Patent Description:
Building panels provided with a mechanical locking system comprising a displaceable and resilient tongue cooperating with a tongue groove for vertical locking is known and disclosed in, e.g., <CIT> and <CIT>, The tongue is a separate part and is made of, e.g., plastic and inserted in a displacement groove at an edge of a panel. The tongue is pushed into the displacement groove during a vertical assembling of the panels and springs back into the tongue groove of an adjacent panel when the panels have reached a locked position.

Also known is a locking system for panels comprising a tongue, which is displaceable along the edge of a panel, see e.g. <CIT>, and cooperates with a tongue groove for vertical locking. The tongue is a separate part and is provided with several protrusions, which initially match recesses of the tongue groove. The panels may be assembled by a vertical movement and the tongue is displaced to a position in which the protrusions no longer match the recesses in order to obtain the vertical locking.

Further known is a locking system comprising a tongue provided with, e.g., a wedge element. Two adjacent panels edges are locked by displacing the tongue along the adjacent edges, see e.g. <CIT>.

Further known locking systems are disclosed in <CIT> , which discloses the features of the preamble of claim <NUM>, and <CIT>.

Although the description relates to floor panel, the description of techniques and problems thereof is applicable also for other applications, such as panels for other purposes, for example, wall panels, ceiling panels, furniture etc..

A drawback with the known systems is that a locking system comprising a displaceable tongue requires a rather thick panel to ensure that the locking system meets the strength requirement.

The above description of various known aspects is the applicant's characterization of such, and is not an admission that any of the above description is considered as prior art.

It is an object of certain embodiments of the present invention to provide an improvement over the above described techniques and known art. Particularly the strength of the known locking system is improved by embodiments of the invention.

A further object of embodiments of the invention is to provide thinner panels with a locking system comprising a displaceable tongue.

At least some of these and other objects and advantages that will be apparent from the description have been achieved by the claimed invention.

A first aspect comprises a set of essentially identical panels provided with a mechanical locking system comprising a displaceable tongue, which is arranged in a displacement groove at a first edge of a first panel and a first tongue groove, at a second edge of an adjacent second panel. The displaceable tongue is configured to cooperate with the first tongue groove for locking in a vertical direction of the first and the second edge. The displacement groove is provided with a first opening and the first tongue groove is provided with a second opening wherein a height of the first opening is greater than a height of the second opening. At least a part of the displaceable tongue is preferably configured to be pushed into the displacement groove during assembling of the first and the second panel and spring back to a position in which an outer part of the displaceable tongue cooperate with the first tongue groove for the locking in the vertical direction.

The height of the second opening may be in the range of about <NUM>% to about <NUM>% of the height of the first opening, preferably in the range of about <NUM>% to about <NUM>% of the height of the first opening.

The first opening and the second opening are preferably horizontally open and a vertical height of the second groove is preferably greater than a vertical height the first opening.

A maximum height of the displacement groove may be greater than a maximum height of the first tongue groove. The maximum height of the first tongue groove may be in the range of about <NUM>% to about <NUM>% of the maximum height of the displacement groove, preferably in the range of about <NUM>% to about <NUM>% of the maximum height of the displacement groove.

An outer part of the displaceable tongue is preferably provided with a recess. The smaller opening of the first tongue groove and the thinner first tongue groove increases the strength of the locking system at the second edge with the first tongue groove. The thicker displacement groove is preferably provided on an edge, i.e., the first edge, with more material available for the displacement groove or a stronger material.

The recess may comprise a first recess surface and a second recess surface, which are arranged at an obtuse angle to each other. The first recess surface of the recess may be a first surface configured to cooperate with the first tongue groove, preferably at a second surface, for locking in the vertical direction. An angle between an upper surface of the displaceable tongue and the first recess surface may be in the range of about <NUM>° to about <NUM>°, preferably in the range of about <NUM>° to about <NUM>°. The recess and the angle may provide the benefit of an increased locking strength, since the first surface and the second surface may be arranged at an angle that requires, in a locked position, an increased force to push the displaceable tongue into the displacement groove.

