In use process of refractory material,  due to a variety of differences of environment, a variety of requirements are proposed on the performance of products, whether to meet the requirements of performance indicators, become the main measure standard of the quality of refractory products, and also prolong its service life, improve the important basis of use value.

Refractoriness

Refractoriness is refractory material resist to high temperature function rather than melting performance, its meaning of refractoriness and melting point are different, melting point is refers to the crystalline phase and liquid phase of pure substance is in equilibrium temperature. And general refractory material is multiphase solid mixture composed of a variety of mineral, has no uniform melting point, but began to produce liquid phase under certain temperature, with temperature rising, the liquid phase ratio increases continuously, to a fixed temperature, solid phase can all melt for the liquid phase. Between the two fixed temperature range, both liquid phase and solid phase exist at the same time.

The chemical composition, mineral composition and its distribution of refractory products are the most basic factors to influence the refractoriness. Impurity elements with strong solvent effect, will seriously reduce the refractoriness of products. Uneven distribution of composition that cannot form an ideal high melting point mineral, will lead to lower refractoriness products, so damage the using performance of products, but the refractoriness of products doesn't mean its use temperature, because refractory material in use, processes through high temperature function at the same time, often with the solvent effect of load and external things and so on. Actually allowable working temperature is much lower than refractoriness, but, after all, the refractoriness index is one of the important reference frame to select reasonably refractory material.

Refractoriness under load

The refractoriness under load of refractory material, also known as the high temperature load deformation temperature, defined as refractory products under persistent overheating conditions, bear deformation temperature under constant load. It said the refractory products at the same time resist the ability of high temperature and load effect.

Linear change on reheating

Linear change on reheating, also known as residual linear change, refers to after the refractory material heated to high temperature, happens the irreversible changes of its length. The specific definition is refractory products sample heated to the specified temperature, heat preservation time, after cooling to room temperature, the length produce residual expansion or contraction. 

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. 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.

4. 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. 

The use performance of corundum brick refers to the corundum brick has the performance when used in high temperature. Including refractoriness, refractoriness under load, linear change rate, thermal shock resistance, slag resistance, acid resistance, alkali resistance, oxidation resistance, resistance to hydration and CO erosion resistance, etc.

1. Increase the refractoriness. 

Refractoriness refers to corundum brick with non-melting performance under resistance to high temperature. Refractoriness is the basis for determining material whether can be used as a refractory brick. The international standardization organization stipulates above 1500 ℃ refractoriness of inorganic non-metallic materials is the refractory material. The significance of refractoriness and melting point is different. Can not take refractoriness as the use of corundum brick temperature. The basic factor of refractoriness to decide is chemical mineral composition and its distribution of corundum brick.

2. Increase the refractoriness under load.

Corundum brick refractoriness under load refers to the products bear constant load deformation temperature under the condition of rise temperature. It shows corundum brick the ability of resistance to high temperature and load effect, to a certain extent, indicates that products in the similar conditions of use case structure strength. The major factors that affect corundum brick refractoriness under load is the chemical mineral composition and microstructure. To improve the purity of raw materials, reduce the content of low melting or flux, increase the molding pressure, made of high density of bricks, can significantly improve products refractoriness under load.

3. Improve the thermal shock resistance

Thermal shock resistance refers to the corundum brick with damage resistance performance to the temperature change rapidly. Generally speaking, the thermal expansion rate of corundum brick is greater, thermal shock resistance is worse. The thermal conductivity of products is higher, thermal shock resistance is better.

Refractory brick's molding in the manufacturing process, refers to the refractory raw materials recuring to outside force and the model, making the blank will be processed into specified dimension and shape. However, the flow castable's construction of the latest development does not need basically external forces. 

The molding of refractory brick, firstly is to satisfy the using demand of the products, when refractory brick masonry, the requirement of products must have a certain shape, precise size, and enough strength. Secondly, molding is also the efficient way to improve the physical and chemical properties of products, by shape can improve the organizational structure of products. Refractory brick has a lot of molding methods, the traditional processing methods according to how much moisture content can be divided into: 

1. Semi-dry method: its blank moisture is around 5%, suitable for blank of different clinker content(50% 100.

2. Plastic method: its blank moisture is around 15%, suitable for manufacturing large or complicated shape of the products.

