How does Chrome Plating work?

[ChrisSarnowski]

Hi Guys,

I'm wondering how hard chrome plating works.

There seems to be some process for chroming car parts, involving copper plate, then nickel plate, then chrome plate.

Is the hard chrome plating for model airplane cylinder liners like that?

Is nickel plating "good enough" since chrome plating chemicals are so nasty? I mean, if we can't get chrome plating done for us, then why not nickel?

Thanks in advance,
Chris

[Phil Krankowski]

OS uses nickle plating.  The nickle is less hard than chrome, so it wears faster.  The piston and liner wear out at about the same time.  With hard chrome several pistons might wear out before the liner wears out.

Hard chrome is a little different from cosmetic chrome.  Cosmetic chrome is a thin layer, and provides significant corrosion protection.  Hard chrome is a much thicker layer, and due to the process of growing crystals has openings to the base metal on a microscopic level, so you get wear protection but not the same corrosion protection.  Engines are full of oil so the corrosion protection is less necessary.

Phil

[John Park]

My 1950 'AeroModeller' Annual contains a fascinating article entitled: 'You Can Chrome Plate Pistons!' by C. O. 'Pop' Wright of Topeka, Kansas.  It was presumably copied from one of the American model magazines, but there is no indication of which one this might have been.  'Pop' described the process in great detail, and it clearly worked for him - I often wonder whether anybody else ever tried it.  As a boy in the mid-1950s, I did once get hold of some chromium trioxide, intending to plate the piston of an old ED 'Bee' diesel, but somehow never got round to it - which was probably as well, in view of what I now hear about chromium plating chemicals!

Regards
John

[ChrisSarnowski]

Hi Guys,

There are probably differences in Nickel plating, too. I read here somewhere that OS nickel is not as hard as Enya's nickel plate for example.

But also - my first question - is there a plating sequence for chroming the brass cylinders, or do you just toss the brass cylinder into the chrome solution?

-Chris
 

[dennis lipsett]

I cannot speak with any knowledge of the chroming process but as a kid I used to go to Franny Wolfs place in Reading and sit on the steps while others did their business. He never allowed anyone near his chroming tanks and I guess that it was because an accidental moving of the parts would probably end up with an out of round cylinder. I do know that one of the waste products was Chromium cyanide. Actually I was more mesmerized by the Dooling 61's and the yellow jacket varieties in particular. Bought my first diesel there, a Mills .08cc(045) that served me well for years.
For the younger set Franny was a pre eminent source of chromed goods in the 40 to 70 era. His fuels were also legendary. Who can for get 'this is it' or purple k actually p+++ and other legendary concoctions.
He never flew airplanes but was totally dedicated to rail and other forms of cars.

Dennis

[Tim Wescott]

Hey Chris, I know that chrome is laid on with an electroplating process, so no, you can't just dump the cylinders into a bucket of chemicals.  You need to have an electrode that goes down through the middle of the cylinder.  Beyond that, I'm in the dark -- I'm not even sure which needs to be the positive and which needs to be the negative electrode.

Have you googled "chrome plating"?

[Brett Buck]

Hi Guys,

There are probably differences in Nickel plating, too. I read here somewhere that OS nickel is not as hard as Enya's nickel plate for example.
 

   Nonetheless, OS nickel plating is good for maybe 3-4000 stunt flights, which is more than most people ever get in their entire lives.

   Brett

[Lauri Malila]

[quote author

There seems to be some process for chroming car parts, involving copper plate, then nickel plate, then chrome plate.

...

[/quote]

It's about decreasing the potential difference and to avoid possible oxydation. Brass can be chromed directly but aluminium requires an nickel layer before chrome. The nickel we have on our AAC cylinders (Mahle#124) is so thin that it's very important to have plating power on allready when the parts are put in chromium acid. Otherwise the nickel is gone in a fraction of a second.
I think our original deposit layer is about 40 microns thick; this thickness is needed to get the desired micro-crack pattern to the surface. Then about 50% is honed away.
In small series, and because I don't like to do grinding in my home-workshop, the chromed cylinders are first pre-honed, then outside shape and ports are milled and then, after final honing the port edges are chamfered & polished by hand.
In mass production I'd prefer making the ports before plating and to raw-finish the chromium by internal grinding.


Is OS & such nickel plating just Nickel or NicaSil?

Lauri

[Douglas Ames]

OS uses nickle plating.  The nickle is less hard than chrome, so it wears faster.  The piston and liner wear out at about the same time.  With hard chrome several pistons might wear out before the liner wears out.

Hard chrome is a little different from cosmetic chrome.  Cosmetic chrome is a thin layer, and provides significant corrosion protection.  Hard chrome is a much thicker layer, and due to the process of growing crystals has openings to the base metal on a microscopic level, so you get wear protection but not the same corrosion protection.  Engines are full of oil so the corrosion protection is less necessary.

Phil

The crevasses also hold oil for lubrication of the rings on a full scale aircraft engine. Hard chrome is ground to the desired finish whereas decorative chrome (triple chrome process) is dependent on the polish job and base metal smoothness. On a cylinder it's the machine work that matters, on a car bumper it's all prep & workmanship.

[Steve Helmick]

George Aldrich wrote that getting the anode centered in the cylinder was crucial...I got the idea that it had to be adjusted off center to compensate for gravity, but it was long ago.

Notice that chromed cylinders are only plated on the bore, while nickled cylinders are plated all over, including the ports.

Howard indicated that he has done some nickle plating at home...electroless, I think. It appears that the major reason for ABN vs ABC is the environmental cautionary specs just cost a heck of a lot more.  Steve

[ChrisSarnowski]

Good information! I didn't know that you had to machine/hone the cylinder bore after the chrome plating. Interesting that the hard chrome has micro-cracks, crystal boundaries, etc., and so holds oil but does not provide corrosion protection.

