Manufacture of bricks (Burning)

Burning of bricks

Clamp burning

Clamp burning is followed by procedure listed below:

1. A piece of ground selected. It is trapezoidal in shape. Short end is below ground level for certain length and wider end above ground level at an angle 15° degree with horizontal from ground surface.
2. Brick wall with mud mortar protection is constructed at shorter end of platform. A layer of fuel is laid on prepared floor. Fuel may be of grass, cow dung, litter and rice husk or ground nuts etc. Thickness of this fuel layer is generally 70-80 cm. Wood or coal dust may be used as fuel.
3. Layer of row bricks on their edges are laid on this fuel layer with some gap between them for air circulation purpose. generally 4-5 layers of bricks are laid over fuel layer.
4. Second layer of fuel and than another layer of brick over it laid and this is continued till 3-4 meter height(restricted). And thickness of fuel layer is decreased towards upward direction staking.
5. When height of clamp reached to 1/3 of its total height, lower layer get burned so that burning operation get started when upper layers are in progress. 
6. When clamp is constructed completely it is covers with mud mortar to all side except bottom, so that heat can not escape from inside during burning. 
7. It will take about 1-2 months to get properly burned.
8. Cooling period will be more or less that of burning.
9. After allowed for cooling, bricks are taken out from clamp.

CLAMP

Advantages and disadvantages of clamp burning

Advantages	Disadvantages
Gradual burning and cooling produce tough and hard bricks	Bricks are not produced of desired shape
Cheap and economical method	Take longer time to burning and cooling
No supervision and skilled labour are required	Once fired it is not controllable
Less fuel optimisation	Quality of bricks are not uniform due to lower bricks get over burnt and upper bricks get under burnt

Kiln burning

Kiln is a large oven type structure used to burn bricks. There are mainly two types of kiln based on their performance are as follow:

a) Intermittent kiln       b) Continuous kiln

Intermittent kiln

This are the kiln which are not run all the time. They are intermittent in operation of burning of bricks, they are loaded, brought to fire, cooled and then unloaded. They may be rectangular or circular in plan as per local convenience. Kiln may be underground or overground.

Again intermittent kiln classified in two ways:

• Intermittent up-drought kiln
• Intermittent down-drought kiln

Intermittent up-drought kiln

This kilns are rectangular in shape with thicker out side walls. Doors are provided at both ends for loading and unloading of bricks into kiln. flues are also provided to get burning process done. While placing raw bricks in kiln top of kiln is covered with some cheap and light roofing material to protect it from rain. Once flues are ignited roof covering is removed and let the fire smoke out.

Working of intermittent up-drought kiln

1. Raw bricks are laid in a row of thickness equal to two to three bricks and height equal to six to eight bricks. Space is left between raw of bricks to allow placing of fuel.
2. Fuels are filled with the material which can take fire easily. Interior part is filled with larger size fuel.
3. An arch like opening is provided by projecting 4 - 5 row of bricks. projection of each row is about 30 to 40 mm.
4. Loading of bricks are carried out by placing bricks on their edge and top is covered by placing bricks flat.
   
5. End doors provided on both side are covered by dry bricks and covered by mud.
6. After this kiln is ignited and firing kept maintain for 3 days. Strong fire is maintained for a period of 2 to 3 days. Drought rises in upward direction from bottom of kiln  and bricks get burned.
7. After burning kilns are allowed to cool down for some time and the bricks are taken out.
8. Above process is repeated for further burning of remained raw bricks.

Intermittent up-drought kiln are superior than clamp burning but, there are some cons which needs to be addressed.

• problem of over-burnt and under-burnt still addressed.
• bricks are not uniform.
• supply of bricks is not continues.
• every time we need to allow cooling of kiln, hence wastage of heat is there.

Intermittent down-drought kiln

In this type of kiln, kiln are of rectangular of circular in shape. This kilns are with permanent walls and air tight doors. This kilns provided with closed tight roof. In this kiln there are openings on floor like up-drought kiln but it is connected with chimney tunnel at bottom so that smoke goes into the chimney from bottom and left the chimney from its opening in atmosphere at a distance from kiln. Due to this arrangement it is known as intermittent down-drought kiln.

