Glue spreader, plywood

Lay-up proceeds by laying down the veneer which is to be the back surface of the panel. Then a sufficient number of pieces of core veneer are passed through the glue spreader to form the next layer of cross-oriented veneer. The glue spreader commonly used in hardwood plywood manufacture is a roU coater in which a pair of opposing mbber roUs are coated with a thin layer of adhesive. As the veneer is passed between the roUs, the adhesive is transferred to the surfaces of the veneer. Adhesive is appHed only to the cross-pfles and in sufficient quantity to provide a continuous layer on both opposing faces of veneer. Thus, in the case of a three-ply panel, only the core layer is spread with adhesive and in that of a five-ply panel, the second and fourth layers both of which are cross-pfles, are spread with adhesive. Then the top surface veneer, which is normally the decorative surface, is placed on the assembly. 

The adhesive is applied to both sides of the alternate ply veneers. They are passed through a glue spreader and then stacked between the uncoated veneers to form the plywood assembly. A product made with urea-formaldehyde adhesive might be pressed at 125 °C and a pressure of 150-300 pounds per square inch for 5-10 minutes to achieve a satisfactory cure. 

Low-viscosity soybean briquetting adhesives are generally applied by spray. Paper and softboard laminating glues are usually applied by curtain coater, knife, or indirect roller. High-viscosity plywood and lumber assembly formulations are fairly well limited to application by spreader roll or extrusion. For very small assembly jobs, soybean glue can easily be applied by brush. 

A widely used, commercially available pine plywood resin was employed as a comparative control throughout all tests. The glue was applied using a (Black Brothers) roller spreader and spread rate was controlled within the range of 83-87 lbs. per 1000 square feet of double glueline (Ibs./MDGL). 

---