casting defects Flashcards
(27 cards)
in which castings solidify before completely filling the mold cavity
misruns
what are the typical causes of misruns?
- fluidity of the molten metal is insufficient
- pouring temperature is too low
- pouring is done too slowly
- cross-section of the mold cavity is too thin
it occurs when two portions of the metal flow together bu there is a lack of fusion between them due to premature freezing
cold shuts
it is a result of splattering during pouring, causing the formation of solid globules of metal that become entrapped in the casting
cold shots
how to prevent cold shots?
pouring procedures and efficient gating system designs
it is a depression in the surface or an internal void in the casting caused by solidification shrinkage
shrinkage cavity
what is the cause of shrinkage cavity?
mainly caused by solidification shrinkage that restricts the amount of molten metal available in the last region to freeze
how is shrinkage cavity prevented?
it is often solved by proper riser design
it consists of a network of small voids distributed throughout the casting caused by localized solidification shrinkage of the final molten metal in the dendritic structure
microporosity
it occurs when the casting is restrained from contraction by an unyielding mold during the final stages of solidification or early stages of cooling after solidification
hot tearing
hot tearing is also called as __________
hot cracking
how is hot tearing manifested?
it is manifested as a separation of the metal at a point of high tensile stress cause by the metal’s inability to shrink naturally
how is hot tearing prevented?
in the expendable mold process, it is prevented by compounding the mold to be collapsible. in the permanent mold process, it is reduced by removing the part from the mold immediately after solidification.
it is a defect consisting of a balloon- shaped gas cavity
sand blow
what causes sand blow?
it is caused by the release of mold gases during the pouring. also: low permeability, poor venting, and high moisture content of the sand mold
what causes pinholes?
it is caused by the release of gases during pouring
it consists of many small gas cavities formed at or slightly below the surface of the casting
pinholes
it is an irregularity in the surface of the casting that results from erosion of the sand mold during pouring, and the contour of the erosion is formed in the surface of the final cast part
sand wash
these are rough areas o the surface of the casting due to encrustations of sand and metal.
scabs
scabs are caused by?
it is caused by portions of the mold surface flaking off during solidification and becoming embedded in the casting surface
it refers to a surface defect that occurs when the fluidity of the liquid metal is high, and it penetrates into the sand mold or sand core
penetration
how is penetration alleviated?
by harder packing of the sand mold
it refers to a defect caused by a sidewise displacement of the mold cope relative to the drag
mold shift
what happens with mold shift?
a step in the cast product at the parting line may be observed
