Abstract:
A novel planking system utilizing an inventive groove design is provided. The novel groove is defined by two opposing side walls and a groove end wall. The groove side walls present two generally opposed tongue-engaging projections that automatically provide a uniform space between planks during installation, and accommodate expansion of the planks after installation by breaking away when force is exerted on the projections by an adjacent plank. The present invention is also concerned with a combination of planks having an inventive tongue-and-groove configuration, as well as inventive methods of assembling planks to accommodate the expansion and contraction of the assembled planks after installation.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention is broadly concerned with a novel planking system utilizing an inventive groove design, combinations of planks having an inventive tongue-and-groove configuration, and methods of assembling planks to accommodate the expansion and contraction of the assembled planks. 
   2. Description of the Prior Art 
   Wood panels and planks are commonly used for various structures, including decks, porches, walls, and the like. Composite materials offer many benefits over natural wood products for these uses, including improved durability and enhanced moisture resistance. However, wood composites still expand and contract with changes in temperature and moisture like natural wood, which can cause unwanted buckling when these products are used in tongue-and-groove arrangements. In particular, tongue-and-groove arrangements are commonly used in the construction of covered porches, where a small uniform space between each plank is desirable, and where wood composite materials have become increasingly popular. There are two main concerns that arise during the assembly and installation of porch planks when wood or wood composites are used. The first problem is efficiently creating a small space between the planks that is uniform and that can be maintained throughout the installation process. The second problem is accommodating the expansion and contraction of the planks after installation is complete. 
   Previous attempts to relieve the pressure between planks upon the expansion of the interconnected boards have utilized a “crush bead” located on the tip of the tongue of the plank in anticipation of it being crushed during expansion. Although these crush beads do create the desired space during installation, they do not always crush wider the compressive forces of the adjacent planks, resulting in buckling of the interconnected boards. This especially common in composite tongue-and-groove configurations due to the high compressive strength of the wood composite materials from which the planks and crush beads are formed. It is therefore desirable to have planks or panels with a tongue-and-groove configuration that create the desired space, while at the same time accommodating the expansion and contraction of the interconnected boards. 
   SUMMARY OF THE INVENTION 
   The present invention solves these problems by providing planks with a tongue-and-groove configuration providing generally opposed tongue-engaging projections on the side walls of the groove, which create the desired space that is maintained during installation. 
   In more detail, the present invention provides a plank configured to be assembled with an adjacent plank having a first edge surface and a tongue extending from the first edge surface. The tongue of the adjacent plank is defined by a tongue end wall and a pair of tongue side walls extending between the tongue end wall and first edge. The plank comprises a body presenting a second edge surface and a groove projecting inwardly from the second edge surface along a groove axis, with the groove being configured to receive the tongue of the adjacent plank. The groove is defined by a groove end wall and a pair of groove side walls that extend between the groove end wall and the second edge surface. The groove side walls present generally opposed tongue-engaging projections that are spaced from the groove end wall in alignment substantially perpendicular to the groove axis. 
   In another embodiment, there is provided a combination of planks comprising a first plank and a second plank utilizing a tongue-and-groove arrangement. The first plank presents a first edge surface, and a tongue extending from the first edge surface. The tongue comprises a tongue end wall and a pair of tongue side walls extending between the tongue end wall and the first edge surface. The second plank presents a second edge surface, and a groove projecting inwardly from the second edge surface along a groove axis and receiving the tongue of the first plank. The groove comprises a groove end wall and a pair of groove side walls extending between the groove end wall and the second edge surface. The groove side walls present generally opposed tongue-engaging projections that are spaced from the groove end wall in alignment substantially perpendicular to the groove axis. 
   In a further embodiment, a method of assembling porch planks to accommodate expansion and contraction of the assembled planks is provided. The method comprises securing a first plank to a support and positioning a second plank adjacent to the first plank. The first plank presents a first edge surface and a tongue extending from the first edge surface. The tongue comprises a tongue end wall and a pair of tongue side walls extending between the tongue end wall and the first edge surface. The second plank presents a second edge surface and a groove projecting inwardly from the second edge surface along a groove axis to receive the tongue. The groove comprises a groove end wall and a pair of groove side walls extending between the groove end wall and the second edge surface. The groove side walls present generally opposed tongue-engaging projections that are spaced from the groove end wall in alignment substantially perpendicular to the groove axis. The planks are assembled by inserting the tongue into the groove so that the tongue is received in the groove and the tongue end wall is engaged by the tongue-engaging projections, thereby providing an interior space between the tongue end wall and groove end wall, and first and second spaces between the first edge surface of the first plank and the second edge surface of the second plank. 
