Note: Descriptions are shown in the official language in which they were submitted.
7;Z0~6
For use in applications such as transformers it is known
that cores can be made from ferromagnetic material, where the
cores are constructed typically of a plurality of laminations made
-from strip material. Generally, the laminations are magnetically
insulated one from the other; this is achieved typically by coating
the laminations with varnish and the like. This prevents in the
assembled core current from circulating between the laminations to
result in excessive core loss. It is also known to provide cores
! made from ferromagnetic ma~erial in powder form. With this
practice, the powder may be pressed and sintered to produce
laminations of the desired thickness which are then assembled to
form the core. Cores constructed from laminations of ferro- ;
magnetic powder provide manufacturing cost advantages over the
practice of constructing the core from laminations made from strip
material. They provide, however, manufacturing disadvantages in
that the sintering of ind;vidual laminations results in poor
utilization of the sintering furnace. If the individual
laminations are assembled prior to sintering this results in a
cumbersome and expensive additional manufacturing operation in the
overall practice.
. .: .
.. . .
. . .
.,
i~ '
,.~ -1 ~
. . .
,:
.,. ~
.,
.,
ili7Zt;)(~6
.,
It is accordingly an object of the-invention to provide
a method for manufacturing cores from ferromagnetic powder that
provides, in combination, a metal core having the improved
properties resulting from the use of ferromagnetic laminations
, 5 achieved by an economic and efficient manufacturing practice.
This and other objects of the invention will be apparent
from the following description and specific examples of the
~ practice of the invention.
'~ ~
The practice of the invention ~ s for the manufac-
: 10 ture of a core for alternating current appl 00 ~ by placing a
plurality of layers of the selected ferromagne~ ~wder into a
container with each layer being separated one from the other.
` - When the desired number of layers, each one constituting a
lamination in the final core, have been provided in the container
tne powder is consolidated to form a core of intermediate density.
This core is then sintered in the conventional manner to achieve
further densification. The ferromagnetic powder used in the
practice of the invention may be an elemental ferromagnetic
powder,a prealloyed ferromagnetic powder or a blend of ferro-
, magnetic powder with one or more alloying elements. The powder
may be made by conventional atomizing techniques, with examples
thereof being atomized low carbon steel, atomized low carbon
silicon-iron, atomized low carbon nickel-iron, or a blend of
atomizing low carbon steel with nickel-molybdenum or cobalt
powders singly or in combination. As is conventional practice a
:
separating medium is provided between the layers or laminations in
the practice of the invention. The separating medium may be in
powder form or solid form, such as conventional alumina fiber
sheet. If a separating medium in powder form is used such may be
:'
:.`
` -2-
.
,~
'`
:
~::
1~7Z~)Q6
aluminum oxide, zirconium oxide or mixtures thereof. In an
alternate procedure with respect to the invention each layer of
ferromagnetic powder may be separately compacted within the
container prior to consolidation to form the core.
More specifically with respect to the practice of the
invention, in the manufacture of a core for magnetic applications
the desired number of core laminations is determined. The total
weight of the metal in powder form for the specific core would be
divided into essentially equal portions in accordance with the
` 10 number of laminations required. Each of the portions would be
introduced sequentially into a mold or die cavity having an
internal cross section conforming substantially to that desired in
- the core to be produced. The die would typically be provided with
movable upper and lower die punches. Between each layer of ferro-
magnetic material there would be provided an insulating medium
: which may be solid or powder form as described hereinabove. When. ` all of the ferromagne~ic layers and insulating medium have been
introduced to the die cavity, the upper and lower punches would
be activated to press the powder material into a laminated core of~
,intermediate density. The density should be sufficient to permit
handling particularly for conventional sintering. Sintering
would be conducted in a furnace wherein the core would be moved
through the furnace and heated to a temperature of, for example
2300F. This would then achieve a core with the final desired
density. By using the alternate procedure of separately compacting
each layer of ferromagnetic powder prior to introducing a succeed-
!::
ing layer and prior to consolidating to form the core, this
` alternate practice insures more uniform compacting throughout the
thickness of the core prior to sintering.
, -3-
.
.,
11720U6
The following constitutes specific examples of the
practice of the invention:
EXA~fPLE A:
Atomized steel powder of -lO0 mesh of the conventional
composition identified as Ancorsteel lOOOB was blended with ferro-
phosphorus powder, which had an average particle size of 13.5~m.
