Note: Descriptions are shown in the official language in which they were submitted.
This application is a division of application
Ser. No~ 353,504, filed ~une 6, 1980
This invention relates to an improved process and
apparatus for control of corner shape in continuous or semi-
continuous electromagnetic casting of desired shapes, such as
for example, sheet or rectangular ingots of castable materials.
The basic electromagnetic casting process had been known and
used for many years for continuously or semi-continuously
casting castable materials including, but not restricted to,
metals and alloys and silicon or other similar semi-metals,
metalloids, and seml-conductors.
- One of the problems which has been presented by elec-
tromagnetic casting of sheet ingots has been the existence of
large radius of curvature corners'thereon. Rounding off of
corners in electromagnetic cast sheet ingots is a result o~
higher electromagnetic pressure at a given distance from the
inductor near the ingot corners, where two proximate faces of
the inductor generate a ~arger field. This is in contrast to
lower electromagnetic pressure at the same distance from the
inductor on the broad face of the ingot remote from the corner,
where o~ly one inductor face acts.
There is a need to form small radius of curvature
corners on sheet ingots so that during rolling cross-sectional
changes at the edges of the ingot are minimized. Larger radius
of curvature corners accentuate tensile stress at the ingot
edges during rolling which causes edge cracking and loss of
material. Thus, by reducing the radius of curvature of the
ingot at the corners there is a maximizing in the production of
useful material~
It has been found in accordance with the present
invention that rounding off of corners in electromagnetically
cast ingots can be made less severe or of smaller radius by
bringing about a net downward displacement of the screening
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~i5~6"3
current at the corner~ of a shield placed at the molten metal
or alloy inpu~ end o~ the casting zone and~or b~ contouring
the field produclng inductor so as to enlarge the a~r gap
between the inductor and the ingot a~ areas between ~he
lnductor and the ingot corners. Thus, since undesirable
rounding off of the corners results from the action of excess
electromagnetic force at the lngot corners, the desired
modification of the ~ield shape can be obtalned by lncreased
local ~creening of the field and/or by contouring ~he
inductor at the corners.
- 10 Various embodiments of the present invention increase
local screening of the electromagnetic field by locally
increasing shield depth~ b~ locally providing deeper displace-
ment of the shield, or by certain local changes in shield
section or orientation.
PRIOR ART STATEMENT
Kno~n electromagnetlc castin~ apparatus comprises a
three part mold consisting of a water cooled inductor, a non-
magnetic screen and a mani~old for applyin~ cooling water to
the ingot being cast. Such an apparatus is exempllfled in
U.S. Patent No. 3,467,166 to Getselev et al. Containment of
the molten metal is achieved without direct contact between
the molten metal and any component of the mold. 5O1idiflcation
of the molten metal is achieYed by direct application of water
from the cooling manifold to the formlng ingot shell.
In some prior art approaches the inductor ls formed as
part of the coollng manl~old so that the cooling manlfold
supplies both coolant to solidify the castln~ and to cool the
lnductor. See United States Patent 4 3 004,631 to Goodrich
et al.
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~ ~ ~ 5 ~ ~
Non-magnetic screens of the priQr art are typically
utllized to ~roperl~ shape the magne~1c ~ieId for con~aining
the molten metal, as ex~mpll~ied in UOS. Patent 3,6Q5,865 to
Getselev. Another approach with respect to use o~ non-
magnetic screens is e~emplified as well in U.S. Patent NoO
3,985,179 to ~oodrich et al. Goodrich et al. ?179 describes
the use of a shaped inductor in con~unction with a screen to
modify the electromagnetic forming field.
It is generally known that during electromagnetic casting
the solidifi~ation front between the molten metal and the
solidiPying ingot at the ingot surface should be maintalned
within the zone of maximum magnetic ~ield strength, i.e. the
solidification front should be located within the inductor.
If the solidification front extends above the inductor, cold
~olding is likely to occur. On the other hand, if it recedes
to belo~ the inductor, a bleed-out or decantation of the liquid
metal is llkely to result. Getselev et al. '166 associate the
coolant application manifold ~ith the screen portion of the
; mold such that they are arranged ~or simultaneous movement
~ 20 relatiYe ~o the inductor. In U.S. Patent 4,156,451 to
Getselev a cooling medium is supplied upon the lateral face
o~ the ~ngot in several cooling tiers arran~ed at various
levels longitudinally of the ingot. Thus, depending on the
pulling velocity of the ingot, the solidification front can
be maintained within the inductor by appropriate selection of
one of the tiers.
