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CASTING DEFECTS
CH. JAYA TEJA M.TECH (PH.D)
ASSISTANT PROFESSOR
DEPARTMENT OF MECHANICAL ENGINEERING
BVC ENGINEERING COLLEGE, ODALAREVU
• 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
Gas Defects
3
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
Gas Defects
4
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.
• 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
• 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
Molding Material defects
• A defect that can be caused by improper mold preparation, inadequate
ventilation, or impurities in the mold material
Pouring material defects
• A defect that can include misruns, which occur when the molten metal
doesn't completely fill the mold cavity
Metallurgical defects
• A defect that can include slag inclusion, which occurs when molten metal
containing slag particles is poured into the mold cavity
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).
10
Air Inclusions
due to absorption
of atmospheric
and other gases
in the molten
metal in Furnace.
11
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.
12
Scar
A shallow blow,
usually found on the
flat casting surface.
13
Blister
Scar covered by
thin layers of a
metal.
14
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.
15
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.
16
Misrun
Freezing of molten
metal before
reaching the
farthest point of the
mold.
Due to insufficient
superheating
of metal.
17
Cold Shut
Misrun at the centre
in case of two gates
is called Coldshut.
18
Hot Tear (Crack due to residual stresses)
19

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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 3 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 4 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). 10
  • 11. Air Inclusions due to absorption of atmospheric and other gases in the molten metal in Furnace. 11
  • 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. 12
  • 13. Scar A shallow blow, usually found on the flat casting surface. 13
  • 14. Blister Scar covered by thin layers of a metal. 14
  • 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. 15
  • 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. 16
  • 17. Misrun Freezing of molten metal before reaching the farthest point of the mold. Due to insufficient superheating of metal. 17
  • 18. Cold Shut Misrun at the centre in case of two gates is called Coldshut. 18
  • 19. Hot Tear (Crack due to residual stresses) 19