I wanted to get your opinions on powdercoating of metal parts such as engine mounts and gear legs. Although powdercoating is durable, I have heard that it may hide cracks and corrosion. What do you think?
Tom
Powdercoating
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Dave Clark
- Posts: 894
- Joined: Mon Apr 22, 2002 6:25 pm
Powdercoating has some great uses. Like for trim items and certain control wheels. (Most 170s aluminum wheels are too porous and show defects though. It's usually better to fill the pinholes and paint them with polyurethane enamel.)
Enamel even has limitations in certain places. Wheels for instance. A cracked wheel can be hidden underneath thick enamel. That's why it's better to use lacquer, because a crack will also crack the lacquer. Also, the lacquer is easily stripped with MEK, Acetone, etc. to inspect the wheel.
Powdercoating is a method of electrostatically applying a "powder" of colored plastic, then baking (melting) it to a glossy finish. This is usually done around 400 degrees, which becomes a factor when you consider the use of the base product and/or any attaching parts that might be adversely affected by the heat. The thin plastic coating can remain undamaged even though an underlying weld cracks. That's why I don't feel it should be used on motor mounts. I want to be able to catch any cracks during preflights and during annual inspections. Same thing with springs. (Which by the way, can also have hidden cracks beneath thickly coated polyurethane enamels, which can also be thought of like a coating of plastic.)
Enamel even has limitations in certain places. Wheels for instance. A cracked wheel can be hidden underneath thick enamel. That's why it's better to use lacquer, because a crack will also crack the lacquer. Also, the lacquer is easily stripped with MEK, Acetone, etc. to inspect the wheel.
Powdercoating is a method of electrostatically applying a "powder" of colored plastic, then baking (melting) it to a glossy finish. This is usually done around 400 degrees, which becomes a factor when you consider the use of the base product and/or any attaching parts that might be adversely affected by the heat. The thin plastic coating can remain undamaged even though an underlying weld cracks. That's why I don't feel it should be used on motor mounts. I want to be able to catch any cracks during preflights and during annual inspections. Same thing with springs. (Which by the way, can also have hidden cracks beneath thickly coated polyurethane enamels, which can also be thought of like a coating of plastic.)
You are so right George! The Jet Glow paint on my airplane, was painted when I bought it, hid a rust spot on the main tail spring. The spot was completely hidden by the paint and over time it radiated outwards and finally fractured and broke, causing substantial damage to the rudder and elevators. Thankfully, it was during a non perfect landing and provided me with a great excuse. 
Joe
51 C170A
Grand Prairie, TX
51 C170A
Grand Prairie, TX
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Tom Downey
- Posts: 285
- Joined: Thu Apr 25, 2002 4:50 am
You folks should talk with Victor Aviation, they have proven you wrong.
Do not confuse powder coating with thick paint, it does not act the same.
Do not think all powders are the same, when used properly it is better than paint in all ways. the proper powder for the application will be better every time.
Do not confuse powder coating with thick paint, it does not act the same.
Do not think all powders are the same, when used properly it is better than paint in all ways. the proper powder for the application will be better every time.
Tom Downey A&P-IA
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Dave Clark
- Posts: 894
- Joined: Mon Apr 22, 2002 6:25 pm
Apologies to Tom. It looks like my knowlege base is very dated. I received my Hemmings Motor News today and it had an insert from Eastwood ( http://www.eastwoodcompany.com ) who is a specialty tool supplier.
In there it shows a number of Powdercoating guns and materials with complete setups going for as little as $129. It makes me want to get one and play with it as I have an industrial oven in my paint shop (bought for $50 at Boeing Surplus years ago). Anyway, it sows a primer that has "impressive corrosion resistance and adhesion". Also listed is powder for High Temp header and exhaust manifold applications in four colors including black. (maybe neat for cylinders?)
In there it shows a number of Powdercoating guns and materials with complete setups going for as little as $129. It makes me want to get one and play with it as I have an industrial oven in my paint shop (bought for $50 at Boeing Surplus years ago). Anyway, it sows a primer that has "impressive corrosion resistance and adhesion". Also listed is powder for High Temp header and exhaust manifold applications in four colors including black. (maybe neat for cylinders?)
