In induction heat treating, the heat pattern is the product. The case depth, the hardness zone and the transition zone all follow from where the coil puts its power. A pattern that misses a fillet or spills onto a shoulder means rejected parts or extra distortion, so pattern control matters as much as efficiency.
Three tools for shaping the pattern
Designers have three levers for shaping an induction coil heat pattern.
- Coupling gap. The closer the coil is to the part, the more intense the heating in a narrower band.
- Coil copper profile. Reshaping the heat face changes how power is distributed. Recessing copper in the center of a coil, for example, can compensate for flux divergence at the coil ends.
- Magnetic flux controllers. SMCs placed near the coil concentrate the field and let designers contour the pattern by profiling the SMC poles themselves.
The first two change geometry and are limited by what the part, fixtures and clearances allow. SMCs add control without changing the copper envelope, which is why they are used where the specification is tight.
How SMCs move the heat
The ASM Handbook describes controllers as providing favorable and unfavorable paths for flux, which increases heating in desired areas and reduces it in undesired ones. On an OD coil the primary pattern benefits are heating fillets, avoiding overheated shoulders and obtaining sharper transition zones. Two behaviors drive this:
- A C-shaped concentrator raises the magnetic field, and the power, under its opening and narrows the power distribution under the coil face.
- A thin SMC plate in the gap between coil and part blocks heating in that region. In that role it is a shield rather than a concentrator.
Examples from heat treating
Crankshaft pins and journals. A bare clamshell coil heats the crankshaft web, wasting energy and adding distortion. Fluxtrol 100 plates on the sides of the coil removed that unintended heating and improved the coil parameters. On U-shaped crankshaft coils, replacing laminations with SMC enabled better pattern control and significantly extended coil life, since copper had been cracking under the concentrators.
Camshaft static hardening. A customer saw unsatisfactory cycle times and back tempering of the adjacent lobe. With Fluxtrol A as the only change, cycle time fell 26%, power fell 30% and back tempering stopped.
S-cam and tractor hub coils. Fluxtrol case studies report a 46% cycle time reduction with pattern improvement on a case-hardened S-cam, and a 42% reduction with positive pattern control on a tractor hub OD coil with integral quench.
Axle scan hardening. In scanning, the main benefit is the pattern at the beginning and end of the part. Where fillet heat treatment drives the design, controllers improved the pattern and delivered 15 to 50% energy savings.
Fluxtrol also published a video comparison of five inductor geometries with and without Fluxtrol 25 .
Placement depends on coil style
Flux flows differently in OD, ID and linear coils, so the same SMC does different work in each. Many real coils are hybrids. Inside the coil and between opposite-direction turns on linear coils, where magnetic resistance concentrates, a controller is especially effective. On seam-annealing inductors, C-shaped controllers over the central turn concentrate heat on the weld seam, and none are used on the return legs because the return current should stay widely distributed.
Predict first, then build
Pattern control is a design problem, and electromagnetic and thermal simulation is how it is solved without trial and error. It shows field lines, power density and temperature before metal is cut, and predicts coil temperature as well. Pair it with the right grade from the SMC product comparison . Fluxtrol’s coil design and engineering team does this work.
Talk to an engineer
Contact Fluxtrol with your part print and heat pattern specification, or order materials through the SMC order form .