Note: Descriptions are shown in the official language in which they were submitted.
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1
SOFT MAGNETIC POWDER COMPOSITION COMPRISING INSULATED
PARTICLES AND A LUBRICANT SELECTED FROM ORGANO-SILANES, -
TITANATES, -ALUMINATES AND ZIRCONATES AND A PROCESS FOR THEIR
PREPARATION.
FIELD OF THE INVENTION
The present invention relates to new metal powder
compositions. More specifically, the invention concerns a
new iron-based powder which is useful for the preparation
of soft magnetic materials having improved properties
when used both at high and low frequencies.The invention
also concerns a method for the manufacturing of soft
magnetic composite materials prepared therefrom.
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 having 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
compaction process.
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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
varying field, energy 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. 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. A high electrical resistivity of
the component is desirable in order to minimise the eddy
currents.
Research in the powder-metallurgical manufacture of
magnetic core components using coated iron-based powders
has been directed to the development of iron powder
compositions that enhance certain physical and magnetic
properties without detrimentally affecting other
properties of the final component. Desired component
properties include e.g. a high permeability through an
extended frequency range, low core losses, high
saturation induction, and high strength. Normally an
increased density of the component enhances all of these
properties provided that a sufficient electrical
resistivity can be maintained. The desired powder
properties include suitability for compression moulding
techniques, which i.e. means that the powder can be
easily moulded to a high density component, which can be
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3
easily ejected from the moulding equipment without
damages on the component surface.
SUMMARY OF INVENTION
The present invention concerns a new ferromagnetic powder
composition, which is suitable of compaction to high den-
sity composite components. More specifically the present
invention concerns a powder composition comprising soft
magnetic iron or iron-based core particles, the surface
of which are surrounded by an electrically insulating in-
organic coating and which composition also includes a lu-
bricating amount of silanes, titanates, aluminates, or
zirconates.
The present invention also includes a method of preparing
high-density green, and optionally heat-treated, compacts
from these compositions. This method comprises the steps
of providing the composition, optionally mixing said com-
position with additives, such as conventional lubricants
(i.e. particular lubricants) and binders as well as flow-
enhancing agents; uniaxially compacting in a die at high
pressure and ejecting the green body, which may subse-
quently be heat-treated.
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3a
According to one aspect of the present invention, there is provided a
ferromagnetic powder composition for die compaction to produce high density
soft
magnetic composite parts comprising soft magnetic iron-based core particles
wherein at least 40% of said iron-based core particles consist of particles
having a
particle size above 106 pm and less than 5% of said iron-based core particles
having a particle size below 45 pm and wherein the surface of the core
particles
are surrounded by an insulating inorganic coating, and a lubricating amount of
a
compound selected from the group consisting of silanes, titanates, aluminates,
zirconates, and mixtures thereof, having the following general formula:
M(Ri)n(R2)m,
wherein M is a central atom selected from Si, Ti, Al, and Zr,
R, is a hydrolysable group,
R2 is a group consisting of a lubricating organic moiety,
wherein the sum of m+n is the coordination number of the central atom;
n is an integer >_1 and
m is an integer >_1.
Brief description of the drawings
Figure 1 demonstrates transverse rupture strength at different
density levels.
Detailed description of the invention
The ferromagnetic powders used herein are made up of iron or
an alloy containing iron optionally in combination with up to 20 % by weight
of
one or more of element selected from the group consisting of aluminium,
silicon, chromium, niobium, molybdenum, nickel and cobalt. Preferably the
new powder is based on a base powder that consists of essentially pure iron.
This powder could be e.g. commercially available water-atomised or
gas-atomised iron powders or reduced iron powders, such as
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sponge iron powders. The powder particle shape could be
round, irregular or flat.
Preferred electrically insulating coatings, which may be
used according to the invention, are thin phosphorous
containing coatings of the type described in
the US patent 6348265. Also other,
preferably inorganic coatings may be used,
for example coatings based on Cr, Mg, Mo, Zn, Ni, or Co.
