COMPOSITE STRUCTURAL PANEL

BACKGROUND OF THE INVENTION

[0001] The present invention generally relates to modular structural panels, and more particularly to an improved structural panel, joint, and method of fabricating the same for constructing interconnected panel systems.

[0002] Modular building components such as composite structural panels with the ability to be interconnected have been used to construct various types of residential, commercial, and industrial structures. For example, the panels may be interconnected to create walls, floors, ceilings, and partitions of a building or various types of enclosures within a building.

[0003] One type of composite panel, commonly known as structural insulated panels (SIPS), has an insulating core that is disposed between an exterior and interior facing sheets. In one method of fabricating a composite panel, a preformed rigid sheet of insulating material such as polystyrene or urethane is sandwiched between the facing sheets. In another type of fabrication used, a light-weight insulating foam is injected between two facing sheets to fill the void between the sheets. Other types of composite structural panels may be uninsulated and have only a structural core or members disposed between the facing sheets to strengthen the panels. The opposing relatively thin face sheets may be made of metal, fiberglass, plywood, gypsum, oriented strand board, or other materials. [0004] The edges of insulated panels are sometimes formed from only the insulating material or foam itself may form an the edge of the panel, which is abutted directly against a complementary edge of an adjacent panel to create a joint. These types of joints, however, may be weak. It is also known to affix metallic types of edging to sides of the panels having complementary mating tongue and groove type arrangements. [0005] The foregoing panels, joints, and methods of fabrication have drawbacks.

The panels and/or joints between adjacent panels may lack sufficient strength to resist axial, torsional, or shear loads imposed by the dead weight of the structure, impact forces, or wind loadings. The foregoing known joining methods often are not sufficiently waterproof or airtight, thereby allowing air and water to infiltrate through the joint and into the panel and/or building formed by the panels without an adequate means of intercepting, directing, or stopping the through- flow of these elements. Water infiltration may result in structural damage to the panel or reduce its thermal efficiency by wetting the insulating material. Air infiltration or exfiltration, depending on whether ambient air pressure is greater inside or

outside of the structure, results in heat loss and energy inefficiency that translates into higher utility costs for heating and air conditioning. In inclement weather situations, ambient pressure differentials between the exterior or interior of a structure may cause panels to bow and joints to partially or completely open and fail. Existing panel fabrication methods are also often complicated and time-consuming, thereby resulting in higher manufacturing and final product costs.

[0006] Accordingly, there remains a need for a composite structural panel, joining system, and method of fabrication that overcomes the foregoing shortcomings of current structural panel systems.

SUMMARY OF THE INVENTION

[0007] The present invention is directed to an improved composite structural panel and joint, and a method of fabricating the same that overcomes the shortcomings of foregoing known panels and joining systems. The invention provides a modular composite structural building panel with increased strength, non-leaking joints, and a unique fabrication process. When combined in a modular system comprising multiple adjacent units coupled together with the joining system disclosed herein, a building or other enclosure may be constructed that is strong, thermally efficient, and weather resistant. Typical applications, without limitation and for illustrative purposes only, may include residential, commercial, and industrial buildings; equipment enclosures; partitions; etc. The invention provides numerous advantages over known panel systems as further described herein.

[0008] According to one aspect of the invention, a composite structural panel may generally include a first sheet including a first outer surface and a first inner surface; a second sheet spaced apart from the first sheet and including a second outer surface and a second inner surface; a stiffening core element disposed between the first and second sheets and defining a plurality of cells; and a rigid foam reinforcing material disposed in the cells. In the preferred embodiment, the foam is a rigid urethane foam. In another embodiment, the panel may further include a first longitudinally-extending edge formed between the first and second sheets, the edge including a deformable foam portion protruding outwards from the edge and extending longitudinally along the edge. In one embodiment, the edge may include a longitudinally-extending window and the foam may protrude outwards through the window to form the deformable foam portion. The deformable foam portion may have a convex-shaped surface.

