Sintered Ferrite Magnet (arc segment)

Process flow

6 main process steps, with the equipment and instruments used at each step, their main suppliers, and the technical control points.

1. 1

   Mixing & calcining

   Iron oxide is mixed with strontium (or barium) carbonate and calcined in a rotary kiln into ferrite clinker.

   ⚙ Rotary Kiln (ferrite calcining)Automated

   International

   To be added

   Mainland China

   To be added

   Technical control points:

   • ▪Raw material purity and ratio — Per formula; Fe₂O₃ purity and impurity limits per specificationCheck: Incoming certificate and lab analysis per lot
   • ▪Calcining temperature and conversion — About 1,250–1,300 °C; full ferrite phaseCheck: Kiln temperature log; magnetic or XRD check of clinker
2. 2

   Wet milling

   Clinker is milled in water with additives (CaCO₃, SiO₂) to a fine slurry.

   ⚙ Wet Ball Mill / AttritorSemi-automatic

   International

   To be added

   Mainland China

   To be added

   Technical control points:

   • ▪Particle size — About 0.8–1.0 µm averageCheck: Fisher sub-sieve sizer or laser diffraction; each batch
   • ▪Slurry solid content — Per process sheetCheck: Drying and weighing; each batch
3. 3

   Wet pressing in a magnetic field

   The slurry is pressed in a die under a magnetic field to align the particles, while water is drawn off by vacuum. This makes the magnet anisotropic.

   ⚙ Magnetic-field Orientation PressAutomatedSemi-automatic

   International

   To be added

   Mainland China

   To be added

   Technical control points:

   • ▪Orientation field — Per process sheet, strong enough to saturate the alignmentCheck: Gaussmeter check each shift
   • ▪Green density and cracks — Per process sheet; no laminations or cracksCheck: Weighing and visual check; sampling
4. 4

   Sintering

   Green parts are sintered in air in a roller or tunnel kiln and shrink to near-final size.

   ⚙ Roller / Tunnel Kiln (ferrite sintering)Automated

   International

   To be added

   Mainland China

   To be added

   Technical control points:

   • ▪Sintering profile — About 1,180–1,250 °C; profile per gradeCheck: Kiln thermocouple log; continuous
   • ▪Shrinkage and warping — Within grinding allowanceCheck: Dimensional sampling each batch
5. 5

   Grinding

   Inner and outer arcs, ends and chamfers are ground to size.

   ⚙ Slicing, Grinding & Wire-cut MachinesAutomatedSemi-automatic

   International

   To be added

   Mainland China

   To be added

   Technical control points:

   • ▪Arc dimensions and thickness — Per drawing (thickness typically ±0.05 mm)Check: Gauges; first piece and sampling
   • ▪Chipping and cracks — Per limit sampleCheck: Visual check; 100% or sampling
6. 6

   Final inspection

   Magnetic properties, dimensions and appearance are checked before packing.

   ⚙ Hysteresisgraph (BH tracer)Test instrumentSemi-automatic

   International

   Magnet-Physik, Brockhaus Measurements

   Mainland China

   To be added

   ⚙ CMM, Roundness & Runout GaugesTest instrumentSemi-automaticManual

   International

   MitutoyoDongguan, HexagonGuangzhou, MarpossShenzhen+1 more →

   Mainland China

   To be added

   Technical control points:

   • ▪Magnetic properties — Per grade, e.g. Y30BH Br about 0.38–0.40 TCheck: Hysteresisgraph on samples per batch

Incoming inspection & approval tests

• Br, HcB, HcJ and (BH)max per gradeIEC 60404-8-1; hysteresisgraph on samples per batch
• Dimensions: arc radii, thickness, length, chamfersPer drawing; gauges and optical measurement
• Appearance: cracks, chips, edge breakagePer drawing or customer limit sample
• Low-temperature demagnetization checkCoercivity at the minimum operating temperature (ferrite HcJ falls when cold)

Buyer FAQ

Why use ferrite instead of NdFeB?

Ferrite costs a fraction as much, does not corrode and does not need plating, and its coercivity rises with temperature. It is the standard for brushed DC motors, fans and appliance motors where size is less critical than cost.

What is the main risk with ferrite arcs?

Demagnetisation at low temperature (coercivity drops in the cold) under high starting or stall current, and chipping during handling and assembly. Check the grade's HcJ at your minimum temperature and inspect edges.

Which tolerances matter?

Inner and outer radius, chord width and length — they set the air gap and how the arcs fit the can — plus magnetic properties (Br, HcJ) per lot.