Paint or powercoat

My struts are starting to get some rust on them. I'm debating which to do. I know epoxy paint will work, but I though about powercoating them. I wonder if the heat needed to cure the powercoat would weaken the strut. Crash, you said you powercoat small parts, what about struts?

Tim

I should have said powdercoat
Tim

Tim,
At work we have a one million dollar plus powder
coating system that is close in length to a football
field (big pizza oven).The curing temperature is
425 to 450 degrees and is not high enough to alter
the molecular structure of aluminum or for that
matter any ferrous or nonferrous material.

Mark

I powder coated the jury struts and other assorted steel parts in the wings. I will do the struts on my next project. When I get done with the fuselage I have been rebuilding it is getting powdercoated. I did find out there is epoxy powder and some other kind. One is softened by MEK and the glue we use on fabric but stands up to UV well. The other stands up to MEK and glue but chalks after time when exposed to UV. Maybe someone can expand on this a bit.

Steve,
I'll talk with our coating suppliers and try to find the info
for you.

Mark

Powdercoating Struts

I have been told by one powdercoat outfit here in Alaska, and several other people, that sealed struts cannot be powdercoated. Some risk of an explosion. Real or only perceived I don't know. I was told I would have to drill a relief hole in mine if I wanted to powdercoat them. Not what I want in a set of lifetime struts. Has anyone had there new struts powdercoated. I am going to have to repaint mine too.
Robert

I would think that a ceramic coating would be more beneficial than powder coating,since it is used to protect the interior side of an enclosed chamber more so than the exterior! Most ceramic exhaust coatings are applied to the interior tubes and the by-product is left on the outer coating for looks.

Dennis

Juat a small word on the subject of powder coating from a MAULE driver, seems there is a problem starting to show up in some of the more stressed aircraft,( bush planes being used to the upper limits), there apparently is a problem with the brittle powder-coating getting microscoptic cracks and allowing corrison to migrate along tubing and show up in most unexpected places. There has been several reported agencys moving away from this pratice and looking for a better, more flexable coating, that is easier to inspect and clean off for repair. Most are looking at a more flexiable paint that can move with the tubing without developing these tiny stress cracks, which is what I get when you guys talk about Maule aircraft I just love to fly

I've been a sandblasting and painting contracter for 23 years, and I think the first question that needs to be asked is what you are looking for in the coating system. Generally I look at what the surface I'm coating needs to be resistant to. (moisture, corrosion, rust, or wearability, UV or IR rays etc.) There is a coating to resist the most aggressive environments, and a specific coating works for a specific job.
Bear with me, because I'm not super familiar with the baked on powdercoating systems. I have noticed a lot of interest in them, and see everything from aircraft parts, fuselages, etc., motorcycle frames, and custom hot rod frames done with it.
To my knowledge, correct me if I'm wrong, the two advantages I see in them is superior resistance to UV and IR rays, very good wearability, and an advantage in production facilities, because they can coat it, cook it, and package it at a fast pace. They have baked on enamels, and they have the advantage of being able to bake cure them quickly, and can go right to the box - The same as pole barn sheeting. I don't think these two coatings will cure without heat.
The weak point I see in baked on systems is that the coatings have no rust inhibitve components in them. (zinc, zinc chromates, epoxy chromates, etc.) They protect from exposure from the outside, but not from the underside or inside, and ferrous metal is porous. Moisture WILL pass through it.
I've seen a lot of powder coated weathergaurd truck accessaries start rusting underneath the powdercoat, and because there is no rust inhibitve component to keep it in check, it is able to rust thru completely, and the coating actually traps the moisture underneath it, so it continues to rust until the metal is gone.
I sandblasted and painted a state highway truck box 10 yrs ago that had a load of salt in it from the year before. They dumped it before they dropped it off. Blasted it to white metal, shot it with an epoxy chromate as a primer, automotive finish. It's still spredding salt and no rust.
Only my opinion, but I'd never apply anything that wouldn't stop ferrous metal oxidation (rust) when it started. Even if it were 10 years after it was redone.
I've got an 18A that's been wrecked more times than I have, and have thought that 10-15 years down the road when I go through it, it'd be a good time to do the new wider fuselage. I won't take one unless it's bare, and I'll blast it and give it a good coat of epoxy zinc chromate.
Wilbur

Wilber, it sounds like you know what you'r talking about. I haven't looked, but where do you buy epoxy chromate, I think that's what I'll use.
Thanks

Tim

paint vs powdercoat

Does anyone out there have experience with gear legs that are powder coated? I am planning on getting 3" extended heavy duty gear, and can either get it bare or powder coated. If it comes bare, I can sandblast and epoxy paint myself, just kind of short on time so getting the gear ready to install would be good.

I agree with the other posts about powder coat and moisture getting underneath, but I have seen some powder coating systems that stick like s**t to a blanket, and in areas that get wacked by branches, rocks etc, the powder coat may work better than the epoxy paint systems.

