Abstract:
A method for producing a bicycle wheel rim having an inner peripheral wall, an outer peripheral wall, two lateral walls joining said peripheral walls, and two circumferential wings, for anchoring a tire, is provided. The method providing a rim made of a single part made of structural fiber based material, preferably carbon fiber material.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to bicycle wheel rims of the type presenting a peripheral inner wall, a peripheral outer wall, two lateral walls joining said peripheral walls and two circumferential wings for anchoring a tyre which radially extend outwards from the two sides of the outer peripheral wall. 
     This invention also relates to a method for producing a rim of the type described above. 
     The Applicant has recently conducted various studies and tests to make bicycle wheel rims using structural fibre based material, typically carbon fibre based material. The advantage offered by this type of material is that of being light in weight with respect to the metallic materials used in the past given equal structural characteristics. Making a rim out of a single part of carbon fibre based material was difficult, at least utilising the technologies available at that time, due to the typical conformation of the circumferential anchoring wings of the tyre. Typically, these wings present peripheral outer edges folded one towards the other thus creating an undercut, which causes the moulding problems. 
     SUMMARY OF THE INVENTION 
     The object of this invention is to overcome this technical problem. 
     In order to attain this object, this invention relates to a rim for a bicycle wheel, comprising an inner peripheral wall, an outer peripheral wall, two lateral walls joining said peripheral walls, and two circumferential wings for anchoring a tyre which radially extend outwards from the two sides of the outer peripheral wall, wherein said rim is made of a single part of structural fibre based material incorporating the two circumferential wings. 
     This invention relates also to a method for producing a bicycle wheel rim of the type presenting an inner peripheral wall, an outer peripheral wall, two lateral walls joining said peripheral walls , and two circumferential wings, for anchoring a tyre, which extend outwards from the two sides of the outer peripheral wall, 
     wherein it comprises the following steps: 
     applying on the inner part of a mould a predetermined number of layers of structural fibre fabric incorporated in a plastic material matrix which are to form the inner wall, the outer wall, the two lateral walls and the wings; 
     arranging an inflatable bag on the layers; 
     folding a first predetermined number of the layers on the inflatable bag; 
     applying at least one core over the folded first predetermined number of layers; 
     folding a second predetermined number of the layers over the core; 
     applying the outer part of the mould so as to enclose the layers; 
     inflating the inflatable bag so as to press the layers against the mould; 
     increasing the temperature of the mould to a value sufficient to cause reticulation of the plastic material matrix; 
     removing the bicycle wheel rim from the mould and removing the core, so as to obtain a bicycle wheel rim formed of a single piece of structural fibre material. 
     The cores are made of a material with a thermal dilation coefficient exceeding 5×10 −5  mm/° C., the moulding process comprising an increase in temperature to a value sufficient to cause the material of said cores to dilate so as to press the layers of fabric forming the tyre anchoring wings against the wall of the mould. 
     Preferably, the material forming the cores has a thermal dilation coefficient exceeding 9×10 −5  mm/° C. and a maximum continuous thermal resistance temperature exceeding 100° C. 
     Again preferably, the material forming the core can be either PTFE (polytetrafluoroethene), or FEP (fluorinated ethene propene), or PCTFE (polychlorotrifluoroethene), or PVDF (polyfluorodivinylidene), or PE-HD (high density polyethylene). 
     The use of PTFE is widely preferred, due to the anti-adherence properties of this material, which are useful for detaching the core, or cores, from the structural fibre moulded body, as well as its high continuous thermal resistance (260° C.), for its good thermal conductivity (0.25W/m° C.) and for its good thermal capacity (specific heat), equal to 1.045 Kj/kg° C. 
     This material presents the characteristic of being subject to high thermal dilation at relatively low temperatures, in the order of temperatures at which the plastic material in which the structural fibre fabric is incorporated reticulates. 
     Structural fibre fabrics incorporated in a plastic material matrix are known and have been used for some time. They are made with yarn obtained from structural fibres, such as carbon fibres, for example. These fabrics are then subjected to an impregnation method to associate them with a plastic material matrix, typically a thermosetting plastic material. 
     According to an additional preferred embodiment of this invention, two ring-shaped cores of said thermally dilating material are used, each split into several sectors if required, which are arranged so as to be spaced from each other around the layers which are to form the peripheral external wall of the rim, each core supporting one of the two tyre anchoring wings. 
