In the production of permanent ferrite magnets—widely used in motors, speakers, and magnetic separators—the sintering process is a critical phase where material quality is determined. One often overlooked but vital component? The sintering tray. While many manufacturers still rely on standard ceramic trays, industry leaders now recognize that high-purity composite corundum-mullite trays are not just an option—they’re a necessity.
During sintering, ferrite magnets are exposed to temperatures between 1150°C and 1250°C in a reducing atmosphere (typically H₂ or N₂ + H₂ mix). Ordinary alumina-based trays may decompose under such conditions, releasing aluminum oxide dust that contaminates the magnet surface. According to internal data from a leading Chinese magnet producer, using substandard trays increased metal impurities by up to 0.7%—a level that directly impacts coercivity and magnetic performance.
| Tray Material | Porosity (%) | Thermal Shock Resistance (°C) | Metal Contamination Risk |
|---|---|---|---|
| Standard Alumina | 12–15% | ≤ 400 | High |
| Composite Corundum-Mullite | ≤ 3% | ≥ 600 | Very Low |
Another hidden failure mode: thermal stress-induced micro-cracks. When trays expand unevenly due to poor thermal conductivity, they can crack during heating or cooling cycles—creating pathways for contaminants. A case study from a European motor manufacturer showed that switching to high-purity trays reduced magnet inclusion defects from 8.2% to 1.5% over six months.
“After implementing corundum-mullite trays, our yield improved by 12%, and we saw fewer complaints about inconsistent magnetic output.” — Lin Wei, Process Engineer at Zhongshan Magnetic Tech
For companies aiming for consistent product quality, especially those exporting to EU or North America, understanding tray chemistry isn’t optional—it’s part of compliance with ISO 9001 and IEC standards. Even minor contamination can lead to rejection at final inspection. The solution? Use trays with ≥98% purity of corundum and mullite phases, which offer superior resistance to both chemical attack and mechanical fatigue.
If you're experiencing issues like surface oxidation, sticking residues, or unexpected cracks in your ferrite magnets, it might be time to re-evaluate your sintering tray selection. Our technical team has helped over 50 global clients optimize their kiln furniture setup—and we’d love to do the same for you.
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