High Frequency Gluing of Wood–What Glue Should I Use?

The form of radio frequency energy being used determines the choice of adhesive. With the perpendicular method, in which the load is placed between two metal plates or electrodes and heated quite uniformly, any thermosetting adhesive can be used. This method has proven excellent in the production of curved plywood. Wooden molds, machined from hard maple, and dried to bone dryness, are sealed with high dielectric varnish and covered with thin sheets of copper to act as electrodes. In parallel heating, the power is concentrated in the glueline, and heating cycle calculations depend on the electrical characteristics of the glue, the density of the species involved, and the curing rate of the glue. In general, flour extensions should be avoided with parallel heating as the water in the glueline increases the heating time. When the voltage is high, the conductivity of the glue must be kept fairly low to prevent arcing. With high density species, viscosity is important. In stray field heating, commonly used for gluing panels to frames, electrodes are placed on the panel side and tack cure spots are formed between the electrodes. The power goes from the hot electrode through the panel to the wet glue-line, then up the panel to the ground electrode. The glueline below each electrode is not cured, but it will normally cure at room temperature within a few hours. As the electrodes are not in contact with the wet glueline, a highly conductive mix can be used, encouraging the power to go through the glue-line rather than the panel. There is little likelihood of burning unless the voltage is very high.

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