Ferrous powder compositions containing a polymeric binder-lubricant blend

Complexable polymeric binder-lubricant blends are disclosed for production by powder metallurgy techniques of ferrous compositions with remarkably high green strength upon compaction, or soft magnetic ferrous powder/resin composites with improved processability and magnetic properties. An exemplary composition consists of a ferrous powder, a thermoset phenolic resin and poly(ethylene oxide), both polymers exhibiting, when intimately mixed, strong intermolecular acid-base interactions giving rise to an interpolymer complex which imparts a high strength to the resulting ferrous powder compact.

FIELD OF THE INVENTION 
The present invention relates to ferrous powder compositions containing 
specific polymeric binder-lubricant blends which can give rise to an 
association product, also known as interpolymer complex, by strong 
intermolecular acid-base interactions. Such compositions can be used to 
produce remarkably high green strength compacts or/and soft magnetic 
composites with improved processability and magnetic properties, together 
with good mechanical properties. 
BACKGROUND OF THE INVENTION 
The Processes for producing metal parts from ferrous powders using powder 
metallurgy (P/M) techniques are well known. Such techniques typically 
involve mixing of ferrous powders with alloying components such as 
graphite, copper or nickel in powder form, filling the die with the powder 
mixture, compacting and shaping of the compact by the application of 
pressure, and ejecting the compact from the die. The compact is then 
sintered wherein metallurgical bonds are developed by mass transfer under 
the influence of heat. The presence of an alloying element enhances the 
strength and other mechanical properties in the sintered part compared to 
the ferrous powders alone. When necessary, secondary operations such as 
sizing, coining, repressing, impregnation, infiltration, machining, 
joining, etc. are performed on the P/M part. 
It is common practice to use a lubricant for the compaction of the ferrous 
powder. The lubricant can be admixed with the ferrous powders or sprayed 
onto the die wall before the compaction. The lubricant is used to improve 
the compressibility of ferrous powders and the uniformity of densification 
throughout the part. It also reduces the metal powder/die wall friction, 
and in turn lowers the ejection force that is required to remove the 
compact from the die, thus minimizing die wear. 
Die-wall lubrication is known to lead to compacts with high green strength. 
Indeed, die-wall lubrication enables mechanical anchoring and 
metallurgical bonding between particles during compaction. However, 
die-wall lubrication is not yet widely used because it increases the 
compaction cycle time, leads to less uniform densification and is not 
applicable to complex shapes. On the other hand, an admixed lubricant most 
often reduces the strength of the green compact by forming a lubricant 
film between the metal particles which limits microwelding and eases the 
slipping of the particles when stresses are applied. 
When complex parts or parts with thin walls are to be produced, as well as 
when green parts have to be machined, parts with a high green strength are 
required. A number of patents describe lubricating components leading to 
compacts with enhanced green strength compared with conventional 
lubricants such as synthetic waxes and metallic stearates. For example, in 
U.S. Pat. No. 5,290,336 Luk discloses iron-based powder compositions 
containing binder-lubricants which increase the strength of green 
compacts, in terms of transverse rupture strength (TRS) values, up to 
about 5,000 psi, and which generally reduce the ejection forces during 
removal of the compacted part from the die cavity. The binder-lubricants 
comprise a dibasic organic acid and one or more additional components such 
as solid polyethers, liquid polyethers, and acrylic resins. Such 
binder-lubricants are added to the iron-based powders preferably in liquid 
form, dissolved or dispersed in an organic solvent. In U.S. Pat. No. 
5,498,276, Luk discloses the use of a polyether or poly(alkylene oxide) in 
a particulate form as a green strength enhancing lubricant. Green compacts 
with transverse rupture strength values of about 6,000-7,000 psi are 
obtained. However, dimensional variations during sintering are higher 
compared to mixes containing conventional lubricants, which may alter the 
sintered properties. 
Non-sintered soft magnetic parts especially for AC magnetic applications 
can also be produced using P/M techniques. In this case, the iron-based 
powder compositions contain an organic dielectric resin which forms an 
insulating coating between the iron particles and also bind those 
particles so as to impart mechanical strength to the pressed parts. A wide 
range of thermoset or thermoplastic resins have been described for the 
production of such magnetic composites, alone or in conjunction with 
inorganic insulating coatings, as diclosed for example in U.S. Pat. No. 
