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Патент USA US3046330

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July 24, 1962
Filed July 10, 1959
3 Sheets-Sheet 1
July 24, 1962
Filed July 10, 1959
3 Sheets-Sheet 3
Jn venfor
HORST 6195554’
Patented July 24, 1962
condition on all sides by means of a preferably metallic
Horst Gassen, Geisweid, Kreis Siegen, Germany, assignor
to Stahlwerke Siidwestfalen, A.G., Geisweid, Kreis
Siegeu, Germany, a corporation of Germany
casing. A transverse slit is de?ned in each casing wall
which nevertheless electrically insulates the voltage and
Filed July 10, 1959, Ser. No. 826,184
Claims priority, application Germany July 22, 1958
rectangular to the EMP induced in the casing in order to
prevent secondary current.
The furnace is generally cylindrical so that the encased
coil may be suitably disposed therein. The material to
11 Claims. (Cl. 13-31)
maintains the vacuum tight condition. This slit must be
be treated is situated within the core space of the coil.
In furnaces conventionally used for inductive heating 10 Hence, the slits are preferably approximately defined in
under decreased pressure, where ‘an electric coil is arranged
the casing Walls parallel to the longitudinal axis of the
in the furnace, electric arcs may be ignited in speci?c pres
coil. The sealing of the coil slits may be effected by
sure ranges ‘as soon as the coil voltage rises above 130-250
any suitable means, such as by arranging the correspond
volts, depending upon the particular type of gaseous en
ing slit edges in ?ush or overlapping position.
vironment. In this connection, unfortunately, great ca 15
Advantageously, the casing of the coil may be made of
pacity may only be obtained with safety where high cur
a nonmagnetic metal or of an alloy of a nonmagnetic metal
rent intensities are employed. Even a comparatively small
vacuum type furnace used for melting steel in 25 kilo
or steel.
batches and operating at 250 volts coil voltage, requires
through a conduit extension of the casing passing through
The power supply lines for the coil are introduced
about 5,000 amperes, in order to supply 70 kilowatts to the 20 the wall of the furnace. This extension is in vacuum
tight communication with the main coil casing and is
To maintain the heat required for a vacuum ladle used
sealed from the furnace proper. Alternatively, the casing
for 50 ton steel batches, a furnace capacity of approxi
may form a part of the power supply line itself, for
mately 1,000 kilowatts would be necessary. Thus, if the
instance by directly attaching one end of the coil to the
furnace voltage were limited to 250 volts, then currents of 25 casing wall and connecting the casing wall to the current
the order of magnitude of 70,000 amperes would be re
quired to attain the necessary Wattage. In practice, how
A particular advantage of such arrangements is that
ever, this can hardly be carried out on an economical and
the coil may be provided as a simple Wire ?lament arrange
efficient industrial scale.
ment or litz, i.e., a high frequency conductor made up of
It is signi?cant with respect to safe operation that 30 a number of strands, each separately insulated and inter
electric arcs in vacuum induction furnaces which are pro
woven, and connected together in parallel at the ends,
duced as a result of higher coil voltages may lead to
whereby electrical losses may be minimized. This feature
is of particular value since the coil and the core space
This explosive tendency of electric arcs in vacuum fur
containing the metallic material to be treated, such as
naces can be avoided nevertheless by insulation of all
molten steel, may possess a diameter which exceeds their
current carrying parts against the vacuum.
height, an arrangement which heretofore was not con
this could be carried out in a manner dependable in oper
veniently possible in conventional induction furnaces. The
use of such dimensions, however, is preferred for metal
ation only with great dif?culty. By limitation of the fur
nace voltage to 130-250 volts, the operation of larger
lurgical reasons, particularly on account of the better
vacuum furnaces, for instance, for the melting of over 40 degasi?cation which results during the operation.
one ton of steel or for the maintenance in heated condi
tion of more than 10 tons of steel, is rendered extraor
dinarily dif?cult.
It is an object of the invention to overcome the fore
going disadvantages and to provide an arrangement of
induction coils for vacuum furnaces which makes possi
ble the utilization in the furnace of coil voltages of the
order of 1,000 volts and more, heretofore customary only
in open furnaces, without ‘the aforementioned electric arc
FIGS. 1 and 2 are sectional views through the coil of
a vacuum furnace in accordance with the invention, trans
versely and longitudinally to the coil axis respectively.
