TECHNICAL DATA
Magnetic Yoke Design and Manufacturing
Why is a magnetic yoke used in an induction furnace?
The coil is surrounded by laminated silicon steel. The stack pulls leakage flux into a closed path through the melt, keeps the steel shell cooler, and braces the coil against electromagnetic force.
How does a magnetic yoke reduce flux leakage?
Grain-oriented sheet has high permeability along the rolling direction. Arc stacking keeps that direction following the coil, so the joint does not saturate locally and no-load loss stays lower. A phlogopite mica sheet separates stainless covers from the laminations.
Directional silicon steel for magnetic yokes
Grades used on current builds include Nippon Steel grain-oriented sheet, Nippon Steel 0.23-80, grade 230, and 23RJ100, alongside WISCO cold-rolled sheet. Each sheet is checked before it goes into the stack.
Water-cooled magnetic yoke structure
Water runs in a channel, a tank, or a dual circuit welded to stainless plate. The 12 ton reinforced channel is made for higher flow and less scale. The 15 ton yoke omits the cover plate so the stainless does not sit as a continuous eddy path on the laminations.
Copper tube embedded magnetic yoke
Copper conducts heat away from the sheet more directly than a distant channel. On the 30 ton yoke the tubes are arranged 4 in / 4 out and 3 in / 3 out. On the 20 ton yoke the cover plate is left off, two shielded copper tubes sit inside, and a copper shield runs beside the leads.
Stainless steel tube embedded magnetic yoke
A welded water pocket can crack, and a stainless plate can pit by electrolytic corrosion. Stainless tubes, clamped rather than used as a water box, avoid both. The 20 ton build also uses step-lap joints and copper shield plates beside the leads. The 3 ton melting-furnace yoke uses the same tube idea with a hydraulic arc stack.
Magnetic yoke cooling system
Every water circuit is pressure-tested and flow-tested before the yoke leaves the shop. The aim is a stack that stays near ambient temperature, so it does not grow, loosen the bolts, or rust on the cut face.
Magnetic yoke assembly and clamping
Sheets are stacked on a locating fixture so the arc matches the coil. Clamps are stainless. Bolt counts on current jobs run from 4 bolts on smaller yokes to 6 bolts, 4–8 bolts, and 10 bolts M20 on the 60 ton yoke. The 5 ton yoke uses 4 demagnetized stainless through-bolts.
Magnetic yoke replacement
A replacement is dimensioned from the furnace that is already installed: capacity, frequency, power, coil diameter and height, number of yokes, cooling method, and photos or a drawing of the old yoke. The new stack is matched to that coil rather than taken from a generic catalogue size.