Note: Descriptions are shown in the official language in which they were submitted.
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Iron powder composition including an amide typ lubricant and
a method to prepare it.
FIELD OF THE INVENTION
The present invention relates to metal powder
compositions. Particularly the invention relates to iron-
based compositions suitable for compaction at elevated
temperatures.
BACKGROUND OF THE INVENTION
The powder metallurgy art generally uses different
standard temperature regimes for the compaction of a
metal powder to form a metal component. These include
chill-pressing (pressing below ambient temperatures),
cold-pressing (pressing at ambient temperatures), hot-
pressing (pressing at temperatures above those at which
the metal powder is capable of retaining work-hardening),
and warm-pressing (pressing at temperatures between cold-
pressing and hot-pressing).
Distinct advantages arise by pressing at tempera-
tures above ambient temperature. The tensile strength and
work hardening rate of most metals is reduced with in-
creasing temperatures, and improved density and strength
can be attained at lower compaction pressures. The ex-
tremely elevated temperatures of hot-pressing, however,
introduce processing problems and accelerate wear of the
dies. Therefore, current efforts are being directed to-
wards the development of metal compositions suitable for
warm-pressing processes.
The US patent 4,955,789 (Musella) describes warm
compaction in general. According to this patent, lubri-
cants generally used for cold compaction, e.g. zinc ste-
arate, can be used for warm compaction as well. In prac-
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tice, however, it has proved impossible to use zinc ste-
arate or ethylene bisstearamide (commercially available
as ACRAWAX~.), which at present are the lubricants most
frequently used for cold compaction, for warm compaction.
The problems, which arise, are due to difficulties in
filling the die in a satisfactory manner.
The US patents 5,744,433 (Storstrom et al) and
5,154,881 (Rutz) disclose metal powder compositions in-
cluding amide lubricants, which are especially developed
for warm compaction.
The lubricant according to the US patent 5,744,433
contains an oligomer of amide type, which has a weight-
average molecular weight Mw of 30,000 at the most. Very
high densities and green strengths may be obtained by
warm compacting powder compositions when the lubricant
has a molecular weight above 4000, the preferred lubri-
cant molecule having a molecular weight of about 6500.
It has however been found that this lubricant has a ten-
dency of sticking to the die wall, which requires fre-
quent cleaning of the die. Another disadvantage is that
the obtained green bodies are stained.
In the US. Patent 5,154,881 the amide lubricant con-
sists of the reaction product of a monocarboxylic acid, a
dicarboxylic acid and a diamine. The only lubricant
tested according to this patent is ADVAWAX~ 450, the com-
position of which is not described in detail but the re-
action product obtained includes i.a. ethylene bissteara-
mide according to Chemis-CIVS. Our experience of this
product is that it is difficult to obtain a constant com-
position and quality, which in turn may result in compo-
nents of varying quality. This may cause problems when
the lubricant is used in large scale industrial produc-
tion.
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SUMMARY OF THE INVENTION
The present invention reduces or eliminates
current problems associated with large scale production.
The present invention provides a new type of lubricant
useful in metal compositions intended for compaction at
elevated temperatures. The present invention also provides
a metal powder for producing components without stains. The
present invention also provides a metal composition
including lubricant, which during the compaction of the
metal powder does not deposit on the die wall.
In one aspect, the present invention provides a
powder composition comprising an iron-based powder and new
oligomer amide type lubricant. The composition may also
include one or more additives, such as binders, flow agents,
processing aids and hard phases.
The warm compaction may be performed by mixing an
iron-based powder with the oligomer amide type lubricant and
optionally a binder, preheating the powder composition and
compacting the metal-powder composition in a pre-heated
tool.
DETAILED DESCRIPTION OF THE INVENTION
The new amide type lubricant used according to the
present invention may be represented by the following
formula:
2 5 D-Cn,a-B-A-B-C~,y,-D
wherein:
D is -H, COR or CNHR, wherein R is a straight or
branched aliphatic or aromatic group including 2-21 C atoms;
C is the group -NH (CHZ) nC0-;
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B is amino or carbonyl;
A is alkylene having 4-16 C atoms optionally
including up to 4 0 atoms;
ma is an integer 1-10;
mb is an integer 1-10; and
n is an integer 5-11.
