Technology

Production Process

Quality Control and Testing

Water Atomization Process

Atomization is the most commercially used process to produce the largest tonnage of metal powders. High-pressure water atomization has proven to be a viable, low-cost process to achieve fine particle size distributions for iron, stainless and low-alloy metal powders. The economic advantages and pre-alloying capability provide desirable advantages over competing technologies. Previous shortcomings relative to powder characteristics, i.e. irregular particle shape, lower tap densities, oxidized surfaces, have been refined to more closely replicate gas atomized powder properties.
In principle the technique is applicable to all metals that can be melted, and is commercially used for the production of iron, copper, including tool steels, alloy steels, brass, bronze and the low-melting-point metals, such as aluminum, tin, lead, zinc, cadmium. If a falling stream of molten metal is impinged by jets of water, then it is broken up into droplets which rapidly freeze to form granules (> 1 mm) or powder (> 1 mm), depending on the composition of the metal alloy, and the water pressure. Classical granulation uses pressures in the range of 2–5 bars (200–500 kPa) and typically produces 1–10 mm size granules. Very large flow rates can be accommodated (in the t/min range), as pumping costs are modest.
To make finer powders, one needs higher pressures (we find median size is approximately inversely correlated with pressure), so it is necessary to use more controlled streams, typically from a tundish arrangement instead of a launder as in many granulators, and to run more modest flow rates, typically using nozzles from 3 mm to 30 mm in diameter to give flow rates from 5 kg/min to ~500 kg/min (up to 30 t/h). Pressures range from 20 bars for coarser powders (say 0.3 mm) to 200 bars for finer powders (say ~50 μm). Elements like sulphur in the melt strongly affect (reduce) the required pressure by reducing melt surface tension. As shown in Figure 2, the atomized slurry can be pumped, either directly to leach tanks, or to a dewatering system which can deliver either a thickened slurry at ~20% moisture or a damp solid at ~5% moisture. This can then be fed to the leach tanks if the water balance is critical. Drying adds significant energy and cost, but may be done if, for instance, a smelter is selling to a refiner.

Water Automization

Atomization is the most commercially used process to produce the largest tonnage of metal powders. High-pressure water atomization has proven to be a viable, low-cost process to achieve fine particle size distributions for iron, stainless and low-alloy metal powders. The economic advantages and pre-alloying capability provide desirable advantages over competing technologies. Previous shortcomings relative to powder characteristics, i.e. irregular particle shape, lower tap densities, oxidized surfaces, have been refined to more closely replicate gas atomized powder properties.
In principle the technique is applicable to all metals that can be melted, and is commercially used for the production of iron, copper, including tool steels, alloy steels, brass, bronze and the low-melting-point metals, such as aluminum, tin, lead, zinc, cadmium. If a falling stream of molten metal is impinged by jets of water, then it is broken up into droplets which rapidly freeze to form granules (> 1 mm) or powder (> 1 mm), depending on the composition of the metal alloy, and the water pressure. Classical granulation uses pressures in the range of 2–5 bars (200–500 kPa) and typically produces 1–10 mm size granules. Very large flow rates can be accommodated (in the t/min range), as pumping costs are modest.
To make finer powders, one needs higher pressures (we find median size is approximately inversely correlated with pressure), so it is necessary to use more controlled streams, typically from a tundish arrangement instead of a launder as in many granulators, and to run more modest flow rates, typically using nozzles from 3 mm to 30 mm in diameter to give flow rates from 5 kg/min to ~500 kg/min (up to 30 t/h). Pressures range from 20 bars for coarser powders (say 0.3 mm) to 200 bars for finer powders (say ~50 μm). Elements like sulphur in the melt strongly affect (reduce) the required pressure by reducing melt surface tension. As shown in Figure 2, the atomized slurry can be pumped, either directly to leach tanks, or to a dewatering system which can deliver either a thickened slurry at ~20% moisture or a damp solid at ~5% moisture. This can then be fed to the leach tanks if the water balance is critical. Drying adds significant energy and cost, but may be done if, for instance, a smelter is selling to a refiner.

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