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PPT On Clay Products (Building Construction Materials)

Home > PowerPoint Slides > PPT On Clay Products (Building Construction Materials)

Published in: Civil

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Clay, Classification of Clay, Bricks, Manufacturing of bricks, Selection of suitable brick earth, Undesirable Components, Preparation of Mud, Molding of Bricks, Drying of bricks, Burning of bricks,

Gaurav T / Ahmedabad

8 years of teaching experience

Qualification: M.Tech (SGSITS - 2007)

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Clay Products Building Construction Material
Introduction • Clay is naturally occurring mineral that is found almost every where on the surface of the earth making the soil cover or the soft ground. • It is so widespread in its occurrence that in common language it is often referred as earth.
Introduction Miner logically pure clay may be composed of one or more minerals of clay group such as Kaolinite, Montmorillonite, illite, vermiculite and Allohane, etc. Kaolite is the most important mineral component of common clays. • Clay occurs universally. Man has used them since ancient times for making earthware of great variety.
Classification of Clays • Clays are classified in two ways: Genesis or their mode of formation and their dominant characteristics. All clays are classified in two ways: • Genesis or their mode of formation and their dominant characteristics The Residual Clays The Transported Clays
Classification of Clays The Residual Clay includes all varieties of clays that are found covering the rocks from which they are formed by natural processes. Such clays are pure in their chemical composition that is related broadly to the parent rock. China Clay is the best example of residual Clay.
Classification of Clays The Transported Clays. These are the most common clays spread on the earth. They are formed by the disintegration and decomposition of the pre-existing rocks by the natural agencies followed by removal and transportation of broken pieces to far off places where they are finally deposited. Hence any such deposit of transported clay will have all the particles transported from many places and different source materials. The transported clay are, therefore quite heterogeneous in mineralogical and chemical composition.
Classification of Clays The transported clays are sometimes further distinguished into glacial clays, marine clays, alluvial clays and lacustarine clay when glaciers, seas, rivers, and lakes respectively have played dominant roles in their formation.
Classification of Clays • On the Basis of their dominant Characteristics, Clays are classified as into four groups: China Clay Fire Clay • Vitrifying Clay • And Brick Clay
Classification of Clays China Clay • It is the purest type of clay containing very high percentage of mineral Kaolinite or Kaolin It is Considered high Grade clay and is used for the manufacturing of crockery and other proclain ware
China Clay
Classification of Clays Fire Clay They are also called refractory clay and contain, besides Kaolinite, Silica and alumina in very high temperature without suffering any deformation off shape given to them at the time of moulding. They are mainly used in manufacturing of refractory bricks that are of great importance in many metallurgical, mechanical and chemical operations
Fire Clay
Classification of Clays Vitrified Clays These clays are rich in fluxing compounds like iron oxide and carbonates of calcium and magnesium. These are easily fusible. i.e. cannot withstand high temperatures above 1100 0 C the fluxes get softened and form glass like material that acts as a strong bonding agent between the other clay particles, This results in the formation of a smooth surfaced hard burnt clay products, The Vitrifying clays called hard burnt clay are specially used for manufacturing of facing brick, flooring tiles, sewer pipe and other similar ornamental and dense clay products,
Classification of Clays The Brick Clays These are low grade clays used most for the manufacturing of building bricks and similar clay products. Brick clay are rich in silica, alumina, oxide of iron, calcium, magnesium and organic matter. It is mutual proportion of these components that define their suitability or otherwise for making good quality bricks for building construction. The oxides of iron, calcium and magnesium act as fluxes that fuse easily at brick-making temperature and bind the alumina and silica particles thoroughly giving the brick desired properties of cohesion and strength.
Bricks • Building bricks may be defined as "Structural units of rectangular shape and convenient size that are made of suitable clays by different processes involving moulding, drying, and burning.
Bricks • It is now established that even in remote ancient civilizations bricks were common material of construction. It is believed that it was in Egypt that bricks were used some 6000 years ago. Excavation in prehistoric sites in our country has revealed that bricks were used abundantly in Indus valley civilization at Mohan jo daro and Harappa.