It is preferred that D is COR, wherein R is an
aliphatic group 16-20 C atoms; C is -NH(CHz)nC0-, wherein n
is 5 or 11; B is amino; A is alkylene having 6-14 C; atoms
optionally including up to 3 O atoms; and ma and mb, which
may be the same or different, are an integer 2-5.
Examples of preferred lubricants to be used in the
iron based compositions according to the present invention
are:
CH,3 ( CHz ) i6C0- [ HN ( CHz ) 1100 ] z-HN ( CHz ) lzNH- [ CO ( CHz ) mNH ]
zC0 ( CHz ) i6CH3 ;
CH3 ( CHz ) 1600- [ HN ( CHz ) 1100 ] z-HN ( CHz ) lzNH- [ CO ( CHz ) mNH ]
sC0 ( CHz ) i6CH3 ;
CH3 ( CHz ) 1600- [ HN ( CHz ) mC0 ] 3-HN ( CHz ) izNH- [ CO ( CHz ) mNH ] sC0
( CHz ) i6CHs ;
CH3 ( CHz ) 16C0- [ HN ( CHz ) mC0 ] s-HN ( CHz ) lzNH- [ CO ( CHz ) mNH ] 4C0
( CHz ) i6CH3 ;
CH3 ( CHz ) 1600- [ HN ( CHz ) 1100 ] 4-HN ( CHz ) lzNH- [ CO ( CHz ) mNH ]
4C0 ( CHz ) i6CH3 ;
2 0 CH3 ( CHz ) 1600- [ HN ( CHz ) 1100 ] 4-HN ( CHz ) lzNH- [ CO ( CHz ) mNH
] sC0 ( CHz ) i6CH3 ;
and
CH,3 ( CHz ) i6C0- [ HN ( CHz ) 1100 ] s-HN ( CHz ) lzNH- [ CO ( CHz ) mNH ]
sC0 ( CHz ) i6CH3 -
Other examples are:
( CH3 ) CO-HN ( CHz ) SCO-HN ( CHz ) zNH-CO ( CHz ) SNH-CO ( CH3 ) having the
MW 370.49;
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CH; ( CHZ ) zoCO-HN ( CH2 ) 1100-HN ( CH2 ) laNH-CO ( CH2 ) liNH-CO ( CHZ )
2oCHs
having the MW 1240.10;
CH j ( CHZ ) zoCO- [ HN ( CHz ) 1100 ] lo-HN ( CHZ ) izNH- [ CO ( CH2 ) mNH ]
ioCO ( CH2 ) 2oCHs
having the MW 8738.04;
5 CH; ( CHZ ) 9C0- [ HN ( CHz ) 1100 ] s-HN ( CH2 ) 12NH- [ CO ( CHZ ) mNH ]
3C0 ( CH2 ) 4CH3
having the MW 1580.53;
CH; ( CH2 ) 4C0- [ HN ( CH2 ) SCO ] ~-HN ( CH2 ) 6NH- [ CO ( CHZ ) SNH ] NCO (
CHZ ) 4CH3
having the MW 1980.86;
CHI ( CH2 ) 2oC0- [ HN ( CHZ ) SCO ] ~-HN ( CHZ ) 6NH- [ CO ( CHz ) SNH ] NCO
( CHz ) zoCH3
having the MW 2429.69; and
CHI ( CH2 ) i6NH- [ CO ( CH2 ) mNH ] 4-CO ( CH2 ) ioCO- [ HN ( CHZ ) 1100 ]
4HN ( CHZ ) 16CH3
having the MW 2283.73.
The chemical differences between the new lubricant
and the lubricant described in the US patent 5,744,433 are
that the new molecule has a central diamine or diacid moiety
and identical terminal groups on both ends. The chemical
difference between the new lubricant and the lubricant
described in the US patent 5,154,881 is that the new lubricant
molecule includes the unit -NH(CH2)nC0-.
