JPS6127146B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a casting method using a belt-and-wheel type continuous casting machine, and is particularly for continuously casting an ingot with high surface quality without causing defects such as cracks on the ingot surface. Conventionally, wire materials such as copper, copper alloy, aluminum, and aluminum alloy have been cast using a belt-and-wheel type continuous casting machine, and then rolled using a continuous rolling mill connected thereto. Therefore, the ingots cast by a continuous casting machine do not have their surfaces polished.
Since it is rolled using a continuous rolling mill, the ingot must be of high quality and free from defects such as surface cracks. In a belt-and-wheel type continuous casting machine, the mold is made up of a rotary casting wheel with grooves on its outer circumferential surface and an endless belt that partially contacts the outer circumferential surface. Molten metal is poured and the ingot is continuously pulled out from the other end, but cracks often occur on the surface of the ingot, so improvement is desired. In view of this, the inventors of the present invention have conducted various studies on the occurrence of cracks on the surface of an ingot during continuous casting, and have found that cracks that occur on the surface of an ingot are caused by the following factors. (1) Grain boundaries are weak. (2) The initial solid phase is reheated during the solidification process. (3) Tension is applied to the initial solid phase. The basic factors (1) to (3) are related to the state of the molten metal poured into the mold. In other words, the above three factors are related to the relative velocity ratio between the molten metal already filled in the mold and the newly poured molten metal, and if the relative velocity ratio is too small, the above (1) and (2) will be promoted and the If it is too long, the above-mentioned (2) and (3) will be promoted and cracks will occur on the surface of the ingot. Therefore, in order to prevent cracks on the ingot surface, it is necessary to maintain the above-mentioned relative speed ratio within an appropriate range, and this relative speed ratio is determined by the ratio of the ingot internal cross-sectional area to the internal cross-sectional area of the pouring spout. It's decided by then. Belt-and-wheel type continuous casting machines perform horizontal pouring, inclined pouring, or vertical pouring, but in horizontal pouring, the relative velocity ratio is small, so the number of nucleations is small and the crystal grains become coarse. The above factors
(1) occurs, and the initial cooling on the belt side becomes excessive, and the solidification shrinkage of the initial solid phase causes factor (2), which causes cracks to occur on the surface of the ingot. In addition, tilt pouring and vertical pouring have a large relative velocity ratio, which is advantageous for factor (1), but the fast pouring flow causes factor (2) and causes initial solidification. There is a large temperature difference between the final solidification zone and the final solidification zone, causing factor (3).
It is recognized that cracks occur on the surface of the ingot. The present invention is based on the above knowledge, and as a result of further studies, we have developed a continuous casting method for ingots with high surface quality without causing defects such as cracks on the ingot surface. A mold is made up of a rotary casting wheel equipped with a rotary casting wheel and an endless belt that comes in contact with a part of the outer circumferential surface. Molten metal is poured into the mold through a spout attached to one end of the mold, and the ingot is continuously drawn out from the other end. In the casting method, the ratio A/a between the cross-sectional area A in the mold and the cross-sectional area a in the spout is 1.05 to
7.5, and the difference U-V between the molten metal flow velocity U in the spout and the molten metal flow velocity V in the mold is 0.25 ~
It is characterized by casting at a casting speed of 110 m/min. That is, as shown in FIG. 1, the present invention comprises a mold 3 consisting of a rotary casting wheel 1 which rotates in the direction of the arrow and has a concave groove on its outer circumferential surface, and an endless belt 2 that partially moves in contact with the outer circumferential surface of the rotary casting wheel 1. A casting method in which a pouring spout 4 is attached to one end of the mold 3, molten metal is poured into the mold 3 through the spout 4, and the ingot is continuously drawn out from the other end of the mold 3, although not shown in the figure. In the above, the cross-sectional area in the spout 4 is a, the molten metal flow rate is U, the cross-sectional area in the mold 3 is A, and the molten metal flow rate is V. Using the spout 4 where A/a is 1.05 to 7.5, the molten metal speed difference is (U-V) is 0.25 to 110m/min
Continuous casting is performed at a casting speed within the range of . In the figure, 5 indicates a presser roll. Therefore, A/a is 1.05 to 7.5, molten metal velocity difference (U
-V) was set to 0.25 to 110 m/min for the following reason. As is clear from Figure 1, in order to perform continuous casting, Ua = VA must be satisfied. Therefore, the relative speed ratio U/V can be considered as A/a. In the present invention, the optimum conditions for this A/a and the molten metal velocity difference (U-V) have been experimentally determined. That is, considering the weakness of grain boundaries, which is the factor (1), the strength T of grain boundaries can be considered as the following quadratic function. T = (Gs, Se) Cs: Grain size Se: Degree of segregation Therefore, if A/a is too small, the crystal grains will become coarse and the number of grain boundaries will decrease, which will easily lead to stress concentration in this area. Furthermore, since the flow of the molten metal is small, the solute-rich phase discharged to the grain boundaries cannot be dispersed, and the degree of grain boundary segregation increases. In order to eliminate this drawback, by providing an appropriate molten metal velocity difference (U-V), the crystal grains are refined by an appropriate turbulent flow effect, avoiding stress concentration at grain boundaries, and at the same time dispersing segregation. A/a is at least 1.05 or more, and the molten metal velocity difference (U-V) is 0.25 m/min.
It is necessary to do more than that. Furthermore, the reheating phenomenon of the initial solid phase, which is the factor (2), is caused by the formation of an air gap between the ingots due to an excessive cooling rate during the initial solid phase formation. Therefore, it is necessary to reduce the degree of this initial cooling, but since this is mostly determined by the temperature of the mold, it is sufficient to raise the temperature of the mold by some method. For this reason, the molten metal poured into the mold is brought into contact with the inner surface of the mold in a fluid state, and is referred to as A/a.
1.05 or more, molten metal velocity difference (U-V) 0.25m/
Must be greater than or equal to min. On the other hand, if A/a and the molten metal velocity difference (U-V) become too large, a reheating phenomenon of the initial solid phase occurs due to another mechanism. That is, as shown in FIG. 2, the initial solid phase 6 already formed on the surface layer is heated from the inside by the molten metal flow from the spout 4 in the direction of the arrow. Therefore, to prevent this, A/a should be 7.5 or less, and the molten metal velocity difference (U-V) should be 110.
It is necessary to keep it below m/min. Next, factor (3), which is stress applied to the initial solid phase, is caused by the same phenomenon as factor (2). That is, since the initial solid phase portion heated by the molten metal flow has a lower cooling rate than other portions, this becomes the final solidification position, and tensile stress is concentrated here. Therefore, to prevent this,
This can be solved using the same method as the countermeasure for factor (2) above. The method of the present invention can be applied not only to the conventional horizontal pouring but also to vertical pouring to prevent cracks on the surface of the ingot. Further, as shown in FIG. 3, the angle θ of the spout 7 of the spout 4 may be varied within the range of 0 to 90 degrees. Next, examples of the present invention will be described. A mold with a cross-sectional area of 3000 mm ² is formed by a casting wheel with an outer diameter of 3 m with a groove on its outer circumferential surface and an endless belt that partially contacts the outer circumferential surface, and a pouring spout is attached to one end of the mold. Continuous casting of aluminum was carried out, and the surface condition of the ingot was investigated when the internal cross-sectional area of the spout and the difference in molten metal flow velocity were varied. Table 1 shows the mold internal cross-sectional area A and the spout internal cross-sectional area a.
The ratio A/a, the velocity difference (UV) between the molten metal flow velocity V in the mold and the molten metal flow velocity U in the spout, and the surface condition of the obtained ingot are shown.

