Casting Defects Foundry All Major casting defects

1. Casting Defects
1. Casting defects are often very difficult to
characterize due to the intrinsic complexity of the
casting process.
2. All defects will fall into one or more of the
established categories of casting defects.
3. The proper identification of a particular defect is the
prerequisite to correcting and controlling the quality
of castings.
4. The nature of a casting defect can only be
determined by correctly categorizing the shape,
appearance, location and dimensions of the defect.
5. Once appropriately classified, the possible causes
can be examined and the corrective action can be
taken.

2.  Casting has often been referred to as "a
process that really knows how to keep a
secret." Even in a controlled process,
defects in the output can occur which defy
rational explanation.
 The complexity of the process is the result of
integrating the varied disciplines of physics,
thermodynamics and chemistry.
 When these factors are combined with the
problems associated with the high
temperature alloys, the root cause of a
casting defect can truly become a mystery.

3. Casting defects in a controlled process will generally fall
into one of two categories.
1. Defects can be chronic, i.e., long-standing, which
require a remedy through a process change usually
via designed experiments
2. Sporadic, which are sudden adverse changes in the
normal capability of the process.
Sporadic defects are probably the most
troublesome for casters. In a controlled process
defects do not just happen, they are caused. "If a
defect occurs, measures must be adopted to
eliminate its cause and prevent its repetition."

4. Defect Characterization
Two distinct journeys must be taken to correct
sporadic defects.
 the diagnostic journey from symptom to cause
 the remedial journey from cause to remedy
There is a temptation to attempt to diagnose a
defect by the possible causes; but, an incorrect
diagnosis of the root cause can lead to an
incomplete or incorrect remedy of the problem. It
is important to correctly identify the defect
symptoms prior to assigning the cause to the
problem.

7.  In general, a casting defect is defined as an
observable and unplanned variation of a
specification.
 The identity of a particular casting defect is based
upon the specific shape, appearance, location and
dimension or profile of the anomaly.
 The proper identification of a specific defect is the
prerequisite to correcting and controlling the quality of
castings.
 A problem solving approach that is characterized by
the unique "morphology of the defects is more logical
than one based upon the causes since it requires no
prior assumptions to be made

8. Categories of casting defects
1. Metallic Projections
2. Cavities
3. Discontinuities
4. Defective Surface
5. Incomplete Casting
6. Incorrect Dimensions or Shape
7. Inclusions or Structural Anomalies

9. DEFECTS IN CASTING
1. Gas defects
2. Shrinkage cavities
3. Molding Material Defects
4. Pouring Metal Defects
5. Metallurgical defects

10. Gas Defects
 Blow Holes
 Open Blows
 Air Inclusion
 Pin Hole Porosity

11. Blow Holes and Open Blows
 Cavities, mostly with smooth walls; bright or oxidised.
 In the case of large blowholes with corrugated walls too.
Always spherical form, even in large expansions (then
always flat cavities). Frequently accompanied by slags
and oxides
 Typical characteristics:
Rounded shapes, location always in the upper part of the
castings and beneath cores or undercuts. Individual
blowholes or large accumulations, then mostly with
different sizes.
Preferred defect locations:
In parts of the casting in the top of the mould, often above
larger cores. In thick parts, but also in thin walls. Beneath
undercuts and large cores.
 Apart from presence of moisture, they occur due to poor
venting and lower permeability of the mold

12. Blow Holes and Open Blows
 Remedial measures:
- Adequately dry cores
- Larger proportion of new sand
- Better gas permeability
- Smaller proportion of binder
- Check casting system
- Reduce moisture content of the sand
- Add a little oxide to the melt (e.g. rusty
insert)

16. Air Inclusions
 The atmospheric and other gases absorbed
by the molten metal in the furnace or during
the flow in the mold, when not allowed to
escape would be trapped in the casting and
weaken it.
 High pouring temperature increase the
amount of gas absorbed
 Or due to poor gating design such as straight
sprues in unpressurized gating, abrupt bends
and turbulence causing practices in the
gating which increase the air aspiration and
 Low permeability of the mold itself.