Dave
N92CP ("Clark's Plane")
1953 C-180
N92CP ("Clark's Plane")
1953 C-180
I have been involved in restoration of many diverse things over the years and have never liked powdercoating. The only way I have figured out to remove it is with a torch. It can't be touched up easily and if it is done by an unskilled or uncaring person, the results are horrible. Bolt holes can get filled and it does fade over the years and I don't know of any way to polish it. In my opinion, powdercoating is good for wheelbarrows and lawn ornaments. It is a great coating, but for things that I do, I would never think of using it. The best corrosion protection you can do is to completely remove all oxidation from the piece and use a good epoxy primer. Randoplate has proven itself to me as the best primer you can use, better than any automotive primer and very reasonable in cost.
Powdercoating is not an approved coating for aircraft engines/cylinders. It retards heat dissipation. It also is not in the coating specifications of the engine overhaul manual.
There are a few engine rebuilders who will sell you a Red/Gold or a Black/Gold or a Purple/Yellow even if you want it and are willing to pay more for it, but what you're paying more for is reduced engine cooling and a cover-up for cracks and defects.
Powdercoating is good for cosmetic things but not functional things. I'll stop repeating myself on this now.
There are a few engine rebuilders who will sell you a Red/Gold or a Black/Gold or a Purple/Yellow even if you want it and are willing to pay more for it, but what you're paying more for is reduced engine cooling and a cover-up for cracks and defects.
Powdercoating is good for cosmetic things but not functional things. I'll stop repeating myself on this now.
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Tom Downey
- Posts: 285
- Joined: Thu Apr 25, 2002 4:50 am
Victor aviation has proven you wrong George, They have proven to the FAAs satifaction that powder coated engines run cooler.
Remember it is not paint, or just powdered plastic, urathane powders actually aid in heat transfer.
Checkem out..
http://www.victor-aviation.com/nav.shtml?company.shtml
Every thing new is not bad.
Remember it is not paint, or just powdered plastic, urathane powders actually aid in heat transfer.
Checkem out..
http://www.victor-aviation.com/nav.shtml?company.shtml
Every thing new is not bad.
Tom Downey A&P-IA
Tom, As you know I have a great deal of respect for you and your knowlege.
But in this case, I believe you've fallen for Victor's sales hoopla. It all reads very nicely. It's B.S. (And even within their sales message, I didn't see them make any claims it "cools" engines. Their claim is primarily that it's simply pretty and remains so.)
Powdercoating is not "paint", it's baked on plastic. Baked paint is just as good, whether it's done chemically (like most catalyst paints) or done by heat (either in an oven or by engine heat.)
The claim Victor makes that IS viable is that a clean surface, either powdercoated OR painted is better protected against corrosion than an untreated or poorly treated (painted) surface. Where they are wrong, in my opinion, is that powdercoating is indeed such a good and durable coating...that it will hide cracks. Not a good thing.
Powdercoating is a relatively thick coating of baked-on plastic. It is not a paint. It will retain heat because it will retain greater amounts of, and not radiate heat as well as paint. (Even the color of the protective coating is important, that's why engines and radiators painted dark colors run cooler than those painted bright colors, and it's why surfaces like interior cowling surfaces are sometimes painted white because they will reflect heat rather than absorb and hold it in the engine compartment. The reflected heat "blows" on out the cowl.) Red/Gold and Black/Gold and powdercoated engines is pure marketing ploy. It's great for show-room looks. It's lousy for parts that need to be cooled and inspected for cracks.
Their claim that the major cause of crankcase cracking is corrosion (allegedly prevented by powdercoating) borders on irresponsible, in my opinion. It's just more unabashed marketing of their product. Surface corrosion due to lack of powdercoating (their implication) is NOT the leading cause, nor even a remote cause of crankcase cracking. Industry-wide accepted causes are: improper annealing subsequent to weld repairs, improper machining operations without stress relief processes, improper assembly, improper bolt torque leading to case-halve working, subsequent cylinder replacement that fails to maintain thru-bolt tensions, and out-of-balance operations due to lack of dynamic balancing. Surface corrosion has never been blamed in any report I've seen, although improper blending of corrosion treated areas might have credence. (But Victor's powdercoating certainly might HIDE any cracks. I guess if you don't see a crack to report it, then it doesn't exist?)
