US 20020178681 A1
Panel for floor coverings and relative floor covering consisting of floor panels made of composite material, wherein the floor covering comprises a plurality of panels (10) arranged adjacent to each other and joined together two by two in correspondence with at least two respective sides and wherein the panels include, on the opposite longitudinal sides, first male coupling means (C) and first female coupling means (D), and, on the opposite butt sides, second male coupling means (E) and mating second female coupling means (F).
The butt end male-female coupling means (E, F) have respective and mating cam-type ends (33, 36) able to cooperate through interference in the butt-wise coupling of two adjacent panels.
1- Panel made of composite material such as MDF, HDF or impregnated chipboard, including at least one upper face or plane (48) and a lower face or plane (49), said panel (10) including two opposite longitudinal sides having respective male means (C) and female means (D) for the reciprocal connection of two panels (10), said male means (C) including at least a projecting portion (11) extending coplanar to said upper plane (48), and said female means (D) including at least a projecting portion (16) extending coplanar to said lower plane (49), the panel having a thickness (1) and a median longitudinal axis (X), characterized in that said male-female means have, in reciprocal cooperation:
i) said male means (C) a wall (112) which begins from the upper plane (48) and is orthogonal thereto, said wall (112) terminating with a tooth (12) protruding towards the outside for a width (40) and substantially parallel to said upper plane (48), said tooth (12) extending downwards for a height (50) substantially equal to the width (40) and connecting with an underlying horizontal plane (13) which extends towards the inside so as to define a bevel (15) inclined by an angle (β) with respect to the vertical, the bevel (15) cooperating with a recess (14) defined by a substantially vertical wall (314) separated from said wall (112) by a width (43), said wall (314) connecting with a horizontal plane (414) of a width (42) which terminates on a wall (22) which extends as far as said lower plane (49), the width (41 =40+42+43) of said projecting portion (11), defined between the outer end of said tooth (12) and said wall (22), being equal to about the value of the thickness (l) of the panel (10);
ii) said female means (D) a first wall (44) beginning from said upper plane (48) and having a height (47) substantially equal to the height of said wall (112) of the male means (C), said first wall (44) including a substantially vertical first upper tract (121) and a second lower tract (221) inclined towards the inside by an angle (γ), said second lower tract (221) extending in a horizontal recess (21) defined by a horizontal wall (321), a vertical wall (421) and a horizontal plane (19), said recess (21) having a length (40) and height (50) mating with the length and height of said tooth (12) of the male means (C), said horizontal plane (19) having a length mating with that of said plane (13) of the male means (C), said plane (19) extending with a groove (20) connected to a tooth (17) comprising a substantially vertical wall (118) which connects with a substantially horizontal upper plane (18), the upper plane (18) connecting to said lower plane (49) with a substantially vertical wall.
2- Panel as in
3- Panel as in
4- Panel as in
5- Panel as in any claim hereinbefore, characterized in that the height (52) of said plane (13) with respect to said lower plane (49) is equal to about ⅓ of the thickness (l) of said panel (10).
6- Panel as in any claim hereinbefore, characterized in that the inclination (β) of said bevel (15) with respect to the vertical is equal to about 45°.
7- Panel as in any claim hereinbefore, characterized in that said wall (22) consists of a first tract (114) orthogonal to said upper plane (48) and a second tract (214) angled rearwards with respect to the vertical by an angle (γ), said angle (γ) being equal to about half of said angle (α).
8- Panel as in any claim hereinbefore, characterized in that the distance (42) between said wall (112) and said wall (314) is equal to about ⅓ of the thickness (l) of the panel (10).
9- Panel as in any claim hereinbefore, characterized in that said upper plane (18) of the female means (D) has a width (42) mating with the width of said plane (414) of said male means (C).
10- Panel as in
11- Panel as in any claim hereinbefore, characterized in that said groove (20) is able to perform an at least partial function of elastic hinge for the terminal end of said female means (D) at least during the coupling phase of two adjacent panels, when said bevel (15) thrusts against said upper plane (18).
12- Panel as in any claim hereinbefore, characterized in that said groove (20) has a minimum section equal to at most a quarter of the total thickness of the panel (10).
