DIY Powdercoating?

DIY Powdercoating?

Curt
Curt

August 1st, 2012, 3:24 pm #1

So I designed an R/C plane a biplane.. 'cause I love doing all the difficult/annoying bits twice *sigh*, which has gone from CAD to my workbench in just a few short months --http://www.rcuniverse.com/forum/m_11096359/tm.htm

It's big enough to make use of a smoke generator so I want to add one, they rely on muffler heat and the muffler I am using is this:

http://www.hobbyking.com/hobbyking/stor ... duct=25277

I haven't gotten it yet because it's shipping form Hong Kong but I'm going to assume its polished aluminum (not chromed)

Problem is polished aluminum dissipates heat quickly, and I want to capture it. I would like a matte-black finish, can I DIY powder-coat it? or is there an inexpensive way to get the finish I want? I'd paint (and re-paint it every few weeks :P) if I thought that would work, but I would expect it to flek off in flight and clog the carburetor, which results in something like this:http://www.youtube.com/watch?v=I_b_jYUM ... re=related (1:50 or so)

Any advice would be appreciated.

-Curt
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Gambit
Gambit

August 1st, 2012, 3:36 pm #2

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Doc Nickel
Doc Nickel

August 1st, 2012, 8:50 pm #3

So I designed an R/C plane a biplane.. 'cause I love doing all the difficult/annoying bits twice *sigh*, which has gone from CAD to my workbench in just a few short months --http://www.rcuniverse.com/forum/m_11096359/tm.htm

It's big enough to make use of a smoke generator so I want to add one, they rely on muffler heat and the muffler I am using is this:

http://www.hobbyking.com/hobbyking/stor ... duct=25277

I haven't gotten it yet because it's shipping form Hong Kong but I'm going to assume its polished aluminum (not chromed)

Problem is polished aluminum dissipates heat quickly, and I want to capture it. I would like a matte-black finish, can I DIY powder-coat it? or is there an inexpensive way to get the finish I want? I'd paint (and re-paint it every few weeks :P) if I thought that would work, but I would expect it to flek off in flight and clog the carburetor, which results in something like this:http://www.youtube.com/watch?v=I_b_jYUM ... re=related (1:50 or so)

Any advice would be appreciated.

-Curt
Powdercoating is a heat-curing (or rather, heat-flowing) coating. When applied, the powdered part is put in an oven and baked at around 400 degrees, where the powder literally melts and flows out over the part.

As you might imagine, this is not a suitable application for an exhaust pipe, which should- not just "can", but should - see in excess of 1100 degrees in service. The powder will burn off in the first flight.

The cheap-and-simple fix is of course some flavor or another of "hi heat" spray paint meant for barbecues. It has to be periodically reapplied, but it'll work.

A more expensive solution would be to send it off to a company that does exhaust plating, like the so-called "Jet Hot" coatings, which are a proprietary metallized ceramic applied with a flame gun. (Think "spray MIG".) They're typically not black, but the ceramic aspect acts as a heat reflector/insulator anyway.

Something in between, you might try one of those bake-on firearm coatings, one of the ones with a heavy moly-disulfide content. They're sprayed on and cure at about the same temps as powdercoating, but the cured coating generally (depending on brand) has a fairly high heat tolerance.

Doc.
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sniper1rfa
sniper1rfa

August 1st, 2012, 9:59 pm #4

glow engines for R/C run ridiculously cool - on the order of 250-300*F EGT.
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sniper1rfa
sniper1rfa

August 1st, 2012, 10:07 pm #5

EGT's are still pretty low though. Under 1000*F for sure.
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Johnny Logan
Johnny Logan

August 2nd, 2012, 1:29 am #6

So I designed an R/C plane a biplane.. 'cause I love doing all the difficult/annoying bits twice *sigh*, which has gone from CAD to my workbench in just a few short months --http://www.rcuniverse.com/forum/m_11096359/tm.htm

It's big enough to make use of a smoke generator so I want to add one, they rely on muffler heat and the muffler I am using is this:

http://www.hobbyking.com/hobbyking/stor ... duct=25277

I haven't gotten it yet because it's shipping form Hong Kong but I'm going to assume its polished aluminum (not chromed)

Problem is polished aluminum dissipates heat quickly, and I want to capture it. I would like a matte-black finish, can I DIY powder-coat it? or is there an inexpensive way to get the finish I want? I'd paint (and re-paint it every few weeks :P) if I thought that would work, but I would expect it to flek off in flight and clog the carburetor, which results in something like this:http://www.youtube.com/watch?v=I_b_jYUM ... re=related (1:50 or so)

Any advice would be appreciated.

