RU2611090C2 - Mechanical locking system for floor panels - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: invention relates to construction, particularly, to locking systems for floor panels. Shown are construction panels, especially floor panels, which are provided with a vertical locking system on adjacent edges including a removable tab, which has the main body of the tab and separate spring parts attached to the body.

EFFECT: technical result is simplification of panels assembling.

10 cl, 18 dwg

Description

The invention generally relates to the field of mechanical interlock systems for floor panels and building panels. The invention shows floor boards, interlock systems, installation methods and manufacturing methods.

Embodiments of the invention are particularly suitable for use in floating floors that are formed from floor panels that are mechanically coupled by means of an interlock system made integrally with the floor panel, i.e. factory mounted, made of one or more top layers of wood or wood veneer, decorative laminate, sawdust-based or decorative plastic material surfaces, an intermediate core of wood-based material or plastic material, and preferably a lower balancing layer on the back side of the core. Included are floor panels with a surface layer of cork, linoleum, rubber or soft wear-resistant layers, for example needle-punched material glued to a board, a printed and preferably also varnished surface, and floors with hard surfaces such as stone, ceramic and similar materials. Embodiments of the invention can also be used to join building panels that preferably comprise plank material, such as wall panels, ceilings, furniture components and the like.

The following description of known technology, problems of known systems, and the objectives and features of embodiments of the invention will therefore, by way of non-limiting example, be directed primarily to this field of application and, in particular, to panels formed in the form of rectangular floor panels with long and short edges intended for mechanical connection with each other at both long and short edges.

Long and short edges are mainly used to simplify the description of an embodiment of the invention. Panels may be square. Embodiments of the invention are preferably used at short edges. It should be emphasized that embodiments of the invention can be used in any floor panel, and it can be combined with all types of known locking system formed on long edges, where the floor panels are intended to be connected using a mechanical locking system connecting the panels in horizontal and vertical directions in at least two adjacent sides.

Laminate flooring usually contains a core of fiberboard from 6 to 12 mm, an upper decorative surface layer with a thickness of 0.2 to 0.8 mm laminate, and a lower balancing layer with a thickness of 0.1 to 0.6 mm laminate, plastic, paper or similar material. The surface of the laminate contains melanin impregnated paper. The most common core material is a high density wood fiber board with good stability, commonly referred to as fiberboard, a high density wood fiber board. Sometimes also MDF - medium density fiberboard - is used as a core.

Traditional laminate floor panels of this type were joined by glued tongue and groove joints. In addition to such traditional floors, floor panels have been developed that do not require the use of glue and are instead mechanically connected by so-called mechanical interlock systems. These systems contain locking means that block the panels horizontally and vertically. Mechanical interlock systems are typically formed by machining the core of the panel. Alternatively, parts of the interlock system can be formed from a separate material, for example aluminum or fiberboard, which is combined with the floor panel, i.e. connected to the floor panel in connection with its manufacture.

The main advantages of floating floors with mechanical interlock systems are that they are easy to install. They can also be easily cleaned again and reused elsewhere.

DEFINITION OF SOME TERMS

In the following text, the visible surface of the installed floor panel is called the “front side”, while the opposite side of the floor panel facing the base is called the “back side”. The edge between the front and back is called the “connecting edge”. By "horizontal plane" is meant a plane that runs parallel to the outer part of the surface layer. The immediately adjacent upper parts of two adjacent connecting edges of the two connected floor panels together define a “vertical plane” perpendicular to the horizontal plane. By “inner vertical plane of the tongue” is meant a plane that is parallel to a vertical plane that intersects the outer and inner most part of the main body of the tongue. By “vertical lock” is meant a lock parallel to a vertical plane. By “horizontal lock” is meant a lock parallel to the horizontal plane.

By "up" is meant towards the front side, by "down" - towards the back side, by "inward" - mainly horizontally towards the inner and central part of the panel and under "out" - mainly horizontally from the central part panels.

By “interlocking systems” is meant interacting connecting elements that connect floor panels vertically and / or horizontally.

