# Patent

## Title
Mechanical locking system for floor panels

## Abstract

Floor panels are provided with a mechanical locking system having small local protrusions which reduce displacement along the joint when the panels are laying flat on the sub floor and locked vertically and horizontally.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
The present application is a continuation of U.S. application Ser. No. 13/426,159, filed on Mar. 21, 2012, which is a continuation of U.S. application Ser. No. 11/822,684, filed on Jul. 9, 2007, which is a continuation of U.S. application Ser. No. 10/908,658, filed on May 20, 2005. The entire contents of each of U.S. application Ser. No. 13/426,159, U.S. application Ser. No. 11/822,984 and U.S. application Ser. No. 10/908,658 are hereby incorporated herein by reference.


TECHNICAL FIELD
The invention generally relates to the field of mechanical locking systems for floor panels and building panels. The invention comprises floorboards, locking systems, installation methods and production methods.
FIELD OF APPLICATION
The present invention is particularly suitable for use in floating floors, which are formed of floor panels which are joined mechanically with a locking system integrated with the floor panel, i.e. mounted at the factory, and are made up of one or more upper layers of veneer, decorative laminate or decorative plastic material, an intermediate core of wood-fiber-based material or plastic material and preferably a lower balancing layer on the rear side of the core. The following description of prior-art technique, problems of known systems and objects and features of the invention will therefore, as a non-restrictive example, be aimed above all at this field of application and in particular at laminate flooring 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. The panels could be square.
It should be emphasized that the invention can be used in any floor panel and it could be combined with all types of known locking systems, where the floor panels are intended to be joined using a mechanical locking system connecting the panels in the horizontal and vertical directions on at least two adjacent sides. The invention can thus also be applicable to, for instance, solid wooden floors, parquet floors with a core of wood or wood-fiber-based material and a surface of wood or wood veneer and the like, floors with a printed and preferably also varnished surface, floors with a surface layer of plastic or cork, linoleum, rubber. Even floors with hard surfaces such as stone, tile and similar material are included, and floorings with soft wear layers, for instance, needle felt glued to a board. The invention can also be used for joining building panels which preferably contain a board material for instance wall panels, ceilings, furniture components and similar.
BACKGROUND
Laminate flooring usually consists of a core of a 6-12 mm fiber board, a 0.2-0.8 mm thick upper decorative surface layer of laminate and a 0.1-0.6 mm thick lower balancing layer of laminate, plastic, paper or like material. A laminate surface may consist of melamine impregnated paper. The most common core material is fiberboard with high density and good stability usually called HDF—High Density Fiberboard. Sometimes also MDF—Medium Density Fiberboard—is used as the core.
Traditional laminate floor panels of this type have been joined by means of glued tongue-and-groove joints.
In addition to such traditional floors, floor panels have been developed which do not require the use of glue and instead are joined mechanically by means of so-called mechanical locking systems. These systems comprise locking means, which lock the panels horizontally and vertically. The mechanical locking systems are usually formed by machining the core of the panel. Alternatively, parts of the locking system can be formed of a separate material, for instance aluminum or HDF, which is integrated with the floor panel, i.e., joined with the floor panel in connection with the manufacture thereof.
The main advantages of floating floors with mechanical locking systems are that they are easy to install. They can also easily be taken up again and used once more at a different location.
DEFINITION OF SOME TERMS
In the following text, the visible surface of the installed floor panel is called “front side”, 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 outer part of the surface layer. 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 in D1 direction. By “horizontal locking” is meant locking parallel to the horizontal plane in D2 direction. By “first horizontal locking” is meant a horizontal locking perpendicular to the joint edges in D2 direction. By “second horizontal locking is meant a horizontal locking in the horizontal direction along the joint which prevents two panels to slide parallel to each other when they are laying in the same plane and locked both vertically and in the first horizontal direction.
By “locking systems” are meant co acting connecting elements which connect the floor panels vertically and/or horizontally in the first horizontal direction D2. By “mechanical locking system” is meant that joining can take place without glue. Mechanical locking systems can in many cases also be joined by gluing. By “integrated with” means formed in one piece with the panel or factory connected to the panel.
RELATED ART AND PROBLEMS THEREOF
For mechanical joining of long edges as well as short edges in the vertical and in the first horizontal direction (direction D1, D2) several methods could be used. One of the most used methods is the angle-snap method. The long edges are installed by angling. The panel is than displaced in locked position along the long side. The short edges are locked by horizontal snapping. The vertical connection is generally a tongue and a groove. During the horizontal displacement, a strip with a locking element is bent and when the edges are in contact, the strip springs back and a locking element enters a locking groove and locks the panels horizontally. Such a snap connection is complicated since a hammer and a tapping block may need to be used to overcome the friction between the long edges and to bend the strip during the snapping action. The friction on the long side could be reduced and the panels could be displaced without tools. The snapping resistance is however considerable especially in locking systems made in one piece with the core. Wood based materials are generally difficult to bend. Cracks in the panel may occur during snapping. It would be an advantage if the panels could be installed by angling of long edges but without a snap action to lock the short edges. Such a locking could be accomplished with a locking system that locks the long edges in such a way that also displacement along the joint is counteracted.
It is known from Wilson U.S. Pat. No. 2,430,200 that several projections and recesses could be used to prevent displacement along the joint. Such projections and recesses are difficult to produce, the panels can only be locked in well-defined positions against adjacent long edges and they cannot be displaced against each other in angled position against each other when top edges are in contact. Terbrack U.S. Pat. No. 4,426,820 describes a locking system with a tight fit in a panel made of plastic material. The tight fit prevents displacement along the joint. A system with tight fit does not give a safe and reliable locking over time especially if the locking system is made of wood fiber based material, which swells and shrink when the humidity varies over time.
OBJECTS AND SUMMARY
