JP4401896B2 - Semi-continuous casting method of aluminum or copper - Google Patents

Description

  The present invention relates to a semi-continuous casting method of aluminum or copper. Aluminum as used herein refers to all aluminum-based metals including so-called pure aluminum and aluminum alloys, and copper refers to all copper-based metals including so-called pure copper and copper alloys.

  In the semi-continuous casting method of aluminum and copper, the molten metal is supplied into a circular or rectangular mold with both ends open, primary cooling to solidify the ingot surface layer in the mold, and cooling water is drawn out from the mold. It is a method of performing continuous casting by performing secondary cooling in which it is directly supplied to the ingot surface and cooling, and is widely used all over the world. In particular, the vertical semi-continuous casting method in which the casting direction is vertical is the mainstream.

In this method, the structure of the solidified shell portion formed in the mold may become non-uniform. For aluminum casting, many improved technologies such as hot top casting and electromagnetic field casting have been developed. This is the same in that direct cooling (secondary cooling) is used.
Water is a cooling medium that can cool an object rapidly and is suitable for continuous casting. However, if the ingot surface is strongly cooled with water, cracks may occur when the ingot center is solidified.
Particularly, in the semi-continuous casting method of aluminum or copper, the cooling from the mold is small, and the solidification inside the ingot is strongly influenced by the direct cooling by the cooling water.

On the other hand, the same casting method is adopted for steel, but mold cooling is dominant for solidification, and there are few problems of internal cracks due to direct cooling water.
As countermeasures against internal cracks, slowing the casting speed is often taken as a countermeasure, which is a major factor that hinders casting productivity.
For this reason, Patent Document 1 proposes that the ingot is gradually cooled with cooling water mixed with a gas such as carbon dioxide. However, in addition to the normal cooling water piping, a gas piping and a mixing device are required, and a device for mechanically controlling the slow cooling region is also required separately. For example, when casting an ingot having a circular cross section, it is common to cast several dozens simultaneously in a narrow space, and this method is not practical. In addition, there are also problems such that a device is required for each different ingot size, the length of the slow cooling region cannot be easily changed, and a large amount of special gas is required.

Japanese Patent Laid-Open No. 58-212849

  The present invention has been made in view of such conventional problems, and it is intended to provide a semi-continuous casting method of aluminum or copper that can increase the casting speed and that does not cause cracks when the center is solidified. It is what.

The first invention is a semi-continuous casting method of aluminum or copper in which a molten metal is poured from one end of a mold whose both ends are released, and a solidified ingot is continuously drawn from the other end of the mold.
After performing the primary cooling for cooling the molten metal or the ingot with the mold, the cooling water collides with the ingot surface drawn from the mold to perform the secondary cooling. The film boiling cooling is performed in a predetermined region on the casting direction side from the collision position, and the nucleate boiling cooling is performed when the predetermined region is exceeded,
And the said ingot is D = 140-600 (mm) when the diameter is set to D, The said predetermined area | region to which the said film boiling cooling is carried out from the position where the said cooling water collides in a casting direction is 0. The method is a semi-continuous casting method of aluminum or copper, characterized in that the range is 2 × D + 20 (mm) to 1.5 × D (mm ).
The second invention is a semi-continuous casting method of aluminum or copper in which a molten metal is poured from one end of a mold whose both ends are released, and a solidified ingot is continuously drawn out from the other end of the mold.
After performing the primary cooling for cooling the molten metal or the ingot with the mold, the cooling water collides with the ingot surface drawn from the mold to perform the secondary cooling. The film boiling cooling is performed in a predetermined region on the casting direction side from the collision position, and the nucleate boiling cooling is performed when the predetermined region is exceeded,
And the starting point of the said nucleate boiling cooling is located in the casting direction side rather than the solidification start point of the center of the said ingot, It exists in the semi-continuous casting method of the aluminum or copper characterized by the above-mentioned.

  In the present invention, as described above, when performing secondary cooling, film boiling cooling is performed in the predetermined region, and nucleate boiling cooling is performed when the predetermined region is exceeded. By positively adopting such a combination of cooling states, the casting speed can be made faster than before and cracks can be prevented from occurring in the ingot.