Another approach to improved ingot sh~pe h~s lncluded
proYisions of more uniform fields at conductor 'DUS connections
(Canadian Patent 930,925 to Getsele~)~
In electromagnetically casting rectangular or sheet
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6S~6~
ingots, the ingots are often cast with high radius of
curvature ends or corners which is indicative of the need for
improved ingot shape control at the corners of such ingots.
Finally, United States Patent 3,502,133 to Carson
teaches utilizing a sensor in a continuous or semi-continuous
DC casting mold to sense temperature variations at a particular
location in the mold during casting. The sensor controls
application of coolant to the mold and forming ingot. Use of
such a device overcomes insta~ilities with respect to how much
extra coolant is required a~ start-up of the casting operation
and just when or at what rate this e~cess cooling should be
~ reduced. The ultimate purpose of adjusting the ~low of
`~ coolant is to maintain the freeze line of the casting at a
su~stantially constant location.
Carson '133 teaches that ingots having a width to
thickness ratio in the order of 3 to 1 or more possess an uneven
cooling rate during casting when coolant is applied periph-
erally of the mold in a uniform manner. ~o overcome this
problem, Carson '133 applies coolant to the wide faces of
the ingot or/and the mold walls and not at all (or at least
at a reduced rate) to the relatively narrow end faces of the
ingot or/and the mold walls.
SUMMARY OF THE INVEN~ION
The present invention comprises a process and appar-
atus for electromagnetic casting of castable materials inc-
luding, but not restricted to, metals and alloys and silicon
or other similar-semi-metals, metalloids, and semi-conductors
into rectangular or sheet ingots and other desired elements of
shape control, having small radius of curvature corners or
portions by modification of the electromagnetic ~ield. In
10052-1~B
particular, a method and apparatus utilizing control or
shaping of the magnetic field by means of controlled or
di~erentlal field screening, particularly at the corners o~
rectangular ingots or other desired elements of shape is
claimed. Control and shaping of the magnetic fleld by means
of contouring o~ the electromagnetlc inductor is also claimed.
In a fur~her embodiment, control or shaping of the
magnetic field by dif~erential screening and/or by inductor
contouring is combined wlth contoured impingement of a
coolant about the surface o~ the ingot being cast such that
the implnging coolant contacts the ingot at a minimum
perlpheral elevation at or near the corners o~ the forming
lngot.
According to the present inventlon, the desired modi~l-
cation o~ the field shape can be obtalned by inductor
contouring and~or by increased local screening of the electro-
magnetlc field at the lngot corners, thereby ma~ing the
roundlng of~ o~ corners ln electromagnetlc cast ingots less
severe or of smaller radius.
In accordance with one embodiment of this invention, a
desired modi~ication of the electromagnetic field is obtained
by contouring the inductor so as to enlarge the gap between the
inductor and the ingot at the ingot corners.
In accordance wlth another embodlmen~ o~ this inventlon,
increased local screening of the electromagnetic field at the
ingot or desired shape corners ls achieved by locally
increasing the shield depth at the corners.
In accordance with another preferred embodiment of this
lnvention, increased local screening o~ the electroma~netic
fleld at ~he desired shape or ingot corners is achieved by
iS9~
locally deeper displacement of the shield section at the
corners.
In accordance with another embodiment of this invention,
increased local screening is accomplished by locally changing
the shield cross-section at the corners of the ingot or
desired shape.
In accordance with yet another embodiment of this
invention, increased local screening of the electromagnetic
field at the ingot corners is achieved by locally altering
the orientation of the shield at the ing~t corners.
All of the aforementioned screening embodiments of
this invention operate via a net-downward displacement of the
screening current at the corners of the shield. It is of
course understood that hybrids of locally increased shield
depth, locally deeper displacement of the shield, local changes
in shield cross-section and local changes in shield orientation
can also be utilized in accordance with the concepts of this
invention.
Other embodiments of this invention contemplate the
combining of the various modi~ied screens with a contoured
inductor and~or with a coolant manifold such that the effects
of field control are enhanced by increased static head at the
ingot corners brought a~out by impingement of coolant at a
lower elevation at or near the corners of the ingot.
