Note: Descriptions are shown in the official language in which they were submitted.
3 ~3
58-203,609
~ COOLING PAD FOR USE IN A CONTINUOUS
CASTING APPARATUS FOR THE PRODUCTION OF CAST S~IEETS
This invention relates to a filmy fluid
(water) flow-forming pad ~hereinafter referred to as a
cooling pad) in a continuous casting apparatus for the
direct production of cast sheets having a thickness of
05 not more than 30 mm (e.g. sheet bar or the like) from
molten metal, particularly molten steel (hereinafter
referred to as a belt caster). More particularly, it
relates to an improvement in the cooling pad which
properly selects the size and arrangement of supply
hole and discharge hole for cooling water so as to form
a desired filmy water flow.
As a continuous casting apparatus for directly
producing steel sheets such as sheet bar or the like
from molten steel, there is a belt caster as disclosed
in Japanese Patent laid open No. 57-100,851. In such a
disclosed synchronous type belt caster~ there are many
systems, a typical example of which is shown in Fig. 1.
This belt caster has usually such a structure that a
casting space is defined by a pair of endlessly circulat-
ing metal belts 4, 5 oppositely arranged to each otherat a given interval for retaining molten steel 2 over a
predetermined distance, each of which being guided and
supported through plural guide rolls 6a, 6b, 6c or 6'a,
6'b, 6'c and cooled by a filmy cooling water flow from
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the back face, and a pair of side plates disposed between the
metal belts 4, 5 and positioned near the side edge portions of
these metal belts.
Moreover, numeral 1 is a tundish, numeral 3 a pouring
nozzle, numerals 7, 8 cooling pads arranged behind the metal belts
4, 5 for cooling these belts and forming a filmy water flow capable
of supporting the static pressure of the poured molten steel,
numerals 9/ 10 springs for tensioning the belts, and numeral 11 a
cast sheet.
Since the static pressure of molten steel or semi-
solidified cast sheet changes from the molten steel surface level
toward the cast sheet-drawing direction, the cooling pads 7, 8 act
to balance the static pressure of molten steel at various stages
of the cast sheet (various positions in the cast sheet-drawing
direction) by the pressure of the filmy cooling water flow. To
this end, each cooling pad is provided at a side facing the respec-
tive metal belt with plural supply holes for the cooling water,
each of which is provided at its top with a storing recess having
a size enough to adjust the flow amount of the cooling water
supplied.
In Figures 2 and 3 is shown a structure adopted in the
conventional cooling pads 7 and 8, wherein each of plural oblong
recesses 12 is disposed on the top portion of the corresponding
water supply hole 15 for injecting the cooling water, which hole
is formed in each of the cooling pads at its side facing the metal
belt 4, 5, whereby a film flow of the cooling water is formed
between the metal belt 4 or 5 and the cooling pad 7 or 8 to counter-
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act the static pressure of the molten steel and to uniformly cool
the metal belt. Moreover, the oblong recesses 12 have usually a
minor axis a of 50-150 mm and a major axis b of 100-200 mm and are
so arranged that a transverse distance (~1) between centers of
minor axes of mutual recesses is 200-400 mm and a longitudinal
distance (~2) between centers of major axes of mutual recesses is
200-600 mm.
In the conventional cooling pad of such a structure, if
it is intended to continuously cast thin slabs and sheets bars, the
flow rate of the cooling water is considerably different between
the water flowing portion 14 formed in the recess 12 and the filmy
water portion 13 formed in an area other than the recess, causing
a difference in the cooling strength, resulting in a wavy deforma-
tion of the metal belt. As a result, the liquid-tight contact
between the metal belt 4, 5 and the fixed side plate is weakened
to produce a gap therebetween, which causes the leakage of molten
steel, casting troubles, and production of cast sheet having a
poor shape such as fin and the like. Also, the surface of the cast
sheet is not smooth, which affects the surface properties of thin
steel sheet after the rolling and causes deterioration in quality.
It is, therefore, an object of the invention to overcome
the drawback of the conventional cooling pad, wherein the rear sur-
face of the metal belt is cooled by the filmy water portion 13 and
the water flowing portion 14, by an arrangement of water supply
hole and water discharge hole for forming a filmy cooling water
flow so as to match static pressure of molten steel as mentioned
later and to prevent the occurrence of accidents in the casting
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operation and the deterioration of qualities in the cast produc-ts.
