Corrosion inhibitor for teflon embedded rod ends. 2

[Urban500]

Hi.

We are flying in highly corrosive environment and we have some problems with corrosion on steel rod ends embedded in Teflon.
Does anyone know how to protect these rod ends from corrosion without damaging the teflon (ordinary grease is of course out of the question). Is there any aviation approved products available?

Thank you.
Urban.

 

[CoryPad]

The rod end is embedded in Teflon? Or there is Teflon embedded in the surface of the bearing elements of the rod end? The rod end is carbon steel? No coating? Need quite a bit more information (strength of rod end, mating part material, etc.) to provide a proper answer. Potenial corrosion protection for parts like this could include cadmium electroplating, IVD aluminium coating, Al-rich coating according to NAS 4006, and others.

 

[Urban500]

Hi.
The teflon is embedded in the surface of the bearing elements, i did not express that correctly sorry. The bearing material is steel. The mission is only for 3-4 months, but the last time we where on that sort of mission we had to scrap all rod ends fitted on that helicopter. What i'm really looking for is some sort of liquid surface protection that won't damage the teflon, i have never heard of such thing but maybe someone else has. There must be people operating aircrafts in this kind of environments all the time.

Thank you.
Urban

 

[WKTaylor]

Urban500.

What harsh environment? Warm, seacoast/abrasive [similar to DNA JP]?

Assume these are self aligning spherical bearing: WHAT [P/N] 'steel rod ends'?

Aren't there equivalent CRES or CRENS rod-ends with the teflon/fabric liner?

Do Your steel parts have corrosion protective plating [cad, Zn-Ni, etc]?

Any value for coating [smothering] exposed metal surfaces with CPC [corrosion preventative compounds]?

Regards, Wil Taylor

Trust Me! I'm an engineer!

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

Unfortunately, in science what You 'believe' is irrelevant – "Orion"

 

[TVP]

Urban,

Just in case you aren't familiar with the term CRES, it means Corrosion Resistant Steel, also known as stainless steel. Any good supplier of aircraft/aerospace bearings will offer a hardenable CRES alloy for aggressive environments.

 

[WKTaylor]

TVP... good point... Abbreviations are a pain without clear definition.

CRES = Corrosion Resistant Steel.
CRENS = Corrosion Resistant Nitrogen [hardened/toughened] Steel.

NOTES.
a. There is a special coating system for bare steel bearing surfaces [spherical and anti-friction, ball, ball/roller-bearings, races, etc] that enhances grease "wetting" for lubrication and [to a significant degree] improved corrosion protection; which is obviously only used for gease lubricated bearings. In a harsh environment, the ability to flush contaminants out the joint with repeted grease lubrication, can be significant for longevity of the bearing.
b. Is there a teflon grease that is compatible with, the teflon liner?

Regards, Wil Taylor

Trust Me! I'm an engineer!

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

Unfortunately, in science what You 'believe' is irrelevant – "Orion"

 

[tbuelna]

Urban500- Can you provide the part number(s) and manufacturer of the rod ends? This will allow us to look at the materials/finishes used.

You noted the rod ends are constructed of a "steel" that did not provide adequate corrosion resistance for your application. I can see where an "economy" type rod end that uses a zinc plated carbon steel body might have corrosion issues on the body surfaces in a humid or marine environment. But even the cheapest rod ends use hard chrome plating on the inner (ball) race, so surface corrosion should not be an issue with this part of the rod end. You can certainly clean, mask and apply some type of paint or coating to surfaces of the existing rod ends that require corrosion protection without damaging the PTFE liner. However you might find that simply buying new rod ends made from corrosion resistant steel would not involve much more cost than coating the existing ones, and it definitely would be less hassle.

For your reference I've attached a catalog page that shows the typical materials and finishes used on an "economy" PTFE lined rod end.

