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Nov. 5, 1946.
2,410,794
D. C. WRIGHT ET AL.
ELECTROMAGNET
Filed Nov. 24, 1942
2 Sheets-Sheet 1
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INVENTORS
Dm/m C. WFHGHT g,
ARTHUR L.WARD
BY
{£01} ATTORNEY3
NOV. 5, 1946.
D. c_ WRlGH-r ET AL
2,410,794
ELECTROMAGNET
Filed Nov. 24, 1942
52
2 Sheets-Sheet 2
60
INVENTORS
DAVI‘D C. WmcgHT K,
BY
'ARTHUR457. WARD
a?wf
6M%Q¢@z£/¢M
7:254; ATTORNEYS;
Patented Nov. 5, 1946
2,410,794
UNITED STATES PATENT OFFICE
2,410,794
ELECTROMAGN ET
David C. Wright, Euclid, and Arthur L. Ward,
Shaker Heights, Ohio, assignors to The Elec
tric Controller & Manufacturing Company,
Cleveland, Ohio, a corporation of Ohio
Application November 24, 194-2, Serial No. 466,732
10 Claims.
(Cl. 175—367)
1
This invention relates to improvements in the
construction of electromagnets and particularly
to improvements in the construction of magnets
used for lifting and transporting material.
The most widely used type of lifting magnet (Fl
comprises a hollow inverted bowl-like yoke or
frame of cast steel having an integral peripheral
?ange and an integral central boss which de?nes
2
aligned with a corresponding opening through
the inner pole shoe to assist in cooling the mag
net and to permit the drainage of water from
a dished portion of the top surface of the mag
net frame.
Heretofore, both pole shoes generally have
been attached to the magnet ‘frame by bolts ex
tending through aligned openings in the pole
with the ?ange an annular channel, the ?ange
shoes and. the magnet frame. The use of bolts
serving as an outer pole piece and the boss serv 10 not only requires the accurate drilling of a great
ing as an inner pole piece. An annular coil unit
number of holes through large castings, but also,
is mounted in the annular channel co-axial with
due to the air gaps around the bolts, reduces the
respect to the inner and outer pole pieces, and
effective area of the magnetic circuit of the
the channel opening is sealed by an annular non
magnet and thereby prevents the attaimnent of
magnetic sealing plate or inner bottom plate 15 maximum lifting capacity. Furthermore, loos
tightly fastened to the inner and outer pole pieces
ening of the bolts due to the stretching thereof
and forming with the magnet frame a complete
causes a further reduction in the lifting capacity
enclosure for the coil unit.
because of the resultant increase in the air gap
To protect the sealing plate and the coil unit
between the pole shoes and the magnet frame,
of this common type of magnet from damage
and such loosening once it starts is aggravated
during operation of- the magnet, a relatively thick
by the repeated slamming of the pole shoes
annular protective plate or outer bottom plate
against the pole faces and bolt heads due to
is usually mounted beneath the sealing plate.
alternate energization and deenergization of the
Generally, the protective plate is formed from
magnet. Alloy steel bolts withstand harder and
high manganese steel because of the high 25. longer usage than soft iron or steel bolts before
strength and the good abrasive resistant and
they stretch enough to cause a large loss of lift,
non-magnetic properties of that alloy. It is com
but, because of the inherently poor magnetic
mon practice to hold the protective plate in posi
properties of suitable alloy steels, the reluctance
tion against the sealing plate by the clamping
of the magnetic circuit is increased by substitu
action of annular shoulders on inner and outer
tion of alloy steel bolts for iron or soft steel bolts.
pole‘ shoes which are fastened to the magnet
Another disadvantage in the use of bolts as a
frame and which engage the faces of the inner
fastening means for the pole shoes is the di?i~
and outer pole pieces, respectively. The protec
culty of removing them from old magnets in
tive plate is clamped in place because high man
order to replace the pole shoes or to inspect the
ganese steel is too hard to be machined or drilled 35 coil, in many cases it being necessary to cut off
and can be welded only with great difficulty.
each bolt because of the rusting and jamming
of the nuts.
Furthermore, welded connections between the
manganese steel protective plate and the mag
This invention in one of its embodiments
net frame would be subjected to destructive
avoids all of the disadvantages of the bolted con
struction by providing welded connections be
tween the pole shoes and the magnet frame.