For the mechanical connection of long edges, as well as short edges, in the vertical and in the first horizontal direction, perpendicular to the edges, several methods can be used. One of the most used methods is a corner snap method. Long edges are installed by angular installation. The panel then slides to a locked position along the long side. Short edges are locked by horizontal snapping. The vertical joint is usually a tongue and a groove. During horizontal displacement, the strip with the locking element bends and, when the edges are in contact, the strip spring back and the locking element enters the locking groove and locks the panels horizontally. Such a snap connection is difficult since a hammer and a tapping block are usually required to overcome friction between long edges and to bend the strip during the snap action.

Similar interlocking systems can also be made with a rigid strip, and they are connected using the method of installation at an angle - installation at an angle where both short and long edges are installed at an angle in the locked position.

Recently, new and very effective interlock systems have been introduced with a separate flexible or movable inseparable tongue at a short edge, which allows installation only by means of an angular installation action, commonly referred to as “vertical stacking”. Such a system is described in WO 03/083234 and WO 2006/043893 (Välinge Innovation AB).

Several options are used in the market. Figures 1a-1c show a locking system comprising a slide tab 30 that slides inwardly into the offset groove 21 and outwardly into the tongue groove 20 when the edges of adjacent panels 1, 1 ′ are displaced vertically relative to each other. Such systems are called vertically snapping systems and they provide automatic locking during the laying operation. An offset tongue 30 locks the panels vertically, parallel to the vertical plane VP, perpendicular to the main horizontal plane of the panels. The locking strip 6 with the locking element 8, which interacts with the locking groove 14 in the adjacent panel 1 ', blocks the edges horizontally, parallel to the main horizontal plane of the HP.

On figa-2e shows one of the most used flexible reeds 30, the so-called tongue with bristles, which are formed as a single unit. Such a movable tongue 30 comprises a tongue main body 31 that is strong and sufficiently rigid, flexible protrusions 38 that provide the necessary flexibility, and friction joints 36 that prevent the tongue from falling out of the offset groove 21 during transportation and installation of the floor panels. Tongues with bristles are made of high quality fiberglass reinforced plastic material. Flexibility should be significant and allow the flexible tongue to bias about 1-2 mm in two directions during locking. The tongues are obtained by injection molding and are formed in the blanks 50 of the tongue, which can contain up to 32 tongues. The tabs are connected to the rails 51, which are used to feed the tabs during manufacture, when they are separated from the blank of the tab and inserted into the edge of the panel.

Although such locking systems, made as a single tongue with bristles, are very effective and provide a strong and reliable locking, there is still room for improvement.

One drawback is that the entire tongue blank 50 is made of high quality plastic material, which is quite expensive. Such high-quality material is necessary only in those parts of the tongue that form flexible protrusions 36. High-quality plastic material reinforced with fiberglass is not required in parts of the tongue that contain the main body 31 of the tongue and the rails 51. About 60% of the workpiece of the tongue is made of material that has higher quality than required for its specific function.

A second disadvantage is that each tongue blank 50 must be individually made for a particular width of the floor panel, and this requires a wide range of expensive tongues obtained by injection molding of the tongues for each width.

A third disadvantage is that the fiberglass reinforced plastic material is difficult to process, and rail waste has a very low material value.

It would be a major advantage if the tongues were performed in a more cost-effective manner with respect to material costs and different lengths of the tongue.

It is known from the aforementioned publications that the displaced tongue may be formed from sheet materials such as fiberboard. This can reduce material costs by about 80% compared to expensive plastic materials. Flexibility can be obtained by means of a flexible rubber strip that is inserted into the inside of the offset groove or attached to the inside of the extruded plastic section. Such a two-part tongue will not provide sufficient strength and flexibility, since compression occurs outside the displaced tongue between the inner part of the bias groove and the inner edge of the tongue body. The groove should be quite deep and this will have a negative effect on the stability of the connection. It is not shown how flexible material should be attached to the tongues in the tongue blank and how frictional joints should be formed that allow the tongue to slide in the groove without the risk that the tongue will fall out of the groove after manufacture. The cost of the flexible material is still quite high since the flexible part extends along the entire length of the tongue.

It is a general object of embodiments of the invention to provide an improved and more cost-effective interlocking system for mainly rectangular floor panels with long and short edges mounted in parallel rows, which makes it possible for short edges to be automatically locked relative to each other by means of a vertical latch an action triggered by a tongue that slides in the groove. More specifically, the goal is to provide a locking system with a separate sliding tongue, which is formed from different materials, so cost and performance can be optimized.

