WO2024132227A1

WO2024132227A1 - Method and apparatus for providing polymeric annular elements, in particular puncture-resistant elements that can be placed inside a wheel

Info

Publication number: WO2024132227A1
Application number: PCT/EP2023/057031
Authority: WO
Inventors: Gianni Franco Alessio
Original assignee: Alessiohitech S.R.L.
Priority date: 2022-12-20
Filing date: 2023-03-20
Publication date: 2024-06-27

Abstract

The invention relates to a method for providing polymeric annular elements (1, 10, 100), in particular puncture-resistant elements that can be placed inside a wheel (R) provided with an inner tube (C), comprising the initial steps of: introducing corpuscles (91) made of expanded polymeric material into a forming chamber (21); melting the expanded polymeric material inside the forming chamber (21); cooling the material, causing it to resolidify so as to form a longitudinal portion of a semi-finished element (l1). The invention also relates to an apparatus (900) for providing the method.

Description

METHOD AND APPARATUS FOR PROVIDING POLYMERIC ANNULAR ELEMENTS, IN PARTICULAR PUNCTURE-RESISTANT ELEMENTS THAT CAN BE PLACED INSIDE A WHEEL

The present invention relates to a method for providing polymeric annular elements, in particular but not exclusively usable as punctureresistant elements inside a wheel, and to a puncture-resistant element that can be provided with said method.

The products to which the present invention relates in particular are useful and practical, particularly but not exclusively, in the field of cycling and motorcycling. Said products in fact find a specific application as puncture-resistant elements for bicycles and mopeds, in particular for road bicycles with narrow tread and provided with an inner tube. However, the method according to the invention allows the provision of polymeric annular products that can also find application in other fields.

As is known, the wheel of a bicycle, like the wheel of a motorcycle, is formed by a rim which is externally covered by a covering (typically called "tire") whose outer surface (called "tread") comes into contact with the road or, more generally, the ground.

In greater detail, bicycle wheels currently use mainly three types of covering:

- the classic tire, termed "clincher," which protects an inner tube;

- the tubular covering, also known as "Palmer," which combines the outer tire with an inner tube, forming a unit;

- the tubeless covering, which is similar to the "clincher" but is used without an inner tube.

One of the greatest problems in amateur and professional cycling and motorcycling is punctures, which occur due to the effect of external elements (nails, glass, etc.) and due to wear (e.g., caused by the relative sliding of the inner tube with the tire during rolling or during the change of direction of the vehicle). The solutions currently proposed to mitigate the problem of punctures are many, but they are always limited to a specific field of application. Thus, there are "road" and "off-road" coverings, targeted specifically to the type of path, or covers for "road bike" or "mountain bike" (MTB), defined according to the vehicle.

Some solutions provide for the adoption of specific puncture-resistant elements within the covering, either directly incorporated into the tire or replacing the inner tube. These solutions, due to their bulk and mass, are mainly indicated for use with "tubeless" and MTB coverings and are unsuitable for other contexts.

Puncture-resistant elements are also known which consist of bands or laminas that can be placed between the inner tube and the inside curve of the tire. Some of these protective laminas are preformed into a ring and are provided starting from a linear band which is closed in a ring by fixing the two ends by thermal bonding or gluing. The ring is therefore provided with a discontinuity that in the long run can cause damage to the tire and may affect the perfect rolling of the wheel.

Other protective laminas are supplied in an open shape, as actual open tapes supplied in roll form which are cut to size by the user at the time of installation.

The materials predominantly used for this type of puncture-resistant element are thermoplastic resins or special fabrics (such as Kevlar). The mechanical characteristics of these materials are an improvable aspect of this type of element: in particular, the use of these known types of element disadvantageously reduces the overall elasticity of the wheel.

Moreover, a further disadvantage of this type of puncture-resistant elements is the structural noise they produce during motion.

Regarding the method of provision, in the background art the annular elements are provided by producing, generally by extrusion, a linear element which is then closed into a ring by welding or adhesive bonding. Monolithic provision in a mold is usually avoided since this would entail the use of a different specific mold for each size, with obvious problems of cost and versatility.

The aim of the present invention is to provide a method for providing polymeric annular elements, in particular puncture-resistant elements, capable of solving the problems and overcoming the limitations of the background art described above.

