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  #11  
Old 12-13-2006, 01:45 PM
FiveNinerTIM FiveNinerTIM is offline
 
Join Date: Jun 2006
Location: Canby, Oregon
Posts: 18
Default Improvements Don't always mean more cost ...

Power Coating Comments from this thread:

"I was just looking at my newly completed elevator, and saw that the white powder coating was peeling off my elevator horn!!!! "

"Same thing happened to my horns...the coating peeled away at the edges...very frustrating. "

"I have also questioned the quality of the powder coated pieces in the kit. My small aileron pushrods were terrible. "

"My 6A kit from 6 years ago had some iffy power coating on many components."

"My 10 kit has awesome powder coating especially on the engine mount where I had to remove it to weld new tubes on- like granite!"

Being a manufacturing engineer for the past 25 years, I've learned that decreasing variation and improving quality often can be achieved at no cost - its just a matter of understanding and eliminating sources of variation within your current process. (no need to do added cost processing like zinc electroplating if you can achieve "terrible" and "granite" results within the same basic process).

I'm still in the dreaming phase of building an RV, but knowing I've gotten the "terrible" powder coat while someone else got the "granite" one at the same cost would be frustrating and just screams of process variation.

The supplier has no incentive to explore this unless Van's actually says something about it to them. Van's is more likely to say something about it if builders say something about it to them.

I've learned a lot from this forum, and appreciate the opportunity to pipe in once in a while.

Thank you
Tim
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  #12  
Old 12-13-2006, 02:26 PM
jcoloccia jcoloccia is offline
 
Join Date: Sep 2005
Posts: 1,110
Default

Incidentally, if you're really worried about it, just do what I would do next time around. Just ask for the parts with no powder coat. It's a pretty sure bet that SOMEONE in your area is building a tube and fabric plane and probably has a sand blaster lying around you can use.

In my case, the powder coating was acceptable mostly (layed on a bit thick at times, but not too bad) but the color scheme I had in mind would have looked silly with all this white stuff hanging all over the place. Much easier for me to just paint it "right" the first time then to strip it and repaint it.

To put it in perspective, though, of the thousands and thousands of powder coated parts flying in 4500+ airplanes, I haven't read one post anywhere about worrisome corrosion on any of Van's steel. So it's not perfect but it's not THAT bad I guess
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  #13  
Old 12-13-2006, 07:41 PM
Captain Avgas Captain Avgas is offline
 
Join Date: Oct 2005
Location: Melbourne, Australia
Posts: 1,868
Default No QC

Quote:
Originally Posted by JohnR
Typically in a manufacturing situation you should buy on specification followed by price, availibility, etc. as they apply to your needs. Price is always very important but without specifications you don't know for sure what you will get.

Just my $.02 worth.
Absolutely 100% correct. Price is always important but ONLY if all subcontractors are quoting on the same thing...otherwise it is meaningless.

The powdercoating industry in particular is full of sharks. If you don't provide a written specification you will always find some-one who will do a crappier job at a cheaper price. They just cut more corners, such as: inadequate or no degreasing, inadequate or no passivation, inferior powders, insufficient oven temperatures/times (to cut overheads), excessive oven temperatures/times (insufficient staff and/or lack of monitoring). It just goes on and on.

For all of the builders who are advocating the use of Sikaflex for bonding on their canopies I recommend they think carefully about what might be the really weak link...the bond of the powdercoat to the steel (and not just today but down the track when there's corrosive undercreep of the powdercoat due to inferior pretreatment).
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  #14  
Old 12-13-2006, 07:51 PM
TShort TShort is offline
 
Join Date: Jan 2005
Location: Indianapolis, IN (KUMP)
Posts: 1,024
Default

Quote:
Originally Posted by Captain Avgas
For all of the builders who are advocating the use of Sikaflex for bonding on their canopies I recommend they think carefully about what might be the really weak link...the bond of the powdercoat to the steel (and not just today but down the track when there's corrosive undercreep of the powdercoat due to inferior pretreatment).
I thought those that were using sikaflex sanded off the powdercoat before bonding the canopy to the frame ... ?