Another specific task is to provide a tongue that can be made with different lengths without the need for individual injection molding tools specifically made for each length of the tongue.

The above objectives of an embodiment of the invention can be achieved in whole or in part by means of interlocking systems and floor panels in accordance with the description of the invention. Embodiments of the invention are apparent from the description and drawings.

A first aspect of the invention is construction panels provided with a locking system for vertically locking the first and second building panels by vertically displacing the panels relative to each other. The biased tongue is secured to an offset groove open on the side provided at the edge of the first panel. Said tongue cooperates with a tongue groove provided on an adjacent edge of the second panel to lock the edges vertically. The strip protrudes below the offset groove and out beyond the top of the edge or below the tongue groove and out beyond the top of the adjacent edge. The biased tongue comprises a tongue main body extending along the edge of the first panel, and a separate flexible spring portion attached to the tongue main body. A separate spring part is located in the inner part of the offset groove.

The tongue may comprise two or more spring parts that are spaced apart from each other in the direction of the length of the main body of the tongue.

The spring parts may be asymmetric in the direction along the edge.

The main body of the tongue and the spring parts can be made of different materials.

The tongue may comprise a mounting groove that is open up or down.

The spring parts may comprise an upward or downward connecting connecting part.

The spring part may, during blocking, shift or contract horizontally beyond the vertical plane of the tongue, which contains the inside of the tongue body.

The spring portion may overlap the tongue portion or body during blocking.

The spring portion may be located in a vertically open bending cavity formed in the body of the tongue.

Building panels are preferably floor panels.

A second aspect of the invention is a tongue blank containing at least two tongues, each of which is configured to insert a construction panel into the groove and lock the construction panel relative to the adjacent construction panel. Part of the tongue is designed to move during locking. The tongues have an elongated shape, and each tongue contains a separate spring part connected to the main body of the tongue.

The individual spring portion may be asymmetric in the direction of the length of the tongue.

Each tongue may comprise two or more spring parts that are spaced apart from each other in the length direction of the tongue.

SUMMARY OF THE INVENTION Disclosure of the invention will hereinafter be described in connection with illustrative embodiments and in more detail with reference to the accompanying illustrative drawings.

On figa-1C shows the locking system in accordance with known technology.

On figa-2e shows a flexible and movable tongue in accordance with known technology.

Figures 3a-3g show a bias tab in accordance with an embodiment of the invention.

Figures 4a-4d show the operation of a spring part in accordance with an embodiment of the invention.

Figures 5a-5g show the formation and separation of a tongue blank in accordance with an embodiment of the invention.

6a-6e show preferred embodiments of biased reeds.

Figures 7a-7c show a vertical locking of two panels comprising a slide tab in accordance with an embodiment of the invention.

On figa-8f shows the formation and fastening of the biased tab in accordance with an embodiment of the invention.

On figa-9g shows the formation of the preform of the tongue in accordance with an embodiment of the invention.

10a-10g show embodiments of the invention.

11a-11g show spring parts made of compressible material in accordance with embodiments of the invention.

12a-12i show spring portions connected in a cavity in accordance with embodiments of the invention.

13a-13f show individual frictional joints in accordance with embodiments of the invention.

On figa-14d shows the spring parts connected in a groove, in accordance with the variants of the invention.

15a-15f show various embodiments of the invention.

On figa-16g shows the spring parts connected to the groove, in accordance with the variants of the invention.

On figa-17g shows various embodiments of the invention.

On figa-18e shows various embodiments of the invention.

For ease of understanding, several locking systems in the figures are shown schematically. It should be emphasized that improved or other functions can be achieved using combinations of embodiments.

All embodiments may be used singly or in combinations. Corners, sizes, rounded parts, gaps between surfaces, etc. are only examples and can be regulated within the basic principles of the invention.

Figures 3a-3g show a first preferred embodiment of a displaceable tongue 30, which is intended to be used to block two adjacent edges of two floor panels by vertically displacing the panels relative to each other.

FIG. 3 a shows a displaceable tongue 30 with a tongue main body 31, a length direction L along the joint, a width W perpendicular to the length and parallel to the horizontal plane, and a thickness perpendicular to the width. The inner vertical plane Tp1 of the tongue and the outer vertical plane Tp2 of the tongue parallel to the direction of the length of the tongue intersect with the outer edges of the tongue.

