Iron powder composition

Details Iron powder composition Iron powder composition

2002-07-25

2004-06-29

Mai, Ngoclan (Department: 1742)

Specialized metallurgical processes, compositions for use therei

Compositions

Loose particulate mixture containing metal particles

C419S010000, C419S031000, C419S036000

Reexamination Certificate

active

06755885

ABSTRACT:

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 temperatures above ambient temperature. The tensile strength and work hardening rate of most metals is reduced with increasing temperatures, and improved density and strength can be attained at lower compaction pressures. The extremely elevated temperatures of hot-pressing, however, introduce processing problems and accelerate wear of the dies. Therefore, current efforts are being directed towards the development of metal compositions suitable for warm-pressing processes.
The U.S. Pat. No. 4,955,798 (Musella) describes warm compaction in general. According to this patent, lubricants generally used for cold compaction, e.g. zinc stearate, can be used for warm compaction as well. In practice, however, it has proved impossible to use zinc stearate 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 U.S. Pat. No. 5,744,433 (Storstrom et al) and U.S. Pat. No. 5,154,881 (Rutz) disclose metal powder compositions including amide lubricants, which are especially developed for warm compaction.
The lubricant according to the U.S. Pat. No. 5,744,433 contains an oligomer of amide type, which has a weight-average molecular weight M
w
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 lubricant molecule having a molecular weight of about 6500. It has however been found that this lubricant has a tendency of sticking to the die wall, which requires frequent cleaning of the die. Another disadvantage is that the obtained green bodies are stained.
In the U.S. Pat. No. 5,154,881 the amide lubricant consists 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 composition of which is not described in detail but the reaction product obtained includes i.a. ethylene bisstearamide according to Chemis-CIVS. Our experience of this product is that it is difficult to obtain a constant composition and quality, which in turn may result in components of varying quality. This may cause problems when the lubricant is used in large scale industrial production.
OBJECTS OF THE INVENTION
An object of the present invention is to reduce or eliminate current problems associated with large scale production.
A second object is to provide a new type of lubricant useful in metal compositions intended for compaction at elevated temperatures.
A third object is to provide a metal powder for producing components without stains.
A fourth object is to provide a metal composition including lubricant, which during the compaction of the metal powder does not deposit on the die wall.
SUMMARY OF THE INVENTION
These objects are achieved by using 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
D—C
ma
—B—A—B—C
mb
—D
wherein
D is —H, COR, CNHR, wherein R is a straight or branched aliphatic or aromatic group including 2-21 C atoms
C is the group —NH (CH)
n
CO—
B is amino or carbonyl
A is alkylen having 4-16 C atoms optionally including up to 4 O atoms
ma is an integer 1-10
mb is an integer 1-10
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 (CH)
n
CO— wherein n is 5 or 11; B is amino; A is alkylen having 6-14 C atoms optionally including up to 3 O atoms, and ma and mb which may be the same or different, is an integer 2-5.
Examples of preferred lubricants to be used in the iron based compositions according to the present invention are:
CH
3
(CH
2
)
16
CO—[HN(CH
2
)
11
CO]
2
—HN(CH
2
)
12
NH—[OC(CH
2
)
11
NH]
2
—OC(CH
2
)
16
CH
3
CH
3
(CH
2
)
16
CO—[HN(CH
2
)
11
CO]
2
—HN(CH
2
)
12
NH—[OC(CH
2
)
11
NH]
3
—OC(CH
2
)
16
CH
3
CH
3
(CH
2
)
16
CO—[HN(CH
2
)
11
CO]
3
—HN(CH
2
)
12
NH—[OC(CH
2
)
11
NH]
3
—OC(CH
2
)
16
CH
3
CH
3
(CH
2
)
16
CO—[HN(CH
2
)
11
CO]
3
—HN(CH
2
)
12
NH—[OC(CH
2
)
11
NH]
4
—OC(CH
2
)
16
CH
3
CH
3
(CH
2
)
16
CO—[HN(CH
2
)
11
CO]
4
—HN(CH
2
)
12
NH—[OC(CH
2
)
11
NH]
4
—OC(CH
2
)
16
CH
3
CH
3
(CH
2
)
16
CO—[HN(CH
2
)
11
CO]
4
—HN(CH
2
)
12
NH—[OC(CH
2
)
11
NH]
5
—OC(CH
2
)
16
CH
3
CH
3
(CH
2
)
16
CO—[HN(CH
2
)
11
CO]
5
—HN(CH
2
)
12
NH—[OC(CH
2
)
11
NH]
5
—OC(CH
2
)
16
CH
3
Other examples are
CH
3
)CO—HN(CH
2
)
5
CO—HN(CH
2
)
2
NH—OC(CH
2
)
5
NH—OC(CH
3
) having the MW 370.49;
CH
3
(CH
2
)
2
OCO—HN(CH
2
)
11
CO—HN(CH
2
)
12
NH—OC(CH
2
)
11
NH—OC(CH
2
)
20
CH
3
 having the MW 1240.10
CH
3
(CH
2
)
20
CO—[HN(CH
2
)
11
CO]
10
—HN(CH
2
)
12
NH—[OC(CH
2
)
11
NH]
10
—OC(CH
2
)
20
CH
3
having the MW 8738.04
CH
3
(CH
2
)
4
CO—[HN(CH
2
)
11
CO]
3
—HN(CH
2
)
12
NH—[OC(CH
2
)
11
NH]
3
—OC(CH
2
)
4
CH
3
 having the MW 1580.53
CH
3
(CH
2
)
4
CO—[HN(CH
2
)
5
CO]
7
—HN(CH
2
)
6
NH—[OC(CH
2
)
5
NH]
7
—OC(CH
2
)
4
CH
3
 having the MW 1980.86
CH
3
(CH
2
)
20
CO—[HN(CH
2
)
5
CO]
7
—HN(CH
2
)
6
NH—[OC(CH
2
)
5
NH]
7
—OC(CH
2
)
20
CH
3
 having the MW 2429.69
and
CH
3
(CH
2
)
16
NH—[OC(CH
2
)
11
NH]
4
—CO(CH
2
)
10
CO—[HN(CH
2
)
11
CO]
4
—HN(CH
2
)
16
CH
3
 having the MW 2283.73
The chemical differences between the new lubricant and the lubricant described in the U.S. Pat. No. 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 U.S. Pat. No. 5,154,881 is that the new lubricant molecule includes the unit —NH(CH)
n
CO—. In contrast to the lubricant known from U.S. Pat. No. 5,154,881 no EBS is formed when the lubricant according to the present invention is prepared. EBS has the chemical formula CH
3
(CH
2
)
16
CO—HN(CH
2
)
2
NH—OC(CH
2
)
16
CH
3
) 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 preferably 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 80% of the amide having the formula described above. Thus up to 20% by weight of other types of lubricants may be added, as long as the advantageous prope

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