Note: Descriptions are shown in the official language in which they were submitted.
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POWDER COMPOSITION, METHOD FOR MAKING SOFT MAGNETIC COMPONENTS AND.SOFT
MAGNETIC COMPOSITE COMPONENT.
FIELD OF THE INVENTION
The present invention relates to iron-based powder compo-
sitions. More specifically, the invention concerns powder
compositions for producing soft magnetic composite compo-
nents by the powder metallurgical production route. The
compositions facilitates the manufacture of the soft mag-
netic composite component having high density as well as
valuable magnetic and mechanical properties.
BACKGROUND OF THE INVENTION
Soft magnetic materials are used for applications, such
as core materials in inductors, stators and rotors for
electrical machines, actuators, sensors and transformer
cores. Traditionally, soft magnetic cores, such as rotors
and stators in electric machines, are made of stacked
steel laminates. Soft Magnetic Composite, SMC, materials
are based on soft magnetic particles, usually iron-
based, with an electrically insulating coating on each
particle. By compacting the insulated particles
optionally together with lubricants and/or binders using
the traditionally powder metallurgy process, the SMC
parts are obtained. By using this powder metallurgical
technique it is possible to produce materials giving a
higher degree of freedom in the design of the SMC
component than by using the steel laminates as the SMC
material can carry a three dimensional magnetic flux and
as three dimensional shapes can be obtained by the
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compaction process.
Two key characteristics of an iron core component are its
magnetic permeability and core loss characteristics. The
magnetic permeability of a material is an indication of
its ability to become magnetised or its ability to carry
a magnetic flux. Permeability is defined as the ratio of
the induced magnetic flux to the magnetising force or
field intensity. When a magnetic material is exposed to a
alternating magnetic field, energy losses, core losses,
occur due to both hysteresis losses and eddy current
losses. The hysteresis loss is brought about by the
necessary expenditure of energy to overcome the retained
magnetic forces within the iron core component and is
proportional to the frequency of the alternating field.
The eddy current loss is brought about by the production
of electric currents in the iron core component due to
the changing flux caused by alternating current (AC)
conditions and is proportional to the square of the
frequency of the alternating field. A high electrical
resistivity is then desirable in order to minimise the
eddy currents and is of especial importance at higher
frequencies. In order to decrease the hysteresis losses
and to increase the magnetic permeablity of a core
component for AC applications it is generally desired to
heat-treat the compacted part.
Research in the powder-metallurgical manufacture of mag-
netic core components using coated iron-based powders has
been directed to the development of iron powder composi-
tions that enhance certain physical and magnetic proper-
ties without detrimentally affecting other properties of
the final component. Desired component properties include
e.g. a high permeability through an extended frequency
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3
range, low core losses, high saturation induction, (high
density) and high strength. Normally an increased density
o_ the component enhances all of these properties.
The desired powder properties include suitability for
compression moulding techniques, which i means that
the powder can be easily moulded into a high density,
high strength component which can be easily ejected from
the moulding equipment and that the components have
smooth surface finish.
Toe present invention concerns a new powder composition
having the desired powder properties as well as the use
of the powder composition for the preparation of soft
magnetic composite components. The new composition can be
compacted (and heat treated) to components having the de-
l5 Sired properties.
Tae present invention also concerns a method for manufac-
turing soft magnetic iron-based components having ecel--
lent component properties as well as the soft magnetic
component per se.
SUMMARY OF THE INVENTION
In brief the powder composition according to the inven-
tion is made up by electrically insulated particles of a
soft magnetic material and a fatty acid amide lubricant.
Optionally a thermoplastic binder is present in the com-
:loci t? on. The method according to the present invention
includes mixing, compaction and optionally heat treatment
of the obtained component resulting in a soft magnetic
iron-based component having excellent properties.
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3a
According to one aspect of the present invention, there is
provided powder composition consisting of irregularly shaped
particles of a soft magnetic material of substantially pure
water-atomized iron or sponge iron, said particles being
provided with an electrically insulating layer, 0.05-2% by
weight of a lubricant selected from the group consisting of
primary amides of saturated or unsaturated, straight fatty
acids having 12-24 C atoms, and optionally polyphenylene
sulphide in a concentration less than 2% by weight.