Bricks • Even at present bricks is the most basic and favorable material for common construction throughout the world. This may be attributed to no of factors:
Bricks Availability of clay Clay suitable for making bricks are available almost universally, Hence brick making can be adopted anywhere in the world. This is not true either for stones or for concrete that are material which compete with clay.
Bricks Size Shape and handling • Bricks are made in ready —to-use sizes and shapes. This affords very convenient handling and use. For stones, however, some dressing is absolutely essential. In case of concrete, an elaborate formwork and shuttering are basic requirements. Moreover transporting and lying of concrete also requires great care, caution and expertise.
Bricks Ciecte Brick Feather End on edge S'de Arch Woe foce / Flot Standard Circle Brick on edqe Ooee oe Scone Souote Vhelp Skev uck
Bricks Cost • Bricks as also brickwork are cheaper compared to stone masonry and construction with concrete in most cases. This is because of the factors mentioned under availability. Size and shape and construction methods
Manufacturing of Bricks The process of manufacturing of bricks is carried out in number of stages It Is essential a sequential process. That is, next stage is reached only when the previous stages have been completed in all respect. No jumping over or omission of stage is possible. Each stage has its own significance in the process.
Manufacturing of Bricks The Stages are listed below: • Selection of suitable type of clay Preparation and tempering of mud Moulding of brick units Drying of moulded bricks • Loading of dried bricks in kilns; Firing or burning of dried bricks; • Cooling of the units; Unloading of the kiln;
Selection of Suitable Brick Earth A good type of bricks cannot be made from every type of clay. A suitable brick earth should have the following composition in the desired proportions: 1) Alumina (20- 30 %) All clays are chemically hydrous aluminum silicates. The alumina content is responsible for giving the plastic character to the clay in wet conditions. When alumina content is higher than 30 % the bricks becomes more plastic and also shrink on drying. But if Alumina Content is Less than 20 %, clay may be difficult to mould to proper shapes. Hence desired content of Alumina is about 20 — 30
Alümina (20- 30 % )
Selection of Suitable Brick Earth Silica ( 50-60 Silica present in Ideal Proportion i.e. 50- 60% imparts the qualities of hardness and strength to the bricks. It is also responsible for resistance against shrinkage and durability of the brick to weather. However while the proportion of silica are exceptionally high in the clay such bricks when burnt would be quite brittle and porous.
Selection of Suitable Brick Earth
Selection of Suitable Brick Earth • Iron Oxide (4-6%) This Oxide act as a flux, i.e. it lowers down Softening temperature of Silica and other clay components during firing. Further, The Iron Oxide in the clays may make their burning difficult and give them yellowish aPPearance.
Selection of Suitable Brick Earth Lime (4-6 %) This Components make the burning of bricks quicker. Provided, ' It should not be more than 4 %, because in this case may result in excessive softening of the clay on heating. ' It must be present only in fine powder form otherwise it may give rise to slaking, which is harmful and may cause slow disintegration of bricks.
Selection of Suitable Brick Earth • Magnesia Which is invariably associated with lime, has similar effect
Undesirable Components brick clay should be free from the following components: The lime modules: • obstruct the proper burning, when bricks are placed in kiln. • If it present, then burnt bricks are likely to cause disintegration of bricks by their slaking action, The organic matter: • Roots of grasses, leaves and other organic matter, which produces carbon on burning within the body ofbrick. • Brick darker in appearance and too porous in nature, remove in preparation stage,
Undesirable Components Sulphides and sulphates: • Iron sulphide in form of pyrite and alkalkies in form of potash and soda are often present in some clays. ' Iron sulphide causes disintegration of the brick during burning stage itself. The alkali salts: • Act as fluxes during burning and create additional softening. If it is present in burnt bricks, it absorbs the moisture from the atmosphere and form the solution within the body of brick. On evaporation, these solution form white patches. This effect is called efflorescence.
