PIG IRON

Pig Iron

Pig irons are produced by blast furnaces from iron ore and from ferrous scrap in cupolas or electric furnaces (refined pig irons), or as by-products from other processes such as vanadium or titanium oxide production. These latter pig irons are usually high purity irons most suitable for ductile iron production.

The composition of refined pig irons can be adjusted to comply with customer requirements, including a known residual content or added alloys with a specified range of alloy content.

Typical pig iron compositions, with the exception of high purity irons, are shown in Exhibit M.

Control

Pig iron is ordered to a given specification range and should be accompanied by a supplier’s certificate of composition which should include the major residual contents.

No two batches are the same and unless the operation can withstand a reasonable tolerance in casting compositional range, each batch (which in the case of blast furnace irons may have variations in the batch) should be kept separate. This ideal may not be possible in large melting plants.

Foundries should insist on a certificate of analysis and also carry out analytical checks to ensure a quality material.

Pig iron is an expensive metallic and should be used as a general quality control in the metallic charge, i.e.:

 provide and even out carbon “pick-up” variations

 provide and even out silicon levels

 control phosphorus levels

 ensure a better mixing in cupola operations which have inadequate wells and fore hearth facilities

 as a control for excessive residual element levels and possible gas levels when high steel charges are used.

Return Scrap

The return scrap of each individual foundry should be of a known and generally consistent composition. It should be used to the maximum consistent with obtaining the desired composition of the castings to be manufactured.

Control

Each grade of scrap should be kept separate. Large pieces should be broken to a size suitable for individual furnace requirements.

c) Ferro-Alloys

Ferro alloys are used as additions to ensure control of elements such as silicon and manganese in the standard non or low alloy irons.

The high alloy irons such as Ni hard, Ni resist and high chromium iron, represent a small percentage of the iron foundry industry and require special attention to their choice of alloys and ferro alloys. Ferro silicon	Most common grades in lump form contain 75–80% and 45–50% silicon levels.
Silicon carbide	In lump form containing 55–60% Si and 25–30% C
Ferro manganese	Usually obtained in lump form and contains 75–80% manganese.

The use of larger amounts of ferro silicon in cupolas can result in excessive silicon variations unless suitable mixing volumes are provided in wells, receivers or ladles.

Do not rely too much on the cupola for mixing purposes as it is very possible to obtain a wide variation in silicon content from the well, even with a tap and bott system.

Control

Ferro alloys should be checked that they comply with the foundry’s specification for size, grading and composition.

In particular, ferro silicon should be checked for fines as this is a source of high silicon losses and hence variation in silicon content in melting operations.

Briquettes should be checked for consistency of weight and friability. Instability of briquette can also lead to high silicon losses in the cupola.

In both cases alloy content should be occasionally checked by the foundry or by an independent laboratory.

Accurate weighing of ferro alloy additions on suitable scales is an absolute essential to control silicon and manganese contents. When briquettes are used, ensure the chargers can count!