A first overall objective of the present invention is to provide a locking system for primarily rectangular floor panels with long and short edges installed in parallel rows, which allows that the short edges could be locked to each other horizontally by the locking system on the long edges. The costs and functions should be favorable compared to known technology. A part of the overall objective is to improve the function and costs of those parts of the locking system that locks in the horizontal direction along the joint when panels are installed on a sub floor.
More specifically the object is to provide a second horizontal locking system on the long edges, hereafter referred to as “slide lock” where one or several of the following advantages are obtained.
The slide lock on the long edges should be activated when a panel is brought in contact with an already installed panel and then angled down to the sub floor.
The slide lock function should be reliable over time and the panels should be possible to lock and unlock in any position when two adjacent long edges are brought into contact with each other.
The slide lock should be strong and prevent that short edges of two locked panels will separate when humidity is changing or when people walk on a floor.
The slide lock should be possible to lock with high precision and without the use of tools.
The locking system and the slide lock should be designed in such a way that the material and production costs could be low.
A second objective is to provide an installation method for installation of floorboards with a slide lock.
A third objective is to provide a production method for a slide lock system.
The above objects of the invention are achieved wholly or partly by locking systems, floor panels, and installation and production methods according to the independent claim. Embodiments of the invention are evident from the dependent claims and from the description and drawings.
According to a first aspect of the invention, a flooring system is provided comprising a plurality of rectangular floor panels to be installed on a sub floor. The floor panels have long and short edges, which are connectable to each other along one pair of adjacent edges of adjacent panels. The connectable adjacent edges have a mechanical locking system comprising a tongue formed in one piece with the panel and a groove for mechanically locking together said adjacent edges at right angles to the horizontal plane of the panels, thereby forming a vertical mechanical connection between the panels. One pair of adjacent edges has a locking element at one first edge and a locking groove at an opposite second edge thereby forming a first horizontal mechanical connection locking the panels to each other in a direction parallel to the horizontal plane and at right angles to the joint edges. Each panel is at said adjacent edges provided with a second horizontal mechanical connection locking the panels to each other along the joint edges, in a direction parallel to the horizontal plane and parallel to the joint edges, when the panels are laying flat on the sub floor. The second horizontal mechanical connection comprises a plurality of small local protrusions in said mechanical locking system which prevents displacement along the joint edges when the panels are laying flat on the sub floor and are locked with the vertical and the first horizontal connections.
Although it is an advantage to integrate the slide locking system with the panel, the invention does not exclude an embodiment in which parts of the locking system are delivered as separate components to be connected to the panel by the installer prior to installation. Such separate components could be applied in the locking system in order to prevent displacement along the joint when two panels are locked by preferably angling. Displacement could also be prevented and additional strength could be accomplished with a locking system which is pre glued.
It is an advantage if the short edges have a vertical locking preferably with a tongue and a groove. The short edges could however be made without vertical locking especially if the panels are narrow. In such a case long edges will also lock the short edges even in the vertical direction.
The invention is especially suited for use in floor panels, which are difficult to snap for example because they have a core, which is not flexible, or strong enough to form a strong snap locking system. The invention is also suitable for wide floor panels, for example with a width larger than 20 cm, where the high snapping resistance is a major disadvantage during installation, in panels where parts of the locking system on the long edge is made of a material with high friction, such as wood and in locking systems which are produced with tight fit or without play or even with pretension. Especially panels with such pretension where the locking strip is bent in locked position and presses the panels together are very difficult to displace and snap. A locking system that avoids snapping will decrease the installation time of such panels considerably. However, a tight fit and pretension in the locked position could improve the strength of the slide lock. An alternative to small protrusions, in some applications, is to use a high friction core material together with a tight fit between as many adjacent surfaces in the locking system as possible. Even a wood based material might be used if normal shrinking and swelling is reduced.
The invention is also suited to lock parallel rows to each other such that the rows maintain their position after installation. This could be an advantage in floors which are installed in advanced patterns such as tiles or stone reproductions where grout lines or other decorative effect must be aligned accurately or in any other installation where it is an advantage if the floor panels cannot slide after installation.
According to a second aspect of the invention a production method is provided to make a mechanical locking system between two edges of a first and second panel containing a wood fiber based core. According to the invention the locking system is formed at least partly in the core and comprises protrusions formed in the wood based core. The protrusions are at least partly formed by embossing.
According to a third aspect of the invention an installation method to install a floor is provided, comprising a plurality of rectangular floor panels laying in parallel rows on a sub floor with long and short edges which are connectable to each other along one pair of adjacent long edges and one pair of adjacent short edges. The panels have a mechanical locking system comprising a tongue formed in one piece with the panels and groove for mechanically locking together said adjacent long and short edges at right angles to the horizontal plane of the panels, thereby forming a vertical mechanical connection between the panels. The panels have also a locking element at one first long edge and a locking groove at an opposite second long edge which form a first horizontal mechanical connection locking the long edges of the panels to each other in a direction parallel to the horizontal plane and at right angles to the joint edges. Each panel is at said adjacent long edges provided with a second horizontal mechanical connection locking the panels to each other along the joined long edges when the panels are laying flat on the sub floor. The second horizontal mechanical connection comprises small local protrusions in said mechanical locking system on the long edges which prevents displacement along the joint when the panels are laying flat on the sub floor and are locked with the vertical and the first horizontal connections. The method comprises five steps:

