JPS586943A - Refractories for blowing of gas for refining of molten metal - Google Patents

Abstract

PURPOSE:To prevent the inclusion of molten metal into holes and to make the intermittent operations of gas blowing possible in a bubbling brick for the purpose of blowing specific gases into molten metal by inserting convergent bodies of refractory fibers into the holes of the brick. CONSTITUTION:In the case of agitating and refining molten metal by blowing various kinds of active gases and inert gases into molten iron or molten steel, a bubbling brick 4 for blowing of said gases is molded of dense refractories 4 of graphite-Mgo type, and refractory fiber bundles 7 of high wettability with molten iron and molten steel such as carbon fibers, silicon carbide base, boron carbide base or the like are inserted and packed into holes 6 for gas blowing. The bundles 7 of sizes having 5-50mm. sectional diameters are inserted in such a way that the unit air permeating sectional diameter attains <=100mu. Refining by intermittent gas blowing is accomplished without inclusion of the molten metal into the holes 6 of the brick 4.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas-blown refractory for molten metal refining that has excellent durability and can be used intermittently.

Increasing the efficiency of molten metal reactions, especially in the steel industry, by injecting active or inert gases into molten pig iron and molten steel has been carried out in various ways since ancient times. The stirring effect has been recognized in both converters and converters. Conventionally, gas blowing methods include the top blowing method, which uses a lance protected by a refractory material to enter the molten metal from above, and the bottom blowing method, which uses a refractory material with ventilation holes (hereinafter referred to as a bubbling brick) at the bottom of the molten metal container. The blowing method etc. are well known.

The latter is more advantageous in terms of bath agitation effect, but there are problems with the durability of bubbling bricks and there are concerns about accidents such as water leakage, so the latter cannot necessarily be said to be advantageous. situation.

The inventors believe that it is most important to improve the durability and reliability of bubbling bricks in order to take advantage of the stirring effect of bottom-blown gas, and after various studies, they developed a fibrous refractory with high fire resistance and high corrosion resistance. Successfully developed a bubbling brick using They will be explained in order below.

Conventionally, the following three types of gas-injected refractories have been used for molten metal containers.

In other words, (1) porous refractories with good air permeability (Figure 2), (2) refractories with multiple through-holes (Figure 3), and (3) refractories with voids at the joints or corners of bricks. It is. These materials and combinations of materials are selected and adopted as appropriate depending on usage conditions and applications, but all have major drawbacks. That is, in (1), in order to obtain a structure with good air permeability due to the particle size structure, a medium particle composition with a small amount of fine powder is used, and the porosity is as high as 3 to 5 times that of ordinary refractory material J, and the strength is low. Therefore, it is susceptible to flow wear of the molten metal due to gas injection, and has poor durability.Although the average pore size can be reduced by selecting small particle sizes, there are restrictions from the perspective of ensuring air permeability. Configuration (often 2-Q,
5 mm), there are relatively large pores (for example, 30% or more of pores are 40μ or more). Therefore, since the molten metal easily enters and solidifies into such pores, it is impossible to interrupt the gas injection while the molten metal is stored and held in the container, which is disadvantageous in terms of durability. If gas injection is interrupted, so-called metal will invade and solidify into the pores, and unless the metal invades the area, subsequent ventilation will not be possible, resulting in poor durability. .

Next, the refractories mentioned in (2) and (3) above are made of bricks with a dense structure like normal refractories, so they have high strength and, combined with the selection of materials, have excellent corrosion resistance. It will be done. But the pores or voids.

Since it is a large material through which molten metal can easily pass if gas injection is interrupted, similar to the refractory described in (1) above,
It is not possible to interrupt the gas blowing while holding the molten metal. For this reason, it is necessary to continue pointlessly blowing gas while the molten metal is being held, resulting in economical disadvantages and disadvantages in terms of durability when using expensive gas.

Molten metals, especially hot metal and molten steel, are often processed at temperatures of about 1,500 to 1,650°C, but according to Cantor's law, the relationship between bath depth and pore size limit for penetration is approximately 1 As shown in Figure (A) 1.1
It is thought that this will not occur at a bath depth of about 1 m if the pore diameter is 40 μm or less, but it is technically extremely difficult to create a large number of such pores during manufacturing or processing. Moreover, it is not economical.

In the figure, a indicates an area where molten metal does not invade.

The present invention provides a highly durable refractory for gas injection that completely prevents molten metal from entering the pores in such a gas injection process and enables intermittent gas injection operations.

The characteristics of the present invention are highly water-resistant fibers such as carbon (both amorphous and graphite), silica carbide, boron carbide, tungsten carbide, molybdenum carbide and other carbides, boron nitride,
Nitride such as silicon nitride, metal, organic fiber, non-oxide fiber such as novolac type phenolic resin, alumina, alumina-silica, zirconia, special glass. Oxide fibers such as fibers, and composite fibers made by mixing or bonding these fibers are referred to in (2) above.

