U.S. patent application number 10/195912 was filed with the patent office on 2002-11-28 for process of and apparatus for ingot cooling during direct casting of metals.
Invention is credited to Belley, Luc, Langlais, Joseph.
Application Number | 20020174971 10/195912 |
Document ID | / |
Family ID | 24866728 |
Filed Date | 2002-11-28 |
United States Patent
Application |
20020174971 |
Kind Code |
A1 |
Langlais, Joseph ; et
al. |
November 28, 2002 |
Process of and apparatus for ingot cooling during direct casting of
metals
Abstract
A process and apparatus for producing a cast and cooled metal
ingot. The process comprises: casting a molten metal by a direct
chill casting operation to form a metal ingot emerging from a
mould, and directing one or more streams of liquid coolant onto an
outer surface of the metal ingot adjacent to the mould at positions
spaced around the periphery of the ingot to achieve a rate of heat
extraction from the ingot. The one or more streams of liquid
coolant are orientated at an angle relative to the outer surface of
the ingot, and the angle is varied during the casting operation to
change the rate of heat extraction from the ingot to minimize
cooling-related defects in the cast and cooled ingot.
Inventors: |
Langlais, Joseph;
(Jonquiere, CA) ; Belley, Luc; (Jonquiere,
CA) |
Correspondence
Address: |
Christopher C. Dunham
c/o Cooper & Dunham LLP
1185 Avenue of the Americas
New York
NY
10036
US
|
Family ID: |
24866728 |
Appl. No.: |
10/195912 |
Filed: |
July 15, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10195912 |
Jul 15, 2002 |
|
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09713593 |
Nov 15, 2000 |
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Current U.S.
Class: |
164/487 ;
164/444 |
Current CPC
Class: |
B22D 11/049
20130101 |
Class at
Publication: |
164/487 ;
164/444 |
International
Class: |
B22D 011/124 |
Claims
What we claim is:
1. A process of producing a cast and cooled metal ingot,
comprising: casting a molten metal by a direct chill casting
operation to form a metal ingot emerging from a mould, and
directing one or more streams of liquid coolant onto an outer
surface of said metal ingot adjacent to the mould at positions
spaced around the periphery of the ingot to achieve a rate of heat
extraction from the ingot, wherein said one or more streams of
liquid coolant are orientated at an angle relative to the outer
surface of the ingot, and said angle is varied during said casting
operation to change said rate of heat extraction from said ingot to
minimize cooling-related defects in said cast and cooled ingot.
2. The process of claim 1 wherein the said angle may be varied
continuously.
3. A process of producing a cast and cooled metal ingot,
comprising: casting a molten metal by a direct chill casting
operation to form a metal ingot emerging from a mould, and
directing one or more streams of liquid coolant onto an outer
surface of said metal ingot adjacent to the mould at positions
spaced around the periphery of the ingot to achieve a rate of heat
extraction from the ingot, wherein said one or more streams of
liquid coolant are orientated at an angle relative to the outer
surface of the ingot, and said angle is varied during said casting
operation to change said rate of heat extraction from said ingot to
minimize cooling-related defects in said cast and cooled ingot and
wherein each of the said one or more streams is formed by the
combination of two or more streams internally within the mould to
form a single stream exiting the mould.
4. A process of producing a cast and cooled metal ingot,
comprising: casting a molten metal by a direct chill casting
operation to form a metal ingot emerging from a mould, and
directing one or more streams of liquid coolant onto an outer
surface of said metal ingot adjacent to the mould at positions
spaced around the periphery of the ingot to achieve a rate of heat
extraction from the ingot, wherein said one or more streams of
liquid coolant are orientated at an angle relative to the outer
surface of the ingot, and said angle is varied during said casting
operation to change said rate of heat extraction from said ingot to
minimize cooling-related defects in said cast and cooled ingot,
with the angle being varied in response to at least one measured
parameter of the casting system.
5. The process of claim 4 wherein the said at least one measured
parameter is selected from the group including ingot surface
temperature measurement, metal sump temperature, starter block
position, casting speed and coolant property.
6. A process as in claim 5 wherein the said coolant property is the
coolant quenchability factor.
7. A process as in claim 5 wherein the said ingot surface
temperature measurement is measured at a predetermined distance
from the point at which the said streams of coolant impinge on the
outer surface of the ingot after the cast has reached a steady
state.
8. A process of producing a cast and cooled metal ingot,
comprising: casting a molten metal by a direct chill casting
operation to form a metal ingot emerging from a mould, and
directing one or more streams of liquid coolant onto an outer
surface of said metal ingot adjacent to the mould at positions
spaced around the periphery of the ingot to achieve a rate of heat
extraction from the ingot, wherein said one or more streams of
liquid coolant are orientated at an angle relative to the outer
surface of the ingot, and said angle is varied during said casting
operation to change said rate of heat extraction from said ingot to
minimize cooling-related defects in said cast and cooled ingot and
wherein the said one or more streams of liquid coolant exit the
mould along a single line.
9. The process of claim 8 wherein the said single line is selected
from the group consisting of a straight line, and a curve having no
more than three inflection points on one side of the mould.
10. The process of claim 1 wherein each individual stream of said
one or more streams is produced by passing liquid coolant through
at least two channels, each channel being orientated at a different
angle with respect to said surface of said ingot, and combining
said coolant from said channels at a common outlet of said channels
to produce said individual stream.
11. The process of claim 10 wherein said angle of said one or more
streams relative to the outer surface of the ingot is varied by
changing the relative flow of the coolant in said at least two
channels provided for each individual stream.