17. Pin Hole Porosity
 Agglomeration of small, rounded cavities up to around 5 mm
in size. Surface of the cavities mostly smooth and polished,
occasionally with graphite. clearly visible pinholes in the
casting skin; surface is often oxidised
 Typical characteristics:
All cavities have the same size and the long form is always
oriented perpendicular to the surface, arranged at outer
edges in the line bisecting the angles.
Preferred defect locations:
Outer edges and corners, as well as work piece surfaces,
defects always in the immediate vicinity of the surface. Often
at mould parting lines or transitions to cores these are
mostly arranged like strings of pearls/beads.

18.  Remedial measures:
- Optimise mould material
Water content
Nitrogen content
- Nitrogen content in iron; set-point
value < 80 ppm

23. Internal Shrinkage cavities
 Defect is almost always identifiable during
machining. Zones of visibly "loose"
microstructure, occasionally sponge-like
structure or an agglomeration of numerous
small pores.
 Remedial measures:
- Check the gate and feeder system
- Increase the degree of saturation
- Reduce the casting temperature
- Carry out a solidification simulation

27. Dispersed shrinkage
 Accumulation of small, crack-like cavities. Only visible
after machining. Cross-sections up to around 8 mm
long and 1-2 mm wide, upto 2 cm deep.
 All cavities are the same size and always oriented
perpendicular to the surface, arranged at the outer
edges of the lines bisecting the angles.
 Remedial measures:
- Minimise core sand intake
- Reduce water content
- Extend mixing time
- Increase casting temperature

31. Molding Material Defects
CUTS AND WASHES
Thickening of the casting at one place.
Typical characteristics:
Sand washout, combined with sand and /or
slag inclusions because of low strength or
molten metal flowing at high speed
Preferred defect locations:
Mostly close to the gate or on edges, which
tend to heat

32. Cuts and Washes
 Remedial measures:
 Choose binder with good properties at high
temperatures
 Greater compaction of the mould sand
 Avoid high flow speeds and long pouring times
 Improve gate design to reduce turbulence and by
increasing size of the gates

33. Metal Penetration
 More or less thick sand adhesions on the
casting, which are held fast on the work piece
by metal penetrations. The metal between the
grains cannot always be identified by the
naked eye.
 Widespread, frequently cushion-shaped form.
 Can often not be removed by blasting.
 Penetrating adhesions in blackened moulds
and cores can often be cracked off the work
piece using a chisel

34.  Typical characteristics:
Metal between sand grains. Can often only be
identified with a microscope.
Preferred defect locations:
Thick parts, zones of inadequately
compacted mould material and zones, in
which cores lie in the hottest parts. Preferably
in the lower parts of the mould (higher casting
pressure).

36. Fusion
 Manifestation:
Surface defect.
Thin sand crusts, which firmly adhere to the
casting.
Typical characteristics:
Rough cast surface.
Sand sintered on the casting, which can only be
removed by grinding.
Preferred defect locations:
Possible on all parts of the casting.
Especially in thick-walled castings.
Near to the gate.

37.  Remedial measures:
- Add more new sand
- Reduce dust fractions in sand
- Uniform compaction
 Reduce pouring temperature

38. Runout
 Manifestation:
During the casting, metal runs out of the box
at the parting.
Typical characteristics:
Casting is incomplete or fully missing
Preferred defect locations:
The upper part of a casting is mostly missing
 Remedial measures:
- Clamp the two halves of the box
- Place weights on mould

40. Rattails
 Manifestation:
The defect involves a sand expansion defect, which can frequently
occur in highly compacted parts of the mould.
Typical characteristics:
Scratches appear on the surface of the casting, which can be partly
arranged in parallel.
Preferred defect locations:
On areas of the mould cavity covers but primarily on the bases. Can be
mostly identified on the surface in the cast condition.
Remedial measures:
- Optimise mould material preparation with the aim of increasing the wet
tensile strength
- Fast mould filling
- Reduce the casting temperature

41. rattail

42. Swell
 Manifestation:
Irregular, widespread thickening of the casting on the outside
or inside.
Typical characteristics:
Gradual, unwanted increase in wall thickness.
Preferred defect locations:
Possible in all areas of the casting, however mostly in the
lower part of the mould.
Remedial measures:
- Higher binder content
- More uniform compaction
- Reduce casting /sprue height