5,268,140 (Rutz et al.), or European Patent 583,808 (Gay). Different 
techniques have been used to electrically insulate particles, as disclosed 
in U.S. Pat. No. 5,211,896 (Ward et al.). Among them, wet techniques, 
which employ soluble resins, have most often been used to obtain a uniform 
coating at the surface of the iron particles for high frequency 
applications. On the other hand, it has been shown that by dry mixing iron 
and phenolic resin powders and compacting the mix using die wall 
lubrication, magnetic parts with good permeability and low losses 
(especially eddy current losses) at frequencies up to 50-100 kHz could be 
easily obtained. After compaction, compacts are heated at temperatures 
between 100.degree. C. and 300.degree. C. to crosslink the thermoset 
resin. The resin has such a low viscosity that it flows inside the compact 
at the very beginning of the curing treatment to wet, bind and isolate the 
iron particles. Good mechanical properties, i.e., TRS values as high as 
17,000-20,000 psi were obtained. 
Even if die wall lubrication can be used to enable the production of soft 
magnetic iron/resin composites, it is often preferable that the iron-based 
powder compositions contain an admixed lubricant to improve the 
processability of such magnetic materials in an industrial environment. 
Standard known lubricants are, e.g., zinc stearate, amide wax, stearic 
acid or PTFE, as well as boron nitride for warm compaction at temperatures 
higher than 250.degree. C. Even if they improve most often the 
processability of iron/resin powder mixtures, they decrease the strength 
of pressed parts significantly. There is thus a need for a lubricated 
powder composition that will give rise to improve processability of soft 
magnetic composites, while maintaining their good magnetic and mechanical 
properties. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide ferrous powder compositions 
containing specific polymeric binder-lubricant blends which can give rise 
to an association product, also known as interpolymer complex, by strong 
intermolecular acid-base interactions. Such binder-lubricant blends may be 
dry mixed in powder form with ferrous powders, or dissolved and sprayed on 
the surface of ferrous powders. 
It is also an object of the present invention to provide ferrous powder 
compositions which when formed by P/M techniques give parts with a high 
green strength and improved sintered properties. 
It is further an object of the present invention to provide such lubricated 
ferrous powder compositions that can also be used to produce non-sintered 
soft magnetic composites, especially for AC magnetic applications, with 
improved processability and magnetic properties, together with good 
mechanical strength. 
In accordance with the invention, there is provided a metallurgical powder 
composition comprising a metallic powder and a polymeric blend comprising 
a binder and a lubricant, the amount of the polymeric blend being from 
about 0.1 wt. % to about 20 wt. % of the composition, the binder and the 
lubricant being selected such that they form an association product by 
strong intermolecular acid-base interactions when mixed with each other, 
whereby the green strength of the powder composition, when compacted, 
exceeds 5000 psi, preferably 8,000 psi. 
Typically, the metallic powder is a ferrous powder such as an iron or 
iron-based material. The composition may further contain, for certain 
applications, an alloying powder in the amount of up to 15 wt. % of said 
composition. The alloying powder may be, for example, one or more of the 
following: graphite, copper, nickel and ferro-alloys. 
Typically, the binder is a thermoset or thermoplastic polymer having a 
strong acid character such as phenolic resins or carboxylic polyacids (for 
example, polymethacrylic acid and copolymers, hydrolyzed or monoester 
maleic anhydride copolymers). 
In a specific embodiment of the invention, the lubricant is a polymer 
having a strong basic character, such as poly(alkylene oxide) having the 
general formula 
EQU --[O(CH.sub.2).sub.x ].sub.y -- 
where x is from 1 to about 7. Preferably, the poly(alkylene oxide) is a 
poly(ethylene oxide) with x=2 and y is selected such that the 
poly(ethylene oxide) has a weight average molecular weight from about 
5,000 to about 8,000,000 and more preferably below 400,000. 