Changing the bolted construction to a satisfac
contraction consequent upon the use of the mag
tory all-welded construction, however, has here
net for lifting hot iron or steel.
tofore presented insupera-ble difficulties, particu
The inner pole shoe of such prior magnets is
larly with respect to the inner pole shoe. For
usually a thick disc having its upper surface
example, welding cannot be accomplished along
?tted against the face of the inner pole piece
the outer periphery of the inner pole shoe be
with a tongue and groove or similar joint. Both
cause the outer periphery is, in contact only with
pole shoes are formed of magnetic iron or steel
the protective plate which is not fastened to the
and in addition to holding the protective plate 50 magnet frame. Attempts have been made to
weld the inner pole shoe to the bottom edge of
in position also serve to carry the working flux
to the load and thereby protect the pole pieces
the innerpole piece at the junction of the aligned
from abrasive wear. Some magnets have an
central openings. However, if in the design of
axial opening extending from the top of the mag
themagnet the central openings are made large
net frame through the inner pole piece and
enough to permit welding at this point, a magnet
forces due to transverse blows against the magnet
and also would not be able to withstand the
stresses resulting from thermal expansion and
2,410,794
3
4
of given diameter must have a reduced magnetic
magnet frame in such a manner that the attach
ment will resist all the forces likely to damage
it and wherein the magnetic reluctance of the
joint between the inner pole shoe and the magnet
frame is minimized.
A more speci?c object is to provide a substan
circuit area or a magnet having a larger outside
diameter than necessary must result. Further
more, a weld near the center of the inner pole
shoe and close to the working face of the magnet
cannot be made strong enough to resist the de
structive forces caused by the transverse blows
to which the pole shoe is subject during the usual
rough handling of the magnet and is subject to
tially all-welded lifting magnet.
Another object is to provide a lifting magnet
in which the coil unit is sealed and protected
abrasive action.
10 without the use of bolts or screws.
A correlative object is to provide a circular lift
In accordance with this invention in one of
ing magnet in which both the inner and outer
the illustrative forms shown a centrally disposed,
pole shoes are Welded to the magnet frame.
upwardly projecting portion of the inner pole shoe
Another object is to provide a lifting magnet in
of a lifting magnet ?ts tightly into and extends
through a central axial opening in the inner pole 15 which a portion of the inner pole shoe extends
into and substantially through an axial opening
piece and the magnet frame. The iron of the
in the magnet frame.
pole shoe replaces substantially all of the magnet
Another object is to provide a lifting magnet in
circuit area lost due to the opening. The up
which an inner pole shoe is welded to the top of
wardly projecting portion of the inner pole shoe
terminates near the top of the magnet frame, and 20 the magnet frame.
the top surface thereof is securely welded to the
magnet frame.‘ A wedge ?t is made between the
magnet frame and the inner pole shoe ‘substan
Other objects and advantages will become ap
parent from the following speci?cation wherein
reference is made to the drawings, in which
tially throughout the main ?ux path by tapering
Fig. 1 is a side elevation, partly in vertical sec~
all or a portion of the mutually engaging surfaces
of the two parts, and a drive ?t is made between
tion, of a lifting magnet embodying the invention;
Fig. 2 is an enlarged fragmentary vertical sec
tion of‘ the central portion of a modi?cation of
the telescoping portions that are not tapered.
the lifting magnet of Fig. 1, and
This construction and resulting cooperation of
Fig. 3 is a diagrammatical sectional view show
parts not only prevents the transmission to the
weld of shearing and other forces caused by blows 30 ing an assembly step preliminary to welding.
The lifting magnet illustrated in Fig. 1 com
against the lower portion of the inner pole shoe,
prises a circular magnet frame Ill having integral
but also results in a joint of extremely low re
therewith a cylindrical inner pole piece l2 and. an
luctance between the magnet frame and the inner
annnular outer pole piece M. The pole pieces
pole shoe. The coil unit is secured and sealed
in the annular coil space in the magnet frame by 35 l2 and M form downwardly projecting concentric
extensions of the frame l0 and de?ne an annular
continuous welded connections between the inner
winding space l6 therebetween which is open at
and outer pole pieces and the sealing plate. The
the bottom to receive an annular coil unit la.
outer pole shoe is welded to the outer pole pro
The pole pieces l2 and l 4 are formed integral with
jection, thus completing the all-welded construc
tion.
