Casting defects occur when undesired irregularities occur in the metal casting process, there are many types of defects in the metal casting industry, such as:
porosity
shrink
Mold material defect
Cast metal defects
metallurgical defects
Since there are many types of casting defects, this article focuses on porosity and shrinkage defects.

Difference Between Porosity and Shrinkage
Porosity
It can be said that porosity is classified as the most common casting defect in the casting process, and there are many factors related to such defects, such as gas, air and shrinkage. Before we start, let's talk about gas and shrinkage porosity.

porosity
Porosity occurs because most liquid materials can hold large quantities of gaseous materials, but not for solid materials, so when the metal fills the cavity, the air disperses in the form of small spheres of high-pressure air.
How to stop blowhole defects?
In short, porosity can be prevented with these solutions, materials can be melted in a vacuum, in a low-solubility gas environment that prevents contact with air, using dry molds and cores and storing dry before use, increasing the rate of solidification (reduces the metal temperature during casting), so blowholes do not occur.

shrink
Shrinkage usually occurs when standard metal feeds cannot compensate for the shrinkage of thick metal as it solidifies. This type of defect will have a jagged-like linear appearance, and we can classify shrinkage into two different types.

1. Open and shrink
First, open shrinkage defects are open to the atmosphere. Air is compensated as shrinkage cavities are formed. There are two types of air contractions. The first is tube shapes, which are open shrinkage defects that form on the surface and drill into the casting. Second, a concave shape is a shallow cavity formed on the surface of the casting.

2. Closing contractions
Second, closure shrinkage is a defect that develops within the casting. Isolated pools of liquid, called hot spots, form inside the solidified metal. Shrinkage defects usually form on top of hot spots. They require nucleation sites, so impurities and dissolved gases can cause closed shrinkage defects.

Linear and jagged appearance due to shrinkage defects.
Linear and jagged appearance due to shrinkage defects.

How to stop shrinkage defects?
In summary, shrinkage defects can be avoided using these techniques:

Using a running gating system design with risers ensures continuous flow of molten metal so shrinkage defects do not occur.
Lower the casting temperature to limit the total volume deficit.
Produce uniformly strong and rigid molds.