   Expansion of the planks after installation pushes the projections off edge-wise, exercising the projections in shear, instead of in compression. In this sense, the tongue-engaging projections are “shearable.” Thus, when a given force is applied to the projections, they break away, relieving the pressure and preventing the buckling of the assembled planks. 
   Additional advantages of the novel tongue-and-groove configuration and method will be appreciated based upon the drawings and detailed description of the preferred embodiments below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates an end view of a preferred plank in accordance with the invention; 
       FIG. 2   a  depicts an enlarged profile view of a preferred groove; 
       FIG. 2   b  depicts an enlarged profile view of a preferred tongue, and illustrates preferred tongue dimensions; 
       FIG. 3  provides an additional view of a preferred groove to illustrate preferred groove dimensions; 
       FIG. 4  depicts the profile of two preferred planks connected using the inventive tongue-and-groove combination; 
       FIG. 5  depicts a top view of the novel planking system and method utilizing the tongue-and-groove combination of the present invention; and 
       FIG. 6  depicts the expansion of the planks after installation, and the shearing off of the tongue-engaging projections that occurs upon expansion. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The following sets forth preferred embodiments in accordance with the present invention. It is to be understood, however, that these preferred embodiments are provided by way of illustration and nothing therein should be taken as a limitation upon the overall scope of the invention that is claimed. 
   Referring to  FIG. 1 , an end view of a preferred plank  10  in accordance with the present invention is provided. The plank  10  comprises a body  12 , presenting a first edge surface  14 , a second edge surface  15 , and an underside  36 . The first edge surface  14  includes a tongue  22  extending from the first edge surface  14 . The tongue  22  comprises a tongue end wall  30  and a pair of tongue side walls  32 ,  34  extending between the tongue end wall  30  and the first edge surface  14 . The second edge surface  15  comprises an upper edge surface  15   a  and a lower edge surface  15   b , and includes a groove  16  projecting inwardly from the second edge surface  15  along a groove axis  18 . The groove  16  is defined by a groove end wall  24  and a pair of groove side walls  26 ,  28 , extending between the groove end wall  24  and the second edge surface  15 . It will be appreciated that although the underside  36  of the plank  10  illustrated in  FIG. 1  is contoured, planks, boards, or panels can be provided with an underside  36  having a different contour, or being flat, without going beyond the scope of the present invention. It will also be appreciated that the present invention is not limited only to planks having a tongue extending from the first edge surface  14  and a groove projecting inwardly from the second edge surface  15 . Rather, planks can be adapted in a number of ways, depending upon the final desired use, in accordance with the present invention. For example, a plank can be configured to have two grooves or two tongues, one on each of the first and second edge surfaces  14 ,  15 , respectively. It is also envisioned that a plank in accordance with the present invention can have a groove or a tongue on one edge surface only with the other edge surface having neither a tongue nor a groove, depending upon the final desired assembly. 
