JPH0369615B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a continuous casting mold and a continuous casting method that prevent defects on the surface of slabs, defects due to non-metallic inclusions, etc. in continuous casting of molten metal. be.

BACKGROUND OF THE INVENTION Continuous casting of molten metal is widely used in the production of metal materials such as steel, aluminum, copper, and gold to improve yields. In order to explain the present invention in detail, continuous casting of steel, which is the most widespread and mass-produced type, will be taken as an example.

Continuous casting of steel (hereinafter referred to as CC) can be roughly classified into the following two types. One type is called an asynchronous CC in which the slab and mold move relative to each other, and the molten steel is received from a ladle into an intermediate container called a tundish, and then continuously poured into the mold from the tundish, allowing it to solidify while cooling. This is a method of completion, and includes vertical type CC, curved type CC, etc. in which the mold and intermediate molten steel container are separated. Since this format is the most productive and popular, it is usually
Call it CC. There is also a horizontal CC in which the intermediate container and mold are directly connected.

The other type is called synchronous CC, in which the mold has a roll-shaped, belt-shaped, or wheel-shaped mold, and the mold and slab move together as a unit to cool and solidify.

Normally, CC molds have the main function of producing solidified shells, so water-cooled Cu is usually used as the mold material. However, it is common to use a lubricant (powder) to prevent the molten steel from adhering to the mold. In order to produce good slabs and stable operation, it is essential to prevent the adhesion of molten steel and form a lubricating film of powder, and a mold vibration device such as mechanical vibration is required in the casting direction.

However, due to powder casting and mold vibration, surface defects such as pull-out marks called oscillation marks, bubbles, and inclusion defects inevitably occur, and as casting speed increases, slab defects occur frequently. Furthermore, there are many problems such as a casting failure called breakout.

These are caused by the fact that the melt level and the point at which solidification starts coincide in principle. In other words, the inclusions observed on the surface or surface layer of the slab are caused by inclusions brought in from the ladle or tundish deep into the mold by the discharge flow of molten steel, and as the discharge flow decreases, the inclusions rise to the surface. This is because they are captured by the slab.
In addition, it has become clear that slab surface defects are caused by changes in the surface shape of the molten metal near the molten metal surface or deformation of the initially solidified shell due to the mold lubricant used during casting, and that these defects occur unavoidably in the normal CC method. ing.

On the other hand, horizontal CC is known to have the advantage of superior quality such as slab inclusions because the molten metal surface and solidification position are separated, but the solidified shell inside the mold is prevented by using break rings etc. Casting is possible only after sufficient development of cast iron, so intermittent drawing and mold vibration are indispensable, and surface defects called cold shatter cracks and cold shatter marks inevitably occur. The establishment of the system has not yet been completed.

Against this background, various improvements have been attempted. For example, JP-A-54-15424 and JP-A-60-
No. 145249 considers a heating device for generating a solidified shell only in the mold in a horizontal CC. In other words, in JP-A No. 54-15424, an induction heating device is installed in the conduit on the mold entry side in order to prevent abnormal solidification (referred to as hot mass) that occurs on the mold entry side and stabilize operations. be. However, the technology
No consideration was given to the fact that molten steel would be inserted into the gap between the mold and the conduit located immediately before it, and the high-temperature molten steel in the conduit section would be cooled by the cooling mold placed immediately after it, resulting in sudden temperature differences. This is not desirable in terms of quality.

In JP-A No. 60-145249, the heating device and the mold body are arranged in sequence, and a temperature sensor is provided in between to control the start of formation of the solidified shell at a desired position. The temperature sensor is installed at a sleeve-shaped end of the heating device on the side of the mold body.

However, this method also has the same drawbacks as described above. In other words, if the solidification start point moves from the tip of the sleeve toward the mold body for some reason, there is a concern that molten steel may enter from the continuous section between the sleeve and the mold body, and the mold is heated from a high-temperature heating device to be cooled. When moving to the main body, rapid temperature changes adversely affect the quality of the slab surface.

