EP4214376B1

EP4214376B1 - Coating cover for roofs of civil or industrial buildings

Info

Publication number: EP4214376B1
Application number: EP21785996.6A
Authority: EP
Inventors: Mauro Menegoli
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-09-18
Filing date: 2021-09-16
Publication date: 2024-04-17
Anticipated expiration: 2041-09-16
Also published as: WO2022058923A1; EP4214376A1

Description

FIELD OF APPLICATION

The present invention relates to a high-performance metal cover for roofs of civil or industrial buildings.
In particular, the metal coating cover according to the invention utilises a plurality of metal slabs adjacent to one another and connected by the special profiling of the lateral edges thereof.
Such edges are fixed on the underlying structure with the use of particular brackets and the system thus made forms a continuous cover that is easy and rapid to install, long-lasting, very resistant to wind and adequate for the protection of the underlying building.
The present invention is advantageously applied in the sector of covers for roofs of buildings in general and panel covers in particular with a metal structure.

PRIOR ART

The use in the civil or industrial construction sector of various types of covers for buildings is known, which in some cases, as in industrial buildings, establishments, airports or the like, are constituted by adjacent panels or slabs.
The cover of roofs with large-surface elements, being panels or slabs, is usual for large surfaces, such as industrial sheds, or production facilities, or large infrastructures, offering greater implementation velocity and low cost thereof.
The panels and slabs for coverings of buildings are prefabricated elements having large surfaces and supplied directly to the worksite, ready to mount and equipped with all the components and accessories for realising the complete cover.
Such panels are made of various metals, aluminium, copper, zinc, steel or the like, or of plastic materials, ABS, Polycarbonate, PVC, or the like.
The slabs that make them up can have various dimensions, both in length (from less than one metre up to hundreds of metres) and in width, which is usually not greater than a metre, both for static reasons and for the limitation in width of the starting laminated strip that is known as a coil.
It is also known in this sector that the lateral edges of the covering panels or slabs can be connected to enable joining thereof in very many ways, from a simple superposing of the edges to very complex geometries with drainage channels in the joint, up to fixing surfaces to the sub-structure, utilising geometries adapted to special fixing systems.
In this case, where geometries adapted to special fixing systems are used, the fixing brackets can be made of metal or plastic materials, can avoid the need for piercing of the slabs, and can allow for dilation of the slabs in the lengthwise direction.
Further, the choice of geometry of the slab and the metal in production determines the frequency of the fixings in the lengthwise direction and the mechanical performance at concentrated positive load, for example so as to support foot traffic, like snow and wind, and at distributed load, and at negative load, as in the typical cases of wind-uplift, i.e. the lifting thrust of the wind.
To complete the system, there exist innumerable systems outside the slabs for fixing, with or without piercing, clamps, hooks etc., made of various materials and suitable for application of various accessories on the roof, such as snow catches, anti-fall systems, solar panels, walkways, plants, etc.
An example of these covering systems is described in document EP 0964114 which proposes providing systems for connecting or constraining accessories to coating panels or slabs for covering buildings which enables joining the overlapped edging of two adjacent panels without any need for piercing the panels to which the assembly is applied.
According to this solution, the use of gripping and hooking components is included, which gripping and hooking components are applicable on the joined edges of two adjacent panels, which are fixable by use of a tightening and constraint component which, in this case has the characteristic of including at least one part being adapted to enable the constraint of an accessory, represented for example by solar panels or other components and accessories located on the cover.
Further, according to the solution proposed in WO2017/214642 , a covering slab is provided that comprises an interconnected mounting component with a cover component, in which the mounting component includes a profile with a shaped base that extends longitudinally and is configured to be fixed to a purlin and a first lateral wall that extends from one side of the base.
The cover component further includes a connecting element that extends from a second shaped lateral wall and is configured to receive a mounting component and a second extension placed in an operating connecting condition with an adjacent cover.
Another solution is known from EP 0634535 A2 .
Although some of the existing systems have good performance characteristics, the prior art nevertheless continuously proposes improvements regarding both the geometric configuration of the edges of the slabs and the means for mutual connection, that are designed, as in the case of the present invention, also by virtue of the constantly increasing requests for higher performance components for covering buildings because of the serious climatic changes that have greatly increased the cases of typhoons and hurricanes and as a result cases of roofs blown off and new architectural and structural needs.

