Rotary Kiln (ferrite calcining)

Selection criteria

Temperature profile control, throughput, fuel and emissions, refractory life.

Supply chain

Built by Chinese kiln and thermal-equipment makers for the domestic ferrite industry, which produces most of the world's ferrite magnets. Motor makers do not buy kilns; the takeaway is that calcining consistency drives batch-to-batch magnet properties.

Buyer FAQ

Why does calcining temperature matter for ferrite magnets?

Too low a temperature leaves the ferrite reaction incomplete, and residual hematite lowers remanence. Too high a temperature produces hard, over-sintered clinker that is difficult to mill and gives coarser particles and lower coercivity. Kilns are therefore run within a narrow band around the 1,250–1,300 °C target.

What should I ask a magnet supplier about calcining?

Ask how kiln temperature is measured and logged, and how each calcined batch is checked, for example by X-ray diffraction for degree of ferritisation or by pressing and sintering test samples to measure Br and Hcj. Batch records should trace finished magnets back to the clinker lot. Large unexplained swings in magnetic properties often start here.

Do fuel and emissions affect supply risk?

Yes. Chinese environmental rules have pushed many kilns from coal to natural gas and require dust collection, and non-compliant plants have faced production stops. When qualifying a ferrite supplier, check that its calcining plant (or its clinker source) has current environmental permits and adequate dust control.

Where it is used