Home /
T.O.C.
FAQs
 
Good
Books
Ref.
Libr.
Advertise
Here
Help
Wanted
Current
Q&A's
Search 🔍
the Site

Problem? Solution? Chime right in!
(perhaps the world's last 'no registration' site)

-----

"Bad powder coating on steel: Poor wet out surface defects"



September 23, 2018

Q. Hello, we are a company working on steel. We are facing many lack of paint issues especially on the edges of the parts with some RAL composed of epoxy-polyester and polyester. At first I thought of Faraday cage effect, but after checking I realized that we use the tribo system, so this effect is not supposed to occur.

Our pre-treatment is a conversion one based on Zirconium nanocoating. Rinse waters have been checked and rust appearance has been mastered, but issues still appear after powder coating application.

Do you have an idea where these issues may come from?

I attach some pictures of defects:

60844-1a   60844-1aZoom   60844-1b   60844-1bZoom

60844-1c   60844-1d   60844-1dZoom

Thank you

Nadia Bankole
- Cairo, Egypt
^


September 24, 2018

affil. link
High Performance Powder Coating
from Abe Books
or

A. This is almost certainly the result of spraying powder onto a wet substrate and then baking it out.
Hope this helps.
Regards,
Bill

William Doherty
Trainer - Salamander Bay, Australia
^


September 24, 2018

Q. Thank you for your reply, actually parts are well dried (oven) before coating application. This point has been already checked thoroughly.

Regards

Nadia Bankole
- Cairo, Egypt
^


September 2018

A. Hi Nadia. If they are not wet, then they are certainly dirty or inactive. This is not a powder quality or curing problem ... it's a substrate which either due to not being dry or not being clean or not being properly acid activated or having a deficient pretreatment is not accepting the powder properly.

"Powder Coating Complete"
by Nicolas Liberto
from Abe Books
or

affil. link

I suggest sandblasting one sample before sending it through you pretreatment line. I am confident that it will come out fine and will remove your worries about Faraday cages, or other doubts about your powder and its application.

You might also try a sample straight from sandblasting to powder coating and, although it will probably won't prove satisfactory for the long run, I doubt that it will peel and pop at edges and corners like this.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
^


September 25, 2018

Q. Hi Ted, in fact the pretreatment encompasses an acid cleaning, the conversion step. Then, there is the coating process. I made a wettability test just after the cleaning process and it was successful (the dropping water test).
We don't use sandblasting before the chemical process but rather a grinding step as a mechanical activation. Maybe I could explore a sandblasting approach.
What I don't get is that this problem only appears with some specific RAL. On some RAL we don't even face this trouble.

It's not a Faraday cage effect as we use a tribo system and not a corona one

Thank you for your help.

Nadia Bankole
- Cairo, Egypt
^


September 2018

affil. link
Powder Coating Systems
from Abe Books
or

thumbs up sign  Hi again. Well, if you know it's the specific powder then it's the specific powder and there's no more to be said. But it does strike me as very surprising based both on the look of the defects and the fact that the color of a powder coating really shouldn't radically affect your ability to apply it.

I'm always happy to learn something knew, but I wish my confidence level in what I just learned was a bit higher :-)

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
^

Q, A, or Comment on THIS thread SEARCH for Threads about ... My Topic Not Found: Start NEW Thread

Disclaimer: It's not possible to fully 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 might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories:

 
Jobshops
Capital
Equipment
Chemicals &
Consumables
Consult'g, Train'g
& Software


About/Contact    -    Privacy Policy    -    ©1995-2021 finishing.com, Pine Beach, New Jersey, USA