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Explanation of some problems about integral casting materials and masonry of ladle

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Explanation of some problems about integral casting materials and masonry of ladle

Answer: The main methods of ladle refining are: slag washing, vacuum, stirring, heating, spraying (including wire feeding and shot peening). At present, the commonly used refining methods at home and abroad are nothing more than the single use or combined application of these methods. The specific methods are shown in the following table 1-1

refractory castable raw materials1

refractory castable raw materials
Note: The symbol “+” indicates the means that can be added and the metallurgical function that can be obtained.

*LF is called LFV after adding vacuum means, which has the same refining means and metallurgical functions as SKF.

 

How is the mixed masonry of the ladle carried out?

Answer: The mixed masonry methods of ladle are divided into:

(1) fiber felt for thermal insulation layer, high alumina brick for permanent layer, aluminum-magnesium castable for working layer;

(2) fiber felt for thermal insulation layer, aluminum-magnesium for working layer High-quality castable;

(3) fiber felt for thermal insulation layer, lightweight high-aluminum castable for permanent layer, bricks for working layer (such as magnesia carbon and brick aluminum-magnesia carbon);

(4) fiber felt for thermal insulation layer, Permanent layer uses high-aluminum self-flowing castable, working layer (such as: magnesia carbon and brick aluminum-magnesia carbon) bricks;

(5) but considering the working layer (such as: a slag line uses magnesia carbon brick, other parts are cast with aluminum-magnesium Material, b slag line uses magnesia-carbon bricks, and other parts of the aluminum-magnesium-carbon bricks should also be a kind of mixing method. The typical mixing method is slag-line magnesia-carbon bricks, and aluminum-magnesium castables are used for low corrosion areas. Masonry slag When lining magnesia carbon bricks, pay attention to the following two points: A. When pouring the ladle wall, measure the slag line part and stop pouring; B. Smooth the ladle wall castable, and use fire mud to put the bricks layer by layer after solidification The masonry is good.

The temperature of the steel shell after the molten steel is poured into the ladle. Explained separately from the three types of bricklaying, integral pouring and comprehensive masonry.

Answer: We know that in order to meet the needs of continuous casting, molten steel must have a certain temperature, especially for refining ladle. Maintaining a certain temperature is a prerequisite for completing the refining operation. However, in the actual operation process, the phenomenon of molten steel radiating heat to the outside through the steel shell is inevitable. We often make up for the temperature loss in two ways: one is to increase the tapping temperature, and the other is to take heating measures after the furnace.

Due to different types of smelted steel, different smelting methods, and different ladle structures and refractory materials, the temperature of the outer surface of the steel cladding is also different, but the premise must be that the surface temperature of the cladding is less than the creep temperature of the cladding material. Generally, it should be less than 300~350℃ to prevent the occurrence of bag wearing accidents. According to experience, the cladding temperature of the brick-built ladle is between 300 and 320℃; the temperature of the integrally cast ladle is below 280℃; the cladding temperature of the mixed steel is 330-340℃.

What is the basis for the selection of brick ladle and integral casting ladle?

Answer: Due to differences in metallurgical processes, operating conditions and application concepts, the lining materials of ladle in different regions and different steel plants are very different. The following four aspects are considered in terms of economy, practicality, smelting method and slag composition:

(1) From economic considerations. Under the same smelting conditions, the general brick ladle refractory material is expensive, the construction consumes a lot of manpower and material resources, and the cost per ton of steel is high. However, the price of the cast ladle refractory material is relatively cheap, the construction consumes less manpower and material resources, and the cost per ton of steel is low.

(2) Considering practicality. Under the same smelting conditions, integral casting is often used for small and medium-sized ladle. Because the overall pouring is simple and quick, and the use of sleeve pouring can shorten the ladle on-line time, increase the turnover rate, reduce the consumption of refractory materials, increase the package service, and reduce the cost of steel per ton.

(3) Consider from the method of smelting. Currently, ladle smelting methods are different. The tapping temperature of the molten steel connected to the ordinary ladle is low, and the residence time of the molten steel is short. After a simple furnace treatment, it reaches the continuous casting platform. The requirements for refractory materials are relatively low, and the integral cast aluminum-magnesium castable can meet the needs. However, the inner lining of refined ladle is often in an environment of heating, stirring, vacuum, slag washing, and spraying, which has strict requirements on refractory materials: high temperature resistance, erosion resistance, corrosion resistance, peeling resistance, thermal shock resistance, low porosity, high Density etc. Especially at the slag line, the requirements for refractory materials are more stringent. This requires some high-grade materials for the working layer: such as MgO-C bricks, MgO-Al2O3-C bricks, MgO-Cr2O3 bricks, magnesia-calcium bricks, etc.