    
    
        a) As a first step a first panel is installed on a sub floor in a first row.
        b) As a second step a second panel in a second row is brought in contact with its long edge against the long edge of the first panel and held at an angle against the sub floor.
        c) As a third step a new panel in a second row is brought at an angle with its long edge in contact with the long edge of the first panel and its short edge in contact with the short edge of the second panel.
        d) As a fourth step the new panel is displaced against the second panel in the angled position and the tongue is inserted into the groove until the top edges at the short edges are in contact with each other.
        e) As a final fifth step the second and new panels are angled down to the sub floor. This angling locks the long edges of the second and new panels to the first panel in a vertical direction and in a first horizontal direction perpendicular to the joined long edges and in a second horizontal direction along the long edges. The locking in the second horizontal direction prevents separations between the short edges of the second and the new panel.
    
    





BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1a-d illustrate two embodiments of the invention.
FIGS. 2a-d illustrate locking of the slide lock with angling.
FIG. 3 illustrates a floorboard with a slide lock on long side.
FIGS. 4a-b illustrates a production method to form a slide lock.
FIGS. 5a-e illustrate another embodiment of the invention.
FIGS. 6a-i illustrate an installation method according to an embodiment of the invention.
FIGS. 7a-i illustrate floor panels, which could be installed in a herringbone pattern and in parallel rows according to an embodiment of the invention.
FIGS. 8a-8d illustrate embodiments according to the invention.



