JPS6313784B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous casting method for aluminum ingots, and more specifically, to stabilization of the quality of ingots continuously cast from molten aluminum or its alloys, and safety of casting operations. It relates to methods for effectively achieving sexual improvement.

In the past, many proposals have been made for casting equipment (including so-called semi-continuous casting equipment) for continuously producing round or square aluminum ingots made of aluminum or its alloys. A typical example thereof has a structure as shown in FIG. i.e. movable mold bottom (bottom plate)
8 is placed at the bottom of a water-cooled cylindrical mold 1, and a molten metal 4 made of aluminum or its alloy is supplied into the mold 1 through a nozzle 2 and a float 3, while gradually lowering the mold bottom 8 to cool the inside of the mold. The mold 1 is cooled based on the cooling of the inner wall of the mold by the cooling water flowing through the flow path 5 and the direct cooling by the cooling water jetted from the slit 6 at the bottom of the mold 1.
The molten metal column formed therein is solidified, and the solidified aluminum ingot 7 is continuously taken out from the lower end of the mold.

By the way, since the molten metal 4 supplied to the mold 1 comes into contact with the inner wall of the mold, it forms a thin solidified shell S through primary cooling through the channel (water chamber) 5 that cools the inner wall of the mold. When this solidified shell S is formed, the aluminum or its alloy therein solidifies and shrinks, creating a gap between it and the inner wall of the mold, which impedes heat radiation, so that the solidified shell S temporarily In the subsequent processing of the ingot, it causes the so-called sweating phenomenon, which locally remelts and causes low-melting point metals to leach out and molten metal to leach out, and cold shatter (cold welding phenomenon) to occur. This causes problematic surface defects. In particular, such undesirable phenomena are likely to occur in an unsteady state at the initial stage of casting (at the start of casting).

In addition, in the initial stage of casting, it is inevitable that the ingot 7 formed on the mold bottom 8 is rapidly and unevenly cooled by the cooling water jetted from the slit 6 when it comes out of the mold 1. A thermal residual stress is generated at the bottom of the ingot 7, which causes deformation in the bottom of the ingot, so-called "warpage". This "warpage" is more noticeable in square ingots than in round ingots, and in large ingots than small ones, but such "warpage" is caused by the subsequent rolling process of the ingot. There was a problem that led to significant scrapping at this stage.

In addition, rapid direct cooling by cooling water
The shape P of the sump (unsolidified molten metal) in the ingot 1 changes, and this causes "warping" (deformation) at the bottom of the ingot 7.
Correspondingly, this significantly increases the risk of metal leakage and poses considerable problems in terms of the safety of casting operations.

The present invention has been made against this background, and its gist is to supply molten aluminum or its alloy to a mold and continuously cool and solidify it. A method in which a predetermined aluminum ingot is continuously cast, and the casting speed is controlled to be gradually increased according to the length of the ingot formed in the mold to reach a final steady speed. and then
The steady speed value of the set casting speed is divided into multiple stages in advance, the ingot length at each speed is set, and casting is started at the speed value of the slowest of the casting speeds. At the same time, the length of the ingot that is gradually formed is detected, and based on the detected value, as the length of the ingot at each of the set speeds is reached, the casting of each of the plurality of stages is performed. While the speed is gradually increased until it finally reaches the steady speed, the amount of cooling water supplied to the mold and jetted from the bottom of the mold to the ingot formed is controlled by increasing the length of the ingot. The water supply amount per unit time is gradually increased to a steady water amount, and this reduces the amount of water that forms at the bottom of the mold at the initial stage of pouring. By making the temperature gradient in the vertical direction (in the casting direction) gentle during the solidification of the ingot and reducing the stress, deformation of the bottom of the ingot was prevented and the ingot was made flat. This has stabilized the quality of the ingot at the initial stage of pouring, improved safety, and enabled automatic pouring operation, resulting in labor savings.