According to another aspect of the present invention, there
is provided a method for making a soft magnetic component
comprising the steps of: a) mixing the particles and the
lubricant as defined herein to obtain a composition,
b) uniaxially compacting the composition to obtain a
component and c) optionally subjecting the obtained
component to heat treatment.
According to still another aspect of the present invention,
there is provided a soft magnetic composite component
obtained by compacting a composition as defined herein
followed by heat treatment of the compacted component,
having; a density >> 7.5 g/cm3 a maximum relative
permeability, max >- 600 a coercive force, He < 250 A/m a
specific resistivity, p _> 20 pQm.
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DETAILED DESCRIPTION OF THE INVENTION
The powder is preferably a substantially pure, water at-
omised iron powder or a sponge iron powder having irregu-
larly shaped particles. In this context the term "sub-
stantially pure" means that the powder should be substan-
tially free from inclusions and that the amounts of the
impurities 0, C an N should be kept at a minimum. The av-
erage particle sizes are generally below 300 pm and above
pm. Examples of such powders are ABC 100.30, ASC
10 100.29, AT 40.29, ASC 200, ASC 300, NC 100.24, SC 100.26,
MH 300, MH 40.28, MH 40.24 available from Hoganas AB,
Sweden.
According to one embodiment of the invention the powders
used have coarser particles than what is normal in common
die pressing. In practice this means that the powders
are essentially without fine particles. The term "essen-
tially without fine particles" is intended to mean that
less than about 10%, preferably less than 5% the powder
particles have a size below 45 pm as measured by the
method described in SS-EN 24 497. The average particle
diameter is typically between 106 and 425 pm. The amount
of particles above 212 m is typically above 20%. The
maximum particle size may be about 2 mm.
The size of the iron-based particles normally used within
the PM industry is distributed according to a gaussian
distribution curve with an average particle diameter in
the region of 30 to 100 m and about 10-30% of the parti-
cles are less than 45 pm. Thus, the powders used accord-
ing to the present invention may have a particle size
distribution deviating from that normally used. These
coarse powders may be obtained by removing the finer
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fractions of the powder or by manufacturing a powder hav-
ing the desired particle size distribution. The invention
is however not limited to the coarse powders but also
powders having the particle sizes normally used for die
5 pressing within the phi industry are included in the pre-
sent invention.
The electrical insulation of the powder particles may be
made of an inorganic material. Especially suitable are
the type of insulation disclosed in the US 6348265,
which concerns par-
ticles of a base powder consisting of essentially pure
iron having an insulating oxygen- and phosphorus-contai.-
ning barrier. As regards the coating it should be espe
cially mentioned that the properties of the composite
component may be influenced by the thickness of the coa-
ting. -Powders having insulated particles are available as
Somaloy "4 500 and 550 from Hoganas AB, Sweden.
The lubricant used according to the invention is selected
from the group consisting of fatty acid amides. Parti;cu-
larly suitable amides a e primary amides of saturated or
unsaturated fatty acid having 12-24, preferably 14-22 C
atoms and most preferably 18-22 C atoms. The lubricants
may be used in amounts less than 2% and preferably less
than 1.5% by weight of the composition. Especially pre-
ferred amounts of the lubricant are 0.05-1%, preferably
0.05-0.8 more preferably 0.1-0.8% and most preferably
0.1-0.5% by weight. Especially preferred lubricants are
stearic acid amide, oleic acid amide, behenic acid amide,
eurcic acid amide, palmitic acid amide, the stearic acid
amide being most preferred. in the US patent 6,531,389
stearic acid amide seemingly in combination with rapeseed
oil methyl ester is mentioned as a lubricant in connec-
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tion with a termoplastic resin, polyphatalamide as a
binder for the compaction of soft magnetic powders.
