The function of Refractory Materials

Refractoriness refers to refractory cone sample in which there are no load cases, resistance to high temperature function and not soften the Celsius temperature. Refractory materials is not less than 1580 ℃ refractoriness of inorganic non-metallic materials. But just to define the refractoriness cannot fully describe the refractory materials, 1580 ℃ is not absolute. Now defined as any physical and chemical properties to allow its use in high temperature environment is called refractory material. Refractory material is widely used in metallurgy, chemical industry, petroleum, machinery manufacturing, silicate, motivation and other industrial area, etc. The dosage in metallurgy industry is the biggest, accounts for 50% ~ 60% of total output.

Although the definition of national regulation is different, for example, the international organization for standardization (ISO) in the official publication of international standard, “refractory material, the refractoriness is at least 1500 ℃ of nonmetallic materials or products (but do not rule out that contain a certain proportion of metal)”, but the basic concept is the same, namely the refractory material is the structure material used for high temperature furnace, furnace thermal equipment, as well as high temperature containers and components of materials used in industry, and can withstand the corresponding physical and chemical change and mechanical action.

According to the refractoriness, can be divided into ordinary refractory products (1580 ~ 1770 ℃), high-grade refractory products (1770 ~ 1770 ℃) and super refractory products (above 2000 ℃).

In metallurgy, silicate, chemical, power, petroleum, machinery manufacturing industry, refractory material is used widely. Metallurgical industry of refractory consumption accounted for about 50 ~ 60% of the total refractory.

What is Silica Brick?

Firstly, the most basic is that the nature of silica brick belongs to acidity.

The true density of silica brick is the smaller, the lime change is the more complete, in the process of the oven, generated residual expansion is the smaller. In silica brick, the true density of tridymite crystal is smallest, the linear expansion rate is small, the thermal stability is better than quartz, thermal conductivity is good, refractoriness under load is high, slag corrosion resistance is strong, is the most stable volume form in quartz. In good firing silica brick, the content of tridymite is the highest, accounted for 50% ~ 80%. Cristobalite takes second place, only accounted for 10% ~ 10%. The content fluctuation of quartz and glass phase is in 5% ~ 5%.

When working temperature is below 600 ~ 700 ℃, silica brick volume change is bigger, the resistance to thermal shock performance is poor, thermal stability is not good. If the long-term work under the temperature of coke oven, masonry is easily broken.

The key to determine whether thermal stability of silica brick is true density, the size of true density is to determine one of the important marks of the quartz.

Silica brick is the ideal refractory products of coke oven, the important parts of the modern large and medium-sized coke oven (such as the combustion chamber, ramps and regenerator) all use silica brick to build.

The Molding and Methods of Refractory Brick

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.

The Characteristics and Application of Lightweight Refractory Materials

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

Several Steps of Fire Clay Brick Production

Our company mainly produces fire clay brick, has advanced technology, strong technical force, complete detection equipment. Fire clay brick production has several steps:

1. Borrow earth. The soil bake brick uses taking from two feet deep of the ancient soil under the earth’s surface. The layer of soil color is slightly deeper than the overburden，it formed in eighty thousand to about eighty thousand years ago. At that time, the earth’s climate is warm and moist, rich biological role makes this period of the formative soil soft and sticky, is good material of fire brick.
2. Dig out of clay, in the process of passing about half a year of open air accumulation, let sunshine illuminate, snow and rain frozen erosion, make its internal decompose and loose, then by manual crushing, sieving, leaving only fine pure soil.
3. Add water into pour soil, make it moist, and then repeatedly refine, or use the cow power trample, make it become thick mud, human through mud and refine need five to  six times, the process plays a crucial role in the quality of the brick.
4. Fill soil into wooden blocking mode, after compaction, use iron wire to scrape off the excess sludge and become blank shape. Before blocking, need to sprinkle a layer of fine sand under wooden underground, in case of mud and ground adhesion.
5. After stripping the brick, need to place sun back to dry in the shade, to prevent exposure to make brick bad and appear crack and deformation.
6. After waiting for adobe completely dry (about one to two months), then into the kiln, the process is one of the most important link in the whole process of brick, common brick uses coal as fuel, while compactness higher feed slurry brick uses wheatgrass, pine slowly burn, etc.