[0009] According to one aspect of the invention, a composite structural panel may include a first facing sheet; a second facing sheet spaced apart from the first sheet; a foam material disposed between the first and second sheets; and a first longitudinally-extending edge having a deformable foam portion protruding outwards from the edge and extending longitudinally along the first edge. The deformable foam portion of the first edge is preferably compressible in response to contact by an abutting surface, such as a surface on a second edge of a second panel that may be inserted into the first edge of the first panel. The deformable portion provides a seal that forms a thermal break and air infiltration barrier when two adjacent panels are interconnected at their respective edges. In other embodiments, the deformable portion of the first edge may mate with and be compressed by contact with a second deformable portion on a second edge of a second panel. The first edge may include a longitudinally-extending window and the foam may protrude outwards through the window from inside the first edge and panel to form the deformable foam portion. In one embodiment, the first edge may have a double ship-lap configuration to complement a double ship-lap edge configuration of a mating second panel which may be inserted into the first panel edge.

[00010] According to another aspect of the invention, a composite structural panel system is provided that includes a first panel including an internal cavity, an insulating material disposed in the cavity, and a first longitudinally-extending edge having a deformable foam portion protruding outwards from the edge and extending longitudinally along the first edge. The panel system further includes a second panel including a second longitudinally-extending edge configured to complement the first edge and receive the first edge in an interlocking relationship. The deformable portion of the first edge preferably compresses upon contact with the second edge when the second edge is inserted into the first edge to form a seal. In one embodiment, the second edge also includes a deformable foam portion protruding outwards from the second edge and extending longitudinally along the second edge. The deformable foam portions of the first and second edges may be arranged to become mutually engaged with each other and compressed when the first edge is inserted into the second edge to form a foam-to-foam seal.

According to another aspect of the invention, a modular composite structural panel system is provided that includes a first panel including a pair of spaced apart sheets each having an outer face and at least one first edge longitudinally-extending between the sheets. The first edge preferably includes an elongated recess and an elongated projection extending along the edge. The panel system further includes a second panel including a pair of spaced apart

sheets each having an outer face and at least one second edge longitudinally-extending between the sheets. The second edge preferably includes an elongated recess and an elongated projection extending along the second edge. Preferably, the second edge is configured complementary to the first edge. The first and second edges may be abuttingly interconnected such that the projection of the first edge complementary engages the recess of the second edge and vice-versa to define a joint; the joint including a pressure equalization chamber to balance ambient pressures on opposite faces of the first and second panels. In one embodiment, at least the first edge includes a first deformable foam portion protruding outwards from the first edge and extending longitudinally along the first edge; the deformable portion being compressed by the second edge when the first and second edges are interconnected to form a first seal. The first edge may further include a first longitudinally-extending gasket or sealant, which is compressed by the second edge when the first and second edges are interconnected to form a second seal. In one embodiment, the first and second seals trap air therein when the first and second edges are interconnected and abutted to define the pressure equalization chamber along the panel edges between the first and second seals.

[00011] According to another aspect of the invention, an improved method of fabricating a composite structural panel is provided. The method may include applying a thickness of foam to a first sheet held in a substantially horizontal position; setting a core having open cells down into the foam; contacting the core with the first sheet; layering a second sheet onto the core to form a panel; and expanding the foam between the first and second sheets to reinforce to the core. In a preferred embodiment, the foam is a rigid urethane foam. The method preferably further includes restraining the first and second sheets from moving relative to each other before expanding the foam. Preferably, the method includes compacting the foam in the open cells which reinforces the core by expanding the foam against and applying pressure to the walls of the core defining the open cells as the foam expands. The method preferably also includes hardening the foam after the foam has expanded. In another embodiment, the method includes providing pressure to hold the sheets and core together, and heating the panel to cure and harden the foam. [00012] Although the preferred structural panel and system of joined panels may sometimes be described herein with reference to a vertically-oriented wall structure, the invention is not limited in its applicability by such reference. Any reference to either orientation or direction is intended primarily for the convenience in describing the preferred embodiments and is not intended in any way to limit the scope of the present invention

thereto. Accordingly, panels and systems according to principles of the present invention may be used without limitation in applications wherein the panels are used as floors, ceilings, or other structures and are oriented in any direction including horizontally or angled or sloped.