Solid lubricants generally have a density of about 1-2
g/cm3 which is very low in comparison to the density of
the iron- based powder, which is about 7.8 g/cm3. As a
consequence, inclusions of these less dense lubricants in
the compositions will lower the theoretical density of
the compacted component. It is therefore essential to
keep the amount of lubricant at low levels in order to
produce high-density components. However, low amounts of
lubricants tend to give ejection problems. It has now un-
expectedly been found that the type of lubricants men-
tioned above can be used in low amounts without ejection
problems.
By replacing the internal lubricants, i.e. lubricants
added to the iron- based powder mix, with lubrication of
the die wall, DWL, in combination with high compaction
pressures high green densities can be reached. One draw-
back with this known method when compacting insulated
iron-based powder at high compaction pressures, is how-
ever that the insulation of the iron-based powder is eas-
ily damaged leading to high core losses at higher fre-
quencies. Furthermore, the use of DWL will add further
process complexibility, it may prolong cycle times and
decrease the production robustness in an industrial envi-
ronment.
According to the present invention the fatty acid amide
may be used as the only additive to the insulated iron
or iron-based powder, although for certain applications
it is advantageous to add minor amounts of a thermoplas-
tic resin, specifically polyphenylene sulfide (PPS). The
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term "minor amounts" should in this context be inter-
preted as less than 2, preferably less 0.8, more prefera-
bly less than 0.6 and most preferably less than 0.5% by
weight of the composition. In amounts lower than 0.05 no
effects of PPS have been observed. Specifically the
amount of PPS could vary between 0.1 and 0.5 and prefera-
bly between 0.2 and 0.5 or 0.4% by weight. The addition
of PPS is of particular interest when good frequency sta-
bility is required.
The combination of PPS and stearic acid is known from the
patent application W001/22448. The examples of this ap-
plication disclose that a soft magnetic material can be
produced by mixing an electrically insulated iron-based
powder with PPS and stearic acid. The mixture is com-
pacted at elevated temperature and the obtained compacted
part is heat treated at 260 C in an atmosphere of nitro-
gen followed by a second heat treatment at 285 to 300 C.
It has now unexpectedly been found that by using the new
powder composition, which includes a fatty acid amide in
stead of a corresponding fatty acid several advantages
can be obtained. Thus it has been found that the new pow-
der has unexpectedly improved lubricating properties,
which results in that lower ejection energy is needed to
eject the compacted part from the die, that higher densi-
ties and that better transverse rupture strength can be
obtained. Furthermore, the compaction step can be per-
formed at ambient temperature. Also the heat treatment
can be facilitated, as the first heat-treating step,
which is required according to the WO publication, can be
omitted.
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Iron-based magnetic powders, which have insulated parti-
cles and which are combined with thermoplastic resins,
are described in the US patent application 2002/0084440.
In contrast to the particles according to the present in-
vention these previously known particles also include a
rare earth element. Furthermore, the thermoplastic resin
is used in relatively large amounts, namely at least 5%
by weight. Additionally, the particle size of the iron-
based powder is quite small (3pm is mentioned as an exam-
ple). A lubricant selected from a wide variety of chemi-
cal compounds may also be included. These powder composi-
tions are taught to be useful preferably for injection
molding, extrusion, injection compression molding and in-
jection pressing for the preparation of highly weather-
resistant bonded permanent magnets.
In order to prepare composite components according to the
present invention the powder composition is first uniaxi-
ally pressed in a die, which normally must not be lubri-
cated, although the powder composition may also be used
in lubricated dies. The compacted component is then
ejected from the die and optionally subjected to a heat
treatment.
The compaction may be performed at ambient or elevated
temperatures and at pressures up to 1500 MPa.
According to a preferred embodiment of the invention the
compaction is performed in a moderately heated tool as in
this way not only the green density and the ejection be-
haviour but also the maximum relative permeability will
be improved. When comparing properties of components com-
pacted at an elevated temperature and at a lower compac-
tion pressure to properties of components compacted to
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the same green density at ambient temperature and at a
higher compaction pressure the component compacted at an
elevated temperature will have a higher permeability. For
larger components it may be necessary to elevate the tem-
perature of the powder as well in order to achieve the
improvements according to the invention.
