GE T
In the Winter 2021 issue of PM Review, we began our four-part series on metal powder atomisation. Over the course of this series, two atomisation experts, Joe Strauss and John Dunkley, have offered our readers a valuable overview of the principles of atomising technology, atomised powders and their applications. In this final instalment in the series, Strauss and Dunkley present those special atomisation methods such as centrifugal, ultrasonic, pressure (single-fluid) atomisation, and two-fluid atomisation with unconventional media. While perhaps not as widely known as gas or water atomisation, each of these specialist methods of metal powder atomisation has its own unique applications – some industrially significant and some highly niche.
Previous instalments of this review have dealt with the most commonly used two-fluid atomisation techniques – that is, when one fluid (molten metal) is broken up by another (water or gas). This section will cover other atomisation methods, including those that produce metal droplets by mechanical disintegration of the melt. Some of these methods are well-established and are industrially significant, with installed capacity of 50–100 kt/y, such as centrifugal atomisation. Ultrasonic atomisation has been commercially used for many decades for low-temperature alloys, but recent developments have extended the operating temperature, which further increases the range of alloys that can potentially be processed. We will also look at pressure – or single-fluid – atomisation, which has very limited use, and will briefly mention some two-fluid methods using unconventional media (oil and cryogenic gas).
© 2022 Inovar Communications Ltd
Centrifugal atomisation This is also sometimes referred to as rotary atomisation and, in principle, means the breaking up of liquid metal by centrifugal forces. A spectacular illustration of one embodiment of the concept is shown
in Fig. 1. Here, a stream of metal – in this case, steel – is falling at 30 t/h onto a rotating disc or cup which is about 600 mm in diameter. As this was rotating at low speed to make very coarse particles, it is easy to see what is happening. The liquid is accelerated to the peripheral velocity
Fig. 1 Centrifugal atomisation on a spinning cup (Courtesy Atomising Systems Ltd)
Autumn 2022
Powder Metallurgy Review
71
F
How to make metal powders. Part 4: Centrifugal and other special atomisation methods
PD
Special atomisation
| contents | news | advertisers | events | website | e-newsletter |