Powder Coating Al80 Tanks

[CuriousRambler]

Unfortunatly I'm afraid tha the 165°F was written by somebody with a dive shop monkey's education. Unfortunatly it happens all the time, and most of the time we believe what they tell us in the gasstation or at the pump.
I had access to the raw data and results of testing done as part of a engineering groups doctoral thesis that was successfully defended.

Michael

I really hope the people designing and manufacturing my tanks are slightly more educated than your "dive shop monkey."

I get it. I work with aluminum all day every day. I send literally tons of aluminum to plating, powder, and anodizing shops every month. No shortage of that is used in critical applications where failure isn't measured in numbers of dollars, because failure of a component means literally irreplaceable loss. I'm not trying to tell you what you do or don't know about material properties, but I also couldn't care less about what information you "had" access to, or who got a PhD as a result. I have access to a wide variety of materials information and national and international standards. I'm pretty intimately familiar with a lot of them. I've submitted corrections to more than one of them. None of that means anything to me, except that I read boring technical stuff and occasionally spot a typo.

Can it be done safely? Sure, with the right powder (not all are created equal), the right oven, the right operator. Plus knowing EXACTLY the alloy and heat treat the tank in question uses.

Can the average coating shop do it safely? Absolutely not.

Can the advanced shop so it safely? Maybe.

If you want to tell the internet and the world that you think it's no big deal - have at it. But don't put others at risk by failing to point out the risk is immense if you're even slightly off.

More to the point; if others reading this want to trust their lives to some internet stranger who says it's OK, go right ahead.

Personally? I'd stick with the recommendations of the tank manufacturer, even if I'm 100% confident they're padded to reduce their risk.

If you want to powder coat your tanks, educate yourself. Learn what powders your shop is using and find the flow temperatures for them. Educate yourself on the powder coat process - for a lot of folks, a scuba cylinder is just about the worst possible geometry to try to effectively bake. Find the alloy and heat treat information for your tanks. Find the information defining what those numbers mean. All of the pertinent information is out there. I'd almost guarantee you can find a perfectly safe solution. To the OP's question; PLEASE do any finish BEFORE you have the tanks hydro tested. You run the risk of spending money to finish a tank that fails, or screwing up your brand new finish. But more importantly, you'll know with certainty if your finishing process compromised the integrity of the tank.

Or you can just live with them as they are, wear the scars and scuffs like badges of experience, pocket a few bucks for more fills, and not worry about risk.

 

[Diving Dubai]

The ONLY way to prove if teh correct temps were adhered to, and for the fill shop to satisfy themselves without doubt would be for them to carry out a Hardness test on the cylinder, or Hardness and perhaps a tensile test on a representative piece of material that has been subjected to exactly the same processes at the same time

Likely hood of the above.....

 

[Superlyte27]

And just so we're clear, I think a lot of shops will refuse to fill it. Ours definitely will not fill it.

 

[Frogkicker]

I have some experience with specialty coatings, and I have never liked powdercoat. The heat cure is one reason, but durability is misleading to me. Once it starts chipping, it looks like hell and goes down hill fast.

Why even coat it at all? If you want a color, I would recommend a vinyl wrap.

If you dont want that, I would recommend air cure Cerakote. It is cured at ambient temps and is quite a durable finish.

I agree that shops won't fill a tank that LOOKS refinished, and I wouldn't either but it makes me want to know.

If the heat used to cure powdercoat is not ok. How is the powdercoat applied at factory? Seriously...

And @Superlyte27 how do you know it has been recoated? I wouldn't use powdercoat for the reasons above, but I doubt that you could tell my finish from a factory finish.

 

[Superlyte27]

I have some experience with specialty coatings, and I have never liked powdercoat. The heat cure is one reason, but durability is misleading to me. Once it starts chipping, it looks like hell and goes down hill fast.

Why even coat it at all? If you want a color, I would recommend a vinyl wrap.

If you dont want that, I would recommend air cure Cerakote. It is cured at ambient temps and is quite a durable finish.

I agree that shops won't fill a tank that LOOKS refinished, and I wouldn't either but it makes me want to know.

If the heat used to cure powdercoat is not ok. How is the powdercoat applied at factory? Seriously...

And @Superlyte27 how do you know it has been recoated? I wouldn't use powdercoat for the reasons above, but I doubt that you could tell my finish from a factory finish.

Almost 30 years in the industry, with nearly 90% accuracy, I can look at most tanks from 10 feet away and tell you what year original hydro was +/- 5 years. Trust me, we can tell.

We know what colors were popular what years. We know which shades of reds, blues, yellows, etc were offered by which manufacturer. I promise, we can spot a tank that looks out of place. Unless you powder coat a tank exactly the color it was new, but then why bother, and will we question a spotless 10 year old tank.

 

[Hickdive]

To paraphrase from EN ISO 18119 17.1.2,

"For heat treated aluminium alloy (e.g. AA6061) cylinders temperatures of 175 deg C shall not be exceeded"

Since powder coating usually involves temperatures between 175 and 200 deg C then it is not advisable to powder coat aluminium alloy cylinders

 

[LanceRiley]

ok. thanks for all the replies. sounds like a dangerous endeavour. no need to start pulling hairs. the powder coating company is just 1km from my office. it was just an idea.

thanks everyone.. i'll do vinyl

 

[Jim Lapenta]

There are powders that cure using UV light. But they are expensive. The pre melt temp is 130 C for 1-2 minutes. Followed by near-instantaneous UV light curing.
The issue is as others have said, powder is not as durable as people think. It looks pretty to start with, but it will hide some defects and highlight others. Then when it does chip it spreads quickly.
Repainted tanks are problematic because you don't know what's under the paint. Original paints are easy to see they are original. I wanted to have a couple of my sidemount cylinders painted to resemble warp nacelle's. Those who know my usual swim speed would get the joke.
Once I started looking into it, it became prohibitively expensive and soon realized that unless I used the right paint, the normal expansion and contraction of the cylinder would result in micro cracking.
A vinyl wrap could be done if I wanted to go to the expense, except that in the vis process, things like that should be removed.

 

[tmassey]

Once I started looking into it, it became prohibitively expensive and soon realized that unless I used the right paint, the normal expansion and contraction of the cylinder would result in micro cracking.
A vinyl wrap could be done if I wanted to go to the expense, except that in the vis process, things like that should be removed.

And that’s why you find most technical divers’ tanks are brushed or shot finished (plain-metal-looking) aluminum or hot-dipped galvanized steel. It’s not that we don’t like pretty colors, but that they only stay that way for something between a few dives to a few dozen dives. And you can’t “fix” it without risking harm to the tank or strong suspicion on the part of a fill station.

At least the metal-looking tanks stay at a relatively even and consistent level of (ugly?) appearance.

(Personally, I’m a huge sucker for the electric blue or candy-apple red tanks — but only when they’re new. Which lasts about three months for an active diver...)

While I’m at it: vinyl wrap or stickers aren’t a great (or, say, danger-free) idea, either. Much safer than other options, but they can trap water. For example, when you vis a tank, you often find that the maximum damage is along the edges of stickers...

 

[broncobowsher]

While on the subject of finishes, Hydro-dip?