Fig. 1. The 20.2-lb. (9.1 kg) alu- minum A356 water turbine blade is 36.6 in. (930 mm) long, with thick- ness ranging from 1.7 in. (44 mm) to 0.5 in. (13 mm).
图1：20.2磅（9.1千克）的A356铝合 金水轮机叶片长度为36.6英寸（930毫 米），厚度从1.7英寸（44毫米）至0.5 英寸（13毫米）。
for the casting process, the Centre de Métallurgie du Québec examined two methods for production—sand casting using traditional gating and sand casting with the direct pour method. If the metallurgical properties were found to be similar for the two filling procedures, direct pour technology would make the molding much easier in a smaller flask while increasing the yield and eliminating finishing costs. In their study, the researchers compared the optimal
operational parameters, such as pouring temperature and pouring time, for both methods. Metallurgical properties, including dendrite fineness (secondary dentrite arm spac- ing) and microporosity along with tensile properties, were measured at 13 locations.
Traditional Gating vs. Direct Pour Mold Filling Te wedge-shaped aluminum blade is a perfect geometry
for casting, as solidification smoothly progresses from the thin end of the part to the thick extremity, providing self- feeding as long as a riser is placed at the hot end of the blade. Te traditional rigging is shown in Fig. 2. It included a sprue, sprue well with a filter at the parting line, two runners and six gates corresponding to an unpressurized gating ratio of 1:2:4 with a resulting filling time of 25 seconds. Te yield was 70%. Te cup of a direct pour system combines a ceramic foam filter held inside an insulating ceramic sleeve (see inset in Fig. 3). Te assembly acts as a pouring cup, filter and riser, allowing the metal to be poured directly into the mold cav- ity, eliminating the traditional sprue-runner-gate system. It considerably simplifies the molding process and promotes directional solidification since the hottest metal is poured
良好的耐腐蚀性。在铸造工艺方面，魁北克金属研究中 心对两种生产工艺进行了检验——传统浇注砂型铸造和 直接浇注砂型铸造。结果表明，如果两种浇注工艺的冶 金性能相似，直接浇注工艺在较小砂箱中的成形更加容 易，同时提高了产量、节省了加工费用。 研究人员比较了二者最佳的运行参数，如浇注温度和 浇注时间。他们还测量了13个点的冶金特性，包括枝晶 细度（二次枝晶间隙）和显微疏松，以及拉伸性能。
传统浇注与直接浇注工艺对比
楔形铸铝叶片是完美的几何形状，因为只需在叶片 的热端放置冒口就可以完成自动给料，叶片从薄的一端 到厚的一端的凝固过程可以顺畅进行。如图2所示，传 统的浇注系统包含一个浇口，浇口和过滤片位于叶片一 侧，2个浇道和6个横浇道，所对应的非承压的浇注比为 1：2：4，充型时间25秒。产出率是70％。 直接浇注系统的浇口杯含有置于绝缘陶瓷套筒内的泡 沫陶瓷过滤器（见插图3）。该组件充当了浇口杯、过 滤片和冒口，使金属液直接浇入模腔中，取代了传统浇 口杯–直浇道-横浇道的浇注系统。温度最高的金属液被 浇入到冒口，大大简化了模塑过程并促进了定向凝固。 直接浇注尤其适合于叶片铸造，因为过滤器下面的金属 液滴大小适中（2 in. [50 mm]）。
Fig. 2. A conventional sprue- runner-gate system is shown.
图2：直浇口-横浇道-内 浇口的传统浇注系统
Fig. 3. In direct pour filling, the metal is poured through a ceramic filter directly into the mold cavity via pouring cups (shown in inset).
图3：采用直接浇注充型工 艺，金属液通过浇注杯的陶瓷 过滤器直接浇入型腔进行充型 （见插图）。
December 2014
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