JPS63126651A - Belt type continuous casting method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for smoothly continuously casting thin slabs using a two-reducing belt type thin slab continuous casting machine.

(Prior art) There are various types of continuous casting machines that continuously produce thin slabs such as sheet bars directly from molten metal, that is, belt-type continuous casting machines for thin slabs. This is described in Japanese Patent Application Laid-Open No. 59-92154.

This belt-type continuous thin slab casting machine is shown in Figure 1. This belt-type continuous thin slab casting machine is of a narrowing type and maintains a gap to hold the molten metal and solidified shell over a predetermined distance. At the same time, a plurality of guide rolls 3a+ 3b+ 3c, 3'a13''b, 3
The long sides of the mold are made up of a pair of opposing metal belts 1.2 which move circularly through the metal belts 1.2 and 1.2. The side mold constitutes the short side of the mold. especially,
The above-mentioned short side mold produces a thin slab with a thickness of 30 mm or less,
Considering the diameter of the injection nozzle 6 of about 100 mm or more, it has a substantially inverted triangular shape that is wide at the top, gradually tapers toward the bottom, and has a constant width at the bottom.

(Problems to be Solved by the Invention) When casting with the above-mentioned belt-type continuous caster, when the casting machine is in a normal casting state, the crater end 11 is cooled to the front as shown in FIG. The curved part of the metal belt provided with the pad 12 is located between the inflection point 10, which becomes the straight part, and the lowest end of the cooling band. However, if the pouring speed and casting speed into the casting space made up of the metal belts 1 and 2 and the short-side mold 4.5 do not match, the crater end 11 will form as shown in FIG. The curved portion of the metal belt may be located above the inflection point 0, which is the straight portion. in this case,
The thickness of the solidified shell is thicker than the thickness of the mold at the inflection point 10, which determines the thickness of the thin slab to be cast, that is, the thickness of the slab.For this reason, the solidified shell becomes an anchor and the metal belt rotates 1 to 20 times. or the water film between the metal belts 1 and 2 and the cooling pad 12 is crushed, causing the metal belt to melt and become impossible to cast.Furthermore, even if casting can be continued, cracks may occur inside the thin slab. or the surface quality of the thin slab may deteriorate.Also, as shown in FIG. 4, the crater end 11 may be located below the lowest end of the cooling pad. In this case, bulging occurs in the thin slab 7 due to the static pressure of the molten metal.This may cause internal cracks in the thin slab, or the amount of bulging may become too large (if the pinch roller overcomes the bulging area). This makes it impossible to continue casting.

The purpose of the present invention is to always position the crater end between the inflection point of the metal belt and the lowest end position of the cooling pad to ensure smooth casting when performing casting with a heald-type continuous caster. The objective is to prevent internal cracks and surface cracks in thin slabs.

(Means for Solving the Problems) The present invention includes a pair of opposing belts that circulate while maintaining a gap for holding the molten metal and solidified shell over a certain distance, and a belt near the side edge of the belt. When continuously casting thin slabs using a belt-type continuous casting machine, which consists of a short-sided mold that is wide at the top, gradually tapered to a constant width at the bottom, and is in close contact with the belt, melting into the mold space is carried out. The above-mentioned problems can be solved by using a belt-type continuous casting method characterized by controlling the solidification thickness at the tapered tip by adjusting the metal meniscus height h(t) and the casting speed v(t). solved.

The conditions necessary to realize the normal casting condition shown in FIG. 2 will be explained based on FIG. 5.

In Figure 5, the inflection point 10 between the R part and the straight part of the belt
The arc length of the belt at time t until it reaches a meniscus is It) The length of the straight part of the belt is m, and the time required to develop a solidified shell half the thickness of the thin slab on the belt is x. , and the casting speed is v(t). In order to maintain the normal casting condition shown in Fig. 2, the following formulas must be satisfied. The above conditions are essential conditions for achieving normal casting. It is. It) in the above formula is given by h(t), where h(t) is the meniscus height at time t from the inflection point 10 between the R section and the straight section of the belt, so (1)
Since the equation (2) can be expressed as follows, it is sufficient that the meniscus height h(t) and the casting speed ν(1) at time t satisfy the following conditions.

By setting the meniscus height h(t) and casting speed v(t) that satisfy the above equation (6) at each time t, the solidified shell as shown in FIG. 3 becomes an anchor, or As shown in FIG. 4, bulging does not occur in the slab.

Otoko Shinl-tori 1 Using the belt-type thin slab continuous casting machine shown in Fig. 5,
85 tons of low carbon aluminum killed steel was cast into a thin slab with a thickness of 30 mm and a width of 500 mm under the casting conditions shown in the table. In addition,
The radius of the R part of the belt-type thin slab continuous casting machine is 1513 m.
m, the length m of the straight portion of the belt is 1150 mm, and the time x 1 for completely solidifying the slab thickness in the continuous casting machine is 22 seconds.

