Patent Description:
Embodiments of the present invention are particularly suitable for use in thin floating floors, which are formed of floor panels which are joined mechanically with a locking system preferably integrated with the floor panel, i.e. mounted at the factory, are made up of one or more upper layers of thermoplastic or thermosetting material or wood veneer, an intermediate core of wood-fibre-based material or plastic material and preferably a lower balancing layer on the rear side of the core. Embodiments of the disclosure can also be used for joining building panels which preferably contain a board material for instance wall panels, ceilings, furniture components and similar. It may also be used to connect ceramic tiles.

The following description of prior-art technique, problems of known systems and objects and features of embodiments of the invention will therefore, as a non-restrictive example, be aimed above all at this field of application and in particular at floor panels and especially at laminate floors and thin resilient thermoplastic floor panels such as so called luxury vinyl tiles, generally referred to as LVT, formed as rectangular floor panels with long and shorts edges intended to be mechanically joined to each other on both long and short edges.

The long and short edges are mainly used to simplify the description of embodiments of the invention. The panels may be square. Floor panels are generally produced with the surface layer pointing downwards in order to eliminate thickness tolerances of the core material. The major part of the embodiments is shown with the surface pointing upwards in order to simplify the description.

It should be emphasized that embodiments of the invention can be used in any floor panel on long and/or short edges and it may be combined with all types of known locking system on long or short edges that lock the panels in the horizontal and/or vertical direction.

Relevant parts of this prior art description are also a part of embodiments of the invention.

Several floor panels on the market are installed in a floating manner with mechanical locking systems formed at the long and short edges. These systems comprise locking means, which lock the panels horizontally and vertically. The mechanical locking systems are usually formed by machining of the core of the panel. Alternatively, parts of the locking system can be formed of a separate material, for instance aluminium or plastic material, which is integrated with the floor panel, i.e. joined with the floor panel in connection with the manufacture thereof.

Laminate flooring usually comprise a <NUM>-<NUM> millimetre, mm, wood based core, a <NUM> thick upper decorative surface layer of laminate and a <NUM> thick lower balancing layer of laminate, plastic, paper or like material. A laminate surface comprises melamine-impregnated paper. The most common core material is fibreboard with high density and good stability usually called HDF - High Density Fibreboard. The impregnated paper is laminated to the core with heat and pressure. HDF material is hard and has a low flexibility especially in the vertical direction perpendicular to the fibre orientation.

Recently a new type of powder based laminate floors, generally referred to as WFF floors (Wood Fibre Floors), have been introduced. Impregnated paper is replaced with a dry powder mix comprising wood fibres, melamine particles, aluminium oxide and pigments. The powder is applied on an HDF core and cured under heat and pressure. Generally, high quality HDF is used with a high resin content and low water swelling. Advanced decors may be formed by means of digital printing. Water based ink may be injected into the upper surface of the powder or injected in several transparent powder layers prior to pressing such that a very wear resistant 3D-print may be obtained. A digital binder and powder printing generally referred to as the "BAP method" may also be used to create advanced 3D-prints. Pigmented powder, or so-called dry ink, may be bonded in several layers with a digitally applied binder pattern comprising blank ink without pigments. The high wear resistance is often used to produce copies of stone and tiles. Such WFF floors may be rather wide and the material cost for the short edge locking system may be rather high.

LVT flooring with a thickness of <NUM>-<NUM> usually comprises a transparent wear layer which may be coated with an ultra-violet, UV, cured polyurethane, PU, lacquer and a decorative plastic foil under the transparent foil. The wear layer and the decorative foil are laminated to one or several core layers comprising a mix of thermoplastic material and mineral fillers. The plastic core is generally soft and very flexible.

Wood Plastic Composite floors, generally referred to as WPC floors, are similar to LVT floors. The core comprises thermosetting material mixed with wood fibre fillers and is generally stronger and much more rigid than the mineral based LVT core.

Thermoplastic material such as polyvinyl chloride, PVC, polypropylene, PP, or polyethylene, PE, may be combined with a mix of wood fibres and mineral particles and this may provide a wide variety of floor panels with different densities and flexibilities.

Moisture resistant HDF with a high resin content, LVT floors and WPC floors comprise stronger and more flexible core materials than conventional HDF based laminate floors and they are generally produced with a lower thickness.

A minimum thickness in several of the above mentioned floor types are mainly required in order to form the locking system. The panel itself is generally strong and flexible and a thickness of about <NUM> - <NUM> would in many applications be sufficient but cannot be used since it is not possible to form strong locking systems in such thin floors.

The above mentioned floor types comprise different core materials with different flexibility, density and strengths. Locking systems must be adapted to such different material properties in order to provide a strong and cost efficient locking function.

In the following text, the visible surface of the installed floor panel is called "front side" or "floor surface", while the opposite side of the floor panel, facing the sub floor, is called "rear side". The edge between the front and rear side is called "joint edge". By "horizontal plane" is meant a plane, which extends parallel to the front side. Immediately juxtaposed upper parts of two adjacent joint edges of two joined floor panels together define a "vertical plane" perpendicular to the horizontal plane. By "vertical locking" is meant locking parallel to the vertical plane. By "horizontal locking" is meant locking parallel to the horizontal plane.

By "up" is meant towards the front side, by "down" towards the rear side, by "inwardly" mainly horizontally towards an inner and centre part of the panel and by "outwardly" mainly horizontally away from the centre part of the panel.

For mechanical joining of long edges as well as short edges in the vertical and horizontal direction perpendicular to the edges several methods may be used. One of the most used methods is the angle-snap method. The long edges are installed by angling. The short edges are locked by horizontal snapping. The vertical connection is generally a tongue and a groove and the horizontal connection is a strip with a locking element in on edge that cooperates with a locking groove in the adjacent edge. Snapping is obtained with a flexible strip.

Similar locking systems may also be produced with a rigid strip and they are connected with an angling-angling method where both short and long edges are angled into a locked position.

Advanced so-called "fold down locking systems" with a separate and flexible tongue on the short edges have been introduced where both the long and short edges are locked with a single angling action. A floor panel of this type is presented in <CIT>. It discloses a floor panel with a short edge locking system comprising a locking element cooperating with a locking groove, for horizontal locking, and a flexible bow shaped so called "banana tongue" cooperating with a tongue groove, for locking in a vertical direction. The flexible bow shaped tongue is inserted during production into a displacement groove formed at the edge. The tongue bends horizontally along the edge during connection and makes it possible to install the panels by vertical movement. Long edges are connected with angling and a vertical scissor movement caused by the same angling action connects short edges. Such a locking is generally referred to as "vertical folding".

Similar floor panels are further described in <CIT>. This document provides a fold down locking system with an improved flexible tongue so called "bristle tongue" comprising a straight outer tongue edge over substantially the whole length of the tongue. An inner part of the tongue comprises bendable protrusions extending horizontally along the tongue edge.

<CIT> describes a locking system having a tongue that is formed of the material of panel edge and is inserted into a groove in order to form a fold down locking system. It is not described how the tongue should be formed in order to obtain sufficient flexibility and how it should be and inserted into a groove in a cost efficient way.