13- Panel made of composite material such as MDF, HDF or impregnated chipboard, including at least one upper face or plane (48) and a lower face or plane (49), said panel (10) including a thickness l and respective male means (E) and female means (F) for the reciprocal butt-wise connection of two panels (10), said male means (E) including a projecting extension (34) extending coplanar to said upper plane (48), and said female means (F) including a projecting extension (30) extending coplanar to said lower plane (49), characterized in that said male-female means (E, F) have, in reciprocal cooperation:
i) said male means (E) a vertical wall (53) beginning from said upper plane (48) and substantially orthogonal thereto, which is connected to a plane (35) facing towards the inside and substantially horizontal, said plane (35) extending terminally in an S-shaped profile lying on a vertical plane, said S-shaped profile defining a cam-type end (36) which extends so as to define a recess-type seat (56) the bottom of which is displaced towards the outside of the panel (10) with respect to the vertical plane passing through the edge of said cam-type end (36), said recess-type seat (56) being connected to a substantially horizontal wall (58), said wall (58) extending with a wall (60) connecting to said lower plane (49);
ii) said female means (F) a first wall (62) beginning from said upper plane (48) and substantially orthogonal thereto, said wall (62) extending with a substantially horizontal wall (31) on which at least the front end of said plane (35) of the male means (E) is able to rest, said wall (31) extending in a groove (32) defining a bottom (132), said groove (32) extending upwards so as to define an S-shaped profile lying on a vertical plane and defined by a cam-type end (33) the edge of which faces towards said vertical wall (62), said cam-type end (33) of said female means (F) being able to cooperate through interference, during the coupling phase of two panels (10), with the mating cam-type end (36) of the male means (E) and to be at least partly housed in said recess-type seat (56), said cam-type end (33) extending in a substantially horizontal wall (63) of a width (64) mating with the width of said wall (58) of said male means (E), said wall (63) being connected to said lower plane (49) by means of a substantially vertical wall (65).
14- Panel as in
15- Panel as in
16- Panel as in any claim from 13 to 15 inclusive, characterized in that the distance (59) between said wall (58) and said lower plane (49) is at least equal to half the thickness (l) of said panel (10).
17- Panel as in any claim from 13 to 16 inclusive, characterized in that said wall (31) has a first tract (131) and a second tract (231) joined by a bevel (331) inclined downwards, so that said second tract (231) is sunken with respect to said first tract (131).
18- Panel as in any claim from 13 to 17 inclusive, characterized in that the bottom (132) of said groove (32) is connected and sunken with respect to said wall (31).
19- Floor covering formed by panels made of composite material, comprising a plurality of panels (10) arranged adjacent to each other and joined two by two in correspondence with at least two respective sides, characterized in that, on a first pair of opposite longitudinal sides, said panels have first male coupling means (C) and first female coupling means (D), and, on the opposite butt sides, second male coupling means (E) and mating second female coupling means (F), the coupling of two adjacent panels being obtained by coupling said first male coupling means (C) of one panel (10) to said first female coupling means (D) of an adjacent panel (10), then by taking into contact the butt edges (37, 38) of said two panels (10), and then by rotating one panel (10) to be positioned with respect to an already positioned panel (10) in a scissor-like manner from up to down, in order to couple, through interference, one cam-type end (36) of said second male coupling means (E) of one panel (10) included in correspondence with the butt side with a mating cam-type end (33) of said second female coupling means (F) of the adjacent panel (10).
 The present invention refers to a floor covering formed by panels of such a material as MDF, HDF or faced-chipboard, ie. manufactured out of board made of fibers or wooden chips impregnated with synthetic resins and faced on their surfaces with either natural or synthetic materials.
 These panels may have different shapes and dimensions, but they are usually rectangular and are joined with each other along all of their perimetral edges.
 According to the present invention, a panel 10 (FIG. 1) has an upper plane 48 and a lower plane 49 defining a thickness l and a median axis x, and has, on two opposite sides thereof, a section with conjugate profiles, respectively male section C and female section D, so that two contiguous panels will then be able to join with each other along engagement surfaces that are orthogonal with respect to each other.
 In fact, on one side, or male section C, the cross-sectional profile of the panel 10 can be noticed to include a projecting portion 11 which has a reduced height with respect to the overall height of the panel and extends horizontally along the same plane as the upper plane of the panel.