Working of intermittent down-drought and operation is same as above up-drought kiln except movement of smoke.

Down-drought kiln has the following advantages.

• uniform burning of bricks.
• this kiln works better than up-drought kiln.
• due to even burning it is used for burning of structural clay products.

Continuous kiln

This kilns are superior to intermittent kilns. Operation carried out in this kiln is continuous i.e. loading>heating>cooling>unloading carried out continuously. This kiln further classified into three types based on their performance.

1. Bull trench's kiln
2. Hoffman's kiln
3. Tunnel kiln

1. Bull trench's kiln

Bull trench kiln may be rectangular, circular and oval shape in plan. It may be underground or partly overground in nature. If it is projecting over ground an earthen ramp should be provided to access the kiln. It is divided into total 12 compartment which are numbered from 1 to 6 in reverse order twice. As shown in figure it has mainly two walls outer brick wall and inner brick wall.

Openings provided in outer walls as a flue holes. Dampers are used in the form of iron plate to divide kiln into compartment. 

BULL TRENCH KILN

Bricks are placed such as flues are formed. Top of bricks are covered with suitable material to prevent heat loss. Fuel is inserted from flues and then ignited to get bricks burn. Chimneys are provided at each 6th compartment to allow drought formation, this chimneys are movable. Each section is allowed to get burnt for a day. After burning employed each flues are closed and bricks are allowed to get cooled.

Another compartment is fired and chimney is moved towards particular compartment to allow formation of drought. As it allows simultaneous loading>burning>cooling and unloading it is able to work continuously. 

Operations are carried out in compartment as follows:

1. loading
2. empty
3. unloading
4. cooling
5. burning
6. heating

2. Hoffman's kiln

Hoffman's kiln if somewhat different than bull trench's kiln in  manner that it is constructed over ground level and circular in shape. This kiln divided into 12 component for its operation. Each component provided with following facilities.

• A main door for loading and unloading of bricks.
• Flue doors in open condition.
• Flues are connected with a vertical central chimney.
• Fuel holes with cover.

As earlier we studied about main door covering here same operation carried out to cover a door with dry bricks and mud after placing of bricks. Dampers are provided for communicating and radial flue doors.

In normal conditions only flues are connected to chimney to established drought.

Same as bull trench's kiln compartment in this kiln are also employed to their functions for loading, burning, cooling and unloading.

1 - Loading

2 to 5 - Drying and Preheating

6 to 7 - Burning

8 to 11 - Cooling

12 - Unloading

HOFFMAN KILN

Though cost of installment of this kiln is high but having following advantages.

1. Bricks are burnt evenly.
2. Good and uniform quality of bricks are achieved.
3. Burning is controllable.
4. Supply of brick is regular and continuous.
5. Less fuel consumption.

Capacity of kiln will depend on dimensions of it, if it is large, more number of bricks are manufactured and if small then less number of bricks are manufactured.

3. Tunnel kiln

In tunnel kiln the shape of structure is of tunnel type which may be straight, circular or oval shape. This kiln contain a stationary zone of fire. In this kiln row bricks are entered from one place and leave from another place. During travelling it will burned sufficiently. Heat is also controllable in this kiln also. This type of kiln operations are used for the large production based projects. They are cheaper for bulk manufacture of bricks. 

Comparison between clamp and kiln

Clamp Burning	Kiln Burning
Larger number of bricks can be prepared	Lesser number of bricks can be prepared
Less fuel requirement	High fuel requirement
Less initial cost	High initial cost
Good quality of bricks is about 60 %	Good quality of bricks is about 85-90 %
During burning of bricks fire is uncontrollable	During burning of bricks fire is controllable
No skilled labour required	Skilled labour required
Temporary structure	Permanent structure
Suitable when bricks requirement is of small scale and demand of bricks is discontinuous	Suitable when bricks requirement is of large scale and demand of bricks is continuous
Large waste of fuel heat	No wastage of fuel heat

"To Be Continued..."