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topic 45155

Powdercoating stainless steel Q&A's, Problems and Solutions


A discussion started in 2007 but continuing through 2018

(2007)

Q. I don't really understand why anyone would want to powdercoat on top of stainless steel, but we recently received an enquiry. The material is very smooth almost polished, and adhesion will not be easy to achieve. Any suggestions? Was considering shotblasting to reprofile the surface for mechanical adhesion.

Geoff Crowley
Geoff Crowley
galvanizing & powder coating shop
Glasgow, Scotland



(2007)

A. Painting stainless is purely cosmetic and won't be resistant to chipping and other adhesion problems. You'll need to CYA if you paint it by making the customer sign something saying that he understands and agree's with the terms. Reprofiling the surface is like taking away the reason the product is made from stainless. Don't do it without his permission unless you want to buy it all back some day.

Sheldon Taylor
Sheldon Taylor
   supply chain electronics
Wake Forest, North Carolina



(2007)

Q. The customer is quite happy to have the SS shotblasted. Like me, he thinks its crazy to powdercoat SS. If PC is the desired finish, then PC over galv mild steel will be adequate. If SS is the desired finish then why PC? (Colour = silver).

Its as crazy as some requests we get to PC over galv steel in "a colour like galvanizing".

Its an interesting point of discussion how far a coater should go in telling a customer that what they want to do is not sensible. We declined a job recently where customer wanted PC on mild steel (not galv) for an indoor swimming pool area. This after long discussions about corrosion.

Geoff Crowley
Geoff Crowley
galvanizing & powder coating shop
Glasgow, Scotland



(2007)

A. Powder coating SS is more common than most would think, powder coating SS gives you many advantages over coating CRS or HRS or all of the pre plated materials out there. The main advantage is that corrosion is at a very small percentage, and SS if prepped correctly it will hold up to adhesion as well as many other destruct test.

DOD/AERO/SPACE

Todd Dirkes
Aero space - Longmont, Colorado


(2007)

A. Hello

I tried to coat over stainless steel sheets using Polyester powder electrostatic spraying & baking.

The stainless steel was brushed finish

We etched the surface with ANTOX

The powder coating was successful.

Phalle MD
- Abu Dhabi, UAE


(2007)

If you have not been able to obtain Antox material try a sample of Anoprime from the UK

Terry Hickling
Birmingham, United Kingdom

----
Ed. note: Chemical names or descriptions of the types of etchants, please, readers -- not proprietary names!



Blisters between stainless steel substrate and powder coating

February 24, 2016

Q. Hi everyone,

We are a painting company from the UK coating mainly automotive parts (interior+exterior). I'm currently trying to figure out the cause of blistering under our paint system on an exterior stainless steel (grade 304) rejected car part from Taiwan.

To put you in context, the process of the part was the following:
- The stainless steel parts were vapour degreased with methylene chloride (no prep before)
- Then degrease wipe
- Powder coating
- Primer
- Basecoat and lacquer

The whole part is covered with blisters. After analysis of the part under the microscope we can see the blisters are coming from the interface substrate/powder (see photos attached).

45155-1a  45155-1b

What do you think caused the blisters ? Is stainless steel porous enough to catch contaminants that couldn't be removed with our cleaning process? (see "holes" in picture)

Thank you very much for your help, please let me know if you need further information to reply to my questions,

Kind Regards,

Audrey Genay
Project engineer - UK


February 27, 2016

A. Sir,
Methylene Chloride is a paint stripper not a solvent degreaser.
That is possibly the beginning of your woes?

William Doherty
Trainer - Salamander Bay


February 2016

A. Hi Audrey. William is deliberately being very gentle :-)

First, as he says, methylene chloride is not a proper degreaser. It sounds quite unusual to me to use it in a vapor degreaser, and I'm not sure whether it is even legal in your jurisdiction. Wiping with a better solvent is sometimes done in unusual situations, but it is not a proper pretreatment.

I would suggest alkaline cleaning or sandblasting, followed by a self-etching primer. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



Durable (Scratch & Chip Resistant) Coatings for Stainless Food Service

March 9, 2016

Q. How are you? I am the Purchasing Manager at a Holloware Manufacturing Co in Bronx, NY. My question is regarding the best fit powder coat solutions for some product line parts. Specifically I have stainless steel food pans that we powdercoat in white. We know for sure that our current supplier is not sandblasting these parts prior to spray coating. That aside we are looking for a more durable coating that is food safe (or that we can certify as such).

