[0001] The present invention relates to an apparatus for producing metal foil from molten
starting material, the apparatus including a movable, cooled substrate and a nozzle
discharging a short distance from the substrate, by means of which nozzle the molten
material is disposed to be applied to the substrate for cooling, for the formation
of the metal foil.
BACKGROUND ART
[0002] An apparatus of the type described above is previously known from, for example, US-A-4,142,571.
The prior art apparatus has a nozzle directed towards the circumferential surface
of a rotary roller or drum, the opening of the nozzle located a short distance from
the circumferential surface being connected to a reservoir for heated molten metal
material disposed above the nozzle through a slot-shaped nozzle channel connecting
the nozzle opening and the reservoir. The reservoir is connected to a pressure source
by means of which molten material may be urged from the reservoir through the nozzle
channel and the nozzle opening out onto the circumferential surface for cooling, for
the formation of a metal foil.
[0003] It is known that the quality of a metal foil which is produced in accordance with
the above-described so-called Planar Flow Casting technique is greatly dependant upon
and varies with fluctuations in the cooling cycle of the melt. In order to achieve
the desired uniform foil quality, it is thus important that the cooling cycle of the
melt take place under as constant conditions as possible. In this instance, a key
factor is the interface layer of air which accompanies the substrate and which may
readily give rise to air pockets between the melt and the substrate which disrupt
the cooling cycle and are thereby detrimental to quality. In order to avoid or minimize
the risk of quality deterioration caused by such air pockets, the air interface must,
therefore, be displaced, which, in the prior art apparatus, is achieved partly by
the proximity of the nozzle opening to the substrate and partly by the pressure of
the melt forced through the nozzle opening against the substrate. Since the melt pressure
against the substrate displacing the interface layer of air in a given nozzle design
(the slot width of the nozzle channel and nozzle opening) is, in all essentials, dependant
upon the pressure applied to the molten material in the reservoir, the applied pressure
must, hence, be kept above a certain minimum pressure level in order to achieve the
desired air displacement. Since the applied pressure, in a given nozzle design, also
influences the quantity of positively discharged melt and ultimately the thickness
of the finished foil, the pressure should, moreover, be kept as constant as possible
in order to ensure a uniform foil thickness.
[0004] However, the problem inherent in the prior art apparatus is that it is difficult
to avoid pressure variations, for example in connection with replenishment of the
reservoir, which results in corresponding thickness variations in the foil. Another
problem inherent in the prior art apparatus is that it does not wholly unconditionally
make for the production of metal foils of thicknesses below a certain value, eg. 50
µm. As has been explained above, the thickness of the metal foil in a given nozzle
design is, in all essentials, dependant upon the pressure which is applied to the
molten material in the reservoir and which in turn determines the quantity of extruded
melt. In increased quantities of discharged melt, the foil thickness increases, while
consequentially diminishing at the same rate as the quantity of dischargedmelt is
reduced. Thus, when the apparatus is to be switched from producing a metal foil of
a certain thickness to producing a metal foil of another, slighter thickness, the
applied pressure (and thereby the quantity of discharged melt) must thus be reduced
correspondingly. Such a pressure reduction entails, at the same time, that the melt
pressure against the substrate which displaces the interface air layer is reduced,
with resultant increased risk of air pockets between the melt and the substrate, which
disrupt the cooling process and thereby impair the quality of the finished foil. In
order to prevent the reduced melt pressure against the substrate from being lower
than is required for achieving desired air displacement as explained above, a modification
of nozzle design (i.e. nozzle channel and nozzle opening with smaller slot width)
is thus required in the prior art apparatus in order to be able to reduce the discharged
quantity of melt to an extent adapted to the desired foil thickness. However, a nozzle
design with reduced slot width of nozzle channel and nozzle opening is highly sensitive
to and places great demands on the purity of the molten starting material which should,
therefore, be pure and wholly free of large-sized impurities in order to be able to
pass through the nozzle channel and nozzle opening without becoming stuck and clogging
the passage. Consequently, using the prior art apparatus, it is not possible to produce
a metal foil of a thickness of less than 50 µm, for example 10-20 µm, without employing
an extremely pure - and thereby expensive - starting material, which is a contributory
factor in drastically raising the price of the finally produced metal foil.
