casting defects
A casting defect is an undesirable irregularity in the process of metal casting.
Some casting defects can be repaired, while others can be tolerated or must be eliminated.
five major categories of casting defects are in this ppt.
CASTING DEFECTS casting defect is an undesirable irregularity in the process of metal casting
1. CASTING DEFECTS
CH. JAYA TEJA M.TECH (PH.D)
ASSISTANT PROFESSOR
DEPARTMENT OF MECHANICAL ENGINEERING
BVC ENGINEERING COLLEGE, ODALAREVU
2. • A casting defect is an undesirable irregularity in the process of metal casting.
• Some casting defects can be repaired, while others can be tolerated or must be eliminated.
five major categories of casting defects are
Gas porosity
Shrinkage defects
Mold material defects
Pouring metal defects
Metallurgical defects
3. Gas Defects
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Caused due to entrapped gases in mold due to
Lower venting
Poor permeability of mold (due to finer grain size, higher clay content, higher moisture
content, excessive ramming of mold)
Improper design of casting
High pouring temperature
4. Gas Defects
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A common defect that occurs when gas is trapped in the metal during solidification, forming voids that are circular, elliptical,
pear-shaped, or waist-shaped
Gas porosity is a common casting defect that occurs when gas bubbles form in a casting as it cools. This happens because
liquid materials can hold more dissolved gas than solid materials.
Some causes of gas porosity:
Gassy heat of metal: The metal may contain dissolved gases from the melting process, such as nitrogen, oxygen, or hydrogen.
Turbulence: Pouring the liquid metal into the mold too quickly can introduce gases.
Dampness: Too much moisture in the air can cause hydrogen to dissolve into the molten metal.
5. • The pores run through the wall of the casting, weakening its structural integrity. Such a
form of gas porosity defect makes the casting unsuitable for automotive or marine
casting applications, where the pressure tightness of parts is usually of prime importance
• This type of porosity form on the surface of the casting and extend into its interior. It usually
doesn’t affect the mechanical strength but can lead to corrosion. Blind porosity is often
exposed during surface finishing
• Such porosity are internal defect formed within the casting. Therefore, it may go
unnoticed unless specialized porosity detection methods like ultrasonic or X-ray
are used
6. • A defect that occurs when there is not enough metal to fill the mold, causing the metal to shrink and
create holes in the casting
Shrinkage cavities
7. Molding Material defects
• A defect that can be caused by improper mold preparation, inadequate
ventilation, or impurities in the mold material
8. Pouring material defects
• A defect that can include misruns, which occur when the molten metal
doesn't completely fill the mold cavity
9. Metallurgical defects
• A defect that can include slag inclusion, which occurs when molten metal
containing slag particles is poured into the mold cavity
10. Blow holes / Open blows
flattened
or
Spherical,
elongate
d inside
the
cavitie
s
castin
g
presen
t
(BLOW
HOLES) or on the
surface (OPEN BLOW).
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11. Air Inclusions
due to absorption
of atmospheric
and other gases
in the molten
metal in Furnace.
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12. Pin Hole Porosity
Caused by hydrogen
in the molten metal.
Picked up in the furnace
or by the dissociation of
water inside the mold
cavity.
at lower temp solubility
of gas decreases and
therefore
hydrogen escapes. It
leaves a pin like
structure at the surface.
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15. Scab
Rough, thin layer of a metal, protruding above the casting
surface, on top thin layer of sand.
The scan results the up heaved sand is separated from the
mold surface and the liquid metal flow into the space
between the mold and the displaced sand.
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16. Wash
A low projection on
the drag surface of a
casting
commencing near
the gate is called
wash.
Due
san
d
to erosion
of by
the
high
velocity liquid metal
in bottom gating.
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