JPH054861A - Refractory brick of magnesia carbon - Google Patents

Abstract

PURPOSE:To obtain magnesia carbon refractory brick useful for lining of smelting device of metal, having excellent heat spalling properties. CONSTITUTION:Magnesia carbon refractory brick having a main blending composition of refractory brick consisting of 50-99.5wt.% magnesia-based refractory, 0.5-5.0wt.% content of mesophase-containing pitch powder and graphite and at least 0.5-15wt.% mesophase-containing pitch powder. The magnesia carbon refractory brick contains metal powder as other blending composition, may be impregnated with pitch or tar during or after burning and mesophase in a liquid crystal state has viscosity and forms strong carbon bond to relax thermal stress and to improve heat spalling properties of refractory brick.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnesia carbonaceous refractory brick having excellent heat spalling property used for lining metal refining equipment.

[0002]

2. Description of the Related Art Generally, a magnesia-carbon refractory brick, which is a mixture of refractory materials such as magnesia and dolomite with carbon as an aggregate, has excellent thermal spalling property regardless of whether it is fired or unfired. Is often used in. However, since carbon is easily oxidized in a high temperature region, various carbonaceous refractory bricks to which metal powder is added have been proposed in order to prevent oxidation of carbon and improve hot strength.

Japanese Unexamined Patent Publication (Kokai) No. 54-39422 discloses a carbon-containing fired refractory in which a refractory raw material powder and carbon or a carbon-containing substance are mixed with a metal powder having a higher oxygen affinity than carbon at high temperatures. Further, Japanese Patent Application Laid-Open No. 54-163913 discloses a carbon-containing unfired refractory in which a refractory raw material powder and carbon or a carbon-containing substance are mixed with a metal powder having a higher oxygen affinity than carbon at high temperature. .

[0004]

Carbon has a high heat transfer coefficient, and the blending of carbon greatly affects the physical properties of refractory bricks. Carbon absorbs stress due to expansion and contraction of the brick structure due to repeated heating and cooling, and improves the heat spalling property of the refractory brick. However, if the carbon content is excessive, the carbon is likely to be oxidized, and the elastic modulus of the brick structure lowers, resulting in brittleness and reduced corrosion resistance.

In conventional carbon-containing refractory bricks,
Although the improvement of heat spalling property is recognized as compared with the refractory bricks that do not contain carbon, it is not sufficient, and the fire resistance with higher heat spalling property is particularly high in hot spots in refining equipment, especially where it is exposed to high temperatures. Brick is required.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention uses a magnesia-based refractory material and a carbon-based refractory material as a main compounding composition of magnesia.
In carbonaceous refractory bricks, the magnesia-based refractory material: 50-99.
5wt%, the total amount of mesophase containing pitch powder and graphite
Disclosed is a magnesia carbonaceous refractory brick having an excellent thermal spalling property, characterized by containing 0.5 wt% to 50 wt% of at least mesophase-containing pitch powder: 0.5 to 15 wt%.

The mesophase is generated by heat-treating the pitch, and the carbon molecules are oriented in a certain direction, and the orientational order imparts strength so that it is expressed in the solid phase, but it is strong enough to suppress fluidity. It is a non-liquid crystalline substance and has a high degree of optical anisotropy. The pitch containing this mesophase has a high softening point of about 400 ° C, compared to about 150 ° C for a normal pitch, and when it exceeds the softening point, bonding between the mesophases proceeds rapidly to form a carbon bond. The carbon bond of this mesophase has a flow structure, is rich in elasticity and fluidity, has high viscosity, and has a strong bonding force, so that the thermal stress generated by heating is relaxed and the thermal spalling property is improved.

If the amount of the mesophase-containing pitch powder blended is less than 0.5 wt%, there is no effect of improving the heat-resistant spalling property, and if it exceeds 15 wt%, impurities such as ash and volatile matter contained in the pitch powder are heated. May result in voids, which is not preferable because of lack of hot strength. When the particle diameter of the mesophase-containing pitch powder exceeds 0.1 mm, it becomes difficult to uniformly disperse the mesophase-containing pitch powder in the refractory brick structure.

As described above, since the mesophase-containing pitch powder contains a small amount of ash and volatile matter, voids may occur in the brick structure due to these impurities. Therefore, in order to minimize the generation of voids, it is preferable to use graphite in combination as the carbon-based refractory material.

Further, carbon is easily oxidized at a high temperature, and the addition of a metal powder having a higher oxygen affinity than carbon suppresses the oxidation of carbon, prevents the brittle structure from being weakened by the oxidation of carbon, and improves the heat spalling property. Make it noticeable. Particularly when high hot bending strength is required in a high temperature range of 1400 ° C or higher, the addition of metal powder is effective. As the metal powder, one or a combination of two or more metal powders selected from Al, Si, Ca, Mg, Fe or Cr, or alloys thereof are added within a range not impairing the function as a refractory. Preferably.