The heat treatment can be performed in one or several
steps. A recommended one step heat treatment is per-
formed for a period of 30 minutes to 4 hours in an oxy-
gen-containing atmosphere (air) at a temperature between
250 and 550 C.
Another alternative is to perform the heat treatment at
250-350 C for a period of 30 minutes to 3 hours in a air
or inert gas followed by a heat treatment for 15 minutes
to 2 hours in an oxygen containing (air) atmosphere at a
temperature between 350 and 550 C.
A somewhat different heat treatment is recommended when
PPS is included in the composition. Thus in this case the
heat treatment may be performed at 250-350 C for 30 min-
utes to 4 hours in an oxygen-containing atmosphere (air).
Another alternative is to perform the heat treatment at
250-350 C for 30 minutes to 3 hours in air or inert gas
followed by 300-500 C for 15 minutes to 2 hours in an
oxygen containing atmosphere (air).
The possibility of performing the heat treatment by using
different atmospheres, periods of time and temperatures
in order to obtain a final component having the desired
properties makes the new powder composition especially
attractive.
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By compacting a composition comprising an iron- based
insulated powder having coarse particles and a lubricant
as described above at high pressures, such as above 800
MPa, followed by heat treatment of the compacted
5 component, soft magnetic composite components having a
density 7.5 g/cm3, a maximum relative permeability,
}max >- 600, a coercive force, He < 250 A/m and a specific
resistivity, p >- 20 pQm. Such components may be of
interest for the demanding applications required in e.g.
10 stator and rotor components in electrical machines.
The invention is further illustrated by following exam-
ples.
EXAMPLE 1.
The following materials were used.
An iron-based, water atomized powder with particles hav-
ing a thin inorganic coating (SomaloyTM 500, available
from Hoganas AB, Sweden) was*used as starting material.
PPS powder,
Stearic acid powder, lubricant A.
Stearic acid amide powder, lubricant B
3 kg of the base powder SomaloyTM 500 was mixed with PPS
and stearic acid amide or stearic acid, according to ta-
ble 1.
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Table 1. Powder mixes: Lubricants and PPS,(percent by
weight)
Sample number PPS Lubricant
A 1 0.60% 0.2% A
A 2 0.50% 0.3% A
A 3 0.50% 0.3% B
A 4 0.30% 0.3% B
A 5 0.30% 0.4% B
A 6 0.30% 0.5% B
A 7 0.1% 0.3% B
A 8 0.2% 0.3% B
A 9 - 0.4% B
The powder mixes were compacted into ring samples with an
inner diameter of 45 mm, outer diameter 55 mm and height
5 mm at 800 MPa at ambient (room) temperature. Ring sam-
ples with a height of 10 mm were also compacted and the
ejection force was measured on these samples. The ejec-
tion energy is shown in Table 2. The results show that
considerably lower ejection energy is obtained by using
the fatty acid amide.
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Table 2. Ejection energy measured on ring samples with
h=10 mm.
Ejection
Sample Energy
number PPS Lubricant (J/cm2)
A 1 0.60% 0.2 %A 52
A 2 0.50% 0.3% A 46
A 3 0.50% 0.3% B 38
A 4 0.30% 0.3% B 37
A 5 0.30% 0.4% B 33
A 6 0.30% 0.5% B 30
A 7 0.10% 0.3% B 41
A 8 0.20% 0.3% B 39
A 9 - 0.4% B 35
After compaction the parts were heat treated at 290 C for
120 minutes in air. The obtained heat-treated rings were
wound with 25 turns. The relative AC inductance perme-
ability was measured with an LCR-meter (HP4284A) accor-
ding to standard IEC 60404-6, 2nd Edition
2003-06.
The drop in initial permeability (frequency stability) is
shown in tables 3 and 4. The drop in initial permeability
is expressed as the difference between the initial perme-
ability at 10 and 100 kHz divided by the initial perme-
ability at 10 kHz. Table 3 shows that by increasing the
amount of the fatty acid amid from 0.3 to 0.5% a better
frequency stability can be obtained. Table 4 shows that
by using the fatty acid amid instead of the corresponding
fatty acid a better frequency stability is obtained.
