US 4,420,670 AGranted

Control for dielectric heating in blow molding machine

AssigneeCincinnati Milacron Industries, Inc.

InventorsFred J. Croswell, Charles P. Shinkle

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Abstract

Apparatus for controlled dielectric heating a plurality of thermoplastic preforms for blow molding is provided. The apparatus controls the energization of a plurality of electrode pairs by a radio frequency generator. The generator is equipped with a load current limit detector and the electrode energization is enabled selectively for a predetermined time or until a predetermined load current magnitude is reached. The choice of control is determined by the anticipated load as reflected by the number of preforms within the heating station. The generator is further provided with overload detecting means indicative of the occurrence of electrical arcing within the heating station and the apparatus has further means responsive to the arc detector for selectively momentarily or indefinitely deenergizing the electrodes.

Claims11

Dependent claims

In an apparatus for dielectric heating a plurality of thermoplastic article preforms having heating station, said heating station having a plurality of pairs of electrodes energizable by a radio frequency generator, the generator being provided with a load current sensor producing a current limit signal at a selectable load current magnitude and an input circuit for selectively energizing and deenergizing the electrodes in response to a control signal, the preforms to be heated being placed between the electrodes of the pairs, an improved control apparatus comprising:

(a) means responsive to the number of preforms resident in the heating station for selecting interval control and current control, current control being selected when the number of resident preforms equals the number of pairs of electrodes;
(b) timing means responsive to the selecting means for producing an interval control signal for application to the input circuit to effect energization of the electrode pairs for a predetermined period of time in response to interval control being selected;
and
(c) current control means responsive to the selecting means and the current limit signal for producing a current control signal for application to the input circuit to effect energization of the electrode pairs until a predetermined load current magnitude is reached in response to current control being selected.

1 more element

In an apparatus dielectric heating a plurality of thermoplastic article preforms having a heating station, said heating station having a plurality of pairs of electrodes energizable by a radio frequency generator, the generator being provided with a load current sensor producing a current limit signal at a selectable load current magnitude and an input circuit for selectively energizing and deenergizing the electrodes in response to a control signal, the preforms to be heated being placed between the electrodes of the pairs, an improved control apparatus comprising:

(a) means for producing a preform resident signal representing the number of preforms resident within the heating station;
(b) timing means responsive to the preform resident signal for producing an interval control signal for application to the input circuit to effect energization of the electrodes for a predetermined period of time when the number of preforms within the heating station is at least one and less than the number of pairs of electrodes;
and
(c) current control means responsive to the preform resident signal and the current limit signal for producing a current control signal for application to the input circuit to effect energization of the electrodes until a predetermined load current magnitude is reached in response to the present signal representing a number of preforms within the heating station equal to the number of pairs of electrodes.

1 more element

In an apparatus for dielectric heating a plurality of thermoplastic article preforms having a heating station, said heating station having a plurality of pairs of electrodes energizable by a radio frequency generator, the generator being provided with a load current sensor producing a current limit signal at a selectable load current magnitude and an input circuit for selectively energizing and deenergizing the electrodes in response to a control signal, an improved control apparatus comprising:

(a) detecting means for producing a signal indicating passage of a preform into the heating station;
(b) counting means responsive to the detecting signal for producing a preform count signal representing the number of preforms within the heating station;
(c) timing means responsive to the counting means for producing an interval control signal for application to the input circuit to effect energization of the electrodes for a predetermined period of time when the number of preforms within the heating station as represented by the count signal is at least one and less than the number of pairs of electrodes;
and
(d) current control means responsive to the counting means and the current sensor for producing a current control signal for application to the input circuit for effecting energization of the electrodes until a predetermined current magnitude is detected in response to the count signal representing a number of preforms resident within the heating station equal to the number of pairs of electrodes.

2 more elements

Dependencies are inferred from the claim text.