Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Heterocyclic ring compound; a heterocyclic ring is one...
Reexamination Certificate
2001-05-24
2002-05-28
McAvoy, Ellen M. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Heterocyclic ring compound; a heterocyclic ring is one...
C508S454000, C508S551000, C508S554000, C419S061000, C419S066000, C072S042000
Reexamination Certificate
active
06395687
ABSTRACT:
FIELD OF THE INVENTION
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
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.
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.
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.
Despite the advantages of using internal lubricants, there are disadvantages. For example, the lubricant generally has a density of about 1-2 (g/cm
3
, as compared to the density of the metal-based powder, which is about 7-8 g/cm
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.
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.
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
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.
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.
A preferred polyamide lubricant useful in the present invention is a reaction product of about 10-30 weight percent of a C
6
-C
12
linear dicarboxylic acid, about 10-30 weight percent of a C
10
-C
22
monocarboxylic acid, and about 40-80 weight percent of a diamine having the formula (CH
2
)
x
(NH
2
)
2
where x is 2-6.
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Hoeganaes Corporation
McAvoy Ellen M.
Woodcock & Washburn LLP
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