Vulcanizing device with radially mobile segments for a tire

Vulcanizing device with radially mobile segments comprising:

This application is a 371 national phase entry of PCT/EP2013/069388, filed 18 Sep. 2013, which claims benefit of French Patent Application No. 1258943, filed 24 Sep. 2012, which is incorporated herein by reference for all purposes.

BACKGROUND

The present disclosure relates to a tire vulcanizing device, more specifically of the type in which the part intended to form the tread of the tire is divided into several segments that can be moved radially in relation to the axis of the mold. In this type of vulcanizing device, the space for molding the exterior surface of the tire is defined by two shells, each one molding one sidewall, and by a ring of segments which mold the tread, these components together forming a curing mold.

2. Description of Related Art

Vulcanizing devices vulcanize the tire by applying pressure and heat energy to a green form of tire. Vulcanizing devices of the segmented type are made as several components which are assembled and driven with suitable dynamics in relation to the curing press.

The methods used for radially closing the segments onto the green form of the tire often involve closing the segments by sliding along the internal surface of a conical closure ring. Of the vulcanizing devices that employ such a conical closure ring those comprising molds referred to as container molds, in which the bottom shell is fixed and the molding cavity is closed by first of all bringing the top shell that molds the sidewall into contact with the green tire, this movement being initiated by the top plate of the container, then bringing the segments into contact with the green tire, are preferred for reasons of ease of access to the molding space when loading and unloading the tire. At the time of opening the mold, the segments accompany the top shell as the latter is lifted.

A container-type curing mold of this kind is described in U.S. Pat. No. 3,779,677. The mold comprises two lateral shells used for molding a sidewall of the tire and a peripheral ring comprising elements for molding the tread, this ring being divided into several segments having lateral faces perpendicular to the axis of the mold and radial transverse faces. The mold is closed by bringing the lateral shells axially closer together and then by moving the segments radially towards the axis of the mold. The radial movement of the segments is performed by a conical closure ring set in motion by the top plate of the press. The closure ring on its radially internal face comprises several T-shaped components, each being made to slide in a channel having an inclined guide surface of corresponding shape made on the radially external surface of a mold segment. Pivoting coupling elements connect the mobile plate that supports the top shell to the segments allowing these to move axially with the plate and to slide radially in radial slots of the plate.

Another example of a segmented vulcanizing device operating on the same principle as that of the previous document is described in document EP-0 170 109, the conical closure plate comprising, on its radially internal surface, guide grooves in which correspondingly shaped coupling pieces borne by the segments of the mold slide. Prismatic coupling elements connect the top faces of the segments to the mobile plate allowing the segments to move axially with the plate and to slide radially in correspondingly shaped prismatic guides belonging to the plate.

The major disadvantage with these vulcanizing devices is that the segments actuating assembly is dedicated to a specific mold, the parts of the device being machined to suit a fixed number of segments each having a predetermined angle and an amplitude of edge cutout which is dictated by the pattern and the circumference of the tire that is to be vulcanized. More particularly, the closure rings of the prior art are equipped with slide ways fixed to the radially internal wall of the ring to collaborate with a given number of mold segments and a pre-established angular positioning thereof. What is more, the mobile upper plate is machined to form the guide parts for returning the segments, these parts being dictated by the number and position of the mold segments. Thus, the closure ring and top plate of the prior art are permanently set up and suited to just one vulcanizing mold. This makes manufacture of the ring and of the plate of the vulcanizing device expensive while at the same time restricting their use to a restricted number of tire types.

Also known is document WO 2010/019134 in the name of the applicant company which proposes a vulcanizing device comprising elements for the attachment of the several adjacent half-segments, the attachment elements being produced in such a way as to be fitted to the periphery of each closure half-ring. However, this solution is specific to a vulcanizing device the closing and opening system of which involves the use of thrusting springs that push each half-segment. That document cannot provide a solution for optimizing the structure of molds of the container type in which each segment needs to be connected to the mobile plate and guided in its radial movement with respect thereto and at the same time able to collaborate with a closure ring.

SUMMARY

The objective of embodiments of the invention is to at least partially overcome these disadvantages and to propose a vulcanizing device with radially mobile segments for a tire that can be used with molds of the container type having a variable number of segments.

