WO2021191555A1

WO2021191555A1 - Drum for building a tire adapter on a rim

Info

Publication number: WO2021191555A1
Application number: PCT/FR2021/050494
Authority: WO
Inventors: Gérard BAUMGARTNER
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2020-03-26
Filing date: 2021-03-23
Publication date: 2021-09-30
Also published as: EP4126521A1; FR3108556A1; FR3108556B1

Abstract

Radially expandable building drum (10) designed for manufacturing a tire adapter blank (1) on a rim, with a central shaft with axis X-X' for a building area (50) provided with a plurality of segments (100, 200), the segments comprising grooves (103, 203) for receiving bead cores, and comprising folding-up devices (30, 40) around bead cores arranged on either side of the building area (50) that are suitable for being moved axially toward one another and apart from one another, each fold-up device comprising a plurality of adjacent fold-up arms (31, 41) arranged circumferentially on the drum, where each fold-up arm has a proximal end (32, 42) suitable for folding-up the components around the bead cores, characterized in that the proximal end (32) of each arm of at least one of the fold-up devices (30) comprises at least two adjacent toroidal spiral springs (321, 322), each being designed to come in contact with the blank.

Description

Drum for making a tire adapter on a rim

The invention relates to a building drum for the manufacture of a tire adapter used for mounting the tire on a rim.

[0002] Document WO2015 / 086662 discloses such an adapter made from reinforced rubber mixtures which are elastically deformable mainly radially in the event of a violent impact suffered by a rolling assembly comprising it. In such a rolling assembly, two adapters are used to connect the rim to the beads of the tire, making it possible to improve the properties of the latter.

[0003] More particularly, such an adapter generally comprises an inner bead which ensures the attachment of the adapter to the rim, an outer bead intended to receive the bead of the tire, the inner and outer beads being connected by a reinforcement frame allowing elastic deformation of the adapter mainly in the radial direction. Such an adapter is made by stacking different rubber compound products on a support and is then vulcanized in a mold inside a vulcanizing press so that it acquires the desired elastic properties.

Given its functions and taking into account the assembly requirements, the adapter has a generally conical tubular shape, with a very specific profile. Indeed, the shape of the section of the adapter is determined by the shape of the section of the rim and by the associated type of tire, and therefore its profile is often complex. In addition, in order to respond to extreme stresses, such as an impact against a sidewalk or a passage in a pothole, the elastic deformation of the adapter must have very precise predetermined values and, therefore, the adapter must meet very strict dimensional conditions. To meet these conditions, it is envisaged to assemble the various components by successive laying on a rigid core, then vulcanization in a suitable mold. With good production precision, this solution must however call for very complex tools, requiring a significant investment. In order to be able to industrially and economically manufacture such an adapter, given its constitution and its structure which are based on reinforcements and rubber products, such as webs or profiles related to those used for the manufacture of 'a tire, the reuse of an assembly drum has also been envisaged. However, such a drum must satisfy several conditions, it must in particular have sites for receiving beads of different diameters. Such a drum is described in document WO 2018/215722 in the name of the applicant. According to this document, one begins by laying different products (rubber-based plies and reinforcing ply) flat on a cylindrical part of the drum to form the radially inner part of the adapter. The rods are then placed and the expansion of the drum is controlled so as to obtain two zones of different diameters relative to each other and thus achieve a clamping inside the rods. The ends of the plies are then folded around the bead wires using winding devices each comprising a spring, arms located at the axial ends of the drum. Operating satisfactorily, however, it has been desired to improve the operation of the roll-up devices of such a drum.

