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 900 

Cadmium Plating

APTICOTE 900 is an electrolytic process that can deposit protective cadmium coatings on to a variety of base materials to produce a degree of corrosion protection unmatched by other sacrificial coating systems.

APTICOTE 900 cadmium plating out-performs coatings based on zinc or aluminium in aggressive corrosion situations, including atmospheric, saline and alkaline conditions.

How cadmium plating works

Cadmium provides corrosion protection by its unique 'sacrificial' action. When applied as a coating on steels or other structural metals, it corrodes preferentially and the substrate remains undamaged, even if the coating is scratched. Normally, the cadmium coating is applied with a thickness between 5 and 25µ and its own corrosion rate is less than one fiftieth of that of steel.

Features of cadmium plating
  • Superb corrosion protection
    (> 2,000hrs salt spray)
  • Low friction (0.15 vs steel)
  • Ductile, self-healing
  • Small volume growth when oxidising,
    lower than zinc or aluminium coatings
  • No final grinding smooth, aesthetically
    Pleasing surface as plated
  • Can be chromate passivated for enhanced corrosion protection
  • Zero effluent processing

Benefits of cadmium plating
  • Provides prolonged corrosion protection to your key components
  • Prevents galvanic corrosion between steel fasteners and aluminium
  • Reduces the tightening torque of fasteners and allows repeated dismantling
  • Prevents jamming of fasteners or delicate mechanisms
  • Accommodates your manufacturing tolerances without finishing
  • Helps guarantee the safety of highly stressed components

Why is Apticote 900 better than other cadmium plating?
Salt mist corrosion

The answer is precise process control, bespoke jigging and racking, rigorous quality systems and comprehensive NDT inspection systems. Poeton have made major investments in plating plant, electrical supply systems, operator training and quality inspectors, so that the coating is right first time, be it on single large items or on batch components.

Because of this precise control, defects and imperfections are virtually eliminated, so that the crucial sacrificial corrosion protection given by the coating is maximised.

Fastening torque
Bolt torque

The graph shows test results for high tensile steel bolt torque with a variety of finishes, performed as part of a DoE sponsored research programme. They are the average of ten tests, to a fixed bolt tension, confirming the superiority of Apticote 900 Cadmium Plate.

Applications

Cadmium plating can be used in aeronautical, aerospace, mining, military & defence, offshore and nuclear applications. Cadmium plating can also be used on SAFETY devices in road vehicles, agricultural vehicles, rolling stock & vessels. The use of cadmium plating on electrical contacts in any sector of use is also not restricted.

Chromate Passivation

After electroplating, and heat-treatment if required, a chromate conversion coating is usually applied, giving the coating its well known iridescent green/brown appearance. Such a treatment can double the corrosion resistance, and 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. Additional protection can be provided by a clear lacquer coating.

De-embrittlement

Like many electroplating processes, cadmium plating could involve hydrogen absorption into the substrate. Highly stressed parts should be heat-treated after coating to minimise embrittlement. The heat-treatment conditions depend on the material, and users should provide a comprehensive specification. For metals with a tensile strength above 1100MPa, specialised pre-treatment and coating procedures are required.

For normal, bright cadmium plate, you should specify Apticote 900N. For a low-embrittlement, a duller variety, you should specify Apticote 900L. This is a Low Hydrogen Embrittlement (LHE) form of cadmium plating. LHE Cadmium Plating uses a higher current density, with no brighteners, and the bath chemistry is modified to produce a more porous structure - duller. After LHE Cadmium Plating, de-embrittling is carried out at 190 Deg C for 24 hours, and this can be verified, for instance, by an ASTM F 519 Sustained Load Test or a ASTM F 326 Electronic Measurement. As an example, LHE Cadmium Plate shows no effect of hydrogen embrittlement when exposed to Maintenance Fluids.

Sizes

Poeton can cadmium plate parts up to 3 metres long.

Health and Safety

There are restrictions on the use of cadmium plating for certain applications, and any plated part should not be welded or similarly heated without the use of effective breathing apparatus. (Cadmium oxide fumes are harmful.)

There are very stringent conditions imposed on the plating process itself, and Poeton are proud to say that the Apticote 900 technique is zero-effluent, with all cadmium residues being returned to the bath.

More information about Cadmium Plating

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