Nodular Pig Iron for Foundries Producing Ductile Iron Castings
Nodular Pig Iron is differentiated from other types of pig iron by its low manganese, phosphorus and sulphur contents, typically maximum 0.05% for each element.
In practice, manganese will be <0.05%, phosphorus <0.04% and sulphur <0.02%.
Nodular Pig Iron constitutes the principal ferrous raw material in production of ductile iron castings (also known as nodular or spheroidal graphite iron).
The Benefits of Using Nodular Pig Iron in Ductile Iron Castings:
Low residual content
Allows dilution of undesirable elements in the melt
Better control and lower variability of melting process
Tighter control of final casting composition = better mechanical properties of castings
Removes requirement for costly heat treatment of castings
Lower melting temperaturethan steel scrap = lower energy requirement in the furnace
Higher bulk densitythan steel scrap = lower storage space needs, fewer charge buckets
required, better electromagnetic effect thus quicker melting and reduced power consumption
Lower surface area:volume ratio than scrap = lower oxide (rust) formation = lower slag
Increasing percentage of pig iron in the charge normally leads to higher nodule countsin
ductile iron castings
Nodular Pig Iron For Producing Ductile Iron Castings
Nodular pig iron is produced in conventional blast furnaces, using either coke or charcoal, and in electric furnaces, as a co-product of titanium dioxide slag production. In some cases, ladle metallurgy is used for further refining.
The blast furnace chemically reduces and physically converts iron oxide into liquid iron called “hot metal”. Further refining of the “hot metal” is carried out to reduce sulphur and phosphorus to acceptable levels for nodular pig iron grades.
Iron oxide can be in the form of raw ore, pellets, or sinter. The ore can be either hematite or magnetite, with iron content ranging from 50-70 percent. The oxygen in the iron oxide is removed by a series of chemical reactions shown below.
The basic reduction reactions in the blast furnace are:
Producers of titanium dioxide slag in Canada, South Africa, and Norway smelt ilmenite in electric furnaces at temperatures ranging from 1650-1700°C, using either coal or another carbonaceous material as reductant. Titanium dioxide slag is largely used as a raw material for producing white pigment, mostly for the paint and plastics industries. The basic reactions in smelting are shown below.
Basic reactions in ilmenite smelting are: