How to choose refractory castables and four factors that must be considered

In addition to price, the selection factors of refractory materials also need to consider the following factors: longer service life; better thermal insulation effect; simpler masonry method and faster masonry speed; fast maintenance speed, etc.
Amorphous refractory materials, also known as bulk refractory materials, are composed of bulk particles and fine powders. They do not need to be fired or formed before use. It can flexibly change the composition properties and processes of the materials according to needs, such as the composition and particle size of refractory materials; the type and amount of binders; the selection and adjustment of admixtures (such as plasticizers, hardening accelerators, hardening retarders, water reducers, etc.) and the diversification of construction methods (pouring, ramming, spraying, projection, plastic construction, etc.), which makes the brick shape of refractory materials develop a big step towards large-scale, special-shaped and integrated structures, and is called the second generation of refractory materials.
Amorphous refractory materials are one of the important basic materials in the application of refractory lining technology in high-temperature kiln industry. Refractory castables are an important type of amorphous refractory materials. Its important features are short supply cycle, no restrictions on equipment shape, and can be used directly after pre-calcination, loose mixture with suitable anchors, on-site molding and baking. Refractory castables can be made into seamless linings, also known as integral refractory materials. Amorphous refractory materials such as high-aluminum castables, high-aluminum low-cement castables, steel fiber wear-resistant castables, and corundum castables have been widely used in the lining design of cement kilns, and have been used as refractory layers of thermal equipment in different parts for many years.

1.Classification of monolithic refractory materials

1.1 Grouting material
A material with good fluidity after adding water and stirring, also known as pouring material. After molding, it needs to be properly cured to make it solidify and harden, and can be used after baking according to a certain system. Grouting material uses aluminum silicate clinker, corundum material or alkaline refractory clinker as aggregate; lightweight pouring material uses expanded perlite, vermiculite, ceramsite, and hollow alumina balls as aggregate. Binders use calcium aluminate cement, water glass, ethyl silicate, polyaluminum chloride, clay or phosphate, etc. The admixture depends on the use situation, and its function is to improve the construction performance and physical and chemical properties.
The construction molding methods of grouting materials include vibration method, pump injection method, pressure injection method, injection method, etc. Grouting materials are often used in conjunction with metal or ceramic anchors for integral lining. If stainless steel fiber reinforcement is added, its resistance to mechanical vibration and thermal shock can be improved. The grouting material is used as the lining of various heat treatment furnaces, ore roasting furnaces, catalytic cracking furnaces, converters, etc. It is also used as the lining of smelting furnaces and high-temperature melt flow channels, such as lead-zinc melting furnaces, tin baths, salt bath furnaces, steel or iron tapping troughs, steel ladle, molten steel vacuum circulation degassing device suction nozzles, etc.

1.2 Plastic
Plastic clay or clay blank. When appropriate external force is applied, it is easy to deform without cracking; after the stress is eliminated, it will no longer deform. Plastic materials include semi-siliceous, clay, high-alumina, zircon, carbon, etc., and there are also lightweight plastics. Plastic materials must be added to plastics, and plastic materials are mostly highly plastic clays. Plasticizers can also be used to improve the plasticity of this clay. Plasticizers include carboxymethyl cellulose, dextrin, lignin sulfonate, etc. The binders used in plastics include plastic clay, phosphoric acid, aluminum dihydrogen phosphate, aluminum sulfate, etc. Alumina plastics with phosphoric acid or phosphate binders will react chemically with alumina during storage to generate insoluble aluminum orthophosphate and harden the clay, so preservatives such as oxalic acid, citric acid, acetylacetone, etc. must be added.
The construction method generally adopts ramming method or vibration method. When using plastic to build an integral furnace lining, metal or ceramic anchors must be configured. Plastics are used as linings for thermal equipment such as soaking furnaces, heating furnaces, boilers, and are also used to wrap water-cooling pipes for heating furnaces.