Hope that helps.
Terry

 

[Urban500]

Hi.
Thank you for your responce, I'm new to this page and this far i'm really impressed.
Now there was many questions i'll try to answer them.
The helicopter will be stationed on ship in the sea surrounded by desserts, so really warm.
During previous missions in this area has caused corrosion damage on a lot of parts of the helicopter including landing gear pistons, varios bearings, new wheel rims, gearbox etc. things that normally never corrods.
There is several different rod ens with teflon liner that has corroded but the worst ones is mounted on the flight control servos. The part number is 28007GR87 alt 1650-15-005-3014 (i will try to find out what manufacturer it is during the day). It might be possible to change to greasable bearings but since we have 20 helicopters we don't really want to change the maintenance program for just a few of them. But I will try to find out if we can replace them with higher quality bearings.
Thank you
Urban

 

[tbuelna]

Urban500-

The part no. you provided looks like it is an OEM component from Agusta Westland. If these rod ends are used on a certified aircraft you should not make any unauthorized part substitutions/modifications. The best thing to do is discuss the issue with the aircraft manufacturer (AW?). If this is a common problem with this aircraft model, it is quite possible that there are already approved alternate parts available with better corrosion protection. Manufacturers sometimes do "marinization" of an existing model that upgrades components for service in a marine environment.

Good luck to you.
Terry

 

[WKTaylor]

Urban5oo... observation...

RE this comment You made...

"...During previous missions in this area has caused corrosion damage on a lot of parts of the helicopter including landing gear pistons, various bearings, new wheel rims, gearbox etc. things that normally never corrode..."

The naval environment is exceptionally severe. It sound like these acft were either: (a) never intended to be flown as naval aircraft (Army or USAF missions primarily)... but were adapted to this naval mission for unique reasons [unknown to us] without appropriate consideration of the corrosive environment; or (b) the OEM/Navy failed to specify/apply rigorous corrosion prevention measures [for the naval environment] such as frequent cleaning [water washes, solvent washes, etc], increased frequency lubrication, special added temp coatings [CPC, etc], wipe coatings of lubricant fluids, etc.

A similar trend was noted with a USAF helo adapted from an Army variant, flown in an abrasive-seacoast environment: massive corrosion issues were noted. Boiled down to the fact that the USN/USCG versions were built with significantly greater corrosion protection for the naval environment [better coatings, assy practices, special maintenance requirements, etc, etc] … which were not applied to the USAF or USA variants… even when they could be operated in a similar environment. Sure’nuf the aircraft deteriorated rapidly.


Regards, Wil Taylor

Trust Me! I'm an engineer!

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

Unfortunately, in science what You 'believe' is irrelevant – "Orion"

 

[tbuelna]

I can't believe that something like a landing gear strut would experience surface corrosion even in a marine environment, since these components are usually chrome plated. The same goes for new aircraft wheel rims, which are typically primed and painted using very durable coatings. However, I could see corrosion problems with a gearbox housing made from magnesium being used in a marine environment. Any little nick or ding in the coating of a magnesium gearbox housing exposed to a marine environment would quickly result in corrosion damage.

 

[AeroStructAnalyst]

@tbuelna,
corrosion underneath chrome is really not new especially for landing gear structures when chrome has been applied to the coating surface with incorrect thickness. Nickel under chrome usually comes handy, however, new environmental regulations in aerospace is pushing most OEM to look for alternatives to chrome. Same goes for wheels primed and painted. Corrosions at tie bolt holes, rim flange underneath beads have been observed on a number of wheels in commercial aircraft.

 

[MikeHalloran]

Is it permissible to apply one of those silicone coatings that dries to a nonsticky film? They did wonders for my Cubco ski bindings, otherwise protected only with cadmium plate and chromates, I think.

The only downside I can think of is that I'd want a colored coating to verify complete coverage after a wipedown after every sortie.

Or maybe something like the red goo that can be used to protect battery terminals.





Mike Halloran
Pembroke Pines, FL, USA