Metal founding – Means providing inert or reducing atmosphere – In continuous casting apparatus
Reexamination Certificate
2001-08-08
2003-03-25
Elve, M. Alexandra (Department: 1725)
Metal founding
Means providing inert or reducing atmosphere
In continuous casting apparatus
C164S417000, C164S428000
Reexamination Certificate
active
06536504
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to and the benefit of Japanese Application Ser. No. 2000-239777, filed Aug. 8, 2000.
TECHNICAL FIELD
This invention relates to a continuous strip casting device and to a method for the use thereof.
PRIOR ART
FIG. 5
illustrates the continuous strip casting device revealed by JP 8-300108 (and also U.S. Pat. Nos. 5590701 and 5960856), such continuous strip casting device being provided with a pair of casting rolls
101
a
and
101
b
that are rotatably supported in such a manner as to be juxtaposed horizontally parallel to each other and as to form roll gap G, with the outer circumferential surfaces of the casting rolls facing the said roll gap G. A molten metal supply means
102
of the casting device supplies molten metal to and between the casting rolls
101
a
and
101
b
, and a strip guide means
112
guides sideways the strip
103
that emerges from the roll gap G through the rotation of the casting rolls
101
a
and
101
b
. A pinch roll stand
105
grips the strip
103
that has passed from the strip guide means
112
. An enclosure wall
107
provides a chamber
106
that is positioned below the casting rolls
101
a
and
101
b
and encloses the moving path for the strip
103
from the roll gap G to the pinch roll stand
105
, with a scrap box
108
whose upper edge is in contact from below with the edge of the chamber
106
of the enclosure wall
107
.
The outer circumferential surfaces of the casting rolls
101
a
and
101
b
are cooled by means of the cooling water that flows through the interiors of the casting rolls and the solidification of the molten metal on the surfaces of the casting rolls
101
a
and
101
b
is accelerated thereby.
Moreover, an actuator (not shown) that holds in close proximity the rotational axes of the casting rolls
101
a
and
101
b
is attached in order to regulate the roll gap G, and in turn the gauge of the strip
103
that is to be manufactured.
The molten metal supply system
102
also possesses a tundish
109
that receives the molten metal, and a nozzle
110
that pours the molten metal from the said tundish
109
to and between the casting rolls
101
a
and
101
b.
The strip guide means
112
is comprised of a support shaft
111
that is disposed below the casting roll
1010
b
and that is pivoted parallel to the said casting roll
101
b
, and a plurality of guide rolls
113
that are disposed laterally and that support the strip
103
that is transported sideways by the movable apron
112
A.
The pinch roll stand
105
possesses a housing
114
through which the strip
103
passes, and a pressure roll
115
a
that is so mounted in the housing
114
as to come into contact with the lower surface of the strip
103
, and a pressure roll
115
b
that is so mounted in the housing
114
as to come into contact with the upper surface of the strip
103
.
The enclosure wall
107
is comprised of a steel outer shell
116
which is intended to impart support to an interior refractory lining
117
which extends across the entire inner surface of the outer shell
116
.
A scrap box
108
is formed of refractory materials, and a seal member
118
is mounted in the top of the scrap box
10
. The scrap box
108
is mounted on the car
121
that has wheels
120
that are able to move over the rails
119
, and has a cylinder
122
that is able to raise the scrap box
108
as provided on the said car
121
.
When strip
103
is manufactured by means of the continuous strip casting device illustrated in
FIG. 5
, the cylinder
122
attached to the car
121
raises the scrap box
108
bringing the upper edge of the scrap box
108
through the seal member
118
into contact with the edge of the chamber
106
of the enclosure wall
107
. The leading edge of the movable apron
112
A is so set as to be positioned below the support shaft
111
. The distance between the rotational axes of the casting rolls
101
a
and
101
b
is set so that a roll gap G corresponds to the gauge of the strip
103
that is to be cast, and the casting rolls
101
a
and
101
b
are rotated in such a manner that their outer circumferential surfaces move from above towards the roll gap G.
Next, molten steel is supplied to the tundish
109
, and when the molten steel is poured through the nozzle
110
to and between the casting rolls
111
a
and
101
b
, a solidified shell forms on the outer circumferential surfaces of the rolls, and as the casting rolls
101
a
and
101
b
rotate, the strip
103
is transported into chamber
106
.
After the strip
103
has been presented in a laterally uniform state, the rotational axis of the casting rolls
101
a
and
101
b
rebounds in a very short time (approximately from 0.1 to 0.5 seconds) such that the roll gap G becomes approximately 1.5 to 3 times the thickness of strip
103
, and then the roll gap G reverts to its original state. The expansion in the roll gap G causes the casting rolls
101
a
and
101
b
to produce areas of imperfect cooling, so that the strip
103
melts again through reheating effectively acting as a hot shear.
In this way, the strip
103
that is transported before the expansion of the roll gap G is broken off in a straight line from the strip
103
that is transported after the roll gap G has reverted to its original state, with the portion of the strip
103
that was remelted through the expansion of the roll gap G forming the boundary of the strip
103
to be transported to the coilers.
Moreover, the movable apron
112
A is disposed laterally, and the strip
103
that is transported from the roll gap G after the break is led by the guide rolls
113
to the pinch roll stand
105
.
The problem addressed by the present invention is that in the continuous strip casting device shown in
FIG. 5
, the space formed by the enclosure wall
107
that encloses the moving path for the strip
103
from the roll gap G to the pinch roll stand
105
, and the scrap box
108
that comes into contact with the lower edge of the of the chamber
106
of the enclosure wall
107
, is not filled with a non-oxidizing or weakly reducing atmospheric gas, and hence scale caused by oxidation develops on the strip
103
.
Moreover, no means is provided for control of the flow of the atmospheric gas (air) between the casting rolls
101
a
and
101
b
and the movable apron
112
A, and between the movable apron
112
A and the guide rolls
113
. The high temperature air that has been heated by the strip
103
blows in a concentrated manner onto the casting rolls
101
a
and
101
b
, while the insulating effect of the refractory lining
117
of the enclosure wall
107
impedes the cooling of the air within the chamber
106
. This causes reheating of the strip
103
immediately after transport from the roll gap G and breakout and instability in casting. The high temperature strip
103
(not less than 1250° C.) is transported to the pinch roll stand with scale, leading to embedded scale damage, and a likely reduction in yield.
Moreover, because the seal member
118
of the scrap box
108
is in contact with the edge of the enclosure wall
107
forming chamber
106
, when an attempt is made to exchange the scrap box
108
during casting, a large amount of air flows into the chamber
106
causing severe strip oxidation. As a result, for practical purposes, it is not possible to exchange the scrap box
108
during the operation of the continuous strip casting device.
Moreover, splashes of molten metal and slag fall onto and accumulate on the seal member
118
between the enclosure wall
107
and the scrap box
108
. As a result, the seal member
118
is deformed and damaged by the raising of the cylinder
122
of the scrap box
108
so that, each time the scrap box
108
is exchanged, the seal member
118
must be cleaned or replaced. Furthermore, it is difficult to restrict the inflow of external air and to maintain a low oxygen content inside the enclosing wall
107
.
The present invention takes account of such deficiencies of the prior art, and enables the efficient manufacture of
Kato Heiji
Matsushita Toshiro
Takeuchi Osamu
Barnes & Thornburg
Castrip LLC
Elve M. Alexandra
Tran Len
LandOfFree
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