U.S. patent application number 09/866013 was filed with the patent office on 2002-02-28 for method of lubricating a die cavity and method of making metal-based components using an external lubricant.
Invention is credited to Hanejko, Francis G..
Application Number | 20020025913 09/866013 |
Document ID | / |
Family ID | 26902966 |
Filed Date | 2002-02-28 |
United States Patent
Application |
20020025913 |
Kind Code |
A1 |
Hanejko, Francis G. |
February 28, 2002 |
Method of lubricating a die cavity and method of making metal-based
components using an external lubricant
Abstract
A method is provided for lubricating a die cavity that includes
applying a lubricant composition containing a high melting point
polymeric wax lubricant to the wall of a die cavity. Preferably,
the lubricant is a polyamide lubricant that has a melting
temperature greater than the temperature of the die wall during
use. The present invention also provides a method of making a
compacted metal part that includes applying the lubricant
composition to an internal wall of a die cavity, introducing a
metal-based powder composition into the die cavity; and compacting
the powder composition at a pressure sufficient to form a compacted
part from the metal powder composition.
Inventors: |
Hanejko, Francis G.;
(Marlton, NJ) |
Correspondence
Address: |
Woodcock Washburn Kurtz
Mackiewicz & Norris LLP
One Liberty Place - 46th Floor
Philadelphia
PA
19103
US
|
Family ID: |
26902966 |
Appl. No.: |
09/866013 |
Filed: |
May 24, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60208175 |
May 31, 2000 |
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Current U.S.
Class: |
508/266 ;
106/38.22; 508/454; 508/554 |
Current CPC
Class: |
C10N 2040/50 20200501;
C10M 2217/044 20130101; C10N 2040/42 20200501; B22F 1/10 20220101;
C10M 149/18 20130101; C10N 2040/38 20200501; C10N 2040/36 20130101;
C10N 2040/40 20200501; B22F 3/02 20130101; C10N 2040/30 20130101;
C10N 2040/44 20200501; C10N 2040/34 20130101; C10M 2217/045
20130101; C10N 2040/00 20130101; B22F 2003/026 20130101; C10N
2040/32 20130101 |
Class at
Publication: |
508/266 ;
508/454; 508/554; 106/38.22 |
International
Class: |
C10M 17/44; C10M 19/02;
C10M 15/68; C10M 15/70 |
Claims
What is claimed is:
1. A method of making a metal based compacted component comprising
the steps of: (a) providing a metallurgical powder composition
comprising at least about 85 percent of a metal-based powder; (b)
providing an external lubricant composition, wherein the external
lubricant composition comprises at least about 10 percent by
weight, based on total weight of the external lubricant
composition, of high melting point polymeric wax lubricant having a
melting point range beginning at a temperature greater than about
100 degrees Centigrade; (c) applying the external lubricant
composition to interior walls of a compaction die in an amount
sufficient to reduce the stripping and sliding pressures upon
ejection of a metal based component; and (d) compacting the
metallurgical powder composition in the die at a compaction
pressure sufficient to form a metal component.
2. The method of claim 1 wherein the high melting point polymeric
wax lubricant comprises (a) an amide lubricant that is the reaction
product of: (i) about 10-30 weight percent, based on total weight
of the lubricant composition, of a C.sub.6-C.sub.12 linear
dicarboxylic acid having the formula HOOC(R)COOH where R is a
saturated or unsaturated linear alphatic chain of 4 to 10 carbon
atoms; (ii) about 10-30 weight percent, based on total weight of
the lubricant composition, of a saturated or unsaturated
C.sub.10-C.sub.22 monocarboxylic acid, and (iii) about 40-80 weight
percent, based on total weight of the lubricant composition, of a
diamine having the formula (CH.sub.2).sub.x(NH.sub.2).s- ub.2
wherein x is an integer from about 2 to about 6; (b) oligomers of a
polyamide; or (c) combinations thereof.
3. The method of claim 2 wherein the monocarboxylic acid is stearic
acid, the dicarboxylic acid is sebacic acid, and the diamine is
ethylene diamine.
4. The method of claim 2 wherein the oligomers comprise: (a)
lactams having the formula:
--[NH--(CH.sub.2).sub.m--CO].sub.n--wherein m is an integer from
about 5 to about 11, and n is an integer form about 5 to about 50;
or (b) oligomers formed from diamines and dicarboxylic acids having
the formula: --[NH--(CH.sub.2).sub.m--NCO(CH.sub.2).sub.n--CO].sub-
.x--wherein m is an integer from about 4 to about 12, n is an
integer from about 4 to about 12, the sum of m and n is greater
than 12, and x is an integer from about 2 to about 25.
5. The method of claim 1 wherein the external lubricant composition
has a weight average particle size of less than about 20 .mu.m.
6. The method of claim 1 wherein the external lubricant composition
comprises at least about 40 percent by weight of high melting point
polymeric wax lubricant comprising: (a) an amide lubricant that is
the reaction product of: (i) about 10-30 weight percent, based on
total weight of the lubricant composition, of a C.sub.6-C.sub.12
linear dicarboxylic acid having the formula HOOC(R)COOH where R is
a saturated or unsaturated linear alphatic chain of 4 to 10 carbon
atoms; (ii) about 10-30 weight percent, based on total weight of
the lubricant composition, of a saturated or unsaturated
C.sub.10-C.sub.22 monocarboxylic acid, and (iii) about 40-80 weight
percent, based on total weight of the lubricant composition, of a
diamine having the formula (CH.sub.2).sub.x(NH.sub.2).s- ub.2
wherein x is an integer from about 2 to about 6; (b) oligomers of a
polyamide; or (c) combinations thereof.
