Information
-
Patent Grant
-
6536504
-
Patent Number
6,536,504
-
Date Filed
Wednesday, August 8, 200123 years ago
-
Date Issued
Tuesday, March 25, 200321 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Elve; M. Alexandra
- Tran; Len
Agents
-
CPC
-
US Classifications
Field of Search
US
- 164 480
- 164 417
- 164 428
- 164 477
- 164 415
- 164 475
-
International Classifications
-
Abstract
Continuous strip casting device comprises a pair of parallel casting rolls onto which molten metal is supplied by metal supply means. Casting rolls are enclosed by a casting chamber into which hot strip is delivered downwardly from the casting rolls. Strip passes downwardly into a cooling chamber where it can either fall into a moveable scrap box at the bottom of chamber or be guided by operation of moveable apron through an exit door from chamber into a heat exchange chamber provided with heaters. A pair of seal rolls are moveable in a seal chamber to form a seal between chambers and are provided with respective gas inlets to admit oxidation inhibiting gas into those chambers. Scrap box is moveable into and out of the bottom of chamber via a scrap box exchange chamber fitted with an airtight door.
Description
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 strip from molten steel with substantially reduced scale.
SUMMARY OF THE INVENTION
According to the invention there is provided apparatus for continuously casting metal strip comprising:
a pair of parallel casting rolls forming a nip between them;
a molten metal delivery system to delivery molten metal into the nip between the rolls to form a casting pool of molten metal supported on the casting roll surfaces immediately above the nip;
roll drive mechanism to drive the casting rolls in counter-rotational directions to produce a solidified strip of metal delivered downwardly from the nip between the casting rolls;
a casting chamber to enclose strip delivered downwardly from the nip;
a cooling chamber disposed below the casting chamber to receive the strip passing through the casting chamber from the nip through a transfer opening between the casting chamber and cooling chamber located beneath the nip between the casting rolls;
interchamber sealing system disposed at said transfer opening and having an open condition in which the opening is dilated and a closed condition in which the opening is contracted about the strip to enhance sealing between the casting and cooling chambers.
The apparatus may further comprise casting chamber gas inlet means to admit an oxidation inhibiting gas into the casting chamber. The oxidation inhibiting gas may be an inert gas or a weakly reducing gas.
There may be cooling chamber gas inlet to admit an oxidation inhibiting gas into the cooling chamber.
The interchamber sealing system may comprise a pair of seal rolls disposed on to either side of said transfer opening and a roll moving mechanism operable to move the sealing rolls between retracted positions and extended positions in which they contract the transfer opening.
The apparatus may further comprise a moveable scrap box to receive scrap strip at the bottom of the cooling chamber and a scrap box exchange chamber communicating with the bottom part of cooling chamber through an exchange opening closable by a moveable air tight door through which the scrap box can be moved in and out of its scrap receiving position at the bottom of the cooling chamber. The scrap box exchange chamber is provided with a moveable air sealing entry door through which the scrap box can pass into the exchange chamber, and with exchange chamber gas inlet through which to supply an oxidation inhibiting gas to the scrap box exchange chamber.
The apparatus may be further possess a heat exchange chamber with radiant tubes that are disposed in the heat exchange chamber. Guide rolls are disposed in the heat exchange chamber and transport laterally the strip that is sent from the cooling chamber. The heat exchange chamber is also provided with an atmospheric gas inlet.
The apparatus may also have a pinch roll chamber that communicates with the exit of the heat exchange chamber and that is able to receive the strip from the heat exchange chamber, and a partition door that is able to expand and contract in cross section the opening of the exit of the pinch roll chamber, and pinch rolls that are disposed in the pinch roll chamber and are capable of gripping the strip.
The apparatus may also have a rolling mill that is disposed in the downstream strip travel direction from the pinch roll chamber, and a strip pass line that runs from the exit of the pinch roll chamber to the rolling mill being typically so set as to lower the strip by between 10 mm and 150 mm for every 1 m distance of travel.
The invention further may provide a continuous strip casting device having a pair of casting rolls that form a roll gap and that are disposed parallel to each other in diametrical juxtaposition, and a molten metal supply system that supplies molten metal from above to and between the casting rolls, and a casting chamber that encloses the strip emerging from between the two casting rolls and in some embodiments the two casting rolls themselves, and an inter-chamber sealing system having a pair of seal rolls that permit the passage of the strip that is emerging from between the casting rolls downwards. A seal roll chamber may enclose the pair of seal rolls and communicate with or be within the casting chamber. A seal member slides the seal guide that is disposed in the seal roll chamber and positions the seal rolls in the path of and on either side of the strip in such a manner as to cause the movement of the seal rolls. A movable apron is so disposed as to guide sideways the strip that is transported downwards from between the seal rolls or alternatively to lower the said strip to a scrap box. The scrap box is disposed below the movable apron. A cooling chamber communicates with the inter-chamber sealing system and possesses an exit that is able to transport the strip that has been guided by the movable apron and that encloses the movable apron. An exit door is able to increase and decrease the cross section of the opening of the exit from the cooling chamber, and a scrap chamber possesses an air sealing door that is able to move the scrap box in and out of the cooling chamber and that encloses the scrap box that communicates with the cooling chamber, and in which the said casting chamber, cooling chamber and scrap chamber each possesses an atmospheric gas inlet.
