JP3464331B2 - Continuous casting method and continuous casting apparatus for non-ferrous metals - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention has a solidus temperature of 90.
In continuous casting (including semi-continuous casting) of non-ferrous metals above 0 ° C, especially copper and copper alloys, casting speed is 10 m / hr.
The present invention relates to a method of performing high speed casting of (166 mm / min) or more.

[0002]

2. Description of the Related Art Conventionally, in continuous casting of non-ferrous metals, especially copper and copper alloys, the casting speed is about 10 m / hr. However, although it is desired to increase the casting speed in order to improve productivity, it is well known that cracking occurs inside the ingot when the casting speed is increased.

First, an outline of a conventional non-ferrous metal continuous casting machine will be described with reference to FIG. As shown in FIG. 1, the molten metal 1 is poured into a mold 2 having a length (Lm) of 350 mm, for example, and gradually drawn downward. The ingot 3 is at the outlet of the mold 2 and usually has a nozzle cooling zone 5 which is cooled by cooling water from a nozzle 4.

The nozzle cooling zone 5 is followed by the pit cooling zone 6
Is provided. The length (Lp) of this cooling zone is 850
It is about mm. Then, the cooling water contained in the pit further cools the pit to complete the solidification.
The ingot is pulled out by a pinch roll 10 provided below the pit cooling zone 6. Since the cooling water from the nozzle always flows into the pit, the cooling water in the pit is usually at room temperature.

In order to prevent cracking of the ingot in the above conventional continuous casting machine, the following means are usually adopted. The first means slows down the casting speed. The second means is to increase the length of the mold and finish the solidification of the ingot to the final solidification portion. A third means is a method of weakly cooling in a secondary cooling zone such as a pit cooling zone below the mold.

Conventionally, in copper and copper alloys,
Although the second means is used, lowering the casting speed generally hinders the productivity. The third means has been put to practical use in continuous casting of steel. Generally, "mist cooling", "spray cooling device" or "air cooling" is performed as the cooling method. Therefore, "mist cooling device" and "spray cooling device" are installed below the mold. There is. However, in order to maintain these devices in a normal state, the maintenance of the tip nozzles of these cooling devices and the cleanliness of water are constantly managed.

[0007]

In the first and second methods, the casting speed is limited in order to prevent internal cracking.
The third method requires the installation of a cooling device in the casting direction, which complicates the equipment configuration. Furthermore, the tip of the nozzle used for these is exclusively thin, and at present the clogging is likely to occur. Therefore, maintenance is required to prevent the nozzle from being blocked.

In the third cooling method, since air is blown onto the surface of the ingot together with the fine droplets, oxide scale is generated on the surface of the ingot. In particular, when hot working (particularly hot extrusion) is performed without cutting the surface of the ingot, there is a problem that the oxide scale on the surface of the ingot is pushed into the processed material.

Further, since this cooling system is extremely weak, there is a problem that the ingot temperature does not drop due to continued insufficient cooling even in a safe state where internal cracking does not occur. . Then, in order to overcome this problem, it is necessary to install a strong cooling device or the like in order to sufficiently cool the ingot below these cooling methods, which further complicates the equipment configuration. Therefore, there is a problem in that the equipment design involves an extremely large equipment configuration, or existing equipment cannot handle it.

[0010]

There is a need for a cooling system which satisfies the above problems and requires no maintenance. Therefore, we first created three-dimensional simulation software that can reproduce the solidification phenomenon in continuous casting, and studied a cooling method that can overcome these problems using this simulation.
As a result, the inventors have made the following inventions.

A first aspect of the invention is to continuously cast a metal having a temperature conductivity (= (heat conductivity) / (specific heat × specific gravity)) of 0.12 m ² / h or more, and cool the ingot immediately after casting by stationary cooling. A method for continuous casting of non-ferrous metal, characterized in that in a method of immersing in cooling water and cooling, the water temperature (t) of the cooling water is controlled according to the temperature conductivity (a) of the ingot which is the material to be cooled. .