Furthermore table 4 discloses that without PPS a larger
drop in frequency stability is obtained. However the ini-
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tial permeability at 1 kHz for A9 was found to be 95 com-
pared with 75 for A3. A high initial permeability at
lower frequencies is advantageous for some applications.
Table 3, drop in initial permeability
Dp 10-100 kHz ( o )
A 4 7.4
A 5 5.2
A 6 4.2
Table 4, drop in initial permeability
Dp 10-100 kHz ( o )
A 2 6.4
A 3 3.9
A 9 20.9
The specific electrical resistivity was measured by a
four point measuring method and is shown in table 5. From
this table it can be concluded that by using the fatty
acid amide in stead of the corresponding acid a consid-
erably higher electrical resisivity can be obtained.
Table S. Resistivity for ring samples
Sample PPS Lubricant Specific electrical re-
number sistance, resistivity
iOhm*m
A 2 0.50% 0.3% A 316
A 3 0.50% 0.3% B 400
Samples were also tested with regard to Transverse Rup-
ture Strength, TRS, after heat treatment at 290 C for 120
minutes in air. The TRS was tested according to ISO 3995.
TRS was also tested on parts at a temperature of 200 C.
The TRS is shown in Table 6. The sample with 0.5% PPS and
0.3% stearic acid amide (A 3) shows significantly higher
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TRS at both room temperature (RT) and 200 C compared with
both the sample with 0.5% PPS and 0.3% stearic acid (A2)
and the sample with 0.2% PPS + 0.6% stearic acid (Al).
The density is higher for a mix with low total organic
content, which will result in higher induction and perme-
ability (pmax).
Table 6. Density and TRS at room temperature and 200 C.
Density TRS TRS
Sample after RT 200 C
number Heat MPa MPa
treatment
PPS Lubricant g/cm3
A 1 0.60% 0.2 %A 7.18 68 51
A 2 0.50% 0.3% A 7.18 46 30
A 3 0.50% 0.3% B 7.19 81 67
A 4 0.30% 0.3% B 7.27 88 73
A 5 0.30% 0.4% B 7.22 87 73
A 6 0.30% 0.5% B 7.17 51 68
A 7 0.10% 0-.3% B 7.35 85 74
A 8 0.20% 0.3% B 7.31 84 71
A 9 - 0.4% B 7.33 87 78
EXAMPLE 2.
The following materials were used.
An iron-based, water atomized powder with particles hav-
ing a thin phosphorus containing inorganic coating
(SomaloyTM 500, available from Hoganas AB, Sweden) was
used as starting material was used as starting material.
PPS powder,
Stearic acid powder, lubricant A
Stearic acid amide powder, lubricant B
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Behenic acid amide powder, lubricant C
Oleic acid amide powder, lubricant D
KenolubeTM.
5 The base powder SomaloyTM 500 was mixed with PPS and
lubricants according to the following table 7.
Table 7. Powder mixes: Lubricants and PPS, percent by
weight.
Sample number PPS Lubricant
B 1 0.50% 0.3% A
B 2 0.50% 0.3% B
B 3 0.50% 0.3% C
B 4 0.50% 0.3% D
B 5 0.30% 0.3% B
B 6 - 0.4% B
B 7 - 0.3% B
B 8 0.1% 0.3% B
B 9 0.2% 0.3% B
B 10 - 0.4% KenolubeTM
The powder mixes were compacted into test bars according
to ISO 3995 at a compaction pressure of 800 MPa at ambi-
ent temperature. After compaction the parts were heat
treated in a two-step heat treatment. The first step was
performed at 290 C for 105 minutes in inert nitrogen at-
mosphere. This step was followed by a subsequent heat
treatment step at 350 C for 60 minutes in air. Samples
were tested with regard to Transverse Rupture Strength,
TRS, according to ISO 3995.