FIG. 3b shows a biased tongue 30 comprising a separate spring portion 40 attached to the tongue main body 31. The spring portion comprises a spring portion body 41, a friction joint 36, preferably formed in the form of a small local protrusion extending vertically from the spring portion body 41, and a fastener connecting portion 42 that is secured to the fastening groove 32 formed in the tongue main body 31.

On figs shows the workpiece 60 of the spring part, when viewed from above, containing several spring parts 40 connected to each other in parallel rows and with rails 61 of the spring part.

On fig.3d shows the workpiece of the spring part, when viewed from below. Each spring portion 40 comprises a fastener connecting portion 42, which in this embodiment is formed as a protrusion extending vertically from the main body 41 of the spring portion and in the opposite direction with respect to the extension of the friction joint 36.

FIG. 3e shows the main body 31 of the tongue, which in this embodiment is formed as a two-dimensional profile with the same cross section along the body of the tongue. Such a tongue body may be formed by, for example, linear machining, extrusion, or injection molding, using fairly simple molding tools.

FIG. 3f shows a displaceable tongue in an external locked position, the tongue comprising a tongue main body 31 and two separate spring parts 40, 40 ′ mechanically connected to the tongue body 31 and spaced apart from each other in the length direction of the tongue 30.

Fig. 3g shows a displaceable tongue in an internal unlocked position when the tongue 30 is pushed into the lateral displacement groove 21. The spring portion is displaced inward beyond the first vertical plane Tp1 of the tongue, but also above the portion of the main body 31 of the tongue. The thickness of the spring portion is less than the thickness of the body 31 of the tongue. This embodiment offers the advantage that the spring portion can easily be connected to the tongue body, which has a fairly simple cross section, and that the depth of the offset groove can be reduced, since the tongue main body 31 and the spring portion body 41 can overlap at a friend in a locked and unlocked position.

Any type of polymeric material can be used to form spring parts, for example PA (nylon), POM, PC, PP, PET or PE or the like, having the properties described above in other embodiments. These plastic materials can be, when injection molding is used, reinforced, for example, with fiberglass, Kevlar fiber, carbon fiber or talc or chalk. The preferred material is fiberglass, preferably extra long, reinforced with PP or POM. Such materials can also be used to form the main body of the tongue.

The body of the tongue preferably contains inexpensive material, which preferably can be machined. Suitable materials are wood fiber based materials combined with thermoplastic or thermosetting binders.

FIG. 4 a shows a portion of a biased tongue 30 comprising a spring portion 40 connected to an upper portion of a tongue main body 31. Fig. 4b shows a spring part 40 from below with a fastening connecting part 42, which is flexible and adapted so as to connect vertically into a vertically open mounting groove 32 formed on the upper part of the tongue body 31. The fastening connecting portion 42 comprises a horizontal friction protrusion 43 which is pressed against the vertical wall of the fastening groove 32.

Fig. 4c shows a flexible tongue 30 in an external position, and Fig. 4d shows a flexible tongue 30 in an internal position. AA shows a cross section of the middle part of the main body of the tongue. BB shows a cross section of the outer part of the main body of the tongue. The figures show that a part of the body 41 of the spring part is located above the upper part of the body 31 of the tongue and is displaced behind the first vertical plane Tp1 of the tongue during blocking so that it overlaps the main body of the tongue.

FIG. 5 a shows a cross-section of a tongue blank 50 comprising several movable tongues that comprise a tongue main body 31 and individual flexible portions 40 connected to the tongue body. Fig. 5b shows a blank 70 of the tongue body containing several tongue bodies 31 that are connected to the rails 71 of the tongue bodies. Such rails can, for example, be formed by punching material from the bodies of reeds. Fig. 5f shows a preform 60 of the spring part, where the spring parts are arranged with substantially the same distance D between each other as the distance between the reed bodies 31. This facilitates the fastening of the spring parts relative to the bodies of the tongues, since the spring parts can be displaced after the separation shown in Fig. 5g, mainly parallel to the bodies of the tongues along the bodies of the tongues and pressed vertically so that the fastening connecting part 42 is included in the mounting groove 32 The tongue blank 50 may be formed as shown in FIG. 5c. Such a formation can be performed as a separate operation, and reed blanks are delivered in the form of combined blanks. The connection can also be made along with the insertion of the tongue with the offset groove. The tongues 30 are separated from the workpiece, as shown in FIG. 5d, and inserted into the offset groove 21, as shown in FIG. 5e. The tabs can be inserted into a groove of a panel of a strip containing a strip, or into a groove formed in another adjacent panel.

