Note: Descriptions are shown in the official language in which they were submitted.
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~THOD OF MAKING A TRANSFOR~ER OR LIXE CORE
F~OM AMORPHOUS STRIP METAL
The present invention relates generally to magnetic cores
for use in transformers or like electrical induction ap-
paratus and more particularly to a specific method of making
a magnetic core from amorphous strip metal.
One common way to make a magnetic core for use in an elec-
trical apparatus such as a transformer is to use magnetic
strip material having a preferred direction of orientation
parallel to the longitudinal direction of the material, e.g.
n-amorphous metal material. This material is relatively
flexible and easy to form into the ultimate shape of the
core, either before or after it is stress relief annealed.
'Therefore, after the core is formed it can be readily-
provided with an unconnected joint, for example by cutting
entirely through one circumferential section and, because of
its flexibility, an associated electrical coil can be easilv
assembled around one section merely by opening the joint and
inserting the coil therethrough. While this technique is
entirely satisfactory when the core is made from non-amor-
phous metal strip material, it has not been proved to besatisfactory when forming a core from amorphous strip
material. This is because the latter, for example METGLASR
(a registered trademark) strip material manufactured by
Allied Chemical Corp., is very thin, very brittle and very
hard. Most attempts to make a core conventionally using
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this matexial have been unsuccess~ul, m~inly bec~use ~mo~-
phous strip metal is difficult to shear without backc~cking
along the shear line. ~toreove~ even if this th~n and
brittle material could be sheared without cracking, the time
S required to make joint cores using the heretofore conVen-
tional approach would be increased significantly due bo the
thinness of the material. Nevertheless, it is desirable to
use amorphous metal to form the core because of the reduced
core losses achieved thereby.
In view of the foregoing, it is a main object of the present
invention to provide a relatively uncomplicated and eco-
no~ical method of making a magnetic core from amorphous
strip metal for use in a transformer or like electrical
induction apparatus and particularly a method which is
reliable in use. As will be described in more detail
hereinafter, the method disclosed starts with a continuous
strip of non-annealed amorphous metal which is initially
wound about a cyclindrical mandrel to form an initially
round core and thereafter clamped in a predetermined way and
cut entirely through a predetermined transverse section.
This cutting procedure, which requires the application of a
rust inhibiting liquid coolant at the cutting section of the
core, results in a plurality of unconnected elongated metal
strips. The unconnected strips are separated into the
number of individual groups which are assembled, one group
at a time, into a substantially oval shaped core and then
formed into its final shape, if not already in its final
shape. Thereafter, the core is annealed and simultaneously
subjected to a magnetic field of predetermined strength.
The method just recited will be described in more detail
hereinafter in conjunction with the drawing wherein:
Figure 1 is a side elevational view of an assembled magnetic
core made in accordance with the present invention; and
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Figures 2a - 2e diagrammatically illustrate a number of
steps in the disclosed method of making the magnetic core
illustrated in Figure 1.
Turning now to the drawing, wherein like components are
S designated by like reference numerals throughout the various
figures, attention is first directed to Figure 1 which, as
stated above, illustrates a magnetic core assembled in
accordance with the present invention. This core which is
generally indicated at 10 and which is especially suitable
for use in a transformer or like electrical induction ap-
paratus initially formed from a continuous strip of amor-
phous metal, for example the METGLASR strip material re-
ferred to previously. The core can be round, rectangular,
somewhat rectangular as illustrated in Figure 1, or any
other suitable shape. In the somewhat rectangular shape
shown, the core includes opposite legs 12 and 14, an upper
yoke 16 and a lower yoke 18. One of these four sections,
for example the upper yoke 16, includes a joint 20 which
serves as an access into and around the core for positioning
an associated electrical coil or coils. One such coil is
shown in Figure 1 at 22.
Joint 20 may be comprised of a planar or straight butt
joint, it may be a stepped joint, a V-notched or it may take
other possible shapes. In addition, the opposite end
sections forming this joint may include protective coatings.
