The making of cast iron begins with a combination of raw
materials. Iron is rarely found in its pure form. Only
meteorites contain pure iron. The iron in use for centuries is
found in the combination of iron and other elements. These
combinations are known as iron oxides. Mining pulls most of the
iron from iron ores which are rocks found on the outer layers of
the earth that contain iron. This iron ore is then converted
into various types of iron but first it is processed in a blast
furnace to produce pig iron. Used by itself, pig iron has few
uses due to its brittle nature. Alloyed with other metals, pig
iron takes on new uses.
Making Cast Iron
The term cast iron is generally used to describe grey cast iron,
but it can also describe a whole group of alloys too. The
surface color of the cast iron is often used to identify it.
Cast iron begins its life as pig iron, which is remelted and
often combined with large amounts of scrap iron and sometimes
with steel. Contaminants are removed from the melted pig iron,
and the iron, once melted, is then cast. Casting is the process
of pouring the iron into a mold thus giving it a shape. Molds
and pouring methods divide this process up. Molds can be made as
expendable molds (sand) or non-expendable molds (metal). Pouring
can happen via gravity, low-pressure or vacuum. Controlling the
pouring process becomes more important the more intricate the
mold is.
Solidifying Cast Iron
After the iron is cast, it is allowed to solidify. If performed
incorrectly, the solidification process can destroy the effort
and the metal is then re-used as scrap metal thus being recycled
and living again as pig metal ready for casting. Controlling the
cooling curve is very important to good solidification practices
and can note the difference between high quality and average
cast iron. Quick cooling produces fine grain construction and
slow cooling produces coarse grain construction. Cast iron that
has not cooled evenly produces a low-quality cast. Other
problems faced during the cast iron process include
contamination of the iron, gas porosity (the forming of bubbles
in the iron), and problems with the fluidity of the metal. The
casting process is an art that must be examined and experienced
to be fully understood.
  
HOME PAGE | CASTING BLOG | CONTACT US |
