Special treatment of melts:
1) Before pouring molten metals are given certain treatment in order to purify them or alter the metallographic structure of castings.
2) Such treatment is preformed either by plunging reagents into the furnace bath / ladle or by injecting etc.
3) Various melt treatment are listed below:
a) Refining (oxidation, deoxidation, degassing and desulphurisation)
b) Inoculation (grain and constituents refinement, eutectic modification)
Refining:
Refining is the process of removing unwanted impurities from the molten metal during its preparation for pouring into the molds.
Degassing:
a) Vacuum degassing
- Static bath treatment
- Induction degassing
- Fractional degassing
- Stream droplet degassing
b) Gas scavenging
- Solid degasser
- Jet degasser
Some of the alloys and scavenging gases employed:
1) Copper base N2
2) Aluminum base N2, Cl2, Ar
3) Magnesium base Cl2, Ar
4) Nickel base O2
Desulphurization:
- Desulphurization means reducing the amount of sulphur.
- Is carried out in ferrous alloys.
- Typical desulphurization reagents are, for
Cast iron…………..soda ash, calcium carbide
Steel………………soda ash
Inoculation:
a) An inoculation is an addition made to molten metal, usually late in the melting operation, for modifying the solidification structure and properties of the cast metals or alloys.
b) Some common inoculation treatments are:
1) Grain and constituents refinements
Alloys typical inoculation
a) Steel Al, Ti
b) Aluminum base Ti, B, Nb, Zr
c) Magnesium base C, Zr
d) Mg- Al C
2) Refinement and eutectic modification
Alloys typical inoculation
a) Al-Si Na
b) Cast iron Si, C
c) Cast iron Mg, Ce
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