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Neodymium Magnets: Melt-Spun Ribbon Milled, Pressed in a Field, Sintered and Magnetised at 30 kOe (Sato, Tokin, US 4,881,986)
Squirting the molten Nd-Fe-B alloy onto a spinning copper wheel freezes it into ribbon with crystals only a tenth of a micron across. Milled fine, lined up in a magnetic field, pressed and sintered, it makes a strong anisotropic magnet, which a 30 kOe pulse then magnetises.
Result: sintered neodymium magnets, above 16 MGOe when the powder is finer than 15 microns.
Source: Sato and Tachiya, US 4,881,986 (Tokin, 1989), Example 1. Not given: magnet shape and size. Picture drawn by Youblob.
Advanced
3 days
Instructions
1
1
Melt the alloy in argon
Melt the alloy in argon
Weigh 35.0 % neodymium, 0.9 % boron (as ferroboron with 20 % B) and the rest electrolytic iron, by weight, and induction-melt them in argon into an ingot. Ours, worked out: 35 parts neodymium, 4.5 ferroboron, 60.5 iron. Sato's neodymium was 97 % (with Ce and Pr); ours is the 99 % metal.
Materials for this step:
Neodymium Metal35 parts
Ferroboron4.5 parts
Electrolytic Iron60.5 partsTools needed:
Balance Scale
Induction Furnace
Pressure Gas Cylinder2
2
Melt-spin a ribbon
Melt-spin a ribbon
Remelt in argon and squirt the alloy through a small orifice onto a copper wheel whose rim moves at 15 m/s. It freezes into ribbon about 5 mm wide and 100 microns thick, with R2Fe14B grains about 0.1 micron.
Tools needed:
Induction Furnace
Melt SpinnerPressure Gas Cylinder3
3
Ball-mill to powder
Ball-mill to powder
Crush and ball-mill the ribbon. Particle size: Sato made 0.5 to 30 microns; below 15 microns the magnet tops 16 MGOe, better below 10, best at 5 microns or less.
Tools needed:
Iron Ball Mill4
4
Press in a 20 kOe field and sinter
Press in a 20 kOe field and sinter
Press the powder at 1 ton/cm² in a 20 kOe field. Sinter at 1,050 °C for 1 hour in vacuum and 1 more hour in argon, then quench; age at 630 °C for 1 hour in argon.
Tools needed:
Magnetic-Field Press
Tube Furnace
Vacuum PumpPressure Gas Cylinder5
5
Magnetise at 30 kOe
Magnetise at 30 kOe
Magnetise the sintered body in a field of about 30 kOe.
Tools needed:
MagnetiserMaterials
3- 35 partsPlaceholder
- 4.5 partsPlaceholder
- 60.5 partsPlaceholder
Tools Required
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