Combating Zinc Growth in Plating Baths

Q: We continually have zinc growth in our chloride zinc plating tank. The costs to cut the bath are killing us. What can we do to prevent this from happening?

A: Chloride-based zinc plating is a ubiquitous metal finishing technology because of its mirror-bright finish, high-temperature tolerance and excellent cathodic current efficiency (>90%). Because of its popular appearance and ability to prolong the life of metal components, the zinc plating market is estimated to grow to $14.1 billion by 2031 (“Zinc Plating Market Size by Product, By Application, By Geography, Competitive Landscape and Forecast,” Market Research Intellect, 2024)

Unfortunately, like all plating systems, acid chloride zinc plating isn’t perfect, and it also suffers from a few drawbacks. The main drawback is metal growth, which results in poor low-current density coverage, or in the case of acid-chloride zinc nickel plating, poor alloy distribution. Metal growth is a result of less-than-ideal current efficiencies (<100%) and spontaneous zinc-anode dissolution due to the acidic nature of these baths.

To combat the inevitable zinc growth in acid chloride plating baths, platers will typically cut the bath to get the zinc concentrations back into range. However, this process not only leads to production downtime, but also lower profit margins through increased chemical consumption and waste treatment. A better way to mitigate zinc growth in chloride zinc and zinc-nickel plating baths is the use of membrane anodes. These innovative technologies use an inert anode that helps lower zin concentrations and a membrane that reduces chlorine evolution for safe operation in chloride-containing plating baths.

Membrane anodes are used in conjunction with zinc anodes and are capable of controlling zinc concentrations by modulating the current split between the two types of anodes. Thus, the use of membrane anodes can eliminate the need for bath cutting. Furthermore, since membrane anodes can be used to mitigate zinc growth, additional strategies may be used to increase production, decrease operating expenses and enhance sustainability.

The ability to control zinc concentrations with the use of membrane anodes enables ideal plating conditions that will aid your plating shop by increasing production. For example, if the bath conditions are tuned just right, a chloride zinc bath can combine excellent thickness distribution (comparable to alkaline zinc) with the high plating rate of chloride zinc. This “Goldilocks” situation leads to higher production and less metal consumption; however, this strategy is not typically adopted because of the resulting decrease in current efficiency and necessity for more frequent bath cuts. This is where membrane anodes can be a game changer. This technology can modulate zinc growth and enable this Goldilocks scenario without the need for excessive bath cutting and wasting of chemicals. In addition, membrane anodes also enable the plater to reclaim the drag-out rinse. This strategy will enable you to reclaim costly commodity chemicals, decreasing your shop’s operation expenses through lowered waste treatment costs and less chemical consumption. Moreover, water reclamation is a great way to enhance your shop’s sustainability, providing a greener future for tomorrow.

Membrane anodes can reduce costly bath cuts, leading to increased profit margins and decreased production downtime. While there is an associated initial investment, the anodes pay for themselves by decreasing waste treatment/chemical consumption and enabling higher production rates. This technology will provide a plating shop with a competitive advantage and the most productive and profitable process available.