Strip casting apparatus and method

Strip casting apparatus including a molten-metal-holding container and a nozzle to deposit molten metal onto a moving chill drum to directly cast continuous metallic strip. The nozzle body includes a slot bounded between a back and a front lip. The slot width exceeds about 20 times the gap distance between the nozzle and the chill drum surface. Preferably, the slot width exceeds 0.5 inch. This method of strip casting minimizes pressure drop, insuring better metal-to-chill-drum contact which promotes heat transfer and results in a better quality metallic strip.

FIELD OF THE INVENTION 
The present invention relates generally to casting of metal and, more 
particularly, is concerned with planar flow casting of metallic strip. 
DESCRIPTION OF THE PRIOR ART 
Planar flow casting of metallic strip is disclosed in U.S. Pat. No. 
4,142,571 for "Continuous Casting Method for Metallic Strips" and in U.S. 
Pat. No. 4,475,583 for "Strip Casting Nozzle", both of which patent 
specifications are incorporated herein by reference. 
In planar flow casting, molten metal (which may be under pressure) is 
deposited onto the moving surface of a chill drum, chill wheel, chill 
roll, endless belt, or other chill body whereon the metal is solidified 
and then removed as a strip from the rotating drum. The process provides 
for direct and continuous casting of metal strips from the molten metal. A 
nozzle having a slot is used to transfer the molten metal from a 
container, such as a tundish or pouring box, to the moving chill drum. The 
nozzles are referred to as strip casting nozzles or planar flow casting 
nozzles. 
Existing strip casting nozzle designs are characterized by slots having a 
width of less than 0.09 inch. For example, the slot of U.S. Pat. No. 
4,142,571 has a width from about 0.2 to 1.01 millimeters (0.0078 to 0.039 
inch), while the slot of U.S. Pat. No. 4,475,583 has a portion with a 
width from about 0.010 to 0.080 inch. Applicants discovered that such 
narrow-width slots restrict the flow of molten metal at a point removed 
from the surface of the chill drum which causes a large pressure loss in 
the molten metal from the container through the slot to the chill drum; 
that when molten metal is deposited on the moving chill drum surface with 
too low pressure, the heat of the molten and solidified portions of the 
metal is not efficiently transferred to the chill drum, and even local 
lift-off of the metal from the drum may result; and that as planar flow 
casting requires rapid cooling of the molten metal, improper heat transfer 
can result in poor strip properties. 
What is needed is a planar flow apparatus design, based on Applicant's 
discovery, which minimizes the pressure drop of the molten metal from the 
container to the chill drum to increase the contact of the metal on the 
drum for efficient heat transfer to produce metallic strip of high 
quality. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a planar flow apparatus design 
which minimizes the pressure drop of the molten metal through the nozzle. 
It is another object of the invention to provide a strip casting method 
which will deposit molten metal onto a moving chill drum with good surface 
contact, so as to allow for efficient heat transfer. 
To achieve the foregoing and other objects and in accordance with the 
purpose of the present invention as embodied and broadly described herein, 
the strip casting apparatus includes a chill body surface and a reservoir. 
The reservoir includes a molten-metal-holding container and a strip 
casting nozzle. The nozzle includes a through slot and a bottom surface. 
The bottom surface is spaced a predetermined distance from the chill body 
surface. The slot interconnects the container and the nozzle's bottom 
surface whereby the container's molten metal is delivered through the slot 
generally perpendicular onto the chill body surface. The slot's 
predetermined width is at least 20 times greater, at its minimum 
dimension, than the predetermined distance between the nozzle's bottom 
surface and the chill body surface at their nearest point. 
In a second embodiment of the invention, the strip casting apparatus 
includes (a) a moving chill body surface, and (b) a reservoir for 
delivering molten metal onto a moving chill body surface. The reservoir 
includes (1) a container for holding the molten metal and (2) a strip 
casting nozzle. The strip casting nozzle includes a nozzle body having a 
slot, a front lip, and a spaced-apart back lip. The nozzle body is 
attached to the container, and the nozzle body is positioned to deliver 
molten metal through the slot perpendicularly onto the chill body surface. 
