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Investment materials
1. Investment Material
Qus:
1.Classify investment & write in detail about the composition and function of each component of a gypsum-
bonded investment material.
Ans:
According to binders used there are three types of investment materials.
A. Gypsum- bonded investment.
B. Phosphate – bonded investment materials.
C. Ethyl – Silicate bonded investment materials.
According to Expansion:
A. Type -1
B. Type -2
C. Type -3
Composition and Function of each component of a gypsum – bonded investment material.
A.Sillica:
Silica is any of its allotropic form , such as cristobalite or quartz or both.
Function of sillica:
1.Acts as a refractory.
2.Regulates mold expansion.
B.Calcium Sulphate:
1.To react with water and on hydration , to bind the silica together.
2.To impart sufficient strength of the mould by providing rigidity.
3.To contribute to the mould expansion by setting expansion.
C.Reducing Agent:
Reducing Agent such as charcoal powder provides a reducing environment and reduces any oxide form in the
metal.
D.Modifres:
For example , sodium chloride and boric acid.