[0006] An objective of the invention is to remedy the aforementioned drawbacks and to provide an original solution for a building drum making it possible to achieve good roll-up of the adapter blank at a lower cost. This objective is achieved by the invention which provides a radially expandable building drum intended for the manufacture of a tire adapter blank on a rim, said drum comprising a central shaft of axis XX 'which is a axis of revolution for a building zone provided with a plurality of segments disposed circumferentially around the central shaft, said segments comprising annular grooves for receiving bead wires, and comprising devices for rolling up the rubber components around bead wires each arranged in on either side of the building zone while being adapted to be displaced axially towards one another and one away from the other, each rolling up device comprising several adjacent rolling up arms arranged circumferentially on the drum where each winding arm has a proximal end capable of turning the components around the rods, characterized in that the prox end imale of each arm of at least one of the devices roll-up comprises at least two adjacent toric helical springs, each being intended to come into contact with the blank.

In other words, the invention provides a roll-up device with several arms arranged in the circumferential direction of an adapter blank making drum in which each roll-up arm comprises at its proximal end (we understand the most close to the drum building zone) two adjacent toric helical springs which are able to roll on the components of the blank in order to roll them up around the rods thereof. By toroidal or toroidal helical spring is understood a helical tension spring whose ends have been joined in a ring so that each spring forms a ring around the drum. Indeed, the spring closest to the preparation area first attacks the components and the second carries out the finishing and the plating of the products one on the other, and one thus obtains an excellent quality of finishing of the blank. .

[0009] The two adjacent springs of each roll-up arm may have different stiffnesses or different diameters. In what follows, the diameter of the spring is understood to mean the average diameter of the ring formed by the helical spring closed around the drum. In a preferred variant of the invention, the rings forming springs have different diameters, the closest to the building zone having a diameter greater than the adjacent spring. Thus, the spring which is located closest to the building zone initiates the turnaround around the bead wire, which is advantageous for large diameter bead wires, while the adjacent spring ensures the plating of the rubber components on each other. by expelling air during taxiing. This makes it possible to obtain a better quality roll-up compared to that carried out with a single spring, as in the state of the art. [0010] In an advantageous variant of the invention, the spring which is located closest to the building zone projects forward with respect to its support and the adjacent one projects towards the rear of its support. Each of the springs thus comes in turn in contact with the components, the first ensuring first the contact and the rise of the products in the direction of the rod and the second being the one which makes the last contact with the products and therefore the finish of the roll-up. [0011] The solution of the invention thus makes it possible to carry out a better quality roll-up of the rubber components around bead wires of large diameter. In addition, by reuse of O-ring springs to perform the roll-up, these springs provide the radial force necessary for a better and progressive plating of the components, they roll on the rubber components while guaranteeing the continuity of the roll-up over the entire circumference of the liner. 'sketch.

[0012] Other features of the invention are set out by the subsidiary claims.

The rings formed by said springs around the drum can have different diameters.

The spring located closest axially to the building zone can form a ring having a larger diameter than the ring formed by the adjacent spring.

The springs can be mounted side by side in a common support.

The spring located closest axially to the building zone can project from its support.

The spring furthest axially from the building zone may project from its support.

The springs can be tensioned in the retracted position of the drum.

The springs can have a tensile stiffness of between 0.1 and 0.5 N / mm.

[0020] The diameter DI of the ring formed by a spring can be between 350 and 500 mm and the diameter D2 of the ring formed by the adjacent spring can be between 350 and 500 mm.

The segments may have an inclined proximal part of downward slope connected to a cylindrical distal part by an intermediate part inclined at upward slope and one spring can be adapted to follow the slope of the intermediate part and the other spring can be adapted to follow the slope of the proximal part.

[0022] The coil diameters of the springs may preferably be equal to each other and be between 10 and 16 mm. [0023] The springs can be held in a housing of the proximal end by means of a spacer.

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 illustrating the building drum at the end of the manufacturing operation of a adapter; FIG. 2 is a partial sectional view of the drum of FIG. 1 illustrated in the start-up position of rolling up; Figure 3 is a partial sectional view of the drum of Figure 1 illustrated in the end position of the rolling up operation.