The displaceable tongue is preferably of a longitudinal shape and an outer longitudinal edge of the displaceable tongue is preferably straight along essentially the whole longitudinal length of the tongue. A bevel may be provide at at least one end of the longitudinal edge, at a short edge of the displaceable tongue, to facilitate assembling of the first and the second panel by an angling movement.

The recess preferably extends along essentially the whole longitudinal length of the displaceable tongue.

The benefits of examples of the disclosure may be more pronounced for thin panels, e.g. thinner than <NUM>. The panels may be in the range of about <NUM> to about <NUM>, preferably in the range of about <NUM> to about <NUM>, and preferably in the range of about <NUM> to about <NUM>.

The mechanical locking system may comprise a first locking strip, at the first or the second edge, provided with a first locking element configured to cooperate for horizontal locking with a first locking groove at the other of the first or second edge.

Since the height of the first opening is greater than the second height of the second opening, the first locking strip is preferably arranged at the first edge and the first locking groove on the second edge. An outer and lower part of the displaceable tongue is preferably provided with the recess.

The panels may be rectangular and the mechanical locking system may comprise a second locking strip, at a third or fourth edge, provided with a second locking element configured to cooperate for horizontal locking with a locking groove at the other of the third or fourth edge of an adjacent third panel. The third or the fourth edge is preferably provided with a second tongue configured to cooperate for vertical locking with a second tongue groove at the other of the third or fourth edge of an adjacent third panel. Each edge provided with a locking groove is preferably provided with a lower edge surface configured to cooperate with an upper surface of a locking strip at an adjacent panel. The lower edge surface is therefore preferably arranged in the same plane as the upper surface of the locking strip at the adjacent panel.

An upper surface of the first locking strip is preferably provided in a same plane as an upper surface of the second locking strip. The mechanical locking system at the third and fourth edge is normally produced before the mechanical locking system at the first and second edge. If said upper surfaces are in the same plane or essentially in the same plane remainders of the mechanical locking system at the third and fourth edge, at the corner of the panels may be automatically removed. The remainders are generally thin and may later come loose, e.g. during packaging, transportation or assembling.

The mechanical locking system at the third and the fourth edge may be configured to be assembled by an angling motion.

The mechanical locking system at the first and the second edge may be configured to be assembled by a vertical motion.

A second aspect is a set of essentially identical panels provided with a mechanical locking system comprising a displaceable tongue, which is arranged in a displacement groove at a first edge of a first panel and a first tongue groove at a second edge of a second panel. The displaceable tongue is configured to cooperate with the first tongue groove, for locking in a vertical direction of the first and the second edge. The displaceable tongue comprises at least two bendable parts, wherein at least one of the bendable parts is provided with a lower and/or an upper friction connection at a distance from the innermost part in the displacement groove of the bendable part. The distance may make it easier to arrange the displaceable tongue in the displacement groove. At least a part of the displaceable tongue is preferably configured to be pushed into the displacement groove during assembling of the first and the second panel and spring back to a position in which an outer part of the displaceable tongue cooperate with the first tongue groove for the locking in the vertical direction.

The displacement groove may comprise an upper wall, a lower wall and an inner wall extending between the lower and the upper wall. The inner wall is preferably of a rounded shape or may comprise a plane section provided with a round section adjacent to the upper and/or lower wall. The rounded shape and the round section/s increase the strength of the mechanical locking system. The benefits of this embodiment may be important for thin panels, e.g. thinner than <NUM>. The panels may be in the range of about <NUM> to about <NUM>, and preferably in the range of about <NUM> to about <NUM>.

The upper friction connection is preferably configured to cooperate with a plane section of the upper wall. The upper friction connection may comprise a protruding part of the bendable part that extends above remaining parts of the displaceable tongue. An upper surface of the displaceable tongue may be configured to be displaced along the upper wall during assembling of the first and the second panel. A lower surface of the displaceable tongue may be configured to be displaced along the lower wall during assembling of the first and the second panel.

The lower friction connection is preferably configured to cooperate with a plane section of the lower wall. The lower friction connection may comprise a protruding part of the bendable part that extends below remaining parts of the displaceable tongue.

The innermost part of the bendable part may be provided with an upper and/or lower bevel. The upper and/or lower bevel facilitates the insertion of the displaceable tongue into the displacement groove.

