Dual roll type continuous casting machine

Cut-out portions or horizontal passages in the form of an inverted T are provided to melt solidified shells grown at triple points at which side seal plates, colling rolls and molten metal are made contact with each other. Pouring holes or slits are provided for inside pouring. Length of the slit in the cast widthwise direction is preliminarily determined so as to maintain temperature distribution in molten bath uniformly. Start of a continuous casting operation is facilitated by movable baffer plates disposed at open ends of the horizontal passage.

BACKGROUND OF THE INVENTION 
The present invention relates to a dual roll type continuous casting 
machine for continuously casting a strip. 
As shown in FIG. 1, a dual roll type continuous casting machine has a pair 
of cooling rolls 1 in parallel with each other and spaced apart from each 
other by a suitable distance as shown in FIG. 1. Side seal plates 2 are 
disposed at the ends of the cooling rolls 1 to define a molten bath or 
pool 13 (in some cases, barrel seal plates are disposed, extending in the 
axial direction of the cooling rolls 1). Molten metal is poured into the 
molten bath 13 and is cooled by the cooling rolls 1 which are rotated in 
the directions indicated by the arrows so that a cast 3 continuously 
emerges out of a roll gap between the rolls 1. 
Solidified shells are developed over the surfaces of the cooling rolls 1 as 
the molten metal in the molten bath 13 is cooled by the cooling rolls 1. 
Abnormal growth of the solidified shells is observed at the so called 
triple points (i.e., the points of contact between the cooling roll 1, the 
side seal plate 2 and the molten metal) since the molten metal tends to 
tarry and thus tends to be sooner cooled at the triple points. The 
abnormally grown solidified shells are pulled by the solidified shells 
developed on the cooling rolls 1 and drops (are separated) into the gap 
between the cooling rolls 1. As a result, not only the surfaces of the 
cast may be degraded, but also the thickness of the cast may be increased 
locally, causing breakdown of the same. In addition, drop of the 
abnormally grown solidified shells may cause damages on the side seal 
plates 2. 
To overcome such triple-point problem, it has been devised and demonstrated 
to pour the molten metal 5 into a core 4 disposed in the molten bath and 
to cause the same to flow through holes 6 on the core 4 into the gap 
between the cooling rolls 1 for prevention of the abnormal growth of the 
solidified shells at the triple points. 
However, even the above-described system cannot satisfactorily overcome in 
practice the triple point problem because it is impossible to effectively 
melt only the harmful solidified shells grown at the triple points. More 
specifically, when the molten metal is directed to flow directly toward 
the triple points, not only the solidified shells at the triple points but 
also the solidified shells on the cooling rolls are melted. 
In view of the above, according to the present invention, of the solidified 
shells grown at the triple points, only the solidified shell which are 
harmful and are grown at the side seal plate is effectively melted away. 
The above and other objects, effects, features and advantages of the 
present invention will become more apparent from the following description 
of preferred embodiments thereof taken in conjunction with the 
accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
First referring to FIGS. 2-4, a first embodiment of the present invention 
will be described. Side seal plates 2 are disposed at opposite 
longitudinal ends of cooling rolls 1 to define a molten bath or pool 13 on 
the rolls 1. A V shaped core 7 is accommodated in the molten bath 13 
between the side seal plates 2. Molten metal 5 within a tundish 8 formed 
integral with an upper portion of the core 7 flows through side pouring 
holes 9 which are formed adjacent to the opposite ends of the core 7 in 
the longitudinal direction thereof (the widthwise direction of the cast 3) 
so that the molten metal 5 is supplied toward the side seal plates 2. 
Furthermore, in order to directly pour the molten metal 5 from the tundish 
8 into the gap between the cooling rolls 1, a plurality of vertical inside 
pouring holes 10 which open to a V shaped leading or lower end of the core 
7 are formed through the longitudinal intermediate portion between the 
ends of the core 7 and are spaced apart from each other by a predetermined 
distance. Each of the pouring holes 10 has a reduced-diameter portion 10' 
so as to retard the flow of the molten metal 5. 
The side pouring holes 9 opens to the corresponding longitudinal end of the 
core 7 and terminates in a cut-out portion 11 to define a passage through 
which the molten metal 5 flow along the side seal plate 2 toward an 
abutment between the side seal plate 2 and the cooling plate. 
Thus, the molten metal 5 from the side pouring hole flows along the side 
seal plate 2 due to the cut out portion 11 toward the abutment (the 
position of the triple point) between the side seal plate 2 and the 
cooling roll 1 so that the undesired solidified shell grown on the surface 
of the side seal plate 2 can be melted. 
The molten metal 5 flowing out of the inside pouring holes 10 is directly 
supplied to the gap between the cooling rolls 1 and the solidified shells 
grown over the cylindrical surfaces of the cooling rolls 1 are not melted. 
