The Kreibaum Process for Extruded Core Board

Discusses history and operation of a vertical extrusion process for manufacturing core stock developed by Otto Kreibaum of Germany in 1947. The wood may be either softwood or hardwood, or a combination of both. Wood waste or cordwood passes through a chipper and is reduced to chips 3/4-inch to 1-1/4-inches long. A milling machine reduces the chips to approximately 1/2-inch long by 1/8-inch. Sawdust is undesirable because it adds weight, and does not add strength to the board. A reasonable percentage of bark is admissible. The chips, which have been dried down to 3 percent moisture content, are mixed with resin glues, extender, water, and a catalyst. After a short flashing period, the chips are fed vertically and downward into the vertical extrusion presses. American plants usually have setups for seven thicknesses, ranging from 1/2 inch to 1-7/8 inches. The plates in the presses are heated by oil. Through resistance, friction, heat, and pressure, the glue-treated chips pass through these vertical presses and emerge as a board 49 inches across by whatever other dimension is desired. In this process the chips are oriented in a vertical position, perpendicular to the two molded surfaces. In this way dimensional stability is achieved in thickness. Also, what might be termed grain direction in the board pertains to the 49-inch direction.

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