40 the frame Ill since greater strength and a better
magnetic circuit are thereby obtained. The inner
Generally, in order to obtain a joint of low mag
p-o-le piece i2 is in the form of a hollow cylinder
netic reluctance between two pieces of iron, the
with a central axial opening l9 extending through
abutting surfaces of the pieces are very accurately
the magnet frame It. Suitable supporting lugs
machined; Heretofore, the joint between the pole
I‘! may be cast integral with the magnet frame
shoes and pole pieces of large lifting magnets has
not been of as low reluctance as desired because
If) as shown.
of the same cooperative relation between the
of which are insulated in the usual manner. The
The coil unit is may be of any suitable type,
of the excessive cost of accurately machining such
and, for purposes of illustration, comprises a
large castings. The novel magnet construction
sleeve 20 which ?ts over the periphery of the
of this invention whereby a portion of the inner
pole shoe is ?tted tightly into and extends through 50 inner pole piece l2, an annular flange 22 welded
to the upper end of the sleeve 20, and a plurality
an axial opening in the magnet frame not only
of suitably insulated windings 24, each of said
permits the pole shoe to be easily and securely
windings being formed of strap copper, the turns
welded to the magnet frame, but also, by virtue
inner pole shoe and the magnet frame, results 55 sleeve '23 and the flange 22 are preferably of mag
netic iron or steel so that they add to the area
in a joint of lower reluctance between the pole
of the magnetic circuit of the magnet.
shoe and the inner pole piece of the magnet frame
The coil unit 58 is supported and sealed in the
than can be obtained without accurate machin
winding space l6 by an annular sealing plate 26
ing. Both the drive ?t obtained as a result of
the cooperation between the cylindrical portion 60 which has its inner peripheral edge fastened in a
shouldered recess in the lower- outer peripheral
of the inner pole shoe and the cylindrical portion
edge of the pole piece [2 by a continuous weld 28
of the axial central opening in the magnet frame
and which has its outer peripheral edge fastened
and the wedge ?t obtained as a result of the co
in a similar shouldered recess in the lower inner
operation between the tapered surfaces of the two
peripheral edge of the outer pole piece M by a
parts cooperate in producing an extremely low
continuous weld 3B. The sealing plate 26 may
reluctance joint substantially through the major
be made of non-magnetic metal such as brass or
flux path of the magnet. Only an extremely small
a chromium steel alloy or it may be made of
portion of the mutually engaging surfaces of the
magnetic iron or steel to facilitate welding. The
inner pole piece and the inner pole shoe are in
contact with the. usual butt joint.
70 total ?ux shunted by a magnetic steel inner bot
tom plate of su?‘lcient thickness to support the
An object of this invention is to provide a new
coil unit has been found to be very small.
and improved electromagnet suitable for use as
a lifting magnet.
- -
A conventional terminal and sealing arrange;
Another object‘ is to provide an electromagnet
ment for the coil unit i8 is illustrated. A pair:
in which the inner pole shoe is attached to the
of circumferentially spaced current conducting
2,410,794
5
leads 3|, only one of which is shown in Fig. 1,
extend from the windings 24 into a chamber 32
of a terminal box 34 formed integral with the
frame In and are attached respectively to cir
cumferentially spaced bolts 36 which pass
through an integral dividing wall 38 into a cham
ber 40 of the terminal box 34. Suitable electri
cal connections (not shown) are made to the
bolts 35 in the chamber 40 from a source of
power through a pair of circumferentially spaced
water tight plugs 42. After the coil unit 18 is
in place and the sealing plate 26 is attached, the
chamber 32 and the winding space It around the
coil unit l8 are preferably ?lled in a well-known
manner with a suitable water-proof insulating
compound (not shown). Openings in the top of
the terminal box 34 which provide access to the
‘chambers 32 and 48 are closed by pipe plugs 44
pole shoe 48 and the magnet frame I 0 substan
tially at the top of the opening IS. The pole
shoe 48 has a small central axial bore 14 which
assists in cooling, permits drainage from the
top of the magnet frame, and serves as a bolt
opening during assembly in a manner to be de
scribed.