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

The construction drum of Figure 1 is suitable for manufacturing an adapter 1 intended to be mounted between a rim and a tire (not shown) to form an assembly of the type described in document WO2015 / 086662 in the name of the applicant . The adapter 1 comprises for this purpose an inner bead 3 for fixing to a rim, an outer bead 2 intended to receive the bead of a tire and a body 4 connecting the two beads. The adapter thus formed is a part of generally annular shape with a radially widening profile, having a symmetry of revolution about a central axis.

The body 4 of the adapter 1 comprises a frame formed on the basis of a main ply of textile cables parallel to each other encompassed in a rubber base, such as a carcass ply. This sheet is arranged so as to form an upturn around the rod of the inner bead 3 (called small rod in what follows) and, on the other hand, is anchored in the outer bead 2 of the adapter, also forming an upturn around the rod of the latter (called large rod in what follows). The main ply is completed by one or more secondary plies, such as a protective ply arranged on the outer face located radially inside the adapter, or even an inner sealing ply or rubber, arranged on the radially face. outside of the adapter, or by other filling or packing gums at the rods. For example, the difference in diameters between the outer bead and the inner bead is about 1 inch. Figures 1 to 3 illustrate, in different operating positions, an assembly drum 10 according to the invention intended for the manufacture of a rim adapter on a tire, the green adapter blank obtained by assembly on this drum being then vulcanized in a mold. For the sake of clarity of the drawings, the drum 10 has been shown with a single set of segments 100, 200 and their related components located on the same generator of the drum, as will be explained later.

The drum 10 is mounted on a frame (not shown) comprising mechanical drive means capable of rotating the drum around a central shaft or barrel 8 of central axis X-X ', for example by coupling a geared motor to one of its ends. In what follows the radial and axial directions are defined with respect to the central axis X-X ’which is also an axis of symmetry, or even of revolution of the drum as a whole.

The drum 1 comprises segments 100 of a first type and segments 200 of a second type which face each other axially or in other words are axially juxtaposed. All the segments 100, 200 of the first and second type are arranged circumferentially on the periphery of the drum to form an outer cylindrical face 50 of the drum which constitutes the working face or assembly area on which the elements or components of the drum are arranged. adapter blank. The segments 100, 200 have the same width in the circumferential direction, their respective length (measured in the axial direction) being chosen as a function of the dimensions of the adapter to be made. The segments of each type are arranged one behind the other so as to form a ring concentric with the axis X-X '. The outer face 50 has, in the retracted position of the drum, a generally cylindrical shape of circular section in a plane perpendicular to the axis X-X '. The segments 100 and 200 are arranged so as to be able to pass from a retracted position to an expanded position and vice versa. In the expanded position of the drum, as seen in Figure 1, the segments 100 form an outer face 51 of cylindrical shape of smaller diameter than that of the outer face 52 of cylindrical shape of the segments 200.

The segments 100 of the first type are all identical to each other. They are, in the present example twenty-seven, distributed uniformly around the axis X-X ’in the circumferential direction, but this number may vary. In this example, each segment is rigid and formed as a single piece having a generally elongated shape, the largest dimension of which is parallel to the X-X axis. As best seen in the sectional view of Figure 1, a segment 100 has a proximal portion 101 of generally inclined shape or in the form of a portion of a cone of downward slope connected to a distal portion

102 of the general shape of a cylinder portion by an intermediate portion 107 having the shape of a cone with an upward slope. The proximal part 101 has a circular groove

103 intended to receive a rod. The groove 103 has as its central axis the axis X-X ’and has a radial section in a semicircle. The proximal part 101 is made in the form of a comb, in this case, comprising teeth interpenetrating with the teeth of the proximal part of an adjacent segment 200 of the second type, which makes it possible to ensure continuity in the axial direction. of the outer face of all segments of the drum. Each segment 100 is fixed to a rigid support 110 by which it is connected to drive and guide means, as will be explained below. The ascending and descending terms of each segment are defined by the movement made by the front part of a roll-up device which traverses said slope when it is set in motion to carry out the roll-up of the blank.

