

[0029] According to the invention, the mold comprises heating elements arranged in all or part of the molding parts and all the molding parts are insulated from the resistant parts of the mold using insulating elements, each insulating element being made of a thermally insulating material, said insulating elements being arranged on the outer sides of said molding parts so as to thermally insulate radially and axially the molding parts with respect to the resistant parts.

[0030] Advantageously according to the invention, the sectors 20 each comprise at least one electric heating element 31. More precisely, several electric heating elements 31, which are four in number in FIG. 5, are inserted into the lining 19 of each sector 20 and receive electrical energy via a power cord 35. Each molding ring, in particular the upper ring 18a and the lower ring 18b, comprises an annular electric heating element 32. In the example shown, the shells 18a and 18b do not comprise a heating element, but in an alternative embodiment of this first mode, each shell comprises one or more annular heating elements, preferably electric. Furthermore, each heating element 31, 32 is preferably associated with a temperature sensor also arranged in the molding part near the heating element whose temperature the sensor is to measure.The various temperature sensors are connected to an automaton which controls the power supply and therefore the temperature of the respective heating elements.

[0031] The lining 19 comprises on its internal face facing the tire blank hollow or protruding patterns constituting the negative of the reliefs or sculptures of the tire. It is produced in a known manner using metal additive manufacturing or by molding, for example using a plaster-aluminum process.

[0032] The other components of a circumferential sector 20 are better visible in Figure 5. Thus, a circumferential sector 20 also comprises a lining support 22 and two prismatic shims 43 whose role is to transmit the compression force coming from the conical crown 14. The lining 19 is held by its support 22 by sandwiching a sheet 40 of thermal insulation. The sheet 40 comprises two axial cutouts 40a communicating with two axial cutouts 28 opposite each other made in the thickness of the lining support 22. The axial cutouts 40a and 28 are through and form passages for the prismatic shims 43. The lining support 22 is metallic, for example made of steel for greater robustness, and has a jaw-shaped profile, comprising in particular two axial edges 22a and 22b which project radially inwards from the main body which extends, itself, circumferentially according to that of the lining 19.Cords 41a and 41b, each made of a thermal insulating material of the DELTHERM ® type, are provided between each axial edge of the lining 19a, respectively 19b, and the axial edges 22a, respectively 22b, of the lining support 22. The lining 19 is fixed to its support 22 using the screws 29 located at the axial edges 22a, 22b of the latter, so as to sandwich the sheet 40 and the cords 41a, and 41b. Furthermore, to connect the assembly thus obtained to the conical crown 14, the prismatic wedges 43 are fixed to the two circumferential ends of the lining support 19. For this, each prismatic wedge 43 is fixed using flanges 25 on the upper face, flanges 26 on the lower face and flanges 27 on the external face and fixing screws provided for this purpose for fixing each flange. The flanges 25, 26 and 27 are metallic. The flange 27 materializes the external surface 21 of the circumferential sector 20.

[0033] Two fins 24 with a triangular lateral profile complete the entire circumferential sector 22 by fixing them, using fixing screws, one opposite the other to the support 22 and at a pre-established distance which thus determines the rail 17 in which the rod 12 secured to the conical crown 14 is caused to slide.

[0034] As better seen in Figures 2 and 3, the circumferential length of a support 22 of circumferential sector 20 is less than that of a lining 19. The support 22 is thus designed so as to have the dimensions strictly necessary for the mechanical stresses to which it is subjected, while making it possible to optimize the thermal insulation capacity offered by the thermal insulation sheet 40 which covers substantially the entire surface of the lining 19. Furthermore, this solution also makes it possible to produce sectors having standardized dimensions and to use them with linings of several different dimensions, which makes it possible to reduce the manufacturing cost of the mold.

[0035] The insulating sheet 40 is preferably made of a flexible thermally insulating material whose thermal conductivity is approximately 0.03 W / mK. Such a material is, for example, insulating foam of the BASOTECT® V3012 type from BASF, or glass wool.

[0036] The prismatic shims 43 are made of a rigid thermally insulating material which has very good mechanical strength properties and a very low thermal conductivity which is approximately 0.3 W / mK. Such a material is for example a composite material made from a glass fiber reinforced epoxy resin, such as DELTHERM®. Thus the prismatic shims 43 are able to absorb the compressive stresses coming from the conical crown 14 during the closing of the mold, while making it possible to thermally insulate the lining 19 with respect to the crown 14. This same material is preferably used to produce the upper 41a and lower 41b beads which absorb axial stresses.

