Any powdercoating experts here? Facing issues with powdercoating on top of zinc plated mild steel.
I've been having issues with powdercoating on top of zinc plated mild steel sometimes. Have issues like small dots visible instead of a smooth texture.
It looks like how a zit or pimple looks on the skin.
After zinc plating, it is pre heated for 15 mins at 150 degrees celsius. Then sand it with some 80 no sandpaper. Finally powder coat it and cure it again for 20 mins.
Amy inputs would be appreciated. Thanks guys.
Attached some images below:
https://cubeupload.com/im/Temporalator/Screenshot2024061610.jpg
https://cubeupload.com/im/Temporalator/18bScreenshot2024061610.jpg
Edit:
Hi guys, I posted recently about facing issues with powdercoating zinc plated mild steel. And I'm really thankful for all the responses I got. The zit like small dots I had last time were pretty much solved with outgassing.
I am now facing another issue where the product has sort of tiny indents or pinholes. I can get my nail in them. Shared some photos below. If you guys could shed some light on what these are and why this is happening despite outgassing, it would be great.
Currently outgassing the parts at 250 degrees celsius for 30 mins. The curing temperature after that is 200 degrees celsius for 20 mins.
https://cubeupload.com/im/Temporalator/WhatsAppImage2024062.jpeg
https://cubeupload.com/im/Temporalator/f15WhatsAppImage2024062.jpeg
https://cubeupload.com/im/Temporalator/15eWhatsAppImage2024062.jpeg
https://cubeupload.com/im/Temporalator/9caWhatsAppImage2024062.jpeg
Thanks everyone.
How are you prepping the surface beforehand? Pinholes are almost always some contaminant on the piece that gets trapped by the powdercoat and then bubbles up during the cure.
Are you outgassing before powdercoating? I haven't personally powdercoated galvanized steel, but in a previous job I was sourcing steel cases for some of our equipment and for a time we used powdercoated galvanized steel (one of our customers both wanted a colored finish and didn't want to pay for stainless, so we bumped down to powdercoating galvanized steel) and my local supplier walked me through their process in their plant and one of the steps was outgassing the case after bending and before coating as it was a necessary step to prevent pinholes just like these.
The product is cleaned with hcl first. Then a sulphuric acid light rinse. Followed by alkaline zinc plating.
After which there's a black colour dip which has some nitric acid. The end product is black colour zinc plating. And on this we do powdercoating. It's becoming a right pain whenever this happens.
The powdercoating department blames the zinc plating department and vice versa. Leads to a loss of time, material and effort basically.
I'm not sure what outgassing means. Would you mind explaining it mate?
Edit: I just searched up about outgassing. I think you're right, this is what might be happening.
What's the timeframe between galvanizing and powdercoating?
Freshly galvanized steel reacts with the surrounding atmosphere to form a series of zinc corrosion products. In air, zinc reacts with oxygen to form zinc oxide layer. Zinc reacts with water (moisture in the air) forming zinc hydroxide. Eventually zinc hydroxide reacts with carbon dioxide in the air to form zinc carbonate which is the ultimate corrosion layer that protects the underlying zinc and ultimately is the product of galvanizing that provides the corrosion resistance.
Heat breaks down these products to re-expose the zinc coating, which is, in my opinion, what's happening with your pin holes. Pre-heating to outgas the zinc prior to powdercoating should solve the problem. Your galvanizers should already know this, but depending on how long the company has been doing this (and no offense to your workers) it's possible they know how to do what's being done but not why as, in my experience, the how remains as older generations leave the workforce, but the why is rarely handed down as it's not something people seek out/ask and management prioritizes in knowledge sharing.
There's atleast a 2-3 hour gap between zinc plating and powdercoating, usually more. I think the issue lies in outgassing. I'm looking for a consultant to be honest, to help streamline the process. Also looking at Cerakote H as a future alternative.
Not an expert in this particular context, but think like the smell you get from a freshly painted room. The fumes from the paints are the paint outgassing after application, releasing the gasses that were mixed in. Once most/all the gasses are released, the odors from the paint go away.
In this case, I'm envisioning very small pockets of gas which get trapped during the prior processes, kind of like an air bubble when applying a screen protector to a phone.
This reminds me of my issues with my powder coated zinc/steal Model F keyboard. There were all kinds of questionable texture and coating issues when it arrived. Apparently this was common, so I decided to just live with it since it took over four years to actually get made and arrive, but a large area of the powder coat pain is now completely rubbed off.
My ducky brand keyboard isn’t custom or fancy in any way, but I had the same issue. The final surface had a bunch of tiny bubbles across part of it, which quickly came off and peeled away through use, and exposed the metal frame underneath.
Apparently this was the first time Ducky had used that material in their keyboards, and they never issued a proper recall but did offer replacements for a short time after the problem was identified.
Unfortunately I’m not the kind of person to keep my ear to the ground on products I bought, and I didn’t realise it was paint coming off for nearly a year after I had it (I thought it was a stain on the surface, so when I finally got around to giving it a deep clean, I stripped even more paint off trying to scrub the “stain” before I realised what I was doing to it) so I ended up missing out on the window of opportunity entirely.
To skip all that background, if you find a way to re-surface in a way that will stick around, let me know because I’m definitely interested in patching up my keyboard!
We refinish stuff all the time mate. We use a small blowtorch to burn the powder off, sand blast the product, clean it with acid, plate it again. And then powdercoat it.
Usually does the job but is quite a bit of time and effort. If you can take your keyboard to a powdercoating job shop I'm sure they'd help you out.
Oh, awesome! I’ll have a look in my area and see if I can find somewhere that can do it! Thank you!
I think the "proper" way would be to completely strip it and do a fresh coat of paint, but I don't know that even following a guide I'd be able to do a good enough job that I'd be happy with it. I may just strip it and leave it as bare metal (I saw pics of these keyboards in the production process and they looked pretty cool that way).
Hi guys,
Thanks for all your help last time. I had another query, so thought I'd ask the kind folks here again. Have edited my original post highlighting the issues that I am facing. Thanks everyone.
As a completely offtopic aside, I appreciate this as one of the most specific niche asks I've seen on Tildes yet, and a decent answer surfaced.
Keep up the good work everyone!