Preparation Of Mud Winning: Obtain brick earth from its natural deposit. Clear off from vegetation, pebbles and other organic matter. Manual digging or mechanical excavation are used to obtain dry soil or brick matter. Clay is spread on even ground for seasoning so that clay is exposed to atmosphere for good time. At this stage, earth is further cleaned off any pebbles, stones lime nodules and visible organic matter. The seasoned clay is ready for making mud by mixing with adequate amount of water.
Winning
Preparation Of Mud ' Tempering: Converting the brick earth to mud of proper consistency by thoroughly mixing with desired quantities of water. Manual tempering: Clay is spread on a platform and thoroughly mixed under feet of either man or cattle. Water is added gradually in small quantities till desired homogeneity and plasticity are obtained. Pug mill tempering (pugging): mechanical device called pug mill.
Manual Tempering
Pug Mill Tempering A simple pug mill consist of steel cylinder covered at top and hole at or near the bottom. Most important part of pug mill is a central vertical shaft provided at the base which can be rotated with the help of long arm through animal or motor power. Central shaft is attached with the horizontal blades, each carries some knives. • Seasoned clay and water are added from an opening provided at the top. The churning effect to the clay-water mixture, that is converted into mud of desired plasticity and consistency. The mud is then taken out from the hole at the base and new charge is field. Iron Tub G >>>> long Arm Knives Clay Vertical Shaft Horizontal Arm Timber Base Ramp for Pugged Clay
Moulding Of Bricks • Moulding: is the process of making green bricks of proper shape and size from thoroughly tempered clay. • Two Main Methods: hand moulding and machine moulding.
Moulding Of Bricks Hand Moulding: Using skilled manpower. Most common method in India. The quality oftempered clay is kept soft. More water content (18-25% by weight). So, we can call this method as soft mud process. Ground moulding: bricks are shaped from such a soft mud by hand on a specially prepared ground. Table moulding: bricks are shaped from such a soft mud by hand on a specially designed table.
Table Moulding
Tools For Hand Moulding A brick mould: wood or steel. Its inside dimensions are kept slightly bigger than the desired dimensions of finished brick because bricks on drying are liable to shrink in size. • It may be a single unit or a multiple unit type. The stock board (moulding board): • Small wooden board with raised central projection carrying the identification marks (frog) of the manufacturer,
Tools For Hand Moulding The Pallets: Thin wooden plates used for handling the green bricks from the moulding boards to the drying field. The Strike: Wood or metal • Has its one edge quite thin to slash surplus mud from the top of the moulded brick, while it is in the mould. • Sometimes a thin wire strung in a wooden block for holding is used for the same purpose, it is called cutting wire,
Ground Moulding • Common method of moulding bricks in India A stretch of land is first flattened, levelling and cleaned and made smooth by mud plastering. • Some sand is sprinkled uniformly over it to make it non-sticky.
Ground Moulding (a) For making ordinary bricks: Mould is either dipped in water (slop moulding) or some sand is sprinkled on its inside surface (sand moulding). Mould is placed on the ground at desired spot, • Lump of mud is dashed into the mould by hand. Mud should reaches to the sides and corners of the mould. • Any surplus mud is removed by using the strike or the cutting wire. The mould is then lifted up with a jerk and leaves behind the moulded brick on the ground below,
Ground Moulding Moulding bricks with frog (pallet moulding) By using a stock board and pallets. The stock board is provided with a raised projection carrying the identification mark. The mould is placed on the stock board (instead of ground) and a brick is moulded. The brick is then taken away using two pallet to the drying field,
Ground Moulding • Frog: an identification mark during the moulding stage with the help of a stock board. It serves following purposes: The name of the manufacture of the brick is easily found and can be known for the quality of the brick. The frog-faced side is placed upward during use, which accommodates some extra mortar, which develops structural grip between upper and lower brick.
Frog
Table Moulding The skilled worker — moulder carries out all the moulding operations on a specially designed table of suitable dimensions, ' Table is large enough to accommodate all the materials required in hand moulding such as stock board, moulds, cutting edge, water, sand and tempered mud.