[0037] These insulating materials perform their functions well at the baking temperature of the tire blank, which is between 120 and 180°C.

[0038] The prismatic shims made of insulating material which resists mechanical stresses occupy 20% of the total surface area of ​​the back of the lining 19, while the insulating sheet 40, made of insulating foam, having thermal insulation properties superior to those of the resin bars occupies the remaining 80%.

[0039] Figure 4 illustrates by an axial sectional view passing through a prismatic wedge 43 of a circumferential sector 20 assembled as previously described. The Figure 1 illustrates a sectional view of the baking mold 1 in the closed position, produced with an axial sectional plane passing through a prismatic wedge 43. It is thus noted in Figure 1 that the lining 19 is insulated in the radial direction by the thermal insulating material of the wedge 43 and in the axial direction by that of the beads 41a and 41b. It is also noted in Figure 1 that the other molding parts which are constituted by the shell 16a and the upper ring 18a, in the upper molding assembly, and by the lower shell 16b and the lower ring 81b, in the lower molding assembly, are also thermally insulated, in the axial direction, with respect to the resistant parts of the mold. More particularly, an upper flat ring 44 is arranged directly in contact with the external faces of the upper shell 16a and the upper ring 18a and it is sandwiched between these two molding parts and the upper plate 2 of the mold.Similarly, a lower flat ring 45 is arranged directly in contact with the external faces of the lower shell 16b and the lower ring 18b and is sandwiched between these two molding parts and the lower plate 4 of the mold. Furthermore, the various parts made of a thermal insulating material having shapes of revolution, the thermal insulation of the molding parts relative to the resistant parts is also done in the radial direction of the mold. Preferably, the external diameter of the upper flat ring 44 and the lower flat ring 45 is extended so that they also thermally insulate the parts of the central part of the internal curing device 25 supporting the curing membrane. This makes it possible to isolate the internal curing cavity for greater efficiency of curing inside the tire blank.

[0040] The upper 44 and lower 45 flat rings are produced from a disc 4a made of a thermally insulating material of the insulating foam type, for example of the BASOTECT® V3012 type from the company BASF, in which disc several rectangular cutouts are made, oriented radially from the center of the disc, and by inserting bars 4b made of a glass fiber reinforced epoxy resin, of the DELTHERM® type, into these cutouts (fig. 9). Figure 9 illustrates, by way of example, an upper flat ring 44 comprising four bars 4b, the number of bars 4b and their dimensions being able to vary with the dimensions of the flat ring. The lower flat ring is produced in a similar manner to the upper flat ring, based on a disc 4a and bars 4b. The upper 44 and lower 45 flat rings being subjected to significant mechanical stresses in the axial direction during the closing of the mold, said bars 4b are preferably made of a material that has good mechanical strength properties, while having low thermal conductivity. It is thus preferred to use, as in the case of the prismatic shims 43, a composite material made from a glass fiber reinforced epoxy resin, such as DEL THERM® whose thermal conductivity is approximately 0.3 W / mK. Thus, the bars made of glass fiber reinforced epoxy resin are able to withstand the pressure stresses exerted in the axial direction, while the rest of the disc ensures very good thermal insulation of the molding parts relative to the resistant parts of the mold. The bars made of insulating material that resists mechanical stresses occupy 20% of the total surface area of ​​the upper 44 and lower 45 flat rings, while the insulating foam, having thermal insulation properties superior to those of the resin bars, occupies the remaining 80%.

[0041] It is clear from what has been described with reference to Figures 1 to 5 that a baking mold 10 thus produced makes it possible to completely isolate the molding parts 19, 16a, 16b, 18a and 18b from the resistant parts surrounding them (conical crown 14, upper plate 2, lower plate 4), so that there is substantially no more metallic contact, and therefore no heat loss, between the molding parts and the resistant parts of the mold. By substantially, it is understood that the ratio between the surface area of ​​the contact part that can cause a heat loss and the surface area of ​​the thermal insulation that surrounds the molding parts is less than 10% and preferably less than 5%. The difference of up to 100% coverage of the molding parts by thermal insulation may be due to the fixings of the parts made of thermal insulating material using metal screws, such as screws 29.