Within this aim, an object of the present invention is to provide a method for providing polymeric annular elements that is more versatile than the background art, allowing the simple provision of annular elements of different sizes.

Another object of the invention is to provide a method for providing polymeric annular elements that is simple and economical.

A further object of the invention is to provide puncture-resistant elements that have a more uniform surface.

Another object of the invention is to provide anti-puncture elements that have improved mechanical characteristics.

This aim, as well as the objects mentioned and others that will become better apparent hereinafter, are achieved by a method according to claim 1.

This aim and these and other objects are also achieved by an apparatus according to claim 11 , as well as by an element according to claim 13.

Further characteristics and advantages of the invention will become better apparent from the description of some preferred, but not exclusive, embodiments of the method for providing polymeric annular products, of an apparatus for providing said method, and of an element that can be provided by such a method, illustrated by way of non-limiting example with the aid of the accompanying drawings, wherein:

Figure 1 is a sectional view of a puncture-resistant element, obtainable with the method according to the invention, inserted into a bicycle wheel;

Figures 2 A, 2B, 2C are transverse sectional views of three possible embodiments of an element obtainable with the method according to the invention;

Figures 3, 4 and 5 are sectional views, taken along a plane that is transverse with respect to the extension of the semi-finished element, of a mold during the provision of a sequence of initial steps of the method according to the invention;

Figures 6, 7 and 8 are sectional views, taken along a longitudinal plane, of the same mold as in the preceding figures, during the provision of a sequence of the successive steps of the method according to the invention;

Figures 9, 10, 11, 12, 13 and 14 are views, in sequence, of intermediate and final steps which follow the steps of the preceding figures, of a possible form of embodiment of the method according to the invention, provided in a unit provided with two molds;

Figure 15 is a view of a first possible arrangement of the guiding elements of a unit for the provision of the method according to the invention;

Figure 16 is a view of a second possible arrangement of the guiding elements of a unit for the provision of the method according to the invention;

Figures 17 A, 17B and 17C are views of three different possible cuts of the ends of the semi-finished element;

Figure 18 is a perspective view of an annular puncture-resistant element provided by means of the method according to the invention.

With reference to the figures, the method according to the invention is used for providing polymeric annular elements 1, 10, 100, in particular but not exclusively puncture-resistant elements that can be placed inside a wheel R equipped with an inner tube C, said elements 1, 10, 100 being suitable to be placed between the inner tube C and the tire B as shown in Figure 1. An example of annular element 1 obtainable with the method is shown in full in Figure 18; Figures 2A, 2B and 2C show three possible variations of the cross-section.

According to the invention, the method comprises a series of initial steps (shown in Figures 3 to 5) designed to obtain a semi-finished element 1' made of expanded polymeric material which is extended longitudinally, and more precisely an initial portion of a semi-finished element 1' designed to be then elongated in subsequent steps.

In the preferred embodiments of the method, the semi-finished element 1' is in practice a strip of expanded polymeric material whose cross- sectional shape can be any as needed, such as for example one of the crosssections shown in Figures 2A, 2B and 2C, which show respectively a polymeric annular element 10 having a rectangular cross-section, a polymeric annular element 1 having a pseudo-elliptical cross-section (i.e., the cross-section of an ellipse deprived of two opposite ends along the major axis), and a polymeric annular element 100 having a concave crosssection (with a concavity).

These initial steps comprise a first initial step (shown in Figure 3) which consists in introducing corpuscles 91 of expanded polymeric material into an (inner) forming chamber 21 of a mold 20.

The term "corpuscle" here refers to any piece of material in solid form having dimensions and volume smaller than the semi-finished element 1' to be obtained. Preferably, these corpuscles 91 consist of beads or balls.

Preferably, the polymeric material is an elastomer and even more preferably a polyurethane elastomer, and therefore in the preferred embodiments the corpuscles 91 consist of expanded polyurethane elastomer beads or balls. According to an optimal solution, the expanded polymer corpuscles 91 are provided by physical foaming.

Following the introduction of such material in the form of corpuscles 91, the material is melted inside the forming chamber 21.

Subsequently, the melted material is cooled, causing it to resolidify so as to form a longitudinal portion of semi-finished element f inside the forming chamber 21 of the mold 20, as shown in Figure 4.