This objective is achieved by an embodiment of the invention which proposes a vulcanizing device with radially mobile segments for molding and vulcanizing a tire comprising: a bottom plate supporting a bottom shell for molding a tire sidewall, an axially mobile top plate supporting a top shell for molding a tire sidewall, an axially mobile closure ring comprising an inclined interior face, a plurality of circumferentially arranged adjacent segments of which the interior radial faces comprise linings for molding the tread of the tire and of which the inclined exterior radial faces are able to collaborate with: first means of coupling with the closure ring which are produced in such a way that the axial movements of the closure ring involve a radial movement of the segments, and second means of coupling the said segments to the top plate which are able to connect the segments to the top plate and to allow their radial movement, the said second means of coupling being adjustable on the circumference of the top plate.

A closure ring means a ring that closes and closely hoops the mold segments, the ring comprising an inclined interior face collaborating with the inclined corresponding part of each segment. A mold means all of the parts intended to come into direct contact with the tire and which form a molding cavity for molding the latter. When the vulcanizing device is mounted in the press, the bottom plate of the device is secured to the fixed bottom platen of the press and the top plate is secured to the top platen of the press and able to move along the axis of the mold. In the vulcanizing device of the invention, the ring is secured to a mechanism which makes it move along the axis of the device and this ring can be raised and lowered independently of the top shell. The radially interior face of the closure ring is generally a frustoconical face. The radially exterior face of the segments which collaborates with the closure ring is also frustoconical and corresponds to the interior face of the ring, the inclination with respect to the axis of the mold providing the dynamic movement of the segments. The device of the invention comprises first means of coupling between the segments and the closure ring, these means of coupling allowing radial movement of the segments towards the outside and towards the inside of the device during the axial movement of the closure ring. Such means of coupling may be guide rods sliding in grooves of, for example, dovetail cross section.

According to an embodiment of the invention, the device comprises second means of coupling between the segments and the top plate, which are able to connect the segments to the top plate and allow them to move radially, the said second means of coupling being adjustable on the circumference of the top plate. Thus, the mobile top plate of the device comprises a radially exterior edge by means of which collaborating with means of attachment of the segments directly or through the intermediary of connecting pieces, this being so for a variable number of segments and different angular positions thereof. A radially outer edge means a circular ring situated on the periphery of the plate at a height lower than that of the top surface of the mobile plate of the device. This ring is produced by peripheral circular machining of the plate and may be a flat surface, a rib or a groove extending from the periphery of the top face of the mobile plate.

That allows the second means of coupling to be fitted to the periphery of the mobile plate, their position being determined by the circumferential position of each segment. Thus, with one single plate and a variable number of coupling pieces the position of the coupling pieces can be adjusted circumferentially in order to allow a variable number of mold segments to collaborate with a single type of mobile top plate.

For preference, the said first means of coupling with the closure ring comprise a plurality of guide pieces produced adjustably on the circumference of the said ring, each guide piece coming to collaborate with a guide groove of a segment.

The vulcanizing device of an embodiment of the invention additionally comprises several guide pieces which are mobile and can be fitted to the circumference of the closure ring and are made to be fixed in a position determined by that of the groove of the mold segments with which each guide piece is made to collaborate. In this way, the position of a guide piece on the closure ring can easily be adjusted circumferentially and the number of guide pieces can be adapted to suit the number of mold segments. It is also possible, for the same diameter of mold, to create a variable number of segments, which can subtend different angles, with different amplitudes of cutout at their transverse faces and then more readily adapt the closure ring. In this way, a simplified closure ring is obtained which can easily be adapted to several type of tire. Moreover, the cross sections of the rods and grooves are the same, disregarding a sliding clearance formed between them making it possible to have a good area of contact of ring with segments, over the entire circumference thereof, thus ensuring good heat transfer between the closure ring and the segments of the device. In this way, using the device of the invention, the mobile plate and also the closure ring can be adapted to suit the angular position and number of molding segments.

In a first alternative form of embodiment of the invention, the said second means of coupling comprise a radially exterior rim of the said top plate against which rim a roller mounted with freedom to rotate about a horizontal axle of a segment comes to press. Thus, the segments are allowed to move radially as a result of the rotation of the roller (or of several rollers arranged on the same axle) along the radially exterior edge of the plate.

For preference, the said horizontal axle is supported by a cranked flange mounted on the top lateral face of a segment. This allows the roller to be kept easily at the level of the top plate.

In a second alternative form of the invention, the said attachment means each comprise a horizontal crosspiece mounted on the top lateral face of a segment, the said crosspiece being able to slide along the rails of a removable jaw collaborating with the said radially exterior rim of the top plate. This solution assumes an arrangement of several removable jaws which will be attached to the radially exterior rim of the plate according to the number and angular position of the segments of the device so as to allow the segments to move radially as the device is closed and opened.

For preference, the said jaw comprises a circular rail able to collaborate with a correspondingly shaped groove of the said radially exterior rim. This allows better orientation and attachment of the jaws on the plate.

