What is the production process of magnesia brick?

The production process of magnesia bricks is the basis for the production of magnesia refractories and even basic refractories. The production process of high-purity magnesia bricks and direct-bonded magnesia-chrome bricks is similar, but the parameters such as the type of raw materials, purity, molding pressure and firing temperature are different. The following mainly introduces the production process of magnesia bricks.

1. Requirements for raw materials

The main raw material for the manufacture of magnesia bricks in my country is ordinary sintered magnesia. This magnesia is calcined by adding magnesite and coke in layers in a shaft kiln. Therefore, the content of SiO2 and CaO, especially SiO2, is higher than that in magnesite. Its requirements are mainly chemical composition and sintering degree. It is generally required that the chemical composition should be MgO content greater than 87%, CaO content less than .5%, SiO2 content less than 5.0%, and good sintering is required, the density should not be less than 3.18 g/cm3, the burning reduction should be less than 0.3%, no nodules The less black blocks the better.

2. Particle composition and ingredients

The particle composition should conform to the tightest packing principle and facilitate sintering. The critical particle size depends on the degree of magnesia sintering and the appearance size and unit weight of the brick, and can be selected from 4 mm, 3 mm, 2.5 mm, and 2 mm. To manufacture single-sized refractory bricks, the critical particle size can be appropriately increased. The particle size composition is generally as follows: the critical particle size to 0.5 mm accounts for 55% to 60%, the 0.5 to 0.088 mm accounts for 5% to 10%, and the smaller than 0.088 mm accounts for 35% to 40%.

In production, part of the crushed waste bricks can also be added, and the addition amount generally does not exceed 15%, or the waste bricks can be smashed during the molding process and directly mixed into the mud for molding.

The binder adopts the waste liquid of sulfite pulp (with a density of 1.2-1.25 g/cln3) or an aqueous solution of MgCl2 (brine).

3. Mix

It is carried out in a wheel rolling machine or a sand mixer. The feeding sequence is: granular material → pulp waste liquid → fine powder, and the total mixing time is not less than 10 min. Since the amount of CaO in the raw material is limited and the sintering degree of magnesia is improved, the trapping process is generally cancelled.

4. Forming

Sintered magnesia is a barren material, and the water content of the green body is low. Generally, there is no overpressure waste produced by the compressed gas. Therefore, high pressure molding can be used to make the green body density above 2.95 g/cm3. This is beneficial to improve the performance of refractory bricks.

5. Dry

During the drying process of the green body, the physical and chemical changes that occur include the evaporation of water and the hydration of magnesia. The initial stage of water removal requires higher temperature, but high temperature will accelerate the hydration of magnesia and cause the green body to crack. Especially in the later stage of drying, since the influence of heat conduction is greater than the influence of moisture conduction, too high temperature is not conducive to the removal of moisture. In the tunnel dryer, the inlet temperature of the drying medium is generally controlled at 100-120°C, and the exhaust gas outlet temperature is generally controlled at 40-60°C. In order to ensure that the green body has a certain strength after drying, the green body should keep about 0.6% moisture after drying.

The waste products that often appear in the drying process are network cracks, which are mainly caused by the formation of a large number of hydrates in the formed green body. However, if the control is properly controlled, generally no waste products will appear. After the green body is dried, it should be fired in a kiln in time. To avoid moisture absorption and powdering.

6 .Fired

The firing of magnesia bricks can be carried out in inverted flame kiln or tunnel kiln. Their load softening temperature is low, and the green body strength is low after the binder loses its effect, so the brick stack should not be too high, generally about 0.8 m.

Since the physical and chemical changes of the material during the calcination process have been basically completed during the raw material calcination process, the main mineral composition of the refractory brick can be considered to be basically the same as that of the sintered magnesia, but the degree of reaction close to equilibrium and the uniformity of the distribution of mineral components are different. improved. The formulation of the sintering system mainly considers the removal of physical water during the sintering process, the decomposition of hydrolysis products and the bonding strength of the green body at different temperatures. Below 200°C, mainly due to the removal of water, the heating rate should not be too fast; 400-600°C hydration products are decomposed and structural water is precipitated, and the heating rate should be appropriately reduced; 600-1000°C binder loses its binding effect, and the liquid phase has not yet Formation, the green body is mainly maintained by the friction between particles, the strength is low, and the heating rate should not be too fast; the liquid phase begins to appear at 1200-1500 ℃, and forms a ceramic bond, and the heating rate can be appropriately increased; above 1500 ℃ to the final firing rate At the temperature, the ceramic bonding is relatively complete, the strength of the green body is larger, and the heating rate can be accelerated. The holding time at the final firing temperature depends on the size of the refractory brick.

In order to prevent the formation of FeO-MgO solid solution, the iron oxide is formed into MF. This can not only promote the sintering of refractory bricks, but also does not significantly reduce the refractory performance, so it is generally fired in a weak oxidizing atmosphere.

During cooling, the brick has the ability to buffer stress before the liquid phase solidifies, and the cooling rate can be very high, but after the liquid phase solidifies, the plasticity of the brick has disappeared. In order to avoid cracks, the cooling rate should not be too fast. However, rapid cooling can be used below 800 °C.

Zhengzhou Shennan Refractory Co.,Ltd are professional in producing high quality magnesia bricks ,any demands,please don't hesitate contact with me. 


Copyright © 2019 HENAN SNR REFRACTORY CO.,LTD All Rights Reserved.