Method of heat treating using eddy current temperature determination
AssigneeTocco, Inc.
InventorsGeorge D. Pfaffmann, Donald E. Novorsky
Life of this patent
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Abstract
A method and apparatus for the heat treating of quench hardenable ferrous alloy workpieces utilizing periodic eddy current excitation and reflection to determine the in-line cooling rate from the critical temperature of the workpiece material and comparing the in-line cooling rate against a standard rate for establishing acceptance or rejection of the quenched workpiece.
Claims9
A method for non-destructively determining satisfactory cooling of a ferrous workpiece after said workpiece has been heated above its critical temperature comprising the steps of:
- (i) rapidly cooling said workpiece from said critical temperature to a lesser temperature which is approximately equal to greater than the M.sub.s temperature of said workpiece;
- (ii) during the time said workpiece is cooling, periodically inducing eddy currents in said workpiece so that a plurality of eddy current pulses are produced in said workpiece during the time said workpiece is cooled;
- (iii) periodically measuring said eddy currents produced in said workpiece at time intervals correlated with each eddy current pulse to produce a plurality of output signals correlated to the varying temperature of said workpiece as said workpiece is cooled;
- (iv) generating a plurality of comparison signals, each comparison signal correlated to a different temperature ranging from the critical temperature to a temperature approximately equal to the M.sub.s temperature of said workpiece with a discrete time interval associated therewith and all comparison signals correlated to the critical cooling rate of said workpiece, said critical cooling rate being determined from the time-temperature-transformation diagram for said workpiece;
- (v) comparing said output signals with said comparison signals on both a temperature and a temperature-time basis and rejecting or accepting said workpiece depending on the deviation between said signals.
Apparatus for non-destructively determining the satisfactory heat treatment of a ferrous workpiece comprising:
- (a) means for heating said workpiece to its critical temperature;
- (b) means for rapidly cooling said workpiece from its critical temperature to a temperature approximately equal to or greater than the M.sub.s temperature of said workpiece;
- (c) a coil adjacent said workpiece and situated within said cooling means;
- (d) means for applying a high frequency current to said coil for a first fixed time period followed by a second fixed time period where no current is applied during the entire time said workpiece is cooling to induce a plurality of eddy current pulses throughout the time said workpiece is being cooled;
- (e) means for measuring said eddy current pulses at periodic time intervals while said workpiece is being cooled to produce a plurality of output signals;
- (f) microprocessor means for comparing each of said output signals with comparison signals previously stored in said microprocessor means and correlated to preferred temperature-time characteristics of said workpiece;
- (g) output means associated with said microprocessor means for indicating the deviation of said output signals with said comparison signals and, accordingly, reject or accept said workpiece.
Dependencies are inferred from the claim text.