Fig. 8. Filling with direct pour from the side is illustrated.
required, particularly the yield strength (Table 2). Te yield strength varied from 154 to 170 MPa, while the mini- mum required was 140 MPa. Tese properties by far exceeded the yield strength of an as-cast blade as previ- ously determined by mechanical test- ing. 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 receiv- ing the hydro-kinetic energy were smooth, as-cast shapes providing optimum hydrodynamic efficiency for the water turbine (Fig. 9). Te direct pour filter cup technol-
ogy studied on the blade highlighted the main advantages of direct pour: 1. Lower metal pouring tempera- ture—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.
This article is based on paper 14-003 presented at the 2014 AFS Metalcasting Congress.
August 2014 MODERN CASTING | 47
Fig. 9. Two faces of a blade filled from the side are pictured.
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