casting procedure

Question 1

what is the procedure for casting

Answer 1

1. emlt alloy
2. add casting flux to molten alloy
3. time allowable for casting should be done once ring removed from furnance to decrease heat loss from investment otherwise insufficeint thermal expansion, prevent premature solidification of molten alloy
4. quench casting only for gold alloy. distortion may occur if quencehd when metal not completely solidified
5. clean casting to remove oxide and tarnished layer using pickling and sandblasting

Question 2

what are the advantages of quenching

Answer 2

-alloy left in softenend condition for burnishing/ polishing

• can easily retrieve casting from investment for gypsum bonded investment

Question 3

what is pickling

Answer 3

heating discoloured casting in acid
50% aq solution of hcl and 50% aq solution of h2so4, can increase action by adding a little potassium dichlorate

Question 4

why is adequate casting pressure required

Answer 4

to prevent back pressure porosity