The invention also provides a method of use of the continuous strip casting device, such method supplying an oxidation inhibiting gas such as a non-oxidizing or alternatively weakly reducing atmospheric gas, to the said casting chamber, cooling chamber and scrap chamber when strip is being continuously cast.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be more fully explained, specific embodiments will be described with reference to the accompanying drawings in which:
FIG. 1
is a vertical cross-section through part of a continuous strip casting installation constructed in accordance with the invention;
FIG. 2
is a vertical cross-section through a further part of the installation of
FIG. 1
;
FIG. 3
is a detail view of part of the installation;
FIG. 4
is a transverse cross-section through part of the installation;
FIG. 5
illustrates part of a prior art installation;
FIG. 6
is a vertical cross-section through part of an alternative continuous casting installation in accordance with the present invention;
FIG. 7
is a top view of part of the installation of
FIG. 6
; and
FIG. 8
is a front view of the installation components illustrated in FIG.
7
.
DETAILED DESCRIPTION OF THE DRAWINGS
FIGS. 1
to
4
are an embodiment of the continuous strip casting device envisaged by the present invention.
The molten metal supply system has tundish
1
that supplies molten metal down from above through the nozzle
2
to between the casting rolls
3
a
and
3
b
. The molten metal supply system may have insulated sealing material
23
positioned between the tundish
1
and the casting chamber
4
, and nozzle
2
inserted into the pool of molten steel that is formed between the casting rolls
3
a
and
3
b.
The outer circumferential surfaces of the casting rolls
3
a
and
3
b
are cooled by cooling water that flows through them, which accelerates the solidification of the molten steel.
Moreover, the casting rolls
3
a
and
3
b
are juxtaposed horizontally in order to form the roll gap G, and the casting rolls
3
a
and
3
b
are so supported that their outer circumferential surfaces revolved from the top towards the roll gap G.
When the molten steel that flows down between the casting rolls
3
a
and
3
b
passes through the roll gap G, the molten steel forms a solidified shell on the outer circumferential surfaces of the casting rolls
3
a
and
3
b
, and strip
10
emerges downwards from the roll gap G.
Immediately after the strip
10
is separated from the outer circumferential surfaces of the casting rolls
3
a
and
3
b
, the strip may not be solidified through to the centre of its thickness, but from 30% to 50% of the central portion of the strip may be still molten steel.
In the continuous strip casting device illustrated in
FIGS. 1
to
4
, any non-solidified centre portion of the strip
10
is solidified after it has separated from the casting rolls
3
a
and
3
b
. However, the leading edge of the strip
10
that is transported from the roll gap G is irregular.
At this time, the seal rolls
6
a
and
6
b
are moved by the cylinders
9
a
and
9
b
to positions as indicated by the double dotted lines in
FIG. 1
, so that they are not affected by splash of molten metal from the roll gap G, and expand the gap between the seal rolls
6
a
and
6
b
to its largest extent. The movable apron
14
is at this time positioned facing downwards as indicated by the unbroken lines in FIG.
1
.
The strip
10
that has initially been transported from the roll gap G passes through the seal rolls
6
a
and
6
b
and faces downwards and enters the scrap box
17
that is disposed inside the scrap chamber
16
.
Next, after the distance between the rotational axes of the casting rolls
3
a
and
3
b
has widened in a very short period of time (typically 0.1 to 0.5 seconds), the roll gap G reverts to its original position. The expansion of the roll gap G causes liquid steel to be admitted between the strip shells and thus cause a portion of a portion of the incompletely cooled strip
10
to reheat and remelt forming a new head end suitable for transportation of the strip to the coilers.
The alignment of the movable apron
14
is then set laterally as indicated by the double dotted lines in FIG.
1
. The strip
10
is thus guided onto the upper surface of the movable apron
14
, onto the guide rolls
18
and passes through the exit door
20
, in an open state, to the heat exchange chamber
19
. The strip
10
moves through the heat exchange chamber
19
to the exit door
21
, in open state, of the heat exchange chamber
20
, and is then gripped by the pinch rolls
22
in the pinch roll chamber
65
so that the desired tension is then imparted to the strip
10
.
The strip
10
is gripped by the pinch rolls
22
and is prevented from falling into the scrap box
17
. Hence the alignment of the movable apron
14
is set in the direction indicated by the unbroken line in
FIG. 1
forming a gently curving moving path for the strip
10
in the cooling chamber
15
, whereby the continuous strip casting device is shifted from activation state to normal continuous casting operation.
