Here, I have listed 10 most common casting defects (with images) that are observed in sand casting.
I have also mentioned the causes and remedies of these casting defects. So that you can avoid them during the metal casting practice.
10 Types of Casting Defects
Let me tell you a few important things about each of these casting defects with images. I have also discussed the causes and remedies of each casting defect below.
10 Types of Casting Defects
Types of Casting defects and their causes and remedies are mentioned below.
Misrun is a type of casting defect that occurs when the metal is unable to fill the mold cavity and thus leaves the unfilled portion in the mold cavity.
- The molten metal may have less fluidity.
- The temperature of molten metal is low.
- Pouring speed is slow.
- Cross section of the mold cavity is thin.
- The pouring temperature should be high.
- Gating system should be modified.
When the metal is melted, the flux is added to it in order to remove the undesirable impurities and oxides present in the metals.
During the time of tapping, the slag should be property removed otherwise if it mixes with molten metal, then it causes a defect called inclusions (slag). Also there are many other reasons which are responsible for slag formation. These causes are mentioned below.
- Improper gating system.
- Improper pouring of molten metal.
- Soft ramming.
- Core sand quality.
- Improper flux.
- Modifying the gating system and pouring technique.
- Use the proper flux.
- Proper ramming of sand should be done.
- Superior sand should be used.
#3) Cold shut
When the two portions of the molten metal flow together, there is a lack of fusion between them due to premature solidification. This defect in casting is called cold shut.
- This defect may occur due to lack of fluidity of molten metal.
- Faulty design.
- Less pouring temperature of metal.
- Design of the gating system should be improved.
- Maintaining the higher pouring temperature of molten metal.
#4) Shrinkage cavity
This defect is caused due to depression in the surface in the casting which is caused by solidification shrinkage that restricts the amount of liquid metal available in the last region to freeze.
- This occurs due to a faulty gating system.
- Also due to improper chilling.
- Gating system should be improved.
- Chilling system should be modified.
#5) Blow holes
Blow holes are like small cavities in a casting.
The holes that appear on the surface of the metal casting are known as open blow holes. While the holes which occur inside the metal casting are termed as blow holes.
- This defect occurs due to unnecessary moisture content in the molding sand.
- It occurs due to low permeability of sand and excessive fine grain sand.
- Excessive binders also cause this defect in casting.
- Improper baked cores also lead to this defect.
- Moisture content should be regulated.
- Cores should be baked properly.
- Cores and moulds should be vented properly.
- Binders should be used in the desired amount.
The porosity is a pin holes type defect seen in the casting. This defect is also called gas porosity as hydrogen gas is responsible for this defect.
Generally the gases remain absorbed by the molten metal. But when the metal solidifies, its solubility decreases and the gases are released which creates small holes throughout the casting.
You can see the schematic image of porosity below.
- This defect occurs due to low permeability of the molding sand as well as high moisture content present in the sand.
- Gases dissolved in molten metal are also responsible.
- This defect may occur due to less amount of flux used in molten metal.
- Also high pouring temperature is responsible for porosity.
- Increase the proportion of flux.
- Proper venting should be done and moisture content of the molding sand should be reduced.
#7) Hot tearing
Hot tearing (also known as hot cracking) occurs when the casting is restrained in early stages of cooling after the solidification process.
- Lack of collapsibility of mold and sand core.
- Very hard ramming also causes this defect.
- collapsibility of mold and sand cores should be improved.
- Soft ramming should be done.
#8) Hard spots
The hard spots are generally developed on the iron castings which are rich in silicon. This is due to the chilling of those spots by the molding sand.
- Improper metal composition.
- Improper casting design.
- Metal composition should be improved.
- Casting design should be improved.
The deformation of the casted components takes place due to internal stress of the casting or due to different rate of solidification in different sections. This results in warpage.
- Improper directional solidification.
- Large flat surface castings also cause warpage.
- Directional solidification should be looked after properly.
- Casting design should be modified to break the continuity.
Sometimes due to high pressure of the molten metal, the mold will enlarge slightly. Because of this the size of cavity increases and so the final casting will be bulgy at that point. This defect is called swells.
- Soft ramming causes this defect.
- Low strength of sand cores.
- Mold is not supported properly.
- Harder ramming should be done.
- Strength of mold and sand cores should be increased.
- Proper support should be provided to the mold.