43. Washout/Erosion
 Manifestation:
Thickening of the casting at one place.
Typical characteristics:
Sand washout, combined with sand and /or slag
inclusions.
Preferred defect locations:
Mostly close to the gate or on edges, which tend to
heat up
 Remedial measures:
- Choose binder with good properties at high
temperatures
- Greater compaction of the mould sand
- Avoid high flow speeds and long pouring times

44. Pouring Metal Defects

45. Mis Runs and Cold shuts
 Metal unable to fill the mold cavity completely
 Cold shut is caused when two metal streams
while meeting in the mold cavity do not fuse
together properly, thus causing a discontinuity
or weak spot.
 Remedial measures:
- Increase casting temperature
- Increase casting speed and make gates
larger

50. Cold shot inclusion/ spray
bead
 Spray beads are pearl or bead shaped inclusions,
which are only loosely bonded with the metal. They
are partly already visible at the surface, they are
often not exposed until the machining.
 The beads are created by turbulences during casting
or by the effect of spray in the mould, metal particles
prematurely solidify in drip or spherical form. These
splashes oxidise very easily and the oxide skin
prevents the spray beads from being re-incorporated
by the subsequent melt flow.

52. Spray bead in micro-section (etched) unetched:

53. Slag inclusion
 Irregular inclusions or cavities left behind by
inclusions, which have fallen out. Mostly on the
surfaces in the top of the mould. Frequently grouped
together with gas cavities, often with particles of
mould material too. Tough slags often form lumps,
the easily fusible slags float that upwards in the
mould form skins, which at times can separate the
whole casting wall. Occasional lustrous carbon on
slag skins.
 Glassy inclusion, several phases can be frequently
identified under the microscope. Skins wrinkled or
creased, often bonded with a large number of mould
material particles (scar like arrangement).

54.  Preferred defect locations:
As coarse slags at places which were in the upper
part of the mould and under large area cores and
core prints. Scar shaped finely distributed, frequently
in the direction of flow on the surface of the work
piece. As slag skin often running in a transverse
direction to the casting wall. Occasionally relatively
coarse slags inside castings too.
 Remedial measures:
- Reduce elements which bond with oxygen
- Properly dry ladles beforehand
- Reduce pouring times
- Increase mixing time

58. Hot Tears
 Material partition in liquid /solid state, which occurred
as the stresses, which occurred in the casting in the
area of the elastic deformations, were larger than the
strength of the material.
 Stresses can occur in case of uneven cooling
conditions (differences in wall thicknesses). Special
design of the casting can prevent contraction. –
shrinkage onto the core -
Hot cracks primarily occur in steel castings.
 preferred defect locations:
- at sudden, steep transitions in wall thicknesses.
- at wall thickness transitions with too small radii
Remedial measures:
- Design suitable for stresses, balance out cross-
sections with large wall thicknesses

63. Core damage
 Unintentional protruding(extension) core parts.
 Typical characteristics:
Parts of the core are displaced relative to each other.
 Preferred defect locations:
At parting lines of the cores.
 Remedial measures:
Check core box guides
- Check core boxes (is there a defect in the core
box?)

65. Dimensional variation
 The casting has larger or smaller dimensions compared to the
dimensionally checked initial pattern released by the customer
and the drawing.
 Typical characteristics:
This defect can conceal a range of casting defects, starting with
pattern wear, so that it is not always possible to quickly narrow
down the defect.
 Remedial measures:
- Check the pattern equipment and core boxes
- Core print clearance
- Check the mould making, mould box guides
- Compact the mould

66. Dross
 Irregularly shaped interruption in the material
Typical characteristics:
Dark scars, foamy dark surfaces, very finely
distributed. Dross worsens the mechanical
properties, Dross mainly consists of magnesium oxy-
silicates and magnesium sulphides, and is a product
of the reaction of magnesium with oxygen, sulphur
and silicon.
Preferred defect locations:
In the upper casting surface or beneath cores. Mostly
in cast iron with nodular graphite, often only visible
after the casting skin has been removed.

67.  Remedial measures:
Dross cannot be prevented, only reduced.
 Melts:
- High temperature
- Low residual Mg contents
- Clean melting of pure raw materials
- Highly concentrated Mg master alloys or pure Mg
- Gas purging(cleaning)
- Refining slags (melt cleaner)
In the work pieces:
- Draw off and restrain treatment slags (large pouring
basin, optimum casting system)
- Filters are very effective
- Dry, closed moulds
- HOT casting

70. Elephant skin
 Irregularly scared and/or creased(bend)
surface with net shaped notches
Typical characteristics:
Parchment(skin) like appearance
Preferred defect locations:
Normally in the top part of thick-walled
castings on horizontal surfaces. The defect
can effectively always be identified in un
machined casting.