BRIEF DESCRIPTION OF THE DRAWINGS

[00013] The features of the preferred embodiments will be described with reference to the following drawings where like elements are labeled similarly, and in which:

[00014] FIG. 1 is a front view of a preferred embodiment of a composite panel according to principles of the invention with a partial cross-section to show the interior structure of the panel;

[00015] FIG. 2 is a top cross-sectional view showing two adjacent panels of FIG. 1 prior to being abutted at the edges to form a joint;

[00016] FIG. 3 is a top cross-sectional view showing two adjacent panels of FIG. 1 after being abutted at the edges to form a joint; and

[00017] FIG. 4 is a perspective view of the panel of FIG. 1 showing an illustrative embodiment of a panel edge.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[00018] It is understood that while the present invention will now be described and illustrated for convenience with reference to particular preferred embodiments, the scope of the invention is not limited to such embodiments. Furthermore, the description and drawings of the invention that follow, and any references to orientation, position, configuration, direction, size or materials, are also intended for convenience and does not limit the scope of the present invention.

[00019] Referring to FIGS. 1 and 2, a composite structural panel 10 generally includes two outer layers such as sheets 12, 13 arranged in substantially facing relationship to each other and an intermediate layer 1 1 spacing the outer layers apart. In one embodiment, intermediate layer 11 includes a generally rigid stiffening or reinforcing core 14 bonded to outer layers 12, 13 to form a unified composite structure. Core 14 preferably has an open structure defining a plurality of open cells 15 surrounded by cells walls 42. In a preferred embodiment, an insulating material 16 is disposed in and fills at least some of the cells, and more preferably fills substantially all of the cells to strengthen and reinforce core 14 and panel 10 as well as to insulate the panel.

[00020] Sheets 12, 13 each generally include an inner surface or face 18, 19, an outer surface or face 17, 20, and four longitudinally-extending and opposing sheet edges extending along each respective sheet. In some embodiments where panels 10 are oriented vertically or sloping, the four sheet edges may be characterized as a generally horizontal top edge 21, an opposing bottom edge 22, and two opposing vertical side edges 23, 24 (see FIG. 1). In one embodiment, sheets 12, 13 may be substantially planar and extend in horizontal and vertical directions. Sheets 12, 13 are preferably arranged in substantially opposing and parallel relationship to each other as shown. In some embodiments, where required by a particular application, sheets 12, 13 may be disposed at an angle to each other to form a panel 10 having a varying thickness from edge to edge. Preferably, sheets 12 and 13 have the same overall dimensions (width, height, and thickness).

[00021] The inner and outer surfaces of sheets 12, 13 may be generally smooth or embossed with a pattern for either aesthetic or practical purposes. For example, if sheet 12 or 13 is to be used for flooring, they may be embossed with a non-slip checkering pattern. In addition to being substantially planar or flat, sheets 12, 13 may also include undulating curved ribs, box ribs, corrugations, or other typical cross-sectional shapes commonly used for building panels in the industry.

[00022] Sheets 12, 13 may be made of any suitable material, including but not limited to ferrous and non-ferrous metals, plastic or polymer, fiberglass, graphite or other fiber composites, plywood, oriented strand board, etc. Suitable metals may include plain steel, galvanized steel, stainless steel, aluminum, etc. In a preferred embodiment, sheets 12, 13 are made of metal, and may have an illustrative typical thickness T2 in the range from about 1/8 to 3/4 inches. It will be appreciated that the type of material used to fabricate the sheets and thickness of the sheets may be varied according to the specific load and design requirements of a particular application. A finish such as paint, epoxy, or other coatings may be applied to the inner and/or outer surfaces of sheets 12 and 13. [00023] Although sheets 12 and 13 may have the same general construction, shape, and size, it will be appreciated that the sheets may differ depending on the intended application for the composite panels. For example, the sheet on the exterior of a building may have different requirements than the sheet facing the interior of the building. Accordingly, panels according to principles of the present invention may be customized to match the intended end use.