DESCRIPTION OF EMBODIMENTS OF THE INVENTION
To facilitate understanding, several locking systems in the figures are shown schematically. It should be emphasized that improved or different functions can be achieved using combinations of the preferred embodiments. The inventor has tested all known and especially all commercially used locking systems on the market in all type of floor panels, especially laminate and wood floorings and the conclusion is that at least all these known locking systems which have one or more locking elements cooperating with locking grooves could be adjusted to a system with a slide lock which prevents displacement along the adjacent edges. The locking systems described by the drawings could all be locked with angling. The principles of the invention could however also be used in snap systems or in systems which are locked with a vertical folding. The slide lock prevents sliding along the joint after snapping or folding.
The invention does not exclude floor panels with a slide lock on for example a long and/or a short side and floor panels with a angling, snapping or vertical folding lock on short side which locks horizontally and where the slide lock on the long side for example gives additional strength to the short side locking.
The most preferable embodiments are however based on floorboards with a surface layer of laminate or wood, a core of HDF or wood and a locking system on the long edge with a strip extending beyond the upper edge which allows locking by angling combined with a tongue and groove joint on the short edges. The described embodiments are therefore non-restrictive examples based on such floor panels. All embodiments could be used separately or in combinations. Angles, dimensions, rounded parts, spaces between surfaces etc. are only examples and could be adjusted within the basic principles of the invention.
A first preferred embodiment of a floor panel 1, 1′ provided with a slide lock system according to the invention is now described with reference to FIGS. 1a-1d. 
FIG. 1a illustrates schematically a cross-section of a joint preferably between a long side joint edge of a panel 1 and an opposite long side joint edge of a second panel 1′.
The front sides of the panels are essentially positioned in a common horizontal plane HP, and the upper parts of the joint edges abut against each other in a vertical plane VP. The mechanical locking system provides locking of the panels relative to each other in the vertical direction D1 as well as the horizontal direction D2.
To provide joining of the two joint edges in the D1 and D2 directions, the edges of the floor panel 1 have in a manner known per se a locking strip 6 with a locking element 8, and a groove 9 made in one piece with the panel in one joint edge and a tongue 10 made in one piece with the panel at an opposite edge of a similar panel 1′. The tongue 10 and the groove 9 provide the vertical locking D1.
The mechanical locking system according to an embodiment of the invention comprises a second horizontal locking 16, 17 formed as small local protrusions on the upper part of the strip 6 and on the lower part of the panel 1′ in the edge portion between the tongue 10 and the locking groove 14. When the panels 1, 1′ are locked together in a common plane and are laying flat on the sub floor as shown in FIG. 1a, the small local protrusions 16, 17 are pressed to each other such that they grip against each other and prevent sliding and small displacement along the joint in a horizontal direction D3. This embodiment shows the first principle of the invention where the local protrusions are formed in the panel material. As a nonrestrictive example it could be mentioned that the upper 17 and lower 16 protrusions could be very small, for example only 0.1-0.2 mm high and the horizontal distance between the protrusions along the joint could be for example 0.1-0.5 mm. The distance between the upper protrusions could be slightly different than the distance between the lower protrusions. In locked position some protrusions will grip behind each other and some will press against each other but over the length of the floor boards there will be enough resistance to prevent sliding. The friction and the locking will be sufficient even in small cut off pieces at the end of the installed rows.
FIG. 1b shows an embodiment where small local protrusions 16 are formed on the upper part of the strip 8 adjacent to the locking element 8. The protrusions have a length direction which is essentially perpendicular to the edge of the floorboard. D1 show the locking in the vertical direction, D2 in the first horizontal direction and D3 in the second horizontal direction along the joint edge. FIG. 1c shows that similar protrusions could be formed on the lower side of the adjacent panel 1′ in a portion which is located between the locking groove 14 and the tongue 10. The protrusions on one edge could be different to the protrusions on the other adjacent edge. This is shown in FIG. 1d where the length direction of the protrusions has a different angle than the protrusions on the strip 6 in FIG. 1b. When two such panels are connected the protrusions will always overlap each other and prevent displacement in all locked positions. A strong locking could be accomplished with very small protrusions. The protrusions in this embodiment which is based on the principle that the protrusions 16, 17 are formed in one piece with the panel material could for example have a length of 2-5 mm, a height of 0.1-0.5 mm and a width of 0.1-0.5 mm. Other shapes are of course possible for example round or square shaped protrusions arranged as shown in FIG. 5a. 
FIGS. 2a-2c show locking of a slide lock system. In this preferred embodiment the panels 1, 1′ are possible to displace even when the locking element 8 is partly in the locking groove. This is an advantage when connecting the short edges with a tongue and a groove
FIG. 2b show that the local protrusions are in contact with each other when the adjacent panels 1, 1′ are held at a small locking angle A for example of about 3 degrees against the sub floor. Lower locking angles are possible but could cause problems when the panels are installed on an uneven sub floor. Most preferable locking angles are 3-10 degrees but of course locking systems with other locking angles smaller or larger could be designed. FIG. 2c shows the slide lock in locked position.