Table Moulding • Process is similar to pallet moulding on ground. The moulder is placed on the stock board and then sprinkles some sand inside the surface of mould. • Dashes a lump of mud into it, press it thoroughly and skillfully. Cuts away any surplus mud with the strike or the cutting edge. Places a pallet over the mould and turn it over. The moulded brick is transferred to the pallet, which is carried away by a helper. This process is repeated for each brick. • Initial cost is slightly higher than ground moulding but more efficient and economical in the long run because production is better in quality and quantity.
Machine Moulding Essential process in all mechanized brick making plants. Cheaper in longer run and gives uniform quality brick. ' Main two methods: Stiff mud method and Dry process method. Stiff mud method: Small quantity of water (8- 12 % by volume) is added to the clay to create plasticity. This stiff mix is made to pass out under pressure from moulding machine.
Machine Moulding
Machine Moulding • Two versions of machines can be used such as: • Worm gear moulding machine A vacuum press for brick moulding. Worm gear moulding machine: consists of • A feeding chamber provided with a worm gear to apply pressure. • A hopper at the top to receive the clay mix from the pug mill • A fixed die provided at the front narrow end • A conveyor belt on a set otrollers • Cutting wire device adjusted in front of the die
Worm Gear Moulding Machine The operation steps on machine consist of ' Feeding the properly mixed stiff mud into the chamber through the hopper • Forcing forward the mud charge using the worm gear. The pressed mud comes out through the die in the form of continuous rectangular ribbon having the height and width of the bricks, This ribbon gets cut into brick lengths by pressing down the cutting wire device, when the conveyor belt is under the device. Capacity of machine: 1000 — 2000 units per hour or more depending upon the machine.
Machine Moulding • Dry press process: a very small quantity of water is added to finely crushed and thoroughly cleaned batch of clay. Mix is almost dry, at best damp, • Such damp clay is fed through hoppers to special brick moulds. • Pressure - 50-150 Kg/cm2 through hydraulic presses. This pressure is sufficient enough to convert the loose damp clay mass into dense and very compact brick unit, Brick is removed from the mould. These bricks are having perfect shapes on all the sides, edges and corners, Such bricks are also called as pressed bricks.
Drying Of Bricks Reasons To Dry The Green Bricks: To Make Green Brick Strong Enough To Bear Rough Handling During Stacking In The Kiln For Burning. To Allow Loss Of Moisture At A Slow Rate To Avoid Disintegration. To Save Fuel During Burning Stage, Drying Artificial method drying in the chamber drying in the tunnel Natural method Air drying and Sun drying
Drying Of Bricks • Natural method (stacking method): there are two different stages involved in the drying process such as: 1) Pre stacking stage: Moulded bricks are laid sidewise and flat wise for 2 — 3 days in the drying fields. So, that they become hard enough to handle for stacking in heaps, 2) Stacking stage: Bricks are arranged in the layers (100 cm wide and 10 brick layer height) by skilled workers. • Staking is done in specially prepared drying ground. • Enough space is left in between the individual bricks and between layers.
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Drying Of Bricks ' Artificial drying: essential in mechanized brick making unit. ' Independent of weather condition. Chamber Drying: • Arrange in stacks in drying chamber by keeping sufficient spaces for free circulation of hot air around them. • Hot air is circulated under control condition of temperature and humidity. 2 — 4 days or more, and then next batch is stacked,
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Drying Of Bricks Tunnel drying: • Bricks are stacked on mobile cars that are made on travel on rails within a specially designed drying tunnel, The tunnel is divided into compartments and each car is made to stay in a particular compartment for pre-fixed duration. The cars come out from other end. 2 — 3 days for a car load of bricks to dry to desired extent.
Tunnel Drying ill"llli
Burning Of Bricks Absolutely essential to develop in brick making the desired building properties such as sufficient strength, hardness, durability and resistance to decay and disintegration.