3. Grouting method: its blank moisture is around 40%, is suitable for all kinds of hollow thin-walled refractory materials in production.

The modeling methods of refractory brick have a lot, the common used molding ways contain organic pressure molding, vibration molding, extrusion molding, ramming forming, isostatic pressure molding, casting molding, grouting, etc.

Choose what kind of molding method, mainly according to the nature of the plaster, body shape, size and other technical requirements. In addition to most of the refractory brick is made of machine pressure forming, vibratory molding is used for special-shaped body, the extrusion molding is generally used in tubular blank, slip casting molding is used for thin wall body shape. 

Refractoriness of magnesia brick high reaches above 2000 ℃, and refractoriness under load with the combination of phase's melting point and at high temperatures result in different liquid phase without great changes. General magnesia brick's load softening temperature is at 1520 ~ 1600 ℃, and high purity magnesium boast a softening start temperature can reach 1800 ℃.

The difference between start refractoriness under load of magnesia brick and collapse of temperature is not big, it is because the main phase composition is periclase magnesia brick, but periclase crystals within the magnesia brick is not crystalline network skeleton, but was cemented by combination. High purity magnesia brick's refractoriness under load start temperature can reach 1800 ℃, mainly due to the combination between the periclase grain is forsterite or dicalcium silicate, it and MgO formed eutectic mixture's melting temperature is high, crystal lattice strength is big and plastic deformation under high temperature is small, crystal particles combined are good.

The linear expansion rate of magnesia brick under 1000 ~ 1600 ℃is generally 1.0% ~ 2.0%, and approximate or linear, in refractory products, thermal conductivity of magnesite brick is next only to carbon brick, it reduces by the rise of temperature. Under the condition of 1100 ℃water, magnesia brick's number of thermal shock is only 1 ~ 2 times. Magnesia brick to CaO and iron oxide's alkaline slag  resistance capability is strong, but to SiO2 and acidic slag's resistance is weak.

So in use can not direct contact with silica brick, and in general will be separated with a neutral brick. Under normal temperature, the conductivity of the magnesia brick is very low, but at high temperature, the conductivity will not be ignored. Property of magnesia brick, because of the differences of adoptive raw materials, production equipment, technology measure have a large difference.

Mullite brick with mullite as phase of high aluminum refractory material. Has higher refractoriness, can reach more than 1790 ℃. So what quality characteristics does Mullite brick have?

1. The brick binder of mullite brick. Mullite brick uses adhesive to connect between contact, therefore, the solid degree of adhesive bonding to give full play to the excellent properties of mullite brick base material, to the final use performance of the products is a very important factor.

2. Bulk density of mullite brick. The density of thermal insulation material generally should be lower than 600 kg/m. Small bulk density of material, generally tears eyes coefficient of thermal conductivity is small, but at the same time decreases in the mechanical strength, so need to reasonably choice.

3. The mechanical strength of mullite brick. To make the insulation material non-deformation and damage under their own weight and external force, so its compressive strength should not be less than 3 kg/cm.

4. The water absorption of mullite brick. After insulation material absorbing water, not only can greatly reduce the thermal insulation performance, but also can accelerate the corrosion of metal, it is very harmful. Therefore, need to choose small bibulous rate of thermal insulation material.

5. The heat resistance and use temperature of mullite brick. According to different situation of use place's temperature to choose different heat insulation performance of thermal insulation material.

Mullite brick with mullite as phase of high aluminum refractory material. Has higher refractoriness, can reach more than 1790 ℃. So what quality characteristics does Mullite brick have?

1. The brick binder of mullite brick. Mullite brick uses adhesive to connect between contact, therefore, the solid degree of adhesive bonding to give full play to the excellent properties of mullite brick base material, to the final use performance of the products is a very important factor.

2. Bulk density of mullite brick. The density of thermal insulation material generally should be lower than 600 kg/m. Small bulk density of material, generally tears eyes coefficient of thermal conductivity is small, but at the same time decreases in the mechanical strength, so need to reasonably choice.

3. The mechanical strength of mullite brick. To make the insulation material non-deformation and damage under their own weight and external force, so its compressive strength should not be less than 3 kg/cm.