Following these initial steps, the method provides for cyclically repeating, one or more times, a series of intermediate steps aimed at elongating the semi-finished element 1' until a semi-finished element 1' of predetermined length is obtained which can then be closed to create the annular element 1. An example of embodiment of these intermediate steps is shown in Figures 5 to 11.

In greater detail, these intermediate steps comprise a first step which consists in moving the longitudinal portion of semi-finished element 1' that has just been formed and/or at least part of the mold 20 so as to clear at least part of the forming chamber 21 and arrange said longitudinal portion of semi-finished element 1' in a position in which it has a front end 11 outside the forming chamber 21 and a rear end 12 inside said forming chamber 21. This position can be clearly seen, for example, in Figure 9, where it can be noted that the rear end 12 remains inside the forming chamber 21, which has free space ready to accommodate additional corpuscles 91 to be melted to increase the length of the semi-finished element 1'.

Advantageously, in order to make the execution of these steps simple and efficient, the forming chamber 21 is partially open, in the preferred and illustrated embodiment the forming chamber is provided with a lateral opening 79 through which the semi-finished element 1' can extend from inside the forming chamber 21 to the outside thereof. Even in the case, which will be described later, in which a same chamber acts as both a forming chamber 21 and a closure chamber, said chamber is provided with at least one lateral opening 79 and possibly two opposite openings (in a manner similar to the closure chamber 31 shown, which will be described hereinafter). The movement of the longitudinal portion of semi-finished element T can be provided, merely by way of example, by virtue of the action of one of the half-shells 23, 24 of the mold (for example the upper one 23), which moves pushing the semi-finished element T, as shown in Figure 8, and then returns to its initial position, or other movement means can be used.

Following this movement, additional corpuscles 91 of the same expanded polymeric material are introduced in the same forming chamber 21, as shown in Figure 6.

The newly introduced expanded polymeric material is then melted (together with the material that forms the rear end 12 of the longitudinal portion of semi-finished element 1') inside the forming chamber 21 and then cooled, causing it to solidify again, so as to increase the length of the longitudinal portion of semi-finished element 1' by forming a new rear end 12 inside the forming chamber 21, as shown in Figure 7 (it should be noted that the longitudinal portion of semi-finished element 1' thus lengthened keeps intact the front end 11 arranged outside the forming chamber 21).

At this point, the longitudinal portion of semi-finished element 1' thus elongated and/or at least part of the mold 20 is moved, so as to clear at least part of the forming chamber 21 and arrange the longitudinal portion with the front end 11 outside the forming chamber 21 and the new rear end 12 inside the forming chamber 21. New corpuscles 91 can then be introduced in the forming chamber 21 and are melted and cooled, together with the rear end 12, inside the forming chamber 21 to further elongate the longitudinal portion of semi-finished element 1', and so on: the intermediate steps just described are repeated cyclically, as shown in Figures 6 to 10, until the longitudinal portion of semi-finished element 1' reaches the desired length, and at this point said portion can be considered a final semi-finished element 1' ready to be closed.

During or after (preferably during) the execution of the intermediate steps just described, the longitudinal portion of semi-finished element 1' (or the portion thereof formed in the meantime) is guided along a curved annular path having a predetermined radius of curvature rl that corresponds to the radius of the annular element 1 that is to be obtained. Preferably, said curved annular path is defined by a series of guiding rollers 7 or other guiding means suitable for the purpose.

Once the intermediate steps have ended, the method comprises a series of final steps aimed at closing the semi-finished element 1' in a ring; an example of these steps is shown in Figures 12 to 14.

The first of the final steps consists of placing both ends, the front one 11 and the rear one 12, of the semi-finished element 1' inside a same closure chamber 31 of a mold 30. Said closure chamber can be the same forming chamber 21 of the same mold used for the intermediate steps or, as in the example shown, a different chamber 31 belonging to a different mold 30.

In the first case (not shown), the same chamber serves as both forming chamber and closure chamber, preferably extends longitudinally along an arc (preferably having a radius of curvature equal to the predetermined radius of curvature rl of the annular element 1 to be obtained) and is, for example, shaped like the closure chamber 31 shown. Thus, in this first case, the semi-finished element T is formed directly in a curvilinear manner.

In the second case, in which the two chambers 21, 31 are different and separate chambers and are each comprised in a respective mold 20, 30, preferably the closure chamber 31 is extended longitudinally along an arc (having a radius of curvature equal to the above cited predetermined radius of curvature rl), while the forming chamber 21 can extend longitudinally along a straight axis, as in the example shown.

