Fig. 4. The casting sur- face adjacent to the silica sand exhibits burn-on, whereas adjacent to the zircon sand the casting surface was smooth.
硅砂形成的铸件表面及圆 柱空腔内都存在粘砂，而 锆砂形成的铸件表面很 光滑
affected by the mold substrate, the differences in applied layer thickness and the penetration of the coating into the mold surface were determined for each substrate. A standard zircon- based coating with an ethanol solvent was used (ISOMOL* 310PE).
Te coating was adjusted to 60 Baume and applied to a stan-
dard test-piece by dipping and dried by a subsequent ignition of the solvent.
Te coating penetration depth into the mold surface was
significantly lower for the synthetic sands when compared with silica sand, while layer thickness was equivalent in all cases (Table 3). Te zircon sand had a significantly lower penetration depth, which also resulted in an increased average layer thickness. Comparing the synthetic sands, there was a marked variation in the penetration depths with synthetic sand 3 being significantly lower than the other two samples; this can be attributed to the slightly lower AFS number, the particle size distribution, form and composition. Te investigation of widely used commercial synthetic sands
has shown that the bonded sand has a lower thermal conductivity than silica, zircon or chromite sand, providing a more insulat- ing molding material. Te refractoriness of the synthetic sand under casting conditions is significantly better than that of silica sand, but the indications are that it does not perform as well as zircon sand and the performance can depend on the particular grade of material. Standard coatings can be applied to synthetic sand molds without problems and similar layer thicknesses are achieved without modification to the coating dilution. However, penetration into the mold surface can be less than with conven- tional sand types and is effected further by the specific grade of synthetic sand. According to these results, it is possible when using synthetic sands that the solidification of the cast material will be retarded and hot spots may be formed in areas not previously observed with conventional sand types. Moreover, since the penetration of the coating into the mold surface is reduced, defects such as burn- on may arise in parts where they have not occurred previously. Consequently when a switchover from conventional sand is
made, it is recommended a coating should be selected that can compensate for the different properties of synthetic sands when compared with conventional sands. By establishing the correct synthetic sand, binder and coating combination it is possible to use a single sand type, eliminating the use of expensive special- ity sands for mold facing. Tis will allow for an optimized sand reclamation process that minimizes new sand purchases and dumping costs, while eliminating the formation of silica dust that may contribute to a respirable hazard.
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www.globalcastingmagazine.com.
涂料ISOMOL .310PE。先将涂料稀释到波美度为 60ºBe，再用标准砂样试片浸涂一遍涂料，然后点燃 干燥。
涂料渗入合成砂铸型表面的深度比硅砂铸型要小 得多，但涂层厚度却相当（表3）。锆砂铸型的渗入 深度也较小，而涂层厚度平均值有所增加。比较几种 合成砂发现，3号合成砂的渗入深度比其他两种合成 砂小得多。这可能是由于其较低的AFS细度、粒度分 布、粒形及成分不同所致。
对广泛应用的各种不同的商品合成砂调查发现， 合成砂粘结形成的砂型具有比硅砂、锆砂及铬铁矿 砂较低的导热率，是一种比较隔热的材料。合成砂 的耐火度在各种浇注条件下都大大好于硅砂，但不 如锆砂。其性能表现取决于材料的特定品级。标准 涂料用于合成砂铸型没有问题，不需改进稀释工艺 即可获得相似的涂层厚度。然而，涂料渗入铸型的 深度可能比传统的几种砂要小，并受到合成砂品级 的影响。
根据这一结果，在应用合成砂时铸件的凝固可能 会被推迟，也可能形成采用传统砂时不曾注意到的热 节。另外，由于涂料在合成砂铸型表面的渗入深度有 所降低，有些缺陷如粘砂可能会出现在原来不曾出现 的部位。
因此，当从传统砂型转换到合成砂时，建议精心 选用一种涂料，以抵消合成砂带来的一些差异。通 过正确地选用合适品级的合成砂、粘结剂及涂料之组 合，有可能实现仅使用单一砂，而避免使用昂贵的特 种砂作面砂。这样可以优化旧砂再生工艺，使新砂采 购及丢弃成本最小化，同时又可避免形成对呼吸系统 有害的硅砂粉尘。
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FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION February 2013
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