The Application of Magnesia in the Refractory Industry

The magnesia made of natural magnesia by one-step or two-step calcination process in a shaft kiln or rotary kiln is called sintered magnesia. The magnesia made of magnesia by melting in an electric arc furnace and then cooling to solid is called fused magnesia. Seawater magnesia is exacted from seawater.

 

Magnesia can also be divided into fused magnesia, intermediate magnesia, high purity magnesia and dead burned magnesia.

 

Dead burned magnesia is made of natural magnesia by firing at high temperature in a shaft kiln. It can be used to produce refractory bricks and monolithic materials for steel smelting in electrical furnaces.

 

Fused magnesia is made of chosen special grade natural magnesia or high purity light burned magnesia particles. It has high purity, large size, dense structure, good slag resistance and good thermal shock resistance. It is a good electronic insulation material and raw material for high grade magnesia brick, magnesia carbon brick and monolithic material.

 

Intermediate magnesia is made of 97% light burned magnesia by ball pressing and high temperature firing in a shaft kiln. It has good degree of sintering and fine crystal. It is used in the production of intermediate magnesia refractories.

 

High purity magnesia is made of natural magnesia by light burning, fine grinding, ball pressing, and ultra-high temperature firing in a shaft kiln.

The raw materials of Refractory Brick and firing methods

Refractory brick has a variety of raw materials, the composition is mainly divide with the six categories: earth, stone, sand, ore, powder and other.

1. Earth: aluminum earth, kaolin earth, clay, diatomaceous earth.
2. Stone: fluorite, kyanite, andalusite, forsterite, vermiculite, mullite, pyrophyllite, chlorite, dolomite, sillimanite, magnesium aluminate spinel, silica.
3. Sand: ceramic sand, zircon sand, quartz sand, magnesia snad.
4. Ore: chrome ore.
5. Powder: metal aluminium powder, silicon powder and silicon metal powder.
6. Other: Asphalt, graphite, phenolic resin, perlite, floating bead, corundum, sulfuric acid silicon, silicon carbide, soluble glass, silica sol, boron carbide, calcium aluminate cement, nitride materials, shale ceramsite, alumina, alumina sol, zirconium oxide, etc.

The firing stages of refractory brick:

1. At room temperature to 200 ℃, the temperature should not be too fast, in case of refractory brick body cracking, in the tunnel kiln firing, the former 4 parking temperature should not exceed 200 ℃.
2. 200 ~ 900℃: the temperature should speed up in the stage, for the organic matter content in the refractory brick and impurities of chemical reactions to conduct. During the period of 600 ~ 900 ℃, should stay stronger oxidation atmosphere in furnace, avoid  the “black heart” refractory waste.
3. 900℃ to the highest firing temperature: in the high temperature stage, should be smooth temperature and steady, continue to maintain the oxidizing atmosphere, make the refractory brick body heated evenly, also need to prevent cracking of refractory brick. Due to above 1100 ℃ high temperature, sintering shrinkage is very strong, shrinkage rate reaches 2-5%, so keep the gentle temperature gradient, eliminate internal stress is very important.
4. Cooling stage: according to the character changes of refractory products in the cooling section, the temperature should be fast cooling above of 800 ~ 1000 ℃ high temperature stage, under 800 ℃, should slow cooling rate, in fact, in the actual production, the cooling speed of actual use will not cause cold cracking risk to refractory products.

The production process of Refractory Materials

The variety quality of refractory materials has a big relationship with production process. The same raw material using different process, can produce need different varieties and quality of products.

The production process of generally block burned into refractory brick:

1. Raw materials

Make different refractory products, need to adopt different chemical mineral composition of raw materials.

Refractory products demand for raw materials are: suitable chemical mineral composition and content of impurities in raw material: fewer and uniform distribution. Facilitate mining processing and manufacturing, and lower cost.

2. The raw material processing

Raw material processing including mineral separation, drying, burning, crushing and screening.

3. Ingredients and mix practice (mixed)

Ingredients are the raw materials (large, medium and small three kinds of particles, raw material and clinker), additive (binder, mineralizer) and water to coordinate according to certain proportion.

4. Molding and drying

The purpose of molding is to make the refractory products with specification density, appearance size and strength. Molding methods can be divided into new moon and semi-dry forming. Metallurgical industry to use the most is the half dry molding in refractory products.

The melting technology of Fused Cast AZS Block

The melting technology of fused cast AZS block is divided with reduction method and oxidation method.

Reduction method is also called submerged arc method, it is the graphite electrode immersed in furnace charge, because the electrode burns under the environment of lack of oxygen, recover in a series of recover reaction, make the melt of some high oxide be in unstable form, together with carbon also enters the melt, this will eventually make the color of melt become dark.