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Turning to Figures 2a through 2e, attention i8 di~ected to a
preferred method of making core 10 made from one or more
cont~nuous strips of amorphous metal, for example the
METGhASR material referred to previously. In Figure 2a, two
S continuous strips 24 are illustrated. These strlps are
initially stored on their own reels 26. The first step ln
the present method calls for winding the continuous strip or
strips about a cylindrical mandrel 28 to form an initially
round core generally indicated at 30. In the preferred
method, it is important that core 30 be wound round so that
the strip or strips 24 are not subjected to a jer~ing or
similar irregular motion that could cause breakage. More-
over, by winding the strips around mandrel 28 without
~` excessive acceleration, the speed of windingJ10 can actually
be increased.
After forming an intially round core 30, the latter is
clamped in the predetermined way illustrated in Figure 2b.
The clamping arrangement generally designated by the re-
ference numeral 32 is shown diagrammatically in this figure
to include a steel or otherwise rigid base plate 34 and two
removable steel or otherwise rigid clamping plates 36.
While not shown, suitable means are provided to maintain the
clamping plates 36 above base plate 34 such that the ini-
t ally round core 30 is maintained therebetween in a some-
what compressed, substantially oval shaped state indicatedgenerally at 38. In t~is regard, the confronting ends of
the clamping plates are spaced from one another in order to
expose a transverse section of the core.
With oval shaped core 38 clamped into the position illus-
trated in Figure ~2b, a cutting tool, preferably a power saw
including an abrasive circular saw blade 40 constructed of,
for example aluminum oxide or silicon carbide with resin or
rubber bond, is used to cut entirely through the previously
mentioned exposed transverse section rom one edge of the
oval shaped core to its opposite edge. In this regard, the
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power saw itself may be a table ox ~adial a~ saW and ~n
appropr~ate steel or otherwise rig~d ~lock 42 is preferably
disposed inside the core, as shown in Figure 2b, to receive
the inwardly projecting edge of saw blade 40 ~or guiding the
latter across the core as the ~lade cuts through the exposed
transverse section thereof. At the sa~e time, block 42
serves as a support between the base plate 34 and clamping
plates 36 for allowing greater compression of the core
laminations on either side of the transVerse section being
cut. This reduces the possibility of backcracking, burrlng
and/or swelling along the cut. In any event, once the cut
is made, a plurality of unconnected elongated strips of the
material result.
An amorphous metal is a non-crystalline material. When the
amorphous metal is overheated, the material degrades its
~uperior magnetic characteristics ~or loses ~ non-crys-
talline characteristics). Therefore, a supply of rust
inhibiting coolant is needed to prevent overheating while
cutting. Contact pressure between the material and the
cutting wheel is critical. ~eat will generate easily un~er
high contact pressure. The contact pressure is controlled
by the wheel running speed and the advance speed of the
work piece. The proper wheel running speed was 100 to
120 ft/sec and the advance speed of the work piece was
2 inch square per hour for cutting in an actual embodiment.
This of course may vary depending upon the cutting wheel
and material being cut. The supply of rust inhibiting
coolant is continuously supplied in the form of a spray by
suitable means including, for example, two nozzles generally
indicated at 44 in Figure 2b. In a preferred embodiment,
the coolant is a water based coolant, specifically water
containing Nu-oil from Pittsburgh Chemical Mfg. Co. as a
rust inhibitor. Nevertheless, in order to further prevent
rusting, the various unconnected elongated strips which
resulted from the cutting operation as discussed above, are
a~ soaked in an alcohol base compound, specifically methyl
,
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alcohol to remove most of the wate$ coolant. The uncon-
nected strips are then heated in an oven, p~efe~r~ly at
125C, for a period of time su~ficient for them to d~y.
While the present invention is not limited to a water b~se
coolant, although it is preferred, and while the present
invention is not limited to the particular parameters used
in the drying of the strips, when a water based coolant is
used, the drying step just mentioned is a very necessary
step in the overall process to prevent excessiVe rustinq and
swelling. The little oxide that is left on the unconnected
strips as a result of the water is so thin that it does not
appreciably affect the space factor between turns of the
ultimately formed core, but does beneficially increase
surface resistance. After this treatment, the unconnected
lS strips will more readily slide past one another and not
stick together so that they can be separated into groups and
provided with the appropriate end shapes to be discussed.