The slot is bounded by the two lips. The chill body surface moves from the 
back lip to the front lip. The front lip has a bottom, inner and outer 
surface. Each of the lips has a slot-facing inner surface, which is 
generally perpendicular to the chill body surface, and a bottom surface 
which faces the chill body surface. The distance between the lips is 
greater than about 20 times the closest distance between the chill body 
surface and each bottom surface of the lips. 
In a third embodiment of the invention, the method for casting continuous 
metallic strip includes orienting the nozzle slot generally perpendicular 
to the chill body surface, positioning the nozzle such that the slot width 
is greater than about 20 times the distance from the nozzle to the chill 
body surface, passing the molten metal through the slot onto the chill 
body surface, moving the chill body surface, and cooling the molten metal 
on the chill body surface to solidify the molten metal into the continuous 
metallic strip. 
In a preferred embodiment of the invention, the distance between the lips 
is greater than about 0.5 inch. 
Several benefits and advantages are derived from the invention. The 
apparatus of the invention minimizes the pressure drop of the molten metal 
through the slot, which increases the contact of the metal with the chill 
body surface, which increases the heat transfer, which results in metallic 
strip of good quality being produced. Also, freeze-up or clogging of the 
nozzle slot due to inclusions is less likely to occur, and more likely to 
be overcome, by using the method of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Reference will now be made in detail to several present preferred 
embodiments of the invention, some examples of which are illustrated in 
the accompanying drawings. In the drawings, like reference characters 
designate like or corresponding parts throughout the several views. 
Referring to FIGS. 1 and 2, the strip casting apparatus 10 is shown in 
operation. Molten metal 12, such as steel, flows, under hydrostatic 
pressure, from the container 14, such as a tundish or pouring box, through 
the strip casting nozzle 16, the container 14 and the nozzle 16 together 
being referred to as the reservoir 18, and onto the surface 20 of the 
moving chill drum 22 sometimes referred to as a chill wheel, chill roll, 
endless belt, or other chill body, which is kept cold, i.e., colder than 
the melting point of the molten metal 12, in a manner well known to those 
skilled in the art. The molten metal 12 is quickly cooled on the moving 
chill drum 22, changing into a solid metallic strip 24 along a 
solidification surface 26. As can be appreciated by the artisan, the 
metallic strip 24 is removed from the chill drum 22 in a continuous 
manner. 
As shown more clearly in FIGS. 3, 4, and 5, the strip casting nozzle 16 
includes a nozzle body 28 having a through slot 30, a front lip 32, and a 
spaced-apart back lip 34. The slot 30 is bounded front and back by the 
front and back lips 32 and 34. The front lip 32 is considered to be that 
portion of the nozzle body 28 which extends from the slot 30 to the front 
end 33 thereof, while the back lip 34 is that portion of the nozzle body 
28 which extends from the slot 30 to the rearward end 35. "Front" and 
"back" are reference terms chosen such that the moving surface 20 of the 
chill drum 22 moves in a direction from the back lip 34 to the front lip 
32. 
The nozzle body 28 is communicably attached to the container 14 so that 
molten metal 12 can flow through the slot 30. The term "attached" includes 
a separate nozzle body attached to the container as well as a nozzle body 
which is integral with the container, i.e., a reservoir of unitary 
construction. The nozzle body 28 is disposed, with respect to the chill 
drum 22, so that the molten metal 12 flowing through the slot 30 from the 
container 14 is deposited generally perpendicularly onto the chill drum 
22. 
The back lip 34 of the nozzle body 28 has an inner surface 36 and a bottom 
surface 38. The inner surface 36 faces generally the back of the slot 30 
and is generally perpendicular to the chill drum surface. The bottom 
surface 38 faces the chill drum surface 20. Likewise, the front lip 32 of 
the nozzle body 28 has an inner surface 40 and a bottom surface 42. The 
inner surface 40 faces generally the front of the slot 30 and is generally 
perpendicular to the chill drum surface 20. The bottom surface 42 faces 
the chill drum surface 20. 
The gap distance is defined as the perpendicular distance from the closest 
point on each of the bottom surfaces 38 and 42 of the lips 32 and 34 to 
the chill drum surface 20. The slot width is defined as the perpendicular 
distance from any point on the inner surface 36 of one of the lips 34 to 
the inner surface 40 of the other one of the lips 32. In Applicants' 
invention, the slot width is greater than about 20 times the gap distance. 