OBJECTS OF THE INVENTION
[0005] One object of the present invention is, therefore, to propose an apparatus of the
type described by way of introduction which permits production of a metal foil of
desired large (eg. 50 µm) or lesser (eg. 10-20 µm) thickness and with uniform foil
qualities without suffering from the consequential drawbacks of the type inherent
in the prior art apparatus.
[0006] Another object of the present invention is to devize an apparatus of the described
type which makes possible the production of an extremely thin (10-20 um) metal foil
using the cheapest concievable starting material (metal scrap), without the risk of
clogging of the channel and/or the opening in the nozzle employed.
SOLUTION
[0007] These and other objects will be attained according to the present invention in that
an apparatus of the type described in the foregoing has been given the characterizing
feature that a space defined between the substrate and the nozzle is communicable
with a vacuum chamber or a pressure chamber, by means of which molten material supplied
through the nozzle is disposed to be sucked or pressed, respectively, into contact
with the substrate.
[0008] With the aid of the pressure difference created by the vacuum chamber or the pressure
chamber, respectively, in the space between the substrate and the nozzle, it is thus
possible to maintain a sufficiently high, constant melt pressure against the substrate,
i.e. a melt pressure which is wholly independent of both the quantity of the melt
supplied through the nozzle opening and any possible pressure variations occurring
in the inflowing melt. The constant melt pressure realized by the pressure difference
creates extraordinarily good pre-conditions for producing a metal foil of uniform
superior surface qualities, at the same time as naturally also contributing to enhancing
the efficiency of contact between the melt and the substrate, and thereby the cooling
cycle of the melt. A further advantage afforded is that the melt pressure against
the substrate may be kept constant irrespective of the quantity of melt which is supplied,
which implies that metal foils of different, both large and small thicknesses, may
be produced without the need for modifying the design of the nozzle (the slot width
of the nozzle channel and the nozzle opening). Hence, metal foils of very large thicknesses,
eg. above 50 µm, as well as metal foils of very slight thicknesses, eg. 10-20 µm,
may be produced employing one and the same nozzle design. In particular, this entails
that the slot width of the nozzle channel and nozzle opening may be very large, of
the order of 2-3 mm, for which reason the nozzle will be less sensitive, or completely
insensitive, to the purity of the starting material employed, even if metal foils
of very slight thicknesses (10-20 µm) are to be produced.
[0009] Further practical and advantageous embodiments of the apparatus according to the
present invention have moreover been given the characterizing features as set forth
in the appended subclaims.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0010] The present invention will be described in greater detail hereinbelow with particular
reference to the accompanying Drawings, in which:
Fig. 1 schematically illustrates in partial section an apparatus according to one
embodiment of the invention;
Fig. 2 schematically illustrates, on a larger scale, the region of the nozzle opening
in the apparatus of Fig. 1; and
Fig. 3 schematically illustrates, on a larger scale, the region of the opening of
a nozzle according to another preferred embodiment of the apparatus according to the
invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0011] The apparatus according to the present invention which is schematically illustrated
in partial section in Fig. 1 has been given the generic reference numeral 1. The apparatus
1 includes a movable, cooling substrate which, in the illustrated embodiment, consists
of the circumferential or casing surface 2 of a roller or drum 3 rotary about a horizontal
axis in the direction of the arrow A. Adjacent the roller 3, there is disposed a nozzle
4 comprising an upper and a lower nozzle lip 4a and 4b, respectively, which therebetween
form the forward end 5a of a nozzle channel 5 which, at the forward end, discharges
in a slot-shaped nozzle opening 4c (slot width 2-3 mm) directed towards the circumferential
surface 2. The nozzle channel 5 is in communication with a reservoir 6 for molten
starting material 7, eg. metal scrap, and is provided with a rear portion 5b extending
beyond the reservoir 6 and being closed by means of an openable hatch or door 8.
[0012] As is apparent from Fig. 1, the nozzle 4 is arranged so that the nozzle channel 5
inclines somewhat upwardly towards the roller 3 in relation to the horizontal plane,
as is intimated by the angle of inclination∝marked at the rear region of the nozzle.
The nozzle 4 is further arranged so that the nozzle opening 4c discharges a very short
distance (approx. 0.3 mm at the lower nozzle lip 4b and the upper nozzle lip 4a) from
the circumferential surface 2 in a region and on a level below the horizontal axis
of rotation (not shown) of the roller 3, i.e. in a region located within the fourth
quadrant of a coordinate system with zero point in the axis of rotation of the roller.