The segments 200 of the second type are all identical to each other. They are, like the segments 100, twenty-seven in number in this example, distributed uniformly around the axis XX 'in the circumferential direction, but their number can also vary, while remaining equal to the number of segments 100. Each segment 200 is rigid and formed in one piece having a generally elongated shape, the largest of which dimension is parallel to the X-X 'axis. As best seen in FIG. 1, a segment 200 comprises a proximal part 201 of generally inclined shape or in the form of a portion of a cone with an upward slope at the same angle as the proximal part 101 of the segments 100 of the first type. In a variant, the upward slope of the segments 200 may be different from the upward slope of the segments 100. The proximal portion 201 is connected by an intermediate portion 207 having the shape of a cone of upward slope to a distal portion 202 of the general shape of a portion. cylinder. The proximal part 201 has a circular groove 203 intended to receive a rod, which groove has as its central axis 1 'axis X-X' and has a radial section in a semicircle. The proximal part 201 is made in the form of a comb, comprising teeth interpenetrating with the teeth of an adjacent segment 100. Each segment 200 is fixed to a rigid support 210 by which it is connected to drive and guide means, as will be explained below.

The drum 10 is made so as to pass from a first retracted position to a second expanded position when the segments 100 cooperate with the ramp 301 of a first cam 300 and the segments 200 with the ramp 401 of a second cam 400, the cams being axially movable by being mechanically connected to a sleeve 71 driven in an axial movement by a mechanism 70 with screw 72 and nut 73. The ramps 301,401 have an inclined profile, the angle of inclination of the ramp 301 being different from the angle of inclination of the ramp 401 over at least part of their profile. More precisely, the supports 110 and 210 of the segments 100, 200 of the drum 10 comprise at their distal end (that opposite to the end which supports the segments 100, 200) rollers 150, respectively 250 which come into contact with the ramps 301, respectively 401 of the cams 300, 400.

In operation, the rotational drive of the central shaft of the drum and therefore of the screw 72 of the screw and nut mechanism 70 drives the axial displacement of the sleeve 71 carrying the cams 300, 400. The axial displacement, at the same speed, cams whose ramps have different inclinations cause the segments 100, 200 to move radially at different radial heights with respect to each other in order to obtain, at the end of travel, the positioning of the segment 100 to a diameter greater than that of the segment 200. This results in a greater radial displacement of the segments 100 of the first type relative to the segments 200 of the second type (FIG. 1). Thus, when a radial expansion different takes place between the two sets of segments, the cylindrical outer face in the retracted position of the drum which allowed the different components to be laid "flat" becomes conical in the expanded position of the drum, which allows the assembly to be finished. , as will be explained later. The drum 10 also comprises, for each segment 100, 200, two roll-up devices 30, 40 comprising roll-up arms coming into contact with the rubber layers of the adapter blank. The drum 10 furthermore comprises means for driving the winding arms, as will be explained below.

The first roll-up device 30 is located in the right part of the drum, it comprises, for each pair of adjacent segments 100, 200, a roll-up arm 31 arranged, in the retracted position, substantially parallel to the X-X axis ', arm which comprises a proximal end 32 intended to come into contact with the adapter blank and a distal end 33 connected to a pivoting articulation of a displacement mechanism 39 of the rolling-up device. In the example illustrated according to the invention, the proximal end 32 comprises a housing for receiving two circumferential winding springs 321, 322 each mounted slightly in tension on the distal part 102 of the segments 100 of the drum 1 when the roll-up device is in the rest position. The arm 31 is mounted so as to pivot around an articulation 33 to which are also pivotally connected two connecting rods 34 and 35. The connecting rod 34 is mounted via an articulation 37 on a straight plate 60 supported by the drum. The connecting rod 35 is mounted on a cylinder plate 650 movable via a joint 38. The axes of the joints 33, 37 and 38 are mutually parallel and perpendicular to the X-X ’axis of the drum. The straight plate 60 and the cylinder plate 650 are generally in the form of a planar disc, they extend in a plane perpendicular to the axis X-X "and are centered on the latter.