DESCRIPTION OF THE INVENTION

The present invention intends to make available a metal coating cover for roofs of buildings which uses a plurality of metal slabs adjacent to one another and connected by the special shaping of the lateral edges thereof which is able to improve the general performance of the system so as to satisfy the demands highlighted above.
In particular, the invention provides a metal coating cover for roofs of buildings according to claim 1, the slabs thereof, positioned adjacent to one another, comprise edges which are fixed on the underlying structure by means of specially shaped brackets and the system thus made forms a continuous cover that is easy and rapid to install, long-lasting, very resistant to wind and perfectly suitable for the protection of the underlying building.
An important objective proposed by the present invention is to significantly improve the performance of the covering system in place, enabling an increase in terms of distance, or span, between successive rests in the lengthwise direction of the slabs, and/or a greater resistance to the wind-uplift value, i.e. the resistance to the lifting thrust of the wind.
A further object of the present invention is to improve the sliding of the slabs into the respective fixing brackets in order to enable free longitudinal dilation of the slabs themselves, enabling the manufacturing of even very long slabs (well above 100 metres), without this compromising and limiting the wind-uplift value, as happens with existing systems.
Another object of the invention is to reduce to a minimum the number of bends of the profile of the edges of the panels to be placed against one another, in the interest of greater production cost effectiveness.
A further object of the invention is to maintain for such folds of the profile of the edges of the panels to be placed against one another a curvature radius that is sufficiently wide as to enable the use of hard metal alloys, for example aluminium alloys, on the one hand avoiding the risk of formation of cracks, which can lead to the breakage of the material, and on the other hand avoiding the possibility of whitening of some types of colouring of the surface, which occurs for example using PVDF paints that may involve so-called whitening phenomena, in particular for dark colours, where this constitutes an unacceptable problem for customers.
Another object of the invention is to facilitate the mounting of external clamps, without any need to pierce the slabs, but guaranteeing great resistance thereof to the lateral, longitudinal and extraction stresses, without however increasing friction between the slabs and the fixing brackets.
This is obtained through a coating cover for roofs with a metal structure of buildings, comprising a plurality of metal slabs adjacent to one another and connected by the particular shape of the lateral edges thereof and locked by brackets, the characteristics of which are described in the main claim.
The dependent claims of the present solution outline advantageous embodiments of the invention.

ILLUSTRATION OF THE DRAWINGS

Further features and advantages of the invention will become apparent from reading the following description of an embodiment of the invention provided by way of non-limiting example, with the aid of the figures illustrated in the appended tables of drawings, in which:

figure 1 illustrates the schematic view in axonometric perspective of three coating slabs of a coating cover according to the invention, connected to one another and to the underlying surface by the brackets shown on the front;
figure 2 illustrates a detail of two edges and two coating slabs of a coating cover according to the invention placed against one another and maintained in retaining position by a mutual interlock;
figure 3 shows a schematic perspective frontal view of three coating slabs of a coating cover according to the invention placed against one another and blocked to the sub-structure by use of respective fixing brackets for connection between the slabs and the sub-structure, not illustrated;
figures 4 and 6 represent schematic views of a portion of one of the coating slabs of a coating cover according to the invention, provided with opposite edges each having a complementary geometric shaping with respect to one another, to enable joining between slabs placed against one another;
figures 5 and 5b show schematic views in axonometric perspective of one of the brackets and the detail of the components thereof, used for securely retaining the edges of the joined panels and for fixing them on the sub-structure, which is not illustrated;
figure 7 shows a schematic view in axonometric perspective of two portions of edges of two distinct coating panels mutually placed against one another and placed at a certain distance, i.e. before joining thereof;
figure 8 illustrates a frontal view of the edges of two different adjacent panels placed against one another prior to being joined;
figures 9, 10 and 11 are detailed frontal schematic views which show the co-penetration of the shaped profiles of two edges placed against one another of the slabs respectively before, during and after introduction thereof into the locking bracket.
figure 12 shows a schematic view in axonometric perspective of a complete bracket in the open position before receiving the slabs;
figures 13 and 14 show schematic views relative to a further embodiment in which the slab is an integral part of a sandwich panel, or glued to the insulating material.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

