Twin drum type continuous casting apparatus and method

A twin drum type continuous casting apparatus is provided for continuously feeding molten metal into a cast portion defined by a pair of water cooling drums that are rotated in opposite directions to each other, thereby continuously casting a plate-like cast piece. A thin portion is formed close to an outer circumferential portion of each of opposite end portions, in a width direction, of each of the water cooling drums. A thin annular member having a hot water flow passage therein is formed in between the thin portion and a shaft with a space relative to an end face of each of the water cooling drums.

BACKGROUND OF THE INVENTION 
1. Field of the Industrial Application 
The present invention relates to an improvement in a twin drum type 
continuous casting apparatus and a continuous casting method in which a 
change in shape caused by a thermal load of water-cooling drums is 
controlled. 
2. Description of the Related Art 
A conventional twin drum type continuous casting apparatus (Japanese Patent 
Laid-Open Application No. Hei 2-104449), which is a kind of a thin plate 
continuous casting apparatus, is shown in FIGS. 9 and 10. 
As shown in these drawings, molten steel R is continuously fed to a casting 
mold portion defined by a pair of water-cooling drums 01 which are rotated 
in opposite directions as indicated by arrows and a pair of side dams 02, 
and is cooled by outer circumferential walls of the water-cooling drums 01 
to thereby continuously cast a thin plate cast piece W. A water feed port 
01a, a water discharge port 01e, a number of water feed passages 01b, a 
water cooling passage 01c along the outer periphery of each water-cooling 
drum 01 and a water discharge passage 01d are provided in an interior of 
each water-cooling drum 01. Heater blocks 03 are internally provided over 
an entire circumferential wall of both end portions of each water-cooling 
drum 01. 
In this casting apparatus, when the molten steel R is fed to the casting 
mold portion, the outer circumferential portion of each water-cooling drum 
01 is thermally expanded with both its ends being extended in a width 
direction of the roll. In accordance with this expansion, the 
water-cooling drum 01 is shrunk and deformed in the radial direction by 
.delta. as indicated by dotted lines in FIG. 11(a). Accordingly, an 
interval between the two water-cooling drums 01 is further increased by 
2.delta. at both ends beyond the interval in the central portion. Also, a 
thickness at both end portions of the workpiece to be cast is increased by 
2.delta., resulting in a worse plate shape. 
Therefore, cooling water is fed from the water feed port 01a to the water 
cooling passage 01c, and at the same time a current is supplied to the 
heater blocks 03 to heat both end portions of each drum. As a result, as 
shown by dotted lines in FIG. 11(b), the end portions are expanded and 
deformed by .delta. in the radial direction to cancel the thermal 
deformation caused by the above-described molten steel R to equalize the 
interval over the entire width of each drum. 
In this case, a planar shape detector (not shown) is provided at the outlet 
of the cast piece W to periodically detect the plate thickness over the 
entire width of the cast piece W. On the basis of the detection signal, 
the amount of heat generation of each heater block 03 is adjusted to 
control the thermal expansion amount at both end portions of each drum and 
to well control the plate shape of the cast piece W. 
As described above, in the conventional continuous casting apparatus, a 
method is adopted in which both end portions of each drum are heated and 
expanded by the heater blocks 03 internally provided in both end portions 
of each drum to thereby perform shape control of the outer surfaces of the 
water-cooling drum. However, since the thermal capacitance of each drum 01 
to be heated is large, a deformation responsibility of the shape of the 
outer surfaces of the drum to be controlled is low, and it would be 
difficult or impossible to timely control the workpiece to be continuously 
cast timely. The conventional apparatus suffers from such a problem. 
Also, since the heater blocks 03 are internally provided in each drum 01, 
the heating with the heater blocks 03 is non-uniform, and it would be 
impossible to suitably control the shape of the workpiece to be 
continuously cast. 
SUMMARY OF THE INVENTION 
In order to solve the problems inherent in a twin drum type continuous 
casting apparatus for continuously feeding molten metal into a cast 
portion defined by a pair of water cooling drums that are rotated in 
opposite directions to each other, thereby continuously casting a 
plate-like cast piece, according to the present invention, a thin portion 
is formed close to an outer circumferential portion of each of opposite 
end portions, in a width direction, of each of the water cooling drums and 
a thin annular member having a hot water flow passage therein is formed in 
between the thin portion and a shaft with a space relative to an end face 
of each of the water cooling drums. 
It is possible to impart a gradient so that a wall surface on the outer 
circumferential side of each drum, which wall surface forms the space, 
expands toward each end face of the drum. 
