casting defects

1. - CASTING DEFECT-
Is defined as irregularity in the metal casting process that is
very undesired
 DISTORTION
Distortion of the casting
probably related to
distortion of the wax
pattern
 Due to hygroscopicandsetting
expansion
 Distortionduringmanipulation
 Manipulationof wax at high
temperature
 Investingpatternwithinone hourafter
finishing
 SURFACE
ROUGHNESS
Defined as relatively
fined space surface
imperfactions whose
height,width and
direction establish the
predominant surface
ptn.
 Airbubblesonthe wax pattern
 HigherW/Pratio
 prolongedheating
 Propermixingof the investment
 Usingcorrect W/P ratio
 Complete the castingassoonas ringis
heated
 POROSITY
External or Internal
External-cause
discoloration of the
casting
Internal-weakens the
restoration
Caused by - Solidificationshrinkage:-
 Localizedshrinkage porosity
 Suck back porosity irregular
 Microporosity inshape
 By Gas:
 Pinhole porosity
 Gas inclusion usuallyspherical
 Subsurface porosity inshape
 Back pressureporosity
:-AvoidBy
 Use investmentof adequate porosity
 Usingadequate castingforce
Minimize distortionby:-
Avoidby:-

2. - CASTING DEFECT-
Is defined as irregularity in the metal casting process that is
very undesired
 INCOMPLETE
CASTING
 Insufficientalloyused
 Premature solidificationof alloy
 Low castingpressure
 Alloynotable toenterthinparts of
mould
 Mouldis notheatedto casting
temperature
 Sprue are blockedwithforeignbodies