JPH0588286B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention belongs to the field of removing minute inclusions contained in molten metal using a ceramic filter in tandem casting. This invention relates to a method for preventing filter clogging. (Conventional technology) As part of high-cleanliness steel manufacturing technology, various methods for removing inclusions in tundishes have been studied, but the representative methods include (1) inclusions caused by improving the shape and increasing the size of tundishes; (2) Agglomeration and flotation separation of inclusions by blowing gas from the bottom of the tundish (3) Controlling and adsorption of inclusions by adding flux (4) Preventing foreign inclusions from entering the tundish by improving the lining material of the tundish There is absorption into the lining, etc. However, with these methods, it is difficult to remove minute inclusions, for example those with a diameter of 50 μm or less. On the other hand, if a ceramic filter is used, the above-mentioned minute inclusions can be removed. (Japanese Unexamined Patent Publication No. 56-62509) A ceramic filter has a three-dimensional network structure, for example, a skeleton structure such as polyurethane foam, and the material is replaced with ceramics such as alumina or zirconia, and it has high performance. Moreover, it has the characteristics of low pressure loss. The present inventors investigated the use of this ceramic filter by installing it in a tandem weir. FIG. 2 shows the installation position of the ceramic filter when applied to the tundish 1. The ceramic filter 6 is supported on a weir 5 as shown in FIG. 3, and the weir 5 is provided between the long nozzle 2 and the immersion nozzle 4. In addition, 3 is a stopper. (Problems to be Solved by the Invention) When casting is carried out in this state, as is well known, the molten steel at the initial stage of casting is filled with fillers (silica sand, etc.) for the initial opening of the ladle sliding nozzle, and peeled off materials from the tandice coating material. , a large amount of large inclusions, etc. are mixed in, and these cause clogging of the ceramic filter, resulting in the problem that not only can the inclusions not be removed, but the molten steel cannot flow downstream and cannot be cast. In view of the above points, the present invention aims to stably exhibit the function of removing minute inclusions without causing clogging of the ceramic filter in the initial stage of casting. (Means for solving the problem) In other words, slag, large inclusions, and refractory debris are brought to the surface as much as possible on the upstream side of the tundish, and then the molten steel that does not contain these is poured into a ceramic filter to remove minute inclusions and molded. In this method, a ceramic filter is installed in a continuous casting tundish to remove inclusions from the molten metal. Invented a method for removing inclusions using a ceramic filter in a tundish by placing a thick metal plate weir on top of the tundish that does not melt until the molten metal reaches the level, and injecting the molten metal at the initial stage of casting into the inflow side. did. Hereinafter, the content of the present invention will be explained in detail. Based on conventional knowledge, it has been known that large inclusions and the like will float if the residence time is sufficient, and this was applied and studied in the present invention. The method of the present invention is the first
As shown in the figure. That is, in order to prevent clogging of the ceramic filter due to slag, large inclusions, refractory debris, etc. in the early stage of continuous casting, an iron plate weir 7 is provided in front of the weir 5 (on the upstream side 8 of the tundish) where the ceramic filter 6 is provided. The molten steel is prevented from contacting the filter until the level of the molten steel containing slag in the initial stage of casting and large inclusions of refractory debris reaches the level of the top surface of the ceramic filter, or for a predetermined floating time in that state. In this way, after flotation treatment, the iron plate is melted, and the molten steel containing only minute inclusions is brought into contact with a ceramic filter and passed through, supplying highly clean steel to the downstream side of the tundish. In addition, to support the iron plate, a supporting refractory 10 is provided as shown in Fig. 3, and this supporting refractory 1
Insert between 0 and weir 5. The iron plate may be a flat plate with a constant wall thickness, but
In this case, in the initial stage of casting, there is a possibility that the lower part melts first and a small amount of molten steel passes through the filter, and it takes time for the specified amount to accumulate in the clean steel sump tank 9 beyond the filter, causing the temperature of the molten steel to drop. There is a risk of connection. Therefore, in order for the molten steel to flow out of all the filters of the weir 5 equipped with filters, the thickness of the iron plate is made into a wedge shape, thicker at the bottom and thinner at the top, as shown in Fig. 3, so that the molten steel sufficiently collects in front of the weir. It is preferable for the iron plate to melt at the same time and for the molten steel to flow out from the entire filter surface, since this does not involve the above-mentioned difficulties. To give a specific example, the bottom thickness is 1.6mm and the top thickness is 1.2mm.
An ordinary steel plate of 1.5 mm was used, but this value varies depending on the molten steel temperature, tundish capacity, shape, etc. (Example) Next, specific examples will be shown. A weir with 8 ceramic filters (diameter 130 mm, thickness 25 mm, cell size 5 to 7 ppi, material ZrO ₂ ) was installed approximately in the center of a 14 t tundish (distance 4 m from the long nozzle), and as a comparative example. Casting continued. About 3 minutes after casting, a problem occurred in which molten steel gradually stopped passing through the ceramic filter. When the filters were observed after cooling, most of the ceramic filters were clogged with refractory debris and large inclusions.
Therefore, we replaced the ceramic filter and installed an iron plate with the same shape as the weir, with a wedge-shaped wall thickness of 1.6 mm at the bottom and 1.2 mm at the top, on the upstream side of the tundish. (The present invention) It takes several seconds for the molten steel to accumulate to the top of the weir, and then the iron plate melts in a few seconds, and the molten steel passes through the entire ceramic filter. Furthermore, casting could be completed stably without clogging after two charges. As shown in Table 1, the fine inclusions in the obtained molten steel are reduced to about 1/2 by the present invention compared to before using the ceramic filter.
It dropped sharply to 10. Furthermore, when the filter was inspected after casting, it was found that many minute inclusions were adhered inside the filter, and there were hardly any large slag inclusions, refractory debris, etc.

[Table] Although the example shows the case where a weir with a ceramic filter is installed vertically to the flow of molten steel, the method of the present invention can be similarly applied when the filter is installed horizontally and the molten steel flows from top to bottom. is applicable. (Effects of the invention) As described above, in the method for producing clean steel using a ceramic filter, a thick iron plate is placed in front of the filter so that it does not melt until slag, large inclusions, refractory debris, etc. at the initial stage of casting are sufficiently floated. This makes it possible to prevent clogging of the ceramic filter due to slag, large inclusion debris, etc. at the initial stage of continuous casting, and to stably filter out inclusions in molten steel.

[Brief explanation of drawings]

FIG. 1 is a side view showing the iron plate insertion situation of the present invention;
FIG. 2 is a side view showing the state of the ceramic filter device in the tundish, and FIG. 3 is a front view of the weir with the ceramic filter. 1...Tandate dish, 2...Long nozzle, 3...
Stopper, 4... Immersion nozzle, 5... Weir with ceramic filter installed, 6... Ceramic filter, 7... Iron plate, 8... Initial casting sump tank, 9... Cleanliness steel sump tank, 10... Steel plate supported refractory.

Claims (1)

[Claims] 1. In a method of removing inclusions from molten metal by installing a ceramic filter in a continuous casting tundish, there is a layer of metal that does not melt until the molten metal level reaches the upper part of the ceramic filter on the front surface of the molten metal inflow side of the ceramic filter. A method for removing inclusions using a ceramic filter in a tundish, characterized by arranging a thick metal plate weir and injecting molten metal at the initial stage of casting into the inflow side.