JPH05337637A - Filter for removing non-metallic inclusion - Google Patents

Abstract

PURPOSE:To improve the quality and the productivity of a steel by forming a filter as a screw shape molten metal passage having plural bending parts. CONSTITUTION:The colliding hole type filter for filtrating molten metal is formed as the screw shape molten metal passage having plural bending parts. The screw shape is made to satisfy the condition of 30-100mm the outer diameter, 10-90mm the inner diameter and 10-20mm the screw pitch and the thickness of the filter is made to be 50-100mm. The material of the filter is suitable to be constituted with a refractory combined of MgO, Al2O3, CaO, MgO-CaO, Al2O3-SiO2 (particularly mullite quality). By action of the plural bending parts formed with female screw type thread ridge, the contact surface of the molten metal in the molten metal passage is increased and the removing efficiency of inclusion is drastically improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonmetallic inclusion removing filter which is disposed in a tundish or the like in a steel continuous casting facility and is used for removing nonmetallic inclusions in molten steel.

[0002]

2. Description of the Related Art In recent years, due to the demand for improving the quality of steel materials, it has become an important subject to remove non-metallic inclusions which adversely affect the workability, mechanical properties and surface quality of steel in molten steel. .. Conventional methods for removing non-metallic inclusions in molten steel (abbreviated as "inclusions" for convenience of description below) are to install a weir in the tundish or to separate the levitation by forming an upward flow of gas-blown bubbles. Most of them were urged, but recently, various filtration techniques using a fireproof filter have been studied as a new technique.

For the filtration method using this fire resistant filter, a through-hole type, impingement hole type, laminated mesh type, refractory-filled type or foam type filter is used. Figure 4
Is an example of the use of the fireproof filter, Tundish 1
In this example, a refractory filter 12 is installed in place of the conventional weir to remove inclusions in the molten steel in the tundish. Among the above various types of fire resistant filters, the through-hole type filter 12 is a conventional weir having a through hole 12-1 having a circular or rectangular cross-section, as shown in FIG. The inclusions are trapped in the flow path in the process of flowing. The collision hole type filter is, as shown in FIG. 6, two through hole type filters 13-1 and 13-.
It is a structure having a through hole 13-3 with a refraction portion formed by stacking two layers, and is designed so that molten metal collides with the refraction portion. The laminated mesh type filter has a honeycomb structure in which a plurality of layers formed in a mesh shape are laminated, and inclusions are captured by each mesh. The refractory material-filled type filter is a structure in which a refractory granular material having a diameter larger than that of the through hole is filled between two weirs having through holes, and inclusions are captured in the process of flowing between the granular materials. (See JP-A-56-47509, etc.). The foam type is an irregular mesh type, so to speak, a filter obtained from a molded product having a sponge structure (see Japanese Patent Application Laid-Open No. 1-218751).

[0004]

However, in the above-mentioned conventional refractory filter, the molten steel processing amount dramatically increased due to the enlargement of the converter in the recent steel process or the increase in the number of castings in the continuous casting machine. This is one of the factors that hinder the improvement of quality and productivity.

That is, the through-hole type filter is structurally low in inclusion removal efficiency. As a method of utilizing this through-hole type filter, in order to obtain the required cleanliness of steel quality, a plurality of weirs or filters are installed in the tundish, or a digestion phenomenon (slakin) is used as a filter.
The material of the remarkable calcia of g) is selected. Therefore, tundish construction, maintenance in terms of furnace body maintenance,
Inspection work is complicated. The collision hole type filter is
Since two through-hole filters are laminated to obtain the required refraction portion, the strength of each filter (plate-shaped molded body) is unstable, and there is a problem with the reliability of the refractory molded body. Yes, a plurality of refraction portions cannot be provided. Further, it is impossible to give an arbitrary shape to a certain filter thickness according to the purpose of use and conditions. The laminated mesh type or foam type has a great effect of trapping inclusions, but if the amount of treatment per treatment exceeds 500 tons, clogging at the inlet of the flow channel becomes remarkable and the treatment itself becomes difficult. On the other hand, while the refractory-filled type is capable of large-scale processing, it is easy for floating and outflow of particulates, and energy required for preheating and heat retention in advance, etc.
The complexity of maintenance is so great that virtually stable operation cannot be maintained.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to propose an inclusion removal filter having a large effect of capturing non-metallic inclusions and capable of stably processing a large amount of molten metal. To do.

[0007]

Means for Solving the Problems The inventors of the present invention have prototyped a collision hole type filter in which a large number of various threads are formed on the inner surface of the flow path of an existing through hole type filter, and various threads (female thread type) As a result of conducting a molten steel passage test on a filter having the above, it is possible to process a larger amount of molten metal than the conventional impingement hole type filter by the action of the refraction part formed by the screw thread, and the size of the screw. It was found that the trapping effect of inclusions varies depending on the pitch, pitch, and filter thickness.

