Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2000-04-20
2001-08-14
Nguyen, Nam (Department: 1722)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S428000, C164S414000, C164S444000
Reexamination Certificate
active
06273178
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a twin roll continuous casting installation wherein molten metal is quenched for solidification and directly molded into a metal sheet.
Prior Art
It is known in the art of continuous casting that quenching of poured molten metal for solidification into a strip will greatly improve characteristics of the material owing to formation of stable phase in the strip, drastic reduction of microsegregation and micronization of the structure and the like.
For casting such strip, there have been proposed installations in which molten metal is poured into a nip between a pair of chilled roll to be quenched into a strip.
Problems during the pouring and quenching of molten metal are deteriorated cleanliness of the molten metal due to oxygen in surrounding atmosphere as well as formation of oxided scale on the strip.
A proposal for overcoming the problems is disclosed in JP-B-3-33053.
FIG. 7
shows a twin roll continuous caster as disclosed in this Japanese patent publication. It comprises an upstream chamber
2
constituting a main-body vessel and a downstream chamber
12
disposed just below the chamber
2
and constituting a strip-delivering vessel. Prior to continuous casting of strip (strip
8
), interiors of the chambers
2
and
12
are substituted into inert gas atmospheres.
Arranged in the upstream chamber
2
in the order named from above are a tundish
5
, a pair of chilled rolls
1
a
and
1
b
and a pair of upper cooling gas sprays
10
a
and
10
b
. Molten metal supplied from a ladle
7
outside and above the upstream chamber
2
to the tundish
5
is poured into the nip between the chilled rolls
1
a
and
1
b
which are rotated, so that the molten metal is cooled by the rolls
1
a
and
1
b
into solidified strip
8
which is continuously delivered downward.
The strip
8
delivered by the chilled rolls
1
a
and
1
b
is cooled at its opposite surfaces by inert gas injected by the upper cooling gas sprays
10
and
10
b
and passed to the downstream chamber
12
.
Arranged in the downstream chamber
12
in the order named from above are a pair of lower cooling gas sprays
15
a
and
15
b
and a pair of pinch rolls
11
a
and
11
b
. The strip
8
delivered from the upstream chamber
2
is cooled at its opposite surfaces by inert gas injected from the lower cooling gas sprays
15
a
and
15
b
and is passed outside of the downstream chamber
12
.
Thus, the twin roll continuous casting installation shown in
FIG. 7
suppresses deteriorated cleanliness of the molten metal and prevents oxidization of the strip surfaces in such a manner that the interiors of the upstream and downstream chambers
2
and
12
are substituted into inert gas atmospheres and the inert gas is injected to the opposite surfaces of the strip by the gas sprays in the chambers
2
and
12
.
Meanwhile, a recent problem on strip in continuous casting is occurrence of bulging on the strip at its widthwise edges (edge bulging), break on the strip at the edges (edge break) and strip fracture (breakout) due to a phenomenon that insufficient cooling on the strip at its widthwise edges may result in the unsoldifified surface of the strip just after the casting being melted again because of heat recuperation. A proposal to overcome the problem is disclosed in JP-A-5-277654.
FIGS. 8 and 9
show a twin roll continuous caster disclosed in this publication and having a pair of dog bone type chilled rolls
17
a
and
17
b
rotatably arranged below the chilled rolls
1
a
and
1
b
. The chilled rolls
17
a
and
17
b
have, at their opposite ends, enlarged roll portions which contact widthwise opposite edges on opposite surfaces of the strip
8
from the chilled rolls
1
a
and
1
b
, so that the widthwise edges of the strip
8
just after the casting is quenched to prevent edge break of the strip
8
.
However, in the twin roll continuous caster as disclosed in JP-B-3-33053 (see FIG.
7
), sealing of the upstream and downstream chambers
2
and
12
for maintaining the inert gas atmospheres in casting of the strip
8
will elevate temperatures in the chambers
2
and
12
, so that the strip
8
must be cooled by the upper cooling gas sprays
10
a
and
10
b
below the chilled rolls
1
a
and
1
b
. Since the inert gas from the sprays
10
a
and
10
b
is injected over the whole surfaces of the strip
8
, cooling effect may be low at the widthwise opposite edges of the strip
8
, disadvantageously resulting in occurrence of edge bulging.
On the other hand, in the twin roll continuous caster as disclosed in JP-A-5-277654 (see FIGS.
8
and
9
), assumption in actual operation may be made such that the chilled rolls
1
a
and
1
b
have outer diameter of 400-600 mm and the enlarged portions of the dog bone type chilled rolls
17
a
and
17
b
have outer diameter of 200 mm. Then, the distance of the dog bone type chilled rolls
17
a
and
17
b
from the chilled rolls
1
a
and
1
b
may be 300-400 mm, which may cause insufficient cooling effect on the widthwise opposite edges of the strip
8
just below the nip between the chilled rolls
1
a
and
1
b
, disadvantageously resulting in occurrence of edge bulging and breakout on the strip
8
.
Further, the inventors experimentally investigated a relationship of perfect solid phase shell thickness near the edge of the strip
8
to distance of the chilled rolls
1
a
and
1
b
from the nip between the chilled rolls
1
a
and
1
b
in the manufacturing conditions that, as shown in
FIG. 6
, atmosphere temperature in the chamber is 1200° C., strip thickness is 2 mm and manufacturing speed is 60 m/min. As a result, it was found out that, in the condition {circle around (1)} in the Figure where no cooling is effected, the perfect solid phase shell thickness of the edge of the strip
8
tends to decrease to zero due to heat recuperation of unsolidified portion in the strip
8
so that edge bulging, edge break and/or breakout of the strip
8
is likely to occur on such portion.
The present invention was made in view of the above and has an object to provide a twin roll continuous casting installation which can alleviate decrease of the perfect solid. phase shell thickness near the edge of the strip caused by heat recuperation of the unsolidified portion.
SUMMARY OF THE INVENTION
According to the invention there is provided a twin roll continuous casting installation comprising pinch rolls for clamping a strip continuously cast by a pair of chilled rolls, a chamber for enclosing travel path of the strip from the chilled rolls to the pinch rolls, said chamber having seal members airtightly in contact with outer peripheries of the chilled rolls and pinch rolls, and a pair of chilled blocks for injecting cooling medium to edges of the strip delivered from the chilled rolls, said blocks being shaped for loose fitting over the edges of the strip, one of the blocks being arranged just below one ends of the chilled rolls, the other block being arranged just below the other ends of the chilled rolls.
It is preferred that each of the chilled blocks has cooling medium passages therein to cool the chill blocks.
Preferably each of the pair of chilled blocks is adapted to be moved between a position where the chilled block is loosely fitted over the edge of the strip just below the chilled rolls and a position where the chilled block is not affected by splashing of metal dropping from the nip between the chilled rolls at the beginning of strip casting.
It is preferred that cooling gas is injected from the pair of blocks toward the edges of the strip positioned near the nip between the chilled rolls, thereby preventing decrease of perfect solid phase shell thickness of the strip due to heat recuperation of unsolidified portion to suppress edge bulging and breaking of the strip.
Preferably cooling medium is passed through cooling medium passages of the respective chilled blocks to enable radiation-cooling of the edges of the strip positioned near the nip between the chilled rolls by the blocks, thereby preventing decrease of perfect solid phase she
Hirata Atsushi
Osada Shiro
Takeuchi Osamu
Ishikawajima-Harima Heavy Industries Company Limited
Kerins John C.
Lin I,-H.
Miles & Stockbridge P.C.
Nguyen Nam
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