Abstract: Four kinds of inorganic ammonium salts such as: NH4F, NH4Cl, (NH4)2SO4 and NH4HCO3 were added on low-temperature sintering vitrified bond CBN wheels at different mass percentage. Their performing effects were evaluated by testing their porosity, bending strength and bending fractures observed using SEM. The experimental results show that NH4Cl is not an ideal pore-forming agent for it causes the wheel cracking; the pore-forming effect of NH4f is not obvious, so it is not a suitable alternative. The mass percentage of (NH4)2SO4 should be controlled to ＜ 5%, when the mass percentage reaches 5%, the porosity of sample is 36.14% and its bending strength is 29.03 MPa; the pore size is small and can be poorly adjusted. The mass percentage of NH4HCO3 should be less than 15%; when the mass percentage is 5%, its porosity is 34.19% and the bending strength is 40.32 MPa; while the mass percentage reaches 15%, its porosity can reach 42.5% and its bending strength is 29.16MPa; and within this amount the proportion of big pore increases as the addition amount increases and the pore sizes are well adjusted.

Keywords: pore-forming agent with inorganic ammonium salts        porosity       bending strength        vitrified bond CBN wheel