A second invention is the continuous casting method for nonferrous metal according to the first invention, wherein the metal is copper or a copper alloy.

In a third aspect based on the above aspect, the water temperature (t) of the cooling water is the temperature conductivity (a) of the ingot which is the material to be cooled.
It is a continuous casting method for non-ferrous metals, which is controlled as follows according to In the case of 0.30 <a: t> −200.0 × a + 90.0 (° C.) In the case of 0.15 ≦ a ≦ 0.30: t> −33.3 × a + 40.0 (° C.) 0. When 12 ≦ a <0.15: t> −2250.0 × a + 372.5 (° C.)

A fourth aspect of the present invention is a continuous casting apparatus for non-ferrous metals, which is provided with the following members. (A) a mold into which molten non-ferrous metal is injected; and (b) a cooling mold that is arranged immediately below the mold so as to circulate the ingot and cools the ingot discharged from the mold. A pit, (c) a thermometer for measuring the temperature of the cooling water, a cooling water supply pipe for adjusting the temperature of the cooling water in the pit, and the temperature measured by the thermometer is cast. A temperature control device for controlling the amount of water in the cooling water supply pipe so that the temperature of the cooling water is determined from the temperature conductivity of the metal.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Unlike the conventional continuous casting machine shown in FIG. 1, in the present invention, as shown in FIG. 2, a pit cooling zone 6 is provided immediately below the mold 2 without providing a nozzle cooling zone. . This length (Lp) is, for example, about 1500 mm. In the pit cooling zone directly below the mold, a thermometer 9 for measuring the temperature of the cooling water, a cooling water supply pipe 10 for adjusting the temperature of the cooling water in the pit, and the temperature A temperature control device 11 is provided to control the amount of water in the cooling water supply pipe so that the temperature measured by the meter becomes the temperature of the cooling water determined from the temperature conductivity of the metal to be cast.

In order to quantitatively evaluate the heat transfer of the ingot in the above continuous casting machine, three-dimensional simulation software for calculating the solidification process was prepared. In this calculation, the direct difference method was used to subdivide the calculation target and evaluate the heat balance between each element. The outline of the calculation will be described below.

Heat transfer amount in the ingot due to heat conduction (Q1)
Can be calculated from the Fourier law. Q1 = S × λ × ΔT / L S: Area adjacent to element λ: Thermal conductivity ΔT: Temperature difference between elements L: Distance between nodes

The heat transfer amount (Q2) associated with mass transfer in continuous casting can be calculated by the following formula. Q2 = S
× n × v × ρ × Cp × ΔT n: normal vector at element boundary v: windward velocity Cp: specific heat ρ: density

The transfer amount (Q3) of latent heat of solidification due to solid phase formation in continuous casting can be calculated by the following formula. Q3 = S × n × v × ρ × H × Δfs H: Latent heat of solidification or phase transformation energy Δfs: Solid phase difference between elements

Heat transfer between different materials such as molds (Q4)
Can be calculated by the following formula. Q4 = S × ΔT / (d1 / λ1 + 1 / h + d2 / λ2) d1, d2: Distance from node to boundary h: Thermal resistance between different materials λ1, λ2: Material No. Thermal conductivity of 1, 2

The heat transfer amount due to cooling water (Q5) can be calculated by the following formula. Q5 = S × h0 × (T−T0) h0: Heat transfer coefficient at the boundary T: Node temperature T0: External temperature (cooling water temperature, etc.)

The heat change (Q6) due to latent heat in each element can be calculated by the following formula. Q6 = V × ρ × H × Δfs ′ V: Element volume Δfs ′: Amount of change of solid phase ratio in the element

The heat quantity from Q1 to Q6 was comprehensively calculated using these basic equations, and the three-dimensional heat transfer quantity in continuous casting was evaluated using the time progress method. This calculation method is a particularly effective calculation method in the case of a copper alloy having a large thermal conductivity. Further, regarding the immersion cooling in the present invention, the cooling ability (heat transfer coefficient) was made into a function with various materials, and this was taken into the simulation, and solidification / heat calculation was performed.

