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Abstract
The development of a process of preparing spherical or flake powders in the size range 100–1500 μm is described. The process has been applied to a wide range of materials, including iron, nickel, cobalt and titanium alloys, refractory metals, carbides, and oxides.
In one mode of operation the feed material is in the form of a consumable rod electrode (cathode) and is melted by a vertical arc struck between the electrode and a rotating crucible. The melted material falls into the crucible, which may be water-cooled, and is forced up and over the walls by centrifugal action. By selecting rotation speeds in the range 500–4000 rev/min, the mean size of the particles formed as the liquid tears off the crucible lip may be varied systematically. Alternatively, granules may be fed through a hollow non-consumable electrode or the crucible may be replaced by a consumable anode.
The conditions controlling particle size and shape have been analysed theoretically in terms of the relevant alloy, atmosphere, and machine parameters, and the results compared with those obtained from experiment.
An important feature of the process is that it permits the preparation of powders of oxyphilic materials, such as high-temperature high-strength alloys and titanium alloys, under conditions where there is no significant increase in oxygen content. Production rates of up to 1kg/min have been achieved and machine designs have been prepared that indicate the economic potential of the process up to the 1000 tonnes/annum scale.
Notes
* Manuscript received 14 May 1973. Contribution to a Symposium on ‘PM Alloys and Properties’, to be held in Eastbourne on 19–21 November 1973.