Victor builds a decent engine. They're even better at marketing them to the unknowlegeable. (Bob Hoover performed for 30 years behind genuine TCM reman engines supplied by Rockwell, long before he did a couple dozen shows with engines paid for by the Victor marketing department. There's a joke in here somewhere about his trademark stunt of making dead-stick landings. Does Victor imagine his using their engines for that stunt somehow makes them appear more reliable?)
But in this case, I believe you've fallen for Victor's sales hoopla. It all reads very nicely. It's B.S. (And even within their sales message, I didn't see them make any claims it "cools" engines. Their claim is primarily that it's simply pretty and remains so.)
Powdercoating is not "paint", it's baked on plastic. Baked paint is just as good, whether it's done chemically (like most catalyst paints) or done by heat (either in an oven or by engine heat.)
The claim Victor makes that IS viable is that a clean surface, either powdercoated OR painted is better protected against corrosion than an untreated or poorly treated (painted) surface. Where they are wrong, in my opinion, is that powdercoating is indeed such a good and durable coating...that it will hide cracks. Not a good thing.
Powdercoating is a relatively thick coating of baked-on plastic. It is not a paint. It will retain heat because it will retain greater amounts of, and not radiate heat as well as paint. (Even the color of the protective coating is important, that's why engines and radiators painted dark colors run cooler than those painted bright colors, and it's why surfaces like interior cowling surfaces are sometimes painted white because they will reflect heat rather than absorb and hold it in the engine compartment. The reflected heat "blows" on out the cowl.) Red/Gold and Black/Gold and powdercoated engines is pure marketing ploy. It's great for show-room looks. It's lousy for parts that need to be cooled and inspected for cracks.
Their claim that the major cause of crankcase cracking is corrosion (allegedly prevented by powdercoating) borders on irresponsible, in my opinion. It's just more unabashed marketing of their product. Surface corrosion due to lack of powdercoating (their implication) is NOT the leading cause, nor even a remote cause of crankcase cracking. Industry-wide accepted causes are: improper annealing subsequent to weld repairs, improper machining operations without stress relief processes, improper assembly, improper bolt torque leading to case-halve working, subsequent cylinder replacement that fails to maintain thru-bolt tensions, and out-of-balance operations due to lack of dynamic balancing. Surface corrosion has never been blamed in any report I've seen, although improper blending of corrosion treated areas might have credence. (But Victor's powdercoating certainly might HIDE any cracks. I guess if you don't see a crack to report it, then it doesn't exist?)
Victor builds a decent engine. They're even better at marketing them to the unknowlegeable. (Bob Hoover performed for 30 years behind genuine TCM reman engines supplied by Rockwell, long before he did a couple dozen shows with engines paid for by the Victor marketing department. There's a joke in here somewhere about his trademark stunt of making dead-stick landings. Does Victor imagine his using their engines for that stunt somehow makes them appear more reliable?)
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Tom Downey
- Posts: 285
- Joined: Thu Apr 25, 2002 4:50 am
If your concerns are valid why did the FAA give them an STC for it??
The second question is, why did a minor change need an STC?
As most of you know I work for DOD as an engine mechanic 40 hours a week, as the supervisor and inspector for the T-56 rebuild center at NAS Whidbey.
We build the P-3 Orion engines.
These turbine engines run much hotter than any recip, and we are finding that after we changed to powder coating (Urathane) the corrosion discrepancies have all but stopped on the aluminum castings, the 14 stage exit guide vane runs at about 650 degrees and was in the past cad. plated, EPA does not like CAD so it had to go away, we now have the under water lab at Keyport Wa recover them with an aluminum powder and bake at 850 degrees, the 2 that have been removed after 2500 hours run time were good enough to return to service.
The external bracketing was in the past cad plated, we now have it all bead blasted to bare metal, and powder coated, any that have cracked are easy seen, the powder coating cracks too. because it is well adheared to the surface and when the surface moves the coating moves with it.
Our burner cans had a failure rate of 1500 hours running bare stainless steel, (as designed) we started to powder coating them with a ceramic powder thay no longer fail. I removed a set this week that have well over 10,000 hours on them, they are good to go for another overhaul period.
