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Powder Coating - fail impact test (160 in-lbs) and Salt Fog Test 500hrs

I have problem to get my sample panel to pass the above requirement after powder coating.
Before coating we had applied required stages of pre-treatment including Zinc Phosphating. The base material used is GI (Galvanized Iron) without chromate. Impact test as per ASTM D2794. Salt Fog test as per ASTM D1654, ASTM B117 and ASTM D610. Please help me if you have any experience like this.

Nur - QA Engineer

Nur H
fabrication and finishing - Malaysia
April 16, 2008

simultaneous replies

This reply is the same as my reply to another similar question on this forum.
Unfortunately, you inform us of the problems you are experiencing but no more. What type of powder (I presume it is not coffee or cocoa-powder°°)? What type of powder? What metal temperature do you achieve (not oven temp)? What film weight is being achieved? Once those bits of information are provided then you may get some answers from the experts.

Terry Hickling
Birmingham, United Kingdom
April 19, 2008

April 20, 2008

Assuming your pretreatment is good, have you checked the paint for proper cure? Contact your vendor for information about the overbake temperature and time. I've run into situations where parts were obviously clean and properly prepped before paint. We could easily scrape the paint off, and they'd fail in NSS in less than 48 hours. However, when we really baked the paint, it stuck like glue and the parts passed NSS without a problem.

If you haven't ruled out pretreatment, try taking some test parts and cleaning/prepping them very, very, very well. Make sure there's no chance of contamination or improper treatment.

If you're unsure of both, make up a quick DOE matrix that considers pretreatment and paint cure to see what the main cause is.

Christian Restifo
- Pittsburgh, Pennsylvania

June 11, 2008

For a powder to be perfect in all the sense, it should meet the following three criteria:
1. Good pretreatment of metal
- This as you mentioned, with zinc phosphating should take care. You can send some sample to labs analyzing Zn phosphate micron thickness coating.
2. Good curing
-Get to know from your supplier on what is the curing temp and time for this powder that you are using.
-Get your oven calibrated to show you the right temperatures.
3. %Resin in powder has to be optimum I guess it is somewhere around minimum of 70% for a good powder.
Lower the specific gravity, better is the powder.
- Ask your suppliers for %resins,plate test,sp. gravity specs and get the one with best cost and lesser sp. gravity,higher resins and higher value of plate test should help you to choose the right powder.

Check with your powder supplier on whether the tests you are doing are passing at their end or no. You may end up changing your powder.

All the best

- Old Goa, Goa, India

Since your dealing with zinc phosphate, check and see if the phosphate coating is coming off with the paint. You may have poor rinsing prior to the phosphate application.

Ron Zeeman
Coil Coating - Brampton, ON, Canada
July 4, 2008

Q. On a plate coated by a powder coating, what should be results of direct and indirect impact test for the electrical panels in normal conditions?

Farshad Amini
consultant - Tehran, Iran
April 29, 2012

A. Hi cousin Farshad.

Your question is a bit out of my area of expertise, but based on the previous answers in this thread, I think you'll get better answers if you can explain the details of your situation. Thanks.


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey
April 30, 2012

May 2, 2012

A. An extremely vague question.
Perhaps flesh the problem out a bit and someone may be able to assist.
Are you referring to reverse impact testing?
What material is the "electrical panel"?
What type & grade of powdercoating is applied?
What specification are you trying to achieve?
Bill Doherty.

William Doherty
Trainer - Salamander Bay, Australia

Q. Hi, I am Farshad from Iran, working in an inspection company in testing and inspection of carbon steel panels coated by epoxy polyester powder coating with specification of of 100 But our test fails at 20 in direct impact and 5 in reverse. Please help me to find the reason.
Thanks a lot

- Tehran, Iran
May 23, 2012

June 5, 2012

A. I would hazard a guess that you have a problem with cure.
It could be inadequate pre-treat but if it were I would expect a more consistent impact vs Reverse Impact failure.
I assume that you are following Powder Manufacturer's recommendations for cure time at metal temperature rather than at air temperature?
Maybe, if you could fully describe your process we could be of more help.

William Doherty
Trainer - Salamander Bay, Australia

Q. Impact test is not successful for 60 kg in powder coating of 2 mm thick MS crc material , the applied powder is str pp, microns is between 80-120. Kindly let me know the proper procedure to pass the impact test

Balu J S
- India
August 7, 2018

A. Hi Balu. There are a number of good suggestions on this page, which start from the assumption that the problem exists despite proper pretreatment since this is probably a more likely cause than poor powder coating. Is your pretreatment zinc phosphating? Thanks.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey
August 2018

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