JPS6092064A - Pouring method of molten metal - Google Patents

Abstract

PURPOSE:To suppress closing of a nozzle and to stabilize continuous operation by acting the DC magnetic field to the molten metal flow passing through the inside of the nozzle and preventing sticking of an inclusion to the inside surface of the nozzle. CONSTITUTION:The molten metal 2 in a tundish 1 flows through the inside of a nozzle 3 and is poured into a casting mold 4. The molten metal 2 passes through the magnetic field of an electromagnet 5 by which the flow is made laminar and the chance at which the inclusion in the metal 2 sticks to the inside surface of the nozzle 3 is decreased. The closing of the nozzle 3 is thus suppressed and the continuous operation is accomplished stably.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel molten metal injection method that can prevent nozzle clogging caused by inclusions mixed in molten metal in a continuous casting machine or the like.

In the field of steel manufacturing, a method of injecting molten metal through a nozzle is widely used. However, there are cases where the nozzle becomes clogged during injection, forcing the injection to be interrupted or abandoned. One of the causes of nozzle blockage is due to solidification of molten metal within the nozzle. This is because the temperature of the molten metal is lowered by the nozzle, which has a temperature lower than the molten metal while passing through the nozzle, and the molten metal solidifies.
To prevent this, heat the nozzle sufficiently before injection.
This problem can be solved by taking thermal countermeasures, such as installing a heat shield on the nozzle or wrapping a heat insulating material such as glass fiber around the nozzle to suppress heat radiation from the nozzle.

Another cause is that inclusions in the molten metal, such as alumina in aluminum quilt steel, adhere to and accumulate on the upper end of the inner surface of the nozzle. In this case, thermal countermeasures cannot be used, and the following two methods have been implemented. One method is to add calcium, which is originally unnecessary to the aluminum killed steel, to change the alumina composition (calcium treatment) and then inject it.The other method is to use a porous nozzle and inject Ar gas into the nozzle. Pass inert gas such as
This is a nozzle bubbling method that forms a gas layer between the nozzle and molten steel to prevent alumina from adhering to the nozzle.

However, in the former case, there is a drawback that the cost of molten steel increases due to the calcium treatment, and in the latter case, although the effect is recognized, it is not perfect.

There is no practically effective solution to such cases of nozzle blockage caused by inclusions, and a solution has been awaited.

The present invention has been made in view of the above circumstances, and its purpose is to provide a molten metal injection method that suppresses the amount of inclusions attached so that molten metal having an aluminum killed composition can be stably injected. It is in.

First, the background and principle leading to the completion of the present invention will be explained below.

The inventor of the present application conducted various studies on the adhesion mechanism of inclusions on the inner surface of the nozzle, and found that movement toward the inner surface of the nozzle is a major factor, that is, the higher the moving speed, the greater the chance of contact between the inclusion and the inner surface of the nozzle. It has been found that the amount of adhesion 8 increases. We also obtained the idea that the speed at which inclusions move toward the inner surface of the nozzle depends on the flow mode of the molten metal flow, and that it is possible to suppress the attachment of inclusions by changing this flow from turbulent flow to laminar flow. reached. In order to make the molten metal flow a laminar flow, the Raynozzle number Re may be made smaller than the critical Raynozzle number Rec for a turbulent single-layer flow. The Ray nozzle number Re is the following (11
It is given by Eq.

η However, ρ: Fluid density U: Fluid velocity d: Nozzle inner diameter η: Fluid viscosity Now, the Ray nozzle number R of aluminum killed steel is determined by equation (1).
Subtracting e, the condition is P = 7000 kg/m
3゜U=0.4m/sec, d=0.05m, 77=
6 xlO” kg/m/sec, so Re is 230
It is about 00. Therefore, the critical Raynozzle number Rec is 20
Since it is about 00 to 3000, Re is larger than Rec. In other words, the conventional molten metal flow was in a turbulent state.

The Ray-nozzle number Re is determined by the properties of the fluid itself and the inner diameter of the nozzle, and it is impossible to change the Ray-nozzle number Re to a value lower than the Rec value. Therefore, the inventor of the present invention came up with the idea that by conversely increasing the critical Ray nozzle number Rec, Rec > Re is achieved and the molten metal flow is made laminar, thereby suppressing the adhesion of inclusions on the inner surface of the nozzle. Ta. In the present invention, this critical Ray nozzle number Rec is increased by applying a DC magnetic field to the molten metal flow in order to make the molten metal flow laminar.

That is, the method for injecting molten metal according to the present invention is characterized in that when injecting molten metal through a nozzle, a DC magnetic field is applied to the molten metal flow within the nozzle.

The present invention will be specifically explained below based on the drawings.