According to the present invention, in the twin drum type continuous 
casting apparatus, since the pair of water cooling drums are provided, the 
thin annular members are immediately heated and expanded when the hot 
water is supplied to the hot water flow passages of the thin annular 
members based upon a signal from cast piece planar shape detectors, 
whereby the thin portions at both ends of the water cooling drums are 
deformed to thereby suitably control the drum outer diameter. 
Since the space is interposed between the thin annular member and the end 
face of the water cooling drum, the profile of the surface of the water 
cooling drum is formed by smooth curved lines, and it is possible to 
control the shape of the cast piece to be flat at its central portion or 
to be projected at the central portion. 
Also, with such a space, it is possible to reduce the thermal stress change 
caused by the expansion/shrinkage of the thin annular member. 
According to the present invention, the apparatus may further comprise a 
crown calculating means for detecting a distribution of plate thickness of 
the plate-like cast piece held immediately below the water cooling drums 
and calculating a cast piece crown, means for calculating a crown 
difference between a cast crown obtained by the crown calculating means 
and a predetermined target crown, and means for controlling a temperature 
of hot water to be supplied to the thin annular member in response to the 
crown difference. 
In the thus constructed twin drum type continuous casting apparatus 
according to the present invention, the crown of the plate-like cast piece 
to be cast and the crown difference are periodically calculated, the 
temperature of the hot water to be supplied to the thin annular member is 
suitably controlled by these values, and it is therefore possible to 
manufacture the plate-like piece having a desired shape. 
The apparatus may further comprise crown change rate calculating means for 
calculating a change rate of the cast crown based upon the cast piece 
crown obtained by the crown calculating means, and means for controlling a 
flow rate of the hot water to be supplied to the thin annular member based 
upon the change rate of the cast piece crown. 
According to this twin drum type continuous casting apparatus, the crown, 
the crown difference and the change rate of the plate-like cast piece to 
be cast are periodically calculated, and the flow rate and the temperature 
of the hot water to be supplied to the thin annular member are suitably 
controlled in accordance with these crown difference and crown change rate 
to thereby manufacture the plate-like cast piece having a desired shape. 
In a twin drum type continuous casting apparatus according to the 
invention, it is preferable to use a method comprising the steps of: 
periodically detecting a difference in thickness between edge portions and 
a central portion of the plate-like cast piece to be continuously cast; if 
the detected value exceeds a range of a control target value, supplying 
water to the annular member by decreasing the water temperature; and if 
the detected value is smaller than the range of the control target value, 
supplying water to the annular member by increasing the water temperature. 
In this case, a constant flow rate of the hot water relative to the thin 
annular member may be used. 
Also, according another aspect of the invention, it is preferable to use a 
twin drum type continuous casting apparatus which uses a method comprising 
the steps of: periodically detecting a difference in thickness between 
edge portions and a central portion of the plate-like cast piece to be 
continuously cast; if a change rate of the detected value exceeds a 
standard range, supplying water to the annular member by increasing the 
flow rate of the water; and if a change rate of the detected value is 
smaller than the standard range, supplying water to the annular member by 
decreasing the flow rate of the water. 
Also, in the twin drum type continuous casting apparatus according to the 
present invention, in addition to the feature that each water cooling drum 
is formed as described above, it is preferable that partition plates are 
provided for dividing the hot water flow passage of the thin annular 
member into a plurality of sections in a circumferential direction and a 
feed port and a discharge port for hot water which are in fluid 
communication with each of the sections are formed in each of the 
sections. 
These partition plates are preferably arranged so as to symmetrically 
divide the hot water flow passage in the thin annular member into a 
plurality of sections in the circumferential direction. 
With the twin drum type continuous casting apparatus thus constructed, 
since the hot water is simultaneously fed and discharged into the 
plurality of divided hot water flow passages of the thin annular member, 
the shaft and the annular member are uniformly thermally expanded in the 
circumferential direction, whereby the thin portion of each end portion of 
the water cooling drum is also uniformly deformed in the circumferential 
direction to thereby perform a more preferable shape control. 
The controlled state is shown in FIG. 6. The start of the control is 
effected immediately after the state where the cast piece crown is out of 
the non-sensitive region has been detected. 
According to the conventional method, since the compensation rate of the 
cast piece crown is slow, the cast piece crown value is changed largely 
away from a non-sensitive band set range. Thus, it takes a long period of 
time to obtain a desired cast piece. However, according to the present 
invention, since the compensation rate is high, it is possible to 
immediately correct the cast piece to the non-sensitive set range. 
