Gas porosity is the formation of gas bubbles within the casting after it has cooled.
This occurs because most liquid materials can hold a large amount of dissolved gas, but the solid from of same material cannot, so the gas forms bubbles within the material as it cools.
Gas porosity may appear itself on the surface as a pore/cavity. Perhaps it trapped inside the metal results in reduction of strength in the vicinity.
In most of the cases, Nitrogen, Oxygen and hydrogen cause gas porosity.
In aluminum castings, only hydrogen gas dissolves in significant amounts, which cause Hydrogen gas porosity
Whether a vacancy in a cast material is a result of gases or shrinkage, sometimes it is hard to tell.
If the vacancies are spherical and smooth, they are most likely a result of gases.
Angular and rough vacancies are most likely a result of shrinkage. Macroscopic voids found in a casting are almost due to shrinkage caused by poor feeding.
Gross absences of material within the metal casting are a result of shrinkage. The largest shrinkage pore of all in any casting is usually the pipe which ideally occurs in the riser.
Whether a vacancy in a cast material is a result of gases or shrinkage, sometimes it is hard to tell.
If the vacancies are spherical and smooth, they are most likely a result of gases.
Angular and rough vacancies are most likely a result of shrinkage. Macroscopic voids found in a casting are almost due to shrinkage caused by poor feeding.
Gross absences of material within the metal casting are a result of shrinkage. The largest shrinkage pore of all in any casting is usually the pipe which ideally occurs in the riser.
Whether a vacancy in a cast material is a result of gases or shrinkage, sometimes it is hard to tell.
If the vacancies are spherical and smooth, they are most likely a result of gases.
Angular and rough vacancies are most likely a result of shrinkage. Macroscopic voids found in a casting are almost due to shrinkage caused by poor feeding.
Gross absences of material within the metal casting are a result of shrinkage. The largest shrinkage pore of all in any casting is usually the pipe which ideally occurs in the riser.
Whether a vacancy in a cast material is a result of gases or shrinkage, sometimes it is hard to tell.
If the vacancies are spherical and smooth, they are most likely a result of gases.
Angular and rough vacancies are most likely a result of shrinkage. Macroscopic voids found in a casting are almost due to shrinkage caused by poor feeding.
Gross absences of material within the metal casting are a result of shrinkage. The largest shrinkage pore of all in any casting is usually the pipe which ideally occurs in the riser.
Whether a vacancy in a cast material is a result of gases or shrinkage, sometimes it is hard to tell.
If the vacancies are spherical and smooth, they are most likely a result of gases.
Angular and rough vacancies are most likely a result of shrinkage. Macroscopic voids found in a casting are almost due to shrinkage caused by poor feeding.
Gross absences of material within the metal casting are a result of shrinkage. The largest shrinkage pore of all in any casting is usually the pipe which ideally occurs in the riser.
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