Sliding plate is the core component of ladle sliding spout, which is the component that directly controls steel pouring and determines the function of sliding spout. If the sliding plate leaks steel in the process of steel pouring, it will cause the continuous casting to break pouring, or cause the vicious accident of burning out the continuous casting machine. Therefore, it is very important to explore the causes of steel leakage accidents between sliding plates and formulate preventive measures.
Analysis of the causes of steel leakage
1. Ladle Slide gate mechanical reasons
According to the formula P = N × μ × ΔX (where: P indicates that the ladle sliding mechanism provides the face pressure of the slide plate, N indicates the number of face pressure springs, μ indicates the spring coefficient of the face pressure spring, and ΔX indicates the compression of the spring at work), it can be seen that when the mechanism of the movable mold frame, the deformation of the fixed mold frame, or the wear and tear of the part of the loaded face pressure exceeds the specified value, the compression of the spring decreases within the specified face pressure loading stroke, and it can not produce Sufficient slide face pressure; and air cooling pipeline connection is not good, air pressure is not enough, pipeline occlusion, etc. caused by insufficient cooling, so that the spring performance is reduced or even failure, resulting in insufficient face pressure; steel static pressure is greater than the slide face pressure, the gap between the slide plate, resulting in pouring process between the slide plate leakage of steel.
2. Sliding plate operation and installation reasons
(1) The installation surface of the slide gate mechanism is not cleaned up debris, or the installation of the mouth of the use of too much refractory mud, excess mud is squeezed into the back of the skateboard, the appearance of the skateboard in the pressurized pressure is not uniform or produce the surface pressure is added to the full illusion, pouring process between the skateboard gaps.
(2) The face pressure of the ladle slide gate is not sufficient;
(3) For the continuous use of the slide plate does not recognize the reaming, hair pulling, clamping steel and other melt damage, resulting in excessive use of the slide plate.
3. the quality of the ladle slide gate itself
(1) Ladle slide gate material can not meet the requirements of steel pouring steel, ladle slide gate in the harmful components exceed the standard, resulting in increased thermal and chemical erosion of the slip sheet.
(2) Cracks in the use of the slide plate, and abnormal expansion, steel along the cracks on the slide plate to produce a “V” type melting damage, the outer edge of the ladle slide plate of the iron hoop offset or fracture, resulting in the use of the ladle slide plate in the process of cracking.
4.Reasons of ladle pouring operation
(1) When the lalde nozzle can not automatically open the pouring need to burn oxygen, in the slide plate is not fully open in place when the oxygen burn, will lead to serious burns on the slide plate surface, and even be burned through.
(2) When the multi-stream continuous casting machine from the normal multi-stream casting steel to single-stream or less stream casting steel, so that the contact surface of the lower slide surface and the steel than normal casting steel increased, and the larger the contact surface of the slide surface and the steel, the faster the steel erosion of the slide. When the slide plate surface erosion groove, the slide plate will produce a thicker layer of sandwiched steel; at the same time, single-stream pouring steel and lead to the slide plate flow control frequently, a short period of time, the number of full-stroke sliding times than the normal pouring of steel greatly increased, so that the slide plate surface of the furring intensified, and the damage to the surface of the slide plate intensified, which led to the leakage of steel.
5.Problems in steel smelting
Although the appropriate material of the ladle slide plate was selected, due to careless control of the steel in the smelting process, the components in the steel that have a strong erosive effect on the slide plate were severely overloaded, and the speed of thermo-chemical erosion of the slide plate was greatly accelerated, resulting in the leakage of steel from the slide plate in a short period of time. The following is a case of pouring calcium treated steel leakage steel after the residual slip plate (aluminum carbonaceous) analysis to discuss the thermochemical erosion of the slip plate.
Observation of the appearance of this residual slide gate found that the back of the upper slide gate is clean and free of debris, while the surface of the residual lower slip sheet has 2 erosion grooves of about 180mm long, 30mm wide and 10mm deep, the erosion grooves are yellowish-brown in surface color, and there are obvious honeycomb-like small holes. These 2 erosion grooves should be the channel for steel outflow. From this, it can be inferred that the abnormal thermochemical erosion led to serious damage to the slide surface. The thermochemical erosion process is as follows.
(1)Formation of decarburized layer
Carbon on the surface of the slide plate in the pouring temperature (1550 ~ 1600 ℃) is oxidized, the formation of decarburization layer, resulting in an increase in the porosity of the working surface of the slide plate, the strength is reduced, and its contact with the liquid steel, the liquid steel in the FeO, MnO, [Ca] through the pores to the slide within the diffusion, infiltration. The oxidation of carbon in the slide plate has three main pathways: one is the ladle water mouth repair burned oxygen is oxidized; the second is the pouring of steel in the steel water [O] oxidation of the slide plate ; the third is the pouring of steel due to the high-speed steel jet, from the upper and lower sliding plate gap between the inhalation of air on the oxidation of the slide plate.