FIG. 2d show a testing method to test the sliding strength F of a slide lock. Test show that even small protrusions could prevent displacement of the short edges 5a and 5b of two panels. A slide lock could prevent displacement of the short edges when a pulling force F equal to 1000 N is applied to the panels with a slide lock length L of 200 mm on both long edges. This corresponds to a sliding strength of 5000 N per 1000 mm of slide lock length. This means that even small pieces with a length of 100 mm could be locked with a locking force of 500 N and this is in most applications sufficient. A slide lock could be designed with a sliding strength of more than 10,000 N per 1000 mm joint length. Even sliding strengths of 20,000 N or more could be reached and this is considerably more than the strength of traditional mechanical locking systems. Such systems are generally produced with a horizontal locking strength of 2000-5000 N per 1000 mm joint length. A preferable embodiment is locking systems where the slide strength of the slide lock in the second horizontal direction exceeds the locking strength of the mechanical locking system in the first horizontal direction. A high sliding strength is an important feature in a floating floor where small pieces often are installed as end pieces against the walls. In some applications a sliding strength of at least 50% of the horizontal locking strength is sufficient. In other applications, especially in public places 150% is required.
FIG. 3 shows a preferred embodiment of a floor panel with long 4a, 4b and short 5a, 5b edges. The long edges have a slide lock (C,D) with upper 17 and lower 16 protrusions over substantially the whole length of the long edges. The short edges have only a vertical locking system (A,B) with a tongue 10 and a groove 9. The lower lip 6 is a strip and extends beyond the upper lip 7.
FIG. 4a shows a production method to form small local protrusions in a wood based material. The protrusions are formed by embossing. This could be done with a press or with any other appropriate method where a tool is pressed against the wood fibers. Another alternative is to brush or to scrape parts of the locking system to form small local protrusions. The most preferable method is a wheel 30, which is rolled against the wood fibers with a pressure such that small local protrusions 16 are formed by compression of wood fibers. Such an embossing could be made continuous in the same machining line where the other parts of the locking system are formed.
FIG. 4b shows that the local protrusions could be formed between the tongue 10 and the groove 9, at the upper part 21 of the tongue, at the tip 20 of the tongue and at the lower outer part 19 of the tongue. They could also be formed between the upper part 18 of the strip and the adjacent edge portion and/or between the locking element 8 and the locking groove 14 at the locking surfaces 22, at the upper part 23 of the locking element and at the outer distal part 24 of the locking element. The local protrusions could be formed on only one edge portion or preferably on both edge portions and all these locations could be used separately or in combinations.
Compression of wood fibers with a wheel could also be used to form parts of the locking system such as the locking grove 14 or the locking element 8 or any other parts. This production method makes it possible to compress fibers and to form parts with smooth surfaces, improved production tolerances and increased density.
FIG. 5a shows another embodiment according to a second principle. The protrusions 16 could be applied as individual parts of a separate material such as rubber, polymer materials or hard sharp particles or grains which are applied into the locking system with a binder. Suitable materials are grains similar to those generally used in sandpaper, metal grains, especially aluminum particles. This embodiment could be combined with the first principle where protrusions formed in one piece with the panel material cooperates with a separate material which is applied into the locking system and which also could have cooperating protrusions. FIG. 5b shows an embodiment where a rubber strip is applied into the locking system. Separate high friction material could create a strong slide lock even without any protrusions but protrusions in the panel and/or in the separate material gives a stronger and safer slide lock. FIG. 5c shows that an embossed aluminum extrusion or wire 15 could be applied into the locking system. FIGS. 5d and 5e shows preferable location of the separate friction material 16, 17, 17′.
The following basic principles to make a slide lock have now been described:
Local protrusions are formed in one piece with the panel material preferably on both adjacent edges and they cooperate with each other in locked position.
A separate material softer than the panel material is applied in the locking system and this material could preferably cooperate with the protrusions which are formed in one piece with the panel.
A separate material harder than the material of the panel is applied in the locking system. Parts of this harder material, which preferably has sharp protrusions or grains, are in locked position pressed into the panel material.
Separate soft and flexible friction material is applied into the locking system with or without protrusions.
All of these principles could be used separately or in combinations and several principles could be used in the same locking system. For example a soft material could be applied on both edges and local protrusions could also be formed on both edges and both local protrusions could cooperate with both soft materials.
FIGS. 6a-6i shows a method to install a floor of rectangular floor panels in parallel rows with a slide lock. The floor panels have long 4a,4b and short 5a,5b edges. The panels have a mechanical locking system comprising a tongue 10 formed in one piece with the panels and groove 9 for mechanically locking together adjacent long and short edges vertically in D1 direction. The panels have also a locking element 8 at one first long edge and a locking groove 14 at an opposite second long edge which form a first horizontal mechanical connection locking the long edges of the panels to each other in a D2 direction parallel to the horizontal plane and at right angles to the joint edges. Each panel is at the adjacent long edges provided with a second horizontal mechanical connection locking the panels to each other along the joined long edges in the D3 direction when the panels are laying flat on the sub floor. The second horizontal mechanical connection comprises small local protrusions 16, 17 in the mechanical locking system on the long edges which prevents displacement along the joint when the panels are laying flat on the sub floor and are locked in D1 and D2 directions. The method comprises five steps:

