Billets

Round billets can be fabricated by spray forming in vertical (Fig. 8) or horizontal (Fig. 9) plants. The two techniques differ only in relation to the collector movement, which is either vertical or horizontal. The former is used currently on aluminum and copper alloy billet plants. Osprey Metals utilizes the horizontal configuration for processing high alloy steels.

Fig. 8 Vertical mode billet fabrication by spray forming. Source: Osprey Metals, Ltd.

Induclion meiter

Fig. 9 Horizontal mode billet fabrication by spray forming. Source: Osprey Metals, Ltd.

Exhaust

Fig. 9 Horizontal mode billet fabrication by spray forming. Source: Osprey Metals, Ltd.

With a melt size of 1.2 tonne, tool steel and precipitation hardened stainless steel billets have been sprayed at diameters up to 400 mm by 1.2 m length (Fig. 10). Significant cost reductions have been achieved by the use of twin atomizers, higher metal dispensing rates, a reduction in gas consumption, and an increase in yield of the deposit.

Fig. 10 Horizontal mode spray formed tool steel billet. Source: Ref 11

Aluminum alloy billets are normally spray formed in the vertical mode (Fig. 8); Sumitomo Light Metals (Japan) uses this configuration on a commercial scale. The spray formed billets are subsequently extruded or forged into the final product configuration. Current billet size is 250 to 400 mm diam by 1 to 1.4 m length. Smaller diameter billets can be extruded without machining because of the tight tolerances achieved. Primary applications for spray formed aluminum-silicon alloys are in the automotive field (e.g., cylinder liners, pistons, connecting rods).

Other spray formed aluminum alloys in billet form are at an advanced stage of development. These include aluminum-zinc alloys, ultralow density aluminum-lithium alloys, and Al-Si-X ternary alloys, which exhibit a low coefficient of thermal expansion (Ref 11).

Copper alloy billets up to 300 mm diam by 2.2 m length are being spray formed on pilot plants in operation at Wieland (Germany) and Swissmetal (Switzerland). Production levels are not high because the emphasis has been on alloy development. Swissmetal produces Cu-Ni-Sn alloys that combine high strength with acceptable levels of electrical conductivity, copper-bronzes with a high tin content that exhibit enhanced levels of hot and cold workability, Cu-Cr-Zr alloys for high-temperature stability, and copper-carbon alloys in which the graphite particles enhance wear properties.

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