Heating device for plastic blanks

摘要

The preform (1) has a region designated for heating and a further region which is not to be heated. The region to be heated is subjected to microwaves in a resonator. All of this region is heated simultaneously. It is alternatively heated progressively in steps or sections. The region is moved and/or heated continuously. The preform is moved longitudinally (A) or at right angles to this direction, into or through the disc- or plate-shaped resonator (11) which completely surrounds it. The path of preform movement, projected into the extended plane of the (TE wave) resonator during heating, is essentially circular. Movement through the resonator takes place repeatedly, no less than twice. This movement is superimposed on the circular movement, which is followed by the resonator. Preform temperature is measured internally and/or externally, once or more times, during the operation. The value is sent to a controller for the following heating process, or to control heating of the present preform. In an adjustment method, by measuring the temperature profile of the preform and comparison with a desired profile, the field strength distribution in the resonator is adjusted accordingly. Variants of these procedures are described, in accordance with the foregoing principles. Salient features include an optionally-moving microwave reflector, delivery to an associated polyethylene terephthalate (PET) stretch-blowing process. Heating may be intentionally non-uniform over the length, thickness and/or circumference. Microwave heating is supplemented by infra red heating. A microwave generator feeds the ring resonator. The equipment is further detailed. An independent claim IS INCLUDED FOR corresponding equipment.