6a-6d show alternative methods for connecting the spring parts 40 to the tongue main body 31. One or more holes 34a or cavities 34b may be formed. FIG. 6e shows that different lengths of displaced tongues can be formed by combining several spring parts that are located along the main body 31 of the tongue.

On figa-7c shows the locking of two panels 1, 1 '. Fig. 7a shows that the tongue 30 deviates downward during blocking, and Fig. 7c shows that the tongue 30 deviates upward in the locked position such that the outer part of the rigid body of the tongue forms an upper contact surface 22 with an offset groove 21, and that the inner part forms the lower contact surface 23. This means that it is an advantage to connect the spring part with the upper part of the main body of the tongue. The spring part, of course, can be connected to the lower part in the mounting groove, which is open in the downward direction.

On figa-8e shows a method of forming and inserting offset tabs in the edge of the panel, which can be used, for example, when the bodies of the tabs are supplied as a separate element or in the form of extruded sections that are cut to a given length. The bodies of the reeds 31 are displaced, for example, in parallel with their lengths, and the preforms 60 of the spring part are displaced towards the bodies of the reeds, where the spring parts 40 are separated and connected to the body of the reed when the body 31 of the reed is displaced in the direction of its length. The biased tabs 30 are then inserted into the bias groove 21.

On figa-9c shows that the preform of the body of the tongue can be formed in the form of an extruded section, figa, b, or by, for example, machining a panel from a machined wood, wooden / plastic or plastic panel, fig.9b, or by injection molding, FIG. 9c.

Figures 9d and 9f show that the tongue blanks can be formed by movable tongues that connect to rails that may comprise an extruded section, Fig. 9e, or molded parts, Fig. 9g.

10a-10d show preferred embodiments of the displaceable tongues 30. FIG. 10a shows overlapping spring parts 40. FIG. 10b shows a spring part that adheres to the body of the tongue. Fig. 10c shows spring parts with the body of the spring part, which is flexible at only one edge. 10d shows spring parts that are connected to each other.

FIG. 10e shows a tongue 30 with a spring portion that is connected to an inclined offset groove 21 in a panel of a strip containing a locking strip 6. FIG. 10f shows a sliding tongue 30 inserted at an edge of a panel with a groove containing a locking groove 14. FIG. .10g shows a locking system that only locks vertically. Strip 6 does not have a blocking element. Horizontal locking can be accomplished, for example, by friction between long edges.

On figa-11g shows that the spring part can also be formed from a flexible material, such as, for example, rubber. The flexible parts in this embodiment are uniformly spaced apart from each other along the main body of the tongue, and the individual parts can be compressed and displaced beyond the first vertical plane Tp1 of the tongue, as shown in FIG. 11c. Preferably, bending cavities 33 are formed in the main body of the tongue to enable such compression. The spring portions 40 are preferably asymmetric in the length direction of the biased tongue 30.

On figa-12i shows that several bending cavities 33 and bending cavities 34 can be formed in the main body 31 of the tongue in order to fix the spring parts and to allow compressive or bending displacement in and out of the vertical plane Tp1 of the tongue. The figures show that the bodies 31 of the reeds and the spring parts 40 are asymmetric in the direction of the length of the tongue.

On figa-13f it is shown that also other parts of the displaced tongue can be connected in separate parts, for example a friction connection 36, which can be attached to the main body 31 of the tongue, as shown in fig.13d. On fig.13e shows that the friction connection 36 can be formed and attached to the main body 31 of the tongue so that it can be displaced with rotation. Such a pivoting device can be used as a link to bias the tongue outward from the bias groove when the tongue is pushed laterally along the joint with lateral pressure.

On figa-14d shows an alternative method of forming a biased tongue, which contains individual spring parts 40. The spring parts are inserted into the groove 21 of the bias. The main body 31 of the tongue is then inserted into the offset groove and connected to the spring parts 40.