(4) Consider from the slag composition. The slag composition of ordinary ladle and refined ladle is different. The slag of ordinary ladle comes from the final slag of converter or electric furnace and belongs to the CaO-MgO-FeOn-SiO2 system; the slag composition of refined ladle generally includes SiO2, CaO, It is composed of MgO, Al2O3, FeOn, MnO, Cr2O3, and its composition only depends on the slagging agent. These oxides will chemically react or dissolve in equilibrium with the chemical components in the refractory material of the working layer at a certain temperature, resulting in erosion of the working layer. When selecting the working lining, it is necessary to avoid the above two reactions of slag and refractory materials.

What are the factors that affect the life of the ladle? Please explain.

Answer: Mainly include: lining material, ladle lining structure design and refractory material selection, construction method and process control, smelting process, converter or electric furnace final slag control, slagging agent, molten steel composition, hot repair and other factors.

What is the corrosion mechanism of the slag line of the ladle? How to determine the upper and lower slag line?

Answer: The damage to the magnesia carbon brick of the refining ladle slag line is firstly the oxidation of carbon in the hot surface of the working lining to form a thin decarburization layer. The oxidation of carbon is due to the continuous iron oxide in the slag and O2 in the air. The result of oxidation of CO2, SiO2, etc., and the gasification of carbon by MgO dissolved in molten steel or bricks; followed by high-temperature liquid slag penetration into the pores of the decarburized layer or cracks caused by thermal stress , It reacts with the magnesium oxide in the brick to form a low-melting compound, causing the surface layer of the brick to change and weaken, and fall off layer by layer under the stress of strong steel slag agitation, mechanical erosion, etc., resulting in the damage of the magnesia carbon brick, and so on: Oxidation → decarburization → porosity → erosion → erosion → shedding → damage.

The method of determining the upper and lower slag lines: find the slag line area, the upper slag line is the part above the interface between slag and molten steel; the lower slag line is the part of the slag line below the interface between slag and molten steel. From the ladle after pouring steel, The upper slag line is more eroded than the lower slag line, and a ring zone will be formed in the upper slag line area.

What is the effect of the in-situ generation of aluminum-magnesium in the aluminum-magnesium castable and the direct addition of aluminum-magnesium spinel during the production process on the corrosion resistance and penetration resistance of the castable?

Answer:

(1) Al-magnesium spinel is pre-introduced into the ingredients during production. It has no obvious hydration reaction with water. It has good volume stability during health maintenance or baking stage. The high-temperature flexural strength, thermal shock resistance and expansion resistance are better than the aluminum-magnesium castable that generates the aluminum-magnesium spinel in situ;

(2) The aluminum-magnesium castable that generates the aluminum-magnesium spinel in situ, because the needle-shaped MA is evenly staggered in the matrix, it can prevent the penetration of slag. For the pre-introduced aluminum-magnesium spinel castable, the slag can easily migrate around the particles, and the corrosion resistance and permeability resistance are not good.

How to judge the initial setting time and final setting time of aluminum-magnesium castables?

Answer: After the unshaped refractory is mixed with water or liquid binder, the property of the mixture gradually losing thixotropy or plasticity and being in a solidified state is called coagulation, and the time required for this process is called coagulation time. The time when the mixture starts to change from visco-plastic or visco-plastic-elastomeric to plastic-elastomeric is the initial setting time, and the time from plastic-elastomeric to elastomeric is the final setting time.

Judgment method of initial setting time: hold the material in hand to form a mass, twist it a few times in the hand, and disperse the material into lumps; there is no flow value when measuring the flow value.

Judgment method of final setting time: The material is completely solidified into a fixed shape, and the material block must be forced to break apart. The section is the aggregate surface.

In order to meet the requirements of construction operation time, it is generally required that the initial setting time should not be earlier than 40min, and the final setting time should not be later than 8h.

Please explain the respective baking systems and baking curves of brick ladle, pouring ladle, and comprehensive masonry ladle.

Answer: (1) Ladle baking system for integral pouring (summer): low-fire baking time: temperature <300℃, 24 hours; medium-fire baking time: temperature 300~600℃, 20 hours; high-fire baking time: Temperature 600~800℃, 12 hours; Temperature 800~1000℃, 8 hours.

