The invention relates to the field of the manufacture of tires for passenger or utility vehicles and is more particularly concerned with the tire building methods and equipment that allow the collection of constituent parts of such a tire to be laid in succession in order efficiently to arrive at a green tire that is ready to be cured.
In the various methods and equipment, all of the operations of building the green tire are performed on a drum the diameter of which preferably corresponds substantially to the interior diameter of the tire (commonly referred to as the “seat diameter” with reference to the standardized diameter of the rim on which the tire will be mounted when used). Thus, not only the carcass, the beads and the sidewalls, but also the crown reinforcers and the tread may be laid onto a tire building drum the diameter of which corresponds substantially to the seat diameter. One advantage of this type of method is that it allows the green tire to be kept on the same drum throughout the process of assembling it. The complete green tire can then be introduced directly into a curing press where it adopts its final external diameter through the action of an internal pressure. One example of this type of method is given in document FR1508652.
Shaping is the name given to the conversion that the green tire blank experiences as it passes from its substantially tubular shape to the generally toroidal shape of a finished tire. During shaping, the central part of the green tire which corresponds to the crown of the tire sees an increase in diameter through the action of an internal pressure, while the beads are kept at the initial diameter. The difference in circumference between the seat diameter and the shaped diameter is generally comprised between 30% and 70%, and for example, commonly of the order of 50% for a passenger vehicle tire.
When it does not take place within the curing press, the operation of shaping the green tire is performed on a tire building drum. Thus methods and equipment referred to as “single-stage” are known, and in these the shaping of the green tire is performed on a single drum. In methods and installations of another type known by the name of “two-stage”, the carcass is manufactured on a first drum with a diameter suited to the seat diameter, and is then transferred onto a second, shaping, drum where it receives the crown unit assembled beforehand on a crown form. The green tire blank obtained at a diameter close to the final diameter of the tire is then introduced into the curing press.
In these various methods and equipment for the manufacture of tires, the tooling is designed according to the architecture of the tire which imposes the order of assembly of the various products that make up the green tire, according to the seat diameter of the tire and also according to the distance separating the two bead wires. As a result, for a range of, for example, passenger vehicle tires, it is necessary to design and produce a plurality of drums, it being necessary to load and set up the various drums on the tire building machine according to the characteristics of the tire that is to be manufactured. One alternative solution is to use a complex drum, as is generally known, but which nonetheless remains suited to the manufacture of green tire blanks within a pre-established range of seat diameters and a pre-established range of distances between the bead wires.
Moreover, after the bead wires have been laid, the ends or edges of the rubber plies that are involved in the makeup of the green tire and are laid beforehand onto the drum, notably the carcass ply, need to be turned around the bead wires. To do that, the drum needs to be provided with ply-turning devices which, for the most part, are equipped with inflatable bladders mounted fixedly on the drum. When these are inflated, they turn the ends of the plies over the bead wires. Such a bladder-type ply-turning device is complex and expensive, especially since it is tailored to a particular size of tire and proves to be tricky to maintain. What is more, a ply-turning device of the inflatable bladder type is unable to correctly fold green tire components of which the length of the ends to be folded over exhibits variations after laying or else when the ends that are to be folded are too rigid, for example when turning a metallic carcass ply.
Ply-turning devices comprising mechanical systems free of an inflatable bladder are also known. Such an example is the ply-turning device of document U.S. Pat. No. 3,887,423, the drum of which comprises a plurality of circumferential fingers mounted with the ability to pivot about an axis perpendicular to the axis of rotation of the drum, and also having the possibility of moving in translation parallel to the axis of the drum. This system has the disadvantage of being mounted on the drum and, therefore, of being restricted to one size of tire. What is more, it is not suitable for use with a multi-workstation tire building machine, the drum then being bulky and expensive.
In order to alleviate this problem, the ply-turning device may be arranged on the outside of the drum. Such a device is described in document U.S. Pat. No. 4,362,592 and is suited to use with an automatic tire-building machine having several tire-building workstations. The device comprises two ply-turning assemblies each comprising several circumferential fingers and arranged near the axial ends of the drum. The end of the fingers of each assembly comprises rollers and the fingers are actuated, by means of a hydraulic actuating cylinder and a cam mechanism, to move radially and axially with respect to the drum so as to lift up the end of the carcass ply and then fold it over the bead wires. While being easier to maintain and admittedly allowing a movement of greater amplitude to be developed than can be achieved with the preceding devices, its use is nevertheless limited to a given architecture of tire and to the presence of just one ply to be turned, the length of which is greater than that of the drum.
