What are the prominent problems in the tundish

 

At present, there are many problems in the tundish used in China, especially in the tundish used for billet caster. 

The specific performance is as follows:

(1) The shape of tundish cavity is unreasonable. Due to the unreasonable shape of the inner cavity, the flow of molten steel in the tundish is unreasonable and the residence time is short, which can not purify the molten steel. The distance from the drop point of the large ladle injection into the tundish to the tundish nozzle is short, or the distance from each nozzle is too different; The volume at the drop point of the ladle is too small, resulting in serious steel slag mixing and lining scouring, affecting the service life of the tundish and polluting the molten steel.

(2) The capacity of tundish is small and the depth of molten pool is shallow, so it is not suitable for high-speed caster. The molten steel stays in the tundish for a short time, which makes it difficult to purify the molten steel and remove inclusions; It is difficult to maintain constant casting speed when changing the package; During pouring, the steel slag in the tundish is agitated seriously, which makes it difficult to float the inclusions and easy to enter the mold, especially when changing the tundish.

(3) The position of tundish nozzle clogging is not properly designed, especially the nozzle on both sides is too close to the two sides, which is easy to cause unsmooth pouring of the two side nozzles.

(4) The tundish nozzle control device is too thin and unreliable, which makes it difficult to accurately control the flow of molten steel, making it difficult to stabilize the liquid level of the mold and often causing out of control accidents.

(5) The large deformation of tundish and the problems of design and manufacturing accuracy result in insufficient centering accuracy of multiple water outlets.

(6) The lifting device of tundish is ineffective, and most of them can not be lifted, which brings difficulties to the continuous casting process and causes many defects of the slab.

(7) The distance from the bottom of tundish to the upper mouth of crystallizer is improperly selected. Most of the distance is too high, which makes it difficult to align the nozzle, and also makes the nozzle too long, which increases the refractory consumption per ton of steel nozzle.

(8) Insufficient attention has been paid to the quick change technology of submerged entry nozzle.

The above tundish can only be used at low casting speed, which is not suitable for the requirements of high casting speed. Modern tundish should not only adapt to the conditions of constant speed casting at high drawing speed, high steel throughput and strength, and intense agitation in the tundish, but also play the role of purifying molten steel and removing inclusions.

 The specific measures adopted include:

(1) Optimize the shape of the inner cavity of the tundish, make the liquid steel flow reasonably in the tundish, expand the volume of the large ladle at the drop point of the tundish and optimize the distance from the drop point of the large ladle to each water inlet under the condition of adapting to the high pulling speed; 

(2) Tundish with large capacity deep melting bath; 

(3) Prevent deformation of tundish shell; 

(4) Adopt firm and reliable tundish nozzle control device; 

(5) Adopt reliable tundish lifting device under load; 

(6) Optimize the distance from the tundish to the upper mouth of the crystallizer.

Article Source: What are the prominent problems in the tundish
Company name: Henan Changxing Refractory Materials Co.,Ltd
More refractory products:https://www.cxrefractories.com/en-product-solution
Email:info@cxrefractories.com
Website:https://www.cxrefractories.com

Five main functions of tundish

 The continuous casting tundish was originally used for the heat preservation of molten steel, and its main purpose was to distribute and rectify molten steel. With the successful development of technologies such as slow cooling of molten steel, molten steel reheating technology, argon gas sealing technology, gas stirring technology, and removal of non-metallic inclusions in molten steel,?continuous casting tundish has become the most important part in the final stage of the steel smelting process. The main refining vessel is developing to a large scale.

1 Purification function

To produce high-purity clean steel, install porous ladle purging plug at the bottom of the tundish or embed a porous tubular gas distributor between the working layer and the permanent layer, or install porous bricks on the slag retaining wall to blow argon to make argon bubbles. Float evenly from the bottom to promote the removal of inclusions. These devices can eliminate the increase of argon in the molten steel and the reduction of oxide inclusions in the molten steel at the initial stage of pouring, and reduce the defects caused by Al203 inclusions on the tin plate.

2 Temperature adjustment function

In order to make the temperature difference of the molten steel before, during and after the tundish be less than 5℃ and close to the liquidus temperature during the pouring process, expand the equiaxed crystal area of the slab and reduce the center segregation, small scrap steel and iron injection can be adopted to the tundish. Powder and other measures to adjust the temperature of molten steel.