The lubricating agent used according to the invention is
a type of organo-silanes, organo-titanates, organo-
aluminates or organo-zirconates. This class of
substances is often referred to as surface modifying
agents, coupling agents, or cross-linking agents
depending on the chemical functionality of their linked
groups. The specific type of organo-silanes, organo-
titanates, organo-aluminates or organo-zirconates which
are used according to the present invention and which may
be referred to as organo-metallic compounds are
distinguished by the presence of at least one
hydrolysable group and at least one lubricating organic
moiety. This type of compounds can be defined by the
following general formula:
M(R1)n(R2)m
,wherein M is a central atom selected from Si, Ti, Al,
and Zr; R1 is 'a hydrolysable group; R2 is a group
consisting of a lubricating organic moiety; wherein the
sum of m+n must equal the coordination number of the
central atom and where n is an integer >l and m is an
integer >_l.
Particularly R1 is an alkoxy group having less than 12 C
atoms. Preferred are those alkoxy groups; which have less
than 6, and most preferred are alkoxy groups having 1-3 C
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atoms. R1 may also be a chelate group, such as a residue
of hydroxyacetic acid (-OC(0))-CH2O-) or a residue of
ethylene glycol (-OCH2CH2O-) .
R2 is an organic group including between 6-30, preferably
5 10-24 carbon atoms optionally including one or more
hetero atoms selected from the group consisting of N, 0,
S and P. R9 is a group consisting of an organic moiety,
which is not easily hydrolysed and often lipophilic and
can be a chain of an alkyl, ether, ester,
phospho-alkyl, phospho-lipid, or phospho-amine. The
phosphorous may be present as phosphato, pyrophosphato,
or phosphito groups. Furthermore, R2 may be linear,
branched, cyclic, or aromatic.
A preferred group of lubricating silanes according to the
present invention are alkyl-alkoxy silanes and polyether-
alkoxy silanes. Furthermore, promising results have been
obtained with hexadecyl-trimethoxy silane, isopropyl-
triisostearyl titanate, isopropyl-tri(dioctyl)phosphato
titanate, neopentyl(diallyl)oxy-tri(dioctyl)phosphato
zirconate, neopentyl(diallyl)oxy-trineoclecanoyl
zirconate, and diisobutyl-acetoacetyl aluminate.
The amount of the compound is preferably present in
amounts above 0.05%, such as in amounts of 0.05-0.5%,
preferably 0.07-0.45%, and most preferably 0.08-0.4% by
weight of the composition. A too low amount of
lubricating agent gives high density but results in poor
ejection behaviour and may thus result in poor surface
condition of the tool and/or SMC parts. A too high
amount, however, may give excellent ejection behaviour
but could render in low component densities. Furthermore
it is preferred that the compound is present as a
lubricating layer on the insulated particles. It should,
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however, be noted that the geometry of the component as
well as the material and quality of the tool, have great
impact on the surface condition of the SMC parts after
ejection.
The use of compounds organo-silanes, organo-titanates, or
organo-aluminates is known from US patents 4820338 and
6537389. According to the US patent 4820338 silanes,
titanates or aluminates are used in order to accelerate a
coupling between the magnetic powder particles and an
electrically insulating organic binder polymer. The
powder particles do not have an inorganic coating.
The US patent 6537389 discloses a wide range of silicon-,
aluminium-, or boron-containing compounds as molecular
precursors for producing electrically insulating ceramics
on soft magnetic powders. The precursor compounds are
converted by thermal treatments into ceramic, metallic or
intermetallic end products to enhance temperature and
solvent resistance. The US patent 6537389 distinguishes
from the present invention i.a. in that the organo-
metallic compounds are used as precursors for producing
chemically and thermally resistant coatings, and not as
the key component that facilitates production of high
density parts. Furthermore, the precursor compounds
described in the examples of US patent 6537389 do not
include a lubricating moiety.
The lubricating compound(s)used according to the present
invention can be used in such a way that it is dissolved
or dispersed in a suitable solvent, e.g. an organic sol-
vent, such as acetone or ethanol. The obtained solution
or dispersion is subsequently added to the iron based
powder during mixing and optionally heating. The solvent
is finally evaporated optionally in vacuum.
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According to one embodiment of the invention the powder
used has coarse particles i.e. the powder is essentially
without fine particles. The term "essentially without
fine particles" is intended to mean that less than about
5 % of the iron or iron-based powder particles have size
below 45 pm as measured by the method described in SS-EN
24 497. So far the most interesting results have been
achieved with powders essentially consisting of particles
above about 106 pm and particularly above about 212 pm.