At this time, the cylinders
9
a
and
9
b
move the pinch rolls
6
a
and
6
b
closer together, as indicated in
FIG. 1
, and the gap between the seal rolls
6
a
and
6
b
is reduced to a value set by the seal guide
8
, and the exit door
20
of the cooling chamber
15
and the exit doors of the heat exchange chamber
21
are lowered to their lowest positions at which they do not come into contact with the strip
10
.
Thus, in the continuous strip casting device illustrated in
FIGS. 1
to
4
through the combination of the gap between the casting rolls
3
a
and
3
b
instantly expanding and reverting to its original state and the appropriate setting of the alignment of the movable apron
14
, operation may be readily repeated, and the casting of the strip
10
may be started and stopped readily, without the necessity for the use of a dummy bar.
During continuous casting operations, the casting chamber
4
is sealed by reducing the gap between the seal rolls
6
a
and
6
b
and the strip
10
. The exhaust control valve
27
, apart from the exhaust vent
26
, permits control of the volume of exhaust gas from casting chamber
4
. Casting chamber
4
may be filled with a mixed non-oxidizing gas such as 99.99% nitrogen or argon or weakly reducing gas such as mixture from 2% to 10% hydrogen with the balance nitrogen. The gas is introduced through the atmospheric gas intake vent
24
and the atmospheric gas is exhausted through the gap between the seal rolls
6
a
and
6
b
to the cooling chamber
15
, thus preventing the surface oxidation of the strip
10
that is at a temperature of between 1300° C. and 1400° C. immediately after casting in the casting chamber
4
.
The casting chamber
4
consists of water cooled panels with cooling water flowing between dual outer and inner plates. The strip
10
that moves through the casting chamber
4
radiates heat to the cooling panels and is continuously cooled.
The seal roll chamber
5
communicates with both the casting chamber
4
and the cooling chamber
15
, and encloses the seal rolls
6
a
and
6
b
is disposed between the casting chamber
4
and the cooling chamber
15
. The seal roll chamber
5
is also constructed of water cooled panels after the fashion of the casting chamber
4
, and continues cooling of the strip
10
as the strip moves from the casting chamber
4
to the cooling chamber
15
.
The outer circumferential surfaces of the seal rolls
6
a
and
6
b
are cooled by cooling water that flows through the interiors of the seal rolls
6
a
and
6
b
and this accelerates the cooling of the strip
10
.
The inter-chamber sealing system with seal rolls
6
a
and
6
b
is intended to reduce and may minimize the atmospheric gas that is communicated from the cooling chamber
15
to the casting chamber
4
and to minimize the movement of the gas in the casting chamber
4
in order to stabilize the casting operation. However, the gap between the seal rolls
6
a
and
6
b
can be extended at the start and finish of casting operations because splashes of molten metal may fall from the roll gap G and strip of indeterminate shape may collide with the seal rolls
6
a
and
6
b
and become entangled with them.
The sealing system with the seal rolls
6
a
and
6
b
may be comprised of sealing members
7
that are positioned on the path traversed by the strip, and which moves with the seal rolls
6
a
and
6
b
. Seal guides
8
may be disposed in the seal roll chamber
5
and extend along the entire circumference of the sealing members
7
.
Sealing members
7
are formed of blocks of materials that are softer than the cast iron, ceramic or polymer resin and the like, which is employed for the seal rolls
6
a
and
6
b
, and are supported in frames sideways to the seal rolls
6
a
and
6
b.
Moreover, the gap between the sealing members
7
and the seal rolls
6
a
and
6
b
may be set at not more than 1 mm.
Furthermore, an electric motor may also appropriately be employed in place of the oil, air or gas fluid hydraulically powered cylinders
9
a
and
9
b
as the means of moving the seal rolls
6
a
and
6
b.
The seal guides
8
performs a sealing function for the sealing members
7
and also sets the magnitude of the gap between the seal rolls
6
a
and
6
b.
The gap between the seal rolls
6
a
and
6
b
and the strip
10
may be set at a maximum of between 1 mm and 20 mm greater than the gauge of the strip
10
, which is to be cast, in order to minimize the ingress of atmospheric gas into the casting chamber
4
, while avoiding rupture of the strip
10
caused by gripping by the seal rolls
6
a
and
6
b.
Moreover, because the gauge of the strip
10
emerging from the roll gap G normally ranges between 1 mm and 5 mm, the seal rolls
6
a
and
6
b
are also capable of being driven by the drive mechanism, for example by a electric motor, in a range of up to 20 mm.
The cooling chamber
15
is also constituted of water cooled panels after the fashion of the casting chamber
4
, and the cooling of the moving strip
10
is continued in the cooling chamber
15
by means of radiant cooling.
Moreover, the outer circumferential surfaces of the movable apron
14
are cooled by cooling water that flows through the interior of the movable apron
14
and thus accelerates the cooling of the strip
10
.
