What are Refractory Bricks?
Refractory bricks are bricks that are developed to withstand high temperatures. Refractory bricks, also called fire bricks, are made using fireproof materials that have a high melting point and are resistant to thermal stress. While the ability to withstand heat is their primary purpose, refractory bricks also have a low thermal conductivity which makes them more energy efficient than other fire-resistant materials. Refractory bricks are most commonly used in high-temperature environments, but there are situations where engineers use them in low-temperature applications due to their insulating properties, chemical resistance, and structural integrity.
Refractory bricks are not subject to decomposition by heat, pressure, or chemicals. They are part of a larger group of substances that materials science defines as refractory material. Refractory bricks are a part of the “shaped” subset of refractory material.
Common Types of Refractory Bricks
Refractory bricks have numerous applications, so manufacturers have created distinct types of bricks to withstand specified conditions. The most common materials they use in the production of fire bricks are alumina, silica, magnesia, and fire clay. Mixed in different proportions, these materials create the main three types of refractory bricks: acid refractory bricks, basic refractory bricks, and neutral refractory bricks.
Listed are some of the most common types of refractory bricks in these three broad categories.
Fire Clay Bricks
Fabricators make fire clay bricks using a combination of crushed clay, sand, silica, and alumina. Builders use fire clay bricks in moderate temperature applications like fireplaces, kilns, stoves, and chimneys. They can withstand heat up to 1600 degrees Celsius. This is the most common type of refractory brick that people use.
High Alumina Bricks
High alumina bricks are ideal for high-temperature settings like steelmaking and incinerators because they have good thermal stability and resistance to chemical erosion. As its name suggests, alumina is the primary component in high alumina bricks.
High-purity silica, or silicon dioxide, is the primary component of silica bricks. This type of refractory brick has a high melting point with a temperature resistance of up to 2000 degrees Celsius. These bricks also have a high resistance to acid, so they are ideal in glass-making furnaces, copper-melting furnaces, and open-hearth steel furnaces.
Fireclay, which consists of magnesium oxide, is the primary component of magnesia bricks. Manufacturers use this brick primarily because of its resistance to slags, including lime and iron-rich slags. These bricks have the widest application in the steel industry. They resist temperatures up to 2100 degrees Celsius.
Fabricators construct chrome bricks using fire clay containing chrome iron ore, iron oxide, bauxite, and silica. These bricks have the greatest application in corrosive environments. This can include specific areas in a kiln or furnace. They can resist temperatures up to 2000 degrees Celsius.
Carbon bricks are a type of neutral refractory brick that is composed of high-quality carbons including anthracite, coke, graphite, and a binding agent. Carbon bricks have excellent shock resistance, low thermal conductivity, and high temperature and erosion resistance. The primary application of carbon bricks is for the metallurgic industry.
Zirconia bricks are a type of acid-refractory brick and are composed of zirconium dioxide. These bricks have excellent shock resistance and low thermal conductivity. Designers use these bricks where rapid changes in temperature require their stability. These applications include metallurgical furnaces, glass furnaces, and ceramic kilns.
Insulating bricks are made from porous materials so they are lightweight refractory bricks. They also have low thermal conductivity so they are ideal to minimize heat loss. Compared to fire clay bricks, these have a lower density and higher thermal resistance. There is a wide variety of insulating refractory bricks. Insulating bricks are often a cost-effective option compared to other refractory bricks.
Refractory Brick Qualities and Characteristics
The quality and characteristics of the material that forms refractory bricks allow them to thrive in high-temperature environments.
- High Melting Point – The materials that form the base of refractory bricks like silica, carbon, alumina, zirconia, magnesia, and chrome oxide all have a high melting point. The composition of this base material allows the bricks to maintain their structural integrity at extremely high temperatures.
- Thermal Stability – Refractory bricks can withstand rapid changes in temperature without cracking or breaking. This is a valuable quality in applications like the glass, steel, and ceramic industries where heating and cooling are an integral part of the production process.
- Chemical Resistance – Certain refractory bricks maintain structural integrity when exposed to chemical substances. This makes them valuable in applications that are exposed to the presence of corrosive agents and slags.
- Thermal Insulation – Some refractory bricks have low thermal conductivity. This allows them to minimize heat transfer, reduce energy loss, and maintain temperature stability. Refractory bricks such as insulating bricks provide effective insulation in high-temperature environments.
