JP2999134B2 - Magnesia chrome refractory and cement rotary kiln - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnesia chrome refractory suitable for lining a cement rotary kiln and a cement rotary kiln lining the magnesia chrome refractory.

[0002]

BACKGROUND OF THE INVENTION magnesia chrome refractories is an excellent service when it is used in the lining Ri refractory cement rotary kiln, it is often used from the conventional to the lining of cement rotary kiln. The refractory used for the lining of the cement rotary kiln has a low melting point containing alkali contained in the cement clinker exposed to a high temperature by the high temperature combustion gas flowing inside the high temperature part of the cement rotary kiln, especially near its baking point. If the components penetrate into the refractory lining and change the quality of the refractory, and if the refractory undergoes structural spalling due to a change in temperature, the service life of the refractory becomes very short.

As a countermeasure to avoid this problem, tends to react with the cement components refractories to be lined rotary kiln, or the addition of cement clinker easily adheres components of the semi-molten state refractories, cement clinker semi Various techniques have been devised for coating the melt on the surface of the refractory.

[0004] For example, alumina spinel refractory not containing chromium as lining Ri refractories cement rotary kiln is disclosed in JP-A 4-310561, a fused magnesia clinker This refractory in the aggregate 10
５０50% by weight and partially stabilized zirconia in the refractory are added in an amount of 0.5 to 10% by weight to make the semi-molten cement clinker easily adhere to the surface of the refractory. Further, as a preferred configuration example of the refractory, it is disclosed that an electrofused magnesia clinker containing 1 to 3% by weight of SiO ₂ and CaO is used for the electrofused magnesia clinker.

[0005] Besides, for the purpose of improving the coating adhesion of the cement rotary kiln lining Ri <br/> brick, the Fe ₂ O ₃ to magnesia chrome-based refractory containing chromium ore 20-40 wt% Magnesium clinker containing 3.5 to 10% by weight and 5 to 10% by weight of CaO
The addition of 70% by weight has been proposed in JP-A-5-238809.

However, in these conventional cements rotary kiln lining Ri refractories, when the various devices to improve the adhesion of the coating, the refractory on the other hand corrosion resistance, heat resistance, heat cycle stability The tendency of the characteristics to degrade remains as a problem.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, to provide a corrosion-resistant and heat-shock resistant coating, and to improve the coating adhesion. It is to provide an excellent refractory.

[0008]

DISCLOSURE OF THE INVENTION The present invention has been made to achieve the above-mentioned object, and a magnesia chromium refractory of the present invention comprises 20 to 40% by weight of chromium ore and 20 to 75 % by weight of a calcined magnesia clinker. % And 0 .
5 to 3% by weight of CaO and 0 . The fused magnesia clinker including a SiO ₂ of 5 to 3% by weight, characterized in that it comprises 5 to 40 wt%.

Here, the content of chromium ore in the refractory is 20
The reason why the content of chromium ore is set to 20% by weight or more is that the corrosion resistance and heat resistance of the refractory are secured and the content of chromium ore is 40% by weight or less. This is because the heat resistance is secured.

Although the fused magnesium clinker is slightly expensive, it has high corrosion resistance due to its fine structure. In the magnesia chromium-based refractory of the present invention, the fused magnesia clinker to be added to the refractory contains 0.5% by weight or more of CaO.
The coating adhesion is improved by containing 0.5% by weight or more of SiO ₂ , thereby obtaining the effect of extending the service life of the refractory lining the cement rotary kiln. These components are composed of electrofused magnesia clinker periclase crystals (MgO crystals).
It is hardly contained in it and is mainly concentrated and distributed at the grain boundaries of periclase crystals, and these function as anchors for cement clinker in a semi-molten state,
Makes the coating easy to adhere.

However, the fused magnesium clinker is Ca
When O to 3 wt.% Or SiO ₂ containing 3% wt, exhibits a tendency to tissue refractory embrittlement when refractory is subjected to a thermal cycle, the respective contents as 3 wt% or less is there. The content of fused magnesia clinker CaO and SiO ₂ to be blended in the refractory is preferably set to 1.0 to 2.5% by weight when considering the balance of properties imparted.

[0012] Normally, calcined magnesia clinkers that are commercially available as raw materials for refractories are of high purity so that the refractories have both heat resistance and corrosion resistance. Since the fused magnesia clinker is usually produced using these calcined magnesia clinkers as raw materials, the purity is also high. Therefore, the electrofused magnesia clinker blended in the refractory of the present invention is produced using low-purity calcined magnesia clinker with a reduced degree of purification of the raw material, and slightly contains both components of CaO and SiO _2. Includes many.

Further, in order to impart a required coating adhesion to the refractory and further enhance the corrosion resistance, the amount of the electrofused magnesia clinker to be added to the refractory is set to 5% by weight or more. Further, when the above fused magnesium oxide clinker is added to the refractory in an amount exceeding 40% by weight, the thermal shock resistance of the refractory deteriorates, so that the content is set to 40% by weight or less.

The fused magnesia clinker to be added to the magnesia chromium refractory of the present invention preferably has an average crystal grain size of periclase of 100 μm or more. When the average crystal grain size of periclase is 100 μm or more, CaO and S contained in the fused magnesium clinker are contained.
When iO ₂ is accumulated at the grain boundaries of periclase, the function as an anchor is enhanced, and the cement clinker in a semi- molten state is more easily adhered to the refractory, so that the coating adhesion to the refractory is further improved. . Also,
There is also a secondary effect that the corrosion resistance of the refractory is improved due to the large average crystal grain size of periclaze.