7. A method of making a metal based compacted component comprising
the steps of: (a) providing a metallurgical powder composition
comprising at least about 85 percent of a metal-based powder; (b)
providing an external lubricant composition, wherein the external
lubricant composition comprises at least about 40 percent by
weight, based on total weight of the external lubricant
composition, of high melting point polymeric wax lubricant having a
melting point range beginning at a temperature greater than about
100 degrees Centigrade; (c) applying the external lubricant
composition to interior walls of a compaction die in an amount
sufficient to reduce the stripping and sliding pressures upon
ejection of a metal based component; and (d) compacting the
metallurgical powder composition in the die at a compaction
pressure sufficient to form a metal component.
8. The method of claim 7 wherein the high melting point polymeric
wax lubricant comprises (a) an amide lubricant that is the reaction
product of: (i) about 10-30 weight percent, based on total weight
of the lubricant composition, of a C.sub.6-C.sub.12 linear
dicarboxylic acid having the formula HOOC(R)COOH where R is a
saturated or unsaturated linear alphatic chain of 4 to 10 carbon
atoms; (ii) about 10-30 weight percent, based on total weight of
the lubricant composition, of a saturated or unsaturated
C.sub.10-C.sub.22 monocarboxylic acid, and (iii) about 40-80 weight
percent, based on total weight of the lubricant composition, of a
diamine having the formula (CH.sub.2).sub.x(NH.sub.2).s- ub.2
wherein x is an integer from about 2 to about 6; (b) oligomers of a
polyamide; or (c) combinations thereof.
9. The method of claim 8 wherein the monocarboxylic acid is stearic
acid, the dicarboxylic acid is sebacic acid, and the diamine is
ethylene diamine.
10. The method of claim 8 wherein the oligomers comprise: (a)
lactams having the formula:
--[NH--(CH.sub.2).sub.m--CO].sub.n--wherein m is an integer from
about 5 to about 11, and n is an integer form about 5 to about 50;
or (b) oligomers formed from diamines and dicarboxylic acids having
the formula: --[NH--(CH.sub.2).sub.m--NCO(CH.sub.2).sub.n--CO].sub-
.x--wherein m is an integer from about 4 to about 12, n is an
integer from about 4 to about 12, the sum of m and n is greater
than 12, and x is an integer from about 2 to about 25.
11. The method of claim 7 wherein the high melting point polymeric
wax lubricant has a weight average particle size of less than about
20 .mu.m.
12. The method of claim 7 wherein the metal-based powder is an
iron-based powder.
13. The method of claim 7 wherein the external lubricant
composition comprises at least about 50 percent by weight of high
melting point polymeric wax lubricant comprising: (a) an amide
lubricant that is the reaction product of: (i) about 10-30 weight
percent, based on total weight of the lubricant composition, of a
C.sub.6-C.sub.12 linear dicarboxylic acid having the formula
HOOC(R)COOH where R is a saturated or unsaturated linear alphatic
chain of 4 to 10 carbon atoms; (ii) about 10-30 weight percent,
based on total weight of the lubricant composition, of a saturated
or unsaturated C.sub.10-C.sub.22 monocarboxylic acid, and (iii)
about 40-80 weight percent, based on total weight of the lubricant
composition, of a diamine having the formula
(CH.sub.2).sub.x(NH.sub.2).s- ub.2 wherein x is an integer from
about 2 to about 6; (b) oligomers of a polyamide; or (c)
combinations thereof.
14. The method of claim 13 wherein the metal-based powder is an
iron-based powder.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/208,175 filed May 31, 2000.
FIELD OF THE INVENTION
[0002] The present invention relates to a method of lubricating a
die cavity using an external lubricant composition, and a method of
making metal components using the external lubricant composition.
The methods of the present invention are particularly useful for
compacting metal-based powders where the die is heated during
use.
BACKGROUND OF THE INVENTION
[0003] The powder metallurgy industry has developed metal-based
powder compositions that can be processed into integral metal parts
having various shapes and sizes for uses in the automotive and
electronics industries. One processing technique for producing the
parts from the metal-based powders is to charge the powder into a
die cavity and compact the powder under pressure. The resultant
green part is then removed from the die cavity and sintered.
[0004] To avoid excessive wear on the die cavity, lubricants are
commonly used during the compaction process. Lubrication is
generally accomplished by either blending a solid lubricant powder
with the metal-based powder (internal lubrication) or by spraying a
liquid dispersion or solution of the lubricant onto the die cavity
surface (external lubrication). In some cases, both lubrication
techniques are utilized.
[0005] An example of an internal lubricant is disclosed for example
in U.S. Pat. No. 5,154,881. The '881 patent discloses the use of an
internal amide lubricant that is the reaction product of a
monocarboxylic acid, a dicarboxylic acid, and a diamine. This amide
lubricant is particularly useful when compacting metal-based
powders at elevated temperatures.
[0006] Despite the advantages of using internal lubricants, there
are disadvantages. For example, the lubricant generally has a
density of about 1-2 g/cm.sup.3, as compared to the density of the
metal-based powder, which is about 7-8 g/cm.sup.3. Inclusion of the
less dense lubricant in the composition lowers the green density of
the compacted part. Also, internal lubricants are generally not
sufficiently effective for reducing the ejection pressures when
manufacturing parts having part heights (the minimum distance
between the opposing punches in the press) in excess of about 1-2
in. (2.5-5 cm). Additionally, when the particles of internal
lubricant burn off during sintering, pore spaces can be left in the
compacted part, providing a source of weakness for the part.
