BACKGROUND OF THE INVENTION
1. Field of the invention:
[0001] The invention relates to an apparatus for casting metal strip. More particularly,
the invention relates to a nozzle assembly.system for mounting a casting nozzle to
a crucible reservoir to cast continuous metal strip.
2. Description of the prior art:
[0002] In the production of continuous metal strip, molten metal has typically been extruded
from a pressurized reservoir through a nozzle on to a high speed, rotating quench
surface. Representative apparatus are shown in U.S. Patent No. 4,142,571 for "continuous
casting method for metallic strips" issued March 6, 1978 to M. Narasimhan.
[0003] When continuously casting metal strip over extended periods of time, it has been
desirable to connect a replaceable nozzle to a separate crucible capable of holding
a large quantity of molten metal. The resultant multipiece assembly has required sealing
means to prevent leakage of molten metal between the component parts. A conventional
nozzle assembly is representatively shown in U.S. Patent No. 4,154,380 issued May
15, 1979 to W. Smith.
[0004] The sealing means of Smith is comprised of a tapered, frusta-conical surface on the
cashing nozzle which is adapted to mate with a corresponding tapered surface along
the outlet passage from the crucible. The weight of the nozzle plus ths. metallostatic
pressure head holds the mated, tapered surfaces together. These tapered surfaces,
however, required precise machining to obtain the required degree of sealing effectiveness.
In addition, the closely mated surfaces do not allow for any differences in thermal
expansion between the crucible and the nozzle body, particularly where the crucible
and nozzle body are constructed from different refractory materials having different
coefficients of thermal expansion. As a result, the nozzle can expand more than the
crucible outlet passage opening, and very large lateral, side to side, forces developed
between the crucible and nozzle have often caused the nozzle to fracture. If the nozzle
should fracture severely, the flow of molten metal is no longer restricted by the
relatively small nozzle extrusion orifice; large volumes of molten metal may then
escape and damage the casting surface and any nearby auxiliary support equipment.
[0005] Thus, conventional nozzle assemblies, such as those taught by Smith, have lacked
a mechanism for preventing nozzle fracture due to thermal expansion of the nozzle
against the crucible and have lacked a safety device to prevent the sudden escape
of large volumes of molten metal from a fractured nozzle.
SUMMARY OF THE INVENTION
[0006] The invention provides an efficient, leak resistant nozzle assembly system for casting
continuous metal strip. The apparatus of the invention includes a nozzle means for
extruding molten metal. The nozzle means has a nozzle body, a nozzle inlet opening,
a nozzle exit orifice and a nozzle mounting surface located on the nozzle body proximate
to the nozzle inlet. A reservoir means for containing the molten metal is in fluid
communication with the nozzle means. The reservoir means has a reservoir opening for
flowing the molten metal therethrough and has a reservoir mounting surface located
proximate to the reservoir outlet. The reservoir mounting surface is adapted to mate
with the nozzle mounting surface and allow a relative, sliding-type movement therebetween
due to a differing thermal expansion of the nozzle relative to the reservoir means.
Heat resistant sealing means between the nozzle mounting surface and the reservoir
mounting surface minimize molten metal leakage therebetween, and a force means for
resiliently urging the nozzle mounting surface toward the reservoir mounting surface
mates the nozzle and reservoir means together.
[0007] In accordance with the invention, there is further provided a method for casting
continuous metal strip. A supply of molten metal is contained in a reservoir means
which has a reservoir mounting surface located proximate to a reservoir outlet. Molten
metal is extruded from a nozzle means which is in fluid communication with the reservoir
means and has a nozzle mounting surface located proximate to a nozzle inlet. The nozzle
mounting surface and the reservoir mounting surface mate together and allow a relative,
sliding-type movement therebetween due to a differing thermal expansion of the nozzle
means relative to the reservoir means. The region between the nozzle mounting surface
and the reservoir mounting surface is sealed to minimize molten metal leakage therebetween,
and the nozzle mounting surface is resiliently urged toward the reservoir mounting
surface to mate the nozzle and reservoir means together.
