Understanding Atomization Method in Powder Metallurgy

April 16, 2019

This phase of the powder metallurgy process hasn’t received adequate attention. Here’s an opportunity to remedy that oversight. Actually, that’s not quite true, past articles have described the electric arc phase, but that’s hardly the only option. Grabbing this chance with both hands, let’s delve deeper into the powder dispersing options.

What Is Powder Atomization?

At the beginning of the procedure, powder medium is broken down into a pile of free-moving grains. Now, since those particles must be homogenized, near identical in shape and size, then no mere grating or grinding mechanism can administer this operation. Rather, advanced manufacturing stages perform highly energized material dispersion actions, which turn larger metal droplets into fine, flour-like mounds of dust. Only, this dust is still metallic, and each powdery neighbour is identical in both size and shape.

There Are Different Atomization Options

Water is one option. A high-pressure jet of water strikes a liquid metal surface. The resulting grains pile up rapidly, but they’re irregularly sized, which is a definite drawback for sintering equipment. An inert gas replaces water in some equipment types. Inert jets of gas eliminate the risk of water oxidization and produce perfect spheroids. Uniform in shape and size, gas-atomized powders neck predictably when they’re sintered. More on atomization technology is upcoming. Before that, however, where is the initial metallic discharge coming from?

It’s an Arc-Gap Melted Stream

Rods of solid metal can’t just enter one orifice and come out magically on the other side as small droplets. No, the rods enter the initial stage, then they’re melted by a high-current arc. The electrode strikes the solid rod, the molten metal flows, and it breaks down into a series of liquid droplets. From here, the stream is hit by water or gas. Alternatively, a finely separated pile of dust-like powder is produced when the droplets strike a rapidly spinning disk. Other atomization methods include centrifugal spinning, ultrasonic atomization, and vacuum dispersion technology. From the arc-electrode fitted orifice to the actual vaporization mechanism, the manufacturing process works away until a mound of metallic grains is volumetrically dense enough to fill the parts-compaction or pressing die.

The properties of the powder load are key, of course. For example, if one atomization method produces larger, pear-shaped particles, then the necking phase in the compaction die will react in a certain manner. Spheroids, as produced by an alternate atomization technique, won’t react in the same way. Then there are oxide layers, powder densities, and alloy differences, all of which can be managed by changes in the arc and/or atomization settings.

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