Furnaces can be classified according to the fuel, the heat flow / circulation fire, shape, heat contact, manner of operation / combustion process, use, and inventor. But of the various classifications will only be explained in part.
a. Furnace classification according to the fuel
Any combustible material can be used to burn ceramics, although it always starts with the burning of wood fuel, while in the recent development of oil and gas combustion using. Now a new heat source for firing ceramics is electricity. Type furnace based fuel (heat source) used can be classified into five types, namely:
1) Furnace gas fuel
This type of furnace using gas fuel, if in Indonesia known as liquefied petroleum gas (LPG). The furnace is very practical and operational costs are quite economical. Reason is what causes many ceramic industries using furnace gas as the main burner. The furnace must be operated with correct procedures and safety standards are high, considering the fuel gas is invisible and extremely flammable. We can set the furnace atmosphere with this gas furnace.
2) Electric Furnaces
Furnaces of this type are widely used in studios or in schools because it is easy to operate. The furnace is equipped with coils that will smolder when electrified. Shape, volume, and specifications of the electric furnace is very varied and each has its own advantages.
3) furnaces solid fuel (wood, coal)
This is the type of furnace that is the forerunner of the ceramic combustion. Until now wood-burning stove is still used in the centers of traditional ceramics. Other solid fuels are wood chips, rice husks, dry leaves and garbage.
4) Furnace fuel oil
When oil prices are dirt cheap, this furnace is very economical. But this time the kerosene stove is rarely used because of the cost of expensive operations.
b. Classification Furnace according Directions Heat Flow / Circulation Fire
1) Furnace fire rises (up draft kiln)
In the furnace of this kind of heat from flowing into the combustion chamber space heating / burning on it and heats the goods there and then out through the chimney at the top. The amount of fuel used in furnaces of this type are relatively large and the temperature difference between the bottom and it was large enough to affect the outcome. Which includes this type are fields and furnace bath furnace. Shape furnace caught fire there were some are square and round. The characteristics of a furnace rises is:
a). rather wasteful fuel consumption,
b). the combustion temperature is relatively low (below 1000 ° C),
c). temperature difference of the top and bottom and the middle is quite large (bottom higher),
d). manner of operation is easy, and
e). costs of construction and maintenance easier and cheaper.
Figure 20. Furnace with flames rising circulation.
2) The furnace fire turned (down draft kiln)
The heat generated from the combustion chamber will flow upwards because there is a bridge of fire (bag wall), touching the roof of the furnace combustion chamber and turned downwards to heat the ceramic objects, then flows into the channel under the floor of the furnace (canal) and out through the chimney. By using this type of furnace combustion chamber temperature will produce a more equitable and can reach higher temperatures, namely 1400 o C. This type furnace is equipped with a damper (skepticism) that is placed on the channel (channel) between the furnace and the chimney. Which includes this type of catenary furnace. The shape of the furnace down this draft there are square and some are rounded.
Figure 21. Furnace fire turned circulation
3) The furnace fire horizontal (cross draft kiln)
The heat generated from the combustion chamber by the type of furnace will flow into the heating chamber that heats the floor parallel ceramic goods, then out through the chimney. The highest temperature is located close to the combustion chamber and decreases towards the chimney.
Figure 22. Furnace fire horizontal circulation.