With reference to the appended figures, and initially in particular to figure 1, 20 denotes in its entirety one of the slabs of a coating cover according to the invention which are used for coating a roof with a metal frame, while 20' and 20ʺ denote the adjacent slabs.
Each slab 20 has a substantially rectangular conformation, indicatively a width of about 0.5 metres and a length that can also be much above 100 metres, which, given the specific conformation thereof, is achievable by using hard metal alloys, for example aluminium.
The slabs 20 are destined to be mutually joined to form the whole cover and for this purpose each pair of consecutive slabs coupled to one another form a longitudinal joint 21.
The connecting element of such longitudinal joint 11 is constituted by the geometry of the edges of the slabs, which are mutually retained, both by the co-penetration thereof and by brackets S which join to one another two consecutive slabs and guarantee fixing of the slabs to the underlying structure, not illustrated.
The brackets S are arranged in relation to the design, and in a normal situation, but not every situation, they would be aligned in both a transverse direction, in each joint 21 between the slabs 20, thus at a distance that coincides with the width of the slab, and aligned in a longitudinal direction at a distance that coincides with the rests of the underlying structure, not illustrated herein.
The joint 21 further guarantees the seal of the roof against penetration of water and air. The described system adapted in the longitudinal direction by the length of the slabs, and in a transverse direction by the multitude of coupled slabs, forms a single continuous surface that constitutes the cover in its entirety.
According to one embodiment shown in figures 5 and 5b, the fixing brackets S comprise a base X, having a conformation generally defined by a flat rest surface 60 which rests on the sub-structure of the roof, an internal rotating element Y (proximal to the middle plane of the bracket S), and an external rotating element Z (distal to the middle plane of the bracket S). The bracket S is a body typically made with a plastic material, or a metal material, or a group of these materials, or other materials.
The bracket S comprises two holes 46 which constitute the housing of the fixing elements to the sub-structure, typically screws, or other suitable elements.
According to the embodiment shown in figures 5 and 5b, the bracket S has a central axis of frontal symmetry and has a shaping that allows fixing two consecutive slabs 20.
Shaping the bracket S defines four opposite indentations 33bs, 34bs, 33as and 34as, formed respectively by four portions 44b, 45b, 44a and 45a protruding upwards and bent in a reciprocally specular direction towards the common middle plane.
The four indentations 33bs, 34bs, 33as and 34as are further parallel to the base of the bracket S and parallel to the rest surface 60. This conformation, as more fully described below, determine the best performance in relation to wind uplift, i.e. the lifting thrust of the wind, relative to existing systems.
With reference to the embodiment illustrated in figure 4, each single slab has two opposite profiled edges A and B which are only partially symmetrical to one another, from the first fold, which is proximal to the central axis of the slab, to the eighth fold.
The folds 30a, 31a, 32a, 33a, 34a and 35a on the shaped edge A and the corresponding 30b, 31b, 32b, 33b, 34b and 35b on the shaped edge B, are symmetrical to one another and coincide with the geometry of the bracket S. In particular, as visible in figures 4, 5 and 5 b, the protrusion that corresponds to the folds 33a, 34a, 33b and 34b of the slab is housed in the indentations 33as, 34as, 33bs and 34bs of the bracket S.
Still symmetrically, the folds 36a and 36b, respectively on the shaped edges A and B of the slab, return the slab to a substantially vertical position with an upward direction, in which the two slabs substantially adhere to one another.
Lastly, the two folds 37a and 37b, respectively on the shaped edges A and B of the slab are also substantially symmetrical. These two folds take the two contiguous slabs in a horizontal direction opposite the middle plane of the bracket S.
At the portion of the two contiguous slabs that substantially adhere to one another, between folds 36 and 37, an external fixing system can be mounted for mounting accessories, such as snow catches, anti-fall systems, solar panels, or others.
The fact that the two slabs adhere to one another enables, with no need for piercing the slab, a very effective and resistant locking by means of an external clamp, not illustrated, which is opposed to both longitudinal and transverse and upwards vertical stresses.
This clamp, when tightened, does not deform the slabs and does not lock them in the support bracket, enabling free longitudinal dilation, even in the case of slabs of significant length.