12. Apparatus for producing a cast and cooled metal ingot,
comprising: a direct chill casting mould having an annular body
defining a casting cavity, for casting molten metal into a metal
ingot having a periphery, and a mould outlet from which said metal
ingot emerges as casting proceeds during a casting operation, one
or more openings in said annular body adjacent to said mould outlet
for directing one or more streams of liquid coolant onto an outer
surface of said metal ingot at positions spaced around the
periphery of the ingot to achieve a rate of heat extraction from
the ingot, and an orientating arrangement within said annular body
for orientating said one or more streams emerging from said
openings at an angle relative to the surface of the ingot, and for
enabling variation of said angle as said casting operation proceeds
to minimize cooling-related defects in the cast and cooled
ingot.
13. Apparatus as in claim 12 wherein the said orienting arrangement
causes the said angle of the said one or more streams to be
continuously variable.
14. Apparatus for producing a cast and cooled metal ingot,
comprising: a direct chill casting mould having an annular body
defining a casting cavity, for casting molten metal into a metal
ingot having a periphery, and a mould outlet from which said metal
ingot emerges as casting proceeds during a casting operation, one
or more openings lying along a single line in said annular body
adjacent to said mould outlet for directing one or more streams of
liquid coolant onto an outer surface of said metal ingot at
positions spaced around the periphery of the ingot to achieve a
rate of beat extraction from the ingot, and an orientating
arrangement within said annular body for orientating said one or
more streams emerging from said openings at an angle relative to
the surface of the ingot, and for enabling variation of said angle
as said casting operation proceeds to minimize cooling-related
defects in the cast and cooled ingot.
15. Apparatus according to claim 14 wherein the single line is
selected from the group consisting of a straight line and a curve
have three or less inflection points along a side of the said
mould.
16. Apparatus for producing a cast and cooled metal ingot,
comprising: a direct chill casting mould having an annular body
defining a casting cavity, for casting molten metal into a metal
ingot having a periphery, and a mould outlet from which said metal
ingot emerges as casting proceeds during a casting operation, one
or more openings in said annular body adjacent to said mould outlet
for directing one or more streams of liquid coolant onto an outer
surface of said metal ingot at positions spaced around the
periphery of the ingot to achieve a rate of heat extraction from
the ingot, and an orientating arrangement within said annular body
for orientating said one or more streams emerging from said
openings at an angle relative to the surface of the ingot, and for
enabling variation of said angle as said casting operation proceeds
to minimize cooling-related defects in the cast and cooled ingot
and wherein the said orienting arrangement comprises, for each of
the said one or more openings, two or more internal channels that
meet internally within the mould body to form a single channel
before exiting the mould.
17. Apparatus according to claim 12 wherein the said orienting
arrangement is selected from the group consisting of a hydraulic
means, a mechanical means, or a pneumatic means.
18. Apparatus for producing a cast and cooled metal ingot,
comprising: a direct chill casting mould having an annular body
defining a casting cavity, for casting molten metal into a metal
ingot having a periphery, and a mould outlet from which said metal
ingot emerges as casting proceeds during a casting operation, one
or more openings in said annular body adjacent to said mould outlet
for directing one or more streams of liquid coolant onto an outer
surface of said metal ingot at positions spaced around the
periphery of the ingot to achieve a rate of heat extraction from
the ingot, and an orientating arrangement within said annular body
for orientating said one or more streams emerging from said
openings at an angle relative to the surface of the ingot, and for
enabling variation of said angle as said casting operation proceeds
to minimize cooling-related defects in the cast and cooled ingot,
said orienting means being controlled so as to cause the angle of
impingement on the said one or more coolant streams to vary in
response to one or more measured casting parameters.
19. Apparatus according to claim 18 wherein the said at least one
measured parameter is selected from the group including ingot
surface temperature measurement, metal sump temperature, stool cap
position, casting speed and coolant property.
20. Apparatus according to claim 19 wherein the said coolant
property is the coolant quenchability factor.
21. Apparatus according to claim 19 wherein the said ingot surface
temperature measurement is measured at a predetermined distance
from the point at which the said streams of coolant impinge on the
outer surface of the ingot after the cast has reached a steady
state.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to the cooling of ingots as they are
formed during metal casting procedures. More particularly, the
invention relates to cooling processes and apparatus that allows
the cooling effect to be varied at different times during the
casting process.
[0003] 2. Background Art
[0004] Direct chill (DC) casting of metals is a well known
procedure that is frequently used for the formation of ingots (i.e.
elongated bodies, sometimes also called billets or slabs) of
non-ferrous metals, such as alloys of aluminum, zinc, magnesium,
etc. The DC casting procedure can be done in the vertical or
horizontal direction. In the vertical procedure, molten metal is
poured into the top of an annular mould and quickly caused to
solidify (at least at the periphery) before the metal exits the
bottom of the mould as an ingot. The procedure is commenced by
positioning a bottom block in the lower opening of the mould during
the initial pouring step, and then lowering the bottom block at a
suitable rate of descent to allow the ingot shell to form and
solidify before it exits the mould. Due to the vertical nature of
the such a casting procedure, the emerging ingot normally descends
into a pit positioned beneath the casting apparatus, and ingots
having a length of 10 to 12 m are normally produced before the
casting procedure is repeated. Horizontal casting procedures are
similar in that a starter-block is used in the opening of a
horizontally oriented annular mould until the initial mould fill
occurs at which time the starter-block is displaced horizontally.
