High temp silver discoloring

[sgunn911]

I am having problems with the Caswell High temp silver discoloring after it heats up. I used two coats and baked according to directions. This is for a major client, and I need to resolve it quickly.







Please HELP! This is after only one flight (about 15 minutes)

[DALE]

My first thought from looking at the pictures is how much was it handled?
It looks like oil from hands burning on the coating.In the photos some spots actually look like finger prints.You may need to run some shorter runs at first to season the coating. This will act as a higher temp baking.

[sgunn911]

How can I prevent the oil from burning on the pipe? As with any engine application, there is going to be oil present. Is there some kind of clear coat available to apply? There has to be a solution to this as this powder is made for headers and hot engine parts.

[DALE]

What did you do to prep it? Was this muffler new?

[sgunn911]

It was chrome, but was stripped and sandblasted prior to coating. The chrome plating on this pipe was flaking, and the manufacturer wanted a solution. The chrom and other plating was completely removed and the aluminum was bead blasted to a shiny finish.

[Noob2PC]

Did you Prebake it after sandblasting? I know that I have to do that or my powder looks like dodo! I have some Valve covers that I have blasted and prebaked 2 times already and I plan on prebaking/outgassing at least one more time.

[sgunn911]

I was under the impression that outgassing is not a problem with aluminum. I didn't prebake, and the coating looked great when it was finished, it was only after using the muffler that it started discoloring. The finish still looks solid, it's just ugly now that it's coloring

[customandsound]

after you out gas clean it again . and the oil from your fingers will show if not cleaned off . i wear rubber toss away gloves when handling all part's ... from what i found about alum. it has alot of little pores and the mixture is not the best on some part's .. the usa part's and coarse and the jap part's are nice to work on

[sgunn911]

The pipe was clean as in the pics even after baking, if the discoloration is from oil, then it came after the final bake while installing and using. The part is going to get dirty during use, and if it's that oil burning there is no way around it. This stuff in person looks like the actual powder is discoloring when you look at it, almost like it's rusting.

[customandsound]

if it is powder form caswell contact them ... you may need to use tech line of it i know them little motors let out some heat ...

[sgunn911]

That's funny, because it is from Caswell and they said to put it on the forum and offered no help.

[bzer1]

To be honest I think your solution is to attack it from the inside. If I remember correctly these heli mufflers are baffels not packed with sound deadeners. You might want to contact the manufacturer and verify. I would use something like a techline thermal barrier (CBC2). What you might be experiencing is wasted fuel burning in the exhaust...very common on R/C helis and planes. Due to the short exhaust manifold the still burning fuel enters the manifold and because it's so short it doesn't have enough time to dispurse the heat. I would try that first. Another problem is that the oil content in the fuel is very high so the thermal barrier might help direct that out as well. I'm wondering weather the exhaust is also settling on the coating and burning in. Hope this helps.

[DALE]

What temp did you bake it on at and for how long?

[Popeye]

Looks burnt to me. Air cooled 4 stroke EGT would be around 1500F.

[Stytooner]

I don't know very much, but I have heard about ceramic coatings for headers. How is this done? What would the color choices be? Just throwing in another monkey wrench.