-Curt
The engine in question is a spark ignition gasoline two stroke. The head and exhaust temps are in the 1000 deg range on the test stand, somewhat lower in flight. Having said that, it has been my experience in three decades of RC flight that the available smoke oils are typically designed to work at the much lower exhaust temps of glow engines, so the higher temps generated by your engine should work plenty well, especially considering the side-to-rear location of the exhaust system. Airflow over the pipe will be limited, thus heat transfer to the air will also be limited. If you wish to paint your pipe, the only thing I can suggest is to paint ONLY the two stacks. Otherwise you will get paint in the carb as it flakes off...

I checked out your design -- As a professional CAD designer, I was pleased to see the detail and thought you obviously put into your drawing. I look forward to seeing the finished model!
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Curt
Curt

August 2nd, 2012, 1:25 pm #7

EGT's are still pretty low though. Under 1000*F for sure.
This is not a glow-powered model, its a gasser which runs at famously high exhaust temperatures. Thats what makes it particularly suitable for smoke, specifically I'll be running a DLE-30cc

http://www.youtube.com/watch?v=YToE-cbD8Q4
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manike
manike

August 2nd, 2012, 2:06 pm #8

So I designed an R/C plane a biplane.. 'cause I love doing all the difficult/annoying bits twice *sigh*, which has gone from CAD to my workbench in just a few short months --http://www.rcuniverse.com/forum/m_11096359/tm.htm

It's big enough to make use of a smoke generator so I want to add one, they rely on muffler heat and the muffler I am using is this:

http://www.hobbyking.com/hobbyking/stor ... duct=25277

I haven't gotten it yet because it's shipping form Hong Kong but I'm going to assume its polished aluminum (not chromed)

Problem is polished aluminum dissipates heat quickly, and I want to capture it. I would like a matte-black finish, can I DIY powder-coat it? or is there an inexpensive way to get the finish I want? I'd paint (and re-paint it every few weeks :P) if I thought that would work, but I would expect it to flek off in flight and clog the carburetor, which results in something like this:http://www.youtube.com/watch?v=I_b_jYUM ... re=related (1:50 or so)

Any advice would be appreciated.

-Curt
Or even aluminum why not simply take it off, media blast it for a matte finish, and then get it anodised black?

Am I missing something? Is there anything inside it other that more aluminium?

That would be a simple and quick solution that would be relatively permanent (although it may go dark brown when it gets hot come to think of it, instead of staying black). That's still better than shiny silver.

Might cost you $10 to get it blasted at a local metal finishing place and $10-20 tops to make it black.
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Curt
Curt

August 2nd, 2012, 2:31 pm #9

if I can get a dark matte finish for $20-$30 that seems reasonable to me.

There is a baffle inside it but I expect that is aluminum too.
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Maker of Toys
Maker of Toys

August 2nd, 2012, 6:17 pm #10

So I designed an R/C plane a biplane.. 'cause I love doing all the difficult/annoying bits twice *sigh*, which has gone from CAD to my workbench in just a few short months --http://www.rcuniverse.com/forum/m_11096359/tm.htm

It's big enough to make use of a smoke generator so I want to add one, they rely on muffler heat and the muffler I am using is this:

http://www.hobbyking.com/hobbyking/stor ... duct=25277

I haven't gotten it yet because it's shipping form Hong Kong but I'm going to assume its polished aluminum (not chromed)

Problem is polished aluminum dissipates heat quickly, and I want to capture it. I would like a matte-black finish, can I DIY powder-coat it? or is there an inexpensive way to get the finish I want? I'd paint (and re-paint it every few weeks :P) if I thought that would work, but I would expect it to flek off in flight and clog the carburetor, which results in something like this:http://www.youtube.com/watch?v=I_b_jYUM ... re=related (1:50 or so)

Any advice would be appreciated.

-Curt
no matter what you do to it.

That said, there's a reason that many heatsinks are **black** and matte finished; for radiative heat transfer, a surface emits heat in direct proportion to its effectiveness as an absorber (emissivity); all other things being equal, a shiny surface has lower emissivity than a matte one. And a rough surface ALSO promotes flow turbulence, which increases convective heat transfer as well.

So, ironically enough, the silvery polished finish may be your best bet for heat retention, unless you want to go to a ceramic coating or a fiber wrap. . . . and if you do that, aluminum isn't my first choice for a substrate, as after insulation, you might get localized hot spots that will soften enough to distort even if it doesn't melt outright.

Unless you want to do something custom in, say, thinwall stainless, a hard silver anodize might be the best/easiest choice. . . . the anodization (aluminum oxide) doesn't conduct heat nearly as well as the bare metal. (of course, with maybe 0.002" of coating the relative effect is going to be miniscule, at best. . . )
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