Ferrite Magnets Manufacturer in China

Step-by-Step Manufacturing Process of Ferrite Magnets

1. Raw Material Preparation

The foundation is high-purity raw materials: iron oxide (Fe2O3, about 80-90%), strontium or barium carbonate (10-20%), and minor additives like silica or calcium oxide for enhanced properties.

• Materials are weighed precisely and often pre-milled to ensure uniformity. Impurities are removed to prevent defects in the final magnet.
• For strontium Ferrite (more common and stronger), SrCO3 is the key additive.

This step sets the stage for a consistent chemical composition, crucial for magnetic performance.

2. Mixing and Calcination

The powders are wet-mixed in a ball mill with water to form a slurry, ensuring even distribution.

• The slurry is dried and then calcined (pre-sintered) in a rotary kiln at 900-1,200°C for 1-2 hours. This decomposes carbonates and forms the ferrite phase (e.g., SrFe12O19).
• Calcined material is crushed into coarse particles, creating a “clinker” ready for finer processing.

Calcination drives off volatiles and initiates the magnetic compound formation—think of it as baking the “dough” for your magnet.

3. Fine Milling and Powder Refinement

The calcined clinker is ball-milled again (wet or dry) to reduce particle size to 0.5-2 microns, producing a fine powder.

• Additives like dispersants or binders may be included to improve flow.
• For anisotropic magnets, the powder is aligned later, but here it’s prepared for pressing.

This ultra-fine powder ensures dense compaction and optimal sintering.

4. Pressing and Compaction

The powder is compacted into shapes using hydraulic presses under 100-500 MPa pressure.

• Dry pressing (with binders) or wet pressing (in slurry form) is used for shapes like blocks, rings, or arcs.
• For anisotropic Ferrites, a magnetic field (up to 10,000 Oe) is applied during pressing to align particles, enhancing magnetism in one direction.

The “green” compact is fragile but holds the desired form, with densities around 50-60%.

5. Sintering

The green parts are sintered in a tunnel or box furnace at 1,100-1,300°C for 1-4 hours in an air or controlled atmosphere.

• This fuses particles into a solid ceramic, achieving 90-95% density.
• Slow cooling prevents cracking, and the process refines the crystal structure for peak coercivity.

Sintering is the heart of the process, transforming powder into a hard, permanent magnet.

6. Machining, Magnetization, and Testing

Ferrites are brittle, so machining uses diamond grinding or ultrasonic tools for final shaping and smoothing.

• The magnet is magnetized in a strong electromagnetic field to align domains.
• Quality testing measures properties like remanence (Br), coercivity (Hc), and energy product using permeameters. Visual inspections check for cracks or uniformity.

Optional coatings (e.g., paint) add protection, and the magnets are ready for use!