Fig. 2. To measure the heat conducting properties of the different sands, test pieces were placed on a heat source.


为测定不同砂的导热性能，将试块放于 某一热源处.


form compared with both silica and chromite sand, and it follows that the performance of the mold coating may differ in terms of application properties and casting surface finish. On determining the composi-


tion of the synthetic sands by means of X-ray diffraction, commercially used silica, zircon, chromite and synthetic sands were all found to be alumina silicates. Furthermore, all of the synthetic sands have a distinct spherical form (Fig. 1). To measure the heat conducting properties of the different


sands, test pieces were placed on a heat source (Fig. 2), and temperature at a set point within the test piece was recorded using a thermocouple and data recorder. When comparing the recorded temperature within the test pieces after they had been located on the heat source for 5 minutes, the temperature was lower with all of the syn- thetic sands than with silica sand. Te highest temperature was achieved with the zircon sand. From these results it was concluded the thermal conductivities of the synthetic sands were lower than that of silica sand and significantly lower than that of zircon sand.


Casting tests with uncoated molds were conducted to evalu-


ate the refractory performance of the synthetic sands. A furan mold was constructed to produce a hexagonal cross-sectioned casting with each side measuring 350mm wide by 720mm high, and incorporating two cylindrical cores in each side (Fig. 3). Te cores forming each side were made of different base sands, including silica, zircon, chromite and synthetic sands. Te cast- ing was poured using standard carbon steel at 1,650C, and the resultant casting weighed 110kg. Te casting surface adjacent to the silica sand exhibits


burn-on, both on the hexagonal face and within the cylin- drical indentation, whereas adjacent to the zircon sand the casting surface was smooth (Fig. 4). Both samples 1 and 2 of the synthetic sands showed some burn-on in the cylindri- cal indentation and on the hexagonal face. Te third sample showed a clean defect free surface. Te chromite sand had a similar performance to the synthetic sand samples 1 and 2, with a rougher surface finish than either zircon or synthetic sand 3 and some minor burn-on defects.


Application of mold coatings to synthetic sand molds To establish whether the application per-


formance of a mold coating could be adversely


应用性能及铸件表面光洁度等 方面的表现也不尽相同。


硅砂、锆砂、铬铁矿砂及合 成砂的性能见表1。为确定合 成砂的成分，通过 X-光衍射 对其进行分析，发现所有合成 砂都属铝硅酸盐。另外，合成 砂都呈独特的球形（图1）。 为测定不同砂的导热性能， 将试块放于某一热源处（图


2），并通过热电偶及记录仪记录试块内特定点的温 度。


试块放置于热源上5分钟后，比较其内部测量点的 温度发现，所有合成砂试块内的温度都低于硅砂试块 内的温度。锆砂试块内的温度最高。这些结果表明合 成砂的导热性能低于硅砂，大大低于锆砂。 为评定合成砂的耐火性能，对未刷涂料的合成砂铸 型进行了浇注试验。用呋喃树脂砂制成一六角截面的 铸件。每个面宽350mm，高720mm ，各有两个圆 柱砂芯。形成每个面的砂芯采用不同的砂子，包括硅 砂、锆砂、铬铁矿砂和合成砂。浇注的铸件均为标准 碳钢材质，重110公斤。


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（图4）。由合成砂制成 的两个砂芯试样1号及2号在圆柱空腔内及平面上都有 一些粘砂。第三个合成砂试样无缺陷。铬铁矿砂结果 与合成砂1，2号相类似，铸件表面比合成砂3号试样 的更粗糙，而且有少量粘砂。


合成砂表面涂料的应用


为了确定铸型基底是否会反过来影响涂料的应用 性能，测定了不同基底情况下涂层厚度及渗入铸型 表面的深度。试验采用了一种标准的乙醇基锆英粉


Fig. 3. A furan mold was constructed to produce a hexagonal cross-sectioned casting with each side measuring 350mm wide by 720mm high.


用呋喃树脂砂制成一六角截面的铸件。每个 面宽350mm，高720mm ，各有两个圆柱 砂芯。


February 2013 FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION | 65


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