     FIGS. 2   a - 2   b  illustrate an enlarged view of a preferred groove  16  and a preferred tongue  22  in accordance with the present invention. In more detail, as shown in  FIG. 2   a , the groove side walls  26 ,  28  present generally opposed tongue-engaging projections  38 ,  40 , respectively, in alignment substantially perpendicular to the groove axis  18 , and spaced from the groove end wall  24 , to define respective spaces  42 ,  43  between the projections  38 ,  40  and the groove end wall  24 . The respective spaces  42 ,  43  are preferably from about 0.50 mm to about 1.8 mm, more preferably from about 0.6 mm to about 1.6 mm, and even more preferably from about 0.8 mm to about 1.0 mm, when measured from the groove end wall  24  to the center of each tongue-engaging projection  38 ,  40 . As shown in  FIG. 2   b , the preferred tongue  22  has a length “L” being defined between the tongue end wall  30  and a plane  44  coinciding with that created by the first edge surface  14 ; a width “W” being defined as the greatest distance between the tongue side walls  32 ,  34 ; and a width “W′” being defined as the shortest distance between the tongue side walls  32 ,  34 . In a particularly preferred embodiment, the tongue side walls  32 ,  34  are inwardly sloped to narrow the distance between the side walls  32 ,  34 , and terminating at the tongue end wall  30 , causing the tongue  22  to be tapered when viewed from the side. In this embodiment, the length of W′ is less than the length of W. More particularly, W′ is at least about 60% the length of W, preferably from about 60% to about 100% the length of W, more preferably from about 70% to about 90% the length of W, and even more preferably at least about 82% the length of W. As shown in  FIG. 2   a , the groove side walls  26 ,  28  are also preferably inwardly sloped to narrow the distance between the groove side walls  26 ,  28 , and terminating at the groove end wall  24 , creating a tapered groove  16  corresponding to the tapered tongue  22 . 
   The dimensions of a preferred groove are shown in more detail in  FIG. 3 . The tongue-engaging projections  38 ,  40 , respectively, extend from the groove side walls  26 ,  28 , but are preferably spaced apart from each other, where “d” is the distance between the projections  38 ,  40 . More preferably, the tongue-engaging projections are spaced apart from each other a distance d that is less than the width W′ of the tongue  22  (shown in  FIG. 2   b ). 
   The tongue-engaging projections  38 ,  40  also preferably have a height “h.” The height h is measured from the highest point of the projections  38 ,  40  to their respective groove side walls  26 ,  28  on the respective sides of tongue-engaging projections  38 ,  40  that are adjacent the groove end wall  24 . The tongue-engaging projections  38 ,  40  also preferably have a width “w,” as measured from the widest portion of the tongue-engaging projections  38 ,  40 . In a particularly preferred embodiment, the tongue-engaging projections  38 ,  40  have a height h of at least about 0.50 mm, preferably from about 0.70 mm to about 0.90 mm, and more preferably about 0.812 mm, and a width w of at least about 0.01 mm, preferably from about 0.02 mm to about 0.05 mm, and more preferably about 0.030 mm. It is also preferred that the height h be greater than the width w, more preferably at least about 2% greater, and even more preferably from about 2% to about 6% greater. 
   As shown in  FIG. 4 , the groove  16  is configured to receive the tongue  22  of an adjacent plank  11 . When assembled, the adjacent planks  10 ,  11  preferably have first and second spaces  46 ,  48 , between the first edge surface  14  and the second edge surface  15  of each plank, and an interior space  52  between the groove end wall  24  and the tongue end wall  30 . More particularly, the assembled planks have a first space  46  above the tongue-and-groove configuration and a second space  48  below the tongue-and-groove configuration. The first and second spaces  46 ,  48 , respectively, should be from about 0.10 mm to about 1.5 mm, preferably from about 0.80 mm to about 1.2 mm, and more preferably from about 1.0 mm to about 1.2 mm. In a further preferred embodiment, the first and second spaces  46 ,  48  are different sizes, as shown in  FIG. 4 , with the lower edge surface  15   b  preferably being undercut and the first space  46  being smaller than the second space  48 . In this embodiment, the second space  48  should be from about 1.0 mm to about 2.54 mm, preferably from about 1.6 mm to about 1.9 mm, more preferably from about 1.78 mm to about 1.9 mm. The interior space  52  between the groove end wall  24  and the tongue end wall  30  should be from about 1.2 mm to about 3.0 mm, preferably from about 1.75 mm to about 2.5 mm, more preferably from about 1.9 mm to about 2.25 mm. 