Further, the casting speed and the internal stress at the center of the ingot were calculated based on the above calculation of the solidification process (solidification profile, temperature gradient in the ingot, etc.). As a result, as shown in FIG. 3, when the casting speed was increased (especially 10 m / mi
It was found that a large internal stress is generated at the center of the ingot. Further, it was also clarified that when the secondary cooling strength was decreased, the internal stress curve moved to the right side in the figure, and when the secondary cooling strength was increased, the curve moved to the left side.

The above calculation was further developed to clarify the relationship between the temperature conductivity, the casting speed, the central crack, that is, the core crack. The results are shown in FIGS. 4 and 5. Figure 4 shows a diameter of 30
The relationship between the temperature conductivity and the casting speed in the case where 0 mm pure copper is continuously cast is shown. The temperature conductivity is 0.12 m ²
It was found that in the case of / h or more, no core crack occurred in the ingot even if the casting speed was set to a conventional casting speed of 10 m / h or more.

FIG. 5 shows the relationship between the temperature conductivity of the ingot and the pit cooling water temperature at the casting speed of 15 m / h under the same conditions as above. From this figure, it has been found that it is necessary to set the temperature of the cooling water to a predetermined temperature or higher in accordance with the temperature conductivity in order to prevent core cracking of the ingot under the condition that the casting speed is constant.

This means that the temperature of the cooling water is set to a predetermined temperature or higher than room temperature (20 ° C. or lower) in accordance with the temperature conductivity of the ingot, so that the casting speed becomes the conventional casting speed (10 m).
/ H or less) is meant.

From FIG. 5, it is clear that it is desirable to control the water temperature (t) of the cooling water as follows according to the temperature conductivity (a) of the ingot which is the material to be cooled. In the case of 0.30 <a: t> −200.0 × a + 90.0 (° C.) In the case of 0.15 ≦ a ≦ 0.30: t> −33.3 × a + 40.0 (° C.) 0. When 12 ≦ a <0.15: t> −2250.0 × a + 372.5 (° C.)

Generally, when the solidification of the central portion of the ingot is completed, the release of the latent heat of solidification is stopped, the high temperature state is not maintained, the cooling capacity of the stationary cooling water rapidly increases, and the ingot is rapidly cooled. To leave. Therefore, the temperature conductivity is 0.12 m ^2.
In order to cast a metal of / h or more, for example, a copper alloy at a higher speed than before, it is necessary to raise the temperature of the pit cooling zone to limit the cooling capacity.

The mold cooling capacity (the amount of cooling water is reduced) and the casting speed are changed (accelerated) so that the final solidified portion exists in the stationary cooling water. As a result, cooling is automatically controlled by the cooling characteristics of the cooling water itself by simply immersing it in the pit cooling water, and cracking at the center of the ingot is completely avoided.

Further, in the continuous casting machine as shown in FIG. 2, since the ingot surface can be completely shielded from the air by the cooling water in the pit, an oxide film on the ingot surface is also generated. Can be prevented. Further, in such a continuous casting machine, there is nothing to maintain due to the equipment configuration, so that the cost can be reduced by eliminating maintenance work.

As described above, the thermal conductivity is 0.12.
When manufacturing ingots of non-ferrous metal of m ² / h or more, particularly copper and copper alloys by a continuous casting machine as shown in FIG. 2, a cooling water pit is provided immediately below the mold, and the cooling water is placed in the pit. It has been found that the method of immersing the ingot immediately after casting is effective. Table 1 shows examples of non-ferrous metals to which the cooling method as described above can be applied, and desirable cooling temperatures for the respective metals.

