JPS6356339A - Dripping type casting device - Google Patents

Abstract

PURPOSE:To obtain an ingot having fine crystal structure and no surface defects by heating the region near a casting mold of the molten metal surface in the mold selectively by a selective heating means at the time of dropping the liquid drops of a molten metal into the casting mold by a liquid drop casting means. CONSTITUTION:The opposed ends of electrodes 11 melt and the liquid drops 14 of the molten metal fall into the casting mold 13 when electricity is conducted between the electrodes 11 to form an arc 12. The liquid drops 14 are cooled before dropping into the casting mold 13 and are cast into the casting mold 13 in the state of having less overheating. An electron beam 21 emitted from an electron gum 20 is projected to the peripheral edge where the melt surface of the molten metal 16 in the mold 13 contacts the mold 13. Then, said part is selectively heated and the solidification boundary between the molten metal 16 in said part and the ingot 15 moves downward. The quick solidification of the part of the molten metal surface in contact with the mold 13 is, therefore, obviated even if the melt surface of the molten metal 16 rises instantaneously upon dropping of the liquid drops 14 into the mold 13. The formation of a recess in the surface of the ingot 15 and the consequent formation of a surface defect are thus prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drip casting apparatus capable of producing slabs and ingots having a fine structure.

[Prior Art] Usually, slabs or ingots, which are intermediate materials for metal products, are manufactured by pouring molten metal into a continuous casting mold or an ingot mold and solidifying it.

However, in these techniques, completely molten metal is cast, so the produced slab or ingot has a relatively large crystal grain size in its solidified structure.

For this reason, when applying a reduction to a slab or the like to ensure mechanical properties, if a large reduction is applied, cracks will occur in the slab or the like. Therefore, it is necessary to apply the reduction blade in multiple steps, but this requires a long processing time and also requires a large amount of thermal energy, resulting in high processing costs. When producing a knot of coagulated tissue in this way, the produced culm becomes extremely complicated.

In order to eliminate these shortcomings in general casting technology, VADER (VacuuIIIArcDou) has recently been developed.
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A casting technique called the vacuum arc two-electrode melting (vacuum arc two-electrode melting) method has been proposed (Japanese Unexamined Patent Publication No. 55-165271). In this VADER method, as shown in FIG. 6, an arc 2 is formed between a pair of electrodes 1 made of a metal having the same composition as the slab to be produced by an appropriate means, and an arc 2 is formed between the opposite ends of the electrodes 1. melt. This droplet 4 of molten metal falls into the mold 3, is cooled by the mold 3, and solidifies. A slab 5 obtained by partially solidifying the molten metal is continuously drawn downward from the mold 4. In this case, the molten metal droplet 3 is slightly cooled in the process of falling from the electrode 1 to the mold 4, and is cast into the mold 3 as molten metal 6 without superheating.

Therefore, solidification occurs in the mold 3 in which the solid-liquid coexistence phase exists uniformly, so that the crystal grain size of the solidified structure of the slab 5 is small. Therefore, even if a large reduction is applied, cracks will not occur in the slab.

[Problems to be solved by the invention] However, in such conventional devices, the seventh
As shown in the figure, in the area of the meniscus (molten metal surface) in the mold 3 that is in contact with the mold 3, the molten metal 6 is rapidly removed heat by the mold and solidifies, causing a bulge in the vicinity of this area. The state will be as follows. When the droplet 4 falls into the mold 3 in this state, the meniscus instantly bulges, as shown in Figure 8, and the molten metal that has been cast comes into contact with the mold 3 and rapidly solidifies. . If this happens, recesses will remain on the surface of the slab 5, and surface defects 7 will be formed.

Such surface defects 7 occur frequently, and their depth is typically 2 mm, but may reach 5 mm in some cases. For this reason, the surface quality of the slab 5 becomes extremely poor, and the surface of the slab 5 is removed by several millimeters before being processed.
For example, when grinding a cylindrical ingot with a diameter of 20 On+m by 5 mm, there will be a loss of about 10% in weight, and the yield will decrease accordingly.

This invention was made in view of such circumstances, and
The object of L1 is to provide a dropping casting apparatus capable of obtaining a slab having a fine crystal structure, no surface defects, and excellent surface quality.

[Means for Solving the Problems] The drip casting apparatus according to the present invention includes a mold, a droplet casting means for causing droplets of molten metal to fall into the mold, and a droplet casting means for causing droplets of molten metal to fall into the mold, and and selective heating means for selectively heating a region.

In this case, the selective heating means can be constituted by an electron gun that irradiates an electron beam.

[Operation] In the present invention, droplets of molten metal are dropped into the mold by the droplet casting means. In this case, the selective heating means selectively heats the area near the mold on the surface of the hot water in the mold.

In this case, a thick layer of molten metal exists in this region, and even if a droplet falls, this region will not solidify rapidly. Therefore, surface defects in the slab are significantly reduced.

[Embodiments] Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings.

FIG. 1 is a sectional view showing a continuous casting apparatus according to an embodiment of the present invention. The mold 13 is made of copper and has a cylindrical shape, for example,
When producing slabs with a circular cross section, they are cylindrical. This mold 13 is water-cooled by an appropriate water-cooling means. Above this mold 13, a pair of electrodes made of metal having the same composition as the slab to be manufactured are arranged at an appropriate length interval. This pair of electrodes 11
is supplied with power from a power supply device (not shown), and an arc 12 is formed between the electrodes 11. This arc 12 causes the opposing ends of the electrodes 11 to melt, forming droplets 14 that fall into the mold 3.

The droplet] 4 that fell into the mold 13 becomes the molten metal 16,
The molten metal 16 is cooled by the mold 13, and the resulting slab 15 is pulled downward by pinch rolls (not shown).

