What are the refining methods 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
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?
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?
What is
the cause of the erosion of the ladle castable by the slag?
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;
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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