Note: Descriptions are shown in the official language in which they were submitted.
~ 1 ~6'122
This invention relates to electromagnetic
stirring apparatus for the provision of a magnetic field
rotating about the path of steel through a continuous
casting mold, the purpose of such field being to cause
rotation of the steel which is still liquid in the mold.
Prior apparatus of this type has included, in
addition to the windings and power sources to produce the
field, pole pieces or teeth of magnetically permeable
material, extending between the windings or some of them,
toward the mold. Such pole pieces or teeth have a useful
function in other applications, e.g. in the stator of an
A.C. motor where the teeth or pole pieces reduce the air
gap between the stator (composed of such teeth or pole pieces
and an outer magnetically permeable path) and a rotor
mainly formed of magnetically permeable material. However,
in the electromagnetic stirring of steel the role of the
"rotor" is replaced by the liquid steel being cast and this
is substantially non-magnetic. Accordingly, the air gap is,
relatively, extremely large, being greater than the trans-
verse dimension of the mold. With the magnitude of the air
gap, in the electromagnetic stirring of steel, the effect
of teeth or pole pieces in reducing the air gap is extremely
small.
This invention, there~ore, provides an electro-
magnetic stirring apparatus for a continuous casting, s~eel
mold comprising a set of windingQ and a magnetically permeable
path extending about said windings and about the mold, the
windings and path being designed for producing a rotating field
in the mold to produce such magnetic stirring, wherein said
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I 1 66~1~2
magnetically permea~le path is totally located outside
said windings: in othèr words: the magnetically permeable
path does not include pole pieces or teeth extending
radially inward between said windings toward said mold.
Another facet of the invention derives from th~
fact that the means for producing the magnetic field does
not require radially (relative to the mold) directed pole
pieces, teeth or equivalent. This allows the windings to
be effectively disposed in the orm of a pluxality of
multiturn loops connected to carry electric current down
one side of the mold, then approximately half-way about the
mold, then up the opposite side, then approximately half way
about the mold to the first side, and so on in repetition
of the above path for the number of turns present in the
multiturn winding. The result iQ a roughly multiturn loop,
wound in a predetermined -~ense: which, with electric current
therein, will produce flux across the mold, transverse to
the steel movement direction and in a direction perpendicular
to the median plane of the loop. A plurality (preferably
two and, next in preference, three) of such multiturn loops
are similarly disposed relative to the mold, at angular
dispositions thereabout. When the energizing alternating
currents are provided to the multiturn loops in the correct
phase relationship, the effect of the flux fields is to
produce the effect of a composite field through the steel and
rotating about the steel travel direction in the mold, at a
frequency determined by the energizing A.C. frequency and the
number of multiturn loops The invention, in this facet
1 ~ 6fi'122
provides an efficient, economic, and compact structure due
to the elimination of pole pieces and teeth and the winding
arrangement.
The previous paragraph describes a mold stator
wherein each multiturn loop comprises longitudinally extending
winding segments carrying current down one side of the mold
and up the other. It is within the scope of the invention
to provide such longitudinally extending winding segments
without the connections going half way round the mold at
each end of the winding segments. In other words the rotating
field may be provided by the properly arranged pairs of
opposed groups of winding segments, with the proper phase
relationship between energization of the pairs, but without
the individual connections between the winding segments of
opposed groups of a pair. Thus a single connection may join
one end of all the winding segments of a group on one side
of the mold to the same end of all the winding segments of
the group on the other side of the mold. Alternatively a
source of the cyclically varying current may be connected to
the group of winding segments on one side of the mold and
to the opposed group (without the connections about the mold),
the connection being in a sense to produce current flow
in opposite directions on opposite sides of the mold and the
phase of the energization for the pairs of groups being
designed to produce the desired rotating magnetic field
having a main component tranæverse to the axis of the mold.