The term "essentially consisting" is intended to mean
that at least 40 %, preferably at least 60 % of the
particles have a particle size above 106 and 212 pm,
respectively. So far the best results have been obtained
with powders having an average particle size about 250 pm
and only less than 3 % below 106 pm. The maximum particle
size may be about 5 mm. The particle size distribution
for iron-based powders used at PM manufacturing is
normally distributed with a Gaussian distribution with an
average particle diameter in the region of 30 to 100 m
and about 10-30% less than 45 pm. Iron based powders
essentially free from fine particles may be obtained by
removing the finer fractions of the powder or by
manufacturing a powder having the desired particle size
distribution.
According to a preferred embodiment of the invention and
contrary to common practise in powder metallurgy, where
conventional PM lubricants are used in the iron powder
mix, or where a lubricant is used in combination with
binder and/or surface treatments the iron or iron-based
powder must not be mixed with a separate (particular)
lubricant before it is transferred to the die. Nor is it
necessary to use external lubrication (die wall
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lubrication) where the walls of the die are provided with
a lubricant before the compaction is performed. The
invention, however, does not exclude the possibility of,
when it is of interest, to utilise conventional internal
lubrication (in an amount up to 0.5% by weight), external
lubrication or a combination of both. The powder to be
compacted may also include additives selected from the
group consisting of binders, lubricants, and flow-
enhancing agents. Examples of inorganic lubricants, which
may be used in addition to organic PM lubricants, are
hexagonal boron nitride, and MoS2.
According to the present invention soft magnetic compo-
site materials having a density of at least 7.45 g/cm3 can
be prepared by uniaxially compacting the new powder com-
positions in a die at high compaction pressures and with-
out die wall lubrication. When the green body has been
ejected from the compaction tool it can be heat treated
up to temperatures of about 700 C.
The term "at high compaction pressure" is intended to
mean at pressures of about at least 800 MPa. More inter-
esting results are obtained with higher pressures such as
pressures above 900, more preferably above 1000, and most
preferably above 1100 MPa. Conventional compaction at
high pressures, i.e. pressures above about 800 MPa, with
conventionally used powders including finer particles are
generally considered unsuitable due to the high forces
required in order to eject the compacts from the die, the
accompanying high wear of the die, and the fact that the
surfaces of the components tend to be less shiny or dete-
riorated. High electrical resistance can be obtained even
though high compaction pressures are used to achieve the
high density. By using the powders according to the pre-
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sent invention it has unexpectedly been found that the
ejection force is reduced at high pressures of about 1000
MPa, and that components having acceptable or even per-
fect surfaces may be obtained.
The compaction may be performed with standard equipment,
which means that the new method may be performed without
expensive investments. The compaction is performed uni-
axially and preferably in a single step at ambient or
elevated temperature. Alternatively, the compaction may
be performed with the aid of a percussion machine (Model
HYP 35-4 from Hydropulsor) as described in patent
publication WO 02/38315.
The heat treatment may be performed at the temperatures
normally used, e.g. up to temperatures of about 700 C in
different types of atmospheres or at reduced pressure and
optionally in the presence of steam. Prior to the heat
treatment the pressed components may optionally be green
machined and/or cleaned.
A main object of the present invention is to achieve high
density products and to this end it is preferred to use
coarse powders as described above. It has, however, also
been found that these lubricating effects can also be
obtained in combination with powders including higher
amounts of fine particles i.e. the type of powders which
are conventionally used in the PM industry today. Example
3 and 5 below illustrates the lubricating effect of the
organo-metallic compounds according to the present
invention on both conventional powders and coarse
powders. As can be observed high densities are obtained
also with a conventional powder including higher amounts
of fine particles. Compositions including iron or iron-
based powders with the particle size distributions which
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are normally used today and the lubricating agents
according to the present invention may be of special
interest for certain applications and are therefore also
within the scope of the invention.
5 The term "high density" is intended to mean compacts
having a density of about at least 7.45 g/cm3. "High
density" is not an absolute value. A typical achievable
density according to the state of the art for single
heat-treated, single pressed components is about 7.2
10 3
g/cm By using warm compaction an increase of about 0.2
g/cm3 may be reached. In this context the term "high
density" is intended to mean compacts having a density of
about 7.45-7.65 g/cm3 and above, depending on type and
amount of additives used, and type of iron-based powder
used. Components having lower densities can of course
also be produced but are believed to be of less interest.