[0042] In operation, when the curing mold 10 is closed on the tire blank, the electric heating elements 31 are regulated, all or each individually, to at least a first set temperature which is the desired curing temperature to ensure the curing of the tread or a part thereof. The annular electric heating elements 32 are also supplied with energy and regulated to a pre-established temperature, desired to achieve the curing of the tire bead. The thermal insulators which surround the molding parts on all their external sides prevent the heat from diffusing towards the parts mold resistance, which means that each area of ​​the tire is baked at the right temperature and efficiently.

[0043] Furthermore, a sleeve 50 made of insulating material, such as an insulating foam mattress of the BASOTECT® V3012 type from the company BASF, makes it possible to isolate the cooking mold 10 from the external environment, the sleeve 50 being arranged around the resistant parts of the cooking mold. This makes it possible to limit heat exchanges outside the mold.

[0044] Figures 5 and 6 illustrate a curing mold 100 according to a second embodiment of the invention, a mold intended for curing a very large tire, such as a tire for a civil engineering vehicle. The curing mold 100 has a symmetry of revolution around a vertical axis Y-Y'.

[0045] The baking mold 100 is intended to be inserted between the upper 2' and lower 4' plates of a baking press 1'. The lower plate supports a lower shell 160b, made of several pieces or elements for large molds, as well as a ring 180b. The elements of the lower shell 160b and the lower ring 180b are rigidly fixed on a lower insulation support plate 4”, also rigidly fixed, by sandwiching an insulation 501, to the lower plate 4'. Similarly, the press comprises an upper plate 2' to which is fixed an upper shell 160a composed of the several parts or elements, as well as an upper ring 180a. The elements of the upper shell 160a and the ring 180a are rigidly fixed on an upper insulation support plate 2” which is fixed, itself, by sandwiching an insulation 502, to the upper plate 2'.The upper plate 2' and the lower plate 4' are mounted to move vertically along the Y-Y' axis. The mold also comprises circumferential sectors 200 which extend peripherally to form a crown in the closed position of the mold. Such a sector 200 is shown in Figure 7. Each sector comprises an internal front face having a molding part or lining 190 extending in a vertical direction and a circumferential direction.

[0046] The mold also includes a clamping ring 150 actuated by a movable ring 145 which is connected to one of the press actuators, a ring which ensures that the sectors 200 are held in position when the molding cavity is pressurized. The clamping crown 150 comprises a conically shaped internal face capable of cooperating with the conically shaped external face 224 of the sectors 200.

[0047] Each sector 200 comprises a flat lower face 220b capable of resting on the flat surface of the upper face of the lower plate 4' and a flat upper face 220a capable of coming into contact with the flat lower face of the upper plate 2'. The components of a sector-forming assembly 200 are held by attachment to a support 220 located in the rear part, on the side opposite the axis Y-Y'. In a similar manner to the first embodiment, the circumferential length of the support 220 is less than that of the lining 190. The support 220 is provided in the lower part of its lateral sides 223, with two plates 221 parallel to each other and spaced apart by the width of the support 220. Each plate comprises a through-orifice 222 in its lower part, an orifice which is intended to receive a tilting pin 146.More particularly with reference to figure 6, it is noted that the tilting pin 146 is able to travel along a ramp 147 inclined outwards (relative to the axis Y-Y') of a cam 148 rigidly fixed to the frame 6 of the press 1'.

[0048] The baking mold 100 of Figure 6 is shown in the closed position, the molding parts 11' formed by the linings 190, the upper shell 160a, the lower shell 160b, the upper ring 180a and the lower ring 180b are brought into contact to close on the tire blank 3 in order to ensure its baking. At the end of the baking, during demolding, the upper plate 2' and the lower plate 4' slide upwards relative to the frame 6. The movable ring 145 causes the clamping ring 150 to slide upwards, moving it away from the sectors 200. During the upward movement of the clamping ring 150, the sectors 200 are caused to perform a radial sliding and outward rotation movement around the axis of the tilting pin 146, which allows the mold to be completely opened in order to remove the baked tire.