The reason is considered as follows.
In general, water cooling is divided into film boiling cooling, film boiling-nucleate boiling transition cooling, nucleate boiling cooling, and forced convection cooling from the high temperature side, depending on the surface temperature of the object to be cooled, and is the strongest during nucleate boiling cooling. The
In a normal semi-continuous casting method, nucleate boiling occurs at a position where the cooling water collides with the ingot surface, and the ingot surface is strongly cooled. For this reason, the cooling rate of the ingot surface becomes maximum before and after the cooling water collision position, and the cooling rate of the ingot surface decreases as the position becomes closer to the casting direction than this position.

  The crack at the center of the ingot is generated because the surrounding solidified layer constrains the shrinkage when the center is about to solidify and shrink. This restraining force is relaxed when the thermal contraction of the surrounding solidified layer is large, and conversely, it becomes remarkable when the thermal contraction of the solidified layer is small. In other words, when the central portion is about to solidify, if the solidified layer around it is slow to cool and the amount of heat shrinkage is small, the above restraining force is generated due to the difference between the amount of shrinkage, and cracks are likely to occur.

In the semi-continuous casting method, as the solidification position at the center moves from the nucleate boiling position toward the casting direction, the amount of heat shrinkage of the solidified layer decreases and cracks are more likely to occur. That is, the ease of cracking is strongly influenced by the relationship between the nucleate boiling position and the central solidification position. Usually, since the central solidification position is on the casting direction side with respect to the nucleate boiling position, cracks are less likely to occur if the central solidification position is moved as far as possible in the anti-casting direction side.
The method of reducing the casting speed is widely adopted because it is an easy and effective method for moving the center solidification position in the anti-casting direction. However, this measure by reducing the casting speed has the greatest drawback that casting productivity is hindered.

  Here, in the present invention, as described above, when performing secondary cooling, film boiling cooling is performed in the predetermined region, and nucleate boiling cooling is performed when the predetermined region is exceeded. Thereby, crack prevention can be achieved by a completely different method from the method of moving the solidification position of the central part to the opposite side to the casting direction as much as possible by reducing the casting speed.

  That is, sudden nucleate boiling cooling is intentionally avoided in the secondary cooling, and film boiling cooling is first performed in a predetermined region, followed by nucleate boiling cooling. Thereby, the nucleate boiling position can be moved to the casting direction side, and the nucleate boiling position can be brought closer to the center solidification position without moving the center solidification position to the side opposite to the casting direction. As a result, it is possible to increase the temperature reduction rate of the surrounding solidified layer during solidification of the central portion and increase the amount of heat shrinkage, and to suppress cracks in the central portion.

  Therefore, if the semi-continuous casting method of the present invention is used, cracks can be prevented without reducing the casting speed as in the prior art, and a high-quality ingot can be obtained with high efficiency.

  In carrying out the present invention, it is necessary to set and manage a casting speed and cooling conditions that can realize the above cooling method. Here, the casting speed and the cooling conditions differ greatly depending on each casting equipment or the size of the ingot to be cast. Therefore, it is necessary to determine the casting conditions in advance, but this can be performed by a method similar to that for ordinary casting conditions in the art, requiring excessive trial and error and complicated advanced experiments. Not what you want. In addition, since the current equipment can be used, the effect of adopting the present invention is enormous.

  In the present invention, when performing the secondary cooling, the film is boiled and cooled by the cooling water collided with the ingot surface, and then nucleate boiled using the cooling water itself used for the film boiling cooling. It is preferable. Thereby, adjustment of cooling conditions can be simplified compared with the case where the cooling water for film | membrane boiling and the cooling water for nucleate boiling are discharge | released separately and each is controlled by another system | strain. Furthermore, since many existing facilities are configured to discharge only one system of cooling water for secondary cooling, the existing facilities can be used as they are.

  In addition, in order to easily realize the cooling conditions for film boiling using this kind of cooling water and further nucleate boiling, vertical semi-continuous with the casting direction from top to bottom in the vertical direction. It is most effective to adopt casting. In this case, since the cooling water can be smoothly lowered along the ingot surface over the entire circumference of the ingot by utilizing its own weight, the adjustment of the predetermined region for film boiling cooling is also possible. Relatively easy.

