News Release

Cadmium Plating - The FAQs and Answers

August 2001

 
Along with eggs, beef, rail travel, disposable nappies and a good few other products in recent years, cadmium has been put under the metaphorical microscope and found wanting. Health warnings followed, and within a very short time a ubiquitous coating has become an industrial pariah!
Now Poeton Industries, a world leader in surface coating technology with a significant investment in and capacity for cadmium plating, thinks it's time to look again at cadmium and lay some of the ghosts of this most versatile of surface coatings.
Explains a Poeton spokesman: "Cadmium has many uses - from batteries to plastic pigments - yet electroplated cadmium coating represents only about 9% of cadmium's total use. And like most other products that have been the subject of a health scare, the real problems lie in mis-use rather than use!"
Over 90% of electroplated cadmium is applied by electro-deposition but it can also be applied by mechanical plating, vacuum deposition and metal spraying. Today, the West's annual consumption of cadmium for coatings is about 1500 tonnes - a very small proportion of total cadmium consumption.
So here are a few Frequently Asked Questions and some Answers.
Is there a significant health hazard?
Put into perspective, cadmium and cadmium electroplated products are safe to deposit, use and handle normally. However in certain processing and manufacturing conditions cadmium can present a health hazard.
For example, effective respiratory equipment and exhaust ventilation must be used when welding or otherwise heating cadmium electroplated products over 250ºC, as the cadmium oxide fumes produced are highly toxic.
Adequate exhaust ventilation must also be used when handling cadmium metal in the form of powders or dusts. However, the routine precautions required under the UK COSHH regulations ensure that risks are properly controlled.
Why all the fuss?
Certainly cadmium, like all metals, needs to be monitored and controlled. However it is difficult to establish with any certainty why cadmium has been singled out as a potential risk to human health.
The environmental goal is to prevent cadmium from entering the food chain, yet there is an increasing volume of evidence to suggest that the levels are not significant and are decreasing rapidly.
Is it harmful?
No. Cadmium can be handled just like any other metal. It is only harmful if absorbed into the bloodstream through, for example, smoking (Yes. There is significant cadmium in tobacco!).
Reputable surface treatment companies will happily provide information covering EEC directives on the use of cadmium electroplating, Health & Safety information and sources of independent advice.
Can I specify cadmium?
Yes. If the use of cadmium is for aerospace, defence, offshore, safety, nuclear or electrical contacts. However, there are many areas in which the use of cadmium is restricted, details of which can be found in EC Directives 91/338/EEC and 76/769/EEC.
Why should I?
Corrosion destroys one-fifth of the world's production of ferrous metals annually!
Most methods of protection involve putting an extra layer of some corrosion-resistant material between steel and the environment. Paints and plastics prevent contact between the atmosphere and the steel, but if there is damage to the protective film corrosion will occur at the break and spread outwards, lifting and destroying the film as it goes. Similar effects will also occur from the inherent pores in paint films.
Metallic coatings on the other hand, isolate the steel from the atmosphere with an impermeable layer. Cadmium, like other anodic metals such as Zinc, even protects the steel where there are small gaps in the coating. So slight damage to the coating causes no loss of protection.
And while Cadmium is itself subject to corrosion, it is 'sacrificing' itself at a predictably slow rate of up to one-fiftieth that of untreated steel. Cadmium coatings also have good lubricity, easy solderability and other properties, which are essential for reliable service life in many engineering components.
How does cadmium electroplate work?
Cadmium electroplate coating such as Poeton's APTICOTE 900 is an electrolytic process that can deposit protective cadmium coatings onto a variety of base materials to produce a degree of corrosion protection unmatched by other sacrificial coating systems.
They out-perform coatings based on zinc or aluminium in aggressive corrosion situations, including atmospheric, saline and alkaline conditions
What are the benefits?
They include superb corrosion protection (more than 2,000hrs salt spray), low friction (0.15 against steel); ductile and self-healing, small volume growth when oxidising, no final grinding required and a facility to be chromate passivated for enhanced corrosion protection. All of which adds up to an attractive package for the engineer looking for versatile and cost effective protection.
A cadmium coating also provides prolonged corrosion protection for key components, prevents galvanic corrosion between steel and aluminium, reduces the tightening torque of fasteners and allows repeated dismantling, prevents jamming of fasteners or delicate mechanisms, accommodates manufacturing tolerances without finishing and helps guarantee the safety of highly stressed components.
Which makes cadmium ideal for aeronautical, aerospace, mining, military & defence, offshore, and nuclear applications. It can also be used for coating safety devices in road vehicles, agricultural vehicles, rolling stock and vessels and to protect electrical contacts in critical applications.
What are the typical applications?
The aerospace industry specifies cadmium plating to prevent bimetallic corrosion between high tensile steel fasteners and aluminium alloys. Aerospace engineers also regard cadmium plating as vital for bolts used with engines, major structural members and landing gear, and for fasteners for aluminium sheet.
Nevertheless Cadmium is not the widely used 'cure all' coating it used to be, mainly because regulation restricts its use to applications where an alternative coating is not available or appropriate.
What of the future?
Together with the National Centre of Tribology, leading academic bodies and aerospace contractors, Poeton was a member of the DTI sponsored "RECAP" project set up to seek substitutes for Cadmium Electroplating.
Yet this versatile treatment still offers a unique range of properties for which no single alternative exists now or in the foreseeable future. It still has an important role to play in key areas of manufacturing and this is expected to continue well into the 21st century.
Specialised surface treatment company's such as Poeton continue to maintain substantial facilities to offer cadmium electroplating as part of their metal finishing service. Reputable specialists, who have invested to ensure full compliance to statutory obligations, will have been issued with a permit to operate by the Environmental Agency.
Certainly Poeton is confident to provide certified cadmium electroplating to the highest standards on exacting applications such as weaponry, civil aviation, offshore and safety related applications.
To discuss sample part processing or technical advice call Poeton Industries now on 01452 300500.

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File: Cadmium - Q&A

For further information contact Rowenna Poeton,
Poeton Industries Limited, Eastern Avenue, Gloucester GL4 3DN
Tel: 01452 300500 Fax: 01452 500400 Email: rowennapoeton@poeton.co.uk

For press information contact Dennis Cantillion,
Cantillion King, 16 The Cornhill, Stroud, Gloucestershire, GL5 1AJ
Tel: 01453 755551 Fax: 01453 751525 E-mail: dennis@cka.co.uk

Editors Note
Other important facts about cadmium
De-embrittlement
Like many electroplating processes, cadmium deposition can result in hydrogen absorption into the substrate; so highly stressed components should be
stress-relieved after coating to minimise embrittlement. For metals with a tensile strength above 1100MPa, specialised pre-treatment and coating procedures are required.
Chromate Passivation
After electroplating (and heat treatment if required) a chromate conversion coating that can double corrosion resistance is usually applied, resulting in the well known iridescent green/brown appearance. A thin conversion coating can also be applied to maintain a bright; 'as-plated' finish that does not appreciably affect the electrical conductivity of the surface, nor its solderability. Additional protection can be provided using a clear lacquer coating.
High Tensile Steels
Most steels are easily electroplated with Cadmium and require no heat treatment, either for stress relief or to avoid embrittlement. Base metals of tensile strength above 1100 MPa should not be cadmium plated with conventional methods. Specialised pre-treatment and coating procedures, such as Apticote 900L, must be used together with stress relief and de-embrittlement.

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