The drum comprises a first annular cylinder 600, for example a pneumatic cylinder which serves as an actuator means in axial translation of the roll-up device 30. The annular cylinder 600 comprises a cylinder body 610 which is arranged in a sealed manner and with possibility of axial sliding along a shank 8a of the drum 1. The annular cylinder 600 comprises an annular piston 620 fixedly mounted on the shank 8a and a rod of locking in rotation (not shown). When the internal chamber of the annular cylinder 600 is supplied with pressurized gas, the cylinder housing 610 moves in axial translation, it drives the rod 35 in motion and causes the forward movement of the arm 31.

When it receives the thrust movement in axial translation of the annular cylinder 600, the arm 31 moves to the left on the fig. 1 and pushes the springs 321, 322 in contact with the blank of the adapter to roll up the plies around the rod placed in the groove 103. At the end of the roll-up, the cylinder 600 is controlled in the opposite direction and the arm 31 is withdrawn into its initial or rest position. In this case, the drum has twenty-seven roll-up devices 30 and the arms 31 are actuated simultaneously by the cylinder 600.

The second roll-up device 40 is similar to the first. It comprises, for each pair of adjacent segments 100, 200, a roll-up arm 41 arranged, in the retracted position, parallel to the axis X-X 'and which is directly connected, at its right end, to a proximal part 42 which maintains a circumferential roll-up spring 43 mounted slightly in tension on the distal part 202 of the segments 200 of the drum 1. The arm 41 is mounted so as to be able to pivot about a joint 46 to which are also pivotally connected two connecting rods 44 and 45 The connecting rod 44 is pivotably mounted via an articulation 47 on a left plate 80. The connecting rod 45 is mounted on a cylinder plate 48 via an articulation 850 (Fig. 1). The axes of the joints 46, 47 and 48 are mutually parallel and perpendicular to the X-X ’axis of the drum. The left plate 80 and the cylinder plate 48 are generally disc-shaped, extending in a plane perpendicular to the X-X "axis and centered on the latter.

The drum comprises a second annular cylinder 800, for example a pneumatic cylinder which serves as an actuator means in axial translation of the roll-up device 40. The cylinder 800 comprises a cylinder body 810 which is arranged in a sealed manner and to possibility of axial sliding along a barrel 8b of the drum 1. The annular cylinder 800 comprises an annular piston 820 fixedly mounted on the barrel 8b and a rotational locking rod (not shown). When the internal chamber of the annular cylinder 800 is supplied with pressurized gas, the cylinder housing 810 moves in axial translation, it drives the rod 45 in motion and causes the lifting movement of the arm 4L. When it receives the thrust movement in axial translation of the annular cylinder 800, the arm 41 moves to the right on the fîg. 1 and pushes the spring 43 on the slope of the intermediate part 207 of a segment 200 in order to roll up the plies around the rod placed in the groove 203. At the end of the roll up, the jack 800 is controlled in the opposite direction and the arm 41 is withdrawn into its initial or rest position. In this case, the drum comprises twenty-seven roll-up devices 40 and the arms 41 are actuated simultaneously by the jack 800.

[0043] The segments 100 and 200 are located one in the extension of the other with a distance between the grooves 103 and 203 of approximately 55mm in the example described. Most of the drum parts are made of metal, for example some of aluminum and others of steel.

This drum is used in the manufacture of a green tire adapter blank. An adapter assembly method using the drum will now be described.

