Wet process - Cement manufacturing -Flow Diagram

Helllo,

Cement manufacturing is done in the following three major processes:
(a) Mixing
(b) Burning
(c) Grinding

(a) Mixing: Mixing can be done in two ways: (1) dry method and    (2) wet method.
Dry method was used in the early periods in between 1913 to 1982. After 1982 all the cement manufacturing plants in India are equipped with the technologies of Dry process, since this is more energy efficient and environment friendly method of cement manufacturing. In this post I am sharing with you the flow diagram of the wet process of the mixing because it is in the syllabus of the many Diploma courses.

Wet Process - Manufacturing of Cement

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Functions of various Constituents of Cement

Functions of various cement ingredients:

•      Lime (CaO) :This is the important ingredient of cement and its proportion is to be carefully maintained.  The lime in excess makes the cement unsound and cause the expansion and disintegration of the cement. On the other hand if the lime is deficient it will decrease the strength of the cement and will cause it to set quickly.
•  Silica (SiO2) :   This is an important ingredient of the cement as it imparts strength to the cement due to formation of di-          calcium silicate and tri-calcium silicate. If silica is present in excess quantity its setting time is prolonged          however strength is increased.
•  Alumina (Al2O3) :      This ingredient imparts quick setting property  to the cement. It acts as a flux and it lowers the clinkering        temperature. However the high temperature is essential for the formation of a suitable type of cement and       hence in alumina should not be present in excess amount as it weakens cement.
• Calcium Sulphate (CaSO4) :This ingredient is in the form of gypsum and its function is to increase the initial setting time of cement.
• Iron Oxide (Fe2O3) :This imparts color, hardness and strength to the cement.
• Magnesia (MgO) :This ingredient, if present in small amount, imparts hardness and color to the cement. A high content of magnesia makes the cement unsound.
• Sulphur(S) :A very small amount of sulphur is useful in making sound cement. If it is in excess, it causes cement to become unsound.
• Alkalies :The most of the alkalies present in raw materials are carried away by the flue gases during heating and the cement contains only a small amount of alkalies. If they are in excess in cement, they cause a number of troubles such as alkali-aggregate reaction, efflorescence and staining when used in concrete, brickwork or masonry mortar.

Harmful Constituents of Cement:

The presence of the following two oxides adversely affects the quality of cement:
        1) Alkali Oxides K2O and Na2O    2)    Magnesium oxide MgO.

    If the amount of alkali oxides exceeds 1 per cent, it leads to the failure of concrete made from that cement.     Similarly, if the content of magnesium oxide exceeds 5 per cent, it causes cracks after mortar or concrete        hardens. It is due to the fact that magnesium oxide, burned at a temperature of about 1500 degree            Celsius, slakes very slowly, when mixed with water.

Reference:


  

Bricks Classification and Specification (IS-1077:1992)

Hi,

According to Indian standard(IS: 1077: 1992) bricks are classified into the following categories:

Classes of common burnt clay bricks:

       Class Designation             Average compressive strength not less than[ (N/mm^2) (kg/cm2)

1. 35                                               35            350
2. 30                                              30                300
3. 25                                              25             250
4. 20                                              20                200
5. 17.5                                           17.5          175
6. 15                                              15                150
7. 12.5                                           12.5              125
8. 10                                               10                100
9. 7.5                                              7.5               75
10.  5                                                5                   50
11.  3.5                                            3.5                35

General Quality

• Bricks shall be hand moulded or machine moulded and shall be made from suitable soils. They shall be from from cracks and flaws and nodules of free lime. 
• Bricks with height of 90 mm or 70 mm will be moulded with a frog of  10 mm to 20 mm deep on one of its flat sides. Bricks with height of 40 mm or less, and as well those made by extrusion process  may not be provided with frogs.
• The bricks shall have smooth rectangular faces with sharp corners and shall be uniform in colour

.For other detailed dimensions and tolerance criteria please visit the IS 1072 : 1992

In some books the classification of the bricks is given as below:

General classification:

(1) First Class Bricks

(2) Second Class Bricks

(3) Third Class Bricks

First class bricks: 

Specifications: 

(1) Plain surface, sharp edges and size with tolerance in dimensions +-3%

(2) Uniform red or brownish colored.

