Grooves are formed in cellular thermoplastic insulation boards using an apparatus having a pair of rotatable knives to first form two continuous slits in the board, and further having a heated tool of specific design which is caused to remove material from between the slits in the form of a continuous strip.
A machine for cutting grooves in foam workpieces includes a plurality of vertically spaced U-shaped cutting wires mounted on pairs of mounting posts. One leg of each U-shaped wire is mounted on one post, while the other leg is mounted on the other post. The posts are mounted on a frame so as to be adjustable in spacing and vertical position with respect to each other, so the widths of the grooves can thereby be adjusted. Horizontal slice-cutting wires are provided behind the groove-cutting wires so that grooves and slices can be cut simultaneously. The slice-cutting wires are aligned at an angle with the vertical so that each slice-cutting wire exits the workpiece before all those beneath it. One version produces tongue-and-groove sheet, while ship-lap sheets are produced by the other version.
Disclosed is a gypsum board having a kerfed edge along substantially the full length of at least one edge wherein the kerf has sidewalls inclined opposingly inwardly toward one another but do not intersect and are joined by a bottom surface of uneven profile characterized by alternately and irregularly spaced projections and depressions. The uneven bottom surface and each sidewall meet at a jagged intersection. Said kerfed edge provides enhanced strength in a direction perpendicular to the sidewalls providing improved board retention by flanged supports over that of conventional mechanically sawn kerfed edge boards. A process for providing kerfed edge gypsum board is also disclosed which comprises projecting into the board edge a first and second fine stream of aqueous liquid which incline toward one another at angles of incidence to a line perpendicular to the board edge which provides a combined angle therebetween of from about 3.degree. to about 20.degree.. Both first and second fine streams of aqueous liquid are projected at a pressure sufficient to cut to substantially the same depth of from about one-quarter to about three-quarter inches. The process is dustless and provides a kerf having two opposing sidewalls inclined toward one another and joined by a bottom uneven jagged surface providing increased strength exceeding that of boards kerfed by conventional mechanical sawing processes.