An atmospheric gas intake vent
29
, an exhaust vent
30
, a chamber internal pressure gauge
31
, a gas analyzer
32
and a strip temperature gauge
33
are disposed in the cooling chamber
15
, with the signals indicating the pressure by the chamber internal pressure gauge
31
, indicating the gas composition by the gas analyzer
32
and indicating the temperature by a strip temperature gauge
33
being sent to a control computer that controls the internal pressure, gas composition and temperature of the cooling chamber
15
.
A door roll
38
that passes cooling water into the exit door
20
of the cooling chamber
15
is attached rotatably to the bottom end of the exit door
20
.
The exit door
20
of the cooling chamber
15
is set to an open state, until the leading edge of the strip
10
passes, by a drive mechanism of a door opening and closing device
37
that is powered by a fluid hydraulic or electric drive motor, and the exit door
20
of the cooling chamber
15
is set to an opening sufficient to leave a gap of between 2 mm and 10 mm to the strip
10
during continuous casting operations.
The exit door
20
of the cooling chamber
15
is constituted of insulation material, and is intended to provide insulation against radiant heat or cold from the heat exchange chamber
19
.
The scrap chamber
16
is composed of water cooled panels after the fashion of the casting chamber
4
in such a manner as to communicate with the cooling chamber
15
. The strip
10
is received in the scrap box
17
immediately after the start of continuous casting operations, and immediately before the conclusion of continuous casting operations.
The scrap chamber
16
is provided with an airtight door
42
to allow the insertion and removal of the scrap box
17
, and a door seal
43
that is attached to the airtight door
42
.
The door seal
43
preferably consists of an O ring that is formed of a heat resistant rubber material such as Viton, and an inflatable seal that expands on contact and which is provided internally with water pressure or gas pressure. The scrap chamber
16
also has an atmospheric gas intake vent
44
.
Moreover, transport rollers
40
support the base of the scrap box
17
. A jack
41
that raises the scrap box
17
is also provided in the base of the scrap chamber
16
. The gap between the upper edge of the scrap box
17
and the edge of the opening at the bottom end of the cooling chamber
15
should be as narrow as possible when the scrap box
17
is raised by means of the jack
41
, in order to prevent air leakage into the scrap box
17
from the exterior.
The scrap box
17
possess refractory materials mounted on the inside surfaces of the outer steel plates, such refractory materials providing buffers against collision when the strip
10
falls and providing insulation around the perimeter of the scrap box
17
.
Moreover, the portion in which the airtight door
42
of the scrap chamber
16
is disposed communicates with the exchange chamber
45
for the placement of the scrap box
17
.
The exchange chamber
45
contains an airtight door
48
for the insertion and removal of the scrap box
17
, a door seal
49
for the airtight-door
48
, an exchange gas intake vent
50
, and a gas exhaust vent
51
.
The door seal
49
preferably consists of an O ring that is formed of a heat resistant rubber material such as Viton, and an inflatable seal that expands on contact and which is provided internally with water pressure or gas pressure.
Moreover, transport rollers
46
and
47
that support the base of the scrap box
17
are disposed in the bottom of the exchange chamber
45
and outside the airtight door
48
.
When the scrap box
17
is to be removed from within the scrap chamber
16
, the jack
41
is retracted, and the scrap box
17
is supported on the transport rollers
40
.
Next, the airtight door
42
is opened, and the scrap box
17
is moved by means of the transport rollers
40
and
46
to the exchange chamber
45
, whereupon the airtight door
42
is closed, and the airtight door
48
is opened. The scrap box
17
is then moved by means of the transport rollers
46
and
47
to outside the exchange chamber
45
.
When the scrap box
17
is to be sent into the interior of the scrap chamber
16
, the airtight door
48
is opened and the scrap box
17
is moved by means of the transport rollers
46
and
47
into the exchange chamber
45
, and the airtight door
48
is closed.
Next, the gas exhaust vent
51
is opened, the air within the exchange chamber
45
is exhausted to the exterior, and non-oxidizing or weakly reducing atmospheric gas is supplied through the exchange gas inlet vent
50
into the exchange chamber
45
. The interior of the exchange chamber
45
is thus filled with atmospheric gas, and then the gas exhaust vent
51
and the exchange gas inlet vent
50
are closed.
Then the air sealing door
42
is opened, the scrap box
17
is moved by means of the transport rollers
46
and
40
into the scrap chamber
16
, and the airtight door
42
is closed, whereupon the scrap box
17
is raised by means of the jack
41
.
Consequently, the scrap box
17
can be exchanged during the operation of continuously casting the strip
10
, without permitting the invasion of the external air, and avoiding oxidation of the strip
10
.
Moreover, by providing an exhaust vacuum pump in the gas exhaust vent
51
, the time required in order to replace the air with the atmospheric gas can be reduced.
If the scrap box
17
is replaced only at the conclusion of the continuous casting operation, there is no need to provide an exchange chamber
45
, and the scrap box
17
can be inserted and removed simply by the opening and closing of the airtight door
42
.
