Chapter 2 : Metal Casting

Lecture 4 : Permanent moulds, Casting Defects

Advantages:
Can produce a wide range of cylindrical parts; good dimensional accuracy and cleanliness
Limitations:
Limited shape; spinning equipment may be expensive
Common metals:
Iron, steel, stainless steel, alloys of aluminum, copper and nickel
Die Casting
Continuous Casting
Casting Defects
Casting Defects

• Metallic projections
– Flash: excess metal solidified outside mold cavity
• Causes: insufficient clamping force, improper parting line
• Cavities (voids)
– Shrinkage cavities: voids inside casting
• Causes: contraction during solidification
• Remedies: use similar (V/A) ratios, use gradually increasing
section modulus toward riser, proper gating/riser design, use of
chills
– Blowholes: void on surface of casting
• Causes: excessive gas entrapment, lack of adequate venting
• Remedies: de-gas melt, add vents
Defects - Hot Tears
• Discontinuities
– Hot tears: intercrystalline failure in casting that occurs at a high
temperature within mold; usually forms in sections that solidify
last and where geometrical constraints are present
• Causes: large differences in section thickness, abrupt changes in
section thickness, too many branching/connected sections, mold
has high hot strength and stiffness
• Remedies: through casting and mold redesign
– Cold shut: incomplete fusion of two molten metal flows that
meet inside the mold from opposite directions
• Causes: insufficient superheat, inadequate risers
• Remedies: increase superheat, add additional risers
• Defective surface
– Scabs: thin layer of molten metal that enters gaps in mold and
solidifies
• Causes: improper mold design
• Incomplete castings
– Misrun: incomplete casting
• Cause: insufficient superheat
• Remedy: increase superheat
• Inclusions
• Remedy: clean melt before pouring, improve strength of mold
1987
Riser is designed so as to
A
Freeze after the casting freezes
B
Freezing before the casting freezes
C
Freeze at the same as the casting
D
Minimize the time of pouring

1988
The contraction allowance provided on the pattern and core boxes compensates for the following type of
contraction.
A
Liquid contraction
B
Solidification contraction
C
Solid contraction
D
All the above three types of contractions.
GATE ME 1989

Chills are used in molds to

A
achieve directional solidification
B
reduce possibility of blow holes
C
reduce the freezing time
D
smoothen the metal for reducing spatter.

GATE ME 1989
Increase in water content in moding sand causes
A
Flowability to go through a maxima
B
Permeability to go through a maxima
C
Compressive strength to go through a maxima
D
strength to go through a maxima
GATE ME 1990
The pressure at the in-gate will be maximum with the gating system
A
4:8:3
B
1:3:3
C
1:2:4
D
1:2:1

GATE ME 1991

Converging passage is used for feeding the liquid molten metal into the mould to

A Increase the rate of feeding

B Quickly break off the protruding portion of the casting
C Decrease wastage of cast metal
D Avoid aspiration of air
GATE ME 1991

When there is no room temp change, the total shrinkage allowance on a pattern is INDEPENDENT OF
A
Pouring temp of the liquid metal
B
Freezing temp of the liquid metal
C
The component size
D
Coefficient of thermal contraction of solidified metal

GATE ME 1992
In a green sand moulding process, uniform ramming leads to
A
Less chance of gas porosity
B
Uniform flow of molten metal into the mould cavity
C
Greater dimensional stability of the casting
D
Less sand expansion type of casting defect
GATE ME 1993

Centrifugally casted products have

A
Large grain structure with high porosity
B
Fine grain structure with high density
C
Fine grain structure with low density
D
Segregation of slug towards the outer skin of the casting

GATE ME 1996

Light impurities in the molten metal are prevented from reaching the mold cavity by providing a
A
Strainer
B
Button well
C
Skim bob
D
All of the above
GATE ME 1999
Which of the following materials requires the largest shrinkage allowance, while making a pattern for casting?
A
Aluminium
B
Brass
C
Cast Iron
D
Plain Carbon Steel
GATE ME 2000

Disposable patterns are made of

A
Wood
B
Rubber
C
Metal
D
Polystyrene
GATE ME 2001

Shrinkage allowance on pattern is provided to compensate for shrinkage when

A
The temperature of liquid metal drops from pouring to freezing temperature
B
The metal changes from liquid to solid state at freezing temperature
C
The temperature of solid phase drops from freezing to room temperature
D
The temperature of metal drops from pouring to room temperature

GATE ME 2002

The primary purpose of a sprue in a casting mold is to

A
Feed the casting at a rate consistent with the rate of solidification
B
Act as a reservoir for molten metal
C
Feed molten metal from the pouring basin to the gate
D
Help feed the casting until all solidification takes place
GATE ME 2002

In centrifugal casting, the lighter impurities are

A
Uniformly distributed
B
Forced towards the outer surface
C
Trapped near the mean radius of the casting
D
Collected at the center of the casting

GATE ME 2003

Hardness of green sand mould increase with

A
Increase in moisture content beyond 66 percent
B
Increase in permeability
C
Decrease in permeability
D
Increase in both moisture content and permeability
GATE ME 2004

Misrun is a casting defect which occurs due to

A
Very high pouring temperature of the metal
B
Insufficient fluidity of the molten metal
C
Absorption of gases by the liquid metal
D
Improper alignment of the mould flasks

GATE ME 2006

An expendable pattern is used in

A
Slush casting
B
Squeeze casting
C
Centrifugal casting
D
Investment casting
GATE ME 2007

Which of the following engineering materials is the most suitable candidate for hot chamber die casting
A
Low carbon steel
B
Titanium
C
Copper
D
tin

GATE ME 2009

Two streams of liquid metal, which are not hot enough to fuse properly, result into a casting defect known as
A
Cold shut
B
Swell
C
Blow hole
D
Scar
GATE ME 2011

Green sand mould indicates that

A
Polymeric mould has been cured
B
Mould has been totally dried
C
Mould is green in colour
D
Mould contains moisture

GATE ME 2013
A cube shaped casting solidifies in 5 min. The solidification time in min for a cube of the same material, which
is 8 times heavier than the original casting, will be
A
10
B
20
C
24

40
 GATE ME 2014 Set 3
Match the casting defects (Group A) with the probable causes (Group
B):
A
P−1,Q−3,R−2,S−4
B
P−4,Q−3,R−2,S−1

P−3,Q−4,R−2,S−1
D
P−1,Q−2,R−4,S−3
GATE ME 2014 Set 3

The hot tearing in a metal casting is due to

A
high fluidity
B
high melt temperature
C
Wide range of solidification temperature
D
Low coefficient of thermal expansion

GATE ME 2015 Set 3

In full mould (cavity-less) casting process, the Pattern is made of

A
Expanded polystyrene
B
Wax
C
Epoxy
D
Plaster of Paris