Page 460 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

440 Chapter 17 Powder-Metal Processing and Equipment

Q Q Atomization. Atomization involves a
liquid-metal stream produced by injecting
molten metal through a small orifice. The
stream is broken up by jets of inert gas
' or air (Fig. 17.5a) or water (Fig. 17.5b),
known as gas or water atomization, respec-
Q tively. The size and shape of the particles
formed depend on the temperature of the
Q* 1100 pm molten metal, rate of flow, nozzle size, and
_
jet characteristics. The use of water results
(a) (D)
in a slurry of metal powder and liquid at
FIGURE l7.4 (a) Scanning-electron microscope image of iron-powder the bottom of the atomization chamber.
particles made by atomization. (b) Nickel-based superalloy (Udimet 700) Although the powders must be dried before
powder particles made by the rotating electrode process; see Fig. 17.5d. they can be used, the water allows for more
Source: Courtesy of PC. Nash, Illinois Institute of Technology, Chicago. rapid cooling of the particles and higher
production rates. Gas atomization usually
results in more spherical particles (see Fig. 17.3c).
In centrifugal atomization, the molten-metal stream drops onto a rapidly
Ladle © <1 1 2 - Tundish
rotating disk or cup, so that centrifugal forces break up the stream and generate par-
ticles (Fig. 17.5c). In another variation of this method, a consumable electrode is

©
Molten metal
E
High-pressure
ma.;
dia /_'
Q Tundish i _ _ water manifold
i-
1
Alomlzing
Water Spray
9:
Atomization tank
__ _ \
A
’
A §ft, x"_$ 5.1
Q ? Atomizing chamber =’.f¢?_`f§;f¥l; Q ff*
V’-sw
Metal particles
Vl/BIBT
il 1* DewaterinQ
atomization L* );¢;%§‘
(21) (D)
m-=1!!-;--
lnert gas
->Vacuum
Ladle --~~r~~
@ Rotating consumable
Molten metal electrode
Nonrotating
Q Tundisn Spindle
/- Liquid metal
tungsten electrode
I
Collection port
Spinning disk
(C) (d)
FIGURE l1.5 Methods of metal-powder production by atomization: (a) gas atomization;
(b) water atomization; (c) centrifugal atomization with a spinning disk or cup; and (d) atomization
with a rotating consumable electrode.