[0007] The use of external, die wall lubricants has generally taken
the form of liquid dispersions of the solid lubricant. U.S. Pat.
No. 5,518,639 discloses the use of an external lubricant
composition that includes a solid lubricant, a binder for the solid
lubricant and a solvent for the binder. Despite the advantages of
the lubricant composition disclosed in the '639 patent, it is
desire to provide alternative lubricant compositions.
[0008] According to the present invention, there is provided an
external lubricant composition that is particularly useful for
compacting metal-based powder compositions where it is desired to
carry out the compaction at elevated temperatures.
SUMMARY OF THE INVENTION
[0009] The present invention provides a method of lubricating a
wall of a die cavity that includes applying a lubricant composition
to the die wall, where the lubricant composition contains at least
one high melting point polymeric wax lubricant, that is preferably
a polyamide lubricant. Preferably, the polyamide lubricant has a
melting point range that begins at a temperature greater than the
temperature of the die wall.
[0010] The present invention also provides a method of making a
compacted metal part, that includes applying the aforementioned
lubricant composition to a wall of a die cavity, introducing a
metal-based powder composition into the die cavity; and compacting
the powder composition at a pressure sufficient to form a compacted
part from the metal powder composition.
[0011] A preferred polyamide lubricant useful in the present
invention is a reaction product of about 10-30 weight percent of a
C.sub.6-C.sub.12 linear dicarboxylic acid, about 10-30 weight
percent of a C.sub.10-C.sub.22 monocarboxylic acid, and about 40-80
weight percent of a diamine having the formula
(CH.sub.2).sub.x(NH.sub.2).sub.2 where x is 2-6.
BRIEF DESCRIPTION OF THE FIGURES
[0012] FIG. 1 is a graph showing ejection pressure, in units of
MPa, versus compaction pressure, in units of MPa, for compacting a
metal-based powder composition using an external lubricant
composition containing 100 wt % PROMOLD.TM. 450 (a polyamide
lubricant). The ejection pressure versus compaction pressure is
shown at spray times of 0.05 seconds, 0.10 seconds, and 0.15
seconds for the external lubricant composition.
[0013] FIG. 2 is a graph showing the effect of green density, in
units of g/cm.sup.3, versus compaction pressure, in units of MPa,
for four compacted metal-based powder compositions containing 0 wt
%, 0.15 wt %, 0.30 wt %, and 0.60 wt % internal lubricant, and
using an external lubricant composition containing 100 wt %
PROMOLD.TM. 450 sprayed onto the die for 0.10 seconds.
[0014] FIG. 3 is a graph showing the effect of green strength, in
units of MPa, versus green density, in units of g/cm.sup.3, for
four compacted metal-based powder compositions containing 0 wt %,
0.15 wt %, 0.30 wt %, and 0.60 wt % internal lubricant, and using
an external lubricant composition containing 100 wt % PROMOLD.TM.
450 sprayed onto the die for 0.10 seconds. The compactions were
carried out at pressures from 410 MPa to 685 MPa.
[0015] FIG. 4 is a graph showing the effect of ejection pressure,
in units of MPa, versus compaction pressure, in units of MPa, for
four compacted metal-based powder compositions containing 0 wt %,
0.15 wt %, 0.30 wt %, and 0.60 wt % internal lubricant, and using
an external lubricant composition containing 100 wt % PROMOLD.TM.
450 sprayed onto the die for 0.10 seconds.
[0016] FIG. 5 is a graph showing the effect of (a) pore free
density, in units of g/cm.sup.3, (line 1), (b) measured density, in
units of g/cm.sup.3, (line 2), and (c) % pore free density (line 3)
versus internal lubricant content in compacted metal-based powder
compositions. An external lubricant composition containing 100 wt %
PROMOLD.TM. 450 was sprayed onto the die for 0.10 seconds prior to
compaction.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The present invention provides lubricant compositions
containing a solid high melting point polymeric wax lubricant,
preferably designed for use in the powder metallurgy industry. The
lubricant composition is generally applied to the walls of a
compaction die before the powder composition is charged into the
die for subsequent compaction into a metallurgical part. The
lubricant composition prevents die scoring during compaction, and
reduces the stripping and sliding pressures upon the ejection of
the compacted part. The lubricant composition of the present
invention can negate the need to supply an internal lubricant,
which is blended into the powder composition prior to compaction,
and thereby eliminates the problems of reduced density in the final
compacted parts that can be caused by use of internal
lubricants.
[0018] In one embodiment of the present invention, a method is
provided for lubricating an internal wall of a die cavity that
includes applying a lubricant composition containing a high melting
point polymeric wax lubricant. By "high melting point" it is meant
a wax having a melting point range beginning at a temperature
greater than about 100.degree. C., more preferably greater than
about 120.degree. C., and most preferably greater than about
150.degree. C. The high melting point polymeric wax lubricant also
preferably has a weight average particle size of less than about
100 .mu.m, more preferably less than about 50 .mu.m, an most
preferably less than 30 microns. Moreover, it is generally
preferred that about 90 weight percent of the particles be below
about 30 microns, preferably below about 20 microns, and more
preferably below about 15 microns. The polymeric wax lubricant is
preferably present in the lubricant composition in an amount of
from about 10 weight percent to 100 weight percent, more preferably
from about 40 weight percent to 100 weight percent, and most
preferably from about 50 weight percent to about 100 weight
percent.
