A tile-leveling spacer device comprising:

TECHNICAL FIELD

The present invention concerns a leveling spacer device for applying sheet-like manufactured products, such as tiles, slabs of natural stone or similar, for coating surfaces, such as walking surfaces, floors, wall or ceiling coatings and similar.

PRIOR ART

In the field of the application of tiles for coating surfaces, such as floors, walls and similar, it is known to use spacer devices that, as well as evenly spacing the adjacent tiles, allow the planar arrangement thereof, such devices being commonly called leveling spacer devices.

Known leveling spacer devices generally comprise a base, able to be positioned below the application surface of at least two adjacent tiles, from which at least one spacer bridge rises up, adapted for contacting, through its side flanks, the facing sidewalls of the two tiles to be arranged close together on the application surface.

The leveling spacer device is also equipped with a pressing wedge adapted for wedging between a cross-member of the spacer bridge and the visible surface of the tiles resting on the base, so as to press the visible surfaces of the tiles towards the base, leveling them.

The bridge is then removed through separation from the base after the solidification of the tile glue leaving the base hidden beneath the surface of application of the tiles themselves incorporated in the solidified glue.

In these leveling spacer devices there is a great need to reduce as much as possible the volume taken by the glue from the portion of leveling spacer device that remains incorporated in it after breaking, in particular in the gap area (channel) defined between the two tiles separated by the separating bridge.

A further great need is to reduce as much as possible the areas of the tile that are not in direct contact with the glue, so as to allow an excellent adhesion of the tile to the surface to be coated through the glue itself.

Furthermore, in these leveling spacer devices there is a great need to make the separation of the bridge from the base particularly efficient and simple once the glue has set and, at the same time, to make the area intended to cause the separation between the bridge and the base sufficiently strong and resilient, so as to avoid or limit the risk of accidental separations between the bridge and the base or during the transportation or storage of the leveling spacer devices or during the use thereof before the desired moment.

A purpose of the present invention is to satisfy the aforementioned requirements of the prior art, in a simple, rational and low-cost solution.

Such purposes are accomplished by the characteristics of the invention given in the independent claim. The dependent claims outline preferred and/or particularly advantageous aspects of the invention.

PRESENTATION OF THE INVENTION

The invention, particularly, provides a tile-leveling spacer device comprising:a base having a lower surface and an opposite upper surface, wherein the upper surface comprises:a central portion defining a support plane for two adjacent tiles arranged at a first distance from the lower surface andtwo opposite side portions with respect to the central portion and each defining a planar surface arranged at a second distance from the lower surface,wherein the second distance is less than the first distance;a spacer bridge equipped with:two legs rising from the base in a direction perpendicular to at least the central portion of the upper surface of the base anda cross-member that joins the top of the two legs and is arranged parallel to and distanced from the upper surface of the base;a through opening delimited perimetrically by the cross-member and the legs of the bridge and by the upper surface of the base, wherein the through opening is suitable for being crossed by a pressing wedge along a crossing direction;wherein each leg of the bridge is connected to the base at a respective side portion of the base in a breakable manner through a predetermined fracture line arranged at a third distance from the intermediate lower surface with respect to the first distance and to the second distance,wherein each side portion has a longitudinal axis parallel to the crossing direction of the pressing wedge and extends for the entire length of the base along such a crossing direction, andwherein the second distance is comprised between 20% and 90% of the first distance.

Thanks to such a solution, each side portion defines a lowered area of the base in which the glue can penetrate and improve the hold of the tile, decreasing the contact surface between tile and base of the device.

Moreover, since the fracture line is arranged in this lowered area beneath the support plane of the tiles, none of the base, once the bridge is removed, is above the surface of application of the tiles, not even the gap (channel) between the tiles.

Advantageously, the second distance can be comprised between 20% and 80%, preferably between 48% and 58% of the first distance.

Alternatively, even more advantageously, the second distance can be comprised between 81% and 90% of the first distance, preferably equal to 88% of the first distance.

Thanks to such a solution, a good compromise between the stability of the base (the strength of the leveling spacer device), i.e. its constant function with respect to the bridge, and the function of a lowered area adapted for receiving the fracture line beneath the support plane of the tiles.

A further aspect of the invention foresees that the upper surface can comprise a pair of opposite inclined surfaces at the ends of the base distal from the bridge and opposite with respect to it, wherein each inclined surface defines a ramp rising from the end of the base towards the bridge, in a direction parallel to the crossing direction, and which connects the lower surface of the base to the support plane of the central portion of the base.