According to the invention, there is provided in a con-
tinuous casting apparatus for the production of cast sheets com-
prising a pair of endlessly circulating metal belts oppositely
arranged at such a gap to hold molten metal and its cast sheet a-t
both long sides of the cast sheet, a pair of side plates each
located at one side near the side edge portions of both belts and
brought into intimate contact therewith, and a cooling pad for
supplying and discharging cooling water to the rear surface of the
metal belt, the improvement wherein said cooling pad is provided
with plural water supply holes and water discharge holes each open-
ing to said metal belt so as to satisfy the following relations:
0.5< Ai < 7
Ai/Ao > 1.1 n
lc < 20,
wherein Ai is a sectional area (cm2) of the water supply hole, Ao
is a sectional area (cm2) of the water discharge hole, n is a
parameter depending on the arrangement of the water supply and dis-
charge holes, and lc is a distance (cm) between the centers of the
water supply hole and the water discharge hole, said water discharge
holes being disposed around said water supply hole in said cooling
pad into a triangular shape at n=0.5, a square shape at n=l or a
hexagonal shape at n=2.
For a better understanding of the invention, reference
is made to the accompanying drawings, in which:
Figure 1 is a schematic view of an embodiment of the
continuous casting apparatus for the direct production of cas-t
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thin sheets;
Figure 2 is a partial sectional view of the conventional
cooling pad as mentioned above;
Figure 3 is a parti.al plan view of the conventional cool-
ing pad viewed from the metal belt;
Figures 4 to 6 are schematic views of embodiments on the
arrangement of water supply and discharge holes in the cooling pad
according to the invention, respectively; and
Figure 7 is a graph showing the influence of the correc-
tion factor in sectional area ratio of water supply hole to waterdischarge hole upon the index of cast sheet form.
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~ ccording to the invention, plural water
supply holes 15 and plural water discharge holes 16
opening to the metal belt 4 or 5 are simultaneously
disposed on each of the cooling pads 7 and 8 in the
05 contin~lous casting apparatus, and the size ànd arrange-
ment thereof are characterized by satisfying the
following requirements as a result of the observation
of flow velocity distribution of filmy cooling water
flow and the measurement of the heat transfer coefficient
in model experiments and actual operation:
(l) The water supply holes 15 are uniformly
dispersed ~s far as possible facing the rear surface of
the metal belt 4 or 5;
(~) The water discharge holes 16 are symmetrically
disposed around each water supply hole 15;
(3) The cross sectional area of the water supply
hole Ai (cm2) and the cross sectional area of the water
discharge hole Ao (cm2) satisfy the following equation:
Ai/Ao > ~n ................ (l)
, wherein n is a parameter depending upon the arrangement
of the water supply and discharge holes. That is, when
the arranging shape of the water discharge holes is
triangular, n is 0.5. Further, n is l in case of the
square shape and 2 in case of the hexagonal shape.
Such arranging shapes are shown in Figs. 4-6.
And also, ~ is a correction factor in a
sectional area ratio of water supply hole to water
discharge hole. If ~<1, the uniform formation of the
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4881-233
filmy water flow is difficult and there is occasionally caused -the
melting loss of the metal belt during the casting. In order to
uniformly and stably form the filmy water flow having a -thickness
of about 300 to 2,000 ~m, ~ is necessary to be not less than 1.1,
preferably not less than 1.2 as shown in Figure 7, in which ~
represents triangular arrangement, ~ represents square arrangement
and o represents hexagonal arrangement;
(4) When the sectional area Ai (cm2) of the water supply
hole 15 is less than 0.5, the clogging of the hole is apt to be
caused due to the adhesion of scale, while when it exceeds 7,
stagnation is produced in the water flow. Therefore, the sectional
area Ai is necessary to satisfy the following relation:
0.5 < Ai < 7; and
(5) The distance ec between the centers of the water
supply hole and the water discharge hole is necessary to be
,ec< 20 cm, preferably ~c< 17.5 cm because it is difficult to ensure
the uniform formation of the filmy water flow distribution as the
value of ec becomes large.