[00024] With continuing reference to FIGS. 1 and 2, core 14 in one embodiment preferably is a rigid or semi-rigid structural member including a plurality of interconnected

walls 42 defining a plurality of open cells 15 formed therein. In some embodiments, the walls 42 may preferably define various shapes including geometric shapes. In one possible embodiment as shown in FIG. 1 , core 14 may have a honeycomb shape created by a plurality of interconnected hexagonal units. It will be appreciated, however, that other suitable geometrically-shaped units such as circular, triangular, trapezoidal, rhombus, rectangular, square, diamond, pentagon, hexagon, heptagon, octagon, nonagon, decagon, and other polygons may be used without limitation depending on the required strength characteristics of the panel so long as open cells 15 are provided. Core 14 abuts sheets 12 and 13 and preferably extends completely therebetween to transfer and evenly distribute external loads between the sheets. Preferably, core 14 may have a relatively rigid structure to reinforce and strengthen panel 10. Core 14 may be made from paper, resin or polymer impregnated paper, metal, plastic, fiberglass, graphite or other fiber-filled composites, etc. depending on the strength requirements of the panel for a particular application. Illustrative typical depths Dl for core 14 defining the panel depth (excluding the thickness of each sheet) as measured from inside of sheet to sheet may range between about 1 to 6 inches in some embodiments. However, the depth of core 14 may be varied above and below the illustrative range according to the strength and insulating properties required for the panel. [00025] In a preferred embodiment, core 14 is reinforced with an insulating material

16 that is disposed in at least some of the open cells 15, and more preferably substantially all of the open cells. Insulating material 16 serves to strengthen and stiffen core 14 to better withstand loads imposed on panel 10 and to thermally insulate the panel. In one embodiment, insulating material 16 is preferably a polymer-based foam, and more preferably a rigid polyurethane foam (commonly also referred to as simply "rigid urethane foam"). Rigid urethane foam provides numerous advantages for use in the construction of panels 10 in contrast to other commercially-available insulating materials sometimes used for insulated panel construction. Rigid urethane foam has one of the highest insulating R- values per inch of commercially available products. Accordingly, with typical values in the range of R 5.6 to R 8 per inch, for example, thinner panels 10 may advantageously be produced using rigid urethane foam while retaining the high insulating efficiency only achievable with thicker panels using some other insulating materials. [00026] In contrast to other insulating materials commonly used in the industry, including flexible urethane foam, rigid urethane foam advantageously has high compressive and shear strengths despite the light-weight characteristics of the rigid foam. This permits panel sheets 12, 13 to have relatively thin overall thicknesses T2 since some of the load-

bearing capacity is provided by the strength of the rigid urethane foam. Accordingly, the unique combination of rigid urethane foam with the reinforced core panel construction features and method of fabrication according to principles of the present invention allows panels 10 to be made thinner than with other insulating materials, but advantageously capable of spanning relatively long unsupported distances. In some embodiments, for example, panel 10 may have illustrative typical total thicknesses Tl in a range from about 1 to 6 inches. Rigid urethane foam is further characterized by advantageous properties such as low vapor transmission, dimensional stability, and moisture resistance. Rigid urethane foam also advantageously has self-adhesive properties allowing it to bond to a variety of substrate materials such as sheets 12, 13 without any additional adhesives or bonding agents.

[00027] It should be noted that rigid urethane foam differs from flexible urethane foam in a number of ways. Rigid urethane foam has a closed cell structure, which typically without limitation is in the range of 90% or greater. By contrast, flexible urethane foam has an open cell structure which provides the material with more resiliency and better sound absorption properties than rigid urethane foam. Accordingly, flexible urethane foam is commonly used in cushioning applications (e.g., seating, bedding, carpet padding, etc.) and for acoustic panels. Rigid urethane foam, however, has a higher compressive and shear strength than flexible urethane foam, thereby providing a more rigid or stiff structure capable of better resisting external loads without significant flexing or deformation. Rigid urethane foam has a higher hardness on the Shore A or D scale than a flexible urethane foam. In sum, due to the superior mechanical strength of rigid foam combined with good thermal insulating values, rigid urethane foam is preferred over flexible urethane foam for reinforcing core 14 of panel 10.

