Patent Application
20170145692
This invention relates to structural insulating panels and more particularly to a chamfered reinforced edge for the panels to provide a finish-ready surface.
Structural insulated panels or SIPS have been in existence since the 1930s in which stress skinned panels have been used for construction. Frank Lloyd Wright was a pioneer in the use of SIPs in an effort to incorporate beauty and simplicity into cost-effective homes. Wright's attempt at the panel contained no insulation; they consisted of layers of plywood and layers of tarpaper. Alden B Dow, an architecture student of Frank Lloyd Wright, experimented with providing proper insulation for the SIPs and created a structural panel with an insulated core in 1950. Dow's earliest SIPs were composed of 1⅝ inch Styrofoam cores with plywood facings to add structural support for loadbearing walls.
In general, the structural insulated panel is a composite building material consisting of an insulating layer of rigid core sandwiched between two layers of structural board. The board can be made of sheet metal, plywood, cement, magnesium oxide board (MgO) or oriented strand board (OSB) in which the core is typically expanded polystyrene foam or EPS. While the SIPs share the same structural properties of an I-beam or I column, the rigid insulating core acts as a web, whilst sheathing fulfills the function of the flanges.
When these panels are placed side by side, a finished surface usually requires covering over the joint between adjacent panels with a fiber tape and applying a compound over the tape. However, this traditional joint treatment creates material build up between the adjacent edges of the board that stands proud of the surface and presents a hump which must be sanded down in order to provide a smooth finish-ready surface on which stucco or paint may be applied.
In summary, the most difficult step in finishing SIPs is treating the joint between the panels before painting. This is done by laying a fiber tape over the joint and applying a joint compound over it. This is a traditional treatment for nonstructural drywall and fiber cement boards that are used as interior and exterior sheathing.
In the past, nonstructural drywall and some fiber cement boards have been provided with tapered edges that allow the application of tape and joint compound without creating material build up that stands proud of the surface. Structural boards used to manufacture SIPs, such as OSB, do not usually have tapered edges because they are covered by another finish layer, such as exterior cladding or drywall. Therefore the joints of the SIP are not finished and do not require a taper. For SIPs that are not covered by another layer, such as SIPs made with MgO boards, the tapered edges are provided by cutting a taper in the finished edge of the skin or board which cuts one or more layers of fiberglass mesh that gives the panel structural integrity.
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Thus, while these tapers provide a recessed edge, the cutting weakens the board so much that the joints between the boards are not robust. Since the boards are produced with two main components, one for instance an MgO cement which gives the board compressive strength; and one or more layers of fiberglass mesh that gives the board tensile strength and flexural strength, when the board is cut, one or more layers of the fiberglass mesh are removed eliminating a key element that gives the edges tensile and flexural strength. In short, the structural integrity of the joints is compromised by virtue of providing the recessed edge by cutting a taper in the edge of the SIP panel.
It is noted that MgO boards have been provided with a recessed edge by cutting the edge at an angle with a saw or other cutting tools. This may work for a nonstructural board, but for a structural board the cutting significantly weakens the edge. Since the edges are where the fastening of the panels one to another occurs, the structural integrity of the panel is severely impacted by the use of a chamfered edge provided by cutting the edge of the panel.
Thus, prior to the subject invention, structural panels either do not have recessed edges or, if they do, the edge is not properly reinforced with the proper amount of fiberglass mesh due to the cutting.
In order to provide SIPs with a reinforced recessed edge to permit a flush finish-ready surface, the SIP board or skin, in one embodiment a cementitious skin, has tapered molded edges that are reinforced. The boards or skins are manufactured by locating an acrylic mold having raised edges at either side, introducing a cementitious slurry onto the acrylic mold, overlaying the slurry with a reinforcing mesh, in one embodiment a fiberglass mesh, introducing more slurry and providing an additional reinforcing mesh on top of the slurry, followed by calendaring or calibrating the top surface of the slurry with rolls to calendar the slurry into the shape defined by the acrylic mold. The result is a flat surface on the rolled side of the skin and a tapered edge on the underside which is reinforced by fiberglass mesh. The wet board or skin is transported still on the acrylic mold into a curing room, where it dries and hardens, after which it is stripped from the mold to provide a SIP panel skin having reinforced recessed tapered edges corresponding to the raised portions of the acrylic mold in which it was formed.