Burning Of Bricks • 3 chemical changes take place during burning process: • Dehydration: complete removal of water from the pores of the bricks. • Completed at the temperature range of 425 — 7650c. • Losses all the free water,
Burning Of Bricks • Oxidation: it start taking place during heating of the bricks at the above temperature and gets completed at about 6500C-9000C. All the organic matter in the brick earth gets oxidized. Carbon and sulphur are eliminated as oxides. • Fluxes (lime, magnesia, iron) become reactive at these temperature. • Brick acquires the red colour due to the oxidation of iron in the clay.
Burning Of Bricks Vitrification: last reaction takes place at temperature range of 9000C to 11000C. The alumina and silica start softening in the presence of the fluxing compounds. The constituent grains get bound firmly.
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Burning Of Bricks Clamp Burning: (Open kiln or Pazawah) Temporary structure, constructed over the ground ' Height - about 4 to 6 m. Used for lower scale bricks, not suitable in monsoon season. Trapezoidal in plan, whose shorter edge among the parallel sides is below the ground and slope angle of about 15 0 A vertical brick and mud wall is constructed at the lower edge to support the stack of the brick.
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Burning Of Bricks Clamp Burning: (Open kiln or Pazawah) First layer - fuel is laid as the bottom most layer with the coal, wood and other locally available material like cow dung and husk. Another layer 4 to 5 rows of bricks Then again a fuel layer is laid over it. Thickness of the fuel layer decreases with the height of the clamp. Top surface - 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. In a clamp of 10 m * 7.5 m sides, about one- lakh bricks can be burnt in two months. Earth layers Aof Raw Bricks l.cct 00 oeooe •ooee
Burning Of Bricks Advantages of Clamp Burning: Easy to erect and operate • Any type of fuel can be used Not requires skilled labour and least supervision after burning Economical Clamp is not liable to injury from high wind or rain
Burning Of Bricks Disadvantages of Clamp Burning: Burning of bricks is not uniform, such as bricks at the bottom are over-burnt while at the top are under-burnt, Bricks loose their shape, and reason may be their descending downward once the fuel layer is burnt, 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, It can not be employed in monsoon season. Time required for burning is too long. No possibility to regulate heat, once it start burning.
Burning Of Bricks (Kiln Burning) Kilns are permanent structures, used for burning. • Fuel - Coal and other locally available materials like wood, cow dung etc. Two types based on their principle of construction:
Burning Of Bricks (Kiln Burning) Intermittent Kilns: periodic kilns, only one process can take place at one time, The brick supply from such kilns is intermittent and not continuous. • e.g. The kiln Continuous Kilns: possible to get supply of bricks almost continuously. Used when the bricks are demanded in larger scale and in short time. Operations in these chambers are so controlled that at any given time, when one chamber is in the loading process, another chamber may be in burning stage, third chamber in the preheating stage, fourth chamber in the cooling stage and fifth chamber in the unloading or supply stage. • e.g. The Bull's trench kiln, The Hoffman's continuous kiln, The Tunnel kiln.
Burning Of Bricks (Kiln Burning) Intermittent Kiln Rectangular, Four Permanent Walls. • Totally Underground Or Partly Underground And Partly Over Ground. The Longer Walls Are Raised Perpendicular To The Direction Of Prevailing Winds. Provided With Number Of Opening Called Flues (F), Exactly Opposite To Each Other For Charging Fuels And Controlling Air. Openings Are Provided With Door Sheets, Which Can Be Raised Or Lowered. The Shorter Walls Are Provided With Doors For Loading And Unloading The Bricks. There Are Four stages In The Working Of Kiln: • Loading Firing Cooling • Unloading
Burning Of Bricks (Kiln Burning) Loading: dried bricks are laid in rows on the raised portions, • Each row - two to three brick thick. Height - 8 to 10 brick layers. • Brick laying in such a manner that make arch-shaped opening for, a) supply of fuel b) supply of air While staking, some space is provided between individual bricks for circulation of air around each brick. • Top layer - covered with thick layer of dry earth, which helps in preventing escape of heat from the kiln during the burning process. Outside Wall Space for fuel
Burning Of Bricks (Kiln Burning) Firing: After loading, fuel is supplied in the opening at the base, is fired through the arch shaped opening provided for this purpose. Low fires: 1 — 2 days for removing moisture left in the brick during the process of drying. Firing is brought to full strength. The flames spread upward baking and burning the bricks stacked within the body of the kiln in 2 — 3 days time.
