①If the difference in moisture content between the inside and outside of the blank is relatively large after the blank is ejected from the mold, the magnet will simply bubble. This is because the initial surface moisture transpiration rate of the blank is faster than the internal moisture dispersion. As time goes by, the surface moisture content decreases, and the difference between the inner and outer moisture content of the blank increases. If there is residual closed water at the base of the blank , It will foam at high temperatures. If the difference between the inner and outer moisture content of the blank is gradually reduced, the blistering is gradually reduced.
② In the second fine grinding, the larger the particle size, the simpler the dispersion of the inner and outer capillary water, and the smaller the foaming rate of the magnet.
③During sintering, there is no blistering below a certain sintering temperature. This temperature is called the blistering critical temperature. Beyond this temperature, the blistering rate will gradually increase with the increase of the sintering temperature. As the pre-sintering temperature increases, the foaming critical temperature also increases.
④ Another reason for bubbling is that after the pre-fired material is mixed with natural Fe2O3 due to crushing and grinding in the crushing technology, it will be sintered according to the reaction formula of 6Fe203 = 4Fe304 + O22Fe2O3 = 4FeO + O2. When Fe2O3 is violently reduced to FeO, if the differentiated O2 cannot be discharged, the blank will also bubble.
⑤The sintering furnace has good air permeability, and its magnets are also prone to blistering.
