Specific analysis of the ventilation performance of the ventilation brick

Breathable brick is a kind of functional refractory material with long lifespan, energy saving, consumption reduction and emission reduction. It is made of high-purity raw materials by firing. Out-of-furnace refining of ferrous metals and smelting of non-ferrous metals.

Today, the editor will introduce to you the analysis of the air permeability of the breathable brick, which mainly includes three aspects. , Do a face-to-face analysis, and after reading the overall content in detail, you will have a very detailed understanding of this content.

1. The effect of smelting conditions on the air permeability of air-permeable bricks

According to BarthelH's findings

r=9.81ρhΠ(-2σCosδ107)

In the formula: r—the width of the slit of the breathable brick (mm);

h—the depth of molten steel (mm);

ρ—the density of molten steel (g·cm3);

σ—surface tension (dyne.cm-3);

δ—Wetting angle (degrees).

For a fixed slit, the molten steel has different surface tensions and wetting angles at different temperatures. When the wetting angle is smaller than the fixed value, the molten steel will penetrate into the slit, and the penetration depth is different from that of the molten steel. The difference between the static pressure generated by the surface height, the atmospheric pressure and the pressure of the residual argon gas in the argon gas pipe is related. In fact, when Maanshan Steel was smelting steel grade A, the temperature of molten steel reached about 1620 degrees Celsius, and the superheating degree reached about 140 degrees Celsius. Without taking maintenance measures, the blow-through rate of ladle permeable bricks was only about 80 percent, while in When smelting B steel, the temperature of molten steel is about 1580 degrees Celsius, and the superheat is about 65 degrees Celsius. Without taking maintenance measures, the blowing rate of ladle breathable bricks is close to 100. According to research data, the carbon in the iron-carbon melt is in the At 0.15% and 0.40%, the surface tension appears to be smaller and larger, reducing the content of non-metallic elements sulfur and oxygen in the steel can significantly increase the surface tension and wetting angle of the molten steel, but these controls are affected by the steel and other There are many limitations due to factors.

2, the effect of airway size on ventilation performance

In the use of slit-type breathable bricks, the slits are easily invaded by molten steel to form sandwiched steel, and the air permeability becomes smaller. It is difficult to blow argon, and the molten steel is small, and it is difficult to achieve the effect of pure molten steel. For the breathable bricks that must be used in large ladle For example, in order to ensure the air permeability, the size and number of slits must be constant and not too small. Clamping steel is unavoidable for slit ventilation bricks. The penetration of molten steel cannot be quantified, but it can be determined from the size and size of the slit airway. The raw material to reduce the steel clip as much as possible, the appropriate slit airway size and the raw material with better thermal stability are beneficial to reduce the clip steel.

After dissection of the remaining bricks, it was found that the thickness of the clip steel sheet is much larger than the thickness of the airway, and the closer it is to the working face, the thicker it is, while the thickness of the steel sheet far from the working face is thin and conical distribution. The reason is that under the action of high temperature molten steel , The area near the distance of the breathable brick for argon blowing is subjected to thermal stress, and the local stress generated is concentrated near the air channel, which makes the size of the air channel change during use, resulting in the easy intrusion of molten steel and affecting the air permeability. There is also the end of refining. If the valve is closed quickly, the molten steel will enter the slit with positive pressure, which will also lead to steel infiltration and affect the air permeability.

3, the effect of cracks on air permeability

The ladle to be used must be baked before use to reduce the temperature difference. But even so, the surface temperature of the breathable brick installed at the bottom of the ladle still does not reach 1000 degrees Celsius, and the breathable brick is directly impacted by molten steel above 1600 degrees Celsius when tapping; When blowing argon, the large flow and high-speed normal temperature argon make the temperature of the slit of the permeable brick drop rapidly, so that a huge temperature difference occurs inside the permeable brick. These two points are the main factors that cause cracks in the permeable brick. The temperature gradient is mainly concentrated in the permeable brick. It is 30mm below the working face, so the cracks caused by thermal stress are also concentrated in this area. During the argon blowing cycle of the breathable brick, due to the generation of cracks, it is very easy for molten steel to invade the brick body along the cracked air channel, forming molten steel penetration. , Seriously will affect the argon blowing fruit.