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Types of refractory materials used in various parts of the heating furnace

Dec 05, 2023

Heating furnace is a thermal equipment used to heat steel billets or small steel ingots when rolling or forging steel. The operating temperature is generally 1300~1400℃. With the large-scale and high-efficiency rolling mills, higher requirements have been put forward for heating furnaces. The development trend is large-scale, low-consumption, pollution-free and automated operation. As a result, the materials for building furnaces have also undergone major changes.

The furnace body consists of furnace walls, furnace bottom and furnace top. An end burner is installed on the end wall of one side of the furnace, there is a discharge door on the end wall of the soaking section, and there is a feed door on the other end wall. In addition to the furnace door and manhole on the side wall, side burners are sometimes installed on the side wall of the heating section; the bottom of the push-steel furnace is composed of a soaking bed and a water-cooling tube slide or ceramic slide brick, and a walking-type furnace The bottom is composed of fixed beam (bottom) and walking beam. Traditionally, the furnace bottom refers to the solid furnace bottom made of bricks or amorphous refractory materials. The stove top is divided into two types: vaulted top and flat top. The top of the furnace is affected by factors such as high temperature, airflow erosion, and thermal stress. In particular, the top of the furnace in front of the heating section and the soaking section is more susceptible to damage and is the weak link of the entire furnace body. therefore. The life of the furnace top represents the service life of the heating furnace.

Item DYSLG-1.0B DYSLG-0.9B DYSLG-0.8B DYSLG-0.7B DYSLG-0.6B
Al2O3 48-60 48-60 48-60 48-60 48-60
Fe2O3 ≤2.0 ≤2.0 ≤2.0 ≤2.0 ≤2.0
Bulk Density (g/cm3) ≤1 ≤0.9 ≤0.8 ≤0.7 ≤0.6
Cold Crushing strength (Mpa) ≥3.92 ≥3.43 ≥2.94 ≥2.45 ≥1.96
Thermal Conductivity Coefficient (W/mk) ≤0.45 ≤0.45 ≤0.35 ≤0.35 ≤0.3
Permanent Linear Change Rate (max 2%) (℃) 1400 1400 1400 1350 1350

(1) Brick furnace body. Furnace lining made of insulating bricks and refractory bricks. The thermal insulation layer of the furnace is built with clay or high-aluminum insulating bricks, floating bead bricks, diatomite bricks and refractory fiber felt, with a thickness of 113~300mm. The working layer of the furnace wall is built with clay refractory bricks, with a thickness of 113~300mm. It is 230~400mm, and the openings can be built with brick arches, special-shaped bricks, or long strips of clay refractory bricks. If the furnace wall is high, high-aluminum tensile bricks must be installed at appropriate intervals to prevent the furnace wall from toppling. At the same time, the bottom of the furnace wall in the heating section needs to be thickened to increase its stability. The furnace wall impacted by the billet is more susceptible to damage. The furnace walls around the burner and side tap holes are most susceptible to damage due to high temperature, rapid cooling, rapid heating, and mechanical effects. The thickness of the working layer at the furnace bottom is 300~400mm. The preheating section is built with clay refractory bricks, and the heating section is built with clay or high-alumina refractory bricks, with a layer of metallurgical magnesia laid on top.

Phosphate High Alumina Brick

In order to resist the erosion of iron oxide scale slag, magnesia bricks or magnesia chrome bricks can also be used to directly build a protective layer. The solid-bottomed soaking bed in the soaking section is damaged quickly due to high temperature, billet impact, movement wear and slag erosion. When high alumina bricks or magnesia bricks are used as the working layer in this part, the service life is about half a year. If fused mullite bricks or corundum bricks are used instead, the service life can be extended to about one year. When the furnace roof is a brick vault, the working layer thickness is 230~300mm, and an insulating brick insulation layer with a thickness of 120~300mm is added. When using a suspended flat roof, the thickness of the working layer is 230~250mm, and the thickness of the insulation layer is about 70mm. Suspension bricks for hanging flat ceilings are divided into single groove type, single side groove type, double side groove type and clamping type. Generally, soil-made hanging bricks are used, and high-aluminum hanging bricks are also used in high-temperature areas. The commonly used special-shaped hanging bricks in the depressed part of the furnace roof do not need to be insulated. The service life of clay refractory brick furnace top is 1 to 2 years, and the service life of high-alumina brick furnace top is slightly longer. After replacing the fired bricks with unfired high-aluminum hanging bricks, the service life can be increased by about 1 times. Under normal operation, the service life of the rolling steel heating furnace is generally 1 to 3 years. Due to intermittent operation, the forging steel heating furnace is greatly affected by thermal stress and mechanical collision, and its service life is 3 to 11 months.

High Alumina Anchoring Bricks

(2) Hoist the furnace body from prefabricated blocks. Precast blocks are manufactured using refractory castables such as aluminate cement, phosphate low cement and water glass. If clay combined with refractory castables is used to make prefabricated blocks, anchor bricks must be provided. Furnace roof prefabricated blocks are divided into arched and strip shapes. If steel bars are used, they must be placed in the non-working layer.

 

(3) The furnace body can be made of refractory plastic. Furnace lining working layer made of refractory plastic hammered with anchors. The gaps between anchor bricks or hanging bricks need to be filled with refractory plastic blanks and compacted with a pneumatic hammer or tamping machine. Refractory plastics, including the furnace bottom, are generally constructed in layers and in sections, and the surface is shaved, vent holes are tied, and expansion joints are cut. The advantages of refractory plastic furnace lining are strong integrity, good sinterability and high high temperature strength. Therefore, the furnace lining generally does not peel off and has a service life of about 13 years.

