Brief Analysis of Production Process of Sunrise Refractory Magnesia Brick

The production process of magnesia bricks is the basis for the production of magnesia refractories and even alkaline refractories. High-purity magnesia brick, directly combined with magnesium.
 

The production process of chrome bricks is similar, except for the types of raw materials, purity, molding pressure and firing temperature.

Different. The following mainly introduces the production process of magnesia bricks.
 

Raw material requirements - particle composition and ingredients - kneading - molding - drying - firing
 

1 raw material requirements

The main raw material for the manufacture of magnesia bricks in China is ordinary sintered magnesia. This magnesia is layered with manganite and coke in a shaft kiln.

Calcined. Therefore, the SiO2 and CaO contents, especially SiO2, are higher than those in magnesite. Mainly for its requirements

Learning composition and degree of sintering. The general chemical composition should be MgO content greater than 87%, CaO content less than .5%, SiO2

The content is less than 5.0%, and the sintering is required to be good, the density should not be lower than 3.18 g/cm3, the burning is reduced to 0.3%, and there is no tumor.

The smaller the black block, the better.
 

2 particle composition and ingredients

The particle composition should conform to the principle of the closest packing and facilitate sintering. The critical particle size is based on the degree of sintering of the magnesia and the appearance of the brick.

Depending on the size and weight, you can choose 4 mm 3 mm 2.5 mm. 2 mm to make a single major refractory brick with a critical particle size.

Appropriate increase in particle size composition is generally: 55% ~ 60% of the critical particle size to 0.5 mm, 5% of 0.5 ~ 0.088 mm

10%, less than 0.088 mm accounted for 35% ~ 40%.

In production, it is also possible to add partially broken waste bricks, which are generally not more than 15%, or in the molding process.

The waste bricks were crushed and directly mixed into the mud for molding.

The binder is a sulfite pulp waste liquid (density of 1.2 to 1.25 g/dln3) or an aqueous MgCl2 solution (brine).
 

3 kneading

In the rim machine or sand mixer, the feeding sequence is: granules - → pulp waste liquid → fine powder, all mixing time is not lower than

10 min, because the amount of CaO in the raw material is limited, and the degree of sintering of the magnesia is increased, the trapping process is generally eliminated.

4 molding

Sintered magnesia is an inert material, and the moisture content of the body is small, and there is no over-pressure waste caused by the compression of the gas.

Therefore, high pressure molding can be employed to make the green body density 2.95 g 'cm3 or more. This is beneficial to improve the performance of the refractory brick.

 

5 drying

During the drying process, the physical and chemical changes that occur during the drying process include the evaporation of water and the hydration of magnesia. Moisture row

The initial stage of the removal requires a higher temperature, but the high temperature accelerates the hydration of the magnesia and causes the body to crack. Especially in dry

Later, because the influence of heat conduction is greater than the influence of wet conduction, too high temperature is not conducive to the elimination of moisture. tunnel

In the dryer, the population temperature of the drying medium is generally controlled at 100~120C, and the exhaust gas outlet temperature is generally controlled at 40~60C.
 

In order to ensure a certain strength after drying the green body, the green body should maintain about 0.6% of moisture after drying.

The waste that often occurs during the drying process is a reticular crack, which is mainly caused by the formation of a large amount of hydrate in the formed body.

However, if properly controlled, there will be no waste, and the green body should be fired in the fashion kiln after drying to avoid moisture absorption.

 

6 firing

The firing of the magnesia bricks can be carried out in a downdraft kiln or a tunnel kiln. Their load softening temperature is low and they are lost in the bonding agent.

After use, the strength of the green body is low, so the bricks should not be too high, generally about 0.8 m.

Since the physical and chemical changes of the materials during the calcination process have been basically completed in the calcination process of the raw materials, the main refractory bricks

The mineral composition can be considered to be basically the same as that of attapulgite, except that the reaction is close to equilibrium and the uniformity of mineral composition distribution.

has seen an increase. The formulation of the firing system is mainly from the elimination of physical water during the firing process, the decomposition of the hydrolysate and the different bodies.
 

The bonding strength at temperature is considered in several aspects. Below 200C, mainly the removal of water, the heating rate should not be too fast, 400

The decomposition of a 600C hydration product, the structural water is precipitated, the heating rate is appropriately reduced, and the 600~1000C binder loses the knot.

For cooperation, and the liquid phase has not yet been formed, the green body is mainly maintained by the friction between the particles, the strength is low, and the heating rate is not too high.
 

Fast; 1200~1500C liquid phase begins to appear, and ceramics are combined, the heating rate can be appropriately increased; 1500C to the final firing temperature, the ceramic combination is relatively complete, the strength of the green body is large, and the heating rate can be accelerated. Burning at the final temperature

The time depends on the size of the refractory brick.

 

In order to prevent the formation of a FeO-MgO solid solution, iron oxide is formed into MF. This will not only promote the sintering of refractory bricks, but also not significant

The fire resistance is lowered, so it is generally fired in a weak oxidizing atmosphere.