     In a first embodiment, the space comprised between said two rings is filled by one wall of the mould. In a second form of embodiment, this space is filled by a third core, which is also a ring formed by several sectors, made of thermally dilating material. The cores being split into several sectors allows easy removal of said cores from the part obtained at the end of the moulding process, after opening the mould, despite the undercut conformation of the two tyre anchoring wings. In a third embodiment, the core is a silicone sheath made in a single continuous piece or in sectors centered by a projection of the outer mould. 
     As shown above, the application of the required pressure inside the mould on the layers destined to form the outer and inner peripheral walls of the rim, as well as the two lateral walls of the rim, is obtained by arranging an inflatable bag in the cavity between these layers. The bag can remain inside the part after the end of the moulding process. This technique was previously tested by the Applicant for making rims of the type above without tyre anchoring wings. This technique cannot be used in a similar fashion for making said anchoring wings in rims of the type comprising said wings. For this reason, the Applicant has additionally developed studies to create this invention. 
     According to an additional preferred characteristic of this invention, the rim can initially be moulded with anchoring wings which are longer than required. In this case, after the moulding process, mechanical machining is carried out to reduce the wings to the required dimensions. This method also has the advantage of preventing superficial defects, which may be present on the circumferential edges of the two wings at the end of the moulding process. This method is an invention in its own right, regardless of the type of moulding process used. 
     Further features of the method of the invention are indicated in the claims. 
     The invention is also directed to the apparatus for carrying out the above described method as well as to the bicycle wheel rim per se. The features of the apparatus and the rim of the invention are also set forth in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This invention will be better explained by the following detailed descriptions with reference to the accompanying figures as non-limiting examples, whereas: 
     FIGS. 1,  2  and  3  illustrate three different phases of a moulding method of a bicycle rim according to this invention, 
     FIGS. 4,  5  illustrate two different phases of the method according to this invention, with the use of a modified mould with respect to the one shown in FIGS. 1-3, 
     FIG. 6 illustrates the end product, which can be obtained either with the mould in FIGS. 1-3 or with the mould of FIGS. 4,  5 , after final mechanical machining required to reduce the tyre anchoring wings to the required dimensions, 
     FIG. 7 illustrates a perspective exploded view of a phase of the method, 
     FIG. 8 is a variant of FIG. 5, and 
     FIGS. 9,  10  show two further variants. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to FIG. 6, the method according to this invention is used to make a rim  1  for a bicycle wheel, which cross section is shown in the figure. The rim comprises an outer peripheral wall  2 , an inner peripheral wall  3 , two lateral walls  4 ,  5 , joining the peripheral walls  2 ,  3  and defining a closed circumferential cavity  50  with the peripheral walls  2 ,  3 , and two circumferential wings  6  for anchoring a tyre, which extend radially outwards towards the sides of the outer peripheral wall  2 . As mentioned above, the rim  1  made with the method according to this invention presents a body made of a single part made of structural fibre based material, preferably carbon fibre material. A plastic material bag  7  is arranged inside the cavity  50 , for the reasons illustrated below. 
     FIGS. 1-3 show three subsequent phases of the method according to this invention, with the use of a first type of mould. In this case, the mould used for moulding the rim comprises two inner elements  8  and an outer element  9 . The inner elements  8  are circumferential elements which overlap on a plane  8   a . They define a circumferential surface  11  destined to delimit, as shown in FIG. 3, the outer surface of the inner peripheral wall and the two sides of the rim. In order to form the rim, a number of layers  12  of the structural fibre based fabric, for example carbon fibre fabric, incorporated in a plastic material matrix, are arranged on the surface  11 , but the structural fibres can be selected among carbon fibres, glass fibres, aramidic fibres, boron fibres, ceramic fibres or any combinations thereof. The arranged layers  12  are destined to assume the conformation shown in FIG.  1 . Firstly, the layers  12  are arranged on the surface  11  so to present sections  12  radially extending outwards from the mould elements  8 , which are arranged in the position illustrated with the dotted line. An inflatable bag made of plastic material  13  is then arranged on the layers. The bag is equipped with an inflating valve (not shown), which communicates externally to the mould by means of a passage (not shown in the figures). The purpose of the inflatable bag  13  is to press the layers of fabric  12  against the walls of the mould during the moulding process while the mould is closed. Again with reference to FIG. 1, after positioning the plastic material bag  13 , a certain number  12   a  of the projecting sections of the layers of fabric  12  are partially folded back, over the bag  13  and another number  12   b  is left free to form edges destined to make the circumferential tyre anchoring wings  6 . Naturally, additional layers C can be applied on the layers  12  positioned over the bag  13 , to achieve any required thickness of the external peripheral wall  2  of the rim, and/or of wings  6 . Further, additional layers D can also be applied to fill the side regions of the outer wall of the rim. 
