Non-cyanide alkaline silver plating, mobile app
Published

Low pH in E-Coat Bath

We are coating parts in a cathodic epoxy electrocoat with a very low pH. How can we increase the pH in our tank and improve the quality of our coating?

Jose Tirado, Consultant, Ti6 Consulting International

Share

Q. We are coating parts in a cathodic epoxy electrocoat with a very low pH. How can we increase the pH in our tank and improve the quality of our coating? M.R.

A. You do not mention the exact pH you have in your system and what is the acceptable range that your electrocoat supplier has determined for your specific electrocoat material and operation. Also you do not mention the process difficulties or quality issues you have as a result of your low pH.

Low pH in your bath indicates that excess solubilizing acid is present in the system. Excessive solubilizing acid can lead to aggressive post rinses and low film builds due to paint re-dissolution. The amount of acid released during coating deposition in the electrocoat bath is directly proportional to the amount of material being coated in square feet or square meters. In other words, the more you coat the more acid the system generates, and thus the more acid that must be removed from the system to maintain the pH within the required limits. Maintaining your electrocoat bath within the recommended ranges will enable you to operate a very stable electrocoat system and obtain the best possible quality and corrosion performance online, as pH is a measurement of paint solubility and overall bath stability.

pH values are expressed as logarithmic values in a logarithmic scale, so what may appear to be a small change in pH actually represents a large change in the overall chemistry of the paint bath. Long term charting and SPC is used to detect unusual pH swings or trends and prevent future problems.

To increase your pH, you must do one or more of the following:

  1. Dump anolyte
  2. Dump permeate
  3. Add new material to the bath.

The best way to increase the pH will depend on many variables, such as the actual pH and the target where it needs to be, the volume of ecoat tank and permeate post rinses, the type of electrocoat technology and the color of electrocoat, the capabilities of your UF system to generate permeate, the capabilities of your anolyte system to generate and store anolyte, the type of parts you coat, and the minimum and maximum mils your quality system allows.

There is no single answer fits all for all low-pH problems. The time and risk your system is allowed to take to correct the pH will drive the direction to take. A system is not designed to drain large amounts of anolyte or permeate, especially over short periods of time, so proper steps must be taken prior to taking a final decision on how to proceed. Excessive permeate draining can lead to an electrocoat system that does not want to coat at low voltages.

Also, you have to be careful to correct the root cause of the problems that got you where you are now with the low pH. If you don’t eliminate the process or systemic root cause(s) that created the low pH, then your system will return to this condition again sometime in the future, and the correction will be temporary and wasteful.

Typical low-pH conditions encountered in an electrocoat system are related to the anolyte system. Leaky anolyte cells with holes and tears or plugged anolyte membranes are typically the root cause of most pH problems in electrocoat systems. In this case, you must fix or replace the damaged anolyte boxes or membranes and allow the system to reach a new equilibrium in pH. Also, you must check the conductivity set-point and control system to make sure it is functioning properly and that you have the proper set-point for your operation that is consistent with your electrocoat supplier recommendations. Your supplier must be closely involved in any decisions you take and must keep a close eye on the stability and recovery of your bath. 

Your Best Finish Starts With Us!
The Finishing Industry’s Education and Networking Resource
Heatmax Heaters ad with immersion heaters
Filtration Systems
OptiCenter All-in-One OC11
PF Podcast
New Acid-Free Bright Nickel Process
Heatmax Heaters ad with immersion heaters
Pretreatment Washer and Finishing Equipment
Gardner Intelligence
plating and surface finishing additives
find masking products online

Related Content

Sponsored

Masking Solutions Provider CFS Dramatically Expands Capabilities and Capacity

Custom Fabrication & Supplies (CFS) completed a new plant expansion packing 10 times the capacity into twice the space. It dramatically enhances the supplier’s custom capabilities to provide extremely precise and cost-effective masking solutions.

Read More
Powder Coating

Coatings Plant Evolves with Market Trends

Expanding its focus from exclusively serving the RV industry, one of this company’s stand-alone coatings plant has successfully extended its services to additional markets.

Read More
Ask The Expert

10 Ecoat Best Practices

Following this list of guidelines can help to increase the performance, cost effectiveness and quality for your ecoat operation. 

Read More
Powder Coating

Take Full Advantage of Industry Events

As travel plans ramp up for the year, what industry events will you attend? Products Finishing offers a quick look at some of the upcoming opportunities for 2024. 

Read More

Read Next

Sponsored

Masking Solutions for Medical Applications

According to Custom Fabricating and Supplies, a cleanroom is ideal for converting, die cutting, laminating, slitting, packaging and assembly of medical-grade products.

Read More
Parts Cleaning

A ‘Clean’ Agenda Offers Unique Presentations in Chicago

The 2024 Parts Cleaning Conference, co-located with the International Manufacturing Technology Show, includes presentations by several speakers who are new to the conference and topics that have not been covered in past editions of this event.   

Read More
Pollution Control

Episode 45: An Interview with Chandler Mancuso, MacDermid Envio Solutions

Chandler Mancuso, technical director with MacDermid Envio discusses updating your wastewater treatment system and implementing materials recycling solutions to increase efficiencies, control costs and reduce environmental impact.

Read More
cfs masking