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In contrast to the lubricant known from US 5 154 881 no
ESS is formed when the lubricant according to the present
invention is prepared. EBS which has the chemical formula
CH3 ( CH2 ) isCO-HN ( CHz ) ZNH-CO ( CH2 ) isCHs is a molecule without
lactam units which is in contrast to the lubricants
according to the present invention.
As regards the molecular weight of the new lubricant
molecule it has been found that the preferred lubricants
have a molecular weight between 1000 and 5000, most pref-
erably between 1500 and 3000.
The lubricant molecule may be prepared according
standard procedures for amide oligomer as described in
e.g. "Principles of Polymerization" third edition by
George Odian (John Wiley & Sons, Inc.). According to the
present invention the lubricant preferably consists of at
least 800 of the amide having the formula described
above. Thus up to 20~ by weight of other types of lubri-
cants may be added, as long as the advantageous proper-
ties of the new lubricant is not detrimentally affected.
This lubricant, which is added to the iron-based
powder is preferably in the form of a solid powder, can__
make up 0.1-to by weight of the metal-powder composition,
preferably 0.2-0.8o by weight, based on the total amount
of the metal-powder composition. The possibility of using
the lubricant according to the present invention in low
amounts is an especially advantageous feature of the in-
vention, since it enables high densities to be achieved.
As used in the description and the appended claims,
the expression "iron-based powder" encompasses powder es-
3o sentially made up of pure iron; iron powder that has been
pre-alloyed with other substances improving the strength,
the hardening properties, the electromagnetic properties
or other desirable properties of the end products; and
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particles of iron mixed with particles of such alloying
elements (diffusion annealed mixture or purely mechanical
mixture). Examples of alloying elements are copper, mo-
lybdenum, chromium, manganese, phosphorus, carbon in the
form of graphite, and tungsten, which are used either
separately or in combination, e.g. in the form of com-
pounds (Fe3P and FeMo). Unexpectedly good results are
obtained when the lubricants according to the invention
are used in combination with iron-based powders having
high compressibility. Generally, such powders have a low
carbon content, preferably below 0.040 by weight. Such
TM TM TM
powders include e.g. Distaloy AE, Astaloy Mo and ASC
100.29, all of which are commercially available from
Hoganas AB, Sweden.
Apart from the iron-based powder and the lubricant,
the new powder composition may contain one or more addi-
tives such as binders, flow agents, processing aids and
hard phases.
The binder may be added to the powder composition in
accordance with the method described in U.S. Pat. No.
5,368,630 and
may be organic compounds such as cellulose ester resins,
hydroxyalkyl cellulose resins having 1-4 carbon atoms in
the alkyl group, or thermoplastic phenolic resins.
A type of flow agent, which can be used according to
the present invention, is disclosed in the US patent
5,782,954.
The flow agent, which is preferably a silicon dioxide, is
used in an amount from about 0.005 to about 2 percent by
weight, preferably from about 0.01 to about 1 percent by
weight, and more preferably from about 0.025 to about 0.5
percent by weight, based on the total weight of the met-
allurgical composition. Furthermore, the flow agent
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should have an average particle size below about 40 nano-
meters. Preferred silicon oxides are the silicon dioxide
materials, both hydrophilic and hydrophobic forms, com-
TM
mercially available as the Aerosil line of silicon diox-
ides, such as the AerosilTM200 and R812TMproducts, from
Degussa Corporation.
The processing aids used in the metal-powder compo-
sition may consist of talc, forsterite, manganese sul-
phide, sulphur, molybdenum disulphide, boron nitride,
tellurium, selenium, barium difluoride and calcium di-
fluoride, which are used either separately or in combina-
tion.
The hard phases used in the metal-powder composition
may consist of carbides of tungsten, vanadium, titanium,
niobium, chromium, molybdenum, tantalum and zirconium,
nitrides of aluminium, titanium, vanadium, molybdenum and
chromium, A12 03, and various ceramic materials.