4. The water absorption of mullite brick. After insulation material absorbing water, not only can greatly reduce the thermal insulation performance, but also can accelerate the corrosion of metal, it is very harmful. Therefore, need to choose small bibulous rate of thermal insulation material.

5. The heat resistance and use temperature of mullite brick. According to different situation of use place's temperature to choose different heat insulation performance of thermal insulation material.

Ceramic Fiber Blanket is the clay clinker of high purity, alumina powder, silica powder and other raw materials melting in high temperature furnace, forming fluid. Fiber cotton can be further processed into fiber blanket, board, paper, cloth, rope and other products. Turn out to be an efficient heat insulation material, with the characteristics of light weight, high strength, oxidation resistance, low thermal conductivity, good flexibility, corrosion resistant, small heat capacity and sound insulation, etc.

Ceramic fiber blanket made from ceramic fiber as the raw material, in recent years become each big kiln dedicated furnace lining materials, because of its simplicity and easy construction, and heat insulation effect is better, become a required insulation material of kiln company. The adiabatic temperature can reach more than 1600 degrees, greatly satisfy the needs of the user.

Energy shortage, various cost increase, are the necessity of  industrialization process, has the construction application of the energy-saving insulation materials, for the enterprise, it is the top priority in development, ceramic fiber blanket improves the conservation of thermal efficiency, but for some special kilns, due to the particularity of chemicals, may temporarily can't use ceramic fiber blanket as insulation materials. 

The performance and application of chrome corundum brick.

Fire resistance of the products

Add Cr2O3 to high purity corundum material, no matter how much the amount is, not only will not reduce refractory performance of materials, on the contrary make fireproof performance of materials improved. The refractoriness of chrome corundum brick (> 1790!) and refractoriness under load (> 1700!) are superior to high purity corundum products.

1. The strength of the products

 Room temperature compressive strength of high purity corundum brick is 70 ~ 100 MPa commonly, room temperature compressive strength of high performance chrome corundum brick is generally more than 150 MPa, the intensity is significantly higher than the corundum brick. This is because the products in the process of burning, between particles and particles, particles and fine powder, powder and powder, formed  Al2O3 — Cr2O3 solid solution, the solid solution connects particles to fine powder particles together, make the strength of the material is greatly increased.

2. Thermal shock resistance

Add Cr2O3 to corundum, when Cr2O3 content is 10% ~ 66%. The raw materials that Chrome corundum series of products used is made from alumina and chromium oxide according to certain proportion matching, after high temperature melting synthesis of a solid solution. Using special refractory materials production technology to produce refractory brick, can improve and enhance internal quality of the products, improve the high temperature performance of products, have the characteristics of high refractoriness, big strength, good thermal shock stability, strong ability to resist erosion. 

Lightweight refractory material is also known as heat insulation refractories and insulation refractories, refer to the high porosity, small volume density, low thermal conductivity, has the thermal insulation performance of refractory materials. It includes insulating refractory products, refractory fiber and refractory fiber products. 

As a kind of refractory material, lightweight refractory has a certain high temperature mechanical properties and good volume stability, is all sorts of high-temperature thermal equipment necessary. Compared with dense refractory material, the lightweight refractory filled with gas shows high apparent porosity, small volume density, good insulation performance, has the screened effect on heat. Therefore, the main characteristics of lightweight refractory material are:

1. High apparent porosity

A main performance index to measure lightweight refractory material quality is the porosity. Pore is made of the pore in the refractory raw materials and intergranular porosity after forming. 

2. Small volume density

The volume density of lightweight refractory is small, no more than 1.3g/cm³. At present, volume density of common lightweight refractory industry is 0.5~1.0g/cm³ in industry.

3. Low thermal conductivity

Under unit the temperature gradient, within the unit time through unit vertical heat. It is the important performance index of lightweight refractory material quality, is also the important index of the design of thermal performance design. It indirectly reflects apparent porosity and bulk density of the products.

4. Low compression strength

Lightweight refractory material, due to large apparent porosity, low bulk density, not form a compact connection between crystals. So relative to the dense refractory material, its pressure strength is low, wear-resisting performance is poor.

Application

Lightweight refractory material is important component part of kiln, boiler, the thermal container and other equipment, is widely used in industry. Because of the lightweight refractory material's high apparent porosity, occupies the irreplaceable position in the high efficiency and energy saving, reducing heat loss.