    
    
        a) As a first step a first panel Fl 1 is installed on a sub floor in a first row R1.
        b) As a second step a second panel Fl 2 in a second row R2 is brought in contact with its long edge 4a against the long edge 4b of the first panel Fl 1 and held at an angle A against the sub floor.
        c) As a third step a new panel Fl 3 in a second row R2 is brought at an angle A with its long edge 4a in contact with the long edge 4b of the first panel Fl 1 and its short edge 5a in contact with the short edge 5b of the second panel FL 2. In this preferred embodiment the tongue 10 is angled on the strip 6 which is an extension of the lower lip of the grove 9. These 3 steps are shown in FIGS. 6a, 6b and 6c. 
        d) As a fourth step the new panel Fl 3 is displaced against the second panel Fl 2 in the angled position and the tongue 10 is inserted into the groove 9 until the top edges at the short edges 5a, 5b are in contact with each other. This is shown in FIGS. 6d-6f. 
        e) As a final fifth step the second panel Fl 2 and new panel Fl 3 are angled down to the sub floor. This angling locks the long edges 4a, 4b of the second Fl 2 and new Fl 3 panels to the first panel Fl 1 in a vertical direction D1 and in a first horizontal direction D2 perpendicular to the joined long edges and in a second horizontal direction D3 along the long edges. The locking in the second horizontal direction D3 prevents separations between the short edges 5a, 5b of the second Fl 2 and the new panel Fl 3. This is shown in FIGS. 6g-6i. 
    