71.  Remedial measures:
- Use pure, base iron with low sulphur and oxygen
contents
- Use a teapot ladle
- Adjust the degree of saturation of the melt
according to the casting temperature
- Possible extension of the dead-melting time after
the magnesium treatment
- Use refining slags
- Use filter

73. Inclusion of foreign metal
 Manifestation:
Material not homogeneously formed.
Typical characteristics:
Visible irregularities in the microstructure.
Preferred defect locations:
On the inside of the casting, partly extending
out to the surface too. during machining, the
inclusions are worn down by the machining
tool.

74.  Remedial measures:
- Adequately high temperature
- Clean melting of pure raw materials
- Gas purging
- Draw off treatment slags and hold back
(large pouring basin, optimum casting
systems)
- Mould fill rising, gently and fast
- Filters are very effective
- HOT casting

77. Mismatch in mold
 Manifestation:
Unintentional protruding(extending) casting parts.
Typical characteristics:
Parts of the casting are displaced relative to each
other.
Preferred defect location:
On parting lines.
 Remedial measures:
- Check box guides, mould assembly and closure
equipment
- Check models

81. Fillet
 Manifestation:
Fillets in castings, especially in wall thickness transitions do not often
occur according to the drawings, or they contain defects.
Typical characteristics:
- Radii at the fillets are considerably smaller in the casting than in the
patterns.
- The surface of the fillets is maculate(unclean).
Preferred defect locations:
Fillets at wall thickness transitions with large agglomerations of mass.
At these places the mould material is subjected to extreme thermal
stresses .
Remedial measures:
- Make radii larger than those given in the drawing.
- Check addition of new sand

84. Mould damage
 Manifestation:
Irregular, widespread thickening of the outside or inside of the
casting. After the pattern has been stripped, areas of the
subsequent cast contour are broken off in the mould material
area of the mould cavity.
Typical characteristics:
Enlargement of the wall thicknesses or change in contour, the
broken off areas of the mould material are then found in the
casting as mould material inclusions, if the defect is caused
when the mould is assembled and closed by pressing core
prints or in the mould joint.
Preferred defect locations:
Joint face or core prints

85.  Remedial measures:
-Re-open the mould after assembling
and closing and check for pressure
points and broken off edges.
-Check pattern and core box, core print
allowance

90. Rough casting surface /
Roughness
 Manifestation:
Roughness must be assessed relative to the
grain size of the casting selected. Under
certain circumstances a workpiece cast in
coarse sand with fully uniform surface must
be assessed as being smooth, although it is
rougher than a “rough area” on a workpiece
cast in fine grained sand.
 Preferred defect locations:
Close to gate, parts deep in the mould, zones
with inadequate compaction

91.  Remedial measures:
- Use finer sand
- Reduce water content
- Increase compaction pressure
- Reduce casting temperature

93. Defect Analysis of castings

94. Reasons for Casting Rejections
Casting Failed
Pressurized
Leak Test
(28%)
Visual
Imperf ection on
Machined
Surf ace (52%)
Casting
Breakage
During
Machining
(16%)
Low Tool Lif e
& Excessiv e
Machined
Surf ace
Roughness
(4%)

95. Defects Causing Surface Imperfection (relative
frequency of each defect found)
Flow Lines
(7.7%)
Cold Laps
(46%)
Lubricant or
Mold Coating
Inclusions on
Surface (16%)
Gas Porosity
(85%)
Shrinkage
Porosity (69%)
Oxide
Inclusions
(38%)

96. Defects Causing Pressurized
Leak Test Failure
(relative frequency of each defect found)
Gas Porosity
(57.1%)
Shrinkage
Porosity
(71.4%)
Cold Laps
(57.1%)
Mechanical
Cracks (14.3%)

97. Defects Causing Casting Breakage at Machining
(relative frequency of each defect found)
Gas Porosity
(75%)
Cold Laps
(75%)
Shrinkage
Porosity (75%)
Oxide Inclusions
(25%)
Mechanical
Cracks (25%)