Thanks to such a configuration of the base, together with the shape of the lowered side portions of the base itself, the insertion action of the bases beneath the tiles is made easier with a translation parallel to the crossing direction of the wedge.

Advantageously, the base can comprise a pair of opposite through slots from the lower surface to the upper surface at the central portion thereof, wherein the slots are open laterally at the respective ends of the base distal from the bridge and opposite with respect to it.

Thanks to such a solution, the volume of glue that holds the surface of application of the tile at the base is accentuated even further.

For example, each slot can be adapted for intersecting a respective inclined surface, dividing it into two separate portions along a direction perpendicular to the crossing direction.

Such a characteristic is even more important when the base is arranged at a joining line of four tiles.

According to an aspect of the invention, the fracture line can be defined by a longitudinal notch defining the area having a smaller section of the entire leg, wherein the longitudinal notch is parallel to the planar surface of the respective side portion of the upper surface of the base and perpendicular to the crossing direction, and wherein the longitudinal notch has a cross-section having a concave shape rounded according to a first radius of curvature.

Thanks to such a solution, the stress concentration to start the breaking between the bridge and the base is optimised.

In particular, the fracture line has been studied so as to allow a high resistance to breaking, i.e. a high resilience, when the bridge undergoes flexing stress with respect to a flexing axis parallel to the mid-plane of the bridge (that cuts through both of the legs and the cross-member thereof), but at the same time a high fragility, i.e. an efficient fracture-starting notch, if stressed through an impulsive traction force (axial).

In particular, all the time that the device does not have to be broken, i.e. in the transportation, storage and manipulation steps and in the first application operations thereof, such a fracture line and the leg as a whole is such as to dissipate possible deformations and react elastically to the deformations (for example allowing the rotation of the leg with respect to an imaginary hinge axis parallel to or coinciding with the fracture line, when the device has to be broken, at the end of the application operations, on the other hand, through an impulsive impact, for example through a kick, directed at the top of the bridge and in a direction parallel to such a hinge line (such as to cause an axial impulsive traction stress on the leg), the fracture line will effectively trigger the separation between the leg and the base along the desired separation plane.

Moreover, the fracture line thus studied is such as to ensure a sufficient resistance to the axial traction in non-impulsive conditions, like in the use of the pressing wedge during the step of use of the device.

Preferably, from the same point of view described above, the longitudinal notch can be joined to the portion of the leg above it through a joining surface rounded according to a second radius of curvature, opposite and greater with respect to the first radius of curvature.

Advantageously, each leg can comprise a central sector arranged between the cross-member and the lower end of the leg, wherein the central sector is equipped with two opposite flanks with respect to the crossing direction and parallel to one another, said flanks being adapted for making contact with the adjacent tiles resting on the central portion of the upper surface of the base defining their distance apart, the central sector being connected to the respective side portion of the upper surface of the base by means of a block having a smaller cross-section than the distance between the two flanks of the central sector, wherein the upper end of the block is arranged at a fourth distance from the lower surface of the base that is greater than the first distance.

Thanks to such a solution, the tapered block is such as to dissipate possible quick deformations. In practice, if the bridge is bent quickly there is the risk of the plastic from which it is made having a non-elastic behaviour, the bridge thus configured is such as to distribute the deformation and, therefore, slow down the deformation of the fracture line that must be kept as intact as possible until the fracture must be deliberately triggered.

Advantageously, the upper end of the block can be joined to the central sector of the leg through a joining surface rounded according to a third radius of curvature, the same way as and greater than the first radius of curvature.

A further aspect of the invention foresees that the upper surface (and/or the bridge) of the base can have a surface roughness comprised between 20VDI-30VDI.

Thanks to such a solution, the hold of the laying glue to the base (and/or the grip of the person tasked with application on the bridge) is improved.

A further aspect of the invention provides a tile-leveling spacer device comprising:a base having a lower surface and an opposite upper surface defining a support plane for two adjacent tiles;a spacer bridge equipped with:two legs rising from the base, wherein each leg of the bridge is connected to the base in a breakable manner through a predetermined fracture line, anda cross-member that joins the top of the two legs and is arranged parallel to and distanced from the upper surface of the base;a through opening delimited perimetrically by the cross-member and the legs of the bridge and by the upper surface of the base, wherein the through opening is suitable for being crossed by a pressing wedge along a crossing direction;

wherein the fracture line is defined by a longitudinal notch defining the area having a smaller section than the entire leg, and wherein the notch has a cross-section with respect to a plane parallel to the crossing direction having a concave shape rounded according to a first radius of curvature.