The following geometries of the two sides are differentiated.
According to the embodiment shown in figure 4, on the shaped edge A of the slab 20, following the fold 37a, a fold 38 proceeds upwards and forms a curve of 180° at a top fold 39, covering, when engaged in the joint 21, the end B of the opposite slab, and ends with a final fold 40 that takes the slab in the direction of the middle plane of the bracket S.
Lastly, the edge B of the slab 20, has, at the end thereof, a fold 41, that, when it is engaged in the longitudinal joint 21, comes to adhere to the fold 40 of the opposite slab.
The coupling between the folds 40 and 41 exploits the elasticity of the construction material of the slabs and represents an element with an excellent seal against water, as the external surface exposed to a pressure determined by the level of the rising water, pushes the shaped edge A and the last fold 40 against the fold 41 with an intrinsically positive cohesion mechanism: the greater the pressure the better the seal.
According to the embodiment shown in figures 4 and 11, at the end B of each slab 20 the last two folds 42 and 43 form a geometry that determines the formation of a channel 61, that is dedicated to collecting the residual water that has possibly penetrated through the coupling of the curves 40 and 41, transferring the residual water to the end of the slab.
As is known from the prior art, the thrust of the wind acts on the entire surface of the cover with pressure in a direction that is orthogonal to the surface and in an ascending direction. When this pressure acts on the covering system, the pressure breaks down to weigh on the points fixing the cover to the underlying structure.
In this model, we can consider that the pressure acting on the flat part of the slab 20 determines upward convexity and accordingly a force acting on the fold 32 tangent to the central part of the slab 20 and a direction in the direction of the middle plane of the slab 20 itself, or distal to the middle plane of the bracket S.
This force on the slab at the folds 32a and 32b is discharged completely onto the processes 44a and 44b of the bracket S and the folds 33a and 33b are accordingly pushed to the inside of the two indentations 3as and 33bs, preventing the release of the slab 20 from the support S.
Through the fact that the anchoring points represented by the brackets S are not continuous and are spaced apart from one another in the direction that is longitudinal to the joint 21, part of the extracting pressure of the wind breaks down into a vertical lifting force of the rib consisting of the two contiguous slabs in the joint 21. This substantially vertical force discharges onto the two sides of the joint 21 at the bracket S on the folds 33a and 33b, that are in turn discharged onto the protruding portions 45a and 45b of the bracket S.
Further, the two folds 34a and 34b are accordingly pushed into the indentations 34as and 34bs of the bracket S, preventing the release of the slab 20 from the support S.
Consequently the seal limit for the wind-uplift, or lifting thrust of the wind, of the coating cover of the present invention is uniquely determined by the resistance of the bracket S, which, if built for example of metal, is extremely high, and by the resistance of the material used for the slabs.
Consequently an increase in the thickness of the metal or the use of very tenacious metals, special aluminium, steel, or other alloys, proportionally increases the resistance of the whole system.
The bracket S, as described in figures 5 and 5 bis consists of three distinct parts, a base X characterised by the recesses 33bs and 34bs and by the protruding portions 44b and 45b, said recesses intended to receive the respective folds 33b and 34b of the slab 20 on the termination B thereof.
The base X, on the side opposite the central axis thereof has two cylindrical indentations 47 and 48 and a further two downward indentations 49 and 50 characterised by a tooth stop geometry.
The other two parts of the bracket S are represented by the two internal Y and external Z rotating elements, which, in the completely assembled position, form the recesses 33as and 34as through the protruding portions 44a and 45a, said recesses being intended to receive the respective folds 33a and 34a of the slab 20 on the termination A thereof.
Further, the two rotating elements Y and Z have respectively the cylindrical portions 51y and 51z that are received respectively by the indentations 47 and 48 of the base X, further, two further protrusions 52y and 52z that are received respectively by the indentations 49 and 50 of the base X.
This conformation of the bracket S, as illustrated in figures 9, 10 and 11, permits assembly in several steps. In the presence of the shaped edge B of a slab 20 the shaped edge A of which has already been mounted, the brackets S can be inserted onto the longitudinal ends of the slab 20 on the shaped edge B. Every single bracket will then be fixed at the sub-structure, which is not shown, by fixing elements, typically screws, through the holes 46 shown in fig. 5.