You see stainless steel will corrode when heated, when coated it does not.
I'll give you that Victor has a sales staff that don't know beans about powder coating.
Paint actually is an insulator, a thick coat will deter the transfer of heat from metal, to the air, urathane, epoxy, aluminum, and ceramic powders are actually bonded well enough to aid in the transfer of heat to the open air.
The second question is, why did a minor change need an STC?
As most of you know I work for DOD as an engine mechanic 40 hours a week, as the supervisor and inspector for the T-56 rebuild center at NAS Whidbey.
We build the P-3 Orion engines.
These turbine engines run much hotter than any recip, and we are finding that after we changed to powder coating (Urathane) the corrosion discrepancies have all but stopped on the aluminum castings, the 14 stage exit guide vane runs at about 650 degrees and was in the past cad. plated, EPA does not like CAD so it had to go away, we now have the under water lab at Keyport Wa recover them with an aluminum powder and bake at 850 degrees, the 2 that have been removed after 2500 hours run time were good enough to return to service.
The external bracketing was in the past cad plated, we now have it all bead blasted to bare metal, and powder coated, any that have cracked are easy seen, the powder coating cracks too. because it is well adheared to the surface and when the surface moves the coating moves with it.
Our burner cans had a failure rate of 1500 hours running bare stainless steel, (as designed) we started to powder coating them with a ceramic powder thay no longer fail. I removed a set this week that have well over 10,000 hours on them, they are good to go for another overhaul period.
You see stainless steel will corrode when heated, when coated it does not.
I'll give you that Victor has a sales staff that don't know beans about powder coating.
Paint actually is an insulator, a thick coat will deter the transfer of heat from metal, to the air, urathane, epoxy, aluminum, and ceramic powders are actually bonded well enough to aid in the transfer of heat to the open air.
Tom Downey A&P-IA
Well, I certainly had hoped this wouldn't deteriorate into some sort of personal slugging match. I feel this resembles a bushwhack attempt, since such sparse info was given in your first messages, and then after my opinion is detailed, suddenly there appears a discourse on high-tech coatings (that do not compare to common plastic powdercoating.)Tom Downey wrote:If your concerns are valid why did the FAA give them an STC for it??
The second question is, why did a minor change need an STC?
As most of you know I work for DOD as an engine mechanic 40 hours a week, as the supervisor and inspector for the T-56 rebuild center at NAS Whidbey.
We build the P-3 Orion engines.
These turbine engines run much hotter than any recip, and we are finding that after we changed to powder coating (Urathane) the corrosion discrepancies have all but stopped on the aluminum castings, the 14 stage exit guide vane runs at about 650 degrees and was in the past cad. plated, EPA does not like CAD so it had to go away, we now have the under water lab at Keyport Wa recover them with an aluminum powder and bake at 850 degrees, the 2 that have been removed after 2500 hours run time were good enough to return to service.
The external bracketing was in the past cad plated, we now have it all bead blasted to bare metal, and powder coated, any that have cracked are easy seen, the powder coating cracks too. because it is well adheared to the surface and when the surface moves the coating moves with it.
Our burner cans had a failure rate of 1500 hours running bare stainless steel, (as designed) we started to powder coating them with a ceramic powder thay no longer fail. I removed a set this week that have well over 10,000 hours on them, they are good to go for another overhaul period.
You see stainless steel will corrode when heated, when coated it does not.
I'll give you that Victor has a sales staff that don't know beans about powder coating.
Paint actually is an insulator, a thick coat will deter the transfer of heat from metal, to the air, urathane, epoxy, aluminum, and ceramic powders are actually bonded well enough to aid in the transfer of heat to the open air.
Firstly Tom, I don't think anyone needs the FAA's approval in order to have valid concerns.
As for your second question re: STC's, I'm not clear on what your point is. So there's an STC. So what? There are STC's for baggage door hold-open springs on Barons that have absolutely no impact on safety or security of the door. Does that make them extra-special-important changes to safety-of-flight items? Of course not. So, suddenly anything the FAA licenses is superfantastic-the-end-of-discussion-and-the-end-of anyone-having-valid-opposing thoughts? Since when has that agency displayed no-fault-thinking prowess?