 This portion 11 further extends downwards with a vertical wall 112, thereby forming a laterally protruding rib or tooth 12 which, in a preferred manner, is interrupted at one or more points, ie. along one or more tracts, along its overall extension. The tooth 12, which has a length 40 equal to about Ό of the thickness l of the panel 10, has a plane upper surface parallel to the upper plane 48 of the panel 10.
 Moreover, the portion 11 has on its lower side a plane horizontal surface 13 and, extending towards the inside of the panel 10, a substantially vertical recess 14, defined by a vertical wall 314 and by a bottom 414 which is also plane and substantially horizontal, parallel to the upper plane 48 of the panel.
 The height 52 of the plane 13 with respect to the lower plane 49 of the panel 10 is equal to about ⅓ of the thickness l of the panel 10, and this conditions to said value the thickness of he resistant projecting section of the female section D, as will be described in detail hereafter.
 The tooth 12 and the plane 13 are connected by means of a bevel 113 directed rearwards and defining an angle α with respect to the vertical. In a preferential embodiment, said angle α is between about 20° and about 30°.
 The tooth 12 has a height 50 substantially equal to its width 40 and therefore it too is equal to about Ό of the thickness l of the panel 10.
 The bevel 113 is located astride the median axis X of the panel 10 and is substantially symmetrical with respect thereto; the bevel 113 encourages the reduction in the width 41 of the projecting portion 11, and consequently of the mating projecting portion 16 of the female section D, since it allows, during the insertion phase through rotation, to bring into greater reciprocal proximity the two panels 10 which are to be coupled.
 The plane 13 extends, in the solution shown here, in a bevel 15 facing upwards and defining an angle β of about 45° with respect to the vertical; this bevel 15 connects to the bottom 414 of the recess 14 by means of a vertical wall 314.
 The bevel 15 also encourages the reduction in the width of the coupling zone since it thrusts, in the way which will be seen later, upon on the elastic terminal part of the female section D, making it bend at least temporarily.
 The vertical wall 314 is separated from the wall 112 by a value 43, while the recess 14 has a width 42 equal to about ⅓ of the thickness l; the projecting portion 11 has an overall width 41, defined by the sum of the widths 40, 42 and 43, equal to a value which is about equal to the thickness l of the panel 10.
 The recess 14 also has a wall 22 connecting to the lower plane 49 which, in this case, is made in two tracts, respectively a first, substantially vertical upper tract 114 and a second lower tract 214, inclined towards the inside of the panel 10 and defining an angle γ with respect to the vertical. The value of the angle γ is equal to about half of the angle α. The other, ie. opposite side, or female section D, of the panel 10 has in turn a projecting portion 16 which has again a reduced height with respect to the overall height of the panel and extends horizontally along the same plane as the lower surface 49 of the panel. The portion 16 further extends upwards with a vertical tooth 17 which extends all along the side of the panel and whose upper surface 18 is substantially horizontal.
 The upper surface 18 has a width 42 which is substantially equal to the width of the recess 14 and is therefore equal to about ⅓ of the thickness l of the panel 10.
 The projecting portion 16 has furthermore, going towards the inside of the panel 10, a horizontal plane surface 19 at a lower level than the level of the surface 18 and connected to the latter through a vertical groove 20 opening upwards and extending in a vertical wall 118. At the end portion of the surface 19 on the opposite side of the groove 20, the side of the panel is provided with a substantially horizontal recess 21.
 The recess 21 is defined not only by the plane 19, but also by a vertical wall 421 and by a horizontal wall 321 which are mating in size with that of the tooth 12.
 The recess 21 is connected to the upper plane 48 by means of a wall 44 which, in this case, consists of a lower tract 221 inclined with respect to the vertical by an angle γ and by a vertical upper tract 121, connected to said upper plane 48.
 A particular importance, as this will be more clearly explained further on, has to be attributed to the groove 20, which is deeply hollowed out, ie. sunken so that the thickness of the panel, as seen across the vertical section thereof, turns out to be considerably reduced with respect to the overall thickness of the panel itself.
 The groove 20 also forms a hinge element which, as can be understood from FIG. 2, allows a partial elastic flection forwards of the terminal end of the female section D when the front tooth 12 of the new panel 10 is inserted into the recess 21 of the already positioned panel 10.