The separate flexible tongue is a vital part of the fold down locking system. It would be an advantage if the flexible and separate tongue could be produced and inserted into the edge in a more cost efficient way. It would also be an advantage if the width and thickness of the tongue could be reduced such that a fold down locking system may be formed in very thin floor panels.

An objective of embodiments of the present invention is to provide an improved and more cost efficient fold down locking system comprising a flexible tongue for primarily adjacent short edges of thin floor panels.

A first specific objective is to provide a separate flexible tongue that is more compact and cost efficient than known tongues and that is suitable for locking thin panels.

A second specific objective, not claimed, is to provide a locking system with a flexible and bendable tongue that may be formed as a simple, straight and rod shaped component.

A third specific objective is to provide a cost efficient method to form an advanced flexible tongue from a core material of a floor panel and to insert the tongue after forming into a groove of the panel, preferably in the same production line.

The above objects, individually or collectively, may be achieved by embodiments of the invention.

According to a first aspect, and in accordance with the invention, a set of essentially identical floor panels is provided with a mechanical locking system comprising a flexible tongue, which is arranged in a displacement groove at a first edge of a first panel and a tongue groove at a second edge of an adjacent second panel. The flexible tongue is configured to cooperate with the tongue groove for locking of the first and the second edge in a vertical direction. The mechanical locking system further comprises a locking strip at the first or the second edge, provided with a locking element configured to cooperate with a locking groove at the other of the first or second edge for locking in a horizontal direction. The flexible tongue is displaceable in the horizontal direction in the displacement groove. An outer part of the flexible tongue comprises two or more curved tongue sections, each comprising a sliding surface, which is configured to cooperate with the second edge during locking, and a locking surface that is configured to lock into and/or against the tongue groove. The tongue sections are spaced from each other in a length direction of the flexible tongue that is curved in a locked and in an unlocked position. A first horizontal distance, from an outer upper edge of the first edge to an outer edge of the flexible tongue, and a second horizontal distance, from the outer upper edge of the first edge to an inner edge of the flexible tongue, varies along a length of the flexible tongue. The tongue sections are configured to be pressed inwardly during locking by the second edge such that the tongue sections are at least partially straightened and deformed to essentially straight rod shaped sections with a width, which is essentially the same along essentially the entire length of the flexible tongue and to move back towards their initial positions in a final stage of the locking such that the locking surface is inserted into the tongue groove.

The curved sections may be straightened and deformed to essentially straight rod shaped sections with a width, which is essentially the same along essentially the entire length of the flexible tongue.

The tongue sections may be configured to spring back towards their initial positions in a final stage of the locking such that the locking surfaces are inserted into the tongue groove.

Here and in the following, the wording "second panel edge" will be used interchangeably with the wording "second edge" or "adjacent edge", unless stated otherwise.

By "essentially straight" is here meant that the curved section has been at least partly straightened towards a straight section. By way of example, the curved section may be straightened to a completely straight section. A first curved section may be straightened towards a straight section by being straightened to a second curved section, wherein the first and second curved sections have a convex or concave outer edge along the length direction of the first and second curved section. During the straightening, an outer edge point of the convex or concave outer edge of the first curved section moves towards the displacement groove, wherein the outer edge point is a point on the first curved section that is farthest away from the displacement groove. Thereby, the outer edge point of the first curved section moves to an outer edge point of the second curved section that consequently is closer to the displacement groove, wherein the outer edge point now is a point on the second curved section that is farthest away from the displacement groove.

In the final stage of the locking, the tongue sections moves back towards their initial positions. In a first example, the tongue sections partly move back to their initial positions. In a second example, the tongue sections move back completely to their initial positions. In a third example, some tongue sections move back completely to their initial positions and some tongue sections move back partly to their initial positions.

The tongue sections may move back towards their initial positions by springing back.

The sliding surface may have a shape that essentially corresponds to a shape of a portion of a lower wall of the tongue groove. Moreover, the locking surface may have a shape that essentially corresponds to a shape of a portion of an upper wall of the tongue groove.

Preferably, the flexible tongue is freely arranged in the displacement groove. Thereby, no part of the flexible tongue is attached to the panel, e.g., by an adhesive or a friction connection.

Alternatively, however, one or more parts of the flexible tongue may be attached to the panel. For example, a first longitudinal end portion and/or a second longitudinal end portion of the flexible tongue may be attached to the displacement groove. The attachment of the tongue may be provided by means of an adhesive, a clip, or by means of inserting it into a slot provided in the panel, such as in the displacement groove.

The tongue may be attached to the panel by means of a friction connection. The friction connection may be provided at one or more upper and/or lower parts of the tongue along a length direction of the tongue.

In a first example, the curved edge sections are essentially identical. In a second example, the curved edge sections are different.

The flexible tongue may comprise a plastic material. The plastic material may be a thermoplastic material or a thermosetting plastic material. In particular, the plastic material may be a cross-linked thermoplastic, such as cross-linked PE. By "cross-linked thermoplastic" is here meant that at least a portion of the thermoplastic material comprises cross-links.

The sliding surface may be an inclined surface. The sliding surface may be essentially planar. The sliding surface may be directed upwards. According to one embodiment, the sliding surface forms an angle between <NUM>° and <NUM>° with respect to the vertical plane.

The locking surface may be an inclined surface. The locking surface may be essentially planar. The locking surface may be directed downwards. According to one embodiment, the locking surface forms an angle between <NUM>° and <NUM>° with respect to the vertical plane.

The width of the flexible tongue may be essentially the same over <NUM>% of the length of the flexible tongue. By "essentially the same" for a measurement is meant within ±<NUM>% of other.

The flexible tongue may comprise tongue sections with cross sections such that the first horizontal distance is essentially the same as the second horizontal distance.

A major part of the flexible tongue may comprise cross sections with a horizontal width and a vertical thickness that are essentially the same. By "major part" is meant at least <NUM>% of a length of the tongue. In examples, the major part may be <NUM>%, <NUM>% or <NUM>% of the length of the tongue. In a specific example, the major part may be an entire length of the tongue.

The vertical thickness of the flexible tongue may be less than about <NUM>.

A curved tongue with a simple cross section and a straight rod shaped geometry in the inner position provides several advantages that may be used to design a very compact flexible tongue suitable for locking of thin floor panels. By a thin floor panel is here meant that a thickness of the panel is between <NUM> and <NUM>. A very thin floor panel has a thickness below <NUM>, for example <NUM>, <NUM> or <NUM>.

According to a second aspect of the disclosure, not claimed, a set of essentially identical floor panels is provided with a mechanical locking system comprising a flexible tongue, which is arranged in a displacement groove at a first edge of a first panel, and a tongue groove at a second edge of an adjacent second panel. The flexible tongue is configured to cooperate with the tongue groove for locking of the first and the second edge in a vertical direction. The flexible tongue comprises a sliding surface and a locking surface. The displacement groove comprises a cavity comprising upper, inner and lower cavity walls and a horizontal opening. The second floor panel comprises a protrusion comprising a sliding edge, which is configured to cooperate with the sliding surface during locking and to press and bend a flexible tongue section into the cavity. The flexible tongue section is configured to move back outwardly such that the locking surface is inserted into the tongue groove.

