Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to lubricants for powder
metallurgy and to the manufacture and use of lubricants.
More particularly the lubricant comprises a micro-
capsule comprising a core of a liquid lubricant enclosed by a
solid shell~
Powdered metals, for example, powdered iron, are used
to make small, fairly intricate parts, for example, gears. The
fabrication of such metallic parts by powdered metal technology
involves the following steps:
a) the powdered metal is blended with a lubricant and
other additives to form a mixture,
b) the mixture is poured into a mould, -
c) the mixture is compacted in the mould to form a part
uxing a high pressure, usually of the order of 30 tons per
square inch,
d) after compaction the part is ejected from the mould,
e) the ejected part is subject:ed to a high temperature ~ -;
to decompose and remove the-lubricant, ;
f) the part i~ heated to a higher temparature to cause
all the particles of metal in the part to sint~r together and
g) the part is cooled, after which it is ready for use,
Commonly used lubricants include zinc stearate and
lithium stearate. ` `;
The lubricant is added to the powdered metal for
several reasons, it increases the bulk density of the uncom-
pacted powdered metal. Thi~ means that the moulds can be ;
shallower, for a given thickness of the final part. The
bulk density is generally referred to as the "apparent
density".
The lubricant allows the compacting pressure to be
reduced to attain a specified density before sintering. This
is very important because it means that for a given pressure a
~ - 1- ~ :
.
larger part can be made. Because of the very large pressures
required to compact powdered metal, only relatively small parts
are made. The density of the compacted part is called the
"green density".
The ejection force to remove the compacted part from
the mould is much lower when a lubricant is present and this
- lower force results in less mould wear.
Unfortunately, the lubricant also has a few adverse
- effects; it often reduces the flow rate of the powdered metal and
therefore the rate at which a mould can be filled; it reduces
the strength of the compacted part, referred to as the "green
strength"; further, it can cause an unattractive surface finish
on the sintered part. Zinc stearate is commonly used as a
lubricant and slowly deposits a thin coating of zinc on the walls
of the oven used to burn off the lubricant or on the walls of
the sintering oven.
This last disadvantage is often serious, and because
of it a wax is sometimes used instead of zinc stearate. The
most commonly used wax is ethylenebisstearamide; however, it
is not as good a lubricant as zinc stearate, especially with
regard to compressi~ility, i.e., it gives a lower green density
for a given compacting pressure, It can only provide tha same
compressibility as zinc stearate if it is ground to a very fine
powder using a special grinding mill which is expensive and
consumes a great deal of energy.
A further disadvantage to customarily used lubricants
is that they are dusty. ~ -
The present invention provides an entirely or almost
entirely organic lubricant for powder metallurgy which is com
parable to zinc stearate, with respect to compressibility of the
lubricant-metal mixture, as well as with respect to other pro-
perties of the mixture and of parts produced therefrom.
2 _
. . .
B3
:"
The invention further provides an organic powdered
metal lubricant which is cheap, dustless, non-toxic, and which
- can be used in quantities no greater than now used for existing
lubricants, for example, zinc stearate, lithium stearate and
waxes.
The in~ention further provides a lubricant composition
which comprises a synergistic mixture of microencapsulated
lubricant and unencapsulated solid lubricant. -~
The invention further provides a process by which the
10 microencapsulated lubricant can be manufactured. ~
The invention further provides a method of pro- ~-
ducing a sintered metal part using the lubricant of the in-
vention.
It has been found that small capsules called micro-
capsules consisting of a liquid lubricant surrounded by a
solid shell material, having certain properties, provide an
excellent lubricant for powdered metals.
:: . . . .
The addition of a liquid lubricant to powdered metal
results in high compressibility and low ejection pressure,
however, it also causes very poor flow and very low apparent
density which are unacceptable.
When the liquid lubricant is encapsulated, however,
according to the present invention,it does not have an ~-~
opportunity to reduce the flow rate or the apparent density of
the powdered metal; however, when the mixture of powdered
metal and encapsulated lubricant is subjected to high pressure
during the compaction stage, the shell of the capsule is
ruptured or broken and the liquid lubri~ant is released to coat
the particles of powdered metal and the die wall, and there-
;~ 30 by results in high compressibility and low ejection pressure.
-- 3 --
.: ~. .
.:
/ - -
According to one aspect of the invention there is pro-
vided discrete pressure-rupturable microcapsules for lubrication
in powder metallurgy comprising a core and a solid shell sur-
rounding said core, said core comprising a non-corrosive organic
liquid lubricant able to wet powdered metals, and said shell
comprising a thin non-atmospherically-degradable polymeric mate-
: rial, said shell being impermeable to said lubricant and having
.
a smooth, slippery, non-tacky, outer surface resistant to
abrasion by sinterable powdered metal to the extent that the
microcapsules can be thoroughly mixed with sinterable powdered
metal without release of lubricant said shell being rupturable,
when said microcapsules are in admixture with sinterable powdered
metal and are subjected to powder metallurgy compacting pres- .
.
sures, said lubricant and said shell being heat decomposable to
~ gaseous products which are non-corrosive to sinterable metal with
a low residùe of carbon at elevated temperatures below the
sintering temperature of a powdered metal to be sintered.
. According to another aspect of the invention there is
provided a free-flowing lubricant composition for powder
metallurgy lubrication ~omprising the discrete pressure-
rupturable microcapsules defined above in admixture with a
..
solid particulate lubricant for example an amide wax or a - ~ :
metal stearate, such mixtures exhibit beneficial synergistic
effacts.
According to another aspect of the invention the~e is
provided a method of producing a sintered metal part from
powdered metal comprising: blending said powdered metal with a
lubricant comprising discrete pressure-rup~urable microcapsules
comprising a core of a non-corrosive liquid organic lubricant
able to wet said powdered metal, and surrounding said core a thin
polymeric solid shell, to form an intimate mixture, compacting
said mixture in a mould at a pressure effective to rupture said
~`t
3~
shell and release said liquid lubricant and to form said mixture
into a self-supporting shaped body, removing said body from ~:
said mould, heating said body to decompose and remove organic
material, and sintering said metal particles.
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According to yet another aspect of the invention there
is provided a process for producing solid lubricant coated dis-
crete pressure rupturable microcapsules, comprising a core of a
liquid organic lubricant and a solid polymeric shell surrounding -
~said core comprising forming a mixture of the liquid lubricant
and a polymerizable monomer soluble therein, forming an emulsion
of the mixture with a polar solvent immiscible with said liquid
lubricant, reacting said monomer with a polar solvent-soluble
monomer or catalyst to produce microcapsules comprising a core of
said liquid lubricant and a shell of polymerized monomer or
monomers, mixing the microcapsules with the solid lubricant at a
temperature above the melting point of the solid lubricant to coat
the microcapsules and recovering coated microcapsules.