The displaceable tongue may be of a longitudinal shape and an outer longitudinal edge of the displaceable tongue is preferably straight along essentially the whole longitudinal length of the displaceable tongue. A bevel may be provided at at least one end of the longitudinal edge, at a short edge of the displaceable tongue, to facilitate assembling of the first and the second panel by an angling movement.

An outer part of the displaceable tongue may be provided with a recess, which preferably extends along essentially the whole longitudinal length of the tongue. A first surface of the recess is preferably configured to cooperate with a second surface of the first tongue groove for locking in the vertical direction.

The mechanical locking system may comprise a first locking strip, at the first or the second edge, provided with a first locking element configured to cooperate with a first locking groove at the other of the first or second edge for locking in a horizontal direction.

A size of the displacement groove at the first edge may be greater than a size of the first tongue groove at the second edge. The first locking strip is preferably arranged at the first edge and the first locking groove on the second edge. An outer and lower part of the displaceable tongue is preferably provided with the recess.

The displacement groove may have a first opening and the first tongue groove may have a second opening, wherein a first height of the first opening is preferably greater than a second height of the second opening.

An aspect of the invention is a set of essentially identical panels provided with a mechanical locking system comprising a displaceable tongue, which is arranged in a displacement groove at a first edge of a first panel and a first tongue groove at a second edge of a second panel. The displaceable tongue is configured to cooperate with the first tongue groove, for locking in a vertical direction of the first and the second edge. At least a part of the displaceable tongue is preferably configured to be pushed into the displacement groove during assembling of the first and the second panel and spring back to a position in which a part of the displaceable tongue cooperate with the first tongue groove for the locking in the vertical direction. The displaceable tongue comprises a first and a third surface and the first tongue groove comprises a second and fourth surface. A first angle between the second surface and a front face of the second panel is greater than a second angle between the fourth surface and the front face. The first surface of the displaceable tongue is configured to cooperate with the second surface of the tongue groove under a first load on the mechanical locking system. The third surface of the displaceable tongue is configured to cooperate with the fourth surface of the tongue groove under a second load on the mechanical locking system. The first load may correspond to a load under normal condition and the second load may correspond to an increased load when for example a chair, a sofa or a bookcase is positioned on the first or the second panel. The first angle may have the advantage that a small displacement of the displaceable tongue pushes the first and the second panel together to the desired locked position, in which the front face of the second panel is essentially in the same vertical position as a front face of the first panel. The second angle may have the advantage that the third and the fourth surface are able to carry a greater load and that the displaceable tongue is prevented from being pushed out from the first tongue groove. Another advantage of the second angle is that a height of an opening of the first tongue may be decreased. A decreased height may increase the strength of the mechanical locking system. The first angle may be in the range of about <NUM>° to about <NUM>° and the second angle may be in the range of about <NUM>° to about <NUM>°. The difference between the first angle and the second angle may be in the range of about <NUM>° to about <NUM>°.

The mechanical locking system described under the first and the second aspect may comprise the first, the second, the third and the fourth surface described under the aspect of the invention.

The panels according to the first and the second aspect or the aspect of the invention may be floorboards, wall panels, ceiling panels, a furniture component or the like.

A core of the panels according to the first and the second aspect or the aspect of the invention may be a wood-based core, preferably made of MDF, HDF, OSB, WPC, plywood or particleboard. The core may also be a plastic core comprising thermosetting plastic or thermoplastic e.g. vinyl, PVC, PU or PET. The plastic core may comprise fillers. The thinner first tongue groove may be easier, for a panel with a layered core, such as a core comprising plywood, to arrange at a favourable position in relation to the layers is the core.

The front face of the panels according to the first and the second aspect or the aspect of the invention is preferably provided with a decorative layer and the back face is preferably provided with a balancing layer.

The edge of the panels, according to the first and the second aspect or the aspect of the invention, of which parts of the locking system, such as the first and the second locking strip, the first and the second locking element, the first and the second locking groove and the first and the second tongue groove, may be made, may comprise the core material.

The present invention will by way of example be described in more detail with reference to the appended schematic drawings, which shows embodiments of the present invention.

