Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Making composite or hollow article
Patent
1982-02-02
1984-05-08
Hunt, Brooks H.
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Making composite or hollow article
419 5, 419 27, 428547, B22F 300
Patent
active
044473893
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for manufacturing tubes by sintering.
It has long been known to manufacture tubes of ceramic material by extrusion and firing (sintering) in a furnace. It is also known to glaze such tubes at one stage of the firing in order to obtain tight surfaces. Fired, glazed or unglazed clay tubes of circular cross-section in general are manufactured in predetermined lengths, but both the molding process and the firing may be performed continuously, i.e. the molding can be effected by injection molding and the firing can be effected during continuous travel through a tube furnace. If the tubes are to be glazed or enamelled, the glaze or the enamel can be applied for instance by dipping or spraying.
The object of the invention is to provide tight and strong metallic tubes by using this per se known technique as well as metal sintering technique and sealing of sintered bodies by infiltration.
One drawback in connection with the manufacture of ceramic products is that, subsequently to molding and prior to firing, the products require a relatively extended drying time and that the products are sensitive to deformation during a considerable part of the drying time. By suitable peptization it is possible to prepare a slurry of high dry content, such as 65-70%, and such a relatively dry, ceramic mass can be molded in that it is deformable to a great extent without breaking, and can retain its shape with a very slight elastic recovery. The drying time for a ceramic mass of relatively high dry content is of course shorter than for a ceramic mass of lower dry content.
A ceramic raw material mixture is normally carried out as a wet mixture to form a slurry having a 30-50% moisture content, whereupon the starting material can be dewatered in filter presses for preparing a molding compound which can be compression molded or extruded to tubular shape.
Another method is to perform isostatic pressing of a dry ceramic powder under such conditions that the powder is fired at the same time.
Another object of the present invention is to make use of these per se known methods in the manufacture of ceramic products, to produce strong, tight tubes of sintered metal powder, and a particular object is to achieve a method for the manufacture of tubes in which the major portion of the tube wall may be of a relatively coarse-grained structure while the tube wall has a very close inner or outer surface structure with a smooth or slick surface.
As infiltration material may be used a material which is liquid or during the sintering process is liquefied for infiltration of the pores of the molded tube and which after the infiltration process is caused to solidify in situ.
When the tube is molded by extrusion, use can be made of a molding compound consisting of metal powder and a wetting agent. As wetting agent may be used a hydrocarbon, for instance alcohol, which readily evaporates by drying prior to the sintering process or which during the sintering process is readily driven off by heat. A wetting agent in the form of a hydrocarbon can be used for giving the metal powder, such as iron or steel powder, a suitable carbon content, the hydrogen part of the hydrocarbon being useful for reducing oxide inclusions and/or for producing a hydrogen gas atmosphere. It is also possible to use carbon- and hydrogen-based binders, such as binders based on starch or cellulose, the carbon and the hydrogen being useful in the above indicated way during the sintering process.
According to the invention, the entire molding and sintering process can be conducted under vacuum or in protective atmosphere.
The method of performing isostatic pressing of a dry powder may be used in such a manner that dry metal powder is pressed to tubular shape under such a pressure that a certain sintering occurs. Pressing can be conducted in a furnace or the pressed and presintered tube from the pressing station can be introduced in a sintering furnace.
When sintering metal powder mixtures of a particle size of about 250 .mu.m and above, it has
REFERENCES:
patent: 2227307 (1939-03-01), Hildabolt
patent: 2695231 (1954-04-01), Causley
patent: 2843501 (1958-07-01), Ellis et al.
patent: 3069757 (1962-12-01), Beggs et al.
Brookes Anne
Hunt Brooks H.
Uddeholms Aktiebolag
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