- Mechanical Strength – Refractory bricks are structurally sound which allows them to resist cracking and strain during constant use and wear.
- Abrasion Resistance – Many of the applications for refractory bricks subject them to flowing materials or mechanical actions. These bricks can withstand this constant abrasion so they will last longer with greater structural integrity.
- Porosity/Density – Specific types of refractory bricks have different levels of porosity which determines their ability to resist the penetration of gas or liquids. Dense bricks have a higher level of resistance to gas and chemicals, but porous bricks have greater insulation capabilities.
- Structural Integrity – Refractory bricks maintain their shape in the harshest chemical and highest temperature environments. This quality ensures the longevity of the refractory lining.
Applications for Refractory Bricks
The qualities of refractory bricks mean that they work for a broad range of applications that involve high temperatures and harsh conditions.
The steel industry is a primary user of refractory bricks in applications such as blast furnaces, steel ladles, and steel converters. Refractory bricks line the walls, roofs, and floors of this equipment to give them the capability to withstand the high temperatures and chemical reactions involved in steel production.
Refractory bricks are used in glassmaking furnaces and glass melting tanks. They provide insulation and resistance to the corrosive properties of molten glass. Refractory bricks also maintain their structural integrity during the changing temperatures present in the heating and cooling of glass.
Non-Ferrous Metal Industry
The non-ferrous metal industry refers to metals that do not contain iron or have a low-iron content. Refractory bricks are common in the non-ferrous metal industry because these metals have a high melting point, corrosive chemical waste, and a wide range of distinct properties that require bricks with versatility.
Fabricators use refractory bricks in applications for catalytic cracking units and ethylene furnaces common in the petrochemical industry. Refractory bricks have strong corrosion and abrasion resistance and the chemical stability required to ensure the longevity of the furnaces. They also have the thermal insulation needed to control the temperatures, optimize process efficiency, and reduce fuel consumption.
Power Generation Industry
Power generation plants use refractory bricks to line boilers, incinerators, and other high-temperature equipment. This provides insulation for this equipment and protects sensitive machines and structures from high temperatures.
Ceramic and Cement Industry
Ceramic and cement plants use refractory bricks to line kilns for firing ceramics, pottery, bricks, and cement blocks.
Foundries use refractory bricks in furnaces and crucibles used for melting and pouring molten metals.
Physical Properties of Refractory Bricks
- Shape – Refractory bricks usually have a square or rectangular shape. This allows for easy stacking, alignment, and stability. There are also specialty brick shapes such as circular, arch, or wedges for particular applications.
- Size – Refractory bricks come in varying but standardized sizes to ensure ease of installation. A typical refractory brick dimension is 9 in x 4.5 in x 2.5 in (LxWxH) or 230mm x 115mm x 75mm.
- Weight – The weight of refractory bricks varies widely according to the exact material used for the brick. Typically, insulating bricks are the lightest-weight refractory bricks and range between 2.2lb-6.6lb (1kg-3kg) per brick. Chrome bricks are heavy because of their dense composition. They range from 8.8lb-17.6lb (4kg-8kg) per brick.
- Color – The color of refractory bricks ranges depending on the material. Common colors include light yellow, beige, light gray, off-white, and black.
- Surface Texture – Refractory bricks are solid and compact. They can have a smooth, slightly rough, or textured surface depending on the manufacturing method or brick type.
- Surface Pattern – Some refractory bricks have patterns or markings on their surface due to the manufacturing process. These markings can help with alignment during the installation phase.
- Compressive Strength – The compressive strength of refractory bricks varies according to their material. In general, refractory bricks have a compressive strength ranging from a few hundred pounds per square inch (psi) to several thousand (psi). Insulating bricks have the lowest compressive strength at 300 psi to 2,000 psi. Chrome bricks have the highest compressive strength from 10,000psi to 30,000 psi.
- Moisture Absorption – Engineers design refractory bricks to have low moisture absorption to minimize its negative effects on their performance. Like all the physical properties, the absorption depends on the exact material of the refractory brick but they all have a moisture absorption rate between 1%-6%. Insulating bricks, due to their porous nature, have the highest absorption range, which is between 2%-6%.