Table 1: Casting speed v(t) and meniscus height h(t
) changes over time were as shown in Figure 6.

Since the pouring speed ■ and the meniscus height h at each time shown in the same figure satisfied the above equation (6), internal cracks in the slab caused by the solidified shell acting as an anchor did not occur, and There were no internal cracks in the slab due to bulging, and good slabs could be cast smoothly.

Further, under the above casting conditions, casting was performed while varying the casting speed V(t) and the meniscus height h(t) as shown in FIG. 35 seconds after the start of casting, that is, after the start of pouring, the casting speed V and the meniscus height h deviated from the conditions of equation (6) above, so it is assumed that the slab was created due to the solidified shell acting as an anchor. An internal crack occurred.

Further, under the above casting conditions, casting was performed while varying the casting speed v(t) and meniscus height h(t) as shown in FIG. After the start of casting, that is, 30 seconds after the start of pouring,
Internal cracking of the slab occurred due to bulging that occurred because the pouring speed V and meniscus height h did not satisfy the conditions of equation (6) above.

Casting was carried out under the same casting conditions as in Example 1, ensuring a casting speed v(t) and a meniscus height h(t) that satisfied the equation (6). The relationship between the thickness d of the solidified shell formed on the belt at the inflection point between the R section and the straight section of the belt and the thickness d of the slab was investigated.

The results are shown in Figure 9. As the thickness dl of the solidified shell at the inflection point between the R section and the straight section of the belt increases, the rate of occurrence of internal cracks in the slab increases, and the ratio of d+/a increases. 0.95
The above has increased dramatically. The reason for this is that when the solidified shell moves from the R part of the belt to the straight part, the thickness d of the solidified shell at the inflection point between the R part and the straight part of the belt increases. In other words, it is estimated that the correction strain rate increases.

Casting was carried out under the same casting conditions as in Example 1, ensuring the casting speed v(t) and meniscus height h(t) that satisfied the above equation (6). The distance 12 from the meniscus to the crater end 11 and the distance 13 from the meniscus to the lower end of the cooling pad shown in FIG. 2, that is, the effective cooling length! ! The ratio of 3 and
Figure 10 shows the results of investigating the relationship with the surface crack index of slabs.

As can be seen from the figure, when the ratio of 12/β is less than 0.7, the surface crack index of the slab is high because the slab has been properly cooled, and when the ratio of β2/23 is 0.7 or more, the surface crack index of the slab is high. When this happens, the temperature of the slab increases, and the surface cracking index of the slab drastically decreases.

(Effects of the Invention) As explained above, according to the present invention, since the crater end is located between the inflection point of the metal belt and the lowest position of the cooling pad, a good thin slab can be smoothly cast. becomes possible.

[Brief explanation of the drawing]

FIG. 1 is an overall view of a belt-type thin slab continuous casting machine. FIG. 2 is a diagram showing a normal casting condition by a belt-type thin slab continuous casting machine, and FIGS. 3 and 4 are diagrams showing abnormal casting conditions by a belt-type thin slab continuous casting machine. FIG. 5 is a diagram showing the state of casting by a belt-type continuous thin cast slab casting machine. FIG. 6 is a diagram showing a normal casting pattern, FIG. 7 is a diagram showing a casting pattern in which a solidified shell serves as an anchor, and FIG. 8 is a diagram showing a casting pattern in which bulging occurs. FIG. 9 is a diagram showing the relationship between the internal cracking index of the slab and d+/d, and FIG. 10 is a diagram showing the relationship between the surface cracking index of the slab and 2□723. 1.2...Belt 3a-30'...Guide roll 4.5...Short side mold 6...Injection nozzle 7...
・Thin slab 8... Molten metal 9... Solidified shell 10... R-S inflection point 11... Crater end 12... Cooling pad Figure 2 Figure 3 Figure 4 Figure 6 Figure 7: [ Figure 8 [ 2 fortune-tama e adult beak 84 槁; Akira

Claims (1)

[Claims] 1. A pair of oppositely arranged belts that circulate while maintaining a gap to hold the molten metal and solidified shell over a certain distance, and a pair of belts that are in close contact with the belt near the side edges of the belt and are wide at the top and sequentially Adjusting the meniscus height and casting speed of molten metal into the mold space when continuously casting thin slabs using a belt-type continuous casting machine consisting of a short side mold that tapers and has a constant width at the bottom. A belt-type continuous casting method characterized by controlling the solidification thickness at the tapered tip.