Method for manufacturing rare earth permanent magnet

A method for manufacturing a rare earth sintered magnet, the method comprising the steps of:

• preparing a rare earth alloy comprising xwt % RE-ywt % B-zwt % TM-bal.wt % Fe wherein RE is a rare earth element, TM is a 3d transition element, x=28˜35, y=0.5˜1.5 and z=0˜15;
• coarsely pulverizing the prepared rare earth alloy;
• finely pulverizing a powder of the pulverized rare earth alloy which has been coarsely pulverized, repetitively 2˜10 times, using a jet mill method;
• aligning and compacting the finely pulverized rare earth alloy powder in a magnetic field, to be magnetized;
• performing a hydrogenation-disproportionation-desorption-recombination (HDDR) process to a compact which has been magnetized;
• sintering the HDDR processed compact;
• and
• loading a sintered alloy into a heating furnace to be heat-treated under a vacuum or in an inert gas atmosphere, thereby forming the rare earth sintered magnet,
• wherein the finely pulverizing step comprises a first pulverizing process and a second pulverizing process,
• wherein, in the finely pulverizing step, classification of the finely pulverized powder of rare earth is carried out at a rotational speed of 2,000˜8,000 rpm in each classifying section and nitrogen gas is supplied to the classifying section at an atmospheric pressure 6˜10 atm,
• wherein, in the first pulverizing process, classification is carried out at a rotational speed of 2,000˜8,000 rpm, such that an average particle size of the rare earth powder discharged at an outlet in the classifying section is 3˜15 μm,
• wherein, after repeating the first pulverizing process 2 to 4 times, classification is carried out at a rotational speed of 8,000 rpm, such that the average particle size of the rare earth powder discharged at the outlet in the classifying section is 1˜4 μm,
• wherein, in the finely pulverizing step, an ultra-fine powder resulting from the pulverizing process is removed through the rotational speed in the classifying section during each pulverizing process whenever jet milling is performed, and
• wherein, in the HDDR process performing step, the magnetized compact is loaded into a vacuum furnace for vacuum-exhaust to be heated at 700˜900° C. and maintained for 1˜3 hours by changing the vacuum furnace atmosphere to a hydrogen atmosphere of 0.2˜0.5 atm, and subsequently to be heated at the same temperature for 10 minutes to 1 hour by changing the hydrogen atmosphere of 0.2˜0.5 atm to a vacuum atmosphere.