Burning Of Bricks (Kiln Burning) Cooling: After visual inspection and ensuring that all the fuel has been burnt, the kiln openings are closed for 7 — 10 days, which helps in natural slow cooling of the burnt lot of bricks. Slow cooling is essential for avoiding development of cracks in the cooling bricks. If cooling at fast rate, cracks are likely to occur and spoil the brick. Unloading: after sufficient cooling, the top layer ofthe dust is removed. • Burnt bricks are removed from the top layer to downwards. The entire kiln is emptied and thoroughly clean for loading next batch. Outside Wall -n h/ Space for Fuel
Burning Of Bricks (Kiln Burning - The Bull's Trench Kiln) Principle: continuous type of kiln, Number of compartments, which can be operated in sequential process. Possible to obtain a regular supply of burnt bricks. Moveable Chimneys Preheating zone Setting green bricks Drawing fired brtcks zone Stoking holes
Burning Of Bricks (Kiln Burning - The Bull's Trench Kiln) • Construction: rectangular, circular or oval shape in the plan. Below the ground level by excavating a trench of the required width for the given capacity of brick manufacturing, • Range of dimension of trench depending upon the desired capacity of the bricks: - Length: 50 -78m - Width: 6-8m — Depth: 1 —2 m A typical trench kiln has two walls: — Inner wall - continuous and close contact with the inner land part. — Outer wall - number of openings or gates provided with dampers or doors which can be opened or closed.
Burning Of Bricks (Kiln Burning - The Bull's Trench Kiln) Exhaust leave kiln here Red area oi kitti whete tucl iz Inscrtx* Ash and rubble on top razintains draught sea' in chamber co of ing down Exhaust nascs "ill Great* Bricks in of fire '*ated by gases Cold air enters here Bricks awaiti'*q war by kilo Strucuure New betches ot dry bricks being in •ho kiln Fired bricks bclne token away Air wa«rnina up as iz passes by bricks
Burning Of Bricks (Kiln Burning - The Bull's Trench Kiln) 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. 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, Drawback: not a permanent roof, so it is not easy to manufacture the bricks in the monsoon seasons,
Burning Of Bricks (Kiln Burning - The Bull's Trench Kiln) Ramp of Earth Section on Inner Bk. Outer Bk. Wall Plan Chimney AB Dampers Wall Flue Holes
Burning Of Bricks (Kiln Burning 16 - The Bull's Trench Kiln) 2 1. COOL BURNT 2. FLUE HOLES 3. FIRING BRICKS PLAN (c) SECTION 4. HEATING BRICKS CHIMNEYS DAMPERS 7. DOOR WAYS outER BRICX WALLS INNER BRECK WALLS
Burning Of Bricks (Kiln Burning - The Bull's Trench Kiln) Working: • first prepare to keep all compartments of the kiln in operation. • Each compartment has to pass through following six stages such as loading, unloading, cooling, burning, preheating and cleaning.
Burning Of Bricks (Kiln Burning - The Bull's Trench Kiln) • Loading: • stacking of brick is done carefully within the kiln boundaries • Enough space is left between any two bricks in a layer for free circulation of hot gases. • Fuel galleries are made in the lower regions that are continuous with the flues in the outside wall. • Vertical flues (holes) are left connecting the fuel galleries and horizontal flues. These holes should be left at approximately every meter during loading. Arched openings are left at the end for placing the chimney,
Burning Of Bricks (Kiln Burning - The Bull's Trench Kiln) The top of the loaded section is thoroughly covered with 20 — 30 cm deep layer of ash and dust. Metal plates may be placed over them during the operation to cover the top.