(2) [Ca] on the destruction of the slide plate
In order to inhibit the Al2O3 in the middle packet immersed in the water mouth at the adhesion, tumor and block the water mouth, in the end of refining need to Ca treatment operation, generally add Ca alloy, such as Ca-Fe line, Ca-Si line, so that it reacts with the steel inclusions of Al2O3 to generate low-melting material, thereby changing the morphology of the aluminum oxide inclusions, with the bottom blowing argon bubbles rising and discharged from the liquid steel. However, when the Ca alloy added in excess, that is, its addition exceeds the amount required to react with Al2O3 in the steel, the excess [Ca] will accelerate the erosion of the slide. The erosion process is as follows: Al2O3 in the skateboard is first reduced by [Ca] in the steel to generate CaO and Al, and then generated CaO and then react with Al2O3 in the slide gate to form Al2O3-CaO system of low-melting-point compounds and washed away by the liquid steel.
Through the tracking of the [Ca] content in the steel water and the degree of erosion of the skateboard, it is found that: when the [Ca] content in the steel water (mass fraction, the same below) <0.003%, the main generation of high melting point CaO-3Al2O3 (melting point of 1850 ℃) and CaO-2Al2O3 (melting point of 1750 ℃), the erosive effect of the slide gate is weaker; when the [Ca] content of the steel water is 0.003% ~ 0.005%, the generation of part of the high melting point of CaO-3Al2O3, CaO-2Al2O3 and part of the low melting point of CaO-Al2O3 (melting point 1600 ° C) and 12CaO-7Al2O3 (melting point 1415 ° C), aggravation of the erosion of the slide gate plate; when the [Ca] content of steel water > 0.005%, the generation of a large number of 12CaO -7Al2O3 low melt and part of CaO-Al2O3, the erosion of the slide plate is very serious, which may lead to the slide plate leakage of steel in a short time.
Preventive measures for steel leakage accidents between ladle slide gate
(1) Strictly control the end point [Ca] content of steel.
From the CaO-Al2O3 system phase diagram, when the steel Ca, Al mass ratio > 0.10, Al2O3-like inclusions basically react with CaO into 12CaO-7Al2O3 or composition close to 12CaO-7Al2O3 low melt, thus easy to discharge from the molten steel. Therefore, in actual production, the control of the amount of calcium wire feeding is mainly based on the requirements of the steel Ca, Al quality ratio to control, but the following reasons may lead to fluctuations in the [Ca] content:.
a) feeding calcium line process ladle blowing argon amount is too large;
b) fluctuations in the amount of steel, did not adjust the amount of feeding line in a timely manner.
c) feed calcium line after premature sampling, steel mixing is not uniform, [Ca] content is not representative;;.
d) add steel core aluminum deoxidation, blowing argon is too small, steel mixing is not uniform or sampling too early, resulting in unrepresentative samples.
e) Calcium wire itself material fluctuations.
Therefore, in order to prevent [Ca] excess, feed calcium line must be temperature sampling, according to the amount of steel, steel temperature, steel [Als] content, calcium line of the collection rate and steel required by the Ca, Al quality ratio to control the calcium line feeding volume (tons of steel 3 ~ 4m), the bottom of the amount of argon blowing (50L-min-1) and feed calcium line temperature (1590 ~ 1605 ℃), to ensure that the end of the steel [Ca] content in the control of the endpoints. Ca] content is within the control range. (Note: Reference data for A steel grade is in parentheses).
(2) Strengthen the maintenance of the slide gate mechanism.
Check whether the mold frame of the mechanism is deformed; whether the surface pressure of the spring loaded sliding plate is appropriate; timely replacement of wear parts; frequent refueling of lubrication parts.
(3) According to the requirements of the steel type to determine whether the ladle slide plate can continue to be used.
Observe whether there is any deep hair pulling, cracks and abnormal fusion damage on the surface of the slide plate; determine whether the effective residual stroke of the ladle slide plate meets the requirements for re-use.
(4)Strictly in accordance with the operating points for the installation of the ladle slide plate.
Clean up the debris on the mold frame, working surface and back of the ladle slide plate; make the slide plate in full open state when burning oxygen.
(5)Operate carefully when pouring.
In the process of pouring steel, try to reduce the number of pulling of the ladle slide plate to reduce the possibility of wear and tear; for the intermediate package of multi-stream steel pouring, if there is more than 1/2 of the casting stream can not be poured, the continuous casting machine should stop pouring; should be satisfied with the normal control of the flow of the ladle slide plate as narrow as possible when the distance between the pulling of the slide plate in order to protect the slide plate of the effective residual stroke; in the end of the pouring period to prevent the slag under the water mouth, in order to prevent the slide plate of the unwanted erosion.
Conclusion
The reasons for steel leakage between ladle slide plates are manifold, and poor control of sliding gate machinery, slide plate installation operation, slide plate quality, ladle steel pouring operation, steel smelting and other aspects may lead to steel leakage between slide plates. For different reasons to formulate corresponding preventive measures, can reduce the chances of steel leakage of the ladle slide plate, improve the good slip rate of the ladle slide plate.