Liquid Lubricant ~
.
With regard to the physical properties of the
lubricant it should be liquid at the temperatures at which it
is used, the melting point should be below room temperature, or
more precisely, below the temperature of the powdered metal
when it is compacted. It should have a low enough viscosity so
20 that when the shell is ruptured the lubricant will rapidly flow
out and envelop the particles of powdered metal. A viscosity
below 300 cp should suffice.
The liquid lubricant must have the ability of wetting
the powdered metal. This is generally dependent on the sur~ace
tension properties and generally if the surface tension of the
lubricant is below about 40 dynes/cm., good wetting should occur.
The liquid lubricant should not dissolve the shell
material or it will tend to slowly diffuse through the shell.
Since lubricants are frequently burned off at 800F. prior to
sintering, almost all the liquid should desirably volatilize
below this temperature. The remaining lubricant should
completely burn off in the sintering oven so that very little
_ 5 _
~ ~ :
black soot is deposited on the surface of the sintered part.
With regard to ch~mical properties the liquid ~ `
lubricant should not be corrosive, and should not yield
corrosive degradation products or yield degradation products
which adversely affect the lining of the sintering furnace or
the properties of the sintered metal parts. These requirements
eliminate such lubricants as chlorinated and sulphonated fats
and oils. ~ ;
Liquid lubricants which have been found to be suitable
are animal and vegetable fats and oils which have the required
low melting points. Examples are rapeseed oil, soya-bean oil, -
peanut oil and coconut oil. Fatty acids and fatty acid esters are
also suitable, provided they have low enough melting points.-
Examples are:oleic acid; methyl laurate and the methyl ester of
lard oil, epoxidized fats and oils which are liquids, such as
epoxidized soya-bean oil. Mineral oils and low melting point
polyethylene glycols and polypropylene glycols can also
be used, but are less preferred.
Small amounts of special additives may be mixed with ;
the liquid lubricant, even though if present in large amounts
they would be deleterious. Examples o~ these are chlorinated ~-
oils, sulphonated oils, tricresyl phosphate, zinc dithiodi-
al~ylphosphates and sodium nitrite. -
The lubricant may also contain small amounts of solid
lubricants, for example, molybdenum disulphide.
The amount of liquid lubricant present in the micro-
capsules should be as great as possible, because the shell
material itself is not a good lubricant. Large amounts may be '
employed, provided difficulties are not encountered in the form-
a~ion of a continuous shell and the shell is sufficiently strong.
Usually the lubricant content varies between 5~/O and 85% by
weight. ,~ ;
- 6 -
-, . . . : . : . . ~
Shell
The chemical properties required of the shell material
are the same as for the liquid lubricant. With regard to
physical properties the shell material must satisfy several
; criteria. The shell should be impermeable to the liquid
lubricant. The surface of the shell must be sufficiently
smooth and slippery so that a good flow rate and apparent
density is obtained for the mixture of powdered metal,
lubricants and other additives Neither moisture in the air
nor oxygen should degrade the shell.
The shell material should be sufficiently abrasion
resistant so that the microcapsules can be thoroughly mixed
with the powdered metal without release of the liquid
lubricant. During this mixing operation
the temperature may reach as high as 130F. and therefore the
shell should be able to withstand this temperature. A further
and rather obvious requirement, is that the shell should
rupture when subjected to the pressure exerted during com-
paction, It is also desirable that the shell material be such
that thin shells can be utilized so that the percentage of
- liquid l~bricant is high.
Microcapsule
The size, shape and colour of the microcapsules are
important. If the microcapsules are too large they will
segregate from the powdered metal. If all of the microcapsules
pass through a 140 mesh sieve there is no danger of segregation.
Generally, it is preferable to have the microcapsules
as fine as possible, for example, 5 microns in diameter.
Coarser microcapsules frequently lead to lower apparent densities
and lower green densities, However, they also lead to
higher flow rates, therefore, when a high flow rate is
paramount, coarse particles should be used, for example,
-- 7 --
~6;~3~ ~
50 microns in diameter. Generally the microcapsule will have a
size in the range of about 1 to 200, particularly 5 to 100, microns;
however, the most suitable microcapsule size is also dependent on
the particular grade of iron or non-ferrous metal powder.
A spherical shape is the most desirable, because this
leads to the highest ~low rate and apparent density. A black
or grey colour is undesirable, particularly when the powdered
metal is iron powder, because it is then impossible to deter-
mine whether the microcapsules have been thoroughly mixed
with the powdered metal; white is the preferred colour.
In one embodiment of the invention the shell of the
microcapsules is coated with a thin layer of a solid which is
a good lubricant for powdered metals, for example, stearic
acid or carnauba wax. This coating can result in an improvement
in the apparent density and flow rate, without harming the
; other properties. Preferably, the coating constitutes between
5% and 15% of the total weight of the microcapsules. If it is
much less, the coating will not completely cover the shell;
if it is much more, the beneficial effects of the encapsulated
' 20 liquid lubricant will be reduced.
In another embodiment o~ the invention the micro-
.. . -
encapsulated lubricant is mixed with an unencapsulated solid
particulate lubricant because ~ynergism occurs with respect to '~
certain properties. For example, the ~ompressibility may reach a
maximum at a particular concentration of microcapsules, and the
ejection force may reach a minimum at another, usually different,
concentration of microcapsules; the values of these concentrations
depend upon the particle size and the composition of the micro-
capsules and of the unencapsulated solid particulate lubricant.
.
. . :
B ~
, ~ ' , ; . ' , , , : . ,
Suitable solid particulate lubricants include waxes,
for example, ethylenebisstearamidewax, Carnauba wax, Fischer-
Tropsch wax, fatty acids, zinc stearate and lithium stearate.
Microcapsule Production
There are several methods of microencapsulating a liquid
and most of these can be applied to the microencapsulation of `-
liquid lubricants. U.S. patents 2,800,457, 3,041,288 and
3,201,353 involve the formation of a shell by the precipitation
- of gelatin; in U.S. patent 3,137,631 other proteins are used
to form the shell. Precipitation of synthetic polymers is
employed in U.S. patent 3,173,878 to produce a shell. U.S.
patent 2,969,330 entails shell formation by the polymerization
of a monomer at the interface of the oil and water in which
the oil i~ emulsified. In U.S.~patent 3,796,669 the shell
formation is by the copolymeriæation of two monomers in an
emul~ion of an oil and water.
~, ,
- 8A -
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.