In horizontal DC casting an essentially continuous ingot is
produced, which is then sawn to length as required.
[0005] The annular mould has a mould body normally defining a
rectangular casting cavity for producing ingots of rectangular
cross-section. The mould body may also be circular, square or any
other suitable shape. The mould body usually has a hollow interior
through which a liquid coolant (e.g. water) may be passed to
provide primary cooling for the metal. The mould body has a mould
surface that contacts and shapes the outer periphery of the ingot
as it is being formed. In addition, casting apparatus of this kind
is provided with a means of secondary cooling (often referred to as
direct cooling) of the metal. For example, jets of water or other
liquid coolant are directed onto the outer surfaces of the metal
ingot as the ingot emerges from the mould. This provides the bulk
of the ingot cooling and has a major effect on the ingot
microstructure.
[0006] However, different rates of cooling of the ingot are
required at different stages of ingot formation. The start of the
casting operation is referred to as the start-up phase (often
referred to as the butt-forming stage) when the bottom or starter
block is positioned at the mould opening and is initially
displaced. After this initial stage, steady state casting may
commence and continue until the ingot is fully formed. During the
start-up phase, heat extraction from the ingot must be lower than
in the steady state casting phase in order to prevent various
problems and defects, e.g. excessive ingot butt curl, hot/cold
fissures, tearing, cold-shut, run out, bleeding, etc. As
steady-state casting commences, the rate of heat extraction can be
increased. However, even during steady-state casting, the cooling
requirements may change due to changes in the casting rate or
surface characteristics of the ingot microstructure.
[0007] There are several ways by which the rate of heat extraction
can be varied. For example, the amount of cooling liquid may be
varied during different production phases, or jets of water may be
pulsed (rapidly turned on and off) at different rates at different
phases to achieve different rates of cooling. Alternatively or
additionally, air or other gases may be entrained or dissolved in
the liquid jets in different amounts to modify the effective heat
transfer co-efficients of the coolant at different times. However,
such methods usually do not produce even cooling effects and can
therefore give unsatisfactory results. They are difficult to
control and produce variable results.
[0008] An alternative arrangement is disclosed in U.S. Pat. No.
5,582,230, which issued on Dec. 10, 1996 to Robert B. Wagstaff, et
al. and was assigned to Wagstaff, Inc. In this apparatus, the mould
body is provided with two series of channels staggered relative to
each other around the periphery of the lower end of the mould body
so that cooling water can be directed as individual streams onto
the emerging ingot surface. The channels of the first series are
all oriented to produce water streams that impinge against the
ingot surface at angles of 45 degrees, and the channels of the
second series are all orientated to produce water streams that
impinge against the ingot surface at angles of 22.5 degrees.
Because of the high angle of incidence of the 45 degree streams,
substantial portions of the coolant rebounds from the ingot surface
and form a region of spray directly in the path of the 22.5 degree
streams. The effect is to widen the bands of turbulence in the
coolant layers in contact with the ingot and to minimize or
eliminate regions of laminar flow of the coolant. By combining
streams of 45 degrees and 22.5 degrees in this way during the
steady-state phase of casting greater heat extraction can be
achieved than in the initial phase, when only the 22.5 degree
streams are employed. However, the degree of control of the rate of
heat extraction is still rather unsatisfactory, and the transition
from the 22.5 degree to 45 degree jet may cause disturbances to the
ingot, since there is an abrupt change in the heat transfer
coefficient as soon as the 45 degree jet is started.
[0009] U.S. Pat. No. 4,351,384, which issued on Sep. 28, 1982 to
David G. Goodrich, and was assigned to Kaiser Aluminum &
Chemical Corporation, also makes use of streams of water arranged
at different angles to the ingot surface to achieve direct cooling.
This patent is particularly concerned with electromagnetic DC
casting in which an electromagnetic effect is used to hold the
solidifying metal a slight distance away from the casting surface
of the annular mould. The invention is concerned in particular with
defects that are characteristic of electromagnetic DC casting. The
coolant streams at different angles are directed to the ingot so as
to intersect a short distance away from the metal surface. By
controlling the velocity and/or volume of one or both of the
coolant streams, the point of impact of the coolant with the metal
surface can be brought closer to the discharge point of the mould,
which is desirable to prevent defects during the start of casting
in the electromagnetic process. By causing the two streams issuing
from the mould to intersect before they strike the ingot surface,
the increased turbulence increases the tendency for the coolant to
remain on the ingot surface.
[0010] Despite these approaches to cooling modification during DC
casting, there is still a need for an improved way of varying
direct cooling effects to allow the formation of cast ingots of
high quality and achieve a better control of the cooling,
especially in the transition from the startup to the steady
state.
SUMMARY OF THE INVENTION
[0011] An object of the invention is to facilitate variation of
cooling of an ingot during DC casting at different times during the
casting procedure.
[0012] Another object of the invention is to provide an improved
means to control the cooling of an ingot during the casting
procedure.
[0013] According to one aspect of the invention, there is provided
a process of producing a cast and cooled metal ingot, comprising
casting a molten metal by a direct chill casting operation to form
a metal ingot emerging from a mould, and directing one or more
streams of liquid coolant onto an outer surface of the metal ingot
adjacent to the mould at positions spaced around the periphery of
the ingot to achieve a rate of heat extraction from the ingot. The
one or more streams of liquid coolant are orientated at an angle
relative to the outer surface of the ingot, and the angle is varied
during said casting operation to change the rate of heat extraction
from said ingot.