Moreover, wheels may be provided on the scrap box
17
in place of the transport rollers
40
,
46
and
47
, whereby the scrap box
17
may be moved.
When the strip
10
passes through the cooling chamber
15
, the strip
10
is cooled through radiant conduction, but the strip
10
can be cooled down to not more than 1000° C. if the continuous casting velocity is low (between 30 m and 100 m/minute according to strip gauge). On the other hand, if the continuous casting velocity is high, the temperature of the strip
10
is not less than 1250° C., and temperature differences are produced laterally across the strip.
A plurality of radiant tubes
53
, which may be formed of heat resistant steel or ceramic, are disposed in the interior of the heat exchange chamber
19
, and insulating material is disposed on the inner surfaces of the heat exchange chamber
19
. The heat exchange chamber
19
provides for correction of such differences in temperature and also controls the temperature of the strip
10
at a desired temperature within the range of from 950° C. to 1200° C., which is suitable for rolling when the strip
10
reaches the entrance to the rolling mill
76
downstream in the movement of the strip
10
.
A temperature gauge
54
for measuring the temperature within the heat exchange chamber
19
, a gas analyzer
55
for measuring the composition of the gas, and a pressure gauge for measuring the pressure are positioned within the heat exchange chamber
19
. An atmospheric gas inlet vent
57
is also disposed within the heat exchange chamber
19
, with the signals from the chamber temperature gauge being sent to the control computer. Accordingly, the fuel
59
and the combustion air
60
mixture that is sent to the burners
58
that may be attached to the radiant tubes
53
is adjusted, and the temperature within the heat exchange chamber
19
is regulated and maintained.
Alternatively, if the temperature of the strip
10
that is transported into the heat exchange chamber
19
is low, the amounts of fuel
59
and combustion air
60
that are supplied to the burners
58
that are attached to the radiant tubes
53
are increased in order to raise and again control the temperature of the strip
10
.
Moreover, if the temperature of the strip
10
that is transported into the heat exchange chamber
19
is high, the supply of fuel
59
to the burners
58
is stopped, and combustion air
60
only is supplied to the burners
58
that are attached to the radiant tubes
53
, in order to cool the strip
10
through the radiant tubes
53
.
Heat-resistant steel rolls, and internally water cooled rolls or internally water cooled rolls to the outer circumferential surfaces of which refractory materials are attached are employed for the guide rolls
18
that are disposed in the heat exchange chamber
19
.
Moreover, the output signals from the gas analyzer
55
and the chamber pressure gauge
56
are sent to the control computer which adjusts the atmospheric gas that is supplied through the atmospheric gas intake vent
57
into the heat exchange chamber
19
in order to prevent the oxidation of the strip
10
.
Door rolls
61
through the interiors of which cooling water passes are rotatably mounted at the lower end of the exit door
21
of the heat exchange chamber
19
.
Until the leading end of the strip
10
has passed through, the exit door
21
of the heat exchange chamber
19
is set to open by means of the door opening and closing device
64
which is operated either by a fluid hydraulic drive or by an electric motor, and the opening of the exit door
21
is so set as to provide a minimum gap in relation to the strip
10
of from 2 mm to 10 mm during the operation to continuously cast the strip
10
.
The exit door
21
of the heat exchange chamber
19
is formed of steel plate to which insulating material is attached, and thus the escape of the radiant heat from the heat exchange chamber
19
is inhibited.
Moreover, a seal trough
63
that holds water may be disposed in a fixed position in relation to the heat exchange chamber
19
, over the exit door
21
to the heat exchange chamber, and a seal plate
62
, whose upper part is linked to the rising and falling part of the door opening and closing device
64
, and whose lower end is always immersed in the seal trough
63
, is also disposed over the exit door
21
of the heat exchange chamber
19
. Such seal trough
63
and seal plate
64
minimize the outflow of the atmospheric gas from the heat exchange chamber
19
to the exterior.
Referring to
FIG. 2
, the pinch roll chamber
65
is also constructed of water cooled panels after the fashion of the casting chamber
4
. The cooling of the strip
10
that is continued as it is moved into the pinch roll chamber
65
.
The outer circumferential surfaces of the pinch rolls
22
are cooled by cooling water that flows through the interiors of the pinch rolls
22
, whereby the cooling of the strip
10
may be accelerated.
Disposed in the pinch roll chamber
65
are transport rolls
66
supporting the strip
10
from below, and plate guides
67
permit accurate insertion of the strip
10
into the pinch rolls
22
.
Also disposed in the pinch roll chamber
65
are atmospheric gas intake vent
68
that supplies atmospheric gas into the interior of the pinch roll chamber
65
, and a drain
69
that drains off to the exterior lubricating oil that is sprayed onto the pinch rolls
22
and drips onto the base of the pinch roll chamber
65
.
