White Film Casting Surface Defect and Its Possible Solutions
A joint research project investigated the possible underlying mechanisms investigated and potential solutions for reducing white film defects.
EKATERINA POTATURINA, ASK CHEMICALS GMBH, WÜLFRATH
铸件表面白膜缺陷的成因及其可能的解决方案 联合研究项目探讨了白膜缺陷产生的潜在机制及其解决方案。
维尔弗拉特, 亚世科化学有限公司，ekaterina potaturina
cases, casting defects can be successfully avoided with small measures such as adding mold material additives, replacing the binder or coating systems, changing the casting param- eters or, at a later point in time, performing additional work on the casting. One casting surface defect that can occur takes the form of white deposits or film, and removal of the defect leaves a pitted surface (Fig. 1). Tis has been a problem in metalcasting facilities for some years now and is extremely costly and time-consuming to resolve. Tis casting defect takes the form of white deposits or
I
film (Figs. 2 and 3a) and is the result of a chemical reaction that takes place in the edge zone between the liquid metal and the heated coating and mold material. Te resulting reac- tion products comprise fibrous silicon-, oxygen- and carbon- containing inclusions and amorphous silicon oxide SiOx theory states that SiOx forms along with silicon, carbon and other elements due to the reduction of silicon dioxide SiO2
. Te .
Tis casting defect can arise on coated and uncoated mold surfaces. A coating is a special substance that is applied onto the surface of the mold and core surface and has the effect of separating the iron from the mold material in order to create a flawless and smooth casting surface. Te resulting layers, which are chemical in origin, are
brittle, porous and easy to remove. Once removed, they leave behind a rough, pitted surface (Fig. 3b). As a result, the pitted surface on the finished casting has to be filled or ground, which can be time-consuming and lead to increased costs.
Fig. 1. Shown is a casting surface defect that takes the form of a white deposit and the resulting pitted casting surface.
n large-scale casting processes, different kinds of cast- ing defects can occur in all chemically bound mold materials. Teir causes lie in not only the smelting area but also the mold material and coating areas. In some
在
大批量铸造过程中，所有的化学粘结剂造型 材料都可能产生不同类型的铸件缺陷。其成 因不仅与熔炼有关，还与造型材料和涂料
有关。在某些情况下，可以通过诸如使用造型材料添加 剂、更换粘结剂或涂料体系、改变铸造参数或铸造之后 对铸件进行处理等简单措施成功避免铸件缺陷。有一种 铸件表面缺陷以白色沉积物或白膜的形式出现，消除该 缺陷会留下麻面（图1）。这是多年来一直困扰铸造厂 的问题，解决这个问题十分昂贵且耗时。 这种铸件缺陷表现为白色沉积物或白膜（图2和图 3a），由金属液与受热的涂层及造型材料之间边缘区 域内发生的化学反应引起。生成的反应产物包括含纤 维状硅、氧和碳的夹渣以及非晶硅氧化物SiOx 指出，SiO2 SiOx
。理论 在硅、碳及其他元素的还原作用下可形成
。这种铸件缺陷在有涂层和无涂层的模具表面上 都可能出现。涂料是涂覆于模具和型芯表面的特殊物 质，用于隔离铁液和造型材料，使铸件的表面光滑且 无瑕疵。
反应产生的化学层易碎、多孔且易于除去。除去后， 铸件上将留下粗糙的麻面（图3b）。因此，最终需要将 铸件上的麻面填平或磨平，这样做不仅耗时而且会增加 成本。此外，这种铸件缺陷还影响结构。例如，在球墨 铸铁中，通常能观察到石墨退化深度达0.5-1mm。石墨
图1. 所示为以白色 沉积物形式出现的 铸件表面缺陷以及 因其而产生的麻面 铸件表面。
December 2014
FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION | 61
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