Electric heating – Metal heating – By arc
Patent
1992-09-09
1995-02-21
Albritton, C. L.
Electric heating
Metal heating
By arc
21912169, 21912182, B27K 2600
Patent
active
053918568
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a cooling drum for use in a twin-drum process, a single-drum process, a drum-belt process or the like for continuously casting thin cast strip and to a method and apparatus for forming dimples in the peripheral surface of the cooling drum.
BACKGROUND OF THE INVENTION
In the field of continuous casting, there is a strong demand for the development of a technique for manufacturing directly from a molten metal a thin cast strip having a shape generally equal to a finished shape of sheet metal for the purpose of reducing the manufacturing cost, creating new metals, and so on. To meet this demand, various methods, for example, a twin-drum method using a pair of cooling drums with internal water-cooling mechanisms, a single drum method using one cooling drum and a drum-belt method based on the formation of a meniscus between a cooling drum and a belt, have been proposed and some of them have been improved to such a level as to be industrially practicable.
In these continuous casting methods, it is important to stably maintain surface characteristics of a thin cast strip at a high level. That is, continuous casting methods of this kind have been developed with the aim of obtaining a thin cast strip which is capable of reducing the rate of rolling in a subsequent step unlike slabs manufactured by the conventional continuous casting facilities. Therefore, if there is a variation in the thickness of a thin cast strip, a crack in the surface thereof, or the like, it would remain as a defect in the surface of the product and there is a considerable risk of impairing the value of the product on the market.
Various methods have therefore been studied and proposed to stably manufacture thin cast strips having good surface qualities. For example, a method of forming irregularities in the peripheral surface of a cooling drum to form air gaps between a cast metal and the cooling drum has been proposed in Japanese Unexamined Patent Publication No. 60-184449. The heat removing capacity of the cooling drum is reduced by the air gaps so that the molten metal is slowly cooled. Consequently, the thickness of the solidified shell is made uniform in the widthwise direction of the shell and it is possible to manufacture a thin cast strip having improved shape characteristics.
However, if a thin cast strip is manufactured by using a cooling drum having surface irregularities or dimples formed in its peripheral surface, transverse creases may be easily formed in the surface of the obtained cast strip. The cause of this phenomenon will be described below with reference to the drawings.
FIG. 5 shows a meniscus portion of one of two cooling drums of a twin drum type continuous casting machine. The same problem is encountered in the case of the single drum process or the drum-belt process.
Molten metal 4 injected into a basin 3 is vibrated by surface irregularities or dimples 2 formed in the peripheral surface of a cooling drum 1 to cause surface waves 5. As the cooling drum 1 is rotated in the direction of arrow A, the molten metal 4 is cooled by the peripheral surface of the cooling drum 1 to form a solidified shell which is fed into the drum gap.
If surface waves 5 occur in the molten metal surface during this process, the state of contact between the molten metal 4 and the peripheral surface of the cooling drum 1 is deteriorated, so that irregular gaps are easily formed at the interface. These gaps act to cause a reduction in the rate of heat transfer to the cooling drum 1, causing irregular changes in the growing speed of the solidified shell and the cooling speed in the lengthwise direction of the cast strip.
Transverse creases are therefore formed in the resulting thin cast strip. Also, even if the generation of transverse creases can be avoided, the heat history of the thin cast strip is locally changed since the conditions of the growth and cooling of the solidified shell are varied by surface waves 5.
Variations in the heat history caused in this manner result in non-uniformity of th
REFERENCES:
patent: 4947023 (1990-08-01), Minamida et al.
Kido Motoi
Minamida Katsuhiro
Nishizawa Fumihiko
Albritton C. L.
Nippon Steel Corporation
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