Advantageously, the said guide pieces are fixed adjustably in a circumferential notch of the said closure ring.

Thus, a guide piece may comprise a catching part to be inserted in a correspondingly shaped circumferential notch of the closure ring, ensuring better attachment in a position determined by that of the groove of a segment of each guide piece.

For preference, the said guide piece comprises a guide rod having at least one guide surface able to slide in the said groove and a hook arranged at one of the ends of the said rod to collaborate with the said circumferential notch.

This means that the assembly of the device can be made easier as the guide rod can be inserted easily between the ring and the segments until it catches on the lip of the notch of the ring. The notch and the projecting part have complementary profiles, for example of conical shape, to allow correct orientation of the guide pieces and make them easier to attach.

Advantageously, the other end of the said guide rod collaborates with means of attachment to a circular lip of the said closure ring. This allows the guide rod to be attached easily to the ring, for example using fixing screws on the lip opposite that of the notch of the ring.

For preference, the said means of attachment comprise a spacer piece comprising a circumferential part for attachment to the said ring and a radial part for attachment to the said rod. This allows the guide rod to be immobilized in terms of rotation on the circumference of the closure ring.

Advantageously, the circumferential part of the said spacer piece comprises a notch which collaborates with a complementarily-shaped circumferential rib belonging to the said closure ring. The rib preferably has a profile of conical shape, which allows the guide piece to be clamped against the closure ring with any clearance taken up.

For preference, the said radial part of the said spacer piece comprises a thrust surface for driving a segment. The segment-driving thrust surface may be a protrusion collaborating with the bottom of a groove of the segment or, conversely, a plane wall which contains a groove made in the guide piece to collaborate with a protuberance of a segment.

Advantageously, the said guide groove is positioned substantially in a circumferential part of the segment corresponding to the projection thereonto of the co-ordinates of the centre of gravity of a segment. It will be understood that the centre of the groove is positioned in the circumferential part of the radially exterior surface of a segment corresponding to the projection onto this face of the centre of gravity of the segment, this allowing forces acting on the segment to be positioned on the axis of the groove thereby balancing the dynamics of the whole.

For preference the said guide surface of the guide rods comprises plates that have a low co-efficient of friction. This improves the sliding of the guide pieces and ensures that the segments are driven smoothly.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

In the various figures, elements that are identical or similar bear the same reference. A description thereof is not systematically repeated.

FIG. 1illustrates a tire vulcanizing device1with radially mobile segments according to the invention which is able to collaborate with a vulcanizing press. The device1comprises a bottom shell2secured to a bottom plate3by means of which the device is mounted on the vulcanizing press. The bottom plate3supports the bottom shell2, centres the device with respect to the vulcanizing press and transmits heat energy to the bottom shell2. The device also comprises a top shell4secured to a top plate5. The top plate5is mobile being secured to the double-acting cylinder of the press. Its purpose is to drive the segments of the device to open and to close. The top plate5supplies heat energy to the top shell4when it is in contact with the heating top platen of the press. The device also comprises a closure ring7which is a heating ring having a conical interior surface6(making for example an angle of 15° with the vertical) and a cylindrical exterior surface8. Heating means (for example a duct for the circulation of steam or electric heating elements) are arranged inside the closure ring7and supply heat energy to the segments of the device so as to allow the tread to be vulcanized. The closure ring7is secured to a mechanism which provides the axial movement thereof, along the axis X-X′ (FIG. 6) of the device, and may be rendered axially mobile independently of the top plate5. The device1comprises a plurality of circumferentially arranged adjacent segments10(just one being illustrated inFIG. 1) each collaborating with the top plate5and the closure ring7. The radially interior part of the segments10form the part that molds the tread of the tire. The number of segments10is determined according to the circumference and tread pattern of the tire; there may, for example, be from seven to twelve of these for a passenger car tire and from eleven to twenty-four for a heavy vehicle tire. The segments with which a mold is equipped may have identical or different sizes in order to adapt to suit the desired characteristics of the tire tread.

As is best visible inFIG. 2, a segment10comprises a body9which on its radially interior face accepts a lining11which is a molding element for molding the crown of the tire, and on its exterior radial face13has a substantially vertically directed guide groove12parallel to the exterior radial surface13(for example making an angle of15° with the vertical) and intended to collaborate with a complementary guide piece belonging to the closure ring7forming the first means30of coupling of the device, as will be explained later on. In the example depicted in the drawings, the guide groove12has a T-shaped cross section. A longitudinal groove18is made parallel to the guide groove12, this is open at one of its ends at the bottom lateral face16of the segment and at its opposite end comprises a transverse wall19which serves to limit the travel of a segment10by collaborating with a corresponding part of a guide piece.