Moreover, the pass line for the strip
10
that is supported by the guide rolls
18
and the transport rolls
66
may be lowered by d
1
only from the exit portion of the heat retention chamber
19
to immediately before the pinch rolls
22
in order to prevent the invasion of the heat exchange chamber by the lubricating oil.
The appropriate extent of the dip in the pass line may be between 10 mm and 100 mm per 1 m of distance travelled by the strip
10
.
The path of movement of the strip
10
between the pinch roll chamber
65
and the entrance portion of the rolling mill
76
is enclosed by the pre-rolling mill chamber
72
. Transport rolls
73
support the strip
10
from below are provided before and after the rolling mill
76
.
The strip
10
that is transported from the pinch rolls
22
passes below the partition door
70
and enters the pre-rolling mill chamber
72
, and after the strip
10
has been rolled in the rolling mill
76
, the strip
10
is passed on to the downstream units.
The pre-rolling mill chamber
72
is also constructed of water cooled panels after the fashion of the casting chamber
4
. The cooling of the strip
10
is continued as the strip is moved into the pre-rolling mill chamber
72
.
The pre-rolling mill chamber
72
is provided with an atmospheric gas intake vent
74
in order to supply atmospheric gas to the interior of the pre-rolling mill chamber
72
. A water tank
77
collects the cooling water that drips down to the base of the pre-rolling mill chamber
72
after being sprayed onto the rolls of the rolling mill
76
, and a waste water drain is provided in order to drain to the exterior the cooling water from within the water tank
77
. The oxidation of the strip
10
in the pre-rolling mill chamber
72
is prevented by filling the pre-rolling mill chamber
72
with atmospheric gas.
The partition door
70
is so constructed as to be internally water cooled. Hence a door roll
71
that causes the cooling water to flow inwardly is mounted rotatably in the lower end of the partition door
70
.
The partition door
70
is set to an open state by a drive mechanism such as a fluid hydraulic device or an electric motor until the leading end of the strip
10
has passed, and the partition door
70
is set to a minimum opening sufficient to leave a gap of between 2 mm and 10 mm to the strip
10
during continuous casting operations.
Moreover, the pass line for the strip
10
that is supported by the transport rolls
66
and
73
may be lowered by d
2
only from the partition door
70
to the entrance portion of the rolling mill
76
, in order to prevent the backflow of the cooling water after it has been sprayed onto the rolls of the rolling mill
76
into the pinch roll chamber
65
.
The appropriate extent of the dip in the pass line may be between 10 mm and 150 mm per 1 m of distance travelled by the strip
10
.
Moreover, disposed over the partition door
70
is a seal trough
80
, which holds water, is disposed in a fixed position in relation to the pre-rolling mill chamber
72
, and a seal plate
79
whose upper part is linked to the rising and falling part of the door opening and closing device
78
and whose lower end is always immersed in the seal trough
80
. Such seal trough
80
and seal plate
79
minimize the outflow of the atmospheric gas from the pre-rolling mill chamber
72
to the exterior.
Moreover, Table 1 shows the changes over time in each portion when nitrogen gas is supplied at a rate of 500 Nm
3
/hr to a continuous strip casting device illustrated in
FIGS. 1
to
4
, and when nitrogen gas is supplied at a rate of 2000 Nm
3
/hr and when nitrogen gas is not supplied to the device revealed by JP 8-300108.
TABLE 1
|
|
Present invention
JP 8-300108
|
After 1 hour
After 6 hours
After 1 hour
After 6 hours
After 6 hours from
|
from
from
from
from
commencement of
|
commencement
commencement
commencement
commencement
casting, with nitrogen
|
Item
of casting
of casting
of casting
of casting
gas injection
|
|
internal pressure (strip
10 Pa
10 Pa
2 Pa
1 Pa
5 Pa
|
pass line)
|
Amount of atmospheric gas
500
500
0
0
2000
|
injected into casting
|
chamber and cooling
|
chamber (Nm
3
/hr)
|
Amount of oxygen in
≦100 ppm
≦100 ppm
10%
18%
6%
|
casting chamber
|
Ternperature of gas in
≦200
≦200
500
1000
1000
|
casting chamber (° C.)
|
Temperature of gas in
≦800
≦800
1300
1100
1200
|
cooling chamber or
|
enclosure (° C.)
|
Thickness of oxidized scale
≦0.02
≦0.02
20-30
30-50
8-20
|
on strip at cooling chamber
|
or exit from enclosure (μm)
|
Yield of cast strip (%)
95
95
85
80
87
|
|
The device envisaged by the present invention and illustrated in
FIGS. 1
to
4
possesses seal rolls
6
a
and
6
b
and is therefore able to maintain a low level of oxygen in the casting chamber, such that it is possible to restrict the formation of scale on the strip
10
due to oxidation to not more than 0.02 microns. It is also possible to provide the temperature within the casting chamber
4
to not more than 700° C.
Thus in the present invention, the path of movement of the strip
10
that is transported from the casting rolls
3
a
and
3
b
is filled with a non-oxidizing or weakly reducing atmospheric gas, such as to enable an increase in the yield of the strip
10
.