    


It is not necessary that the second and the new panels are held in the same angle since some twisting of the panels may occur or may even be applied to the panels.
The installation method and the locking system according to the embodiments of the invention make it possible to install floor panels in a simple way without tools and without any snap action on the short sides. The locking system could be designed in such a way that the upper part of the locking element keeps the floorboards in an angled position until they are pressed down to the sub floor.
If the short edges do not have a tongue, installation could be made by just angling the floor boards to the sub floor. Even the traditional installation with angling the new panel Fl 3 to the sub floor and thereafter displacing the new panel towards the second panel Fl 2 could be used. The disadvantage is that a hammer and a tapping block should be used to overcome the resistance of the slide lock. This could be done without damaging the slide lock or substantially decreasing the sliding strength since the panels will be pushed upwards into a small angle by the small local protrusions.
FIGS. 7a-7i show preferred embodiments of floorboards which are only A panels and which could be installed in a herringbone pattern and in parallel rows. FIGS. 7a-7d show a locking system where the horizontal locking in D2 direction is obtained by a strip 6, a locking element 8 and a locking groove 14. In FIGS. 7e-7h the horizontal locking D2 is obtained by a tongue lock where a locking element 41 on the upper part of the tongue locks against another locking element 42 in the upper part of the groove 9. The figures show long edges 4a, 4b short edges 5a, 5b and long edges 4a or 4b locked against the short edges 5a, 5b. The advantage of such a locking system is that a herringbone pattern could be created with only one type of A panels. The locking elements 41, 42, 8 and the locking groove 14 locks both short edges 5a, 5b of one panel to both long edges 4a,4b of a similar panel. The disadvantage is that such panels cannot be installed in parallel rows since the short edges cannot be locked horizontally. This is shown in FIGS. 7c and 7g. This problem could be solved however with a slide lock 16 on the long edges. The invention comprises one type of panels which could be installed in parallel rows and in a herringbone pattern and which at the long edges have a slide lock according to the described embodiments above.
FIG. 7i shows a strong locking system with a slide lock and with a locking element 8 and a locking groove 14 and with locking elements 41,42 in the upper part of the tongue 10 and the groove 9. The locking element 42 in the locking groove could be formed with a scraping tool.
FIG. 8a shows a floor panel with a surface layer 31, a core 30 and a balancing layer 32. Part of the balancing layer has been removed under the strip 6 to prevent backwards bending of the strip in dry or humid environment. Such bending could reduce the strength of the slide lock especially in laminate floors installed in dry environment.
FIG. 8b shows an embodiment with a separate wood based strip 6 which has a flexible friction material 16.
FIGS. 8c and 8d shows a separate strip of aluminum. Small local protrusions 16, 16′ are formed on the upper and lower parts of the strip 6. These protrusions prevent sliding between the strip and the two adjacent edges 4a and 4b. 
It will be apparent to those skilled in the art that various modifications and variations of the present invention can be made without departing from the spirit and scope of the invention. Thus, it is intended that the present invention include the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

## Claims

1. A flooring system, comprising a plurality of rectangular floor panels adapted to be installed on a sub floor, said panels having long and short edges which are connectable to each other along one pair of adjacent edges of adjacent panels having a mechanical locking system comprising a tongue formed in one piece with the panels and a groove for mechanically locking together said adjacent edges at right angles to the horizontal plane of the panels, thereby forming a vertical mechanical connection between the panels, and a locking element at one first edge and a locking groove at an opposite second edge thereby forming a first horizontal mechanical connection locking the panels to each other in a direction parallel to the horizontal plane and at right angles to the joint edges, wherein:
each panel is made up of one or more upper layers of decorative plastic material and an intermediate core plastic material,
each panel at said adjacent edges being provided with a second horizontal mechanical connection locking the panels to each other along the joint edges, in a direction parallel to the horizontal plane and parallel to the joint edges, when the panels are laying flat on the sub floor,
said second horizontal mechanical connection comprises a plurality of protrusions in said mechanical locking system which reduces displacement of the panels along the joint edges when the panels are laying flat on the sub floor and are locked with the vertical mechanical connection and the first horizontal mechanical connection, the protrusions extending in a direction that traverses a line along the joint edges.

2. The flooring system as claimed in claim 1, wherein the locking groove is open towards the rear side.

3. The flooring system as claimed in claim 1, wherein the protrusions are formed on both the first edge and the second edge.

4. The flooring system as claimed in claim 1, wherein the first horizontal mechanical connection comprises a strip which is an extension of the lower part of the groove and the locking element is formed on the strip.