An electron gun 2o is installed above the mold 13. This electron gun 20 is powered by a high voltage power source (not shown) of, for example, 30 KV.
Electricity is supplied from the mold 13, and an electron beam 21 is irradiated onto the peripheral edge where the surface of the molten metal 16 in the mold 13 comes into contact with the mold 13.

In the dropping casting apparatus configured as described above, first, an electric current is applied between the electrodes 11 to form an arc 12, thereby melting the opposing ends of the electrodes 11, and droplets 14 of the molten metal are poured into the mold 13. fall inside.

The droplet 14 is cooled down before it falls from the electrode 11 into the mold 3, and is cast into the mold 13 with a low degree of superheating. The molten metal 16 cast into the mold 13 is
The solid-liquid coexistence phase is cooled and solidified by the mold 13 in a state where the solid-liquid coexistence phase exists uniformly within the mold.

Therefore, the crystal grain size of the solidified structure of the obtained slab [5] is small.

In this case, as shown in FIG. 2, an electron beam 21 emitted from an electron gun 20 is irradiated onto the peripheral portion of the mold 13 where the surface of the molten metal 16 contacts the mold 13. Then, that part is selectively heated, and the solidification interface between the molten metal 16 and the slab 15 in that part moves downward. That is, the thickness of the molten metal 16 becomes thicker at and near the peripheral edge where the surface of the molten metal 6 contacts the mold 13. Therefore, even if the droplet 14 falls into the mold 13 and the level of the molten metal 16 rises momentarily, the molten metal 16
The part of the molten metal surface in contact with the mold 13 will not solidify rapidly. Therefore, it is possible to avoid the occurrence of surface defects due to the formation of recesses on the surface of the slab 15. Thereby, a slab with good surface quality can be obtained.

Next, a specific example of producing a Ni-based super super heat-resistant alloy using the apparatus according to this embodiment will be described. Table 1 shows the composition of the alloy used in this example.

Table 1 (% by weight) In this specific example, a cylindrical mold with an inner diameter of 100+nm is used, an electron gun with a maximum output of 60KV is used, and the electrodes are round rods with a diameter of 100n+n+ having the composition listed in 1. Using. Then, a current of 160 OA was applied to the electrode (current density: 2 OA/cm 2 ) to melt the opposing ends of the electrode, and droplets of molten liquid were dropped into the mold. In addition, the output of the electron gun was increased to 30K.
The voltage was set to V and an electron beam was irradiated. In this case, the scanning speed of the electron beam was set so that the electron beam went around the periphery of the molten metal surface in the mold in 0.002 seconds.

The surface of the slab produced by casting under these conditions was observed, and the number of surface defects per 1,000 cm2 was investigated. FIG. 3 is a graph showing the number of surface defects on the slab in this example compared to the conventional one.

As shown in this figure, in the case of the conventional device, 100 cm2
While the number of surface defects per unit is distributed between 1 and 6, in the case of this example, the number is 2 or less, which is extremely small. It was also confirmed that the depth of surface defects in this example was shallower than in the conventional case.

FIG. 4 is a diagram showing the surface shape of a slab manufactured by the apparatus according to this embodiment, and FIG. 5 is a diagram showing the surface shape of a slab manufactured by the conventional apparatus. As is clear from these figures, the slab produced using the conventional equipment has extremely many surface defects, but the slab produced using the equipment according to this example has almost no surface defects observed and has an extremely excellent surface quality. have.

In this example, the droplets were generated by forming an arc between a pair of electrodes, but the present invention is not limited to this, and any method may be used as long as suitable droplets can be produced. Although an electron gun is used as the selective heating means, any means may be used as long as it can selectively heat the area near the mold on the surface of the mold. Furthermore, although this example shows the case where slabs are produced by continuous drawing using a mold for continuous casting, the present invention can also be applied to the case where an ingot is produced using a mold for ingot making. Can be done.

In this invention, it is important to heat only the area inside the mold near the mold.

If the entire area of the hot water surface is heated, a completely liquid phase region with a high degree of superheating will be formed on the hot water surface. When a completely liquid phase region is formed in this way, it becomes impossible to solidify the molten metal in a state where the solid-liquid coexistence phase exists uniformly within the mold, and the crystal grain size of the solidified structure becomes finer. I can't. Therefore, as described above, only the area near the mold of the molten metal surface in the mold is heated.

[Effects of the Invention] According to the present invention, droplets of molten metal are dropped into a mold to selectively heat a region of the molten metal surface in the mold near the mold. For this reason, it is possible to obtain a slab or an ingot having a fine crystal grain size in the solidified structure and excellent surface quality. Therefore, this invention has extremely high practicality.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing a dropping casting apparatus according to an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the part irradiated with an electron beam, and Fig. 3 is the number of surface defects on a slab in this embodiment. Fig. 4 is a graph showing the surface shape of the slab manufactured by the apparatus according to this embodiment, Fig. 5 is a graph showing a comparison with the conventional method.
The figure shows the surface shape of slabs produced using conventional equipment.
The figure is a schematic diagram showing a conventional device, and FIGS. 7 and 8 are enlarged views showing the inside of the mold. 11; electrode, 12; arc, 13; mold,] 4; droplet,
15; Slab, 16; Molten metal, 20; Electron gun, 21; Electron beam Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 4 Figure 1 Toki FI8G3-56339 (5) Figure 6

Claims (2)

[Claims] (1) Dripping characterized by having a mold, droplet casting means for dropping droplets of molten metal into the mold, and selective heating means for selectively heating a region of the molten metal surface in the mold near the mold. Type casting equipment. (2) The continuous casting apparatus according to claim 1, wherein the selective heating means is an electron gun that irradiates an electron beam.