~ ccordingly, it is an object of this invention to pro-
vide an improved process and apparatus for electromagnetic
casting of castable materials into sheet ingots, or other de-
sired elements of shape control, characterized by small radius
of curvature corners or portions thereon.
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1005Z~
S~36~3
This and other ob~ects will become more apparent from
the following description and drawings.
..~ _~
Flgure 1 ls a schematic cross-sectional representation of
a prior art electro~agnetic casting apparatus utilizing a
uniform depth, cross-section and orientation non-magnetic
shield.
Figure 2 is a perspective vlew o~ the prior art non-
magnetlc shield o~ Figure 1.
Figure 3(a) ls a perspectiYe view of a non-magne~ic shield
in accordance with this lnvention showing increased local depth
of the shield at the corners. Figure 3(b) is a partial section
through the face Or the shield of Figure 3(a) showin~ the
shield positioned between an inductor and an ingot being cast.
Flgure 3(c) ls a partial section through the corner o~ the
shleld, inductor and in~ot of Figure 3(b).
Flgure 4(a) is a perspective ~ie~ Or a non-magnetlc shield
in accordance with another embodiment o~ this lnvention sho~ing
areas o~ locally deeper displacement of the shi~ld at the
corners. Figure 4(b) is a partlal section tArough the face of
the shield of Figure 4(a) showing the shield positioned between
an inductor and an ingot belng cast. Figure 4(c) is a partlal
sectlon through the corner of the shield, inductor and ingot of
Figure 4(b).
Figure 5(a) is a perspectiYe view o~ a non-magnetic shield
ln accordance with another embodiment of this invention showing
areas of locally inclination to the screen axis at the corners.
Figure 5(b) is a partial sectlon through the ~ace o~ the shield
of Figure 5(~) showing the shield positioned between an
inductor and an ingot being cast. Figure 5(c) is a partlal
r7~
r o 10052~
~ ..S~
sec~ion through the corner o~ the shield, inductor and ingot
of Figure 5Cb). Figure 5~d) is a bottom vlew o~ ~he shleld o~
Figure 5(a).
Figures 6~a) and 6(d) are top and bottom views, respec-
tively, of a non-magnetic shield in accordance with another
embodiment o~ this invention showing a shield of tapered
section havlng increased thlckness at the bottom o~ the screen
corners. Figure 6(b) is a partial sectlon through the ~acè of
the shield of Figure 6(a) showing the shield positioned between
an inductor and an ingot being cast. Figure 6(c) is a partial
section throu~h the corner of the shleld, inductor and lngot
of Figure 6(b).
Figure 7 is a partlal schematic cross-sectional repre-
sen~ation of the shield of Figure 3(a) being utilized as part
of a coolant manifold ln an electromagnetic casting apparatus.
Figure 8 is a partial schematic cross-sectional repre-
sentation of the shield of Figure 4(a) being utilized as part
of a coolant mani~old in an electromagnetic castin~ apparatus.
Figure 9 is a partial schematic cross sectional repre-
sentation of the shield of Figure 5(a) being ut~llzed as part
of a coolant mani~old in an electromagnetlc castlng apparatus.
Figure 10 is a partial schematlc cross sectional repre-
sentatlon o~ a shield similar to the shield depicted ln
Figures 6(a)-(d) being utilized as part of a coolant mani~old
; ln an electroma~ne~ic casting appara~us.
Figure 11 ls a partlal top Yiew showlng the iso~lux llne
contour for a prior art rectangular inductor.
Flgure 12 is a p~rtial top view showing the lso~lux line
contour for a contoured inductor in 2ccordance wlth one
embodiment o~ this in~ention.
1~ 0 5 2 ~ lB
i5~k~
Flgure 13 is a partial top view showing a cont.oured
inductor in accordance with another embodiment of thl's
inventlon .
Figure 14 1~ a partial top view showing the lsoflu~ line
contour for a contoured lnductor ln accordance wlth yet another
embodiment of this inYention.
DETAIL~D DESCRIPTION OF PREFERRED EMBODIMENTS
In all drawing figures alike parts are designated by
alike numerals.
Ref'errlng now to FIGURE 1, there is shown therei~ a prlor
art electromagnetic casting apparatus in accordance with U.S.