 When the insertion and coupling of the panels 10 has been completed, and when the panel to be inserted has been taken to a position coplaner with the panel already inserted, the elastic flection of the tooth 17 is released and the two panels 10 are coupled without being under tension.
 The groove 20 also forms a balanced union joint specially adapted to lead towards the floor, underneath the neutral axis of the panel, the strains induced by expansions which the panel itself may undergo in use, thereby maintaining the coplanarity of the treading surface. The minimum section of the panel under the groove 20 shall at most be equal to one fourth of the overall thickness of the panel.
FIG. 2 is a partial cross-sectional view of the longitudinal sides of two panels 10 in the phase in which the respective profiles thereof are mutually engaging.
 As can be seen, the panel that has to be inserted (the one shown on the right side of the Figure) is drawn in an inclined position alongside the already arranged matching panel, while the insertion is made by simply rotating the edge portion 11 of the panel to be inserted with respect to the edge portion 16 of the matching panel already arranged in position.
 The tooth 12 and the corresponding accommodating seat 21 hereby form the fulcrum about which the rotary motion for assembling and disassembling the panels is performed, whereas the action of thrust caused by the bevel 15 on the plane wall 18 determines the elastic flection forwards of the end of the female section D which allows to introduce the tooth 12 into the recess 21 even when there is a limited rotation space.
 The upper resting plane between the tooth 12 and its seat 21 is horizontal and positioned very close to or coinciding with the neutral axis of the cross-section of the panel. The insertion is facilitated not only by the elastic flexibility of the tooth 17, but also, as said, by the fact that the vertical engagement profiles, that is to say, the walls 22 and 44, of the two panels are relieved, ie. slightly beveled in order to prevent them from mutually interfering when they are coupled together and enter into contact with each other.
 The insertion of the front tooth 12 inside the recess 21, and the simultaneous insertion of the raised tooth 17 into the seat 14, are facilitated by the fact that the reciprocal sizes of teeth and recesses allow to maintain a certain coupling play, that is to say, the coupling does not occur with the shapes coinciding, but free spaces remain which allow a reciprocal movement without friction and rubbing.
FIG. 3 is a partial cross-sectional view of the detail shown in FIG. 2, however in the phase in which the engagement, ie. coupling between the two contiguous panels has been completed. It should be noticed that, when coupling is terminated, the panels turn out to be simply resting on each other along a horizontal plane on which the lower surface 13 of the portion 11 of a panel (ie. the one shown in the left side of the Figure) and the upper surface 19 of the portion 16 of the other panel (ie. the one shown on the right side of the Figure) come to meet with each other.
 The tooth 12 engages the recess 21, and the tooth 17 in turn engages the recess 14, in a loose manner since they only serve a locating and retaining purpose when positioning and assembling the panels. Since the edges of the panels are not joined to each other by any kind of forced coupling, but taking merely advantage of the elasticity of the materials, it clearly emerges that two contiguous panels are in this manner capable of freely sliding with respect to each other, thereby facilitating the assembly as well as the butt joining of contiguous panels.
 As the afore cited FIG. 3, FIGS. 4 to 6 illustrate the detail of the longitudinal coupling of two panels with each other under differing conditions of load applied to the floor.
 In particular, FIG. 4 illustrates the case in which a force F, applied to the upper end portion of the panel on the right side of the Figure, triggers a reaction R of the slab under the floor, wherein said reaction is transmitted through the mutual contact surfaces along the path indicated by the arrows inside the panels. In a fully similar manner can be noticed to behave the two so engaged when the force F is applied on to the upper end portion of the panel on the left-hand side in FIG. 5. Finally, when both upper end portions of the two panels are loaded with a force F, as shown in FIG. 6, the reaction R of the slab under the floor is transmitted inside the panels where it balances at the vertical contact surfaces.
FIG. 7 is an interrupted longitudinal-section view of the panel illustrated in FIG. 1, while FIG. 8 is a partial sectional view of the butt sides of two contiguous panels 10 with the respective profiles in a fully engaged condition. A panel (ie. the one on the left-hand side of the Figure) is provided with a female element F comprising a projecting extension 30, which is aligned with the lower surface 49 of the same panel and whose profile, when seen across its section, includes a vertical wall 65, a horizontal wall 63 with a width 64, a substantially horizontal resting and reference plane 31, as well as a groove 32, defining a bottom 132 which follows a sunken contour with respect to, ie. is lower than the plane 31, and a cam-shaped end portion 33 and a vertical wall 62.