[0008] The invention advantageously allows differential thermal expansion between the nozzle
body and reservoir. In particular, the lateral clearance avoids lateral contact between
the nozzle and reservoir, and the planar mounting surfaces allow an amount of relative
movement along the mated, parallel mounting surfaces to avoid the build up of excessive
lateral stresses that could fracture the nozzle or crucible. Additionally, the force
means, which resiliently urges the nozzle and reservoir means together, allows a lengthwise,
longitudinal thermal expansion of the nozzle without a buildup of excessive internal
stresses. The safety device prevents a sudden escape of excessive amounts of molten
metal if the nozzle should become inadvertently fractured.
[0009] Thus, compared to conventional nozzle assembles without planar mounting surfaces,
without a resilient force means or without a safety device, the present invention
more reliably and more efficiently casts continuous metal strip. The invention minimizes
nozzle fracturing due to thermal stresses developed between the nozzle and the reservoir
means and minimizes the escape of molten metal from the reservoir if the nozzle should
become inadvertently fractured.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The invention will be more fully understood and further advantages will become apparent
when reference is made to the following detailed description of the preferred embodiment
of the invention and the accompanying drawings in which:
FIG. 1 shows a representative prior art apparatus for casting continuous metal strip;
FIG. 2 shows a representative cross-sectional view of a nozzle mounted internally
to a crucible;
FIG. 3 shows a representative cross-sectional view of a nozzle mounted externally
to a crucible;
FIG. 4 shows a side elevational view of a nozzle mounted externally to a crucible
with a force means comprised of springs;
FIG. 5 shows a side elevational view of a nozzle mounted externally to a crucible
with a forced means comprised of a pneumatic actuator;
FIG. 6. shows a bottom plan view of the pheumatic actuator mechanism taken in the
direction A-A. of FIG. 5; and
FIG. 7 shows a representative cross-sectional view of the apparatus shown in FIG.
5.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0011] The present invention is suitable for casting continuous strip of crystalline or
amorphous metal. While the preferred embodiments are described with respect to casting
amorphous metal alloy strip, it is readily apparent that the invention can be easily
adapted to cast crystalline metal strip as well.
[0012] For the purposes of the present invention and as used in the specification and claims,
a "strip" is a slender body in which the transverse dimensions are much smaller than
the length. Thus, a strip includes wire, ribbon and sheet of regular or irregular
cross-section.
[0013] FIG. 1 shows a typical prior art apparatus for the continuous casting of metal strip
to point out the general use of the present invention. Molten alloy contained in crucible
101 is heated with a heating element 4. Pressurization of the crucible with an inert
gas extrudes a stream of molten metal from nozzle 102, located at the base of the
crucible, onto quench surface 5 of rotating quench wheel 6. The solidified moving
strip 8 after its break-away point from the quench wheel is routed onto a winding
wheel (not shown).
[0014] When casting a strip of amorphous, glassy metal or when casting a strip of certain
crystalline metal alloys, the extruded metal is quenched at an extremely rapid rate
of at least about 10
4°C/sec, and the solidified strip moves rapidly off the quench wheel at a speed ranging
from about 400-2200 m/min. The cast strip is quite thin, typically about 25-100 microns
thick, but considerable selectivity may be exercised with respect to the width and
cross-section.
[0015] FIG. 2 shows a representative nozzle assembly for casting continuous metal strip
in which a nozzle means for extruding molten metal is shown generally at 2. The nozzle
has a nozzle body 12, a nozzle inlet opening shown generally at 14, a nozzle exit
orifice 16 and a nozzle mounting surface, such as substantially planar surface 24.
A reservoir means, comprised of crucible 1, contains molten metal and includes a reservoir
outlet opening, shown generally at 10, for flowing the molten metal therethrough.
A reservoir mounting surface, such as substantially planar surface 22, is located
on the reservoir means proximate to the reservoir outlet. Reservoir surface 22 is
adapted to mate with nozzle surface 24 and allow a relative, sliding-type movement
therebetween due to a differing thermal expansion of nozzle 2 relative to crucible
1. In addition, the reservoir crucible is adapted to provide a lateral clearance distance
3 between nozzle 2 and crucible 1. The lateral clearance prevents lateral contact
caused by a differing thermal expansion of nozzle 2 relative to crucible 1. A safety
device is comprised of a cover member 26 having a constricted passage 28 therethrough.