[0019] A preferred high melting point polymeric wax lubricant is a
solid polyamide lubricant. In one embodiment of the present
invention, the polyamide lubricant is preferably a condensation
product of a dicarboxylic acid, a monocarboxylic acid, and a
diamine, such as those described in U.S. Pat. Nos. 5,154,881 and
5,368,630, the disclosures of which are hereby incorporated by
reference in their entireties.
[0020] In such an embodiment the dicarboxylic acid is preferably a
linear acid having the general formula HOOC(R)COOH where R is a
saturated or unsaturated linear aliphatic chain of 4-10, preferably
about 6-8, carbon atoms. Preferably, the dicarboxylic acid is a
C.sub.8-C.sub.10 saturated acid. Sebacic acid is a preferred
dicarboxylic acid. The dicarboxylic acid is present in an amount of
from about 10 to about 30 weight percent of the starting reactant
materials.
[0021] The monocarboxylic acid is preferably a saturated or
unsaturated C.sub.10-C.sub.22 fatty acid. Preferably, the
monocarboxylic acid is a C.sub.12-C.sub.20 saturated acid. Stearic
acid is a preferred saturated monocarboxylic acid. A preferred
unsaturated monocarboxylic acid is oleic acid. The monocarboxylic
acid is present in an amount of from about 10 to about 30 weight
percent of the starting reactant materials.
[0022] The diamine preferably has the general formula
(CH.sub.2).sub.x(NH.sub.2).sub.2 where x is an integer of about
2-6. Ethylene diamine is the preferred diamine. The diamine is
present in an amount of from about 40 to about 80 weight percent of
the starting reactant materials.
[0023] The condensation reaction is preferably conducted at a
temperature of from about 260.degree.-280.degree. C. and at a
pressure up to about 7 atmospheres. The reaction is allowed to
proceed to completion, usually not longer than about 6 hours. The
polyamide is preferably produced under an inert atmosphere such as
nitrogen. The reaction is preferably carried out in the presence of
a catalyst such as 0.1 weight percent methyl acetate and 0.001
weight percent zinc powder. The lubricants formed by the above
condensation reaction are polyamides characterized as having a
melting range rather than a melting point. As those skilled in the
art will recognize, the reaction product is generally a mixture of
moieties of varying molecular weights, and therefore properties
dependent on such, will vary. As a whole, this polyamide lubricant
preferably begins to melt at a temperature between about
150.degree. C. (300.degree. F.) and 260.degree. C. (500.degree.
F.), and more preferably between about 200.degree. C. (400.degree.
F.) to about 260.degree. C. (500.degree. F.). The polyamide will
generally be fully melted at a temperature about 250.degree. C.
above this initial melting temperature, although it is preferred
that the polyamide reaction product melt over a range of no more
than about 100.degree. C.
[0024] A preferred such polyamide lubricant is commercially
available as ADVAWAX.TM. 450, or PROMOLD.TM. 450, polyamide sold by
Morton International of Cincinnati, Ohio, which is an ethylene
bis-stearamide having an initial melting point between about
200.degree. C. and 300.degree. C.
[0025] In another embodiment of the present invention the polyamide
is an oligomer of a polyamide as described in for example U.S. Pat.
No. 5,744,433 ("'433 patent"), the disclosure of which is hereby
incorporated by reference in its entirety. The polyamide oligomers
described in the '433 patent include lactams containing the
repeating unit:
[NH--(CH.sub.2).sub.m--CO].sub.n--
[0026] where m is in the range of from about 5 to about 11, and n
is in the range of from about 5 to about 50.
[0027] The polyamides in the '433 patent also include oligomers
formed from diamines and dicarboxylic acids to contain the
following repeating unit:
--[NH--(CH.sub.2).sub.m--NCO(CH.sub.2).sub.n--CO].sub.x--
[0028] where m and n are in the range of from about 4 to about 12,
where the sum of m and n is greater than about 12, and where x
ranges from about 2 to about 25.
[0029] These oligomers preferably have a weight average molecular
weight of less than about 30,000 and a melting point ranging
beginning at about 100.degree. C. to about 220.degree. C. Moreover,
one skilled in the art will recognize that the aforementioned
oligomers may be terminated with various functional groups, such as
those terminal groups described in the '433 patent.
[0030] Specific examples of the oligomers of polyamides useful in
the present invention include Orgasol.TM. 3501, Orgasol.TM. 2001,
and Orgasol.TM. 2002 supplied by Elf Atochem of France.
[0031] In addition to the high melting point polymeric wax
lubricant, such as the polyamide lubricant, the lubricant
composition can also optionally contain other high melting point
solid lubricants, such as inorganic lubricants. For example,
graphite, molybdenum disulfide (MoS.sub.2), boron nitride, or
combinations thereof may be present in the lubricant composition.
The weight average particle size of the optional solid lubricant is
preferably below about 20 microns, more preferably below about 10
microns, and most preferably below about 7 microns. Also, it is
generally preferred that about 90 weight percent of the particles
be below about 20 microns, preferably below about 15 microns, and
more preferably below about 10 microns. Preferably, these optional
lubricants are present in the composition in an amount of from 0
weight percent to about 75 weight percent, more preferably from
about 1 weight percent to about 60 weight percent, and most
preferably from about 5 weight percent to about 50 weight
percent.
