EP0449895A1 - Procede pour fabriquer des elements permeables poreux mecaniquement stables en aluminium pulverise ou granule - Google Patents

Procede pour fabriquer des elements permeables poreux mecaniquement stables en aluminium pulverise ou granule

Info

Publication number
EP0449895A1
EP0449895A1 EP19900900751 EP90900751A EP0449895A1 EP 0449895 A1 EP0449895 A1 EP 0449895A1 EP 19900900751 EP19900900751 EP 19900900751 EP 90900751 A EP90900751 A EP 90900751A EP 0449895 A1 EP0449895 A1 EP 0449895A1
Authority
EP
European Patent Office
Prior art keywords
aluminum
shape
sintering
porous
sintered
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19900900751
Other languages
German (de)
English (en)
Inventor
Werner Jasny
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
KWW GESELLSCHAFT FUER THERMOTECHNIK MBH
Original Assignee
Kww Gesellschaft fur Thermotechnik Mbh
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Kww Gesellschaft fur Thermotechnik Mbh filed Critical Kww Gesellschaft fur Thermotechnik Mbh
Publication of EP0449895A1 publication Critical patent/EP0449895A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • B22F3/11—Making porous workpieces or articles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • B22F2003/1042—Sintering only with support for articles to be sintered

Definitions

  • the invention relates to a method for producing mechanically strong, porous, flowable components from untreated oxidized aluminum powder, granules or granules.
  • porous bodies find e.g. Use as filters, silencers or heat exchanger elements.
  • porous components used in this way are made of sintered bronze or stainless steel. These commonly used materials have a high density and lead to relatively high costs per volume or structural unit. Considerations are known for replacing these materials with aluminum, the pulverized or granulated starting material per unit of weight being cheaper to obtain and, owing to its low density per unit, leading to significantly more favorable weight ratios compared to steel or bronze.
  • a major problem with the sintering of aluminum powder is that aluminum is coated with an oxide layer in contact with oxygen. This oxide layer initially prevents sintering due to its high thermal stability and chemical resistance.
  • additives so-called sintering aids
  • sintering aids By rubbing the aluminum powder with the additives, fractures occur in the oxide layer, so that the additives contact the aluminum and form a eutectic.
  • Eutectics have significantly lower melting points than pure aluminum.
  • the aluminum particles can be mechanically firmly bonded by sintering if the temperature range of the pour point of the respective eutectic is set.
  • the sintering process itself must also be carried out under an inert gas atmosphere.
  • the mode of operation of this process has to be imagined in such a way that the respective additives diffuse through the broken oxide layer, so that a mixture of aluminum / additives can form a eutectic structure which, after cooling, ensures a mechanically firm bond between the aluminum particles .
  • the setting of the furnace temperature to the pour point of the eutectic which e.g. when using silicon as an additive, depending on the weight proportion of silicon in the overall system, between 577 ° and a maximum of 635 ° C (at 0.5% Si), it must not be exceeded, since otherwise the desired porous structure of the powder layer ver ⁇ running. Since the necessary maximum furnace temperature is sensitive to the quantity and type of additives, great care must be taken on the one hand when mixing the aluminum starting material with the additives and on the other hand this care is also required when regulating the maximum furnace temperature . Both lead to the fact that this known method is comparatively expensive. In addition, with this known method, the residence time in the furnace is comparatively long, which also leads to an increase in the cost of the manufacturing process.
  • Anodization direct current / sulfuric acid anodization
  • the oxide layer forming by reaction of the pure aluminum with atmospheric oxygen.
  • this oxide layer is consequently also formed. Since this automatically forming layer is very thin, it makes sense to reinforce this oxide layer in order to damage the sintered body when the aluminum sintered body comes into contact later with corrosive substances that do not have a neutral pH to avoid.
  • GS anodization with subsequent densification of the oxide layer, however, high surface qualities can be achieved.
  • the oxide layers that form after the furnace process have a structure that is dependent on the previous production process, with an oxide layer interrupted by elemental silicon being interrupted, particularly when using silicon as additives. Even with downstream GS anodization, a closed oxide layer cannot easily be produced.
  • the disturbances in the oxide layer in the form of elemental silicon lead to the formation of silicic acid, AL hydroxide and basic aluminum sulfate in the form of efflorescence upon contact with air and H2O.
  • the GS anodization may therefore have to be carried out several times. This also leads to an increase in the cost of the sintered bodies produced.
  • DE-A-30 13 659 describes a sintering process by means of which simple geometric shapes are described, plates are heated and sintered under pressure (pressing) and direct current flow (resistance principle). Instead of sintering aids, the oxide layer is broken up by mechanical action - pressure. Information on the activating effect of pressing can be found in the manual "Powder Metallurgy; Sintered and Composite Materials" by Werner Schatt, page 117.
  • the process described in DE-A-30 13 659 is based on sintering in a free atmosphere. Completely shaped sintered parts cannot be produced in this way, since uniform pressurization is not possible with complicated shapes. In particular, it must be assumed that such strongly pressed solid components derive the electrical currents (short circuit) and that the powder is not sintered.
  • the oxide layer surrounding the aluminum would have to prevent a metallic bond or break open at higher temperatures, which should then lead to the melt flowing into one another.