[0033]

[Table 1]

In the above continuous casting machine, the water temperature in the pit is measured by the thermometer 9, and the temperature control device 11 cools and drains the mold by the temperature control device 11 or supplies cooling water to the pit from the outside with cooling water. It is injected from the tube 10. It is more preferable to provide, for example, a water flow blocking plate 7 in the pit so that the water flow does not directly collide with the ingot. Since the ingot is immersed in cooling water immediately after leaving the mold, it is possible to prevent the generation of oxide scale on the surface of the ingot.

[0035]

EXAMPLE A copper and copper alloy 300 mm billet is shown in FIG.
A casting experiment was carried out in the continuous casting machine shown in FIG. The structure is such that the cooling water drainage from the mold does not directly contact the ingot. The cooling water in the pit was cast by raising the water level just below the mold. In the pit, a makeup water pipe 10 for controlling the pit water temperature so as not to rise was provided, and the pit cooling water temperature was controlled by the temperature control device 11.

Table 2 shows the results of comparison between the occurrence of core cracks inside the ingot and the results of the simulation by calculation while changing the casting speed variously. Calculation result is "core crack"
It was confirmed that the core cracking can be prevented under the cooling condition based on the calculation.

[0037]

[Table 2]

[0038]

As described above, when non-ferrous metals, especially copper and copper alloys are continuously cast by the method and continuous casting machine of the present invention, center cracking, that is, core cracking occurs even if the casting speed is increased more than ever before. It is possible to cast a sound ingot without causing it to occur.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a conventional non-ferrous alloy continuous casting machine.

FIG. 2 is a diagram showing an outline of a continuous casting machine according to the present invention.

FIG. 3 is a diagram showing a relationship between a casting speed and an internal stress in continuous casting of copper.

FIG. 4 is a diagram showing a relationship between temperature conductivity and casting speed in continuous casting of copper.

FIG. 5 is a diagram showing a relationship between temperature conductivity, cooling water temperature, and core crack in continuous casting of copper.

[Explanation of symbols]

1 molten metal 2 molds 3 ingot 4 nozzles 6 pit cooling zone 7 Water flow shield 9 thermometer 10 Cooling water supply pipe 11 Temperature control device

Front page continuation (58) Fields surveyed (Int.Cl. ⁷ , DB name) B22D 11/00 B22D 11/124 B22D 11/16 104 B22D 11/22

Claims (4)

(57) [Claims] 1. Thermal conductivity (= (thermal conductivity) / (specific heat ××
Continuous casting of metal having a specific gravity of 0.12 m ² / h or more,
In a method of cooling an ingot immediately after casting by immersing it in still cooling water, the temperature (t) of the cooling water is controlled so that the final solidified portion is present in the still cooling water by the temperature conduction of the ingot as the material to be cooled. A continuous casting method for non-ferrous metals, characterized by controlling according to the degree (a). 2. The continuous casting method for a non-ferrous metal according to claim 1, wherein the metal is copper or a copper alloy. 3. The water temperature (t) of the cooling water is controlled as follows according to the temperature conductivity (a) of the ingot which is the material to be cooled. Continuous non-ferrous metal casting method. In the case of 0.30 <a: t> −200.0 × a
+90.0 (° C.) 0.15 ≦ a ≦ 0.30: t> −33.3 × a +
40.0 (° C.) 0.12 ≦ a ≦ 0.15: t> −2250.0 ×
a + 372.5 (℃) 4. A continuous casting apparatus for non-ferrous metals, comprising the following members. (A) a mold into which molten non-ferrous metal is injected, and (b) arranged to orbit the ingot immediately below the mold to be discharged from the mold and cool the ingot,
A pit containing cooling water; (c) a thermometer for measuring the temperature of the cooling water; a cooling water supply pipe for adjusting the temperature of the cooling water in the pit; The temperature of the cooling water is determined by the temperature conductivity of the metal to be cast.
Temperature control apparatus for controlling the amount of water of the cooling water supply pipe.