Casting defects are unwanted irregularities that occur in cast products due to improper mould design, poor material control, or incorrect process parameters. Common casting defects include blowholes, shrinkage cavities, cold shuts, and misruns, and they can be reduced by proper mould preparation, controlled pouring temperature, adequate venting, and correct gating design.

Casting Defects and Their Remedies

Casting defects are imperfections in the cast product caused by improper mould design, melting, pouring, or solidification.

1. Blow Holes

Description

Smooth, round cavities inside or on the surface of casting
Caused by entrapped gases

Causes

High moisture in moulding sand
Poor permeability
Gas dissolved in molten metal
Turbulent pouring

Remedies

Reduce moisture content in sand
Improve sand permeability
Proper venting of mould
Degas molten metal
Smooth and controlled pouring

2. Porosity

Description

Small, distributed gas holes throughout casting

Causes

Hydrogen or gas absorption
Inadequate degassing
High pouring temperature

Remedies

Proper degassing
Use dry moulds and cores
Control pouring temperature
Use vacuum casting if required

3. Shrinkage Cavity

Description

Irregular internal cavities formed during solidification

Causes

Improper feeding of molten metal
Absence or improper size of riser
Poor solidification control

Remedies

Provide proper risers
Use chills to control solidification
Proper gating system design
Directional solidification

4. Misrun

Description

Incomplete filling of mould cavity

Causes

Low pouring temperature
Slow pouring rate
Poor fluidity of metal
Thin sections

Remedies

Increase pouring temperature
Increase pouring rate
Improve metal fluidity
Modify casting design

5. Cold Shut

Description

A line or seam where two metal streams meet but do not fuse

Causes

Low metal temperature
Oxidation of molten metal
Improper gating design

Remedies

Increase pouring temperature
Improve gating system
Reduce turbulence
Ensure proper metal flow

6. Hot Tears (Hot Cracks)

Description

Cracks formed during solidification at high temperature

Causes

Restricted contraction
Sharp corners in casting
Poor mould collapsibility

Remedies

Provide fillets and rounded corners
Improve mould collapsibility
Proper riser placement
Uniform cooling

7. Inclusions

Description

Non-metallic materials trapped inside casting

Causes

Slag, sand, or oxide inclusions
Turbulent metal flow
Poor metal cleaning

Remedies

Use slag traps
Proper fluxing and skimming
Smooth metal flow
Clean mould cavity

8. Sand Drop

Description

Lumps of sand fall into molten metal creating cavities

Causes

Weak mould strength
Improper ramming
Excessive metal velocity

Remedies

Proper sand ramming
Improve sand strength
Reduce metal pouring speed

9. Scab

Description

A rough, raised area on casting surface

Causes

Expansion of mould sand
High moisture content
Weak mould surface

Remedies

Reduce sand moisture
Use proper sand additives
Improve sand strength

10. Metal Penetration

Description

Metal enters sand interstices, causing rough surface

Causes

Coarse sand
High pouring temperature
Low mould hardness

Remedies

Use finer sand
Increase mould hardness
Reduce pouring temperature

11. Flash

Description

Thin excess metal at mould joints

Causes

Poor mould alignment
Improper clamping
High metal pressure

Remedies

Proper mould assembly
Adequate clamping
Reduce pouring pressure

Summary Table

Defect	Main Cause	Remedy
Blow holes	Gas entrapment	Venting, degassing
Porosity	Dissolved gas	Degassing
Shrinkage	Lack of feeding	Risers, chills
Misrun	Low fluidity	Higher temp, faster pour
Cold shut	Poor fusion	Better gating
Hot tears	Restricted contraction	Fillets, collapsibility
Inclusions	Slag/sand	Fluxing, slag traps
Sand drop	Weak mould	Better ramming
Scab	Sand expansion	Control moisture
Penetration	Coarse sand	Finer sand
Flash	Poor alignment	Proper clamping