Thus, with requirements imposed by the assembling of a complex product, the tire industry is dependent on there being a stock of drums of greater or lesser complexity that need to be stored, mounted on a tire building machine or replaced and set up when starting a tire or series of tires of a given range. That entails high manufacturing costs and long cycle times.
It is therefore an objective of the invention to alleviate at least one of the disadvantages described hereinabove.
For that purpose, the invention proposes a method and an equipment that allow the laying of the various components of a green tire blank, namely the components of a carcass or of a complete green tire, on a simplified expandable drum. Carcass is the name used to denote that part of the green tire that does not comprise the crown unit.
The invention therefore proposes a method of assembling a green tire, comprising in succession steps involving:
Thus, according to the invention, it becomes possible to lay on a drum that can be expanded in terms of diameter one or more component(s) of the green tire (inner liner, carcass ply, protectors in the form of strips of rubber, etc.) in the desired order, it being possible for the various products to be secured to one another by rollering over their entire length by applying pressure to the external circumferential face of the drum. Once the bead wires have been laid on the drum, the ends of the various products laid on the drum are lifted up using the wings, then folded using the elements involving rollers. Because the drum segments are slotted, the wings can lift up several products laid on the drum and supported thereby, notably with a view to rollering. What is more, because the device for folding or turning the plies around the bead wires has been made independent of the drum, it can be used for turning the edges of the plies around the bead wires while at the same adapting to accommodate a plurality of distances between the bead wires. As a result, the drum lends itself to the building of a plurality of tire sizes.
What is more, the edges lifted up and turned over according to the method of the invention may comprise several plies stuck together, it being possible for the plies each to comprise textile or metallic reinforcers. The wings of the device of the invention are rigid and robust enough to be able to lift a complex of plies with a view to ply-turning by a device independent of the drum. The drum and the associated devices in the context of the method of the invention can therefore be used to create tires of different architectures (the architecture being defined by the arrangement and composition of the collection of plies that make up the green tire) in addition to the possibility offered by this method of varying their size, thus further increasing the number of manufacturing options offered by the tire building method of the invention. It thus becomes possible to propose a tire building method according to the invention which is highly flexible and adapts to various manufacturing requirements.
For preference, the various components that are to be assembled are laid on a drum free of grooves. This makes it possible to sever the connection with distance between bead wires and therefore, since the drum is also expandable in terms of diameter, to build several sizes of tire on the one same drum, for example by laying the bead wires using the arm of a robot at a pre-established location on the drum.
For preference also, the bead wires are formed by winding a metal cord onto the drum. That makes it possible to form a bead wire in situ and, through a suitable choice of the number of turns to be wound, better adapt the bead wire to suit the tire that is to be built.
For preference also, the laying of at least one first product begins at a diameter smaller than that of the seat. That allows tension to be introduced into the first product or products laid on the drum, which is then inflated to the seat diameter which corresponds to the laying of the reference products including the bead wires.
In one advantageous embodiment of the invention, a wavy strip is wound in a helix on the green tire in order, in a plurality of turns, to form a tire crown hooping ply, the wavy strip having a given over length to allow the green tire to be shaped. This allows all the components of the green tire to be built up, flat, on the one same drum before the tire is shaped.
For preference, all the components of the crown unit are laid and the green tire is finalized before the drum is collapsed. At least one wavy reinforcing strip is thus laid by winding around the drum, as well as at least one metal reinforcing ply, the tread and the sidewalls in order to obtain a green tire that can be shaped directly in a curing press. The drum is then collapsed so that the green tire can be extracted and sent for curing.
The invention also proposes an equipment for implementing such a method, the said equipment comprising a drum driven in rotation about a main axis, the said drum being able to support a green tire blank created by the successive laying of raw components on the external circumferential face of the drum which face is made up of segments which are radially mobile between a drum-expanded and a drum-collapsed position, the said drum being positioned facing a ply-turning device independent of the drum, the said device being able to turn the edges of the rubber plies laid on the drum around a bead wire using elements involving rollers which are mounted with the ability to move in the axial direction on the circumferential face of the drum, in which each end of segment comprises a longitudinal cut running parallel to the axis, the cut being made to collaborate with a wing which runs parallel to the axis and is made to move in the said cut in order to lift up the edges of the rubber plies extending axially beyond the bead wires towards the ends of the drum so that they can be turned over.