We have stumbled upon nylon (Corvel) but don't know enough about it, as well as a "rubber" e-coating that we have heard could possibly be better.

I would like to know your opinions and thoughts regarding.

Thanks in advance for your support.

Kurell Julien
Purchasing Manager - Bronx, New York, US



December 20, 2017

Q. Is there is any problem in Powder coating on polished stainless steel?

Thanks
Akshay

Akshay Patel
Bison Pumps - Conway, Arkansas, USA


December 2017

A. Hi Akshay. I don't think there's any problem in powder coating onto polished stainless steel which has been properly pretreated. But if you are talking about simply powder coating directly onto polished steel, I think I'd expect terrible adhesion problems.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


January 3, 2018

A. Akshay,
I don't think there's any problem per se, but keep in mind you are:

1. Paying extra for stainless steel and then covering it over, making your choice of alloy a moot point.

2. Paying extra for a polished surface which, if anything, probably reduces the adhesion of the powder.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
stellar solutions banner


January 9, 2018

A. It seems to me that this is an ill defined question.
The metal finishing industry in the western world can and has overcome very many challenges over the centuries.
We always come back to the points that:
(1) you must fully define the substrate and it's condition.
(2) you must assess what facilities are available to the artisan.
(3) you must quantify the performance factors required of the finished article.
In this instance it is highly unlikely that organic coating wet or powder is going to provide any mechanical properties, i.e., Adhesion, impact resistance or abrasion resistance.
On the other hand if a purely aesthetic appearance is the key performance criterion then that is achievable.

"A little knowledge is a dangerous thing.
Drink deep or taste not the pierian spring.
There, shallow draughts intoxicate the brain and drinking deeply sobers us again"

In other words fully define the problem and the desired outcome before you can hope for a result.
Hope this helps.
Regards,
Bill

William Doherty
trainer. - salamander bay nsw australia



February 8, 2018

Q. Hello.
I had some work done by a well renowned powder coating company on a stainless steel radar arch.
Now it's gone a year and I can see rust coming on edges and on a few small cracks here and there.
The company says to me that the work he's done is impossible to get that rust.
I've had a other company sandblast it and it had white powder coating on before.
So my question to you is what do you think has happened?

Alex Larsson
- Gothenburg Vastragotaland Sweden


February 2018

A. Hi Alex. Sounds to me like the stainless wasn't passivated before powder coating. If iron from previously used sand contacts stainless steel it will rust. The powder coating probably protected it for a year and that's all.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


March 15, 2018

A. It also sounds like there are microcracks in the stainless. Look at the coating carefully. Good luck.

Harry Hudson
- Durham, North Carolina



April 23, 2018

Q. My question is:
Is there a method other than sand blasting to configure a stainless steel surface for powder coating?

Mahmoud Hassan Okasha
El Sewedy electric industries co - Cairo , Egypt



July 3, 2018

A. I live/work in Florida and we Powder coat all of out exterior 304 stainless steel enclosures to reduce heat. A stainless steel enclosure, unpainted,in the direct sun will reach 300 °F inside the cabinet, but powder coat it bright white and the temperature will stay below 120 °F in full sun. The electronics last much longer if you keep it cooler.

Phil Marjason
Paralee Company Inc - Orlando, Florida


July 2018

thumbs up sign  Excellent point, Phil. Thanks!

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


Want Stainless shiny for looks but etched for powder coating adhesion

July 25, 2018

Q. My situation: I appreciate all of the great knowledge and forum posts that I've had a chance to read through. I'm hoping someone can help me out with a somewhat unique problem. I am powder coating small polished 316ss parts more for decoration then anything. The parts are so small that bead blasting has proven futile. I was trying to find answers towards a chemical etch product that might be available that would help give me more tooth to the polished 316ss but still keep some of the shiny polished look. This is so that I don't have to apply a chrome powder then a topcoat candy powder. My knowledge with all the chemical options is limited.

Thank you for your time

Adam Lathrop
small business/hobbyist - Houston, Texas, USA


July 2018

A. Hi Adam. You already recognize what the actual problem is: that you seek diametric opposites, a very smooth finish for looks and a very toothy finish for adhesion.

We have numerous threads about etching stainless steel, which can be easily found by just using the search term "etch stainless" in the google custom search engine. Ferric chloride is probably the most common and universal etch, but a silver bullet that can both etch and not etch doesn't sound possible. And even if it were, expecting really good adhesion without any pretreatment, which will obscure the shine, doesn't sound promising.

Your idea of chrome-look paint/powder reasonable to me.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



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