The importance and importance of industrial refractories
The performance of industrial furnaces is affected by the type of refractories and refractories used. The quality and durability properties of the consumables, together with their proper installation, are factors that determine the useful life and efficiency of the furnaces. The accurate and scientific study of refractories as a major indicator in the mother country’s industries, which is their main consumer, is essential. Of course, the proper use and proper installation of them will not be suitable. Studies on raw materials and manufacturing technology, especially modern technology and the use of refractories, indicate that our country is heavily dependent on this sector of the ceramic industry. On the other hand, due to foreign currency and foreign purchases, without domestic refrigeration, many domestic industries that can not continue to work without refractory materials will face serious problems. The refractory susceptibility in many industries is such that its unavailability will result in complete production stoppage.
The production of refractory products is of particular importance due to the widespread use and high dependence of various industries on them, especially in the infrastructure industries such as steel, cement, aluminum, copper and glass. For this reason, the production of refractory materials has always been a strategic commodity, and the advanced technology of refractory products in the world is unique to several industrialized countries. With the growth and development of metallurgy industries in Iran, which almost consumes 70% of refractories in the country, refractory products were considered. The need for refractometers is not just related to heat, but also other factors, such as strength (especially high temperature strength) and corrosion resistance (chemical-physical). Several industries in the production process need to use the refrigeration, which are referred to below as part of them.
Ø Iron and Steel Industries
Ø Non-ferrous metal industries (copper, aluminum, lead, zinc, etc.)
Ø Glass industry
Ø Gas industry
Ø Power plants
Ø Furnaces and furnaces in the ceramic industry
Ø Gas turbines
Ø Nuclear reactors
Ø Cement and Lime Furnaces
Ø Trash bins…
Refractories can be classified according to the chemical composition and production process or their physical form. In addition to these divisions, refractories can also be classified according to their use, for example, blast furnace refractories. These refractories are constantly being revised and changed.
Below are some of the refractory categories:
Classification of refractories based on chemical composition
From a chemical point of view, refractories are divided into three categories:
Ø Acid reflux
Ø Game refreshments
Ø Neutral Neutrality
Various minerals and stones are in the group of refractories or refractories, including Olivine, Zircon, Chromite, Mesquite, Graphite, Andalosite, Duston, Silimanite, Wollastonite, Asbestos (Chrysotile, Thermolite, Teaching, etc.) Magnesite, clay, dolomite, bauxite and latitudinal. Other than the above materials, synthetic compounds such as silicon carbide are also used as refractories. Refractories can be classified based on the chemical conditions of the operating environment, the degree of reflux and the composition of the raw materials. Based on chemical conditions, refractories are divided into three types of acid, neutral and alkaline.
These refractories are used in areas that are atmospheric and acid slag. These refractories are resistant to acids, but are not strong enough to attack alkaline materials. The primary material of this group of refractories is RO2 (such as silica) (Sio2) Under the cone (Zro) and clay alumina silicates (Al2O3.2zio2.2H2o).
These refractories are used in places where slag and atmospheres do not have a certain state and are sometimes playful or acidic. These refrains remain stable against acidic and playful factors. The major raw materials of these refractories belong to the R2O3 group. Of course, the chemical composition of neutral refractometers is not limited to the R2O3 group; typical examples of these materials are: alumina (Al2O3), chromium oxide (Cr2O3) and carbon (c)
These refractories are used in areas that are atmospheric and slag. These refractories are resilient to the openings but react with acid. The main raw materials in this group of refractories belong to the RO group. Magnesium oxide (Mgo) is the most common example of these refractories. Other examples of these refractories include dolomite reflux and chromium magnesite reflux.
Game refreshments are very famous because these refractories have good corrosion resistance to game slugs and chemical or chemical at high temperatures. Some refracting games have been developed that have excellent resistance to acid slag.
Magnesium oxide (mgo) is a binary metal oxide of magnesium. This oxide, when high in purity, has a high boiling point. Magnesium magnesium magnesium magnesium is known as periclase. The impurities present in natural magnesium oxide It makes it possible to combine with a low melting temperature, which greatly reduces drainage.
Magnesium-chromite compounds have good mechanical strength and very good stability at a very high temperature. Magnesia-chromite refractories have good corrosion resistance against slag and are suitable for steel and masonry industries.
Magnesium-chromite compounds have lower thermal expansion than compounds with high levels of magnesium oxide. High purity and chrome-free compounds of magnesium oxide derived from seawater and saline water have the highest refractive index and are resistant to iron oxide.
Carbon monoxide compounds contain from 5 to 35% carbon. The added carbon to these refractories is obtained by adding natural graphite, carbon monoxide refractories have a high resistance to steel slag.
Theoretically, acid reflux should not be directly in contact with gambling slugs, gases, or bottlenecks. While game refills are the best option for use in game environments. In fact, for the most part, these theoretical rules are often broken down. Hence, the chemical classification of refractories is largely academic, and it only helps us to understand the real uses of refractories. Also, the existence of an overflow that is really neutral can be dubious. Refractories are divided into three groups based on the stability temperature:
ü Low temperature refractories such as clay firefighters and silica refractories with a thermal resistance of 1580 to 1780 ° C.
ü Moderate heat fluxes such as siliciclastic 1, bauxite 2, kaolinite and Foresterite 3 with heat resistance of 1780 to 2000 ° C.
ü High temperature refractories such as graphite refractories, carbide 4, aluminum and magnesia 5 with thermal resistance of over 2000 ° C.
