There are many bricks in the construction market; however, not every brick can be used for every purpose. Bricks differ based on the raw materials used, shape, size, characteristics, and purposes. One such special brick is Fire Brick, which has unmatched resistance to fire and decomposition. Here, we take a look at Fire Brick, its types, uses, production, and grades.
What is Fire Brick?
Fire Bricks or Refractory bricks are made exclusively to withstand extremely high temperatures. These bricks resist fire, water, chemicals, and mechanical stresses. They are made like other ordinary clay bricks, however, they use fire clays and get exposed to high temperatures while curing, which makes them more durable. They are generally employed in places with fire like kilns, reactors, and furnaces.
Types of Fire bricks
Acidic Fire Bricks
Acidic fire bricks or acid-resistant bricks are exclusively designed to withstand chemical attacks caused by acids and other climatic conditions. There are three types of acidic fire bricks based on the composition of raw materials.
- Ordinary Fire Bricks- These bricks are made from natural fire clay mixed with crushed clay and sand. They consist of 50-75% Silica and 20-40% alumina and liquifying agents below 10%. Used for acid refractory linings in furnaces and has temperature resistance up to 1600℃.
- Silica Bricks- These bricks contain 95% silica. They are made from sandstones or quartzite, 2-3% lime. They are used in furnaces for glass manufacturing, steel furnaces, acid furnaces, and copper melting furnaces. They can resist up to 2000℃ of temperature.
- Ganister Bricks- The main ingredients of these bricks include 85% silica, 10% clay, and 2% lime. They are highly dense and can withstand high temperatures up to 2100℃.
Neutral Fire Bricks
These bricks are made from a well-balanced amount of alumina and silica. These bricks can resist both acids and bases and are durable against any chemical attacks.
- Chromite Bricks- These bricks are made from fire clays of 50% chrome iron ore, 30% iron oxide, and 20% bauxite with a minimum amount of silica. They have a temperature resistance of up to 2000℃.
- Carborundum- These bricks are made from fire clays of higher silicon carbide content. These bricks are used in electric furnaces. They can resist temperatures up to 1900℃.
- Chrome Magnesite Bricks- These bricks are made by using a chrome and magnesite mixture.
- Spinal Bricks- These bricks are made from a mix of alumina and magnesia in balanced proportions.
- Forsterite Bricks- These bricks are made from magnesium silicone oxide mineral.
Basic Fire Bricks
These bricks are made from clay that is rich in magnesium and lime. These bricks are highly resistant to corrosion and other chemical reactions.
- Magnesite Bricks- These bricks contain 85% magnesium oxide, 3-5% iron oxide, and a limited amount of lime and alumina. They are commonly used in furnaces for linings, as they have fire resistivity from 1800 to 2100℃.
- Dolomite Bricks- These bricks consist of high dolomite. They are a cheaper alternative to magnesia bricks and can withstand temperatures from 1400 to 1600℃.
- Bauxite Bricks- These bricks are made from fire clays that have 86% Bauxite and can resist up to 1600℃.
Uses of Fire Bricks
- Fire Bricks are used for lining in places with high temperatures such as fire kilns, burning furnaces, chimneys, etc.
- Used for building fire-resistant structures to prevent fire accidents and other extreme climatic conditions.
- These bricks are applicable for wood-fired ovens, steel manufacturing units, glass-making factories, etc.
Manufacturing Process of Fire Brick
Digging & Cleaning
Fire Clay that is rich in silica, alumina, and magnesia is extracted from mines. The extracted clay is cleaned to eliminate impurities and vegetable matter.
Weathering
The materials are then dried, and exposed to open-weather conditions, to reduce the moisture content and increase durability.
Tempering
The weathered raw materials are mixed with water and kneaded to form a homogeneous mixture, ready to get moulded.
Moulding
The plastic-like mixture is transferred to the moulds of the required shape and size. They are moulded using different methods such as extrusion, pressing and casting. This process reduces the pore gaps and makes the brick more dense and hard.
Burning
The bricks are kept in fire and burnt at very high temperatures that range from 1300℃ to 1800℃ to provide density and durable properties.
Pros and Cons
Pros
- Fire bricks have extraordinary insulation properties that stop the heat from passing through the brick, protecting the structure from external climatic conditions.
- They are more durable compared to ordinary bricks.
- They are denser than other clay bricks.
- These bricks can withstand heavy chemical reactions compared to common bricks.
Cons
- They use heavier materials compared to other masonry bricks, which could increase the overall weight and cost of the structure.
- These bricks are highly compact and cannot effectively isolate sound within the structure.
- Using natural resources such as silica and alumina, along with the release of smoke during the burning process, negatively affects the environment.
What are the Grades of Fire Bricks?
Fire Bricks vary based on the composition of raw materials used, properties and applications. Grades are determined for the most efficient use in construction projects.
Low Duty
The fire bricks that contain 24-36% of alumina, and have a maximum resistance of 1750℉ are termed low-duty bricks. They are primarily used in chimneys.
Medium Duty
Medium-duty fire bricks consist of 34-38% alumina and can withstand high temperatures up to 2700℉. These bricks are used in low-temperature ceramic kilns and chimneys.
High Duty
These are first-quality fire bricks that consist of 36-40% alumina. They can withstand high temperatures up to 2850℉. These bricks can be used in the construction of boilers, ceramic kilns, chimneys and lining processes.
Super Duty
These bricks contain 40-44% alumina and have a resistivity of 2900℉. The temperature of these bricks can be reduced by several hundred degrees and the same can be applied for higher temperatures.
High-Fired Super Duty
These bricks have 40-44% alumina and can withstand very high temperatures ranging from 3000℉ to 3150℉. It is the superior version of fire bricks that have low porosity, high physical strength and extreme resistance to alkali attack and carbon disintegration.
What are the Differences Between Common Brick & Fire Brick?
Manufacturing Process
Both common brick and fire brick use clay, sand and other natural additives as the raw materials, made quite similarly. However, fire bricks are exposed to extreme burning and thermal shocks to maintain their structural integrity.
Properties
Common bricks have high compressive strength, are versatile, affordable, strong and excellent for a variety of construction processes. On the other hand, firebricks have high heat resistance and are suitable for fireplaces. Although common bricks have thermal properties, they cannot withstand high temperatures. Common bricks are comparatively less in weight and less smooth than fire bricks.
Applications
Common bricks have numerous applications and can be used in several construction projects such as load-bearing walls, fences, chimneys and other commercial structures. On the other hand, firebricks are ideal for places with high temperature such as kilns, chimneys, wood-burning ovens and industrial furnaces.
Conclusion
Fire bricks are ideal for fireplaces and places that require high thermal resistance. There are several bricks in the market that have thermal resistance, but they cannot withstand temperatures as high as fire bricks. If thermal resistance is not the only priority, there are many other bricks to consider, as these bricks are comparatively priced high and have very limited applications compared to common bricks.