Castting defect

1. Casting Defects and Solidification
ABP
Prof. Aniket B.Pawar
Mechanical Engineering Department
RAJARAMBAPU INSTITUTE OF TECHNOLOGY, RAJARAMNAGAR
Unit : 2

2. 2
➢ Types of fuel fired melting Furnaces- Cupola furnace, oil/gas fired furnaces, crucible
furnaces, Electrical furnaces.
➢ Metal pouring equipment.
➢Introduction to permanent mould casting Process- Gravity and pressure die-casting,
Centrifugal casting, Continuous casting. shell Molding, CO2 Molding, Investment casting
➢ Solidification control devices: chills, ceramics bricks, directional solidification .
➢ Pollution Control in foundries, Cleaning- fettling and inspection of casting.
➢ Defects in casting
Content

3. 3
CASTING DEFECTS
➢ A casting defect is an irregularity in the metal casting process that is undesired.
➢ It may sometimes be tolerated sometimes eliminated with proper moulding practice or
repaired using methods such as welding, metallization etc.
➢ There are many types of defects which result from many different causes. Some of the
remedies to certain defects may be the cause for another type of defect.
➢ Defects in castings occur due to various causes. Although it is quite difficult to establish a
relationship between defects & causes casting defects are roughly broken down into five
main categories :
➢ Gas defects, Solidification of metal, Sand problems, Moulding making problem.

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CASTING DEFECTS
➢ Gas Defects
• Blow hole
• Porosity
• Pin hole
➢ Solidification of metal
• Miss Run
• Cold Shunt
• Hot Tears
• Shrinkage Cavity
➢ Sand problems
• Penetration
• Swell
• Fusion
• Drop
➢ Moulding making problem - Shift

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BLOW HOLES
➢ Balloon shaped gas cavities caused by release of mould gases during pouring are known
as blow holes.
➢ Causes : • Ramming is too hard. • Cores are not sufficiently baked. • Excess moisture
content. • Low sand permeability. • Excessive fineness of sand grains. • Rusted chills,
chaplets & inserts. • Presence of gas producing ingredients.
➢ Remedies : • Baking of cores properly. • Control of moisture content in moulding sand. •
Use of rust free chills, chaplets & inserts. • Provide adequate venting in mould and cores. •
Ramming the mould less harder.

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POROSITY
➢ Porosity is in the form of cavities caused due to gas entrapment during solidification.
➢ Causes : • High pouring temperature. • Gas dissolved in metal charge. • Less flux used.
• Molten metal not properly degassed. • Slow solidification of casting. • High moisture and
low permeability of mould.
➢ Remedies : • Regulate pouring temperature • Control metal composition.
• Increase flux proportions. • Ensure effective degassing. • Modify gating and risering. •
Reduce moisture and increase permeability of mould.

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MISRUN & COLD SHUTS
➢ When the metal is unable to fill the mould cavity completely & thus leaves unfilled
cavities it is called as misrun defect.
➢ When two metal streams meeting in the mould cavity do not fuse together properly
causing discontinuity or weak spot inside casting it is called as cold shuts.

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MISRUN & COLD SHUTS
➢Causes : • Low pouring temperature. • Faulty gating system design. • Too thin casting
sections. • Slow and intermitted pouring. • Improper alloy composition. • Use of damaged
pattern. • Lack of fluidity in molten metal.
➢ Remedies : • Smooth pouring with the help of monorail. • Properly transport mould
during pouring. • Providing appropriate pouring temperature. • Modifying the gating
system design.

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SHRINKAGE CAVITY
➢ Shrinkage cavity is a void on the surface of the casting caused mainly due to uncontrolled
and haphazard solidification of the metal.
➢ Shrinkage defects can be split into two different types:
1) External shrinkage 2) Closed shrinkage defects.

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SHRINKAGE CAVITY
➢ Causes :
• Inadequate and improper gating & risering system.
• Too much high pouring temperature.
• Improper chilling.
➢ Remedies :
• Ensure proper directional solidification by modifying gating, risering & chilling
system

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HOT TEARS or HOT CRACKING
➢ Hot tears are ragged irregular internal or external cracks occurring immediately after the
metal have solidified.
➢ Causes : • Lack of collapsibility of core & mould. • Hard ramming of mould. • Faulty
casting design.
➢ Remedies : • Providing softer ramming. • Improve casting design. • Improve collapsibility
of core & mould.