How to Solve the Excessive Shrinkage Cavity Problem of Fused Cast AZS

For the excessive shrinkage cavity problem of fused cast AZS, can carry on the improvement in the mold design, the control of sodium oxide content, the casting operation.

1. The design method of improvement

The residual shrinkage cavity of no shrinkage cavity fused cast AZS is closely related to the mold design, excessively increase the size of the AZS brick, cut off more shrinkage cavity, but the AZS brick has high incidence of crack, rising costs. Therefore, by a large number of tests, grasp different shapes and the use of the best parts of the product design, reached a reasonable balance in all respects.

2. Control of sodium oxide

The content of sodium oxide has close relationship with the short of bulk and excessive shrinkage cavity of fused cast AZS, through the theoretical analysis and experiment validation, ultimately determine the appropriate add amount.

3. The improvement of the casting operation

For a large no shrinkage cavity fused cast AZS, sometimes first time casting is not able to complete, need secondary casting.

The physical properties of the Refractory Materials

Structural properties

Macroscopic organization structure of refractory material is heterogeneous body composed of solid material and gas hole. Porosity is the important factors influencing the products under normal temperature and high temperature performance, especially under the condition of high temperature, is products to the outside world of erosion resistance ability is greatly reduced. Reason of gas hole formation: when products molding, the air in the material is completely ruled out. After material moisture ruled out, leaving space. Raw material calcined is inadequate, some should decomposition of salt is the complete decomposition, should be burning ingredients to burn completely. The material composition is uneven, when high temperature firing, contraction is uneven, etc.

1. porosity

The porosity of refractory can be divided into: closed porosity, closed in the products is not connected with the outside world. Open pores, closed at one end and the other end connected with the outside world, for fluid filling. Cut-through pore, The two sides of the cut-through products, get through for the fluid.

2. Bibulous rate

Bibulous rate is absorbed by all the open pores in the products of water quality and the quality of the dry sample ratio. Because the bibulous rate of determination method is simple, in actual production often used for identifying the quality of raw material calcined. The raw material calcined is the better, the bibulous rate value is the lower.

3. Bulk density

The definition of bulk density is the ratio of dry weight and total volume of products, also known as a volumetric weight. Volume density intuitively reflects the degree of the density of the products, it is an important measure indicator of  dense refractory products quality. But in the production of  lightweight insulation products, in order to reduce the heat capacity and thermal conductivity, people use various means to reduce the products volume density.

4. True proportion

The quality of dry material and its true volume (not including pore volume) ratio. The true proportion of refractory material, can reflect the material composition of purity or the degree of crystal structure transition, proportion, etc.

The thermal properties

1. Thermal expansion
2. Thermal conductivity

What requirements should Refractory Materials meet?

Refractory materials used for all kinds of high temperature equipment, it is the high temperature condition of the physical and chemical erosion and mechanical damage, so the performance of refractory materials shall meet the following requirements:

1. High refractoriness. Modern metallurgical furnace and other industrial kiln‘s heating temperature are generally between 1000 ~ 1800 ℃. Refractory material should have no easy to melt performance under the action of high temperature.
2. High temperature structural strength is large. Refractory materials should not only have high melting temperature, but also should not happen softening deformation and collapse under the stove masonry load or other mechanical shock.
3. Thermal stability is good. Metallurgical furnace and other industrial kiln are in operation, due to temperature shock caused by uneven temperature of each part of refractory material, masonry internal stress and make the material fissile and peeling. Therefore, refractory materials should have the ability to resist the damage.
4. Slag resistance ability is strong. Refractory material in use process, often by high temperature furnace slag, metal and chemical erosion of furnace dust. Therefore, must have the ability to resist erosion of refractory material.
5. High temperature volume is stable. Refractory materials at high temperature for a long time use, bricky system internal can produce volume shrinkage or expansion, causes the damage of refractory masonry.

What are the unique advantages of Sillimanite Brick?

Sillimanite brick is refractory brick made of sillimanite minerals. Commonly using high temperature burning method and mud casting method to product.

Sillimanite brick has five big advantage of using:

1. The application of non-ferrous metal smelting industry

Use silicon carbid, high temperature resistance, big strength, good heat conduction performance, impact resistance, high-temperature indirect heating material, such as strong retort furnace. Distillation furnace tray, aluminium electrolyzer, copper melting furnace lining, furnace zinc powder with arc plate, the thermocouple protection tube, etc.

