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Casting defects may be dened Those characteristics that create adefciency or imperection to quality specifcations imposed by design

and service requirements.

Reduces total output, increases the cost of production.

Even in modern foundries the rejection rate as high up to 20 of the numberof casting produced.

Surface defectsInternal defects

ncorrect chemical compo. Unsatisfactory mech.properties

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+ell - enlargement of the mould cavity by metal pressures, results locali$ed or overall enlargement of castings

Causes

nsu/cient ramming of the sand. Rapid pouring of molten metal. lso due to insu/cient +eighting of mould.

Remedies void rapid pouring. provide su/cient ram on sands. proper +eighting of moulds.

thin projection of metal not a part of cast.

1sually occur at the parting of mould or core sections.Causes

ncorrect assembly of cores and moulds,

mproper clamping.

mproper sealing.

Remedy

Reduces by proper clamping of cores and mould.

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Gas HOLE

Gas Holes

Clean, smooth +alled rounded holes of varying si$e from pin heads to fullsection thicness, often e3posed during machining.

Causes

4o+ pouring temperature. 5ases blo+ing from the mould.

E3cessive turbulence during pouring.

"oisture condensed on densors and chills.

Remedies

Use correct pouring temperature and check with pyrometer.

ncrease permeability of sand and chec grinding.

6arm densors and chills.

"odify gating to reduce turbulence, use sive3 lter

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t is a void or depression in the casting caused mainly by uncontrolled solidication.

Causes:

7. 8ouring temperature is too high causing li)uid shrinage.

2. *ailure to supply li)uid feed metal.

9. 8re mature solidication.

Remedies :

pply principles of casting, reduce the pouring temperature and provide ade)uate

risers, feeders, +hich supply the molten metal to compensate the shrinage.

:ne of the main defects is hot tearing or hot cracing, or hot shortness.rrespective of the name, this phenomenon represents the formation ofan ;irreversi

ble ailure crac/0 in the still semisolid casting.1

Cause:

&he inade)uate compensation of solidication shrinage by melt %o+ inthe presence of thermal stresses.

Remedy

void e3cessive ramming.

Controlled ramming should be done.

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Castings not fully form heaving lines or seam

of discontinuity or holes +ith rounded edgesthrough casting +alls.

Causes: ncomplete fusion +here t+o streams of metal

meat. "etal free$es before mold is lled. (ie too cold.

Remedies:

ncrease pouring temperature. ncrease die temperature or improve venting. ncrease permeability of sand.

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Casting Defects

ME 6222: Manufacturing Processes and Systems 6Prof. J.S. Colton