1.3 Gunning material
A refractory mixture used for gunning or spraying with a jet machine. According to the gunning method, it can be divided into wet gunning (or mud gunning), semi-dry gunning and fire (flame) gunning. Wet gunning uses compressed air to spray mud containing 20-40% refractory powder, which can achieve higher atomization and high adhesion rate, and can be used for more uniform thin layer gunning. Semi-dry gunning is to add water to the nozzle to moisten the refractory powder sprayed by compressed air. The amount of water added is 11-14%, the adhesion rate is lower, and thicker layers can be gunned. Fire gunning belongs to dry gunning, which sends the gunning material to the flame of the fuel-oxygen spray gun. The gunning material partially melts in the nozzle flame and adheres to the brick lining.
The materials of gunning materials include aluminum silicon, aluminum silicon zirconium, magnesium, magnesium calcium, magnesium chromium, etc. The binders used are sodium silicate, phosphate, polyphosphate, asphalt, resin, etc. In order to improve the adhesion rate, clay, bentonite, lime and other additives are added. In order to ensure that the gunning material can achieve good sintering, sintering aids such as serpentine, pure olivine, lime, refractory clay, iron oxide and the like are also added.

1.4 Refractory coatings
The materials applied to the refractory brick lining. According to different use requirements and construction methods, refractory coatings can be prepared in the form of mud paste and mud. The binder used varies according to the material. For example, phosphate, polyphosphate, and magnesium sulfate are used to prepare alkaline coatings for continuous casting tundishes; clay, aluminum dihydrogen phosphate, aluminum chromium phosphate, water glass, etc. are used to prepare high-alumina coatings. In order to improve the coating’s spreadability, plasticizers and other additives are generally added. The coating is mainly used as a protective coating for the lining of various thermal equipment, or for repairing local damage to the brick lining.

1.5 Ramming material
A bulk refractory material with very low plasticity or no plasticity. The materials include siliceous, clay, high alumina, corundum, zircon, silicon carbide, carbon, magnesium, etc. According to the material and use conditions of the ramming material, inorganic or organic binders similar to the pouring material can be used, such as water-soluble dextrin, carboxymethyl cellulose, lignin, sulfonate, polyvinyl alcohol; water-resistant and thermoplastic paraffin, asphalt, tar, phenolic resin, random polypropylene, etc.
The ramming material is constructed by forced ramming, with low porosity and high density. Therefore, among the amorphous refractory materials, the ramming material is particularly suitable for the lining of the smelting furnace and various containers for high-temperature molten metal. Such as the hearth of the open hearth and electric furnace, the lining of various induction furnaces, the iron ditch of the blast furnace, the steel ladle, etc.

1.6 Projectile
A kind of semi-dry mud material that is projected by a projector to build the lining. It is mainly used to build the lining of the integral steel drum. The materials include silica, wax stone, clay, high alumina and zircon. High silica and high alumina projectiles are more commonly used.

2.Application of monolithic refractory materials

2.1 Characteristics of castable prefabricated blocks
Casable prefabricated blocks only need to be heat treated at a relatively low temperature. They are low-carbon and green refractory materials and are a unique technology in refractory lining technology. They can improve the performance of refractory linings, reduce the consumption of refractory materials, and have stable quality and reliable performance. We know that the purpose of adding steel fiber to castables is to improve the mechanical properties of castables, inhibit the generation of cracks, or limit the expansion of cracks when they are formed. The following figure is a picture of steel fiber castables. Steel fiber castable prefabricated blocks are made using special processes. They are made into certain shapes according to the process parts and needs, and heat treated according to their working conditions after demoulding.

