Casting Defects
Gas
Molding material
Metallurgical
Pouring Metal
Shrinkage cavities
Lower permeability
Improper design
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Air inclusion
Pin hole porosity
Blow holes
due to moisture trap in the mold/core
spherical, flattened, elongated cavity inside/on surface inside called blow holes, on surface called open blow
lower venting and low permeability
due to high pouring temperature, poor gating design ( such as straight sprue
atmospheric /other gases absorb by molten metal in the furnace/can’t escape
low permeability
high pouring temperature
critical, cause fluid leakage under high operating
pressure.
caused by hydrogen in the molten metal (pick up in furnace)
Metal penetration
Fusion
Cut and washes
Run out
Rat tail and buckles
caused by erosion of sand molding (low strength of sand mold, high velocity metal flow
choice correct molding sand, increase the gates size, using multiple ingates.
rough spots and areas excess metal
molten metal enter gaps between sand
due to sand too coarse, high pouring temperature
due to low refractoriness character of clay, pouring temperature too high
appropriate type, amount of bentonite
fusion of sand grains with the molten metal, giving brittle, glassy appearance.
molten metal leaks out of the mold
due to faulty mold making, faulty mold flask
excessive heat of molten metal, sand expand
poor expansion properties and hot strength, heat in pouring metal too high, facing sand not enough carbonaceous (cushioning effect)
Cold shuts
Slag Inclusion
Misrun
metal unable to fill the mold cavity completely
‐ two metal streams, not fuse together properly, causing discontinuity or weak spot
lower fluidity of the molten metal, section thickness too small
flux add to remove oxides/impurities ‐
gain slag
use slag trapping
slag must be remove. Otherwise, if enter in mold cavity, weakening, spoil the surface
required proper feeding ( proper casting design)
cause by liquid shrinkage during
solidification
Hot tear
Hot spots
unwanted stress during cooling ‐
cause rupture
caused by chilling of the casting ‐ chilled surface (certain element on the surface ‐ hard – difficult for machining)