Hard Anodising

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or Email anodise@btconnect.com
Company No. 997950
VAT No. 274441654

Properties

HARDNESS

The natural hardness of deposited Nickel Phosphorous gives rise to a tough abrasion resistant surface. Reducing the Phosphorous content down to around 2% maximizes the as plated surface hardness. This can be further enhanced by heat treatment and even further by nitrogen ion implantation. Further improvement in these properties can be gained, please see ‘SPECIAL PROCESSES’

CORROSION RESISTANCE

The Nickel Phosphorous alloy has good, natural corrosion and chemical resistance. Increasing Phosphorous content to 10% or above maximizes this property.  Furthermore full ‘encapsulation’ of the substrate is critical therefore elimination of porosity is necessary. To ensure this, coating thicknesses need to be above 30 microns for the coating to provide protection for use in arduous conditions.

New processes are being developed with our chemistry suppliers to improve corrosion resitance. Please see ‘SPECIAL PROCESSES’.

The chemistry of the solution can be varied to give the coating different properties:

MEDIUM PHOSPHOROUS:  
The most commonly applied E.N. coating
6-9% Phosphorous
Roughly 500 Vpn as plated and up to 800Vpn heat treated
Bright (usually not RoHS compliant)
RoHS compliant (not so bright)
Very stable and reliable with fast plating rates (20-25 uM per hour)
Normal Plating thickness range 3-50 microns

LOW PHOSPHOROUS:
Less than 3% Phosphorous
Very hard coatings in the region of 1000Vpn after heat treatment
Normal Plating thickness range 10-25 microns
Silver-Grey colour

HIGH PHOSPHOROUS
>10% Phosphorous
Very high corrosion and chemical resistance
Non-Magnetic
Normal plating thickness range 25-75 microns.
Silver-Grey Colour.
Slow plating rates 10-12 microns per hour. Short solution life

SPECIAL PROCESSES

ELECTROLESS NICKEL BORON       A boron based reducing agent is used instead of the hypophosphite hence a Nickel Boron alloy is produced. This gives very high as plated hardnesses up to 1100 vpn without the need for heat treatment. Also very good for solderability. A very specialist process with a slow plating rate and very sensitive to substrate.

ELECTROLESS NICKEL TIN             

A new process in which tin is analogous to Phosphorous or Boron . Its specialty is high corrosion resistance for low plating thicknesses. We have had reports of 2000 hours salt spray resistance for as low as 5 microns on some substrates.

It is possible to get a black colour with suitable post treatment.

ELECTROLESS NICKEL PTFE         

In this case fine particles of PTFE are dispersed within the plating solution. The resultant coating has PTFE trapped in the Nickel Phosphorous matrix providing a low coefficient of friction surface. Hardness is about 350 vpn as plated increasing to 450vpn after heat treatment.

This process has a very slow plating rate. 5- 8 microns per hour. The coating is usualy applied over the top of one of the more conventional E.N. coatings. 

ELECTROLESS NICKEL WITH OTHER COMPOSITES

Particles of Silicon Carbide, Tungsten Carbide  and diamond, may be dispersed within the plating solution to achieve hardnesses of in excess of 10,000 vpn.

Because of the nature of the particles involved these processes are very sensitive and require very special manipulation of the workpiece during the plating process

POST TREATMENTS

HEAT TREATMENT

It is said that low temperature (100-120 C) Heat Treatment of Electroless nickel is used to enhance adhesion we think it more likely that the resulting expansion and contraction can expose poor adhesion, ie. If its still ok after heat treatment then adhesion is good!

As higher temperatures are reached 200-400C the plating hardness increases up to around 1000-1100 vpn for low phos. plating.

PTFE DISPERSION

A simple immersion in an aqueous dispersion gives a very thin layer of low co-efficient of friction PTFE which is useful on all reciprocating components, especially in closed systems. In this case the PTFE is present only at the surface of the coating and not throughout  the nickel matrix.

GENERAL CONSIDERATIONS

PRESENTATION:Pieces to be processed must be extremely clean and free of contamination and corrosion damage. We have a multi stage cleaning line with different options for different materials. If our cleaners are unable to remove contamination then either plating will not occur or the plating will loose adhesion to the substrate. It is often the case that such contamination is not visible prior to plating

Surface defects such as pits or cracks may not be fully plated. These features can cause gassing which drives fresh plating solution from the immediate vicinity, or can trap depleted solution both resulting in locally reduced plating thickness. Similarly our cleaning solutions can become trapped and depleted giving rise to poor adhesion.

In short these processes require components to be clean and contamination free, with mechanically even, open surface finish.

COATING THICKNESS:

The various Electroless Nickel solutions plate at different rates, from 25 microns per hour down to 5 microns per hour. Theoreticaly there is no limit to the coating
one could grow, however at high thickness, tiny defects in the substrate seem to be magnified. We have been successful on salvage plating operations in excess of 200 microns, but have found the finish on other jobs to be poor at 100 microns.

The more coating, the more corrosion resistance. ‘Encapsulation’ is the all important goal of plating for corrosion resistance, so at least 30 microns and 50 for belt and braces. Of course cost and coating thickness are pro rata.

Unlike anodising, the plating is entirely additive e.g. 25 micron coating thickness, you must make 50 micron allowance on plain features and 100 microns on threads.

Coating thicknesses can be controlled to +/- 2 microns.