The lining11is generally made of aluminium by an injection molding technique and the body9is preferably produced by machining from a cast iron ring. The lining11(made as a single piece or as several independent elements) is fixed to the body9by rods and fixing screws (not depicted). Other ways of embodying the lining1and of assembling it with the body9of the segment may be envisaged, it being possible for example for the lining to be made as one piece (for example by injection molding) with this body. The transverse faces14,15of the segment10are cut to a given profile and produced in such a way that two adjacent segments10can nest together when the mold is in the closed position. The guide groove12is made on the radially exterior surface of a segment10and its centre is situated in a circumferential part corresponding more or less to the projection of the centre of gravity of a segment10onto the exterior radial face thereof, with a tolerance of 1°, so that forces acting on the segment at the moment of the closing and opening of the mold are balanced. The bottom lateral face16is the face via which the segment10presses against the bottom plate3and the top lateral face17accepts means20of attachment to the top plate5of the device.

According to an embodiment of the invention, the top plate5of the vulcanizing device1is adapted to suit the number and angular position of the segments10so that it can be used with various configurations of mold, notably by using second means20of coupling between the top plate5of the device and the segments10which are adjustable on the circumference of the top plate5. According to one advantageous aspect of the invention, the closure ring7of the device is also adapted to suit the number and angular position of the segments10, notably by using first means of coupling between the segments10and the closure ring7which are adjustable on the circumference of the closure ring7. That means that the closure ring7and the top plate5can be standardized and then used with different molds.

A closure ring7of the invention is best visible inFIGS. 1 and 3. The closure ring7is an annular component comprising a circumferential notch30′ in which the catching parts of the guide pieces31can slide. In the example depicted in the figures, a guide piece31is a component mounted removably with respect to the closure ring7; it comprises a guide rod33ending at its top end in a hook32. The hook32is preferably V-shaped and the circumferential notch30′ has a profile of complementary shape. The bottom end34of the guide piece31collaborates with a spacer piece35allowing it to be attached in the bottom part of the closure ring7. The guide rod33comprises plates45with a low co-efficient of friction which are mounted on the guide surfaces that come into contact with the complementary surfaces of the guide groove12. The guide rods33of the closure ring7and the guide grooves12of the segments10form the first means30of coupling.

According to one advantageous aspect of the invention, the closure ring7is made from nitrided steel and closes around segments10which are themselves made of cast iron. It has thus been found during the tests carried out that, for a good surface finish, the two components had good properties of sliding and, for this reason, the practice, generally employed in the prior art, of covering the interior surface of the closure ring7with plates of low co-efficient of friction has been abandoned. That makes it possible to avoid having to resort to additional interfaces and to obtain good thermal contact between the closure ring7and the segments10.

As is best visible inFIG. 4, the spacer piece35comprises a circumferential part36for attachment to the lip of the closure ring7and a radial part37for immobilizing a guide piece31.

The circumferential part36comprises a circumferential channel39having a cross section of the same shape as that of the bottom lip40(ofFIG. 3), preferably a V-shape, of the closure ring7. Two oblong slots43allow the spacer piece35to be attached using the screws41in orifices44made uniformly on the bottom lip of the closure ring7. The attachment of the guide pieces31to the closure ring7at the top (in the circumferential notch30′) and bottom (in the bottom lip40) thereof is on a dovetail contact profile allowing clamping against a conical surface with assembly clearances taken up.

In the example illustrated inFIG. 4, the radial part37comprises a protuberance38able to collaborate with the groove18of a segment10, the top part of the protuberance38coming into abutment against the transverse wall19of the segment10(FIG. 2) in order to limit the travel of the segments10at the top. A screw42attaches the guide piece31to the spacer piece35.

In another exemplary embodiment visible inFIG. 5, the guide piece31comprises a longitudinal groove60collaborating with an insert61mounted on the exterior radial face13of a segment10, for example using a fixing screw. The bottom part62of the insert61collaborates with a flat38′ of the radial part37to form a thrust surface for axially driving the segments10. In this example, the position of the insert61can be adjusted in order to limit the opening travel of the segments10.

The guide rod33has a T-shaped cross section and is able to collaborate with the guide groove12of the segment10. Other shapes of cross section for the grooves12and the guide rods33can be envisaged, such as dovetail cross sections or other types of cross section comprising two surfaces for guiding a guide rod33in longitudinal translation in a guide groove12in a direction that is inclined with respect to the axis of the device while at the same time allowing the segments10to move radially inwards and outwards.