After placing the rear end 12 and the front end 11 in the closure chamber 31, the method provides for melting, inside said closure chamber 31, the polymeric material that constitutes said ends 11, 12 and then cooling it, again inside the closure chamber 31, so as to join in practice the two ends, forming a continuous annular element 1 of expanded polymeric material.

In this way, an annular element 1 is obtained which has no joining elements or discontinuities, by virtue of the fact that the closure (or joining) of the annular element 1 occurs by means of the same forming process as the semi-finished element 1'.

Optionally, before melting the material that constitutes the two ends 11, 12, additional corpuscles 91 of expanded polymeric material are introduced into the closure chamber 31 in which the two ends 11, 12 are present, as shown in Figure 12.

Optionally, after the intermediate steps and before the final steps, the semi-finished element 1' obtained with the intermediate steps is cut by means of a cutting tool 41, as shown in Figure 11; more precisely, this operation consists in cutting a portion of semi-finished element 1' that lies outside the internal chamber 21 so as to obtain a final semi-finished element 1' of predetermined length.

More in detail, the cutting tool 41 can be configured to cut one or both ends 11, 12 of the semi-finished element 1' with cuts of any shape chosen according to the requirements; preferably, both ends 11, 12 are cut with complementary cuts designed to form a joint (i.e., by shaping the two ends 11, 12 so that they can join by shape mating) before being melted in the closure chamber 31, for example, with cuts such as those shown in Figures 17A, 17B and 17C: curvilinear cuts (Figure 17A), dovetail cuts (Figure 17B), linear cuts (Figure 17C), straight cuts (Figure 17C).

Advantageously, while the final steps are performed, the semifinished element 1' is kept in an annular shape by means of the rollers or other guiding means 7.

With reference to some optimal constructive details, in the embodiments in which the forming chamber 21 and the closing chamber 31 are separated into two different molds 20, 30, the forming chamber 21 is extended along a horizontal longitudinal axis and the guiding rollers 7 have a horizontal axis X, being arranged along a circumference that lies on a vertical plane, as shown in Figure 15. Preferably, in these embodiments there is also a pair of conveyance rollers 71 , an upper one and a lower one, configured to convey the semi-finished element 1' from the first mold 20 (containing the forming chamber 21) toward the second mold 30 (containing the closure chamber 31).

Optionally, a support and conveyance plane 72, substantially aligned with the forming chamber 21 (and aligned with the lateral opening 79 thereof), is also provided in order to support and guide the semi-finished element 1' exiting the first mold 20 in the direction of the second mold 30.

According to a particular embodiment, the curved annular path along which the semi-finished element 1' is guided passes through the second mold 30, so that the semi-finished element 1' is guided to pass through the closure chamber 31, while it is kept open, during the intermediate steps or in any case before the final steps, as shown in Figures 10 and 11.

In the embodiments in which the same chamber acts as forming chamber and closure chamber, the guiding rollers 7 preferably have a vertical axis and are arranged along a circumference lying on a horizontal plane, as shown in Figure 16. In this case, the forming and closure chamber extends along an arc that is part of this horizontal circumference. Also in this case, according to an optional and advantageous characteristic, there is also a second series of rollers 77 having a horizontal axis, or a supporting surface, whose function is to support the semi-finished element 1' from below.

The forming chamber 21 and the closure chamber 31 can have any transverse cross-section depending on the annular element 1, 10, 100 to be obtained, for example a rectangular or pseudo-elliptical or concave transverse cross-section. Conveniently, when the forming chamber 21 and the closure chamber 31 are distinct, they have a transverse cross-section of the same shape.

Preferably, the corpuscles 91 are inserted into the forming chamber 21, and optionally into the closure chamber 31 when required, with the mold 20, 30 in an at least partially open condition and then, before being melted, the mold 20, 30 is closed so as to put the corpuscles 91 under pressure in the chamber 21, 31.

In the preferred embodiments, the polymeric material is melted inside the forming chamber 21 and in the closure chamber 31 by means of a heat transfer fluid, preferably a vapor, even more preferably steam.