A blend of these powders, identified as Blend A2, was made to
produce a 0.75 weight percent phosphorus-iron composition. The
blend also contained 0.5% by weight zinc stearate, which was
provided as a lubricant to facilitate ejection of the pressed
powder material from the mold. From Blend A2 three powder charges
of 24 grams, two of 12 grams and three of eight grams were
- provided. From the 24-gram charge a single lamination in the form
of a toroid was produced by double action pressing at 45 tons per
square inch. The toroid had a nominal outside diameter after
pressing of 3.75 centimeters and an inside diameter of 2.50
centimeters. The 12-gram and eight-gram charges were similarly
pressed to form toroids. All of the toroids so produced were
sintered for 60 minutes at 2300F in a vacuum furnace. A pressure
jof 0.1 Torr (13.3 Pa) was maintained with a hydrogen atmosphere
during sintering. The toroids were furnace cooled to room
temperature. The characteristics of these samples are summarized
in Table I.
117~ 6
TABLE I
Outside Inside
Sample Weight ~iameter Diameter Thickness Density
No. grams cm. cm. cm. g/cm3
3 1 23.7897 3.726 2.550 0.567 7.24
2 11.8440 3.726 2.550 0.285 7.17
3 11.8691 3.724 2.550 0.284 7.22
4 7.9080 3.726 2.550 0.192 7.17
5 7.8882 3.725 2.550 0.189 7.21
6 7.8991 3.723 2.550 0.190 7.23
The toroid identified as Sample No. 1 produced from the
24-gram charge was prepared and magnetically tested. The toroids
produced from the two 12-gram charges were combined and identified
as Sample Nos. 2 and 3 to provide a two-lamination core with a
- single air gap. l'he three toroids produced from the three eight-
. gram charges were combined to provide a three-lamination core with
two air gaps and`are identified as Samples Nos. 4, 5 and 6.
The cores were magnetically tested in identical fashion
by placing them in fiber cases. The cores were uniformly wound
with 100 turns primary and 100 turns secondary winding. The
density of each core was determined from its weight and physical
dimensions. The cross-sectional area for the voltage and
` induction level was determined from the core weight, mean magnetic
path length and density in accordance with conventional practice.
The peak magnetizing force was determined by calculations from
peak-peak voltage reading across a small series resistance. The
cores were demagnetized using 60 Hertz voltages slowly decreased
from a value well over the knee of the induction-peak magnetizing
force curve to zero voltage. The core loss values were determined
by testing the samples from the lowest to the highest induction
levels using conventional ~S~ test procedures recommended for the
purpose.
1~72~)6P6
Table II lists the 60 Hertz peak magnetizing force at
induction levels of one to 10 kilogauss in one kilogauss increments.
TABLE II
60 HERTZ PEAK ~IAGI~ETIZING FORCE (Hp) IN OERSTEDS
AT VARIOUS INDUCTION LEVELS
Sample~lagnetizing Force-Oersteds
No.1 KG 2 KG 3 KG 4 KG 5 KG 6 KG 7 KG 8 KG 9 KG 10 KG
1 .969 1.607 2.563 3.889 5.865 8.441 11.552 15 045 19.635 26.138
2~3 .778 1.150 1.556 2.193 3.047 4.055 5.457 7.204 9.308 11.935
4,5,6 .663 0.946 1.229 1.543 2.002 3.576 3.366 4.144 5.202 6.566
Table III lists the 60 Hertz core loss in watts per
pound at induction levels of one~to 10 kilogauss in one kilogauss
increments.
TABLE III
60 HERTZ CORE LOSS IN WATTS PER POUND
AT VARIOUS INDUCTION LEVELS
.
Sample Core Loss - Watts Per pound
No 1 KG 2 KG 3 KG4 KG 5 KG 6 KG 7 KG 8 KG 9 KG 10 KG
1 .0820 .274 .624 1.34 2.37 3.92 6.759.88 14.08 --
2&3 .0603 .189 .395 0.713 1.28 2.02 3.054.45 6.78 9.27
4,5,6 .0486 .152 .304 0.520 0.891 1.33 1.92 2.71 3.74 5.07
EXAMPLE B:
The ferromagnetic powder, Blend A2 of Example A, was
used with tabular alumina powder containing A12O3 in excess of
99.5% by weight with a particle size of -28/+48 mesh as a
separating medium in powder form in accordance with the practice
of the invention. Two 12-gram charges and three 8-gram charges
were prepared from Blend A2. A core was produced using a mold
of the dimensions described in Example A by providing a layer of
12 grams of Blend A 2 in the mold and 2.50 grams of the tabular
117Z(~Q6
alumina powder was placed on top of the layer of Blend A2. This
operation was repeated and then the powder was pressed at 45 tons
per square inch to form a double laminate core with alumina
powder insulation between each layer. With a similar operation, a
core of three eight-gram laminates separating the alumina powder
was made. The two-laminate core is identified in Table IV as
Sample No. 14 and the three-laminate core is identified as Sample
No. 10. Both cores were vacuum sintered for 60 minutes at 2300F.