A known mechanical locking system for building panels, which comprises a displaceable tongue <NUM> at a first edge of a first panel <NUM> and a first tongue groove <NUM> at a second edge of a second panel <NUM>', is shown in <FIG>. The displaceable tongue is configured to cooperate with the first tongue groove for locking in a vertical direction. The displaceable tongue <NUM> is a separate part and is made of, e.g., plastic, and inserted in a displacement groove at the first edge of the first panel <NUM>. The tongue is pushed into a displacement groove during a vertical assembling of the first and the second edge of the first and the second panel. The displaceable tongue springs back and into a first tongue groove <NUM> at the second edge of the second panel <NUM>' when the panels have reached a locked position. A third and a fourth edge of the panels are provided with a locking system, which enables assembling to an adjacent panel <NUM>" by an angling movement, to obtain a simultaneous assembling of the first and the second edges and the third and the fourth edges.

<FIG>and <FIG> show cross sections of different embodiments of the known displaceable tongue <NUM> during assembling of a first and a second panel <NUM>, <NUM>'. The second panel <NUM>' with the first tongue groove is displaced in relation to the second panel with the displaceable tongue <NUM>, which is pushed into a displacement groove <NUM> by an edge of the second panel. The displaceable tongue <NUM> springs back, and into the first tongue groove <NUM>, when the panels have reached an assembled position, and locks the first and the second panels vertically.

Examples of the disclosure are shown in <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG> <FIG>, <FIG>, <FIG> and <FIG>. A mechanical locking system is formed at a first and a second edge of essentially identical first and second panels <NUM>, <NUM>'. The mechanical locking system is configured for locking the first edge of the first panel to the second edge of the second panel, in a vertical and/or horizontal direction. An embodiment of the mechanical locking system enables assembling of the first and the second panels by a vertical displacement of the second edge of the second panel relative the first edge of the first panel. The mechanical locking system is preferably formed by mechanical cutting, such as milling, drilling and/or sawing, of the edges of the panels and provided with a displaceable tongue <NUM>, preferably of plastic. The displaceable tongue may be bendable and provided with protruding bendable parts, such as the displaceable tongues disclosed in <CIT> and <CIT>. The displaceable tongue may also be configured to be locked by a movement along the first and the second edge, such as the displaceable tongues disclosed in <CIT> and <CIT>.

Embodiments comprise a displaceable tongue <NUM> arranged in a displacement groove <NUM> at the first edge of the first panel <NUM>. The displaceable tongue <NUM> cooperates with a first tongue groove <NUM>, which is formed at the second edge of a second panel <NUM>', for locking of the first and the second edge in a vertical direction. A first locking strip <NUM> with a vertically protruding first locking element <NUM> is formed in the first edge of the first panel. The first locking element <NUM> cooperates with a first locking groove <NUM>, formed in the second edge of the second panel <NUM>', for locking of the first and the second edge in a horizontal direction. A lower edge surface of the second edge may be arranged in the same plane as a first upper surface of the first locking element. The lower edge surface may be configured to cooperate with the first upper surface for locking the first and the second edge in a vertical direction. <FIG> and <FIG> show that the height <NUM> of the opening of the first tongue groove <NUM> is smaller than the height <NUM> of the displacement groove <NUM>. Preferably, also the maximum height of the first tongue groove <NUM> is smaller than the maximum height <NUM> of the displacement groove <NUM>. The tongue groove and the displacement groove may be provided with a guiding bevel or rounding that are not include in the height of the opening or the maximum height of the groove when measuring the heights of the grooves. Such a first tongue groove has the effect that the distance <NUM> between a lower side of the second panel and the bottom of the first tongue groove may be increased and the distance <NUM> between the first tongue groove <NUM> and the locking groove <NUM> may be increased. The increased distance <NUM> between the first tongue groove <NUM> and the locking groove <NUM> increases the strength of the locking system. In order to further increase the distance and the strength the displacement groove and the displaceable tongue may be angled, as is shown in e.g. <FIG> and <FIG>. The outer part of the displaceable tongue is preferably provided with a recess <NUM>, so that the outer part may be displaced into the first tongue groove <NUM>.

With the smaller first tongue groove <NUM> the distance <NUM> between a front face of the first panel and the displacement groove <NUM> may be increased and/or the thickness of the locking strip <NUM> may be increased with the same or increased distance <NUM> between the first tongue groove <NUM> and the locking groove <NUM> for the same thickness of the first and second panel, as is shown in <FIG>.

