JPH03193249A - Method for starting continuous casting - Google Patents

Abstract

PURPOSE:To prevent casting defect caused by involution of flux and to stably obtain a sound cast slab by executing the initial charging of the mold flux after the time of point when the molten metal spouting hole in a submerged nozzle perfectly dips into the molten metal in a mold. CONSTITUTION:Supplying of the molten metal 5 into the mold is started and under condition, where the molten metal spouting hole 4 in the submerged nozzle 3 perfectly dips into the molten metal 1 in the mold, the mold flux 6 is charged into the mold. By this method, disturbance of the molten metal surface caused by the molten steel flow spouted from the nozzle 3 is restrained and the involution of the mold flux into the molten metal can be prevented.

Description

[Detailed description of the invention] [Industrial application field] The present invention is applicable to continuous casting of metal slabs.

The present invention relates to a method for starting continuous casting for stably casting a healthy slab without causing casting defects due to entrainment of mold flux into the slab at the start of casting.

[Conventional technology]

In the continuous casting method, the molten metal in the tundish or the molten metal tapped from the melting furnace into the trough is supplied from one end of a water-cooled copper mold through a submerged nozzle attached to the bottom of the tundish or the gutter, and the molten metal is cooled in the mold. This is a method in which the slab is solidified one after another, and the slab is continuously pulled out from the other end of the mold, and is widely used as a casting method for steel and nonferrous metals.

Generally, when starting the casting of slabs using the continuous casting method, as shown in Fig. 2, a dummy bar or disk 2 is inserted into the through-hole mold 1 to block the lower part of the mold, and then the supply of molten metal is started. When the molten metal inside reaches a certain height, drawing begins.

Conventionally, mold flux 6 was added immediately upon supply of molten metal.
The molten metal supplied into the mold was prevented from oxidizing by charging the molten metal into the mold and coating the exposed surface of the molten metal with mold flux.

As shown in FIG. 3, when the supply into the mold 1 starts, mold flux 6 is introduced into the mold 1 to coat the surface of the molten metal 5, and as shown in FIG. Pulling out the disk 2 from the mold 1 was started with the disk 4 completely buried in the molten metal 5.

However, as shown in FIG. 3, when mold flux is introduced when the level of the molten metal 5 is lower than the molten metal spout 4 of the immersion nozzle 3, the molten metal flow 7 spouted from the spout 4 falls, causing the mold flux 6 and The surface of the molten metal 5 is violently disturbed, and mold flux entrainment 8 occurs, and the entrainment 8 is captured by solidification of the molten metal and remains in the slab as a casting defect.

The reason why mold flux is normally added at the same time as the supply of molten metal starts is to prevent oxidation due to contact between the molten metal and air, and to melt the mold flux supplied in the form of powder before the start of drawing.

[Problem to be solved by the invention]

However, if mold flux is introduced when the molten metal level is lower than the spout hole of the immersion nozzle.

The molten metal flow ejected from the nozzle violently disturbs the surface of the molten metal in the mold, and as shown in Figure 3, the falling molten metal flow causes the mold flux to be caught in the molten metal, and when it solidifies, it becomes a slab. It remained within the mold, resulting in a casting defect.

For this reason, casting defects occur frequently in slabs at the start of casting, and the casting defects are usually prevented from flowing out by cutting the affected parts, but the amount of cutting is, for example, 200 to 300 nm in the case of copper alloy slabs. In the case of steel, it can extend up to several meters, contributing to a decrease in yield.

On the other hand, when continuously casting metals or alloys that do not significantly generate inclusions due to oxidation of the molten metal.

There was no major problem even if the timing of coating the surface of the molten metal in the mold was delayed, and the molten metal spout 4 of the immersion nozzle 3 was completely buried in the molten metal 5 in the mold 1 as shown in Fig. 1. By charging the mold flux in this state, it is possible to prevent severe disturbances on the surface of the molten metal and the entrainment of the mold flux into the molten metal.

The present invention has been made in view of the above circumstances, and is a continuous casting method that can stably supply healthy slabs without causing mold flux to be caught in the molten metal in the mold when starting continuous casting. It is intended to provide a way to get started.

