JPS6152118B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a slide plate for controlling the flow rate of molten steel. In recent years, slide valve systems have been widely used to control the flow rate of molten steel in steelmaking ladles and tundishes. Applications to converters, etc. are also being attempted. The structure of the slide valve system is shown in Figures 1 and 2. The sliding surfaces 3 of the two plates, the fixed plate 4 and the sliding plate 5 in FIG. 1, are precisely polished and are sufficiently smooth to allow easy sliding. Of these two plates, the lower sliding plate 5 can slide in the left-right direction in FIGS. 1 and 2, thereby changing the cross-sectional area of the molten steel passage hole 2 and adjusting the flow rate. In order to satisfy such a function, defects such as cracks, chips, wear, erosion, etc. must not occur in the molten steel passing hole 2 of the plate during the passage of molten steel. Furthermore, the sliding surface needs to have sufficient smoothness to prevent molten steel from entering through the molten steel passage section. When molten steel is charged into the molten steel container, the slide valve is in a state where the molten steel passage hole 2 is closed as shown in FIG. At this time, the molten steel passing hole and the upper nozzle hole of the fixed plate 4 are filled with sand, so the two plates do not come into direct contact with the molten steel. Next, by moving the sliding plate 5, the molten steel passing hole 2
It will be in the state shown in Figure 1, where it is open. At this time, the filling sand falls due to the weight of the molten steel, and at the next moment, high-temperature molten steel flows through the molten steel passage hole 2 at high speed. That is, this instantaneous molten steel passage hole is subjected to a sudden thermal shock. Furthermore, while the molten steel passes through it, it is subject to wear and erosion by the molten steel flow. After a predetermined amount of molten steel has flowed out of the molten steel container, the sliding plate 5 is slid to return the molten steel passage hole 2 to the closed state as shown in FIG. 2. In this process, the sliding surface 3 of the sliding plate 5 sequentially and continuously slides while contacting the molten steel in the molten steel passage hole of the fixed plate 4, so that only a small portion of the sliding surface 3 receives a thermal shock. After similar operations are repeated 2 to 4 times, the fixed plate and sliding plate are discarded. In addition, in the figure, 1 is the upper nozzle,
1' indicates the lower nozzle. The process until a conventional slide valve plate is discarded is as follows. As shown in FIG. 3, radial cracks 6 occur in the molten steel passage hole due to the initial thermal shock. This crack grows continuously with repeated use and spreads throughout the plate. Additionally, during the passage of molten steel, the diameter of the molten steel passage hole expands due to wear and erosion caused by the molten steel flow.
Moreover, the cracks caused by the thermal shock described above induce peeling 7 of the edge portion and promote the expansion of the pore diameter. In this condition, the plate loses its ability to accurately control flow, and is therefore discarded. On the other hand, on the sliding surface of the sliding plate, repeated thermal shocks on the surface cause surface layer peeling 8 and loss of smoothness. This is facilitated by the growth of cracks that occur in the molten steel passage holes. A sliding surface that has lost sufficient smoothness can no longer be stopped from entering the molten steel through the molten steel passage hole even if it is pressed under high pressure, and is discarded. Conventional slide valve type plates generally contain Al ₂ O ₃ , MgO, Al ₂ O ₃ -C, or MgO.
- Press-molded products of refractories such as C quality are used, but they are not fully satisfactory. It is clear that longer life can be achieved by making plates from refractory ceramics, which have better thermal shock, abrasion and erosion resistance than traditional refractories; This is a property that is contradictory to the property, and high-grade refractory ceramics that have both of these properties are extremely expensive and are not put into practical use. Since a conventional slide plate is made of a single piece (one refractory brick) press-molded from a refractory material, one plate is homogeneous throughout. For this reason, the following drawbacks can be cited. First, damage to the molten steel passage holes and sliding surfaces is the direct cause of plate scrapping. In other words, damage to a small portion of the plate that comes into contact with molten steel will determine the lifespan of the entire plate. For this reason, most of the plates that do not come into contact with molten steel are discarded without sustaining much damage, resulting in a lot of waste and hindering the use of high-grade refractory ceramics. Secondly, since the entire plate is homogeneous, cracks generated in the molten steel passage holes grow continuously. Thirdly, the molten steel passage hole, sliding surface, and other parts are press-formed as one piece even though the forms of damage they receive are different, so optimal materials with different properties are applied to each part. difficult to do. The present invention relates to a slide valve plate characterized by a low-expansion ceramic body and a surface of the body coated with ZrO ₂ containing 3 to 10 mol% MgO. In the present invention, the term "slide valve plate" includes a case where a lower nozzle is attached. An example of its configuration is shown in FIG. The sliding plate main body 10 is made of low-expansion ceramic and has the same shape as a conventional plate. Suitable ceramic materials for this purpose include fused silica, syamoto, cordierite, and the like. It is important that the main body itself withstands large thermal shocks when adjusting the flow rate of molten steel, and for this purpose low-expansion materials such as fused silica, Shamots, cordierite, etc. are used. However, fused silica, syamoto, and cordierite have poor wear resistance, corrosion resistance, and heat resistance against molten steel, and cannot be used in areas where molten steel comes into direct contact with them. For this reason, it is necessary to coat the areas directly in contact with the molten steel with ceramic, which is resistant to thermal shock and has excellent abrasion resistance, corrosion resistance, and heat resistance. After examining various ceramic materials, we found 3 materials that could satisfy the above characteristics.
We found that _ZrO2 partially stabilized with ~10 mol% MgO is the best. This ZrO ₂ 12 partially stabilized with MgO (hereinafter referred to as MPSZ) is thermally sprayed onto the sliding parts. Further, a cylindrical or hollow truncated conical molded body 11 made by sintering or thermal spraying is fitted into the molten steel passage hole. At this time, the thickness of the sprayed film 12 on the sliding part is 0.2 to 15
mm, the thickness of the molded body 11 to be fitted into the molten steel passage hole is
0.5~20mm is good. The sprayed coating thickness on the sliding part is 0.2mm.
If it is less than that, the ceramic of the slide valve plate body may be thermally changed, leading to cracking damage and peeling of the sprayed film. If the thickness exceeds 15 mm, the spraying time will be long and productivity will be poor, which is not preferable. The molded body 11 of the molten steel passage hole has a wall thickness of 0.5 mm.
If it is less than that, no matter how excellent the wear resistance of MPSZ is, the expected service life cannot be obtained because the wear damage caused by molten steel is large. The wall thickness of the molded body should be 20 mm or less, as it will harmonize well with damage to the sliding parts.
There is no need to exceed. The reason why the MgO content of MPSZ is desirably 3 to 10 mol% is as follows. Various _ZrO2 materials were tested, including stabilized _ZrO2 and partially stabilized _ZrO2 with CaO, _partially stabilized _ZrO2 with _Y2O3 and even fully stabilized _ZrO2 with CaO, MgO, _{Y2O3 .}
All of these cracks occur during rapid heat tests.
It has been found that only the MPSZ of the present invention can withstand repeated rapid heating tests, does not crack, and has excellent abrasion resistance and corrosion resistance. The reason for its excellent thermal shock resistance
It is said that monoclinic crystals precipitated within MPSZ transform during rapid heating, causing thermal contraction and eliminating thermal stress. FIG. 4 shows a schematic diagram of the groove formation of the slide valve plate of the present invention. The MPSZ coating can be applied to the entire sliding area (Figure b), or only to the areas where it actually slides (Figure a).
(Fig.) But there is no groove. From an economic point of view, it is desirable to spray only the areas that will actually slide. Furthermore, after thermal spraying, the sliding surfaces are polished to make them smooth to prevent molten steel from leaking. The MPSZ molded body 11 in the molten steel passage hole is fixed by the sprayed film, but it is desirable to fit a cylinder with an inclination as shown in FIG. 4 to prevent it from falling off. Examples will be described below. The plate body 10 was molded with syamoto, cordierite, and fused silica, and a molded body 11 of MPSZ was fitted into the molten steel passage hole as a covering material, and MPSZ was sprayed on the sliding surface. For comparison, a conventional slide valve plate and one in which ZrO ₂ completely stabilized with Al ₂ O ₃ or CaO is inset and thermally sprayed are shown. The tests included a thermal shock test and an erosion test. The thermal shock test heated the plate with an oxygen-acetylene flame. At this time, the surface temperature of the plate is
Adjust the temperature to 1700℃, heat the plate sliding surface and molten steel passage hole for 5 minutes, and let it cool for 30 minutes.
The operation was performed once. This operation was repeated and the number of rotations until cracks appeared on the plate surface and the number of times until peeling was observed in some areas were compared. The test was stopped after 20 repetitions. The erosion test was conducted using an induction furnace at 1650°C for 4 hours to compare the amount of erosion caused by molten steel in the molten steel passage hole. The amount of erosion was measured after the test was completed. The quality and test results of the slide plate according to the present invention and the conventional slide plate are shown. Table 1 shows the thermal shock test results of a thermally sprayed coating on the sliding surface of a slide valve plate. Conventional products without thermal spray coating are also shown. 3-10 mol%
ZrO ₂ partially stabilized with MgO has better thermal shock resistance than other conventional products. Table 2 shows the results of an erosion test of the molten steel passage hole of the slide valve plate. Product 1 of the present invention is a dense sintered body of MPSZ. Others were formed by thermal spraying. It is clear from this that the parts of this invention have better corrosion resistance than conventional products.