The first locking groove may also be arranged on the first panel with the displacement groove. Such embodiments are preferably provided with a displaceable and flexible tongue, which is fixed to parts of the displacement groove by glue. An inner part of the flexible and displaceable tongue is preferably glued to a bottom surface of the displacement groove. The inner part may also be glued to an upper and/or lower surface of the displacement groove <NUM>.

Embodiments comprise a set of essentially identical panels comprising the first panel <NUM>, the second panel <NUM>' and a third panel <NUM>", as shown in <FIG>. Each panel may be of a rectangular shape and the mechanical locking system may comprise a second locking strip <NUM>, at a third edge 5a, provided with a second locking element <NUM>, and a second locking groove <NUM> at a fourth edge 5b, as is shown in e.g. <FIG> and <FIG>. The second locking element <NUM> is configured to cooperate with the second locking groove <NUM> for locking of the third and the fourth edge in a horizontal direction. The mechanical locking system may comprise a second tongue groove <NUM> at a third edge 5a and a second tongue <NUM> at a fourth edge 5b. The second tongue and the second tongue groove are configured to cooperate for locking of the third and the fourth edge 5a, 5b in a horizontal direction. The fourth edge 5b is preferably provided with a lower edge surface configured to cooperate with a second upper surface of the second locking strip. The lower edge surface is therefore arranged in the same plane as the second upper surface of the second locking strip at the adjacent panel.

<FIG> shows an assembling of the second panel <NUM>' to the first and the third panel <NUM>, <NUM>". The second panel <NUM>' is angled around the fourth edge 5b of the second panel <NUM>' to obtain simultaneously locking of the fourth edge 5b of the second panel <NUM>' to the third edge 5a of the third panel <NUM>" and the second edge 4b of the second panel <NUM>' to the first edge 4a of the first panel <NUM>'.

The first upper surface <NUM> of the first locking strip is preferably provided in a same plane as the second upper surface <NUM> of the second locking strip <NUM>. The mechanical locking system at the third and the fourth edge 5a, 5b is normally produced before the mechanical locking system at the first and the second edge 4a, 4b. If said first and second upper surface are in the same plane or essentially in the same plane remainders of the mechanical locking system at the third and fourth edge 5a, 5b, at corners of the panel may be automatically removed. The remainders are generally thin and may later come loose, e.g. during packaging, transportation or assembling. An embodiment is shown in <FIG> with a first corner 2a, between the fourth edge 5b and the first edge 4a, and a second corner 2b between the third edge 5a and the second edge 4b. The remainder of the mechanical locking system at the fourth edge and the first corner 2a are automatically removed when forming the mechanical locking system at the first edge. The remainders of the mechanical locking system at the third edge and the second corner 2b are automatically removed when forming the mechanical locking system at the second edge.

<FIG> shows a cross section of the third edge of the first panel <NUM> and the fourth edge of the third panel <NUM>". The mechanical locking system at the third and the fourth edge comprises the second tongue <NUM> at the fourth edge and the second tongue groove <NUM> at the third edge. The third edge is provided with the second locking strip <NUM>, protruding from the third edge, with the second locking element <NUM>, and the fourth edge is provided with the second locking groove. The second upper surface <NUM> of the locking strip <NUM> is in contact with the lower surface of the fourth edge for locking in a vertical direction. The shown mechanical locking system at the third and the fourth edge is configured to be assembled and locked by an angling motion. The second upper surface is positioned in a horizontal plane <NUM>. <FIG> shows a cross section of the first edge of the first panel and the second edge of the second panel. The first edge is provided with the first locking strip <NUM>, protruding from the first edge, with a first locking element <NUM>, and the second edge is provided with the first locking groove. The first upper surface <NUM> of the first locking strip is in contact with a lower surface of the second panel for locking in a vertical direction. The remainders of the mechanical locking system, at the third edge and the second corner and at the fourth edge and the first corner, may be automatically removed if said first and second upper surfaces are in the same horizontal plane <NUM>. Unremoved remainders, such as the remainders <NUM> at the second corner shown in <FIG>, are generally thin and may later come loose, e.g. during packaging, transportation or assembling.

