Intermittent KilnsIntermittent kilns work by firing cool wares using a heat source, where the temperature is slowly increased throughout the firing process . Traditionally, intermittent kilns were nothing more than a trench drug in the ground filled with a fuel source and unfired pots. Intermittent kiln may be either rectangular circular or oval shaped. Types of intermittent kilns: There are two types of intermittent kilns: 1- Up draught intermittent kiln 2- Downdraught intermittent kiln 3- Clamp 4- Scove 1) Up draught intermittent kiln: Updraft kilns are those in which the flame is introduced into the bottom of the kiln, at or below floor level, and exhausted out the top. Updraft kilns consist of three basic components: the firebox, the damper, and the stack area. The firebox is where the flame enters. The damper is at the top of the kiln and controls the exhaust (and by association, the kiln's atmosphere). The stack area is where the pots are set and is between the firebox and damper. Although an updraft kiln tends to be less fuel efficient than a downdraft kiln, most commercially built fuelburning kilns are updrafts. This is mainly due to their internal structure of up draught Simplicity to build, packs, and ship. kiln Disadvantages of up draught kiln: Up draught kiln have following disadvantages:1- Burning of bricks is not uniform. 2- The supply is not continuous. 3- There is a loss of heat from top most layers of bricks. 4- There is waste of fuel heat as the kiln is to be cooled down. 5- The cost of manufacture is more. Channels were often made in the floor and filled with fuel. . The floor had to be level and was made of burnt brick.2) Downdraught intermittent kiln: Downdraft kilns are designed to force the flame and heated air to circulate through the kiln.cotta etc. terra .Heat can be controlled in a better way and hence such kilns are most useful for burning of structural clay tiles. Clamps varied from yard to yard but there were general rules which most followed.The burning of bricks is less or more uniform. It is 4000 BC old. Flame is introduced at the bottom of the kiln and naturally flows upward. charcoal was also used. 2. usually breeze but any fuel would suffice and wood. to exhaust at the bottom of the kiln. The addition of the chimney helps create draw. furze.The thermal performance is much better and heat loss is much less. Internal structure of down draught kiln Advantages of down draught intermittent kiln: The following are the advantages of down draught kiln over the up draught intermittent kiln: 1. or air flow. Downdraft kilns consist of four main components: the firebox. 3) Clamp: Clamp kiln One of the oldest methods of firing bricks is by clamp. The construction forces the flame back downward. the stack area. 3. Sprung arch downdraft kilns are probably the commonly potter-built kiln type in the United States. and the chimney. the damper. A clamp is a temporary construction of unfired or green bricks which is dismantled after firing and could be erected near the clay source. Two short tunnels A coal fired scove clamp (e.000 to 150. The construction of a scove requires a level. followed by a course . After this. This is a suitable method of burning wood. a course of headers. tunnels cannot be longer than approximately 6 m. with mud.e. Thus. flat surface. the outer surface of the piled-up bricks is scoved. Three or four layers of bricks are used to form the bottom of the tunnels. Most clamp bricks had a small percentage of breeze added to the clay during manufacture. tunnels can be built through the base of the pile in order to feed additional fuel. lay bed face down to form a good. 4) The scove kiln: A widely used adaptation of the clamp is the scove kiln. dry area of land. Alternate courses are laid at right angles to each other (i.g. the name of the scove kiln. Three lengths of bricks separate the tunnels. the latter being one of the most frequently used fuels for small-scale brick making in developing countries. The width of each tunnel is approximately equal to that of two brick lengths.000 bricks. Usually. approxima tely 2 m long) may be sufficient for a small number of bricks. although larger ones could take as much as ten or twelve weeks. Previously fired bricks. Sometimes the outside was sealed with wet pug. .Next came three or four layers of green bricks which were placed on edge and then another layer of fuel was added. For large numbers of bricks. This helped to 'self fire' them and ensured that a good temperature was reached. that is to say plastered all over its sides. Clamps contained 30. if available. An average size would take two or three weeks to burn out. green bricks were packed closely together to a height of 14 or 15 feet. also mistakenly called a clamp. The bricks were 'dished' or tilted inward to prevent injury to workmen during firing. If the fuel available is of a type which cannot be spread as a thin bed at the base of the kiln and/or is not in sufficient quantity to burn all the bricks without the need for replenishment. including the blocking of the centre of the tunnel during construction. cooling bricks down. On the top of the green bricks. This is easy to achieve although a narrower spacing may be satisfactory. Some of the top bricks half-way between the tunnels must not be scoved so that they may be lifted out to increase air flow through the kiln as required. in alternate courses of headers and stretchers up to a height of at least 3 m above the ground. . two or three courses of previously fired bricks should be laid. Turves are sometimes laid on top to reduce heat losses. In the latter case. Small spaces are left between the bricks to allow the hot gases from the fires to rise. Such winds may increase fuel consumption by 25 per cent. fuel inserted from both ends will not reach the centre of the tunnel. The fourth and successive courses of bricks are laid in such a way that rows of brickwork finally meet. It should preferably be at least 10 cm across. one end may be bricked up and fire set at the other end. In the middle of the picture. As the scove is built up. Firewood is set into the tunnels for firing. each course is stepped in a centimeter or so. Once the fire is well alight. to provide insulation. This will also allow the proper firing of the outer layers of green bricks. Kindling should be set in the mouth and bottom of the tunnel. an outer layer of previously burnt bricks is laid. it is essential that strong winds do not blow through the tunnels. Large numbers of bricks are dealt with by extending the number of tunnels to cope with the requirement. the first corbelled-out course of green bricks is partly set.6. Since the heat of the fire is to rise up into the bricks. and wasting heat. marking out the tunnel positions. At the edge of the scove. while further back several courses are laid. The required maximum spacing between bricks is a ‘finger width’. in pieces about 1 m in length. that end may be bricked up while the previous one is opened and lighted. a few courses of fired bricks are set. The wet mud should not contain a high fraction of clay if cracks are to be avoided during firing. bed face down and closely packed. The whole structure should then be scoved with wet mud to seal air gaps. A number of measures may be taken to avoid this waste of heat. The provision of this adjustable ventilation can be most useful in controlling the rate of burning. The progression of the early stages of construction of a scove is shown in figure VII. or the temporary blocking of tunnel mouths with bricks. to give a sloping side. Green bricks are set above tunnel level.otherwise. and tunnels are thus completed. In the foreground.