To specify Zinc Nickel Plating correctly, it is necessary to have an understanding of the thickness and the finish options that are available.
Typical Thickness Ranges
The typical thickness of zinc nickel plating is between 5 microns and 25 microns depending on the requirements of corrosion protection. The lightest thicknesses are in the order of 5 microns to 8 microns. These are suitable for lower usage corrosion protection situations where dimensional change to a part is a major concern. For general engineering the typical plating thicknesses are in the range of 8 microns to 15 microns.
How Thickness Is Measured
The thickness of the zinc nickel coating is usually measured by X-ray fluorescence (XRF) and can be specified on the drawing. Typically the thickness is measured on a flat surface, but on drawings for complex parts, cross-section metallography can be called up where necessary, e.g. inside a deep bore.
Surface Finish Options
Zinc Nickel can be coated with a variety of finishes. We have bright, mid-bright and dull (matte) finish. The bright finish is sometimes specified for visible or decorative parts. We would normally specify a mid-bright finish for engineering parts as it gives a good, uniform grey appearance without having too much reflectivity. The dull finish does not have too much glare and topcoats and sealers penetrate better for longer lasting coatings.
Passivation and Topcoat Sealing
Passivation: The plating is passivated with a trivalent chromate layer to enhance corrosion protection. A sealer or topcoat can then be applied to the treated surface to seal the passivation film and to enhance performance in salt-spray testing to in excess of 500 hours. If you are looking for Zinc Nickel Plating, see www.poeton.co.uk/surface-treatments/plating/zinc-nickel-plating/.
What to Put on Your Drawing
Set out thickness (in microns) with a tolerance (e.g. 8-12µm); Finish Type; Trivalent Passivation required; and a reference to a sealer if needed. By also outlining the method of measurement and where measurements are to be taken, you can prevent possible problems when the item is inspected.
Setting specifications on a drawing ensures that the rework that would inevitably follow if left to individual interpretation was avoided in the first place and ensures that good quality is maintained throughout subsequent production batches.
Leave a Reply