skip to main content
 
  Cadmium Plating  

Cadmium plating plays an important role in a number of key manufacturing areas. Poeton expect this to continue well into the future. We are therefore committed to maintaining our substantial facility to offer Cadmium plating as a key part of our complete metal finishing service. Poeton is registered with the appropriate authorities and is licensed to this effect, having invested to ensure better than full compliance with statutory obligations.

Equally, we are committed to investigate alternatives, coatings that can match the performance of cadmium without the accompanying environmental problems. To this end, Poeton play a key role within the aerospace industry and the European Community, participating in research and development initiatives to investigate new processes.

Certainly, careful evaluation of applications can often permit use of other coatings that the metal finishing industry offers, indeed as are also carried out by Poeton. However, this is very selective and depends much on the priority property for which cadmium plating was originally selected. So, Poeton continue with confidence to provide certified cadmium electroplating to the highest standards on many exacting applications including weaponry, civil aviation, offshore and safety-related applications.

Some Important Points About Cadmium Plating

Cadmium has many wide and varied uses from batteries (Nickel/Cadmium) to plastic pigments. Electroplated Cadmium coatings represent approximately 9% of Cadmium's total use (December 2007) and as a process of significance to Poeton (Apticote 900L & 900N) we are motivated to ensure our customers have the best information available regarding its properties and uses.

Background

Corrosion destroys one-fifth of the world 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, for example, prevent contact between the atmosphere and the steel. However, if there is damage to such a protective film, corrosion will occur at the break and spread outwards to lift and destroy the film. Similar effects will also occur from the inherent pores in paint films.

Metallic coatings, on the other hand, isolate the steel from the atmosphere by a truly impermeable layer. Cadmium, like other anodic metals such as Zinc, still protects the steel at small gaps in the coating. Slight damage to the coating causes no loss in protection, and while the cadmium itself is subject to corrosion, it is "sacrificing" corroding at a predictably slow rate - up to one-fiftieth that of bare steel, and even less in some severe marine environments.

Cadmium coatings also have good lubricity, easy solderability and other properties that are essential for reliable service life of many engineering components. Cadmium is normally applied by electro-deposition from cyanide or acid solutions in barrels or vats. It can also be applied by mechanical plating, vacuum deposition and metal spraying, but generally only electroplated cadmium is of commercial importance.

Cadmium is a by-product of Zinc production, and it was not until the 1920's that electroplating of cadmium became widely used as a protective coating. Today, the Western World annual consumption of cadmium for coatings is about 1000 tones, which is a relatively small proportion of total cadmium consumption. Over 90 per cent of all Cadmium coatings are deposited by electroplating.

Coating Properties

Cadmium as an electroplated metallic coating has the following advantages:

High Tensile Steels

Most steels are readily electroplated with cadmium and require no heat- treatment, either for stress-relief or for avoidance of embrittlement due to hydrogen entrapped during the process. Base metals of tensile strength above 1100 MPa should not be electroplated with cadmium by conventional methods. Instead, specialised pre-treatment and coating procedures have to be used (Apticote 900L) along with stress-relief and de-embrittlement by way of specific heat-treatment cycles.

Chromate Coatings

After electroplating, and heat-treatment if required, a chromate conversion coating is usually applied, giving the coating its well known iridescent green/brown appearance. A chromate conversion coating adds corrosion resistance, and the protective value increases with the mass of the coating. A thin conversion coating can maintain a bright as-plated finish and does not appreciably affect the electrical conductivity of the surface, nor its solderability. A full chromate conversion coating can double the life of a typical cadmium coating in most atmospheres. Additional protection can be provided by a clear lacquer coating.

Uses of Cadmium Plating

Cadmium coatings are used principally to impart corrosion resistance to steels, and in a great variety of applications which call for other engineering properties of cadmium. The aerospace industries specify cadmium plating to prevent bimetallic corrosion between high tensile steel fasteners and aluminium alloys. Aerospace engineers regard cadmium plating as important 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 for all applications" coating it used to be, primarily due to regulatory actions restricting its use on applications where an alternative coating is not appropriate.

Health Warnings

Cadmium and cadmium plated products are safe to deposit, use and handle normally. However, under certain conditions, cadmium can present a health hazard. Effective respiratory equipment and exhaust ventilation must be arranged when welding or otherwise heating cadmium electroplated products over 250 Deg C, as the cadmium oxide fumes produced are highly toxic. Adequate exhaust ventilation must also be arranged when handling cadmium metal in the form of powders or dusts. Routine precautions taken under the UK COSHH regulations will ensure risks are properly controlled.

Contact us for complete information regarding EEC directives on the use of Cadmium Electroplating, Health & Safety information and reputable sources of independent advice.
Can I Specify Cadmium Plating?

Yes, if the use of cadmium plating is for aircraft, defence, offshore, safety, nuclear or electrical contacts. There are many areas in which use of cadmium is or will be restricted, such as food handling, sanitary and household goods.

Back to the Apticote 900 page