BEST EMBODIMENT OF THE INVENTION

With particular reference to such figures, reference numeral10globally indicates a leveling spacer device adapted for facilitating the application of sheet-like manufactured products, such as tiles and similar, globally indicated with the letter P, and adapted for coating surfaces, i.e. floors, walls, ceilings and similar.

The device10comprises a base20of widened shape, for example polygonal.

The base20, in the example depicted, is a monolithic body that has an irregular shape (in plan), for example substantially octagonal.

The base20comprises a lower surface21, for example flat.

The lower surface21is adapted for being rested on a layer of glue arranged on the block that is intended to be coated by the tiles P.

The base20also comprises an upper surface wholly indicated with reference numeral22.

The upper surface22comprises a central portion220defining a support plane221for two adjacent tiles P.

The support plane221, i.e. the higher flat surface of the upper surface22that defines the central portion220, is arranged at a first distance d1from the lower surface21.

The support plane221is the surface of the base20furthest from the lower surface21.

In practice, the maximum thickness of the base20is defined by the first distance d1.

The support plane221is a plane substantially parallel to the lower surface21(planar).

The upper surface22of the base20also comprises two mutually opposite side portions222with respect to the central portion220, for example symmetrical (and the same) with respect to a mid-plane M of the base20perpendicular to the support plane221and cutting through the central portion220and the side portions222.

Each side portion222defines a planar surface223arranged at a second distance d2from the lower surface21, wherein the second distance d2is less than the first distance d1.

In practice, the thickness of each side portion222of the base20is defined by the second distance d2and is less than the thickness of the central portion221of the base itself.

For example, the second distance d2is comprised between 20% and 90%.

In a possible embodiment of the base20, the second distance d2is comprised between 20% and 80%, preferably between 48% and 58%, of the first distance d1.

In such a case, for example, the first distance d1can be comprised between 2.55 mm and 2.7 mm and the second distance d2can be comprised between 1.15 mm and 1.35 mm.

In a preferred (and alternative) embodiment of the base20, the second distance d2is comprised between 81% and 90%, preferably equal to 88%, of the first distance d1.

In such a case, for example, the first distance d1can be comprised between 2.4 mm and 2.5 mm, preferably equal to 2.48 mm and the second distance d2can be comprised between 2.1 mm and 2.2 mm, preferably equal to 2.18 mm.

Each side surface223is a plane substantially parallel to the lower surface21(planar) and to the support plane221(distinct from them).

The upper surface22comprises a joining surface224arranged between each planar surface223and the support plane221.

The joining surface224is substantially perpendicular to the planar surface223and to the support plane221, defining the rise of one step between them.

Each side portion222of the upper surface22, i.e. each planar surface223, has a longitudinal extension, i.e. it has a main direction of extension, along a longitudinal axis A, which is perpendicular to the mid-plane M of the base20that cuts through the central portion220and the side portions222.

In practice, each planar surface223defines an elongated strip (having a length greater than the width) with longitudinal axis A perpendicular to the aforementioned mid-plane M of the base20and arranged at a lower level with respect to the level defined by the support plane221defined by the central portion220of the base20.

The planar surface223has a substantially trapezoidal shape in plan, for example shaped like an isosceles trapezium, wherein the larger base is proximal to the support plane221, i.e. it is joined to it through the joining surface224, and the smaller base, opposite to it, defines the (free) side end distal from the central portion220of the base20.

The upper surface22of the base20comprises a pair of opposite inclined surfaces225with respect to the mid-plane M of the base20that cuts through the central portion220and the side portions222.

Each inclined surface225defines a ramp rising from the end of the base20towards the aforementioned mid-plane M in a direction perpendicular to the mid-plane M and that connects the lower surface21of the base20to the support plane221of the central portion220of the base20.

Each inclined surface225has a maximum distance from the lower surface21equal to the first distance d1and a minimum distance from the lower surface21comprised between zero and the second distance d2, preferably equal to the distance d2.