Alternatively, the lubricant is a polymer having also a strong basic 
character, such as a poly(alkylene ester) having the formula 
EQU --[O(CH2).sub.x O--C(O)--(CH2).sub.y --C(O)--].sub.n -- 
EQU or --[O(CH2).sub.z --C(O)--].sub.n 
for instance 
##STR1## 
where x, y or z is from 1 to about 18 and n is such that said 
poly(alkylene ester) is solid at room temperature, for example a 
polycaprolactone (z=5) having a number average molecular weight from about 
43,000 to about 80,000. 
The compositions of the present invention are preferable to those described 
in the U.S. Pat. Nos. 5,290,336 and 5,498,276 in that higher green 
strength together with better sintered properties can be obtained. 
DETAILED DESCRIPTION OF THE INVENTION 
The metallurgical powder compositions of the invention comprise a mixture 
of metal powders having a maximum particle size of generally about 600 
microns. Optionally, an alloying powder in the amount of less than 15 
weight percent can be admixed. The compositions include a blend of 
polymeric binder and lubricant, which can give rise to an association 
product or interpolymer complex by strong intermolecular acid-base 
interactions. The binder may be a thermoset or thermoplastic polymer 
having a strong acid character such as phenolic resins or carboxylic 
polyacids. The lubricant may be a polymer with a strong basic character 
such as a poly(alkylene oxide), e.g. poly(ethylene oxide), or a 
poly(alkylene ester) e.g. polycaprolactone. 
Using these metallurgical compositions, it has been found that compacts 
with remarkably high green strength can be produced together with sintered 
properties superior or equivalent to those obtained from metallurgical 
compositions containing other lubricants. Such lubricated ferrous powder 
compositions can also be used to produce non-sintered soft magnetic 
composites, especially for AC magnetic applications, with improved 
processability and magnetic properties, together with a good mechanical 
strength. 
The ferrous powders employed in the present invention are any of the pure 
iron or iron-containing (including steel or ferromagnetic) powders 
generally used in P/M methods. Essentially any ferrous powder having a 
maximum particle size less than about 600 microns can be used in the 
composition of the invention. 
Typical ferrous powders are iron and steel powders including stainless 
steel and alloyed steel powders. Atomet.RTM. 1001 steel powders 
manufactured by Quebec Metal Powders Limited of Tracy, Quebec, Canada are 
representative of such iron and steel powders. These Atomet.RTM. powders 
contain in excess of 99 weight percent iron, less than 0.2 weight percent 
oxygen and 0.1 weight percent carbon, and have an apparent density of 2.50 
g/cm.sup.3 and a flow rate of less than 30 seconds per 50 g. Virtually any 
grade of steel can be used. 
Considering the production of soft magnetic composites, typical ferrous 
powders are preferably high purity iron powders, preferably at least 97% 
pure, more preferably at least 99% pure, and most preferably at least 
99.75% pure. Suitable iron powders are commercially available. For 
example, Quebec Metal Powders Limited of Tracy, Quebec, Canada 
manufactures and markets a number of high purity iron powders, including 
Atomet.RTM. 1001 HP, Atomet.RTM. 110HP and Atomet.RTM. 68. Those skilled 
in the art will readily be able to identify alternative suitable iron 
powders. 
In accordance with the present invention, the metal powder is admixed with 
a polymeric binder-lubricant blend. The blend comprises a polymeric 
lubricant with a strong basic character such as poly(alkylene oxide), or 
poly(alkylene ester). 
The poly(alkylene oxide) for the purposes of the present invention has the 
following general formula: 
EQU --[O(CH2).sub.x ].sub.y -- 
wherein x is from about 1 to about 7 and y is selected such that the 
poly(alkylene oxide) has a weight average molecular weight greater than 
5,000. Preferably, the poly(alkylene oxide) is a poly(ethylene oxide) with 
x=2, and y is selected such that the poly(alkylene oxide) has a weight 
average molecular weight from about 5,000 to about 8,000,000, more 
preferably below 400,000. Commercially suitable poly(ethylene oxide) is 
for instance POLYOX.RTM.N-10 available from Union Carbide Canada of 
Willowdale, Ontario, Canada. 