     Again with reference to FIG.  1  and also to FIG. 7, two cores  14 , each made of a ring which may be split into several sections (for example into three sections)  15 , to facilitate the subsequent extraction of the cores  14  from the mould, are arranged over the layers  12  destined to form the outer peripheral wall  2  of the rim. The two rings  15  are arranged over the layers  12 , destined to form the wall  2 , in a reciprocally distanced position, so to allow folding one of the edges  12   b  on it in order to make the tyre anchoring wings  6  (see FIG.  2 ). In the form of embodiment shown in FIGS. 1-3, the space between the two rings  14  is filled by a circumferential ribbing  16  of the outer element  9  of the mould, as shown in FIGS. 2,  3  (the latter figure shows the mould in the closed condition with the bag inflated). 
     As extensively described above, the material forming the cores  14  is a material presenting a relatively high thermal dilation coefficient, such as PTFE, for example. The mould is thus closed with the layers  12  arranged inside, placed in an oven and subjected to a heating and cooling cycle so to cause the reticulation of the plastic material matrix in which the carbon fibre fabrics are incorporated, on one hand, and the thermal dilation of the cores  14 , on the other hand, to press the layers of fabric  12   b  against the walls of the mould. The pressure required to make the outer and inner peripheral walls and the sides of the rim is ensured by letting pressurised air into the inflatable bag  13 . The temperature to which the mould must be taken in order to complete the process is preferably comprised in the range from 80° C. to 200° C. The mould is preferably maintained at a temperature in this range for a time comprised in the range from 10 minutes to three hours, preferably from 30 minutes to three hours. 
     After the moulding process, a cooling phase follows, then the mould is opened and the cores  14  are removed. 
     It is important to note that any number, conformation and arrangement of cores used for moulding the wings  6  can be used, also entirely different from the cores illustrated in the drawings provided as non-limiting examples. The case of a single core made of deformable material may also be envisaged to allow extraction from the mould (FIG.  8 ). FIG. 9 shows a further variant in which a single core  14  is provided in form of a silicone sheath made in a single continuous piece or in sectors. This sheath is deformable and kept in a centered position by a projection  140  of the outer mould. At the end of the process the silicone sheath is extracted with the aid of pliers 
     According to an additional important characteristic of the invention, the edges  12   b  of the layers destined to form the wings  6  are arranged to form a length exceeding the required dimensions. Consequently, at the end of the moulding process, the parts are mechanically machined to reduce the wings  6  to the required length and/or shape. The method also has the advantage of eliminating any surface defects which may be present on the ends of the edges  12   b  at the end of the moulding process in the mould. This characteristic can be used regardless of the moulding process used, and is consequently an invention in its own right. 
     FIGS. 4,  5  illustrate a second type of mould in the open condition and in the closed condition. In this case, the space comprised between the two ring-shaped cores  14  is occupied by a third ring-shaped core  17 , also made of high thermal dilating material, for example PTFE. 
     Finally, FIG. 10 shows the case of a rim with asymmetrical cross-section obtained according to the principles of the present invention. In this case the layers of fibre fabric material include first layers A extending so as to contribute to define the inner wall, the side walls and the two wings of the rim, second layers B arranged so as to contribute to define the inner, side and outer walls of the rim, third layers C arranged to define the outer wall and the two wings of the rim, and fourth layers D wound to fill the side regions of the outer wall of the rim from which the wings depart. 
     Naturally, numerous changes can be implemented to the construction and forms of embodiment of the invention herein envisaged, all comprised within the context of the concept characterising this invention, as defined by the following claims.