As shown in fig. 10, in this step two rotating elements Y and Z are in the open position, and in particular the internal rotating element Y is rotated anticlockwise, such that the protruding portion 45a moves to the position that is the most proximal to the middle plane of the bracket S, and the external rotating element Z is rotated clockwise such that the protruding portion 44a moves to the most distal position from the middle plane of the bracket S.
This position of the protruding portions 45a and 44a leaves space free for assembling from above the shaped edge A of the subsequent slab 20', and in particular the portion characterised by the folds 33a and 34a of the slab. During the introduction of the shaped edge A of the slab 20' the pressure exerted from above determines the rotation of the two rotating elements Y and Z, and in particular the element Y rotates clockwise taking the protruding portion 45a to a position that is distal to the middle plane of the bracket S and at the fold 35a of the shaped edge A of the slab 20' and the element Z rotates anticlockwise taking the protruding portion 44a to a position that is proximal to the middle plane of the bracket S and at the fold 32a of the shaped edge A of the slab 20'.
When rotation has been completed, the two protrusions 52y and 52z respectively of the rotating elements Y and Z are located respectively in a definitive position in the indentations 49 and 50 of the base X of the bracket S. It should be noted that the definitive closure position in the solution shown is irreversible, so as to give system resistance, in particular to the extraction action of the wind, at the maximum possible levels.
Dismantling is still possible, by using tools to break the protrusions 52y and 52z, which are thus sacrificed, at minimal cost, in the rare occasions of necessity.
It is pointed out that the bracket shown is one of the possible systems. Other bracket systems, with more or fewer rotating elements, with magnetic, mechanical or fixed systems and the numerous variants thereof which are technically equivalent are possible, provided they fall within the scope of the claims.
With reference to fig. 12 it should be noted how the insertion of the screws into the holes 46 that are present on the base X and on the rotating elements (47y and 46z) prevents the longitudinal sliding of the rotating elements Y and Z relative to the base X of the bracket S.
Further, the solution of the present invention determines an interference stress between the slab 20 and the bracket S only in the moment of mechanical stress, for example during a meteorological event with very strong winds. This leaves total freedom between slabs 20 and brackets S in normal conditions and significantly improves the longitudinal sliding necessary for the free heat dilation of the slabs, even in the event of extremely long slabs.
The embodiment shown in figure 13 refers to a variant in which the slab 20 is an integral part of a sandwich panel 70, i.e. it is glued to the insulating material (polyurethane, polystyrene or other insulating material)
It should be noted that the absence of folds 30, 31, 32 and 33 should be noted is due to the fact that as a panel does not flex during the extraction stress of the wind, it exerts only an upward thrust and does not therefore require a distal pocket in relation to the joint.
Assembly is a roto-translation, i.e. the panel 70' to be interlocked has a movement from top to bottom to assemble the outer part and a clockwise rotation to interlock the protrusion 34 in the corresponding pocket of the bracket.
The embodiment of figure 14 is identical to the preceding embodiment with the sole difference that the upper geometry has been varied, whilst maintaining the sealing area and the drainage channel, so that assembly can occur with a longitudinal translation from right to left of the panel 70'.
In this manner, both the outer closing part and the protrusion 34 go into place and there is no need to raise the panel, which is usually rather heavy.
Note that the illustrations are merely indicative, and the various dimensions and inclinations can be freely changed, customised and set up and conceived without influencing the basic concepts and the protective purpose of the following claims.
Further, the drawings show ideally a system of slabs that are provided with shaped edges A and B on each slab, but this can be reversed on the two sides or slabs can be conceived that are totally symmetrical with end edges A on both sides that are coupled with symmetrical slabs characterised by shaped edges B on both the sides, which are mounted alternately.
The invention has been described in the foregoing with reference to a preferential embodiment thereof and a variant. However, it is clear that the invention is susceptible to numerous variants which fall within the scope of the claims