The vacuum chamber 7 of the furnace is cyclindrically
arranged and has the same center axis as that of induc
tion coil 1. Coil 1 is completely surrounded by cylindri
cal casing 2 on all sides and its power supply lines 4 are
completely enclosed by the casing extension portion 5.
Casing 2 is provided with a slot opening or slit 3, de?ned
50 in both walls so arranged that no current corresponding
Other and further objects will become apparent from
a study of the within speci?cation and accompanying
to the coil current may ?ow therethrough.
drawings, in which:
3e of the casing are connected together with insulated
screws 3a in pressing contact with a suitable packing
FIG. 1 is a sectional view, transverse to central axis of
At the slit
3, the two corresponding side wall edges 3d, 3d and 3e,
an embodiment of an induction furnace in accordance 55 material, for instance, rubber, 3b and 3c, disposed there
between. Extension portion 5 passes out of the vacuum
with the invention;
FIG. 2 is a sectional view longitudinally of the central
axis of said embodiment;
chamber 7 via opening 6 de?ned in the outer wall of
chamber '7, allowing supply lines 4 to communicate with
FIG. 3 is a sectional view similar to that of FIG. 1
the current supply source.
of a further embodiment of the invention;
By constructing the slit 3 as well as the opening 6 for
FIG. 4 is a sectional view of a further embodiment of
the extension portion 5 of the casing vacuum tight
an induction furnace arrangement showing pouring means
with respect to the vacuum tank 7, such as by means of
as well as heat and induction current insulation means;
rubber or silicon packing material 3b, 30 disposed along
FIG. 5 is a partial sectional view of a further embodi
the slit 3 in both walls of the casing 2 and rubber or
ment of the casing and coil arrangement for an induction 65 silicon packing material 6n disposed along the opening 6
furnace illustrating an alternate form; and
between extension portion 5 and chamber '7, the space
FIG. 6 is a partial sectional view similar to that of FIG.
Within the induction furnace may be readily evacuated
5, wherein the casing is horizontally divided.
as desired. As a consequence, the interior of casing 2
It has been found in accordance with the invention that
containing coil 1 may be kept at any desired pressure,
these objects are realized by providing the coil, with which 70 for instance one atmosphere, without affecting the Vac—
the induction of currents into the metallic material to be
uum conditions in the furnace. The coil voltage may
treated under vacuum is ‘carried out, in vacuum tight
then be maintained just as high as that of conventional
open furnaces. Since the electromagnetic ?eld of the
coil is not essentially disturbed by the slit covering ar
attendant bubbling. The coil 1", for instance, may have
rangement, the insert crucible 9 containing the material
8 to be treated may be heated just as easily as if no cas
ing existed.
In accordance with the invention, the support of the
crucible is no longer effected by the coil itself, but more
advantageously by the casing instead.
38 loops of copper pipe with a cross section of 50 x 20
mm. and the wall thickness of 2 mm. or copper strip with
the cross section of 50 X 5 mm. and be adapted to attain,
from a power source of 50 cycles/ sec. at a coil voltage of
2,000 volts and a current intensity of 4,600 amperes, a
capacity of 1,700 kilowatts. The inside diameter of the
coil may be 250 cm., and its height 210 cm. The pipe
The coil itself may be made of any suitable material
conductor is suitably separated from the surrounding
such as copper pipe and the same may be cooled by
circulating water therethrough. The spool conductor or
coil may also be made of flexible wire or litz carried
cooling water provided by a 2 mm. thick insulating layer
12". The casing 2" is made of nonmagnetic steel with
within an insulating jacket capable of being cooled with
a wall thickness of 5 mm. and has an inside diameter of
246 cm., an outside diameter of about 256 cm. and a
a cooling agent, for instance water, in the same way.
height of 215 cm. From casing 2” top and bottom pipes
The casing, and particularly the slit, may also be con
veniently cooled, for instance by circulating water or oil.
