The benzoxazines used for precoated sand were optimally synthesized at 95℃ for three hours by measuring its gel time and soften point.The results reveal that molten viscosity keeps about 0.5 Pa·s by measuring molten viscosity-gel time curves at 90 ℃.The relationship between temperature and gel time of the benzoxazines with and without accelerating agent was investigated.In addition

the DSC curves of benzoxazines were examined.It was found that there exists a apparent thermo-positive peak

and the cured degree of the pre-coated sand is more than 90% at 200 ℃.The gel time of the resin becomes slow with temperature more than 200 ℃.The soften and cured properties of synthesized benzoxazines can meet the preparing requirement of pre-coated sand.