Refractory materials, as their name suggests, can maintain their physical and chemical stability at extremely high temperatures. Not only are these materials resistant to high temperatures, they are also effective against thermal shock and chemical erosion, making them the preferred materials for heating furnace linings and working surfaces. However, refractory materials are not a single type, but a large group with a variety of different properties and characteristics. How to select the most suitable refractory material from these many options is actually a rather complicated task.
1.Refractory materials for furnace body
As a key equipment for heating steel and other materials, the structural design of the heating furnace is directly related to production efficiency and material quality. From a professional point of view, the heating furnace is mainly composed of three parts: furnace wall, furnace bottom and furnace top, each of which carries specific functions and challenges.
On one side of the end wall of the furnace body, an end burner is installed to provide heat, and a discharge door is also provided on this side of the soaking section to facilitate product output. On the other side of the end wall of the furnace body, a feed door is provided to achieve smooth input of raw materials.
In addition to considering necessary openings such as furnace doors and manholes, the design of the furnace wall also adds side burners to the side walls of the heating section when necessary to enhance the heating effect. The furnace bottom part varies according to different types of heating furnaces. For example, the furnace bottom of the push-steel furnace is mainly composed of a soaking bed and a water-cooled pipe slide or ceramic slide bricks, while the walking furnace adopts a combination of fixed beams and walking beams. The furnace bottom mentioned here usually refers to a solid furnace bottom made of brickwork or amorphous refractory materials.
As an important part of the heating furnace, the furnace roof is mainly divided into two shapes: arched roof and flat roof. However, the furnace roof is often affected by multiple factors such as high temperature, airflow scouring and thermal stress, especially the furnace roof in the front of the heating section and the soaking section is more susceptible to damage. Therefore, the service life of the furnace roof often directly determines the service life of the entire heating furnace. In order to improve the overall performance and life of the heating furnace, it is necessary to pay attention to the design and maintenance of the furnace roof.
① Brick-built furnace body: As the core equipment in the industrial field, the internal structure of the heating furnace, especially the application of refractory materials, is particularly critical. The following will deeply analyze the refractory structure of the heating furnace and take you to appreciate the professional beauty.
The heating furnace is mainly composed of refractory bricks and insulation bricks, which jointly undertake the insulation and working layer tasks of the furnace body. First of all, the insulation layer of the furnace body, its main materials include clay or high-alumina insulation bricks, floating bead bricks, etc. These materials have excellent insulation properties and can effectively reduce the heat loss in the furnace. The thickness of the insulation layer is usually between 113 and 300 mm, which is adjusted according to the specific working temperature and requirements of the furnace.
The working layer of the furnace wall is built with clay refractory bricks, and its thickness is between 230 and 400 mm. These refractory bricks have excellent high temperature resistance and can maintain stable physical and chemical properties under high temperature environment. At the opening of the furnace wall, the designer cleverly uses brick arches, special-shaped bricks and other methods to reinforce it to ensure the overall stability of the furnace wall.
The working layer of the furnace bottom is also made of refractory bricks, with a thickness of 300 to 400 mm. The preheating section and heating section use clay and high-alumina refractory bricks respectively to meet the working requirements of different temperature sections. In order to protect the furnace bottom from the erosion of iron oxide slag, a layer of metallurgical magnesia sand is laid on the furnace bottom or a protective layer is directly built with magnesia bricks, magnesia-chrome bricks, etc.
In the heating furnace, the furnace wall around the burner, the side steel outlet and other areas, and the solid bottom soaking bed of the soaking section are the most severely damaged parts. These areas are subject to multiple effects such as high temperature, rapid cooling and heating, mechanical impact and slag erosion, so more durable materials are needed for protection. For example, high-alumina bricks or magnesia bricks can be used as the working layer of the soaking bed, but their service life is relatively short, about half a year. The use of high-performance materials such as fused mullite bricks or corundum bricks can extend the service life to about 1 year.
As an important part of the heating furnace, the furnace top is also very particular about its structure. The working layer thickness of the brick vault is between 230 and 300 mm, and an insulating brick insulation layer with a thickness of 120 to 300 mm is added. The suspended flat roof adopts a lighter structure, with a working layer thickness of 230 to 250 mm and an insulation layer thickness of about 70 mm. There are various types of hanging bricks used for suspended flat roofs, including single groove type, single-sided groove type, double-sided groove type and clamping type, etc., which are selected according to specific needs.