How do you get the chrome only on the inside of the cylinder for brass cylinders? Also not in the ports? I am thinking about the spares that I have that are like that. I guess you could seal the bottom of the cylinder and plate before you cut the ports. Or maybe lacquer the areas you don't want to plate?

Tim, I did do some googling on chrome plating and the first try wasn't very satisfying. I figured we had some experts here that could answer my layman's questions, and others might be interested. I'm just a lowly electronics guy, mostly lost in a machine shop.

-Chris

[Motorman]

The cylinder is held vertical in a polypropylene or similar fixture that stops off the OD and also holds the anode. It has a screw in top to make connection and stop off the top of the sleeve. The brass ring connection also acts as a thief to keep chrome from building up on the top edge. the fixture is open top and bottom and bath agitation keeps fresh solution moving through.

The bath has to have a very fine density, chemical composition, temperature range and current density and this is what makes throwing chrome more difficult than other metals.

Depending on the port shape the chrome will plate the port to some extent which is no problem except more chrome will build up on a port edge which is one reason you need to hone afterwards.

The anode to sleeve surface area is a bad mismatch which makes hexavalent chromium build up in the bath. If you want to try it I suggest getting several books on the subject and learn the safety aspects first. Putting electric to dangerous chemicals can produce deadly nerve gas.

MM

[Dave Rolley]

Here is one person's experience chroming model engine parts:

http://www.nclra.org/TechTopics/WayneTrivin/Chroming.html

Dave

[Lyle Spiegel]

I suggest google to find  plating shops that offer hard chrome plating for various industrial applications-
They should be  familiar with industry spec AMS 2460 which defines technical requirements.
One shop I found in Ohio is Techmetals.

[Randy Ryan]

My 1950 'AeroModeller' Annual contains a fascinating article entitled: 'You Can Chrome Plate Pistons!' by C. O. 'Pop' Wright of Topeka, Kansas.  It was presumably copied from one of the American model magazines, but there is no indication of which one this might have been.  'Pop' described the process in great detail, and it clearly worked for him - I often wonder whether anybody else ever tried it.  As a boy in the mid-1950s, I did once get hold of some chromium trioxide, intending to plate the piston of an old ED 'Bee' diesel, but somehow never got round to it - which was probably as well, in view of what I now hear about chromium plating chemicals!

Regards
John

John, yes indeed!! My Dad got the chemical from the lab where he worked and found a rheostat, hot plate and all the other stuff. Over the years we have plated many pistons with great success. The real beauty of it is that in iron/steel cylinder sets, the piston an liner wear in mating patterns. The hard chrome basically follows that surface profile. Of course this only applies to wristpinned engines. We also did some ball socket types with good success. I still have all the stuff and a pile of engines to plate. its a very drawn out process so it doesn't make semse to try unless you do batches. It's been several years no I've been meaning to set up. If I get to it next spring, I'll post a how to with pics. Just to be clear, we plated the pistons though cylinders could be done if you held the anode dead centered in the bore, but that's another bit of tooling to be made.

[Andrew Tinsley]

Yes Pop's method does work. I tried it once but had an advantage of modern power supplies. I plated pistons such as the ones in O&R engines. It worked far better than I had any reason to expect.
  I have also tried experimental cylinder chroming. The central electrode needs to be spot on and I found that the chrome "throwing power" could be very variable. I was lucky to obtain the necessary chemicals to try plating, it isn't something I would recommend people to try.

 

[Andrew Tinsley]

Just to clarify the nickel plating process, there are two types in use for our model engines. the OS process is simply a dip method and no electroplating is used. This method produces a thin layer of nickel.It has two drawbacks. The nickel is soft and adhesion is relatively poor. Great care needs to be taken to ensure the adhesion is adequate.
By contrast electroplated nickel is much harder and has far better adhesion. The layer is also much thicker than the electroless layer. Magnum use nickel that is electroplated and their liners are much better than those of OS.

[ChrisSarnowski]

Hi Andrew,

Good info on the OS vs Magnum nickel plating processes.

Is there a reason why an electroless low phosphor nickel plating method is not used? It seems to have the advantage of a uniform coating thickness (as compared to electoplating thickness varying with current density).

Hi Dave,

Thanks for sharing the link!!

Here is one person's experience chroming model engine parts:

http://www.nclra.org/TechTopics/WayneTrivin/Chroming.html

Dave

[Jim Thomerson]

I watched George Aldrich chrome the cylinder on what was probably the last engine he worked on.  I don't remember details, but he chromed the cylinder, measured it, dechromed it and chromed again.  He did this three times before he got it to suit.  He was literally exhausted and we left the shop with the engine in pieces.  We had been going to go to the club meeting together, but George was not up to it.

[Dave Rolley]

If you want to go into the details of chrome plating as applied to model engines look for back issues of Strictly I. C. (S.I.C) magazine.  Issues 22, 23, 24, & 25 (1991 & 1992) have a series of articles written by E. D. Cox that go into great detail on techniques, mixes, and times for different liner materials (steel, brass, & aluminum).  I've been told that the basis of Russian/Ukrainian plating of AAC liners is contained in this series of articles.

http://www.strictlyic.com/

Dave

[Steve Helmick]

Hi Andrew,

Good info on the OS vs Magnum nickel plating processes.

Except that Magnum engines are chromed and not nickel plated. Andrew must be thinking of Thunder Tiger engines. I've always been PO'd at Thunder Tiger because they were too cheap or arrogant to put a sticker on their boxes to cover the "ABC" (which they are NOT) with "ABN", which they are.  Steve