Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Compound of indeterminate structure – prepared by reacting an...
Patent
1996-11-29
1998-04-28
Howard, Jacqueline V.
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Compound of indeterminate structure, prepared by reacting an...
508103, 508551, 75252, 75231, 419 31, 419 38, 419 53, 419 54, C10M14918
Patent
active
057444331
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/SE95/00636, filed Jun. 1, 1995.
FIELD OF THE INVENTION
This 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, as well as the use of the lubricant in a metal-powder composition in warm compaction. Particularly, the invention concerns lubricants which, when warm-pressed, result in products having high unsintered strength (green strength).
BACKGROUND OF THE INVENTION
In industry, the use of metal products manufactured by compacting and sintering metal-powder compositions is becoming increasingly widespread. A number of different products of varying shapes and thicknesses are being produced, and the quality requirements placed on these products are continuously raised. Thus, it is of paramount importance that the manufactured metal products have high density as well as high strength.
In metal compaction, different standard temperature ranges are used. Thus, cold pressing is predominantly used for compacting metal powder (the powder has room temperature). Use is also made of hot isostatic pressing (HIP) and warm pressing (compaction at temperatures between those used in cold pressing and HIP). Both cold pressing and warm pressing require the use of a lubricant.
Compaction at temperatures above room temperature has evident advantages, yielding a product of higher density and higher strength than compaction performed at lower pressures.
Most of the lubricants used in cold compaction cannot be used in high-temperature compaction, since they seem to be effective within a limited temperature range only. An ineffective lubricant considerably increases the wear of the compacting tool.
How much the tool is worn is influenced by various factors, such as the hardness of the material of the tool, the pressure applied, and the friction between the compact and the wall of the tool when the compact is ejected. This last factor is strongly linked to the lubricant used.
The ejection force is the force required for ejecting the compact from the tool. Since a high ejection force not only increases the wear of the compacting tool but also may damage the compact, this force should preferably be reduced.
However, the use of a lubricant may create problems in compaction, and it is therefore important that the lubricant is well suited to the type of compaction carried out.
In order to perform satisfactorily, the lubricant should, in the compacting operation, be forced out of the pore structure of the powder composition, and into the gap between the compact and the tool, thereby lubricating the walls of the compacting tool. By such lubrification of the walls of the compacting tool, the ejection force is reduced.
Another reason why the lubricant has to emerge from the compact is that it would otherwise create pores in the compact after sintering. It is well-known that large pores have an adverse effect on the dynamic strength properties of the product.
BACKGROUND ART
U.S. Pat. No. 5,154,881 (Rutz) discloses a method for making sintered products on the basis of a metal-powder composition containing an amide lubricant. Apart from the lubricant, which consists of the reaction product of a monocarboxylic acid, a dicarboxylic acid and a diamine, the composition contains iron-based powder. The amide lubricant thus consists of an amide product mixture chiefly made up of diamides, monoamides, bisamides and polyamides (of column 4, lines 55-56). Especially preferred as a lubricant is ADVAWAX.RTM. 450 or PROMOLD.RTM. 450, which is an ethylenebisstearamide product.
Furthermore, U.S. Pat. No. 4,955,789 (Musella) describes warm compaction more 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 ethylenebisstearamide (commercially available as ACRAWAX.RTM.), which at pre
REFERENCES:
patent: 3647694 (1972-03-01), Swanson
patent: 5154881 (1992-10-01), Rutz et al.
patent: 5368630 (1994-11-01), Luk
patent: 5429792 (1995-07-01), Luk
patent: 5476534 (1995-12-01), Ogura et al.
Johansson Bjorn
Storstrom Helge
Hoganas AB
Howard Jacqueline V.
Toomer Cephia D.
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