(3) High crushing strength, not less than 10.7 N/mm2

(4) Machine moulded

(5) Efflorescence- NIL

(6) Water absorption less than 15%.

USE: They are used for the exterior wall brick works, short columns and arches.

Second class bricks:

Specifications:

(1) Slightly uneven faces and edges with tolerance in dimensions +-8%

(2) Uniform colored but may be slightly over burnt.

(3) High crushing strength, not less than 7 N/mm2

(4) Hand moulded

(5) Efflorescence- Little

(6) Water absorption less than 20%.

USE: They are used for internal walls and compound walls.

Third class bricks:

Specifications:

(1) May be distorted with blunt edges.

(2) Over burnt or under burnt and non uniform color.

(3) High crushing strength, not less than 3.5N/mm2

(4) Hand moulded

(5) Efflorescence- Large

(6) Water absorption less than 25%.

USES: They are used for flooring, paving, small brick foundations and brick bat lime concrete(B.B.L.C.).

Relevant books:   

  

Drying, Burning of Bricks- Bull's Trench Kiln, Hoffman's kiln

Hello!

The Manufacturing of bricks is consists of  following processes:

1.  Preparation of brick clay
2.  Moulding of Bricks
3.  Drying
4. Burning of bricks

First two operations are already discussed in the previous two parts of the article in the same blog. In this blog I am going to discuss with you the Drying and the Burning of the bricks:

• Drying Of Bricks: 

Drying of the bricks at lower temperature is done to strengthen the bricks to have sufficient strength so that they do not crack or crumble while holding and carrying them in hand.

Finally bricks are to be stacked in the kiln, but they must possess the sufficient strength to maintain their shape while the transportation and loading operations, so drying of the bricks is important process. Drying of the bricks can be done in two ways:

(a) Natural Drying: Natural drying is done by putting the bricks in the under the air circulation, generally avoided to direct Sun-light.

(b) Artificial Drying: In artificial burning bricks are put under a temperature of about 120 degrees Celsius in a tunnel like structure where arrangements are there to maintain the temperature.

 These tunnel kilns can be period or continuous. In periodic kilns the bricks are dried periodically but in the continuous they are put continuously at one end and dried bricks are taken out at the other end.

• Burning of Bricks: 

Bricks are burned at high temperature to gain the strength, durability, density and red color appearance.

All the water is removed at the temperature of 650 degrees but they are burnt at an temperature of about 1100 degrees because the fusing of sand and lime takes place at this temperature and chemical bonding takes between these materials after the temperature is cooled down resulting in the hard and dense mass.

 Bricks are not burnt above this temperature because it will result in the melting of the bricks and will result in a distorted shape and a very hard mass when cooled which will not be workable while brickwork. Bricks can be burnt using the following methods:

(a) Clamp Burning

(b) Kiln Burning

•   Clamp Burning: 

Clamp is a temporary structure generally constructed over the ground with a height of about 4 to 6 m. It is employed when the demand of the bricks is lower scale and when it is not a monsoon season.

 This is generally trapezoidal in plan whose shorter edge among the parallel sides is below the ground and then the surface raising constantly at about 15 degrees to reach the other parallel edge over the ground.

 A vertical brick and mud wall is constructed at the lower edge to support the stack of the brick. First layer of fuel is laid as the bottom most layer with the coal, wood and other locally available material like cow dung and husk.

Another layer of about 4 to 5 rows of bricks is laid and then again a fuel layer is laid over it. The thickness of the fuel layer goes on with the height of the clamp.

After these alternate layers of the bricks and fuel the top surface is covered with the mud so as to preserve the heat.

Fire is ignited at the bottom, once fire is started it is kept under fire by itself for one or two months and same time period is needed for the cooling of the bricks. 

