JPS5941951B2 - Manufacturing method for magnesia-alumina refractories - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a magnesia-alumina refractory material suitable for lining materials for cement rotary kilns and the like.

In general, this type of lining material is required to have clinker ring properties and to have excellent alkali resistance, clinker resistance, thermal shock resistance, and volume stability under hot conditions.

By the way, alumina refractories, magnesia refractories, or magnesia-chromium refractories are used as lining materials for conventional cement rotary kilns.

However, these refractories have advantages and disadvantages as shown below, and are not fully satisfactory as lining materials.

That is, the alumina refractory reacts relatively easily with alkali, forms a reaction layer, peels off and is damaged, and becomes unusable in a short period of time.

In addition, although magnesia refractories are relatively inexpensive,
It has the drawbacks of a large coefficient of thermal expansion, poor thermal shock resistance, and large deformation during hot conditions.

Furthermore, although magnesia-chromium refractories have greater resistance to alkali and cement clinker reactions than the above two refractories, they also produce harmful romate during use, which poses a pollution problem. There are also drawbacks such as clinker ring easily adhering to the clinker ring, which impedes transportability of the clinker.

For this reason, the present inventor conducted various studies to eliminate the above-mentioned drawbacks without using harmful ROM, and found that the amount of magnesia was higher than the theoretical blending ratio of magnesia and alumina that forms the spinel structure (MgO・At203). It was found that a refractory with a low coefficient of residual thermal expansion could be obtained by molding and firing the mixed powder blended into the mold.

However, this refractory has not always been fully satisfactory in terms of alkali resistance, clinker resistance, and thermal shock resistance.

As a result of further intensive study based on the above research process, the present inventor formed the magnesia-alumina mixed powder with the above composition into a pellet shape, fired it, pulverized the synthetic fired pellets obtained, and obtained this as the main component. By molding and firing the raw material, it reduces the adhesion of clinker rings and has superior alkali resistance, clinker resistance, and thermal shock resistance compared to conventional magnesia-chromium refractories. We have discovered a method by which a magnesia-alumina refractory can be obtained which has no inferior volumetric stability and has no risk of inducing pollution.

That is, in the method of the present invention, a mixed powder consisting of 35 to 65 weight percent magnesia powder and 65 to 35 weight percent alumina powder is fired to form synthetic fired pellets, and then a raw material containing the pulverized powder of this pellet as the main component is regularly Form into the desired shape according to the law,
It is characterized by being fired.

As the magnesia powder used in the present invention, pulverized seawater magnesia clinker with a purity of 94 or higher is suitable.
The particle size is desirably 250μ or less.

The alumina powder used in the present invention is preferably pulverized calcined alumina by electrofusion or Bayer method with a purity of 97% or more, and the particle size is preferably 250 μm or less.

The reason why the blending ratio of magnesia powder and alumina powder is limited in the present invention is that if the amount of magnesia powder is less than 35% by weight, the alkali resistance, clinker resistance, and thermal shock resistance will decrease. This is because if the amount exceeds 65% by weight, not only the porosity increases and the compactness decreases, but also the thermal shock resistance decreases.

The molding conditions for producing the synthetic fired pellets in the present invention are preferably a molding pressure of 300 Kg/ca or more, and the firing conditions are preferably in the temperature range of 1,600 to 2,000°C.

The raw material used in the present invention is one consisting only of pulverized powder of synthetic fired pellets, or one in which magnesia powder is blended with this pulverized powder, and the pulverized powder of synthetic pellets used is one consisting of coarse particles, medium particles, and fine particles. This is desirable.

In addition, when creating a raw material from pulverized powder of synthetic fired pellets and magnesia powder, add 85% magnesia powder to the pulverized powder.
It is desirable to mix the weight ratio or less.

By using such a two-component raw material, it is possible to obtain a refractory with further improved compactness and compressive strength.

The means for molding and firing the raw material in the present invention may be carried out under substantially the same conditions as those for molding and firing the synthetic fired pellets.

Next, the present invention will be explained in detail.

Example 1-1 Magnesia clinker with a purity of 97 and a particle size of 250μ or less
To a mixed powder consisting of 60 parts by weight of powder and 40 parts by weight of fused alumina powder with a purity of 98 parts and a particle size of 250 μm or less, 3 parts by weight of lignin sulfonic acid solution was added and kneaded, and then this was formed into pellets, Synthetic calcined pellets were prepared by processing at a temperature of 1750° C. for 6 hours.

