Chrome plating on prop spinner

[Zreyn]

I have my 1954 170B in the paint shop as I speak & mentioned that I thought it would look good with a chrome plated prop spinner & got a very negative response from the painter. So Iam wandering about the legality of a chrome spinner & why it would be illegal,as the spinner is not structure. Any thoughts? PS it has a 180 lyc & CS Hartzel prop.

[N2865C]

Are you sure you are not thinking about a polished spinner? Just about anyone that doesn't know about polished aluminum and looks at my spinner and prop (and most of the rest of the plane) thinks it's chrome. (Not that I'm braggin or nothin... ) As far as I know the only chrome spinners are on the big Pratt & Whitney’s and the like, although there may well be others. You might not think of the spinner as structural until it flies off in flight due to cracks caused by hydrogen embrittlement, or some other factor that may be caused by the plating process.

Polished props became an issue with the FAA a few years ago, and while they don't seem to be tagging them anymore, prop shops out here won't return a polished prop. I didn't strip and polish my prop....... I just cleaned it really, really, really well until it shined.
If you are interested in stripping and polishing there is good info here.
http://perfectpolish.com/

[blueldr]

I've seen a good many chrome plated spinners, particularly on twins.

[GAHorn]

Polished aluminum and stainless is more common, I believe. Chrome plating existing spinners is tricky, not only for the aforementioned embrittlement issues but also because chrome doesn't do well on aluminum, (most common spinner-material.) I beleive it requires an alloying of a copper-wash before chrome-plate and that creates corrosion issues.
However, I seem to recall that at least one facility has approval to do it on certain spinners.

[GAHorn]

Polished aluminum and stainless is more common, I believe. Chrome plating existing spinners is tricky, not only for the aforementioned embrittlement issues but also because chrome doesn't do well on aluminum, (most common spinner-material.) I beleive it requires an alloying of a copper-wash before chrome-plate and that creates corrosion issues.
However, I seem to recall that at least one facility has approval to do it on certain spinners.

[Zreyn]

I am way too lazy to have a polished anything,that is why I was curious about chrome on the spinner.I certainly dont know anything about chrome plating although have seen many chrome spinners, probably they were all steel,dont kow that either.That being said, there are lots of chrome alum. "things" out there ,probably not on airplanes & maybe they are all thicker than the spun alum of a prop spinner.I have never noticed any of these chrome items having a corrsion issue ie boats, motorcycles,cars etc.But if that in fact is an issue or embrittlement either that would be enough of course to stop that idea in its tracks.I would like to know for sure if it is for real or speculation.Does anyone know for sure or know where I could find out?

[doug8082a]

But if that in fact is an issue or embrittlement either that would be enough of course to stop that idea in its tracks.I would like to know for sure if it is for real or speculation.Does anyone know for sure or know where I could find out?

Hydrogen embrittlement is a "natural" by product of chroming. It is alleviated by baking for at least 3 hours @ 350-400 deg. F.

Here are some excerpts and a link to a good explanation of it:

http://www.moldmakingtechnology.com/art ... 40208.html

When preparing a part for electroplating, the steel needs to be ground and cleaned - usually with an acid. The mineral acid becomes absorbed into the steel, which is then put into the tank to be chromed. In electroplating, only about 20 percent of the electricity used in the process is utilized to apply the chrome. The other 80 percent of the electricity helps to create a side reaction called hydrolysis, which is a chemical process of decomposition involving the splitting of a bond and the addition of the hydrogen cation (a positively charged ion) and the hydroxide anion (a negatively charged ion) of water.

Unfortunately, this hydrolysis is unavoidable during the electroplating process. When chrome plating, the chrome is applied in layers to assure the proper buildup of chrome throughout the piece. However, this means layers of trapped hydrogen, which at the molecular level is creating hydrogen blisters. When the piece is removed, that hydrogen wants to escape, and does so by creating micro-cracks in the surface - greatly impairing the strength of the piece.


Hydrogen embrittlement is putting an overabundance of stress on the steel, so it makes sense to say that a "stress relief process" to alleviate this unwanted tension is very necessary. Timing is crucial at this point. It is imperative that within one hour of a piece's withdrawal from electroplating that it be put through the relief process. One hour is the maximum permitted wait time - but in dealing with this realistically, sooner is better. What the stress relief process does is basically temper - heat or bake - the piece to allow the hydrogen that is trapped within the chrome to escape with virtually no stress, cracking or weakening, ensuring a strong, efficient part.

[GAHorn]

The process used to alleviate hydrogen embrittlement is known as QQ-P-416 , and is commonly specified when new mfr or rebuilding of landing gear components. I first encountered this issue about 1979 when helping a friend restore a Stearman which had seat rail/tubes which needed re-chroming due to wear.
Dixie Plating (Houston) was selected to de-plate and re-plate the tubes and it was their expert workmen to asked my friend if he wanted them baked per QQ-P-416 . We didn't have a clue what they were talking about, and they sat us down and ... " 'splane to you two whut you need to know 'bout these thangs!"

Spinners may also be nickel plated with a vacuum process that does not cause embrittlement. Just because something is shiney don't mean it's chrome.

[blueldr]

Maybe I stand corrected. I've seen a good many shiney spinners that were obviously plated, not polished, but they may well have been nickle, rather than chrome, plated. I really don't know how I'd tell them apart.

[Zreyn]

Well that certainly is enough info to convince me.Thanks everybody for your comments & info.Iguess I will just have to live with a boring painted spinner with my brand new paint job!Sure wouldn't like the feeling I'm sure I would get in the event of my spinner departing the A/C during flight!