Perhaps the best type of refrigeration is to classify them based on the raw materials and composition of their constituents. Accordingly, refractory materials can be divided into 12 following groups:
Ø Silica refrains
Ø Magnificent refusals
Ø Dolomite refrains
Ø Graphite refractories
Ø Chromatic refrains
Ø Bauxite reflux
Ø Silanite reflexes
Ø Forrestrial refreshments
Ø Clay clay
Ø Silicon carbide refueling
Ø Aluminum reflux
Oxidizing refractories such as beryllium oxide, cesium, zirconium, tantalum and niobium.
Here is a brief overview of the most important types of refueling mentioned above.
Silica refrains: These refractories contain more than 90% SiO2 alumina, titanium, iron, and calcium oxides totaling less than 8.5% in their copper. These refractories come from quartz, quartzite, and silica sandstone (quartz arnite). The presence of alkali-sodium and potassium elements reduces the melting temperature of silica bricks. These bricks are more stable in dry environments.
Magnesium reflux magnesite MgCo3 is the most important ingredient in the manufacture of magnesium reflux. Its melting temperature is about 1860 ° C. It may add up to 15% chromite to increase the resistance of magnesia refractories to thermal shock. Dolomite refrains: The primary substance of these refractories is dolomite (Ca, Mg (CO3) 3) 2, and the melting point of these refractories is about 1700 ° C and has a low resistance to electric shocks. The presence of CaO causes it to crack when in contact with water and hydrated lime is produced. Adding serpentin can reduce the effect of the action. Graffiti refractories: These refractories are made of graphite and a small amount of sticky clay and have very high thermal resistance.
Chromite reflux: The main part of these refractories is from chromite (FeCr2O5) 4. Except for chromite, aluminum oxide, magnesium, silicon, and calcium are used in their composition. Aluminum refractories (aluminum silicate): These refractories are mainly composed of Al2O3 and SiO2. The percentage of Al2O varies from at least 25% (Shamot 1) to 100 (Kronedy firewalls). The materials needed to produce these bricks include clay, bauxite, silimanite, andalusite, kyanite and corundum. As Al2O3 increases and SiO2 decreases, thermal resistance increases. In high-alumina refractories, siliconite, andalosite, diestin, bauxite and corundum are used.
Silica Carbide Refills: These refractories are made of SiC (SiC). A mixture of sand, silica, coke, salt and sawdust is heated in an electric furnace and heated to 2700 ° C. The salt evaporates coke and silica sand. The sawdust creates porosity, and the carbon monoxide generated through the pores. These refractories have high thermal resistance and abrasion resistance and stand against thermal shocks. The heat transfer coefficient of these refractories is high. Oxidizing refractories: The most important of these refractories is refractory oxidation. These refractories are resistant to temperatures up to 2500 ° C. Due to its high thermal and abrasion resistance and resistance to thermal shock, it is very good because of its high price, it is more limited than other refractories. The thermal expansion of this reflux is relatively high.
Classification by production method
Refractories can be produced in one of the following ways.
Ø Dry dress process
Ø Mold casting (fused cast)
Ø Manual Moldes
Ø Cooked, raw or chemical bindings
Ø Unformed (Monolithic-Plastic-Crushing-Typical – Mouldable and Sprayable
Classification based on physical form
Refractories can also be classified according to their physics. These materials can be formulated or non-shaped refractories. Generated refractories are commonly referred to as monolithic refractories as limestone bricks and shapeless refractories. Shaped refractions. The formed refractories are those that, when delivered to the consumer, have a certain shape, we call these refractories brick.
The shape of the bricks may be divided into two types: one of them is standard and the other is a particular form. The standard shapes are dimensional that are accepted by most refractory manufacturers. These manufacturers follow these dimensions. These refractories are generally Can be used in identical furnaces.
The formed refractories are produced mainly by stamping. Thus, their properties are expected to be homogeneous. Some of the formed refractories produced by manual molding have non-homogeneous properties.
The shapeless refractories do not have a certain geometric shape and are formed during application. These latencies are known as monolithic refractories. These refractories are sub classified.
A) PBStic refractories
Plastics refueling is a mixture that is prepared in a plastic and abrasive state. These types of refractories are delivered to the consumer in the form of masses that are wrapped in polyethylene wrap. During the massive use of this type of refractory to parts The smaller one is cut and no other action is applied to it at the desired location. It is done by a winder. This plastic material is easily converted to any desired shape and form.
B) Ramming Mixes
Crushing refractory materials are those that are carefully sized to particle size, so that they can be easily applied. These materials are generally delivered to the consumer in a dry form. When needed, the consumer mixes the refreshments with a little water and then uses them. There are also cobwebs that are delivered to the consumer in a wet state. And at the same time, they can be used. They are used by windmills.
C) Castable blends
A disassembly suggests that these materials naturally have hydrogel capability. These refractories are materials that contain a percentage of cement (usually alumina cement). These refractories have a hydraulic capability when mixed with water. Calcium aluminate adhesives should be well bonded to these refractories to prevent moisture absorption into refractories. In addition, the strength of this binder begins to decrease after 6 to 12 months. These materials are also used as a molding. They are also known as refractory concrete.
D) Gunning Mixes
Spray mixtures are refractory materials that are made in granules. These granules are sprayed onto the surface. Sprayed with these materials, various guns air plocemen are used. These refractories are produced by Heat is strengthened and used for repair and repair work in ovens and pellets.
E) Fettling Mixes
Protective mixtures of refractory materials are in the form of granules whose performance is similar to dispersion mixes. But these blast-molds are poured into the furnace by the pit so that the damaged areas of the furnace are repaired.
Mortars are a group of refractories that are not part of a refractory batch, rather than a monolithic refractory group. These refractories are refractory materials that are found to be plastic because of their combination when mixed with water. These materials are used to create bonding between bricks in the bricks process They are used to create bricks to irregular surfaces of the bricks. Also, the layer formed in the bricks does not accept the spaces created in the bricks. They prevent slag penetration and corrosive agents into the refractory structure.