Manufacture of bricks 🧱

How bricks are made? 

In the previous blog we have studied about brick, its composition, impurities and its comparison to stonework. Today in this blog we will further discussed on how bricks are made and what care taken while manufacturing.

There are mainly four operations are involved in manufacture of bricks.

1. Preparation of clay
2. Moulding
3. Drying
4. Burning
5. Dispatching

1. Preparation of clay

Brick making clay is not directly available in market, we need to obtained it by various operations like.

• Unsoiling
• Digging
• Cleaning
• Weathering
• Blending
• Temping

Unsoiling

Location of which clay is meant to be used for brick manufacturing the top 20 centimetre layer is taken and thrown away, as top most layer contains impurities in large amount which will affect formation of bricks and final product quality. Hence unsoiling need to done before getting clay from a particular location.

UNSOILING

Digging

After unsoiling operation clay is dig out and spread on a levelled ground. Generally heaps of 600 mm to 1200 mm are allowed to stake.

DIGGING

Cleaning

During this operation there are chances of clay obtained with stone, pebble and other vegetable matter which are harmful and unexpected. So it is necessary to clean soil from this unsuitable matters and lumps of clay need to be powdered if any.

Weathering

Weathering mean to get in contact with atmosphere. After all above operations clay is allowed to get soften in atmosphere. The weathering time may vary from weeks to months or say seasons. For small projects it is okay to have less period of weathering but in case of large projects clay is dug out before monsoon and allowed to get weathered full monsoon season.

WEATHERING 

Blending

Before the use of next operation clay is need to be well mixed so that it could passes a uniform property at all. Hence clay is made loose by adding some agents and blend well by moving it in vertical direction up and down, a small amount of clay in succession. 

Tempering

In tempering operation clay is brought to a hardness level and make it fit to moulding operation. Necessary water is added to the clay and pressed or kneaded with the help of men fit or cattle. Temping is done to get homogeneous and uniform mass of clay for making bricks. 

TEMPERING

Temping by human fit or cattle is work for small scale of bricks production, but any how we are not able to make it happen for large scale, so that we need machinery for those large scale project where uniform quality is essential. A pug mill is used for large scale temping operation.

PUG-MILL

Process of mixing/grinding of clay with water is known as pugging.

How Pug Mill works

• Fist hole of pugged clay is kept closed
• Mixture of clay and water is added from top to pug-mill.
• After adding mixture pug-mill kept closed at top.
• Rotation of vertical shaft is started and horizontal arm/ knives on it assist in pugging operation.
• Rotation of shaft is employed by mechanical or any other means.
• Once clay is pugged sufficiently bottom hole is opened and clay is taken out for further moulding operation.

Check:- If pugged clay can be rolled into 3 mm diameter thread, that means it is pugged properly.

2. Moulding

Moulding is an operation to give proper required shape to brick. Moulding operation can be done in two ways, either hand moulding or machine moulding

Hand Moulding

In case of hand moulding rectangular blocks are used which are opened at top and bottom with extra handle facilities.

They are made up of either wood or steel, wooden blocks are less durable then steel blocks and having less uniformity of shape also, to increase its durability brass/metal strip is wounded around the blocks at edges, while steel blocks are made up of steel plates and channels.

Steel blocks are more durable and used for large scale works. Bricks shrink during drying and burning operations, hence it is necessary to used larger blocks than required size, almost 8 to 12 percent extra size blocks are used for mfg. of bricks. 

Exact extra size of blocks for bricks will never be fixed due to certain parameters, so it is always obtained by actual experiment at a particular location for particular kind of earth.

Hand moulding is done in two ways:

• Ground moulded bricks 
• Table moulded bricks

Ground moulded bricks

In this method ground is leveled before operation of moulding

• Fine sand layer sprinkled over leveled ground.
• Mould dip into water and placed over it.
• Pugged clay fill in the mould in such a manner that every space in it filled with clay, even a corner should also filled properly.
• Extra clay at top is removed by wooden or metal flat.
• After this mould is lifted up and placed at another location and process repeated(every time mould need to dipped into water once).
• After sufficiently dry, brick placed at drying sheds.

