Lockheed Corporation

Andrew Zsolnay

Leiv H Blad

Kelly M Perkins

This invention is directed to a method of automatically controlling curing of a thermosetting polymeric material. The method comprises the steps of (a) applying heat to the polymeric material to initiate curing; (b) measuring a selected characteristic of the polymeric material at various times during the cure cycle thereof; (c) generating a set of signals corresponding to the measurements made; (d) determining from the signals the optimum time for applying pressure to the polymeric material; and (e) automatically applying pressure to the polymeric material at the optimum time, in a closed-loop system. The selected characteristic measured may be the capacitance or the dissipation of the polymeric material. In general, the pressure is automatically applied immediately after the minimum capacitance level is reached but before hardening of the polymeric material.

Automatic process control system for curing polymeric material

The invention is directed to an apparatus and method for curing polymeric materials by use of a closed-loop, automatic process control technique. A dielectric monitoring device (15) senses the electrical characteristics which are analogous to viscosity changes taking place in an uncured or partially cured polymeric material (10) while heat is applied thereto. The generated analog signal, which changes in response to variations in the capacitance and dissipation of the polymeric material, is fed into a microcomputer (21) which determines from the direction and amplitude of the generated wave form both the maximum and minimum levels of capacitance and dissipation developed. When a predetermined condition is reached, the microcomputer (21) sends a control signal to processing equipment (24,25) to apply pressure, heat and/or vacuum to the polymeric material (10) at or near the onset of gelation but prior to the hardening point. The microcomputer (21) is programmed so as to discard random electrical signals and questionable data such as from short-term burst noises. The system can be used for curing various polymeric materials having differing characteristics.

Automatic process control system and method for curing polymeric

A sample of polymeric composite material is cured using conventional curing methods. The optimum time during the cure cycle for applying pressure to the sample is determined by standard resin advancement measuring techniques. A dielectrometer monitoring device (15) is then attached to another material of the same type which is cured under the same conditions to develop an analog signal denoting variations in dissipation of the material. The dissipation curve characteristically has a first and second maximum value, with the latter occurring in the general vicinity of the optimum time for applying pressure for a particular frequency. Thus by changing the frequency, the dissipation is shifted along the time axis so that the second maximum coincides with the optimum time for applying pressure. The generation of a readily recognizable and repeatable feature on the analog wave form, a minimum or maximum, is a prerequisite to triggering process control functions. Thereafter, a voltage at that particular frequency is applied to other similar materials during their cure cycles to obtain a dissipation curve which has a second maximum value coinciding with the optimum pressure application point. The dielectric monitoring unit (15) is connected to a microprocessor ( 20) which determines the time at which such maximum value is reached, in response to which a command signal is sent to a pressure control system (24) connected to the microprocessor (20) for applying pressure to the material, all in an automatic, closed-loop system.

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Manhattan Beach, CA, United States of America

Andrew Zsolnay