Although the symmetry is lost or some of the above
requirements are not satisfied in the marginal portion of the
cooling pad, it is not of importance because the metal belt corre-
sponding to the marginal portion of the cooling pad does not
directly cool the cast sheet. Further, the arrangement of the
water discharge holes determining the value of n need not
necessarily be exactly held at the triangular shape or the like,
and can be changed to the extent that a large change of heat flow
distribution is not caused. Moreover, the invention is applicable
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4881-233
to not only belt caster comprising a pair of fixed side pla-tes but
also belt caster comprising a pair of side plates moving synchron-
ously with the metal belts.
The following examples are given in illustration of the
invention and are not intended as limitations thereof.
Example 1
A continuously cast sheet of low-carbon aluminum killed
steel having a thickness of 100 mm and a width of 500 mm was pro-
duced through the belt caster shown in Figure 1, wherein each of
the cooling pads 7, 8 used was provided with plural water supply
and discharge holes 15, 16 having a sectional area of water supply
hole Ai=l.l cm2 (hole diameter di=12 mm), a sectional area of
water discharge hole Ao=0.38 cm2 (hole diameter do=7 mm), a
distance between water supply and discharge holes ec=12 cm and n=2
~hexagonal shape shown in Figure 6). In this operation, the temper-
ature of molten steel 2 in the tundish 1 was 1,560C and the
maximum drawing speed was 3.0 m/min. As the metal belt 4 or 5 was
used a thin steel having a thickness of 1.2 mm.
The resulting cast sheet, after the cooling from the
back surface of the metal belt using the above cooling pad was even
and smooth at its surface as compared with the cast sheet obtained
by using the conventional cooling pad shown in Figures 2 and 3,
from which was obtained a rolled thin steel sheet having a beauty
surface. Even after the casting of about 30 tons, the metal belt
was normal and did not produce deformation and the formation of fin
accompanied therewith.
Example 2
The same procedure as described in Figure 1 was repea-ted,
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4881-233
except that the arrangement of water supply and discharge holes in
the cooling pad had Ai=0.79 cm2 (di=10 mm), Ao=0.79 cm2 (do=10 mm),
~c=10 cm and n=0.5 (triangular shape), to produce a cast sheet,
which was subjected to the usual rolling treatment to obtain a thin
steel sheet of 1.2 mm in thickness. In this case, the surface of
the cast sheet was smooth, and the surface properties of the thin
steel sheet were excellent.
Example 3
A continuously cast sheet of aluminum killed steel having
a thickness of 30 mm and a width of 1,000 mm was produced through
a belt caster comprising a converged-type side face tapering toward
the casting direction and a cooling pad having that arrangement of
water supply and discharge holes which has Ai=3.1 cm2 (di=20 mm),
Ao=0.79 cm2 (do=10 mm), ~c=17.5 cm and n=l (square shape). The
maximum drawing speed was 5.3 m/min. As a result, the sheet bar
obtained was good in shape and in surface properties as in the cases
of Examples 1 and 2.
Comparative Example 1
A continuously cast sheet oE aluminum killed steel having
a thickness of 30 mm and a width of 1,000 mm was produced at a
drawing speed of 4.7 m/min through a converged-type belt caster,
wherein the arrangement of water supply and discharge holes in the
cooling pad had Ai=3.1 cm2 (di=20 mm), Ao=0.79 cm2 (do=10 mm),
~c=23 cm and n=l (square shape). In this case, only the distance
between holes ~c was outside the range defined in the invention
(ec S 20 cm). When the inner surface of the steel belt (having a
thickness of 1.2 mm) was observed after the casting of about 5 tons,
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unevenness was locally produced, so that it was necessary to replace
the steel belt with a new one.
As mentioned above, according to the invention, the
filmy cooling water flow can be uniformly and stably formed on the
rear surface of the metal belt, whereby cooling unevenness in the
belt can be avoided and hence wavy deformation of the belt is pre-
vented. As a result, contact between the metal belt and the fixed
side plate is improved, whereby not only are accidents in the cast-
ing avoided, but also the qualities of the cast sheet and
finished sheet are improved.