The known mechanical locking system at the first and the second edges, as is shown in <FIG>, is provided with a first upper surface <NUM> at a lower horizontal plane <NUM> than the second upper surface at the third and the fourth edge. For the known mechanical locking system an additional operation is required to remove the remainder. The example makes it possible to increase the thickness of the first locking strip and thereby arranging the first and the second upper surface in the same horizontal plane <NUM> without decreasing the distance <NUM> between the first locking groove <NUM> and the first tongue groove <NUM>. This has the effect that the strength of the mechanical locking system is increased.

A preferred embodiment of the displaceable tongue <NUM> is shown in <FIG>. The displaceable tongue comprises several bendable parts <NUM>. The bendable parts are provided with a lower and an upper friction connection <NUM> at a distance from the innermost part of the bendable part. The innermost part of the bendable parts <NUM> is provided with an upper and a lower bevel <NUM>. The tongue is of a longitudinal shape and an outer edge of the displaceable tongue is preferably straight along essentially the whole longitudinal length of the displaceable tongue. An outer part <NUM> of the displaceable tongue is provided with a recess <NUM>, which preferably extends along essentially the whole longitudinal length of the tongue. A first recess surface <NUM> of the recess is configured to cooperate with a first surface of the first tongue groove for locking in the vertical direction. A bevel <NUM> is provided at each end of the longitudinal edge, at a short edge of the displaceable tongue, to facilitate assembling of the first and the second panel by an angling movement. The tongue comprises a groove <NUM> at each bendable part <NUM>. At least a part of the bendable part <NUM> is pushed into the groove <NUM> during assembling. The recess <NUM> may comprise a second recess surface <NUM>, which is arranged at an obtuse angle to the first recess surface <NUM>. An angle between an upper surface of the displaceable tongue and the first recess surface <NUM> may be in the range of about <NUM>° to about <NUM>°, preferably in the range of about <NUM>° to about <NUM>°.

The displaceable tongue is preferably produced by injection moulding and <FIG> shows casting gates at the short edges of the displaceable tongue.

<FIG> shows displaceable tongue <NUM> arranged in the displacement groove <NUM> in a position during an assembling when the tongue is pushed into the displacement groove. The displacement groove <NUM> comprises an upper wall, a lower wall and an inner wall extending between the lower and the upper wall. The inner wall is of a rounded shape. The inner wall may as an alternative comprise a plane section provided with a round section adjacent to the upper and/or lower wall. The upper friction connection is configured to cooperate with a plane section of the upper wall. The lower friction connection is configured to cooperate with a plane section of the lower wall. An upper surface of the displaceable tongue may be configured to be displaced along the upper wall during assembling of the first and the second panel. A lower surface of the displaceable tongue may be configured to be displaced along the lower wall during assembling of the first and the second panel.

<FIG> shows another known mechanical locking system and <FIG> shows an improved version according to examples of the disclosure presently not claimed. The displaceable tongue <NUM> is provided with a recess at the outer part and the first tongue groove <NUM> is made smaller. The thickness of the locking strip <NUM> is increased and a bottom of the displacement groove <NUM> is provided with rounded corners. <FIG> shows that the upper and the lower outer part of the displaceable tongue may be provided with a recess. Particularly for floorboards of soft material, e.g. comprising a plastic core such as PVC, the joint is made stronger if both the upper and the lower outer part of the displaceable tongue are in contact with first tongue groove.

Further examples of the disclosure presently not claimed are shown in <FIG>. The benefits of the smaller first tongue groove <NUM> and the displaceable tongue <NUM> provided with a recess at the outer part are in the embodiment in <FIG> utilized to make the locking strip <NUM> thicker. <FIG> shows an embodiment with a displacement groove <NUM> provided with rounded corners and a locking groove <NUM> and locking element <NUM> provided with chamfered surfaces in order to further increase the strength of the locking system.

<FIG> shows an embodiment which is of the type disclosed in <CIT> with the displaceable tongue <NUM> arranged at the edge of the panel provided with the locking groove. The recess at the outer edge of the displaceable tongue is shown on the lower edge of the displaceable tongue but the recess may also be provided at the upper and outer edge of the displaceable tongue.