~ lthough encapsulation methods using gelatin are the
most popular and have been thoroughly investigated, they are
not particularly suitable for the present application because,
in addition to other reasons, the gelatin shells are moisture
sensitive and the surfaces are often tacky; a tacky surface
causes low flow rates and low apparent densities.
U.K. patent 950,443 involves a method which is
similar to that preferred in the present invention. In this
case, microcapsules are formed by a condensation polymerization
reaction between a monomer which is soluble in a water phase
and a monomer soluble in a water immiscible phase.
The microcapsules may be manufactured by a method ~
comprising the following steps: (1) If necessary, mix an
emulsifying agent with either the liquid lubricant, the water
` phase, or both; (2) mix a lubricant soluble monomer with the
liquid lubricant, (3) add the resulting mixture to the water
phase, (4) mix at room temperature usin~ vigorous agitation to
form an emulsion of the desired fine droplet size, (5) to the
emulsion add, with mixing, a water soluble monomer react1ve with
the lubricant soluble monomer or a polymerizationicatalyst for
the lubricant soluble monomer, (6) mix, but not so vigorously
that the capsules are destroyed, for several hours with heating
- to about 80C. to accelerate the reaction, (7) filter the mixture
to separate the microcapsules from the water, (8) wash the micro-
capsules to remove emulsifying agent and any excess water soluble
monomer and (9) dry the microcapsules. -
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The liquid lubricant should, of course, be inert to
and not interfere with the polymerization.
In this respect fatty acids should be avoided as the liquid
lubricant when the isocyanate/amine reaction is employed
because the fatty acids and amines tend to react together
preventing or hindering the formation of microcapsules
and the fatty acid can also react with the isocyanate.
To coat the microcapsules with a thin layer of a
solid lubricant, the mass of dried microcapsules is heated
to a temperature a little above the melting point of the
solid lubricant, the solid lubricant is then added, preferably
as a fine powder, and the mixture is mixed gently for about
an hour while the temperature is held constant. Finally, with
continuous mixing, the temperature is allowed to slowly
decrease to that of the room. It is generally found that
several aggregates of microcapsules have formed during this
process because of the bonding nature of the solid lubricant.
These can easily and completely be broken by grinding lightly
in a hammer mill.
In the preferred method a di- or polyfunctional
i~ocyanate is dissolved in the liquid lubricant; the resulting
solution is emulsified in water containing an appropriate
emulsifying agent, and an aqueous solution of a di- or poly-
functional amine is added. Among the isocyanates that can ~e
used there may be mentioned: -
toluene diisocyanate
dianisidine diisocyanate
xylylene diisocyanate
bitolylene diisocyanate
hexamethylene diisocyanate
o,m and p-phenyléne diisocyanate
methylene bisphenylisocyanate
B` ~
-- 10 --
. - ` : .
. ; :
. :,; .
.
polymethylene polyphenylisocyanate
1, 6- hexamethylene diisocyanate
methylcyclohex~lene diisocyanate -
. trimethylhexamethylene diisocyanate .
Examples of amines that can be used in the method
are the following~
. ethylene diamine
methane diamine
.~ 1,3 diaminocyclohexane
m-xylylenediamine
diethylenetriamine
iminobispropylamine ~,
propylenediamine
trieth~lenetetramine
tetraethylenepentamine
m-phenylenediamine ::
. 4,4'-methylenedianiline
Examples o~ liquid lubricants which can be used in the
: preferred encapsulation method are as follows:
rapeseed oil .~ :
soyabean oil ; :
epoxidized soyabean oil . -
methyl lardate
methyl laurate -:
peanut oil
methyl oleate ~
corn oil .
-- 11 --
.'' ' '.i~ ' .
- When mixed with metal powders, the concentration of
the microcapsules or of microcapsules plus unencapsulated
solid lubricants, is suitably in the range of 0.1% to 5% by
~ weight, preferably from 0.3% to 1% by weight.
- Test data on lubricant compositions of the invention
are illustrated with reference to the accompanying drawings in
which
FIGURE 1 shows graphically the variation in
flow time, green density, apparent
density and ejection pressure for
: iron powder (MP-32, trademark)
; containing 1% by weight of
lubricant comprising microcapsules
admixed with particulate ethylene-
bisstearamide, with microcapsule
concentration, for the micro-
capsule of Example IV.
- 12 -
.. .
: . . . . .
... . .
.-- --
y:~
FIGURE 2 shows graphically the variations in
ejection pressure, apparent density and
green density for iron powder (MP-32, trade~
mark) containing 1% by weight of lubricant
comprising microcapsules admixed with ethylene-
bisstearamide, with microcapsule concentration,
for the microcapsules of Example VIII.
FIGURE 3 shows graphically the variation in
ejection pressure, apparent density and
green density for iron powdex (Atomet 29,
trademark) containing 1% by weight of
lubricant comprising microcapsules
. .- . .
admixed with ethylenebisstearamide, with ~-
microcapsule concentration, for the micro-
capsules of Example X, and
FIGURE 4 shows graphically the variation in ejection
pressure, apparent density and green density
for brass powder (CZ-2, trademark) containing
1% by weight of lubricant comprising micro-
capsules admixed with ethylenebisstearamide,
with microcapsule concentration, for the -~
microcapsules of Example VIII.
The following examples serve to illustrate the
invention, but they are not intended to limit it thereto. - -
.
~ EXAMæLE I Rapeseed oil encapsulated in the reaction
; product from eth~lene diamine and toluene
diisocyanate.
30 g. of toluene diisocyanate (Nacconate 80, trade-
mark from Allied Chemical) was dissolved in 120 g. of refined
rapeseed oil. This solution was added with stirring to a
- solution of 3 g. of Siponic 218 ( trademark for a polyoxyethylene
thioether from Alcolac, Inc.) in 700 g. of water. When the
emulsification was complete, the stirring rate was reduced and
~ i '
.. .. . . . . . .
30 g. of ethylene diamine dissolved in 70 g. of water was
added. The temperature was then increased to 80C. and
maintained constant while the mixture was stirred for 4 hours.
The resulting dispersion of microcapsules in water
was filtered and the microcapsules dried at 60C. Aggregates
of microcapsules were broken by light grinding through a
hammer mill.
The microcapsules were white, spherical, free flowing,
had an average particle size of about 50 microns and contained
about 66% by weight of rapeseed oil.
EXAMPLE II Methyl oleate encapsulated in the reaction
product from ethylene diamine and toluene
diisocyanate.
30 g. of toluene diisocyanate was dissolved in 120 g.
of methyl oleate~ This solution was added with stirring to a
solution of 3 g. of Siponic 218 (trademark) in 700 g. of water.
When the emulsification was complete the stirring rate was
reduced and 30 g. of ethylene diamine dissolved in 70 g. of
water was added. The temperature was increased to 80C. and
maintained constant while the mixture was stirred for 4 hours.
