Jet Milling: Refinement Technique for NdFeB Powder

In our previous newsletter, we learned that we can obtain the magnetic powder with a diameter of approximately 100μm after hydrogen decrepitation of NdFeB metal ribbons. However, that is not enough, for the production of NdFeB magnets, further refinement of powder granularity is required. Hence, to achieve this, the powder refinement technique of "jet milling" has been developed.

Jet milling is a novel powder production method that utilizes high-pressure airflow (typically high-purity nitrogen gas) to accelerate powder particles to supersonic speeds within the jet milling chamber, causing them to collide and shatter. The process involves mixing the hydrogen-broken metal ribbons with a certain proportion of grinding aids, then adding them into the jet milling feed hopper. A precise amount of powder is fed into the milling chamber, where high-pressure nitrogen gas is ejected from nozzles, accelerating the material to supersonic speeds, forming a fluidized bed. The particles collide and break, resulting in particle diameters of less than 10μm. By controlling parameters such as milling time, pressure of chamber, the speed of wind-selection-wheel, specific average particle sizes can be achieved through jet milling.

The powder produced by jet milling is non-uniform and requires further mixing. Before mixing, a certain proportion of additives is added to the tank according to the process, to control oxygen content and improve molding orientation performance.

Stay tuned for more in-depth knowledge of NdFeB by following us.