Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1997-09-24
2000-06-13
Lin, Kuang Y.
Metal founding
Process
Shaping liquid metal against a forming surface
164459, 164480, B22D 1106, B22D 1110
Patent
active
060736798
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to the casting of steel strip.
It is known to cast metal strip by continuous casting in a twin roll caster. In this technique molten metal is introduced between a pair of contra-rotated horizontal casting rolls which are cooled so that metal shells solidify on the 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 term "nip" is used herein to refer to the general region at which the rolls are closest together. The molten metal may be poured from a ladle into a smaller vessel from which it flows through a metal delivery nozzle located above the nip so as 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 and extending along the length of the nip. This casting pool is usually confined between side plates or dams held in sliding engagement with end surfaces of the rolls so as to dam the two ends of the casting pool against outflow, although alternative means such as electromagnetic barriers have also been proposed.
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 encountered in the casting of mild steel in a twin roll strip caster is the propensity for molten mild steel to produce solid inclusions, in particular inclusions which contain aluminates, and these solid inclusions clog the very small metal flow passages required in the metal delivery system of a twin roll caster. As fully described in our New Zealand Patent Application 270147 we have determined by an extensive programme of strip casting various grades of steel in a twin roll caster that aluminium killed mild steels or partially killed mild steel, with an aluminium residual content of 0.01% or greater cannot be cast satisfactorily because the solid inclusions agglomerate and clog the fine flow passages in the metal delivery system to form defects and discontinuties in the resulting strip product. This problem can be overcome by keeping the aluminium content below 0.01% by weight and by using a silicon/manganese killed steel having a manganese content of not less than 0.20% by weight and a silicon content of not less than 0.02% by weight. However, such silicon/manganese killed steels have a very much higher oxygen content than aluminium killed steels and this gives rise to a problem of carbon dissolution from the refractories of the metal delivery system. Specifically, the carbon combines with oxygen from the molten steel to produce carbon monoxide. This can degrade the surfaces of the fine flow passages in the delivery nozzle. Moreover, in casters in which the delivery nozzle dips into the casting pool, the pool is disturbed by carbon monoxide bubbles generated by the reaction between carbon in the submerged delivery nozzle and oxygen in the molten metal of the casting pool.
Silicon/manganese killed steels will have an oxygen content in the range 50-155 ppm at typical casting temperatures of the order of 1600-1700.degree. C. whereas the oxygen content of aluminium killed steels will generally be less than 10 ppm and the carbon leaching problem is a very significant one when endeavouring to cast silicon/manganese killed steel.
We have now determined that this problem can be solved by the controlled addition of sulphur to the silicon/manganese killed steel melt at least in the start-up phase of a casting operation. After start-up a surface slag forms on the delivery nozzle which is dipped into the casting pool. This slag reduces the availability of carbon to react with the oxygen in the immersed areas of the delivery nozzle which is the part of the metal delivery system most vulnerable to carbon leaching.
The addition of sulphur also enables the avoidance of "chatter" and "crocodile skin" defects in the strip due to he
REFERENCES:
patent: 5345994 (1994-09-01), Kato et al.
patent: 5701948 (1997-12-01), Strezov et al.
Derwent Abstract Accession No. 90-330626/14, Class P53, JP 02-236254 A (Nippon Steel Corp.) Sep. 19, 1990.
Derwent Abstract Accession No. 89-367752/50, Class M27, JP 01-275736 A (Nippon Steel Corp.) Nov. 6, 1989.
Derwent WPAT Online Accession No. 02022Y/02, BE 844818 A (Centro Speri Metal Spa) Dec. 1, 1976.
Patent Abstracts of Japan, M138, p. 74, JP 57-41847 A, (Sumitomo Kinzoku Kogyo KK) Jan. 30, 1992.
Patent Abstracts of Japan, C57, p. 24, JP 56-29658 A, (Kawasaki Seitetsu KK) Mar. 25, 1981.
Patent Abstracts of Japan, C715, p. 50, JP 02-47242 A (Kobe Steel Ltd) Feb. 16, 1990.
Patent Abstracts of Japan, C273, p. 9, JP 59-205453 A (Daido Tokushuko KK).
BHP Steel (JLA) Pty. Ltd.
Ishikawajima-Harima Heavy Industries Ltd. Company Limited
Kerins John C.
Lin Kuang Y.
LandOfFree
Casting steel strip does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Casting steel strip, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Casting steel strip will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2060996