The density of both cores was determined to be 7.20 g/cm3. The
cores were magnetically tested in the same manner as those of
Example A. Table IV lists the 60 Hertz magnetizing force at
induction levels of 1 to 10 kilogauss and in one kilogauss
increments for each core.
TABLE IV
60 HERTZ PEAK MAGNETIZING FORCE (Hp) IN OERSTEDS
AT VARIOUS INDUCTION LEVELS
., .
SampleMagnetizing Force-Oersteds
No.1 KG 2 KG 3 KG 4 KG 5 KG 6 KG 7 KG 8 KG 9 KG10 KG
14 1.071 1.811 2.665 3.570 4.501 5.763 7.204 8.861 10.965 13.009
0.859 1.377 1.964 2.563 3.251 3.927 4.794 5.789 6.936 8.313
Table V lists the 60 Hertz core loss in watts per pound
at induction levels of one to 10 kilogauss in one kilogauss
increments for each core.
TABLE V
`~ 60 HERTZ CORE-LOSS IN WATTS PER POUND
AT VARIOUS INDUCTION LEVELS
::`
~ Core Loss - Watts Per Pound
; Sample
` 30 No. 1 KG 2 KG 3 KG 4 KG 5 KG 6 KG 7 KG8 KG 9 KG 10 KG
14 .0885 .307 .658 1.22 1.92 2.82 3.965.97 7.89 10.31
.0634 .229 .485 0.899 1.38 2.00 2.783.7~ 4.87 6.82
--7--
.
~ .
. .,
117ZO~!6
It may be seen that at lower induction levels the
magnetizing force and core losses of the cores of Example B
produced in accordance with the invention are relatively high;
however, at an induction level of about 5 kilogauss and greater
these properties approach the values for the two- and three-
laminate cores of Example A.
EXAMPLE C:
Blend A2 was used to produce cores having two laminations
and cores having three laminations with the practice being
identical to that described and used in Example ~, the only
variation being tha~ in this example the insulating medium was
alumina fiber sheet. The cores were sintered under conditions
identical to that used and described with respect to Example B.
The density of the cores was 7.21 g/cm3. A one lamination core
was also produced in accordance with this practice but without an
insulating layer. This core is identified as Sample No. 2-0; the
two-lamination core is identified as Sample No. 2-1 and the three-
lamination core is identified as Sample No. 2-2-1. These three
core samples were magnetically tested in the manner described with~
` respect to Example A. Table VI lists the 60 Hertz magnetizing
force at induction levels of one to 10 kilogauss in one kilogauss
increments for each core.
TABLE VI
60 HERTZ MAGNETIZING FORCE (Hp) IN OERSTEDS
AT VARIOUS INDUCTION LEVELS
Sample Magnetizing Eorce-Oersteds
No. 1 KG 2 KG 3 KG 4 KG 5 KG 6 KG 7 KG 8 KG 9 KG 10 KG
2-0 .983 1.58 2.53 3.93 5.75 8.36 11.43 14.94 19.92 25.80
2-1 .830 1.28 1.83 2.55 3.47 4.47 6.07 7.79 9.00 12.51
2-2~ 86 1.02 1.33 1.72 2.23 2.~3 3.55 4.44 5.48 6.90
117Z(~1~6
Table VII lists the 60 Hertz core loss in watts per
pound at induction levels of one to 10 kilogauss in one kilogauss
increments for each core.
TABLE VII
60 HERTZ CORE LOSS IN WATTS PER POUND
AT VARIOUS INDUCTION LEVELS
Core Loss - Watts Per Pound
Sample
No. 1 KG 2 KG 3 KG 4 KG 5 KG 6 KG 7 KG 8 KG 9 KG 10 KG
2-0 .0657 .222 .515 1.31 2.34 3.88 6.50 9.61 13.91 19.35
2-1 .0674 .222 .473 0.890 1.47 2.28 3.40 4.89 7.35 9.96
2-2-1 .0471 .155 .314 0.536 0.986 1.46 2.08 2.90 3.97 5.34
It may be seen from the results in Tables VI and VII
that both the magnetizing force and core loss values are lower at
all induction levels than for the cores of Example B and that
they approach these values determined for the core samples of
Example A.
_g _
.