Cover 26 has a peripheral, outwardly extending cover flange 29 adapted to mount at
the inlet portion 14 of nozzle 2 to limit the flow of molten metal from crucible 1
into the nozzle. A resilient, heat resistant sealing means, such as a boron nitride
paste adhesive 21, is interposed between nozzle mounting surface 24 and crucible mounting
surface 22 to minimize molten metal leakage therebetween. Force means 30 resiliently
urges the nozzle mounting surface toward the crucible mounting surface to mate the
nozzle and crucible together.
[0016] The apparatus of the invention advantageously minimizes any stresses caused by differing
amounts of thermal expansion between nozzle 2 and crucible 1. In particular, lateral
clearance 3 avoids lateral contact between the nozzle and crucible, and the planar
mounting surfaces 22 and 24, disposed substantially parallel to each other, allows
relatively free, sliding-type movement between the nozzle and the crucible. Surface
shear stresses are present, but bulk stresses that could crack and break the nozzle
are minimized. in addition, the resilient force means allows longitudinal thermal
expansion while mating and holding together nozzle 2 and crucible 1 with a force sufficient
to prevent molten metal leakage therebetween.
[0017] The nozzle assembly illustrated in FIG. 2 is an internally mounted nozzle. Thus,
the reservoir mounting surface is an inwardly facing surface 22 of crucible 1, and
the nozzle mounting surface is a nozzle body surface 24 facing in the direction of
the intended flow of molten metal. Preferably, nozzle mounting surface 24 is located
on a surface of a nozzle flange 15 which extends radially outward along a peripheral
edge of nozzle body 12. While force means 30 can be comprised of a distinct mechanical
mechanism, the force means in this embodiment is preferably provided by the weight
of nozzle 2 and cover 26 along with the metallostatic pressure head of any molten
metal contained in crucible 1.
[0018] FIG. 3 shows an externally mounted nozzle which compared to the internally mounted
nozzle is more easily removed and serviced, particularly when there is molten metal
in crucible 1. A stopper rod 66 can be employed to block passage 28 while the nozzle
is being preheated or serviced. In this embodiment, the reservoir mounting surface
is an outwardly facing surface 25 of crucible 1, and the nozzle mounting surface is
a nozzle body surface 20 facing opposite to the direction of the intended flow of
molten metal. Preferably, nozzle mounting surface 23 is located on a surface of nozzle
flange 15 to increase the mated surface area between the nozzle and crucible. The
sealing means for the externally mounted nozzle is preferably comprised of a gasket
composed of a ceramic fiber, such as alumina silica. Such a gasket is easier to handle
than a paste material and still allows the needed amount of movement between planar
surfaces 20 and 25. The externally mounted nozzle advantageously eliminates the need
for a separate cover for the safety device. With this embodiment, the cover member
of the safety device is comprised of the bottom wall 64 of crucible 1, and constricted
outlet passage 28 which communicates through bottom wall 64 limits the flow of molten
metal from crucible 1. The externally mounted nozzle, however, does require a force
means 30 comprised of a distinct mechanical mechanism 33 to hold the nozzle and crucible
together and maintain alignment therebetween.
[0019] FIG. 4 shows an embodiment of the invention which employs an optional nozzle heater
means 18 disposed about nozzle 2 to preheat the nozzle and maintain the temperature
of the molten metal as it passes therethrough. FIG. 4 further shows a force means
comprised of springs.
[0020] In this embodiment of the invention, a support member, such as frame 32, is configured
to be substantially immobile with respect to crucible 1. A displacement member, such
as plate 34, is spaced a distance away from support frame 32 and is movable relative
to the frame. Spring means, such as compressible springs 36, are operably connected
to plate 34 and support frame 32. Springs 36 provide a selected force which is adapted
to move plate 35 toward nozzle 2 and resiliently urge the nozzle mounting surface
23 toward crucible mounting surface 25. Adjustment means, comprised of threaded studs
38, nuts 42 and washers ,40, adjust springs 36 to provide a selected spring force.
[0021] As shown by FIG. 4, threaded studs 38 are attached to frame 32 by suitable attachment
means, such as welding. The studs extend through holes in plate 34 and are adapted
to slide freely through those holes. Additionally, frame 32 has openings which allow
nozzle 2 and heater 18 to extend therethrough without interference from the frame.
