Nitrogen, oxygen and hydrogen are the most encountered gases in cases of gas porosity. Gas porosity may present itself on the surface of the casting as porosity or the pore may be trapped inside the metal, which reduces strength in that vicinity. This occurs because most liquid materials can hold a large amount of dissolved gas, but the solid form of the same material cannot, so the gas forms bubbles within the material as it cools. Gas porosity is the formation of bubbles within the casting after it has cooled. The defects are broken up into macroporosity and microporosity (or micro shrinkage), where macroporosity can be seen by the naked eye and microporosity cannot. They require a nucleation point, so impurities and dissolved gas can induce closed shrinkage defects. The shrinkage defect usually forms at the top of the hot spots. Isolated pools of liquid form inside solidified metal, which are called hot spots. Ĭlosed shrinkage defects, also known as shrinkage porosity, are defects that form within the casting. Pipes form at the surface of the casting and burrow into the casting, while caved surfaces are shallow cavities that form across the surface of the casting. There are two types of open air defects: pipes and caved surfaces. Open shrinkage defects are open to the atmosphere, therefore as the shrinkage cavity forms, air compensates. Shrinkage defects can be split into two different types: open shrinkage defects and closed shrinkage defects.

Shrinkage defects usually occur in either the cope or drag portion of the casting. Shrinkage defects will have jagged or linear appearance. Most of these also occur in other casting processes.Ĭan occur when standard feed metal is not available to compensate for shrinkage as the thick metal solidifies. The following defects can occur in sand castings. Some of the solutions to certain defects can be the cause for another type of defect. There are many types of defects which result from many different causes. Therefore, if the casting is less than perfect, but still useful and in tolerance, the imperfections should be deemed 'discontinuities'. Discontinuities, also known as 'imperfections', are defined as 'interruptions in the physical continuity of the casting'. Defects are defined as conditions in a casting that must be corrected or removed, or the casting must be rejected. The terms 'defect' and ' discontinuity' refer to two specific and separate things in castings. They are broken down into five main categories: gas porosity, shrinkage defects, mould material defects, pouring metal defects, and metallurgical defects. Some defects can be tolerated while others can be repaired, otherwise they must be eliminated.

For the practice of working during an ongoing strike, see Strikebreaker.Ī casting defect is an undesired irregularity in a metal casting process.

Hot brass casing burn