64
No cadmium? Not yet!
By Dr John Newnham
Confederation of British Metalforming
Manufacturers of automotive and industrial on the use of cadmium, so for fasteners of and GARTEUR that were running for over a
components may be excused for thinking 1250 MPa strength, alloy steel was specified, decade. The major problems for aerospace are
that cadmium plating is a thing of the past. with cadmium always used as sacrificial firstly that there is no coating that behaves
For these industry sectors, cadmium plating coating. For the later variants, such as A340- exactly the same as cadmium. Possible
was eliminated many years ago, and 600 in 2001, most of the steel parts were alternative coatings have problems such as
replacement coatings have been the carried over into the new plane, and only corrosion resistance on steel, lack of coverage
standard for a generation. where strengthening was required to support in sockets and recesses, torque-tension, or
the extra load were alternate materials high friction in interference fits. Secondly, the
Throughout this time the aerospace industry chosen. zinc based coatings that were the
has continued to be exempt from this ban, replacements for cadmium in the automotive
and designers have specified cadmium, as a After these, the next major Airbus project was industry cannot be used in contact with
sacrificial coating to prevent galvanic A380, and initially restrictions on the use of aviation fuel. So the steel or stainless steel
corrosion, in successive new projects. Millions cadmium were imposed. But alternative fasteners in aircraft wings or tails, which are
of fasteners are cadmium plated every year standards had not been developed, and there also the fuel tanks, cannot use the normally
for aircraft use. A few years ago, the electrical are still many cadmium plated bolts, nuts and accepted replacement formulations.
and electronics industries were the largest studs in the design. Normally, if any variants
of A380 are designed, In the absence of a satisfactory replacement
the existing fasteners are coating for use on steel, aircraft manufacturers
always specified except if have turned to alternate fastener materials
higher strength is an such as stainless steels, high strength
issue, so there is titanium, and nickel based alloys, which are
potential for future A380 much more expensive than alloy steels. It
variants to have would be very expensive to retrospectively
cadmium also. engineer these new materials into the existing
alloy steel applications. It remains to be seen
The military transporter whether further European community bans are
Courtesy of Airbus S.A.S A400M has fewer imposed which affect the aerospace industry.
applications with
users of cadmium, but the European ban on cadmium. Here, many alternate materials
cadmium in new electrical products from July have been selected instead of alloy steel, for
Trent 900 engine
2006 means that aerospace is probably the example nickel based alloys. Alternative nuts
biggest user since then, with cadmium plated were a problem however, because the
fasteners almost certainly the biggest alternative standard parts had not been
individual class of items. However, the developed, so there are cadmium plated steel
manufacturers of large commercial aircraft nuts and some bolts and studs also in the
now have self-imposed restrictions, and design.
cadmium is only specified in special
circumstances. The philosophy for A350, due to fly in 2012, is
for a total ban on cadmium. So this self
Aircraft engine manufacturers have virtually imposed restriction is now aligned with the
eliminated cadmium plated fasteners from external bans. However, it can be expected
their products. The last remaining threaded that Airbus will be manufacturing some of the
fasteners with cadmium plating were, existing aircraft for at least another 20 years,
eliminated from new designs over twenty so unless bans are imposed on the actual
years ago, so it is only rarely that they are plating operation, cadmium will be required
manufactured for spares for old engines. for that period.
The main European airframe manufacturer, Aircraft manufacturers have sought to find a
Airbus, has gradually changed its philosophy replacement coating for many years. In
towards cadmium in new designs over the Europe, British Aerospace and Airbus have had
last few years. A330/A340 were designed in many research programmes to evaluate
the late eighties / early nineties, and the possible alternative coatings, for example in
Courtesy of Airbus S.A.S
A320 series before that, all without restriction group sponsored projects like RECAP, REFOCUS,
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