T.
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RV-10 N410TS bought / flying
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1948 Cessna 170 N3949V
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  #15  
Old 12-13-2006, 08:01 PM
Low Pass's Avatar
Low Pass Low Pass is offline
 
Join Date: May 2006
Location: Houston
Posts: 2,012
Default

Quote:
Originally Posted by Captain Avgas
Absolutely 100% correct. Price is always important but ONLY if all subcontractors are quoting on the same thing...otherwise it is meaningless.

The powdercoating industry in particular is full of sharks. If you don't provide a written specification you will always find some-one who will do a crappier job at a cheaper price. They just cut more corners, such as: inadequate or no degreasing, inadequate or no passivation, inferior powders, insufficient oven temperatures/times (to cut overheads), excessive oven temperatures/times (insufficient staff and/or lack of monitoring). It just goes on and on.

For all of the builders who are advocating the use of Sikaflex for bonding on their canopies I recommend they think carefully about what might be the really weak link...the bond of the powdercoat to the steel (and not just today but down the track when there's corrosive undercreep of the powdercoat due to inferior pretreatment).
Tell us (me) more about this zinc coating before PC. Is this for adhesion or sacraficial corrosion coating? What role does anchor pattern play in PC bonding?

The points made about application and prep specifications for PC systems are good, but are equally applicable to other coating systems. And then it can be said that even the tightest spec may be useless without proper QA from the owner or end user.

Good info.
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  #16  
Old 12-14-2006, 03:43 AM
Captain Avgas Captain Avgas is offline
 
Join Date: Oct 2005
Location: Melbourne, Australia
Posts: 1,868
Default

Quote:
Originally Posted by Low Pass
Tell us (me) more about this zinc coating before PC. Is this for adhesion or sacraficial corrosion coating? What role does anchor pattern play in PC bonding?

The points made about application and prep specifications for PC systems are good, but are equally applicable to other coating systems. And then it can be said that even the tightest spec may be useless without proper QA from the owner or end user.

Good info.
Firstly I doubt that many of the builders who are opting for the Sikaflex canopy technique remove the powdercoating...none of the ones that I have personally seen have removed it...they just apply the Sikaflex to the existing powdercoat...and hope for the best.

In response to your question above. The problem with powdercoat is that it is purely a barrier protection. Once the barrier is broken (scratch, crack,etc) the steel underneath can oxidise (rust) and the oxidisation runs underneath the powdercoat destroying the adhesion. That's why powdercoaters normally apply a passivating pretreatment (typically iron or zinc phosphate). Iron and zinc phosphates are a non-metallic coating that inhibits corrosion undercreep and increases the adhesion and durability of the powdercoat.

However iron and zinc phosphates are a relatively poor passivation. If you take a piece of steel that is iron or zinc phosphated and put it in a salt spray cabinet it will rust within a very short time.

Zinc electroplating on the other hand provides far superior corrosion protection of the steel and therefore is significantly better at preventing corrosion undercreep.
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  #17  
Old 12-14-2006, 11:16 AM
az_gila's Avatar
az_gila az_gila is offline
 
Join Date: Jan 2005
Location: 57AZ - NW Tucson area
Posts: 10,011
Question My engine mount

Interestingly enough, I had my engine mount powder coated in Los Angeles near all of the aerospace companies.

The shop said they would prime it before powder coating it, and when asked what the primer was, they said it was military primer - turned out to be the MIL-P-23377 primer mentioned in "primer wars...

Since they had large drying ovens (one car garage size with open gas flames at the bottom), it didn't take long for the primer to dry/cure....

Since this primer is strontium chromate, I guess it provides the sacrificial coating mentioned in the previous post.

However, I hadn't heard of priming before powder coating before, perhaps it's an aerospace thing?

gil in Tucson
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Half completed RV-10 QB purchased
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Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ

Last edited by az_gila : 12-14-2006 at 11:16 AM. Reason: spelling
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