It is noted that the slot width may vary at different points along the 
inner surfaces of the nozzle body 28 as long as the 
slot-width-to-gap-distance ratio, for any point on an inner surface, 
always is greater than or equal to 20. A recommended range for the ratio 
of the slot width to the gap distance is from about 25 to 200. Preferably, 
the slot width exceeds about 0.5 inch, and an exemplary slot width is one 
from about 1 to 24 inches. The strip casting apparatus design of the 
invention minimizes the pressure drop of the molten metal 12 through the 
slot 30 which provides for good surface contact between the metal, molten 
metal 12 and solidified metal 24 portions, and the chill drum surface 20 
which improves the heat transfer rate as well as the surface quality of 
the resulting metallic strip 24. 
The front lip 32 also has an outer surface 44. An imaginary line 
perpendicular to the outer surface 44 forms an acute angle with respect to 
the direction of motion of the chill drum surface 20 at the point of 
molten metal deposition on such surface. Preferably, the outer surface 44 
faces generally in the direction of motion of the chill drum surface 20. 
The inner and bottom surfaces 40 and 42 intersect at an inner edge 46, and 
the bottom and outer surfaces 42 and 44 intersect at an outer edge 48. 
Each such edge may be a radiused edge having a radius of, for example, 
about one-eighth inch. 
The inner surfaces 40 and 36 of the lips 32 and 34 can bound a slot 30 
having an oval or other shape rather than the rectangular shape shown in 
FIG. 4. For example, the inner surface 40 of the front lip 32 may be 
concave in shape, looking down into the slot 30 from the top, to 
compensate for edge effects of the metal flow so as to produce strip of 
uniform thickness. 
Preferably, for the front lip 32, the distance from the inner edge 46 to 
the chill drum surface 20 is greater than the distance from the outer edge 
48 to the chill body surface 20. With this feature, the flow of molten 
metal 12 is restricted at a point on the chill drum 22 by the gap between 
the outer edge 48 and the chill drum surface 20. In an exemplary 
embodiment, the bottom surface 38 has a concave shape. 
Depending on the application, the front and back lips 32 and 34 can have 
side portions 50, sideways bounding the slot 30, which extend lower than 
the bottom surfaces 42 and 38 of the lips 32 and 34 (see FIG. 5), to 
better contain the molten metal 12, as can be appreciated by those skilled 
in the art. Also, these side portions 50, as well as the bottom surface 38 
of the back lip 34, may have resilient gaskets, such as ceramic paper 
gaskets 52, compressibly contacting the chill drum surface 20 to further 
contain the molten metal flow (see FIGS. 5 and 6). 
In a test run of the apparatus of the invention, 0.547 pounds of 
low-carbon, silicon-killed steel were induction melted and pressurized 
with 0.5 psig argon. The boron nitride nozzle, having a 0.750 inch 
diameter generally circular slot and a concave tapered front lip 32, was 
oriented generally perpendicular to the chill drum surface 20 and 
positioned to leave a gap therebetween of 0.014 inch for the back lip's 
bottom surface 38, 0.058 inch for the inner edge 46 of the front lip's 
bottom surface 42, and 0.028 inch for the outer edge 48 of the front lip's 
bottom surface 42. The molten metal (heated to about 1,615 degrees C) was 
passed through the slot onto the chill drum surface, the chill drum being 
a 14.2-inch-diameter, 1.2-inch-wide OFHC (oxygen free high conductivity) 
copper solid wheel rotating at 150 rpm and having a before-run temperature 
of 72 degrees C. A fiberfax gasket 52 was used between the nozzle and the 
moving chill drum surface. The molten metal cooled and solidified on the 
moving chill drum surface producing a continuous metallic strip which was 
0.020 to 0.025 inches thick and 0.75 inches wide. 
The above-described elements of the planar flow apparatus work together to 
produce a continuous direct casting metallic strip. It is clear other 
dimensions of the elements, such as the length of the front lip 32 as well 
as the casting operating parameters, such as the speed of the moving chill 
drum surface 20 are to be chosen to best meet the demands of the 
particular metallic strip composition, thickness, etc., as is within the 
purview of those skilled in the art. 
It will be apparent that many modifications and variations are possible in 
light of the above teachings. It, therefore, is to be understood that 
within the scope of the appended claims, the invention may be practiced 
other than as specifically described.