[0014] The angle of the liquid coolant streams is preferably varied
continuously during said casting operation. It is preferably in
between predetermined limits and is preferably varied in response
to at least one measured parameter of the casting system. The
liquid coolant streams preferably exit the mould along a single
line, which may be a straight line, or a simple curve. Preferably,
each of the one or more streams is formed by the combination of two
or more streams internally within the mould to form a single stream
exiting the mould.
[0015] According to a preferred embodiment, this provides a process
of producing a cast and cooled metal ingot, comprising: casting a
molten metal by a direct chill casting operation to form a metal
ingot emerging from a mould, and directing one or more streams of
liquid coolant onto an outer surface of the metal ingot adjacent to
the mould at positions spaced around the periphery of the ingot to
achieve a rate of heat extraction from the ingot. The said one or
more streams of liquid coolant are orientated at an angle relative
to the outer surface of the ingot, and the angle is varied during
said casting operation to change said rate of heat extraction from
said ingot to minimize cooling-related defects in said cast and
cooled ingot. Each of the one or more streams is formed by the
combination of two or more streams internally within the mould to
form a single stream exiting the mould.
[0016] It is further preferred that the one or more streams of
liquid coolant exit the mould along a single line.
[0017] According to another aspect of the invention, there is
provided an apparatus for producing a cast and cooled metal ingot,
comprising: a direct chill casting mould having an annular body
defining a casting cavity, for casting molten metal into a metal
ingot having a periphery, and a mould outlet from which said metal
ingot emerges as casting proceeds during a casting operation. One
or more openings are provided in the annular body adjacent to the
mould outlet for directing one or more streams of liquid coolant
onto an outer surface of the metal ingot at positions spaced around
the periphery of the ingot to achieve a rate of heat extraction
from the ingot. An orientating arrangement is provided within the
annular body for orientating the one or more streams emerging from
the openings at an angle relative to the surface of the ingot, and
for enabling variation of the angle as the casting operation
proceeds.
[0018] In the above apparatus, the orienting arrangement preferably
causes the angle of the one or more streams to vary continuously.
The one or more openings preferably lie along a single line, which
may be a straight line or a simple curve.
[0019] Preferably, the orienting arrangement comprises, for each of
the one or more openings, two or more internal channels that meet
internally within the mould body to form a single channel before
exiting the mould. This orienting means is controlled so as to
cause the angle of impingement on the one or more coolant streams
to vary in response to one or more measured casting parameters. The
orienting arrangement is preferably selected from the group
consisting of a hydraulic means, a mechanical means, or a pneumatic
means or a combination of such means.
[0020] Thus, a further preferred embodiment comprises an apparatus
for producing a cast and cooled metal ingot, comprising: a direct
chill casting mould having an annular body defining a casting
cavity, for casting molten metal into a metal ingot having a
periphery, and a mould outlet from which the metal ingot emerges as
casting proceeds during a casting operation. One or more openings
are provided in the annular body lying in a single line adjacent to
said mould outlet for directing one or more streams of liquid
coolant onto an outer surface of the metal ingot at positions
spaced around the periphery of the ingot to achieve a rate of heat
extraction from the ingot. An orientating arrangement is provided
within the annular body for orientating the one or more streams
emerging from the openings at an angle relative to the surface of
the ingot, and for enabling variation of the angle as the casting
operation proceeds to minimize cooling-related defects in the cast
at an angle relative to the surface of the ingot, and for enabling
variation of the angle as said casting operation proceeds to
minimize cooling-related defects in the cast and cooled ingot.
[0021] According to a further preferred embodiment, the above
orienting arrangement comprises, for each of the one or more
openings, two or more internal channels that meet internally within
the mould body to form a single channel before exiting the
mould.
[0022] The one or more streams of liquid coolant may comprise a
plurality of streams of coolant or only a single stream of coolant
from a continuous slot outlet running around the mould periphery.
The single slot outlet may be connected to a series of internal
coolant channels or to a pair of internal slot-like coolant
channels.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a simplified sketch showing a casting and cooling
operation using apparatus according to one preferred form of the
present invention;
[0024] FIG. 2 is a cross-section of the annular body of the mould
at one side of the apparatus as shown in FIG. 1;
[0025] FIG. 3 is a cross-section of the annular body of the mould
at one side of the apparatus as shown in FIG. 1 illustrating a
further embodiment of the present invention;
[0026] FIG. 4 is a view similar to FIG. 1 showing a position where
coolant liquid is supplied to the upper chamber of the annular
body;
[0027] FIG. 5 is an underneath plan view of the annular body of
FIG. 1;
[0028] FIG. 6 is an additional schematic view showing how the
coolant exit holes in the annular body of FIG. 1 may be placed;
[0029] FIG. 7 is a partial view on an enlarged scale of part of the
annular body of FIG. 5;
[0030] FIG. 8 is a partial cross-section of the part of the annular
body of FIG. 6 rotated through 90 degrees, and also showing part of
an adjacent cast ingot;
[0031] FIG. 9 is a cross-section of the annular body of the mould
at one side of the apparatus showing further embodiment of the
present invention; and
[0032] FIG. 10 is a cross-section of the annular body of the mould
showing yet a further embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] FIG. 1 of the accompanying drawings shows a simplified
representation of a casting and cooling operation according to the
present invention employing apparatus according to one preferred
embodiment. The illustrated embodiment is particularly suited for
casting and cooling aluminum and aluminum alloys, but could be
employed with other metals capable of being DC cast.
