Casting Defects
Casting Defects:
Some defects are common to any and all process. These defects are illustrated in figure briefly described in the following:
[pic]
A) Misruns: A Misrun is a casting that has solidified before completely filling the mold cavity.
Typical causes include
1) Fluidity of the molten metal is insufficient,
2) Pouring Temperature is too low,
3) Pouring is done too slowly and/or
4) Cross section of the mold cavity is too thin.
b) Cold Shut: A cold shut occurs when two portion of the metal flow together, but there is lack of fusion between them due to premature freezing, Its causes are similar to those of a Misruns.
c) Cold Shots: When splattering occurs during pouring, solid globules of the metal are formed that become entrapped in the casting. Poring procedures and gating system designs that avoid splattering can prevent these defects.
d) Shrinkage Cavity: This defect is a depression in the surface or an internal void in the casting caused by solidification shrinkage that restricts the amount of the molten metal available in the last region to freeze. It often occurs near the top of the casting in which case it is referred to as a pipe (Figure 12.7). The problem can often be solved by proper riser design.
e) Microporosity: This refers to a network of a small voids distributed throughout the casting caused by localized solidification shrinkage of the final molten metal in the dendritic structure.
The defect is usually associated with alloys, because of the protracted manner in which freezing occurs in these metals.
f) Hot Tearing: This defect also called hot cracking occurs when the casting is restrained or early stages of cooling after solidification. The defect is manifested as a separation of the metal (hence the terms tearing or cracking) at a point of high tensile stress caused by metal’s inability to shrink naturally. In sand casting and other expandable mold processes, compounding the mold to be collapsible prevents it. In
Some defects are common to any and all process. These defects are illustrated in figure briefly described in the following:
[pic]
A) Misruns: A Misrun is a casting that has solidified before completely filling the mold cavity.
Typical causes include
1) Fluidity of the molten metal is insufficient,
2) Pouring Temperature is too low,
3) Pouring is done too slowly and/or
4) Cross section of the mold cavity is too thin.
b) Cold Shut: A cold shut occurs when two portion of the metal flow together, but there is lack of fusion between them due to premature freezing, Its causes are similar to those of a Misruns.
c) Cold Shots: When splattering occurs during pouring, solid globules of the metal are formed that become entrapped in the casting. Poring procedures and gating system designs that avoid splattering can prevent these defects.
d) Shrinkage Cavity: This defect is a depression in the surface or an internal void in the casting caused by solidification shrinkage that restricts the amount of the molten metal available in the last region to freeze. It often occurs near the top of the casting in which case it is referred to as a pipe (Figure 12.7). The problem can often be solved by proper riser design.
e) Microporosity: This refers to a network of a small voids distributed throughout the casting caused by localized solidification shrinkage of the final molten metal in the dendritic structure.
The defect is usually associated with alloys, because of the protracted manner in which freezing occurs in these metals.
f) Hot Tearing: This defect also called hot cracking occurs when the casting is restrained or early stages of cooling after solidification. The defect is manifested as a separation of the metal (hence the terms tearing or cracking) at a point of high tensile stress caused by metal’s inability to shrink naturally. In sand casting and other expandable mold processes, compounding the mold to be collapsible prevents it. In