A New Method for Selecting Glues for RF Heating

When radio frequency heating is used to accelerate the setting rate of synthetic resin adhesive in a wood-glue composite, the heating rate of the glue, compared with that of the wood, is dependent on the relative values of two electrical constants: 1) the permittivity (dielectric constant) and 2) the loss tangent. These constants can be determined for wood, but the measurement technique cannot be applied to a glueline. A new method was devised utilizing the GL and TR Conductivity Ratios. This method allows, for the first time, the glue maker to compare quantitatively and scientifically his existing range of adhesives and evaluate any improvements which may result from modifications in formulation. The wood adhesives in use at the present time appear to vary considerably in their electrical suitability for radio-frequency heating and, while all can undoubtedly be made to set very rapidly by present-day standards, many could be considerably improved electrically, so that less of the available radio-frequency power is wasted in heating the wood and more is employed for raising the temperature of the glueline.

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