The equipment of the invention makes it possible to optimize the functions of each device of which it is composed and also the functionality of these devices as a whole so that it is flexible and suited to the building of a plurality of green tires in terms of dimensions and architectures of tire to be manufactured.
For preference, the equipment comprises an expandable drum free of grooves.
For preference also, the said wings are mounted on a lifting device comprising drive means able to move the wings in an axial direction and/or in a radial direction.
For preference also, the said lifting device is independent of the drum.
For preference also, the said ply-turning device comprises a plurality of circumferential articulated arms comprising the rollers, the said arms being mounted with the ability to move radially and axially with respect to the drum.
For preference also, the elements involving rollers and the wings are mounted on a common support able to move in longitudinal translation with respect to the drum and secured to the drive means designed to move the elements involving rollers and the wings in the same direction, but with a temporal offset.
The following description allows a better understanding of the method according to the invention and of the structure and operation of an equipment according to preferred embodiments of the invention, and is supported by
In the various figures, the elements that are identical or similar bear the same references. The description of the structure and of the function of these identical or similar elements is therefore not systematically repeated.
The drum 6 has external segments 8 or tiles which run around the periphery of the drum to form the external circumferential face 10 of the drum which defines the working face on which the components of the green tire are arranged. This face has a cylindrical overall shape of circular cross section in a plane perpendicular to the axis 6. This face allows the various components of the green tire to be laid “flat”. The segments 8 are all identical to one another, are arranged in the circumferential direction of the drum and, in this particular example, there are 24 of them, although this number may vary. In this example, each segment is rigid and formed of a single piece having the overall shape of a comb. The segment 8 has a rectangular overall shape of length (which means longest direction) parallel to the axis 6 and the longitudinal edges of which are cut to form toothings so that the teeth of the edge of one comb can imbricate with the teeth of the edge of the adjacent comb. Because the segments are able to move in a radial direction with respect to the axis 6, the comb shape of the segments means that their distance from the axis can be varied while at the same time ensuring a certain continuity of material between the combs in the circumferential direction of the drum.
The segments 8 are connected to the drum by members which guide and drive them. In the example illustrated in the figures, these members comprise two cams 12 centred on the axis 6 of the drum and each having two lateral faces perpendicular to the axis 6 between them delimiting a conical surface 14. The cams 12 are identical and are arranged as a mirror image of one another about a central mid-plane of the drum perpendicular to the axis 6 thereof, one in the right-hand part and the other in the left-hand part of the drum and with the possibility for axial movement. Each segment 8 is fixed rigidly to a segment support 16. In the example depicted, there are 24 of these supports 16 although the number of them may vary. The support 16 has an elongate shape in a direction parallel to the axis 6 and near each end has a follower 18 which follows the inclined circumferential surface 14 of the cam 12. Each support 16 is connected by two rigid rods 20 to a ring 22 centred on the axis 6 of the drum mounted with the ability to rotate with the latter. The rods 20 slide in radial openings made for this purpose within the ring 22 and radially guide the segments 8. The segments are kept in contact with the cams by means of an elastic means (not illustrated), for example a flexible bladder. The cams are driven in an axial movement that is symmetric on each side of the mid-plane of the drum, for example by connecting them to a mechanism of the screw-nut type, one of the ends of the screw having a right-hand thread and the other a left-hand thread, and the screw being turned with the drum 2. The cams 12, the supports 16, the rods 20 and the rings 22 form means of expanding/collapsing the drum 2. In order to move the drum from the collapsed position into the expanded position, the cams 12 are made to move axially in the direction that brings them closer together, something which occurs symmetrically with respect to the mid-plane of the drum and along the axis 6. This movement causes the support 16 and therefore the segment 8 to slide radially in the direction perpendicular to the axis 6. This movement is the same and takes place simultaneously for all the segments 8 of the drum, which means that the drum 2 maintains its cylindrical shape during all the changes in diameter of the drum.
The drum components are made of metal, or of material most being made of steel or of aluminium, the surface of the segments 8 that is in contact with the rubber being treated according to the operating conditions (for example in order to make it sticky or non-sticky towards the rubber). In an alternative, certain components may be made of a plastic or composite material for greater rigidity.
Other segment drive systems for making the transition from the collapsed position to the expanded position and vice versa may be envisaged, such as electric or hydraulic actuating cylinders that move the cams axially, or even rotary cams with grooves in which followers connected to the segments run, etc.
