Evaluation of An Oil-Fired Veneer Dryer–Its Effect on Glue Bond Quality

An oil-fired dryer was suspected as the source of trouble in a glueline quality problem in cold press production using soybean adhesives and Douglas-fir 1/10-inch veneers. The study was divided into two phases. Phase I was to determine if high-temperature drying of Douglas-fir veneer in a direct oil-fired dryer was detrimental to the glue bond quality of interior type cold-press plywood. The results indicated that a higher temperature control setting of 450?F developed significantly lower bond quality than a modified schedule using a 375?F setting. The 3-cycle (soak-dry) evaluation of both dryer control settings showed adhesive durability test ratings of 62 percent for the 450?F setting and 99 percent for the 375?F setting. The steam-dried controls received 100 percent and 99 percent ratings, respectively. Phase II was concerned with collecting temperature data at various locations in the dryer and the development of a drying schedule that would develop satisfactory glue bonds. It was recommended that drying temperatures be maintained below 425?F. This would require, in this particular dryer, a control setting of no higher than 400?F. Unbalanced temperature conditions in the supply manifold section were corrected by means of a damper positioned in the heater duct and adjusted to minimize temperature variations.

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