Next, the synthetic fired pellets are crushed and classified into 1 to 5
rItm coarse grain 50wt, 0.25-1mm medium grain 1
A raw material consisting of 5 weight and 35 weight of fine powder of 0.25w or less is prepared, and lignin sulfonic acid solution is added to this raw material by 3 weight.
After adding weight coefficient and kneading, this was 300 Kg/crA
The molded product was made into a molded product under the pressure conditions of 1750
A magnesia-alumina refractory was obtained by firing for 6 hours at a temperature of .degree.

Comparative Examples 1-3 to 3-1 A mixed powder consisting of 80 parts by weight of magnesia clinker powder and 20 parts by weight of fused alumina powder [Comparative Example 1-1]
, one consisting of 28 parts by weight of magnesia clinker powder and 72 parts by weight of fused alumina powder [Comparative Example 2-II], one consisting of 10 parts by weight of magnesia clinker powder and 90 parts by weight of fused alumina powder [Comparative Example 3-1] ] Three types of magnesia-alumina-based refractories were obtained by processing under the same conditions as in the previous example.

Therefore, the porosity, bulk specific gravity, compressive strength, bending strength at 1400°C, and 1000°C of the magnesia-alumina refractories of Example 1-1 and Comparative Examples 1-1 to 3-1 were found.
The thermal expansion coefficient, alkali resistance, clinker resistance, and thermal shock resistance were investigated.

The results are shown in Table 1 below.

In the thermal shock resistance test, one cycle was a rapid heating and cooling operation in which the refractory was rapidly heated to 1200° C. and then cooled in water, and it was examined at which cycle peeling occurred.

Example 1-2 and Comparative Examples 1-2 to 3-2 Classified powder of synthetic fired pellets produced in Example 1-1 and Comparative Examples 1-1 to 3-1 (15% coarse particles of 1 to 51 rtm) , 0.25-1 mm medium grains (5 parts by weight), magnesia clinker classified grains with a purity of 97% (35 parts by weight of coarse grains of 1-5 bodies, 15 parts by weight of medium grains of 0.25-1 mm, 0.25 m Four kinds of raw materials were prepared by blending the following fine powder (30 weight cl)), and these raw materials were treated under the same conditions as in the above example to obtain four kinds of magnesia-alumina refractories.

Therefore, the porosity, bulk specific gravity, compressive strength, alkali resistance, clinker resistance, thermal shock resistance, and appearance of the magnesia-alumina refractories of Example 1-2 and Comparative Examples 1-2 to 3-2 were investigated. Ta.

The results are shown in Table 2 below.

In addition, the magnesia-alumina refractories of Examples 1 and 2 above were lined in the desorption zone of a 5.4 mφ x 95 Lm rotary kiln equipped with a suspension preheater,
As a result of approximately 4,000 hours of operation, (1) the wear rate of conventional high-temperature fired magnesia-chromium refractories was approximately 0.5
~0.6 mm/day, whereas the wear rate was 0.
．． 4mm and 7 days, extending the lifespan by about 1.5 times.

(2) The adhesion of the cement clean car was reduced to about 1/3 of that of the magnesia-chromium refractory, and the inhibition of the transportability of the clean car due to the formation of clinker rings was reduced.

(3) The amount of clean car adhesion is small and the adhesion force is weak, making it easier to remove the clean car coating when the car is not running.

As detailed above, the present invention not only does not generate chromate, but also reduces the adhesion of clean cars, and has better alkali resistance and clean car resistance than conventional magnesia-chromium refractories. Magnesia-alumina, which has excellent thermal shock resistance but poor volumetric stability under hot conditions, can be used extremely effectively as a lining material for cement rotary kilns and other various steelmaking containers, and is highly safe. It is possible to provide refractories of this type.

Claims (1)

[Claims] 1 Magnesia powder 35~65 weight and alumina powder 65~
A magnesia-alumina refractory characterized by firing a mixed powder consisting of 35% by weight to form synthetic fired pellets, and then molding and firing a raw material whose main component is the pulverized powder of the pellets according to a conventional method. manufacturing method.