As described above, according to the present invention, the casting speed is gradually increased according to the length of the ingot formed by cooling in the mold, in other words, the casting length; l (see Fig. 1). Therefore, at the start of pouring, the molten metal column formed on the bottom of the mold accommodated in the mold is gradually solidified by primary cooling by cooling water through the inner wall surface of the mold, and As the solidified ingot has been cooled, as the bottom of the mold descends, the ingot is directly cooled by jets of cooling water, which causes deformation (warpage) of the bottom of the ingot, cold shatter, and This effectively suppressed localized cracking and remelting of low-melting components, thereby stabilizing the quality of the ingot. In addition, the risk of leakage caused by warping of the bottom of the ingot, changes in the shape of the sump, remelting, etc. has been significantly reduced, and the safety of the casting operation has been greatly improved.

By the way, a specific example of the change in casting speed (lowering speed of the mold bottom) with respect to the casting length (l) in the present invention is shown in FIG.
In this process, the casting speed is gradually increased from the start of casting, and the casting speed is changed in steps until it reaches a steady speed, which is a continuous casting operation. That is, more specifically, the steady casting speed of 50 mm/min is divided into 5 stages (1st speed to 5th speed; 5th speed is the steady speed), and while the casting length (l) reaches 50 mm,
The casting speed is increased in sequence from speed to second speed to third speed to fourth speed to fifth speed to reach the final steady speed (fifth speed).

In addition, the length of the ingot (casting length; l) when the casting speed reaches a steady speed is generally 10 to 500 mm,
The casting length is preferably about 30 to 300 mm, and the casting speed is gradually increased to a steady state while reaching such a casting length. If the casting length is allowed to reach a steady state speed while the casting length is too short, problems such as "warping" at the bottom of the ingot, local cracking, cold shatter, and remelting will occur, which is undesirable. If the casting length required to reach a steady speed is too long, it is undesirable because it will cause problems in controlling the casting speed during that time, as well as problems in productivity and casting operations.

In addition, the gradual increase in casting speed as described above
This is preferably carried out as shown in FIG. That is, a descending member (the mold bottom itself or a mold bottom attached) 10 for the mold 1
When the value of the descending speed (casting speed) in the steady casting state is determined from the material, size, etc., that value (steady speed) is set by the casting speed setting device 11. By setting this steady speed, the percentage setting device 12 sets the speed of each speed from 1st speed to 5th speed as a percentage of the steady speed. Further, the casting length (l) reached at each speed from the first speed to the fifth speed is set in the casting length setting device 13, respectively.

When starting casting, the casting machine control device 14 controls the descending member 10 by the descending member moving mechanism consisting of the DC motor 15 and the drum 16 so as to follow the first speed set value set by the percentage setting device 12. The descent of is controlled. Further, the length (l) of the ingot produced by the descent of the descending member 10 is indirectly measured by detecting the rotational speed of the DC motor 15 with the tachometer 17. Furthermore, the indirect information of the casting length (l) detected by the tachometer 17 is sent to the casting length setting device 1.
3 is input. In the casting length setting device 13, based on the input casting length (l) information, it is set to 1.
When the speed reaches the set value, an output is provided to switch from the first casting speed setting in the percent setting device 12 to the second speed setting, and according to the second speed setting of the percent setting device 12. Then, the DC motor 15 is controlled by the casting machine control device 14.
is controlled, and the lowering member 10 is lowered at the second casting speed.

In this way, the percentage setting device 12, the casting machine control device 14, the DC motor 15, the tachometer 17
The descending speed (casting speed) of the descending member 10 is determined by the control circuit configured with the casting length setting device 13 and the casting length (l) at each preset speed.
Accordingly, the speed is increased sequentially from 1st speed to 5th speed, and then a steady speed is reached in a stepwise manner.Thereafter, the casting operation is continued while maintaining the steady speed.

In particular, by adopting such a control system, automatic control of the casting speed becomes possible, which reduces the work load at the initial stage of casting, making it possible to save labor.

Furthermore, in the present invention, by controlling the casting speed with respect to the casting length, the temperature gradient in the vertical direction during solidification at the bottom of the ingot is made gentle. In addition, the amount of cooling water supplied to the mold 1 and jetted from the bottom of the mold 1 toward the ingot is controlled in accordance with the detected length of the ingot, so that the amount of cooling water is adjusted to the steady water amount (steady water amount). The effect can be further increased by increasing the amount of cooling water stepwise to the amount of cooling water at the casting speed to reduce the heat transfer to the sub-mold being formed at the bottom.

