Means for and method of cutting thermoplastic materials

1,048,378. Cutting thermoplastic materials. G. M. PFAFF A.G. Oct. 20, 1964 [Oct. 23, 1963], No. 42666/64. Heading B5A. In a method of cutting or severing thermoplastic material a cutting or severing tool is brought to a first temperature range within the plasticizing range of the material to contact and cut the material after which its temperature is raised to that of decomposition of the material to effect cleaning of the tool. As described, the or each tool which is of a metal or alloy of high electrical resistivity is connected in series with a variable resistor across the secondary winding of a transformer, the primary of which is connected via a switch to the supply terminals 1 and 2. After cutting, a switch is closed to energize a relay which is then held by closure of a holding switch to connect a tap point of the primary winding of transformer to the supply terminals so that the current to the tool is increased and its temperature rises to that of decomposition of the material. A time delay relay energized on closure of the holding switch determines the duration of the excess heating of the knife and thereafter a time delay relay is de-energized to restore the circuit to its initial condition.