I ( Paten~ 4,158,479.
The electromagnetic castin~; mold 10 is comprised o~ an
inductor 11 which is water cooled; a coolant manifold 12 for
applying cooling water to the peripheral surface 13 of the
metal belng cast C; and a non-ma.gnetlc screen 14. Molten metal
is continuously lntroduced into the mold 10 during a castlng
~, run, in the normal manner using a trough 15 and down spout 16
and conventlonal molten metal head controlO The inductor 11 is
excited ~y an alternatlng current from a suitable power source '
~not shown).
The alternating current ln the inductor 11 produces a
magnetic ~ield which interacts wlth the molten metal head 19
to produce eddy currents therein. These eddy currents in turn
lnteract wi'h the magnetic field and produce forces which
apply a magnetic pressure to the molten metal head''l9 to
contain it so that it solldifie~ in a desired ingot cross-
sectlon.
An air gap e~ists during casting~ between the molten metal
head 1~ and the inductor 11. The molten metal head''l9 1s
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~ti~
formed or molded lnto the same general shape as the induc~or 11
thereby proYiding the deslred ingot cross-section. The
inductor may haYe any known standard shape includlng circular
or rectangular as required to obtain the desired lngot C
cross-sectton, but may also ln accordance wlth this invention
be glven a specific contour as depl cted for example ln
Figures 12 3 13, and 14.
The purpose of the non-magnetic screen 14 is to fine tune
and balance the magnetic pressure wl~h the hydrosta~ic pressure
of the molten metal head 19. The non-magnetic screen 14
comprises a separate e~ement as shown and is not a part of the
manifold 12 for applying the coolant.
Initially~ a conventional ram 21 and bottom block 22 is
held in the magnetlc containment zone o~ the mold 10 to allow
the molten metal to ~e poured into the mold at the start o~
the casting run. The ram 21 and bottom block 22 are then
uniformly withdrawn at a desired casting rate.
Solidi~ication of the molten metal which is magnetlcally
contained ln the mold lG is achie~ed by direct appllcation of
water from the cooling manlfold 12 to the ingot surface 13.
The water is shown applied to the lngot surface 13 within the
con~ines o~ the inductor 11. The water may be applied,
however, to the ingot surface 13 from above, within or below
the inductor 11 as desired.
m e solidlficatlon front 25 of the casting comprises the
boundary between the molten metal head 19 and the solidlfled
lngot C. The locatlon of the solldiflcation front 25 at the
lngot surfaee 13 results ~rom a balance of the heat lnput
from the superheated liquld metal 19 and the resistance
heating from ~he lnduced currents ln the lngot sur~ace layer,
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;
10052`l~B
~ 3
with the longitudinal heat extractlon resulting ~rom the
cooling water application.
Coolant manifold 12 is arranged abo~e the inductor 11 and
lncludes a~ least one discharge port 28 at the end of extended
portion 30 ~or directing the coolant against the surface 13 of
the ingot or castlng~ The discharge port 28 can comprise a
slot or a plurality o~ individual orifices for directing the
coolant again~t the surface 13 of the lngot C about the entire
periphery of that surface.
Coolant manifold 12 is arranged for movement along
vertically extending rails 38 and 39 a~ially of the ingot C
such that extended portion 30 and discharge port 28 can be
mov~d between the non-magnetic screen 14 and the inductor 11.
Axlal ad~ustment of the discharge port 28 positlon is provided
by means of cranks 40 mounted to screws 41.
The coolant is discharged against the surface of the
casting in the dlrection ind+cated by arrows 43 to de~ine the
plane o~ coolant application.
