type heaters and suitable jigs for holding, moving, and maintaining pressure on the sheets during
bonding. A weld of this type has the same strength value as the plastic sheet itself. The heated-tool
welding method is most applicable to the polyolefins discussed in this handbook.
INDUCTION WELDING
Induction welding of plastic, as the name implies, is fusion of two pieces of plastic by electrically induced
heat.
The heat of fusion is obtained by causing a high-frequency electric current to flow in a metallic insert such
as a wire screen, a coil of wire, a die-stamped metal foil, and/or metallic conducting particles intermixed
with the base resins near the face of the plastics to be joined together.
The localized heat caused by the flow of the electric current through the metal insert is sufficient to bring
the surrounding area to fusion temperature. Pressure is then applied to the two pieces of plastic, bonding
them together.
Induction welding is one of the fastest and most versatile methods of joining plastics together, and it
results in an acceptable bond.
The disadvantages of induction welding are: the metal insert remains in the finished product; the cost of
induction-welding equipment is high and the weld is not as strong as that obtained with other methods of
heating.
Although the weld-strength of induction welding is not as high as that obtained by other plastic welding
methods, it is satisfactory for many applications. Using a wire screen insert, a weld-strength of 50% of the
strength of the plastic itself may be realized.
FRICTION WELDING
In friction welding (or spin welding, as it is known in plastic trades), two thermoplastic surfaces are rubbed