Why do nickel-iron alloy furnace lining refractories choose magnesium-chromium?

March 06, 2021

Nickel-iron alloy refining converters and copper-smelting converters are similar in structure, tuyere arrangement, blowing, smelting temperature, and slag composition. The lining of the nickel-smelting converter also has problems similar to those encountered in copper-smelting converters, and various factors have caused damage to the refractory materials. The refractory life in the tuyere area is only one-third of that of other parts. The erosion of the refractory material in this part is mostly mechanical impact and slag penetration erosion. Therefore, we have studied the suitable refractory materials for these characteristics by adding chromium micropowder to the magnesia to form a magnesia-chrome refractory material to resist slag erosion, thereby extending the service life of the nickel alloy charge.
1 test

1.1

raw material

Using medium-grade sintered magnesia as aggregate, adding medium-grade sintered magnesia, Cr2O3, silica micropowder, plus different proportions of silicon carbide aggregate, CA-50 cement as binder, and Sodium Tripolyphosphate as subtraction Aqueous agent.

The chemical composition and sample distribution of the main raw materials are shown in Table 1 and Table 2.

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Table 1 Chemical composition of raw materials
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Table 2 Experimental formula

1.2

Sample preparation and testing

The aggregate, the powder, the binder and the water reducing agent are accurately weighed according to the formula, and the prepared aggregate is poured into the mixer to be uniformly mixed, and then the powder, the binder and the water reducing agent are added and then dry mixed for 60 seconds. Add the vector water temperature for 120 seconds, discharge, and mix the uniform warm material into the mold quickly. During the vibration process, add the material according to the amount, until the bubbles appear, the slurry will appear, and the formed sample will be naturally cured. After the hour, the mold was released, and the sample after demoulding was cured at room temperature for 24 hours. The cured sample was placed in a dry box and dried at 110 ° C for 24 hours, and then fired in a high temperature electric furnace at a firing temperature of 1500. °C, holding time is 3 hours.

1.3

Performance Testing

The bulk density and apparent porosity of the sample after drying and burning were measured by the drainage method. The pressure resistance test was carried out by the WHY-600 microcomputer-controlled automatic hydraulic pressure testing machine, and the DKZ-6000 cement electric bending test machine was used for bending resistance. For strength testing, the slag resistance was tested by static enthalpy method.

2 Results and discussion

Each sample was subjected to a normal temperature and high temperature heating test to obtain the following table data.

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Table 3 Sample performance test data after 110 ° C * 24 h
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Table 4 Sample performance test data after 1500 ° C * 3 h

It is found from Tables 3 and 4 that the overall performance of the second formulation in the first scheme is relatively stable, and the values ​​of body density, flexural strength, compressive strength, apparent porosity and firing rate before and after the high temperature heating of the second formulation are There is not much variation and fluctuation before and after heating at high temperature.

2.1 Permanent line rate of change

Magnesia-chromium refractories Due to the increase of chrome green powder, the permanent line change of the material first decreases and then increases, and the permanent line change rate of the chrome green fine powder of Formula 1 is 4%.

2.2 Analysis of bulk density

The bulk density of the magnesia-chromic refractory material after firing becomes larger, because the liquid phase is generated during the firing process, and the liquid phase is filled into the voids, and the magnesia-chromic refractory material of the third formulation is found to have the largest bulk density. .

2.3 apparent porosity

After the magnesia-chromium refractory material is heated at 1500 °C*3 h and high-aluminum refractory material at a temperature of 1350 °C*3 h, it is obvious that the apparent porosity of the refractory after firing is significantly higher than that of the post-drying.

2.4 Normal temperature flexural strength

After the magnesia-chromium refractory material is heated at 1500 °C*3 h and high-alumina refractory material at a temperature of 1350 °C*3 h, the strength of the magnesia-chromium refractory material decreases, the structure becomes loose, and the bending strength decreases. When the amount of chrome green powder added in Formula 3 is 8%, the flexural strength is the largest.

2.5 坩埚 method test slag corrosion resistance

First, 140 g of nickel-iron alloy slag was separately charged into the dried magnesia-chromium slag pot and the high-aluminum slag pot, and then the magnesia-chrome slag pot was heat-treated at 1500 ° C for 3 h. Finally, it was found that the bottom of the magnesia-chrome slag tank was eroded to a thickness of 10 mm, and the chromium was oxidized at 1500 ° C, which was formed in an acidic and semi-acid atmosphere. This was beneficial to increase the viscosity of the slag and inhibit the slag during slag attack. Continue to erode into the brick, and form a buffering transition layer between the dense layer of the reaction zone and the internal loose layer, which is beneficial to improve the slag corrosion resistance of the magnesia chrome brick and reduce the structural spalling erosion of the magnesia chrome brick. .

3 Conclusion

1) With the increase of CA-50 cement addition and the decrease of silica micropowder addition, the flexural and compressive strength of high alumina refractories increases, when CA-50 cement is added 4%. When the amount of silica fine powder added is 8%, the slag resistance of the high alumina refractory material is relatively good.

2) With the increase of the amount of chrome green micropowder, the flexural strength and compressive strength of magnesia refractory materials are reduced. When the amount of chrome green micropowder is 6%, the slag resistance of magnesia chrome refractories is better. .

3) Magnesia-chromium refractory material has good slag corrosion resistance, because magnesia-chromium refractory material should be used as the lining of nickel-iron alloy furnace.

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