The poly(alkylene ester) suitable for the purposes of the present invention 
has the following general formula: 
EQU --[O(CH2).sub.x O--C(O)--(CH2).sub.y --C(O)--].sub.n -- 
EQU or --[O(CH2).sub.z --C(O)--].sub.n 
wherein x, y and z is from 1 to about 18 and n is such that the 
poly(alkylene ester) is in solid form at room temperature. The melting 
temperature will vary depending on its structure, i.e on the value of x, y 
and z. Commercially available poly(alkylene esters) are polycaprolactones 
(z=5) from Union Carbide Canada of Willowdale, Ont., TONE.RTM. P767 and 
TONE.RTM. P787. These polymers have a melting point of about 60.degree. C. 
and have respectively a number average molecular weight of 43,000 and 
80,000. 
In accordance with the present invention, the polymeric lubricant is used 
in conjunction with a thermoset or thermoplastic polymeric binder having a 
strong acid character. Typical thermoset resins are phenolic resins, 
specifically resoles (one step) or novolacs (two-step). Typical 
thermoplastic resins are poly(4-vinylphenol) or carboxylic polyacid 
polymers such as polymethacrylic acid and copolymers, as well as 
hydrolyzed or monoester maleic anhydride copolymers. Suitable thermoset 
phenolic resins for these applications are commercially available, for 
instance, from the Occidental Chemical Corporation: VARCUM.RTM. resin 
series 29217, 29306, 29318, 29338, 7716 and others. 
In accordance with the present invention, the polymeric binder and 
lubricant to form the blend to be admixed with the metal powder, are those 
that are capable of complexing by intense intermolecular interactions 
between donors (acid) and acceptors (basic) groups of each polymer, which 
act like a physical crosslinking. Such intermolecular interactions may 
happen by intimate mixing of the two polymers during either dissolution, 
compaction or heat curing of the binder in case of thermoset resins. As 
well as providing good processability to the metal powders, the 
binder-lubricant blend improves the green strength of pressed parts. The 
formation of interpolymer complexes between polymers having strong 
acceptors and donors groups is well documented in the prior art. For 
instance, I. A. Katime et al. made a review in The Polymeric Materials 
Encyclopedia, 1996 (CRC Press, Inc.) on hydrogen-bonded blends, on the 
detection and characterization of hydrogen bonds and how they affect the 
properties of the mixtures. U.S. Pat. No. 3,125,544 (Winslow et al.) 
describes the possibility of forming an association product between a 
polyether and a phenolic resin. The authors report that, depending on the 
ratio thermoplastic polyether/thermoset phenolic resin used, tougher 
thermosets or more rigid thermoplastics can be produced. Such polymeric 
blends were obtained preferentially by mixing a phenolic resin with an 
aqueous solution of a polyether, e.g. poly(ethylene oxide). Blending in 
the melt state using a thermoplastic blending equipment such as an 
extruder was also described. 
The metallurgical powder compositions of the invention can be prepared by 
various methods. The first method involves dry mixing metallic and 
alloying powders with the other additives and the polymeric binder and 
lubricant powders. The second method consists of dissolving the polymeric 
binder-lubricant blend and spraying the resulting solution on the powder 
mix in a rotating blender. The solvent is then evaporated under vacuum 
while heating the blender shell. The third method involves, first, making 
a dry mix, then spraying a solvent into the mixture while the blender is 
still rotating. This procedure dissolves partially the binder-lubricant 
particles, which adhere to the metal particles. The blend is then dried by 
evaporating the solvent, preferably under vacuum pumping while heating the 
blender shell. After drying, a free-flowing powder is obtained. 
Another alternative is to produce a dry mix of metallic and alloying 
powders with the other additives and the polymeric binder and lubricant 
powders and to treat the obtained mix with another polymeric binder in 
order to improve the flowability, the resistance to dusting and to reduce 
segregation of the constituents. In this case, a polymeric binder such as 
polyvinylpyrrolidone dissolved in a solvent is sprayed in the dry mixture, 
desirably while the blender is still rotating. This procedure desirably 
binds the fine metal, alloying and binder-lubricant blend particles to the 
metal particles. Any type of polymeric binder known in the prior art to be 
suitable to produce segregation-free mixes can be used as for example 
polyvinylpyrrolidone or polymethacrylate and copolymers.

