Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION 121~314
In the process o~ continuously casting steel strands,
molten metal is poured into the open upper end o~ a hollow box-
like mold. As the molten metal flows downwardly through the
mold~ the metal is partiall~ cooled. The partially cooled metal
continues to flow downwardly through the open bottom end of the
mold in the form of a continuous slab or billet or the like. The
molds used in this ~rocess generally comprise spaced apart,
parallel front and rear walls and a pair of opposed side walls.
Each of the walls is made of a relatively heavy, outer back plate
construction and an inner copper or copper-like plate liner. The
exposed inner surfaces of the liner form the inner casting face
of the mold.
Examples of types of molds used in the continuous
casting process are disclosed in prior patents of Floyd R.
Gladwin: U.S. Patent No. 3,964,727 issued June 22, 1976; U.S.
Patent No. 3,978,910 issued September 7, 1976; U.S. Patent No.
4,124,058 issued November 7, 1978; and U.S. Patent No. 4,129,175
issued December 12, 1978.
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1217~4
1185.0~8 In the continuous casting operation, a metal strand is produced by
pouring molten metal into the open upper end of the mold so that the metal in
contact with the casting surfaces is cooled or chilled. This cooling forms a thin
skin on the metal which skin surrounds an interior molten core. As the metal
moves downwardly through the mold, due to the gravity, the thic~ness of the skin
increases until the s~in is relatively rigid and self-sustaining. Further movement
of the strand downwardly, out of the bottom of the mold, produces a
substantially self~ustaining form, like a sla~ or billet, etc., comprising a thick
skin surrounding a still-molten core. The strand is then cooled as it travels
further from the mold until the strand is completely solidified. Once solidified,
the strand is cut into useful lengths.
In this type of continuous casting mold, the molten metal and the
mold walls are cooled by means of passing water through passageways formed
within the mold liners and backing plates. The water cooling removes heat from
the molten metal which is transmitted through the liners from their inner casting
or molding surfaces.
It is important to cool the skin rapidly in order to thicken the skin
so that the skin is reliably self-sustaining. Thus as the strand exits from the
bottom of the mold, the skin will not rupture or burst or distort because of the
pressure from the still molten core. However, as the metal cools in the mold,
the skin tends to shrink away from the mold walls. While the skin is thin and
pliable, the ferrostatic pressure of the molten core forces the skin outwardly into
contact with the casting surfaces of the mold. But, as the skin thickens, the skin
tends to stiffen and resist the ferrostatic pressure so that it shrinks inwardly,
away from the casting surface, to provide a gap. Then the ferrostatic pressure
forces the skin outwardly again and the cycle repeats. This results in a
roughened, corrugated or wavy surface on the metal strand and uneven wear on
the mold liner casting faces.
121~31D~
1185.008 The gap, which is referred to as an air gap, is not necessarily
uniform around the periphery of the strand. For example, sometimes the gap
may appear more at the corner areas of the mold than at the centers of the mold
walls. Such air gap, in effect, acts like an insulation between the transfer of
heat from the solidifying metal skin to the casting wall surface of the liner. This
reduces the amount and rate of heat which is transferred from the metal
outwardly through the mold and away through the cooling fluid.
Thus, it is desirable in the casting process to ~ceep the slcin in
direct contact with the casting or inner face of the mold liner, throughout the
entire height of the mold and to prevent the air gap effect which may occur due
to shrinkage of the skin. One prior art technique for reducing these air gaps isdescribed in my prior application. A second technique for reducing air gaps is to
taper the mold walls inwardly as described in some of the prior art cited by theExaminer in the aforementioned prior application. However7 none of these
techniques have been successful.
The invention herein contemplates cooling the mold liner in a
manner which reduces air gaps and permits the ferrostatic pressure of the moltencore to hold the newly forming skin outwardly against the casting walls
throughout the entire length of the mold.
SUMMARY OF THE INVENTION
The invention herein contemplates substantially reducing the air
gaps between the mold walls and the metal strand. Specifically a thin facing is
applied to the interior of the mold walls and the facing is of gradually increasing
thickness from its top toward its bottom. The facing is of a material such as
nickel which has a substantially lower thermal conductivity than the mold wall.
While the use of a nickel facing is old, as illustrated for example in the Von Jan
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11B5.005 et al U.S. Patent 4,197,902 of April 15, 1980, cited by the Examiner in my prior
application, the prior art does not disclose the wlique idea where a facing may be
of increasing thickness for gradually reducing the size of the mold cavity and
gradually reducing the rate of cooling of the molten strand, to thus provide thethree benefits of (a) reducing air gaps, (b) providing an improved ~uality metalstrand surface, and (c) providing a uniform temperature on the mdd cavity
facing thus reducing excessive mold wall wear.
