Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Making articles of indefinite length
Patent
1991-05-31
1994-05-24
Walsh, Donald P.
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Making articles of indefinite length
419 66, 419 67, 419 61, 266102, B22F 302
Patent
active
053146557
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and apparatus for producing continuous powder metallurgy compacts, for example, metal rods, tubes and the like, of handleable strength.
A variety of techniques are currently employed to produce metal products from metal powders. One of the major technologies in this field is directed to the production of discrete, identical objects from metal powders utilizing fixed forming dies. The essence of this technique may be understood from the following simplified description of the production process.
A known amount of metal powder is introduced into, for example, the bore of a cylindrical tubular die. The powder is then compressed between two punches placed one in each end of the bore, by applying a force to each punch along the direction of the longitudinal axis of the bore. The compressive force consolidates the powder which forms a "green" compact having sufficient strength to allow handling. This compact is then subjected to a high temperature diffusion process, usually in a protective atmosphere, to bond together the separate powder particles in the compact to form a strong component.
The nature of this process is such that it is, in practice, limited to use in the production of discrete components for the following reasons. Due to friction between the die walls and the powder, the pressure transmitted to the powder during compression of the punches gradually decreases in a direction away from the punches. Since the compression forces are directed along the longitudinal axis of the compact, the density of the resulting compact is greatest at each end and gradually decreases to a minimum at the middle of the compact. If this process is to be made continuous, the punches must first be removed leaving the compact in place in the die, more powder added above the compact, and the top punch replaced. A force must then be applied to the top punch so as to consolidate the freshly added powder, while at the same time causing the original compact to be ejected from the bore of the die. Due to the frictional effects discussed above, the compressive force is, in practice, insufficient to eject the original compact from the die since the force is not effectively transmitted through the mass of unconsolidated powder. Increasing the force applied to the punch simply results in further consolidation of the newly added powder and does not result in ejection of the original compact. The process described above is therefore limited to the production of discrete compacts.
Since continuous production processes are, in general, more economical than discrete or batch processes a method of producing continuous powder metallurgy compacts would be of significant commercial advantage.
According to the present invention there is provided apparatus for producing continuous powder metallurgy compacts, which apparatus comprises a forming die providing a powder consolidation region disposed between an inlet in the forming die for introduction of metal powder into the said region and an outlet in the forming die, the consolidation region being tapered in a direction towards the outlet;
means for stopping the outlet in the forming die to retain in the consolidation region metal powder introduced initially into the said region;
means for effecting high frequency, preferably ultrasonic, radial vibrations of said forming die about an axis passing through the consolidation region and in a plane transverse to the intended direction of movement of metal powder through the forming die, and
restrainer means for preventing movement of the metal powder within the consolidation region away from the outlet in the forming die during the said radial vibration of the forming die.
As the die moves radially outwards during vibration, powder tends to move towards the narrower end of the consolidation region and is further compacted during the inward movement of the die. Powder is thus progressively densified during its passage through the die, and emerges through the outlet at the density desired.
The said restrainer
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patent: 4005956 (1977-02-01), Inoue
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Sears, Zemansky, and Young. University Physics. Addison-Wesley (1976) p. 398.
Greaves John N.
Manganese Bronze Limited
Walsh Donald P.
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