There is sufficient clearance between nozzle 2 and frame 32 to eliminate any lateral,
side to side contact therebetween due to thermal expansion of the nozzle. Plate 34
is adapted to operably contact nozzle heater 18 and move nozzle 2 toward crucible
1. Plate 34 also has an opening 61 therethrough which is configured to allow extrusion
of molten metal from nozzle 2 onto a suitable quench surface. A spring 36 and a washer
40 are assembled about each stud 38. Each spring is interposed between a washer 40
and the frame 32, and a nut 42 is then threaded onto each stud 38. Thus, by selectively
turning nuts 42 up onto stud 38 to compress springs 36, plate 34 is drawn up against
heater 18, which contacts nozzle 2 to urge the nozzle mating surface 23 toward crucible
surface 25 and hold the nozzle and crucible together. By adjusting the amount of compression
imparted to springs 36, the amount of mating force can be adjusted to a selected magnitude.
The resilience of the springs also allows longitudinal movement of plate 32 along
studs 38 in response to the thermal expansion of nozzle 2 and heater 18, and prevents
the buildup of excessive stresses within the nozzle.
[0022] During certain casting operations, however, the ambient high temperatures, which
can exceed 1,000°C, can cause a relaxation of the force exerted by springs 36. The
force between nozzle 2 and crucible 1 may become too low to maintain an adequate seal
therebetween, and leakage of molten metal may occur.
[0023] To minimize this problem, the force means is preferably comprised of a pneumatic
actuator mechanism as shown in Figures 5 and 6. By employing a pneumatic actuator
46 operated by a pressurized fluid, such as compressed gas, one can advantageously
monitor and continuously adjust the gas pressure in the actuator to provide a substantially
constant force that operates to hold nozzle 2 and crucible 1 together and maintains
an adequate seal therebetween.
[0024] As shown in FIG. 5, support frame 32 is substantially immobile with respect to crucible
1 and has openings configured to accommodate placement of nozzle 2 and heater 18 therethrough
without interference from the frame. A displacement member is comprised of lever arms
54, a cross member 52 connected between two end portions of the lever arms and a pivot
plate 35. The displacement member is movable relative to frame 32. In particular,
pivot means, comprised of pivot brackets 52 and pivot bearings 56, connect to support
frame 32 and are adapted to pivot the displacement means thereabout. Pivot brackets
52 are rigidly connected to support frame 32 by suitable fasteners or by welding and
are adapted to support pivot bearings 56. Pivot bearings 56 pivotably connect each
lever arm 54 to its respective pivot bracket 52. A neumatic actuator means, such as
a dual action pneumatic actuator 46, is adapted to pivot the displacement member about
the pivot means to move a portion of the displacement member, particularly plate 35,
toward nozzle 2. Actuator 46 further provides a selected force that resiliently urges
the nozzle mounting surface 23 toward mounting surface 25 of the crucible reservoir
to mate and hold the nozzle and crucible together. As illustrated in FIG. 5, actuator
brackets 50 are rigidly connected to frame 32 and adapted to support actuator 46.
Actuator 46 operably connects to cross member 62 an-I when operated, provides a force
that moves cross member 62 downwards to pivot lever arms 54 about pivot pins 56. As
the lever arms rotate, they move plate 35 upward against nozzle heater 18 which in
turn, contacts nozzle 2. The preselected force provided by.actuator 46 urges surface
23 toward surface 25 to mate the nozzle end crucible together.
[0025] Pressure regulator means 48 controls the gas pressure supplied to actuator 46 to
adjust the force directed against heater 18 and nozzle 2. Advantageously, the regulated
gas pressure in actuator 46 provides a resiliency which allows thermal expansion of
nozzle 2 and downward movement of plate 35 while still maintaining a constant, stable
force between nozzle 2 and crucible 1 that is sufficient to preserve the liquid seal
therebetween. As a result, leakage is minimized and excessive thermal stresses that
could fracture the nozzle are avoided.
[0026] Having thus described the invention in rather full detail, it will be understood
that these details need not be strictly adhered to but that various changes and modifications
may suggest themselves to one skilled in the art, all falling within the scope of
the invention as defined by the subjoined claims.