[0034] This apparatus (which in this embodiment is arranged for
so-called vertical casting, i.e. for casting operations wherein the
ingot descends vertically from the mould as it is cast) includes an
axially vertical annular mould 10 (open at its upper and lower ends
11 and 12, respectively) to which molten metal 14 is supplied
through a dip tube 15 for casting an ingot 20. The mould 10 is in
the form of an annular body 18. The annular body 18 has a vertical
inner wall 19 providing a casting surface 21 of desired horizontal
cross-section (in this case, rectangular). A parting layer
(lubricant) may be applied to the casting surface 21 to reduce
sticking. The casting surface 21 defines a casting cavity 22 for
the molten metal. It will be understood that the inner wall
configuration determines the cross-sectional shape of the resulting
ingot.
[0035] The lower end of the mould 10 is provided with a plurality
of outlets through which a cooling liquid 28 is projected as
individual streams onto the outer periphery 29 of the ingot 20
immediately adjacent to the mould 10 for extracting heat from the
ingot emerging from the mould to cool and solidify the metal. This
cooling arrangement is described in more detail later.
[0036] At the start of a casting operation, the lower end of the
casting cavity is closed by a bottom block 30, which is supported
by a hydraulic ram 31. As molten metal poured into the casting
cavity 22 solidifies at the lower end of the cavity, the bottom
block 30 is drawn vertically downwards by operation of the ram 31.
The solidifying base of the ingot 20 being cast, then resting on
the bottom block 30, then begins to emerge from the lower end of
the casting cavity 22.
[0037] Molten metal is continuously supplied to the upper end of
the casting cavity 22 through dip tube 15 that opens downwardly
into an upper portion of the casting cavity 22, so as to maintain
the pool of molten metal 14 in the casting cavity at a
substantially constant level as the solidifying ingot is
progressively withdrawn from the mould, i.e. as the bottom block 30
is moved downwardly.
[0038] During the DC casting operation thus described, molten metal
14 within the casting cavity 22 solidifies around the periphery of
the casting surface 21 and is cooled in part by heat transfer to
the externally chilled mould inner wall 19 but mainly by
impingement of coolant 28 directly on the initially formed solid
shell. This solidification progresses sufficiently far inward
towards the centre of the mould that the ingot emerging from the
lower end of the mould has an externally solid and self-sustaining
shell 33 even though the central portion or core 34 of the emerging
ingot is still molten. With an effectively continuous supply of
molten metal to the mould, and correspondingly continuous downward
advance of the cast ingot from the mould, the molten central core
34 of the ingot emerging from the mould extends downwardly as a
molten metal sump (constituting the lower end of the molten metal
pool in the mould) of progressively decreasing cross-section in the
downward direction, until the ingot becomes entirely solid.
[0039] The mould 18 contains two internal chambers 54, 55 used to
provide cooling to the mould body and to deliver coolant 28 via
channels 60, 61 to impinge on the ingot surface. The arrangement of
internal chambers and channels is described in detail in the
following.
[0040] A source of coolant is provided to each chamber via pipes
83, 84 and control valves 81, 82.
[0041] FIG. 2 is an enlarged cross-sectional view of the annular
mould body 18 as shown at the left-hand side of the apparatus of
FIG. 1. The mould body 18 is made up of three main pieces, a
central portion 37, and top and bottom plates 38 and 39,
respectively. These pieces are held together by upper and lower
bolts, 40 and 41, respectively, that pass through sleeves 42 and
43, respectively, and are secured at their free ends 44 and 45,
respectively, in opposite ends of a threaded hole 46 located in a
central divider 47 of the central portion 37. The enlarged heads 48
and 49, respectively, of the bolts 40 and 41 are recessed as shown
in short bores 51 and 52, respectively, in the top and bottom
plates 38 and 39. Elastomeric O-ring seals 53, 54 and 55 are
provided between the central portion 37 and the top and bottom
plates 38 and 39 to prevent leakage of coolant.
[0042] The central portion 37, in cooperation with the top and
bottom plates 38 and 39, forms upper and lower chambers, 54 and 55,
respectively, within the annular body 18. These chambers are
separated from each other by the central horizontal divider 47. The
chambers each continuously encircle the central casting cavity 22
of the mould, but are separate from each other. At regularly spaced
positions around the annular mould 18, coolant channels 60 and 61
are provided within the central portion 37 of the mould. At their
respective inner ends, coolant channels 60 communicate with the
upper chamber 54, and coolant channels 61 communicate with lower
chamber 55 via narrow cross channels 64 and 65, respectively.
Larger encircling grooves 66 and 67, provided for ease of
manufacture, are sealed by O-rings 68 and 69, respectively. The
channel 60 from the upper chamber 54 is orientated downwardly and
inwardly at an angle of 22 degrees relative to the vertical casting
surface 21 (i.e. relative to the adjacent surface 29 of the ingot
20). The channel 61 from the lower chamber 55 is orientated
downwardly and inwardly at an angle of 45 degrees to the vertical
casting surface 21.
[0043] In all cases, the outer ends 68 and 69 of the channels 60
and 61 overlap or coincide to form a single combined outlet 70 for
both channels. The single outlet 70 is located in an inwardly and
downwardly sloping undercut wall 72 at the lower end of the casting
surface 21. The horizontal distance between the inner and outer
ends of the undercut wall (as shown by arrows A) is typically about
6 mm. The inner end surface of the bottom plate 39 slopes slightly
outwardly and downwardly at 73 (e.g. at an angle of typically 12 to
15 degrees to the vertical) beneath the undercut wall 72. The
horizontal distance and angle is chosen to avoid any tendency for
the coolant streams to "attach" to the mould wall, particularly
when they are directed downwards at the smallest angles from the
vertical. The channels 60 and 61 may be in the form of circular
holes and join to form a single outlet 70. However, adjacent single
outlets may be joined together to form a continuous slot, such a
continuous slot being fed from several pairs of channels 60 and 61.