Burning Of Bricks (Kiln Burning - The Bull's Trench Kiln) Preheating: ' hot and waste gases from a preceding burning chamber are made to pass to the loaded chamber by raising the dampers between the two chambers. • Gases are not very hot, ' To make the bricks completely dry and make them ready for final burning. • Burning: required volume of air is supplied by regulating the opening by raising of the gates provided in the outer wall. Additional quantities of fuel may be added from the flues provided at the top, 24 — 30 hours for perfect burning.
Burning Of Bricks (Kiln Burning - The Bull's Trench Kiln) Cooling: All the outer gates are closed by lowering the dampers. The interdepartmental gates are opened up for leading the hot gases to the preheating section. 3 — 4 days to cool down completely before unloading. • Unloading: The top layer of ash and dust are first removed from the top of the section,
Burning Of Bricks (Kiln Burning - The Bull's Trench Kiln) Advantages : 1) Cost of fuel is less as heat of hot gases is fully utilized for pre-heating of bricks 2) Continuous supply 3) High percentage of first class bricks Disadvantages : 1. High initial cost 2. Constant skilled supervision is essential
Burning of bricks (Kiln Burning - The Hoffman's continuous kiln) ' Principle: modern and more refined type of brick kiln, • For large number of bricks. • Control condition of temperature. Roof fuel Holes G-Chimney Communicating Doors Section on AB Commånicating Doors Main Doors Plan Damper
Burning of bricks (Kiln Burning - The Hoffman's continuous kiln) Construction: over ground • It is sometimes known as flame kiln, Circular in plan and it is divided into a 12 number of chambers. • Permanent roof - can be worked throughout the year. The adjacent chambers are inter connected by doors which can be open or closed by raising or lowering dampers. • Central chimney is provided, which is connected to all twelve chamber. • Each chamber is also provided with separate gate in the outer wall through which it can be loaded, unloaded and fired.
Burning Of Bricks (Kiln Burning - The Hoffman's Continuous Kiln) • Working: at any time, some chambers can be in burning, other in the preheating, still others in cooling and some in the unloading stage. The most important condition for the working is establishment of upward current of air within the kiln, which can be done by closing all the outer gates except of the chamber, which is being unloaded, • Natural air enters the kiln through this gates.
Burning Of Bricks (Kiln Burning - The Hoffman's Continuous Kiln) Impression of the Hoffman Rotary kiln when Working Jar
Burning Of Bricks (Kiln Burning - The Hoffman's Continuous Kiln) • It is made to pass through different chambers by opening their interconnecting doors. The flue at the back of each chamber is kept closed. The air will do the job of cooling, burning and pre- heating. The air is then enter the chimney for pre-heating stage. A scheme of cyclic operation is prepared in advance for working. There are many possibilities, Based on time requirement for each stage, we can decide the operation ofthe kiln.
Burning of bricks (Kiln Burning - The Hoffman's continuous kiln) Advantages . 1 , High percentage of first class bricks 2, Regular out-turn of bricks 3, Bricks are evenly burnt 4, Economy in fuel as all the heat of combustion is utilized 1. 2. 3. Disadvantages : High initial cost Constant skilled supervision is essential Economy demands regular consumption of its output, which may not be possible everywhere,
Burning Of Bricks (Kiln Burning - The Tunnel Kiln) In form of tunnel. ' Continuous type and highly efficient. The tunnel is provided with rail tracks for cars. ' Raw bricks are placed in trolleys which are then moved from one end to the other end of tunnel. Tunnel efractory terial Brick stacked here Sand seal Car mechanism
Burning Of Bricks (Kiln Burning - The Tunnel Kiln) Three sections: pre-heating section, the burning section and the cooling section. The car loaded with raw bricks is moved into the pre- heating chamber. The bricks are heated by the waste gases coming from the burning section. After few hours stop, the car is moved into the burning chamber for 20 to 24 hrs. Then the car is moved to the cooling chamber. When bricks are sufficiently cooled, they are unloaded. The kiln proves to be economical when the bricks are manufactures on a large scale. As temperature is under control, uniform bricks of better quality are produced.
Thanks... BHT

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