The ladle sliding gate is an important element of continuous casting, which is used to control the flow rate of steel from the ladle to the intermediate ladle to realize the smooth operation of continuous casting. The ladle lower nozzle is an important part of the sliding spout system, the lower end is connected to the long nozzle to realize the protection pouring and avoid the secondary oxidation of steel. In the process of using the ladle under the mouth of the transverse break, perforation, clamping steel, sticky steel and other problems, affecting the continuous casting production. This article analyzes the problems existing in the use of ladle lower nozzle.
Problems in the use of ladle lower nozzle
The ladle lower nozzle is prone to transverse cracks during steel pouring , which brings safety hazards to continuous casting operation. It is generally believed that the thermal stress in the lower spout is the main factor leading to its fracture, when pouring steel in the outer wall of the ladle lower nozzle to produce tensile stress, in the location of stress concentration is prone to cracking.
The external force on the ladle lower nozzle is another important cause of its fracture. The ladle lower nozzle is connected with the ladle mechanism, long nozzle and other parts, and the stress situation is more complicated. The lower end of the ladle lower nozzle is partially inserted into the bowl of the long nozzle. When the slide plate is opened at the beginning of pouring, when the slide plate controls the flow during pouring, and when the ladle slide plate is closed at the end of pouring, the ladle downspout is subjected to the transverse shear force from the ladle sliding mechanism, the long nozzle and the manipulator, which leads to transverse cracks in the downspout.
In order to avoid transverse cracks, take the following measures:
① Improve the thermal shock resistance of the material of the ladle lower nozzle;
② Increase the wall thickness of the ladle lower nozzle;
③ Improve the density and strength of the ladle lower nozzle;
④ Prevent the installation of the long nozzle incorrectly.
Sometimes, during steel pouring, a localized area of the ladle lower nozzle is damaged by melting, forming a hole through which the steel passes out , which seriously affects the normal operation of continuous casting.
Possible reasons for perforation:
(1)Sliding plate for a long time half-open pouring steel, steel in the underwater mouth of the serious bias flow, in the underwater mouth of the inner wall of the formation of spinning, local position scour erosion is serious, easy to form a pit, serious when the steel will be worn out from this position; also does not exclude the underwater mouth molding, local position is more loose, lower strength, easy to be eroded by the scouring of the possibility of erosion.
(2) Under the ladle lower nozzle in many times after use, undergoes the violent temperature difference, produces the thermal shock crack in the ladle nozzle, the crack crosses and so on the place is easy to form the air channel, because of the negative pressure inside the mouth, causes the crack to absorb oxygen and be oxidized, the resisting material structure is lax, is the steel scouring and erosion, the formation of the hole, causes the perforation.
3. Steel trap
Sometimes in the use of the ladle lower nozzle, and the lower sliding plate gap between the steel penetrates into the gap to form a steel clip , and in serious cases will be worn out from here, resulting in safety accidents.
There may be the following reasons for the steel pinched in the ladle lower nozzle:
(1) During hot repair, if the downspout rotating sleeve is not tightened in place or expands under high temperature, a gap is created between the ladle lower nozzle and the downspout, resulting in the loosening of the ladle lower nozzle. Deformation of the spinning sleeve, or poor contact between the ladle lower nozzle and the spinning sleeve, and the spinning sleeve does not play a good role in fixing, may also cause the ladle lower nozzle to pinch the steel, or even leakage of steel.
(2) It may be that the joints between the ladle lower nozzle and the lower slide plate are too thick, the bond strength is poor, and the contraction is large when sintering, which makes the ladle lower nozzle resistant material move down and loose, which may easily lead to the pinching of steel, or even leakage of steel.
(3) Installation of long nozzle of many repeated operations, so that the long nozzle to the ladle lower nozzle moment, if after many round-trip movement, may also make the ladle lower nozzle loose. In particular, if the sealing of steel is serious, take down the long nozzle too much force, may make the lower spout loosening, thus causing the ladle lower nozzle and the lower slide plate joints of steel, steel leakage.
Therefore, after replacing the lower spout during hot repair, we should pay attention to tighten the spinning sleeve, check whether the ladle lower nozzle is loosened during continuous sliding, and replace the deformed spinning sleeve in time; improve the quality of fireclay; and standardize the operation of the set of long nozzle to prevent the set of long spout from being deviated.
4. Sticky steel
The place where the ladle lower nozzle and the long nozzle bowl fit together is prone to sticky steel after pouring steel , especially when the seal between the two is not tight (such as the long nozzle and the ladle lower nozzle with the irrational design, the long nozzle installation is not in place, incorrect, or the gasket is of poor quality, etc.), which makes the long nozzle difficult to be removed after the pouring of steel, and the damage to the ladle lower nozzle may be caused when it is taken off. On the other hand, the infiltrated steel will melt the steel shell of the ladle lower nozzle, and in serious cases, it will cause the erosion of the end of the downspout and the falling off of the block, which will reduce the service life of the ladle lower nozzle and increase the consumption of refractory material.
Now, most of the domestic continuous casting production of ceramic fiber made of sealing elements, in the use of the process is easy to be crushed and pulverized, its sealing effect is poor, and easy to bonding of the lower nozzle and the long nozzle, easy to clean up the surface of the refractory material, so the sealing deterioration, it is difficult to meet the requirements of the continuous casting production of clean steel and other high-grade steel. The new solid sealing gasket has good plasticity, plays a good sealing effect in the process of pouring steel, is not easy to bond the refractory material, and after pouring steel, it is easy to separate the long nozzle when it is removed, and it is not easy to damage the long nozzle and the lower nozzle.
When the ladle lower nozzle is used, it is easy to have problems such as transverse breakage, perforation, steel folder and adhesion, which affects the continuous casting production. In view of the problems, on the one hand, it is necessary to improve the material and quality of the ladle lower nozzle, and reasonably carry out the design of the product shape and fit; on the other hand, it is necessary to standardize the operation of hot repair and continuous casting, and enhance the sealing measures between the ladle lower nozzle and the long nozzle.