The inner cavity wall may be a curved surface or a planar surface. The upper, inner and lower cavity walls may start and end in the displacement groove along a length direction thereof. The upper, inner and lower cavity walls may be continuous upper, inner and lower cavity walls, whereby the walls are smooth and connected to the displacement groove by means of a smooth transition, without any disruptions. The continuous walls may be formed by means of a rotating carving or jumping tool.

The flexible tongue may be straight. Thereby, a simple and cost-effective tongue is provided. Alternatively, however, the tongue may be curved.

The cross-section of the tongue may be constant along its length direction.

In a first example, the tongue section moves back partly to an initial shape of the tongue section. In a second example, the tongue section moves back completely to the initial shape of the tongue section.

The locking system may comprise two or more cavities and protrusions.

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

According to a third aspect of the disclosure, not claimed, a set of essentially identical floor panels is provided with a mechanical locking system comprising a flexible tongue, which is arranged in a displacement groove at a first edge of a first panel, and a tongue groove at a second edge of an adjacent second panel. The flexible tongue is configured to cooperate with the tongue groove for locking of the first and the second edge in a vertical direction. An outer part of the flexible tongue comprises a protrusion comprising a sliding surface and a locking surface. The displacement groove comprises a cavity comprising upper, inner and lower cavity walls and a horizontal opening. The second floor panel comprises a sliding edge, which is configured to cooperate with the sliding surface during locking and to press and bend a flexible tongue section into the cavity. The flexible tongue section is configured to move back outwardly such that the locking surface is inserted into the tongue groove.

The upper, inner and lower cavity walls may be continuous upper, inner and lower cavity walls.

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

The cavities offer the advantages that the tongue may be formed as a very simple essential straight rod shaped component with a compact geometry suitable for locking of thin floor panels.

According to a fourth aspect of the disclosure, not claimed, a method for producing a locking system at edges of building panels comprising a core is provided. The method comprises the steps of.

The tongue is configured to cooperate with the tongue groove for vertical locking and the locking element is configured to cooperate with the locking groove for horizontal locking.

The method may comprise the step of forming the tongue at the outer and lower part of the first edge.

The method may comprise the step of forming the tongue with a lower part and an upper part, wherein the lower and the upper part is vertically and horizontally offset in relation to each other.

The method may comprise the step of displacing the tongue with rotating wheels.

This production method offers the advantages that the tongue may be formed from the core material of the floor panel and no additional separate material is needed to produce a flexible tongue that always will have a suitable length that corresponds to the short edge of a panel.

According to a fifth aspect of the disclosure, not claimed, a set of essentially identical floor panels is provided with a mechanical locking system comprising a flexible tongue, which is arranged in a displacement groove at a first edge of a first panel and a tongue groove at a second edge of an adjacent second panel. The flexible tongue is configured to cooperate with the tongue groove for locking of the first and the second edge in a vertical direction, wherein the mechanical locking system further comprises a locking strip at the first or the second edge provided with a locking element configured to cooperate with a locking groove at the other of the first or second edge for locking in a horizontal direction. The flexible tongue comprises a lower part and an upper part. The lower and the upper part are vertically and horizontally offset in relation to each other and the lower part comprises a lower protrusion extending vertically downwards.

The lower part may comprise at least two lower protrusions along its length.

The lower part may comprise at least two inner protrusions extending horizontally inwardly and being spaced from each other along the displaceable tongue.

A tongue with offset upper and lower parts offers the advantages that protrusions and cavities may be formed on the tongue in a cost efficient way when the tongue is formed in line from the same core material that is used to form the locking system.

It is emphasized that all embodiments disclosed above may be partly or completely combined with each other.

The disclosure will in the following be described in connection to exemplary embodiments and in greater detail with reference to the appended exemplary drawings, wherein:.

<FIG> show flexible tongues <NUM> and locking of a first <NUM> and a second <NUM>' panel edge with vertical displacement according to known principles. A flexible bristle tongue <NUM> comprising a tongue body <NUM> and flexible protrusions <NUM> at its inner part as shown in <FIG>, or at its outer part as shown in <FIG>, is displaced inwardly into a displacement groove <NUM> during locking as shown in <FIG> and outwardly during the final stage of the locking such that the outer parts of the flexible tongue <NUM> are inserted into a tongue groove <NUM> and the adjacent edges of the first <NUM> and the second <NUM>' panel are locked vertically parallel to a vertical plane VP. The panel edges comprise a strip <NUM> with a locking element <NUM> in one of the edges that cooperates with a locking groove <NUM> formed in the adjacent edge and locks the edges in a horizontal direction parallel to the panel surface and perpendicularly to the vertical plane.

<FIG> shows a bristle tongue <NUM> with a tongue body <NUM> and flexible protrusions <NUM> at its inner part. <FIG> shows a bristle tongue <NUM> with a tongue body <NUM> and flexible protrusions <NUM> at its outer part.

The flexible tongue has a length direction L along the edge, a width W extending horizontally perpendicular to the edge, and a tongue thickness TT in the vertical direction. The tongue thickness TT is generally the same as the groove thickness GT of the displacement groove <NUM>. The maximum width W is larger than the groove depth GD of the displacement groove <NUM>.

The flexible tongue comprises a complex geometry and is therefore formed as an injected moulded thermoplastic-based component comprising glass fibres that are used to accomplish high strength combined with flexibility. A bending of the protrusions in the length direction of the tongue is an essential feature of such advanced flexible tongues.

<FIG> show that the flexible tongue <NUM> is produced and delivered as a tongue blanks <NUM> comprising for example <NUM> - <NUM> tongues. Plastic material is injected into a tool through injection channels <NUM>, generally from one side only in order to reduce production costs. The channel material is removed after the injection forming and may be re-melted and used again.

Injection moulding with thermoplastic material comprising glass fibres is a cost efficient method that provides high quality components with very low production tolerances. However, the production method and the geometry of the flexible tongue has several disadvantages that limits the possibilities to produce cost efficient locking systems comprising a flexible tongues in new type of floor panels and core materials where a fold down installation is desirable.

One disadvantage is that a flexible tongue must have a length L that corresponds to the width of the panel since it is inserted into a groove formed at the short edge.

Plastic material must flow through a tongue body <NUM> along the length L of the tongue <NUM> and there must be a space S between the protrusions <NUM> and the tongue body <NUM>, see <FIG>. This provides certain cost related limits to the geometry of the tongue. For example, the production time and the tool cost may increase considerably if the width W is lower than <NUM>, the thickness TT is lower than <NUM> and the length exceeds about <NUM>.

Another problem is that it is difficult to form a displacement groove with a groove thickness GT that is smaller than about <NUM> if the groove depth GD is about <NUM>.

Mechanical locking systems are generally formed with large rotation tools that form grooves and protruding parts parallel to an edge and along the whole edge.

<FIG> show embodiments of production methods that may be used to form locking systems and tongues comprising cavities <NUM> and protrusions <NUM> arranged perpendicularly to an edge <NUM> according to an aspect of the disclosure.

<FIG> is a top view showing a tool comprising rotating saw blades <NUM> that are displaced against a panel edge <NUM> and back again. Alternatively, the panel <NUM> may be displaced against the saw blades <NUM> and back again. This production method may be used to form cavities <NUM> or protrusions <NUM> as shown in <FIG>, wherein the upper figures illustrate perspective views and the lower figures illustrate top views of the panel edge <NUM>.

