Steam-Injection Knife Improves Veneer Quality

Block conditioning chambers to facilitate veneer cutting are expensive to construct, expensive to operate, and create pollution. Also, veneer block temperature is very difficult to control. A new approach to cutting veneer at elevated temperatures overcomes these disadvantages by thermally softening the wood fibers an instant before they contact the knife tip; a heated conditioning fluid, such as steam, is directed into the cutting region of the knife tip. Steam is available in plywood plants and has no detrimental effects on veneer. For a laboratory veneer lathe, which was tested on western white spruce and western redcedar, an adaptor plate containing a steam chamber and orifice network was bolted behind the veneer knife; the orifices–1/32 inch in diameter, spaced every 2 inches–direct jets of steam under pressure into the wedge-shaped areas formed by the knife back and the veneer. For a commercial apparatus, which was tested using Douglas-fir at two plywood plants steam chambers and orifice network were machined into the knife backing bar, with orifice diameter increased to 0.050 inch to provide more heat to the knife tip. Insulation between the lathe-carriage frame and the knife backing bar was added. Veneers with depressions greater than 0.020 inch were considered degrade and unsatisfactory for plywood manufacture. In peeling western redcedar veneer produced with a standard knife was 27.1 percent degrade, and veneer produced with the steam knife was 2.1 percent degrade. For western white spruce, roughness degrade was reduced from 7.4 percent to 2.3 percent by steam injection. For Douglas-fir, roughness degrade was reduced from 29.6 percent to 10.7 percent at one mill, and from 10 percent to 2.9 percent at another. Commerical tests of the steam knife are continuing and a patent has been applied for.

You must be logged in to download any documents. Please login (login accounts are free) or learn how to Become a Member