How to mix refractory castable with low cement reasonably and scientifically?（1）

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How to mix refractory castable with low cement reasonably and scientifically

Judging from the variety of low-cement castables, low-cement castables include Al2O3 series and Al2O3-MgO series. The use of high-quality raw materials, according to the scientific and reasonable mixing ratio of ingredients to meet the excellent performance and use requirements of low cement castables. The raw materials used as low-cement castables can be divided into the following four categories.

(1) Aggregate and fine powder of low cement castable
The low-cement castable is made of high-quality high-alumina calcined by rotary kiln and corundum smelted at high temperature in an electric furnace as aggregate and fine powder, and adopts a reasonable gradation composition to ensure that the low-cement castable is closely packed and improves the density.

(2) Fine powder of low cement castable
Ultra-fine powder technology is the key technology of low-cement castable, its main role is to optimize the matrix to improve the performance of the castable.
The main varieties of ultrafine powder and fine powder are active SiO2 fine powder, α-Al2O3 fine powder, white corundum powder, brown corundum powder, mullite powder, magnesium aluminum spinel powder and so on. Due to the sharp increase in the specific surface area, surface atom number and surface energy of micropowders and ultrafine powders, the chemical reaction rate is significantly increased, which lowers the firing temperature of the products and shortens the sintering time. Due to the bulking, adsorption, rheological properties of the ingredients, The meltability has changed, so the strength, toughness, density, electrical properties, magnetic properties, etc. of the products have changed. The fine powder used in low cement castables is mainly α-Al2O3 fine powder, activated SiO2 fine powder, and calcium aluminate cement (CAC) used as a hydraulic binder. The three constitute the matrix part of the low cement castable and its composition The adjustment of the ratio affects the rheological properties and serviceability of the castable.

SiO2 ultrafine powder is an amorphous SiO2 with an average diameter of about 0.15μm and good surface activity. SiO2 ultrafine powder has multiple functions in castables: firstly, it can reduce the amount of cement by about 1%; secondly, it can reduce water consumption, so as to obtain low water consumption and high density castables, and improve the construction rheology when the matrix design is reasonable And high temperature performance; at the same time can also play a role in the combination of low temperature. However, in water systems, SiO2 ultrafine powder usually has a negative surface charge. On the other hand, α-Al2O3 fine powder shows a positive charge, which causes the particles in the binding system to attract each other, resulting in flocculation, which increases water consumption. Use a suitable water-reducing agent to change the charge state of the particles, make the particles repel each other, and reduce water consumption.

The average particle size of α-Al2O3 micropowder is about 1 ~ 5μm. It is generally believed that hydration does not occur during drying at room temperature or 110 ° C, showing inert properties. It is mainly used to improve the sintering performance of casting materials in high-tech casting materials.

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