3 fine-tuning of ingredients

The center hole of the tundish stopper rod feeds cored wires such as aluminum, titanium, boron, etc. To the mold to realize the fine adjustment of the microalloy composition in the steel, which not only improves the yield of easily oxidized elements, but also avoids nozzle blockage.

4 Refining function

Add double-layer slag to the surface of the tundish molten steel to absorb the floating inclusions in the molten steel, or feed the calcium line to the tundish to change the form of AL2O3 inclusions to prevent clogging of the nozzle.

5 Heating function

In the tundish, induction heating and plasma heating are used to accurately control the molten steel pouring temperature within ±.3-5°C. In the initial stage of continuous casting, the tundish heating is used at the end of ladle pouring to compensate for the decrease in molten steel temperature and keep the molten steel temperature near the target. This is conducive to the stability of the pouring operation and improves the quality of the cast slab. During the pouring period, proper heating can compensate for the natural cooling of molten steel. The heating method uses induction heating and plasma heating.

Article Source：Five main functions of tundish
Company name: Henan Changxing Refractory Materials Co.,Ltd
More refractory products: https://www.cxrefractories.com/en-product-solution
Email:info@cxrefractories.com
Website:https://www.cxrefractories.com

Causes and avoiding methods of open pouring breakout

 

Reason:

(1) The head of the tundish stopper rod and the bowl of the upper water inlet are poorly baked. Because the bowl is low, the baking flame of traditional baking method can't reach the bowl, so the temperature of the bowl is 100 ~ 200℃ lower than that of other parts. The low temperature of molten steel can easily cause cold steel to pad bars and steel flow to get out of control, which leads to insufficient solidification of billet head and breakout during casting.
(2) The paper rope is loose, and molten steel leaks from its gap; Paper rope is damp, and it explodes after meeting molten steel, resulting in cracks, and molten steel leaks from the cracks.
(3) The iron scrap layer is too thin, which causes the molten steel to burn the paper rope and seep out from the gap; If the iron chip layer is too thick, the strength of the blank head will be insufficient and the blank shell will be broken; Iron filings are affected with damp, greasy or sundries, and explode or burn after encountering molten steel. The molten steel burns paper ropes and seeps out from gaps or the strength of billet head is insufficient, and the billet shell is broken.
(4) The traditional way of blocking dummy ingot is to plug the gap between dummy ingot head and crystallizer with paper rope. When molten steel arrives at the station for temperature measurement, iron nail chips with a thickness of 20 ~ 30 mm are evenly spread on the dummy ingot head, and then steel strips are placed on the iron nail chips in a cross way according to regulations. If the steel strip is not placed well, the molten steel will directly wash away the iron filings and paper ropes; If the steel strip is not melted sufficiently, the primary shell will be too thin, which will cause the shell to tear when drawing.
(5) There are the following problems in the operation: the steel flow in the casting is too large, which flushes iron chips or splashes molten steel on the crystal wall and corner joints to form steel clips; The starting speed is too fast, each time it exceeds 0.1m/min, and the primary shell can not bear its tensile force; Foreign matter enters the crystallizer and bites into the primary shell.
(6) There are the following problems in equipment: the dummy bar slides over 20mm; The mold corner gap is too large, exceeding 0.30mm .

In order to prevent steel leakage before pouring, adequate preparation and inspection should be made before pouring, with the following points to be paid attention to:

(1) Check the compaction of dummy ingot head and stacking of cold materials;
(2) Check the alignment between nozzle and crystallizer;
(3) Check whether there is cold steel on the crystallizer copper plate and whether the taper is appropriate;
(4) Check whether the secondary cooling nozzle is unblocked and intact;
(5) Understand the fluidity of molten steel, the temperature state of molten steel, the baking state of tundish nozzle, and the quality of mold powder. The upper water inlet and immersion water inlet shall be fully baked to ensure that the temperature of immersion water inlet is above 800℃ within 2.5 hours, and the temperature of upper water inlet stopper is above 1100℃.
(6) The size of injection flow and the residence time of molten steel in the mold should be determined according to the section of slab.
(7) Once the initial drawing speed is generally kept at 0.5m/min, and the growth rate is slower (0.15m/min), so as to prevent excessive fluctuation of crystallizer liquid level.

Article Source:Causes and avoiding methods of open pouring breakout
Company name: Henan Xinmi Changxing Refractory Materials Co.,Ltd
Email: info@cxrefractories.com
Website:http://www.cxrefractories.com