   The first and seconds spaces  46 ,  48 , and the interior space  52  are determined by the placement of the tongue-engaging projections  38 ,  40  along the groove side walls  26 ,  28  in relation to the second edge surface  15 . Referring again to  FIG. 3 , the tongue-engaging projections  38 ,  40  are preferably spaced from the second edge surface  15  a distance “D,” as measured from the center of the tongue-engaging projections to a plane  50  extending along the second edge surface  15  of the plank  10 . More preferably, the distance D is less than the length L of the tongue  22  of the adjacent plank  11 . In particular, the distance D is preferably from about 40% to about 95% the length L, more preferably from about 60% to about 90% the length L, even more preferably from about 80% to about 85% the length L. In this embodiment, when the tongue  22  is received in the groove  16 , the tongue-engaging projections  38 ,  40  engage the tongue  22 , and more preferably the tongue end wall  30 , to provide the desired spaces  46 ,  48 ,  52 , respectively. Accordingly, the tongue-engaging projections  38 ,  40  should be strong enough to prevent the tongue  22  of the adjacent plank  11  from being forced past the tongue-engaging projections  38 ,  40  and into the groove end wall  24  during installation of the plank system. It is also preferred that the tongue-engaging projections  38 ,  40  are integrally formed with the material forming the plank  10 . In other words, the entire plank  10  unitarily formed. 
   The planks can be made from any suitable material including sized lumber, synthetic materials, and wood composites. When formed from natural woods, the novel tongue-and-groove configuration can be formed for example, by conventional routering methods. A preferred method for forming wood composites with the novel tongue-and-groove configuration is by extrusion so that the tongue-and-groove configuration, including the tongue-engaging projections, are integrally formed with the material forming the planks. 
   In particular, a preferred method for making wood composites can be found in U.S. Pat. No. 6,737,006, incorporated by reference herein. In more detail, the products are formed by introducing ingredients including respective quantities of a fibrous or cellulosic material and polypropylene into the inlet of an extruder (preferably a twin screw extruder). Preferably, the weigh blender is positioned immediately above the extruder, at the extruder inlet, so that the blend of ingredients is formed immediately prior to entering the extruder, thus minimizing or preventing separation of the ingredients. 
   The screw(s) is then rotated at a rate of from about 10-50 rpm, and preferably from about 15-34 rpm to advance the ingredients through the extruder barrel and out the extrusion die to form the composite product. The die is configured to present an orifice configured to correspond to the desired plank or board profile, including the tongue-engaging projections  38 ,  40 . Preferably, the screw(s) has a compression ratio of from about 2:1 to about 4:1, and more preferably from about 2.8:1 to about 3.6:1. 
   The temperature of the ingredients in the extruder barrel is preferably from about 150-260° C., and more preferably from about 175-230° C. The retention time of the ingredients in the barrel should be from about 20-120 seconds, and more preferably from about 40-80 seconds. Finally, the ingredients should be advanced through the barrel at a rate of from about 500-2,000 lbs/hr., and more preferably from about 1,000-1,500 lbs/hr. 
   The fibrous material is preferably present in the ingredients at a level of from about 20-80% by weight, more preferably from about 30-70% by weight, and even more preferably from about 50-70% by weight, based upon the total weight of the ingredients taken as 100% by weight. The polypropylene is preferably present in the ingredients at a level of from about 20-80% by weight, more preferably from about 30-70% by weight, and even more preferably from about 30-50% by weight, based upon the total weight of the ingredients taken as 100% by weight. 
   Preferred fibrous materials include those selected from the group consisting of sawdust, newspaper, alfalfa, wheat pulp, wood scraps (e.g., ground wood, wood flour, wood flakes, wood chips, wood fibers, wood particles), wood veneers, wood laminates, cardboard, straw, cotton, rice hulls, paper, coconut shells, peanut shells, bagasse, plant fibers, bamboo fiber, palm fiber, kenaf, and mixtures thereof. Furthermore, the average particle size of the fibrous material should be less than about ½ inch, and more preferably from about 1/16-¼ inch. Finally, the particles of the fibrous material should have an average aspect ratio (i.e., the ratio of the length to the widest thickness) of at least about 10:1, preferably at least about 20:1, and more preferably from about 30:1 to about 50:1. The use of such long particles increases the flexural modulus of the product as compared to products with lower aspect ratios by at least about 25%, and preferably at least about 40%, thus causing the final composite product to have a stiffness comparable to natural wood. 