The invention is further illustrated by the follow-
ing examples, which are to be interpreted only as exam-
ples but should not limit the scope of protection.
wTrrtnr a ~
The following tables disclose a comparison of prop-
erties between components prepared from powder mixtures
including the lubricant according to the present inven-
tion and the amide type lubricant disclosed in the US
patent 5,744, 433.
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Table 1
Lubricant Compaction GD Ejec- Ejec- Spring-
Pressure (g/cm3) tion tion back
(MPa) Force Energy (o)
(N/mm2) (J/cm2)
Invention 500 7.14 11.5 19.3 0.147
" 600 7.29 11.4 23.3 0.162
" 700 7.38 11.8 24.6 0.192
OrgasolTM 500 7.09 11.9 29.9 0.191
3501*
600 7.22 13.8 40.0 0.187
700 7.30 16.0 48.5 0.229
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Table 2
Lubricant Compac- Appearance
tion
Pressure
(MPa)
Green compact Die V~lall
Invention 500 No stains No deposit
" 600 Few stains No deposit
700 Few stains No deposit
Orgasol 500 Many stains Some deposit
3501*
600 Many stains More deposit
700 Many stains More deposit
Temperature Powder/Die: 120°C/120°C
* lubricant preferred according to US patent 5,744, 433
5 The iron-based powder was Distaloy AE available from
Hoganas AB, Sweden. This powder was mixed with 0.3% by
weight of ultrafine graphite and 0.6% by weight of a lu-
bricant according to the present invention. A flow en-
hancing agent Aerosil~ 200 was added in an amount of
10 0.06% by weight.
As can be seen the new oligomer amide type lubricant
according to the present invention is superior not only
as regards the ejection force, the ejection energy, the
springback but also when it comes to the appearance of
the compacted component. Additionally the lubricant does
not deposit on the die wall.
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nvTrrtr~r n
The following table discloses a comparison of prop-
erties between components prepared from powder mixtures
including the lubricant according to the present inven-
tion and the amide type lubricant disclosed in the US
patent 5,154,881.
As can be seen the lubricant according to the pre-
sent invention is superior as regards the ejection force,
the ejection energy and the springback.
Table 3
GD Ejection Ejection Springback
(g/cm3) Force Energy (%)
(N/mm2) (J/cm2)
Lubricant 7.46 9.7 20.9 0.121
according
to the
present
invention
Lubricant 7.40 15.4 21.9 0.201
according
to US
patent
5 154 881
Compaction pressure 700 MPa
Temperature powder/Die 130°C/150°C
The iron-based powder was Distaloy AE available from
Hoganas AB, Sweden.
This powder was mixed with 0.3% by weight of ultra-
fine graphite and 0.6% by weight of a lubricant according
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to the present invention. A flow enhancing agent Aerosil
was added in an amount of 0.06% by weight.
nvTwrtnr n
The following example discloses a comparison of den-
sities of green bodies obtained with the oligomer amide
lubricants which are used according to the present inven-
tion and which have different molecular weights.
The iron-based powder was Distaloy AE available from
Hoganas AB, Sweden.
This powder was mixed with 0.3% by weight of ultra-
fine graphite and 0.6% by weight of a lubricant according
to the present invention. A flow enhancing agent Aerosil
was added in an amount of 0.060 by weight.
The powder was heated to a temperature of 130°C and
the temperature of die was 150°C. The compaction pressure
was 700 MPa.
Molecular V~leight of
Lubricant GD (g/cm')
2000 7,44
3000 7,41
4000 7,31
If the molecular weight of the oligomer amide
lubricant is lower than (about) 2000 the properties of
the powder composition becomes worse with regards to
flow, and the lubricant will have a tendency of sticking
to the die wall and the surface of the ejected compact.
The sticky nature of such surfaces increases the risk of
formation of rough surfaces on the final part owing to
powder which may be collected onto the ejected compact.