Alternatively, channels 60 and 61 may be elongated slot like
channels joining to form a single elongated slot outlet 70.
[0044] FIG. 3 is an enlarged cross-sectional view of the annular
mould body 18 as shown at the left-hand side of the apparatus of
FIG. 1, but shows a further preferred embodiment of the invention.
The embodiment is similar to that illustrated in FIG. 2 except for
the following details. Baffle plates 100 and 101 are placed within
the upper and lower chambers 54, 55 mounted at one end within
grooves machined in the top and bottom faces of central portion 37
and sealed with elastomeric seals 102, 103 against the top and
bottom plates 38 and 39. The baffle plates divide each of the
chambers 54, 55 into an outer section 54a, 55a and an inner section
54b, 55b. Each baffle plate is provided with a series of uniformly
spaced, uniformly sized holes 104, 105 to provide fluid
communication between the outer and inner sections. The coolant
channels 60 and 61 as previously described terminate in the inner
section of the upper and lower chambers. Coolant is delivered to
the outer sections of the upper and lower chambers, and flows
through the holes in the baffle plate to the inner sections and
from there via to coolant channels to the exterior of the
mould.
[0045] FIG. 4 shows how cooling liquid 26 can be supplied to the
upper chamber 54 from below. A tubular element 75 passes through a
hole 76 in bottom plate 39, completely through the lower chamber 55
and the central divider 47, and communicates with the upper chamber
54 at the free end 77 thereof. Elastomeric O-rings 78 and 79 seal
the tubular element 75 to prevent coolant leakage from the lower
and upper chambers 55 and 54. The tubular element 75 is attached at
its outer end 80 to a coolant supply pipe (not shown) so that
coolant can be supplied under pressure to the upper chamber 54.
[0046] Coolant is supplied to the lower chamber 55 from below in a
similar manner via a tubular element (not shown) that extends
through the bottom plate 39 into the lower chamber 55.
[0047] FIG. 5 is an underneath plan view of the annular body 18 of
the previous drawings showing the outlet (lower) side of the mould.
As shown, the annular body 18 and the casting cavity 22 are
rectangular so that an ingot (not shown) of rectangular
cross-section is produced. The vertical casting surface 21
terminates at the sloping undercut wall 72 in which the combined
outlets 70 of the channels 60 and 61 (not visible in FIG. 4) are
located. As shown, these outlets 70 are spaced at regular intervals
around the periphery of the casting cavity 22. The tapering inner
end wall 73 of the bottom plate 39 are also visible in this view.
The outlets also all lie in a single line, i.e. do not lie
vertically one above the other. In the case of circular moulds, the
single line is most often a straight line. In FIG. 5, the outlets
70 are all shown to lie on a single straight line along each side
of the rectangular. However, in such moulds, or in square, T-shaped
and similar moulds, the single line may be most advantageously in
the form of a simple curve particularly along the long faces of the
ingot.
[0048] Although the outlets lie on a single line, that line can be
in the form of any convenient curve. FIGS. 6A-6D show in
exaggerated form preferred embodiments of the kinds of single lines
that may be employed. FIG. 6A shows a straight line (as used in
FIG. 5). FIGS. 6B through 6D show various curved lines that may be
employed along a side (generally the long side) of a rectangular
mould. FIGS. 6B and 6C illustrate forms of such lines have a single
maximum or minimum along a side of the mould, and FIG. 6C shows a
form having three maxima or minima, which is the maximum number of
such points that would be used along each side of a mould.
[0049] The secondary or direct cooling of the ingot is effected by
streams 28 of liquid coolant (see FIG. 1) exiting outlets 70 and
contacting the periphery 29 of the ingot 20 emerging from the
annular body 18. Although each of these streams contains coolant
from both channels 60 and 61, only a single stream 28 of coolant
liquid emerges from each outlet 70 and projects onto the ingot 20.
The angle at which each stream is projected against the ingot 20 is
determined by the relative rate of flow of coolant liquid in the
channels 60 and 61. When the rate of flow through the upper channel
60 is much greater than the flow through the lower channel 61, the
stream 28 emerges from the outlet 70 at an angle similar to the
angle of the upper channel 60, i.e. 22 degrees. On the other hand,
when the rate of flow of coolant through the lower channel 61 is
much greater than the rate of flow through the upper channel 60,
the stream emerges from the outlet 70 at an angle that approximates
the angle of the lower channel, i.e. 45 degrees. Relative flow
rates intermediate these two conditions produce streams that emerge
at particular angles within the range of 22 to 45 degrees.
[0050] The relative rates of flow of coolant through the channels
60 and 61 is controlled by valves 81 and 82 and in the coolant
supply lines 83 and 84 to the chambers 54 and 55 within the annular
body 18 (see FIG. 1). These lines are fed with coolant from a pump
85 fed with cooling liquid 26, after filtration, from a sump (not
shown) where coolant collects after use. Fresh coolant may be added
to the sump to replace coolant lost to evaporation. The relative
rates of flow may be adjusted either to maintain a constant total
flow or allow variations in total flow as well as the relative
flow.