In short, the early stage of casting is an unsteady state, and it is extremely important to control the casting speed and the amount of cooling water. In other words, cooling in steady state is only from around the mold, while cooling in unsteady state is from the bottom (bottom plate).
This is because cooling is applied from both directions, and the mold itself remains at room temperature.In a steady state, there is a gap between the mold and the ingot due to solidification shrinkage, but in an unsteady state Sometimes, due to the molten metal, no such gap exists. Because of these circumstances, controlling the casting speed and cooling water amount together is important in terms of quality (cracking, rough casting surface, cold shunt, etc.), safety (molten metal leakage),
Furthermore, it achieves a remarkable improvement in terms of labor saving (automation).

Specifically, to control the amount of cooling water, for example, the amount of cooling water supplied is increased in a stepwise manner as shown in FIGS. In addition to the method, Figure 4c
It is preferable to adopt a method in which this is done by periodically stopping the supply of cooling water, and the stopping time is gradually shortened, eventually reaching zero and transitioning to a steady state. Become. In addition, in Fig. 4c, the water flow time x and water stop time y are set at a constant ratio in section A, and the water stop time y is gradually shortened in section B, and the water stop time y is gradually reduced to a steady state. It's summery.

This control of the amount of cooling water is performed by controlling the ON/OFF time by the output from the casting length setting device 13 based on the casting length information from the tachometer 17, as shown in FIG. 3, for example. This is performed by inputting the information to the control device 18 and opening and closing the valve (three-way) 19 under the control of the ON/OFF time control device 18. In addition,
The flow rate of the cooling water flowing through the flow path 21 is controlled by the flow rate control valve 20.
The valve 19 is simply turned ON and OFF to allow or shut off the cooling water.

Although specific examples of the present invention have been described above,
The present invention is by no means limited to the illustrative examples, and various modifications and changes can be made based on the knowledge of those skilled in the art without departing from the spirit of the present invention.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view showing a typical example of a continuous casting device, Fig. 2 is a graph showing an example of changes in casting speed with respect to casting length, and Fig. 3 is an example of a control method for casting speed. FIGS. 4a, 4b, and 4c are graphs each showing an example of a method of changing the amount of cooling water. 1: Mold, 4: Molten metal, 7: Ingot, 8: Mold bottom,
l: Casting length, 10: Lowering member, 11: Casting speed setting device, 12: Percentage setting device, 14: Casting machine control device, 13: Casting length setting device, 15: DC motor, 16: Drum , 17: Tachometer, 18:
ON/OFF time control device, 19: Valve, 2
0: Flow control valve.

Claims (1)

[Scope of Claims] 1. When a predetermined aluminum ingot is continuously cast by supplying molten aluminum or its alloy to a mold and continuously cooling and solidifying it, the cast formed in the mold is The casting speed is gradually increased according to the length of the ingot to reach the final steady speed, and the amount of cooling water is gradually increased according to the length of the ingot formed in the mold to reach the final steady speed. By using a method that controls the amount of water so as to reach a steady water volume, the steady speed value of the set casting speed is divided in advance into a plurality of stages, and the length of the ingot at each speed is set. The casting is started at the speed value of the slowest one of the casting speeds, and the length of the ingot that is gradually formed is detected, and based on the detected value, the casting is started at the speed value of the first speed that is the slowest. As the ingot length is reached, the casting speed of each of the plurality of stages is sequentially increased to finally reach the steady speed, while the ingot is supplied to the mold and formed from the bottom thereof. The amount of cooling water spouted to the ingot is controlled in accordance with the detected value of the length of the ingot, and the amount of cooling water supplied per unit time is gradually increased to a steady water amount. Continuous casting method for aluminum ingots. 2. The method according to claim 1, wherein the casting speed is made to reach the steady speed while the length of the ingot becomes 10 to 500 mm. 3. The method according to claim 1, wherein the amount of cooling water is controlled by periodically stopping the supply of cooling water, and the stopping time is gradually shortened to zero.