(3) The unit ventilation cross-sectional diameter for pores or voids is 100
The reason is that it is filled so that it is less than μ, preferably less than 40 μ.

The material of the refractory fiber to be filled depends on the usage conditions.
It is also possible to use a species or a combination of two or more species. In the case of molten steel, the high temperature and slag erosion must be taken into account, so non-oxide fibers such as carbonaceous and carboxylic fibers, and high melting point and highly corrosion resistant oxide fibers such as pure alumina and zirconia are used. Otherwise, durability is often not achieved, but it has been found that hot metal such as silica-alumina and glass fiber can be used satisfactorily.

To fill the pores or voids with refractory fibers, the refractory material (fired or unfired bricks or amorphous refractory block) that constitutes the body of the bubbling brick can be used, and the material may be oxide-based or non-oxide-based. , carbon-based refractories) is molded or charged so that a bundle of the refractory fibers exists so as to maintain continuous air permeability from the gas supply side to the gas discharge side.

It is desirable that the longitudinal direction of the refractory fiber coincides with the gas flow direction, but when using a processed fiber, for example, woven fabric, string, felt, etc. are not limited to this. These cases are also included in the present invention.

In addition, a bundle of refractory fibers set in advance in a refractory tube separate from the main body, or a bundle of refractory fibers covered with the same or different types of refractory fibers, can be placed in a predetermined thin tube provided in the refractory of the main body. A method of fitting into a hole or a gap may be used, and this is also included in the present invention.

The material of the refractory fiber used in the present invention may be one that is generally commercially available, but it is preferable that the material has a lower wettability with molten metal.

It is an absolute requirement that the contact angle be 908° or more by the 5esile drop method, but preferably 150° or more.

In FIG. 1(B), the formula r--2γe CO8θ/1・
ρ is given the following value.

le = 1.733 (lit/cJ), ρ
=7.6 Cf1cd) θ = 150 Table 1 (Quality characteristics of commercially available refractory fibers) shows an example of a material that satisfies the requirements listed in item 7.

The cross-sectional diameter of the refractory fiber bundle is not particularly limited as long as it is within the range of the bubbling brick cross-sectional diameter, but if it is too large, it will be difficult to manufacture the bundle9, and if it is too small, it will be difficult to ensure ventilation. Therefore, 5 *yn ~50 m
m, preferably 101m to 3Q dragon is suitable. Further, it is also possible to use a slit-shaped gas discharge port depending on the purpose, and the present invention can be applied to this slit portion.

Next, the density of this refractory fiber bundle (in this case, the number of fibers per unit cross-sectional area) is such that the unit ventilation cross-section is at least 100μ or less based on the penetration limit pore diameter shown in Figure 1, which prevents the penetration of molten metal. Preferably, the number of bundles is 40μ or less, and in conjunction with the above range of cross-sectional diameter of the bundle,
100-20000/-1 preferably 1000-1o
oo.

Book/jIj is appropriate. If the number of gas pipes is too small, molten metal will enter the pipes, which will interfere with subsequent gas injection.
This is because removing the entire intrusion part may result in shortening the wear and tear of the bubbling brick), while if there is too much, it becomes difficult to secure a ventilation cross section.

With the development of the Nopu-Pull Brick that satisfies the above requirements, it has become possible to perform the gas blowing process from the bottom of the molten metal holding container intermittently at the necessary times without any trouble, resulting in no-pull bricks. The durability of the bricks has also been further improved because the actual gas injection time can be shortened, making it possible to ensure the same lifespan as regular bottom bricks.

Examples of the present invention are shown below.

Example 1 In a bubbling brick for gas blowing made of magnesia-graphite unfired bricks, in which bundles of air-permeable carbon fibers with a diameter lQM were installed at 10 locations, carbon fibers (0, l
We prototyped bundles of 5ad (1 piece) with densities ranging from 50 to 30,000 pieces/- in 10 levels, and repeated 3 10 times in a test ladle to compare them with conventional porous type magnesia yarn porous plugs. The results were as shown in Table 2.

Based on these results, a fiber density of 5,000 fibers/- was selected, and as a result of using it in an actual furnace with a conventional product in a ladle of 250 fibers, it was confirmed that the product had a durability of 25 cycles or more, compared to the average durability of the conventional product, which was 15 cycles.

The 25 times were due to the replacement of the paving bricks, and it was determined that it could be used for more than 40 times based on the remaining condition.

When using the product of the present invention, gas injection was interrupted as necessary while holding the molten steel, but the cross-sectional condition after use showed that there was almost no intrusion of metal, and only a small amount of metal adhered to the surface. was confirmed.

