Non-cyanide alkaline silver plating, mobile app
Published

Corrosion Blisters

After 500 hours of salt spray SS testing of our electrocoated parts, we see many blisters but little corrosion increase from the test X-Cut.

Jose Tirado, Consultant, Ti6 Consulting International

Share

Q. After 500 hours of salt spray SS testing of our electrocoated parts, we see many blisters but little corrosion increase from the test X-Cut. Our parts are made of cold rolled steel CRS with 25µ of black epoxy e-coat paint. What causes the blisters if the overall corrosion protection of the part is good? What can we change in the process to make it better? R.M.

 


A. Blisters are one of the major corrosion problems encountered by automotive companies in the field after parts have been electrocoated. Many corrosion analysis and root cause investigations of failed salt spray SS parts by blisters indicate that most common root causes are poor part cleaning and/or rinsing. Both mechanisms leave oils or salt deposits on the part surface that get trapped before the final electrocoat is applied. Those residues, when exposed to the various environmental chemical conditions in the field, or salt spray solution SS in your situation, react with the chemicals in the testing solutions, causing swelling of the electrocoat at the surface. Potential solutions to reduce or eliminate blisters in electrocoated parts could involve one or several of the following:


1) Improving cleaning capability. Cleaning is always one of the most critical steps in the electrocoat process. Ensure that the cleaner you use is the most compatible with the type of oils and contamination present on your parts, and that you maintain the proper concentration, temperature, level of impingement and agitation. Also, you have to make sure you maintain a good dumping cycle for the specific rates and loads of your process. Your pretreatment supplier should be able to help you optimize your cleaner so that the parts are properly cleaned. Ensuring your parts are properly clean is a guarantee your finished product will maintain the corrosion protection needed for your specific application.


2) Improving rinsing and rinse conductivity. The rinses help in removing the residues of process chemicals used prior to electrocoat (cleaners and phosphate).


To minimize the amount of chemical residues left during rinsing, it is recommended that you establish the proper overflow rate and maintain as low of a rinse water conductivity as possible. Typically this is accomplished by using online conductivity meters, automatically feeding fresh or DI water, depending on the rinse tank, and by implementing counterflow rinsing.


By using automatic conductivity meters with a control set point (eliminating the conductivity highs and the lows), the rinse stages are maintained with more consistency. Typically the rinses prior to phosphate are made up of towns or city water, whereas the rinses after the phosphate stage are made up of DI or RO water. Care must be taken to ensure effective rinsing without excessive water use. While it is not always economically feasible to heat or cool a rinse stage, the effects of temperature on the effectiveness of rinse stages should be taken into consideration.


3) Improve or start using your process sealer. Sealers are used as one of the final rinse stages to aid in the prevention of blisters. The sealer passivates any bare metal left by voids in the phosphate coating, as well as neutralizing or inactivating any salts left on the parts by process chemicals from previous stages. The end result is that a sealer further improves a substrate’s corrosion resistance. To obtain the most out of your sealer, it is important to maintain the concentration and pH levels of the sealer bath.


4) Improve final rinse conductivity. Ensure that your last water rinse—after sealer and before electrocoat—is made up with DI or RO water and that the conductivity does not exceed 50 microhms/cm. This will ensure your parts entering the electrocoat tank are clean and without any residues that will be detrimental during corrosion testing or outside exposure.


Regards and good luck! 

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

Related Content

Electrocoating

ECOAT24 Attracts Both Serious Electrocoaters and Novices Alike

The conference, held April 2-4, 2024, in Orlando, Florida, provides the ecoating industry with educational sessions, supplier exhibits and networking with colleagues.

Read More
Electrocoating

CFS Unveils New Hook Locks Parts Racking Solution

New product from Custom Fabricating & Supplies (CFS) prevents part loss during coating processes.

Read More
Electrocoating

An Altruistic Growth Strategy Puts People First

Professional Plating emphasizes investing in its team and fostering a supportive environment on the shop floor.

Read More
Electroplating

Looking Back to Look Forward

Products Finishing reflects on a year of reporting on the surface finishing industry and looks ahead to what may be in store for 2023.

Read More

Read Next

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
regulation

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
Sponsored

Delivering Increased Benefits to Greenhouse Films

Baystar's Borstar technology is helping customers deliver better, more reliable production methods to greenhouse agriculture.

Read More
OptiCenter All-in-One OC11