The processes you described regarding exotic and sophisticated coatings of turbine engine components are unrelated and not relevant to this discussion of common powdercoatings. (And Victor does not rebuild P-3 Orion engines, nor do they use the exotic processes described in that particular application. Further, if they have approval for powdercoating, that approval will not transfer to any other application. But you know that.)
Ceramic coatings are not common powdercoatings available out here in the real world. Same thing with metallic coatings. You are promoting the taste of apples to a group purchasing oranges.
Those types of powdercoatings are not plastic powdercoatings commonly available in the automotive industry which is the process we've been discussing. And even if they were, aluminum jet engine castings are nothing like welded tubular steel engine mounts.
The corrosion resistance benefits of coatings, (virtually any coating by the way) is better than non-coatings. Common knowlege. So what?
Corrosion is not the only concern we have when it comes to engine mounts and other structures. As I previously noted, a thick coating of enamel paint will also hide cracks. I'm glad we agree on that.
If a thick coating of paint will hide a crack, a thick coating of plastic will hide it with even greater durability.
Tom, as you are certainly an experienced mechanic, you are (or should be) acutely aware of the sometimes long-reaching and unexpected effects of minor changes in materials and methods. Powdercoatings (common, plastic powder, electrostatically applied and baked coatings) are durable synthetic coatings that will cover and hide defects in underlying materials. That happens to be one of it's main selling points.
For that reason it is unsuitable for engine mounts and certain other critical structures. For good looking trim cosmetics it's superior (yes, partly because it coats so evenly and completely that it retards corrosion. That's exactly why it's used.)
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Tom Downey
- Posts: 285
- Joined: Thu Apr 25, 2002 4:50 am
GA says
Those types of powdercoatings are not plastic powdercoatings commonly available in the automotive industry which is the process we've been discussing. And even if they were, aluminum jet engine castings are nothing like welded tubular steel engine mounts
Our Air intake housing is 2400 series aluminum. just like the cases in your C-145. we bead blast alodine and powder coat, corrosion is stopped for the life of the engine. abrasion is no longer a problem.
All the T56 brackets are welded 4130 steel. and we use urethane powders that are common market products. Some have cracked, we can see it easy.
What is special about an engine mount? it is a 4130 tube structure. when powder coated it will show cracks just like any structure. Powder coat does not stretch like you think. it will crack right along with the structure under it.
GA says
Ceramic coatings are not common powdercoatings available out here in the real world. Same thing with metallic coatings
WE buy from local suppliers in Seattle, you can too.
OBTW the ceramic coatings are not new the old 3350 & 1820 Wright had ceramic coated exhaust stacks, its nothing more than a ceramic glaze the is used on china dishes.
Granted we should not use the powder that is on your lawn chair, but that does not mean we can't powder coat aircraft structure.
The reason we can't powder coat aluminum structure is simply heat treatment. It will be altered.
Those types of powdercoatings are not plastic powdercoatings commonly available in the automotive industry which is the process we've been discussing. And even if they were, aluminum jet engine castings are nothing like welded tubular steel engine mounts
Our Air intake housing is 2400 series aluminum. just like the cases in your C-145. we bead blast alodine and powder coat, corrosion is stopped for the life of the engine. abrasion is no longer a problem.
All the T56 brackets are welded 4130 steel. and we use urethane powders that are common market products. Some have cracked, we can see it easy.
What is special about an engine mount? it is a 4130 tube structure. when powder coated it will show cracks just like any structure. Powder coat does not stretch like you think. it will crack right along with the structure under it.
GA says
Ceramic coatings are not common powdercoatings available out here in the real world. Same thing with metallic coatings
WE buy from local suppliers in Seattle, you can too.
OBTW the ceramic coatings are not new the old 3350 & 1820 Wright had ceramic coated exhaust stacks, its nothing more than a ceramic glaze the is used on china dishes.
Granted we should not use the powder that is on your lawn chair, but that does not mean we can't powder coat aircraft structure.
The reason we can't powder coat aluminum structure is simply heat treatment. It will be altered.
Tom Downey A&P-IA