This invention also provides an electromagnetic
stirring apparatus wherein the windings are placed directly
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1 1 66~2~
adjacent the mold sleeve. The mold sleeve is contained in
the water jacket which extends about the outside of the
moldO The sleeve is designed to surround the mold and to
be narrowly spaced therefore to define a narrow water layer
between mold and sleeve. The sleeve is non-magnetic and
preferably non-conducting being preferably constructed of
plastic or of stainless steel. By the term "plastic"
herein, I include fibreglass although, as well known, it
f~J~-s *
13 contains glass filaments. ~breglass is one of the
preferred construction materials for the sleeve. By the
term "winding" in this application I include the conductor,
its insulation and protective cover and, if a number of
conductors are formed in a bundle, the means for maintaining
the arrangement of such bundle. The windings, applied
directly to the sleeve do not have magnetically permeable
material in the form of teeth, pole pieces or the like
between them. It is therefore possible to get more ampere
turns in the same space than with prior designs and the
cost of the assembly is decreased since the design is
simplified. The sleeve may be indented to form recesses to
at least partially receive the windings. In electro-
magnetic stirring apparatus a magnetically permeable path
surrounds the windings. In the inventive arrangement the
material forming such path is preferably used to assist in
~r~d e ~ ~r~
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I ~66~22
retaining the windings on the sleeve. Preferably, in one alter-
native, such path is formed in the inventive construction by
winding steel strapping, of suitable magnetic permeability, about
the windings. The assembly comprising : sleeve, windings, and
strapping; is designed to be contained in the water jacket
customarily provided. Such strapping, as previously implied, may
be used as part of the means to hold the windings in place.
By the term "non-magnetic" in relation to this application,
I include not only plastics but substantially non-magnetic metals
including stainless steel. Stainless steel with fiberglass,
constitutes, herein one of the preferred non-magnetic materials
from which the mold sleeve may be made.
By the term "non-conducting" in relation to this appli-
cation, I include plastics. Stainless steel, although of higher
resistivity than copper is a conducting material and is so
considered in the terminology of this application.
other advantages of the invention, both generally and
with reference to the specific embodiments, will be discussed
hereafter.
In drawings which illustrate a preferred embodiment of
the invention :
Figure 1 shows a side cross-section of a mold indicating
the inventive stator in place thereon,
Figures lA and lB indicate schematically, the stator
winding arrangement,
Figure 2 shows a cross-section of the mold and stator
along the lines 2-2 of Figure 1,
Figure 3 shows an enlargement of a portion of the cross-
`~ ~ section of Figure 2,
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13~6~
Figure 4 shows a perspective view showing the
application of steel strapping to the outside of the windings,
Figure 5 is a perspective view of similar attitude
to Figure 4 but showing the use of a bolted magnetically
permeable path,
Figure 6 is a horizontal cross-section of an alternate
arrangement of the magnetically permeable path and windings,
Figure 7 shows a side cross-section of a mold where
the parts are physically identical to Figure 1 but the input
electrical leads are differently labelled for the description
of two phase operation,
Figures 7a and 7b show, schematically, the stator
winding arrangement for two phase operation,
Figure 8 shows a cross-section of a mold along the
lines 8-8 of Figure 7~ The parts physcially shown in Figure
8 are identical to those shown in Figure 1. Figure 8 however
shows schematic labelling indicating the winding turn
allocation for two rather than three phase operation,
Figure 9 is a horizontal cross-section of an alternate
arrangement of the magnetically permeable path and windings.
Figure 9 shows members physically identical to Figure 6 but
shows schematic labelling indicating the wind ing turn
allocation for two rather than three phase operation.
In the drawings: Figure 1 shows a mold for the
continuous casting of steel, wherein the copper mold wall
10 is designed to receive molten steel at its upper end
and to provide, from its lower end, steel which is solid
at least on the outer skin. The mold is water cooled and
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the thickness of the outer skin ~herefore gr~ws in thickness
with the passage of the steel therethrough from the top to
the bottom of the mold. All this is well known to those
s~illed in the art including the provision of a water jacket
1~ means for circulating cooling water in the jacket including
a -Qleeve 12 which is narrowly spaced from the wall of the
mold. The designed circulation path and circulating means
for the water in the jacket are not shown completely as they
are well known to those skilled in the art.
In accord with the invention the sleeve 12 is not
only constructed of non magnetic material but preferably of
F~ b~ r~J /aS
non conducting material, here ~i~e~ as~. and is provided
D
with spaced small inward projections 15 to establish the
mold sleeve Qpacing. It will be noted that the use of a
sleeve material which is non-conducting as well as non-
magnetic prevent~ the development of eddy currents in the
sleeve and thus strengthens the effective value of the
magnetic field in the mold.