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Results from testing of transverse rupture strength are
shown in table 8. As can be seen from table 8 samples
prepared with mixtures including the fatty acid amide
give sufficient TRS-values. A higher density after heat
treatment is reached, which is beneficial in terms on in-
duction and permeability. If the PPS content is reduced
to 0.3% or less the TRS is increased to values above 80
MPa. The samples without PPS and with the stearic acid
amide lubricant even have TRS values above 100 MPa. The
use of KenolubeTM, which is a conventionally used lubri-
cant, does not result in the required transverse rupture
strength.
Table 8. Density and TRS at room temperature
Sample PPS Lubricant Density TRS-RT
numbers after HT
g/cm3 MPa
B 1 0.50% 0.3% A 7.18 73
B 2 0.50% 0.3% B 7.22 68
B 3 0.50% 0.3% C 7.23 73
B 4 0.50% 0.3% D 7.24 74
B 5 0.30% 0.3% B 7.32 83
B 6 - 0.4% B 7.37 108
B 7 - 0.3% B 7.41 113
B 8 0.1% 0.3% B 7.35 88
B 9 0.2% 0.3% B 7.32 79
B 10 - 0.4% 7.42 32
KenolubeTM
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EXAMPLE 3
This example shows that, in comparison with the commonly
used Zinc Stearate and Ethylene bis stearamide lubri-
cants, low ejection forces during ejection of compacted
components and perfect surface finish of the ejected com-
ponent are obtained, when the fatty acid amide lubricants
according to the invention are used in low amount in com-
bination with coarse powders and high compaction pres-
sures.
Two kilos of a coarse soft magnetic iron-based powder,
wherein the particles are surrounded by an inorganic in-
sulation according to US 6,348,265 were mixed with 0.2%
by weight of lubricants according to table 9. The par-
ticle size distribution of the coarse iron- based powder
is shown in table 10. Mix E and F are comparative examp-
les containing known lubricants.
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Table 9.
Mix Lubricant
A Behenamide
B Erucamide
C Stearamide
D Oleylamide
E Zinc Stearate
F Ethylene bis stearamide
Table 10.
Particle Weight %
size (pm)
>425 0.1
425-212 64.2
212-150 34.0
150-106 1.1
106-75 0.3
45-75 0.2
<45 0
The obtained mixes were transferred to a die and com-
pacted into cylindrical test samples (50 grams) with a
diameter of 25 mm, in an uniaxially press movement at a
compaction pressure of 1100 MPa. The used die material
was conventional tool steel. During ejection of the com-
pacted samples the ejection force was recorded. The total
ejection energy/enveloping area needed in order to eject
the samples was calculated. The following table 11 show
ejection energy, green density and the surface finish.
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Table 11
Mix Ejection energy Green density Surface finish
(J / cm2) (g / cm3 )
A 90 7.64 Perfect
B 83 7.65 Perfect
C 93 7.63 Perfect
D 70 7.67 Acceptable
E 117 7.66 Not Acceptable
F 113 7.64 Perfect
EXAMPLE 4
The following example illustrates the effect of the par-
ticle size distribution of the soft magnetic iron-based
powder on ejection behaviour and green density. A
"coarse" powder according to example 3 was used. The par-
ticle size distribution of the "fine" powder is given in
table 12. The mixes were prepared using 0.2% stearamide
by weight according to the procedure in example 3. The
mixture based on the "fine" powder is marked sample H and
were compared with sample C.
Table 12.
Particle Weight %
size (pm)
>425 0
425-212 0
212-150 11.2
150-106 25.0
106-75 22.8
45-75 26.7
<45 14.3
The mixes were compacted into cylindrical samples accor-
ding to the procedure used in example 3. The following
table 13 shows green density and the surface appearance.
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Table 13
Mix Green density Surface finish
(g/cm3)
C 7.63 Perfect
H 7.53 Acceptable
As can be seen from table 13 the composition containing
5 fine powder results in a lower green density and deterio-
rated surface finish.
EXAMPLE 5.
This example compares a known lubricant, ethylene bis-
stearamide (EBS), and an example of the lubricant steara-
10 mide. A "coarse" powder according to example 3 was used
was mixed with EBS and stearamide, respectively, accor-
ding to table 14. The samples were prepared according to
the procedure in example 3.
