Induction hardening
Induction hardening turns up in 2 fields: heat treating, gears. Here is what it means to the people in each one.
Induction hardening in heat treating
Heating only the surface of a steel part with an alternating magnetic field, then quenching for a hard case.
Surface hardening in which a water-cooled copper coil induces eddy currents that heat a shallow layer in seconds, followed at once by a spray or immersion quench, usually polymer. Frequency sets depth: high frequency (100 kHz and up) gives shallow cases on small parts, while 1 to 10 kHz heats deeper for shafts and large gears. Medium-carbon steels such as 1045, 1050 and 4140 are typical, reaching 50 to 60 HRC over a tough core.
"Induction hardening on the axle shafts: scan at 10 kHz, single-shot the spline, polymer at 10 percent."
Induction hardening in gears
Hardening gear teeth by heating them locally with an induction coil and quenching immediately.
A selective hardening process in which a coil induces current that heats the tooth surface in seconds, followed by a water-polymer quench. Small gears are spin hardened all at once, while large gears are hardened tooth by tooth or gap by gap with a shaped inductor. The hardened pattern matters: a contour pattern that runs through the root gives bending strength, while a flank-only pattern can leave the root weaker than before.
"Induction hardening pattern has to wrap the root, a flank-only pattern on this girth gear is asking for broken teeth."