15a-15f show a preferred embodiment of a spring portion that is suitable for insertion into the offset groove 21. FIG. 15 a shows a spring portion 40 from above, and FIG. 15 b is a side view. The spring portion comprises a friction joint 36, a snap joint 44 and a holding joint 45 located vertically on opposite upper sides of the spring portion. The snap and hold connections move along the body 41 of the spring portion. The main body 31 of the tongue is automatically latched relative to the spring part, which is connected by means of a friction connection 36 to the offset groove. Figures 15e and 15f show cross sections during blocking. The snap connection 44 is attached to the main body of the tongue, and the holding connection slides over the body 31 of the tongue during locking. The spring portion 41, of course, can also be attached to the main body of the tongue before being secured to the offset groove 21.

On figa-16g shows the spring part 40, for which it is possible only to snap relative to the main body 31 of the tongue, when the spring part is already in the groove 21 of the bias, since the spring part contains only the snap connection 44 and does not contain a holding connection. On figa shows the spring part when viewed from above, and on fig.16b shows a side view. It is preferred that the snap connection 44 is located on top of the spring portion 40.

On figa-17g shows that the bending cavity 33 can be formed in the main body 31 of the tongue, and this embodiment provides the possibility that the main part of the body 41 of the spring part can move beyond the vertical plane Tp1 of the tongue.

On figa-18e shows that the body 31 of the tongue can be formed in the form of a three-dimensional molded component and optimized for snapping in relation to the spring part. The material savings are mainly due to the fact that the plastic material of the tongue body 31 can be less expensive since flexibility is not required. Fig. 18e is a side view of Fig. 18d. The protrusions 46, 46 'of the spring part during disengagement are displaced in the displacement cavities 33, 33'.

The tabs described are primarily intended for use on the short edges of panels containing locking systems on long edges that can be locked by angular installation. However, tongues can be used on short and / or long edges.

The principles of the invention can also be used to form two-part reeds that are not flexible and which, for example, are used to bias along the joint during blocking. The individual parts can be used, for example, as wedges, which during movement create a movement of the tongue perpendicular to the edge.

Claims (16)

1. Building panels made with a locking system for vertically locking the first (1) and second (1 ') building panels by vertically displacing said first and second building panels (1, 1') with respect to each other, with a displaced tongue (30) fixed in the side opening of the offset groove (21) made on the edge of the first building panel, while the displaced tongue is configured to interact with the groove (20) for the tongue made on the adjacent edge of the second building panel (1 '), for blocking ki edge and adjacent vertical edges, wherein the strip (6) serves: below the offset groove and out beyond the top of the edge; or below the tongue groove and out beyond the top of the adjacent edge, characterized in that the displaced tongue (30) contains the main body (31) of the tongue extending along the edge of the first building panel and individual flexible spring parts (40) attached to the main body (31) of the tongue, individual spring parts (40) are located in the inner part of the offset groove (21) and are located at a distance from each other in the direction of the length of the main body (31) of the tongue, while the individual spring parts (40) comprise a fastening connecting part (42) extending up or down. 2. The building panels of claim 1, wherein the spring parts are asymmetric in the direction along the edge. 3. Building panels according to claim 1 or 2, in which the main body (31) of the tongue and the spring parts (40) are made of different materials. 4. Building panels according to claim 1, in which the tongue body (31) comprises a mounting groove (32) open up or down. 5. Building panels according to claim 1, in which the spring parts (40) during blocking are displaced or compressed horizontally beyond the vertical plane Tp1 of the tongue, which contains the inner part of the body (30) of the tongue. 6. Building panels according to claim 1, in which the spring parts (40) overlap the part or body (30) of the tongue during blocking. 7. Building panels according to claim 1, in which the spring parts (40) are located in a vertically open bending cavity (33) formed in the body of the tongue. 8. The building panels of claim 1, wherein the building panels are floor panels. 9. A blank (50) of a tongue, comprising at least two tongues (30), each of which is configured to insert into the groove (21) of the construction panel and lock the construction panel relative to the adjacent construction panel, while a portion of each tongue is configured to displacements during locking, characterized in that the tongues (30) are elongated, each tongue containing two or more separate spring parts (40), which are located at a distance from each other in the direction of the length of the tongue, and the spring parts (40) comprise a fastening connecting part (42) extending up or down. 10. The blank (50) of the tongue according to claim 9, in which the spring part (40) is asymmetric in the direction of the length of the tongue.

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