15 Table 14.
Mix EBS (weights Stearamide
(weights)
1 0.20 --
2 0.30 --
3 0.40 --
4 0.50 --
5 -- 0.10
6 -- 0.20
7 -- 0.30
The powder mixes were compacted into rings with an inner
diameter of 45 mm, an outer diameter of 55 mm and the
height 10 mm at 1100 MPa. During ejection of the com-
20 pacted samples, the total ejection energy/enveloping area
needed in order to eject the samples from the die was
calculated. The following table 15 shows the calculated
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ejection energy/area, green density and the surface ap-
pearance.
Table 15. Ejection energy, green density, the surface ap-
pearance
Ejection Density
Mix energy [g/cm3] Surface appearance
[J/cm2]
1 54 7.65 Not acceptable
2 40 7.61 Acceptable
3 33 7.56 Perfect
4 28 7.51 Perfect
5 73 7.67 Acceptable
6 38 7.64 Perfect
7 37 7.59 Perfect
As can be seen from table 15 the new lubricant can be
added in amount as low as 0.2% and still a perfect sur-
face finish can be obtained whereas the for the reference
lubricant, EBS, the lowest addition is 0.4% for obtaining
a perfect surface finish.
EXAMPLE 6
This example compares the magnetic properties of compo-
nents manufactured with a minimum amount of the lubrica-
ting components stearamide and EBS respectively, in order
to achieve similar values of ejection energy. Components
made from mix 2 and mix 6 according to example 5 were
compared regarding magnetic properties after heat treat-
ment.
Ring samples according to example 5 except that the
height were 5 mm were compacted. The green samples were
heat treated at 300 C for 60 minutes in air followed by a
second step of heat treatment at 530 C for 30 minutes in
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air. The obtained heat-treated rings were wounded with
100 sense and 100 drive turns and tested in a Brockhaus
hysterisisgraph. The following table 16 shows the induc-
tion level at 10 kA/m, maximum relative permeability, co-
ercive force H,: and core loss at 400 Hz, 1T.
Table 16. Soft magnetic properties.
Sample 2 Sample 6
Max. Permeability 480 750
B at 10000 A/m [T] 1.58 1.66
He [A/ml 218 213
Core loss 400 Hz, 1 T [W/kg] 78.4 42.1
As can bee seen in table 16 the soft magnetic properties
are superior for components according to the present in-
vention.
EXAMPLE 7
The following example shows the influence of die tempera-
ture on the ejection properties and green density of com-
pacted samples. In this example the primary amide,
stearamide, was selected as the amide lubricant according
to the invention. 0.2% of stearamide was added to 2 kg of
a coarse soft magnetic electrically insulated iron-based
powder according to the procedure of example 3.
The powder mixes were compacted into rings having an in-
ner diameter of 45 mm, an outer diameter of 55 mm and a
height of 10 mm, at a compaction pressure of 1100 MPa.
During ejection of the compacted samples the ejection
forces were recorded. The total ejection en-
ergy/enveloping area needed in order to eject the samples
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from the die was calculated. The following table 17 shows
ejection energy, green density and the surface appearance
of the samples compacted at different temperature of the
die.
Table 17. Ejection energy, green density, surface appear-
ance at different die temperatures
Ejection Green Surface
Die temperature energy density appearance
( C) (J/cm2) (g/cm3)
25 38.4 7.64 Perfect
50 31.5 7.66 Perfect
60 30.6 7.67 Perfect
70 29.3 7.67 Perfect
80 27.5 7.69 Perfect
As can be seen from table 17 the ejection energy and the
green density is positively influenced by increasing die
temperature.
EXAMPLE 8
This example compares component properties of components
manufactured according to the present invention to
properties of components compacted with the aid of DWL.
In both the inventive example and the comparative example
a "coarse" powder according to example 3 was used. As lu-
bricant in the inventive example 0.2% by weight of
stearamide was used and the obtained powder composition
was compacted at a controlled die temperature of 80 C
into ring samples having a green density of 7.6 g/cm3. In
the comparative example no internal lubricant was used,
instead DWL was applied. Ring samples were compacted to a
density of 7.6 g/cm3 at ambient temperature.
