Monolithic refractory/ Unshaped refractory is a mixture composed of a certain grade of refractory aggregates, powders, binders and admixtures in a certain proportion. It can be used directly according to the delivery state without firing or with appropriate additions. The liquid (water in most cases) is mixed evenly before use.
Refractory aggregate generally refers to granular refractory raw materials with a particle size greater than 0.088mm. It plays a skeleton role in unshaped refractory materials and plays a decisive role in the performance of the material. Powder, also known as fine powder, generally refers to materials with a particle size less than 0.088mm, which plays the role of filling the pores between aggregates and connecting aggregates. Fine powders with particle sizes less than 5 μm are usually called ultrafine powders or micropowders.
Binder is a substance that can bind refractory aggregates and powders together and produce sufficient strength after curing, drying and heating. Binder is an important component of amorphous refractory materials, and can be used with inorganic substances, organic substances, etc. The binding agent, under certain conditions, makes the mixture have sufficient strength through hydration, compounding, polymerization, adhesion and cohesion.
Admixture (Additive) is a small amount of substances added to unshaped refractory materials that can improve construction performance and usability. Admixtures are generally added during or before mixing of unshaped refractory materials, and the amount of admixture is generally very small. Admixtures can be single substances or composite substances. There are many types of admixtures used in unshaped refractory materials, mainly including dispersants, water reducing agents, retarders, accelerators, plasticizers, expansion agents, etc.
What are the types of unshaped refractory materials?
There are many varieties of unshaped refractory materials. In order to convey certain information and distinguish them from each other in terms of names or names, it is necessary to classify them. There are many classification methods due to different focus areas. In practice, monolithic refractory materials are generally classified according to their materials, binder types, construction methods, uses and usage characteristics.
Classification by material
Classification according to the materials of the main raw materials that make up amorphous refractory materials can help us understand their chemical and mineral composition. This provides a more intuitive understanding of the chemical properties of materials. Amorphous refractory materials such as clay, high alumina, magnesite, mullite, corundum, alumina-magnesite, Al2O3-SiC-C, Al2O3-MgO-C, etc. are classified according to this method.
Classification of Refractory according to type of bindingformingformationthe types of binders used vary according to the main binders. The classification is based on the primary mode of binding/binder. Such as cement-bonded castables, low-cement, ultra-low-cement, non-cement castables, water glass-bonded castables, phosphate-bonded castables, resin-bonded ramming materials.
Classification by construction method
Different construction methods have different requirements for the rheological properties and construction performance of materials, as well as different requirements for construction conditions and equipment. Unshaped refractory materials classified according to this method include vibration castables, self-flowing castables, sprayed materials, plastics, ramming materials, spreadable materials, pressed materials, dry ramming materials, etc. This classification is relatively common in practical applications.
Classified by use
Different usage occasions and usage conditions have different requirements for unshaped refractory materials. Unshaped refractory materials such as blast furnace tap trough ramming materials, converter gunning materials, ladle castables, tundish coatings, heating furnace castables, heating furnace plastics, etc. are classified based on their uses. .
Classified by usage characteristics
This classification method is mainly based on the physical and chemical properties that unshaped refractory materials must have to meet specific use requirements, such as wear-resistant castables, acid-resistant castables, alkali-resistant castables, lightweight castables, and bake-free castables. Ramming materials, etc.
However, in practice, it is difficult for people to use a single classification method to make a more comprehensive description of amorphous refractory materials, so composite classification is often used. For example, the title "ultra-low cement Al2O3-SiC-C blast furnace tap trough castable" is a composite classification from the four aspects of combination method, material, use and construction method, conveying the information of these four aspects.
What are the main unshaped refractory materials?
In view of the fact that the classification based on the construction methods of amorphous refractory materials is more commonly used in practice, this section introduces the existence forms and varieties of several important amorphous refractory materials according to this classification, including refractory castables, spray materials, plastics, Spreading materials, ramming materials, pressed materials, refractory mud, etc.
Refractory castable
Refractory castable is a mixture composed of refractory aggregates, powders, binders, admixtures and water (can also be other liquid binders) in a certain proportion. It has certain properties under the action of external force or gravity. It has good fluidity. It is solidified and hardened by pouring, compacting and curing, and then baked according to a certain system to form an unshaped refractory material with sufficient strength and structural stability for use.
There are three construction methods for filling and compacting refractory castables: vibration method, gravity flow method and wet spray method.