EXAMPLES 
High Green Strength Iron Based Powder Compacts 
Example 1 
The polymeric binder-lubricant blends comprises a thermoset phenolic resin 
and a poly(ethylene oxide). Using conventional dry-mixing blenders, 
different powder mixtures were prepared containing 98.65 wt % ATOMET 1001 
steel powder (Quebec Metal Powders Ltd.), 0.6 wt % graphite powder (South 
Western 1651) and different combinations of phenolic resin and 
poly(ethylene oxide) powders as described in Table 1. The phenolic resin 
was a resole-type phenolic resin from Occidental Chemical Corporation 
(Varcum.RTM. 29217). The poly(ethylene oxide) is POLYOX.RTM. N-10 from 
Union Carbide. 
Transverse rupture strength bars (3.175.times.1.270.times.0.635 cm) were 
compacted at 65.degree. C. and 45 tsi in a floating compaction die, and 
ejection pressures were recorded for each mixture. After a curing 
treatment (1h/175.degree. C. in air), the density and strength (transverse 
rupture strength according to MPIF 15 Standard) were evaluated. Results 
are compared in Table 1 with a similar mixture containing the same 
constituents except that the binder-lubricant of the present invention was 
replaced by 0.75 wt % of an amide wax lubricant (Atomized ACRAWAX C from 
Lonza) and no curing was applied. 
TABLE 1 
______________________________________ 
POLYOX Varcum ACRAWAX Ejection 
N-10 29217 C Pressure Density TRS 
% % % Tsi g/cm.sup.3 psi 
______________________________________ 
-- -- 0.75 2.75 7.12 2,004 
0.75 0 -- 2.4 7.20 6,057 
0.65 0.1 -- 2.7 7.18 10,399 
0.45 0.3 -- 3.0 7.16 11,127 
0.35 0.4 -- 3.4 7.14 12,044 
______________________________________ 
While maintaining low ejection pressures, the replacement of a part of the 
polymeric lubricant POLYOX N-10 by the phenolic resin Varcum 29217 enables 
the production of pressed and cured parts having a much higher mechanical 
strength than parts containing the polymeric lubricant alone or the 
conventional amide wax lubricant ACRAWAX C. 
Example 2 
Two different polymeric binder-lubricant blends are used: phenolic 
resin--poly(ethylene oxide) blend and phenolic resin--polycaprolactone 
blend. The thermoset phenolic resin and poly(ethylene oxide) were the same 
than those used in example 1 and TONE.RTM. P767 from Union Carbide was 
used as the polycaprolactone lubricant. The two blends, consisting of 0.1 
wt % of phenolic resin and 0.65 wt % of polymeric lubricant were dissolved 
in a solvent and mixed with a dry mixture of 98.65 wt % ATOMET 1001 steel 
powder (Quebec Metal Powders Ltd.) and 0.6 wt % graphite powder (South 
Western 1651). The mixtures were then dried by evaporating the solvent. 
TRS bars were compacted at 65.degree. C. and 45 tsi in a floating 
compaction die and ejection pressures were recorded for each mixture. 
After a curing treatment (1h/175.degree. C. in air), the density and 
strength (TRS) were evaluated. Results are given in Table 2. 
TABLE 2 
______________________________________ 
Varcum .RTM. 
POLYOX TONE .RTM. 
