One stop service for steel industry

The purpose and method of slag blocking and tapping in oxygen top-blown converter steelmaking – slag ball

Table of Contents

In converter steelmaking, the alloying of molten steel is mostly carried out in the ladle. The flow of highly oxidizing slag in the converter into the ladle will cause an oxidation reaction between the molten steel and the slag, resulting in a reduction in the yield of alloying elements and an increase in phosphorization and inclusions in the molten steel. At the same time, slag also corrodes the lining of the ladle. Especially when molten steel is subjected to refining treatments such as argon blowing, the slag (FeO) content in the ladle must be less than 2% to improve the refining effect.

The purpose and method of slag blocking and tapping in oxygen top-blown converter steelmaking

The purpose of slag blocking for steel tapping is to accurately control the composition of molten steel, effectively reduce phosphorization, increase the absorption rate of alloy elements, and reduce alloy consumption; for the use of ladles as refining vessels outside the furnace, it is beneficial to reduce the erosion of the refractory materials of the ladles , significantly increasing the life of the ladle; it can also increase the life of the refractory material at the converter tap hole.

There are many methods to stop slag, including slag stopping ball method, slag stopping rod method, slag stopping plug method, slag stopping cap method, slag stopping material method, pneumatic slag stopping method and so on.

A slag ball

The slag-blocking ball method is a slag-blocking method successfully developed by Nippon Steel Corporation of Japan. The density of the ball is between that of molten steel and molten slag. When the steel tapping is over, it is thrown into the furnace near the tapping port. As the molten steel liquid level decreases, the slag retaining ball sinks and blocks the tapping port, preventing the subsequent molten slag from entering the ladle.

The reasonable density of slag retaining balls is generally 4.2~4.5g/cm3. The shape of the slag retaining ball is spherical. The center is generally made of cast iron blocks, pig iron scrap pressed blocks, small scrap steel billets and other materials as the skeleton. For external coating of refractory mud, high-alumina refractory concrete, high-alumina vanadium refractory concrete or magnesia refractory mud with refractory brick powder as admixture can be used. As long as the process requirements for slag blocking are met, the structure should be simple and the cost low.

Taking into account the problem of the taphole becoming larger due to erosion, the diameter of the slag retaining ball should be slightly larger than the diameter of the taphole to play a role in retaining slag. ​

The slag-blocking ball is generally put in when the steel tapping amount reaches 1/2 to 2/3, and the slag-blocking hit rate is high. The slag is too sticky, which may affect the slag retaining effect of the slag ball. The viscosity of the molten slag is high, so putting in the slag-blocking ball appropriately in advance can improve the slag-blocking hit rate. ​

The structure and function of the slag-stopping plug and slag-stopping rod are the same as those of the slag-stopping ball, but their shapes are different.

slag ball -The purpose and method of slag blocking and tapping in oxygen top-blown converter steelmaking

B slag blocking cap

A cone-shaped slag-blocking cap made of thin steel plate is plugged outside the tapping port to block primary slag at the beginning of tapping. Wuhan Iron and Steel Co., Ltd. and Handan Iron and Steel Co., Ltd. both use this method.

C Pneumatic slag stopper

The principle of the pneumatic slag stopper is to use a mechanical device to block the taphole with a slag stopper from outside the converter when tapping is about to end, and blow air into the furnace to prevent molten slag from flowing out. This method is used by factories such as VAI in France, Western Europe, and has also been adopted by Shanghai Iron and Steel Factory No. 5 and Shougang Iron & Steel Co., Ltd.

D Use covering residue

After the slag is tapped, in order to keep the molten steel warm and effectively process the molten steel, a ladle should be prepared to cover the slag as needed and added to the ladle after the steel is tapped. The ladle covering slag should have the characteristics of good thermal insulation performance and low phosphorus and sulfur content. For example, the covering slag used by a certain factory consists of 30% to 35% aluminum slag powder, 15% to 20% processed wood chips, and 10% to 20% expanded graphite, perlite, and fluorite powder. The usage amount is about 1kg/t. This slag remains in a liquid state after pouring the steel and is easy to pour into the slag tank. At present, carbonized rice husk is widely used as covering slag in production. Carbonized rice husk has good thermal insulation performance, low density and light weight. It does not stick to the ladle after pouring the steel, so it is popular in use.

E The effect of slag blocking during tapping and the use of covering slag

The converter has achieved good results after adopting the slag-blocking tapping process and covering the slag:

Reduce the amount of slag in the ladle and the amount of molten steel rephosphorized. The use results of domestic and foreign manufacturers show that after slag blocking is used to tap steel, the amount of slag entering the ladle is reduced, and the amount of molten steel rephosphorized is reduced. When steel is tapped without slag blocking, the thickness of the slag layer when the slag enters the ladle is generally 100 to 150 mm, and the amount of phosphorization of the molten steel is 0.004 to 0.006%. After using slag blocking to tap steel, the thickness of the slag layer entering the ladle is reduced to 40~80mm, and the amount of phosphorization of the molten steel is 0.002~0.0035%.

Improved alloy yield. Slag blocking reduces the amount of highly oxidizing slag entering the ladle, thereby reducing the oxidation loss of the added alloy in the ladle. Especially for medium and low carbon steel types, the alloy yield will be greatly improved. When tapping without slag blocking, the manganese yield is 80-85% and the silicon yield is 70-80%. After using slag blocking to tap steel, the manganese recovery rate is increased to 85-90%, and the silicon recovery rate is increased to 80-90%.

Improved alloy yield. Slag blocking reduces the amount of highly oxidizing slag entering the ladle, thereby reducing the oxidation loss of the added alloy in the ladle. Especially for medium and low carbon steel types, the alloy yield will be greatly improved. When tapping without slag blocking, the manganese yield is 80-85% and the silicon yield is 70-80%. After using slag blocking to tap steel, the manganese recovery rate is increased to 85-90%, and the silicon recovery rate is increased to 80-90%.

Improve the service life of the ladle. At present, the lining of ladles in my country is mostly made of clay bricks and aluminum-magnesium materials. Due to the high alkalinity and high oxidation of the final converter slag, the lining of the ladle will be corroded and the service life of the ladle will be reduced. After using slag blocking to tap steel, the amount of slag entering the ladle is reduced. At the same time, low oxidation and low alkalinity covering slag is added, which reduces the erosion of the slag on the ladle and increases the service life of the ladle.

Facebook
Twitter
LinkedIn
Reddit

As professional one-stop solution provider, LIAONING MINERAL & METALLURGY GROUP CO., LTD(LMM GROUP) Established in 2007, and focus on engineering research & design, production & delivery, technology transfer, installation & commissioning, construction & building, operation & management for iron, steel & metallurgical industries globally. 

Our product  have been supplied to world’s top steel manufacturer Arcelormittal, TATA Steel, EZZ steel etc. We do OEM for Concast and Danieli for a long time.

LMM Main product series

Need For Some Help ?

Professional engineers provide solutions and technical drawings

phone

86(411) 84174804

mail

lmme-business@lmmgroup.com.cn

Special product design, please send specific data and drawings to our mailbox or form.

As professional one-stop solution provider, LIAONING MINERAL & METALLURGY GROUP CO., LTD(LMM GROUP) Established in 2007, and focus on engineering research & design, production & delivery, technology transfer, installation & commissioning, construction & building, operation & management for iron, steel & metallurgical industries globally. 

Our product  have been supplied to world’s top steel manufacturer Arcelormittal, TATA Steel, EZZ steel etc. We do OEM for Concast and Danieli for a long time.

LMM GROUP Certification

LMM GROUP Service

Get A Free Consultation
And Estimate