As Qh~wn in Figure 4, the outer surface of the
sleeve is Qhaped to define vertically extending grooves 19
which are shaped to partially receive winding segments 14
shown as circles in cross-section therein. Each winding
~r
segment 14 may represent a single insulated conductor of a
bundle of conductors. Moreover the outer shape of the
conductor or bundle of conductors may be of other than
circular shape and the outer shape of the sleeve comple-
mentarily contoured to receive such windings or bundles.
The winding segments in one embodiment 14 are arranged
~ J ~
in three phases as indicated in Figure 2. As indicated in
Figure lb. Such windings for a single phase, e.g. "Pl +"
anld "Pl -" are electrically part of a multiturn winding
where the segments 14 ar~ arranged to carry current down
one side of the mold (as indicated by the - sign) approximately
half-way about the mold and up the opposite side (as indicated
by the ~ sign), then approximately half-way about the mold to
the first -Ride and so on for the same manner for the number
of turns in the multiturn winding.
The path of a single turn of the phase 1 winding is
shown and the remaining phase 1 windings (alongside that shown
as indicated in Figure 2) are omitted for clarity in Figure
la. Figure la Qhows a similar single turn of the phase 2
and phase three windings. Figure 1 does not indicate the
connections of the windings to each other as this is well
known to tho~e skilled in the art and shown schematically
in Figure la. The wind ing segments are connected above and
below the vertical extents shown, by connections C (only
schematically shcwn) on one or the other sides of the mold
path so that for each phase there is a multiturn winding,
wound and energized in a sense to direct magnetic flux
across the steel path in the mold in a direction determined
by the orientation of the winding and in an instantaneous
sense and of strength determined by the phase of the current
1 ~ 66~I22
in the winding. In this embodiment three such windings
are provided, angularly arranged about the mold. The multi-
turn windings are, as previously indicated, energized by
a three phase source, labelled phase 1+, phase 2+, and phase
3+, phase 1- etc., where each phase of the current in each
phase of winding segments will be 120 from the next. The
current in the winding segments labelled 'phase 1+' is
considered to be in phase with the current in the winding
~egments labelled 'pha~e 1-', which are located on the
opposite side of the mold, in the sense that it is the same
current which is energizing these opposite segments. The
current in opposite segments is 180 out of phase in the
sen~e that, relative to the axis of the mold, the currents
in opposed -~egments are running in oppo~ite directions. A
similar relationship exists between the positive and negative
sides of the pha~e 2 and phase 3 segments. In view of the
phase relationship of the three phase currents, the magnetic
flux fields rotate in the mold at a rate proportional to the
frequency of the three phase supply. With the winding arrang~
~ent shown, there is produced, in the mold, a magnetic field
rotating about an axis parallel to the steel path, where the
rotation frequency is that of the A.C. frequency of the
three phase supply. As is well known with other winding
arrangements, the rotational frequency may be designed to be
different from the A.C. frequency.
As shown schematically in Figure la the three multi-
turn windings are preferably delta connected to three phase
A.C. by leads K, L, M which leads are also indicated in
Figures 1 and 2.
As best shown in Figure 4 the magnetically permeable
path i~ preferably provided by steel strapping 22
l~6~2
about the outside of the windlng~ to provide the
magnetically permeable path extending thereabcut. As
shown, the ~trapping also acts to ma~ntain the windings
mechanically in place. Other means not shown may ~e used
to mechanically support the windings.
Figure 5 show~ aR alternative means of forming
the magnetically permeable path to that ~hown in Figures
1-4, the remaining elements of the developments being the
same as those shown in Figure~ 1-4.
The alter~ative of Figure 5, instead of using
strapping to for~ tho magnetically permeable path, uses
plates of magnetically permeable iron, bolted together to
form a path over the ~ame vertical extent subject to
~ariation for pasticulas applications a~ the strapping of
_ Figur~ 1. The plate~ 122 may, like the strapping, be used
to r~tain the windings 14 in position on sleeve 12. Sleeve
12 is located on mold wall 10 as in ~igure 1.