In brief the advantage obtained by using the powder and
method according to the present invention is that high-
density SMC parts can be cost-efficiently produced. SMC
parts with remarkably high magnetic induction levels
together with low core losses can be obtained. Other
advantages are that the mechanical strength after heat
treatment is increased and that, in spite of very high
densities, compacted parts with high electrical
resistance can be successfully ejected from the dies
without negatively influence the finish of the die walls
and/or on the surfaces of the compacted SMC parts. It is
thus possible to obtain parts having excellent surface
finish. These results can be obtained with a single
compaction step. Examples of products of special
interest for the new powder compacts are inductors,
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stators and rotors for electrical machines, actuators,
sensors and transformer cores.
The invention is further illustrated by the following
examples. It is understood that the present invention is
not limited thereto.
EXAMPLE 1
An iron-based water atomised powder (Somaloy 550TM,
available from Hoganas AB, Sweden) was used as starting
material. This powder has an average particle size
between 212 and 425 pm and less than 5% of the particles
have a particle size below 45 pm. This powder, which is a
pure iron powder, the particles of which are electrically
insulated by a thin phosphorus containing barrier, was
treated with 0.2% by weight of a hexadecyl-trimethoxy
silane as a lubricating agent. The addition of the
lubricating agent was performed as follows: hexadecyl-
trimethoxy silane was diluted in ethanol to a 20%
solution by weight and the solution was stirred during 60
minutes. An amount of this solution corresponding to 0.2%
by weight was added during mixing to the iron powder,
which had previously been heated to 75 C in the mixer. An
intensive mixing was carried out in the same mixer during
3 minutes followed by mixing at a lower speed during 30
minutes and during vacuum in order to evaporate the sol-
vent. A corresponding powder mixed with a conventional
lubricant was used as comparison. This powder was mixed
with KenuolubeTM before the compaction. The amount of the
lubricant used was 0.5% of the composition, which is
generally considered as a low amount of lubricant for
components compacted at high pressures.
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Rings with an inner diameter of 47 mm and an outer
diameter of 55 mm and a height of 4 mm were uniaxially
compacted in a single step at different compaction
pressures 800, 1000 and 1200 MPa, respectively. Despite
the low amount of the organo-metallic lubricating agent
and high compaction pressures the surfaces of the
components showed no sign of deterioration.
After compaction the parts were heat treated at 500 C
for 30 minutes in air. The obtained heat-treated rings
were wound with 25 sense and 112 drive turns. The
magnetic properties were measured in an LDJ 3500
Hysteresigraph. Table 1 summarizes the maximum relative
permeability and the magnetic induction at 1500 and 6900
A/m respectively, measured under DC conditions. The core
loss/cycle has also been measured at 1 T and at 50 Hz and
at 400 Hz, respectively.
The following table 1 demonstrates the obtained results:
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Table 1
Core Core
Compaction Density loss/cycle loss/cycle
B1500 B6900
Sample Pressure Pmax at IT and at IT and
MPa g/cm3 (T) (T)
50 Hz 400 Hz
(J/kg) (J/kg)
According
to the 800 7.45 720 1.08 1.53 0.134 0.178
invention
1000 7.59 790 1.15 1.59 0.126 0.163
1200 7.64 820 1.18 1.62 0.124 0.165
Comparative
800 7.39 620 0.95 1.46 0.142 0.200
example
1000 7.47 590 0.95 1.49 0.140 0.198
1200 7.49 550 0.92 1.48 0.140 0.193
As can be seen from table 1 the green density is
significantly higher for the powder according to the
invention and magnetic properties are, hence, improved
compared with the materials used in the comparative
examples. The comparative example also demonstrates that
no or only minor improvements of the magnetic properties
can be obtained by increasing the compaction pressure to
1000 MPa and 1200 MPa.
Despite the obtained high density of the samples the core
losses are maintained at a low level even at 400 Hz,
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which shows that the electrical insulating layers are
maintained.
Samples produced according to Example 1 were tested with
regard to transverse rupture strength (TRS) after heat
treatment at 500 C for 30 minutes in air. The transverse
rupture strength was tested according to ISO 3995. Figure
1 demonstrates the transverse rupture strength at
different density levels. It should be noted that, even
at the same pressed density, the strength is unexpectedly
higher for the material according to the invention.