Claims

A coating cover with a metal structure for roofs of buildings , the coating cover comprising a plurality of slabs (20) of substantially quadrilateral shape each of which is provided with shaped edges (A, B) that are parallel and opposite to one another intended for mutual connection between slabs (20) that are adjacent in the longitudinal direction and are intended for the formation of a joint (21) positioned between each of the adjacent slabs (20), wherein said shaped edges (A, B) comprise folds (30, 31, 32, 33, 34, 35, 36, 37) at least partially symmetrical on the two edges (A, B) and further folds (38, 39, 40) that are made on at least one of the shaped edges (A) and yet further folds (41, 42, 43) on at least the other one of the shaped edges (B), and wherein said shaped edges (A, B) of two adjacent slabs are joined by a bracket (S) of the coating cover having at least two recesses (33as, 34as, 33bs, 34bs) that are symmetrical to one another defined respectively by portions (44a, 45a, 44b, 45b) protruding upwards and folded in a reciprocally specular direction relative to a middle plane of the bracket (S) perpendicular to a base (X) of the bracket (S), in which the curves that are formed by the folds (33a, 34a, 33b, 34b) placed respectively on the edges (A, B) of the adjacent slab are housed, where said recesses (33as, 34as, 33bs, 34bs) of the bracket (S) are substantially parallel to the base (X) of the bracket (S), wherein said base (X) has a conformation defined by a flat surface (60) that is intended to rest on the sub-structure of the roof to which it can be fixed by fixing elements passing through holes (46), and characterized in that the bracket comprises an internal rotating element (Y) and an external rotating element (Z) that rotate on an axis placed at a cylindrical portion (51y, 51z) thereof around respective cylindrical housings (47, 48) of the base (X), wherein the rotating elements (Z) define at least two of said recesses (33as, 34as, 33bs, 34bs).
The coating cover according to claim 1, characterized in that at their base these rotating elements (Y, Z) have protrusions oriented vertically downwards (52y, 52z) that interlock in respective housings (49, 50) of the base (X).
The coating cover according to one of the preceding claims, characterized in that said bracket (S) has a middle plane of symmetry and a shaping configured to fix two consecutive slabs (20) by the folds (33a, 34a, 33b, 34b) thereof that penetrate respective opposite recesses (33as, 34as, 33bs, 34bs) formed respectively by said portions (44a, 45a, 44b, 45b) protruding upwards and folded in a reciprocally specular direction towards the common middle plane.
The coating cover for roofs of buildings according to one of the preceding claims, characterized in that said recesses (33as, 34as, 33bs, 34bs) on the shaped edges (A, B) are specular and opposite one another in pairs and with respect to the common middle plane, this arrangement being configured to prevent the uncoupling of the slabs even against the wind uplift.
The coating cover for roofs of buildings according to one of the preceding claims, characterized in that it comprises folds (30a, 31a, 32a, 33a, 34a, 35a, 36a) placed at the end (A) and corresponding folds (30b, 31b, 32b, 33b, 34b, 35b, 36b) at the other end (B), that are symmetrical to one another and specular, coinciding partially with the geometry of the bracket (S) and in that the profile curve that corresponds to the folds (33a, 34a, 33b, 34b) of the slab is housed in the recesses (33as, 34as, 33bs, 34bs) of the bracket (S) .
The coating cover for roofs of buildings according to one of the preceding claims, characterized in that it comprises symmetrical folds (36a, 36b), placed respectively at the ends (A, B) of the slab (20), which return the edges of the slab to a substantially vertical position with an upward direction and further folds (37a, 37b) placed respectively on the shaped edges (A, B) of the slab, which carry the edges of the slab in a direction that is distal to the middle plane of the bracket (S) .
The coating cover for roofs of buildings according to claim 5, characterized in that the symmetric portions of adjacent slabs comprised between folds (36a, 36b) substantially adhere to one another.
The coating cover for roofs of buildings according to one of the preceding claims, characterized in that at the end (A) the slab (20), starting with the fold (38), continues upwards to then form a curve of 180° at a top fold (39), covering, when engaged in the joint (21), the end (B) of the opposite slab.
The coating cover for roofs of buildings according to one of the preceding claims, characterized in that the edge (A) of the slab (20) has, at the end thereof, a fold (40), that, when it is engaged in the longitudinal joint (21), comes to adhere to the fold (41) of the opposite slab.
The coating cover for roofs of buildings according to one of the preceding claims, characterized in that at the end (B) the last folds (42, 43) take on such a shape that when it is engaged in the joint (21) it defines a channel (61) that is designed to collect the residual water that has possibly penetrated through the coupling of the curves (40-41).
The coating cover for roofs of buildings according to claim 1, characterized in that the bracket (S) is made of at least one base (X) and of the rotating elements (Y, Z), wherein the base (X) comprises a rest surface (60) to the sub-structure and the indentations (47, 48) intended to house the respective cylindrical portions (51y, 51z) of the rotating elements (Y, Z), further characterized in that the base has further indentations (49, 50) with a portion provided with a locking tooth intended to receive corresponding protrusions (52y, 52z) of the rotating elements (Y, Z), this shape enabling the system to be fitted fast and safely.