The microcapsules were separated ~rom the water by
filtration and then dried at 60C. Aggregates of dried
microcapsules were broken by light grinding with a hammer mill.
The microcapsules were white, spherical, free flowing,
:. .
had an average particle size of about 50 microns, and contained
about 66% by weight methyl oleate.
EXAMPLE III Testing of Microcapsules prepared in Examplès
I and II.
The microcapsules prepared in Examples I and II were
tested as lubricants for two different powdered metals using
the following formulations: ~
;. :
,
- 14 -
., . , .
,
. :: ,. . . ...
. . .
Formulation A Formul_tion B
Iron Powder Iron Powder
(QMP's Atomet 29*) 95.10~/o (Domtar s MP32*) 96~28%
Graphite (South~ Graphite (South-
western's 1845*) 0.94% western's 1845*) 0~9~/O -
Copper (Alcan's Copper (Alcan's
MD151*) 2~96~/o MD151*) 1.98%
Lubricant 1. 0~/o Lubricant 0~75%
Standard test methods were used to deter~ine the
effects of the lubricant, namely apparent density by ASTM B212-
48, compressibillty by ASTM B331-64~ green strength by ASTM
B312-64~ transverse rupture strength by ASTM B528-70 and tensile
strength by ASTM E8.
A compacting pressure of 27.5 tons/sq.in. was used to
prepare specimens of Formulation A for tensile strength deter-
minations and of 30 tons/sq.in. for transverse rupture. A
compacting pressure of 25 tons/sq.in. was used to prepare
specimens of Formulation B for tensile and transverse rupture
strength determinations.
Following compaction the samples were subjected to
1000F. in a pure hydrogen atmosphere for 20 minutes to burn
off the lubricant, and subsequently to 2050F. for 30 minutes -
to sinter the metal.
Tables I and II present the results, along with the
corresponding results for two commercially used lubricants,
zinc stearate and ethylenebisstearamide wax. It can be seen
that compared to the stearate and the wax the use of micro-
capsules leads to much lower ejection force, to lower apparent
` density and to greater shrinkage. With regard to the other
parameters the results are comparable. ~ high shrinkage is
frequently desirable, and although the tensile strength
obtained using encapsulated rapeseed oil is low, it is still `~
acceptable. `~
* trademark
- 15 ~
` . . ~ ' : . : ,
-
TABLE I
Comparison Between Effects of Standard
Lubricants and Microcapsul0 Lubricants
for Formulation A
Zinc Ethylenebis- Microcapsules from
Stearate stearamide Wax Example I Example II
Apparent Density
in g/cc 3.08 2.66 2.30 2.37
Ejection Force
in t.s.i. 4.2 4.9 4.2 4,0
Green Density
; in g/cc 6.S7 6.53 6.49 6.49
Shrinkage in
in./in. X 10
Length 7 13 24 39
Width 6 10 24 36
Thickness 29 26 55 93
Tensile
Strength in
p.s.i. 54,140 61,050 57,00056,390
j 20 Transverse
Rupture
Strength
in p.s.i. 111,130 111,180 111,080 121,230
-~
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- 16 -
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TABLE II
Comparison Between Effects of Standard
Lubricants and Microcapsule Lubricants
for Formulation B
_ . . . . . .. .... .
Zinc Ethylenebis- Microcapsules from
Stearate stearamide Wax Example I Example II
Apparent Density
in g/cc 2.73 2.57 2.15 2.25
Ejection Force
-in t~.s.i. 4.3 4.8 3.2 306
` Green Density
in g/cc 6.35 6.30 6.30 6.28
Shrinkages in
in./in. X 10-4
Length 20 6 6 16
Width 12 6 4 14
Thickness 23 13 43 60
Tensile
Strength
in p.s.i. 37,890 , 37,260 28,640 37,730
- Transverse
Rupture
Strength
- in p.s.i. 77,410 80,360 74,930 79,290
EXAMPLE IV Soyabean oil encapsulated in the reaction
product from Ethylenediamine and toluene
~ diisocyanate.
.
30 g. of toluene diisocyanate was dissolved in 60 g.
of soyabean oil (from Canlin Limited). This solution was added
with stirring to a solution of 3 g. of Siponic 218 (trademark)
in 700 g. of water. When the emulsification was complete, the
. . .
~ stirring rate was reduced and 30 g. of ethylene diamine dissolved
.
in 70 g. of water-was added. The temperature was then increased
to 80C. and maintained constant while the mixture was stirred -~
for 4 hours.
The microcapsules were separated from the water by
filtration and then dried at 60C. Aggregates of dried micro-
capsules were broken by lightly grinding in a hammer mill.
... . .
- 17 -
"': ''
,
The microcapsules were white, spherical, free fl,owing
had an average diameter of 50 microns, and contained about 50%
by weight soyabean oil.
EXAMPLE V Soyabean oil encapsulated in the reaction
product from ethylene diamine and toluene
diisocyanate.
The same procedure was followed as in Example IV
except that more soyabean oil was added so that the microcap-
sules contained about 75% by weight oil.
EXAMPLE VI Effect of mixtures of ethylenebisstearamide
- wax and microcapsules from Examples IV and V
on Iron Powder.
Rather than using only microcapsules as a lubricant for ~ '
powdered metals, blends of microcapsules with customary lubricants
can be used. Figure 1 gives the results for blends of ethylene-
bisstearamide wax (from H. L. Blachford, Limited) with micro~
capsules from Example IV where the total concentration of lubri-
', cant system is kept constant at 1% and the powdered metal is iron
powder MP-32 (trademark) from Domtar. It is surprising to see that ~,
the curve for green density shows a maximum, which occurs at ~ '
, approximately 20% microcapsule content. Similarly, the curve for '' --~
'
ejection force shows a minimum, which occurs at approximately 75%
,, microcapsule content. These two separate synergistic effects are
beneficial, because a high green density and a low ejection force ', -~
are desirable.
! . ' . .
Blends were also prepared using microcapsules from ~;
Example V to determine the effect of increasing the oil content
from 50% to 75% by weight. Although the results are not shown
in Figure 1, it was found that with the microcapsules containing '
more oil the apparent densities, flow rates, and ejection
pressures were lower, but, the green densities were higher. ,' '`
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EXAMPLE VII Soyabean oil encapsulated in the reaction product
from ethylene diamine and toluene diisocyanate
The same procedure was followed as in Example IV
except that the amount of soyabean oil was increased to 120 g.
so that the microcapsules contained about 66% by weight oil.
- EXAMPLE VIII Soyabean oil encapsulated in the reaction
product from ethylene diamine and toluene
diisocyanate.