2. The application of iron and steel industry

The use of silicon carbide corrosion resistance. Thermal shock resistance to wear and tear. Good characteristics of thermal conductivity, for large blast furnace lining to improve the service life.

3. The application of metallurgical mineral processing industry

Silicon carbide hardness is second only to diamond, strong wear resistance, is wear-resisting pipe, the impeller, pump room, cyclone, ore bucket lined with ideal material, its wear resistance is  5 to 20 times than the service life of cast iron,rubber,  is one of the aviation flight track ideal material.

4. The application of building materials ceramic, grinding wheel industry

Using the coefficient of thermal conductivity.The characteristics of thermal radiation, high strength, manufacturing sheet kiln furniture, not only can reduce the capacity of kiln furniture, also improves the loading capacity of the kiln and the product quality, shorten the production cycle, is the ideal indirect materials of ceramic glaze baking sintering.

5. The application of energy saving

With good thermal conductivity and thermal stability, heat exchanger, burnup decreased by 20%, saving fuel by 35%, to improve productivity by 20-30%.

The Classification of Fused Cast AZS Block

Fused cast AZS block is the largest consumption species of fused refractory material at present. Glass erosion resistance is strong, with different composition of the glass can adapt. The product categories of fused cast AZS block are as follows:

1. According to zirconia content, refractory fused cast AZS block is divided into three grades: 33 # AZS, 36 # AZS, 41 # AZS.

In general, with the improvement of zirconium dioxide content, baddeleyite mineral content increased, improved glass erosion resistance and high temperature softening property.

2. By casting method, AZS is divided into four types: ordinary casting (PT), tilted casting (QX), Quasi no shrinkage casting (ZWS), no shrinkage casting (WS).

Cast hole is a scourge of fused cast AZS block. When using the general pouring brick, cast hole will account for a third to half of the brick. In order to reduce or remove the cast hole, often used by pouring casting hole cut off without shrinkage cavity brick, increase the density of fused cast AZS block, enhanced ability to resist erosion.

3. According to production process method, products are divided into oxidation (Y) and reduction method (H) oxidizing atmosphere. Main impurity in fused cast AZS block is Fe3 +, Ti4 +, glass phase seepage temperature is high, greater than 1400 ℃. Reducing atmosphere,  main magazine in AZS is Fe2 +, Ti3 +, more than 1100 ℃, fused cast AZS block is easy to be eroded.

The Manufacture Process of Fire Clay brick

Refractory fire clay brick mainly contains a few steps:

 

1. Take soil. Brick takes soil from the surface of the ancient soil with two feet deep, the layer of soil color slightly deeper than the overburden, it formed in eighty thousand to about one hundred and twenty thousand years ago. At that time, the earth’s climate warm and moist, rich biological role make this period of the soil soft and sticky, is good material to burn bricks.

 

2. Dig out of clay, in the process of going through about half a year of open air accumulation, let sun shine, snow and rain frozen erosion, make its internal decomposition loose, after manual crushing, sieving, leaving only fine pure soil.

 

3. Add water to moist pure water, then again and again to refined, or make the cow dint, make its become thick mud, human through mud and refined to roughly five to six times, the process play a crucial role in the quality of the brick.

 

4. The soil filled into wooden blocking mode, after compaction, scrape off the excess sludge using a wire bow and blank shape. Before blocking, under a wooden underground sprinkle a layer of fine sand, mud and ground adhesion in case.

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 chrome 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 product properties of Mullite Insulation Brick

The refractoriness of mullite insulation brick is very high. The highest can resist high temperature of 1800 degrees Celsius, but when from 1600 to 1700 degrees Celsius, heat preservation brick will begin to soften, will not burn. And then it also has a high degree of pressure, presumably in the 260 M/pa. Mullite brick is to adopt high quality high purity refractory powder, according to the requirements of products, to add the organic composite fillers, by vacuum extrusion forming, through high temperature sintering synthetic complex lightweight mullite product.

1. Low thermal conductivity, have very good heat insulation effect.
2. Mullite insulating brick low melt, due to the low thermal conductivity, the accumulation of mullite series light insulating brick has little heat, energy saving effect is obvious in the intermittent operation.
3. Low content of impurities, with very low content of iron boxes alkali metal oxide, therefore, refractoriness is high. Higher aluminum content makes it still keep good performance under the reducing atmosphere.
4. The thermal stage crushing strength of mullite insulation brick is high.