 The sunken groove 32 extends upwards, connecting with the horizontal wall 63, so as to define an S-shaped profile lying on a vertical plane and defined by a cam-type end 33 the edge of which faces towards the inside of the panel 10. The sunken groove 32 also performs the function of a hinge element to allow a partial elastic flection of the cam-type end 33 during the coupling phase of two contiguous panels.
 Correspondingly, the other panel (ie. the one on the right-hand side of the Figure) has a male element E comprising a projecting extension 34 aligned with the upper surface 48 of the same panel, whose profile features a vertical wall 53, a substantially horizontal resting and reference plane 35 which extends upwards in an S-shaped profile lying on a vertical plane and defining a cam-shaped appendix 36, mating with the cam-type end 33 on the other side. The cam-type end 36 then extends into a recessed seat 56, displaced towards the outside and connected to a horizontal wall 58, which is connected to the lower plane by means of a substantially vertical wall 60.
 The planes 31 and 35 can be noticed to be mutually coupled by simply resting on each other when the two panels are assembled, while the cam-type end portions 33 and 36 engage each other with interference on a vertical plane, so as to prevent reciprocal movements between the two panels 10 when they are engaged with each other (FIG. 8).
 In the solution shown here, the wall 60 comprises a substantially vertical first tract 160 and a second tract 260 inclined towards the inside by an angle of γ1.
 Moreover, the plane 31 has a first tract 131 and a second tract 231 connected to each other by a bevel 331 inclined downwards, so that said second tract 231 is sunken with respect to the first tract 131.
FIG. 9 is a partial perspective view the positioning phase for the butt assembly of the panels of FIG. 8. This assembly is facilitated by the fact that, as we have seen above, the panels 10 can be made to slide longitudinally with respect to each other, without friction and rubbing, even when they are already coupled together with the respective long sides.
 As it can be seen, the assembly is carried out by bringing the longitudinal edge of a panel 10 to rest, according to the arrow A, on the corresponding edges of the contiguous panels, while bringing the butt edges 37 and 38 of the panels to be assembled into mutual contact. Then, the panel 10 is rotated according to the arrow B, while causing, with a scissor-like motion according to a vertical plane, the edge 37 to close against the edge 38, until the panel 10 is fully coplanar with the contiguous panels.
 During the rotation and coupling phase, the cam-type appendix 36 of the panel 10 to be inserted exerts on the mating cam-type end 33 a thrust which determines a partial elastic flection forwards of said end 33.
 When the two panels 10 have reached a position of coplanarity, the elastic flection of the cam-type end 33 is released, so that, even in correspondence with the respective butt ends, the two panels 10 are coupled without tensioning. Moreover, the undercuts consisting of the inclined bevel 331 and the inclined tract 260 determine a coupling with play, which prevents tensioning between two coupled panels 10.
 The respective projecting extensions, male 34 and female 30, have respective heights 54 and 59 equal to at least half of the thickness l of the panel 10, so as to ensure a sufficient mechanical resistance which prevents unwanted breakages and flections.
 It clearly emerges that all panels have the same form, with two adjacent edges having a male profile and the other two adjacent edges having a female profile, as shown in FIGS. 1 and 7. From the same Figures it can be further noticed that contiguous panels are coupled by both mutual support 13, 19 and 31, 35 and double-hook coupling 14, 17 and 33, 36, respectively, however without being in a tension state. It is also clear that the presence of the grooves 20 and 32, which function as hinge elements respectively for the raised tooth 17 and the end 33, allows to achieve easy couplings, side-wise and butt-wise, thus reducing to a minimum the width of the face intended for coupling.
 Both the assembly and the disassembly of the panels are thereby facilitated, without any need for tools of any kind to be used, along with the adaptation to possible settlings of the plane on which the flooring rests.
 As a result, the floor covering according to the present invention, as obtained by assembling panels having the afore described profile and coupled together by simply rotating and laying them down to rest on each other, without any forced engagement of the edges, is self-levelling and self-stabilizing under load conditions.