Based on this finding, the present invention has found an impingement hole type filter that enables a large amount of molten metal to be processed by forming a bent portion by a plurality of screws in a molten metal flow path. Is characterized in that the molten metal flow path has a thread shape having a plurality of bending portions, and the thread shape is 100 mm at an outer diameter of 30 mm or more.
It is a filter for molten metal filtration which satisfies the conditions of mm or less, an inner diameter of 10 mm or more and 90 mm or less, a screw pitch of 10 mm or more and 20 mm or less, and a filter thickness of 50 mm or more and 100 mm or less.

[0009]

According to the present invention, the contact area of the molten metal in the molten metal flow channel is increased by the action of the plurality of refraction portions formed by the female thread, and the inclusion removal efficiency is remarkably improved.

The thread shape of the molten metal channel has an outer diameter of 3
0 mm or more and 100 mm or less, inner diameter 10 mm or more and 9
The reason why the screw pitch is limited to 0 mm or less and the screw pitch is 10 mm or more and 20 mm or less is as follows. That is, when the outer diameter of the screw is less than 30 mm, clogging with the adsorbed inclusions is likely to occur, which makes large-scale processing difficult. On the other hand, when it exceeds 100 mm, the strength of the filter itself as a molded body becomes low and it is difficult to put it into practical use. Therefore, the outer diameter (valley) of the screw is 30
It is limited to not less than 100 mm and not more than 100 mm. Also,
The internal diameter of the screw is limited to 10 mm or more and 90 mm or less (the unevenness of the screw portion is 5 mm or more and 20 mm or less)
If it is less than 0 mm, there is a problem that the pores of the refractory raw material are likely to be clogged and the required profile is difficult to obtain. This is because it is easy to do. Also, for the same reason, the interval between the uneven surfaces as the screw pitch is 10 m.
It is desirable that the distance is m or more and 20 mm or less.

Further, the filter thickness is 50 mm or more 10
The reason for limiting the length to 0 mm or less is that if the thickness is less than 50 mm, the strength of the filter itself becomes insufficient, while if it exceeds 100 mm, preheating before use becomes insufficient and molten metal may solidify in the holes.

The material of the filter is required to have a refractory degree that can withstand the use temperature and a strength that can maintain its shape, and it is preferable that it does not contain SiO ₂ for the purpose of melting molten steel. Al ₂ O ₃ , CaO, MgO
-CaO, Al ₂ O ₃ -SiO ₂ (especially mullite) -based combination is preferably used as the refractory raw material.

The filter may be molded by any of press molding, casting, and vibration molding. The bulk density varies depending on the material, but the apparent porosity is 20 to 30%.
It suffices that a molding state of a certain degree be obtained.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a method for molding a filter for removing non-metallic inclusions according to the present invention, in which 1 is a lower mold, 2 is an upper mold, 3 is a thread-forming core rod, 4 is an outer frame, and 5 is an outer frame. Is an outer frame receiver, 6
Is the Oshiage stand.

That is, when molding the filter, the lower end of the thread-forming core rod 3 is screwed onto the lower mold 1, and the raw material is put into the outer frame 4. Thereafter, the upper mold 2 is pressed from above to obtain the required bulk density. After molding, the upper mold 2 is removed, the screw forming core rod 3 is rotated in the opposite direction to pull out from the molded body, and then the lower mold 1 is pushed up by the push-up base 6 and the molded body is taken out from the outer frame. .. The molded body can be heat-treated as necessary to increase its strength.
Therefore, the filter according to the present invention can be manufactured by either a non-firing or firing method. Also, by using a flammable and easily extinguishable material (for example, wood) for the thread forming core rod 3, the extraction step can be omitted. According to such a molding method, the cross-sectional shape of the filter hole, that is, the molten metal flow channel can be arbitrarily determined by the outer shape of the thread forming core rod 3.

2A and 2B exemplify the cross-sectional shape of the molten metal channel according to the present invention. FIG. 2A is a square thread channel, FIG. 2B is a trapezoidal thread channel, and FIG. A saw-tooth channel, FIG. (D) shows a round screw channel. In the figure, 9 is a filter body, 9-1 is a square thread type flow path, 9-2 is a trapezoidal thread type flow path, 9-3 is a sawtooth shape flow path, 9-4 is a round thread type flow path, D ₁ Is the outer diameter, D ₂ is the inner diameter, h is the recess / protrusion of the threaded portion,
l is the screw pitch, and L is the thickness.

That is, by making the cross-sectional shape of the thread-forming core rod 3 into a square thread shape, a trapezoidal thread shape, a sawtooth shape, and a round thread shape, the square thread type flow path (A) of FIG. ) It is possible to easily obtain a trapezoidal screw-shaped flow channel, a (C) serrated flow channel, and a (D) round screw-shaped flow channel. In each of these thread shapes, in the present invention, the outer diameter D ₁ is 30 mm or more and 100 mm or less, the inner diameter D ₂ is 10 mm or more and 90 mm or less, the screw pitch 1 is 10 mm or more and 20 mm or less, and the thickness L is 50 mm or more and 100 mm or less.