During the normal operation of the heating furnace, its service life is affected by many factors. Among them, the quality and selection of refractory materials are one of the key factors. For example, the service life of the clay refractory brick furnace roof is usually between 1 and 2 years, while the high-alumina brick furnace roof has a relatively longer service life due to its higher high temperature resistance. In addition, reasonable furnace design and operation and maintenance also have an important impact on the service life of the heating furnace.
In short, the refractory structure of the heating furnace is a comprehensive subject, which involves many fields such as material science, thermodynamics, and mechanical design. Only by deeply understanding and properly applying this professional knowledge can we ensure the stable operation and long life of the heating furnace in a high temperature environment.
② Prefabricated blocks hoisting furnace body:
Prefabricated blocks are an indispensable and important part of the construction of the heating furnace. They are made of specific refractory castables, including aluminate cement, phosphate low cement and water glass, which have excellent stability and durability in high temperature environments.
Prefabricated blocks are widely used in furnace bodies. They are precisely designed and manufactured to adapt to various furnace types and process requirements. Compared with traditional brick-built furnace bodies, prefabricated blocks have higher construction efficiency and better overall performance.
In the furnace roof part, prefabricated blocks are usually designed in an arched or long strip shape. The choice of these shapes is determined according to the structure and stress conditions of the furnace roof to ensure the stability and sealing of the furnace roof. At the same time, if steel bars are required in the prefabricated blocks to enhance their structural strength, these steel bars must be placed in the non-working layer to avoid being directly affected by high temperatures.
It is worth mentioning that when using clay combined with refractory castables to make prefabricated blocks, anchor bricks are also required. The function of the anchor bricks is to enhance the bonding force between the prefabricated blocks and the furnace body to prevent them from falling off or shifting at high temperatures.
③ Refractory plastic ramming furnace body:
In the field of furnace body construction, refractory plastic is a highly respected professional material. With its unique refractory properties and plasticity, it plays an important role in the production of the working layer of the furnace lining.
The construction process of refractory plastic furnace lining requires delicate operation and professional technology. First, install anchors inside the furnace body, which play the role of fixing the furnace lining. Then, fill the gaps between the anchor bricks or hanging bricks with refractory plastic blanks, and use a pneumatic hammer or a tamping machine to ram them to ensure their density. In this process, the layered and segmented continuous construction of refractory plastic is crucial. At the same time, it is also necessary to scrape the surface, set exhaust holes and cut expansion joints to ensure the stability and safety of the furnace lining in a high temperature environment.
The reason why refractory plastic furnace lining is popular is mainly due to its excellent performance. It has excellent integrity and can effectively resist thermal and mechanical stresses in high temperature environments. At the same time, its good sintering and high temperature strength ensure the long-term and stable use of the furnace lining, and it is not easy to peel off or damage. Therefore, the furnace body constructed with refractory plastic has a longer service life, generally up to about 13 years.
④ Lining castable pouring furnace body:
As a key component inside the furnace, the furnace lining bears the important responsibility of protecting the furnace body, maintaining a high temperature environment, and ensuring the normal chemical reaction in the furnace. As the main material of the furnace lining, the performance and application technology of refractory castable directly affect the service life and operating efficiency of the furnace.
The working layer of the furnace lining is usually poured on site with refractory castables. This process ensures the close combination of the furnace lining and the furnace body and excellent refractory performance. The structural design of the furnace wall and furnace roof is similar to that of the refractory plastic furnace body to ensure the stability and high temperature resistance of the overall structure.
During the construction process, the anchor bricks or hanging bricks need to be installed in place first. These bricks can effectively fix the furnace lining material to prevent it from falling off or shifting. Next, the refractory castable mixture is arranged from one side, and a vibrator is used to vibrate and compact it to ensure the uniformity and density of the furnace lining. This step requires continuous construction and timely maintenance to ensure that the furnace lining material can give full play to its performance.
In the selection of refractory castables, high-alumina cement or phosphate refractory castables were mainly used before 1980. However, these materials are prone to structural peeling in the working layer of the furnace lining in the high-temperature area, which affects the service life of the furnace. Therefore, the life of the furnace was generally short at that time, generally 2-4 years.
With the advancement of technology and the improvement of materials, after 1980, the furnace body was generally cast with various clay-bonded or low-cement series refractory castables. These new materials have higher refractory performance and better stability, which effectively extends the service life of the furnace. At the same time, for special parts such as the furnace bottom in the high-temperature area, slag-resistant corundum, mullite or magnesia-chromium refractory castables will be used for casting to further improve the durability of the furnace. In addition, key parts such as the soaking bed are cast with wear-resistant heat-resistant steel fiber refractory castables to ensure the long-term and stable operation of the furnace.