In short, the skin of the SIP is provided with recessed edges that contain fiberglass mesh layers for proper reinforcement and structural use, with the recessed edges adapted to receive tape and a joint compound in the recess to a level flush with the remainder of the skin. When the reinforced tapered edges of the SIPs are screwed into underlying shims at the edges of adjacent panels to join adjacent panels, the joint has significant structural integrity.
The result is the ability to provide a finish-ready joint that is flush with the skin surface without compromising the structural integrity of the joint which would occur through removal of a reinforcing mesh at the edge.
In summary, a reinforced tapered edge cementitious skin for use in a SIP panel provides a recessed edge having an underlying reinforcing web. When panels having the reinforced tapered edges are to be joined together and fastened to underlying shims, the resulting joint has both structural integrity and a recess for receiving joint compound that can be made flush with said skins.
Moreover, a method is provided for molding a SIP skin so as to provide a tapered recess by using a mold having raised edges; introducing a cementitious slurry onto the mold; embedding reinforcing webbing in the slurry; calendaring the slurry to compress the slurry onto the mold such that the top surface of the slurry is flat and such that the bottom surface of the slurry conforms to the raised edge mold; curing the slurry on the mold; and removing the cured slurry as a SIP skin having a recessed tapered edge that is reinforced with the webbing.
These and other features of the subject invention will be better understood in connection with the Detailed Description in conjunction with the Drawings, of which:
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The result is that adjacent SIP panels can be joined together securely with SIP skins having mesh reinforced tapered edges to accommodate tape and joint compound to provide flush finishing for the panels.
It will be noted that the subject invention is described in terms of the use of magnesium oxide for the skin material, although other moldable skins having reinforced mesh 56 are within the scope of this invention. Moreover, the shims that are utilized may also be made of magnesium oxide.
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While the subject invention is described in terms of fiberglass as the mesh utilized for the reinforcement, other reinforcing webs are within the scope of this invention.
After the MgO slurry has been compressed onto the molds by the calendaring rolls, the molds exit the production line as illustrated at 88. Thereafter, the slurry is air cured and the skins with the tapered edges are pulled off of the molds.
From a process perspective, in one embodiment MgO slurry is deposited, then a layer of fiberglass, then another layer of slurry, then anther of fiberglass, etc. The minimum number of fiberglass mesh layers is 2, but there can be up to 4 layers normally, depending on the thickness of the board. The layers are normally toward the surface and the back. That is to say, they are not evenly distributed in the board. Specifically, they are located more toward the surface areas as they are most useful there.
Some of the slurry does drip off of the edges of the mold. However, the MgO slurry has a very high viscosity, so it maintains the desired thickness for all but the last 1-2 centimeters from the edge.
The edge trimming is 3-5 cm. from each edge, so the last bit that is irregular is sawn away. That sawing is done in one embodiment with a double ended trim saw. 5-10 boards are stacked on top of each other and they are run through on a carrousel, between two saws separated at the width the panel is to have, usually 1220 mm. Then another set of saws is set at a 90 degree angle to that of the first trim saws. The second set of saws trim the boards top and bottom.
It will be appreciated that the mold surface provides a raised edge platten onto which the slurry is deposited. As mentioned above, the slurry has sufficient viscosity that, properly metered, does not roll off the mold. After the multiple deposits of slurry along with the fiberglass mesh reinforcement, the skin has a ragged edge. In one embodiment, these ragged edges are trimmed by the above-mentioned double ended trim saws, with the tops and bottoms of the skins being trimmed with trim saws oriented at 90 degrees to the double ended trim saws.
Note that the acrylic sheet is placed directly on the conveyor and is sufficiently rigid, such that it supports the wet MgO skin at the end of the line when it is removed and is placed on racks for drying and curing. The acrylic mold is made approximately 5 cm wider than the final board width, since there are no vertical sides to the molds. Thus, the very ends of the boards are irregular but, because of the high viscosity of the slurry, it holds its shape well enough not to need vertical mold sides. After the board is cured, the edges are cut to remove the irregularity, giving the board its final exact width, and ensuring the edges are perfectly parallel.
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While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications or additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.