 

(4) The furnace body is poured with fire-lining castables. Furnace lining working layer poured on-site with refractory castables. The structure of the furnace wall and furnace top is the same as that of the refractory plastic furnace body. After the anchor bricks or hanging bricks are installed in place, spread the refractory castable mixture from one side, and then use a vibrator (holding) to vibrate and compact. It should be constructed continuously and maintained in time. Before 1980, high-alumina cement or phosphate refractory castables were generally used to cast the working layer of the furnace lining. However, the working layer of the furnace lining in high-temperature areas is prone to structural spalling, which affects its use. Life span is generally 2 to 4 years. After 1980, various clay-bonded or low-cement series refractory castables are generally used to pour the furnace lining working layer in the furnace body. Corundum, mullite or magnesia-chromium refractory castables that are resistant to slag corrosion are sometimes used at the furnace bottom in high-temperature areas. The hot bed is poured with wear-resistant heat-resistant steel fiber refractory castables. The oven time takes about 8 days. Under normal operation, the service life of the rolling steel heating furnace can reach 4 to 10 years, and the service life of the forging steel heating furnace is 2 to 4 years.

 

Burner bricks are refractory products used in various burner parts and mainly play the role of organizing flames. The flat flame burner is installed on the furnace roof, and the other burners are installed on the furnace wall. The burner brick is in the shape of a bell mouth, consisting of one or several pieces, and is embedded in the furnace lining. Its center must be aligned with the center of the burner to ensure effective mixing and preheating of fuel and air, and organize and stabilize the flame shape. burning process. The brick and its surrounding lining are often subjected to high temperatures, sudden temperature changes, and airflow erosion. Destroyed faster. The service life of clay burner bricks used for burning coal gas is about 1 year. When heavy oil is used as fuel, its service life is only 3 to 6 months. When switching to high alumina or sillimanite burner bricks, the use effect is improved; burner bricks made of high alumina cement or phosphate refractory castables on gas heating furnaces have a service life of 1 to 2 years . Burner bricks made of corundum or mullite low-cement series refractory castables are used on oil-fired heating furnaces and have a service life of 6 months to 3 years.

 

Heating furnaces used for burning coal are divided into various types such as reciprocating grate type and cyclone combustion type. They are generally composed of bottom, wall and roof. The lining of an ordinary combustion chamber is usually built with clay bricks or high-aluminum bricks. Due to the high operating temperature and large temperature fluctuations, slag erosion and mechanical damage during slag cleaning, its service life is about one year. When the lining is poured with refractory castables such as special high-alumina clinker, corundum, mullite or magnesia-aluminum spinel, the integrity is good, no slag sticks, and the service life can be extended to 1 to 3 years. The lining of the cyclone combustion chamber is cast with silicon carbide refractory castable with high strength and high thermal conductivity, and has a service life of 1 to 2 years. The waist furnace is the passage between the combustion chamber and the heating furnace hearth. The operating temperature is about 1600°C. When built with sillimanite bricks or corundum bricks, its service life is only about 0.5 years.

It is used to close the holes in the furnace wall and is divided into two types: side-opening type and lifting type. Furnace doors are generally lined with clay bricks, refractory castables or refractory plastics, high-aluminum insulating bricks or refractory fiber felt; side-opening furnace doors can use a furnace door, and lift-type furnace doors are affected by temperature fluctuations. Affected by factors such as mechanical collision, the service life is about 1 year.

 

The tapping trough is used for heating furnaces that tap out billets from the side. In addition to the water-cooled cast iron tapping trough, it is generally built with high alumina bricks or magnesia bricks, with a service life of 3 to 6 months. When large bricks made of sintered or fused mullite are used for construction, they have high strength and good wear resistance, but have poor thermal shock resistance and are easy to crack. Their service life is about 1 year. The corundum refractory castable reinforced with heat-resistant steel fibers is poured on site to form an integral tapping trough, with a service life of more than 2 years.

The small push-steel heating furnace has a ceramic slideway composed of brown corundum-silicon carbide slide rail bricks, and 2 or 4 rows of refractory bricks are used to build the base wall along the length of the furnace. High-alumina silicon carbide bricks are laid on the base wall, and then the slide rail bricks are installed to form a ceramic slide. The billet moves on the slide to achieve heating on the upper and lower sides. It has the advantages of low energy consumption and no black marks on the billet. Ceramic slides bear the effects of high temperature, steel billet load, high temperature wear and iron oxide scale erosion, etc. The use conditions are harsh and their service life is about 1 year.

For large and medium-sized push steel type or walking beam type heating furnaces, the water-cooled tubes at the bottom of the furnace are composed of thick-walled water-cooled tubes distributed longitudinally and transversely and supporting. The purpose of thermal insulation is to reduce the heat taken away by the cooling medium, reduce the black marks on the billet and improve the heating quality. The insulation methods include special-shaped clay brick inlays or horseshoe-shaped brick hangings, welding of welded tile-type prefabricated blocks made of refractory plastic or refractory castable materials, and on-site bandaging with refractory fiber felts. The service life is generally 3 to 12 months. Use high-quality refractory plastics, ultra-low cement or cement-free refractory castables for on-site bandaging, with a service life of more than 1 year.

The flue lining is generally built with clay bricks, or can be hoisted with prefabricated blocks of refractory castables or poured on site. Sometimes it can also be constructed with refractory spray coatings. Red brick or concrete chimneys are built with refractory bricks in high temperature areas. The inner wall of the metal chimney is welded with metal anchor nails, sometimes with a metal mesh, and is lined with lightweight refractory castables or refractory spray paint. It is easy to construct, has strong integrity, and has a long service life.

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