The bolted plates 122 have the advantages ovo
the ~tsapping 22 in bein~ easier to assemble and di-~-
assemble for construction or repair. The strapping in
~ome ca~e~ will allow economy of iron ince, with the strap
la~i~at~ons extending longitudinally in the direction of flo~
of ~agnoti~ flux about the coil assembly, somewhat le5s
~aterial may ~e needed in ~ome applications.
It wsll be noted that, although a fibreglass
~lee~e iq preferred in the embodiment of Pigures 1-4, on
the one hand, and Fi~re 5 on the other, a stainlesc steel
sleeve ~ay De used, with the realization that the rotating
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]~6~
magnetic ~ield applied to the mold will be somewhat
dimini~hed in the conducting (although non-magnetic)
stainle3s steel sleeve.
Figure 6 shows an alternative wherein the
magnetically permeable path is provided by a m~gnet~cally
permea~le iron weldment 222. Thi~ weldment will, subject
to variation for particular a~plications have the same
ve~tical extent a-~ the path forming membess 22 a~d 122
in o~her embodiments. The weld~ent 222 is shape'~as shown
in ~igure 6 to provide, on each ~ide of a square or
recta~gular mold wall and corresponding slee-~e, a recess
224 extending along each ~ide of the ~guare or rect-
angula~ mold wall, for group of windings 226 suitably
arranged (h re) for three phase operation and designed to
be connected to provide the rotating field. The arrange-
ment allows for the compact housing of a large number of
windings. A thi~ rctainer layer of in-~ulation (not shown)
may be pro~ided over the inner sur~ace o_ each of the
envelope~ of windings 226 along each side. The sleeve 216
~ not scalloped and may be made of stainless steel or
pla~t~ The ~old and mold wall wate_ jac'.~et used with
th~ alte~native of Figure 6 ~ay be the ~ame as illustrated
in Figure 1
Although th~ pref-rred forms of the inv~ntio~
~hown indicate i~wardly airected ~ump~ 15 on the sleeve 12
or 216 to a~.hieve spacing from the mold waLl 10, it will
ba noted that I al~o conte~plate usi~g the alternative
where ;he spacing is achie~ed by outwa~dly directed pro-
_ 1`1 _
I lB~22
jections on the mold wall 10 contacting an inwardly smooth
sleeve 12 or 216; or where the spacing is otherwise achieved.
The three embodiments shown all provide a mag-
netically permeable path surrounding the windings, where
the path is not provided with pole pieces, teeth or
equivalents projecting inwardly through the windings, but
where the magnetically permeable path is wholly outside
the windings.
The following material has as its principal
purpose the full presentation of this development with two
phase operation. Three phase operation, as described in
the previous page, represents an efficient use of electrical
power as is well known from basic electrical power theory.
However many of the m~lds with which the invention is
used are four sided, i.e. either square or rectangular.
With such four sided molds the wiring for three phase
operation is complex since the winding extents do not
correspond to the mold sides. Moreover with the turns of
a phase extending about corners of a mold the application
of classic electro-magnetic theory is difficult and practical
results are difficult to predict. For these reasons and due
to the large proportions of square or rectangular molds, it
is believed tnat the two phase arrangement hereinafter
described will be more commonly used than three or larger
number phase arrangements.
The winding turns may be arranged so that there is
one phase per side on a rectangular mold. With a rectangular
mold an effort will usually be made to balance the field
4 ~ ~
effects on the long and the short sides of the rectangle.
Thus the turns on the long sides of the rectangle may, if
desired, be arranged in an arrangement where the turns on
the long side of the rectangle encompass the same geometrical
envelope as the turns on the short side, i.e. the winding
envelope does not encompass as much of the length of the
long sides as of the short.
In Figure 7 the physical arrangement of the coils
and the mold is identical to Figure 1. However for the
two phase connection the exterior connections are labelled
P, N and Q. As Figure 7a indicates, the coil turns will
be connected 30 that phase 1 will be applied across leads
P-~ and phase 2 will be applied across leads Q-N. Phase 1
and phase 2 will be 90 out of phase as would be expected
for tW.o phase operation. Figure 8 is physically identical
to Figure 2 but the windings are connected in a two phase
relationship with opposite sides of the mold corresponding
to a phase. The preferred winding arrangement for the phase
distribution in Figure 8 is shown in Figure 7b. Such windings
for a single phase e.g. "Pl+" and "Pl-" are electrically part
of a multiturn winding where the segments 14 are (as in
previous embodiments) arranged to carry current d~wn one side
of the mold (as indicated by the - sign approximately half-
way about the mold and up the opposite side as indicated by
the + sign) then approximately half-way about the mold to the
first side and so on in the same manner for the number of
turns in the multiturn winding.
