Metal Casting Zone Info Blog

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Today we learn about the different types of casting furnaces.

In Metal Casting, the type of furnace you have at your foundry, or
workshop determines a lot of the work you can or can not do.
Many metal casters enjoy making their own furnaces and have done
so quite successfully. The plans for home made furnaces are eagerly
shared among the enthusiasts so finding blueprints and instructions
should not be difficult. But before you rush off to find the
blueprints you may want to take time to learn about the types of
casting furnaces available to help determine which one will suit
your needs. This is not saying that you should only have one
furnace at any given time, but this way you will know what project
will work best for which furnace.

Cupola
Cupola furnaces are among the most popular with backyard foundries.
Many casters construct their own cupola which proves to be cost
effective and highly efficient if done properly. Since cupola
furnaces can achieve high melting temperatures they are primarily
used for the melting of iron and bronze, though aluminum can also
be melted when attention is paid to keeping the temperature low.
The primary fuel source for cupola furnaces are coke using limestone
for flux.

By not using a crucible, the Cupola furnace is able to melt the
metal at a faster rate. While individual designs of these furnaces
differ due to varying resources and design ideas, the basic
component of a cupola furnace is the same. The cupola furnace must
be elevated above the ground and installed with a drop bottom
usually hinged, which will allow the excess metal, fuel source, and
other waste to drop from the furnace. The tap hole and shaft which
will allow the molten metal to flow from the furnace and into the
ladle and air shafts are also required.  A slag tap hole can be
placed on the furnace usually in the back, higher then the tap hole,
which will allow the slag to flow out easily.

With most small home foundries, the cupola furnaces are preferred
over that of other furnaces for its high melting rates and for how
easily the construction of such a furnace can be.

Reverberatory
The Reverberatory Furnaces are commonly found in industrial plants
but there have been quite a number of home grown foundries that
have used this furnace type with much success. The basic idea of a
Reverbeatory Furnace is to use the heat reflecting off a surface,
usually brick, to heat the metal, which is aluminum in most cases.
This way, the metal does not come into contact with the fuel or the
flame. This process is also used in Puddling Furnaces. The name
Reverberatory and Puddling are often used interchangeably. By placing
the metal in a shallow depression and then directing an intense flame
over that depression and to the wall, the heat rebounds to melt
the metal. Many casters will adjust the length of the flame since
a longer path will mean that the heat will be more intense.

There are many designs for the reverberatory furnace, all of which
will include exhaust ports and the rear of the furnace must be
able to withstand the intense heat and be able to bounce it back
into the chamber.

Bronze, aluminum, tin, and many other ores can be melted in a
reverberatory furnace all depending on the construction of the
actual furnace and the heat of the flame. This type of furnace has
been around since at least the Middle Ages and was used primarily
for bronze work.

Electric Arc
Electric Arc furnaces are normally used in Industrial foundries.
Most hobby casters do not use these furnaces due to cost, space issues,
and a general inconvenience. There are two forms of the electric
arc furnace, the direct and indirect.

The direct arc has three electrodes which are used to heat metal by
way of the arc. This creates an incredible amount of heat and so
water jackets and other cooling devices will be needed for operation.

The indirect arc just uses one electrode and works in much the same
way as the direct arc furnace.

Electric Induction
Electric Induction furnaces are becoming all the more popular with
large industrial size foundries that enjoy the clean burning and
efficiency of an electrical furnace. Copper coils surround the
crucible with the metal inside which can reach extremely high
temperature suitable for melting most metals.

Rotary
The Rotary style furnaces are hailed for their ease of use being
fully or at the very least partially automatic. These furnaces tend
to be harder to construct though there are resources and companies
online that sell rotary furnace.

The different furnace types do affect the quality of the work being
produced, so it is important to keep that in mind as you cast.
With a little trial and error, you should find the perfect furnace
to fit your needs so you can start building one of your very own.

Here is a link to a Web Page that provides more information about this
Metal Casting topic:

http://www.metalcastingzone.com/casting-furnaces/

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