  • the sintering or furnace temperature is maintained precisely up to or just below the melting temperature of the aluminum powder used, metal bridges are formed between the aluminum particles over a certain period of time without that the structure of the powder filling is changed.
  • Heating up to shortly before the melting point means that the furnace temperature is selected so that the individual sintered particles are in the form of a viscous core which is held together by the oxide layer.
  • Liquid, highly oxygen-affine aluminum emerges from the cracks in the ceramic oxide layer, which are caused by thermal stresses, and does not oxidize only because of the extremely low oxygen or water vapor content in the furnace atmosphere, and thus with reduction the free enthalpy forms the sinter necks or bridges between the individual particles.
  • the temperature in the sintered material is empirically set in such a way that the core does not become so soft that it is crushed by the weight of the sintered particles on it, that is, it retains its shape.
  • this temperature is e.g. between 642 ° and 650 ° C (solidification range according to Al-Taschenbuch, aluminum center 646-657 ° C).
  • the alloy AI Mg Si 05 for example, between 625 ° and 645 ° C (solidification range according to the AI paperback, aluminum center 585-650 ° C).
  • this effect leads to an increase in the batch cycle in a furnace system, the improvement not being readily quantifiable in absolute terms, since the sintering time is influenced, among other things, by the powder fraction used and the weight of the respective sintered body.
  • the holding time can be set to the maximum temperature of about 30 minutes in the conventional method with additives to about five minutes in the method according to the present invention.
  • the apparatus structure is considerably reduced in comparison to press sintering processes.
  • complicated components of non-porous design such as. B. Integrate pipes and create molds with undercuts.
  • the solution according to the invention according to claim 1 represents a way of maintaining the porosity given by the shape of the granulate used, even after sintering, which is not possible in the pressing process.
  • the new method described here is suitable for the production of porous components without the use of sintering aids, also from spherical Al particles up to at least 5 mm in diameter, with no downward limitation of the particle size and other particle shapes.
  • Another advantage of the present invention is that the aluminum bridges have better thermal conductivity than the eutectic bridges in sintered bodies according to the prior art.
  • the main advantage of the present invention is the possibility of sintering untreated pure aluminum powder, the method according to the invention in principle also enables the use of aluminum powder with any alloy constituents, the respective melting or flow temperature of the alloy then being noted must be tet.
  • the sintering temperature is set such that melting or flow temperatures of dense or non-porous components to be sintered with the sintered body or powder, e.g. Aluminum tubes with powder or granular bulk can be taken into account.
  • an aluminum tube made of pure aluminum can be sintered with a granulate or powder filling of any shape in one work process without the risk of the non-porous component being deformed.
  • This is not possible with known sintering processes with additives, since the type and amount of additives have to be selected with regard to the (optimal) sintering. However, this also defines the sintering temperature and cannot be adapted to the melting temperature of the dense component. If an aluminum alloy is used as the starting material in the method according to the invention, the alloy can be selected with regard to its composition such that the pour point of the eutectic is below the melting point of the dense component.
  • the non-oxidizing furnace atmosphere can be generated by a protective gas, for example argon, in accordance with the development according to claim 3.
  • a protective gas for example argon
  • inert gas or protective gas conditions with an O 2 content of less than 5 ppm are sufficient, so that in this regard no higher requirements than with the known sintering processes with additives have to be met.
  • the shape in which the loose starting material is located is designed as a heating element or as an oven.
  • the size of the sintering plant and thus the volume of the furnace atmosphere can be considerably reduced.
  • a smaller volume of the furnace atmosphere is easier to control, ie the quality of the furnace atmosphere is improved.
  • the installation of a furnace system in the inert gas range can be dispensed with and, moreover, rapid and uniform heating with optimum temperature control of the sintered goods is possible.
  • the shape used in the sintering consists of carbon or graphite (claim 5) or highly heat-conducting engineering ceramics, in particular aluminum nitride and boron nitride (claim 7).
  • carbon or graphite claim 5
  • highly heat-conducting engineering ceramics in particular aluminum nitride and boron nitride (claim 7).
  • the mold made of graphite or carbon is used at the same time as an oven or heating element by using the molding material as an electrical resistor.
  • a heating element for example in the form of a heating coil, is integrated into the mold made of good heat-conducting but electrically non-conductive engineering ceramics, or the heating element is in direct thermal contact with the mold.
  • the embodiment according to claim 4 or according to claim 6 or 8 is important insofar as the functional standardization of the mold and the furnace leads to an optimally small volume and thus considerably reduces the effort required to achieve the optimum furnace atmosphere.
  • the aluminum sintered bodies produced according to the invention are passivated anodically, which is possible without any problems owing to the lack of silicon defects in the oxide layer.
  • Other successfully tested passivations were carried out in the form of nickel plating, yellow chromating and anodic oxidation with spark discharge.
  • aluminum powder with a pure aluminum content of 99.5% was filled into a mold made of carbon or graphite.
  • the mold with the aluminum powder was heated to a maximum of 642 ° C and this maximum temperature was held for about five minutes.