[0013] In order to make possible run-off of the molten material 7 from the reservoir 6 via
the inclining nozzle channel 5, 5a out through the nozzle opening 4c by force of gravity,
the reservoir 6 is kept filled to such an extent that the surface of the molten material
in the reservoir lies at a level (h) above the nozzle opening 4c. According as the
reservoir 6 is emptied, the surface sinks and, in order to prevent the surface from
sinking to a level flush with the nozzle opening 4c (i.e. h = 0), the reservoir 6
is disposed to be replenishable with new molten material from a tiltable smelting
furnace (not shown) disposed above the reservoir.
[0014] As is apparent from Fig. 2, which schematically illustrates the region of the nozzle
opening 4c on a larger scale, there is provided, between the forward end of the lower
nozzle lip 4b and the circumferential surface 2, a space 9 which is in communication
with or communicable with a vacuum chamber 10. In the illustrated embodiment, the
space 9 is of elongate, slot-shaped design with a substantially constant slot width
(approx. 0.3 mm) throughout its entire axial extent. There is further provided, between
the circumferential surface 2 and the forward end of the upper nozzle lip 4a, a slot-shaped
elongate space 11 of the same slot width (i.e. approx. 0.3 mm) as the space 9. In
order to maintain the molten material 7 at a constant temperature above the melting
point of the material (eg. 950
oC) throughout the entire passage through the channel 5 from the reservoir 6 to the
nozzle opening 4c, heating devices 12, for instance glowing kanthal tubes, are provided
in both the upper and lower nozzle lips 4a, 4b, respectively, by means of which tubes
the molten material is prevented from cooling before exiting from the nozzle 4.
[0015] Fig. 3 shows the discharge portion of a nozzle according to another embodiment of
the present invention and, for purposes of clarity, the same reference numerals as
in Fig. 2 have been employed for corresponding parts, with the addition of a primo
symbol. The nozzle 4' in Fig. 3 thus includes an upper and a lower nozzle 4a' and
4b', respectively, which therebetween define a nozzle channel 5'. Between the forward
end of the lower nozzle lip 4b' and the surface 2' of the substrate, there is provided
a similarly elongate space 9' which is in communication with or communicable with
a vacuum chamber 10'. The space 9' differs from the space 9 of Fig. 2 in that it displays
a rearwardly tapering (seen in the direction of movement of the substrate) or v-shaped
cross section, i.e the distance between the nozzle lip 4b' and the circumferential
surface 2' (the slot width) diminishes in a direction from the nozzle opening 4c'
and rearwardly. The space 11' between the upper nozzle lip 4a' and the surface 2'
is, on the other hand, substantially of constant slot width throughout its entire
axial extent.
[0016] The apparatus 1 in Figs. 1 and 2 produces a web-shaped metal foil 13 in the following
manner. The space 9 is placed in communication with the vacuum chamber 10 and molten
material 7 runs by force of gravity from the reservoir 6 through the nozzle channel
5 out through the nozzle opening 4c for forming a so-called melt puddle 7' in the
region of the nozzle opening. Because of the pressure (eg. 70-90cm water column) which
prevails in the space 9, the rear portion of the melt puddle will be sucked into the
space 9 and thereby against the circumferential surface 2 at constant, sufficiently
high pressure to displace the interface layer of air which accompanies the circumferential
surface moving in the direction of the arrow A (eg. at 30 m/s). On contact with the
cooling (approx. 170
oC) substrate, the melt puddle is cooled from beneath for the formation of a metal
foil 13 accompanying the circumferential surface 2, the metal foil being, after passage
through the space 11, unwound from the circumferential surface and wound up into a
roll of foil.
[0017] Using the apparatus 1, metal foils may be produced in this manner with varying, but
in every individual case uniform thicknesses and of uniform superior surface qualities.
If, for example, a metal foil of a given thickness (50 µm) is desired, the quantity
of supplied melt is correspondingly regulated, while, if a metal foil of a lesser
thickness (10-20 µm) is to be produced, a correspondingly reduced quantity of melt
is supplied. The quantity of melt which is supplied in each individual case is, to
all essentials, determined by the level difference (h) between the surface of the
melt in the reservoir 6 and the nozzle opening 4c, which is easy to regulate by the
controlled supply of new melt from the smelting furnace (not shown).