In the process of ablation, the furnace charge of circuit of the burden were not carburizing or fused impregnation carbon decarburization before casting, this makes the melt contains no carbon technology, called oxidation method, also called Ming arc method. Because recovery method with the presence of carbon in AZS, when used in glass kiln, high-temperature charcoal burning, gas will squeeze soft glass phase out, speeds up the glass liquid on brick corrosion , so the existence of carbon on the corrosion resistance of AZS is bad, now more choose oxidation instead of recovery method, the history of charcoal in AZS is mainly graphite electrode during discharge not burning with arc into the furnace, so need to find a way to prevent the coal into the furnace. Here are several common methods:

Long arc method

The electrode does not melt in the furnace and eliminate the carbon transfer between the electrode and melt.

Join oxidizing agent method

Add some oxygen enrichment in ingredients material, it can release oxygen in the melting process, the molten liquid on the surface of carbon burned evaporation, however, usually is to use bright arc melting,  with arc melting during refining。

Through oxygen method

Has many same ways, but oxygen blowing melt later after recovery melting. Some will lunge oxygen gun from the furnace top, some set of oxygen gun in the furnace mouth, make the furnace body forward to melt submerged drum oxygen lance, the melt of trace carbon burning escape by touch with oxygen.

How to distinguish High Quality Corundum Brick

Corundum brick is with corundum as main material of refractory products, aluminum oxide content > 90%, corundum brick resorts its good chemical stability, good erosion resistance, good wear resistance, be widely used in petrochemical industry, metallurgical industry, coal gasifier residual oil gasifier, pulp waste liquid gasifier, carbon black reacting furnace and other industrial furnace lining.

The packing density of corundum brick has a relationship to abrasive particle size, particle composition, particle brand, particle size, particle shape and other factors. In general coarse granularity is smaller than fine-grained density, the gap between particles is the smaller, the density is the larger. Hybrid particle packing density is greater than the single particle. The density of particles directly affects the density of corundum brick, The density of the particle is the larger, the density of corundum brick is the larger, the real density of corundum brick refers to the quality of the abrasive contained  in unit volume .

Corundum brick is a kind of important refractory brick, the application is very wide, so what are the properties of high quality corundum brick?

1. Alumina oxide content, common alumina oxide content is the higher, fire resistance is the higher.
2. Corundum brick has high room temperature compressive strength, compression effect is good, directly affects the quality of corundum brick.
3. High temperature resistant effect is good, the starting softening temperature is high.
4. Chemical performance is good, has acid resistance, corrosion resistance, salt resistance and other properties.

 

The advantages of Chrome Corundum Brick

Chrome corundum brick is alumina – chrome oxide as the main raw material production of high-performance chrome corundum brick, has the characteristics of high refractoriness, great strength, good thermal shock stability, strong ability to resist erosion. In use, the scouring resistance, wear resistance, resistance to flake structure, has been in metallurgy, glass, carbon black and the petrochemical industry, has obtained the good using effect. Chromium corundum brick raw material is used by the ratio of alumina and chromium oxide according to certain proportion, go through high temperature melting synthesis of a solid solution. Using special refractory production technology made of refractory brick, can improve internal quality of the product, improve the high temperature performance of products.

1. The refractory properties of chrome corundum brick

In high purity corundum material add Cr2O3,  no matter how much the amount, not only will not reduce the fire performance of materials，can make refractory performance of material improved.

2. The strength of chrome corundum brick

Compressive strength of high purity corundum brick at room temperature is 70 ~ 100 MPa commonly, room temperature compressive strength of high performance chromium corundum brick is generally larger 150 MPa, the intensity is significantly higher than the corundum brick. This is because the products in the process of burning, between particles and fine powder, between powder and powder are formed Al2O3 – Cr2O3 solid solution, calcium solid solution like bridge connect fine powder with particles together, make the strength of the material is greatly increased.

3.  Application

For use in the iron and steel industry, chrome corundum brick material is above double longer than service life extended of corundum material, such as ladle air brick, etc. For use in nonferrous smelting industry, the wear resistance and erosion resistance of chrome corundum brick  is superior to other bricks.

4. Thermal shock resistance

Add Cr2O3 in corundum, when Cr2O3 content is 10% ~ 66%, material of thermal shock resistance decreased with increasing content of Cr2O3, namely the Cr2O3 content low chrome corundum brick, the thermal shock stability is better than Cr2O3 content high chrome corundum brick.

The application of Ceramic Fiber Blanket

The typical applications of ceramic fiber blanket：

1. Aerospace, steel, petrochemical, electric power of high temperature heat insulation
2. Equipment fire insulation
3. Industrial furnace, heating device wall lining, backing insulation
4. High temperature equipment insulation, heat pipe heat insulation
5. Electrical components heat insulation fire, high temperature gaskets
6. Inorganic fire shutter fire-resistant layer
7. Module, folded piece of raw materials

Technical characteristics:

Low thermal conductivity, low thermal capacity

No corrosive substances

Excellent heat insulation, sound-absorbing

Range of application

Industrial building materials furnace, heating equipment, high temperature pipe wall lining

Power boiler, steam turbine and nuclear heat insulation

High temperature reaction chemical industry equipment and wall lining of heating equipment

High-rise building fire prevention and heat insulation

Kiln stove, roof insulation

High temperature filter material