Example 2 A structure for blowing gas from the bottom of a converter was manufactured by the method of the present invention. The base brick is made of Magnenur graphite brick.
Its shape and dimensions are 700X150X150/l 30
It is w. Ten carbon fiber bundles (density: 3000 fibers/-) having a diameter of 30 am were arranged in a staggered manner over the entire edge surface so as to reach from the edge surface of 150 x 150 nm to the edge surface of 150 x 130 nm. Four of these bubbling bricks were installed at the bottom of a converter furnace, and Ar gas was intermittently blown into the furnace.

Conventional gas injection methods have used fired magnesia porous refractories or through-hole refractories with fine holes in magnesia-graphite bricks, but the former suffers from spalling and abrasion erosion of hot metal or molten steel. It was so intense that it only lasted about 100 times. In the latter case, since molten steel invades the pores (1 to 3 unφ), it is necessary to constantly blow Ar gas at high pressure, and the durability also varies widely, ranging from 400 to 900 times.

Since the pores of the product of the present invention are filled with carbon fiber, intermittent gas injection is possible, and gas injection only needs to be performed when stirring is required. The bubbling brick can now be used stably for more than 1,500 times.

In Example 3 and Example 2, it was observed that the carbon fiber filled part was slightly damaged in advance, and in such cases, the bubbling brick was worn out, and the carbon fiber became oxidized and damaged. It was inferred that

As a countermeasure, carbon fibers and silicon carbide fibers are combined at a ratio of 7/3 (weight ratio) and bundled (A), and carbon fibers and zirconia fibers are combined at 6/3 (weight ratio) and bundled together.
/4 (weight ratio) was produced in the same manner as in Example 2, and the oxidation resistance test results showed that it was good, so 100 was used at the bottom of the converter. .

As a result, there were no problems with bubbling bricks.
(A) and (B) each showed a service life of 1100 and 1200 times (this was the same level of damage to the bottom and wall of the furnace as in the case of a conventional LD).

In addition, the preliminary erosion of the gas discharge port was slight in both cases (
Between (A) and (B), (A) showed a higher tendency to melt away).

Although only the case of iron refining has been described above, the present invention is fully predicted to be effective for gas injection in non-ferrous refining, and its application is also possible.

FIG. 2 shows an example of a conventional porous type gas blowing resistor, in which 1 is a porous plug, 2 is an exterior holding plate (for example, a steel plate), and the bottom is connected to a blowing gas pipe 3. There is.

FIG. 3 shows a dense refractory 4 such as M2O-graphite brick, in the axial direction of the refractory ('gas injection direction).
This figure shows a conventional through-hole type gas blowing resistant person provided with an appropriate number of gas blowing holes 5.

FIG. 4 shows an embodiment in which the present invention is applied to a ladle for a gas-injected refractory body, in which the shaft of a dense refractory such as Mg0 = graphite brick is formed into a truncated conical shape. direction(
For example, a refractory fiber bundle 7 such as carbon fiber is inserted into the gas injection hole 6 provided in the gas injection direction).
This shows a gas-injected refractory filled with .

FIG. 5 and FIG. 6 are perspective views showing an example of another embodiment of the present invention applied to a converter. Similarly, a gas injection hole 6 provided in the axial direction (gas injection direction) of a dense refractory such as a MgO-graphite brick preferably formed in a block shape is filled with a material such as carbon fiber. The case where a 1° eyebar bundle 7 is inserted and filled is shown.

By configuring and using the present invention as described above,
When blowing gas into the molten metal in the container using a gas injection refractory provided in the container body below the molten metal surface of the molten metal storage (holding) container.

The gas injection process can be carried out intermittently at the required times without any problems, and therefore the life of the gas-injected refractories can be expected to be extended, and ventilation gas for maintaining the gas-injected refractories is no longer required. As a result, the cost of barking gas can be reduced, which has an extremely large effect on improving productivity, equipment maintenance, and operating costs.

[Brief explanation of the drawing]

Figure 1 (A) is a diagram of the relationship between bath depth and penetration limit.
B) is a schematic diagram of pores, FIGS. 2 and 3 are schematic diagrams showing an example of a conventional gas-injected refractory, and FIGS. 4, 5, and 6 are an example of an embodiment of the present invention. It is a schematic diagram showing an example. l: Porous plug 2: Exterior holding plate 3: Gas injection pipe 4: Dense refractory 6: Gas injection hole 7:
Fireproof fiber Figure 1 (A) 2I27 3rd page 442nd 51st field 6th field

Claims (1)

[Scope of Claims] 1. A dense refractory substrate formed into an appropriate shape, with one end facing the molten metal contact surface and the other end facing the molten metal contact surface along the gas injection direction of the substrate. 1. A gas-blown large object for refining molten metal, characterized in that a long cylindrical hole communicating with a supply system is provided, and a refractory fiber bundle is inserted into the long hole. 2. The gas-blown large resistant material for molten metal refining according to claim 1, characterized in that a wettable refractory fiber with a unit ventilation cross section of 100 μm or less is used as a 5-50 m convergence body.