In the present invention, in order to realize film boiling cooling with the cooling water, it is preferable that at least the value of the cooling water flow rate / casting speed is less than a predetermined value.
For example, when cooling water is supplied into a hollow mold and the cooling water is discharged from a slit provided in the mold, the flow rate of the cooling water (equal to the amount supplied to the mold) is set to f (mm ³ / min ) If the width dimension of the slit is sw (mm) and the circumferential length of the slit is sl (mm), the cooling water flow velocity V (mm / min) can be obtained by V = f / sw / sl. When the casting speed at this time is CV (mm / min), this V / CV (cooling water flow rate / casting speed) is less than 700 when the temperature of the cooling water is 5 to 50 ° C. In order to increase the film boiling cooling region and enhance the effect of film boiling cooling, it is more preferable to set it to 500 or less. When the above value is less than 200, solidification is not sufficiently performed, and a trouble called hot water leakage is likely to occur.

Further, the optimum range of the predetermined region to be cooled by film boiling in the present invention varies depending on the size and material of the ingot to be cast.
For example, when the diameter of the ingot is D and D = 140 to 600 (mm), the predetermined region to be cooled by film boiling is from a position where the cooling water collides in the casting direction. , 0.2 (mm) × D + 20 to 1.5 × D (mm) (Claim 1) .
Although there are various sizes as the ingot, the effect when the cooling method of the present invention is employed is particularly effective in a cylindrical ingot whose diameter D is in the above range. If D is less than 140 mm, cracks hardly occur. Moreover, there exists a problem that casting will become difficult when D exceeds 600 mm. When the range of the predetermined area is less than 0.2 × D + 20 (mm), the effect of adopting the film boiling cooling is small, and the film boiling cooling is stable because the film boiling cooling is short. There is a problem that it is difficult to form. On the other hand, when it exceeds 1.5 × D (mm), there is a problem in that the slow cooling region due to film boiling cooling becomes too long, so that leakage of molten metal or a defect of solidified structure is likely to occur.

Moreover, it is preferable that the starting point of the nucleate boiling cooling is located on the casting direction side with respect to the solidification starting point at the center of the ingot ( claims 2 and 3). In this case, particularly when the central solidified portion is thermally contracted, the thermal contraction rate of the surrounding solidified layer can be reliably increased, and the crack suppressing effect at the central portion is extremely increased.

The cooling water is preferably industrial water, tap water, seawater, river water, or groundwater (Claim 4). That is, as the cooling water, it is possible to apply the various waters mainly composed of water, and to realize low-cost operation. In addition, it is preferable not to actively mix components having an effect of slow cooling such as CO ₂ with these waters. In addition to the impurities such as gas and oil which are inevitably contained in the cooling water, it is preferable not to actively contain other components. In the case of performing control depending on other components, it is necessary to control the content of the component, which complicates the apparatus and the control method. Further, when the slow cooling effect due to film boiling and the rapid cooling effect due to nucleate boiling are realized by a single system of cooling water, it is preferable not to mix a special component in the cooling water because it becomes easier to control.

A casting method according to an embodiment of the present invention will be described with reference to FIGS.
In this example, an ingot-type semi-continuous casting facility for aluminum was used, and ingots were actually cast under several casting conditions to investigate the presence or absence of cracks. An example employing the method of the present invention is shown in Example No. 1 to 4 and what was performed for comparison was Comparative Example No. 5-10.

In any of the examples and comparative examples, as shown in FIG. 1, the molten metal 8 is poured from the upper end of the mold 1 having an inner diameter of 200 mm with both ends released, and the solidified ingot 81 is continuously formed from the lower end of the mold 1. A cylindrical ingot 81 was produced by the vertical semi-continuous casting method.
And, at least, in Example No. adopting the method of the present invention. In 1-4, after performing the primary cooling which cools the molten metal 8 or the ingot 81 with the casting_mold | template 1 as shown in the same figure, the cooling water 7 is made to collide with the ingot surface 810 pulled out from the casting_mold | template 1 and two. When performing the next cooling, film boiling cooling is performed in the predetermined region L on the casting direction side from the position P _{1 at} which the cooling water 7 first collides with the ingot surface 810, and when the predetermined region L is exceeded (P ₂ ) And nucleate boiling cooling.

