Materials Processing TMET 3343
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This 8 page Class Notes was uploaded by Jennyfer Gutkowski on Monday October 12, 2015. The Class Notes belongs to TMET 3343 at Georgia Southern University taught by David Williams in Fall. Since its upload, it has received 35 views. For similar materials see /class/222018/tmet-3343-georgia-southern-university in MET & Materials Engineering at Georgia Southern University.
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Date Created: 10/12/15
Expandable Pattern Casting LostFoam Casting polystyrene patterns Expandable Pattern casting oAlso known as evaporativepattern or lostpattern casting o Uses a polystyrene Styrofoam pattern that evaporates upon contact with molten metal oTrade name Full Mold process o Hs become one of he most important casting processes of both ferrous and nonferrous metals especially in the automotive industry The Process o Raw expandable polystyrene beads are 5 8 pentane volatile hydrocarbon are placed in a aluminum pre heated die for forming into a pattern shape o Re heated to fuse beads together then cooled and opened oPattern removed and additional elements are bonded hot melt adhesive to the surface to obtain complete shape o Pattern is coated with a water based refractory slurry o Dried o Placed in a flask oThe flask is then filled with a loose fine sand surrounds amp supports pattern o Sand is typically compacted at intervals oThen pour molten metal directly onto the polystyrene sprue oThe pattern is instantly vaporized ablation process and the mold filled 4 o The heat degrades depolymerizes the polystyrene and the byproducts are vented into the sand 0 Flow depends on the degradation rate of the polymer o Flow is basically laminar nonturbulent 9 And can be controlled by having hollows in the pattern similar to sand casting o Molten metal cools faster than if poured into a cavity because of the energy consumed to decompose the pattern 9 Fluidity therefore is less Advantages of lost foam 9 Process is simple o No parting lines cores risers 9 Excellent design flexibility oInexpensive flasks o Polystyrene is inexpensive o Polystyrene can be formed into virtually any complex shape 9 Finished casting requires minimum finishing and cleaning Advantages of lost foam o Economical for long production runs o Excellent process for automation oONE DOWNSIDE oThe cost of producing aluminum mold for production runs of parts is very expensive for expanding the beads to produce the patterns o over lostwaxquot no carbon residue left from burning out of pattern Replicast C S process Typical applications
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