[00028] Although rigid urethane foam is preferred for use with the present invention, it will be appreciated that other insulating materials including flexible urethane foam may alternatively be used depending on the specific requirements of the intended application. Accordingly, the invention is not limited by the type of insulating material used. [00029] The rigid urethane foam is formed from a two component reactive resin system in which the components expand when mixed together and then hardens as the resins cure. The rigid urethane foam preferably fills cells 15 for the entire depth Dl of the core 14 to optimize reinforcement of the core, and the strength and insulating value of entire panel 10. The urethane foam readily bonds with core 14 and serves to reinforce the core as the foam expands, cures, and hardens. Accordingly, core 14 is essentially embedded in the

expanded hardened urethane foam. Advantageously, due to reinforcing core 14 with rigid urethane foam, the core and panel 10 is better able to resist both axial in-plane loads acting on the edge of panel 10 and out-of-plane loads acting normal or perpendicular to the outer surfaces 17, 20 of the panel.

[00030] With reference to FIGS. 2-4, at least one longitudinally-extending panel edge

31 is provided on panel 10 which preferably is configured and adapted to mate with a complementary-shaped edge on an adjacent panel, which forms a panel joint 30 when the two adjacent panels are abutted together. Panel 10, however, may include as many edges as required for a particular application to mate with any desired number of corresponding abutting panels. In a preferred embodiment, edge 31 may be configured to form a double ship-lap offset joint as shown and further described herein. Edge 31 may be formed as an integral part of sheet 12 or 13 in one embodiment. For example, in one possible embodiment where sheets 12, 13 are formed of metal, edge 31 may be roll-formed in one- piece as part of sheet 12 and/or 13. In other embodiments, edge 31 may be formed as a separate component that is attached to panels 12 and 13 by any suitable technique known in the art depending on the material from which the panels are fabricated. Accordingly, edge 31 may be attached to the panels by welding, with fasteners, with adhesives, heat fusion for polymers or fiberglass, etc. without limitation.

[00031] Panel edge 31 defines first and second projections 32 and 33 extending longitudinally along the edge. Panel edge 31 also preferably defines a recess 34 in one embodiment which extends longitudinally along the edge. In one possible embodiment as shown, recess 34 is located between projections 32 and 33. Projection 32 may include a step 35 which is cooperatively designed to fit into a corresponding and mating recess 34 on an abutting panel 10. Since panel edges 31 form a double ship-lap offset joint having an asymmetric shape, it will be appreciated that panel edges 31 on abutting panels 10 are preferably arranged and configured in an opposite orientation such that the projections and recesses in one panel may be received in the projections and recesses of the abutting panel, as shown in FIG. 3.

[00032] In a preferred embodiment, panel edge 31 preferably also includes a longitudinally-extending flexible or deformable portion that serves as a primary joint seal and means for locking two adjacent panels together. In one possible embodiment, as shown in FIGS. 2-4, the flexible portion may be a configured as convex surface 36 which extends longitudinally along panel edge 31. As shown in FIG. 3, convex surface 36 is preferably arranged on the panel edge 31 so that a pair of opposing convex surfaces become mutually

aligned and engaged with each other when two panels 10 are joined together. The convex surfaces 36 on each of panels 10 deform and are compressed when mutually engaged to lock the panels together by a friction fit.

[00033] In a preferred embodiment, convex surface 36 is formed by providing a longitudinally-extending window 50 in edge 31 so that the insulating material 16 may protrude through the window and above the surface of recess 34 with a generally convex or arcuate shape. In some illustrative embodiments, window 50 preferably may be at least 1/2-inch wide, and more preferably at least 3/4-inch wide. Since the mating convex surfaces 36 are both formed of insulating material 16, the surfaces advantageously also form and provide a thermal break and air infiltration barrier in addition to serving the function of locking the panel together. Because convex surface 36 is preferably formed as an integral part of insulating material 16 itself, as opposed to being a separate component that must be affixed to edge 31, fabrication of the convex surface is economical and the convex surface is inherently strong being an integral part of a larger mass of insulating material disposed within panel 10. It is contemplated that in other possible embodiments, however, convex surface 36 may alternatively be formed as a separate component that is affixed to panel edge 31.

