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Fig. 2. This is a casting defect that takes the form of a white film with black inclusions.


图2. 以带有黑色夹渣 的白膜形式出现的铸件 缺陷。


Te casting defect also affects the structure. In the case of iron with nodular graphite (nodular casting), for example, graphite degradation to a depth of 0.5–1 mm normally can be observed. Graphite degradation describes a degraded graphite layer, in the form of a lamellar graphite seam, on the surface of the nodular casting. Tis casting defect usually arises on chemically bound


furan and phenolic resin mold materials, in iron with nodular graphite and in cast iron with lamellar graphite. Te furan resin process is a self-curing process with organic binding agents. Te furan resin mold materials are cured through the addition of para toluene sulfonic or phosphoric acids at room temperature. Te binders pyrolize when the molds made from furan resin mold materials are cast. Pyrolysis refers to the thermochemical decomposition of organic compounds. Gasification and combustion occur due to the effects of


heat, without the addition of oxygen. Te carbon reacts with free oxygen and forms toxic gases such as CO. Te remaining carbon stays in the system and continues to undergo reac- tion. Here, the carbon can reduce the SiO2


content, leading


to the formation of SiO. Te SiO compound is stable at high temperatures and, at room temperature, can disproportionate in line with the Boudouard equilibrium of the carbon [3]: 2SiO ↔


Si + SiO2 .


Te casting defect that takes the form of white film/ deposits with black inclusions usually occurs under the con- ditions described in Table 1. Figure 4 shows the white film. Te piece was examined


under a scanning electron microscope (SEM) from the mold material side in the direction of the iron. In preparation for the examination, this single piece was cut into three small pieces, which were adhered onto the stage, metallized with gold and subsequently analyzed. Te enveloped


sand grains with coatings can be seen in Figure. In


退化表现为退化的石墨层,以层状石墨层的形式出 现在球墨铸铁表面。


在球墨铸铁中呈片状石墨,这种铸件缺陷通常出 现在化学粘结剂的呋喃和酚醛树脂造型材料上。呋 喃树脂工艺是使用有机粘合剂的自硬化工艺。室温 条件下,呋喃树脂造型材料通过添加对甲苯磺酸或 磷酸固化。由呋喃树脂造型材料制成的砂型在成型 时粘合剂会热解。热解是指有机化合物受热分解。 无需加入氧气粘合剂就会受高温影响发生气化 和氧化。碳与游离氧发生反应,产生如CO的有毒 气体。剩余的碳保留在体系中,继续发生反应。在 此,碳元素会还原SiO2


在高温下非常稳定,但在室温下会按照对应的碳平 衡发生歧化反应[3]:2SiO↔Si+〖SiO〗2





这种表现为白膜/沉积物、带有黑色夹渣的铸件缺 陷通常在表1所述的条件下出现。


图4所示为白膜。在扫描电子显微镜(SEM) 下,从造型材料一侧,向铁金属方向检测铸件。在 检验的准备过程中,该铸件被截为三片,并粘合在 一起,使用黄金将其金属化后进行分析。 图中可以看到被涂层包裹的砂粒。在详图(图 5a)中,光谱1显示了附着碳和铁夹渣的砂粒。此 外,从分析中还能看到含有硫和碳成分的砂粒(光


,导致生成SiO。化合物SiO


Fig. 3. In the left image, the casting defect is shown on the casting. In the right image, the cast- ing surface following the removal of the casting defect is shown.


图3. 左图所示为铸 件上的缺陷。右图所 示为除去铸件缺陷后 的铸件表面。


62 | FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION December 2014


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