Further, depending on the part of the refractory brick used in the refining equipment, the magnesia-carbon refractory brick is dried and then fired in a non-oxidizing atmosphere at 1500 ° C. or less, or the fired magnesia-carbon refractory. It is also preferred that the refractory brick is impregnated with pitch or tar.

[0012]

[Function] Pitch powder containing mesophase has a softening point of about 400
It is as high as ℃, and when it exceeds the softening point, the bonding between the mesophases proceeds rapidly, forming carbon bonds. The carbon bond produced by carbonization of an organic binder found in conventional carbon-containing refractory bricks is glassy and has excellent strength, but it has a brittle property.On the other hand, the carbon bond produced by this mesophase has a flow structure with elasticity and fluidity. Rich in properties, highly viscous, and has a strong binding force.

Therefore, by using the mesophase-containing pitch powder as the carbon-based refractory material, a strong carbon bond is formed in the brick structure, and the thermal stress generated by the expansion of magnesia due to heating is absorbed and alleviated, whereby the refractory brick is manufactured. Improves heat spalling.

Further, if a part of the carbon contained in the refractory brick is mesophase carbon, the above-mentioned thermal stress relaxation effect can be obtained. Therefore, high-purity graphite having a large fixed carbon content is also used as the carbon-based refractory material. By,
Generation of voids due to impurities contained in the mesophase-containing pitch powder can be minimized.

When high hot bending strength is required in a high temperature region, addition of a metal powder having a higher oxygen affinity than carbon suppresses the oxidation of carbon and prevents brittleness of the brick structure due to oxidation of carbon. be able to.

If it is expected to be used in the temperature range of 400 to 800 ° C., the refractory brick should be fired at an appropriate temperature in advance to form a carbon bond effective for improving the heat spalling property. Good. Further, impregnation with pitch or tar to fill the voids generated by firing is effective in improving the heat spalling property.

[0017]

EXAMPLES Next, specific examples of the present invention will be described.

In order to obtain a desired magnesia-carbon refractory brick having excellent thermal spalling properties, it is preferable to use a magnesia-based refractory material used in the present invention having a high purity of MgO component of 99% or more. If the amount of impurities is large, a low-melting material is likely to be formed, which causes deterioration of the corrosion resistance of the obtained refractory brick. Also, the carbon-based refractory material of the mesophase-containing pitch powder and graphite is also preferably a fixed carbon content of 85% or more, and if it is less than 85%, a large amount of impurities will cause a gap around the aggregate, resulting in a fire brick Physical properties deteriorate. In this example, mesophase-containing pitch powder and scaly graphite with a fixed carbon content of 99% were used together as the carbon-based refractory material. The pitch powder containing mesophase has a particle size of 0.1 mm or less and a softening point of about 400 ° C, and the composition of components is fixed carbon: 85%, ash: 0.5%, volatile: 14.5%. If a part of the fixed carbon contained in the pitch powder is mesophase carbon, the thermal spalling property is improved, and about 35% (about 41% of the fixed carbon) of the pitch powder used is mesophase carbon. .

The metal powder is also preferably of high purity.

Magnesia / carbonaceous refractory brick of the present invention having excellent heat spalling resistance (hereinafter referred to as the present invention product)
In the preparation of, each raw material was blended in the blending ratio shown in Table 1, phenol resin was mixed as a binder, kneaded with a fret mixer, and molded by a friction press machine. The obtained molded body was dried at 150 ° C for 24 hours to obtain a refractory brick. Further, No. 13 was fired at 1200 ° C. in a non-oxidizing atmosphere for 5 hours, and No. 14 was fired at 1200 ° C. in a non-oxidizing atmosphere for 5 hours, and then impregnated with pitch. Further, as a comparative example, the mixing ratio deviates from the present invention, a magnesia-carbon refractory brick (hereinafter referred to as a comparative product), a conventional example of a magnesia-carbon refractory brick containing no mesophase-containing pitch powder (hereinafter referred to as a conventional product) ) Were prepared in the same manner as in the present invention, and their compounding ratios are shown in Table 1.

In Tables 1 and 2, () indicates the total amount of magnesia, mesophase-containing pitch powder and scaly graphite.
It represents the blending amount of 100% by weight. With respect to these magnesia / carbonaceous refractory bricks, heat spalling resistance (visual and elastic retention rate), corrosion resistance, and bending strength were measured by the methods described below, and the results are also shown in Tables 1 and 2. .

[Table 1]

[Table 2]

[Thermal Spalling Property] The thermal spalling property was evaluated by the following two methods. (Visual inspection) A 40 × 40 × 114 mm test piece was cut out from a parallel-shaped refractory brick, the 40 × 40 mm surface was immersed in molten steel at 1650 ° C to a depth of 40 mm, held for 5 minutes, then taken out, and heated at room temperature for 30 minutes. Forced air cooling with compressed air. This cycle was repeated 15 times, and the degree of cracking was visually evaluated relatively as follows. ◎: No cracks ○: Fine cracks △: Large cracks ×: Peeling off

(Elasticity Maintenance Ratio) The elastic moduli were measured before and after the above-mentioned visual heat spalling property test, and these ratios were taken as the elastic maintenance ratios. The elastic modulus was 114 mm, the ultrasonic wave transmission time was measured, and the elastic maintenance ratio was calculated by the following formula. Elasticity retention rate = T ₁ / T ₂ × 100, where T _{1 is the} transmission time after the heat-resistant spalling property test (visual) T ₂ is the transmission time before the heat-resistant spalling property test (visual). When the cracks are generated in the brick structure by repeated heating and cooling to form voids, the ultrasonic wave transmission time is delayed, and thus the larger the elastic maintenance rate, the better the heat spalling property.