[00034] Joint 30 further includes a secondary sealant or gasket 37 which extends longitudinally along panel edge 31 as shown in FIGS. 2-4. Preferably, sealant or gasket 37 is disposed on each side of the convex surface 36, and more preferably is located in a corner of step 35. When two adjacent panels 10 are joined together, projections 33 engage and compress sealant or gasket 37 to form a seal. Any suitable commercially-available gasket or sealant material may be used. For example, sealants may include without limitation silicon or vinyl caulking in which case a bead of caulk is run longitudinally along panel edge 31. Suitable gasket materials may include without limitation rubber, neoprene, polymers, natural or synthetic fabrics, etc.

[00035] A pressure equalization chamber 38 may be formed by panel edge 31 on either side of convex surface 36 between the convex surface and sealant or gasket 37 when two adjacent panels 10 are abutted together to form joint 30. Pressure equalization chamber 38 acts as an air lock trapping air therein and functions to offset unbalanced ambient pressures Pl and P2 on either side of joint 30 to help prevent partial or complete opening and failure of the joint if the pressure differential becomes unduly large across the joint. For example, if Pl and P2 represent exterior and interior building pressures, respectively, the effect of wind or storm conditions on outer face 17 of sheet 12 would create a greater

pressure Pl than P2. This would flex panels 10 and tend to bow joint 30 towards the interior of the building if not properly supported by the building superstructure. Pressure equalization chamber 38 compensates for the pressure differential across joint 30 to help protect the integrity of the joint and panels 10.

[00036] A preferred method of fabricating panel 10 will now be described. In the preferred embodiment, panels 10 are made with rigid urethane foam as the insulating material 16. Preferably, the rigid urethane foam is made using a two component reactive system in which two urethane base resins are mixed together, undergo a chemical reaction, and expand during the reaction. A restrained rise process is preferably used with the rigid urethane foam to fabricate panel 10. In contrast to the free rise foam process wherein foam is allowed to freely rise and increase in volume, the restrained rise process constrains the maximum volume that the foam can reach as it expands. This results in good compaction of the foam and ensures the panel is thoroughly filled with foam to the greatest extent practicable.

[00037] The panel fabrication process begins by manufacturing the facing sheets 12,

13 with the required dimensions by any suitable technique known in the art depending on the specific type of material used. Where sheets 12, 13 are made of metal, such as steel or aluminum for example, the process may include forming the sheets by roll forming. At least one of the sheets 12, 13 is preferably rolled formed to include panel edge 31 with the double ship-lap offset joint configuration described herein. In other possible embodiments, sheets 12, 13 may be thermal formed or extruded if made of plastic. [00038] In the next step of the panel fabrication process, one of the sheets 12, 13 is selected to be a bottom sheet that is positioned horizontally within a fixture or form that generally approximates the final size (i.e., thickness, width, and length) intended for the finished panel 10. The fixture or form helps to ensure that the foam is contained therein. Assuming for convenience of description only that sheet 12 is the one used in this step, sheet 12 is oriented so that outer surface 17 is facing downwards and inner surface 18 is facing upwards. An adhesive 40 is next applied to inner surface 18 to help bond core 14 to sheet 12 in a subsequent step and ensure the structural integrity of the panel 10. It should be noted, however, that the adhesive application step is optional and need not be used to fabricate panel 10. Particularly if rigid urethane foam is employed, which by its chemical properties bonds somewhat like an adhesive to surfaces in contact with the foam, the adhesive step may be omitted without adversely affecting structural integrity to panel 10.

However, the adhesive step is preferably used with rigid urethane foam as an added measure of precaution.