If the nickel facing was of uniform thickness, as in the prior art,
the rate of cooling therethrough would ~e constant but the metal strand would
shrink away causing both air gaps and non-uniform temperature (and hence non-
uniform wear) on the mold cavity walls.
If the nickel facing was of uniform thickness, as in the prior art,
but positioned at an angle inwardly and downwardly, although the rate of coolingwould be constant, the mold cavity surface temperature would vary considerably.
Therefore, too rapid cooling of the strand and thickening of the skin tend to talce
place in the middle of the mold, resulting in shrinkage, air gaps, and uneven mold
wear.
The invention herein further comtemplates varying the thickness
of the mold cavity by downwardly and inwardly tapering only the facing but not
the inner plate or the outer backing plate. Thus facings according to the present
invention may be retrofit onto existing mold plates.
By varying the facing thickness and angle as descri~ed above, the
skin formed on the solidifying strand within the mold tends to remain in direct
contact with the facing for a longer period of time. Air gaps are substantially
reduced, resulting in direct transfer of heat from the skin to the facing without
an intervening air insulation. Moreover, the rate or speed of removal of the
strand from the mold can be somewhat increased, thus increasing overall casting
efficiency.
12~7 1~
1185.008 DESCRIPTION OF THE DRAWINGS
These and other objects and advantages of this invention will
become apparent upon reading the following description t~ken in conjunction
with the drawings. In the drawings, wherein like reference numerals identify
corresponding components:
Figure 1 is a perspective view, schematically showing a continuous
casting mold, according to the present invention;
Figure 2 is a perspective view of the liner plate illustrating the
cooling channels or grooves in the outer face thereof;
Figure 3 is a perspective view of the backing plate illustrating the
innner face thereof;
Figure 4 is an enlarged cross-sectional view through the mold wall
taken in the direction of arrows 4 4 of Figure l;
Figure 5 is a schematic fragmentary, cross-sectional view, drawn
to an enlarged scale, illustrating the problem of air gaps according to the use of
the prior art; and
Figure 6 is a schematic, fragmentary, cross-sectional view, drawn
to an enlarged scale, showing the relationship between the skin and the mold
according to the principles of the present invention.
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1185.008 DETAILED DESCRIPTION OF THE INVENTION
Figure 1 schematically il~ustrates a continuous casting mold 10
~ccording to the principles of the present invention. The mold is formed of a
front wall 11, a rear wall 12, and a pair of opposed side walls 13 and 14. The
walls are fastened together to ma~e up a rectangular shaped box-like
configuration haYing an open top and an open bottom. The center portion of the
box-like mold forms the casting cavity 15 into which the molten metal is poured
for solidification.
The front and rear walls each include a face plate 17, which is
often referred to as a sheath or liner plate, and which is usually made of copper
or of a copper-like material for high heat conductivity. Each liner plate is
fastened in face to face contact with an exterior, thicker, steel backing plate 18.
The steel bac~ing plate actually may be a fabricated construction comprising a
relatively thick wall and an outer backing framework. However, for purposes of
this diclosure, it is illustrated schematically as a relatively thick monolithic
plate.
The spaced apart side walls 13 and 14 are located between the
front and rear plates and are clamped in position with a suitable clamping or
fastening mechanism which is not shown since it forms no part of the invention
hereof. Each side wall includes a side wall interior face plate (or sheath or liner
plate) 2~, which like the liner plates 17 used for the front and rear walls, are
made of copper or a copper-like material. Likewise, each side wall liner plate is
secured in face to face relationship to an exterior, thick, steel backing plate 21.
The liner plates 17, 20 may be bolted to their respective outer
backing plates 18 or 21 with suita~le bolts or mechanical fasteners. Thus, each
of the walls ~nsist of a pair of plates, i.e., the thinner copper liner and the
outer, backing plate.
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~2~73~
1185.008 ~ach of the liner plates 17 and 20 is provided with an outer (i.e.,
positioned away from the mold cavity 15) face 22 within which vertically
arranged, groove-like channels 23 are formed. These channels carry & cooling
fluid, such as water, which circulates through the channels for removing heat
transmitted through the liner plates.
The inner (i.e., positioned toward the mold cavity 15) faces 24 of
each of the backing plates 18 and 21, may ~e provided with horizontally arrangedupper and lower pockets or depressions 25 and 26 which act as headers for the
passage of the cooling fluid. Conduits 27 are formed in the front and rear wall
backing plates 18 and conduits 28 are formed in the backing plates 21 of the side
walls. Typically, the water is circulated through the lower pockets 26, and thenthrough the channels 23, and out through the upper pockets 25.
