Hints on investment casting: troubleshooting casting problems
Defect
cause
solution
Cracking
Quenching too soon
Wait 15-20 minutes
Cracking
Metal cast too soon
Increase casting temperature
Cracking
Flask too cold
Increase flask temperature
Cracking
Incorrect sprueing
Modify sprueing
Cracking
Contamination of gold or alloy
Refine metal
Cracking
Oxide build up in metal, over-use
Refine metal
Cracking
Hydrochloric acid di-vesting
Use alternative di-vestor
Incomplete fill
Metal too cold
Increase casting temperature
Incomplete fill
Flask too cold
Increase flask temperature
Incomplete fill
Insufficient vacuum
Check vacuum for leaks and seal
Incomplete fill
Wrong speed on centrifugal caster
Adjust speed
Incomplete fill
Insufficient burn out
Modify sprue
Incomplete fill
Incomplete burn out
Use proper burn out schedule
Inclusions in castings
Sharp corners or bends in sprueing
Round out sharp corners and bends
Inclusions in castings
Crucible old and deteriorating
Replace crucible
Inclusions in castings
Oxide build up in crucible
Clean or replace crucible
Inclusions in castings
Foreign particles or oxides in metal
Refine metal
Inclusions in castings
Investment erosion or breakdown
Follow investment manufacturerâs mixing instructions
Brittle prongs on castings
Improperly alloyed metal
Pre-allay gold and master alloy
Brittle prongs on castings
Flask temperature too cold
Increase flask temperature
Shrinkage prorsity
Incorrect sprueing
Sprue to heaviest area of casting
Shrinkage porosity
Inadequate sprueing
Use larger sprue or multiple sprues
Shrinkage porosity
Flask too hot
Use lower flask temperature
Shrinkage porosity
Castings too close to sprue button
Leave 1" space on tree above main sprue button
Gas porosity
Metal overheated
Reduce casting temperature
Gas porosity
Inadequate burn out
Increase top end burn out time
Gas porosity
Inadequate air supply during burn out
Assure oven has good air supply & exhaust
Gas porosity
Flask too hot
Reduce flask temperature
Gas porosity
Scrap reused too many times
Refine metal
Gas porosity
Too much oxygen on torch flame
Use reducing flame when melting
Gas porosity
Investment residue on remelted scrap
Remove investment residue before remelting scrap
Rough castings
Flasks not cured before burnout loading
Let flasks set 1-2 hrs. before burnout loading
Rough castings
Incorrect water-powder ratio in invest. mix
Follow investment manufacturerâs instructions
Rough castings
Flasks heated too rapidly
Follow investment manufacturerâs instructions
Bubbles/nodules on castings
Investment not mixed, vacuumed or vibrated sufficiently
Follow investment manufacturerâs instructions
Bubbles/nodules on castings
Vacuum pump not working properly
Bubbles/nodules on castings
Wax patterns not coated with wetting agent
Coat wax patterns with wetting agent
Andy " The Tool Guy" Kroungold
Tool Sales / Technical
Stuller Inc
Phone 800-877-7777 ext. 94194
Fax 337-262-7791