 In prior-art floor coverings, and particularly in floor coverings of the kind described in WO 97/47834, possible breakages, due to coupling edges being put under tension both during assembly and in practical use, occur inside the body of the panel and tend to develop in a horizontal direction, with the practical result of the edges of the panels becoming exposed both at the lower surface and the upper surface thereof. While such an edge exposure at the lower surface is generally not critical in itself, since it is absorbed by the layer of elastic material arranged between the flooring and the slab therebeneath, the upper edge exposure is on the contrary very annoying, since it causes people to stumble and the flooring itself to incur damages.
 These drawbacks are done away with in the floor covering according to the present invention, as it can be easily inferred from the above description and the accompanying Figures. The advantage derives mainly from the non-forced coupling along the horizontal plane of the panels. Furthermore, in correspondence of the grooves 20 and 32 in the lower extension portions 16 and 30 of each panel 10, zones are formed which have a lower strength than the main panel body owing to the reduced cross-section size. Therefore, even in the case that a panel eventually suffers an accidental breakage, the latter would occur in correspondence of the groove 20 and/or the groove 32 and would further develop in a vertical direction without involving the central portion of the panel.
 As a result, the resulting damage would only be limited in its extent and would not be transferred on to the upper surface of the panel.
 Anyway, features and advantages of the present invention will be more readily and clearly understood from the description that is given below by way of non-limiting example with reference to the accompanying drawings, in which:
FIG. 1 is an interrupted cross-sectional view of a panel according to the present invention;
FIG. 2 is a partial cross-sectional view of the longitudinal edges of two panels in the phase in which the respective side profiles engage each other;
FIG. 3 is a partial cross-sectional view of the longitudinal edges of the two panels of FIG. 2 in their fully engaged condition;
 FIGS. 4 to 6 are partial cross-sectional views of the longitudinal edges of the two panels of FIG. 3 under different load conditions;
FIG. 7 is an interrupted longitudinal sectional view of the panel of FIG. 1;
FIG. 8 is a partial cross-sectional view of the butt sides of two contiguous panels with their respective profiles fully engaging each other; and
FIG. 9 is a partial perspective view of a floor covering in the phase in which the butt profiles of the panels are assembled.
 The present invention refers to a floor covering formed by panels constituted by boards of cellulose fibers or wood shavings bound with synthetic resins, generally known in the art as MDF (Medium Density Fiberboards), HDF (High Density Fiberboards) and faced chipboards.
 Floor coverings of the above cited kind have been known for a long time now, while a number of different solutions have been proposed to keep the panels joined to each other.
 In a first example, the edges of the panels are profiled so as to bring about tongue-and-groove joints between contiguous panels. In order to prevent assembled panels from possibly separating from each other, thereby creating unwanted gaps or clearances, additional measures are quite often taken such as glueing the edges or using metal or plastic interconnecting profiles.
 In an improved example, the edges of the panels have profiles that are so shaped as to feature snap-fit joining elements, in such a manner as to do away with the need for additional components or materials to be used for strengthening the joints. This solution, which is described in WO 94/1628, WO 96/27719 and WO 96/27721, is however not effective in ensuring an adequate and firm stability along all sides of the panels.
 Of these, WO 96/27719 provides a coupling of the long sides of two contiguous panels achieved by two pairs of mating teeth with plane surfaces, parallel and orthogonal to each other.
 A first panel has a first front tooth, with plane and parallel surfaces, suitable to be inserted through rotation and sliding into a recess with plane and parallel surfaces made inside the second panel; in a terminal position and on the lower face, the second panel has a compartment comprising a tooth facing towards the base which is inserted in an inner recess made on the extension of the base of the first panel and in an intermediate position of a ridge cooperating with the compartment.
 This type of coupling causes a rigid constraint, forced and without play between the panels, which are not therefore able to slide longitudinally and freely with respect to each other once they have been assembled. Moreover, the coupling is not able to compensate production tolerances and/or deformations of the material with the passing of time, and is not able to allow reciprocal lateral movements of adjustment. Furthermore, to achieve such a coupling it is necessary to provide at least three different types of material, with obvious problems of reciprocal attachment and different shrinkage.