After careful construction and maintenance, the furnace takes about 8 days to bake. Under normal operation, the service life of a rolling mill heating furnace can reach 4-10 years, and the service life of a forged steel heating furnace can reach 2-4 years. These significant improvements are mainly due to the improvement of refractory castables and the improvement of application technology.
Burner bricks, as the core refractory products in the furnace combustion system, undertake the important task of organizing the flame shape and stabilizing the combustion process. These special bricks are usually designed in a trumpet shape to optimize the mixing and preheating effect of fuel and air. In the construction of the furnace, flat flame burners are generally installed on the furnace roof, while other types of burners are installed on the furnace wall, and the burner bricks are tightly embedded in the furnace lining to ensure that their center is accurately aligned with the center of the burner.
The working environment of the burner bricks and the surrounding linings is extremely harsh, and they are often subjected to the combined effects of high temperature, rapid temperature changes and air flow scouring, so their damage speed is relatively fast. The choice of materials has a significant impact on the service life of the burner bricks. For example, burner bricks made of clay can usually only be used for about 1 year in a gas combustion environment, and their life is even shorter under heavy oil combustion conditions, only 3 to 6 months.
In order to extend the service life of burner bricks, engineers continue to explore and adopt new materials. Practice shows that burner bricks made of high-alumina or sillimanite materials have improved performance. Especially on gas-fired heating furnaces, the life of burner bricks made of high-alumina cement or phosphate refractory castables can be extended to 1 to 2 years. The service life of burner bricks made of corundum or mullite low-cement refractory castables on oil-fired heating furnaces is between 6 months and 3 years.
2.Refractory materials for combustion chamber
Coal-fired heating furnaces, as important equipment in the industrial field, have a direct impact on the service life and combustion efficiency of the furnaces due to their structural design and material selection. According to different combustion methods, coal-fired heating furnaces are mainly divided into reciprocating grate type and cyclone combustion type. These furnaces are usually composed of bottom, wall and top parts, each of which has a specific function.
The lining of ordinary combustion chambers is generally built with clay bricks or high-alumina bricks. These materials have good stability in high temperature environments, but due to multiple factors such as high operating temperature, large temperature fluctuations, slag erosion and mechanical damage during slag cleaning, their service life is relatively short, about 1 year.
In order to extend the service life of the combustion chamber, researchers and engineers are constantly exploring new refractory materials. When refractory castables such as special high-aluminum clinker, corundum, mullite or magnesia-aluminum spinel are used to cast the lining, these materials can form a dense and strong protective layer that effectively resists high temperature and erosion. Therefore, the service life of the combustion chamber using these refractory castables can be extended to 1 to 3 years.
The cyclone combustion chamber is a special combustion chamber, and its lining needs to withstand higher temperatures and stronger thermal shocks. Therefore, the lining of the cyclone combustion chamber is usually cast with high-strength, high-thermal conductivity silicon carbide refractory castables. This material has excellent high-temperature resistance and thermal stability, which can ensure the long-term stable operation of the cyclone combustion chamber in harsh environments, and its service life can generally reach 1 to 2 years.
The waist furnace is the key channel connecting the combustion chamber and the furnace of the heating furnace, and its operating temperature is as high as about 1600℃. In such a high-temperature environment, even if high-performance materials such as sillimanite bricks or corundum bricks are used for masonry, the life of the waist furnace is relatively short, only about 0.5 years. This is mainly because the waist furnace is subject to large thermal and mechanical stresses, which makes the material prone to breakage and failure.
3.Refractory materials for furnace doors and steel spouts
As an important industrial thermal equipment, the design and material selection of the furnace door and steel spout of the heating furnace are crucial. They are not only related to the thermal efficiency of the furnace, but also directly affect the safety and continuity of production.
Furnace doors, as components for closing the holes in the furnace wall, are mainly divided into two types: side-opening and lifting types. Side-opening furnace doors are easy to operate and suitable for smaller holes; while lifting furnace doors are suitable for large holes, and their vertical movement design helps to reduce heat loss. The lining materials of the furnace door are usually clay bricks, refractory castables or high-alumina insulation bricks, which can remain stable at high temperatures and effectively isolate the heat in the furnace. However, since the lifting furnace door is often affected by temperature fluctuations and mechanical collisions, its service life is relatively short, about one year.