The path of a single turn of the phase 1 winding is
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shown and the remaining phase ~161fin~gs (alongside that shown
as indicated in Figure 8) are omitted for clarity in Figure 7a.
Figure 7b shows a similar single turn of the phase 2 winding.
Figure 7 does not indicate the connections of the windings to
each other a~ this is well known to those skilled in the art and
~holwn schematic311y in Figure 7a. The winding segments are
connected above and below ~he vertical extents shown by connec-
tions C (only schematically shown) on one or the other side of
the mold path so that for each phase there i9 a multiturn winding,
wound and energized in a source to direct magnetic flux across
the Qteel path in the mold in a direction determined by the
orientation in the winding and in an instantaneous sense and of
strength determined by the phase of the current in the winding.
In this embodiment two such windings are provided, each such
winding corresponding to the opposite sides of the mold. The
multiturn winding~ are, a~ previously indicated, energized by a
two phase source, labelled phase 1l, phase 2+, phase 1-, phase 2-
where each phase of the current in each pha~e of winding segments
will be 90 from the next. The current in the winding segments
labelled 'phase i~' is con~idered to be in phase with the current
in the winding segment~ labelled 'phase 1-', which are located
on the opposite side of the mold, in the sense that it is the
~ame current which is energ~zing these opposite segments. The
current in opposite segments may be considered to be 180 out
of pha~e in the ~ense that, relative to the axis of the mold,
the currents in the opposite segments are running in opposite
directions. A similar relationship exists between the positive
and negative sides of the phase 2 segments. In view of the phase
relationship of the two phase currents, the magnetic flux fields
rotate in the mold at a rate proportional to frequency of the two
phase supply. With the winding arrangement shown, there is
I ~ &~2~
produced, in the mold, a magnetic field rotating about an
axis parallel to the steel path, where the rotation fre-
quency is that of the A.C. frequency of the two phase supply.
As is well known with other winding arrangements the
rotational frequency may be designed to be different from
the A.C. frequency.
As shcwn schematically in Figure 7a the two multiturn
windings are connected to two phase A.C. by leads P, N, Q
which leads are also indicated in Figures 7 and 8.
Figures 4 and 5 apply equally to the two phase
arrangement of F~gures 7 and 8 as to the arrangement of
Figure~ 1 and 2. ~ence the description of Figures 4 and 5
applies to the two phase arrangement.
Figure 9 shcws an alternative which is identical
to that described in connection with Figure 6. However the
alternative of Figure 9 is indicated as wound for two phase
operation, with each phase corresponding to opposite sides
of the mold. Thus the e~bodiment of Figure 9 is wound by
analogy to the arrangement demonstrated in Figure 7b with
the winding system for each phase being continued until the
desired depth of windings i obtained.
In relation to the embodiments both of lb and of
7b it should be noted that a pair of groups of winding segments
14 correspond to a phase with each group of winding segments 14
being on the opposite side of the mold from its paired group.
The pairs of groups of winding segments energized in accord with
the multi phase supply creates current flowing in opposed long-.
itudinal directions along the molds in the respective opposed
. - 15 -
I ~ fi~
paired groups and a rotating field about the axis of the
mold. It is noted that it is within the scope of the
invention to provide such opposed current flow in opposed
groups and the rotating field, without the use of the multiple
connectors C indicated in Figures lb and 7b. For example
all the longitudinal winding segments 14 in a group may be
connected in parallel and connected by a single connector to
the opposed group of winding segments also connected in
parallel. Alternatively each groupof winding segments may
be individually supplied from a cyclically varying sourceO
In either of these latter alternatives, the connections
may be made so that the cyclically varying current flows in
opposite longitudinal directions along the mold in opposed
groups of winding segments 14, and the energization of pairs
of opposed winding groups may be related in phase as
indicated in accord with the various embodiments herein to
produce the desired transverse field; rotating with respect
to the mold axis.
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