Guest Editorial -For Plateworld.com
Don Baudrand, Don Baudrand Consulting, e-mail:firstname.lastname@example.org
Chromium plating problems
There are a number of trouble shooting papers and charts already published in the chrome plating literature. Mostly they deal with adjusting the solution parameters including catalyst ratio, temperature, current density, and chloride contamination. The knowledge of the variables is essential to good chromium plating from hexavalent chrome solutions.
Here are other considerations important to chromium plating.
1. Contamination with iron, nickel, copper, and tri-valent chromium accumulation. Of these only tri-valent chrome can be removed by use of the "porous pot" method.
2. Current source. Ripple. This is the amount of variation from straight line DC. Chromium is particularly susceptible to ripple. 5% is the maximum for good chrome plating. If certain types of rectifiers are used, the ripple percentage goes up as the load on the rectifier goes down. Silicon controlled rectifiers are the worse for ripple. They only have low ripple at full load; the result of ripple is poor coverage and burning. Tap switch rectifiers will have high ripple if the three controls are not at the same setting. Saturable reactor rectifiers have lower ripple at higher loads. Variac (variable transformer) rectifiers keep low ripple even at low loads. These were widely used years ago, less now because of the limited capacity. Up to about 2000 amps. The larger the amperage the larger the transformer must be thus higher cost.
3.Current interruption during plating results in "white areas.
4. High brightener in the nickel solution or organic impurities in the nickel can cause poor chrome coverage in the low current density areas.
5. Very good electrical contact is required to have good covering power. Proper maintenance of racks is important.
6. Chromium contamination of the nickel-plating solution due to entrapment of chromium in splits in the rack coating or nodules of built up nickel and chrome, and generally poor rack maintenance.
I would consider all these before modifying the chrome plating solution.
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