Furthermore, in the twin drum type continuous casting apparatus according 
to the present invention, in addition to the feature that each water 
cooling drum is constructed as described above, an initial crown may be 
formed on an outer circumferential surface of the water cooling drum. 
Since the compensation deformation of the water cooling drum caused by the 
thin annular member may be reduced so that the maintenance of the cast 
piece shape may readily be performed by a small temperature change by the 
hot water. 
It is therefore possible to reduce a load to be imposed on the water 
cooling drum and the thin annular member and the durability of the 
apparatus may be remarkably enhanced.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An apparatus according to each embodiment of the invention will now be 
described by way of example with reference to the accompanying drawings. 
(First Embodiment) 
FIGS. 1 through 5 show a primary part of a twin drum type continuous 
casting apparatus according to one embodiment of the invention. In the 
apparatus, molten steel R is fed to a casting portion defined by a pair of 
water-cooling drums 1 which are rotated in opposite directions as shown in 
FIG. 5 and a pair of side dams 2, and is cooled down and solidified by the 
outer surfaces of the water-cooling drums 1 to continuously cast a thin 
plate cast piece W. 
Plate shape detectors 12 (12a, 12b, 12c) each of which is composed of a 
radioactive ray thickness meter are disposed at an outlet of the apparatus 
for detecting thicknesses at three or more points, for example a central 
point and both edges, to thereby control the profile shape of the outer 
surfaces of the water-cooling drums 1 on the basis of the signals detected 
periodically and to thereby perform the shape control of the cast piece W. 
The difference 2.times..delta.' in thickness between the central portion 
and both edges of the planar cast piece W, i.e. the cast piece crown 
measured periodically by the plate shape detectors 12, is compared with a 
target crown value 2.times..delta..sub.0, and the difference 
.DELTA..delta. therebetween is fed to a controller 13. 
The controller 13 controls a hot water feeder 16 in response to the crown 
difference .DELTA..delta.=(2.delta.'-2.delta..sub.0)/2 and the crown 
change rate .DELTA..delta./.DELTA.t=(2.delta.'-2.delta..sub.0)/.DELTA.t to 
thereby adjust the temperature T and the flow rate Q of the hot water to 
be supplied to thin annular members 5 provided in the water-cooling drums 
1. 
Incidentally, the target crown value 2.times..delta..sub.0 is determined by 
the drum initial crown value, the drum shape change value, the thickness t 
of the planar cast piece and the target plate shape .alpha.. 
As shown in FIGS. 1 to 3, a diameter of each water-cooling drum 1 is set at 
1,200 mm and a width thereof is set at 1,330 mm, and thin portions 1A 
having gradients 15, with a central side thickness of 120 mm and with both 
end portions of 100 mm, is formed at both end portions of the drum. A 
water feed passage 1b, a water discharge passage 1d and a water cooling 
passage 1c along the outer circumferential surface are formed within each 
water cooling drum 1. The cooling water is fed from a cooling water feed 
pipe 7 through a water feed port 1a and the water feed passage 1b to the 
water cooling passage 1c to thereby cool the outer circumferential surface 
of each drum 1, and the water is discharged through a water discharge 
passage 1d and a water discharge port 1e from a cooling water discharge 
pipe 8. 
Incidentally, partition parts 6a, 6b and 6c constitute a partitioning wall 
6 for partitioning the flow-in chamber and discharge chamber of the 
cooling water in each water-cooling drum 1. 
An annular member 5 in which a hot water flow passage 5a having a gap of 5 
mm is formed is inserted in a space B defined between the shaft 4 and the 
above-described thin portion 1A. The annular member has a post portion 5b 
having a thickness of 20 mm. A space is formed at an interval of 60 mm in 
the axial direction of each drum 1 between the annular member 5 and the 
drum end face within the space B. 
The hot water is supplied from the hot water feed pipe 9 through a water 
passage 9a to the hot water passage 5a in the annular member 5 to thereby 
thermally expand the latter and is discharged from the hot water discharge 
pipe 10 through the water discharge passage 10a. 
FIG. 2 is a view showing a fluid communication passage for the hot water. 
The hot water flow passage 5a is divided in the circumferential direction 
into two sections by partition plates 11. The hot water fed from the hot 
water feed pipe 9 is caused to uniformly flow into the respective divided 
grooves from the respective feed ports 5c through the water feed passages 
9a and to be discharged from the respective discharge ports 5d through the 
water discharge passages 10a to the hot water discharge pipes 10. 
In the embodiment shown, the hot water flow passage 5a is divided into two 
sections by the partition plates 11. The divisional manner of the hot 
water flow passage 5a with the partition plates 11 may be adopted suitably 
in order to uniformly heat the annular member by dividing it into a 
further plural number of sections in the circumferential direction as 
desired. 