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METAL PENETRATION
➢ Penetration occurs when the molten metal flows between the sand particles in the
mould.
➢ Causes : • Low strength of moulding sand. • Large size of moulding sand. • High
permeability of sand. • Soft ramming.
➢ Remedies : • Use of fine grain with low permeability. • Appropriate ramming.

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SWELL
➢ A swell is an enlargement of mould cavity by localized metal pressure.
➢ Causes : • Insufficient or soft ramming.
• Low strength mould & core.
• Mould not being supported properly.
➢ Remedies : • Sand should be rammed evenly and properly.
• Increase strength of mould & core.

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Fusion and Drop

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MISMATCH
The casting that does not match at the parting line is known as Mismatch or Mould shift.
➢ Causes : • Worn out or bent clamping pins. • Misalignment of two halves of pattern. •
Improper location & support of core. • Faulty core boxes. • Loose dowels.
➢Remedies : • Increase strength of mould & core. • Provide adequate support to core. •
Proper alignment of two halves of the pattern. • Proper clamping of mould box. • Repair or
replace dowels & pin causing mismatch.

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CASTING DEFECTS

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Cleaning- fettling and inspection of casting
➢ Cleaning and inspection of castings are the processes through which products called
castings are made neat and then subjected to examination before they are applied to
particular use.
➢ Without cleaning and inspection of castings the castings can fail when used for certain
purposes.
➢To avoid the failures, castings must be cleaned and inspected.
➢ Many buildings and constructions have failed today because proper inspections were not
conducted on the metallic materials before their use.

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Cleaning- fettling of casting
The series of operations performed in cleaning shop may be grouped as follow:
• Decoring
• Removing of gates and risers.
• Stripping off adhered sand from the castings.
• Trimming burrs, rib.
• Scale after heat treatment.
• Straightening and painting of the castings if necessary.
• Inspecting for acceptance after cleaning and cutting.

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Inspection of casting
Inspection in this context involves the operations that check the quality of castings and results
to rejection or acceptance of the castings. Fundamental types of inspection are
➢ Visual inspection.
➢ Dimensional inspection
➢ Metallurgical inspection.
➢ Pressure test, Magnetic particle inspection, Radiographic test, Ultrasonic inspection etc. are
used

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➢ The properties of the casting significantly depends on the solidification time cooling
rate.
➢ Shrinkage of casting during cooling of solidified metal should not be restrained by the
mould material otherwise internal stresses may develop and form cracks in casting.
➢ Proper care should be taken at the design stage of casting so that shrinkage can occur
without casting defects.
Solidification and Cooling

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Solidification control devices
➢ A chills are the metal inserts used to increase the solidification rate.
➢ They are placed in critical regions of the mould.
➢ They are placed where the faster metal solidification is required for reducing shrinkage
porosity.
➢ They are made up of same material as castings.
➢ It is used where it is impossible to provide riser for a part which is heavy. This may be
due to complex shape of casting
➢ Metallic chills have the capacity of increasing the solidification rate as high as 14 times
than sand moulds of same condition.

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External Chills
➢ It is Rammed in mould sand walls.
➢ It is a good way of controlling cooling rates in critical regions of casting.
➢ Direct external chill is in level with mould cavity wall and thus comes in direct contact with the
liquid metal.
➢ Indirect external chill is placed behind the mould cavity wall and is fully buried in sand.
➢ It does not come in direct contact with the liquid metal.
➢ Sometimes indirect chill is placed at an angle to casting surface. So its chilling effect decreases
as the chill tapers away from casting
➢ Direct chills are more effective than indirect Chill.
➢ Normally made up of steel, cast iron and copper.
➢ Helps to eliminate porosity (micro and micro) at the portions of casting which is difficult to fed
by riser.

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Internal Chill
➢ Internal chills fuse into and become part of the casting. So these are made of the same
metal which is to be cast.
➢ It is rarely used because structural homogeneity is less due to improper fusion which
results in poor casting quality.
➢ Normally used in the area where it is used is to be removed after solidification. For
example bosses to be drilled/bored.
➢ One end of these remain hanging in mould cavity and the other end is supported in sand.

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25. Materials that
• Withstand high temperatures and sudden changes
• Withstand action of molten slag, glass, hot gases etc.
• Withstand load at service conditions
• Withstand abrasive forces
• Conserve heat
• Have low coefficient of thermal expansion
• Will not contaminate the load
What are Refractories
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26. Refractories
Refractory lining of a
furnace arc
Refractory walls of a
furnace interior with
burner blocks
(BEE India, 2005)
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