Patchy / stained Nickel chrome deposit
We do duplex nickel chrome plating of automobile wheel rims in an automatic plating plant using horizontal rack loading using both cylindrical central anode basket within the rack and external anode baskets. Anode baskets are titanium filled with nickel squares. The nickel plating is traditional Watts bath and the chrome is conventional Chromic acid/sulphuric acid.We have been facing a peculiar type of defect. This appears in the form of bluish white patchy/stained deposit. We have tried the following without much success :
1. Activating chrome dip before Chrome plating
2. Discard of Nickel Drag out more frequently
3. Improved rinse flow after nickel
4. Minimize transfer time from Semi-bright to Bright
5. Addition of Sodium lauryl sulphate to Bright Nickel
The brightener supplier has given us a proprietary salt which he calls Nickel Sequestrant. Addition of this gives relief albeit temporarily. The problem reappears after a couple of days. Can someone suggest what I need to do ?Vijay Rao
an electronics company - BANGALORE, INDIA
You really didn't specify whether you saw this in the Nickel or only after Chrome plating. If the Nickel looks fine then a close look at the Chrome is necessary. Temperature imbalances can cause this.
There is also a common problem called whitewash. This usually occurs with older solutions with high levels of metallic contamination. These trace metals seem to plate out in the lower current densities causing a haze. My troubleshooting rule of thumb has always been to work my way back from the process where the defects first become obvious.
Anoplex - Dallas, Texas USA
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