[0051] Two flow valves 81 and 82 may be used for control as
described above. However, it is possible as well to leave the valve
81 (controlling coolant flow to the upper chamber and to the
channel at 22 degrees) fully open at all times (or even eliminated
altogether), and control the angle of coolant stream exiting the
mould solely by adjusting valve 82 (controlling the flow through
the channel at 45 degrees).
[0052] Since the angle of contact of the streams 28 with the
periphery 29 of the ingot can be varied at will within the range of
angles mentioned above, and since the rate of heat extraction of
the ingot is dependent on the angle of the streams 28, the rate of
cooling of the ingot can be varied during the casting operation. As
noted above, it is generally necessary in DC casting to reduce the
rate of cooling during the initial start-up procedure (when the
bottom block 30 may be moving slowly) as the ingot butt emerges
from the mould, and then to increase the rate of cooling during the
steady state casting operation. It may sometimes be desirable to
vary the rate of cooling during the steady state casting operation,
e.g. if the surface of the ingot becomes unusually hot or cool, or
if undesirable surface effects appear.
[0053] As shown in FIG. 1, it may be desirable to link the control
of the angle of the streams 28 with apparatus for measuring casting
parameters such as ingot surface temperature, metal sump
temperature, casting rate, starter block position, or coolant
properties. A coolant property may include coolant temperature,
coolant chemical composition, including gas content, or coolant
quenchability coefficient. In FIG. 1 apparatus for measuring
surface temperature and for measuring coolant quenchability
coefficient is shown. Thus, a temperature sensor 90 may be provided
in permanent or temporary contact with the surface of the ingot 20
at a suitable distance from the lower end 12 of the mould 10.
Signals from the temperature sensor may fed via line 91 to a
controller 92 (e.g. a computer) that adjusts the relative flow
rates of coolant in the channels 60 and 61 by actuating the flow
control valves 81 and 82 via lines 93 and 94. The rate of
adjustment required for any sensed temperature may be programmed
into the controller 92 for filly automatic operation. An apparatus
for measuring ingot surface temperature is described for example in
U.S. Pat. No. 6,056,041 assigned to Alcan International Limited and
incorporated herein by reference. The preferred location for
measuring the ingot surface temperature is at a predetermined
location with respect to the point at which the coolant stream 26
impinges on the ingot outer surface once the steady state casting
has been achieved (sometimes referred to as the "normal" secondary
coolant impingement point).
[0054] Similarly the quenchability coefficient of the coolant
stream can be measured by extracting a portion 95 of the coolant
stream 26 and passing it through an apparatus 96 for measuring this
coefficient. An apparatus for measuring coolant quenchability
coefficients is described for example in U.S. Pat. No. 5,918,473
assigned to Alcan International Limited and incorporated herein by
reference. The output signal from the coolant quenchability
apparatus may be similarly fed via line 97 to the controller
92.
[0055] The surface temperature and coolant quenchability
coefficient may be used alone or in combination with each other or
with other measured parameters to continuously control the angle of
the coolant discharging on the ingot surface and thereby
continuously and smoothly control the rate of heat removal.
[0056] Although, in the above embodiment, the upper channel is set
at an angle of 22 degrees to the ingot surface 29 and the lower
channel is set at an angle of 45 degrees, the angles of these
channels may be varied, if required. For example, the angle of the
lower channel 61 may be chosen from the range of greater than the
angle of the upper channel 60 up to about 90 degrees but preferably
up to about 60 degrees. The upper channel 60 may be chosen from a
range of less than the angle of the lower channel 61 to a minimum
of about 15 degrees (more preferably, a minimum of about 18
degrees). The angles of the upper and lower channels should, of
course, be sufficiently different that a large variation in the
angle of the emerging coolant stream may be obtained.
[0057] As shown more clearly in FIGS. 7 and 8, the outer ends 68
and 69 of upper and lower channels 60 and 61 coincide at a common
outlet 70. The ends of each channel 60 and 61 may be perfectly
concentric at the common outlet 70, but there may be some variation
as long as there is a significant overlap. Most preferably, the
centre X of the end of one channel does not extend beyond the
periphery Y of the end of the other channel. When this occurs, the
outlet 70 may take on the shape of a "figure of 8", i.e. with a
substantially narrow waist portion positioned between two enlarged
ends. The two channels 60 and 61 actually become one single channel
at a distance B from the outlet 70 within the annular body 18. This
distance B depends in practice on geometrical factors, e.g. the
diameters of the channels and the angle of their convergence.
[0058] The stream 28 preferably has a diameter (or approximate
diameter as the stream may not be quite cylindrical) in the range
of about 3-13 mm, and preferably about 5 mm. The number of outlets
70 provided around the casting cavity 22 of the mould may be the
same as in a conventional mould, e.g. evenly spaced with a distance
of 4 to 12 mm centre to centre.
[0059] The outlets 70 are preferably formed in undercut sloping
surfaces 72 so that the streams 28 emerge from the annular body at
a steep angle to the adjacent surface 72 and at a distance C from
the adjacent surface 29 of the ingot. This distance allows the
coolant to emerge as the required single streams and to impinge
upon the metal surface at a distance D from the lower end of the
casting surface 21 of the mould.
[0060] The sloping wall 73 immediately below the outlets 70
preferably slopes rearwardly and downwardly away from the outlets
70 to prevent coolant streams from "attaching" to this surface and
therefore emerging at an incorrect angle of approach.
