casting and forging discontinuities
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Casting Discontinuities
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Casting
• Casting is a product obtained by pouring themolten metal in a cavity called mould andallowed to solidify to get the desired shapeand size.
• Sand casting
• Permanent Mould Casting
• Die Casting
• Centrifugal Casting
• Investment Casting
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rigin of defects• !he casting design
• !he techni"ue of manufacture
• #or$manship
• Shaping faults arising in pouring• Inclusion and sand defects
• %as defects
• Shrin$age defects due to volume contractionin li"uid state during solidification
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Casting Discontinuities• Surface roughness& !oo coarse a moulding Sand'
Pouring temperature too high' surface reaction.
• Scabs or buc$les& Due to some sand shearing from
the cope surface and ma$ing a metal layerseparated from the casting by a layer of sand.
• (low )oles& Internal voids produced by e*cessive
gaseous material that could not escape.
• Sand Spots& Impurities collected at one or more
locations.
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• Swells& Swelling of casting resulting from
enlargement of mould cavity when molten
metal is poured.
• Shrin$age& Contraction of the metal during
solidification
• )ot tears& )indered contraction occurring
+ust after solidification.
• Cold crac$s& )ydrogen induced crac$s in
highly stressed casting.
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• Cold shorts& !oo streams of metals that are too
cold to fuse properly' slow pouring.
• ,ifts and shifts& Misalignment of pattern parts.
• Sponginess or )oney Combing& - number of
cavities in close pro*imities' open to surface'
because of dirt in molten metal• Pour Shorts& Incomplete filling of the mould
• %as Porosities& ounded voids due to gas
dissolved in molten metal.
• un outs and (ust outs& Drainage of metal from
cavity' gives incomplete casting.
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• Metal Penetrations& Penetration of metal inthe interstices of sand grains' fused
aggregate of metal and sand.• /ins& - thin pro+ection of metal not intended
as apart of casting
• Misruns& Improper filled corners and mouldcavities' low poring temperature.
• Dimensional error& 0ariation in size
• Compositional error and segregation&0ariation in chemical composition of thecasting metal.
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Cold shuts
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Cold shuts
Cold shuts
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Shrin$age cavity
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/orging Discontinuities
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/orging• Controlled plastic deformation of metals at
elevated temperature into pre determinedsize or shape using compressive forcese*erted through some type of die by a
hammer' a press or a upsetting machine'rolling and e*trusion etc.
• /orgings have high strength and ductilityand offer greater resistance to impact and
fatigue loads due to e*tra wor$ing duringthe process and the opportunity of aligningthe grain flow.
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• (ecause of intense wor$ing flaws areseldom found in forging and components
have high reliability.• -lmost all metals can be forged' but the
metals which has low yield point can be
forged with ease.• Materials li$e -luminium' Copper and their
alloys' steels' !itanium and many other alsocan be forged.
• )igh initial costs' rapid o*idation of diesurface.
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/orging Discontinuities• Mismatch• Scale pits
• 1nfilled sections
• Defects resulting from improper heatingand cooling of the forging such as burntmetal' decarburised steel and fla$es
• Dirt ' slag and blow holes• Ingot defects' pipes' crac$s' scabes'
segregation
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• Seams
• Cold crac$s
• ,aps
• Cold shuts
• #rin$les• verlaps
• Distortion
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