 When the floor covering has been laid, it is extremely difficult to separate the panels from each other, so that every intervention of maintenance and repair entails risks of breakage and damage.
 Moreover, this document does not describe how the butt-wise coupling of two adjacent panels is achieved.
 Document EP-A-698162 provides a coupling through rotation and sliding similar to that described in WO'719, but without the tooth and mating inner recess. In this case too, at least two different types of material are necessary, with problems of reciprocal anchorage and problems of different shrinkage.
 In EP'162 the coupling of two panels is achieved so as to maintain a certain play orthogonal to the axis of the coupling, so that, even after assembly, the panels are free to slide longitudinally with respect to each other and to move laterally, using the free spaces.
 However, the solution shown in EP'162 has the disadvantage that no component of the coupling can be elastically deformed, not even temporarily.
 Moreover, the section of the panel in the coupling zones does not have any undercut or bevel which can facilitate the insertion through rotation.
 This leads to the disadvantage that, in order to be able to insert the front tooth of the first panel into the recess of the second panel, simultaneously taking the compartment to couple with the mating recess, it is necessary to provide a great projecting length of the lateral zones of the panels on which the respective coupling elements are made.
 Given the very limited thickness of the panel, the size of the projecting teeth present on the sides of the panels cannot be reduced to less than a minimum value, both because of problems of mechanical resistance, and also because of geometric problems of rotation and insertion. A great width of the lateral projecting zones, where the panels are coupled together, entails, in the first place, a constraint of minimum width of the panel below which it is not possible to go.
 Moreover, it entails a greater fragility and risks of breakage of the projecting parts, which are thinner compared with the overall thickness of the panel.
 This is even more true when we consider that the tendency at present is to try to obtain the panels in a composite material based on pressed wood shavings (for example with a product known commercially as MDF or HDF).
 Furthermore, it entails bands of structural weakening of the panels in correspondence with the coupling zones, which are characterized by a much lower capacity to resist localized loads applied to the floor covering.
 To overcome this problem, EP'162 provides an auxiliary element of metal reinforcement to support the floor covering, but this creates problems in the processing, problems of costs, of coupling of the materials and of laying.
 In this document too, there is no mention of the procedure to couple the butt sides of the panels.
 A solution has been proposed (WO 97/47834) in which the edges of the panels are provided with mutually engaging elements in the form of tongues and grooves, which are provided with mechanical locking means adapted to prevent the edges from possibly separating from each other. These locking means are provided integrally with the related panel and the coupling is brought about laterally along the edges by just snap-fitting and/or rotating them into fastening. The locking means are represented by inclined-plane profiles that are forced elastically into coupling. The preferred inclination of the coupling surfaces is indicated to lie anywhere between 30° and 70° with respect to the horizontal plane. The contours of the edges of such panels appear to be rather complex, since the aim is to obtain the coupling along the longitudinal edges through a rotary movement and subsequent snap-fit engagement, while the butt joints are obtained directly by snap-fitting, preferably with the use of tools. In substance, it therefore ensues that, when the panels are so assembled, the locking means exert a tension that forces contiguous panels against each other.
 Such a solution as disclosed in WO 97/47834 has a number of drawbacks. In the first place, since the coupling of the panels with each other is forced by means of a mechanical tension, the need arises for very solid, strong materials to be used in the construction of said panels, such as in particular high-density compressed fiberboards (HDF), to be further specially reinforced along their edges.
 Moreover, such a forced fitting brings about a certain extent of downward bending of the tongues of the panels that remain or are put under load. This has a twofold negative consequence, ie. (i) the need for an elastic support layer to be always provided under the floor covering in order to dimensionally absorb the deflection of the tongues in view of preventing them from breaking, and (ii) a constant possibility of fracture due to the strain to which the tongues are submitted along a horizontal plane in a central section of the panel in correspondence with the bottom of the groove. Such a possibility of the panels breaking along a central portion thereof arises still more easily when the panels are butt joined, ie. when use must be made of a wall abuttal wedge or a wooden block, driven with an appropriate tool such as a hammer, in order to bring about the forced coupling. Of course, owing to the surface tensioning of the panels due to the melamine layers of the surfaces, any rupture within the same panels would unfailingly cause the edge thereof to raise with respect to the plane of the floor, with negative consequences not only from an aesthetical point of view, but also in connection with arising risks of stumbling and the weardown of the upper surface of the so exposed edge. Finally, a floor covering in which the panels are kept joined to each other by forced snap-fit coupling and under constant tension, cannot be disassembled to modification or repair purposes without incurring the risk of seriously damaging it.