<FIG> shows a side view of a so-called rotating jumping tool head <NUM> that may be displaced vertically or horizontally against a moving panel edge <NUM>.

Thereby, local cavities <NUM> may be formed.

<FIG> shows a cost efficient method to form cavities <NUM> with a rotating carving tool <NUM>. The carving tool <NUM> comprises teeth <NUM> which are arranged along an outer edge of the carving tool <NUM>. The tool rotation speed is synchronized with the displacement of the panel <NUM> and each tooth <NUM> forms one cavity <NUM> at a predetermined position and with a predetermined horizontal extension along an edge of a panel <NUM>. It is not necessary to displace the tool vertically. A carving tool <NUM> may have several sets of teeth <NUM> and each set may be used to form one cavity. The cavities <NUM> may have different cross sections depending on the geometry of the teeth <NUM>.

<FIG> shows a top view of a so-called screw cutter <NUM>. This is an advanced production technology that allows high precision and cost efficient forming of protrusions and cavities perpendicular to an edge that is displaced in a high speed against the screw cutter <NUM>. <CIT> provides a detailed description of the screw cutter principle.

<FIG> shows a flexible tongue <NUM> according to an embodiment. A width W of the flexible tongue <NUM> is essentially the same over substantially the whole length L of the flexible tongue <NUM>.

<FIG> show an enlarged picture of a tongue portion Ts1 shown in <FIG> and a cross section A-A of the flexible tongue <NUM> inserted in a displacement groove <NUM> provided in the panel edge <NUM>.

<FIG> shows the flexible tongue <NUM> in an unlocked and in a locked position. The unlocked position is illustrated by the upper panel edge <NUM>' which is indicated by an unbroken line while the locked position is illustrated by the lower panel edge <NUM>' which is indicated by a broken line. The flexible tongue <NUM> is inserted in a displacement groove <NUM> comprising an upper lip <NUM>. A vertical plane VP intersects the upper and outer part of the upper lip <NUM>. The tongue comprises at least two tongue sections Ts1, Ts2, each comprising a sliding surface <NUM>, that during locking cooperates with a sliding edge <NUM> of the adjacent edge <NUM>', and a locking surface <NUM> that locks into the tongue groove <NUM>. According to the present embodiment, the sliding surface <NUM> is provided in an upper part of the flexible tongue <NUM>. More specifically, the sliding surface <NUM> is an outer and upper inclined part of the flexible tongue <NUM>. Moreover, according to the present embodiment, the locking surface <NUM> is provided in a lower part of the flexible tongue <NUM>. More specifically, the locking surface <NUM> is an outer and lower inclined part of the flexible tongue <NUM>. The sliding surface <NUM> is arranged above the locking surface <NUM>. The tongue sections Ts1, Ts2 are spaced from each other in the length direction L of the flexible tongue <NUM>. The tongue is curved in a locked and in an unlocked position such that a first horizontal distance D1 from the vertical plane VP and to the outer part of the flexible tongue <NUM> and a second horizontal distance D2 from the vertical plane VP to an inner part of the flexible tongue <NUM> varies along the length L of the tongue.

The shape of the flexible tongue <NUM> may be further defined by a third horizontal distance D3 from the inner part of the tongue to an inner horizontal line connecting the innermost points of the tongue. The inner line is essentially parallel with a length direction of the flexible tongue <NUM>. The inner line is a straight line if each of the tongue sections Ts1, Ts2,. have the same shape. In a first example, D1 corresponds to D3 along the entire length direction of the flexible tongue <NUM>, thereby providing a constant width W of the flexible tongue <NUM>. In a second example, D1 differs from D3 at least along a portion of the length direction of the flexible tongue <NUM>, thereby providing a varying width W.

It is clear that the illustrated embodiments of the present application are non-limiting with regard to the number of tongue sections. Indeed, there may be one or more tongue sections Ts1, Ts2,. , TsN, where N is an arbitrary integer larger than or equal to one, i.e. N=<NUM>, <NUM>, <NUM>, <NUM>,.

<FIG> shows the flexible tongue <NUM> in an inner position during locking. According to the present embodiment, the adjacent edge <NUM>' is displaced essentially vertically downwards towards the first panel edge <NUM> during locking, such that the locking groove <NUM> provided in the adjacent edge <NUM>' is lowered towards and cooperates with the locking element <NUM> provided in the first panel edge <NUM>. The flexible tongue <NUM> is pressed inwardly by the sliding edge <NUM> of the adjacent panel <NUM>' and the curved sections Ts1, Ts2 are straightened such that the flexible tongue <NUM> is formed to an essentially straight rod shaped component with a tongue width W that is essentially the same along the major part of the flexible tongue. In an embodiment, during locking of a tongue section, the distance D3 may change from an unlocked distance to less than <NUM>% of the unlocked distance. It is noted that the sliding surface <NUM>, which protrudes outwardly beyond the vertical plane VP in a locked position as well as in an unlocked position, as illustrated in <FIG>, is pressed towards the displacement groove <NUM> during locking as illustrated in <FIG>. Thereby, the sliding surface <NUM> may be pressed inwardly of the vertical plane VP during locking - partly or entirely.

As shown in <FIG> the flexible tongue <NUM> comprises inner protrusions 21a and outer protrusions 21b arranged along a length direction of the tongue at an inner part and an outer part of the tongue, respectively. In <FIG> it may be seen that the tongue section Ts1 comprising an outer protrusion 21b has been straightened to an essentially straight section.

<FIG> shows an embodiment according to which the panels comprise short edges <NUM>, <NUM>' and long edges <NUM>. A scissor movement of the adjacent short edge <NUM>' caused by the angling of the long edge <NUM> of the panel will gradually press the tongue sections inwardly along the panel edge and deform the flexible tongue <NUM> towards an essentially straight component. For example, at least one tongue section of the flexible tongue <NUM>, which has a convex or concave outer edge along the length direction of the tongue section, may become straightened so that an outer edge point of the convex or concave outer edge moves towards the displacement groove <NUM>, wherein the outer edge point is a point on the tongue section farthest away from the displacement groove <NUM>. In <FIG> the outer edge point is located in a centre portion of the convex tongue section Ts1 along its length direction where a distance XM to the inner wall of the displacement groove <NUM> is maximal. It is noted that in a concave tongue section Ts0, as shown in <FIG>, the outer edge point may be located in an edge portion of the concave tongue section along its length direction where a distance to the inner wall of the displacement groove <NUM> is maximal. By way of example, the outer edge point may move towards the displacement groove <NUM> at least by a distance corresponding to <NUM>-<NUM>% of a maximal width of the tongue <NUM>, preferably <NUM>-<NUM>%. In particular, the flexible tongue <NUM> may be straightened to an essentially straight component, for example a straight component along its entire length. Preferably, the outer parts of the flexible tongue <NUM> and the tongue groove <NUM> are configured such that an inner part of the edge 1a and a first tongue portion Ts1 is located close to its final locked position, as shown in <FIG>, when an outer part of the edge 1b and a second tongue portion Ts2, preferably a tongue portion that is most distant to the first tongue portion Ts1, is located in its inner position as shown in <FIG>. The edge sections Ts1, Ts2 will gradually move into the tongue groove <NUM> during the vertical folding and locking resistance and separation forces, that may press the short edges away from each other due to the bending of the tongue, will be reduced. This facilitates an easy locking.