[Means to solve the problem]

In order to achieve the above object, the present inventor has conducted intensive research on the behavior of the molten metal flow in the mold at the start of continuous casting, and on the timing and method of introducing mold flux, and as a result, selected the timing of introducing mold flux. It was found that this suppressed the mold flux from being entangled in the slab at the start of casting, and based on this knowledge, the present invention was accomplished.

That is, by starting the supply of molten metal into the mold and putting the mold flux into the T4 mold with the molten metal spout of the immersion nozzle completely buried in the molten metal in the mold, the flow of molten metal spouted from the nozzle is This suppresses disturbances on the molten metal surface and prevents mold flux from being drawn into the molten metal.

〔Example〕

The details of the present invention will be explained below with reference to the drawings.

In continuous casting, as shown in FIG. 2, with a start bar or disk 2 inserted into the mold 1, supply of molten metal into the mold 1 from a tundish or gutter (not shown) through an immersion nozzle 3 is started.

Next, an experiment in which the method according to the present invention was carried out was conducted along with a comparative example.

As shown in Fig. 1, a continuous casting method using an inverted T-shaped two-hole immersion nozzle 3 that spouts molten metal perpendicular to the casting direction and a rectangular penetrating water-cooled copper mold 1 has a diameter of 650 mm and a thickness of 150 mm.
In the continuous casting of class III brass slab slabs, in this embodiment, the initial injection of mold flux 6 at the start of continuous casting is carried out after the molten metal spout 4 of the immersion nozzle is completely submerged in the molten metal 5 in the mold. A mold flux having a viscosity shown in Table 1 was initially charged in the form of melt or powder.

From the start of supply of molten metal into the mold until the start of drawing, the molten metal supplied into the mold undergoes unsteady solidification, which is different from continuous casting. evaluated.

The occurrence of mold flux entrainment was caused by the entrainment of mold flux exposed on the surface of the rolled plate corresponding to the slab length of 200 mm from the starting end of the casting when the continuously cast slab slab was hot rolled to a plate thickness of 8 mm. The evaluation was made by counting the number of defects. In addition, in order to evaluate the viscosity of the flux and the method of adding the flux, the surface of the slab slab 200 m from the casting start end was visually evaluated.

The results are shown in Table 1 together with comparative examples. The number of defects is expressed as the number of defects generated per IM of the rolled plate surface.

Table 1 The 0 mark above is good, the Δ mark is normal, and the x mark is bad. For example, the entrainment of mold flux into the slab at the start of continuous casting is drastically reduced.
Furthermore, it has become clear that casting surface can be improved by initially adding a molten mold flux with low viscosity.

The mold flux to be initially added may be in powder form, but there may not be much time between the injection of the mold flux and the start of drawing, and the mold flux may not fully melt and spread to the metal body in the mold. figure,
Since the lubricity between the mold and the solidified shell may be impaired, it is desirable that the initial mold flux be added in a molten state. Preferably, mold flux with a low viscosity is used so that it quickly spreads between the mold and the solidified shell. It is desirable to add flux initially.

〔Effect of the invention〕

According to the method for starting continuous casting according to the present invention described above, it is possible to stably cast a sound ingot without causing casting defects due to the entrainment of mold flux in the slab at the start of casting.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of an example of the initial injection timing of mold flux according to the present invention, Fig. 2 is a state diagram when a disk is inserted into the mold before the start of molten metal supply, and Fig. 3 is a diagram at the start of conventional casting. FIG. 3 is an explanatory diagram showing the state of entrainment of mold flux in the mold. 1...Water-cooled copper mold, 2...Disc. 3... Immersion nozzle, 4... Molten metal spout, 5... Molten metal, 6... Mold flux, 7... Molten metal flow, 8... Entrainment of mold flux.

Claims (1)

[Claims] (1) When starting continuous casting using a mold with both ends open and an immersion nozzle, the initial injection of mold flux should be performed after the molten metal spouting hole of the immersion nozzle is completely submerged in the molten metal in the mold. A method for starting continuous casting, characterized by: