As described in material science, a refractory or refractory material is a material that can combat the highest level of heat, chemical attacks, and pressure with an ability to retain its original form showing no proneness to decomposition at all.
Refractory solutions are considered to be the lifeblood of many industries particularly those that work under extreme temperatures. Whatever we see around us has either a direct or indirect connection with refractory materials or simply refractories.
Refractories are non-metallic, porous, polycrystalline, polyphase, inorganic, and heterogeneous. They are typically made up of oxides or carbides, nitrides etc. of the materials that include the following:
• Silicon
• Aluminium
• Magnesium
• Calcium
• Boron
• Chromium, and
• Zirconium.
As per ASTM C71, refractories are "non-metallic materials with incredible chemical and physical properties. These materials make the perfectly suitable to be applied in structures exposed to environments above 1,000 °F (811 K; 538 °C)". Refractory solutions find applications in the following:
• Furnaces
• Kilns
• Incinerators
• Reactors
• In the making of crucibles and molds for casting glass and metals, and
• Surfacing flame deflector frameworks for rocket launch structures.
The metal casting sector is the biggest consumer of approximately 70% of all refractories produced
As per the latest information available, approximately 70% of all refractories produced are used by the metal casting sectors and the iron and steel industry the world over. Refractories find applications in high-temperature processes due to their heat-safe properties and dependability at high temperatures. They are mainly utilized as linings for high-temperature furnaces and other handling units, for example, kilns, incinerators and reactors since they can endure physical wear, extreme temperatures, and erosion by different types of chemical agents. They are also used to make melting pots. They serve broad purposes in the iron and steel industry.
Some salient general requirements that form the refractories
The characteristics of refractories are reliant upon their substance, and physical, mineralogical and thermal properties. Refractory solutions have a scope of properties to meet the necessities imposed by a large number of processes.
The general requirements that form the refractories include the following:
• Capacity to endure high temperatures and trap heat inside a restricted region like a furnace
• Capacity to endure unexpected changes in temperature
• Capacity to endure load in a variety of service conditions
• Capacity to endure chemical and harsh activity of the materials like fluid metal, fluid slag, hot gases and so on interacting with the refractories
• Capacity to resist tainting of the material with which it comes into contact
• Capacity to keep up with adequate layered security at high temperatures and in the wake of/during rehashed heat cycling
• Capacity to conserve/save heat
• Capacity to endure load and grating powers, and low coefficient of thermal extension.
The concept of special refractories
When it comes to special refractories, they are produced through special
refractory casting methodology and often include the following:
• High melting point oxides
• High melting point non-oxides
• Derived composite compounds
• Cermet
• High-temperature coating
• High-temperature fibre, and
• Reinforcing materials.
Non-oxides having a high melting point are often known as refractory compounds that also include borides, silicides, carbides, nitrides, and sulfides.
The cost quotient associated with special refractories
Although the cost quotient of special refractories is high when compared to standard refractory materials, they are considered to be indispensable and irreplaceable solutions in a large number of industrial sectors because of their versatile properties. Special refractories replace standard refractory solutions in many significant parts in various new technologies as well as fields, which can incredibly improve not only the service life but also increase the economic advantages.
The classification of special refractories at a glance
When it comes to the classification of special refractories, it can be roughly made based on the following aspects concerning many different properties of raw materials:
• Oxides having a very high melting point as well as their specific composites
• Compound materials that mainly include carbides, nitrides, borides, silicides, etc. along with their composites
• Oxides’ composite materials and refractory metals having a high melting point (cermet)
• Inorganic coating and high-temperature amorphous material, and
• High-temperature fibre as well as its reinforcing material.
Classification of refractories based on the method of manufacture
• Un-formed (monolithic-plastic, ramming and gunning mass, castables, mortars, dry vibrating cement.)
• Dry press process
• Fused cast
• Hand moulded
• Formed (normal, fired or chemically bonded)
• Un-formed dry refractories.
Classification based on the place of use
As stated earlier, the iron and steel industry is one of the major consumers of refractory solutions as more than 70% of total refractories produced are consumed by this industry. The primary reason lies in the fact that different manufacturing processes in this industry are heavily exposed to extreme temperatures, slags, and sulfur gases. This variety in the operating conditions associated with different tools and equipment calls for different grades of refractory solutions. Apart from it, each production floor has specific refractory requirements that need special shapes and technical particulars to fulfill the process requirements of the particular shop. Therefore, the refractories often get names after the shop names.
Under this category of classification, they are classified in the following ways:
• Coke oven refractories
• Blast furnace refractories
• Steelmaking refractories
• Ladle refractories
• Tundish refractories
• Calcining plant refractories, and
• Reheating furnace refractories etc.
As
refractories have always been the lifeline of many industries, Indian refractory producers have risen to the occasion to meet the demand of their customers both in India and around the globe. These Indian manufacturers have got unmatched abilities to produce refractories as per the exacting requirements of their customers.
Concluding Remarks
RHI Magnesita India is one of the top producers and suppliers of high-grade
refractory products, systems and solutions. The refractory solutions provided by the company are indispensable for industrial high-temperature processes exceeding 1,200°C. These refractory materials find applications in a comprehensive range of industries that include non-ferrous metals and glass, steel, and cement. Right since its inception, the company has been a frontrunner concerning all the leading innovations within the field and always strives hard to come up with new kinds of products. For more details, get in touch with the company.