The flexible tongue <NUM> may comprise friction connections <NUM>, preferably located at an upper and/or a lower part of tongue. The friction connections <NUM> may be elongated. The required flexibility is mainly obtained by a curved tongue body <NUM> of the tongue that during locking bends mainly horizontally and inwardly into the displacement groove <NUM>.

The flexible tongue <NUM> may comprise tongue portions with cross sections wherein the first horizontal distance D1 is essentially the same as the second horizontal distance D2 such that the tongue width W may be about <NUM> times the width of the sliding surface <NUM> that protrudes beyond the vertical plane VP. The flexible tongue <NUM> may be formed with a very compact cross section such that the tongue width W is essentially the same as the tongue thickness TT.

The described embodiment offers several advantages. The straight inner position makes it possible to form displacement grooves with a very small depth. The simple geometry of the tongue allows a cost efficient production since plastic material may float easily during the injection moulding and this makes it possible to decrease the tongue width W and the tongue thickness TT and to increase the tongue length L. It is possible to produce an injection-moulded tongue with a thickness TT that is less than <NUM>, for example with a thickness of about <NUM> - <NUM> and with a width W of about <NUM> - <NUM>. It is also possible to produce extremely thin flexible tongues with a tongue thickness TT of <NUM> - <NUM>. Such tongues may be used to lock very thin floor panels, for example LVT or WPC floor panels with a thickness of about <NUM>.

A stiffness of the flexible tongue may be specified by a transverse spring constant. According to a non-limiting example, the transverse spring constant of the flexible tongue is between <NUM>-<NUM> N/mm per <NUM> length of the tongue. According to another non-limiting example, the transverse spring constant is between <NUM>-<NUM> N/mm per <NUM> length of the tongue. The transverse spring constant of the flexible tongue may be tested by standard methods known to a person skilled in the art.

<FIG> illustrates a top view and a cross-sectional view of a tongue blank <NUM> according to an embodiment. <FIG> show that the flexible tongue <NUM> may be formed from a tongue blank <NUM> that is an extruded plastic or metal component comprising an identical cross section along the whole length of the tongue blank. In particular, the tongue blank <NUM> has a constant width along its length direction. A punching wheel <NUM> may form curved parts of the flexible tongue <NUM>. The curved parts are formed by removing material from the tongue blank <NUM>. According to the present embodiment, material is removed from an inner part and from an outer part of the tongue blank <NUM> in such a way that a width of the resulting flexible tongue <NUM> becomes essentially constant along a length direction of the flexible tongue <NUM>. The flexible tongue <NUM> may have friction connections <NUM> protruding vertically upward or downward. This is illustrated in the top view of the flexible tongue <NUM> according to the embodiment in <FIG>.

According to an alternative embodiment, material may be removed from an inner part and/or from an outer part of the tongue blank <NUM> in such a way that the width of the resulting flexible tongue <NUM> becomes non-constant along the length direction of the flexible tongue <NUM>. Examples of flexible tongues <NUM> having non-constant widths will be described further below in relation to the embodiments in <FIG> and <FIG>.

According to alternative embodiments, the curved parts of the flexible tongue <NUM> may be formed by other means, such as cutting, carving, punching or milling, or any combination of these means.

The tongue blank <NUM> and/or the flexible tongue <NUM> may be formed by means of injection moulding, extrusion, 3D printing by forming successive layers, or pultrusion with a reinforcement material.

Generally, the tongue blank <NUM> and/or the flexible tongue <NUM> may comprise at least one material chosen from the group consisting of a plastic, such as a thermoplastic or a thermosetting plastic, a WPC, a metal, or a panel material, such as a panel core material or material from at least one layer of a panel. The material may further comprise a reinforcement material. Thereby, the material may become more rigid. For example, the reinforcement material may comprise fibres or resins, such as thermosetting resins. Alternatively, or additionally, the material may comprise a cross-linked material, such as a plastic with cross-linked polymers.

The thermoplastic may comprise PVC, PE, PP, CPVC, or similar materials. In non-limiting examples the polyethylene may be a low-density PE, a linear low-density PE, a medium-density PE or a high-density PE. In particular, the thermoplastic may be a cross-linked thermoplastic, such as cross-linked polyethylene, also called PEX or XLPE. Moreover, the thermoplastic may be a reinforced thermoplastic. The reinforced thermoplastic may comprise a reinforcement material, such as fibres. The fibres may comprise at least one of glass fibres, carbon fibres, aramid fibres, wood fibres, basalt fibres, nonwoven fibres, or textile fibres. Alternatively, the fibres may comprise metal fibres, such as magnetic metal fibres, e.g. iron or a magnetic alloy. Thereby, the fibres may be separated from the plastic more easily during recycling. The fibres may have a specific orientation. For example, the fibres may be oriented along a length direction of the flexible tongue <NUM>. Alternatively, the fibres may be randomly oriented. The fibres may be randomly distributed in the flexible tongue <NUM>. Alternatively, the fibres may be arranged in the form of a mat-shaped layer in the flexible tongue <NUM>, such as a fabric, for example in a centre portion of the flexible tongue <NUM>.

Thus, the flexible tongue <NUM> preferably comprises a low-creep material that does not creep or deform to any considerable extent over time. Thereby, the locking function does not deteriorate over time, for example after <NUM> month, <NUM> year, or <NUM> years. The reinforced and the cross-linked materials described above may both counteract creeping. <FIG> show that tongues blanks <NUM> may be formed from a sheet shaped material <NUM>. The sheet shaped material <NUM>, which is illustrated in <FIG> in the case of a single-layer sheet, may be a thermoplastic material, preferably comprising mineral or wood fillers. Preferably at least three layers are laminated or fused together. Glass fibres or any other fibres described above may be used to reinforce the sheet shaped material. The sheet shaped material may also comprise thermosetting resins preferably mixed with wood fibres. <FIG> shows a sheet shaped material <NUM> comprising at least three layers. The upper 51a and the lower 51c layers comprise thermoplastic material and the middle layer 51b is a reinforcement layer comprising fibres, for example glass fibres. The middle layer 51b is a mat-shaped layer comprising fibres. It is clear, however, that other materials described above may be used for the layers 51a-c. For example, the upper 51a and the lower 51c layers may comprise a thermosetting plastic and/or the middle layer 51b may comprise randomly distributed fibres. According to the embodiment in <FIG>, the flexible tongue <NUM> comprises at least three layers of materials with different material properties. The layers and reinforcement layers may be joined to each other by means of heating and/or pressing. Hot embossed rollers may be used to form straight 52a or curved 52b sheet grooves in the sheet shaped material <NUM> that after separation form outer and/or inner parts of a flexible tongue <NUM>. The grooves may also be formed with rotating cutting or carving tools. A punching tool <NUM>, or punching wheel <NUM>, may also be used to form the flexible tongues <NUM>. All these production methods may be combined. Flexible tongues <NUM> may also be formed with conventional 3D-printing methods. In relation to <FIG>, three layers have been chosen for illustrative purposes only and it is clear that any number of layers may be chosen, for example <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM> layers. Additionally, there may be a plurality of reinforcement layers. For example, there may be a centre layer sandwiched between inner surfaces of a first and a second reinforcement layer, and an upper and lower layer arranged on outer surfaces of the first and second reinforcement layer, respectively.