According to an optional and advantageous embodiment, in order to allow optimal melting of the material directly in the molding chamber 21 and in the closure chamber 31, the mold or molds 20, 30 is/are provided with steam passage holes 27, for the passage of the steam inside the chamber 21, 31. In order to obtain an optimum result, the dimensions, number and spatial density of said steam passage holes 27 are such as to ensure a passage area of at least 1 square millimeter over a molding area of 10 square millimeters.

In the preferred embodiments, including the embodiment shown, each mold 30, 20 comprises at least one and preferably two steam accumulation chambers 28A, 28B, 38A, 38B, and the steam passage holes 27 are configured to allow steam to pass from at least one steam accumulation chamber 28A, 28B, 38A, 38B to the forming chamber 21 and/or closure chamber 31.

Appropriately, the molds 30, 20 are provided with a steam inlet passage 51 and one steam exit passage 52 for each steam accumulation chamber 28 A, 28B, 38 A, 38B.

With reference now in greater detail to the preferred characteristics of the molds 20, 30, they each comprise a pair of half-shells 23, 24, 33, 34 that define between them the forming chamber 21 (in the first mold 20) or the forming and closure chamber (when the mold is single for both functions) and the closure chamber 31 (in the second mold 30 when present). The steam passage holes 27 are preferably provided in said half-shells 23, 24, 33, 34.

Each half-shell 23, 24, 33, 34 can be supported by a respective mold supporting surface 25, 26, 35, 36. In this case, the steam accumulation chambers 28 A, 28B, 38 A, 38B are preferably formed between each halfshell 23, 24, 33, 34 and the respective mold supporting surface 25, 26, 35, 36, as in the embodiment shown.

Conveniently, each mold 20, 30 comprises a material injection channel 29, 39 for introducing the corpuscles 91 in the forming chamber 21 and/or closure chamber 31. Advantageously, said material injection channel 29, 39 is adapted to be functionally associated with a flow control element configured to close it; for example, in the embodiment shown, the injection channel 29, 39 is provided with an enlarged inlet adapted to be closed by a flow control element.

In the preferred embodiments, including the one shown, the material injection channel 29, 39 passes through one of the two half-shells 24, 34.

In the preferred embodiments, the polymeric material, after melting, is cooled inside the internal chamber 21 and the closure chamber 31 by means of a cooling fluid, preferably liquid, even more preferably water (for example cold waterjets).

With reference now in more detail to the expanded polymeric material used (which constitutes the corpuscles 91 and then the annular element 1, 10, 100), it is preferably an expanded polymer of the type known as "ETPU" (Expanded Thermoplastic Polyurethane Elastomer), i.e., a hybrid material of thermoplastic polyurethane elastomer containing air and advantageously free from toxic ingredients.

In even greater detail, preferably a material with a melting range of 125 °C to 230 °C is chosen. Preferably, a material having a density between 0.08 and 0.3 g/cm³ is chosen. A further advantageous property of the material thus chosen is that it is capable of immediately returning 2/3 of the energy absorbed in deformation, behaving like an elastic spring. The main physical and mechanical characteristics of the expanded polymeric material that has been found to be optimal for the provision of the method are shown in the following table.

The present invention also relates to an apparatus 900 for the provision of the method, which has already been described in detail. The apparatus 900, in its main elements, comprises at least one first mold 20 which comprises inside it a forming chamber 21 and is provided with an injection channel 29 for introducing corpuscles 91 of polymeric material into the forming chamber 21. As already explained, in some embodiments the apparatus 900 also comprises a second mold 30 comprising the closure chamber 31; as an alternative, the forming chamber 21 is configured to also act as a closure chamber, being adapted also to accommodate two ends of a semi-finished element T to join them following melting and resolidification.

As already explained in detail, the apparatus 900 also comprises heating means to induce melting of the polymeric material within the forming chamber 21 and the closure chamber 31, if any, such as for example a system for steam injection via the steam passage holes 27.

As already explained in detail, the apparatus 900 also comprises cooling means for inducing resolidification of the polymeric material in the forming chamber 21 and in the closure chamber 31, if any, such as a cooling liquid feeding system.

As already explained in detail, the apparatus 900 also comprises movement means configured to move the semi-finished element 1' with respect to the forming chamber 21, or vice versa, at least to position it in a processing position in which it is partially outside and partially inside the forming chamber 21.

As already explained in detail, the apparatus 900 also comprises a series of guiding elements (for example rollers) 7 for the semi-finished element 1' which define a closed annular path.