30 y. of toluene diisocyanate was dissolved in 120 g.
of soyabean oil. The solution was added with stirring to a
solution of 3 g. of Siponic 218 (trademark) in 700 g. of water.
The resulting coarse emulsion was then mixed very vigorously
in a high intensity colloid mill to produce an emulsion
containing very fine droplets of oil. The stirring rate was
then reduced and 30 g. of ethylene diamine in 70 g. of water
was added. The temperature was then increased to 80C. and
maintained constant while the mixture was stirred for 4 hours.
The microcapsules were separated from the water by
filtration and dried at 60C. Aggregates of dried micro-
capsules were broken by gentle grinding.
The microcapsules were white, spherical, free flowing,
- had an average diameter of 5 microns and contained about 66%
by weight oil.
EXAMPLE IX Effect of mixtures of ethylenebisstearamide wax
and microcapsules from Examples VII and VIII
on iron powder.
Rather than using only microcapsules as a lubricant for
powdered metals, blends of microcapsules with customary lubricants
can be employed. Figure 2 gives the results for blends of
ethylenebisstearamide wax with the fine particle size capsules
from Example VIII. The total concentration of lubricant was
held at 1% and the powdered metal was iron powder MP-32 (trademark)
from Domtar. It is surprising to see that the curve for green
density shows a maximum, which occurs at microcapsule content of
19
.
approximately 50% by weight. The results show that synergism
occurs between the two different kinds of lubricant.
Blends were also prepared and tested using micro-
capsules from Example VII to determine the effect of micro-
capsule particule size. Although the results are not shown, it
was found that using the coarser microcapsules resulted in a
maximum in the green density, but it occurred at around 3~/O by
weight microcapsule content, rather than 5~O by weight as with
the finer microcapsules. Furthermore, the apparent densities
were lower. The ejection pressures were lower at low con- - -
centrations of microcapsules, but higher at high concentrations. ~ ~;
EXAMPLE X Rapeseed oil encapsulated in the reaction
product from ethylene diamine and toluene
diisocyanate.
The same procedure was used as in Example VIII, except
that rapeseed oil was used in place oE soyabean oil. The
microcapsules formed had an average diameter of approximately
5 microns and contained 66% by weight oil. ;
,.:
EXAMPLE XI Effect of Mixtures of ethylenebisstearamide wax
and microcapsules from Examples I and X on
iron powder.
Blends of microcapsules and a conventional lubricant
were prepared and tested in iron powder Atomet 29 ttrademark),
from Quebec Metal Powder Company. Figure 3 gives the results ~or
blends of ethylenebisstearamide wax with the fine particle size
capsules from Example X. The total concentration of lubricant
was kept constant at 1% by weight. The results are similar to
- those given in Examples VI and VIII. A maximum green density
occurs at a microcapsule concentration of approximately 40% by
weight. As in Example VI there is a minimum in the curve for
ejection pressure. Beneficial synergism occurs here also, with
regard to both green density and ejection pressure.
- 20 -
' ' ~. .
. . ~ , . .
~. :
: . . . . . .
-
3~
Blends were also prepared and tested using micro-
capsules from Example I. These capsules are identical to those
from Example X, except that khey are much larger. Although the
results are not shown, it was found that the green density reaches
a maximum at a lower microcapsule concentration. The ejection
pressures and apparent densities are higher.
.
EXAMPLE ~II Coating of microcapsules from Example VIII with
thin layers of lubricants.
A 166 g. sample of fine microcapsules from Example -
VIII was heated to 150F. and to half of this was added, with
mixing, 17 g. of double pressed stearic acid and to the other
half was added, with mixing, 17 g. of a Fischer-Tropsch Wax
(Paraflint - trademark). The samples were held at 150F.
and mixed for 30 minutes. The heat source was then removed
and the samples allowed to cool to room temperature, at which
point the mixing was stopped. The aggregates that had formed
as a result of this treatment were broken by light grinding.
I'he coated microcapsules were tested as lubricants
for iron powder, Atomet 29 (trademark) using a lubricant con-
centration o 0.75~/~ by weight.
~ ,
;
'~'.,~ .
; ~
TABLE III
Effect of Thin Coating on Lubricant Properties
-
EthyIene Coated Capsules
Zinc bissteara- Uncoated Stearic : -
Stearate mide Capsules Acid Wax
Flow Rate
in sec./50
g, 34~5 41.0 no flow no flow no flow
Apparent
Density -
in g./cc 3,24 2.94 2.58 2.95 2.6~ - -
Green
Density
in g./cc 6.60 6.55 6.55 6.60 6.52 ~-~
Ejection
Force in
t.s.i. 5.4 6.4 5.6 4.9 5.7 ~ ~ -
Green
Strength
in p.s.i. 1664 2218 1437 1175 1423
. . _ . . .
The results show that the stearic acid coated micro-
capsules give higher apparent densities and green densities than
~o the uncoated.
.. ~ .
- .
EXAMPLE XIII Coating of microcapsules from Example VII with
thin layers of lubricants.
Four samples, each weighing 83 g., of coarse micro-
capsules from Example VII were heated to 150F. and to each
was added 17 g. of a coating material. Four materials were
used: double pressed stearic acid, Fischer Tropsch Wax,
hydrogenated castor fatty acid and carnauba wax. The samples
were held at 150F. and mixed for 30 minutes. They were then
~allowed to cool at room temperature with constant mixing. Any
aggregates of coated microcapsules that had formed were broken
by light grinding.
- 22 -
." '
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~, :. . ~ ~ .
, ,: . . . -
The coated microcapsules were tested as lubricants for
iron powder Atomet 29 (trademark) using concentrations of 0.50%
and 0.75% by weight. Table IV presents the results along with -~-
those for customarily used lubricants.
The results show that when coarse microcapsules are
coated there is a spectacular improvement in the flow rate
and apparent density. Although no results are shown, it was
found that coating the capsules increased the green strength,
but had no significant effect on other properties.
I0TABLE IV
Effect of Various Coatings on Lubricant Properties
. . ., _ _ .
Concentration Flow Rate Apparent Density
of Lubricant in sec./50 G. in g./cc.