Also, as shown in FIG. 4, the hot water flow passage 5a may be formed into 
a plurality of rows in the annular member 5. 
The operation of the apparatus in accordance with the embodiment will now 
be described. 
when the molten steel R is fed into the above-described casting portion 
defined by the pair of water-cooling drums 1 and side dams 2 to 
continuously cast a thin strip cast piece W, the casting portions of the 
pair of water-cooling drums 1 are subjected to thermal loads and deformed 
as described above (see FIG. 11(a)). As a result, the thickness of the 
opposite edge portions of the thin plate cast piece W is increased to 
2.times..delta. at maximum (i.e., about 30% of the entire width), 
resulting in a degradation of the plate thickness shape. 
Therefore, in the apparatus according to the invention, the cooling water 
is supplied from the cooling water feed pipes 7 to thereby cool the outer 
circumferential surface of each cooling water drum 1, and the maximum 
plate thickness difference 2.times..delta.' between the edge portions and 
the central portion of the plate of the cast piece W which is continuously 
cast is periodically detected by the plate shape detectors 12 (FIG. 5). 
The difference between the target crown value 2.delta..sub.0 and the 
detected value is fed to the controller 13. If the detected crown value 
2.delta.' falls within the control target range, the temperature and the 
flow rate of the hot water to be supplied from the hot water feeder 16 to 
the annular member 5 is kept unchanged. 
If the detected crown value 2.delta.' of the planar cast piece W exceeds 
the target crown value 2.delta..sub.0, the water temperature drop rate and 
the flow rate are set based upon the relationship between the drum shape 
change rate and the water temperature difference between the drum cooling 
water, which is measured in advance, and the hot water. The hot water is 
fed to the annular member 5. 
On the other hand, if the detected crown value 2.delta.' is smaller than 
the target crown value 2.delta..sub.0, the water temperature increase rate 
and the flow rate are set in the same manner. The cooling water is fed to 
the annular member 5. 
The magnitude of the crown change rate 
.DELTA..delta.=(2.delta.'-2.delta..sub.0)/2 is determined by setting the 
temperature of the hot water, but the crown change rate 
.DELTA..delta./.DELTA.t=(.delta.'.sub.1 -.delta.'.sub.i-1)/.DELTA.t may be 
rapidly adjusted within the target crown value or may be gradually 
adjusted within the target crown value by detecting changes in case crown 
amount on a time basis for several seconds and increasing/decreasing the 
water flow rate. 
As described above, the flow rate of the hot water to be supplied to the 
hot water flow passage 5a of the annular member 5, the water temperature 
and the like are set and controlled based on the relationship between the 
predetermined water temperature difference and the drum change amount. 
Thus, the annular member 5 is thermally expanded to deform the edge 
portions of each water cooling drum 1 in the radial direction by .delta.. 
Since the space B is provided in each water cooling drum 1 and at the same 
time, the thickness of the thin portion 1A thereof is small at 120 mm, the 
outer circumferential surface of each drum is deformed along a smooth 
curve. Thus, the deformation .delta. of edge portions of the water cooling 
drum 1 caused by the molten steel R is canceled, and the interval of the 
casting portion is somewhat increased at the central portion so that a 
thin planar cast piece W having a good plate shape may be continuously 
cast. 
In this case, since the thickness of the post portion 5b of the annular 
member 5 is small at 20 mm, the thermal responsiveness caused by the hot 
water which is flowing through the hot water flow passage 5a is good. 
Also, since the opposite end portions of the water cooling drum 1 are 
thin, the deformation responsiveness caused by the thermal expansion 
deformation of the annular member 5 is good. Accordingly, .delta. is 
changed at a deformation rate of about 2 .mu.m/sec in an on-line manner in 
accordance with the control signal of the controller 13, which signal is 
periodically fed. As a result, it is possible to perform shape control of 
the profile of the cast piece in a good manner. 
Also, since the hot water flow passage 5a of the annular member is divided 
circumferentially into two sections by the partition plate 11, the hot 
water is simultaneously fed into the divided sections and the annular 
member 5 is uniformly expanded in the circumferential direction. As a 
result, both the end portions of the drum 1 is uniformly deformed, and 
hence it is possible to perform a shape control of a profile of the cast 
piece in a good manner. 
The shape control of the water cooling drum in accordance with the first 
embodiment may be rapidly performed as explained in conjunction with FIG. 
6. 