The present invention also relates to a puncture-resistant element 1, 10, 100 for wheels obtainable with the described method. Such a punctureresistant element 1, 10, 100 is shaped so that it can be arranged inside a wheel R between an inner tube C and a tire B, as in Figure 1. The punctureresistant element 1, 10, 100 comprises, and preferably consists of, a single continuous annular body of expanded polymeric material of the type previously described.

The puncture-resistant element 1 shown in Figure 18 has an outer surface 16 adapted to face the tire B, in contact with it, and an inner surface 15 adapted to face the inner tube C. The inner surface 15 is accessible through an internal circumferential slot 18.

The cross-section of the puncture-resistant element 1, 10, 100 (meant as the transverse cross-section of the strip of material when it spread on a plane) can be chosen as required: a cross-section with constant thickness (such as the rectangular one of Figure 2 A) offers a uniform protective barrier to the inner tube C; a section with a greater thickness in the middle region (such as the pseudo-elliptical one of Figure 2B) better protects the central region of the inner tube and protects less the shoulders of the tire B; a concave cross-section (such as the one of Figure 2C) adapts better to the shape of the inner tube C.

Fitting inside the tire B is achieved by simply resting on the inside curve surface of the covering and does not require adhesive bonding systems.

The puncture-resistant element 1 thus provided is particularly suitable, by virtue of its limited weight and the mechanical characteristics of the material of which it is made, for use as a puncture-resistant band for road bicycles with particular reference to the racing bike category.

Its insertion in the wheel covering allows a reduction by about 20% (from 8 atm to 6.5 atm) in the inflation pressure of the inner tube, consequently reducing the stress state of the latter and further contributing to its durability.

The elasticity of the material and the particular surface quality obtained from the process for providing the puncture-resistant element 1 improve the adhesion of the inner tube C to the tire B. Advantageously, the puncture-resistant element 1 is able to either reduce the structural noise of motion by virtue of the material's acoustic insulation and damping ability.

Moreover, the puncture-resistant element 1 thus provided is able to improve the elasticity of the wheel in case of deformation, since it is able to return 2/3 of the energy absorbed in deformation.

In general, all the polymeric annular elements provided by means of the method according to the invention are recyclable and do not deteriorate in water.

Advantageously, the apparatus 900 and the method are able to provide a closed ring made of polymeric material without adhesive joining bonding by means of other materials (for example glues) and without variations in the surface and technical characteristics in the region of the joint.

In practice it has been found that the method and the apparatus according to the present invention achieve the intended aim and objects, since they are more versatile than the background art and allow the simple provision of annular elements of different sizes.

Another advantage of the method and of the apparatus according to the invention resides in that they are simple and inexpensive to provide.

A further advantage of the method and of the apparatus according to the invention resides in that they allow the providing of puncture-resistant elements with improved mechanical characteristics.

The method, apparatus and element thus conceived are susceptible to numerous modifications and variations, all of which are within the scope of the appended claims.

All the details may furthermore be replaced with other technically equivalent elements.

In practice, the materials used, as well as the contingent shapes and dimensions, may be any according to the requirements and the state of the art.

The disclosures in Italian Patent Application No. 102022000026028 from which this application claims priority are incorporated herein by reference.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

1. A method for providing polymeric annular elements (1, 10, 100), in particular puncture-resistant elements that can be placed inside a wheel (R) provided with an inner tube (C), comprising the initial steps of: al. introducing corpuscles (91) made of expanded polymeric material into a forming chamber (21) of a mold (20); a2. melting said expanded polymeric material inside said forming chamber (21); a3. cooling said material, causing it to resolidify so as to form a longitudinal portion of a semi-finished element (T) within the forming chamber (21) of the mold (20); wherein, after said initial steps, the following intermediate steps are repeated cyclically one or more times until a semi-finished element (T) of predetermined length is obtained: bl. moving said longitudinal portion of semi-finished element (T) and/or at least part of said mold (20) so as to clear at least part of the forming chamber (21) and position said longitudinal portion of semifinished element (T) with a front end (11) outside the forming chamber (21) and a rear end (12) inside the forming chamber (21); b2. introducing additional corpuscles (91) of said expanded polymeric material into the forming chamber (21); b3. melting said expanded polymeric material inside said forming chamber (21); b4. cooling said material, causing it to resolidify so as to elongate said longitudinal portion of semi-finished element (1'), forming a new rear end (12) within the forming chamber (21); b5. moving said longitudinal portion of semi-finished element (T) and/or at least part of said mold (20) so as to clear at least part of the forming chamber (21) and position said longitudinal portion with the front end (11) outside the forming chamber (21) and said new rear end (12) inside the forming chamber (21); during or after said intermediate steps, said semi-finished element (T) being directed along a curved annular path; after said intermediate steps, the method comprising the final steps of: cl. placing the front end (11) and the rear end (12) of the semifinished element (T) within a same closure chamber (31) of a mold (30); c2. melting the polymeric material that constitutes said rear end (12) and front end (11) inside said closure chamber (31); c3. cooling said polymeric material inside said closure chamber (31), forming a continuous annular element (1, 10, 100) made of expanded polymeric material.