Figure 2 shows a prior art screen 14 of constant height
and section as shown in Figure 1. Rounding off o~ corners in
electroma~netic casting of rectangular ingots and other shapes
having corners from higher electromagnetic pressure at a ~iven
distance from the inductor near the corners, where two
pro~lmate faces of the slngle turn inductor generate fleld, as
compared to the pressure at the same dlstance from the inductor
on the broad faces of the ingot or other sh2pes remote from
the corner, where only one inductor face acts. Solution to
the problem may be sought ln accordance with this lnvention
through electromagnetlc ~ield modification. This lnYention
relates to a method and apparatus which is utilized to control
11--
- iO052-MB
or shape the mag~etic ~ield by means of controlled or
differential ~ield screening, particularly a~ the corner~ o~
rec~angular ingots~
Use o~ screens ~or field modification such as shown in
~lgures 1 and 2 is known in the art. Getselev '865 describes
a sc~een or shield in the form o-f ? closed ring positioned
wlthln the inductor with its lower edge located approximately
at the level of half of the height of the inductor. The
thickness of thls shield is changed along its height in an
a~ial or vertical direction to obtain a balance between the
hydrostatic pressure and the electromagnetlc forces while
maintaining a vertical side wall on the liquid immediately
above the solidi~lcation ~ront. Thls technlque is designed to
preven~ formation of a wave-shaped ingot sur~ace due to
variations in its transverse dimensions. Accordlngly, shaping
in this form o~ screening is restricted to control o~ the
llquid contour along the vertical axls o~ the casting. No
consideratlon is given to shaping in the horlzontal axis such
as could be used for corner definition in casting of
`20 rectangular ingots.
Since rounding off o~ ingot and other casting shape
corners results to a large extent from the action of excess
electromagnetic force at the corner, the desired modl~lcation
of the field shape can be obtained by increased local screening
of the f~eld at the corner. In accordance with this invention,
increased local ~creenlng can be achleved by locally increased
shield depth, by locally deeper displacement o~ the shield,
by locally changing the shield section, or by locally chansing
shield orien~ation. All of the above embodiments operate via
3o
-12-
10052-MB
~;t~
a net downward displacement of the screening current at the
corners of the shleld.
Figure 3(a~ shows a non-magnetic shield in accordance with
the present invention. Sh~eld 32 ls provlded with areas 34 of
greater depth at the corners. Figure 3(b~ shows a partial
section through a face of inductor 11, screen 32, and ingot 20
while Figure 3(c) shows a partial section through a corner of
these elements. For reference purposes elevatlon I I ls shown
passing through the crltical point where liquid (L) - solid (S~
front 37 intersects the periphery of ingot 20. It can be seen
that at the ingot corners, Figure 3(c), screen 32 pro~ects a
greater depth with respect to elevation I-I than does the
remainder of the screen along the faces o~ ingot 20, Figure 3(b),
This greater screen depth at the ingot corners causes the
screening of more electromagnetic field from the ingot 20 at
elevation I-I a~ the corners than along the faces of ingot 20.
Figure 4(a) shows a modi~ication of the screen depicted
ln Figure 3(a). Screen 35 is provided with greater depth 36
at the corners by displacement of the whole screen section
downward at the corner locations. Figure 4(b~ shows a section
through a face of lnductor 11~ screen 35 and ingot 20, while
Fi~ure 4(c) shows a ~ection through the corner of these
elements. The greater depth 36 of screen 35 as can be seen
in Figure 4(c) provides further enhanced screening at
elevation r-I at the corners of ingot 20 than through the
broad face deplcted in Figure 4(b).
Figures 5(a) and 5(d) illustrate another embodiment of
this invention. Screen 52 ls an inclined member of constant
section having a lower angle o~ inclination at the corners
with respect to the axis o~ ingot 20. As can be seen ~rom
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.. . .. .. . ....
10052-MB
~ ~ ~,iti~
Figure 5(b), a section through'the 'face of ingot 20, inductor
''li, and screen'52, and Figure '5~c), a section through the
corner o~ these elements, the base o~ screen 52 nearest to
elevation _-I is closest to inductor ll at the corner of
ingot 20. The closer a shieId is to an inductor the more
current is induced in the shield'. Thus, the change in shield
angle at the corners modulates the containment field at and
near ele~ation I-I at the 'ingot corner depicted in Figure 5(c)
more than along the ingot faces depicted by Figure 5~b~.
A further embodiment of a screen which can be utilized
ln accordance with this invention to provide modified
! ( screening at the ingot corners is depict~d in Figures 6(a)
through (d). Screen 54 is a tapered section along the faces
of the ingot'20 (Figure 6tb)) owe~er, screening of the
corner at and near elevation I`-I is increased by increasing
the screen thickness at the bottom '56 of screen 54 as shown
in section in Figure 6~c). If necessary, the angle of taper
can be reduced to zero.