Ladle baking system for integral pouring (winter):
Low-fire baking time: temperature <300℃, 36 hours; medium-fire baking time: temperature 300~600℃, 36 hours; high-fire baking time: temperature 600~800℃, 24 hours; temperature 800~1000℃, 8 hour.

Where is the installation position of the breathable brick in the ladle?

Answer: When selecting the position of the blowing element at the bottom of the ladle, it should be determined according to the purpose of ladle processing. The water model test shows that the air-permeable bricks installed at the center of the ladle bottom and deviated from the center of the ladle (the blowing point is at a radius of 1/2 to 1/3 from the center of the ladle) have different mixing effects on molten steel. Blowing is conducive to the reaction between the slag and gold in the ladle and the desulfurization reaction of the top slag, while the eccentric bottom blowing is conducive to the mixing of molten steel in the ladle, the homogenization of the temperature and the floating of inclusions.

Therefore, for the purpose of uniform molten steel composition, temperature and promotion of inclusions floating up, breathable bricks should be installed at a distance of 1/2 to 1/3 radius from the bottom of the bag (subject to the lining of the bag), and avoid impact The area is located on both sides of the vertical center line of the bottom of the package with the nozzle block bricks.

What is the effect of moistening the peeled surface material with water before pouring the peeling sleeve?

Answer: The role of water spray:

(1) When re-pouring, prevent the dry original layer from absorbing the moisture of the new pouring material, which will affect the construction performance;

(2) Wetting the original layer is conducive to forming a close combination with the new castable, and is conducive to sintering at high temperature to form a whole;

(3) suppressing dust and improving the construction environment;

(4) accelerating the cooling effect.

What is the cause of the erosion of the ladle castable by the slag?

Answer: The process of slag erosion is mainly the melting process of the castable into the slag and the process of the slag intruding into the castable. During the intrusion process, the slag agent composition reacts with the refractory material to form a metamorphic layer. As the molten slag penetrates into the castable and expands its reaction area and depth, the composition and structure of the material surface and nearby undergo qualitative changes, forming a metamorphic layer with high solubility and accelerating damage. In the end, the permeable layer after the structural change is peeled off due to the differential expansion.

How to position the tire mold at the center of the bottom of the new ladle for pouring the new ladle?

Answer: In the actual application of the ladle, the erosion of the ladle wall is irregular, and it is difficult to determine the center and radius at the bottom of the ladle. At this time, the center can be determined from the top of the ladle:

(1) First take a line equal to the diameter of the ladle and take another A line with a heavy hammer at one end is used as the vertical center line of the first line. The point of the heavy hammer is the center of the circle, and the circle is made with the radius of the fetal membrane; then the fetal membrane is hoisted into the ladle to match the circle made. Sit together.

(2) First hoist the fetal membrane into the ladle, measure the thickness of the bag wall, and calibrate it with a hoist.

How to evaluate the performance of ladle castable after use?

Answer: Consider from two aspects:

(1) Construction performance: water addition, flow value, initial setting time, final setting time, ease of demoulding, and whether there are cracks after baking;

(2) Use performance: the peeling resistance of the package wall, the erosion resistance of the side wall of the breathable brick, the erosion resistance and erosion resistance of the slag line, the erosion resistance and erosion resistance of the impact area of the bottom of the package;

Combining the above aspects, can we reasonably evaluate the comprehensive performance of ladle castables.

What data need to be recorded in the field test?

(1) Before the ladle goes online: water addition, initial setting time, final setting time, demolding time, natural curing time, baking time, wall thickness of ventilated brick side/to bread wall thickness, side slag line thickness of ventilating brick/opposite Thickness of slag line, thickness of impact zone at the bottom of bag/thickness of non-impact zone at the bottom of bag:

(2) Ladle online: Ladle serial number, number of furnaces used in ladle, steel connection time, argon blowing time after furnace, pouring time of continuous casting platform, turnover time, intermittent time:

(3) After the ladle is off the assembly line: bag wall residual: (residual thickness of the side wall of the ventilating brick/residual thickness of the bread wall), residual thickness of the slag line (residual thickness of the slag line on the side of the ventilating brick/residual thickness of the opposite slag line), and bottom of the bag Residual thickness (residual thickness in the impact area of the bottom of the bag / residual thickness in the non-impact area of the bottom of the bag).

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