2. The method according to claim 1, wherein said expanded polymeric material is a thermoplastic polyurethane elastomer.

3. The method according to claim 1 or 2, wherein said expanded polymeric material has a density comprised between 0.08 and 0.3 g/cm³.

4. The method according to one or more of the preceding claims, wherein said final steps also comprise the step of:

- introducing additional corpuscles (91) of said expanded polymeric material into the closure chamber (31) before melting the material.

5. The method according to one or more of the preceding claims, characterized in that it comprises, after the intermediate steps and before the final steps, the step of:

- cutting a portion of semi-finished element (T) that is outside the internal chamber (21) so as to obtain a final semi-finished element (T) of predetermined length.

6. The method according to one or more of the preceding claims, wherein the polymeric material is melted inside the forming chamber (21) by the action of a heat transfer fluid, preferably steam.

7. The method according to claim 6, wherein the polymeric material is cooled within the forming chamber (21) by means of a cooling fluid, preferably water.

8. The method according to one or more of the preceding claims, wherein said curved annular path is defined by a series of guiding rollers (7).

9. The method according to one or more of the preceding claims, wherein said forming chamber and said closure chamber are the same chamber, which extends longitudinally along an arc.

10. The method according to one or more of the preceding claims, wherein said forming chamber (21) and said closure chamber (31) are two separate chambers, each comprised in a respective mold (20, 30); said closure chamber (31) extending longitudinally along an arc; said forming chamber (21) extending longitudinally along a rectilinear axis.

11. An apparatus (900) for providing a method according to one or more of the preceding claims, comprising:

- at least one first mold (20) comprising internally a forming chamber (21) and being provided with a channel (29) for injection and for the introduction of corpuscles (91) of polymeric material into said forming chamber (21);

- heating means to induce the melting of the polymeric material within the forming chamber (21);

- cooling means to induce the resolidification of the polymeric material in the forming chamber (21) so as to form a semi-finished element (r);

- movement means configured to move the semi-finished element (T) with respect to the forming chamber (21), or vice versa, at least to position said semi-finished element (T) in a processing position in which it is partially outside and partially inside the forming chamber (21);

- a set of guiding elements (7) for the semi-finished element (T) which define an annular path; wherein: a. said apparatus (900) comprises a second mold (30) comprising a closure chamber (31) adapted to accommodate two ends (11, 12) of a semifinished element (T) to join them following melting and resolidification, said second mold (30) being provided with heating means to induce the melting of the polymeric material within the closure chamber (31) and cooling means to induce resolidification of the polymeric material in the closure chamber (31), or b. said forming chamber (21) is configured to also act as a closure chamber, being also adapted to accommodate two ends of a semi-finished element (T) to join them following melting and resolidification.

12. The apparatus (900) according to claim 11, wherein said at least one mold (20, 30) comprises steam passage holes (27) for the passage of steam within the forming chamber (21).

13. A puncture-resistant element (1, 10, 100) for wheels, shaped to be arrangeable within a wheel (R) between an inner tube (C) and a tire (B), comprising a single continuous annular body made of expanded polymeric material comprising a thermoplastic polyurethane elastomer.

14. The puncture-resistant element according to claim 13, wherein said expanded polymeric material has a density comprised between 0.08 and 0.3 g/cm³.

15. The puncture-resistant element according to claim 13 or 14, wherein said continuous annular body has a transverse cross-section having a rectangular or pseudo-elliptical or concave shape.