 It therefore is a main purpose of the present invention to provide a floor covering made of MDF, HDF or faced-chipboard panels which is simpler as far as both the construction of the panels and the assembly thereof are concerned, wherein the coupling and attachment means are obtained directly from the material of the panel without other additional materials, which has tensionless coupling means that enable the same panels to slide both longitudinally and along their butt joints relative to each other. Such sliding not only facilitates the assembly and disassembly, it also allows the floor covering to be laid without difficulty.
 Another purpose of the invention is to reduce the width of the projecting coupling parts, reducing the risks of unwanted deflection and breakage, and also the amplitude of fragile zones subject to deformation when there are localized loads.
 The attachment means are embodied in a partly elastic front element which temporarily bends during the insertion and rotation of two adjacent panels, thus facilitating the laying operations, the coupling of the panels and, also, possible later operations to disassemble them.
 When the operation to couple one panel with the contiguous one has been completed, and when the panels are in a coplaner position, the elastic flection of the material is released, so that the two panels are coupled without any reciprocal tension.
 Thanks to the geometry of the attachment means, this solution allows to keep free spaces between the coupling surfaces, in order to allow two adjacent panels to slide freely in longitudinal manner, and also to make lateral movements of adjustment to recover play, tolerances and deformations of the material.
 On two opposite longitudinal sides, each panel has first male attachment means and mating first female attachment means, which comprise projecting portions with a width substantially equal to the thickness of the panel.
 The first male attachment means have a tooth protruding towards the outside and lying on a substantially horizontal plane, and the first female attachment means have a substantially horizontal mating recess; the height and width of the protruding tooth are substantially equal, that is, about Ό of the thickness of the panel.
 The first male attachment means and/or the first female attachment means have bevels and/or undercuts on the vertical plane which facilitate the insertion through rotation of two adjacent panels during the coupling phase, allowing to further reduce the width of the projecting portions.
 The floor covering according to the present invention therefore allows for materials without any particular solidity characteristics to be used in manufacturing said panels, as well as for the use of any kind of tools whatsoever to be done away when assembling and disassembling the same floor covering. From a functional point of view, it is then important to notice that the panels are provided with an appropriately profiled edge, so that any breaking or rupture that might possibly occur in use, would develop at the base thereof, and along a vertical section, so as to avoid any projection or prominence of the edge with respect to the plane of the floor, and the related loss of planarity.
 These and further aims are reached in a floor covering according to the present invention which is characterized according to what is set forth in the main claim.
 The floor covering according to the invention has the corresponding longitudinal edges of two contiguous panels which are associated with each other by overlapping and engage each other without any interference along at least a vertical plane, so as to bring about a self-levelling and self-stabilizing connection under load, with the possibility for the edges to longitudinally slide relative to each other, and with the effect of a slight reciprocal elastic attraction, during the coupling phase, between one panel and the other.
 The self-levelling and self-stabilizing effect is obtained thanks to the geometric constraint created between the respective first male-female attachment means and thanks to the planarity of the surfaces of reciprocal coupling, which are parallel to each other and parallel to the surface on which the floor covering rests.
 In correspondence with the butt sides of the respective panels, the floor covering according to the invention has second male coupling means on one side and second female coupling means on the opposite side, able to be taken into a position of reciprocal constraint by means of a movement of scissor-like rotation of the new panel with respect to the one already in position.
 Said coupling means of the butt sides have at least a partly elastic element which can partly bend during the assembly of two adjacent panels, and is released when coupling is complete; in the coupling zones between the butt sides free spaces are formed between reciprocally cooperating surfaces.
 At least some of the second male and female coupling means of the butt sides, according to a characteristic of the invention, are defined by rounded cam-type profiles reciprocally mating and coupling in forced manner, thus achieving an interference on the vertical plane which, when the panels are in the coplaner position, prevents movements of reciprocal lifting of two coupled panels.