Method for producing mono-dispersed spherical granules

Details Method for producing mono-dispersed spherical granules Method for producing mono-dispersed spherical granules

2000-03-08

2001-09-04

Wyszomierski, George (Department: 1742)

Specialized metallurgical processes, compositions for use therei

Processes

Producing solid particulate free metal directly from liquid...

C075S340000

Reexamination Certificate

active

06284015

ABSTRACT:

TECHNICAL FIELD
The present invention relates in general to powder metallurgy, more specifically to methods for preparing monodisperse materials used in regenerative heat exchangers, and has particular reference to a methods for preparing monodisperse spherical granules.
BACKGROUND ART
Known in the present state of the art is a method for preparing metal granules (SU, A, #532,472) by a forced capillary disintegration of a stream of melt under the action of regular perturbations. A device disclosed in the aforementioned reference operates by the method mentioned before. However, the method leaves out of account the thermal characteristics of the process which involves low quality of the resultant granules as to spherical shape and monodisperse nature thereof.
The closest to the proposed method is a method for preparing monodisperse spherical granules (RU, A, 2,032,498) which is based on the effect of forced capillary disintegration of a stream of melt under the action of perturbation applied thereto. The drops resultant from dispersion of said stream of melt are cooled, under optimum conditions, with an inert gas that fills the flight chamber. The prepared granules are taken out in the outlet section of the heat-exchanging chamber after the process has reached steady-state operating conditions of drop generation. When the stream of a chemically active melt flows through a die the surface of the flow-through orifice thereof gets eroded, whereby the die orifice diameter increases with time. This in turn results in that the stream diameter increases incessantly and the diameter of drops into which the stream is disintegrated.
Furthermore, the method under discussion suffers from a low quality of dispersed material obtained from dispersing chemically active melts to which, particularly, can be related rare-earth metals and alloys thereof.
DISCLOSURE OF THE INVENTION
It is a principal object of the present invention to provide a method for preparing monodisperse spherical granules which makes possible attaining higher quality of dispersed material resulting from dispersing chemically active melts so that the root-mean square (standard) deviation of the granule diameter from the preset value should be within 2% and the ratio between the greater and lesser granule diameters be within 1.02.
The foregoing object is accomplished due to the fact that in a known method for preparing monodisperse spherical granules, according to which the stream of melt outflowing from the die is dispersed under the effect of perturbations applied thereto at an optimum temperature of the cooling gas and the resultant granules are taken out in the outlet section of the heat-exchanging chamber after the process has reached steady-state operating conditions of drop generation, according to the invention, the inert gas is freed from oxygen to a maximum content of 0.0001 mol. %, the die is made of a refractory metal, and the length ‘l’ of the die flow section is within the range of 2d<1<20d, while the stream perturbation frequency is selected from the relationship:
f=Wk
o
/&pgr;d
o
(1+
c&tgr;
)
2
where:
&tgr;—is the dispersion time (equal to zero at the initial instant of time),
c—is the empirical coefficient characteristic of the die material resistance to the effect of stream perturbation,
w—is the stream outflow velocity,
d
o
—is the initial stream diameter value,
k
o
—is the initial value (0.7) of the dimensionless wave number, use being made of a material subjected to dispersion comprising at least one of the following rare-earth metals: Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb.


REFERENCES:
patent: 4818279 (1989-04-01), Chaleat et al.
patent: 5403375 (1995-04-01), König et al.
patent: 5445666 (1995-08-01), Peschka et al.
patent: 5480470 (1996-01-01), Miller et al.
patent: 532472 (1977-03-01), None
patent: 2032498 (1995-04-01), None

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