Te detailed casting defect investigation and the theory behind this phenomenon show that the primary cause of this defect is the organic binding agent in the mold mate- rial. If this were to be completely removed from the equa- tion, this defect could be avoided or its severity reduced. To test this, a series of experiments were conducted with the inorganic binder. A second cause to be considered is the melt. Te greater the proportion of alloy elements such as cop- per, manganese, etc. in the melt, the less severe the casting defect, if it occurs at all. In practice, however, the options are limited because a different kind of alloy with different properties would be created. Another cause to be considered is the coating. Of course, this plays a more important role in the process because it can have both a positive and negative impact on the severity of the casting defect. Several series of experiments were conducted in order to identify and remove the “pollutants” in the coating. Te experiments were divided into three main groups: binder experiments in the mold material area; testing of the coatings with a primary and secondary component of silicon; and admixture of different fireproof materials in the coatings. Following the experiments, the metallization layers under- went SEM, macro image and mapping analyses because the casting defect was hardly observed at all on the cast side and instead only a pitted casting surface was formed. Figure 8 shows a diagram illustrating the severity of the defect with respect to the mold material and casting surface. In the experiments in the mold material area with inorganic rather than organic binders, a positive effect on reducing the severity of the defect was observed. Te casting surface was free of defects and did not exhibit any holes or pitting. Tese experiments confirmed that the carbon- containing atmosphere that forms when organic binders are combusted has a negative influence on the emergence of this casting defect. Inorganic technology is currently limited in its application because the use of inorganic binders under extreme thermal conditions leads to severe sintering of the mold material.
Summary Te casting defect that takes the form of a white film
usually occurs with chemically bound furan and phenolic resin mold materials. Te alloy also plays an important role:
解决方案。
详细的铸件缺陷研究及该现象背后的原理表明， 该缺陷的主要成因是造型材料中的有机粘结剂。如 果从反应式中完全移除有机粘结剂，应该可以避免 该缺陷或降低其严重程度。为此，使用无机粘结剂 进行了一系列的实验测试。该缺陷的次要原因是熔 体。熔体中合金元素如铜、锰等的含量越高，铸件 缺陷（如果出现的话）的严重程度越低。但在实际 中，该选项的应用非常有限，因为会产生性质不同 的合金。另一个需要考虑的原因是涂层。当然，涂 层在铸造工艺中有着更重要的作用，因为它对铸件 缺陷的严重性可能产生积极或消极的影响。为了识 别并消除涂层中的“污染物”，进行了大量实验。 这些实验主要分为三组：造型材料方面的粘结 剂实验；测试以硅作为主要和次要成分的涂料；以 及在涂料中掺杂不同防火材料。实验后，对金属化 层进行SEM、放大影像和图解分析，因为很难在铸 件侧观察到铸件缺陷，它只在铸件表面形成一个麻 面。图8所示的图表说明了缺陷的严重程度与造型材 料和铸件表面的关系。
在造型材料的实验中，使用无机粘结剂替代有机 粘结剂时可观察到其对降低缺陷严重程度的积极作 用。铸件表面无缺陷，也没有出现洞或孔。这些实 验表明，有机粘结剂氧化时产生的含碳环境对这种 铸件缺陷的出现有不利影响。但目前，无机粘结剂 技术的应用仍然存在限制，因为在极端热条件下， 使用无机粘结剂会导致造型材料的严重烧结。
总结
表现为白膜的铸件缺陷通常在使用化学粘结剂 呋喃和酚醛树脂造型材料时出现。合金的作用也很
Fig. 8. The diagram illus- trates the development of the casting defect from the mold mate- rial and casting surface sides.
图8. 该表展示了因造 型材料和铸件表面的铸 件缺陷的形成。
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FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION December 2014
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