As just stated, once the oval core 38 is cut and the re-
sulting 1mconnected strips are dried (assuming a water based
coolant is used) the individual unconnected strips are
assembled into a number of groups having specifically shaped
ends depending upon the particular type of joint 20 desired
in the end product. One group of unconnected strips is
shown in Figure 2c and generally indicated at ~6. This
group is shown having tapered ends 46a and 46~ necessary to
provide the ultimately shape2 joint shown in Figure 1. This
particular configuration may be provided by initially
taking the full stack of unconnected strips and lining them
up square on one end by tapping the ends with a flat block.
If more slope is required, the stacks can be shifted by
alternately clamping one end of the stack and then the other
end, synchronized with flexing of the stack. For some types
of joints, such as an alternate butt lap joint, this shift-
ing is unnecessary. ~ith the exception of a square butt
joint or a sloping butt joint, the stack is eivided into the
previously mentioned indivi2ual groups 46. In any case, if
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~he ends of each group are to ha~e the co~tings descxihed in
- the above-recited Lin et al patent application~ such co~t-
ings would be provided at this ti~e.
Once the indi~idual groups 46 are provided, the outermost
group, e.g. the group of longest unconnected strip~
fixedly maintained in an oval ~preferably ellipt~c41~ shape
with its ends brought together and taped to remain in place,
as illustrated in Figure 2d. As seen there, outermost group
46 is held in the position just descri~ed by suitable means,
for example a pair of confronting clamping plates 4~. Once
outer group 46 i5 SO positionea, the remaining groups are
successively placed, one at a time, inside the oute D st
group starting with the next longest group of unconnècted
strips and ending with the shortest group. This is ac-
complished by flexing each individual group into its self so
~ that the latter may be located concentrically within thelast assembled qroup. The group being so assembled is then
allowed to snap back into position such that its oppos~te
ends engage one another in the manner shown ~n Figure 2d.
20. While not shown, a wire, band or other suitable means may be
provided to prevent disassembly of the ultimately formed
oval (or elliptical) core formed between the clamping plates
48 when the latter are ved. The oval ~or elliptical) core
is generally indicated at 49.
Once core 49 has been formed, if its oval or elliptical
shape is not the shape desired for end core 10, the end
shape is provided. This is best accomplished using a
series of clamps which may be readily provided. For ex-
ample, Figure 2e illustrates a series of inner and outer
clamping plates 50 which comprise part of an overall clamp-
ing apparatus 52 readily pro~ided by those with ordinary
skill in the art. While not shown, the overall apparatus
will include means or adjusting the space between the
~arious confronting plates and the location of the plates
relative to one another to provide the desired shape for the
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core. In Figure 2e, the oval or elliptical core 48 in
Figure 2d is shown converted to the somewhat rectangular
shape of Figure 1. This rectangularly shaped core which is
generally designated by the reference numeral 53 is provided
with a current coil 54 which is wound around one section
thereof. This coil which is indicated generally at 54 is
connected to a source current, either direct current or
alternating current 56 resulting in the passage of current
generally indicated at I through the coil. This current, in
turn, subjects the coil to a magnetic field. In a preferred
embodiment, this field is between 5 and 20 oersteds, speci-
fically 10 oersteds in a most preferred embodiment. At the
same time, the entire core is annealed, preferably in a
protective atmosphere, for example, a vacuum, an inert gas
such as argon or a reducing gas such as a mixture of
nitrogen and hydrogen. In a preferred embodiment, the core
is annealed for between 1 and 3 hours, most preferably for
two hours, at a temperature between about 340C and 370C
(the range of these temperatures is suitable for Allied
Chemical Corp's METGLASR materials 2605S and 2605SC). The
core is cooled down preferably gradually specifically at a
rate of 1.67C per minute until the core is 150C. By
annealing the core and subjecting it to a magnetic field as
described, its core losses are reduced, as is known. Once
the core 52 has been annealed and subjected to the magnetic
field, the coil 54 can be removed and the final electrical
coil or coils 22 can be placed around one section thereof in
a suitable manner.
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