Ejection 
29217 .RTM. N-10 P767 Pressure Density TRS 
% % % tsi g/cm.sup.3 psi 
______________________________________ 
0.1 0.65 -- 2.2 7.26 8,909 
0.1 -- 0.65 3.0 7.19 13,800 
______________________________________ 
Varcum .RTM. 29217: thermoset phenolic resin 
POLYOX .RTM. N10: poly(ethylene oxide) 
TONE .RTM. P767: polycaprolactone 
The results show that even when dissolved in a solvent and coated on the 
surface of the steel powders, the binder-lubricant blends of the invention 
produce green parts having significantly higher green strength after 
curing than comparable prior art compositions, while the ejection 
pressures are at a low level. The phenolic resin--polycaprolactone blend 
gave a green strength higher than the phenolic resin--poly(ethylene oxide) 
blend. This suggests that the basic ester groups of the polycaprolactone, 
interacting strongly with the acidic phenolic groups of the phenolic 
resin, adhere more to the surface of the iron particles than the ether 
groups of the poly(ethylene oxide). 
Example 3 
Effect of Sintering 
Two different materials were pressed and sintered: Mix A containing 98.65% 
ATOMET 1001+0.6% graphite+0.1% Varcum.RTM. 29217 phenolic resin 
powder+0.65% POLYOX.RTM. N-10 powder and a conventional Mix B containing 
98.65% ATOMET 1001+0.6% graphite+0.75% Atomized ACRAWAX C. 
TRS bars were compacted at 65.degree. C. and 45 tsi in a floating 
compaction die. After compaction, green compacts made from Mix A were heat 
treated during one hour in air at 175.degree. C. to cure the phenolic 
resin. For both Mix A and Mix B, compacts were sintered for 30 minutes at 
1120.degree. C. in a dissociated ammonia atmosphere. The density, 
dimensional change from die size (according to MPIF 44 Standard) as well 
as the transverse rupture strength (MPIF 41) after sintering were 
measured. Data are reported in Table 3. 
TABLE 3 
______________________________________ 
Property Mix A Mix B 
______________________________________ 
Green Density (g/cm.sup.3) 
7.16 7.12 
Green Strength (psi) 9,206 2,004 
Sintered Density (g/cm.sup.3) 7.13 7.09 
Dimensional change (%) 0.26 0.25 
Sintered Strength (psi) 105,569 99,358 
______________________________________ 
As well as increasing the green density and green strength of compacts, the 
results show that the use of the polymeric binder-lubricant blend of the 
invention (Mix A) gives sintered parts with properties equivalent of 
better than those of parts made from mixes containing a conventional 
ACRAWAX C lubricant (Mix B). 
The good sintered properties obtained by using the polymeric blend of the 
invention may be attributed to the formation of the interpolymer complex 
between the polymeric lubricant and polymeric binder that minimizes 
dimensional change during sintering. 
Soft Magnetic Iron/Resin Composites 
Example 4 
Soft magnetic iron/resin composites using only a phenolic resin as binder 
exhibit good mechanical and magnetic properties, but they necessitate 
lubrication of the die walls during compaction of parts. The use of a 
polymeric lubricant such as polyethylene oxide in conjunction with a 
phenolic resin improves the processability of such soft magnetic 
composites, while maintaining good performance properties. 
Using conventional dry-mixing blenders, two different powder mixtures were 
prepared containing 99.2 wt % ATOMET 1001 HP (High Purity powder 
manufactured by Quebec Metal Powders Ltd.) and either 0.8% of phenolic 
resin or 0.4 wt % /0.4 wt % of phenolic resin/poly(ethylene oxide) 
powders. The phenolic resin was a resole-type phenolic resin from 
Occidental Chemical Corporation (Varcum.RTM. 29217). The poly(ethylene 
oxide) was POLYOX.RTM. N-10 from Union Carbide. 
TRS bars were compacted at 65.degree. C. and 45 tsi in a floating 
compaction die and ejection pressures were determined. After a curing 
treatment (1h/175.degree. C. in air), the density and transverse rupture 
strengths were evaluated. Results are given in Table 4. 