Ethylene 0.50/O 32.0 2 73
Bisstearamide 0.75% 35.0 2 62 ~ -
Uncoated 0.50/0no flow 2.38
Micro-
capsules 0.75% no flow -
Stearic Acid 0.50/0 39.5 2.71
Coated
Capsules~ 0.75% 37,5 2,67
Fischer
Tropsch 0.50O/o30.5 2.61
Wax Coated
Capsules 0,75% 35,0 2.54
Castor Fatty 0.50/0
Acid Coated
Capsules 0.75% 38.5 2.60
Carnauba Wa~ 0.50/0 - - -
Coated
0.75% 37.0 2.61
EXAMPLE XIV Methyl Lardate encapsulated in the reaction
product from Ethylene Diamine and Trimethyl ~ -
Hexamethylene Diisocyanate~
30 g. of trimethyl hexamethylene diisocyanate was
dissolved in 120 g. of methyl lardate. This solution was added
with stirring to a solution of 3 g. of Siponic 218 (trademark)
in 700 g. of water. When the emulsification was complete,
; the stirring rate was reduced and 30 g. of ethylene diamine
- dissolved in 70 g. of water was added. The temperature was
10 then increased to 80C. and maintained constant while the
mixture was stirred for 4 hours.
The resulting dispersion of microcapsules in water
was filtered and the microcapsules dried at 60C. Aggregates
of microcapsules were broken by light grinding.
The microcapsules were white, spherical, free flowing,
had an average particle size of 50 microns and contained
; approximately 66% by weight methyl lardate.
EXAMPLE XV Methyl lardate encapsulated in the reaction
product ~rom propylenediamine and trimethyl
hexamethylene diisocyanake.
.. ,
The same procedure was followed as in Example XIV
except that 32 g. of propylene diamine were used instead of 30
g. of ethylenediamine. ~ -
The resulting microcapsules were white, spherical,
free flowing, had an average particle size of 50 microns and -
contained approximately 66% methyl lardate.
EXAMPLE X~I Rapeseed oil encapsulated in polymerized
divinylbenzene.
- 25 g~ of divinylbenzene were dissolved in 60 g. of
rapeseed oil. This solution was added with vigorous stirring
to a solution of 0.5 g. of Siponic 218 in 700 g. of water.
When the emulsification was complete, the stirring rate was
reduced and the temperature raised to 80C. Then, 2 g. of
.. . .
- 24 -
: . .. . .
potassium persulphate were added and the mixture stirred at
80C. for 6 hours. The temperature was allowed to drop to
25C, At this point, the mixture was filtered, and the
microcapsules washed and then dried at 45~C. The dried
capsules were gently ground to break any aggregates.
The final microcapsules were white, spherical, free
flowing, had an average particle size of 20 microns and
contained approximately 7~/0 by weight rapeseed oil.
EXAMPLE XVII Isostearic acid encapsulated in polymerized
divinylbenzene.
The same procedure was followed as in Example XVI,-
except that 60 g. of isostearic acid was used instead of 60 g.
of rapeseed oil.
The resulting microcapsules were white, spherical, free
flowing, had an average particles size of 20 microns and con-
tained approximately 70/0 by weight isostearic acid.
EXAMPLE XVIII Effect of mlxtures of ethylenebisstearamide wax
and microcapsules from Example VIII on bxass powder.
Blends of microcapsules and a conventional lubricant
~; 20 were prepared and tested using CZ-2 (trademark) brass powder
(from Canada Metals Limited). Figure 4 gives the results for
; blends of ethylenebisstearamide wax with the fine particle siæe
microcapsules prepared in Example VIII. The total concentration
of lubricant was he~d constant at 1% by weight. Here again
synergism occurs and there is a maximum in the green density,
which in this case occurs at a concentration of microcapsules of
approximately 60% by weight. In contrast to the results for
iron powders, the-ejection pressure increases with the addition
of microcapsules.
EXAMPLE XIX Epoxidized soyabean oil encapsulated in the
reaction product from ethylene diamine and
polymethylene polyphenylisocyanate.
13.5 g. of polymethylene polyphenylisocyanate (Mondur
MRS, trademark from Mobay Chemical Company) was dissolved in
76.5 g. of epoxidized soyabean oil (Paraplex G-62, trademark -
from Ro~n and Haas). The solution was added with stirring to
a solution of 3 g. of Siponic 218 (trademark) in 700 g. of water.
The resulting coarse emulsion was then mixed very vigorously in
a high intensity colloid mill to produce an emulsion containing
very fine droplets of oil. The stirring rate was then reduced
and 3~5 g. of ethylene diamine in 10 g. of water was added. The
temperature was then increased to 80C. and maintained constant
while the mixture was stirred for 4 hours.
The microcapsules were separated from the water by
filtration and dried at 60C. Aggregates of dried microcapsules
were broken by gentle grinding.
The microcapsules were white, spherical, free flowing, -
had an average diameter of 5 microns and contained 85% oil.
When tested as lubricants for powdered metals they gave results
similar to those obtained with unepox:idized soyabean oil. ;
; EXAMPLE XX Effect of mixtures of zinc s-tearates and
microcapsules from Example VIII on iron
powder.
Blends of zinc stearate (from H. L. Blachford, Limited)
and microcapsules from Example VIII were prepared and tested
- using Atomet 29 (trademark) from Quebec Metal Powder Company.
The total concentra-tion of lubricant was held constant at 1%
by weight. Although, no maximum occurred in the plot for green
density, a minimum occurred in the ejection force at approximately
60% microcapsule content, showing once again the existence of
~;~ synergism.
:;' ' .
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- 26 -
' '
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. - .,
SUPPLEMENTARY DISCLOSURE
This disclosure and the original disclosure are
concerned with lubricants for powder metallurgy and with
the manufacture and use of such lubricants; and more
~ especially are concerned with microencapsulated lubricants.
- As described in the original disclosure the
microcapsules of the invention comprise a core and a
solid shell surrounding the core.
Liquid _ubricant
The core comprises a liquid lubricant. The
lubricant should have a low enough viscosity that
when the shell is ruptured, the lubricant will rapidly
flow out and envelop the particles of powdered metal.
In this respect the viscosity is suitably less than 1500
centipoises, preferably less than 600 centipoises
and most suitably below 300 centipoises.
:
Generally the surface tension of the lubricant
is below about 50 and preferably below about 40 dynes/cm
so as to achieve good wetting of the powdered metal.
Lubricants are frequently burned off at about 1200F
or below prior to sintering and so in general it is
~, appropriate that at least 90% of the liquid should volatize
or decompose below 1200F.
. .
; Examples of specific liquid lubricants in the
invention, in addition to those mentioned in the original
disclosure include fatty acid esters of polyols such as
glycerol, trimethylolpropane, pentaerythritol, poly-
ethylene glycols, (for example polyethylene glycol dioleate),
polypropylene glycols, and copolymers formed by addition of
ethylene oxide and propylene oxide to a glycol or
amine base. Generally synthetic fatty acid esters or
- 27 -
~J '
,
:; :
mixtures of synthetic fatty acid esters or mixtures of `
synthetic and natural fatty acid esters are preferred~
Mineral oils and low melting point polyethylene
glycols and polypropylene glycols can also be used, but
are less preferred.
