Overview of basic knowledge of monolithic refractories
According to the definition of GB/T 18930-2002 "refractory materials", Unshaped refractory (monolithic refractory) refers to a mixture consisting of aggregates, powders, binders, and additives. Use directly for delivery or participate in one or more suitable liquid applications that do not affect their fire resistance. The British ASTM Standard C71-01a is defined as "A refractory which may be installed in situ, whithout joints to form an integral structure" (refractory material that can be constructed in-situ on the site and does not produce joints to form an integral structure). The meaning of "unshaped" refers to the delivery of dry or wet mixture, which can have no fixed shape. However, castables can also be made into prefabricated parts. It is not appropriate to call "unshaped". Therefore, at home and abroad, monolithic refractories are also referred to as "monolithic refractory materials" in recent years. In 1977, China officially adopted the name "unshaped refractories".
Second, the classification of amorphous refractory
1. Castable refractory
Refractory castables can be made of aluminosilicate clinker, corundum or basic refractory clinker; lightweight castables are expanded aggregates of perlite, vermiculite, ceramsite, alumina hollow spheres as aggregate. Calcium aluminate cement, water glass, ethyl silicate, polyaluminum chloride, clay or phosphate and the like are used as binders. The additive depends on the conditions of use, and its role is to improve the construction function and advance physical and chemical functions.
Refractory gunning mixes consist of fire-resistant aggregate powder, binder, admixture and water. They are transported by compressed air to obtain kinetic energy. They are projected onto a cold or hot surface by special lances. Refractory material.
Fire-resistant sprays can be used to repair linings as well as to build new linings and to form protective coatings. The construction method of sprayed material is practically a solidification process of transporting, pouring, and pouring into a single process. It does not require a bracket, does not require or requires a single-sided template, has a simple process, high efficiency, and has a wide range of practicality. When used to repair part of the lining where premature damage occurs, and most of the lining is still better, it can effectively extend the overall service life of the lining and reduce the consumption of refractory materials.
Refractory plastic is composed of fire-resistant aggregate powder, binder, plasticizer (mostly clay) and liquid (water). It is in mud paste form and has higher plasticity in a longer period of time. Unshaped refractories.
Compared with fine, high-strength refractory castables, fire-resistant plastics have the characteristics of small bulk density, good thermal resistance, good thermal shock resistance, and good drop resistance, and can be used in various heating furnaces, soaking furnaces, annealing furnaces, and infiltration. Carbon furnace, electric furnace and sintering furnace. The operating temperature can be from 5000C to 19000C, depending on the application requirements and its own material.
Refractory coating mixes are paste-like or paste-like monolithic refractories composed of relatively small particles of refractory aggregates, powders, binders, admixtures, and essential liquids.
The use of refractories in the high-temperature industry is mainly in three aspects: the production of linings, such as the center package lining; used as a protective layer, such as the coating of the refractory lining surface; for sealing.
5 refractory ramming material
Fire-retardant ramming materials are generally used in sites requiring fast construction, small construction volumes, and narrow constrictions. It is mainly used in blast furnace iron ditch such as single iron outlet, steel furnace bottom, tapping tank, induction furnace lining, electric furnace roof, rotary kiln blanking area, and petrochemical furnace inner lining.
6. Fire pressure feed
The refractory refractory is mainly used for blast furnace shaft, blast furnace taphole, rotary kiln lining sought-after site, RH rise pipe and top-bottom re-blowing STB converter hearth bottom, converter tapping port, etc.
Refractory mortar is a paste-like or slurry-shaped monolithic refractories consisting of powdery refractory materials, binders, admixtures and essential liquids. It is primarily used for joints or grouting in brick linings.
Third, the characteristics of amorphous refractory
(1) The preparation process is simple, the production cycle is short, and labor produces high yields;
(3) good integrity, good airtightness, large thermal resistance, can reduce the heat loss of industrial furnaces, provincial power;
(5) Damaged industrial furnace linings are easily repaired with monolithic refractories, the service life of the extended linings is reduced, and the consumption of refractory materials is reduced.
The preparation process of monolithic refractories, including the selection of materials, the determination of particle grading, the selection of binders and admixtures, and the determination of the processing flow, are based on the conditions of use, the operating environment, and the construction method selected. . The granular material from which the monolithic refractories are made is collectively referred to as a refractory aggregate.
Binder refers to a substance that can combine the refractory aggregate and the powder and cause it to have a satisfactory strength after being protected, monotonous, and heated. Bonding agents are an important part of monolithic refractories. Under certain conditions, the binding agent can achieve satisfactory strength by hydrating, compounding, polymerizing, and agglutination.
Binding agents for monolithic refractories vary depending on the nature of the material to be cemented and the conditions of use, and are numerous in nature, and are generally categorized according to the chemical nature of the binder and the hardening conditions of the binder.
(1) The hydraulic binder refers to the mixture after mixing with the bulk fire-resistant aggregate, adding water, kneading, and molding, under the condition of normal temperature and humidity
(2) After the gas-hard binder is mixed with the bulk refractory aggregate and molded, the binder that can be aggregated and hardened can be protected under natural temperature and dry conditions. However, the use of accelerators (hardeners) is generally required for the aggregation and hardening of such binders, such as the use of sodium fluorosilicate accelerators when using water glass binders, and the participation of aluminum monophosphate binders. Calcium aluminate cement or magnesium oxide is used as a coagulant.
The selection principle of binder:
(1) The properties of the binder must be matched to the properties of the bonded refractory material. Acidic, neutral refractories can be used with acidic, neutral and weakly alkaline binders, while basic refractories can not be used directly with acidic binders, only neutral or alkaline binders, if under reductive conditions The use of semi-permanent organic binders can also be used. Carbon- and silicon-carbide monolithic refractories are mostly made of high residual carbon organic binders.
(3) The binding agent used must be compatible with the high temperature application of the material. It should not reduce or reduce the high temperature structural strength, resistance to erosion (corrosion), and penetration resistance of the material. For example, high alumina or clay castables can use general calcium aluminate cement or combined clay as binding agent, while corundum or high purity corundum-agile stone castables should use pure calcium aluminate cement or reactive alumina. As a binding agent.
Additives (additive), also known as admixtures, are materials that are added to the amorphous refractory mix to improve the performance and utility of the work.
The monolithic refractories admixtures are classified according to their chemical composition and properties and their function.
(1) Inorganic substances:
The ionic type can be further divided into anionic, cationic and amphoteric surfactants.