Stock material or miscellaneous articles – All metal or with adjacent metals – Having metal particles
Patent
1980-06-26
1983-02-08
Hunt, Brooks H.
Stock material or miscellaneous articles
All metal or with adjacent metals
Having metal particles
425 78, 294205, 29 422, 419 1, 419 9, 419 5, B22F 300
Patent
active
043730124
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a further development of the process for the production of stainless tubes described in German printed application DE-AS No. 24 19 014, corresponding to U.S. Pat. No. 4,143,208.
The German printed application DE-AS No. 24 19 014 and the corresponding U.S. patent relate to a process for the production of tubes of stainless steel having a uniform structure, uniform physical and chemical properties and good further processing properties, in which powder-form steel of the type in question is introduced into metallic capsules; the capsules are closed and compressed by a pressure acting on all sides thereof and the pressing obtained is extruded into tubes, steel powder of predominantly spherical particles produced by sputtering melt in an inert gas atmosphere being used and the capsules used being thin-walled capsules of a ductile metal having a maximum wall thickness corresponding to approximately 5% of the external diameter of the capsule; the density of the steel powder introduced into the capsule is increased to between about 60 and 70% of the theoretical density by vibration and/or ultrasound; the density of the steel powder is increased to at least 80% and preferably to between 80% and 93% of the theoretical density by isostatic cold pressing of the capsule under a pressure of at least 1500 bars; the pressing is heated and subsequently hot-extruded, preferably at temperatures of at least about 1200.degree. C., to form the required semi-finished product.
According to the German printed application DE-AS No. 24 19 014 it can be of advantage to evacuate the metallic capsules filled with the steel powder before they are closed and/or to fill them with a gas, particularly an inert gas, for example argon.
According to the German printed application DE-AS No. 24 19 014, it is preferred to use metallic capsules of which the wall thickness amounts to less than 3% and more particularly to less than 1% of the external diameter of the capsule, metallic capsules having a wall thickness of from about 0.1 to 5 mm and preferably from about 0.2 to 3 mm being particularly preferred.
According to said German printed application DE-AS No. 24 19 014, it is also possible to produce composite tubes using thin-walled metallic capsules which are separated by one or more concentric partitions into two or more compartments. The predominatly spherical powder particles of the various steel qualities are respectively introduced under vibration into one of these compartments, after which the partitions are removed and the capsules closed, followed by isostatic cold pressing and extrusion at elevated temperature. For extruding the pressings into tubes, glass is normally used as the lubricant. Since stringent demands are imposed on the lubricant in the extrusion of, in particular, stainless steels at elevated temperatures, the pressing is required to have a substantially flat end face so that the lubricant applied to the end face of the pressing in the form of a glass disc is effectively utilised.
It has now been found that the pressings frequently show deviations from the ideal shape and thus lead to difficulties and to rejects in the extrusion process.
The object of the present invention is to produce a capsule and a pressing with which these difficulties of the known embodiments are avoided and with which the number of rejects and of defective products is as low as possible.
According to the invention, this object is achieved in that at least the outer wall of the capsule has substantially the same strength properties in the axial direction over its entire circumference. According to the invention, at least the outer wall of the capsule is preferably formed by a thin-walled, spiral-welded or extruded tube. Forming the outer wall of the capsule in this way affords the advantage that extruded products, particularly tubes, characterised by a considerably reduced number of faults and, hence, rejects are obtained.
It has further been found that extrusion is accompanied by the development of surface faults in the fr
REFERENCES:
patent: 3620059 (1971-01-01), Nilsson
patent: 3832100 (1974-08-01), Baxendale
patent: 4131463 (1978-12-01), DePierre
patent: 4143208 (1979-03-01), Aslund
Aslund Christer
Eriksson Hans
Tornberg Claes
Granges Nyby AB
Hunt Brooks H.
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