EXAMPLE 2
A very high purity water atomised iron-based powder, the
particles of which were provided with a thin insulating
coating and which had a mean particle size above 212 m
was treated with 0.1% and 0.2% of hexadecyl-
trimethoxysilane, respectively, according to the
procedure in Example 1. The same iron-based powder
without any lubricating agent was used as a reference.
Cylindrical samples with a diameter of 25 mm and a height
of 4 mm were compacted in an uniaxially press movement at
a compaction pressure of 1000 MPa.
Table 2 shows the ejection energy needed for ejecting the
components and the green density obtained. The ejection
energy is expressed as percentage of the ejection energy
for the sample without lubricating agent.
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TABLE 2
Amount of Green Relative Surface finish
silane density Ejection
(g/cm3) Energy %
0% 7.66 100 Seizure
0.1% 7.67 58 Good
0.2% 7.66 48 Good
10 From table 2 it can be seen that the energy needed for
ejection is considerably reduced and the surface finish
is improved by minor additions of an organo-metallic
lubricating agent according to the present invention. It
can also be observed that an increase from 0.1% to 0.2%
15 by weight of a lubricating agent has a positive impact on
the ejection energy.
EXAMPLE 3
This example demonstrates the effect of the chain length
of the unhydrolysed group or groups (R2) of the organo-
metallic compound on the lubricating properties at
ejection after compaction with high pressures. In this
example various types and amounts of alkyl-alkoxy silanes
(central atom Si) are used as lubricating agent. Two
kinds of high purity water atomised iron-based powder
provided with a thin insulating coating with two
different particle size distributions were used to show
the influence of the particle size. The S-powder has
about 14 % of the particles less than 45 m and a weight
average particle size of about 100 m. The C-powder has a
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significantly coarser particle size distribution with a
weight average size of about 250 m and less than 3%
below 106 }am.
Five different kinds of organo-silanes were used (A-E):
A Methyl-trimethoxy silane
B Propyl-trimethoxy silane
C Octyl-trimethoxy silane
D Hexadecyl-trimethoxy silane
E Polyethyleneether-trimethoxy silane with 10 ethylene
ether groups
Five different alkyl-alkoxy silanes in the range 0.05 to
3.0% by weight were added to the insulated iron-based
powder and the obtained mixtures were compacted at 1100
MPa in a uniaxial press movement into slugs with a
diameter of 25 mm and a height of 12 mm. During ejection
the dynamic ejection force per unit sliding area was
measured and after ejection green surface finish was
evaluated and density was measured as is shown below in
table 3.
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TABLE 3
Powder Powder Powder Powder Powder Powder Powder Powder
C C C S C S C C
Silane 0.05% 0.1% 0.2% 0.2% 0.4% 0.4% 1.0% 3.0%-
A Seizui
B Seizure
C 58
Seizure N/mm2
Poor
7.60
g /cm3
D 89 69 38 N/mm2 63 47 54
N/mm2 N/mm2 OK N/mm2 N/mm2 N/mm2
Poor OK 7.68 Poor OK OK
7.70 7.70 g/cm3 7.65 7.57 7.54
g/cm3 g/cm3 g/cm3 g/cm3 g/cm3
E 80 35 N/IM2 75 32 49
N/mm2 OK N/mm2 N/mm2 N/mm2
Poor 7.69 Poor OK OK
7.70 g/cm3 7.64 7.59 7.60
g /cm3 g /cm3 g /cm3 g /cm3
As can be seen from table 3 a chain length below 8 carbon
atoms in the alkyl chain does not give satisfactory
results, even though the added amount is high. Hence, at
least 8 atoms in the lubricating (alkyl, or
polyethyleneether,) chain group or groups are needed in
order to successfully eject the component. An added
amount above 0.5% is believed to be of less interest, as
the density of the green component will be negatively
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influenced. The table also shows, that when the organo-
silane content is less than 0.05%, ejection without
damaging the component and the surface of the die is not
possible for the silane "D" that contains 16 atoms in the
lubricating alkyl group. However, the geometry of the
component as well as the quality of the tool have a great
impact on the surface condition of the component after
ejection. Therefore, lower amounts than 0.05% lubricant
agent, optionally mixed with conventionally used i.e.
particular lubricants, can be of interest for some
applications.