[0032] Other optional components in the lubricant composition will
depend on, for example, the method of application of the lubricant
composition to the die wall. These other optional components will
be described in more detail hereinafter.
[0033] The lubricant composition useful in the present invention
may be applied in various ways to the die cavity. For example, the
lubricant composition may be applied as a powder to the die wall or
may be dispersed and/or dissolved in a liquid prior to application.
Preferably, the lubricant composition is applied as a powder to the
wall.
[0034] Any method known to those skilled in the art may be used to
apply the lubricant composition as a powder to the die wall.
Preferably, the method of application results in the die wall being
uniformly covered with at least a monolayer of lubricant
composition. Preferred application rates are in an amount that
lowers the ejection pressure to a suitable value, but does not
adversely affect the properties of the component being formed in
the die. A preferred method of applying the lubricant composition
as a powder uses a powder spray gun that imparts a charge to the
powder, that is opposite to the charge of the die wall. A preferred
powder spray system is Gasbarre Die Wall Lubrication System
available from Gasbarre, located in St. Mary, Pa.
[0035] Alternatively, the solid lubricant composition containing
the solid polymeric wax lubricant may be dispersed and/or dissolved
in a liquid and sprayed onto the die wall using any technique known
to those skilled in the art. Preferably, the solid lubricant
composition is dispersed in the liquid as opposed to being
dissolved. The amount of the lubricant composition sprayed onto the
die is generally left to the discretion of the parts manufacturer,
however an amount sufficient to uniformly wet the surface of the
die cavity should be employed. Examples of liquids include for
example water, organic solvents such as aliphatic and aromatic
organic solvents, or combinations thereof. Examples of useful
solvents include ketones such as acetone; C.sub.1-10 alcohols such
as ethanol, propanol, and isopropanol; C.sub.5-10 alkanes such as
hexane; aromatic alcohols; benzene; cyclohexanone; and mixtures
thereof. Preferably, the amount of liquid in the lubricant
composition is that amount needed for applying the polymeric wax
lubricant uniformly. Typically, the level of liquid will be from
about 30 weight percent to about 90 weight percent, and more
preferably from about 50 weight percent to about 90 weight percent,
based on the total weight of the lubricant composition containing
the liquid.
[0036] The lubricant composition containing the polymeric wax
lubricant may also be applied using the techniques disclosed in
U.S. Pat. No. 5,518,639, which is hereby incorporated by reference
in its entirety. In this embodiment the solid lubricant
composition, containing the polymeric wax lubricant useful in the
present invention, may be applied in a composition containing a
binder, and a solvent (e.g., the organic solvents previously
described) for the binder. Examples of suitable binders include
polyethylene glycols having a weight average molecular weight of
from about 3000 to about 35,000; polyethylene glycol esters having
a weight average molecular weight of from about 500 to about
10,000, where the ester functionality is formed from saturated or
unsaturated C.sub.12-36 fatty acids; partial esters of C.sub.3-6
polyhydric alcohols where the ester functionality is formed from
saturated or unsaturated C.sub.12-36 fatty acids; polyvinyl esters
having a weight average molecular weight of at least about 200,
where the ester functionality is formed from saturated or
unsaturated C.sub.12-36 fatty acids; polyvinyl pyrrolidones having
a weight average molecular weight of at least about 200; or
combinations thereof.
[0037] In the above embodiment, the binder is generally present in
an amount of from about 1-30, preferably about 1-20, and more
preferably about 5-10, weight percent of the total lubricant
composition (including the polymeric wax lubricant). The organic
solvent constitutes the balance of the composition, and is
generally present in an amount of from about 30-90, preferably
about 50-90, and more preferably about 55-80, weight percent of the
total lubricant composition.
[0038] In another embodiment of the present invention, a method is
provided for compacting a metal-based component that includes
applying the lubricant composition useful in the present invention
to an internal wall of a die cavity, introducing a metal-based
powder composition into the die cavity after applying the lubricant
composition to the wall; and compacting the powder composition at a
pressure sufficient to form a compacted part from the metal-based
powder composition.
[0039] The compaction of metal-based powder composition is
accomplished by well known conventional methods. The lubricant
composition is applied to the die cavity wall according to the
techniques previously described. If a liquid lubricant composition
is used, the liquid is preferably allowed to evaporate prior to
charging the die with the powder composition. Additionally, the die
may be preheated prior to, or after applying the lubricant
composition to the die wall, depending upon the type of lubricant
composition used. For example, if a powder lubricant composition is
used, preferably the die cavity is preheated prior to its
application.
[0040] Once the die cavity has been coated with the lubricant
composition of the present invention, the powder composition is
typically fed via a hopper into a portion of a die cavity, the die
cavity is then closed, and a pressure is applied to the die.
Typical compaction pressures are at least about 5 tsi, up to about
200 tsi, and conventionally from about 40-60 tsi. Additionally,
heat may be applied to the die during compaction to enhance the
properties of the compacted component. Typical compaction
temperatures range from about ambient temperature to about
400.degree. C., and more preferably from about 50.degree. C. to
about 250.degree. C., and most preferably from about 50.degree. C.
to about 150.degree. C. The die is then opened and the green part
is ejected from the die cavity.
[0041] The lubricant composition useful in the present invention
reduces the ejection pressures of the compacted green part from the
die cavity. Additionally, the use of the external lubricant
composition permits one to lower the amount of internal lubricant
in the metal-based powder composition being compacted, resulting in
improved green properties.
