Table 1. Composition of the Alloy in the Furnace, Inside the Steel Tube and in the Runner Si


Fe


Furnace Fill tube Runner


7.0 6.9 6.8


0.14 0.16 0.14


Cu Mn


0.082 0.017 0.075 0.016 0.097 0.021


Mg


0.39 0.38 0.38


Zn


0.019 0.016 0.018


Ti


0.14 0.15 0.14


Sr


0.013 0.014 0.013


mold. A single operator can repeat- edly fi ll the mold for a 600-lb. cast- ing at the push of a button, com- pared to the manpower necessary to fi ll the mold by gravity through multiple sprues. T e fi lling metal is also cleaner. Solidifi cation times are typically


Fig. 6. The recordings of the thermocouples are indicated for the tube (gray), gate (orange) and riser (blue).


fi ve times longer in sand casting than in permanent mold. T is is why the low pressure sand mold- ing is no match to LPPM when castings are small enough to be produced on a LPPM press. Since the majority of aluminum cast- ings are relatively small, the LPPM process is much more widely used than low pressure sand casting. But when the dimensions are too large for LPPM, low pressure sand casting is a viable option. Dozens of casting facilities are capable of this process and often cater to the aerospace industry. A good candidate is illustrated


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With so much riding on your parts, you simply don’t have time for inferior-performing solutions. As the industry leader in providing austempered ductile iron (ADI), Applied Process develops parts that meet the most stringent industry standards…time and time again. ADI parts are stronger, lighter, quieter, more uniform and have greater wear- resistance—providing increased performance with decreased production costs. It’s time to put the power of Applied Process to work for you.


through the following case study of a cast A356 aluminum mold used to make plastic parts for the food container industry. The overall dimensions of the


casting are 32 x 18 x 66 in. (800 x 460 x 1700 mm). Its inner surface will be polished to a 60 grit fin- ish, so the as-cast surface rough- ness must be less than 250 RMS. For the same reason, subsurface porosities greater than 150 µm are not acceptable. In Figure 3, the quiescent fi lling


is illustrated by showing the melt temperature at three seconds, 10 seconds, 20 seconds and 40 seconds after the start of fi lling. T is rate of fi lling was obtained by applying a rise in pressure of 10 mB per sec- ond inside the crucible enclosure. Figure 4 presents a map of the


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38 | METAL CASTING DESIGN & PURCHASING | Jan/Feb 2016


metal front temperature anywhere in the casting. It indicates no risk of cold shuts (seams in the casting) exists because the liquid metal front temperature never drops below 1,159 F (626 C). (Alloy A356 begins to solidify at 1,135 F [613 C].)


The molten aluminum is fed from the furnace to the runners


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