叙述了添加己内酰胺改性剂的树脂合成工艺，测得改性酚醛树脂性能为：软化点85～90℃，聚速50～60s，游离酚〈6％，粘度40～45s。介绍了热法覆膜工艺，用SWY型液压强度试验机测定了覆膜砂的抗拉强度和抗弯强度，结果表明：在相同的树脂加入量下与采用未改性的树脂比较，覆膜砂的抗拉强度提高15％，抗弯强度提高20％以上，同时型砂的溃散性得到改善，发气量也降低。
The synthesizing process of adding ethyl lactam as modifying agent to modify phenol resin was introduced： The characteristics of the modified phenol resin were test as follows： softening point 85-90℃, polymerizing time 50-60 s, dissociative phenol 〈 6%, viscosity 40-50 s. The hot coating process to make coated sand was described, and the tensile and bending strengths of the coated sand were test. The test result showed that, compared with the unmodified resin coated sand under the condition of same resin addition amount, the modified resin coated sand had higher tensile strength and bending strength by 15% and 20% respectively, and, at the same time, its collapsibility was improved, gas evolution was also reduced.