Steel spout, as a channel for the steel billet to be discharged from the heating furnace, its material selection and design are equally important. Traditional steel spouts are mostly made of water-cooled cast iron or high-alumina bricks and magnesium bricks. Although these materials have certain high temperature resistance, they are still affected by wear and thermal shock during long-term use, and their service life is relatively short, generally 3 to 6 months. In order to extend the service life of the steel spout, more advanced materials and technologies have been adopted in recent years. For example, the steel spout built with sintered or fused mullite bricks has higher strength and wear resistance, but its thermal shock resistance is poor and it is easy to crack. In contrast, the use of heat-resistant steel fiber reinforced corundum refractory castables poured on site into an integral steel spout has better comprehensive performance, and its service life can reach more than 2 years.
4.Refractory materials for furnace bottom water cooling pipes
In large heating furnaces, such as pusher or walking beam heating furnaces, the water cooling pipes at the bottom of the furnace are arranged in a complex pattern, consisting of thick-walled pipes that are distributed longitudinally and transversely and supportive. Insulating these water cooling pipes is essential to optimize thermal efficiency, reduce energy losses and improve heating quality.
The main purpose of insulation is to reduce the heat carried away by the cooling medium, thereby reducing the black mark phenomenon of the steel billet in the furnace and further improving the uniformity and quality of heating. To achieve this goal, a variety of insulation methods are applied in practice: Special-shaped clay brick inlay or horseshoe brick hanging: These traditional refractory materials are covered on the surface of the water cooling pipe by precise inlay or hanging to form an insulating layer.
Welding of prefabricated blocks made of refractory plastic or refractory castables: Using modern refractory technology, prefabricated blocks that perfectly fit the shape of the pipe can be made and fixed to the water cooling pipe by welding.
On-site wrapping: Use flexible materials such as refractory fiber felt, combined with refractory plastic or refractory castables, to wrap the water-cooled pipes on-site to form an efficient insulation layer.
The choice of these insulation methods depends on the specific application requirements and the operating conditions of the heating furnace. Typically, the service life of these insulation materials is between 3 and 12 months. However, by using advanced materials such as high-quality refractory plastic, ultra-low cement or cement-free refractory castables for on-site wrapping, the service life can be significantly extended to more than one year.
5.Refractory materials for ceramic slides
In small pusher heating furnaces, ceramic slides play a vital role. This slide is mainly composed of brown corundum-silicon carbide slide bricks, which can maintain excellent stability and wear resistance in high temperature environments.
To build a ceramic slide, first use refractory bricks to build two or four rows of base walls in the length direction of the furnace. These base walls provide a solid foundation support for the slide. Then, high-aluminum silicon carbide seat bricks are precisely built on the base walls. The function of these seat bricks is to provide a stable installation position for the slide bricks. Finally, the slide bricks are installed on the seat bricks to form a complete ceramic slide.
During the movement of the steel billet on the slide, uniform heating can be achieved on both the upper and lower sides, which not only improves the heating efficiency, but also reduces energy consumption and avoids quality problems such as black marks on the surface of the steel billet.
However, the working environment of the ceramic slide is extremely harsh, and it needs to withstand high temperatures, heavy pressure of steel billets, long-term wear and tear, and erosion by iron oxide slag. Despite these challenges, ceramic slides can still maintain a relatively long service life, usually around one year, due to the excellent performance of the slide tiles.
6.Refractory materials for flues and chimneys
In industrial production and daily life, flues and chimneys, as important channels for emitting smoke, are subjected to extremely high temperatures and chemical erosion. In order to ensure their long-term stable operation, we need to use professional refractory materials (refractory materials) for protection and reinforcement.
For flues, their lining is usually built with clay bricks. This brick has excellent fire resistance and stable chemical properties, and can effectively resist the erosion of high-temperature flue gas. In addition, refractory castable prefabricated blocks are also a common choice for flue linings. They are installed by hanging or pouring on site to form a solid protective layer. In some cases, refractory spray coatings are also used in the construction of flue linings, which can quickly form a dense protective film to improve the overall fire resistance of the flue.
For chimneys, especially red brick or concrete chimneys, refractory bricks are used for masonry in high-temperature areas. This brick has higher fire resistance and stronger mechanical strength, and can withstand the high temperature environment inside the chimney and the wind pressure outside. For metal chimneys, metal anchor nails are welded on the inner wall to enhance the adhesion of the lining material. At the same time, lightweight refractory castables or refractory spray coatings are used as lining materials, which have the advantages of convenient construction, strong integrity, and long service life. They can effectively isolate the erosion of high-temperature flue gas on metal chimneys and ensure the long-term stable operation of chimneys.