[0042] The metal-based powder compositions useful in the present
invention comprise metal-based particles of the kind generally used
in the powder metallurgy industry, such as iron-based powders and
nickel-based powders. The metal-based particles constitute a major
portion of the metal-based powder composition, and generally
constitute at least about 80 weight percent, preferably at least
about 85 weight percent, and more preferably at least about 90
weight percent based on the total weight of the metal-based powder
composition.
[0043] Examples of "iron-based" powders, as that term is used
herein, are powders of substantially pure iron, powders of iron
pre-alloyed with other elements (for example, steel-producing
elements) that enhance the strength, hardenability, electromagnetic
properties, or other desirable properties of the final product, and
powders of iron to which such other elements have been diffusion
bonded.
[0044] Substantially pure iron powders that can be used in the
invention are powders of iron containing not more than about 1.0%
by weight, preferably no more than about 0.5% by weight, of normal
impurities. Examples of such highly compressible,
metallurgical-grade iron powders are the ANCORSTEEL 1000 series of
pure iron powders, e.g. 1000, 1000B, and 1000C, available from
Hoeganaes Corporation, Riverton, N.J. For example, ANCORSTEEL 1000
iron powder, has a typical screen profile of about 22% by weight of
the particles below a No. 325 sieve (U.S. series) and about 10% by
weight of the particles larger than a No. 100 sieve with the
remainder between these two sizes (trace amounts larger than No. 60
sieve). The ANCORSTEEL 1000 powder has an apparent density of from
about 2.85-3.00 g/cm3, typically 2.94 g/cm3. Other iron powders
that can be used in the invention are typical sponge iron powders,
such as Hoeganaes' ANCOR MH-100 powder.
[0045] The iron-based powder can incorporate one or more alloying
elements that enhance the mechanical or other properties of the
final metal part. Such iron-based powders can be powders of iron,
preferably substantially pure iron, that has been pre-alloyed with
one or more such elements. The pre-alloyed powders can be prepared
by making a melt of iron and the desired alloying elements, and
then atomizing the melt, whereby the atomized droplets form the
powder upon solidification.
[0046] Examples of alloying elements that can be pre-alloyed with
the iron powder include, but are not limited to, molybdenum,
manganese, magnesium, chromium, silicon, copper, nickel, gold,
vanadium, columbium (niobium), graphite, phosphorus, aluminum, and
combinations thereof. Preferred alloying elements are molybdenum,
phosphorus, nickel, silicon or combinations thereof. The amount of
the alloying element or elements incorporated depends upon the
properties desired in the final metal part. Pre-alloyed iron
powders that incorporate such alloying elements are available from
Hoeganaes Corp. as part of its ANCORSTEEL line of powders.
[0047] A further example of iron-based powders are diffusion-bonded
iron-based powders which are particles of substantially pure iron
that have a layer or coating of one or more other metals, such as
steel-producing elements, diffused into their outer surfaces. Such
commercially available powders include DISTALOY 4600A diffusion
bonded powder from Hoeganaes Corporation, which contains about 1.8%
nickel, about 0.55% molybdenum, and about 1.6% copper, and DISTALOY
4800A diffusion bonded powder from Hoeganaes Corporation, which
contains about 4.05% nickel, about 0.55% molybdenum, and about 1.6%
copper.
[0048] A preferred iron-based powder is of iron pre-alloyed with
molybdenum (Mo). The powder is produced by atomizing a melt of
substantially pure iron containing from about 0.5 to about 2.5
weight percent Mo. An example of such a powder is Hoeganaes'
ANCORSTEEL 85HP steel powder, which contains about 0.85 weight
percent Mo, less than about 0.4 weight percent, in total, of such
other materials as manganese, chromium, silicon, copper, nickel,
molybdenum or aluminum, and less than about 0.02 weight percent
carbon. Another example of such a powder is Hoeganaes' ANCORSTEEL
4600V steel powder, which contains about 0.5-0.6 weight percent
molybdenum, about 1.5-2.0 weight percent nickel, and about 0.1-0.25
weight percent manganese, and less than about 0.02 weight percent
carbon.
[0049] Another pre-alloyed iron-based powder that can be used in
the invention is disclosed in U.S. Pat. No. 5,108,493, entitled
"Steel Powder Admixture Having Distinct Pre-alloyed Powder of Iron
Alloys," which is herein incorporated by reference in its entirety.
This steel powder composition is an admixture of two different
pre-alloyed iron-based powders, one being a pre-alloy of iron with
0.5-2.5 weight percent molybdenum, the other being a pre-alloy of
iron with carbon and with at least about 25 weight percent of a
transition element component, wherein this component comprises at
least one element selected from the group consisting of chromium,
manganese, vanadium, and columbium. The admixture is in proportions
that provide at least about 0.05 weight percent of the transition
element component to the steel powder composition. An example of
such a powder is commercially available as Hoeganaes' ANCORSTEEL 41
AB steel powder, which contains about 0.85 weight percent
molybdenum, about 1 weight percent nickel, about 0.9 weight percent
manganese, about 0.75 weight percent chromium, and about 0.5 weight
percent carbon.
[0050] Other iron-based powders that are useful in the practice of
the invention are ferromagnetic powders. An example is a powder of
iron pre-alloyed with small amounts of phosphorus.
[0051] The iron-based powders that are useful in the practice of
the invention also include stainless steel powders. These stainless
steel powders are commercially available in various grades in the
Hoeganaes ANCOR.RTM. series, such as the ANCOR.RTM. 303L, 304L,
316L, 410L, 430L, 434L, and 409Cb powders.
