Plating Springs and Clips – one of the toughest tasks for plating parts with complex geometry.
Watch Coating Distribution in Tight Coils
Access into the inside of a wound coil is difficult for the plating electrolyte. Thus the centre of the coil will have a thinner coating than the outer surfaces. This coating needs to be of a sufficient thickness to afford adequate corrosion protection. Specifying a minimum thickness at the thinnest point is more relevant than specifying an average thickness.
Address Hydrogen Embrittlement Before It Becomes a Problem
Some materials, especially high-tensile spring steel, are prone to hydrogen embrittlement when subjected to plating processes. Parts can be baked within a few hours of plating at temperatures around 190 to 200°C for several hours to drive out absorbed hydrogen, which can cause cracking at a later time. Springs made from very hard material require special care and baking must be treated with the same seriousness as other processes that could affect the parts and need to be checked for defects. Refer to information on spring material grades and their mechanical properties for harder materials that have tensile strength greater than 1800MPa.
Allow for Coating Build-Up on Functional Dimensions
As to functional dimensions such as pivot pinholes, these need to be plated to a fixed thickness, reflecting the desired functional tolerance. This should be shared with the plater at the outset so that they are plotting from the start to achieve the required thickness. Zinc Nickel typically builds up to surface thicknesses of 8-15 microns.
Choose Passivation to Match the Environment
The corrosion protection of the zinc/nickel coating can be enhanced by a passivation layer. Most automotive components and articles to be used in industrial environments are coated with a trivalent chrome passivation layer, which can be sealed to increase the salt spray resistance up to 1,000 hours or more. Zinc Nickel Coating is covered in more detail at poeton.co.uk/surface-treatments/plating/zinc-nickel-plating.
Prepare Surfaces Carefully Before Plating
Oil, scale, cutting coolant, and heat treatment residues must be removed from all surfaces before plating to ensure good adhesion. Mechanical pre-cleaning is generally recommended, although it is sometimes possible to use pickling. Pickling must, however, be limited to the minimum time required to remove surface contamination to prevent hydrogen embrittlement.
Getting these points right in advance of processing your parts for plating helps to save a lot of time and inconvenience at the inspection stage.
