Power control for densification of one or more porous articles
View Patent ↗A method of controlling power applied to an induction coil assembly used for densifying porous articles with a liquid matrix precursor. The control of applied power addresses dynamic changes in the electrical characteristics of the porous article being densified as it becomes denser. In particular, the power applied is controlled in accordance with changes in resonant frequency of the coupled system of the induction heating system and the porous article.
1. A method for densifying one or more porous articles, comprising:
loading the one or more porous articles in a reaction chamber having one or more induction coils and a tuning capacitor;
submerging the one or more porous articles and the one or more induction coils in a liquid precursor for a densifying matrix material so that the liquid precursor infiltrates pores in the one or more porous articles;
inductively heating the one or more porous articles using the one or more induction coils to a temperature sufficient to cause a vapor layer to form at an interior surface of the pores of the one or more porous articles, and sufficient to cause vapor in the vapor layer to pyrolize and deposit the densifying matrix material within the pores of the one or more porous articles; and
controlling a densification kinetic of each of the one or more porous articles, the densification kinetic being weight gain by a porous article per densification time,
wherein inductively heating and controlling the densification kinetic of the one or more porous articles comprises matching a resonant frequency of the tuning capacitor with that of the one or more induction coils so as to actively control AC electrical power supplied to drive the one or more induction coils during densification,
wherein actively controlling electrical power supplied to drive the one or more induction coils during densification includes periodically changing a resonant frequency variation in the AC electrical power supplied to the one or more induction coils during densification, and
changing the resonant frequency variation of the AC electrical power includes:
periodically measuring a resonant frequency of the AC electrical power being supplied to the one or more induction coils;
calculating a variation in the measured resonant frequencies of the AC electrical power being supplied;
comparing a respective calculated resonant frequency variation with a resonant frequency variation set point, the resonant frequency variation set point being a predetermined change in resonant frequency over time; and
adjusting the AC electrical power level in accordance with the comparison between the calculated resonant frequency variation and the resonant frequency variation set point.
2. The method of claim 1 , wherein the resonant frequency variation set point is constant over a given densification cycle.
3. The method of claim 1 , wherein the resonant frequency variation set point is variable between minimum and maximum limits.
4. The method of claim 3 , wherein the minimum resonant frequency variation set point corresponds to a minimum core temperature of a given porous article at which densification can occur.
5. The method of claim 4 , wherein the maximum resonant frequency variation set point corresponds to a maximum core temperature of a given porous article, beyond which densification proceeds so quickly as to result in incomplete densification at a interior part of the porous article.
6. The method of claim 3 , wherein the resonant frequency variation set point increases over the course of a densification cycle.
7. The method of claim 1 , wherein adjusting the AC electrical power being supplied in accordance with the resonant frequency variation set point is performed dynamically during a densification cycle.
8. The method of claim 7 , wherein adjusting a resonant frequency of the electrical power being supplied so as to correspond to a resonant frequency variation set point is performed dynamically and automatically during a densification cycle, using a computer control system.
9. The method according to claim 1 , wherein a plurality of induction coils are provided in correspondence with a plurality of porous articles, the plurality of induction coils being electrically connected to a common power source.
10. The method according to claim 9 , wherein the plurality of induction coils is electrically connected to a common power source by a single electrical bus.