FIGS. 6
to
8
illustrate a modified embodiment of the invention in which the inter-chamber sealing system between the casting and cooling chambers has a pair of pivoting closures rather than sliding closures as in the previous embodiment. Moreover, in this modified construction, the casting chamber
4
does not enclose the casting rolls
3
a
and
3
b
, but is sealed against the underside of those rolls so as to enclose the strip
19
as the strip emerges from the gap between the casting rolls
3
a
and
3
b.
In the modified caster illustrated in
FIGS. 6
to
8
, the casting chamber
4
is substantially sealed against the underside of those rolls by seal plates
81
. Further, in this modified construction the seal rolls
6
a
and
6
b
are mounted on a pair of pivoting flaps
82
hanging from horizontal pivots
83
about which they are pivotable from positions below the casting chamber
4
and open to the positions shown in
FIG. 6
in which their lower parts are swung inwardly toward the strip
10
to close the transfer opening
84
through which the strip passes from the casting chamber
4
to the cooling chamber
15
.
As shown in
FIGS. 7 and 8
, the pivot shafts
83
for flaps
82
extend to one side of the chambers
4
and
15
, where they are fitted with actuator links
85
by which they can be actuated by a pair of actuating cylinder units
86
to swing the flaps
82
between their retracted positions and the positions in which they tend to close the opening between the casting chamber
4
and cooling chamber
15
. In all other respects the casting installation may be generally in accordance with the previous embodiment as illustrated in
FIGS. 1
to
4
.
Claims
- 1. Apparatus for continuously casting metal strip comprising:a pair of parallel casting rolls forming a nip between them; a molten metal supply system to delivery molten metal into the nip between the rolls to form a casting pool of molten metal supported on the casting roll surfaces immediately above the nip; roll drive mechanism to drive the casting rolls in counter-rotational directions to produce a solidified strip of metal delivered downwardly from the nip between the casting rolls; a casting chamber to enclose strip delivered downwardly from the nip; a cooling chamber disposed below the casting chamber to receive the strip passing downwardly from the casting chamber from the nip through a transfer opening between the casting chamber and cooling chamber; an inter-chamber sealing element disposed directly adjacent to said transfer opening and movable between an open condition in which the opening is dilated and a closed condition in which the opening is contracted about the strip to enhance sealing between the casting and cooling chambers to reduce transfer of gas therebetween.
- 2. Apparatus as claimed in claim 1, further comprising a casting chamber gas inlet to admit an oxidation inhibiting gas into the casting chamber.
- 3. Apparatus as claimed in claim 1 further comprising a cooling chamber gas inlet to admit an oxidation inhibiting gas into the cooling chamber.
- 4. Apparatus as claimed in claim 1, wherein inter-chamber sealing element comprises a pair of seal rolls disposed one to either side of said transfer opening and a roll moving drive operable to move those rolls between retracted positions and extended positions in which they contract the transfer opening.
- 5. Apparatus as claimed in claim 4, wherein the seal rolls are moveable in a seal roll chamber disposed between the casting and cooling chambers and containing seal members moveable with the seal rolls to provide sealing between the casting and cooling chambers when the seal rolls are moved to their extended positions.
- 6. Apparatus as claimed in claim 4, wherein the inter-chamber sealing element comprises a pair of pivoting flaps hanging from horizontal pivots about which they are pivotable from positions in which the bottom of the casting chamber is open to positions in which their lower parts are swung inwardly toward the strip to close the transfer opening.
- 7. Apparatus as claimed in claim 6, wherein the lower parts of the flaps are fitted with seal rolls to provide the sides of the transfer opening.
- 8. Apparatus as claimed claim 1, wherein the casting chamber encloses the casting rolls.
- 9. Apparatus as claimed in claim 1, wherein the casting chamber is sealed against the underside of the casting rolls.
- 10. Apparatus as claimed in claim 1, wherein the cooling chamber is provided with a strip outlet disposed below and laterally to one side of the nip between the casting rolls, and the apparatus further comprises a moveable strip guide apron disposed within the cooling chamber and operable to guide the strip delivered through the transfer opening into the cooling chamber to the laterally displaced strip outlet of the cooling chamber.
- 11. Apparatus as claimed in claim 10, wherein the strip guide apron is moveable to an inoperative position in which it allows strip to pass downwardly to the bottom of the cooling chamber, and the apparatus further comprises a moveable scrap box to receive scrap strip at the bottom of the cooling chamber.
- 12. Apparatus as claimed in claim 10, further comprising a scrap box exchange chamber communicating with the bottom part of cooling chamber through an exchange opening through which to move the scrap box in and out of its scrap receiving position at the bottom of the cooling chamber, the opening of scrap box exchange chamber being provided with a moveable air sealing entry door through which to pass the scrap box into the exchange chamber and exchange chamber gas inlet means through which to supply an oxidation inhibiting gas to the scrap box exchange chamber.
