Metal strip casting

Details Metal strip casting Metal strip casting

1994-08-15

1996-05-28

Lin, Kuang Y.

Metal founding

Process

Shaping liquid metal against a forming surface

164479, 164480, 164428, 164429, 164416, B22D 1106, B22D 1104

Patent

active

055202438

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to the casting of metal strip. It has particular but not exclusive application to the casting of ferrous metal strip.
It is known to cast metal strip by continuous casting in a twin roll caster. Molten metal is introduced between a pair of contra-rotated horizontal casting rolls which are cooled so that metal shells solidify on the 10 moving roll surfaces and are brought together at the nip between them to produce a solidified strip product delivered downwardly from the nip between the rolls. The molten metal may be introduced into the nip between the rolls via a tundish and a metal delivery nozzle located beneath the tundish so as to receive a flow of metal from the tundish and to direct it into the nip between the rolls, so forming a casting pool of molten metal supported on the casting surfaces of the rolls immediately above the nip. This casting pool may be confined between side plates or dams held in sliding engagement with the ends of the rolls.
Although twin roll casting has been applied with some success to non-ferrous metals which solidify rapidly on cooling, there have been problems in applying the technique to the casting of ferrous metals. One particular problem has been the achievement of sufficiently rapid and even cooling of metal over the casting surfaces of the rolls. We have now determined that the cooling of metal at the casting surface of the rolls can be dramatically improved by taking steps to ensure that the roll surfaces have certain smoothness characteristics in conjunction with the application of relative vibratory movement between the molten metal of the casting pool and the casting surfaces of the rolls.
It has previously been proposed in metal casting techniques to apply ultrasonic vibrations to the casting equipment or to the molten metal in that equipment. However these proposals have usually been advanced simply to prevent sticking of solidifying metal on the casting surfaces, to enhance release of gases from the molten metal, to reduce non-metallic inclusions and to promote some internal grain refinement.
U.S. Pat. No. 4,582,117 of Julian H Kushnick discloses the application of ultrasonic vibrations to a casting surface in a continuous casting apparatus. In that case the casting surface is a continuously moving chilled substrate in the form of a moving endless belt extending between a pair of end rolls. The ultrasonic vibrations are applied to the underside of this belt beneath a puddle of molten metal formed where the metal flows onto the belt from a casting nozzle. Kushnick discloses that application of ultrasonic vibrations through the substrate to the melt puddle prior to the critical period of solidification has the effect of enhancing wetting of the substrate and improves heat transfer between the melt puddle and the chilled substrate. These improvements are said to result from the release of trapped air from the molten metal which increases the molten metal/substrate contact area and enhancing wetting of the substrate by the molten metal. As a result, improved heat transfer between the chilled substrate and the molten metal is achieved. As in other prior art proposals to apply ultrasonic vibrations to casting techniques, the vibrations contemplated are in the ultrasonic frequency from 20 to 100 kHz.
The improvements obtained by the application of ultrasonic vibrations simply to enhance wetting and the release of trapped gases and to prevent sticking, although valuable, do not result in a particularly dramatic improvement in the heat transfer between the molten metal and the casting surfaces. We have discovered that by employing casting roll surfaces which are particularly smooth in conjunction with the application of vibratory movements of selected frequency and amplitude it is possible to achieve a totally new effect in the metal solidification process which dramatically improves the heat transfer from the solidifying molten metal. The improvement can be so dramatic that the thickness of the metal being cast at a particular ca

REFERENCES:
patent: 5390726 (1995-02-01), Fukuda et al.

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