   The preferred polypropylene for use in the invention is reactor flake polypropylene (i.e., the polymer flakes as they are produced in the reactor), preferably without any further treatment (e.g., without the addition of chemical additives or modifiers) to the polypropylene. The preferred polypropylene has a melt index at 230° C. of from about 0-10 g/10 min., preferably from about 0.1-4 g/10 min., and more preferably from about 0.1-1 g/10 min. Furthermore, it is preferred that the polypropylene has a bulk density of from about 20-40 lbs/ft 3 , and more preferably from about 28-32 lbs/ft 3 . The average fiber length or particle size of the polypropylene flakes utilized should be from about 350-1,000 μm, and preferably from about 500-700 μm. 
   The resulting composite product is in the form of a self-sustaining body and has an ASTM D-6109 flexural modulus of from about 600-1,100 psi, and preferably from about 800-1,100 psi. The product should have an actual density of from about 40-60 lbs/ft 3 , and preferably from about 50-58 lbs/ft 3 . 
   A number of optional ingredients can also be added to modify or adjust the properties of the final composite product. Examples of such ingredients include acrylic process aids (e.g., Rohm and Haas K175, Kaneka Kane-AcePA-101), UV stabilizers (e.g., CYTEC 38535, CYTEC 3346), and coloring agents. If a process aid is utilized, it is preferably present in the ingredients at a level of from about 0.5-5% by weight, and more preferably from about 1-2% by weight, based upon the total weight of the ingredients taken as 100% by weight. Unexpectedly, these acrylic process aids are particularly useful in the present invention in spite of the fact that they are intended to be used in PVC products rather than polypropylene products. 
   In use, the planks can be assembled and secured using traditional methods, including by securing through the face of the board, or through the tongue and/or groove, depending upon the final desired use. With reference to the plank system illustrated in  FIG. 5 , a preferred method of assembly comprises the steps of securing a first starter plank  56  to a support (not shown). Preferably, the starter plank is secured through the face of the board using any suitable fastening device  58  (e.g., deck screws, nails, etc.). Next, a second plank  60  is positioned adjacent the starter plank  56  and the tongue  22  of the starter plank  56  is inserted into the groove  16  of the second plank  60  until the tongue end wall  30  is engaged by the tongue-engaging projections  38 ,  40  in the groove  16 . The second plank is then secured, preferably, through the tongue of the second plank (see  FIG. 6 ). More preferably, the second plank is secured by countersinking a nail, screw, or other fastening device  58  into the tongue  22 , so that it does not obstruct the tongue from being subsequently received into the groove of the next adjacent plank  62 . This preferred method automatically provides the desired first and second spaces  46 ,  48 , respectively, between each plank, with the first space  46  between the planks being above the tongue-and-groove configuration and the second space  48  between the planks being below the tongue-and-groove configuration. 
   With reference to  FIG. 6 , the tongue-engaging projections  38 ,  40  should be configured to shear or break away when a given force is generated by expansion of planks  10  and/or  11  after installation. As shown in  FIG. 6 , the assembled planks  10 ,  11  utilizing the novel tongue-and-groove configuration have swelled and expanded. In particular, the second edge surface  15  of the plank  10  has expanded into the first edge surface  14  of the adjacent plank  11 , and the tongue-engaging projections  38 ,  40  have been sheared or broken away by the tongue  22  of the adjacent plank  11  to permit this expansion. In this manner, the novel plank system and method allow for the planks to expand during temperature and/or moisture level changes, thereby preventing buckling of the assembled planks, in particular, when the planks are formed of high compressive strength composite materials. 
   It will be appreciated by those skilled in the art that although the foregoing description has been given with reference to planks having a length and respective end portions, the novel tongue-and-groove configuration and spacing system can be adapted to a wide number of areas, in addition to porch planking. In particular, the novel tongue-and-groove arrangement can be adapted to accommodate any application where wood and/or wood composites are commonly used, such as in wood and simulated wood flooring, decking, wall paneling, and roof paneling, door sills and jambs, fascia board, window edging, window sills, decorative architectural trim (e.g., deck or patio railing), and landscaping products (e.g., raised bed edging, flowerbed edging, driveway edging). It will also be appreciated that the inventive tongue-and-groove configuration can extend along the length of the planks, panels, or boards. However, the tongue-and-groove configuration can also be segmented along the length of the planks, panels, or boards, without going beyond the scope of this invention.