In addition, a temperature sensor is installed between the heating section and the mold body, which is the cooling section, but since a solidified shell has already formed at this temperature detection position, the temperature is measured through the solidified shell. , the sensitivity is extremely reduced due to the heat transfer resistance of the solidified shell, making it difficult to control the solidified position. Furthermore, due to the nature of the electric heating coil, the temperature is generally highest at the longitudinal center of the coil, so it is clear that the temperature measured downstream of the electric heating coil will be lower than the actual molten metal temperature. Furthermore, if we also take into account that the measurement is performed through the solidified shell as described above, the indicated temperatures will show significantly different values, which is impractical.

For example, in order to improve mold segregation, it is necessary to minimize the degree of superheating of molten steel, but due to poor detection sensitivity and dynamic changes in the temperature field due to drawing, the solidification position It is difficult to identify the casting temperature, and heating may be performed more than necessary, leading to high superheat casting, resulting in quality deterioration and failure to achieve the purpose.

Furthermore, Japanese Patent Application Laid-open No. 61-63348 discloses a means for preventing solidification of molten steel at the meniscus by providing a heater in the upper part of the mold in a normal CC. However, this technique also has exactly the same difficulties as the former two.

Problems to be Solved by the Invention The present invention has been made in view of the above circumstances, and aims to solve the problem of surface defects and inclusions in the slab during the casting process of molten metal. The object of the present invention is to provide a continuous casting mold and a casting method that control the formation of shells, stably separate the molten metal surface from the solidification start point, and have excellent slab surface properties and operability.

Means for Solving the Problems The present invention was made with the aim of completely preventing defects on the surface of slabs and preventing the intrusion of inclusions, which had been difficult with conventional methods, and its characteristics are as follows: In a mold for continuous casting, a heating zone with poor conductivity and a cooling zone are formed from the side where the molten metal enters, and a molten metal introduction pipe preferably made of a material with low conductivity is arranged throughout the inside of the mold. A continuous casting mold is characterized in that it has an integral structure and is equipped with a temperature detector downstream of the meniscus of the heating zone, and a molten metal temperature detector provided downstream of the meniscus of the heating zone of the continuous casting mold. The basic invention is a continuous casting method characterized by maintaining the detected temperature above the molten metal liquidus temperature and locating the solidification start point downstream from the installation position of the molten steel temperature detector.

and a structure in which a plurality of electromagnetic induction coils are provided as heating sources for the heating zone of the mold of the present invention, and the frequency of each induction coil can be arbitrarily changed;
It also includes appropriately selecting and utilizing the characteristics of the heating force and molten steel stirring force, which vary depending on the power frequency of the electromagnetic induction coil that is the heating source.

The present invention will be further explained below using the figures. The drawings show an embodiment of the present invention, and FIG. 1 is an overall configuration diagram of the apparatus, FIGS. 2 and 3 are explanatory diagrams of the casting method,
FIG. 4 is an explanatory diagram of another embodiment, and FIG. 5 is an explanatory diagram showing the relationship between power frequency, heating power applied to molten steel, and stirring power in the present invention.

In Fig. 1, 1 is a ladle (or intermediate container);
2 is an immersion nozzle, 4 is a mold, and is composed of a heating zone 5, a cooling zone 6, and a molten steel introduction pipe 7. The heating zone 5 is
It is preferable that a heating element such as an electromagnetic induction coil 8 be incorporated therein, and that the material of the heating zone 5 itself is poorly conductive to prevent absorption of the electromagnetic force of the electromagnetic induction coil 8.