J00039] The two component rigid urethane foam base resins are next mixed together which begins a chemical reaction to form the foam. Preferably, the foam base resin mixture is then applied to inner surface 18 of bottom sheet 12 (on top of adhesive 40) concurrently with or immediately after the two base resin components are mixed since the foam will begin to form and expand upon mixing the two resins. The rigid urethane foam is filled to a sufficient depth on bottom sheet 12 so that after the foam completes its expansion, the height of the foam will reach the desired depth Dl of panel 10.

[00040] After the rigid urethane foam has been added to bottom sheet 12, core 14 is next lowered and set into the foam and on top of sheet 12 before the foam hardens and is still flowable. Preferably, core 14 contacts inner surface 18 of sheet 12 and adhesive 40 previously applied thereto. As core 14 is lowered into the foam, the foam comes up through and completely fills open the open cells 15 of the core. Advantageously, this approach ensures good penetration of the foam into open cells 15 to provide maximum reinforcement of core 14.

[00041] Top panel 13, which may or may not have adhesive 40 applied to inner surface 19, is set down on top of and into contact with core 14. Outer surface 20 of panel 13 is thus facing upwards and outwards. The various components of soon-to-be finished panel 10 are now all in place; however, the rigid urethane foam has not stopped expanding and is not as of yet completely cured.

[00042] Partially finished panel 10 is preferably next placed in a commercially- available laminator or similar fixture that provides heat to finish curing the rigid urethane foam and provides pressure to hold the panel components together against the force of the expanding foam. Expanding rigid urethane foam may exert typical forces of about 17,000 lbs in a 4' wide by 10' long panel, which would otherwise force the panel components apart if not restrained by some means until the foam cures and stops expanding. Accordingly, the laminator or other fixture that may be used has structural members which serve as clamps to restrain the sheets and assembled panel components so as to prevent them from moving excessively while the foam expands. This also keeps the panel sheets positioned to achieve the final intended dimensions for the panel (e.g., panel total thickness Tl) and is known as a restrained rise process. Advantageously, as the expanding foam exerts pressure within core 14, the foam pressure acting on cell walls 42 tightly compacts the foam within open cells 15 thereby tightly embedding the core within the foam to provide substantial structural

reinforcement of the core. Core 14 essentially becomes an integral component of the rigid urethane foam that allows the core and panel 10 to better withstand external loads and forces than other panel constructions known in the art, thereby creating a very strong, yet light-weight structural composite panel.

[00043] Depending on quantity of panels required for a specific project, a continuous laminator that works in a conveyor-like manner or a platen laminator/press in which a plurality of panels may be vertically stacked on top of each other may be used. However, it should be noted that the invention is not limited to the use of any particular type of laminator.

[00044] Preferably, convex surface 36 may conveniently be formed on panel edge 31 during the foregoing process by placing an adhesive -backed tape over window 50 before the foam is applied to the panel. As the foam expands, it will force the tape to bulge and the foam will protrude slightly above the surface of recess 34, thereby forming convex or arcuately-shaped surface 36. Since convex surface 36 is formed during the basic panel fabrication process and does not require a separate step, the cost of forming the convex surface is negligible. It will be appreciated that convex surface 36 may be formed by other techniques or as a separate component that is subsequently affixed to panel edge 31. Accordingly, the invention is not limited to the preferred method of making convex surface 36.

[00045] While the foregoing description and drawings represent the preferred embodiments of the present invention, it will be understood that various additions, modifications and substitutions may be made therein without departing from the spirit and scope of the present invention as defined in the accompanying claims. In particular, it will be clear to those skilled in the art that the present invention may be embodied in other specific forms, structures, arrangements, proportions, sizes, and with other elements, materials, and components, without departing from the spirit or essential characteristics thereof. One skilled in the art will appreciate that the invention may be used with many modifications of structure, arrangement, proportions, sizes, materials, and components and otherwise, used in the practice of the invention, which are particularly adapted to specific environments and operative requirements without departing from the principles of the present invention. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being defined by the appended claims, and not limited to the foregoing description or embodiments.