Each inclined surface225lies on a plane inclined by an acute (inner) angle with respect to the lower surface21.

The base20comprises a pair of opposite slots23passing from the lower surface21to the upper surface22, which are arranged at the central portion220of the upper surface22.

Each slot23has an elongated shape, i.e. it has a main direction of extension, along a longitudinal axis perpendicular to the mid-plane M of the base20that cuts through the central portion220and the side portions222.

In practice, each slot23has a longitudinal axis parallel to the longitudinal axis A of the side portions221of the upper surface22of the base20.

Each slot23is laterally open at a respective end of the base20distal from the mid-plane M.

Each slot23defines a longitudinal through crack of the base20from the end distal from the mid-plane M towards it and with main direction perpendicular to it.

The length of each slot23is less than half the length of the base20in the direction perpendicular to the mid-plane M, for example it is comprised between 0.4 times and 0.55 times half of the length of the base20in the direction perpendicular to the mid-plane M, for example 0.54 times half of the length of the base20in the direction perpendicular to the mid-plane M.

For example, each slot23is adapted to intersect a respective inclined surface225dividing it into two separate portions along a direction parallel to the mid-plane M and to the lower surface21.

The base20, in particular the upper surface22thereof (with the exception of the inclined surfaces225), has a surface roughness substantially comprised between 20VDI-30VDI.

The device10comprises a spacer bridge30, which is adapted, in use, for contacting at least one portion of the adjacent flanks of the at least two tiles P resting on the support plane221of the upper surface22of the base20.

The bridge30comprises two legs31each rising from a side portion222of the upper surface22of the base20in a direction perpendicular to at least the central portion220of the upper surface22of the base itself.

The bridge31also comprises a cross-member32that joins the top of the two legs31and is arranged with longitudinal axis parallel to and distanced from the upper surface22of the base20.

The bridge30is for example made in a single body with the base20, for example through injection moulding of plastic material.

The bridge30is globally defined by a plate-like body arranged parallel to the mid-plane M of the base20, so that the mid-plane M of the base20is also a mid-plane of the bridge30itself.

Each leg31of the bridge30has a lower end fixed to the planar surface223of the respective side portion222.

Each leg31of the bridge30is connected to the planar surface223of the respective side portion222of the base20in a breakable manner through a predetermined fracture line310.

The fracture line310, visible in the details ofFIGS. 5 and 6, is parallel to the planar surface223(and to the mid-plane M) and is arranged at a third distance d3from the intermediate lower surface with respect to (comprised between) the first distance d1and to the second distance d2.

For example, the third distance d3is closer to the second distance d2than to the first distance d1.

The third distance d3is substantially equal to or slightly greater than the second distance d2.

Each leg31of the bridge30is substantially sheet-like and has a longitudinal axis (main direction) perpendicular to the planar surface223of the side portion222from which it branches.

Each leg31has a height (in a direction parallel to its longitudinal axis) that is greater than the thickness of the tiles P to be arranged at adjacent to one another, so that the cross-member32of the bridge30is always at a greater level (distance from the lower surface21) than the level of the visible surface of the tiles P to be arranged at adjacent to one another.

The device10can be of the type shown inFIG. 1-4 or 7, characterised by a low height of the legs, or of the type shown inFIG. 8, characterised by a greater height of the legs31, in relation to the format of tiles P to be applied.

Each leg31has a width, by width meaning the dimension parallel to the mid-plane M (that cuts through both of the legs31and the cross-member32of the bridge30), smaller than the width of the planar surface223of the respective side portion222.

In practice, each leg31(i.e. its edge facing towards the other leg31) has a (non-zero) distance from the joining surface224of the upper surface22of the base20, i.e. between each leg31and the joining surface224a gap is defined.

Each leg31has a variable thickness (for example in sections) along the longitudinal axis thereof.

The term thickness of the leg31is meant to indicate the dimension of the leg31in the direction perpendicular to the mid-plane M of the bridge30that cuts through both of the legs31and the cross-member32of the bridge30.

Each leg31comprises a central sector311arranged at axially between the cross-member32and the lower end of the leg31, wherein the central sector311is equipped with two opposite flanks312with respect to the mid-plane M and parallel to one another.

The flanks312of the central sector311are the area of the leg31that comes into contact with the adjacent tiles P resting on the central portion221of the upper surface22of the base20defining their distance apart in a direction perpendicular to the mid-plane M.