We begin laying the products by bringing the drum in the retracted position, a position in which the outer face 50 of the drum is cylindrical. The segments 100 and 200 have their external faces at the same level, which allows the products to be laid "flat". Thus, we begin by laying the different rubber-based plies (by different plies we include at least one protective ply and a carcass ply provided with reinforcing threads), then the bead packing, by assembling them while the drum 1 is rotating around the X-X 'axis. The small rod of the inner bead 3 and the large rod of the outer bead 4 are then positioned opposite the grooves 103 and 203, then the expansion of the drum is controlled to arrive in the expanded configuration shown in Figure 1.

After placing all the components on the drum, the expansion of the latter is controlled to achieve this configuration, the central shaft is rotated and one obtains, thanks to the axial displacement of the sleeve 71 and the cooperation of the rollers 150 with the ramps 301 and of the rollers 250 with the ramps 401, for all the segments simultaneously, the radial expansion but asymmetric with respect to a vertical median plane passing at the junction of the two sets of segments. When expanding the drum, given the greater thickness of the plies in the vicinity of the small bead wire, the latter is the first to be immobilized in the groove 203 of the segments 200, which makes it possible to control the sliding of the plies on the conical part of the expanded drum. At the end of the expansion, the two bead wires are clamped, with the rubber components in the grooves 103, respectively 203 of the segments 100, 200 of the drum, the roll-up devices 30, 40 still being retracted under the rubber components.

[0047] Figure 2 illustrates the start of the roll-up operation on the right side of the adapter blank 1 by means of the roll-up device 30 actuated in a forward motion relative to the blank. The proximal part 32 of the arm 31 of the device receives an actuation in an axial translational movement coming from the jack 600. The arm 31 moves the proximal part 32 to the left so that it can mount the inclined intermediate part 107 of the segments 100 for lift the edges of the components above the large rod of the outer bead 2.

More particularly according to the invention, the proximal part 32 of the arm 31 supports two adjacent springs 321 and 322. The springs 321, 322 are helical springs in the form of a torus forming around the drum and the axis XX 'of the rings with a diameter slightly smaller than that of the portion 102 of the segments 100. The springs 321 and 322 are tension helical springs whose ends abut so as to form rings around the drum and the axis X-X '. The ring formed by the spring 321 has an average diameter DI greater than the average diameter D2 of the ring formed by the spring 322 (Fig. 1). The springs 321, 322 are each held over an arc of about 180 ° of its cross section within a housing located at the proximal end 32 of the arm 31, which housing has two annular cavities 331, 332 of semi-section. circular of corresponding shape, so that they are driven in motion at the same time as the arm 31. By way of example, the diameter DI is equal to approximately 489.5 mm and the diameter D2 to approximately 474 mm. The coil diameters of the springs 321 and 322 are preferably equal and between 10 and 16 mm. In a variant, the spring 321 which is closest to the building zone 50 has a larger winding diameter than the adjacent spring 322. The tensile stiffness of the springs 321 and 322 is approximately 0.12 N / mm. As shown in Figure 2, the spring 321 is arranged frontally in front of the edges of the cavity 331 (it is understood that the front end of the spring 321 protrudes a few mm from the front end of the edges of the cavity 331 ) so that it can come into contact with the rubber products first. The spring 322 is, for its part, arranged so as to protrude from the rear edges of the cavity 332 so that it can finish the rolling up, as best seen in FIG. 3 (it will be understood that the rear end of the spring 322 exceeds by a few mm the rear end of the edges of the cavity 332) and so that the proximal end 32 of the arm 31 does not come into contact with the rubbery products. The springs 321 and 322 are held in the housing of the proximal part 32 by means of a spacer 330.

The springs 321, 322, which are mounted slightly in tension in the retracted position of the drum, thus make it possible to exert the necessary pressure on the folded edges of the components in order to ensure their adhesion with those of the central part of the blank the adapter and expel the air when they are driven by the arm 31 to roll over the components. At the end of the rolling up, the device 30 performs a withdrawal movement by being actuated in the opposite direction by the jack 600, until it returns to the position illustrated in FIG. 1.