Example 1 An alumina raw material having an average particle diameter of 200 μm was kneaded with a phosphate, and a molding pressure of 200 was obtained by the uniaxial pressing method shown in FIG.
A cylindrical molded body (outer diameter 40 mm, length 50 mm) molded at kg / cm ² is heat-treated at a temperature of 200 ° C. to form three types of molten metal: a square screw shape, a sawtooth shape, and a taper shape (conventional example). An internal type filter 9 having a flow path is manufactured, and each filter is loaded in a lower nozzle 10 of a stopper 8 opening / closing system of a small molten steel storage tank 7 shown in FIG. The adhesion situation of the object was investigated. Table 1 shows the dimensions of the above three kinds of molten metal channels.

[0019]

[Table 1]

In this embodiment, the small molten steel storage tank 7 has a temperature of 1
When the molten steel at 550 ° C. was stored in the 500 mm head, the molten steel was simultaneously discharged, the molten steel was allowed to pass through while maintaining a constant head for 10 minutes, the stopper 8 was closed, the storage tank 7 was tilted, and the residual hot water was discharged and discharged. Chilled After cooling, the filter was recovered, the adherent metal was dissolved with an acid, and the adherent was recovered as a solution residue, weighed, and the form was investigated. As a result, the recovery rate of the Al ₂ O ₃ -based deposits by the conventional tapered channel is 2.3 times that of the square screw channel of the present invention and 1.9 times that of the saw tooth channel. And the effectiveness of the filter of the present invention was confirmed.

Example 2 A square threaded filter was placed in front of one casting port (with a slide gate opening / closing mechanism) of a tundish (two strands) for a T-shaped Bloom CC having a capacity of 30 tons, and aluminum killed steel was cast. The cleanliness of steel when loaded into the tundish is shown in FIG.
The results are shown in Table 2 in comparison with the case of casting with a weir (conventional example) consisting of 2). The filter of the present invention is an alumina non-fired refractory material (Al ₂ O ₃ 95%) and has a thickness of 55 m.
m, height 800 mm, upper bottom 500 mm, lower bottom 800 mm
It is a kind of inverted trapezoidal weir. There are 20 molten steel flow paths,
The molten steel inlet side (square screw outer diameter) was 75 mm, the outlet side (square screw inner diameter) was 50 mm, and the screw pitch was 15 mm.

In this embodiment, the total number of castings is 5 when the number of castings is 4
A sample of 00 tons of molten steel was cast, and a sample was collected from a slab of a steady portion cast at a predetermined drawing speed for each casting. The cleanliness of steel is compared by JIS-G0555 by the amount of inclusions,
The cleanliness without an ordinary weir was set to 100 and indicated by the compared index.

As is clear from the results shown in Table 2, by using the filter of the present invention, the cleanliness of the steel can be remarkably enhanced, and the influence of the mother molten steel for each casting can be averaged to adsorb inclusions. It turned out to show Noh.

[0024]

[Table 2]

[0025]

As described above, since the collision hole type filter of the present invention has a high ability to adsorb inclusions, it is possible to process a large amount of molten metal which cannot be dealt with by the conventional filter, and the size of the converter is increased. Alternatively, it can sufficiently cope with molten steel treatment by increasing the number of castings in a continuous casting machine, and has a great effect on improvement of steel quality and productivity. Further, structurally, since it is composed of an integrally molded body, the strength as a refractory molded body is stable even if it is provided with a plurality of refraction portions, and not only it has a reliable effect, but also a certain filter. The filter is extremely excellent as a filter for removing inclusions in steel because it has the advantage that it can provide an arbitrary flow path shape depending on the purpose of use and conditions with respect to the thickness.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing an example of a method for molding a non-metal inclusion removal filter according to the present invention.

2A and 2B are views exemplifying a cross-sectional shape of a molten metal flow channel according to the present invention, where FIG. 2A is a square thread channel, FIG. 2B is a trapezoidal thread channel, and FIG. Tooth-shaped flow channel, FIG. (D) is a vertical cross-sectional view showing a round screw type flow channel.

FIG. 3 is a vertical sectional view showing a nozzle portion of a small molten steel storage tank according to an embodiment of the present invention.

FIG. 4 is a schematic perspective view showing an example of using a tundish of a fireproof filter.

FIG. 5 is a vertical sectional view showing an example of a sectional structure of a conventional through-hole filter.

FIG. 6 is a vertical cross-sectional view showing an example of the cross-sectional structure of a conventional impingement hole filter.

[Explanation of symbols]

 1 Lower mold 2 Upper mold 3 Screw forming core rod 4 Outer frame 5 Outer frame receiver 6 Push-up base 7 Small molten steel storage tank 8 Stopper 9 Lower nozzle

Claims (2)

[Claims] 1. A non-metallic inclusion removal filter, which is a collision hole type filter for molten metal filtration, and has a screw-shaped molten metal flow path having a plurality of refraction portions. 2. A molten metal filtering filter having a screw-shaped molten metal channel, the screw-shaped filter having an outer diameter of 3
0 mm or more and 100 mm or less, inner diameter 10 mm or more and 9
A non-metal inclusion removal filter characterized by satisfying conditions of 0 mm or less, a screw pitch of 10 mm or more and 20 mm or less, and a filter thickness of 50 mm or more and 100 mm or less.