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.
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