Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Making porous product
Reexamination Certificate
2000-05-24
2002-09-03
Jenkins, Daniel J. (Department: 1742)
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Making porous product
C419S029000
Reexamination Certificate
active
06444166
ABSTRACT:
BACKGROUND OF THE INVENTION
Foam structures are known in industry and the number of applications for metallic foam structures is continually increasing. For example, aluminium foam metal having a continuously connected, open celled (reticulated) geometry is available and employed in energy/impact absorbers, heat exchangers and lightweight composite panels.
When used with heat exchangers the high surface to volume ratio allows for a compact design and the high specific stiffness, that is, high strength to weight ratio makes the material useful in aerospace and car applications.
Low-cost aluminium foam panels can be produced by a continuous casting process. The foam is machinable by common aluminium metal working techniques (sawing, drilling, milling) and maybe joined by brazing or adhesive bonding. As previously indicated aluminium foam produced by this method finds application as lightweight cores for sandwich panels and as components in energy absorbing structures.
However, when gas containment vessels are required and in particular when irregular complex shapes are required then metal foams are formed typically by mixing small quantities of a gasifier e.g. titanium nitride with aluminium powder and subjecting the mixture to heat and pressure to form a sintered sheet.
The sintered sheet or a portion thereof is then placed in a mold which is then heated to a higher temperature at which the metal melts and nitrogen is released from the titanium nitride to provide an even dispersion of bubbles.
The hot metal is allowed to solidify and then shock heat treated by dropping it into a cryogen such as liquid nitrogen which causes small fractures to occur between adjacent bubbles so that the mass becomes reticulated. However, by subjecting the mass to a violent heat shock said small fractures may be prone to brittle fracture and also create areas of crack propagation particularly if cyclic loading is applied to the object made from the mass.
It is an aim of the present invention to mitigate against these disadvantages by employing a hot inert gas which is passed through the mass such that thin metal adjacent the fractures melts slightly and is drawn in to a more circular cross-section by surface tension.
SUMMARY OF THE INVENTION
According to the present invention a method of making a metal foam object includes the steps of mixing a gasifier with metal powder and subjecting the mixture to an elevated temperature T
1
and pressure P
1
to form a sintered sheet, placing at least a portion of the sintered sheet in a mold and subjecting the mold to a temperature T
2
where T
2
is greater than T
1
at which the metal melts and the gas is released from the gasifier quenching the metal foam object thus formed by the mold and passing a hot inert gas through the metal foam object.
Preferably, the hot inert gas is argon which is passed through the metal foam object by means of at least one header tube.
REFERENCES:
patent: 3847591 (1974-11-01), Niebylski et al.
patent: 4099961 (1978-07-01), Patten
patent: 5151246 (1992-09-01), Baumeister et al.
patent: 962 565 (1957-04-01), None
patent: 0 903 415 (1999-03-01), None
Cohen Joshua L.
Jenkins Daniel J.
Pace Salvatore P.
The BOC Group plc
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