Solutlon to the problem of rounded off corners caused by
~0 higher electromagnetic pressure near and' at ingot corners in
electromagnetic casting may also be sought through metal head
or pressure modification. Rounding off of corners in
electromagnetic casting results in part from higher electro-
magnetic pressure near and at the corners of the forming
ingot and in part from excess cooling or higher heat
extraction rates at the corners as a result of geometrlc and
higher heat transfer characteristics.
-14-
Prior art uniform rate and height peripheral coolant
flow directed at the surface of a forming ingot leads to
excess cooling at ingot corners and results in -the solidif-
ication front rising at the corners of the ingot as compared
to the position of the solidification front along the faces
of the forming ingot. Stated another way, the height of the
solidification front from the point of coolant impingement
at the corners of a uniformly cooled electromagnetically cast
ingot is greater than the height of the solidification front
from point of coolant impingement along the faces of the
forming ingot~ Thus, the combination of higher solidification
front (lower head) and increased magnetic pressure at the
corners of the forming ingot causes the pushing of molten
castable materials away from the corners leading to a highly
undesirable rounding off of the corners.
Control of coolant application may also be utilized
to produce controlled differential static head to thereby
obtain refinement of ingot shapes at the corners, and in
particular to form smaller radius of curvatures at ingot
corners. This control is effected by selection of the rate
and/or location of cooling water application to forming
ingot shells. Rounding off of corners in electromagnetic
casting can be made less severe or of smaller radius by
contouring the water application rate ~nd/or elevation so
that the rate andfor elevation is a minimum at the corners of
the ingot. Reduction of the water application rate and~or
lowering of the application level serves to reduce the local
heat extraction rate along an ingot transverse cross-section
line of constant height. This in turn lowers the position
of the solidification front at the ingot corner and
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correspondingly raises the ~etal static head or pPessu~e at
the corneP. This increased pressure results in the liquid
metal approaching the inductor more closely at the corner
and thus filling the corner to form a smaller radius of
curvature at the corner before the increased static pressure
ls counterbalanced by the increased electromagnetic force.
In a further embodiment of this inYention~ aspects of
two solutions to rounding oP~ of ingot corners, namely
solution through èlectromagnetic ~ield modification utilizing
lQ modi~ied screens and solution through metal head or pressure
modification by coolant control are combined in one apparatus
( and process. Figures 7 through 10 de~ict utiliæation o~ the
modified screens of this invention in con~unction with or as
part o~ a coolant maniPold.
Figures 7 and 8 show screens 32 (Figures 3(a))~ and 35
tFigure 4~a)) utilized as a part oP or as an element of
coolant manifolds 18. Line 29 divides Figures 7 and 8 into
sides (A~ and (B), (A) being a partial sectlon through a
face of the ingot 20, the inductor 11 and manifold 18, while
( ~0 shield tB) represents a partial section t~lrough a corner of
these elements. It can be seen that screers 32 and 35, when
utilized as a part of coolant manifolds 18~ serve the dual
function of modifylng and reducing the magnetic field at the
corners of in~ot 20 while simultaneously calslng a lowering
Or the elevation of lmpingement of coolant on the surface 13
of ingot 20, thereby lowering the solidific~tion front 25 at
the corners of ingot 20. In accordance Wit'l the principles
discussed hereinaboYe, the combination of hieher metal static
head 19 and lower electromagnetlc Pield at the corners oP
3o
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10052~
ingo~''20 bring about added corner shaping and a reduction of
the radius of curvature at the ingot corners~
Flgure 9 show~ scree'n '52 ~Figure 5(a)) utilized as part
o~ or as an element of coolant manlfold 18 t . Again, screen 52
is utilized as a part of manifold 1'8' to direct coolant flow
at the surface '_ of ingot 20 such that the effects of
increased screening at the corners, side ~B~, would be
enhanced by the lower eleYation of water impingement on the
surface of the ingot corner. The' lower eleYation of impinge-
ment of coolant at the ingot corners is brought about as a
result of the shallow angle of screen '52 to the ingot surface
at the corners thereof.
Finally, Figure 10 depicts a slight variation of the
screen depicted in Figures 6(a) through 6(d) utilized as part
of a coolant manifold 18. Screen'54' directs coolant at ingot
surface 13 at a lower elevation at the corners (slde' B) than
at the broad faces of ingot 20 (side A~. Thus, increased
screening at the corners is enhanced by the lower eleYation
c of coolant impingement and consequent lowering of solldlfi-
cation fron~ 25 at the ingot corners.