The drawing is a schematic diagram showing the implementation state of the present invention, and in the drawing, 2 indicates molten metal stored in the tundish 1. 3 indicates a nozzle suspended on the tundish 1, and the nozzle 3 consists of an upper nozzle 3a, a sliding nozzle 3c incorporated in the upper nozzle 3a, and a lower nozzle 3b. The sliding nozzle 3c is slidable in the front and back directions of the drawing, and is driven by an opening adjuster (not shown).

The bottom surface 1a of the tandish 1 is composed of a concave core 56 with a part of one long side of the rectangle cut out in plan view, and two coils 5a+5a' wound around the part near the cutout. The nozzle 3 is positioned in the notch so as to receive the magnetic field from the magnetic pole on the end face of the notch. A DC power source (not shown) is connected to the coils 5a+5a', and the magnetic field of the electromagnet 5 is applied in a direction perpendicular to the axis of the nozzle 3.

The molten metal 2 in the tundish 1 flows through the nozzle 3 with its flow rate adjusted by adjusting the opening of the sliding nozzle 3C. The molten metal 2 then passes through the magnetic field of the electromagnet 5 and is poured into the mold 4.

When a magnetic field having a direct current component is applied to the molten metal flow in this manner, the aspect of the molten metal flow is controlled by the Hartmann number tea and the Raynozzle number Re.

The Hartmann number 11a is expressed by the following equation (2).

However, σ: Electrical conductivity Bo: Magnetic flux density On the other hand, the above-mentioned critical Reynozzle number Rec is a function of Ha, and is expressed by the following equation (3).

Rec ≧5000011a ・-(31However, Ha≧
Equation (3), which is 20, is the equation CProc, Roy, Soc, (Lo
ndon) Set, ^203. (1955)).

Now let us consider the electrical conductivity σ of the molten metal, for example, σ=7, 14
x 105 seconds/m, and if a magnetic field is applied to the molten metal flow so that the magnetic flux density Bo = 0.04T, (2
1, (from formula 31, Ha is 21.8 and Rec is +l
ec = 1.09X106> 23000 (=Re)
Therefore, sufficient laminar flow is possible.

By making the molten metal flow laminar, the chances of the inclusions in the molten metal flow coming into contact with the inner surface of the nozzle are reduced, and the upper end A of the inner surface of the nozzle, which conventionally caused nozzle blockage, as well as other locations. The amount of inclusions adhering to the nozzle is reduced, and nozzle clogging is suppressed.

In the above explanation, the magnetic field of the electromagnet 5 is set perpendicular to the axis of the nozzle 3 because laminar flow can be achieved with the minimum magnetic flux density in this direction. The direction may be diagonal or even parallel to the axis of No. 3, but in this case, a considerably large magnetic flux density is required and the efficiency is poor. Furthermore, it goes without saying that the present invention can be implemented in the same manner using permanent magnets instead of electromagnets.

Next, the effects of the present invention will be explained. Dimensions are 180゜mm
X300m quotient coils 5a, 5a' and 100 *yh
Using an electromagnet 5 consisting of a yoke 56 of X 300 as, aluminum killed carbon steel with a composition of C: 0.08% and Mn: 0.8% was injected at an average injection rate of 18T/hour with three levels of magnetic flux density. did. The degree of superheating of the molten steel was +30°C to +40°C relative to the solidification temperature. First, when a magnetic field was not applied, that is, when injection was performed using the conventional method, the upper end of the inner surface of the nozzle was clogged approximately one hour after the start of injection, making injection impossible.

Next, the magnetic flux density is 0.1T (Re
c = 2.73XIO'). In this case, the nozzle was clogged approximately 3 hours after the start of injection, and a slight effect was observed.

Furthermore, the magnetic flux density was set to 0.2 for the upper nozzle 38 at the same location.
Injected as T (Rec = 5.45X106).

In this case, nozzle blockage did not occur even after 8 hours had passed after the start of injection, and the multiple charges of molten steel scheduled for injection could be completely injected.

By applying a DC magnetic field to the molten metal flow in this manner, nozzle clogging does not occur, and the effects of the present invention are obvious.

It goes without saying that the present invention can be practiced with any conductive fluid.

As detailed above, the present invention applies a DC magnetic field to the molten metal flow flowing through the nozzle, so the molten metal flow becomes a laminar flow, reducing the amount of inclusions attached to the inner surface of the nozzle. Blockage can be suppressed, thereby achieving excellent effects such as stabilizing continuous casting operations.

[Brief explanation of drawings]

The drawings are schematic diagrams showing the implementation state of the present invention. 2... Molten metal 3... Nozzle 5... Electromagnet patent Applicant Sumitomo Metal Industries Co., Ltd. agent Patent attorney
Noboru Kono

Claims (1)

[Claims] 1. A molten metal injection method characterized by applying a direct current magnetic field to the molten metal flow within the nozzle when injecting the molten metal through the nozzle.