[0061] It would be possible to combine more than two channels, e.g.
three channels, for even finer control over the angle of the
emerging single combined stream 28, in which case the annular body
would be provided with three coolant chambers. However, it is
normally suitable to combine just two streams, as in the
illustrated embodiment.
[0062] As noted above, the relative rates of flow of coolant liquid
through the respective channels 60 and 61 is adjusted to manipulate
the angle of the resulting single streams emerging from the outlets
70. It is preferable always to maintain at least a minimum rate of
flow in each channel 60 and 61, i.e. the flow to one of the
channels 60 or 61 should preferably not be entirely shut off or a
venturi effect may be created, drawing liquid or air from the
closed channel, and causing an uneven liquid flow from the outlet
70.
[0063] The above description represents the preferred embodiment of
the coolant stream orienting arrangement of this invention. Other
orienting arrangements may also be used.
[0064] In FIG. 9, the annular mould body 110 is provided with a
single internal chamber 111. The chamber communicates with the
mould exterior via a tapered channel 112 which terminates in a
series of holes 113 or a continuous slot for delivering coolant to
the surface of the ingot. The upper wall of the chamber 112 is set
at an angle of 22 degrees from the vertical and the lower wall at
an angle of 45 degrees from the vertical. A deflecting plate 114 is
mounted within the tapered channel on a pivot 115 located near the
end adjacent the holes 113. An internal baffle 117, containing
uniform, spaced holes 118, in mounted within the chamber 111 and
divides it into an inner section 111a and an outer section 111b.
Coolant is delivered to the outer section of the chamber from a
single source 116. In use, the deflector plate is rotated about the
pivot 115 so that the amount of coolant flowing through the upper
portion of the tapered channel can be varied with respect to that
flowing through the lower portion of the tapered channel. The
streams are joined prior to exiting the holes 113 so as to form a
single stream having a direction dependent on the relative flows
through the top and bottom channel sections.
[0065] In FIG. 10, the annular mould body 110 is provided with a
single internal chamber 111. The chamber is divided into an inner
111a and outer 111b portion by means of a baffle plate 117
containing a series of equally spaced uniform holes 118. The inner
chamber communicates with the exterior of the mould by means of two
channels 120, 121, which terminate in a single hole 122 for
delivery of coolant to the ingot surface. The upper channel 120 is
oriented downwardly and inwardly at an angle of 22 degrees relative
to the vertical casting surface and the lower channel 121 at an
angle of 45 relative to the same surface. Two sliding valves 123,
124 are mounted between the inside surface 125 of the inner portion
of the chamber and the baffle plate, and these valves are moved in
the vertical direction by shafts 126, 127 passing through the upper
and lower sides of the mould body, and sealed to the mould body by
means of elastomeric seals 128, 129. The valves extend along the
entire inside face of the chamber so that the upper valve 123 can,
in its lowest position, cover all the upper channels 120 along the
length of the mould, and the lower valve 124 can, in its highest
position, cover all the lower channels 121 along the length of the
mould. In operation, the vertical positions of the valves is varied
to control the relative flow through the upper and lower channel
and thereby to change the direction of the coolant stream exiting
the mould. The sliding valves 123, 124 can in another embodiment,
be replaced by pneumatically activated elastomeric bladders, that
are controlled by air/vacuum valves external to the mould so as to
expand and contract and thereby alternatively cover or uncover the
openings to the channels.
[0066] The embodiments of FIGS. 9 and 10 both use internal
mechanical or pneumatic orienting arrangements to change the angle
of the coolant stream exiting the mould. As a result they are less
preferred embodiments of the invention than that depicted in FIGS.
2, 3 and 4 which provide a continuously adjustable fluidic
orienting arrangement with no internal moving parts.
[0067] Without wishing to be bound by any theory, it can be stated
that, when secondary or direct cooling is employed during DC
casting, the cooling achieved by the liquid coolant passes through
at least four stages. First, at high temperature, the coolant is
vaporized on contact with the hot metal surface and the vapour may
insulate the metal from further contact with the coolant, so that
the overall cooling rate is low. As the metal cools somewhat there
is a transition phase leading to a nucleate boiling phase in which
bubbles form in the coolant film present on the metal surface. In
this phase, the rate of heat extraction may be quite high, but is
somewhat uneven. Finally, the coolant forms a continuous film on
the metal surface that cools by convection, whereby even cooling
can be achieved. The use of a high angle of approach of the cooling
streams onto the metal surface helps the cooling to transition
quickly from the vapour phase, through the nucleate boiling phase
and to the convection phase. During the start-up it is desirable to
provide a continuous, smooth and reproducible increase of the angle
of approach of the coolant streams to ensure that a controllable
cast startup can be achieved for a wide variety of alloys and that
cast failures are minimized. The control over the approach angle of
the streams according to the present invention makes this rapid
transition possible.
[0068] The invention may, if desired, be used in combination with
conventional procedures for varying the rate of cooling of an ingot
during DC casting, e.g. by pulsing the streams rapidly on and off
during one phase of the casting procedure (e.g. during start-up),
or by introducing a gas into the coolant liquid at various stages
of the casting procedure to vary the cooling coefficient of the
combined cooling medium.
[0069] It has been found that the invention works with several
alloys that are difficult to cast with conventional means. The
invention is therefore suitable for use with most other DC castable
metals and alloys.
[0070] While the invention has been described in connection with a
vertical DC casting apparatus, it could also be used equally
effectively with the so-called horizontal DC casting apparatus that
is capable of casting longer ingot lengths.
* * * * *