If I was asked to make a customer wish list, “get my alkaline zinc bath brighter,” would most definitely be near the top of that list. This request would be followed by the comment, “And…while you’re at it, make sure that my bath:
- …does not sacrifice efficiency and throughput, and;
- …continues to maintain consistent metal distribution over a range of current densities”
Making an alkaline zinc bath brighter seems straight forward e
nough. Just add more brightener and you’re all set. Right? If it were only that simple. In reality, brightener additions are more often than not extremely problematic for platers.
Today’s alkaline non-cyanide zinc technology is based exclusively on the use of synthesized complex polymers that are cationic in nature. They carry a positive charge on some portion of the polymeric chain and are co-deposited along with the zinc ions from the cathode film onto the work. These polymers not only provide brightening and leveling, but reduce the bath efficiency especially at high current densities (HCD).
Maintaining HCD is somewhat of a double – edged sword in the plating process. On one hand, the polymeric-based brightener additions enable HCD deposition without burning. However when too much brightener is added to the plating bath, the overall efficiency can be diminished significantly resulting in reduced plating speeds. In the plater’s quest for a brighter product, it becomes very easy to overload the bath and consequently lower plating speed and overall productivity.
Given these concerns, the following recommendations are provided so that your quest for a bright alkaline zinc plating bath will deliver the brightest performance:
- Follow the operating and consumption guidelines as published in the supplier’s technical data sheet.
- When in doubt, laboratory testing can easily be performed by means of a Hull cell. —It will become your best friend.
- Run a Hull cell of a new bath lab sample of the additive system being used. Typically, this would be a 2 ampere 5 minute panel. Pick two points approximately .25 inches from both the HCD edge and low current density (LCD) edge and measure the thickness of deposit. This will establish a baseline and give a ratio of deposition in the HCD vs. the LCD areas.
- Do the same for your working bath. If both of the ratios are close and the panel is of sufficient brightness, then no additional additive is necessary.
- If more brightness is needed, an appropriate addition should be made to the working bath in the Hull cell and another panel should be run. Typically, this should increase the brightness. The thickness at the same HCD and LCD point should be taken and compared. If that ration is similar, then it is appropriate to add more additive.
- If the HCD thickness is significantly reduced, as indicated by a reduced ration of HCD-to-LCD thickness, the polymeric-containing additive should not be added to the bath. Instead, a purifying material or water conditioner additive should be considered.
Following these simple testing procedures should eliminate the problem of additive overload and thus an inefficient and slow depositing alkaline zinc bath. As always, Asterion stands ready to support and optimize all your zinc plating requirements.