amenable to the LPPM process. In low pressure sand casting, the sand mold rests on top of a pressur- ized enclosure as shown on Figures 1 and 2. T e similarity between LPPM and low pressure sand casting is in the controlled tranquil fi lling of the mold with a dross-free melt. Both processes also share the ability to produce thinner walls than gravity pouring would. However, in contrast with the


LPPM process, in low pressure sand casting no excess pressure is applied at the end of fi lling. Feeding from the bottom is interrupted early and long before the casting is fully solidifi ed, so risers are necessary, just as in gravity casting. Low pressure sand casting eliminates liquid metal handling, so the process is also advantageous over gravity sand casting when pouring large parts. Size, quality and wall thickness


will be the primary considerations when deciding between LPSM and gravity sand casting. Compared to gravity sand cast-


ing, the low pressure sand molding process simplifi es the fi lling of the


Fig. 3. The temperature of the melt at three seconds, 10 seconds, 20 seconds and 30 seconds after start of fi lling is illustrated.


Fig. 4. The temperature of the liquid metal front everywhere in the mold cavity can be seen here.


Fig. 5. The location of the three thermocouples (green dots) were, from bottom to top, inside the feeder tube, in one of the ingates and inside the taller open riser.


Jan/Feb 2016 | METAL CASTING DESIGN & PURCHASING | 37


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