[0052] The iron-based powder have a distribution of particle sizes.
Typically, these powders are such that at least about 90% by weight
of the powder sample can pass through a No. 45 sieve (U.S. series),
and more preferably at least about 90% by weight of the powder
sample can pass through a No. 60 sieve. These powders typically
have at least about 50% by weight of the powder passing through a
No. 70 sieve and retained above or larger than a No. 400 sieve,
more preferably at least about 50% by weight of the powder passing
through a No. 70 sieve and retained above or larger than a No. 325
sieve. Also, these powders typically have at least about 5 weight
percent, more commonly at least about 10 weight percent, and
generally at least about 15 weight percent of the particles passing
through a No. 325 sieve. As such, these powders can have a weight
average particle size as small as one micron or below, or up to
about 850-1,000 microns, but generally the particles will have a
weight average particle size in the range of about 10-500 microns.
Preferred are iron-alloy particles or substantially pure iron
particles having a maximum weight average particle size up to about
350 microns; more preferably the particles will have a weight
average particle size in the range of about 25-150 microns, and
most preferably 80-150 microns. Reference is made to MPIF Standard
05 for sieve analysis.
[0053] The metal-based particles can also include nickel-based
powders. Examples of "nickel-based" powders, as that term is used
herein, are powders of substantially pure nickel, and powders of
nickel pre-alloyed with other elements that enhance the strength,
hardenability, electromagnetic properties, or other desirable
properties of the final product. The nickel-based powders can be
admixed with any of the alloying powders mentioned previously with
respect to the iron-based powders. Examples of nickel-based powders
include those commercially available as the Hoeganaes
ANCORSPRAY.RTM. powders such as the N-70/30 Cu, N-80/20, and N-20
powders.
[0054] The metallurgical powder compositions of the present
invention may also include any additive commonly used with
metallurgical compositions such as alloying powders, binding
agents, machining agents, and plasticizers. The types and amounts
used of these additives are described in for example U.S. Pat. Nos.
5,368,630; 5,498,276; and 5,782,954; the disclosures of which are
hereby incorporated by reference in their entireties.
[0055] The metal-based powder composition may also contain an
internal lubricant. Examples of typical powder metallurgy internal
lubricants include the stearates, such as zinc stearate, lithium
stearate, manganese stearate, or calcium stearate; synthetic waxes,
such as ethylene bisstearamide or polyolefins; or combinations
thereof The lubricant may also be a polyamide lubricant as
previously described herein, particulate ethers disclosed in U.S.
Pat. Nos. 5,498,276, and 6,039,784 to Luk, or a metal salt of a
fatty acid disclosed in U.S. Pat. No. 5,330,792 to Johnson et al.,
the disclosures of which are hereby incorporated by reference in
their entireties. Preferred lubricants are ethylene bisstearamide,
zinc stearate, Kenolube.TM. (supplied by Hoganas Corporation,
located in Hoganas, Sweden), Orgasol.TM. oligomers, Ferrolube.TM.
(supplied by Blanchford), and polyethylene wax. The lubricant may
also be a combination of any of the aforementioned lubricants
described above.
[0056] The lubricant is generally added in an amount of from about
0.1 to about 1.5 weight percent, more preferably from about 0.1 to
about 1.0 weight percent, and most preferably from about 0.1 to
about 0.6 weight percent, of the metallurgical powder composition.
Moreover, the level of internal lubricant is preferably lower than
what would normally be needed without the use of the external
lubricant composition employed in the present invention.
EXAMPLES
[0057] Some embodiments of the present invention will now be
described in detail in the following Examples. Metal-based powder
compositions were compacted using external lubricants useful in the
present invention to form metal-based components. The metal-based
components were evaluated for green strength, green density, green
expansion, and ejection pressure.
[0058] Metal-based powder compositions were prepared by admixing
Ancorsteel.RTM. 85 HP powder, previously described herein, 2.0 wt %
nickel powder, 0.6 wt % graphite, and varying amounts of
PROMOLD.TM. 450 as an internal lubricant. The PROMOLD.TM. 450 was
supplied by Morton International of Cincinnati, Ohio, and is an
ethylene bis-stearamide having an initial melting point between
about 200.degree. C. and 300.degree. C. The nickel powder used was
grade Inco 123 having a weight average particle size of -5 .mu.m,
supplied by International Nickel Inc. The graphite was Asbury grade
3203 having a weight average particle size of 2 to 6 .mu.m,
obtained from Asbury Graphite Mills, Inc., located in Asbury,
N.J.
[0059] The powder compositions that were prepared are shown below
in Table 1:
1TABLE 1 Metal-Based Powder Compositions PROMOLD .TM. Ancorsteel
.RTM. 85 Ni Graphite 450 Composition HP (wt %) (wt %) (wt %) A
Balance 2.0 0.60 0.0 B Balance 2.0 0.60 0.15 C Balance 2.0 0.60
0.30 D Balance 2.0 0.60 0.60
[0060] External lubricant compositions were also prepared having
the compositions shown in Table 2.
2TABLE 2 Compositions of Powder External Lubricants Chemtrend
Graphite PROMOLD .TM. 450 Composition (wt %) (wt %) (wt %) E
(comp.) 100 0.0 0.0 F 0.0 0.0 100 G 0.0 50 50
[0061] The Chemtrend.TM. die wall lubricant used was Chemtrend.TM.
101, supplied by Chemtrend, located in Howell, Mich. The graphite
and PROMOLD.TM. 450 was the same as that used for the metal-based
powder compositions in Table 1.