The mold 1 has an annular shape, and the inner peripheral diameter D is 200 mm as described above. As shown in FIG. 1, the inside of the mold 1 is hollow, and cooling water 7 is sequentially supplied into the mold 1 to cool the mold 1, and the cooling water is introduced from the slits 15 provided on the entire periphery of the bottom of the mold 1. 7 is emitted obliquely toward the mold surface 810. The inclination angle α of the slit 15 is set to 65 ° with respect to the horizontal direction. Further, the width dimension sw of the slit 15 was set to 1.5 mm. Further, JIS6063 alloy was used as an alloy to be cast. The molten metal 8 made of this alloy was poured into the mold 1 at a temperature of 680 ° C. Moreover, the distance E (molten metal surface height) from the casting_mold | template lower surface of the molten metal 8 to the molten metal surface was controlled so that it might be set to 60 mm.
Table 1 shows the casting conditions, casting results, and the like for each example.

From past experience, in the case of conventional cooling conditions, that is, conditions in which nucleate boiling cooling is performed at the time of secondary cooling, in order to produce an ingot of the above size from JIS6063 alloy, the casting speed is around 100 mm / min. It is common.
Comparative Example No. 1 shown in Table 1 Nos. 5 and 6 are close to the casting speed, but are the conventional cooling method, that is, nucleate boiling cooling immediately after the cooling water 7 is collided. In this case, as shown in FIG. 2, no crack was generated in the cross section 815 of the obtained ingot 81. This is considered due to the sufficiently low casting speed.

  However, Comparative Example No. 1 in which the casting speed was increased with the same amount of cooling water. 7 and 8, as shown in FIG. 3, the crack 9 occurred at the center of the cross section 815 of the ingot 81. In this case, as shown in Table 1, nucleate boiling cooling was performed through the film boiling cooling region, but the casting direction distance L (FIG. 1) in that region was as small as 20 mm or less, so that the film It is thought that the boiling cooling effect was not sufficiently obtained.

In contrast, Example No. 1 and 2 are Comparative Example Nos. Although the casting speed is the same as 7 and 8, the nucleate boiling position is moved to the casting direction side by adjusting the cooling water amount. In this case, the casting direction distance L of the film boiling region was as large as 70 mm or more, and no crack was generated (see FIG. 2).
In addition, Example No. 3, 4 and Comparative Example No. Nos. 9 and 10 are casting speeds significantly increased. Example No. 1 in which the casting direction distance L in the film boiling region is long. No cracks were observed in FIGS. 3 and 4 (FIG. 2). Cracks occurred at 9 and 10 (FIG. 3).
From these comparisons, it can be seen that the presence or absence of cracks depends on the difference in the casting direction distance L of the film boiling region, and that the crack suppression effect is higher as the film boiling region is larger.

4 to 6 show typical examples of cooling curves of the central portion and the ingot surface (actually, 20 mm from the ingot surface) during casting.
The example shown in FIG. This is an example in which the casting boiling rate is high and the cooling capacity is sufficiently increased to reduce the film boiling cooling region.
The example shown in FIG. 5 and 6 are examples in which crack generation is suppressed by reducing the casting speed.
The example shown in FIG. 1 to 4 is an example of the present invention in which the casting speed is high, the film boiling cooling region is enlarged, and the slow cooling region is lengthened.

In both figures, the distance from the molten metal surface when casting is taken on the horizontal axis, the temperature is taken on the vertical axis, the center temperature A, the temperature on the ingot surface side (inside 20 mm from the ingot surface) B, and the center solidification. The starting point a ₁ , the center solidification completion point a ₂ , and the temperature drop Δt on the ingot surface during the center solidification were taken.
As can be seen from these figures, in the case where cracks occurred (FIG. 4), the temperature drop amount Δt on the ingot surface during solidification of the central part was very small, while no cracks occurred. In the case of (FIG. 5, FIG. 6), it turns out that the temperature fall amount (DELTA) t of the ingot surface during center part solidification is large, and a temperature fall rate is high.