As an alternatiYe or in addition to lower elevation
coolant lmpingement, the manl~old and screens o~ this
invention could be combined so as to deliver a lower,rate of
coolant application, includlng a zero rate at the corners of
the ingot. Such a lower rate also leads to a lowering of
the solidification front at the corners of the forming ingot
leading to formation of corners having a smaller radius o~
curvature.
The manifolds o~ this invention are typically constructed
of non-metalllc materials such as plastics, in particular
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1~052~
re~n~orced phenolic~, whil~ th~ screens in accordance with
thls invention are typicall~ constructed o~ a non-~agnetic
metal such as for example austenitic stainless steel.
In accordance ~ith ano~her aspect of the present inven
tion, it h~s been ~ound possible to reduce and control corner
radius in electromagnetically cast ingots by inductor shaping.
When an ingot is being cast with an electromagnetic mold, the
ingot will assume ~hatever shape ls necessary to balance the
hydrostatic pressures against the containment force. The
containment force at any point is gi~en b~ the vector product
o~ the field tB) and the induced current density (J), i.e.
. the force is BxJ. Thus, that component Bc of the vector B
whlch contributes to the containment force is hereln denoted
contai~ment field. Since the current density ~J) is induced
by the field ~B), the containment force is roughly proportional
to BC2. Accordingly, to a flrst approximatlon a load with
unl~orm head at equilibrium in an EM mold will ha~e a unlform
Bc field around i~s perlmeter at some eleYakion Z above the
solidification front. Whatever shape the lines of constant
20 contalnment field map the load wlll conform to. Where the
contours o~ containment ~ield 8c map into a rectangle9 so
will the load. An exception to thls general rule ls ~ound
when a corner of radius less than the penetration depth (~)
exists. Here, current tends to short circult the corner.
Hence, at and near the corner J is reduced below what would
be expected ~rom the magnitude of the Bc field, and the
force Bc~J i~ also reduced causlng a further bulging effect.
Thls bulging tends ~o further reduce the corner radlus.
In accordance with this aspect o~ the present invention
in order to improve the corner shape of the containment field
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contour llnes, lt is necessary to change the shape of the
inductor in the vicinity of that corner.
Figure 11 shows a contalnment field contour for a typical
rectangular inductor, the inslde surface 61 of which is shown
in the drawing. As can be seen from the plot, the containment
contour line 63 in the vicinity o~ a corner, for example
corner 65, can be characterized by a cur~e with a ma~or and
minor radii, Rl and R2, respectively. Points A-A' mark the
intersectlon o~ the two cur~es formed by Rl and R2 and serve
as the re~erence for basic modificatlon o~ the induc~or.
Points B-B' on the inductor face are opposite Points A-A'. By
changing the shape of the inductor to the shape of inductor
61' illus~ra~ed ln Figure 12, whereln the lnductor corners 62
are provlded with a generally tr~angular cross-section, Rl
can be significantly reduced with the containment contour 63'
more closely approaching the ldeal contalnment contour 64.
As the parametric ratio dl/d2, with d2 being the normal alr
gap, increases, R3 decreases asymptotlcally. By ad~usting
the break points B-B' along the axis and adJusting the radiu~
dl/d2, corners wlth various degrees of curvature can be
obtalned.
To reduce the corner radii R3 ln Flgure 12 beyond lts
asymptotlc llmit, an additlonal modi~lcation to the inductor
corner is necessary. Such a modlflcation is shown ln Flgure 13
whereln an lnductor inside surface 71 lndicates the general
shape o~ such ~ modi~ied lnductor. In this modlfication the
inductor corners 74 are provided so as to have a generally
reGtangular shaped cross~-section. Again, the parameters dl,
d3, and B-B' are a function of the normal air gap d2 desired
and the ingot geometry. The asymptotic limit o~ load corner
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t~
radii o~ this modi~lcation appears to be nearly an order o~
m~gnitude bet~er than ~or the u~modifie~ prior ar~ inductor
61 depicted ln Figure 11.
