酚醛树脂结构对树脂砂强度的影响

为提高树脂砂的强度 ,分别在 p H=14、p H=8和p H =3下 ,合成 3种碱性酚醛树脂 ,采用氢核磁谱图 (1 HNMR)和红外谱图 (IR)分析了树脂分子结构 ,并将所合成的树脂应用于 CO2 气硬冷芯盒中。结果表明 ,在 p H=14下合成的树脂分子中具有大量活性羟甲基且部分苯环以甲醚桥相连 ,其树脂砂具有较高的即时强度与终强度 ,其中最大初强度为 0 .6 4 MPa,终强度为 0 .80 MPa。在 p H=8下合成的树脂分子中虽存在大量活性羟甲基但苯环间基本上以亚甲基桥相连 ,其树脂砂抗拉强度较低。而在 p H=3下合成的树脂中基本没有活性羟甲基 ,其树脂砂即时强度最低

Influence of the phenol-aldehyde resin structure on the tensile strength of cast products

The tensile strength of foundries was improved using three alkaline phenol-aldehyde resins prepared at pH of 14, 8 and 3 as binders in the CO_2 cold-box process. The polymer structures were characterized by IR and ~1H NMR analysis. The results showed that the resin formed at pH=14 contains a large amount of active hydroxymethyl groups with the phenyl groups linked by both ether linkages and methylene bridges. Thus, the cast product had high tensile strength with the highest initial strength of 0.64 MPa and 24 h strength of 0.80 MPa. In addition to the active hydroxymethyl groups, the resin obtained at pH=8 had very few ether linkages with the phenyl groups connected mainly by methylene bridges. As a result, the cured product has low tensile strength. The resin prepared at pH=3 has very few active hydroxymethyl groups in the molecules. The resulting product has the lowest initial tensile strength of the three samples.