Because of the wedge and drive ?ts between
the inner pole piece l2 and the inner pole shoe
48, forces due to transverse and upward blows
against the pole shoe 48 are not transmitted to
the welded connection 12, and because of the
drive ?t alone, the weight of the inner pole shoe
48 is not supported entirely by the welded con
nection “i2. When the magnet is energized and
the pole shoe 48 is subjected to the strongest
downward forces, the pole shoe 43 is, of course,
held strongly against the magnet frame It} by
and 45, respectively.
magnetic attraction and no downward forces
An annular non-magnetic protective plate 43 20 are transmitted to the weld T2. Furthermore,
preferably cast from high manganese steel has
even though the pole shoe 48 is only attached
to the magnet frame ii) near the center, the
its inner and outer peripheries which abut against
outer marginal portion of the pole shoe 48 can
the inner and outer marginal areas of the bottom
not be bent away from the protective plate 46
of the sealing plate 26 and is held in position by 25 as a result of the strongest forces likely to be
the clamping action of an inner pole shoe 48 and
encountered in service since the thickness of the
outer pole shoe 5!). The protective plate 4'5 is
pole shoe 43 increases progressively inwardly due
preferably of hollow ribbed construction as sug~
to the frusto-conical portion 68.
gested at the left in Fig. 1 to provide greatest
The welded connection 12 can be made strong
strength and rigidity for unit weight and to in
enough to support the weight of the pole shoe _
sure a sound casting, and clearance 52 is pro
48 without the drive ?t. For example, in the
vided at the top of the ribs so that ?nishing of
modi?cation: Fig. 2, an inner pole shoe ‘it has a
the entire top surface of the plate 46 is not
lower cylindrical portion ‘48 and an upwardly ex
annular ?nished areas on its upper surface near
required.
tending centrally disposed portion 80 entirely of
The top inner marginal portion of the outer
upright frusto-conical shape which is inserted
in a cooperating frusto-conical axial opening 82
through an inner pole piece 83 integral with a
nal portion of the protective plate 45, and has
magnet frame 84. The magnet of Fig. 2 differs
an upwardly extending annular ?ange 55 around
from that of Fig. 1 principally in that the comple
its outer periphery which ?ts into an annular 40 mentary frusto-conical surfaces of the inner pole
shouldered recess 58 cut in the outer periphery
shoe and the inner pole piece are relatively larger
of the outer pole piece l4 adjacent its lower face.
in Fig. 2 and in that the complementary cylin
A suitable Welded connection 65 is made between
drical surfaces for a drive ?t are omitted.
the pole shoe 59 and the pole piece l4 along the
It may be noted in Fig. 2 that the lesser angle
top of the ?ange 56. The top surface of the 45 of convergence upwardly of the complementary
pole shoe 50 thus is held tightly against the
frusto-ccnical surfaces eliminates the necessity
face of the pole piece l4 while the shouldered
for ?tted cylindrical surfaces such as on the por
recess 54 assists in holding the protective plate
tion ‘Ii and adjacent frame portion of Fig. l. in
45 against the sealing plate 26. Bolt carrying
order to prevent horizontaliy applied forces on
?anges and bolts around the periphery of the
the inner pole shoe l6 from tending to break the
magnet are thereby rendered unnecessary.
weld ‘l2. Such forces in Fig. 2 would be concen-‘
The inner pole shoe 4% comprises a lower cylin
trated in directions approximately normal to the
drical or central disc portion 62 the top outer
frusto-conical surfaces.
marginal area of which is cut away to form an
Referring to Fig. 3, which shows one method
annular shouldered recess £53 which receives the
by which the inner pole shoe 48 may be positioned
pole shoe El! is cut away to form an annular shoul
dered recess 54 which receives the outer margi
inner marginal portion of the protective plate 48
against the magnet frame it": preparatory to mak
and also comprises a centrally disposed, upward
ing the weld it’, a bar 86 laid across the top of
ly extending projection 64 which ?ts into the
the magnet frame :8 supports the pole shoe 48
axial opening [8 in the center of the magnet
during assembly by means of a threaded bolt
frame id. The projection 54 comprises a lower 60 88 which passes through the axial bore 14 in the
upright frusto-conical portion 68 which ?ts tight
pole shoe 48 and opening 89 in the bar 86. A head
ly and wedges into a complementary frusto-coni
96 of the bolt 83 abuts against the lower surface
cal portion ‘iii of the opening 59. Above the
of the pole shoe ‘i8 and a nut 92 is threaded onto
frusto-conical portion 63 of the pole shoe the
the end of the bolt 88 above the bar 88. By
projection ea has a substantially cylindrical por
turning the nut 92 the inner pole shoe 48 is lifted
tion 1! which ?ts tightly with a drive ?t into a
into position and great pressure between the pole
complementary upper cylindrical portion '53 of
shoe 48 and the magnet frame i5 is thereby
the opening 49. The diameter of the opening
exerted.