An antioxidant may be included in admixture with
the liquid lubricant as a special additive.
Usually the lubricant content of the micro-
capsule varies between 50% and 90%, preferably 50% to 85%,
by weight, of the microcapsule.
Shell
The chemical properties required of the shell
material are similar to those for the liquid lubricant.
; The surface of the shell must be sufficiently smooth `
and non-tacky so that a good flow rate and apparent
' density is obtained for the mixture of powdered metal,
; lubricants and other additives. The flow rate and apparent
density are desirably at least ninety percent of the
correspondin~ values for the powder without lubricant, and
should preferably be greater. Desirably in obtaining the
best results the shell should have a smooth, non-tacky
outer surface such that the flow rate and apparent density
of a mixture of the microcapsules and powdered ferrous
.~ ~ . . .
`~ metal which mixturecomprises the microcapsules in an -~
amount of 0.1% to 1%, by weight, are at least 90% of
the corresponding values for the free powdered ferrous
metals. Values less than 90% may be satisfactory for some ` -;
purposes although less preferred. -
The shell-should rupture when subjected to the
pressure exerted during compaction. This pressure can
range from as low as one t.s.i. (tons per square inch)
- 28 -
, ~
; . . ', . ', ,. ' . :' ~ : '' : . , .' ,
to as high as one hundred t.s.i., and even slightly above
this at times. For iron and steel pressures of 20 - 60
t.s.i. are most commonly used, while for brass and bronze
- somewhat lower pressures are generally used, and for aluminum
the usual range is 10 - 30 t.s.i. It is also desirable that
the shell material be such that thin shells can be utilized so
that the percentage of liquid lubricant is high. Shell thick-
ness is usually in the range 0.01 to 50 microns, preferably 0.1
to 20 microns, depending on capsule size.
Microcapsule
Fine capsules are not always preferable since
they fit more easily into interstices between the metal -
particles and a greater degree of compaction is re~uired
before they break. Also, in capsules prepared by the inter-
facial method, the wall thickness is proportional to the
capsule diameter, so smaller capsules are less resistant
~`~` to abrasion.
- In the synergistic mixtures of microcapsules and
unencapsulated solid particulate lubricant the optimum
microcapsule concentration is dependent upon the particle
size and the composition of the microcapsules and of the un-
encapsulated solid particulate lubricant. The compositions
giving optimum properties can vary over a wide range, depend-
ing on the property considered and the powder used, but usually
the microcapsule content is from 1 to 99, preferably 5 to 95,
percent.
Microcapsule Production
As described in the original disclosure the
microcapsules may be manufactured by a method comprising
the following steps~ If necessary, mix an emulsifying
agent with either the liquid lubricant, the water phase,
- - 29 -
:
or both. (2) Mix a lubricant soluble monomer with the liquid
lubicant. (3) Add the resulting mixture to the water phase.
(4) Mix at room temperature uslng vigorous agi~ation to form an
emulsion of the desired droplet size, as discussed above. (5)
To the emulsion add, with mixing, a water soluble monomer
reactive wiih the lubricant soluble monomer or a polymerization
catalyst for the lubricant soluble monomer. (6) Mix, but not
so vigourously that the capsules are destroyed, for several hours,
with heating to about 80C. if desired, to accelerate the
reaction. (7) Filter the mixture to separate the microcapsules
from the water. t8) Wash t'ne microcapsules to remove emulsify-
. .
ing agent and any excess water soluble monomer and (9) dry
the microcapsules.
'! I As llndicated in the original disclosure polyurea shells
derived from the polymerization of a di- or polyisocyanate
with a di- or polyamine are especially preferred.
In particular it is preferred to employ a shell de-
; rived from the polymerization of a polyisocyanate with a poly- ~ ;
amine' such shells are found to be stronger and to provide
better flow characteristics. -
. .
' ' ' :','
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- . . .
~ 3 b.~
The microcapsules themselves represent a total
lubricant system in that not only does the core act as
a lubricant on rupture of the microcapsules but the unbroken
microcapsules themselves act as lubricant. When the
microcapsules are mixed with a powdered metal, for example
powdered iron, the bulk density (i.e. the apparent density,
as it is generally called) of the iron powder/microcapsule
mixture is greate~ than that bf the iron powder alone; this
is in spite of the fact that the specific gravity of the
microcapsules is much lower than that of the iron.
; The apparent density is directly related to the
ease with which the particles of iron powder can slide over
one another. The more easily that the iron particles slide
over one another, the higher the apparent density will be,
because of the greater extent to which the particles of
iron can be packed or nested together. One advantage of
the microcapsules is that they produce an increase in the
bulk density of the uncompacted powdered metal. This
means that the molds can be shallower, for a given thick-
ness of the final part.
Thus, not only does the core of the microcapsule
provide a lubricant on rupture of the microcapsule, but
also the smooth non-tacky shell of the microcapsule acts
as a lubricant prior to rupture of the microcapsules.
- 31 - ~
.
-
3~ .
A further importantcriterion of the microcapsules
of the present invention which is important to the utility
in powder metallurgy is that the outer surface of the micro-
capsules must be resistant to abrasion by sinterable
powdered metal to the extent that the microcapsules can be
thoroughly mixed with sinterable powdered metal without
any substantial release of lubricant: at the same time the
shell must be rupturable when the mixture is subjected to
powder metallurgy compacting pressures. The abrasion
resistance required of the microcapsules is very high.
Particles of iron powder are angular and have sharp - -
edges and are very heavy having a specific gravity of
about 7.9. It is surprising that microcapsules could
be developed which withstand the abrasive treatment
received, when being mixed with iron powder.
Before compaction of the mixture, there are two
important properties of the powdered metal-lubricant mixture
which are greatly affected by the lubricant. One is the
apparent density, and the other is the flow rate. Customarily
used lubricants such as zinc stearate and ethylenebisstear- ;
amidewaxalmost always reduce the flow rate to a ~mall
~ ' . ', .
:
.. .
.''' '`
- 32 -
. .
:,
extent. If more than a very small amount of a liquid
lubricant is added directly to a powdered metal, the
flow rate is substantially reduced and this is a
very serious disadvantage because it then becomes impossible
to fill the mold completely. A great many different
materials have been tested which give good lubrication as
far as, say, apparent density and compressibility and
maybe also ejection pressure are concerned, which materials
fail completely with regard to flow rate because they
reduce the flow rate drastically. The microcapsules of the
invention do not reduce the flow rate drastically and indeed
sometimes they improve it. When they do reduce it, the reduction
is less than with zinc stearate or ethylenebisstearamide wax,
which are the materials conventionally employed as lubricants
in powder metallurgy techniques.
