SLURRY BEHAVIOUR(浆料的性能)

本文节选自《INVESTMENT CASTING》一书中Investment Material and Ceramic Shell Manufacture一节。

Although most slurry compositions are simply mixtures of binder and ceramic powder, with small quantities of additives to enhance slurry behaviour in specific ways, their rheology is highly complex and is influenced not only by the ingredients but by a number of external factors.

尽管大多数浆料组合只是粘结剂和陶瓷粉末的简单混合物，并添加少量添加剂以特定方式增强浆料性能，但其流变学特性非常复杂，不仅受成分影响，还受多种外部因素影响。

Primary and secondary coat slurries have slightly different requirements for the manufacture of the mould. Perhaps the most important slurry is that for the primary coat, because much of the non-conformance that can be attributed to the mould is derived from deficiencies in this coat. Only in those processes where moulds are expected to hold large volumes of metal, or to withstand very high temperatures for long periods (as in directional solidification) do we see casting non-conformance, particularly dimensional control, being influenced significantly by the back-up coats.

面层和第二层浆料在型壳制造中的要求略有不同。也许最重要的浆料是面层浆料，因为型壳中出现的大多数缺陷都源于面层涂层的缺陷。只有在那些型壳需要容纳大量金属液或长时间承受高温（如定向凝固）的工序中，我们才会看到铸造出现缺陷的情况，特别是尺寸控制方面，受到背衬涂层的显著影响。

From the aspect of maintaining a stable, homogeneous mixture in the slurry tank, we have already noted some major differences in binder chemistry as between alcohol and water based slurries, that can affect changes in the slurry due to external influences. Because most primary coat formulations use a water based colloidal silica sol, only this type of primary coat will be considered, but comments will be extended to both binder systems for secondary coats.

从保持浆料桶中呈稳定且均匀的混合物角度来看，我们已经注意到，醇基和水基的黏结剂在化学方面存在一些主要差异，这些差异可能导致浆料在外部影响下发生变化。由于大多数面层涂层配方都使用水基胶体二氧化硅溶胶(硅溶胶)，因此仅考虑这种类型的面层涂层，但关于二层涂层的讨论将扩展到两种黏结剂体系。

The primary coat slurries eventually provide the ceramic face of the mould in contact with the molten alloy, and as surface finish will be an important characteristic of the casting, great attention must be given to the nature of the ceramic filler. The density of the filler and its particle size distribution will affect slurry behaviour. The higher-density fillers such as zircon or alumina will tend to sediment faster than alumino-silicate or silica fillers. As might be expected, the design and agitation characteristics of the mixing tank will also influence the homogeneity of the slurry. It is obviously highly desirable in all slurries to ensure full dispersion and to avoid sedimentation and entrapped air.

面层浆料最终为型壳提供与熔融金属液接触的型壳表面，并且由于表面光洁度将是铸件的重要特性，因此必须高度重视面层粉料的性质。面层粉料的密度及其粒径分布会影响泥浆的性能。高密度粉料（如锆英或氧化铝）的沉淀速度往往比铝硅酸盐或二氧化硅粉料快。不出所料,浆筒(搅拌桶)的设计和搅拌特性也会影响浆料的均匀性。显然，在所有浆料中，确保充分搅拌均匀，避免沉淀、空气滞留都是非常必要的。

Because there are endless permutations and combinations of slurry composition, mixing method and external influences, it is possible to create a'knife edge'situation, whereby a number of factors unite to create conditions in which the slurry is difficult to maintain in a homogeneous state. These critical combinations of variables can lead to sudden sporadic increases in cast scrap although 'nothing has been altered'.

由于浆料配比、混合方法和外部影响的排列组合的方式无穷无尽，因此可能会出现“刀刃边缘”情况，即多个因素共同作用，导致浆料难以保持均匀状态。这些关键变量组合可能导致铸件废料突然零星增加，尽管我们觉得“未进行任何更改”。（1）

上面最后一段可以解释我们经常说的，我们一直没有变，但为什么产品出现了变异。熔模铸造影响因素繁多，各种各样的因素排列组合的方式同样不可胜数，所以，抓细节就是熔模铸造的核心。