5” conduct the ends 4” of the coil into and out of the
furnace. A further pipe 5” provides a conduit for the
The power supply for the coil may be formed as a
For easier mounting of the coil, a part of the casing, for
instance, the top ring-shaped portion 2a may be provided
distribution within the casing space of circulating cooling
water which may easily pass through coil and casing and
out of the arrangement between top and bottom pipes 5”
and ends 4/’. Each wall of the casing is provided with a
slit opening 3", the edges of the slit being sealed together
as a removable cover, permitting insertion of the coil
by suitable packing material and electrically insulated
from the furnace.
concentrically arranged cylindrical line. Part 5 of the
casing in this case may serve as a suitable outside line.
This cover may be suitably sealed against the
vacuum furnace by means of a rubber or adhesive sealant.
The removable cover of the casing, after the mounting
of the coil, may alternatively be Welded or bonded to the
remaining portion of the casing. Instead of providing
a removable cover, inasmuch as the coil Will not normally
be removed after insertion into the casing, the casing
may be manufactured with a suitable opening for this
purpose, and upon placing the coil within the casing, the
same may be sealed in place by welding or soldering.
FIG. 3 shows a preferred form of an induction coil
furnace such as that to be used for the melting of 500
kilo batches of steel under vacuum. Coil ll’ may have,
for example, a diameter of 70 cm., a height of 28 cm. and
seven coil windings. The coil conductor may be made
of copper pipe having a wall thickness of 2 mm. and may
be covered with an insulating hose of 1 mm. thickness
Coil 1' is situated within the casing 2' having a wall thick
ness of 3 mm. comprising brass sheeting so that between
the coil and the casing there is still su?icient space for
cold water to circulate therethrough, especially along the
side facing the material to be heated. Casing 2.’ in this
case may have an inside diameter of 68.6 cm., an out
In order to prevent the induction of
too high current to the furnace jacket 7”, casing 2" and
coil 1" are surrounded by a number of L-shaped packets
13', 13" of transformer sheets. The lining of the furnace
is rendered ?reproof by the provision for magnesite bricks
10" having a wall thickness of, for example, 20 cm. Space
8" is de?ned within bricks 1.0" which is constructed and
arranged to contain the material to be treated, stopper
2% preventing loss through stopper outlet 24 at the bot~
tom of space 8". Below the stopper outlet of the furnace,
there is provided a socket 14-" having a lid 15", in order
to tightly close off the furnace during the degasi?cation
operation. Alternatively, several outlets for the molten
material may be provided so that the material may be
poured under vacuum into tightly arranged cooling molds
16. Due to the possibility of heating, while pouring, the
molten material may be poured very slowly so that very
long ingots may be obtained having a small diameter and
a structure similar to parts obtained by continuous cast
ing techniques.
In addition, the cooling molds may be suitably water
cooled and connected directly to the pouring spouts via
side diameter of about 72.4 cm., and a height of 34 cm.
The furnace may be provided with a lid to which may
At the slit 3’ the two corresponding side wall edges of
be advantageously attached pumping nozzles, feed sluices,
the casing are connected together with insulated screws
blowing devices, measuring and observation devices, and
in pressing contact with a suitable packing material, for
the like.
instance rubber, disposed therebetween. The upper coil
With respect to FIG. 5, a construction is shown in
end of the coil conductor is connected via power supply
which casing 2”’ is provided with inlet and outlet means
line 4’ toward the exterior of the furnace through the
119" and 20" for a coolant to be circulated within the in
tubular appendage ‘5’ of casing 23’. The lower coil end
terior of casing 2"’. The coil in this embodiment is made
is connected for conduction at 21' directly to the casing
up of a litz 17'”, i.e., a high frequency conductor having
2’ so that the appendage 5’ may act as the second power
a number of strands, in this instance 7 strands, each sepa
supply line. Appendage 5' is suitably sealed by packing
rately insulated and interwoven, and connected together
material 611' at its seating in the opening 6' of the wall
in parallel at their ends. Because of the particular con
of the vacuum furnace 7’. On the other side, the projec
struction utilizing a litz or litzendraht, the AC. response
tion 9’ of the coil is insulatedly seated by packing mate
is less than that of the equivalent cross-section of an
rial 6a’ in its opening 6’ on the furnace wall 7’. For 60 analogous solid conductor, owing to the reduction in skin
support of the crucible 10’ which may be made of ceramic
effect. Surrounding the litz coil 17"’ is an insulation
material casing 2’ carries at its lower end a supporting
jacket 18"’ which protects the litz 17"’ ‘from the circulat
frame 11’. Within crucible 10’ lies a block of material
ing coolant which, in this instance, may be water. More
to be heated 8’, which has a diameter of 56 cm. and a
importantly, such insulated or insulation jacket 18"’ serves
height of 28 cm. If the coil is connected to a 1,000 kilo 65 to insulate electrically the coil 17"’ from the surrounding
cycle power source with a voltage of 900 volts, the fur
wall of casing 2" so that no short circuits Will occur be
nace will attain with a current of 6,000 amperes, a capac
tween these elements. It will be seen from this ?gure that
ity of 480 kilowatts.
