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How do you atomise a jet engine?

James May and jet engine and engine in atomised form
From this to this - Roger Hiorns' atomised jet engine, right

WHO, WHAT, WHY?
The Magazine answers...

Among the works unveiled at this year's Turner Prize exhibition is a jet engine which has been reduced to a fine powder.

To the Times's art reporter Ben Hoyle it is "troubling but beautiful", while the Guardian's Adrian Searle sees it as a "desert of wadis, dunes and rills... a landscape of entropy and death". Over at the Sun, Rob Singh is more blunt - "a heap of dust".

The artwork in question is an atomised passenger aircraft engine - one of several exhibits unveiled at the Tate Britain gallery in London by artist Roger Hiorns, a Turner Prize nominee.

But how is a jet engine reduced to a pile of dust-like particles?

THE ANSWER
Heat it to liquid form
Pour the molten metal through a nozzle
As it falls, bombard it with water or gas

Although there are many variations to the process, depending on the type of metal being handled and the purity of the particles needed, in essence it's a two-stage process:

  • 1. The metal is heated until it reaches liquid form
  • 2. It is then dropped through a funnel and sprayed with a fine stream of water or gas, which breaks it into granules

Breaking a hunk of solid metal into tiny particles is a process that's been around for at least 900 years, when gold was granulised. Atomisation, or powdered metallurgy, dates back about 100 years, says John Dunkley, founder and chairman of Atomising Systems Limited.

It has a "surprising number of applications", says Keith Murray, of metal atomiser Sandvik Osprey. "Cars, aeroplanes, boilers... sprockets and gear wheels."

HOW ATOMISING WORKS
Atomiser
Thin stream of molten metal falls through funnel
It is bombarded by purified gas released from nozzle
The impact disintegrates the liquid into tiny droplets
These cool as they fall and collect at the bottom

Atomised metal can be used as a coating for decorative purposes - the silvery flecks in a car's metallic paint - or compressed into a mould to make components. It's more expensive than moulding from liquid metal but the result is lighter. Atomised aluminium is also used in rocket fuel and other explosives.

And some components of jet engines - those made of very tough metals which do not break down easily - would commonly be be atomised to enable recycling, says Mr Dunkley.

But the atomising of an entire jet engine?

It's not the first time Mr Dunkley has had to consider the question, having received a call from an artist several months ago who was investigating the possibility. He is reasonably sure it was Hiorns he was talking to. Hiorns, himself, was unavailable for comment for this article.

"We don't have many artists phoning us up," says Mr Dunkley. "I had to say that we weren't tooled up to do that job. But I gave him some names and numbers of those who might be able to help him."

The main stumbling block would be finding a furnace big enough to melt the entire engine in one go, says Mr Dunkley. And the components used in a jet engine would not always liquefy easily.

While a soft metal such as aluminium melts at a relatively modest 661°C, a jet engine, particularly the combustion parts, would need to be able to withstand the fierce temperatures generated by burning kerosene - jet fuel.

For Hiorns' project, the engine would need to have been melted at between 1,400°C and 1,500°C, producing a "brilliant white heat". Nickel, stainless steel, cobalt would all melt at this temperature although titanium, which can be found in jet engines, is so tough it would have to be handled separately.

Once in molten form, the metal is then poured through a funnel into a sealed chamber, known as an atomiser, and bombarded with a thin jet of water or gas sprayed through a fine nozzle.

The effect of being hit by water breaks the molten metal into tiny spherical or near spherical particles - anything from 4 microns (four millionths of a metre) to 1mm. As they fall, the particles cool and form a powder.

WHO, WHAT, WHY?
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A regular part of the BBC News Magazine, Who, What, Why? aims to answer some of the questions behind the headlines

"I recommended water for being simpler and more economical," says Mr Dunkley, recalling his conversation with the artist. Gas is used when the atomised metal needs to be produced in highly controlled circumstances - if, for example, the powder is to be moulded into high-grade components.

So what does Mr Dunkley make of seeing the product of his craft being shovelled on a wooden floor and presented as art?

"The last thing we would do would be to scatter powder around the place and contaminate it with dust. Some of it has got oxidised - that's where it is black. The grey stuff is where it's cleaner."

Looking at a picture of the work, Mr Dunkley is not unimpressed.

"It's pretty grim stuff [but] quite a pleasing effect."



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