According to an embodiment of the invention, each segment10comprises second means20of coupling to the top plate5which are designed so that the segments10can collaborate with a radially exterior rim5′ of the top plate5so as to be able to follow the axial movement thereof and so as to be able to move radially with respect to the top plate5.

In a first alternative form of embodiment of the invention best visible inFIGS. 1 and 3, the second means20of coupling comprise two rollers21mounted with the freedom to rotate about a horizontal axle22supported by a cranked flange23which is itself fixed, by means of the screws24, to the top lateral face17of the segment10. The rollers21are able to come to press against the radially exterior rim5′ of the top plate5and, by rolling, allow the segments10to move radially as the device of the invention is opened and closed. The radially exterior rim5′ is a horizontal peripheral ring produced below the top surface5″ via which the force of the press is transmitted to the top plate5. The top plate5has the shape of a two-tier circular podium.

In a second alternative form of embodiment of the invention, as best visible inFIGS. 6 and 7, the second means20of coupling comprise a horizontal crosspiece50which slides on the longitudinal rails51of a jaw52fixed removably to the plate5. The surface of contact of the rails51with the crosspiece50is provided with plates that have a low co-efficient of friction. The horizontal crosspiece50is fixed by means of the screws58to the top lateral part17of a segment10. The jaw52comprises a circular rail53able to collaborate with a circular rib54of the radially exterior rim5′ of the plate5. The jaw52is produced in two parts, a top part55and a bottom part56, which sandwich the circular rib54of the plate5when they are attached to the top plate5using the screws57. When the device of the invention is being assembled, a number of removable jaws52which is identical to the number of segments10that the device comprises are arranged radially at the periphery of the top plate5, the position of each segment10determining where these jaws are fixed on the circumference of the plate5.

Assembling a vulcanizing device of an embodiment of the invention begins with selecting the number of segments10needed to create a tire of given size and given tread pattern, and arranging them in a ring around the bottom shell2. The closure ring7is then placed around the segments and the guide rods33are inserted in the guide grooves12of the segments10with their hook42pressing in the circumferential groove30′ of the closure ring7. Each guide rod33is then fixed in position on the circumference of the closure ring7by tightening the screws41,42of the spacer piece35onto the bottom lip40of the closure ring7. The first means30of coupling are thus in place and the second means20of coupling are then mounted.

The mounting of the second means20of coupling which are produced according to the first alternative form of embodiment of the invention (FIG. 1) is performed by assembling the top plate5and the top shell4and attaching this to the assembly described previously. The screws24are then used to attach the cranked flanges23bearing the rollers21, after the rollers21have been positioned beforehand on the radially exterior rim5′ of the top plate5.

The second means20of coupling produced according to the second alternative form of embodiment (FIGS. 6 and 7) are mounted by first of all placing the bottom parts56of the jaws52around the top parts of the guide rods33already in position. A crosspiece50is also attached, using the screws58, to the top lateral part17of each segment10. The top plate5and the top shell4are assembled and these are then attached to the assembly previously described. The top part55of the jaw52is then attached to the bottom part56by fixing using the screws57.

The vulcanizing device1thus assembled is then mounted on a curing press. When a green form of a tire is to be vulcanized, to start off with the device is opened by axially actuating the top plate5and the closure ring7. The segments10thus find themselves in a closed position in the top part of the press and the device can be fed with a green tire which is placed in the molding cavity on the bottom shell2. The top plate5is actuated in a downwards axial movement and it drives the segments10which are lowered with the plate while at the same time parting radially into the open position (by virtue of the combined action of the second means20of coupling and of the first means30of coupling). The segments10in their turn drive the closure ring7, from the moment at which the guide grooves12come into abutment against the guide rods33. The top plate5continues its downward travel until it comes into contact with the green tire. The closure ring7is then actuated in a downwards axial movement and the action of the first means30of coupling causes the segments10to close around the crown of the green form of the tire. The closure ring7holds the segments10in the closed position and contains the pressure during the vulcanizing of the tire. After curing, the vulcanizing device1is actuated to open by first of all moving the closure ring7in an upwards axial movement in order to open the segments10. When the guide rods33of the closure ring7come into abutment (via their protuberance38against the thrust surface19inFIG. 4or via the flat38′ against the bottom part62of the insert61inFIG. 5) in the guide grooves12of the segments10, the latter accompany the ring in its upward movement. An upwards axial movement is then imparted to the top plate5which returns the segments10to the closed position in the top part of the press. The molding cavity is thus completely clear so that the tire can be taken away easily.

Other alternative forms and embodiments of the invention may be envisaged without departing from the scope of these claims.