The cooling zone 6 is preferably internally water-cooled and made of copper, which is commonly used. The introduction pipe 7 is provided over the entire inner length of the heating zone 5 and the cooling zone 6, and is preferably made of a material that is difficult to conduct electricity for the same reason as the heating zone 5. Specifically, corrosion resistance can be achieved by using one or a mixture of two or more of oxides such as zirconia, alumina, silica, and magnesia, graphite, carbides, nitrides, borides, and the like.

Furthermore, it is most preferable that the portion of the introduction tube 7 that comes into contact with the heating zone 5 is poorly conductive, and the portion that comes into contact with the cooling zone 6 is conductive. By providing the introduction pipe 7 over the entire length of the heating zone 5 and the cooling zone 6, it is possible to prevent molten steel from entering the gap between the heating zone 5 and the cooling zone 6, and to prevent the molten steel from entering the gap between the heating zone 5 and the cooling zone 6. It is also possible to prevent rapid temperature changes (rapid cooling) when molten steel transfers, and is effective in preventing surface defects in slabs.

9 is a temperature detector that penetrates the heating zone and the introduction pipe and is located downstream of the molten steel meniscus (lower in the figure)
Provided for.

10 represents a guide roller, 11 represents a cooling water spray, and 12 represents a solidified slab.

2 and 3 are explanatory diagrams of the continuous casting method of the present invention, in which the temperature detected by the temperature detector 9 shown in FIG. 2 is compared with the target set temperature by the comparator 13, and the frequency is adjusted according to the difference. The controller or power controller 14 determines the appropriate frequency or input power, changes the frequency or power of the power source 15, and inputs it to the electromagnetic induction coil 8. That is, the temperature at the detection point of the temperature detector 9 is set to be equal to or higher than the melting point of the molten steel.

This allows the temperature sensor 9 to detect the solidification start point of the slab.
It can be controlled to be located lower in the figure than the installation position of. That is, the solidification start point can be located below the meniscus, and the occurrence of surface defects in the slab can be prevented.

Fig. 3 shows an example of the above-mentioned method in a diagram along with the passage of time. After preheating the heating zone, the input power is changed according to the temperature detected during casting of molten steel, and the molten steel temperature is always maintained at the liquidus level. This is to control the temperature (melting point) or higher.

FIG. 4 shows that by providing multiple sets of electromagnetic induction coils built into the heating zone 5 and connecting each set to a different power source,
This controls the amount of heat generated by each coil.

That is, an upper temperature detector 9-1 is provided near the upper coil 8-1, and the upper comparator 13 is connected to the upper temperature detector 9-1.
-1, upper frequency controller 14-1, upper power supply 1
5-1 will be provided. Separately from these, a lower temperature detector 9-2 is provided near the lower coil 8-2, and connected to this, a lower comparator 13-2, a lower frequency controller 14-2, and a lower power source 15-2 are installed. will be established.

With this configuration, the temperature distribution in the length direction of the heating zone can be set to a desired value. In particular, in the case of a set of electromagnetic induction coils 8 as shown in FIG.
As a characteristic of the coil, the temperature is higher at the center, and the temperature at both ends (upper and lower ends in the figure) is relatively low.

On the other hand, by adopting the structure shown in FIG. 4, it is possible to make the temperature uniform in the length direction of the heating zone, and furthermore, it is possible to obtain arbitrary temperatures at the upper and lower parts.

FIG. 5 shows the degree of heating applied to the molten steel when using the mold of the present invention, and the stirring force of the molten steel that is generated as a secondary effect by using the electromagnetic induction coil.