[0049] According to the invention, the baking mold 100 comprises electric heating elements arranged in the molding parts. In the case of a very large baking mold, at least one electric heating element is arranged in each of the molding parts 190, 160a, 160b, 180a, 180b, such as the annular-shaped electric heating elements 132 arranged in the molding shells or rings (Figure 6) or the coil-shaped heating elements 131 arranged in a groove 191 of the lining 190 of a sector 200 (figure 8). Furthermore, preferably, each heating element is associated with a temperature sensor also arranged in the molding part near the heating element whose sensor is to measure the temperature. The various temperature sensors are connected to an automaton for controlling the power supply and therefore the temperature of the respective heating elements. In order to make the curing of the tire with a curing mold 100 efficient, all the molding parts 190, 160a, 160b, 180a, 180b are thermally insulated from the resistant parts of the mold.

[0050] Thus, as regards the insulation of the linings 190, strips of thermal insulation are arranged on the back of each lining, fixing them to the lining 190 of each sector 200. More particularly, first strips 140 are used alternating with second strips 143 arranged side by side, one in the extension of the other in the vertical direction of a lining 190 in order to completely cover its rear face. The second strips 143 have good mechanical strength and are capable of resisting the compressive stresses coming from the clamping ring 150. In a variant, the shape of the strips 143 is limited to that of the imprint of the support 220, in other words, the second strips 143 are replaced by shorter second strips, their length being that of the width of a sector support 220.In order to ensure good thermal insulation of the lining 190, the part left free by the strips 143 of the surface of the back of the lining 190 is covered with a sheet of thermal insulation having a better thermal insulation capacity.

[0051] An upper cord 141a and a lower cord 141b, each made of a thermally insulating material, are fixed between the upper edge, respectively lower edge of the lining 190, and the upper face 220a, respectively lower face 220b of each sector 200.

[0052] The first strips 140 are made of a flexible thermally insulating material whose thermal conductivity is approximately 0.03 W / mK. Such a material is, for example, insulating foam of the BASOTECT® V3012 type from the company BASF, or glass wool.

[0053] The second strips 143 are made of a rigid thermally insulating material which has very good mechanical resistance properties and a very low thermal conductivity which is approximately 0.3 W / mK. Such a material is for example a composite material made from an epoxy resin reinforced with glass fibers, such as DEL THERM®. Thus the strips 143 are able to withstand the compressive stresses coming from the clamping ring 150 when the mold is closed, while allowing the lining 190 to be thermally insulated from the ring 150. This same material is preferably used to produce the upper 141a and lower 141b beads which absorb axial stresses.

[0054] It is also noted in Figure 6 that the other molding parts which are constituted by the shell 160a and the upper ring 180a, in the upper molding part, and by the lower shell 160b and the lower ring 180b, in the lower molding part, are also thermally insulated, in the axial direction, with respect to the resistant parts of the mold. More particularly, a first upper flat ring 44' is arranged directly in contact with the external faces of the upper shell 160a and a second upper flat ring 44” is arranged directly in contact with the upper ring 180a, the rings 44' and 44” being sandwiched between these two molding parts and the upper platen 2' of the mold.Similarly, a first lower flat ring 45' is arranged directly in contact with the external faces of the lower shell 160b and a second lower flat ring 45” is arranged directly in contact with the lower ring 180b, the rings 45' and 45” being sandwiched between these two molding parts and the lower insulation support plate 4” of the mold. Furthermore, the various parts made of a thermal insulating material having shapes of revolution, the thermal insulation of the molding parts with respect to the resistant parts is also done in the radial direction of the mold. As visible in Figure 6, flat rings 44' and 45' may have a stepped section to better conform to the parts of the mold between which they are inserted.Each of the upper flat rings 44', 44” and lower flat rings 45', 45” is made from a disc made of a thermally insulating material of the insulating foam type, for example of the BASOTECT® V3012 type from the company BASF, in which disc are made several rectangular cutouts oriented radially from the center of the disc, and by inserting bars of a glass fiber reinforced epoxy resin, of the DEL THERM® type, into these cutouts, in a manner similar to the ring 44 illustrated in Figure 9, adapting the dimensions and sizing the rings and the bars according to the forces supported. These parts. being subjected to significant mechanical stresses in the axial direction during the closing of the mold, are preferably made of a material which has good mechanical resistance properties, while having a low thermal conductivity. It is thus preferred to use, as in the case of the prismatic shims 43, a composite material made from a glass fiber reinforced epoxy resin, such as DELTHERM® whose thermal conductivity is approximately 0.3 W / mK. Thus, the bars made of glass fiber reinforced epoxy resin are able to withstand the pressure stresses exerted in the axial direction, while the rest of the disc ensures very good thermal insulation of the molding parts relative to the resistant parts of the mold.The bars made of insulating material that resists mechanical stress occupy 20% of the total surface area of ​​the upper 44', 44” and lower 45', 45” flat rings, while the insulating foam, having thermal insulation properties superior to those of the resin bars, occupies the remaining 80%.