1. An apparatus for casting continuous metal strip comprising:
(a) nozzle means for extruding molten metal, which has a nozzle body, a nozzle inlet
opening, a nozzle exit orifice and a nozzle mounting surface located proximate to
said nozzle inlet;
(b) reservoir means in fluid communication with said nozzle means for containing said
molten metal, said reservoir means having a reservoir outlet opening for flowing said
molten metal therethrough and having a reservoir mounting surface located proximate
to said reservoir outlet which is adapted to mate with said nozzle mounting surface
and allow a relative, sliding-type movement therebetween due to a differing thermal
expansion of said nozzle means relative to said reservoir means;
(c) heat resistant sealing means located between said nozzle mounting surface and
said reservoir mounting surface for minimizing molten metal leakage therebetween;
and
(d) force means for resiliently urging said nozzle mounting surface toward said reservoir
mounting surface to mate said nozzle and reservoir means together.
2. An apparatus as recited in claim 1, wherein said nozzle mounting surface and said
reservoir mounting surface are substantially planar.
3. An apparatus as recited in claim 1, further comprising a safety device comprised
of a cover member having a constricted passage therethrough.
4. An apparatus as recited in claim 1, wherein said reservoir mounting surface is
an inwardly facing surface of said reservoir means and said nozzle mounting surface
is a nozzle body surface facing in the direction of the intended flow of molten metal
into said nozzle.
5. An apparatus as recited in claim 1, wherein said reservoir mounting surface is an
outwardly facing surface of said reservoir means and said nozzle mounting surtace
is a nozzle body surtace facing opposite to the direction of the intended flow of
molten metal into said nozzle.
6. An apparatus as recited in claim 1, wherein said force means comprises:
(a) a support member which is substantially immobile with respect to said reservoir
means;
(b) a displacement member which is spaced a distance away from said support member
and movable relative thereto;
(c) spring means operably connected to said displacement member and said support member
for providing a selected force which is adapted to move said displacement member toward
said nozzle means and urge said nozzle mounting surface toward said reservoir mounting
surface; and
(d) adjustment means for adjusting said spring means to provide said selected force.
7. An apparatus as recited in claim 1, wherein said force means comprises:
(a) a support member which is substantially immobile with respect to said reservoir
means;
(b) a displacement member which is movable relative to said support member;
(c) pneumatic actuator means for moving said displacement member toward said nozzle
body and for providing a selected force that urges said nozzle mounting surface toward
said reservoir mounting surface; and
(d) pressure regulator means for controlling a fluid pressure supplied to said pneumatic
actuator to adjust said force.
8. An apparatus as recited in claim 1, wherein said force means comprises:
(a) support member which is substantially immobile with respect to said reservoir
means;
(b) a displacement member which is movable relative to said support member;
(c) pivot means connected to said support member for pivoting said displacement number
thereabout;
(d) pneumatic actuat.- means for pivoting said displacement member abcut said pivot
means to move portion of said displacement member toward said nozzle body and provide
a selected force that resiliently urges said nozzle mounting surface toward said reservoir
mounting surface to mate said nozzle and said reservoir means together; and
(e) pressure regulator means for controlling a gas pressure supplied to said pneumatic
actuator to adjust said force.
9. An apparatus as recited in claim 1, further comprising heater means disposed about
said nozzle for heating molten metal contained therein.
10. A method for casting continuous metal strip, comprising the steps of:
(a) containing a supply of molten metal in a reservoir means which has a reservoir
mounting surface located proximate to a reservoir outlet opening;
(b) extruding said molten metal from a nozzle means which is in fluid communication
with said reservoir means and has a nozzle mounting surface located proximate to a
nozzle inlet opening;
(c) mating together said nozzle mounting surface with said reservoir mounting surface;
(d) allowing a relative, sliding-type movement between said nozzle and reservoir mounting
surfaces due to a differing thermal expansion of said nozzle means relative to said
reservoir means;
(e) sealing the region between said nozzle mounting surface and said reservoir mounting
surface to minimize molten metal leakage therebetween; and
(f) resiliently urging said nozzle mounting surface toward said reservoir mounting
surface to mate said nozzle and reservoir means together.