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Fig. 8. Filling with direct pour from the side is il- lustrated.


图8:侧边直接浇注充型图


erably; however, it had to be verified that the mechanical properties still exceeded the minimum values specified. After the modified heat treatment was applied to a


blade, the quality index dropped by about 50 MPa, but the yield strength and elongation remained above the minimum required, particularly the yield strength (Table 2). Te yield strength varied from 154 to 170 MPa, while the minimum required was 140 MPa. Tese properties by far exceeded the yield strength of an as-cast blade as previously determined by mechanical testing. Te modified mild heat treatment more than doubled the yield strength of the as-cast blade.


Side Fill Direct Pour In order to avoid a rough finish on the blade’s surface,


the direct pour cup was modified to fill the cavity by the side rather than from the top (Fig. 8). Tis arrangement avoided the grinding of the blade surface at the cup-casting connection and provided a less turbulent liquid metal flow into the mold cavity. Te surfaces receiving the hydro- kinetic energy were smooth, as-cast shapes providing opti- mum hydrodynamic efficiency for the water turbine (Fig. 9). Te direct pour filter cup technology studied on the


blade highlighted the main advantages of direct pour: 1. Lower metal pouring temperature—1,274F (690C) vs. 1,364F (740C).


2. Simpler molding operation and a reduction of 25% in sand usage.


3. Lower finishing costs and a near net shape as-cast product, especially when using filling from the side.


4. Improved yield, from 70% to 85%. 5. Reduced distortion in the as-cast condition as the fast-cooling runners and gates pull on the solidifying casting when the conventional rigging is used. ■


Tis article is based on paper 14-003 presented at the 2014 AFS Metalcasting Congress.


值,尤其是屈服强度(表2)。屈服强度在154-170 MPa之间,而所需的最低值为140 MPa,超过了铸 造叶片先前通过机械测试确定的屈服强度。改进的 温和热处理工艺使铸态叶片的屈服强度变为之前的 两倍多。


侧边直接浇注


为了避免叶片的表面粗糙,直接浇注的浇口杯改 为开在侧边而不是在顶部(图8)。这样的设计避免 了浇口杯和铸件连接处叶片表面的打磨,而且使液 态金属充型时紊流更小。叶片在水力作用下表面变 得光滑,这样的铸态形状使水轮机发挥最佳的水力 效率(图9)。


采用直接浇注及过滤杯技术对叶片进行的研究突 出了直接浇注的主要优点:


1.降低了金属液的浇注温度,从1,364℉(740℃) 降低到1,274℉(690℃)。


2.简化了造型作业,减少25%的砂子使用。 3.降低了清理成本且得到近净形的铸态产品,尤其是 改为侧边充型后。


4.产出率从70%提高至85%。


5.减少铸造时的变形,采用传统浇注系统时,由于 直浇道和横浇道的快速冷却影响了凝固中的铸件形 态。 ■


本文出自2014年美国铸造协会铸造大会上发表的14-003 号论文。


Fig. 9. Two faces of a blade filled from the side are pictured.


图9:侧边浇注叶片的两面 50 | FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION December 2014


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