【table】

[Table] As described above, the product of the present invention is significantly superior to conventional slide valve plates in terms of thermal shock resistance and corrosion resistance, and can be expected to last more than three times as long in actual use.

[Brief explanation of the drawing]

Figures 1 to 3 relate to conventional slide valves, in which Figure 1 is a schematic vertical cross-sectional view when the slide valve hole is open, Figure 2 is a schematic vertical cross-sectional view when the slide valve hole is open, and Figure 2 is a schematic vertical cross-sectional view when the slide valve hole is open. FIG. 3 is a schematic plan view showing damage to the slide valve plate, and FIG. 4 is a schematic plan view of the slide valve plate according to the present invention, with a and b showing a plan view and a vertical cross-sectional view, respectively. . In the figure, 10 is a sliding plate main body, 11 is a molten steel passing hole formed body, and 12 is a sliding surface thermal spray coating.

Claims (1)

[Claims] 1. 3 to 10 mol% of the low-expansion ceramic body
Slide valve plate for controlling the flow rate of molten steel coated with ZrO ₂ semi-stabilized with MgO. 2. The slide valve plate for controlling the flow rate of molten steel according to claim 1, wherein the sliding portion of the slide valve plate is entirely or partially covered. 3. The slide valve plate for controlling the flow rate of molten steel according to claim 1, wherein the inner peripheral surface of the molten steel passage hole is coated with ZrO ₂ semi-stabilized with 3 to 10 mol% MgO.