-- The Home Page of the Finishing Industry
A website for Serious Education, promoting Aloha,
& the most FUN smiley you can have in metal finishing.
    no popups, no spam
on this site
current topics

topic 4296

Spotting out in Rack plated Acid Zinc components.


Hi and thanks for looking in,

Our Chloride Zinc plated steel pressings are sometimes spotting out with grey dots appearing like a rash after two or three months in store.

Whilst porosity in the steel sheet cannot be ruled out, our experience tells me that spotting does not generally occur in steel pressed components in sheet metal parts not more than 2.00 mm thick. There is something we are doing wrong in our bath maintenance which is causing this. Our normal conc. is like this: Metal 25 -30 gms/lit, Boric likewise, Potassium Chloride 120 -135 gms/lit. Is the brightener system to blame or could any other criteria be the cause of this ?

Many thanks in advance and all the best to readers for the new milennium.

Khozem Vahaanwala
Khozem Vahaanwala
Saify Ind supporting advertiser
Bangalore, Karnataka, India

saify logo


Is this in barrel plating? Do the spots look like they could be lining up with the barrel perforations. This could be perhaps a very mild case of the well known measles of iron contamination.

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


First I would check the iron as Ted recommended. The iron that is able to cause this kind of problem is iron plus 2. Take a small sample (like 100 ml) and add a few drops of hydrogen peroxide. If you get a brown precipitate it means that you have a lot of iron plus 2 contamination. The way to get rid of it is adding hydrogen peroxide or potassium permanganate to turn the iron plus 2 into plus 3 and then to filter out the sludge.

In case you find no iron, raise the concentration of your make up addition agent.

sara michaeli
sara michaeli signature 
Sara Michaeli
chemical process supplier
Tel-Aviv, Israel

Feb. .

Duh. I should have read the title before I asked whether this was barrel plating, huh?

Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


Hey K Vahanwala,

The bath chemistry does not know the difference between the thick and thin metals. The difference is in the steels (pores and / or inclusions). If the steel is spotting out after a few weeks, it's salts in the pores of the steel that is the problem. Surface roughness needs to be limited (spec it out)use a surface profiler to measure the surface of the two steels and use your results to find a pass/fail number for the steels. Other controls may be: better rinsing (alternate hot and cold water rinses can pump out the pores), more thickness in the pores (better throwing power).


Fred Mueller, CEF
- Royersford, Pennsylvania


Thank you all, Sometimes my common sense goes holidaying. It was on vacation when I posted the question!

Khozem Vahaanwala
Khozem Vahaanwala
Saify Ind supporting advertiser
Bangalore, Karnataka, India

saify logo


Dear Sir/Madam.

We are in the business of Electr-Galvanizing of Mild Steel Wires using the Zinc Sulphate solution. We are having a problem of the finished goods getting rusted too soon. We also want to know what we should use as brightener for good finshing and texture.

We really appreciate your kind cooperation in this regard. Thank You.

Mohammad Noor Ali
- Karachi, Pakistan

This public forum has 60,000 threads. If you have a question in mind which seems off topic to this thread, you might prefer to Search the Site

ADD a Comment to THIS thread START a NEW threadView CURRENT TOPICS

Disclaimer: It's not possible to diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations may be deliberately harmful.

  If you need a product/service, please check these Directories:

JobshopsCapital Equip. & Install'nChemicals & Consumables Consult'g, Train'g, SoftwareEnvironmental ComplianceTesting Svcs. & Devices

©1995-2018, Inc., Pine Beach, NJ   -   About   -  Privacy Policy
How Google uses data when you visit this site.