(Second Embodiment) In a twin drum type continuous casting apparatus 
constructed in the same manner as in the first embodiment, the diameter of 
the water cooling drum is set at 1,200 mm, and the width, at 1,330 mm. A 
dimension of each component of the water cooling drum and the thin annular 
member shown in FIG. 7 is selected as indicated in Table 1. Then the 
effect of the invention was confirmed. According to the invention, since 
the compensation rate after the start of the compensation control for the 
water cooling drums was high, the cast piece crown was rapidly returned 
back to a regular level. 
Also, in any one of the examples 1-8, effective compensation amounts 
.delta.' were obtained and the flat cast piece shape or the shape where 
the central portion was somewhat projected was obtained. 
TABLE 1 
__________________________________________________________________________ 
compensation 
compensation 
t g L.sub.1 
h L.sub.2 
amounts .delta. 
rate 
Ex. 
(mm) 
(mm) 
(mm) 
(mm) 
(mm) 
(.mu.m) 
(.mu.m/sec) 
note 
__________________________________________________________________________ 
1 5 6 100 80 50 50 10 invention 
2 8 5 100 100 60 90 8 " 
3 20 5 100 100 60 120 2 " 
4 25 5 100 100 60 130 1.5 " 
5 40 5 100 100 60 140 0.8 " 
6 30 5 100 100 60 135 1.0 " 
7 15 6 80 90 50 80 2.8 " 
8 25 6 100 100 60 110 1.5 " 
9 -- -- 100 100 -- 30 0.1 prior art 
__________________________________________________________________________ 
(Third Embodiment) 
As shown in FIG. 8, an initial crown is machined or worked on each water 
cooling drum prior to the casting work. Thereafter, the casting is carried 
out. Thus, it is possible to carry out the casting work for obtaining a 
precise cast piece shape by reducing temperature changes of the hot water, 
i.e. the load to be imposed on the drum sleeve and the thin annular 
member. In the third embodiment, the features other than that of the 
provision of the initial crown 1X on the outer surface of the drum are the 
same as those of the first embodiment. 
When the casting is started by using the water cooling drums 1 with the 
initial machined crown 1X, the casting portion of the water cooling drums 
1 are subjected to the thermal load and deform so that the edge portions 
of the cast piece W are deformed to increase the thickness up to about 
2.delta.. However, since the initial crown 1X is formed to meet the value 
that is somewhat smaller than .delta., the compensation deformation caused 
by the thin annular members 5 may be made small. In other words, since it 
is possible to obtain a desired cast piece crown with a small temperature 
change .DELTA.T due to the hot water, the load to be imposed on the water 
cooling drums 1 and the thin annular members 5 may be small, and the 
durability is considerably enhanced. 
As described above in detail, in the twin drum type continuous casting 
apparatus and the method therefor according to the present invention, the 
thin portions are formed close to the outer circumferential portions at 
the opposite end portions in the width direction of each water cooling 
drum; the thin annular members each having the hot water flow passage 
therein are formed in between the thin portions and the shaft; the crown 
value of the cast piece to be continuously cast is periodically detected; 
the flow rate of the hot water to be supplied to the hot water flow 
passage within the thin annular members, the water temperature and the 
like are controlled in response to the signal; and the space is formed 
between each drum sleeve and the thin annular member is formed. 
Accordingly, the shape of the end portions of each water cooling drum is 
smoothly corrected and controlled so that the shape of the casting portion 
is made parallel or the interval of the central portion thereof is 
somewhat increased. As a result, it is possible to continuously cast the 
thin plate cast piece having a good plate shape. 
Also, the fluid that flows through the hot water flow passage in each thin 
annular member is hot or cool water, and the annular member is of the thin 
type. Accordingly, a period of time for the heat transmission to the 
annular member is shortened, and it is possible to compensate for the 
shape of the cast piece crown in an on-line manner for a control period, 
i.e., several seconds. 
Further, by adopting the structure in which the hot water flow passage in 
the annular member is divided into a plurality of sections in the 
circumferential direction, the hot water is supplied simultaneously to the 
divided sections to thereby deform the end portions of each water cooling 
drum uniformly in the circumferential direction in accordance with the 
thermal expansion of the annular member whereby the shape control of the 
cast piece may be effected well. 
Furthermore, if the initial crown is formed on the outer circumferential 
surface of the water cooling drum, it is possible to compensate for the 
shape of the drum with a low temperature control. 
Various details of the invention may be changed without departing from its 
spirit nor its scope. Furthermore, the foregoing description of the 
embodiments according to the present invention is provided for the purpose 
of illustration only, and not for the purpose of limiting the invention as 
defined by the appended claims and their equivalents.