Thermal contact sealing
Unlike the previously described method the temperature of the sealing tools is kept at a constant preset level (permanent heating).
It is true that this method is not suitable to process all types of film materials optimally, but in many aspects it is superior to the impulse sealing method. It is especially suitable for multilayered films (laminates) which can be processed on heavy-duty machines at high speeds. Unlike the film sealing, only the layers facing each other are fused in this method. Unilayered films are mostly sealed-cut with a permanent heating. Here, too, using different speeds. Heating of the tools is carried out indirectly via heating cartridges.
In flat sealing the surface of the tools is often shaped for the optimum effect or for reasons of tightness.
All in all, permanently heated tools have a simpler design and are more robust in service. A disadvantage of this method is the high energy consumption and the unavoidable heating of neighbouring machine parts. In practice, the size of the tools is limited by possible distortion.