Additives selection added into refractory brick

Resin-bonded carbon magnesia brick because of their excellent thermal shock resistance and slag resistance has been applied in the steel industry in particular, basic oxygen furnace and electric arc furnace. Carbon has excellent performance: as high thermal conductivity, low coefficient of thermal expansion, high thermal shock resistance, while the poor wettability slags it has good resistance to corrosion and erosion resistance.

Ceramic material ( SiC, carbon silicon oxide) to make coatings on graphite or carbon fiber sheet, impregnated with phosphate, cement foam board price and the use of the surface glaze. These expensive methods have certain limitations in the use of the refractory bricks and a method of fine particles by a steam treatment to boron, TiB2, ZrB2, and SiC and other materials for thermal barrier coating on a graphite or carbon composite material.

One method commonly used in refractory bricks is to add the antioxidant materials of fine-grained, such as adding SiC, B4C, metal Al, Mg, and (or) Si or the like to prevent or limit the carbon MgO-C bricks at a high temperature (> 1400 ℃) oxidation. Similarly, these additives are expensive, and can not completely prevent the oxidation of the carbon at a low temperature. The coating solution of 60% solids and 40% of the liquid blend, wherein the liquid binding agent is a mixture of phosphoric acid and ethanol (30% liquid solution). After the MgO-C bricks overcoat thickness of about brushing 0.8mm, samples was coated with the coating were dried at room temperature of about 10min. In practice, pre-heating the ladle after 5h to 1200 ℃, due to some difficulties in the steel making process may take longer.

How much water should added to castable

Various castable binder containing all the appropriate amount of water fittings, which can be composed of mixtures of water and then added to the binding agent with acidic materials, such as condensation and faster Yasumizu of calcium aluminate cement would often order kind of form. May be previously mixed with a binding agent made ​​of a concentration of an aqueous solution or sol added in the form, such as pre-hydrolysis in order to be combined with bonding agent has such properties are mainly in the form. When there is no deterioration of the reaction casting compound binding agent and water, the bonding agent is evenly distributed in the casting compound, are often pre-mixed with water, acid and water glass as described above is so treated.

The cement binding agent, the setting and hardening speed and strength of the hardened cement and cement properties in addition to the outside, is mainly determined by the amount of water (water-cement ratio) decision. According to the most appropriate varieties of cement and water-cement ratio should accordingly in its water-cement ratio – the intensity curve selected, and nearly at the peak were appropriate. Castable refractory cement ratio – are all their intensity curves are generally characterized by a single peak curve, but the peak is not the same (see Figure 7-1). Not only does it vary depending on the type of cement, water absorption and pellets, shape, surface features and construction means when densification is not the same, the peak has also been changed. In production, in order to ensure the strength of castable, in the selection of appropriate water-cement ratio, should fully consider all aspects of the above. Alumino silicate generally binding by ordinary alumina cement clinker made ​​castable cement ratio used mostly 0.4-0.65. Among those who often take 0.5-0.65 vibration molding, mix the water about 8% -10%; pressure molding machine who often take about 0.4, about 5.5% water mixture -6.5%. In order to reduce the moisture castable, increasing the density of hardened body, should be added in castable appropriate plasticizing water reducer.

The organizational structure of refractory materials

Influence of refractory materials under various physical, chemical interaction in high temperature in the process of using, produce corrosion, wear or crack damage. Therefore, the chemical composition is the basic characteristics of refractory materials; the main components are the basic characteristics of refractory material, so the composition and quantity directly determines the performance of refractory materials.

Refractory products at the same time, mineral composition, product nature is the comprehensive reflection of mineral composition and microstructure, therefore can not only from the chemical composition analysis of the effect on the properties of products. Refractory mineral composition and depends on the chemical composition and process conditions. Although the same chemical composition. If the different processing conditions. The formation of amorphous phase, the number and types of minerals will also have the difference, the performance of refractory materials are also different. However, it must be stressed that the refractory material macro organizational structure is an important factor which influences the use performance, and the performance index can reflect the inner structure of refractory products.

For example: the degree indicates the nature of dense – porosity, bulk density, true density; said gas-permeable nature of the degree of difficulty – Porosity: indicates the nature of the thermal properties – the linear expansion coefficient, thermal conductivity, heat capacity, and temperature conductivity; indicates the nature of the mechanical properties – normal and high temperature compressive strength, high temperature flexural strength, high temperature torsional strength, high temperature creep resistance and modulus of elasticity; said high-temperature performance of a – refractoriness, high temperature load softening temperature , High temperature volume stability, thermal shock resistance and slag resistance.

Heat treatment of electric melting refractory materials

The heat treatment process of fused cast refractories, the general heat treatment can be divided into two stages of crystallization and annealing:

1. Crystalline stage

The general hope exists a certain size and uniform distribution of internal grain products. And the precipitation of crystal to a certain temperature range and enough time, so in the crystallization temperature range (crystalline phase) should be insulated for a period of time, let the crystal full precipitation and growth.

2. Annealing stage

After casting electric melting refractory products in the cooling process, because each part of the heating is not uniform, the casting internal temperature gradients, the great stress, causing cracking products. The cooling speed is high, the internal temperature difference is bigger, will produce stress are larger, causing the cracking tendency is even more. Therefore, casting should slow cooling, heat treatment. There are two kinds of annealing methods, namely natural annealing and external heating annealing.

(1) Natural annealing

In the heat preservation, heat insulation layer using casting types of external (diatomaceous earth and rock hit) and thickness, the casting cooling slowly.

In the heat preservation of annealing is to rely on the heat of casting itself. Adjust the cooling system is very limited, only from the thickness and thermal physical properties and the thermal insulation box mold insulation layer choice adjusting casting early cooling conditions, and the later stage (about the cooling time of 80% ~ 90%) with different time intervals to adjust, in fact is not possible. Moreover, thermal insulation filler dust, the assembly and disassembly of the mold to manual labor, small volume or special-shaped product quality can not be guaranteed, the insulation box low turnover rate, low rate of finished products.

(2)External heating annealing

Using annealing tunnel kiln, which can reduce the temperature gradient of electric melting refractory products surface layer and the center, so that the quality product rate of not less than 80%.

The causes and prevention methods of refractory brick cold burst

Refractory brick is to cold and hot, will burst, burst, the reason is very simple, when the cold and hot temperature, which burst due to thermal expansion and contraction, prone to refractory brick burst including following several types of refractory brick.

1, refractory brick minerals quartz, tridymite, cristobalite composition, due to the temperature change and also accompanied by quartz crystal type conversion, volume change, so the refractory brick thermal shock easily burst.

2, refractory brick by brick and magnesia chrome brick, due to thermal expansion coefficient, when the thermal shock, prone to burst.

Methods of prevention of refractory brick burst:

1, using the insulating fire brick, the insulating refractory brick has the function of heat insulation refractory brick inside, low and stable, is not easy to burst.

2 avoid cold and hot, slow heating and cooling is effective in the prevention of refractory brick burst.

3, the selection of heat coefficient is relatively high, refractory brick toughness is good, can reduce the probability of burst.