TABLE 4 
__________________________________________________________________________ 
POLYOX 
Varcum Ejection 
Before curing 
After curing 
.RTM. N-10 
.RTM. 29217 
Die wall 
Pressure 
Density 
TRS 
Density 
TRS 
% % lubrication tsi g/cm.sup.3 psi g/cm.sup.3 psi 
__________________________________________________________________________ 
0 0.8 No 4.6 7.14 
3,196 
7.14 
16,319 
0 0.8 Yes 2.4 7.17 -- 7.16 17,607 
0.4 0.4 No 2.9 7.27 5,471 7.27 14,178 
__________________________________________________________________________ 
Even if the strength after curing is slightly reduced compared to a mix 
containing 0.8% phenolic resin, the mix containing 0.4% phenolic 
resin/0.4% POLYOX.RTM. N-10 gives a low ejection pressure and is therefore 
effective to improve processing of parts without the need of die-wall 
lubrication. This binder-lubricant blend enables pressing of parts with a 
very high density while maintaining good mechanical properties. As 
described previously, the high strength results from the intense 
intermolecular reaction that occurs between the phenolic resin and the 
poly(ethylene oxide) polymers admixed with the metal powder. Indeed, 
infrared measurements revealed the existence of strong hydrogen bonds 
between hydroxyl phenolic groups of the phenolic resin and ether groups of 
the poly(ethylene oxide) polymer. 
Example 5 
Comparison of Different Phenolic Resin/Lubricant Systems 
Soft magnetic iron/resin composites were produced with different phenolic 
resin--lubricant blends. The resole-type phenolic resin VARCUM.RTM.29217 
from Occidental Chemical Corporation was used in conjonction with three 
different lubricants: Poly(ethylene oxide) POLYOX.RTM.N-10 from Union 
Carbide, lithium stearate (Li-St) from Blachford Inc. and 
Polytetrafluoroethylene (PTFE) S-5742 from Shamrock Technologies. 
Using conventional dry-mixing blenders, three different powder mixtures 
were prepared containing 99.1 wt % ATOMET 1001HP (High Purity iron powder 
manufactured by Quebec Metal Powders Ltd.), 0.6 wt % of phenolic resin 
powder and 0.3 wt % of poly(ethylene oxide) or lithium stearate or 
polytetrafluoroethylene powders as described in Table 5. TRS bars were 
compacted at 65.degree. C. and 45 tsi in a floating compaction die. After 
a heat treatment (1h/175.degree. C. in air), the density and transverse 
rupture strengths were evaluated. 
TABLE 5 
______________________________________ 
Binder Lubricant Density TRS 
0.6% wt 0.3% wt g/cm.sup.3 psi 
______________________________________ 
phenolic resin 
PTFE 7.17 12,220 
phenolic resin Li-St 7.15 7,700 
phenolic resin POLYOX N-10 7.20 14,890 
______________________________________ 
Results in Table 5 show that the polymeric binder-lubricant blend of the 
present invention gives soft magnetic composites with the highest density 
and strength. Inferior properties are obtained when using other 
conventional lubricants such as polytetrafluoroethylene or lithium 
stearate in conjonction with the same phenolic resin. 
Example 6 
Magnetic Properties 
Using the mixtures described in Example 4, rings were compacted at 45 tsi 
and 65.degree. C. in order to measure the magnetic properties of the 
composites at frequencies of 60 and 400 Hz and a magnetization of 0.5 
Tesla. The results are shown in Table 6. 
TABLE 6 
______________________________________ 
POLYOX Varcum 
.RTM. N-10 .RTM. 29217 Density Frequency Permeability Core Loss 
% % g/cm.sup.3 Hz .mu. W/lb 
______________________________________ 
0.4 0.4 7.29 60 541 1.6 
400 533 10.9 
0 0.8 7.20 60 394 1.6 
400 389 11.8 
______________________________________ 
* Magnetization of 0.5 Tesla 
Besides improving the processability of parts, the polymeric 
binder-lubricant blend of the present invention (0.4% 
Varcum.RTM.29217/0.4% POLYOX.RTM. N-10) enables the production of 
iron/resin parts with similar or better magnetic properties (permeability 
and core losses) than those obtained using the binder phenolic resin alone 
(0.8% Varcum.RTM.29217). The improvement of the magnetic properties may be 
explained by the increase in density of parts pressed from the mix 
containing the polymeric binder-lubricant blend of the invention. Indeed, 
it is known that the permeability is strongly influenced by the effective 
length of distributed air-gaps in soft magnetic iron/resin compacts which 
is related to the density.