10 Things to Consider When Buying tundish refractory lining

Although there is new refractory insulation technology, discuss with your refractory contractor first.This is because trends may seem too good to be true. Avoid asking for new types of furnace bricks for your refractory contractor to use.The engineering contractor will suggest a material that suits your refractory insulation.

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Basically, everyone thinks they are the best. But, in the end, the most experienced engineer will make the correct decision. Therefore, choose a refractoryfactory that fits your criteria. Then, they will provide refractory products and services that suit your refractory lining.

1. Castables must always be stored in a cool and dry area.
2. One must ensure that the mixers and tools are free from old castable or any other material that can contaminate the product. Such contamination could affect the strength of the castable mix.
3. Only drinking suitable water should be used to mix castable. The temperature of the mix should be optimal as well.
4. Be careful while mixing castable, like castable refractory cement. Too much mixing generates heat and speeds up the setting time.
5. The forms should be covered with oil or grease to prevent moisture loss.
6. After placing the mix, the castable needs to be cured for 18 to 24 hours straight. Cover it with polyethylene sheets and spray it with cold water periodically. It will maintain the moisture of the mix and promote uniform curing at the applied area.

Molten steel refining refers to the metallurgical process of refining molten steel that has been refined in a converter or electric furnace to another vessel, also known as ladle metallurgy or secondary metallurgy, which divides the traditional steelmaking process into primary refining and Refining in two steps.

In the initial refining, the charge is melted, dephosphorized, decarburized, removed, and main alloyed in an oxidizing atmosphere to obtain the initial molten steel; the refining is to use the molten steel in a vacuum, an inert gas or a reducing atmosphere. Degassing, deoxidation, desulfurization, removal of inclusions, inclusion denaturation, fine-tuning of components, and control of the temperature of the molten steel are carried out in the vessel. External refining of the lining furnace can improve the quality of the steel, shorten the smelting time, optimize the process and reduce the production cost.

What is the basis for selecting refractory materials outside the furnace?

01. Temperature

Generally, the temperature of refining outside the furnace is as high as - °C, even reaching °C. A measurement of the AOD furnace has found that when the maximum temperature of refining is increased by 10 ° C, the life of the refractory material is reduced by 30%. The refractory material is required to have high fire resistance, can withstand the highest refining temperature and local overheating shock, and the amount of liquid phase occurring at this temperature is small, and can resist the erosion of low viscosity slag. Therefore, alkaline bricks with high purity and direct bonding rate should be selected.

Intermittent operation will cause temperature fluctuations, causing the lining to peel off. Of course, the temperature fluctuation is as small as possible. Generally, the intermediate baking is used to shorten the stop time between the furnaces, and the temperature change of the ladle is reduced to improve the life of the lining. Under the conditions of smelting, it is better to use magnesia-carbon bricks or magnesia-chrome bricks with the best thermal shock resistance. If the temperature changes rapidly, but the interval time is short, it is better to use magnesium dolomite bricks. For example, LF (V) ladle, the slag line is made of MgO-C or MgO-Cr203, the side wall is made of MgO-GaO or MgO-Cr203, and the bottom is generally made of high quality high alumina brick.

02. Stirring

All furnace refining methods are equipped with a molten steel agitator. VOD, VHD (VAD), AOD, etc. are argon gas agitation. Generally, the furnace wall blowing argon and the furnace wall closer to argon blowing are more seriously damaged. Electromagnetic induction agitation (SKF), generally in the agitator position and the symmetrical position of the agitator, the lining is damaged. Due to the stirring effect, the molten steel and the slag are vigorously boiled, and the damage of the lining is accelerated. Therefore, high-temperature refractories such as magnesia, high-purity magnesia, and chrome corundum should be used in areas severely eroded by scouring.

03. Processing time

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The refining time can be as long as 1-4 hours. The longer the treatment time of molten steel in the ladle, the more serious the lining damage. Therefore, refractory materials with good slag resistance and low temperature creep should be used.

04. Vacuum

The volatilization rate of the refractory material increases with the increase of temperature and vacuum, and the slag penetration rate and quantity also increase. For example, the vacuum degree of LF (V) under high temperature vacuum can reach 67Pa or more, thereby accelerating the damage of the lining. The stability of the refractory oxide in vacuum is related to its vapor pressure dissociation energy and the activation energy of the combined phase. Among several oxides of common refractories, Al203 and CaO are most stable. If A is added to MgO bricks or magnesia chrome bricks, the evaporation rate of bricks can be significantly reduced. At ° C, 10-1 Pa, A volatilization rate is only l / 100 of MgO, MA spinel is l / 44 of MK spinel. It can be seen that magnesium adolescent bricks with high CaO and magnesia chrome bricks with A are better only from the viewpoint of vacuum volatility.

05. Positive arc heating

The refining furnaces such as ASEA-SKF, VHD (VAD), and LF are all heated by electric arc. The former is stirred by electromagnetic stirring and the latter is stirred by argon. In the hot spot near the arc, the direct high-temperature thermal radiation is as high as ° C, and the slag splashing causes the lining damage rate to increase sharply.

The larger the operating voltage, the longer the arc, and the smaller the distance between the electrode and the lining, the more severe the lining damage. Therefore, try to use lower voltage, high current, short arc operation, and the smaller the control electrode core circle, the better.

06. Refined steel grade

The magnesia-chrome brick is operated under an alkaline slag of a reducing atmosphere, and Cr203 in the brick is easily reduced to Cr. Therefore, when refining chromium-free or low-chromium steel grades, it is not advisable to use magnesia-chrome brick lining, but magnesium dolomite brick or magnesia brick should be used. When refining ultra-low carbon steel, in order to avoid the possibility of carbon increase, it is not advisable to use magnesia carbon bricks, and it is better to use magnesia chrome bricks or magnesium dolomite bricks.

07. Slag properties

The refractory material should be adapted to the slag as much as possible to minimize the erosion rate and improve the life of the lining. When n(C)/n(S) is greater than 2, the MA spinel is unstable, and the pure magnesia brick has better slag resistance than the magnesia chrome brick. It is preferable to use magnesia brick, magnesium dolomite brick and magnesia carbon brick. When n(C)/n(S) is less than 2, magnesia chrome brick or magnesium dolomite brick should be used.

The erosion of the lining depends on the contact area of the slag and the refractory product, and the larger the contact area, the more severe the slag corrosion. Under the condition that the product has a certain porosity, the fluidity of the slag is better, and the slag amount in the infiltrated brick is larger, and the slag corrosion is more serious. The viscosity of the slag is determined by its composition and temperature. Generally, the viscosity of the acidic slag is greater than that of the alkaline slag. Controlling the amount of flux, such as CaF2, is beneficial to reduce the erosion of the lining. However, the alkalinity of the slag is too small to be desulfurized, and both need to be taken into consideration; the higher the temperature of the slag, the smaller the viscosity, the greater the fluidity, and the more severe the slag corrosion.

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