I9 at the lower face of the pole piece I2 is
Due to the large force by which the pole shoe
preferably just slightly smaller than the out
and the frame It are urged together by this
side diameter of the pole piece [2 so as to leave
procedure, full advantage is taken of the wedge
as small a butt joint as possible between the
?t between the complementary tapered portions
pole shoe 48 and the frame ID. '
.
68 and ‘m of. the projection 64 and the opening IS
A suitable welded connection '52 is made be
respectively, and the drive ?t is easily made be
tween the top of the portion 64 of the inner
tween the cooperating portions ‘ii and ‘E3 of the
2,410,794
7
projection 66 and the opening l9, respectively.
The tight ?tting of the projection 65 into the
Opening l9 not only prevents the transmission of
all destructive forces to the weld 12, but also
greatly reduces the reluctance of the magnetic
circuit of the magnet. After the pole shoe 63
and the magnet frame I i] are tightly clamped to
gether by the action of the bolt 83, part or parts
8
largest cross-sectional area of said opening being
nearest the lower face of said inner polar pro
jection, a pole shoe extending below the lower
face of said inner polar projection and having
a frusto-conical portion ?tting tightly into said
opening, and means at the upper end of said pole
shoe for securing said frame and said pole shoe in
flux conducting contact.
of the weld 72 are made and then the bar 85 is
5. A lifting magnet comprising a frame having
removed. The weld ‘l2 then can be completed. 10 concentrically arranged inner and outer polar
The same method of assembly, of course, is ap
projections extending downwardly therefrom and
plicable to the modi?cation of Fig.v 2, it being
de?ning an annular winding space therebetween,
noted that in Fig. 2 it is essential, due to the ab
an axially directed cylindrical opening extending
sence of a drive ?t, to have the ‘car 86 so shaped
through said inner polar projection and said mag
that the weld 12 can be partially effected before 15 net frame, said opening having a tapered counter
the bar 85 is removed.
bore extending inwardly from the lower face of
Removal of the inner pole shoe 48 and the outer
said inner polar projection, a pole shoe associated
pole shoe 59 can be accomplished by chipping or
with said inner polar projection and having a
otherwise machining out the welds 60 and 72,
tapered portion extending into and ?tting tightly
respectively. It has been found that such pro 20 against the counterbored portion of said open
oedure is much simpler than the loosening of a
ing and a cylindrical portion ?tting into the re
great many nuts which have become ?rmly at
mainder of said opening, and a securing con
tached to the usual pole shoe bolts during the
nection between said frame and the top of said
period of service of the magnet.
pole shoe.
We claim:
25 ' 6. A lifting magnet comprising a magnetic
1. A lifting magnet comprising a magnetic
frame member provided with an inner depending
frame member having an annular peripheral
pole piece having a bottom working face, a wind
?ange projecting downwardly therefrom, an
ing surrounding said pole piece and having its
axially directed opening through said frame with
lower face surface above the lowermost portion
in and spaced from said ?ange and having a
of said bottom working face, an axially directed
tapered portion, an inner or central pole unit
opening through said pole piece, a homogeneous
projecting downwardly from said frame and hav
and unitary magnetic pole shoe having a portion
ing a tapered portion ?tting tightly into said
extending outwardly from the lower peripheral
tapered portion of said opening, said pole unit
edge of said opening and below the said bottom
working face and also having a portion ?tting
?tting into the other portion of said opening, the
into said opening and with its peripheral surface
peripheral walls of said portions constituting the
in intimate flux conducting relation to surfaces
major ?ux path between the frame member and
de?ning said opening, said surfaces constituting
the inner pole unit, and a welded connection be
the major flux path between the frame member
tween said pole unit and said frame at the top
and pole shoe, and a securing connection entirely
of said pole unit.
