casting defects

Question 1

in which castings solidify before completely filling the mold cavity

Answer 1

misruns

Question 2

what are the typical causes of misruns?

Answer 2

1. fluidity of the molten metal is insufficient
2. pouring temperature is too low
3. pouring is done too slowly
4. cross-section of the mold cavity is too thin

Question 3

it occurs when two portions of the metal flow together bu there is a lack of fusion between them due to premature freezing

Answer 3

cold shuts

Question 4

it is a result of splattering during pouring, causing the formation of solid globules of metal that become entrapped in the casting

Answer 4

cold shots

Question 5

how to prevent cold shots?

Answer 5

pouring procedures and efficient gating system designs

Question 6

it is a depression in the surface or an internal void in the casting caused by solidification shrinkage

Answer 6

shrinkage cavity

Question 7

what is the cause of shrinkage cavity?

Answer 7

mainly caused by solidification shrinkage that restricts the amount of molten metal available in the last region to freeze

Question 8

how is shrinkage cavity prevented?

Answer 8

it is often solved by proper riser design

Question 9

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

Answer 9

microporosity

Question 10

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

Answer 10

hot tearing

Question 11

hot tearing is also called as __________

Answer 11

hot cracking

Question 12

how is hot tearing manifested?

Answer 12

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

Question 13

how is hot tearing prevented?

Answer 13

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.

Question 14

it is a defect consisting of a balloon- shaped gas cavity

Answer 14

sand blow

Question 15

what causes sand blow?

Answer 15

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

Question 16

what causes pinholes?

Answer 16

it is caused by the release of gases during pouring

Question 17

it consists of many small gas cavities formed at or slightly below the surface of the casting

Answer 17

pinholes

Question 18

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

Answer 18

sand wash

Question 19

these are rough areas o the surface of the casting due to encrustations of sand and metal.

Answer 19

scabs

Question 20

scabs are caused by?

Answer 20

it is caused by portions of the mold surface flaking off during solidification and becoming embedded in the casting surface

Question 21

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

Answer 21

penetration

Question 22

how is penetration alleviated?

Answer 22

by harder packing of the sand mold

Question 23

it refers to a defect caused by a sidewise displacement of the mold cope relative to the drag

Answer 23

mold shift

Question 24

what happens with mold shift?

Answer 24

a step in the cast product at the parting line may be observed

Question 25

it is similar to mold shift, but it is the core that is displaced, and the displacement is usually vertical

Answer 25

core shift

Question 26

core shift is caused by?

Answer 26

caused by buoyancy of the molten metal

Question 27

it occurs when mold strength is insufficient, and a crack develops, into which liquid metal can seep to form a ‘fin’ on the final casting

Answer 27

mold crack