Specialized metallurgical processes – compositions for use therei – Processes – Spheroidizing or rounding of existing solid metal particles
Reexamination Certificate
1995-10-12
2001-04-24
Kastler, Scott (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Spheroidizing or rounding of existing solid metal particles
C075S255000
Reexamination Certificate
active
06221125
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to spherical metal powders suitable for use in metal injection molding, and to a method for producing such powders.
2. Description of the Prior Art
Of the powdered raw materials used for metal injection molding, powdered alloys are produced by water-atomization or gas atomization.
When a melt of metal or alloy is formed into particles by water in the process of water atomization, the melt is cooled very rapidly so that the particles formed have a non-spherical shape. Their tap density ratio is therefore only 40-46%, and they cannot be used as a raw material for injection molding unless a large amount of an organic binder is blended with them. However, when the blending proportion of an organic binder is high, a long debinding time is needed and problems such as blistering or distortion arise with considerable frequency during the debinding process.
On the other hand, in the case of a gas-atomized powder, the particles produced are perfect spheres so that their tap density ratio is of the order of 60% and a sufficient injection moldability can be ensured, even with a low blending proportion of an organic binder. However, in this case, there is no interaction at all between particles after the debinding process. Thus, the strength of the debound body is reduced. Further, the gas-atomized powder is also more costly to produce than the water-atomized powder.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention to simultaneously overcome the disadvantages associated with a high blending proportion of organic binder required for the injection molding of non-spherical water-atomized particles having a tap density ratio as low as 40-46% and the problems caused due to the poor strength of molded debound bodies of gas-atomized particles. More specifically, an object of the present invention is to modify the non-spherical particles of a water-atomized powder into spherical particles so that the particle shape of the water-atomized powder becomes close to the particle shape of the gas-atomized powder and the blending proportion of organic binder can therefore be reduced compared to the proportion normally required for a conventional water-atomized powder in the injection molding process. A further object of the present invention is to provide debound bodies having a higher strength than in the case of the gas-atomized powder. As a result, there is provided a water-atomized spherical metal powder which ameliorates all the problems encountered in both types of atomized powders, i.e., water-atomized powder and gas-atomized powder.
Accordingly, this invention provides a water-atomized pherical metal powder having a spherical particle shape, an average particle size of 25 &mgr;m or less and a tap density ratio of 50-60%.
The present invention further provides a method for producing the above-mentioned water-atomized spherical metal powder wherein metal particles of non-spherical shape produced from molten metal by water-atomization are formed into particles of spherical shape by means of a high speed gas stream which causes high speed collisions to occur between the particles and between the particles and a collision target.
REFERENCES:
patent: 4209326 (1980-06-01), Klein et al.
patent: 5006164 (1991-04-01), Kiyota
Soda Yuji
Tokuyama Yukio
Usui Hiroshi
Flynn ,Thiel, Boutell & Tanis, P.C.
Kastler Scott
Mitsubishi Steel Mfg. Co. Ltd.
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