Part 5 of the Investment Checkoff List Series we will cover using investment.
This is meant to serve as a reminder or quality-control list. The information in parenthesis is a possible condition which may result from lack of, or improper control of the parameter.
- Fresh to scrap ratio...........................Too much scrap is never good; 60 scrap/40 fresh for yellow and 50 scrap/50 fresh for white
- History of metal melting....................Overheated metal or dirty metal is trouble
- Type of metal, freezing range, grain refined, etc.....Know your metal's properties
- Crucible, stopper rod, stir rod, cement types and ages.....Reactions with metal may occur causing many problems; avoid graphite with nickel whites
- Calibrated thermocouple/pyrometer......Too hot a melt causes shrinkage; too cold incompletes
- Metallurgical properties of metal............Know your metals properties
- Crucible designated for metal type.........Avoid graphite with nickel whites, if possible
- Cleanliness of scrap/fresh metal free of investment.....Investment in metal will cause porosity or discoloration
- Melt temperature...................................Too hot a melt causes shrinkage; too cold incompletes
- Flask temperature.................................Too hot a melt causes shrinkage; too cold incompletes
- Vacuum achieved vaccumm assist.........Insufficient vacuum causes incompletes
- Rotation speed centrifugal....................Too slow may cause incompletes; too fast may cause investment to fracture or pieces to break off
- Protective gas covers used melt/flask....Air will oxidize metals decreasing their life
- Travel distances and flow paths of metal....The longer the distance the cooler the metal will become and the more unstable the flow becomes
- Possible contamination sources.............Iron, investment, rouge, etc. are never good in a melt
- Pressure assists used............................If you have it, take advantage of it
- Acceleration rate centrifugal.................Too slow may cause incompletes; too fast may cause investment to fracture or pieces to break off
- Type and duration of heating used........Gas flames should always be gas rich
- Reactivity of metal and investment......Too hot a metal and/or flask may result in reactions causing porosity or dark sulphate regions
- Time before flask is moved..................Let it sit until metal is solid, if moving is required, be gentle until bottom loses its red glow
- Time before metal solidifies in flask.....Button should solidify in 15-45 seconds
- Flux type used and condition...............Use only fluxes recommended for golds(boric acid/borax mix)
- Quantity/when flux is used.................Too much flux may end up in your pieces (bright spots)
- Rate of pour........................................Too slow may cause incompletes on hand pours