  Table 1 shows the solidification position obtained from the temperature measured by casting so that the thermocouple is embedded in the center of the ingot. As is clear from the comparison of the central solidification position, the example No. In 1-4, the position has shifted | deviated to the casting direction rather than before. Thereby, the surrounding solidified layer in the central solidification position can be disposed at a position where the cooling rate is high, and the shrinkage rate is increased to obtain a crack suppressing effect.

Table 1 also shows the value of cooling water flow rate / casting speed in each example, that is, the flow rate of cooling water is f (mm ³ / min), the width dimension of the slit 15 is sw (mm), and the circumferential length of the slit. Is obtained by calculating V / CV when the casting speed is CV (mm / min), and the above cooling water flow velocity V (mm / min) = f / sw / sl is obtained. Value was shown.
As can be seen from the table, by setting at least the above V / CV value to less than 700, it is possible to form at least a region in which film boiling cooling is performed, and to suppress cracking by setting it to 500 or less. It can be seen that a film boiling cooling region as much as possible can be secured.

In this example, as described above, whether or not cracks occurred was determined depending on the casting direction distance L of the film boiling cooling region. And, at least, when casting a cylindrical ingot like this example, the predetermined region to be cooled by film boiling with respect to the diameter D is from a position where the cooling water collides in the casting direction. It turned out that it is necessary to set it as the range of 0.2xD + 20 (mm) or more.
Needless to say, when casting ingots of different materials, shapes, sizes, etc., the optimum conditions for the length of the film boiling cooling region are different.

Explanatory drawing which shows the casting method in an Example. Sectional drawing of the normal ingot in an Example. Sectional drawing of the ingot in which the crack produced in the Example. Explanatory drawing which shows a cooling curve in case an casting speed is high in an Example, and cooling capacity is also high enough. The cooling curve at the time of casting speed reduction in an Example. Explanatory drawing which shows the cooling curve at the time of a casting speed being high in an Example and enlarging a film | membrane boiling cooling area | region and lengthening a slow cooling area | region.

Explanation of symbols

1 Mold 7 Cooling Water 8 Molten Metal 81 Ingot 810 Ingot Surface 9 Crack

Claims (4)

In the semi-continuous casting method of aluminum or copper, the molten metal is poured from one end of the mold whose both ends are released, and the solidified ingot is continuously drawn from the other end of the mold.
After performing the primary cooling for cooling the molten metal or the ingot with the mold, the cooling water collides with the ingot surface drawn from the mold to perform the secondary cooling. The film boiling cooling is performed in a predetermined region on the casting direction side from the collision position, and the nucleate boiling cooling is performed when the predetermined region is exceeded,
And the said ingot is D = 140-600 (mm) when the diameter is set to D, The said predetermined area | region to which the said film boiling cooling is carried out from the position where the said cooling water collides in a casting direction is 0. A semi-continuous casting method of aluminum or copper, characterized in that the range is 2 × D + 20 (mm) to 1.5 × D (mm) .   2. The aluminum or copper semi-continuous casting method according to claim 1, wherein the nucleate boiling cooling start point is positioned on the casting direction side of the solidification start point at the center of the ingot.   In the semi-continuous casting method of aluminum or copper, the molten metal is poured from one end of the mold whose both ends are released, and the solidified ingot is continuously drawn from the other end of the mold.
  After performing the primary cooling for cooling the molten metal or the ingot with the mold, the cooling water collides with the ingot surface drawn from the mold to perform the secondary cooling. The film boiling cooling is performed in a predetermined region on the casting direction side from the collision position, and the nucleate boiling cooling is performed when the predetermined region is exceeded,
  And the starting point of the said nucleate boiling cooling is located in the casting direction side rather than the solidification starting point of the center of the said ingot, The aluminum or copper semi-continuous casting method characterized by the above-mentioned.   4. The aluminum or copper semi-continuous casting method according to claim 1, wherein the cooling water is any one of industrial water, tap water, seawater, river water, and groundwater.

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