su?icient space is provided between the adjacent turns of
FIG. 4 is a the longitudinal section through a vacuum
coil 17"’ as well as between said coil and the surrounding
furnace which may be used to carry out the degasi 70 casing wall to permit suf?cient passage of coolant so as
?cation of molten metals, such as 50 ton steel batches.
to carry out the desired heat exchange.
By using the induction coil arrangement in accordance
Concerning FIG. 6, a similar embodiment is shown to
that of FIG. 5, wherein a litz coil 17”’ enclosed wlthm
steel during degasi?cation is prevented and the molten ma
an insulation jacket 18”’ is provided within a casing hav
terial is maintained in agitated condition by the constant 75
with the invention, a decrease in the temperature of the
ing cooling inlet and outlet means 19" and 2t)". The
8. An induction furnace according to claim 1 wherein
casing 2"" in this embodiment, however, is horizontally
induction current insulation means are provided around
divided to form an upper portion 2a"" and a lower portion
2b”". These portions are connected together by means
wardly through the Walls of said chamber.
of strips 23 of sealing or packing material.
Of course,
said casing whereby to prevent passage of current out
in place of strips 23, the connection between the top
9. An induction furnace according to claim 1 wherein
?reproo?ng means are provided along the walls of said
and bottom portions may be effected by means of solder
chamber surrounding said casing.
ing or welding together the appropriate edges.
10. An induction furnace according to claim 1 wherein
I claim:
a pouring outlet for molten metallic material is provided
1. An induction furnace for heating metallic materials 10 in said furnace chamber.
under vacuum conditions by means of induction current
11. An induction furnace for heating metallic materials
which comprises a furnace chamber capable of being
under vacuum conditions by means of induction current
maintained under vacuum conditions, an induction coil
which comprises a furnace chamber capable of being
means disposed Within said chamber, a metallic casing
maintained under vacuum conditions, an induction coil
enclosing said coil means in vacuum sealed condition with 15 means disposed within said chamber, a metallic casing
respect to said chamber and having an open core space
having an inner and an ‘outer Wall concentric with one
axially de?ned therethrough constructed and arranged to
another and connected at their upper and lower edges
receive therewithin metallic material to be treated, said
enclosing said coil means therebetween in vacuum sealed
casing having a transverse slit opening de?ned therein,
condition with respect to said chamber, an open core
said slit opening being in vacuum sealed condition with
respect to- said chamber, and means for supplying induc
tion current to said coil means.
2. An induction ‘furnace according to claim 1 wherein
the casing is made of non-magnetic metallic material.
3. An induction furnace according to claim 1 wherein
a portion of the casing is provided as one of the means
for supplying induction current to said coil means.
4. An induction furnace according to claim 1 wherein
the coil means is litz.
5. An induction furnace according to claim 1 wherein
a crucible supporting means is provided lbelow said casing
for retaining the material to be treated.
6. An induction furnace according to claim 1 wherein
means for circulating a cooling agent around said coil
means and through said casing is provided.
7. An induction furnace according to claim 1 wherein
the coil means is a tubular coil and means are provided
I for circulating a cooling agent through said coil.
space being de?ned by said inner wall constructed and
arranged to receive therewithin metallic material to be
treated, said casing having a transverse slit opening de
?ned through said inner and outer walls, said slit opening
being in vacuum sealed condition with respect to said
chamber, and means for supplying induction current to
said coil means.
References Cited in the ?le of this patent
Brace _______________ __
Tama _______________ __
Van Embden __- ______ __
Tudbury _____________ __
Mar. 15, 1932
June 27, 1933
Jan. 19, 1943
Oct. 20, 1959
Switzerland ___________ __ Sept. 1, 1934
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