Jet Mill (N2 protected)

Selection criteria

Classifier speed, oxygen content of the gas, throughput.

Supply chain

Jet mills for fine NdFeB powder are led by German / Japanese powder-technology groups (Hosokawa Alpine), with Chinese makers supplying many domestic magnet plants. Particle-size distribution and oxygen control here strongly affect coercivity, so mature magnet makers invest heavily in this step.

Buyer FAQ

What particle size and distribution should the jet mill deliver?

Sintered NdFeB powder is typically milled to a median size of about 3–5 µm, controlled by classifier speed and feed rate. A narrow distribution, often tracked as D90/D10, matters as much as the median: fines oxidise and promote abnormal grain growth, while coarse particles lower coercivity. Ask for laser particle-size reports per batch.

How low must the oxygen level be?

Grinding gas is usually nitrogen with oxygen kept to a few tens of ppm or less, because fine NdFeB powder oxidises quickly and can ignite. Oxygen picked up here ends up in the magnet: conventional magnets often contain around 2000 ppm, while low-oxygen processes reach below about 1000 ppm and gain coercivity. Ask for magnet oxygen content when comparing suppliers.

What utilities and ancillaries does a jet mill need?

Plan for a nitrogen supply (PSA generator or liquid nitrogen), a gas-recirculation compressor with cooling, cyclone and filter collection, oxygen analysers and an inert-gas powder transfer system. Throughput falls sharply as target particle size gets finer, so size the mill at your finest grade. Classifier wheels and nozzles are wear parts to stock.

Where it is used