This latter feature of the microcapsules is
illustrated later in Table V from which can be compared
the flow time of powdered metals containing microcapsules
of the invention with powder metal mixtures con-
taining zinc stearate and ethylenebisstearamide wax,
respectively, as the lubricant. It will be seen that in
each case the flow time for the mixture containing
microcapsules of the invention is lower than the flow time
for the mixtures containing zinc stearate or ethylenebis-
stearamide wax; indeed the microcapsules of the present
invention,which can be considered an organic lubricant,
produce a flow time considerably faster than the conven-
tional organic lubricant, namely ethylenebisstearamide.
Further, the flow time for each of the mixtures
containing microcapsules in Table V is less than that for
the powdered metals alone. In particular the flow time
- 33 _
,~'\~ , '' :
; ~'
for the Atomet 28 by itself is 27.1 seconds and the flow
time for Atomet 29 by itself is 24.2 seconds. The corres-
ponding figures for the mixtures with microcapsules of
the invention are 24.6 and 23.4 seconds respectively.
On the other hand the flow times for the mixtures with
zinc stearate and ethylenebisstearamide wax are shown to
be higher than the flow times for the powdered metals
. .
alone. From this it can be seen that the microcapsules
of the invention are superior to zinc stearate and
ethylenebisstearamide wax with regard to flow rate.
It is really very surprising, and certainly not obviQus,
that microcapsules should produce such good results. This
is especially so when one considers that the especially
preferred shell material is a polyurea, which is produced
by reacting an isocyanate with an'amine, since polyurea
is not known as a lubricant.
Production of Sintered Metal Article
The microcapsules of the invention or mixtures
of the microcapsules with solid particulate lubricants are
advantageously employed in the manufacture of sintered
. !
metal articles from powdered metal.
In this method the powdered metal is mixed or
blended with the microcapsules, or a mixture of the micro-
capsules with a conventional solid particulate lubricant,
to form an intimate mixture.
The mixture is compacted in a mould at a pressure
effective to rupture the shell of the microcapsules and
release the liquid lubricant, and to form the mixture into
a self-supporting shaped body. The compacting pressure
will depend too on the particular metal powder and may be
from 1 t.s.i. to 100 t.s.i. or even higher; generally
compacting pressures of 10 t.s.i. to 75 t.s.i. will be
*trademark - 34 -
.~ ~ ;.
'~ ,. .
satisfactory.
The self supporting body is removed from the
mould and is heated to decompose and remove the lubricant
and shell and to sinter the metal particles. This heating
operation may take place in two separate stages, most of
the lubricant and shell and any solid particulate
lubricant being removed in a first heating stage and any
residual material subsequently being removed in the
sintering furnace. The lubricant and shell could be
removed entirely in the sintering furnace but this
results in deposits on the interior of the sintering
furnace which may serve to decrease the efficiency of the
furnace over à period of time.
When mixed with metal powders, the concentration
of the microcapsules or of microcapsulès plus unencapsulated
solid lubricants is suitably in the range of 0.1% to 5%
by weight, preferably from 0.3% to 2% more preferably 0.~/0
to 1% by weight.
The method can be employed in the manufacture
of sintered metal parts from a variety of powdered
sinterable metals including ferrous metals, for example,
iron and steel,and non-ferrous metals, for example, aluminium,
copper and zinc, as well as mixtures of metal powders, for
example mixtures of iron and copper, and powdered alloys,
for example, brass powder. It will be understood that
such sinterable metal powders may also include conventional
additives, for example, graphite, which is often employed
in admixture with iron.
The microcapsules may also be employed in the
manufacture of sintered parts from sinterable metal oxides,
. ~ , . .
and sinterable metal salts, for example, uranium oxide `
and barium ferrite.
. . , ::
- 35 -
~ :; . ::
.,
-
In a further aspect of the invention there
is provided a novel composition of matter for the -
manufacture of sintered iron articles comprising a sinterable
mixture comprising powdered metal, for example iron, and
discrete pressure rupturable microcapsules of the invention.
The invention is further illustrated by reference
to the following examples directed to particular and
preferred embodiments. ;
EXAMPLE XXI
Epoxidized soyabean oil encapsulated in
the reaction product -from triethylene-
tetramine and polymethylene p~lyphenyl-
isocyanate. ~-
19.6 g of polymethylene polyphenylisocyanate
(Mondur MRS, trademark, from Mobay Chemical Company),
was dissolved in 75.0 g of epoxidized soyabean oil (Plasto-
lein 9232, trademar~ from Emery Industries, Inc~) together
with 3.0 g~ of a tallow fatty acid diester of polyethylene
; glycol of molecular weight 600. The solution was added
with vigorous stirring to 700 ml. of water. When the
emulsification was complete, the stirring rate was reduced
and 10.0 g of triethylenetetramine dissolved in 100 ml. of
water was added. The mixture was heated to 80C. for two
hours with continued stirring, cooled, and filtered. The
- microcapsules were dried at 60C. and disaggregated by
sieving through a 60 mesh sieve. They were white, spherical,
free-flowing, had an average diameter of about 70 microns,
and contained about 75% by weight of oil.
EXAMPLE XXII
Testing of microcapsules prepared in ~ -
Example XXI.
The microcapsules of Example XXI were tested in
the iron powders Atomet 28 (trademark, from Quebec Metal ;
- 36 -
) ., ~ -;
,~ . ,
Powder Co.) and Atomet 29, and results were compared with
those obtained for zinc stearate and ethylenebisstear-
amide wax. Lubricant and iron powder were thoroughly
mixed and transverse rupture specimens pressed using a
pressure of 67200 psi. The parts were subjected to lubricant
burn-off at 1000F. for 30 minutes in an atmosphere of
hydrogen-nitrogen (50:50), followed by sintering at 2050F.
for 30 minutes. Properties were measured according to
standard ASTM procedures and are shown in Table V.
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EXAMPLE XXIII
Testing of microcapsules prepared in Example XXI
The microcapsules of Example XXI were tested in
Iron Powder MH-100 of Hoeganaes to determine the flow
time, flow rate and apparent density. The results are
tabulated in Table VI.
TABLE VI
MH-100 M~I-100
MH-100 alone + 1% + 5%
microcaps. microcaps.
_
.. ;
Flow time (sec./50 g.) 31.3 25.7 33.9
Flow rate (as % of
rate for pure MH-100) 100% 122~ 92%
Apparent density (g./cm. ) 2.582 2.603 2.283
Apparent density (as % of
- apparent density for pure
, MH-100) 100% 101% 88%
".
The results demonstrate that 0ven with higher
concentrations of microcapsules of the invention satisfactory
flow rate and apparent density values were ob~ained.
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