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The ring samples outer diameter was 55 mm, inner diameter
45 mm and height 5 mm.
After compaction heat-treatment was done according to ta-
ble 18. The specific electrical resistivity was measured
by a 4-point method. Prior to magnetic measurements in
the hysteresis graph the ring samples were wound with 100
drive and 100 sense turns. The DC properties were ac-
quired from a loop at lOkA/m. The core loss was measured
at different frequencies at 1T. In figure 1 the core
loss/cycle is plotted as a function of frequency.
Table 18: Magnetic properties
Sample Heat- BlokA/m HC P Core loss
treatment [A/m] [pcm] @1 T, 400Hz
[W/kg]
Present in- 530 C, 30min 1.65 192 103 41
vention air
DWL- method none 1.66 305 60 60
DWL- method 530 C, 30min 1.66 189 3 109
air
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From the table 18 and figure 1 it can be concluded that
the present invention gives significantly lower core loss
5 in alternating fields due to lower HC and higher resis-
tivity compared to the DWL-method.
EXAMPLE 9
10 In this example it is shown that iron-powder cores with
excellent magnetic properties can obtained by the present
invention. The positive effect of elevated die tempera-
ture on the maximal relative permeability is also shown.
15 A "coarse" powder according to example 3 was mixed with
various contents and types of lubricants. Both ring sam-
ples (OD=55, ID=45, h=5mm) and bars (30x12x6 mm) were
manufactured with the process conditions given in table
19.
The density was determined by measuring the mass and di-
mensions of the ring samples. The specific electrical re-
sistivity was measured by a 4-point method on the ring
samples. Prior to magnetic measurements in a Brockhaus
hysterisisgraph the ring samples were wound with 100
drive and 100 sense turns. The DC-properties such as }.1max
and He were acquired from a loop at 10kA/m while the core
loss was measured at 1T and 400Hz. The transverse rupture
strength (TRS) of the heat-treated parts was determined
on the test bars by a three-point bending method.
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Table 19: Process conditions for ring samples
Com-
Amount pacting Die
Type of Lubri- pres- tempe-
Sample lubricant cant sure rature Heat treatment
(%wt) (MPa) ( C)
Stearamide 300 C 45 min, air+
1 0.2 1100 25 520 C*, air
Stearamide 300 C 45 min, air+
2 0.2 1100 80 520 C*, air
3 Stearamide 0.2 800 80 530 C, 30 min, air
4 Stearamide 0.2 1100 25 530 C, 30 min, air
Stearamide 0.2 1100 80 530 C, 30 min, air
6 Stearamide 0.1 1100 85 530 C, 30 min, air
Stearamide 300 C, lh, air +
7 0.3 800 25 530 C, 30 min, air
Stearamide 300 C, 1h, air +
8 0.3 800 80 530 C, 30 min, air
Stearamide 300 C, lh, air +
9 0.3 1100 25 530 C, 30 min, air
Stearamide 300 C, lh, air +
0.3 1100 80 530 C, 30 min, air
330 C, 2h, air +
11 Erucamide 0.2 1100 25 530 C, 30 min, air
340 C, 2h, N2 + 530 C,
12 Erucamide 0.2 1100 25 30 min, air
*increasing temperature approx 4 C/min in the component
up to 520 C
5
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Table 20: Measurments of component properties
Core loss at 1T
Density HC Resistivity 400 Hz TRS
Sample (g/cm3) Amax (A/m) (}Ohm*m) (W/kg) (MPa)
1 7.62 754 209 473 42 93
2 7.63 852 204 230 40 97
3 7.60 718 208 103 43 n.a
4 7.62 602 198 591 39 59
7.65 861 178 98 37 68
6 7.71 918 177 66 38 78
7 7.49 669 228 574 46 70
8 7.53 880 202 33 48 81
9 7.56 672 224 515 44 67
7.62 860 203 64 43 76
11 7.62 633 192 414 38 54
12 7.68 738 205 614 39 67