【table】

[Table] As you can see from Table 1, A/a is 1.05 to 7.5, U
-V was within the range of 0.25 to 110 m/min, and no defects such as cracks were observed in the ingots that were continuously cast by the method of the present invention. On the other hand, A/a is 1.05
In comparison method No. 9, where A/a is smaller than 7.5, and comparison method No. 10, where A/a is larger than 7.5, cracks occur on the ingot surface.
Comparison method No. 1 where UV is less than 0.25m/min.
11, U-V is greater than 110m/min Comparison method No. 12
Cracks also occurred on the surface of the ingot. As described above, according to the method of the present invention, the belt-and-wheel type continuous casting machine, which is caused by weak grain boundaries, reheating of the initial solid phase, tension applied to the initial solid phase, etc. This method has the remarkable effect of improving the root of the surface defects of the ingot caused by molding, and preventing the occurrence of surface cracks, etc.

[Brief explanation of the drawing]

FIG. 1 is an enlarged explanatory diagram of the main part showing one embodiment of the method of the present invention, FIG. 2 is an enlarged explanatory diagram of the main part showing the defect occurrence situation in the comparative method, and FIG. 3 is a diagram showing another embodiment of the present invention. FIG. 2 is an enlarged explanatory diagram of main parts. 1... Casting wheel, 2... Endless belt, 3...
...Mold, 4...Spout, 5...Press roll, 6
...Initial solid phase, 7...Pouring port.

Claims (1)

[Claims] 1 A mold is constructed of a rotary casting wheel with grooves on its outer circumferential surface and an endless belt that partially contacts the outer circumferential surface. Molten metal is poured into the mold through a spout attached to one end of the mold, and cast from the other end. In a casting method in which a lump is drawn out continuously, a spout is used in which the ratio A/a of the cross-sectional area A in the mold to the cross-sectional area a in the spout is 1.05 to 7.5, and the flow rate U of the molten metal in the spout and the molten metal in the mold are The difference U-V from the flow velocity V is 0.25 to 110 m/
A continuous casting method characterized by casting at a casting speed of min.