<FIG> shows that the flexible tongue <NUM> may be formed as a straight rod shaped component. <FIG> shows that cavities 22a, 22b may be formed at the inner part of the displacement groove <NUM> of a first panel <NUM> and that protrusions <NUM> may be formed in the adjacent second panel <NUM>'. The cavities 22a, 22b and the protrusions <NUM> are formed along portions of the side edges of the panels <NUM>, <NUM>' in their length direction. Each cavity comprises a continuous upper <NUM>, inner <NUM>, and lower <NUM> cavity wall and a horizontal cavity opening <NUM> towards the vertical plane VP. The cavity walls are preferably continuous along the edge since they are preferably formed with a rotating carving or jumping tool. At least a portion of the inner cavity wall <NUM> is curved. Each protrusion <NUM> comprises an upper horizontal wall and an outer wall. According to the present embodiment, the outer wall is inclined. According to an alternative embodiment, however, the outer wall may be vertical and the protrusion may also comprise a lower horizontal wall that is essentially parallel with the upper wall. The cavities 22a, 22b may have the same vertical extension as the displacement groove <NUM>. Alternatively, the cavities 22a, 22b may have a larger vertical extension than the displacement groove <NUM>. This provides a more cost efficient production since larger and more efficient jumping tools or saw blades may be used and production tolerances may be increased without negative effects on the locking function. According to an alternative embodiment, the cavities 22a, 22b may have a smaller vertical extension than the displacement groove <NUM>.

<FIG> show that the protrusions <NUM> and the cavities <NUM> are located along the panel edges and adjacent to each other such that a protrusion <NUM> may displace and bend a part of a tongue section Ts1 into the cavity <NUM>.

<FIG> shows a cross section A-A comprising a cavity 22a that has about the same vertical extension or cavity thickness Ct as the thickness GT of the displacement groove <NUM>. <FIG> shows an alternative embodiment of the cross-section A-A wherein a cavity 22b has a larger cavity thickness than the displacement groove <NUM> and is offset vertically below the upper or lower parts of the displacement groove. The displaceable tongue <NUM> may have an outer portion with a larger outer tongue thickness TTa than a tongue thickness TTb of an inner portion. An advantage is that the inner part of the tongue may be displaced into a cavity even if the vertical position of the forming tool is not aligned with the upper part of the displacement groove <NUM>. According to an alternative embodiment, the cavity 22b may have a smaller cavity thickness than the displacement groove <NUM>. <FIG> shows a cross section B-B where no cavity and protrusion are formed and where essentially no displacement of the flexible tongue <NUM> in the displacement groove <NUM> takes place. This part of the edge is used as a support for the inward bending of the tongue section Ts1.

<FIG> show in detail the displacement of a flexible rod shaped tongue <NUM> according to <FIG>. <FIG> shows a top view of a first <NUM> and a second <NUM>' edge section at horizontal planes HP <NUM> and HP <NUM>' according to <FIG>. Here, the tongue is essentially straight. <FIG> show the flexible tongue <NUM> in a bended inner position wherein parts of the flexible tongue <NUM> has been pressed into the cavities <NUM> by means of the protrusions <NUM>. <FIG> show the flexible tongue <NUM> in an outer and locked position wherein the tongue groove <NUM> and the displacement groove <NUM> are vertically aligned so that the outer parts of the flexible tongue <NUM> has been inserted into the tongue groove <NUM>. According to the present embodiment, the flexible tongue <NUM> is essentially straight in the outer and locked position. According to an alternative embodiment (not shown), however, at least a portion of the flexible tongue <NUM> may be bended in the outer and locked position. For example, the flexible tongue <NUM> may be bended in sections.

<FIG> show a method to form a tongue, preferably a flexible tongue <NUM>, from an edge part of a panel <NUM> and to insert the tongue into a groove, preferably a displacement groove <NUM>, preferably in the same production line that is used to form the locking system. The flexible tongue <NUM> is in this embodiment formed at an outer part of the strip <NUM>. Pressing wheels 44a, 44b and 44c may be used to separate the tongue <NUM> from the edge <NUM> and displace the tongue vertically and horizontally into the groove <NUM>. It is preferred that a part P1 of the tongue is connected to the edge <NUM> when another part P2 is inserted and fixed into the groove <NUM>. The tongue <NUM> may also be released from the edge <NUM> and displaced with the wheels 44a, 44b, preferably at the same speed as the panel edge <NUM>, and inserted into the displacement groove <NUM> with wheels 44c or some pressing units. Upper and lower support units may be used to align and position the tongue into the groove. The tongue may be used in a locking system as described in <FIG>.

Such production method offers several advantages. Tongue blanks are not needed and the tongue <NUM> will always have an appropriate length that corresponds to the panel edge. A wide variety of core materials have been introduced on the market, such as HDF, high density water resistant HDF comprising an increased resin content, thermoplastic material mixed with mineral or wood fibre fillers, so called LVT or WPC material, foamed thermoplastic material etc. Any of the above-mentioned materials may be used for forming the flexible tongue <NUM> according to the embodiment in <FIG>. Thermoplastic floor materials are often reinforced with glass fibres in order to decrease thermal shrinking and expansion. Glass fibres <NUM> may be located in the part of the core <NUM> where the flexible tongue <NUM> is formed and may contribute to increase the strength and spring properties of the flexible tongue <NUM>. Such materials have a sufficient flexibility and may provide a strong and flexible tongue body. Engineered wood floorings have generally a separate material such as plywood on the short side and this separate material may also be used to form the flexible tongue. Thermoplastic floor materials are often reinforced with glass fibres in order to decrease thermal shrinking and expansion. Such glass fibre layers are positioned in the middle parts of the core <NUM>. Glass fibres <NUM> may be positioned in the part of the core <NUM>, preferably the lower part, where the flexible tongue <NUM> is formed and may contribute to increase the strength and spring properties of the flexible tongue <NUM>.

<FIG> show that rather complex curved tongues <NUM> may be formed with screw cutters, jumping tool heads or punching wheels and that cavities and protrusions formed in the panel edges are not needed to displace a flexible tongue <NUM> in a displacement groove <NUM>. <FIG> shows a tongue <NUM> formed and connected to an outer part of a strip <NUM>. <FIG> shows the flexible tongue <NUM> which is released from the strip <NUM> and <FIG> shows the displaceable tongue <NUM> inserted into a displacement groove <NUM>.

By a curved tongue is meant that at least a section of the tongue is curved. The curved tongue may comprise any number of curved sections, for example, <NUM>, <NUM>, <NUM>, <NUM>,. The curved sections may be directly connected to each other. Optionally, however, straight sections may connect the curved sections.