[0015] Cement kiln magnesia chrome refractories is lined hot parts including the higher true sintered point temperature of the present invention is a coating deposition of the semi-molten cement clinker good corrosion resistance, thermal shock resistance Also, it is excellent in structural spalling resistance, so that it is a cement rotary kiln exhibiting excellent cost performance. As the refractory to be lined with the cement rotary kiln, preferably used is a shaped refractory which has been molded and fired in advance.

[0016]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples.

Baking with a purity of 99% by weight or more and a particle size of 5 mm or less
Forming magnesia clinker, at a purity of 97 wt% 1. It contains ₂ % by weight of CaO and 1.5% by weight of SiO _{2 and} has a particle size of 1%.
To 5 mm, an average grain size of about 250μm fused magnesia clinker A, a purity of 99 wt% 0. 45% by weight of C
It contains aO and 0.25% by weight of SiO _{2 and} has a particle size of 1 to 5
mm, an electrofused magnesia clinker B having an average crystal grain size of about 250 μm , and 30% by weight of Cr in terms of Cr ₂ O ₃ and F
e containing 15% by weight in terms of Fe ₂ O ₃ and having a particle size of 5 mm or less .
A chromium ore was used as a raw material for refractories.

These raw materials were blended according to the formulation shown in Table 1, and a 20 ° Be ′ (referred to as degree Baume, 20 ° Be ′ corresponding to 15% by weight) aqueous magnesium sulfate solution was applied to each as a binder. And add 3% by weight and mix.
Press molding at 000 kg / cm ² and after drying 1780 ° C
And baked for 10 hours to measure 230mm x 114m
A prototype of a m × 65 mm brick (JIS standard dimensions) was produced.

Table 1 summarizes the physical properties measured for each of the prototype bricks. In Table 1, the apparent porosity, water absorption, bulk specific gravity, and apparent specific gravity are values measured by a water immersion method, and the air permeability K is 50 m cut from a prototype brick.
Using a test piece of mx 50 mm x 50 mm, the cross-sectional area of ventilation A
(Cm ² ), the air pressure difference ΔP (cmH ₂ O) when the sample thickness is L (= 50 mm), and the air flow rate Q (cc /
sec) is measured and K = L × Q / (A × ΔP).

The thermal shock resistance was measured by inserting one end of a regular-sized brick (114 mm × 65 mm surface side) into an electric furnace maintained at 1400 ° C. for 15 minutes, removing it, and allowing it to cool in air. Evaluation was made by the number of insertions of the brick until the portion was lost by 5% or more (method prescribed in the DIN method). The results are shown in Table 1. The hot bending strength of each brick was 40 mm × 40 mm × 160.
cut out mm bending test piece, and the average value was obtained by measuring four point bending strength at 1500 ° C. in a fulcrum between distance 1 300 mm.

[0021] For coating adhesion, and processing each brick hollowed with a diameter 50 mm, a disk-shaped test piece height 30 mm, then the powder of Portland cement 5
A mixture of ₄ % by weight of KCl and 6% by weight of K ₂ SO ₄ was formed into a disk having a diameter of 50 mm, and placed on the above-mentioned test piece and placed in an electric furnace maintained at 1530 ° C. Then, the cement mixture in a semi-molten state was heated for about 10 hours, and the adhesion property to the test piece was examined (commonly called a button method). In other words, after removing the test piece from the electric furnace and allowing it to cool, the coating that adheres to the surface of the test piece is not exfoliated when a force of 10 kg is applied from the lateral direction, and the same force is applied. Those peeled when added to the portion were evaluated as poor, and the results are shown in Table 1.

[0022]

[Table 1]

Examples 2 to 4 in Table 1 are examples of the present invention, and others are comparative examples. As can be seen from Table 1, in Examples 1 and 6 in which electrofused magnesia clinker A was not blended, the coating adhesion was lower than in Examples 2, 3, 4, and 5 in which electrofused magnesia clinker A was blended. Inferior. However, the blending amount of electrofused magnesia clinker is 5
The refractory of Example 5 as large as 5% by weight has low thermal shock resistance and is not suitable for practical use.

From the above test results, the bricks (refractory) of Examples 2 to 4, which are examples of the present invention, have physical properties including thermal shock resistance in a numerical range suitable for practical use as a refractory, In addition, 5 to 40% by weight of electrofused magnesia clinker A incorporated in the refractory contains 0.5 to 3% by weight of CaO and S
The iO ₂ by those containing 0.5 to 3 wt%, it is found that the coating adhesion to the refractory of the semi-molten cement clinker is excellent at high temperatures.

[0025]

The magnesia chromium-based refractory of the present invention comprises:
Physical properties of refractories including thermal shock resistance are practically preferable, and when used for lining high-temperature parts of cement rotary kilns, cement clinker in a semi-molten state has good coating adhesion to refractories. is there. Therefore, a cement rotary kiln magnesia chrome refractories lined on the high temperature portion of the present invention exhibits a coating adherent to lining Ri <br/> refractory is stabilized, also excellent useful as a cement rotary kiln, Kosutopafu It has excellent performance.

Claims (3)

(57) [Claims] 1. A with chromium ore 20 to 40 wt% and a sintering magnesia clinker 20-75 wt%, 0. 5
~ 3 wt% CaO and 0 . Magnesia chrome refractories which comprises 5 to 40% by weight of fused magnesia clinker including the 5 to 3% by weight of SiO _2. 2. Peliclay in electrofused magnesia clinker
Claim average crystal grain size of's crystal is 100μm or more 1
A magnesia chromium refractory according to item 1. 3. A cement rotary kiln characterized in that the magnesia chromium refractory according to claim 1 or 2 is lined in a high temperature part.