The document discusses various types of casting defects including their forms, causes, and prevention methods. It covers shaping faults from pouring like misruns and cold shuts caused by low metal temperature or moisture in sand. Shrinkage defects from inadequate gating and risering are described. Contraction defects like hot tears occur when thin and thick sections cool at different rates. Gas defects result from entrapped gases or gases evolving during solidification. Inclusions and sand defects enter the melt during pouring. Dimensional errors occur from mold distortions. Compositional errors and segregation vary the alloy composition.

1. CASTING DEFECTSCASTING DEFECTS
By: yaser elkelawyBy: yaser elkelawy
From: united company forFrom: united company for
foundries.foundries.

2. General Origin of Defects
in Casting
• 1. Casting Design.
• 2. Technique of Manufacture
(Method).
• 3. Application of Technique
(Workmanship).

3. Defects Grouped According
to their Origin
1. Shaping faults arising in pouring.
2. Inclusions and sand defects.
3. Gas defects.
4. Shrinkage defects.
5. Contraction defects.
6. Dimensional errors.
7. Compositional errors and
segregation.

4. Shaping faults arising in
pouring.
• The liquid metal should satisfactorily
fill the mould cavity and develop a
smooth skin through intimate contact
with the mould surface.
• The type of defects that might arise
if this requirement is not met are:
Misrun; Shortrun; Cold laps; Cold
shuts.

5. Shaping faults arising in
pouring.
• Misrun or Shortrun: the metal
solidifies prematurely and some limb
or section of the casting is missing.
• Cold Laps: a less severe
manifestation of misrun.
• Cold shuts: the discontinuity extends
through the casting member.

6. Shaping faults arising in
pouring.
These defects appear due to the following
reasons:
Low metal temperature.
Excessive chilling from the mould face.
Too high moisture content in green sand.
A method developed for dry sand used in
conjunction with green sand.
Occurrence of rounded corners and edges
and a general lack of definition of sharp
features and fine mould detail.

7. Shrinkage Defects
• Shrinkage defects arise from failure
to compensate for liquid and
solidification contraction so their
occurrence is usually a symptom of
inadequate gating and risering
techniques.
• Types of shrinkage defects:
o Major shrinkage cavity.
o Discrete porosity:
o Sinks and surface punctures.

8. Shrinkage Defects
• Major Shrinkage Cavities
Appear in those alloys of short freezing
range i.e. solidify by skin formation.
• Discrete Porosity
The longer freezing range alloys are
subjected to scattered porosity,
susceptible alloys include: bronzes, gun
metals, and numerous light alloys and
phosphorous containing cast irons.
Chilling by inserting chills in the moulding
material is used to combat surface
porosity in these alloys.

9. Shrinkage Defects
• Sinks and surface punctures:
The solidified skins deform under
atmospheric pressure due to the
occurrence of low pressure
conditions within the casting.
This defect can be avoided by
ensuring access of atmospheric
pressure to the liquid metal in the
feeder head.

10. Contraction Defects
• Contraction occurs upon cooling from the solidus
to room temperature. Unlike the liquid and
solidification shrinkages, which can be
compensated by by influx of liquid, solid
contraction affects all linear dimensions of the
casting, hence standard pattern allowances are
made.
• However, under practical cooling conditions,
castings usually have thin and thick sections, so
they do not contract freely and the metal
develops cohesive strength to overcome
significant resistance or hindrance to contraction
which is offered by the mould or other parts of
the casting itself which vary in their thickness.

11. Contraction Defects
• Hot Tears:
Hot tears or pulls are one form of this
type of defect often located at junctions
where changes in section occur, as the thin
part cools more rapidly then the thick part
and when the thick parts cool and start to
contract they cannot contract freely
because the thin section has cooled enough
to become hard and rigid so the material
tears at the junction separating the thin
part from the thick part.

17. Gas Defects
• Defects of this type take the form
of internal blow holes, surface blows,
airlocks, surface or subcutaneous
pinholes or intergranular cavities.

18. Gas Defects
They result from:
• Entrapment of air during pouring.
• Evolution of water vapour on contact
between liquid metal and moulding
material.
• Precipitation during solidification as
a result of chemical reaction or
change in solubility.

19. Gas Defects
• Gases enter liquid metal during
melting as temperature increases
the solubility of gases in the liquid
increases, and vice versa.
• The sources of gases are either:
• mould gases,
• Gases evolving from the metal upon
solidification.

20. Gas Defects
The preventive measures are:
Melting precautions:
• preheating of charge materials to
evaporate surface moisture, also
preheating any material added to the
liquid bath during melting.
• Fast melting.
• Using protective fluxes.