• Disadvantages of Clamp burning: 

1. Bricks at the bottom are over-burnt while at the top are under-burnt. 
2. Bricks loose their shape, and reason may be their descending downward once the fuel layer is burnt.
3. This method can not employed for the manufacturing of large number of bricks and it is costly in terms of fuel because large amount of heat is wasted.
4.  It can not be employed in monsoon season.

• Kiln Burning: 

Kiln is a large oven used for the burning of bricks. Generally coal and other locally available materials like wood, cow dung etc can be used as fuel. They are of two types:

(a) Intermittent  Kilns.

(b) Continuous Kilns.

• Intermittent Kilns 

are also the periodic kind of kilns, because in such kilns only one process can take place at one time. Various major processes which takes place in the kilns are:

Loading, unloading, Cooling, and Burning of bricks.

There are two kind of intermittent kilns:

(i) Up-draught Intermittent Kilns

(ii) Down draught Intermittent Kilns

Down draught kilns are more efficient because the heat is utilized more by moving the hot gases in the larger area of the kiln. In up draught kilns the hot gases are released after they rise up to chimney entrance.

• Continuous Kilns: 

These kilns are called continuous because all the processes of loading, unloading, cooling,  Heating, pre-heating take place simultaneously. They are used when the bricks are demanded in larger scale and in short time. Bricks burning is completed in one day, so it is a fast method of burning.

There are two well known continuous kilns:

• Bull's Trench Kiln: 

Bull's trench kiln consist of a rectangular, circular or oval plan shape. They are constructed below the ground level by excavating a trench of the required width for the given capacity of brick manufacturing.

This Trench is divided generally in 12 chambers so that 2 numbers of cycles of brick burning can take place at the same time for the larger production of the bricks. Or it may happen that one cycle is carried out at one time in all the 12 chambers by using a single process in the 2-3 chambers at the same time.

The structure is under-ground so the heat is conserved to a large extent so it is more efficient.  Once fire is started it constantly travels from one chamber to the other chamber, while other operations like loading, unloading, cooling, burning and preheating taking place simultaneously.

Such kilns are generally constructed to have a manufacturing capacity of about 20,000 bricks per day. The drawback of this kiln is that there is not a permanent roof, so it is not easy to manufacture the bricks in the monsoon seasons.

• Hoffman's Kiln:

The main difference between the Bull's trench kiln and the Hoffman kilns are:

1.  Hoffman's kiln is an over the ground structure while Bull's Trench Kiln is an underground structure.
2. Hoffman's kiln have a permanent roof while Bull's trench Kiln do not have so it former can be used in 12 months a year to manufacture bricks but later is stopped in the monsoon season.

coutesy: http://www.llanymynech.org.uk/html/hoffman_kiln.html

Layout Plan

Hoffman's kiln is generally circular in plan, and is constructed over the ground. The whole structure is divided into the 12 chambers and all the processes takes place simultaneously like in Bull's trench Kiln.

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Manufacturing of Bricks -part II (Moulding and Drying)

Hi,

Preparation of the brick clay is already discussed in the earlier post, is this post I am going to discuss the second operation of brick manufacturing i.e. Moulding

Moulding: Moulding of the bricks into the proper shape and size can be done manually with the hands or it can be done with the help of machines. Hand moulding can take more time as compare to the machine moulding. Hand moulding is employed when the cheap labor available to us and less numbers of bricks are required to be manufactured and machine moulding can be employed when the labor is costly and the large numbers of bricks are required. Machine moulding is more accurate than the hand moulding.

Hand Moulding: It is again can be done in the following two manners:

(a) Moulding on the ground.

(b) Moulding on the table

In hand moulding on the ground following instruments are used:

       (a) Mould

       (b) Pallet

       (c) Strike

       (d) Clay

Mould of the size about 10 to 12% greater dimensions than the standard brick size for the allowance of the shrinkage of the brick, is used which can be made either of the seasoned wood or with the steel plates and the angle. Pallet is used to in-script the frog in the bricks. Frog is necessary for the proper bonding of the bricks and for the advertisement of the manufacturer.