Refractory castables are the largest type of unshaped refractory materials, accounting for about 50% of the entire unshaped refractory materials. In addition to having the common feature of being used directly without firing, among the many types of unshaped refractory materials, their production process is relatively simple, the production cost is lower than that of machine-pressed or pounded shaped products, and the construction is simple and highly mechanized. , high work efficiency and high material utilization rate. In addition, refractory castables can also be made into various prefabricated parts and installed on site, simplifying on-site construction operations and greatly saving on-site construction and maintenance time, thereby increasing the turnover rate of thermal equipment. and utilization.
Refractory spray material
Refractory gunning mixes are composed of refractory aggregates, powders, binders, admixtures and water. They are transported by compressed air and gain kinetic energy. They are projected onto cold or hot surfaces through a specific spray gun for construction. Amorphous refractory materials. Refractory spray materials for cold materials can be divided into three types: dry method, semi-dry method (tidal type) and wet method.
Refractory blasting materials can be used not only to repair furnace linings, but also to construct new linings and form protective coatings. The construction method of spray material actually combines transportation, pouring and tamping into one process. It does not require brackets, no or only one-sided template. The process is simple, high efficiency and has wide practicality. When used to repair partially prematurely damaged furnace linings but most of which are still in good condition, it can effectively extend the overall service life of the furnace lining and reduce the consumption of refractory materials. For example, in the steel industry, refractory blasting materials can be used in blast furnace linings, blast furnace tap troughs, ladles, converters, electric furnaces, ladles, vacuum degassing devices, tundishes, heating furnaces, etc.; in the cement industry, refractory blasting materials can be used in kilns External decomposition system; in the industrial alumina industry, refractory blasting materials can be used in suspension roasters.
Fire-resistant plastic
Refractory plastic (Refractory plastic) is composed of refractory aggregates, powders, binders, plasticizers (mostly clay) and liquids (water) and is in the form of mud. It has a high Plastic amorphous refractory material.
Refractory plastics are suitable for construction in small, narrow and complex parts and parts that require lightweight structures. The construction of refractory plastics generally uses pounding and pressing to make them dense, and then hardened after heating.
Compared with dense and high-strength refractory castables, refractory plastics have the characteristics of smaller volume density, good thermal toughness, thermal shock resistance and spalling resistance. They can be used in various heating furnaces, soaking furnaces, annealing furnaces, etc. Carburizing furnace, electric furnace and sintering furnace, etc. The operating temperature can range from 500℃ to 1900℃, depending on the usage requirements and the material itself.
Refractory coating
Refractory coating mixes are paste or slurry amorphous refractory materials composed of refractory aggregates with smaller particles, powders, binders, admixtures and necessary liquids. It can be constructed by manual troweling or mechanical spraying, and is coated on other refractory material linings. The thickness of the construction layer is generally not large.
The application of refractory coatings in high-temperature industries is mainly in three aspects: making linings, such as tundish working linings; used as protective layers, such as coatings on the surface of refractory fiber linings; and used for sealing.
This type of material is usually required to have good spreadability, adhesion and matching with the material to be protected, good thermal shock resistance and chemical stability, avoid cracking and peeling during use, and try not to chemically react with the parent material, etc. .
Refractory ramming material
Refractory ramming mixes are composed of refractory aggregates, powders, binders and necessary liquids that have no adhesion, low plasticity or no plasticity before use and can be compacted only by strong ramming. Material.
Refractory ramming materials are generally used in narrow and complex locations that require fast construction pace, small construction volume. It is mainly used in blast furnace tap troughs with single tap openings, steelmaking furnace bottoms, tap troughs, induction furnace linings, electric furnace tops, rotary kiln blanking parts, petrochemical furnace linings, etc. It can either form an integral furnace lining or be made into prefabricated components.
Refractory pressed material
Refractory injecting mixes are composed of fine refractory aggregates, powders, binders, admixtures and necessary liquids that can be extruded and filled with special pumps under the action of compressed air or mechanical pressure. Shaped refractory materials.
Refractory press-in materials are mainly used for blast furnace shafts, blast furnace main tapholes, rotary kiln lining hot spots, RH rising tubes, top and bottom double-blown STB converter small furnace bottoms, converter tapholes, etc.
Refractory mud
Refractory mortar is a paste or slurry amorphous refractory material composed of powdery refractory materials, binders, admixtures and necessary liquids. It is mainly used for joints or grouting of brick linings.
Refractory mud can be widely used in brick linings of hot blast furnaces, blast furnaces, coke ovens, torpedo tanks, ladles, converters, electric furnaces, ladles, heating furnaces, soaking furnaces, glass kilns, non-ferrous metal smelting furnaces, petrochemical furnaces, etc. Refractory mortar is required to have good constructability and matching with the base material to avoid penetrating damage due to the lack of durability of brick joint refractory mortar.
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