Therefore, growth of the solidified shell over the cylindrical surface of 
each cooling roll 1 is accelerated while growth of the solidified shells 
over the surfaces of the side seal plates 2 is prevented so that a high 
quality cast 3 can be obtained. 
In the first embodiment described above, in order to prevent the 
solidification at the upper surface of the molten metal in the molten bath 
13 due to residence or retardation of the molten metal, it is very 
effective that the depth H of the molten metal in the molten bath is 
shallowed. 
Next referring to FIG. 5, a second embodiment of the present invention will 
be described. The second embodiment is substantially similar in 
construction to the first embodiment described above except that the core 
7 is formed, at its respective longitudinal end abutting on the side seal 
plate 2, with a horizontal passage 12 which is in the form of an inverted 
T for communication with the side pouring hole 9 and extends horizontally 
and oppositely to open at positions slightly lower than a normal surface 
level of the molten metal in the molten bath 13. In the second embodiment, 
the molten metal 5 poured from the tundish 8 into the core 7 is supplied 
through the horizontal passages 12 to the triple points in the molten bath 
13 so that abnormal growth of the solidified shells at the triple points 
can be prevented. The horizontal flows of the molten metal 5 into the 
molten bath 13 due to the horizontal passages 12 reduce the possibility of 
the solidified shells for the cast 3 below the core 7 being influenced by 
the molten metal flows. 
Referring next to FIGS. 6 and 7, a third embodiment of the present 
invention will be described. The third embodiment is substantially similar 
in construction to the first embodiment described above except that 
provided in lieu of the inside pouring holes 10 and their reduced diameter 
portions 10' defined in the core 7 are an upper slit 14 and a lower slit 
15 which is narrower in width than the upper slit 14. The upper slit 14 is 
communicated with major pouring holes 16 which control the flow rate of 
the molten metal from the tundish 8. 
In the third embodiment, the upper slit 14 serves as inner molten bath and 
the flow rate of the molten metal flowing out of the major pouring holes 
16 becomes uniform and gentle so that the molten metal is gently poured in 
the form of a sheet without causing clogging into the molten bath 13. 
Therefore, prevented are melting of the solidified shells growing over the 
cylindrical surfaces of the cooling rolls 1 as well as disturbance of the 
surface level of the molten metal in the bath. 
In the third embodiment, instead of each cut-out portion 11, the horizontal 
passage 12 may be employed as in the case of the second embodiment. 
FIG. 8 shows a fourth embodiment of the present invention which is 
substantially similar in construction to the third embodiment just 
described above and in which the horizontal passages 12 are defined on 
opposite side surfaces of the core 7 and the ratio of the flow rate 
through the major pouring holes 16 to the sum of the flow rate of the 
molten metal flowing through the side pouring holes 17 for controlling the 
side flow rate and the flow rate of the molten metal flowing through the 
major pouring holes 16 for controlling the flow rate over the major area 
is made equal to the ratio of the length of the lower slit 15 to the 
length of the core 7 in the cast widthwise direction. The total sectional 
area of the lower slit 15 is made greater than the total sum of the areas 
of the major pouring holes 16. The diameter of each side pouring hole 17 
and the diameter of each major pouring hole 16 are evaluated depending 
upon width and thickness of a cast to be produced and in view of 
production rate per unit time interval. Furthermore, the flow rate of the 
molten metal which can prevent the growth of the shell at each triple 
point is evaluated by rule of thumb so as to evaluate the diameter of each 
side pouring hole 17. 
In this embodiment, the molten metal 5 in the tundish 8 having a 
predetermined head flows through each side pouring hole 17, each side 
pouring hole 9 and each horizontal passage 12 to each triple point on each 
side seal plate 2 so that the solidified shell which tends to be grown at 
the triple point is melted. The horizontal passages 12 guide the molten 
metal in the horizontal direction so that melting of the solidified shell 
of the cast can be avoided. 
The molten metal 5 flows through the major pouring holes 16 into the upper 
slit 14 of the core 7 and is streamlined. Thereafter the molten metal 5 
flows through the lower slit 15 into the molten bath 13 gently in the form 
of a sheet and uniformly in the cast widthwise direction without causing 
turbulence. Therefore the flow of the molten metal in the molten bath 13 
becomes uniform so that melting of the solidified shells over the 
cylindrical surfaces of the cooling rolls 1 due to partial increase in 
flow rate of the molten metal can be avoided. 
Furthermore, the ratio of the length W of the lower slit 15 to the length 
of the molten bath 13 in the cast widthwise direction is so selected as to 
be equal to the ratio of the flow rate of the molten metal flowing through 
the major pouring holes 16 to the overall flow rate so that the total side 
flow rate : flow rate at the major area=2S : W (where S represents a side 
length). As a result, the flow rate per unit time interval of the molten 
metal flowing into the molten bath 13 becomes uniform in the cast 
widthwise direction and temperature distribution in the cast widthwise 
direction also becomes uniform. 