An analytical approach to the problem of obtain~ng ingots
with small radii corners suggests an induc~or from 81 as
outlined in Figure 14. As can now be seen, the inductors 61'
and 71 shown in Figures 12 and 13 are piecewise llnear approx
imations to the inductor 81 in Figure 14. The inductor 81 is
shown pro~ided with generally rectangular shaped cross section
corners 85 having curved transition sections 67 which ~oin the
corners 85.to the sides 68 o~ ind~ctor 81. This inductor
( produces a containment field contour 63'' with nearly ideal
corners. The actual curvature of the inductor is basically a
function o~ deslred ingot geometry, air gap d2 and the amount
of lngot shrinka~e.
As stated hereinabove, corners of ingots which have been
electromagnetically cast can be characterized by a curve having
ma~or and minor radii Rl and R2, respectively. Such an ingot
can be utillzed to determine the locatlon of the points A-A',
which points then serve as the ~asic polnts ~or modification
o~ the inductor. Having determined the location of the points
A-A', t~e points B-B' are then established on the inductor
opposite points A A'.
In the embodlment of Figure 12, it is desirable to make
the value of dl significantly greater than the value o~ d2~
and at least twlce as great as d2. In known electromagnetlc
cast~ng proces~e~ the value of d2 i~ typlcally between about
1/2 and 1-1/2 inches. Thus, the value of dl in accordance
~ith this in~ention might ranæe anywhere ~rom about 1 inch to
in~inity. For practical reasons~ a pre~erred value o~ dl
~0--
10052
would be in the range o~ 2 to 4 inches. Referring to Flgure 1
ha~ing established the location of the points ~ B' and the
value o~ dl, the value o~ d3 becomes set implicitly and is
seen to be approxi~ately equal to the distance between the
point3 B~B'.
It should be noted that the optimum contour for a given
EM castln~ process as exemplified by 639 63', and 63" ln
Figures 11, 12, and 14, respectively, is embedded into a family
of non-optimum contours represen~ing decreasing containment
fields toward the interior of the inductor. Contours near the
inductor will tend to simulate the shape o~ the inslde perim-
eter of the inductor while contours further removed from the
lnside perlmeter o~ the inductor wlll tend to be elliptic.
Typical EM casting inductors have a heigh~ of ~rom
approxlmately 3/4 o~ an lnch to 2 inches, and the inductors
are typically maintained anywhere ~rom about 1/2 lnch to 1-1/2
inches from the ~orming ingot surface. The above de~cribed
techniques for obtalning optlmum contours o~ constant con-
tainment ~lelds are most e~ective when applied to lnduc~ors
~- 20 whose heights do nok exceed about 10 times the gap between
the inner sur~ace of the inductor and the outer sur~ace o~ the
forming ingot.
Accordingly, corner control by inductor shaping can
produce ingots wlth small radii corners, and this p~ocedure
constitutes an alternative to using shield shape modi~ications.
However, lt should be understood that either method can be
; used singularly or ln concert to produce ingots with lmproved
corner definitlonO
A further advantage o~ the inductor shaping procedure of
this invention relates to inductor lead connection~. Such
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tj~
lead connectlons are known to cause non-unlformlty of ~ield and
consequent ingot shape perturbations (U.S. 3~7a~,155 to
Getsel~v). Such problems are readily solved by making ~he lead
connections at a corner such as corners 66 and 66' a shown in
Figures 12 and 14, respectively, wherein inductors 51' and'81
in accordance with this invention are shown at~ached to power
sources 69. The lncreased separation of the lead connections
~rom the ingot surface a~orded by this procedure serves to
diml nish the ~ield non-unlformity so produced to a negllgible
level.
The novel method and apparatus of the present invention
find applicabllity in the electromagnetlc casting o~ any
shapes wh~reln'it is deslred to form portions thereon of low
radius of curvature.
It is app~rent that there has been provlded with this
inventlon a novel process and means ~or utilizing modl~led
lnductor contours and/or modifled local screening of electro-
magnetic fleld~ to obtain refinement of ingot shape during
electromagnetic casting which fully satis~y the ob~ect~, means
and ad~antages set forth herelnabove. While the lnvention has
been described in comblnation with speclflc embodiments thereo~,
lt ls evident that many alternatives, modlfications, and
variations wlll be apparent to those skllled in the art in
light of the foregoing description. Accordingly, it ls
intended to embrace all such alternatives, modifications, and
variations as fall within the spiriS and broad scope of the
appended claims.
3o
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