Strike is used to strike off the excess clay from the top of the mould after it is filled with the brick. Following procedure is followed to carry the moulding of the bricks on the ground:

 First of all a dried plane ground is chosen on which dry sand is sprinkled to check the adherence of the brick clay to the ground. mould with the pallet is put on the ground. Clay is taken in lumps in hands and it is slashed on the mould with force so that every corner of the mould is filled with the clay. Excess of clay is struck off with the strike which can be wooden or wired. Mould is turned upside down and it is removed leaving the moulded brick in its place. It is kept at a near place and whole procedure is followed again.

Hand moulding on the table: Here the moulding is done on the table which is generally of the size 2 m * 1m. It may take somewhat longer time than the ground moulding.

Machine Moulding : As the name suggests, machine moulding is carried out with the help of a machine. It produces them in faster rate and in a better shape than that in the hand moulding.

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Relevant Books:

  

        

Manufacturing of Bricks - Part I (Preparation of brick clay)

Hello there,
how you doing? Please read on:

Manufacturing of bricks

Selection of the brick field:

Selection of the brick field where you have to establish your small scale  industry is done correctly when you check the following things:

1.  Site should be well connected with the road transportation facilities so as to transport your product.
2. There should be plenty of the clay available which is to be used for the manufacturing of the bricks.
3. All the necessary facilities for the workers should be checked and made available before starting the work.
4. Site should be of plane topography.

  

After the site selection and establishing the plant you can carry the manufacturing process in the following four processes:

•  Preparation of the brick earth
•  Moulding
• Drying
• Burning

• Preparation of the brick clay:  

Preparation of the brick clay can be done by completing the following processes:

(1) Un-soiling

(2) Digging

(3) Cleaning

(4) Weathering

(5) Blending

(6) Tempering

(Ref: Civil Engineering materials by Rangawala)

To be continued.....     

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Composition of a Good Brick Earth

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How you doing? Well, here is what you searched for:

Composition of a good brick earth:

Following are the constituents of a good brick earth:

(1)    Alumina (Al2O3):

 It is the chief constituent of a good brick earth. A content of about 20% to 30% is necessary to form the brick earth of a good quality. It imparts plasticity to the earth so it helps in the moulding of the brick earth. 

If alumina is present in excess with inadequate quantity of sand then the raw bricks shrink and warp during drying, on burning they become too hard. So it is important to have an optimum content of alumina.

(2)    Silica (SiO2):  

It exists in the brick earth either free or combined. As free sand it is mechanically mixed with clay and in combined form it exists in chemical composition with alumina. A good brick earth should contain about 50% to 60% of silica. 

The presence of this constituent prevents the shrinkage, cracking and warping of raw bricks. It thus imparts uniform shape to the bricks. The durability of bricks depends upon proper composition of silica in brick earth. The excess of silica destroys the cohesion b/w particles and brick become brittle.

(3)    Lime(CaCO3):

A small quantity of lime not more than 5% is desirable in good brick earth. It should be present in very fine state, because even small particles of size of a pin-head can result in the flaking of the brick. 

The lime prevents shrinkage of the raw bricks, sand alone is infusible, but it slightly fuses at kiln temperature in presence of lime. Fused sand acts as a hard cementing material for brick particles. 

The excess of lime causes brick to melt and therefore its shape is lost.  The lumps of lime turns into quick lime (CaO) after burning and this free lime can later react with water  to form slaked lime. This process is called slaking it may result in splitting of the brick into pieces.

(4)    Oxide of Iron (Fe2O3):

Iron oxide performs two functions, first it helps in fusing of the sand like lime and second it provides the red color to the bricks. It is kept below 5 to 6% because excess of it may result in the dark blue or black color of brick.

(5)    Magnesia:

It is used to provide a yellow tint to the bricks. Its content is only about 1% or less.

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