Landscapes

  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Mechanical Engineering (AREA)
  • Powder Metallurgy (AREA)

Abstract

Procédé de fabrication d'éléments frittés à partir de poudre d'aluminium oxydée non traitée. Le matériau de base est versé en vrac dans un moule, sans adjonction d'adjuvants de frittage, et chauffé dans une atmosphère protectrice non oxydante jusqu'à la température de fusion du matériau de base. Ces éléments frittés ont une porosité proche de la porosité de départ puisque le prétraitement, par compression par exemple, n'est plus nécessaire.
EP19900900751 1988-12-14 1989-12-13 Procede pour fabriquer des elements permeables poreux mecaniquement stables en aluminium pulverise ou granule Withdrawn EP0449895A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE3842103 1988-12-14
DE3842103 1988-12-14

Publications (1)

Publication Number Publication Date
EP0449895A1 true EP0449895A1 (fr) 1991-10-09

Family

ID=6369156

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19900900751 Withdrawn EP0449895A1 (fr) 1988-12-14 1989-12-13 Procede pour fabriquer des elements permeables poreux mecaniquement stables en aluminium pulverise ou granule

Country Status (3)

Country Link
EP (1) EP0449895A1 (fr)
AU (1) AU4663489A (fr)
WO (1) WO1990006828A1 (fr)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4403801A1 (de) * 1994-02-08 1995-08-10 Kww Thermotechnik Verfahren zum Herstellen gesinterter Bauteile sowie deren Verwendung
GB0024046D0 (en) * 2000-10-02 2000-11-15 Porvair Technology Ltd Method of making porous articles

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3359095A (en) * 1964-02-19 1967-12-19 Dow Chemical Co Sintering of loose particulate aluminum metal
US4992233A (en) * 1988-07-15 1991-02-12 Corning Incorporated Sintering metal powders into structures without sintering aids

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9006828A1 *

Also Published As

Publication number Publication date
WO1990006828A1 (fr) 1990-06-28
AU4663489A (en) 1990-07-10

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