Specialized metallurgical processes – compositions for use therei – Compositions – Loose particulate mixture containing metal particles
Reexamination Certificate
1999-02-01
2001-05-15
Wyszomierski, George (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Loose particulate mixture containing metal particles
C508S528000, C508S537000, C508S554000
Reexamination Certificate
active
06231635
ABSTRACT:
The present invention relates to a lubricant for metallurgical powder compositions as well as a metal-powder composition containing the lubricant. The invention further concerns a method for making sintered products by using the lubricant.
The powder metallurgy industry has developed iron-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 base powders is to charge the powder into the die cavity and compact the powder under high pressures. 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 iron-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 techniques are used. Almost all currently used lubricants are derived from naturally occurring long-chain fatty acids.
The most common, fatty acid it stearic acid (C
17
H
35
COOH) consisting of an aliphatic chain CH
3
.(CH
2
)
16
combined with the carboxylic acid group —COOH. When mixed with metal powders, it provides fast flow, high apparent density and good lubricity. Its low melting point (64° C.) car lead to softening during blending with the powder causing problems. Therefore, salts of stearic acid, i.e. metallic soaps are more popular. The major drawback of the soaps is their metal content. On burn-off, the fatty acid chain volatilizes readily but the metal remains behind as oxide or carbonate, although this may undergo reduction to the metal in a reducing atmosphere.
The most widely used metallic soap is zinc stearate because of its good flow properties. In reducing atmospheres, the zinc oxide remaining after initial decomposition is reduced to zinc, which readily volatilizes because of its low boiling point (907° C.). Unfortunately, on contacting the cooler parts of the furnace or the outside atmosphere, the zinc tends to condense, forming some zinc oxide as well. A consequence of this condensation is that the production has to be interrupted as the furnace has to be cleaned regularly.
The problems associated with metallic soaps can be avoided by the use of completely organic materials such as waxes. The one most widely used in powder metallurgy is ethylene-bisstearamide (e.g. Acrawax C). This material has a high melting point (140° C.) but it burns off at relatively low temperatures and leaves no metallic residue. The most serious disadvantage is its poor flow behaviour in metal powders.
Furthermore, mixtures of zinc salts of fatty acids and fatty acid bis-amides have not been accepted the P/M industry because of the poor performance of such mixtures.
It has now unexpectedly been found that a lubricant enabling the manufacture of compacted products having high green strength and high green density in combination with low ejecting force can be obtained with a lubricant comprising a lithium and optionally a zinc salt of one or more fatty acids and a fatty acid bisamide product. More specifically the amount of the metal salts of the fatty acids should constitute about 10-60% by weight of the lubricant according to the invention. The amount of the lithium salt is 10-60% by weight and the amount of the zinc salt is 0-40% by weight. Preferably the amount of the zinc salt is at least 10 and most preferably at least 15% by weight of the lubricant. The amount of the bisamide product is 40-60% by weight.
Typical examples of lithium salts of fatty acids are lithium laurate, lithium myristate, lithium palmitate, lithium stearate, lithium behenate, lithium montanate and lithium oleate which are lithium salts of fatty acids having 12~28 carbon atoms.
Typical examples of zinc salts of fatty acid are zinc laurate, zinc myristrate, zinc palmitate, zinc stearate, zinc behenate, zinc montanate and zinc oleate which are lithium salt of fatty acids 12~28 carbon atoms.
Typical examples of fatty acid bis-Amides are methylene bis-lauramide, methylene bis-myristamide, methylene bis-palmitamide, methylene bis-stearamide, ethylene bis-behenamide, methylene bis-oleamide, ethylene bis-lauramide, ethylene bis-myristamide, ethylene bis-palmitamide, ethylene bis-stearamide, ethylene bis-behenamide, ethylene bis-montanamide and ethylene bis-oleamide.
The lubricant is preferably prepared by mixing and melting the components and the obtained mixture is sub-sequently cooled and micronized to a suitable particle size.
The invention is further illustrated by the following non limiting examples.
REFERENCES:
patent: 3827980 (1974-08-01), Thompson et al.
patent: 3980572 (1976-09-01), Dodo et al.
patent: 4106432 (1978-08-01), Blachford
patent: 5256185 (1993-10-01), Semel et al.
patent: 5498276 (1996-03-01), Luk
patent: 5989304 (1999-11-01), Ozaki et al.
patent: 6001150 (1999-12-01), McCall et al.
patent: 54/117873 (1979-09-01), None
“Influence of Lubricants on Dimensional Changes and Mechanical Properties of Sintered Ferrous Compacts” M. Ward, Powder Metallurgy, vol. 22, No. 4 (1979) pp. 193-200. [Abstract provided by STN International, File CAPLUS, CAPLUS Accession No. 1980:114330.]
Saitoh Hiroyasu
Serita Toshio
Suzuki Masa-aki
Ukai Norio
Burns Doane , Swecker, Mathis LLP
Hoganas AB
Wyszomierski George
LandOfFree
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