I've powder coated the gear legs and have not had any problems. The coating cracks around clips that hold the brake lines but wire ties work fine. I don't have fabric on the gear.

This discussion should be expanded to the rust protection of the tube's interior. I've had to replace tubes that rusted from the inside out. At minimum the longerons should be line oiled with a rust preventive oil, I would expect the oiling would be after any powder coating.

I had my airframe powdercoated, did a lot of research and decided to go with it. I specified in my purchase order for a zinc rich base primer first, followed by Solar Black Epoxy. I had no trouble with glueing fabric other then you need to wipe it down with acetone before you start because there is a boil off in the oven.

Greg

Correct me if I am wrong, but I am told that there is not a good way to make a repair to a powdercoated part, short of sand blasting it off and starting over? That would be ok if we knew we were never going to have to repair a fuselage before recovering again?

It seems that if one could use a Zinc or Chromate primer, then powdercoat then it would be the way to go on parts like struts, jury struts, gear, steps, wing metal part, (flap hangers, aileron hangers? I can't imagine the heat being a problem, as surely the oven isn't as hot as my Gas Axe?

Tim

I'm working on a source for the 2 part epoxy primers, my past source was Glidden, but they discontinued their product because of the chromates that the regulators are trying to eliminate. There product rep indicated that there might be mil spec source for a product like the old one.

I'm checking all the product suppliers. Glidden's product was $45 a gallon for a 2 gal kit. PPG might still make the DP 40 (or 90) that was similar, but it was $95 a gallon.

I could see the zinc / zinc chromate / powdercoat combination as being a good one, since the powdercoat would have a lot more abrasion resistance than paint in exposed areas, and you'd have rust inhibitve qualities, but Greg's project is the first one where I've heard someone powdercoat and bake over primer without comprimising the primer. It does sound like the way to go if it works.

Mark - Have you had any situations where you needed an epoxy primer underneath the baked on powdercoating? How does the powdercoating industry deal with the corrosion underneath?

Wilbur

I would suggest that some of the problems can be traced back to poor preparation, not chemically cleaning the corrosion (Dupont 5717 S metal conditioner) or waiting to long to prime and/or contamination of the surface by handling bare handed. Dupont (Corlar primer) and PPG (the DP series) are excellent products but must be applied correctly or problems occur. Stits epoxy primer is also an excellent product. I am not convinced that there is a need to use anything else. But as Ray says in the video "follow the manual". How many of us fail to chemically clean the rust, handle the steel with bare hands, or otherwise cause our own problems. Anyone ever start with a wash primer first? Jim

cruiser

wash primers work great in situations where you can't prep the metal in a better way, becuase the do etch the surface, and they're main prupose is to improve adhesion. Blasting is best, because it cleans the surface, removes the oxidized metal, and leaves a profile, or anchor pattern, and gives the primer a "tooth" to improve adhesion. The other advantage is that your rust inhibitive components attach directly to the ferrous metal, instead of having an intermediate coat in between.

I use wash primers anywhere blasting isn't practical, and used it on my ski's because I didn't want the 80 to 100 grit surface left after blasting, and didn't want to set up all the blast equip for a small project.

the dupont and PPG products you mentioned are both good high end primers, I've got to research everything out there again, since the glidden product is gone. And your definetly right about preparation and handling.
I've always said two things- don't build a house on a poor foundation, and- any idiot can paint, (I should know), it's all in the preparation and product.

Wilbur

I've attended a couple Clyde Smith's seminars and he is adamant about avoiding powdercoated parts on a cub. The reasons he cited were exactly what as above -- any damage or scuff to the coating and moisture will penetrate and actually wick between the coating and the metal. There are probably "good", "better", and "best" versions of powdercoating that would minimize the effect, but I'd put my money in a can epoxy chromate.

delete

Paint or Powdercoat

Allright 1st. post here, no flames please! I'm now a Powder Coater & also been building Cubs for quite along time now. Solvent coating a fuselage is a major pain in the butt, alot of tubing & small channel to get into.
First off no paint job is going to preform if not prepaired correctly. Our procedure is to blast with a fine blasting media to the substrate or white metal, then you NEED (this is whats needed for superior powder adhesion) to apply a conversion coating ( or Phosphate ). We are now ready for primer & Top Coat whether it be Powder OR Solvent paint.
Properly applied Powder paint is alot tougher & alot more corrosion resistance. Proven in numerous Salt water test.
If not preped correctly, yes corrosion can travel under the powder & not show immediately due to the fact that the Powder is that much tougher & won't allow the blistering to show so quickly.
Bill; You must thing were a bunch of animals up here ("there is a problem starting to show up in some of the more stressed aircraft,( bush planes being used to the upper limits), there apparently is a problem with the brittle powder-coating getting microscoptic cracks").
If the powder is not cured properly ( long enough ) & allowed to cross link yes it can get microscoptic cracks. If applied & baked correctly it will not crack.
Bye the time we see the tubing flex that far we have Alot bigger problem than worrying about micoscoptic cracks in the powder!!!
If I can help anyone make a decision on which way to go, solvent or powder, please call. I'm not much on this puter thing!
Advanced Powder Coating 1-907-892-3200 Mark

delete

Mark---I know you aren't much on the puter but you might want to explain a little more about your primer. I was real impressed. I was reading these posts and was hoping you would show up as I am not up on the process enough to give these guys the info they need.

