Glue Spreading By Spraying Method

An improved spreader to spray-apply glue uniformly to veneer moving in a continuous line at a rate of about 80 fpm was developed and found feasible in an evaluation study. Present roller spreaders develop about 15 to 25 percent glue waste. In addition there is a veneer loss of about 5 percent due to thin veneer. Spray spreading methods investigated in various steps to develop a usable spray application method included: 1) a reciprocating crosshead machine, 2) a rotary arm machine, and 3) a rotating arm machine. Problems involved in glue-air blending, variability, and spray patterns were progressively overcome. Overlapping was found to be a requisite of uniform spray spreading, and moving spray guns posed mechanical problems. A staggered stationary gun setup was then explored. Using smaller fluid nozzles good spray patterns 12 inches wide were obtained. Optimum arrangement was with guns spaced 3 inches laterally and 6 inches along the conveyor at a height of 18 inches. This provided a 3/4 overlap and four coats to any one point sprayed. With an exterior phenol-formaldehyde adhesive the system gave very uniform spread on the central 20 inches of samples conveyed through the spray area. Matched panels produced by a laboratory roll spreader and the spray spreader gave similar shear and wood failure values in a standard boil test. Glue wastage in air spraying was about 7 percent. This loss is not prohibitive as some of this glue might be recovered, and 10 to 20 percent (over trim) loss is now tolerated with roll spreaders. The spray spreader had a distinct advantage in control of and uniformity of spread over a roller spreader. The stationary spray spreader’s ability to continuously spread veneer, regardless of grain direction, moving about 80 fpm, should facilitate the development of continuous layup systems for plywood.

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