located at the end of said pole shoe remote from
2. An electromagnet having an inner pole piece,
said working face and holding said pole shoe and
an outer annular pole piece surrounding said
said pole piece together in said ?ux conducting
inner pole piece and de?ning a winding space
relationship.
therebetween, an axially directed opening through
7. A lifting magnet comprising a magnetic
said inner pole piece and having a tapered por
frame member provided with an inner or central
tion, and pole shoes associated with said pole
depending pole piece, an axially directed opening
pieces respectively, the pole shoe associated with
extending through said pole piece and said frame
the inner pole piece having a tapered portion ex
member, a homogeneous and unitary pole shoe
tending into said tapered portion of said open—
ing and in ?rm face to face contact therewith and 60 having av cylindrical portion ?tting snugly into
said opening and a lower portion extending out
having a projection ?tting into the other portion
wardly from the periphery of said opening, and a
of said opening, and means located at the end of
welded connection entirely located substantially
said projection remote from the face of said inner
at the outer marginal portion of said cylindrical
pole piece for holding said pole shoe and said
inner pole piece together in flux conducting 55 portion at the end thereof remote from said lower
portion for holding said pole shoe and said frame
contact.
member together in ?ux conducting relationship,
3. An electromagnet comprising a frame hav~
said cylindrical portion having a diameter which
ing spaced inner and outer polar projections de
is at least equal to one-fourth of the diameter
?ning a winding space therebetween, an axially
directed opening in said inner polar projection 60 of said lower portion thereby preventing stretch
ing of said cylindrical portion due to the weight
extending through said frame, at least a part of
of said pole shoe and the attracted magnet load
said opening being tapered with the largest area
and reducing the loading per lineal unit of said
of said opening nearest the face of said inner
polar projection, and a pole shoe associated with
welded connection.
8. A lifting magnet comprising a frame having
said inner polar projection and having a portion 65
spaced inner and outer polar projections de?ning
?tting into said opening, at least a part of said
pole shoe being tapered and ?tting tightly into
a winding space therebetween, an axially directed
opening in said inner polar projection extending
the tapered part of said opening with its pe
ripheral wall constituting a principal flux path
through said frame, a homogeneous and unitary
70 pole shoe extending into said opening and in drive
between the frame and said pole shoe.
(l. A lifting magnet comprising a frame having
_ ?tted ?ux conducting relation to surfaces de?ning
said opening to provide a principal ?ux path from
concentrically arranged inner and outer polar
the inner polar projection to the unitary pole
projections de?ning a winding space therebe~
shoe for conducting to. a load efficiently the ?ux
tween, a frusto-conical opening in said inner polar
projection extending through said frame, the 75 created by said magnet, and means further se
2,410,794
9
curing said pole shoe to said frame and located
at the inner end of said pole shoe.
9. A lifting magnet comprising a magnetic
frame member having upper and lower face sur
faces, an opening in said frame member extending
between said surfaces, a homogeneous and unitary
pole shoe forming the principal means for con
ducting ?ux i mm the central region of the magnet
10
10. A lifting magnet comprising a frame having
spaced inner and outer polar projections de?ning
a winding space therebetween, an axially directed
opening in said inner polar projection extending
through said frame and having a tapered portion
and cylindrical portion, a homogeneous and uni
tary pole shoe extending into said opening and
having a cylindrical portion and a tapered por
tion, said tapered portions of the opening and
said opening and in drive ?tted ?ux conducting 10 pole shoe ?tting together in ?ux conducting rela
tion, and the wall of said cylindrical portion of
relation to surfaces of said frame de?ning said
the opening and the cylindrical wall of the pole
opening, said surfaces constituting the major ?ux
shoe being drive ?tted together, and constituting
path from the frame to the unitary pole shoe, a
a principal ?ux path for conducting to a load
second portion extending outwardly from the axis
substantially all of the flux created by said
of said opening in ?ux conducting relation to said
magnet.
lower surface, and a securing connection between
said ?rst portion and said frame member located
DAVID C‘. VJRIGHT.
at the top of said first portion and holding said
ARTHUR L. WARD.
pole shoe and said frame member together in said
20
?ux conducting relation.
to a load and having a ?rst portion extending into
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