[0055] Furthermore, a sleeve 500 made of insulating material, such as bagged rock wool, makes it possible to insulate the baking mold 100 from the ambient temperature outside the mold, the sleeve 500 being arranged around the resistant parts of the baking mold. Insulating rings 501 in the upper part and 502 in the lower part of the mold, made of the same material as the sleeve 500, also make it possible to thermally insulate the mold from the upper 2' and lower 4' plates respectively. This makes it possible to limit heat exchanges outside the mold.

[0056] Other variations and embodiments of the invention may be contemplated within the scope of the invention as claimed.

Claims

Claims 1. Baking mold (10, 100) for a tire comprising molding parts (11) formed by - an upper shell (16a, 161a) for molding an upper tire sidewall, - a lower shell (16b, 161b) for molding a lower tire sidewall, - an upper ring (18a, 181a) for molding an upper tire bead; - a lower ring (18b, 181b) for molding a lower tire bead; - a ring of radially movable circumferential sectors (20, 200) for molding a tire tread, where each sector comprises a lining (19, 190) for molding a portion of the tire tread, characterized in that the mold comprises heating elements arranged in at least one of said molding parts (11, 11') and in that the mold comprises several insulating elements (40, 41a, 41b, 43, 44, 45; 44', 44”, 45', 45”, 140, 141a, 141b, 143) where each insulating element is made of at least one thermally insulating material, said insulating elements being arranged on the external faces of said molding parts so as to thermally insulate them substantially completely from the other parts of the mold.

2. Mold according to one of the preceding claims, characterized in that it comprises first insulating elements made of a first thermally insulating material so as to ensure the transmission of mechanical forces to the molding parts which they thermally insulate.

3. Mold according to the preceding claim characterized in that said first thermally insulating material is a composite material comprising glass fibers in an epoxy resin matrix.

4. Mold according to one of claims 2 or 3, characterized in that the thermal conductivity of said first thermally insulating material is between 0.2 and 0.4 W / mK.

5. Mold according to one of the preceding claims, characterized in that it comprises second insulating elements made of a second thermally insulating material having a thermal conductivity of less than 0.03W / mK.

6. Mold according to the preceding claim, characterized in that the surface occupied by said first insulating elements is at most 30% of the surface of the molding parts with which they come into contact and that said second insulating elements occupy the remainder of the external surface of said molding parts.

7. Mold according to one of the preceding claims, characterized in that said heating elements are electric heating elements (31, 32, 131, 132).

8. Mold according to one of the preceding claims, characterized in that each molding part comprises at least one electric heating element (31, 32, 131, 132).

9. Mold according to one of claims 7 or 8, characterized in that each molding part comprises at least one temperature sensor.

10. Mold according to the preceding claim, the temperature sensors are connected to a control unit capable of controlling said electric heating elements.

11. Mold according to one of the preceding claims, characterized in that it comprises means for actuating the sectors (20, 200) in a radial movement, said means comprising a hooping ring (14, 150) whose internal surface is inclined to cooperate with the inclined external surface of the sectors (20, 200) and in that, for each sector, the hooping ring transmits the clamping force to prismatic shims (43) or to insulating strips (143) bearing directly on the lining (19, 190) of the sector (20, 200).

12. Mold according to one of the preceding claims, characterized in that the mold comprises central parts for actuating a cooking membrane and in that the mold comprises thermally insulating elements arranged axially outside said central parts.

13. Method for molding a tire blank using a baking mold comprising molding parts according to one of the preceding claims, characterized in that at least one of said molding parts is heated by at least a heating element and in that all molding parts are thermally insulated substantially completely from other parts of the mold.

14. Molding method according to the preceding claim, characterized in that said heating elements are electric heating elements to which temperature sensors are associated.

15. Molding method according to the preceding claim, characterized in that each heating element is controlled at a pre-established cooking temperature, at least two heating elements being controlled at different temperatures relative to each other.

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