Radio frequency heating system for heating thermoplastic material preforms

摘要

This relates to a radio frequency heating system for heating PET preforms. The system includes two parallel applicator plates or electrodes and the coupling of a radio frequency power supply thereto. Both the radio frequency applicators are isolated from radio frequency oven cavity and are electrically balanced and operated in a push-pull manner so as the net induced currents in the adjacent transport system are maintained to a minimum level and also the electric field strength between either the applicator plate and the transport system is half of that between the applicator plates. It also includes the use of inductors or stubs at specific points to provide for more uniform radio frequency voltage by reducing the voltage standing wave radio. Finally, it includes the proposal that the radio frequency oscillator vacuum tube may be mounted on one of the stubs or inductors and that the oscillator circuit need not be balanced in view of the very small proportion of the energy required by the load as compared to the overall energy in the applicator tank circuit and also that there is no need for the frequency tracking of the oscillator circuit to the load tank circuit.