5. The flooring system as claimed in claim 1, wherein the mechanical locking system comprises a separate material, other than the material of the core of the panels, which is connected to the panels.

6. The flooring system as claimed in claim 5, wherein the protrusions are formed in each panel such that the protrusions cooperate with the separate material when two panels are locked in the same plane.

7. The flooring system as claimed in claim 5, wherein the protrusions are formed in the separate material.

8. The flooring system as claimed in claim 5, wherein the protrusions are formed in the separate material and in the panels.

9. The flooring system as claimed in claim 5, wherein the separate material is aluminum.

10. The flooring system as claimed in claim 1, wherein essentially the whole length of an adjacent edge comprises protrusions.

11. The flooring system as claimed in claim 1, wherein there is a space between the protrusions and the adjacent edge of the adjacent panel when the adjacent panels are in an angled position relative each other.

12. The flooring system as claimed in claim 11, wherein the adjacent panels are displaceable along the joint edges when an upper part of the joint edges are in contact and when said adjacent panels are in an angled position relative each other.

13. The flooring system as claimed in claim 12, wherein the panels are displaceable at an angle of less than 45 degrees when top edges of the panels are in contact with each other.

14. The flooring system as claimed in claim 1, wherein the locking system is integrated with the panel.

15. The flooring system as claimed in claim 1, wherein the plurality of protrusions in said mechanical locking system prevents displacement along the joint edges when the panels are laying flat on the sub floor and are locked with the vertical mechanical connection and the first horizontal mechanical connection.

16. The flooring system as claimed in claim 1, wherein the protrusions are arranged in a pattern that repeats in a direction along the joint edges.

17. A flooring system, comprising a plurality of rectangular floor panels adapted to be installed on a sub floor, said panels having long and short edges which are connectable to each other along one pair of adjacent edges of adjacent panels having a mechanical locking system comprising a tongue formed in one piece with the panels and a groove for mechanically locking together said adjacent edges at right angles to the horizontal plane of the panels, thereby forming a vertical mechanical connection between the panels, and a locking element at one first edge and a locking groove at an opposite second edge thereby forming a first horizontal mechanical connection locking the panels to each other in a direction parallel to the horizontal plane and at right angles to the joint edges, wherein:
each panel is made up of one or more upper layers of decorative plastic material and an intermediate core plastic material,
each panel at said adjacent edges being provided with a second horizontal mechanical connection locking the panels to each other along the joint edges, in a direction parallel to the horizontal plane and parallel to the joint edges, when the panels are laying flat on the sub floor,
said second horizontal mechanical connection comprises a plurality of protrusions in said mechanical locking system which reduces displacement of the panels along the joint edges when the panels are laying flat on the sub floor and are locked with the vertical mechanical connection and the first horizontal mechanical connection,
wherein the protrusions are formed in one piece with each panel.

18. A flooring system, comprising a plurality of rectangular floor panels adapted to be installed on a sub floor, said panels having long and short edges which are connectable to each other along one pair of adjacent edges of adjacent panels having a mechanical locking system comprising a tongue formed in one piece with the panels and a groove for mechanically locking together said adjacent edges at right angles to the horizontal plane of the panels, thereby forming a vertical mechanical connection between the panels, and a locking element at one first edge and a locking groove at an opposite second edge thereby forming a first horizontal mechanical connection locking the panels to each other in a direction parallel to the horizontal plane and at right angles to the joint edges, wherein:
each panel is made up of one or more upper layers of decorative plastic material and an intermediate core plastic material,
each panel at said adjacent edges being provided with a second horizontal mechanical connection locking the panels to each other along the joint edges, in a direction parallel to the horizontal plane and parallel to the joint edges, when the panels are laying flat on the sub floor,
said second horizontal mechanical connection comprises a plurality of protrusions in said mechanical locking system which reduces displacement of the panels along the joint edges when the panels are laying flat on the sub floor and are locked with the vertical mechanical connection and the first horizontal mechanical connection,
wherein sliding strength of the second horizontal mechanical connection exceeds horizontal locking strength of the first horizontal mechanical connection.