[0018] In a corresponding manner, a metal foil 13' is produced using the nozzle 4' illustrated
in Fig. 3. The advantage inherent in this nozzle is that the vacuum in the space 9'
need not be of such magnitude as the corresponding vacuum in the space 9 to achieve
the contemplated sufficiently high melt pressure against the circumferential surface
2', since the tapering cross section of the space gives rise to a pressure composant
directed towards the circumferential surface and increasing in a direction rearwardly
from the nozzle opening 4c'. In the same manner as using the nozzle 4, the nozzle
4' can be instrumental in producing metal foils of varying, but in each individual
case uniform thicknesses and of uniform superior surface qualities. For example, a
metal foil may be produced of a thickness of approx. 50 µm by the supply of a certain
adapted quantity of molten material, while a thinner metal foil, eg. of the order
of 10-20 µm, is produced in that the quantity of supplied molten material is kept
at a correspondingly lower level.
[0019] It should finally be observed that the apparatus according to the present invention
may, instead of the vacuum chamber described in the foregoing and specifically shown
on the Drawings, be provided with a pressure chamber between the nozzle and the substrate,
in order to press the melt at constant pressure against the substrate. The pressure
chamber should ideally be disposed ahead of the melt supplied through the nozzle (seen
in the direction of movement of the substrate). Thus, according to the present invention,
the constant high melt pressure against the substrate is catered for by the pressure
difference which the apparatus creates between the nozzle and the substrate and which
is either achieved by means of the space communicable with the vacuum chamber or the
space communicable with the pressure chamber, as described above.
[0020] As will be apparent from the foregoing description, it is possible, according to
the present invention, to produce, from molten starting material, both thick and thin
metal foils using an apparatus which is extremely simple in both design and operative
mode and which, in particular, makes it possible to produce extremely thin metal foils
(10-20 µm) employing the cheapest possible starting material, for example metal scrap,
without the risk of clogging of the nozzle channel and/or nozzle opening because of
particles present in the starting material.
[0021] The present invention should not be considered as restricted to that described above
and shown on the Drawings, many modifications being conceivable without departing
from the spirit and scope of the appended Claims.
1. An apparatus for the production of web-shaped metal foil (13; 13') from molten starting
material (7), the apparatus including a movable, cooling substrate (2; 2') and a nozzle
(4; 4') discharging a short distance from the substrate and by means of which the
molten material is disposed to be applied to the substrate for cooling, for the formation
of the metal foil, characterized in that it is provided, between the nozzle (4; 4') and the substrate (2; 2'), with a space
(9; 9') which, for the purpose of creating a pressure difference between the substrate
and the molten material supplied through the nozzle, is communicable with a vacuum
chamber (10; 10') or a pressure chamber in such a manner that the molten material
is pressed against the substrate by this pressure difference.
2. The apparatus as claimed in Claim 1, characterized in that the space (9; 9') is elongate, with the longitudinal axis of the space substantially
parallel to the substrate.
3. The apparatus as claimed in Claim 2, characterized in that the space (9') tapers in a direction away from the opening (4c') of the nozzle.
4. The apparatus as claimed in any one of the preceding Claims, characterized in that the substrate (2') consists of the circumferential surface of a rotary roller or
drum (3).
5. The apparatus as claimed in Claim 4, characterized in that the nozzle (4; 4') is disposed at a level beneath the axis of rotation of the roller.
6. The apparatus as claimed in any one of the preceding Claims, characterized in that the nozzle (4; 4') includes an upper (4a; 4a') and a lower (4b; 4b') lip which together
define a nozzle opening (4c; 4c') directed towards the substrate (2; 2'), the space
(9; 9') communicable with the vacuum chamber (10; 10') being disposed between the
substrate and the lower lip.
7. The apparatus as claimed in Claim 6, characterized in that the distance between the substrate (2; 2') and the lower lip (4b; 4b') is less than
the distance between the substrate and the upper lip (4a; 4a').
8. The apparatus as claimed in Claim 6 or 7, characterized in that both the upper and the lower nozzle lips include heating devices (12; 12') for maintaining
the nozzle (4; 4') at a temperature in excess of the melting temperature of the starting
material.
9. The apparatus as claimed in any one of the preceding Claims, characterized in that the portion of the channel disposed towards the reservoir (6) has a rear section
extending beyond the reservoir and closed by means of an openable hatch or door (8).