[Corrosion Resistance] A trapezoidal pillar-shaped test piece was cut out from a parallel-shaped refractory brick and lined in a drum, and an oxygen-propane flame was blown in the axial direction of the drum while rotating the drum to heat it to 1650 ° C. While the drum was heated, a basic slag of C / S (CaO / SiO ₂ ) = 3 was added as an erosion agent and erosion was performed for 15 minutes. Then drain the erosion agent,
Forced air cooling was performed with pressurized air at room temperature for 15 minutes. This cycle from heating to forced air cooling was repeated 10 times with the erosion agent replaced, and the test piece was cut to measure the amount of erosion loss in mm units.The conventional product No. 21 was set to 100% and the wear ratio was expressed as a percentage. Indicated. The smaller this wear ratio, the better the corrosion resistance.

[Hot bending strength] From a refractory brick having a parallel shape
A 20 × 15 × 114 mm test piece was cut out, heated at 1400 ° C. for 1 hour in a coke breeze, and the maximum load was obtained by a load three-point bending method with a span length of 100 mm on a 20 × 114 mm plane. The larger the maximum load, the better the hot bending strength.

As is clear from Tables 1 and 2, the products of the present invention to which mesophase-containing pitch powder is added as a carbon-based refractory material are all excellent in heat spalling property.
Even if the mesophase-containing pitch powder content is within the range of the present invention as in Comparative Product No. 15, if the content of scaly graphite is too large and deviates from the range of the present invention, thermal spalling is performed. Even if it has excellent properties, the hot bending strength will be low,
The function as a refractory brick is low.

Further, in order to clarify the effect of adding the mesophase-containing pitch powder, it was tested by the method described below.

Refractory bricks having different blending ratios of mesophase-containing pitch powder were prepared with the carbon-based refractory material (mesophase-containing pitch powder and scaly graphite) being mixed in a constant amount, and the elastic maintenance factor was measured by the same method as described above. The carbon-based refractory material was tested for the total amount of mesophase-containing pitch powder and scaly graphite of 7 wt%, 15 wt%, and 35 wt%. Tables 3 to 5 show the blending compositions, and FIGS. 1 to 3 show the relationship between the blending amount of mesophase-containing pitch powder and the elastic maintenance rate.

[Table 3]

[Table 4]

[Table 5]

As is clear from Tables 3 to 5 and FIGS. 1 to 3, the elastic maintenance ratio increases and the thermal spalling property improves as the blending amount of the mesophase-containing pitch powder increases. To be

[0030]

EFFECT OF THE INVENTION By using mesophase-containing pitch powder as a part of the carbon-based refractory material, a magnesia-carbonaceous refractory brick excellent in heat spalling property could be produced.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the mesophase-containing pitch powder blending amount and the elastic maintenance rate when the carbon refractory material blending amount is fixed at 7 wt%.

FIG. 2 is a graph showing the relationship between the blending amount of mesophase-containing pitch powder and the elastic maintenance rate when the blending amount of carbon refractory material is fixed at 15 wt%.

FIG. 3 is a graph showing a relationship between the blending amount of mesophase-containing pitch powder and the elastic maintenance ratio when the blending amount of carbon refractory material is fixed at 35 wt%.

Claims (4)

[Claims] 1. In a magnesia-carbonaceous refractory brick having a magnesia-based refractory material and a carbon-based refractory material as a main blending composition of its raw materials, the total amount of these main blending compositions is 100 wt%, and the magnesia-based refractory material is: 50-99.5
wt%, the total amount of mesophase-containing pitch powder and graphite is 0.
A magnesia carbonaceous refractory brick, characterized in that it is 5 to 50 wt% and contains at least mesophase-containing pitch powder: 0.5 to 15 wt%. 2. The composition containing Al, Si, Ca, Mg, Fe or
The magnesia carbonaceous refractory brick according to claim 1 or 2, which contains one or a combination of two or more kinds of metal powders selected from Cr or an alloy thereof. 3. The magnesia-carbon refractory according to claim 1, wherein the magnesia-carbon refractory brick is dried and then fired in a non-oxidizing atmosphere at 1500 ° C. or lower. brick. 4. The magnesia carbonaceous refractory brick is dried, then fired in a non-oxidizing atmosphere at 1500 ° C. or lower, and further impregnated with pitch or tar. Magnesia carbon fireproof brick described in any of the above.