A cutting technology used to dismantle cold-war
nuclear missile installations is now even better thanks to a CRAFT project.
High-speed water jets can cut through many materials from steel to concrete
but suffer from low efficiency. Research carried out under the BRITE-EURAM
Industrial and Materials Technologies programme has shown how adding suitable
polymers to the water can more than double efficiency.
The industrial use of water jets for cleaning and
cutting began in the 1970s. More powerful abrasive water jets, which use
water mixed with abrasive particles, arrived in the early 1980s but only
became commercially important in the 1990s. The most powerful modern jets,
known as abrasive water suspension jets, have jet speeds of hundreds of
metres per second and can cut through 30 cm of steel or one metre of concrete.
"The major application for these jets is in dismantling
and decommissioning redundant plant," explains project co-ordinator
Christoph von Rad of the Institute of Materials Science (Institut
für Werkstoffkunde or IW) at the University of Hanover. "These
include, for example, offshore structures, demilitarisation, or the dismantling
of nuclear power stations."
||Polymers in the water
A few years ago a company known as ANT
(formerly Alba Industries) approached Professor Hartmut Louis's
research group at IW to see if they could help improve the efficiency
of abrasive suspension water jets. "We have very close contacts
with industry because our institute concentrates on research close
to application," says Mr von Rad. "The question came up
whether it was possible to increase the stability of abrasive water
suspension jets by adding polymers to the water."
One problem with water jet cutting is that the
narrow jet breaks up into droplets, drastically reducing the cutting
efficiency. When pure water jets were first developed in the 1970s,
researchers tried adding polymers - large organic molecules - to
the water in the hope of preventing the stream breaking up. Polymers
were considered again for abrasive water suspension jets in the
early 1990s but not pursued since the jet technology itself was
Now, the time was ripe to try again, so the
partners assembled a group of companies and research institutes
to put together a CRAFT project. The project, led by IW and ANT,
included two Italian research institutes: the University
of Cagliari and the neighbouring laboratory of the Consiglio
Nazionale delle Ricerche (National Research Council). Italian
SMEs included FIP
Industriale , a manufacturer of water jet machinery for civil
, which makes water jet cutters for manufacturing industry, and
Sonsub , a
builder of remotely controlled underwater vehicles. PS Watercut,
a Danish firm using abrasive water suspension jets, and French company
, which supplied the polymers, completed the consortium.
After two years of research with different polymers,
the partners have been able to improve cutting efficiency greatly,
mainly because the jet holds together better. "The water becomes
viscous because of the polymer and therefore the jet does not disintegrate
into droplets so much and stays coherent for longer," Mr von
Rad explains. "This is especially advantageous for deep cutting.
The acceleration of the abrasive particles in the nozzle is also
improved, but this effect is not as strong."
As a result, cutting efficiencies have been
improved by as much as a factor of 2.6, depending on the polymer
and the design of the jet nozzle.
The main remaining problem is that the polymers
are normally supplied as powders or granulates, which are not directly
usable in water-cutting machinery. If the chemical industry can
be persuaded to supply them in the form of concentrated solutions
or emulsions then the market for the improved technology should
"There are many offshore structures which
have to be dismantled and also nuclear power plants which will be
taken out of use within the next few decades," Mr von Rad notes.
ANT has even been using water jets to dismantle nuclear missile
silos in the Ukraine, as part of the implementation of the START
I disarmament agreement. This is not a huge market but will provide
a lot of business for specialised firms working within it. And so
far there seem to be no competitors supplying this technology, though
that is likely to change as the market grows.
Meanwhile, IW is applying for EU funding for
another project, this time to introduce polymer technology into
another kind of abrasive water jet, the injection jet, used in the
manufacture of products from very hard, brittle or heat-sensitive
"The superiority of abrasive water jets
is obvious when cutting materials such as ceramics, reinforced plastics
and all kinds of composites, because they do not bring in any heat,"
explains Mr von Rad. "This is of even higher commercial interest.
We did some small scale tests during this last project and got a
very promising result of 20% increase in efficiency without any
modification of the cutting heads, so we are hoping to get a lot