From table 3 it can also be concluded that extremely high
densities can be obtained. The coarse powder shows
superior ejection behaviour compared to the standard
powder. Even powder with a standard particle size
distribution can be compacted to high density (about at
least 7.60 g/cm3). As is noted above, the ejection
behaviour is also here greatly dependent on component
geometry and tool material and quality. Thus, powders
with a standard size distribution can be of interest in
some applications.
EXAMPLE 4
This example demonstrates the lubrication effect of
organo-metallic compounds with different central atoms.
In this example the lubrication effect of four different
agents have been examined i.e. silane, titanate,
zirconate and aluminate, having Si, Ti, Zr and Al as the
central atom, respectively. The various central atoms
have different coordination numbers and chemical
properties. However, the chemical structure of the
organo-metallic compound was selected so that the chain
length of the lubricating group or groups (R2) would'-'show
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comparable properties which can be compared with those
obtained with hexadecyl-trimethoxy silane (D).
A high purity water atomised iron-based powder with a
thin insulating coating were treated with 0.2% by weight
of each organo-metallic compound as lubricating agent.
The obtained mixtures were compacted at 1100 MPa in a
uniaxial press movement into slugs with a diameter of 25
mm and a height of 12 mm. During ejection the dynamic
ejection force per unit sliding area was measured and
after ejection green surface finish was evaluated and
density was measured as is shown below in table 4.
Four different types of organo-metallic agents were
examined (A-D):
A Isopropyl-triisostearoyl titanate
B Neopentyl(diallyl)oxy-trineodecanonyl zirconate
C Diisobutyl(oleyl)aceto-acetyl aluminate
D Hexadecyl-trimethoxy silane
TABLE 4.
Organo-metallic
A B C D
compound
Ejection force
[N/mm2] 35 44 50 39
Denisty [g/cm ] 7.68 7.68 7.68 7.68
Ejection and
part quality OK OK OK OK
As can be seen from table 4 the lubricating properties of
all compounds are satisfactory. Hence, the type of
central atom shows only minor influence on the
lubricating properties. The chain length, and to some
extent the chemical structure, of the unhydrolysed group
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or groups are shown to provide the lubricating properties
according to the present invention.
EXAMPLE 5
The influence of average particle size and particle size
5 distribution was further investigated. Three different
high purity iron-based powders with different particle
size distributions, according to table 5, all of them
insulated with a thin phosphate-based electrical
insulation were prepared. All samples were treated
10 according to the present invention with 0.2 wt% of
hexadecyl-trimethoxy silane according to the procedure
descried in Example 1.
Cylindrical samples with a diameter of 25 mm and a weight
of 50 grams were compacted in an uniaxially press move-
15 ment at a compaction pressure of 1000 MPa and green den-
sities above 7.6 g/cm3for all the samples were obtained.
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TABLE 5
Particle size Sample Sample Sample
distribution A B C
(0) (0) M
-45 m 8.4 0.0 0.1
45-106 m 52.7 15.5 1.0
106-212 m 30.0 84.3 37.4
212-315 pm 0.1 0.2 51.0
+315 m 0.1 0.0 10.5
Density [g/cm3] 7.61 7.63 7.62
Surface finish Poor* OK Good
* Higher amount of lubricant agent improves surface
finish.
It could be observed that the surface finish of the
sample C was superior to those of the samples A and B,
respectively.
EXAMPLE 6
This example illustrates the importance of the inorganic
insulation.
A high purity iron powder, the particles of which are
electrically insulated by a thin phosphorus-containing
barrier was compared with an identical powder without the
phosphorous-based inorganic insulation. Both types of
powders were subsequently treated with 0.2% by weight of
CA 02505381 2005-05-06
WO 2004/056508 PCT/SE2003/002067
22
hexadecyl-trimethoxy silane as a lubricating agent
according to the invention.
Rings with an inner diameter of 45 mm and an outer
diameter of 55 mm and a height of 5 mm were uniaxially
compacted in a single step at compaction pressure 1100
MPa. After compaction the parts were heat treated at
500 C for 30 minutes in air. The electrical resistivity
was measured by the four-point method.
The following table 6 shows electrical resistivity and
density of composite components prepared of powders with
and without insulated particles.
TABLE 6
Electrical Resistivity Density [g/cm3]
[}Ohm*m]
According
to the 150 7.68
invention
Comparative
0.5 7.68
example
