A New Method for Observing Gap-Filling of Wood Adhesives

The characteristics of thick glue lines are described in terms of the activity of the adhesive. Factors that must be controlled in a method for observing gap-filling properties are thus defined and reduced to: 1) absolute fluid pressure on the adhesive, 2) thickness of the adhesive layer, and 3) rigidity of the bonded members. Data are presented showing the behavior of typical assembly adhesives as they react to the imposed conditions of test. The test specimen is a modification of the cross-lap specimen currently under study at the University of Michigan. The upper member of the specimen is drilled through the center with a 7/16-inch hole and counter-bored 3/4-inch to a depth of 5/16-inch. Inserted in this counterbored hole is a flange and nipple through which compressed air is applied directly to the glue as bonding pressure. Pressure to hold the two members of a specimen together is brought to bear by means of clamping arrangement. Modified urea, casein, animal, polyvinyl, and resorcinol adhesives were studied. Results indicate that useful criteria of gap-filling properties may be obtained.

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