Method and an apparatus for manufacturing an R-Fe-B sintered magnet

A method of manufacturing a plurality of R—Fe—B sintered magnets using a plasma flame apparatus and a furnace, the plasma flame apparatus having a plasma torch connected to a chamber and including a reaction gas, a carrier gas, and a cooling gas connected to the plasma torch, said method comprising the steps of:

• providing a sintered magnet block having a composition of R1-T-B-M1 with R1 being present between 25 wt. % and 40 wt. % based on the total weight of the composition, M1 being present between 0 wt. % and 4 wt. % based on the total weight of the composition, B being present between 0.8 wt. % and 1.5 wt. %, and the balance being T, wherein R1 is at least one rare earth element selected from a group consisting of Sc and Y, T is a transition metal selected from a group consisting of Fe and Co, B is Boron, M1 is at least one element selected from a group consisting of Ti, Zr, Hf, V, Nb, Ta, Mn, Ni, Cu, Ag, Zn, Al, Ga, In, C, Si, Ge, Sn, Pb, N, P, Bi, S, Sb, and O;
• machining the sintered magnet block to form a plurality of machined magnets;
• cleaning surfaces of the machined magnets to form a plurality of cleaned magnets;
• depositing a plurality of spherical droplets of a heavy rare earth powder selected from a group consisting of Dy and Tb on the surfaces of the cleaned magnets in the chamber of the plasma flame apparatus under an inert atmosphere of Argon and in a predetermined pattern to produce a plurality of magnets including a uniform film of Dy or Tb;
• and
• sintering the magnets including the uniform film in the furnace under a negative atmosphere or an inert atmosphere and at a sintering temperature and a sintering pressure to diffuse the uniform film into the magnets through grain boundary phases of the magnets to produce the R—Fe—B sintered magnets;
• wherein said step of depositing further comprises the steps of:
• subjecting the heavy rare earth powder having a mesh size of between 50 mesh and 200 mesh to a plasma spheroidization process using the plasma flame apparatus to form the plurality of spherical droplets:
• transferring the heavy rare earth powder to the plasma torch using a carrier gas, a reaction gas, and the cooling gas, the carrier gas at a flow rate of between 2 L/min and 10 L/min, the reaction gas at a flow rate of between 8 L/min and 20 L/min, and the cooling gas at a flow rate of between 10 L/min and 30 L/min, whereby the heavy rare earth powder is being transferred at a flow rate of between 5 g/min and 20 g/min;
• maintaining a predetermined Argon pressure of between 0.1 k Pa and 0.1 MPa and an oxygen content of between 0 ppm and 500 ppm in the chamber:
• and adjusting a position of the plasma torch relative to the cleaned magnets to define a distance of between 5 mm and 20 mm between the cleaned magnets and the plasma torch.