The distance between the flanks312defines the width of the channel (inter-space) between the tiles P.

The device10can be of the type shown inFIG. 1-4 or 8, characterised by a low distance between the flanks312, or of the type shown inFIG. 7, characterised by a greater distance between the flanks312, in relation to the format of tiles P to be applied.

In this last case, as illustrated inFIG. 8, at the flanks312there can be weight-reducing hollows or recesses (blind or passing right through).

Each leg31also comprises a block313adapted for interconnecting the central sector311with the planar surface223of the respective side portion221of the base20.

The block313has a thickness, i.e. a cross-section carried out with respect to a plane perpendicular to the mid-plane M, smaller than the distance between the two flanks312of the central sector311.

The block313has an upper end connected to the central sector311and a lower end, which coincides with the lower end of the leg31as a whole, connected directly to the planar surface223of the respective side portion222of the base20. The fracture line310is defined at the block313, in an area proximal to the lower end thereof.

The fracture line310, as shown in the detail ofFIG. 6, is defined by a longitudinal notch defining the area having the smaller cross-section (in whichever direction and in particular in the direction perpendicular to the mid-plane M) than the entire leg31.

The longitudinal notch that defines the fracture line310defines the fracture-starting area of the bridge30with respect to the base20.

The longitudinal notch has a longitudinal axis parallel to the planar surface223of the respective side portion222and to the mid-plane M and is fully developed, i.e. it occupies the entire width of the leg31(i.e. of the block313).

The longitudinal notch has a constant cross-section (i.e. with respect to a plane perpendicular to the mid-plane M) along the entire length thereof and having a concave shape rounded according to a first radius of curvature R1.

In practice, the shape of the longitudinal notch is substantially semi-cylindrical.

The first radius of curvature R1is substantially comprised between 0.4 and 0.2 mm, preferably equal to 0.3 mm.

The depth along the thickness of the block313of the longitudinal notch is substantially comprised between 0.01 mm and 0.02 mm.

Each leg31, i.e. each block313, comprises a pair of identical fracture lines310, i.e. of longitudinal notches, symmetrically arranged with respect to the mid-plane M of the bridge30(and of the base20).

In practice, the minimum section of the leg31, that starts the fracture of the bridge30) is defined at the joining plane of the minimums of the concave shape rounded according to a first radius of curvature R1defining the two longitudinal notches.

Advantageously, each longitudinal notch is joined to the portion of the leg31(i.e. of the block313) above it through a joining surface rounded according to a secondo radius of curvature R2, opposite and greater with respect to the first radius of curvature R1(for example comprised between 0.3 mm and 0.5 mm, preferably equal to 0.4 mm).

The upper end of the block313, i.e. the area in which the block313joins with the central sector311, is arranged at a fourth distance d4with respect to the lower surface21of the base20, said fourth distance d4being greater than the first distance d1.

In practice, the upper end of the block313projects above the level defined by the support plane211of the central portion210of the upper surface22of the base20.

For example, the fourth distance d4is substantially equal to the sum of the first distance d1and the second distance d2.

The upper end of the block313is joined to the central sector311of the leg31through a joining surface rounded according to a third radius of curvature R3, which is the same way as and greater with respect to the first radius of curvature R1(for example equal to the second radius of curvature R2), and/or by inclined V-shaped walls.

The cross-member32comprises a cross-section (with respect to a plane perpendicular to the mid-plane M) defining an area with greater thickness in an area proximal to the upper end of the legs31and with full longitudinal extension. Such an area with greater thickness defines a reinforcing beam for the bridge30. Such an area with greater thickness has a thinner grip portion on top of it and joins to the legs31through inclined joining surfaces.

The reinforcing beam, in the area arranged between the legs31, i.e. juxtaposed over the central portion220of the upper surface22of the base20, ends at the bottom with a shaped edge, for example V-shaped.

The distance of the shaped edge from the central portion220of the upper surface22of the base20is (much) greater than the thickness of the tiles P to be applied.

The bridge30, with its portal shape described above, and the base20joined to it delimit a through opening40that passes through the bridge30and the base20in a direction perpendicular to the mid-plane M thereof.

The through opening40is delimited perimetrically by the cross-member32and the legs31of the bridge30and by the upper surface22of the base20.