<FIG> show preferred embodiments of locking systems and the flexible tongues <NUM>. <FIG> shows a straight rod shaped flexible tongue <NUM> comprising locking surfaces <NUM> and sliding surfaces <NUM> inserted in a displacement groove <NUM> of an panel edge <NUM> comprising cavities <NUM>. <FIG> also shows an adjacent edge <NUM>' comprising protrusions <NUM>. <FIG> shows that the protrusions on the adjacent edge <NUM>' may be replaced by outwardly extending protrusions <NUM> formed on the outer part of the flexible tongue <NUM>. Such protrusions <NUM> are easy to form on a flexible tongue <NUM> produced by extrusions or produced from a sheet shaped material. Only a cost efficient rotating carving tool may be sufficient to form a high quality locking system. According to the embodiment in <FIG>, the flexible tongue <NUM> is insertable into the cavities <NUM> of the displacement groove <NUM> with the protrusions <NUM> facing away from the cavities <NUM>. Thereby, an outer surface of the panel edge <NUM>', such as the sliding edge <NUM>, may contact the protrusions <NUM> and displace and bend a part of a tongue section of the flexible tongue <NUM> inwardly. <FIG> shows that the cavities <NUM> may be replaced with inner protrusions 21a formed on the inner part of the tongue <NUM>. Thereby, the protrusions <NUM> on the panel edge <NUM>' may displace and bend a part of a tongue section of the flexible tongue <NUM> inwardly. The displacement may occur between the inner protrusions 21a where there is a space between the tongue <NUM> and an inner wall of the displacement groove <NUM>. In this embodiment, the inner wall is a planar surface, but other shapes are equally conceivable. <FIG> shows that both cavities and protrusions may be replaced with a curved flexible tongue <NUM> comprising inner protrusions 21a and outer protrusions 21b at the inner and outer parts of the flexible tongue <NUM>, respectively. Thereby, the outer surface of the panel edge <NUM>', such as the sliding edge <NUM>, may contact the protrusions <NUM> and displace and bend a part of a tongue section of the flexible tongue <NUM> inwardly towards the inner wall of the displacement groove <NUM>. In this embodiment, the inner wall is a planar surface, but other shapes are equally conceivable.

In non-limiting examples, the inner part and/or the outer part of the flexible tongue <NUM> may be shaped essentially as a part of a sine wave, a part of a saw-tooth wave, have a step-wise constant profile, or have a straight profile.

In all of the embodiments above and in the following, it is clear that each protrusion <NUM>, 21a, 21b may be provided at a lower vertical portion, an upper vertical portion, or a centre portion of the flexible tongue <NUM>.

<FIG> shows that a curved tongue as shown in <FIG> may for example be formed with a screw cutter <NUM> and a jumping tool head <NUM>. <FIG> shows that a tongue <NUM> may be formed at an upper part of the edge with jumping tool heads <NUM>. Such an embodiment will save material. <FIG> shows that the tongue <NUM> may be formed above the outer part of the strip <NUM> with a screw cutter <NUM> and a jumping tool <NUM>. Jumping tools <NUM> may in all embodiments of the disclosure be replaced with rotating carving tools <NUM>.

<FIG> shows a panel <NUM> comprising a surface layer <NUM> and a core comprising an upper core layer 5a and a lower core layer 5b. In a non-limiting example, the panel <NUM> may be an LVT panel. The lower core layer 5b comprises a higher content of thermoplastic material than the upper core layer 5a. A flexible tongue <NUM> is formed from the lower core layer 5b. This means that the flexible tongue <NUM> comprises the same material composition as the lower core layer 5b. <FIG> also shows a flexible tongue <NUM> that has been inserted into the displacement groove <NUM>.

<FIG> shows that a curved flexible tongue <NUM> may be formed in a cost efficient way with two screw cutters: a first screw cutter 42a and a second screw cutter 42b. The flexible tongue <NUM> preferably comprises an inner and lower part 10a and an upper and outer part 10b that are displaced vertically and horizontally in relation to each other. The upper part 10b is preferably more distant to the inner part of the displacement groove <NUM> than the lower part 10a. An outer protrusion 21b is formed at the upper part 10b when a first screw cutter 42a removes material from the tongue and an inner protrusion 21a is formed at the lower part of the tongue 10a when a second screw cutter 42b removes material from the lower part of the tongue 10a. The inner part of the tongue may also be formed as an upper part and the outer part may also be formed as a lower part. Such tongues may for example be used when the tongue is inserted into an edge of the second panel <NUM>' comprising a locking groove <NUM>.

<FIG> provide a more detailed description of the locking system shown in <FIG>. <FIG> shows an edge section of a panel <NUM> comprising a part of a locking system formed at one of two adjacent panel edges. A groove <NUM>, a strip <NUM> with a locking element <NUM> and a tongue <NUM> is formed with rotating tools. The tongue is preferably formed at an outer part of the strip <NUM>. The locking system and the tongue <NUM> comprise an essentially identical and continuous cross section along a length direction of the panel edge <NUM>. The tongue <NUM> comprises upper 10b and lower parts 10a displaced vertically and horizontally in relation to each other. The upper part 10b comprises a locking surface <NUM>. The lower part 10a comprises lower protrusions 21c extending downwards. <FIG> shows that a first screw cutter 42a and a second screw cutter 42b may be used to remove material from the outer and upper parts 10b and inner and lower parts 10a of the tongue <NUM> such that outer protrusions 21b and inner protrusions 21a are formed. <FIG> shows a flexible tongue <NUM> that is released from the strip <NUM> such that it may be inserted into the displacement groove <NUM> during production of the locking system. The flexible tongue is characterized in that the inner protrusions 21a are located vertically below the upper part of the tongue <NUM>.

<FIG> show that the tongue <NUM> could be formed with a tongue body <NUM> that is inclined against a horizontal plane Hp1 in order to facilitate an easy machining in a double-end tenor machine comprising a chain <NUM> and an upper belt <NUM>. The panel <NUM> is positioned in the double-end tenor with the surface layer <NUM> pointing downwards. The horizontal distance D4 from the tongue <NUM> and to the upper belt <NUM> may be smaller than a radius R of the jumping tool head <NUM>, the screw cutter tool head <NUM> or of the screw cutter <NUM>.

<FIG> show different embodiments. <FIG> shows a locking system comprising a flexible tongue <NUM> on the second panel <NUM>', the fold panel, which comprises a locking groove <NUM> that cooperates with a locking element <NUM> formed on a strip <NUM> of the first panel <NUM>. <FIG> show that the flexible tongue <NUM> may be formed from a core section of the fold panel <NUM>', which may be located at the upper, middle or lower part of the core <NUM>. <FIG> shows a locking system with a flexible tongue <NUM> attached to a displacement groove <NUM> formed at an inner wall of the locking groove <NUM> on the second fold panel <NUM>'. The tongue <NUM> may be formed from a core section located at a lower part of the core as shown in <FIG> shows a locking system comprising a displacement groove <NUM> formed at an outer part of the strip <NUM> of the first panel <NUM>. <FIG> shows that the tongue <NUM> may be formed from a core portion located above the strip <NUM>.