Suitable pipes are provided to connect a source of cooling water
to the conduits. However, these pipes are omitted as not ~eing part of the
invention herein. Likewise, the liner plates must each ~e sealed to the backing
plates to prevent water leakage between the plates. An example of a sealing
system is described in the above mentioned l~.S. Patent No. 3,978,910 issued
September 7,1976 to Floyd ~. Gladwin.
The inner or casting or molding surfaces of the liners 17, 20, i.e.,
the surfaces facing the mold cavity, are each coated with a wear resistant,
thermally conductive facing or coating 29. An example of a suitable coating for
this purpose is commercially available 201 type niclcel.
The invention herein contemplates first that the copper or copper-
like plates 17, 20 are of uniform thickness along their vertical lengths and theinner cavity f~cing surfaces thereof are vertically oriented. By way of example,with a 3 foot high mold, each of the liners 17, 20 may be approximately one inchthick.
lZ~3~4
1185.008 The nickel facing or coating ag is tapered downwardly and
inwardly of the mold cavity 15. For example, with the 3 foot high mold, the
thickness of the nickel coating 29 would be about 0.125 inches at the top 33
thereof and about 0.250 inches at the bottom 34 thereof. Of course the nickel
facing has a substantially lower thermal conductivity than the copper or copper-like facings.
The thinner upper edge 33 of each facing tends to transmit heat
faster than the thicker lower edge portions 34 of each facing. Thus, heat
transmission rate is gradually slower going from top to bottom of the facing. But
the temperature of the cast metal is decreasing going from the top to the bottomof the cavity and thus less heat transmission is necessary as the strand progresses
toward the bottom of the mold. Consequently, a more uniform temperature can
be maintained at the mold-strand interface. Such temperature can be somewhat
higher than that used in the past. Therefore, the skin formed remains pliable
longer and because of the taper of the facing the skin is maintained in face to
face contact with the facing by the ferrostatic pressure of the molten metal
core. Thus there is a substantial reduction in air gaps.
By way of example, with the aforementioned wear material
tapered facing formed of the 201 nickel, the mold cavity surface temperature
can be maintained at roughly 1,500 degrees F. At this temperature, commonly
used low melting point fluxes, lubricants and the like, will not deposit out upon
the mold walls.
Figure 5 illustrates the prior art problem in the past where a mold
wall lla, which is schematically shown as comprising an outer backing plate 18a,a uniform thickness inner liner 17a and a uniform thickness facing 29a receives
the molten metal 35 ~gainst its surface. The skin 36a tends to gap away from
the inner casting face of the facing 29a to produce an air gap 37, which functions
lZ173~4
1185.008 as ~n insulator. ~uch an insulator actually reduces heat removal from the molten
core and requires the strand to remain in the mold longer. The result is the same
if the facing 29a is of uniform thickness and the inner face plate 17a is tapered
inwardly and downwardly.
13y way of comparison, Figure 6 shows the improved construction
herein where the facing 29 is tapered. Now, as the molten metal 35 is cooled,
the skin 36 remains substantially in full contact with the casting suu face or inner
wa~l surface of the facing throughout the height of the mold. The heat transfer
from the molten core is at a greater rate at the top of the mold but the rate
decreases along the length of the mold thus reducing the opportunity for strand
shrinkage and reducing the likelihood of air gaps 37.
With this tapered facing construction, producing a more uniform
temperature throughout the height of the mold, so-called "fire cracking" on the
surface of the nickel facing is substantially reduced. That is, there is otherwise
a tendency for cracks to form on the nickel facing at the upper part of the mold,
where the free surface or meniscus of the poured molten metal is located.
Although the sizes of the molds may vary considerably, for
example purposes, the mold wall could be of a height of about 30-36 inches9 withthe width of the front and rear walls being on the order of about 4 feet and thewidth of the end walls being on the order of about 9 inches, and face plates
between about from 1 to 3 inches in thickness. Of course, the dimensions may
change, depending upon requirements, with the dimensions set forth above being
for illustrative purposes to show relative sizes of the parts.
lZ~73~L4
1185.008 With a mold of the general size and shape shown, a steel slab can
be cast at a somewhat faster rate using the improved tapered facing, even
though the transfer of heat from the s~in into the wall is somewhat slower
overall. Because of $he greater uniformity of heat transfer, the skin tends to be
thicker at the lower end of the mold than in the prior devices where air gaps
appeared, so that the casting process can be speeded up while still obtaining
either the same thicl~ness or a somewhat greater thiclcness skin where the sla~
emerges from the bottom of the mold.
The invention herein can be applied to existing continuous casting
molds. That is, the copper liners can be removed and their outer faces can be
covered with the nickel facing. This nickel facing may be secured or deposited in
various ways as, for example, described in the aforementioned patent to Von Jan
et al.
Having fully described an operative embodiment of this invention,
I now claim:
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