In greater detail, the through opening40is delimited on top by the shaped edge of the reinforcing beam of the cross-member32, at the bottom (almost totally) by the support plane221of the central portion220of the upper surface22of the base (i.e. the area thereof under the cross-member32) and laterally by the facing edges of the legs31.

The through opening40has an overall substantially rectangular shape.

The device10also comprises a pressing wedge50, separate from the base20and from the bridge30(seeFIGS. 9 and 10).

The pressing wedge50is a rectangular wedge, for example it is equipped with a flat lower surface51and adapted for being arranged, in use, parallel to the support plane221of the central portion220of the upper surface22of the base20and an upper surface52inclined with respect to the lower surface51and equipped with abutment elements, such as teeth53or knurlings.

The pressing wedge50also comprises two parallel flanks.

The pressing wedge50has variable (and constantly increasing) thickness along its longitudinal axis from one end towards the opposite end.

The pressing wedge50is configured to be able to be slotted with clearance through the through opening40defined between the base20and the bridge30of the device10along a crossing direction B (seeFIG. 10) that is perpendicular to the aforementioned mid-plane M of the bridge30and of the base20.

For example, the maximum height of the pressing wedge50(maximum distance between its lower surface51and its upper surface52) is less than the height of the through opening40defined by the distance between the cross-member32(i.e. its shaped edge) and the upper surface22of the base20(i.e. its support plane221).

The shaped edge of the cross-member32is adapted for engaging the substantially pop-up teeth53during the translation inside the through opening40along the crossing direction B.

The width of the pressing wedge50is substantially equal to (or slightly less than) the distance between the two legs31(i.e. between the two facing edges thereof). The pressing wedge50is adapted for being slotted inside the through opening40and sliding, with the lower surface51resting on the visible surfaces of the tiles P resting on the support plane211defined by the upper surface22of the base20, so that the upper surface52of the pressing wedge50goes into forced contact with the shaped edge of the cross-member32and the same pressing wedge50is thus pressed against both of the tiles P, arranged on opposite sides with respect to the bridge30, to thrust them towards the base20and level them.

In light of what is described above, the operation of the device10is as follows.

The device10allows tiles P to be applied according to different application schemes as illustrated inFIGS. 11a-11c.

In order to coat a surface with a plurality of tiles P it is sufficient to apply a layer of glue on top and, then, it is possible to apply the tiles P on it.

In practice, where the first tile must be arranged it is sufficient to position a first device10, the base20of which is intended, for example, to be arranged below four corners of respective two/four tiles P.

Once the base20has been positioned it is sufficient to position the two/four tiles P so that each of them has a portion of the sidewall in contact, respectively, with a flank312of one or both of the legs31.

In this way, the equal spacing between the two/four tiles P that surround the bridge30is ensured and they rest on the support plane221of the base20.

When for example the tiles P are particularly large in size, then it is possible to position a device10also at a middle area of the sidewall of the tile itself. In doing so, the tile P rests on one or more support planes221of respective bases20.

Generally, firstly a tile P is applied and then a base portion20of the device10is inserted under it at the corner or at a sidewall thereof.

In this circumstance, the inclined surfaces225and the elongated shape in a direction perpendicular to the mid-plane M of the side portions222of the upper surface22(lowered with respect to the central portion220) and, for example, the slots23play an important role in (jointly) facilitating the wedging of the base20under the surface of application of the tile P in any case allowing the glue not to be scraped entirely away from the application surface itself.

Once the various based20have been positioned with the respective bridges30that rise up above the visible surfaces of the adjacent tiles P as described above, as long as the glue is in any case still not entirely solidified the various pressing wedges50are inserted inside each through opening40, which, by pressing on the visible surface of the tiles P, locally in the various (middle or corner) points, allow the perfect leveling of the visible surfaces of the tiles themselves.

Finally, when the glue has hardened and set, the long bridge30is broken causing, for example through an impulsive force directed parallel to the mid-plane M, the start of the fracture along fracture line310and the same bridge30(disposable) and the pressing wedge50(reusable) are thus removed to be able to putty the channels between the tiles P without the base20being visible on the finished surface and no part of the base20is arranged between the tiles themselves.

The invention thus conceived can undergo numerous modifications and variants all of which are covered by the inventive concept.

Moreover, all of the details can be replaced by other technically equivalent elements.

In practice, the materials used, as well as the contingent shapes and sizes, can be whatever according to requirements without for this reason departing from the scope of protection of the following claims.