FIELD OF THE INVENTION

This invention relates to lumbers products and more particularly to engineered plywood panels used in the construction of concrete forms.

BACKGROUND OF THE INVENTION

When pouring concrete slabs, tilt-up walls and other flat structures, the peripheral edges of the forms are commonly constructed with various types of milled lumber components such as planks or beams which are often discarded after the forms are broken down.

Plywood panels used in the construction of concrete forms are commonly engineered in several laminated plies or layers of diverse woods. The layers are dried and joined under pressure with glue. The grain of successive layers are alternated in order to equalize strain and minimize shrinkage and warping. More recently, panels are also made of fragmented and scattered wood chips pressed together after being saturated with glue. The instant invention result from an attempt to apply some of the technology developed in connection with construction plywood to the manufacture of edging forms that define the perimeter of poured concrete structures.

SUMMARY OF THE INVENTION

This invention yields an engineered concrete plywood board that can be reused a number of times. The board is strong, but relatively inexpensive due to the use of wood sheets that are peripherally finger-joined to one another within each layer or ply with a PVAc exterior adhesive. The sheets are of unequal sizes, but arranged in rows or columns of a constant height so that joint lines are not aligned between layers. The layers are laminated with a water-repellent adhesive. Each sheet is made from a solid rectangular fragment of wood, and are all made of a single species selected for its high strength-to-weight ratio.

In a first embodiment of the invention, the board consists of only two layers in which the grains of all sheets run in the same direction. In an alternate embodiment a third sheet is sandwiched between two external ones with the grain running in a direction orthogonal to the grain in the other sheets.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective view of a preferred embodiment of the plywood board according to the invention;

FIG. 2 is a detailed perspective view of a segment of the board of FIG. 1; and

FIG. 3 is an exploded view of the board.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

Referring now to the drawing, there is shown an engineered plywood board 1made of three layers 2,3,4 laminated under pressure, and secured together by a water-repellent exterior adhesive.

The board has dimensions of 1.20 by 4.80 meters (4 by 16 feet) and a thickness T of approximately 3.175 centimeters (1.25 inch). It must be understood that other overall dimensions and thicknesses can be used within the scope of the invention.

The exterior layers 2,4 are essentially similar, each made of a patchwork of solid wood sheets 5 that are attached to one another around each sheet's periphery by finger-joints 6. The finger joints use an emulsion PAVc exterior adhesive.

The sheets 5 have different dimensions, but, in the exterior layers they are arranged in latitudinal (running across the longest dimension of the board) rows 7 of a constant height H, the sheets having all the same length and a variety of widths. In the middle layer 3, the sheets are arranged in longitudinal (running with the longest dimension of the board) columns 8 of constant width W. Rows between the respective external layers do not line up so that the joint-finger seams or lines do not either.

Each sheet 5 consists of a single solid wood fragment having a thickness of approximately 10.58 millimeters (0.417 inch) or 15.875 millimeters (0.625 inch). The length and width varies from a few centimeters to about 50 centimeters (20 inches).

The species of wood is selected for its high strength-to-weight ratio of no less than 1.000 where the strength is defined in kilograms per cubic meter, and the weight as the specific gravity, meaning the ratio of oven-dry weight over the green volume.

Preferably, the sheets are made of Paulownia wood, or other high strength-to-weight ratio species.

The edge 9 is sealed with an oily composition to prevent drying or a release agent.

The 10.58 millimeter thick board exhibits the following characteristics:

Weight: 56.35 kilograms (124 lbs.)

Tensile strength: More than 372 atmospheres (5,740 psi)

Average number of uses without significant deterioration: 50

An alternate and lighter version of the board may be manufactured by omitting the middle layer 3. The sheet patchwork design is deemed sufficient to assure adequate strength in spite of the two layers having the same grain orientation.

While the preferred embodiment of the invention has been described, modification can be made to it and other embodiments may be devised within the spirit of the invention and the scope of the appended claims.