Ferromagnetic abrasive shot for treating printed circuit boards - in magnetic field, consists of aluminium and silicon oxide, carbide, nitride, and phosphide in ferrous alloy

摘要

The abrasive consists of a ferromagnetic alloy contg. by wt. 75-97% Fe, 0.2-16% Al, 0.2-18% Si, 0.005-1.5% P, 0.005-4% C, 0.05-3% O2, and 0.01-0.5% N2; and included in the above is 0.01-5% of the oxides, carbides, nitrides and phosphides of Al and Si as abrasives. The abrasive is pref. made by melting an alloy of Fe-Al-Si-P and heating it to 50-200 degrees C. above its initial crystallisation temp.; carbon is added to the melt, which is then converted into shot of below 1.5mm size by the gas stream. The gas contains by wt. 99.999-75% N2 and 0.001-25 wt.% O2, and is used at 2-20 atmos. and a speed of 150-500 metres/second to make the shot, which is cooled to room temp. The abrasive polishes the surface of components and produces very low surface roughness if required. Compared with known abrasives used in magnetic grinding, the invention uses only a small amt. of diamagnetic particles, and the shot has high hardness and strength.