- 13. Apparatus as claimed in claim 10, further comprising a heat exchange chamber to receive strip from the cooling chamber through the cooling chamber exit opening, strip temperature control means within the heat exchange chamber operable to heat or cool strip passing through the heat exchange chamber to control the temperature of the strip, and a heat exchange chamber gas inlet to admit an oxidation inhibiting gas into the heat exchange chamber.
- 14. Apparatus as claimed in claim 13, wherein the heat exchange chamber has a strip outlet opening provided with a moveable door operable to increase and decrease the size of the strip outlet opening.
- 15. Apparatus as claimed in claim 13, further comprising a pinch roll chamber to receive strip from the strip outlet opening of the heat exchange chamber, a pair of pinch roll within the pinch roll chamber operable to draw the strip through the pinch roll chamber and a pinch roll chamber gas inlet to admit an oxidation inhibiting into the pinch roll chamber.
- 16. Apparatus as claimed in claim 15, wherein the pinch roll chamber has a strip outlet opening provided with a moveable door operable to increase and decrease the size of that opening.
- 17. Apparatus as claimed in claim 10, wherein the strip outlet opening from the cooling chamber has a moveable door operable to increase and decrease the size of the opening.
- 18. Apparatus as claimed in claim 11, wherein the strip outlet opening from the cooling chamber has a moveable door operable to increase and decrease the size of the opening.
- 19. Apparatus as claimed in claim 12, wherein the strip outlet opening from the cooling chamber has a moveable door operable to increase and decrease the size of the opening.
- 20. A continuous strip casting device characterized by being provided with a pair of casting rolls that form a roll gap and that are disposed parallel to each other in diametrical juxtaposition, and a molten metal supply system that supplies molten metal-from above to between the casting rolls, and a casting chamber that encloses the two casting rolls, and a pair of seal rolls that permit the passage of the strip that emerges from between the casting rolls, and a seal roll chamber that encloses the pair of seal rolls and that communicates with the casting chamber, and a seal member that slides a seal guide that is disposed in the-seal roll chamber and that is positioned on the path of the strip in such a manner as to cause the movement of the seal rolls, and a movable apron that is so disposed as to guide sideways the strip that is transported from between the seal rolls and alternatively to lower said strip to a scrap box that is disposed below the said movable apron, and a cooling chamber disposed below the seal roll chamber that possesses an exit that is able to transport to the exterior the strip that has been guided by the movable apron and that encloses the movable apron that communicates with said seal roll chamber, and an exit door that is able to increase and decrease the cross section of the opening of the exit of said cooling chamber, and a scrap chamber that possesses an air sealing door that is able to move the scrap box in and out and that encloses the scrap box that communicates with the cooling chamber, and in which said casting chamber, cooling chamber and scrap chamber each possesses an atmospheric gas inlet.
- 21. A continuous strip casting device as in claim 20, further characterized by possessing an exchange chamber that possesses an air sealing door that is able to move the scrap box in and out and that communicates with the scrap chamber, and an air sealing door that is able to divide said exchange chamber and the scrap chamber.
- 22. A continuous strip casting device as in claim 20, further characterized by possessing a heat exchange chamber that possesses an exit that is able to send to the exterior the strip from the cooling chamber and that communicates with the exit of the cooling retention chamber, and radiant tubes that are disposed in the heat exchange chamber, and guide rolls that are disposed in the heat exchange chamber and transport laterally the strip that is sent from the cooling chamber, the heat exchange chamber being provided with an atmospheric gas inlet.
- 23. A continuous strip casting device as in claim 22, further characterized by possessing a pinch roll chamber for the cooling apparatus that communicates with the exit of the heat exchange chamber and that is able to send to the exterior the strip in the heat exchange chamber, and a partition door that is able to expand and contract in cross section the opening of the exit of said pinch roll chamber, and pinch rolls that are disposed in the pinch roll chamber and that are capable of gripping the strip.
- 24. A continuous strip casting device as in claim 23 further characterized in that a rolling mill is disposed in the downstream strip travel direction from the pinch roll chamber, the strip pass line that runs from the exit of the pinch roll chamber to the rolling mill being so set as to lower the strip by between 10 mm and 150 mm for every 1 m distance of travel.
Priority Claims (1)
Number |
Date |
Country |
Kind |
2000-239777 |
Aug 2000 |
JP |
|
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Number |
Name |
Date |
Kind |
5590701 |
Fukase |
Jan 1997 |
A |
5660224 |
Barbe et al. |
Aug 1997 |
A |
5816311 |
Osada et al. |
Oct 1998 |
A |
5960856 |
Blejde et al. |
Oct 1999 |
A |
6079479 |
Osada et al. |
Jun 2000 |
A |
6209620 |
Pleschiutschnigg |
Apr 2001 |
B1 |
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Number |
Date |
Country |
0 780 177 |
Dec 1996 |
EP |
9402269 |
Feb 1994 |
WO |