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Image by Bernard Hermant


(Appropriate for Bengal)

1.0  Details of manufacturing process to be adopted:


a. Clay winning (or excavation)  is done using a JCB / Backhoe Loader. Care is taken to expose the entire vertical clay profile reaching up to the maximum depth to which clay occurs. Clay is dug vertically from top to bottom of the exposed face so that material in all intermediate strata gets mixed in the process. The excavated clay is transported in trucks or tractor trolleys to the plant. Plastic clay and non-plastic clay are stocked one above the other in thin layers in such a way that thickness of each layer is proportionate to its desired proportion in the raw-mix.  The raw-mix is then kept soaked - by spraying water over the heap - for at least 1 week in advance. This improves homogeneity of the mix by allowing sufficient time for the water to penetrate evenly into the material.


b. Shaping:


The soaked raw-mix is then dug vertically from top to bottom by using a JCB and is fed to Box Feeder. The raw-mix then falls on to the belt conveyor fitted below the Box Feeder and is carried to hopper of ‘Ishtika’ Mixerpress (IMP) by a belt conveyor. The IMP consists of a mixer, a mould chain, a press block, a mould washing station and an all-side sander (including exhaust box).  Final adjustment of water content in the raw-mix can be done by adding 5 to 7 % water in the mixer.  The Ishtika Mixerpress requires about 92.00 KW (125 HP) connected load.  7 bricks are shaped every stroke on a metal pallet. The mixerpress can operate at a speed of up to 15 strokes per minute. Thus, the capacity of the Ishtika Mixerpress is 6,300 bricks (of 250 x 120 x 75 mm fired size) per hour. 


c.  Drying:


Loaded pallets coming out of the Ishtika Mixerpress on its Chain Conveyor are then transferred manually to battery-operated cars which are carried inside Drying Shed.  Pallets are unloaded manually from the battery-operated cars and placed on fired bricks placed in regular rows inside drying sheds. This ensures at least a few inches air gap between the pallets and the shed floor for air circulation.   

After 3 or 4 days, bricks are manually turned on their edges for faster drying.  Thereafter, bricks dry inside the shed on edge for another 1 or 2 days.  They are then arranged in stacks of 288 bricks on m. s. pallets and carried by fork lift to open yard for further drying, i.e. till their moisture content is reduced to below 7 per cent.  The dry brick stacks are then carried by fork lift inside the setting area of High Draft Zig-zag Kiln (HDZK) through its wickets (or doors). 

d. Firing:


Dry bricks are manually set in a pre-determined zig-zag pattern with trace holes, fuel shafts, flues, etc. kept in accordance with set practice.  HDZK is a continuous kiln working on induced draught created by a fan.  Crushed 'B' or 'C' grade steam coal or imported coal is used as main fuel for firing bricks. Saw dust may be used as additional fuel for advancing the fire.  Fuel is fed through feed holes provided in the kiln-top.  Firing temperature ranges between 1050 Degree Celsius and 1100 Degree Celsius. Fully fired and cooled bricks are manually unloaded and carried to the Open Brick Yard or are directly loaded into trucks and dispatched.  

  1. Unlike ‘hand-moulding’ operation, soft mud machine moulding provides much better occupational health and safety conditions to workers.  It also reduces labour intensity of the traditional shaping and drying operations and eliminates dependence on skilled ‘moulders’ by delinking quality of green bricks from human skill levels. 

  2. Machine-moulded all-side-sanded bricks are uniform in size and shape and have perpendicular faces and sharp edges.  Therefore, use of these bricks in walling saves up to 15 % mortar and plastering expenses.

  3. Thorough mixing of raw-mix components in the mixer results into uniform firing, better crushing strength and lower breakages during handling. 

  4. Unlike extruder, the mixerpress exerts only the bare minimum pressure required for proper shaping of green bricks thereby ensuring a reasonably ‘open’ brick body which can be dried under shed without fear of cracking.  Also, soft mud machine molding can have frogs and name / trademark of the manufacturer which extruded bricks cannot have and which are always preferred by the market.

  5. Soft mud machine moulding process can incorporate much higher percentage of 'non-plastic' wastes, fuels and / or soils as compared to extrusion.   The wastes could be from agriculture, urban waste treatment plants and industries like coal processing, textile, tanning, sugar, liquor, petroleum, paper, wood-processing, agro / food processing, etc.

    This solves the disposal problem of the waste generating agencies; minimizes the requirement of primarily extracted clays and fossil fuels; increases the porosity of fired bricks making them lightweight and thermally / acoustically more insulating and improves the enterprise profitability by saving costly external fuel, which forms 25- 40 % of cost of production of bricks.  Lightweight bricks also require less transportation energy and can be handled easily by laborers thereby improving their comfort level and speed of work. 

    We are now developing a technique on pilot-scale which - like extrusion - can introduce circular holes in the soft mud moulded bricks.  When introduced commercially in the near future, this feature will also make the soft mud moulded bricks lightweight, less energy and resource intensive and less costly. 

  6. Ishtika Mixerpress is ideal for manufacturing paving blocks with chamfered edges – which are very difficult to be made by extrusion and which fetch much better value addition on weight basis than ordinary fired clay bricks.

2.0 Advantages of the soft mud moulding process:

 It is assumed that the promoter owns at least 5 acres of land required  for the project with apropriate electrical connection and facilities for water pumping / storage and coal crushing. 

3.0 Project Feasibility:

3.1 Production:

a) Green bricks moulded / hour = 7 bricks / stroke x 15 strokes / minute x 60 minutes / hour = 6,300 nos.
 Assuming about 70 % working efficiency, green bricks moulded / day / shift = 6,300 x 8 x 0.70 = 35,000 nos. 

​b)  Assuming 2 % production loss during drying and 3 % during firing; 140  firing days / season (i.e. 20 weeks / year x 7 days / week) and 144  moulding days / season (i.e. 24 weeks / year x 6 days / week),

      Green bricks moulded / season = 35,000 x 144 = 50,40,000;
      Production of saleable fired bricks / season = 50,40,000 x 0.98 x 0.97 = 48,00,000 nos.      
      Production of saleable fired bricks / day = 48,00,000 / 140 = 35,000 nos.  

3.2  Estimated Additional Investment:

3.3  Cost of production @ 48,00,000 fired saleable bricks / year or 35,000 bricks / day:

 * 7 KW Box Feeder + 2.20 KW Conveyor + 92 KW Ishtika Mixerpress  
            + 7.50 KW Coal Crusher + 3.75 KW Raw Water Pump

   4.4 Expected Selling Price (ex-works): Rs. 12,000.00 / 1000 bricks (minimum)

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