[0062] The powder compositions shown in Table 1 were compacted in a
compaction device at various compaction pressures ranging from 410
MPA to 690 MPA to form test bars in accordance with the following
procedure. The die was preheated to 145.degree. C. and the desired
powder in Table 1 was preheated to a temperature of 140.degree. C.
After preheating the die, the desired external lubricant in Table 2
was charged into a Gasbarre Die Wall Lubrication System supplied by
Gasbarre, located in St. Mary, Pa. The lubricant was then sprayed
onto the die for a desired spray time at a desired lubricant air
pressure and charge gun pressure. Following spraying of the
external lubricant, the desired metal-based powder composition in
Table 2 was charged into the die and compacted at the desired
pressure to form a test bar. Following compaction, the ejection
pressure was measured as the test part was ejected from the die.
The test bar obtained was then evaluated for various green
properties.
[0063] The ejection pressure is a quantitative measurement of the
ejection force required to start moving the compacted part from the
die. The method for determining the ejection pressure is set forth
for example, in U.S. Pat. No. 5,154,881, which is hereby
incorporated by reference in its entirety.
[0064] The test bars were evaluated for green density, green
strength, and green expansion. The test methods used for
determining green density and green strength were as follows:
3 Property Test Method Green Density ASTM B331-95 Green Strength
ASTM B312-96
[0065] Green Expansion was determined according to the following
equation: 1 Green Expansion ( % ) = 100 [ ( green bar length ) - (
die length ) ] die length
Example 1
Effect of Spray Time on Ejection Pressure
[0066] Composition C in Table 1, containing 0.3 wt % PROMOLD.TM.
Lubricant, was compacted according to the procedure described above
at various compaction pressures and at external lubricant spray
times ranging from 0.05 seconds to 0.15 seconds to determine the
effect of spray time on ejection pressure. The external lubricant
was 100 wt % PROMOLD.TM. 450 (composition F in Table 2). The
results are shown in FIG. 1. FIG. 1 is a graph showing the relation
of compaction pressure (x-axis, in MPa) and ejection pressure
(y-axis, in MPa) at spray times of PROMOLD.TM. of 0.05 seconds,
0.10 seconds, and 0.15 seconds. FIG. 1 shows that while there is
large benefit in reducing ejection pressures by increasing the
spray time from 0.05 seconds to 0.10 seconds, there is only a small
benefit gained in reduced ejection pressures by increasing the
spray time from 0.10 second to 0.15 seconds.
Example 2
Effect of Green Properties and Ejection Pressures in Varying the
Internal Lubricant Level
[0067] Compositions A through D were compacted at pressures ranging
from 410 MPa (30 tsi) to 685 MPa (50 tsi) according to the above
procedure to determine the effect of the level of internal
lubricant on green properties and ejection pressure. The spray time
for the external lubricant in all cases was 0.10 seconds and the
external lubricant was PROMOLD.TM. 450 (composition F in Table 2).
The effect on green properties and ejection pressure by varying the
level of internal lubricant are shown in FIGS. 2 to 5. FIG. 2 is a
graph showing the effect of green density (in g/cm.sup.3) versus
compaction pressure (in MPa) for Compositions A through D in Table
1. FIG. 3 is a graph showing the effect of green strength (in MPa)
versus green density (in g/cm.sup.3) for Compositions A through D
in Table 1 at various compaction pressures ranging from 410 MPa to
685 MPa. FIG. 4 is a graph showing the effect of ejection pressure
(in MPa) versus compaction pressure (in MPa) for Compositions A
through D. FIG. 5 is a graph showing the effect of (a) pore free
density, (in g/cm.sup.3, line 1), (b) measured density, (in
g/cm.sup.3, line 2), and (c) % pore free density (line 3) for
Compositions A through D in Table 1 (plotted on the x-axis as %
lubricant content). The data in FIG. 5 is shown at a compaction
pressure of 685 MPa. These Examples demonstrate the effectiveness
of the external lubricant composition useful in the present
invention.
Examples 3 to 8
Effect of Other External Lubricants on Green Properties and
Ejection Pressures
[0068] External lubricants having the compositions described as
Composition E (comparative) and G in Table 2 were evaluated by
compacting the metal-based powder compositions B to D shown in
Table 1. The procedure for spraying the external lubricant and
compacting the metal-based powder was the same general procedure as
described above. The green properties and ejection pressures
obtained for test bars produced are shown in Table 3. For all
examples in Table 3 the compaction pressure was 545 MPa (40 tsi).
The spray time was varied in some examples and is shown in Table
3.
4TABLE 3 Green Properties of Compacted Metal-Based Powder
Compositions Metal- Spray Ejec. Green Green % Based Ext. Time Press
Density Strength Green Example Powder Lub. (sec) (MPa) (g/cm.sup.3)
MPa Exp. Comp. 3 D E 0.0 35 7.31 24 0.33 Comp. 4 D E 0.10 32 7.27
17 0.36 Comp. 5 D E 0.15 30 7.24 15 0.40 6 D G 0.10 27 7.28 17 0.32
7 C G 0.10 40 7.27 18 0.25 8 B G 0.10 50 7.23 21 0.25
[0069] The above data shows that the external lubricant composition
useful in the present invention permits the use of lower levels of
internal lubricant to improve green properties. For Comparative
Examples 3 through 5, the green properties became worse as more
external lubricant was applied to the die wall due to the external
lubricant melting on the die wall.
* * * * *