When used as the poorly conductive heating zone and introduction pipe of the present invention,
The heating power and stirring power show larger values compared to conventionally used steel molds, and both the heating power and stirring power draw a unique curve as the power frequency changes. Further, by setting the power supply frequency to approximately equal to or higher than the commercial frequency as shown in FIG. 5, it is possible to combine heating and stirring effects. Stirring becomes dominant from the commercial frequency to about 500Hz, and heating becomes dominant above 500Hz. Therefore, if you want to raise the molten steel temperature higher, operate the power supply frequency at a higher value, and when the molten steel temperature exceeds the target value and heating is no longer required, reduce the power supply frequency to a lower value and reduce the stirring power. It is used to promote the floating of non-metallic inclusions by increasing the

Effects of the Invention As explained above, according to the present invention, (1) Intrusion of molten steel into the gap between the heating zone and the cooling zone is prevented by providing an introduction pipe, and low-temperature cooling is carried out from the high-temperature heating zone. The rapid temperature change during the transfer of molten steel and slab to the strip can be alleviated by the introduction pipe, and the quality of the slab surface can be improved.

(2) By installing a temperature sensor in the heating zone downstream of the meniscus, the temperature of molten steel before solidification can be detected.
The starting point of solidification can be reliably located downstream of the meniscus.

(3) When the heating zone and the inlet pipe are made to be poorly conductive, the heating power and stirring power for molten steel can be increased, and the characteristics of the heating power and stirring power that change depending on the power supply frequency can be utilized. , the necessary heating and stirring can be obtained when desired.

[Brief explanation of drawings]

The drawings show embodiments of the present invention, in which Figure 1 is an overall configuration diagram of the apparatus of the present invention, Figures 2 and 3 are explanatory diagrams of the casting method of the present invention, and Figure 4 is an illustration of a plurality of electromagnetic coils. FIG. 5 is an explanatory diagram showing the relationship between the power frequency and the heating power and stirring power applied to molten steel when the mold of the present invention is used. 1... Ladle (or intermediate container), 2... Immersion nozzle, 4... Mold, 5... Heating zone, 6... Cooling zone,
7...Introduction pipe, 8...Electromagnetic induction coil, 8-1...
...Upper coil, 8-2...Lower coil, 9...Temperature detector, 9-1...Upper temperature detector, 9-2...
... Lower temperature sensor, 10 ... Guide roller, 1
1... Cooling water spray, 12... Slab, 13...
Comparator, 13-1... Upper comparator, 13-2...
Lower comparator, 14... Frequency controller, 14-1...
...Upper frequency controller, 14-2...Lower frequency controller, 15...Power supply, 15-1...Upper power supply, 1
5-2...Lower power supply.

Claims (1)

[Claims] 1. In a mold for continuous casting, a heating zone with low conductivity and a cooling zone with conductivity are formed from the molten metal entry side, and the entire inner length of the heating zone and the cooling zone is melted. What is claimed is: 1. A continuous casting mold having a heating function, characterized in that a metal introduction pipe is arranged, and a temperature detector is further provided downstream of the meniscus of the heating zone. 2. A patent characterized in that an electromagnetic induction coil is used as the heating source of the heating zone, a plurality of the electromagnetic induction coils are provided, each connected to a separate power source, and the power frequency can be changed for each electromagnetic induction coil. A continuous casting mold having a heating function according to claim 1. 3 A non-conductive heating zone and a conductive cooling zone are constructed from the side where the molten metal enters, and a molten metal introduction pipe is arranged along the entire inside length of the heating zone and the cooling zone. In a method of continuous casting of molten metal using a mold configured with a temperature sensor installed downstream of the meniscus, the molten metal in the heating zone is A continuous casting method characterized by casting metal while heating it. 4 A non-conductive heating zone and a conductive cooling zone are constructed from the side where the molten metal enters, and a molten metal introduction pipe is arranged along the entire inside length of the heating zone and the cooling zone. In a method of continuous casting of molten metal using a mold configured by installing a temperature detector downstream of the meniscus and using an electromagnetic induction coil as the heating source of the heating zone, the power frequency applied to the electromagnetic induction coil is controlled to control the temperature of the molten metal. If you want to raise the temperature higher, operate the power supply frequency at a higher value, and when the molten metal temperature exceeds the target value and heating is no longer required, lower the power supply frequency and increase the stirring power. A continuous casting method characterized by different uses.