2.2 Application of unshaped refractory materials in blast furnaces
Blast furnaces are an important equipment for ironmaking. Small blast furnaces used to be built by hoisting prefabricated blocks of high-alumina cement and high-alumina phosphate refractory castables, but now resin-bonded aluminum-carbon unburned bricks are commonly used for masonry. The water-cooled walls of large blast furnaces are made of SiC castables, and the bottom cushion and surrounding brick joints are made of refractory castables and silicon nitride fillers. One of the development trends of refractory materials for furnace walls is to use castables. The No. 2 blast furnace of the Fukuyama Plant of Japan Steel Pipe Company used a high-density castable of Al2O350%, SiO245% on the upper part of the furnace body. After 6 years of use, it was found that spalling rarely occurred. Image.
At present, the amorphous refractory materials used for blast furnace tapping channels at home and abroad are mainly Al2-O3-SiC-C (ASC for short), in addition to mullite-SiC-C, Al2O3-C, magnesia-alumina spinel and other types. my country mainly uses corundum-SiC castables. Most of the blast furnace tapping channels in Japan now use ASC castables and repair gunning materials, and some small blast furnace tapping channels use alumina or synthetic mullite-SiC-C ramming materials. The blast furnace tapping channels in Germany and France generally use ASC ramming materials. France has developed self-flowing castables to increase the service life of the working lining of the main tapping channel.

2.3 Application of amorphous refractory materials in ladle
The increase of tapping temperature and the extension of steel liquid’s residence time in ladle have brought about great changes in refractory materials for ladle. Ladle used to be mainly made of shaped refractory materials, but now it is replaced by amorphous refractory materials. The amorphous shape of ladle can save labor, realize factory automation construction and drying, and improve the overall economy. When the side wall of ladle is amorphous, the maintenance work can save 40% of labor hours. When the ladle lining is all amorphous, the labor saving effect is 70%. Due to Al2O3- Spinel castable has the advantages of good corrosion resistance, small structural spalling, long service life and improved steel quality, making it the main refractory material for current ladles. However, its use is limited by temperature and residence time of molten steel. The Al2O3-MgO castable developed by Kawasa-ki Company of Japan has improved material strength and slag permeability resistance, and its service life is 20% longer than that of Al2O3-spinel castable. At present, the trial use of magnesium refractory castables and aluminum-magnesium-carbon refractory castables on ladles has also achieved initial results.

2.4 Application of amorphous refractory materials in nonferrous metallurgy
Aluminum reverberatory furnaces are the largest consumers of refractory materials in aluminum plants. The refractory materials used in the furnace have changed from brickwork to integral structures. The refractory materials in contact with the hot metal surface of the furnace are usually acid-bonded plastics, phosphate-bonded bricks, and low-cement castables. The composition of the hot surface refractory materials of the lower side wall is usually the same as that of the furnace. The insulation materials can be lightweight insulation castables, insulation clay bricks, or ceramic fibers; the furnace roof materials are usually high-quality refractory materials such as ramming materials and burning injection materials; the furnace door is usually made of dense castables or lightweight castables, or a mixture of the two.

In electrolytic aluminum smelting, amorphous refractory materials are mainly used in aluminum drums. Refractory materials for aluminum drums are required to be resistant to the erosion of aluminum water, withstand the effects of rapid cooling and heating, and have good thermal insulation performance. The non-working lining of aluminum drums generally uses lightweight castables or lightweight high-alumina bricks. If the aluminum liquid in the aluminum drum is to be placed for a long time, insulating castables are usually used to prevent the aluminum liquid from solidifying during transportation. Now, in order to reduce the dead weight of the tank and enhance the thermal insulation effect, the non-working lining uses alumina hollow ball refractory castables. The working lining is generally built with high-alumina bricks with low SiO2 content. In some tanks, corundum refractory casting is used.

In the copper smelting industry, because CuO as a component of slag is highly corrosive, basic refractory materials are widely used in roughing furnaces. For example, all parts of reverberatory furnaces, converters, flash furnaces and rotary anode furnaces use basic magnesia-chrome bricks or basic ramming materials based on MgO, especially for repairing and repairing furnaces. In the refining part, since the slag volume and temperature are reduced, aluminum silicate refractory materials such as casting materials, plastic materials, spray coatings and high-alumina bricks can be used.