<FIG> show that a core material <NUM> may be locally modified such that it becomes more suitable to form a flexible tongue <NUM>. The method may be used to increase the strength and flexibility of any kind of mechanical locking systems, even such systems that are formed as one-piece locking systems without a separate flexible tongue. <FIG> shows that a resin, for example a thermosetting resin <NUM>, such as for example melamine formaldehyde, urea formaldehyde or phenol formaldehyde resin, may be applied in liquid or dry powder form on for example a melamine formaldehyde impregnated balancing paper <NUM> or directly on a core material <NUM>. <FIG> shows that a core material <NUM>, preferably a wood based panel, for example a HDF board or a particle board, may be applied on the impregnated paper <NUM> with the added resin <NUM> prior to lamination. <FIG> shows a floor board after lamination when the surface layers <NUM> and the balancing layer <NUM> have been laminated to the core <NUM>. The resins <NUM> have penetrated into the core <NUM> and cured during lamination under heat and pressure. <FIG> shows an edge of a first panel <NUM> comprising a tongue <NUM> formed in one piece with the core <NUM>. The tongue <NUM> is more flexible and comprises a higher resin content than other parts of the core <NUM>. The increased resin content provides a material that is very suitable to form a strong flexible tongue <NUM> that during production may be inserted into a displacement groove <NUM>.

<FIG> shows that a flexible tongue <NUM> and a locking system according to each embodiment of the disclosure may be used to lock furniture components <NUM>, <NUM>' perpendicularly to each other. Cavities <NUM> may be formed in an inclined displacement groove <NUM> and protrusions may be formed below the tongue groove <NUM>. The flexible tongue may be a curved, rod shaped component as described above, and it may also be formed from a core portion of the panel core.

<FIG> shows that a flexible tongue <NUM> and a locking system according to each embodiment of the disclosure may also be used to lock ceramic tiles <NUM>, <NUM>'. The strip <NUM> and the locking element <NUM> may be formed as a separate plastic or metal part that is attached to an edge of a first tile <NUM>. Cavities <NUM> and protrusions <NUM> may also be formed in ceramic material with diamond tools. All embodiments of the disclosed flexible tongue <NUM> may be used. A second tile <NUM>' comprises a tongue groove <NUM> and a locking groove <NUM>. The flexible tongue <NUM> is configured to cooperate with the tongue groove <NUM> as described above for locking of the first and the second edge in a vertical direction. Moreover, the locking element <NUM> of the separate strip <NUM> is configured to cooperate with the locking groove <NUM> for locking in the horizontal direction.

All shown locking systems may be adapted such that they may be locked with vertical displacement and/or angling and/ horizontal snapping. They may also be released with upward angling or displacement along the edge. The vertical locking may be combined with a flexible strip <NUM> and preferably a flexible locking element <NUM> that is bended during locking. Preferably, the outer part of the strip <NUM> is bended downwards and the upper part of the locking element <NUM> is bended or turned horizontally outwardly.

As illustrated schematically in <FIG>, the curved flexible tongue <NUM> may be formed by first providing a tongue blank <NUM>, or an essentially straight tongue, and then bend it into a curved flexible tongue of a desired shape by means of deformation. The tongue blank <NUM> is made of plastic, preferably a thermoplastic material or a thermosetting, with or without reinforcement, as has been described above. However, other materials are equally conceivable.

This method is particularly suitable for producing curved flexible tongues having an essentially constant cross-section along the length direction of the tongue. However, the tongue blank <NUM> may also have a varying cross-section along the length direction of the tongue. Optionally, the tongue blank <NUM> may comprise inner and/or outer protrusions along its length direction.

As shown in <FIG>, the tongue blank <NUM> is provided on a roll <NUM> and is fed into a bending device <NUM> according to a feeding method known to a person skilled in the art. The tongue blank <NUM> is then arranged in a bent state as shown in <FIG>. According to the present embodiment, the tongue blank <NUM> is arranged in a sequence or matrix of bending elements <NUM> so that portions of the tongue blank become bent. In <FIG> the bending elements <NUM> are rods, nails or screws that are fixed to a substrate <NUM> and the tongue blank <NUM> is arranged in a zig-zag pattern between the bending elements <NUM>. Alternatively, however, the bending elements <NUM> may be rollers or cylinders. Optionally, the end points of the tongue blank <NUM> may be fixed, e.g. to the substrate <NUM>. The final shape of the tongue is determined by the pattern of the bending elements <NUM>. The horizontal and/or vertical distances between the bending elements <NUM> may be constant or, alternatively, varying.

The tongue blank <NUM> is then fixed in the bent state for a period of time. Optionally, heat may be provided to the tongue blank <NUM> in a heating process before and/or during the bent state by a heating device <NUM>. Thereby, the forming of the curved tongue may be speeded up. Optionally, the tongue blank may also undergo a cooling process after the heating process by means of a cooling device <NUM>. The heating and cooling process may be implemented by means of methods well known to a person skilled in the art. After a critical period of time has elapsed, the tongue blank <NUM> assumes a bent shape and becomes deformed permanently, or semi-permanently, and becomes a curved tongue element. The deformation may occur due to tensile forces, compression forces, shear, bending or torsion. A permanent deformation may be a plastic, irreversible, deformation. By semi-permanently is here meant that the bent shape provided directly after forming is essentially preserved at least during a minimum amount of time, such as <NUM> month, <NUM> year or <NUM> years. The curved tongue element is finally cut by a cutting device <NUM> into one or more curved flexible tongues <NUM> having predetermined lengths. A curved flexible tongue <NUM> resulting from the above process is schematically illustrated in <FIG>.

Claim 1:
A set of essentially identical floor panels (<NUM>, <NUM>') provided with a mechanical locking system comprising a flexible tongue (<NUM>), which is arranged in a displacement groove (<NUM>) at a first edge of a first panel (<NUM>), and a tongue groove (<NUM>) at a second edge of an adjacent second panel (<NUM>'), the flexible tongue (<NUM>) being configured to cooperate with the tongue groove (<NUM>) for locking of the first edge and the second edge in a vertical direction, wherein the mechanical locking system further comprises a locking strip (<NUM>), at the first or the second edge, provided with a locking element (<NUM>) configured to cooperate with a locking groove (<NUM>) at the other of the first edge or the second edge for locking in a horizontal direction, wherein:
the flexible tongue (<NUM>) is displaceable in the horizontal direction in the displacement groove (<NUM>),
an outer part of the flexible tongue (<NUM>) comprises two or more curved tongue sections (Ts1, Ts2), each comprising a sliding surface (<NUM>), which is configured to cooperate with the second edge during locking, and a locking surface (<NUM>) that is configured to lock against the tongue groove (<NUM>),
the tongue sections (Ts1, Ts2) are spaced from each other in a length direction (L) of the flexible tongue (<NUM>),
the flexible tongue (<NUM>) is curved in a locked and in an unlocked position, a first horizontal distance (D1), from an outer upper edge of the first edge of the first panel (<NUM>) to an outer edge of the flexible tongue (<NUM>), and a second horizontal distance (D2), from the outer upper edge of the first edge of the first panel (<NUM>) to an inner edge of the flexible tongue (<NUM>), varying along a length (L) of the flexible tongue (<NUM>),
the tongue sections (Ts1, Ts2) during locking are configured to be pressed inwardly by the second edge of the second panel (<NUM>') such that the tongue sections are at least partially straightened and deformed,
the tongue sections (Ts1, Ts2) are configured to move back towards their initial positions in a final stage of the locking such that said locking surface (<NUM>) is inserted into the tongue groove (<NUM>),
characterised in that
the tongue sections (Ts1, Ts2) during locking are at least partially straightened and deformed to essentially straight rod shaped sections with a width (W) that is essentially the same along essentially the entire length (L) of the flexible tongue (<NUM>).