FIG. 3 illustrates the final part of the operation of rolling up the right side of the adapter using the rolling up device 30. The rolling up of the left side of the blank is done using the roll-up device 40. The proximal part 42 of the device receives an actuation in an axial translational movement from the cylinder 800. It moves the spring 43 to the right, which makes it possible to raise the edges of the components above the small one. rod of the inner bead 3. When pushing the arm 41, the proximal part 42 pivots around the articulation 46, which allows it to climb the slope of the intermediate part 207 of the segment 200 by pushing the edges of the plies in. rubber which thus pass over the small rod. The proximal part 42 drives the spring 43 in motion, which exerts the necessary pressure on the folded edges of the components in order to ensure their adhesion with those of the central part of the adapter blank and to expel the air. At the end of the roll-up, the cylinder 800 controls the withdrawal movement of the device 40 in the retracted position (as shown in Figure 1).

After returning the two roll-up devices to the retracted position, the central shaft of the drum is actuated in the opposite direction and the drum is returned to the retracted configuration in order to extract the adapter blank 1 from the drum. The green blank thus obtained is then vulcanized in a mold.

Of course, many modifications can be made to the invention without departing from the scope of its claims.

In a variant, one can consider more than two adjacent winding springs of different diameters and, of course, the winding arms of each winding device (right side and / or left side of the drum) can be equipped.

Claims

1. Radially expandable building drum (10) intended for the manufacture of an adapter blank (1) for a tire on a rim, said drum comprising a central shaft of axis X-X 'which is an axis of revolution for a building zone (50) provided with a plurality of segments (100, 200) disposed circumferentially around the central shaft, said segments comprising annular grooves (103, 203) for receiving rods, and comprising rolling up devices (30, 40) rubber components around bead wires each arranged on either side of the building zone (50), being adapted to be moved axially towards each other and away from each other. the other, each roll-up device comprising several adjacent roll-up arms (31, 41) disposed circumferentially on the drum where each roll-up arm has a proximal end (32, 42) capable of turning the components around the rods, characterized in that that the extrem Proximality (32) of each arm of at least one of the roll-up devices (30) comprises at least two adjacent toric coil springs (321, 322), each intended to come into contact with said blank.

2. Drum according to claim 1, characterized in that the rings formed by said springs (321, 322) around the drum have different diameters.

3. Drum according to one of claims 1 or 2, characterized in that the spring (321) located closest axially to the building zone (50) forms a ring having a diameter greater than the ring formed by the spring ( 322) adjacent.

4. Drum according to one of the preceding claims, characterized in that said springs (321, 322) are mounted side by side in a common support.

5. Drum according to one of the preceding claims, characterized in that the spring (321) located closest axially to the building zone (50) projects relative to its support.

6. Drum according to one of the preceding claims, characterized in that the spring (322) the most distant axially from the building zone (50) projects relative to its support.

7. Drum according to one of the preceding claims, characterized in that said springs (321, 322) are tensioned in the retracted position of the drum.

8. Drum according to one of the preceding claims, characterized in that said springs (321, 322) have a tensile stiffness of between 0.1 and 0.5 N / mm.

9. Drum according to one of the preceding claims, characterized in that the diameter DI of the ring formed by the spring (321) is between 350 and 500 mm and in that the diameter D2 of the ring formed by the spring ( 322) is between 350 and 500 mm.

10. Drum according to one of the preceding claims, characterized in that the segments (100) have a proximal part (101) inclined with a downward slope connected to a distal part (102) cylindrical by an intermediate part (107) inclined with an upward slope and in that the spring (321) is adapted to follow the slope of the intermediate part (107) and the spring (322) is adapted to follow the slope of the proximal part (101).

11. Drum according to one of the preceding claims, characterized in that the coil diameters of the springs (321,322) are preferably equal to each other and between 10 and 16 mm.

12. Drum according to one of claims 4 to 11, characterized in that the springs

(321,322) are held in a housing in the proximal end (32) by means of a spacer (330).