There are two types of bricks by ground moulding technique.

1. Slop moulded bricks

Bricks are made by dipping block in water every time is called slop moulded bricks.

2. Sand moulded bricks

When bricks are made by sprinkling fine sand or fly ash on the inner surface of mould, instead if dipping in water is called sand moulded bricks.

This bricks have straight & sharp corners and edges.

In ground moulded bricks lower surface is rough.

Frog:- Indentation make on the surface of brick is called frog. It is of 10 to 20 mm depth in bricks.

Main two purpose of frog:

1. Indicate trade name of manufacturer

2. Formed key bond between mortar and bricks.

Table moulding bricks

In table moulding of bricks process involved is same as hand moulding of bricks, difference is that only a table of 2 m X 1 m is used for moulding purpose and sent them to drying shed for further process.

Clay, mould, water pots, stock boards, strikes and pallet boards are placed on this board.

Bricks are placed on its longer side for drying in sheds, it will take less space and dries quickly.

Machine moulding

When requirement of bricks at large scale hand moulding does not prove economical, hence we need to use machine for moulding of bricks for large scale production in less time as well as less costly. 

Machine moulding also proves useful for hard and strong clay, which needs lots of energy for breaking. machine moulding done in two ways:

1. Plastic clay machine

2. Dry clay machine

1. Plastic clay machines

This machines contains opening of brick size in length and width. Pugged clay is filled in this machine and it comes out from the opening and cut into strips by wire attached in the frames. Strip thickness is kept as bricks size to obtain a bricks of desired shape and size. 

This bricks are also termed as wire cut bricks.

2. Dry clay machines

In this machines hard clay is made powdered by mechanical means, after that required amount of water added in the machine and form and stiff paste. This paste is then moulded and pressed to form a brick of desired shape.

This bricks are also termed as pressed bricks. 

Bricks made by dry clay machine moulding do not required drying.

Advantages of machine moulded bricks over hand moulding.

• Bricks having sharp edges and corners
• Denser bricks obtained.
• Smooth surface bricks can be manufactured.
• Uniform texture and clear shaped frog.

3. Drying

If bricks are burnt directly after moulding operation it will get cracked and distorted due to moisture present in it in the form of damp. Hence before burning operation of bricks we need to dry it. Bricks are laid longitudinally to get dried. 

All the bricks are paced on edges as stated earlier it will take less space and time too.

Drying of bricks depends on following:

• Artificial drying
• Circulation of air
• Drying yards
• Period of drying
• Screens

Artificial drying

Generally drying process is of two type i.e. artificial drying and natural drying. In case of large scale and shortage of time we need to go for first option that is artificial drying, in this process moulded bricks which are need to be dried before burning are passed through drier in the form of tunnels. And these driers are heated to maintained temperature for drying of bricks at optimum.

Circulation of air

For easy and fast drying of bricks it is necessary to stack bricks in a manner that a good circulation of air get maintained to all side of bricks. 

Drying yards

Drying of bricks is an essential operation and it is done carefully. For drying purpose drying yards prepared at a higher level then ground level and this platform/yard(surface) covered with fine sand sprinkling. This is done to prevent accumulation of air.

Period of drying

Drying period depends upon weathering condition, as it takes more time in monsoon and winter, while take less time in summer. Average it takes about 3 to 10 days for drying.

Screens

Bricks are not in direct contact to sun or wind, screens are provided to avoid certain situations.

4. Burning

Burning is very important operation involved in bricks manufacturing. Burning provides strength and hardness to the bricks. Durability and denseness of bricks also depends on how bricks are burned. Bricks may be sometime overburnt or underburnt.

Overburnt

If bricks are burned greater than its optimum requirement it leads to become brittle in nature and hence break easily

Underburnt

If bricks are burned lesser than its optimum requirement it leads to become soft in nature and hence it cannot carry the loads.

Burning operation of bricks is done either in clamp or kiln. In our next blog we will study in detail about clamp and kiln .

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"To Be Continued..."