Getting back to the original question RPURCELL brought the point up about the sealed lifetime strut going into the oven and being damaged by expanding gasses. I have been told the same thing and if you drill the strut to eliminate this problum the strut is no longer sealed. Have you altered a FAA/PMA part? I would get a answear to this before I spent $$$$ on struts and powder coating.

Cub_Driver

Powder coating struts

Maule has been powder coating there sealed struts for a long time now.

Greg

Powder Coating Lift Struts

Dan Hollingsworth of Dan's Aircraft powder coated a set of front struts. They came out of the oven shaped like a hot dog. The inside pressure made them round. If you put a pressure relief hole in them they then fall out of the "life time" strut catagory and need to be X rayed every two years. The new rear heavy duty Airframe Inc. struts can be powder coated without a pressure relief hole. If you want to powder coat the front struts. Pull the blinds so no one can see what you're doing, unscrew the fork from the barrel, insert a long 1/8" bit and drill a hole in the bottom of the barrel, the barrel comes to a point at the bottom so the hole is automaticly centered. Stand the strut up in the corner with a pan under it to let the oil drain out. Take a 8x32 long tap and tap threads into the hole you drilled. Powder coat the struts. Squirt a 1/8 can of AFT-50 into the struts. Install a 3/8" long 8x32 stainless steel screw with a nylon washer (seal) to plug the strut. Screw the fork into the barrel and tell no one what you did. Not that I would ever do this....I, I, I just heard about it. Crash

P.S. Airframes Inc. has Advanced Powder Coating (Skidmark) powder coat their fuselages and rear lift struts. I powdercoat everything I can, and have been for 10 years. You guys that are still painting need to get a life. One day your liver is going to give up getting all that crap out of your system and you won't have a life.... Super Cub parts are cheap if you've ever priced out a new liver.

Wilbur- Have you found a good primer yet?? I liked Huskys system best, but don't know what it was. They sent me some in a Martin Senior paint can.(10 yrs ago) Last time I used Ditzler, I covered couple days after and it lifted the paint( small area repair).

I'll start diggin for one. I have the mil spec for the epoxy chromate I used to use. Will get back as soon as I find one.
Wilbur

I have powdercoated the fuselage, tailfeathers, gear legs etc. on my L-18C.

The shop I went to never powdercoat bare steel. First coat is always a special Zinc primer which contains 94-96% Zinc. They put on 150-200 um (microns) of Zinc within 1 hr after bead blasting and as soon as possible after the Zinc primer has cured they spray the powdercoat and bake it. All this is done in a controlled environment.

In coastal climate the Zinc primer only (on steel, no powdercoat on top) is consumed at a rate of 20-30 um/yr. That has been verified on those huge oil tanks they have at oil refineries on the Swedish west coast. With powdercoat on top the rate is something like 5-10 um/yr - and that's outside...

A good thing with the Zinc primer is that it "heals" by itself if you get a scratch through the powdercoat and into the Zinc.

I have seen farming machines powdercoated by this shop 20 years ago and they still look like new.

/Mattias

Well I finally did a ton of research on the zinc chromate and epoxy chromate primers. The true zinc chromates are almost non existant. The original ones that worked so well (in my opinion) contained strontium chromate, (the most rust inhibitive component out there, excluding organic or inorganic zinc). Strontium chromate is a known carcinagine (sp) and has been pulled from almost all of the "epoxy chromates" and "zinc chromates". In my opinion, it takes any advantage out of the product. The single component zinc chromates could always be softened with solvent, the polyamine/polyamide two component epoxy chromates generally wouldn't unless you soaked them with mek.
Called Consolidated Aircraft Coatings (who I think bought Poly Fiber, who bought Randolph Products) and they said their EP420/430 contained no chromates, along with PPG, who said their DP-40 and DP-90 contained none.
Here's the particulars on the company I found, and although haven't used the product, am sure would perform better as a rust inhibitor than any other epoxy primer. I don't know how to include a link on this thing, but you can do a search with their name. Their product rep told me they didn't carry a more rust inhibitve primer. Fisheries Supply, Seattle, WA, 1-800-426-6930. U-1201 Yellow Strontium Chromate Epoxy Primer. It's a two part 1 to 1 mix. U-1201 base, U1202 catalist, U-1289 reducer.
I'm not plugging their product, just the fact that this is a true epoxy chromate primer. I couldn't find any others that were.
Wilbur