According to one advantageous feature of the invention, the drum 2 has an external circumferential face 10 of cylindrical overall shape free of bead wire-housing grooves. When used to build passenger or utility vehicle green tires, the drum of the invention preferably has a diameter greater than 250 mm and a length greater than 700 mm or, more generally, the length/diameter ratio for the drum needs to be greater than 2.5.
Such a drum not only allows the building of green tires in a broad range of seat diameters but also, because of the absence of grooves, in a broad range of dimensions of the space between bead wires (which means the distance separating the two bead wires during the building of the green tire). The bead wires are then laid in a precise position on the drum using a robot-controlled arm or are produced in situ during the laying on the drum.
For the next operations, the drum 6 collaborates with a ply-turning device 60 which is independent of the drum and which folds the ends of the components of the carcass around the bead wires and presses them down with a roller.
More particularly according to the invention, the drum has several longitudinal cuts 40 which are slots uniformly distributed on its circumference and are there to collaborate with mobile wings 45 which are designed to be able to move with respect to the cuts 40 so as to be able to lift up the longitudinal edges of the green tire 1 so that they can be turned around the bead wires. The cuts 40 are longitudinal slits made in the centre of each segment 8, over a pre-established distance at each of the longitudinal ends of a segment. The length of a slit is preferably less than one quarter of the length of a segment 8. The slits may or may not be open-ended, depending on how the wings move, and they all have the same width.
In one embodiment of the invention and as is better visible in
In the example depicted in the figures, the wings 45 have a flat overall shape of trapezoidal profile and comprise a leading edge part oriented in the direction of the drum 6 which has an inclined edge 43 forming an angle of between 30 and 45° with the axial direction. The wings are identical and uniformly circumferentially distributed. The thickness of a wing 45 is less than that of a cut 40 so that the wing can move in the cut. This angle is chosen so as to be able to lift up the edges of the plies in such a way that the edges can be driven by the rollers of the ply-turning device. According to the invention also, the wings 45 are mounted with the ability to move axially and/or radially. To this end, use is made of a first actuator such as, for example, an electric actuating cylinder which moves the support 52 in longitudinal translation alone, or in combination with an actuator which moves the conical ring 46 in longitudinal translation.
In the example depicted in the figures, the lifting device 50 is incorporated into the ply-turning device 60 which is independent of the roller, as will be explained hereinafter. However, in an alternative form of embodiment (not depicted) of the invention, the lifting device may be mounted on the drum 6, being arranged with its actuators at the ends and on the inside thereof. In an exemplary embodiment which is not depicted in the figures, when the device is incorporated into the drum, the wings 45 are replaced by rods which project through the cuts 40 to the outside of the drum, beyond the bead wires. These rods are then made to move axially to get into position and radially to lift the edges of the components, it being possible for these two movements either to be combined or separate.
The structure and operation of the ply-turning device 60 will now be explained with reference to
The members that connect the articulated arms 80 to the support and that guide and drive them will be introduced in what follows. A detailed description will be given of the members situated in the right-hand part of the drum in
The equipment 100 of the invention is illustrated in
In order to perform good ply turning, and as is better visible in
The operation of the equipment 100 of the invention will be described in what follows. The drum 2 comes into the vicinity of the ply-turning workstation of the tire building machine, as visible in
In an alternative form, the choice is made to move the rollers 90 over the external face of the drum without applying pressure, so as to facilitate the passage of the bead wires, and then to apply pressure to the turned-over edges of the plies in order to expel the air bubbles trapped between the plies.
Preferably before the drum is withdrawn, rollering means apply additional pressure by running over the turned-over plies or edges in order to finish expelling air and better bond these to the surface of the green tire.
In order to complete the building of the carcass of the green tire, the edges of the plies N1, N2 need to be turned around the bead wires T using the ply-turning device of the invention. The start of the ply-turning operation is illustrated in
Other rubber-based plies can then be laid on the carcass thus formed, for example plies constituting the sidewalls, a wavy strip of reinforcer, a reinforcing ply and the tread so as to obtain a complete green tire blank 1.
Other alternative forms and embodiments of the invention can be envisaged without departing from the scope of these claims. Thus, the ply-turning device and the lifting device of the invention may be used with any other type of drum provided that it has cuts suited to collaborating with wings of the lifting device so as to allow the action of the rollers of the ply-turning device.
Number | Date | Country | Kind |
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1463030 | Dec 2014 | FR | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2015/080882 | 12/21/2015 | WO | 00 |