<FIG> shows embodiments provided with a protruding part <NUM> at the lower side of the second edge. The protruding part <NUM> is configured to cooperate with a recess <NUM> at the upper side of the first locking strip and with the first locking element <NUM>. Such configurations may increase the thickness of an inner part of the locking strip and the strength of the mechanical locking system.

<FIG>shows an embodiment comprising a displaceable tongue <NUM>, which is configured to be locked by a displaceable element <NUM>. The displaceable element may comprise a wedge shaped element (not shown) that pushes the displaceable tongue <NUM> into the first tongue groove <NUM> for vertical locking of the first and the second edge. The displaceable element may be displaced by pushing the displaceable element into <NUM> the displacement groove <NUM> along the second edge or by pulling the displaceable element along the second edge and out of the displacement groove <NUM>. <FIG> shows the embodiment in and unlocked position and <FIG> shows the embodiment in a locked position.

<FIG> shows a displaceable tongue comprising three sections, an inner section 30b, an outer section 30a and a middle section 30c connected to each other. The sections are preferably formed from a plastic material. The outer and inner sections 30a and 30b are formed from a more rigid material than the middle section that provides the major flexibility to the flexible tongue. The middle section may be a rubber like material and may also be used as a friction connection in order to prevent that the flexible tongue falls out from the groove <NUM> after connection to a panel edge. The flexible middle section 30c is preferably located at a lower part of the flexible tongue. The middle section 30c comprises an upper part 31a that is compressed during locking and a lower part 31b that expands during locking. The outer part 30a protrudes preferably outside a vertical pane VP that intersects the upper adjacent joint edges of the panels <NUM>, <NUM>'. The locking system allows locking with low horizontal separation forces during locking. The vertical extension of the tongue groove <NUM> may be less than <NUM>,<NUM> times the vertical extension of the displacement groove <NUM>. The inner part 30b comprises a fixing edge <NUM> that may be located at an upper or a lower part of the flexible tongue.

The flexible tongue may also be formed with only two sections, preferably without the more rigid inner section 30b. An outer section 30a may be connected to an inner section 30d that may have the same function as the above described middle section 30c and flexibility may be obtained with compression and extension of upper and lower parts of the flexible inner section when the outer section is turning inwards. This allows that the displacement groove may be smaller. Such a two sections tongue may also be used to lock panel according to the principles shown in <FIG>. The outer part 30a may point downwards when the flexible tongue <NUM> is located on a panel edge comprising a strip <NUM> (strip panel) and a locking element <NUM> and the flexible inner part 31d may be locate at an upper part of the flexible tongue <NUM>. The outer part 30a may point upwards when the flexible tongue <NUM> is connected to a panel edge comprising a locking groove (fold panel) and the flexible inner part 30d may be located at a lower part of the flexible tongue <NUM>.

Claim 1:
A set of essentially identical panels (<NUM>,<NUM>'), such as building panels, provided with a mechanical locking system comprising a displaceable tongue (<NUM>), which is arranged in a displacement groove (<NUM>) at a first edge of a first panel (<NUM>), and a first tongue groove (<NUM>) at a second edge of an adjacent second panel (<NUM>'), the displaceable tongue (<NUM>) is configured to cooperate with the first tongue groove (<NUM>) for locking of the first and the second edge in a vertical direction, wherein:
at least a part of the displaceable tongue is configured to be pushed into the displacement groove during assembling of the first and the second panel and spring back to a position in which a part of the displaceable tongue (<NUM>) cooperate with the first tongue groove (<NUM>) for the locking in the vertical direction,
characterized in that
the displaceable tongue comprises a first and a third surface (<NUM>, <NUM>) and the first tongue groove comprises a second and fourth surface (<NUM>,<NUM>),
a first angle between the second surface and a front face of the second panel is greater than a second angle between the fourth surface and the front face,
the first surface (<NUM>) of the displaceable tongue (<NUM>) is configured to cooperate with the second surface (<NUM>) of the tongue groove under a first load on the mechanical locking system,
the third surface (<NUM>) of the displaceable tongue is configured to cooperate with the fourth surface (<NUM>) of the tongue groove under a second load of the mechanical locking system, and wherein
the second load is greater than the first load.