Glue Spreading Efficiency of Roll Spreaders

A study of the spreader roll application of phenolic resin adhesives to plywood core veneers–using resin source, adhesive formulation, roll-groove pattern, degree of wear on the roll, and variations of veneer thickness as variables–led to the development of a method for defining and measuring the spreading efficiency of roll-grooving/adhesive combinations. The method permitted studying the effect of roll-groove pattern design variables on spreading efficiency. Wear of the roll grooving caused a marked reduction in spreading efficiency, and variations in veneer thickness also had a marked effect on glue spread levels. There was a direct relationship between the ratio of the volume of the groove and the amount of glue transferred at minimum compression and the included angle of the groove. The variation in spreading efficiency on varying widths of veneer is related to the amount of compression of the roll grooving required to transfer the required volume of glue to the veneer. If the combination of spreading variables is such that the initial spreader setting for 12-inch wide test pieces results in compression of the grooves, then a variation in the glue spread level will result for any variation in the width of the veneer, because the pressure between the rolls, or the resistance of the rolls to being pushed further apart, is set at a constant level. The amount of compression or distortion of a roll grooving as a piece of veneer passes through the rolls will vary with the width of the veneer, causing a variation in the volume of glue transferred. The effect of wear of the spreader roll grooving reduces the volume of glue available, requiring additional nip pressure to obtain the initial spread level, further reducing the spreading efficiency on different widths of veneer.

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