21. Follow Melting
Precautions:
• Following proper melt treatment:
oxidation-deoxidation reactions.
• Maintaining the metal temperature as low
as possible.
• Drying and preheating all spouts, ladles,
shanks, and furnace tools.
• Vacuum melting if justifiable.
• Degasing molten metal: gas scavenging by
argon, nitrogen, or chlorine, or by vacuum
degasing for non-ferrous metals.

22. Inclusions and Sand
Defects
• Non-Metallic inclusions in castings
may be considered in two Min groups:
• Indigenous arising from reactions
within the melt (may not be regarded
as defects).
• Exogenous resulting from
entrainment of non-metallics during
pouring (dross, slag, flux residues, or
moulding material).

23. Inclusions and Sand
Defects
• Inclusions are frequently
concentrated at or immediately below
the upper surfaces of castings,
where they are revealed on machining
or after scaling in heat treatment. It
is advisable that the most important
faces be placed downwards.
Increased machining allowances are
usually made on top surfaces of
castings.

24. Inclusions and Sand
Defects
The types of these defects are:
• Erosion scabs: A rough projection on
the casting as sand is washed away.
• Expansion defect: results from
penetration of liquid meatal behind
the surface layer of the sand.
• Rat tail: Surface fissure or line
defect.
• Surface roughness and sand

25. Dimensional Errors
• Such errors can occur in pattern
making, moulding, and casting, or
fettling.
• Principal causes are misalignment of
mould parts and cores, mould
distortion, anomalous contraction and
distortion in cooling.

28. Compositional Errors and
Segregation
• The main causes for variation in composition from
desired one are:
 Melting losses.
 Incorrect furnace charge.
• Careful melting practice is essential.
• Segregation is unavoided (macro or micro) in cast
alloys.
• Homogenisation treatment is necessary for
castings and it eliminates concentration gradients
by diffusion.

29. SPHERICAL HOLESSPHERICAL HOLES
CO-gas Defects
Gas holes on top surface only, revealed by
machining.
More severe type of the gas hole defects shown
in previous figure with inclusion of slag
particles.
Form: on the top surface, revealed during machining – sometimes discovered underneath a core.
Causes:
•Low pouring temperature
•High Mn and S contents
•Dirty ladles, lacks of skimming, poor refractory quality

30. SPHERICAL HOLESSPHERICAL HOLES
Hydrogen Pinholing
Small, spherical holes with shiny surface occurring
just below casting surface
Shiny graphite film appearing on surface of
defect type shown in previous figures.
Form: small spherical holes on all faces of the casting adjacent to the mould – with shiny surfaces.
Causes:
•Contamination of iron with Al.
Form:
- Scrap
- Inoculates
•Too high moisture content in sand
•Too long runner system

31. SPHERICAL HOLESSPHERICAL HOLES
Nitrogen Defects
Occurrence of small spherical holes adjacent to core,
often revealed immediately after knockout
Form: small spherical holes (sometimes more elongated) adjacent to cores
Causes:
•Nitrogen containing binders
•Too much addition of resin
•Too high N2-content in resin

32. ROUNDED HOLESROUNDED HOLES
Shrinkage Defects
Surface depression occurring at hot spot
Form: surface sink often with exuded bead of metal inside them or small depressions at hot spots with associated subsurface hole
Causes:
• too low mold rigidity causes yielding under ferostatic or solidification pressures
• too high pouring temperature
• too low carbon content

33. ROUNDED HOLESROUNDED HOLES
Gas Blowholes from Cores, Molds, or Inserts
Blowholes in plate casting
Causes:
• Excessive moisture content of sand
• Vents of cores are blocked
• Cores are underbaked or with excessive binder content
• Rusty or contaminated chills (denseners) or chaplets
Blowholes in cored casting resulting from
metal entering core vent. The metal extracted
from the core vent is also shown.

34. IRREGULAR HOLESIRREGULAR HOLES
Shrinkage Defects
Micrograph illustrating dendritic form of
internal porosity
Form:
• open metal, often interconnected areas
• has a dendritic form
• generally occurs in the heavier sections or hot spots such as positions adjacent to ingates or risers
Causes:
• lack of mold rigidity
• high pouring temperature
• over inoculation
• high phosphorous content

35. IRREGULAR HOLESIRREGULAR HOLES
Gas Defects from Molten Iron
Form: discrete fissures rather than areas of interconnected open metal may be widely dispersed or more isolated
Causes:
• Too much gas content in molten iron
• The more widely dispersed holes are due to N2
• The more isolated cavities are due to high H2 - content
Widely dispersed fissure defects
Larger, isolated fissure defects