Thus, the temperature of the molten metal which flows gently and uniformly 
in the cast widthwise direction becomes uniform in the cast widthwise 
direction so that the growth rate of the solidified shell over the 
cylindrical surface of each cooling roll 1 becomes uniform in the cast 
widthwise direction. Therefore, continuous casting can be carried out 
under the same conditions in the cast widthwise direction. 
The flow rate of the molten metal required for melting the solidified 
shells grown at the triple points on the side seal plates 2 which cause 
damages to the cast products and for inhibiting the growth of the same is 
preliminarily determined or evaluated depending upon the diameter of each 
side pouring hole 17. When the side flow rate varies in a practical 
operation due to variations of casting conditions, the flow rate can be 
adjusted by suitably selecting the head of the molten metal 5 in the 
tundish 8. Overall variations in flow rate due to the variations of the 
head can be controlled by varying the rotational velocity of the cooling 
rolls 1. 
The fourth embodiment may attain the same effect by employing the cut out 
portions 11 in the first embodiment instead of the horizontal passages 12. 
FIGS. 9-11 show a fifth embodiment of the present invention which is a 
modification or variation of the second or third embodiment or is similar 
in construction to the fourth embodiment and in which a vertically movable 
baffle plate 18 is adapted to be located in front of the corresponding 
open end of the horizontal passage 12 and is driven by a cylinder 19. 
At the start of the continuous casting operation, the cylinder 19 is 
energized to lower the baffle plate 18 to a position in front of the open 
end of the horizontal passage 12 and then the molten metal is poured. In 
response to increase of the surface level of the molten metal during the 
molten metal being gradually stored in the molten bath 13, the baffle 
plate 18 is raised and is maintained at a position slightly higher than 
the normal surface level of the molten metal as shown in FIG. 11. 
Therefore, at the initial stage of the molten metal pouring with no molten 
metal being in the molten bath 13, the molten metal flows discharged 
horizontally from the horizontal passage 12 are screened by the baffle 
plates 18. When the molten metal 5 is stored in the molten bath 13, the 
flows of the molten metal discharged horizontally from the horizontal 
passage 12 are interrupted by the stored molten metal. Thus, in either 
case, the molten metal flows are prevented from directly contacting the 
cooling rolls 1. 
It is to be understood that the present invention is not limited to the 
above described embodiments and that various modification may be effected 
without leaving the true spirit of the present invention. 
As described above, according to the dual roll type continuous casting 
machine of the present invention, the molten metal flowing through the cut 
out portions defined at the opposite longitudinal ends of the core can 
effectively melt the solidified shells grown over the surfaces of the side 
seal plates and the molten metal is directly fed into the gap between the 
cooling rolls through the inside pouring holes. As a result, the 
solidified shells over the cylindrical surfaces of the cooling rolls can 
be protected and the triple point problem can be avoided so that the 
continuous casting operation can be carried out under better conditions. 
Instead of the cut-out portions of the core, the horizontal passages may be 
used to guide the molten metal horizontally to the molten bath so that the 
downward flows are controlled and there is no fear of the solidified 
shells over the cylindrical surfaces of the cooling rolls being melted. 
As a result, surface degradation of the cast due to stripped solidified 
shells, local variations in thickness, disconnection of cast sheet metal, 
damages to the side seal plates due to separated and dropping solidified 
shells can be prevented. 
The inside pouring passage means of the core may be in the form of a slit 
in lieu of the pouring holes so that the molten metal in the tundish can 
be poured into the molten bath uniformly and gently in the form of a sheet 
without causing clogging. Therefore, nonuniform solidification resulting 
from the melting of the solidified shells grown over the cylindrical 
surfaces of the cooling rolls can be also prevented. Furthermore, 
disturbance of the surface level in the molten bath on the dual rolls can 
be reduced to a minimum. Thus, cast quality is considerably improved. 
Since the ratio of the length of the slit to the length of the core in the 
cast widthwise direction is made equal to the ratio of the major area 
pouring rate to the overall pouring rate, the flow rate per unit time 
interval of the molten metal flowing into the molten bath in the cast 
widthwise direction can be made substantially uniform and therefore 
temperature distribution in the molten bath in the cast widthwise 
direction can be made substantially uniform. As a result, the solidified 
shells are grown over the cylindrical surfaces of the cooling rolls always 
under predetermined conditions so that a high quality metal sheet with 
uniform properties in both the widthwise and lengthwise directions can be 
continuously produced. 
The baffle plates are movably disposed at the open ends of the horizontal 
passage on each end face of the core prevent the molten metal flow from 
directly contacting the cylindrical surfaces of the cooling rolls at the 
initial stage of the casting operation so that local growth of the 
solidified shells over the cylindrical surfaces of the cooling rolls can 
be avoided. As a result, leakage of molten metal in the molten bath can be 
prevented.