Has anyone plated steam locomotive piston or valve rods to restore original dimensions, or to repair surface imperfections caused by rust and corrosion from years of sitting outside? I am considering hard chroming our piston rods to repair twenty years of corrosion, and possibly some other bright parts to restore their surface and maintain the finished without alot of constant polishing.

What would be the preservation issues regarding having a plated surface instead of a polished steel surface?

The Tod Engine
todengine@woh.rr.com

> Has anyone plated steam locomotive piston or
> valve rods to restore original dimensions,
> or to repair surface imperfections caused by
> rust and corrosion from years of sitting
> outside? I am considering hard chroming our
> piston rods to repair twenty years of
> corrosion, and possibly some other bright
> parts to restore their surface and maintain
> the finished without alot of constant
> polishing.

> What would be the preservation issues
> regarding having a plated surface instead of
> a polished steel surface?
Plating is no better then the finish of the metal it is applyed to. Plating will tend to make defects more visable. Hard chrome is an excellent way of protecting the rods but the rods should be ground round, centerless ground, if the rods are deeply pitted they could be welded, then ground.
As for other parts, you have to decide what your aim should be, restoration to original condition is unlikely to be possably, but likely to be expensive. It is your decision, for what very little my personal idea is worth, I think the rust and corrosion is a record of the history of the engine and I would use nothing more then emery cloth and oil on the engine excepting the rods where more extensive restoration may be required.

http://www.themachineryworks.com
hgorin@ix.netcom.com

Tried it once, didn't like it. Started out fine, but over the course of about a year, it all flaked off, in pieces about the size of dimes, a few a day. I have heard that plating can set up stresses in the rod possibly making it more prone to failure, but I can't back that up. My advice, leave them plain, and oil or grease them when out of service.

Plating can cover defects in rods that could be easily detected in polished steel. With the age of our equipment and crystalization, I feel that plating could be dangerous
Tom

ironbartom@aol.com

It was once explained to me that Chrome plating can change the composition of the metal, and allow the creation of weak areas. This person (a metalurgist) told me that he did not recommend Chrome Plating the rods on a locomotive. Does anybody know if this is true? If so, it would be one major reason not to plate the rods.

wilkidm@wku.edu

> It was once explained to me that Chrome
> plating can change the composition of the
> metal, and allow the creation of weak areas.
> This person (a metalurgist) told me that he
> did not recommend Chrome Plating the rods on
> a locomotive. Does anybody know if this is
> true? If so, it would be one major reason
> not to plate the rods.

Are you talking about hydrogen embrittlement? I read about that being a problem plating safety valve springs, the process makes the steel brittle and prone to breakage. However, this problem must have been solved as hard chrome plating rods, hydraulic rams, seamless tube mill mandrels and thousands of other parts by industry.

I think the problem the other poster had with the plating coming off may have been caused by poor surface preparation. Again there is just too many places that plating is used to make me think that the process is as unsatisfactory as some may think.


The Tod Engine
todengine@woh.rr.com

Yeah, it was hydrogen embitterment. The person that told me was very "old school" in the metal industry.

wilkidm@wku.edu

A few notes on plating to my knowledge...

TVRM has plated piston rods for air pumps and pistons with good success. Use industrial grade hard chrome plating process and material (whatever that means, but that's what the resident plating expert/chemist says...).

NEVER plate side, main, or other drive rods with chrome process as this sets up the stresses that HKA and others mention. NS originally plated the N&W J 611's rods with chrome, but later found many imperfections and more knowledgeable folks who came along afterward had it removed and continued to find imperfections developing for some time after that. Mind you, these were very tiny flaws, so they were ground and polished out as nondestructive tests revealed them, but there was potential for bigger problems to develop, I would assume. The N&W did have some kind of plating on the rods originally, but the process seems to be lost to time from my understanding. I recall that it involved nickel. Nickel plating does not set up the stresses that chrome does as is my recollection.

I'm not sure, but I think that the fact that the cross section is not round has something to do with setting up the stresses that can cause cracking, but some of the engineer-types can clarify.

Going on memory, but that's my 2 cents....
Mike

> Has anyone plated steam locomotive piston or
> valve rods to restore original dimensions,
> or to repair surface imperfections caused by
> rust and corrosion from years of sitting
> outside? I am considering hard chroming our
> piston rods to repair twenty years of
> corrosion, and possibly some other bright
> parts to restore their surface and maintain
> the finished without alot of constant
> polishing.

> What would be the preservation issues
> regarding having a plated surface instead of
> a polished steel surface?


Tennessee Valley Railroad Museum
newriver400@cs.com

Michael:

Do you have metallic piston rod packing running on chromed piston rods? And, if so, have you seen any differences from that running on non-plated rods?



Oregon Railroad & Navigation 197

Yes... It is Paxton-Mitchell design metallic packing on the 610, as the original is no longer available, as I recall. Mark will have to help out about answering the part about non-chrome rods and their performance as I have not had personal experience with such, but my memory again serves to say that the chrome rods yield longer packing life.

Mike

> Michael:

> Do you have metallic piston rod packing
> running on chromed piston rods? And, if so,
> have you seen any differences from that
> running on non-plated rods?


Tennessee Valley Railroad Museum
newriver400@cs.com

Hard Chrome Plating is an electrodeposition process. The substrate material is put in a chromic acid bath that is electrified with the proper polarity to pull material off the substrate. This "etches" the substrate to obtain a good surface for deposition of chrome. Then the electrical polarity is reversed. This deposits hard chrome on the substrate. The longer the current is maintained, the thicker the chrome layer. The resulting plating is tough and durable.

Most chrome surfaces are only a few thousands of an inch thick. Chrome is hard and brittle. If it is too thick it will tend to fracture and delaminate from the substrate. Also, excessive strain (deformation) of the substrate may cause the plating to flake off because the chrome has a much higher modulus of elasticity than carbon steel. Most chrome plating is intended to provide a longer wearing rubbing surface where shafts slide or through or rotate around seals. It actually detracts from the strength of the substrate because it creates tiny surface imperfections that can spawn stress cracks if the part is stressed too highly beyond the fatigue threshold.

Several pointers on steam locomotive piston rods: Remember, chrome plating is common on hydraulic cylinder rods, but these rods are usually brand new when plated. They have no history that might include fatigue or incipient cracks. Chrome plating will hide these imperfections on an old rod that is being built up. Steam locomotive piston rods are critical, high stress components. They should not be masked by chrome plating. They should be visually and NDT inspected at reasonably frequent intervals to look for trouble in the early stages. Plating inhibits the ability to watch out for problems.

Furthermore, thin chrome plating works best. This means that the rods must be machined and ground to eliminate the imperfections before chrome plating and ground after plating to achieve a good, reliable surface finish without resorting to a thick chrome plate. Many times old, worn rods should not be turned smaller because they will no longer have the required cross sectional area to withstand the stresses they will see in service, thus aggravating the fatigue problem.

Someone posted a suggestion that pits be built up with welding. NEVER, NEVER WELD ON STEAM ENGINE MOTION WORK!!! Such activity will essentially ruin the metallurgy of the part and create incipient cracks in most cases. This is setting up for disaster at some unpredictable time down the road. I have condemned motion work parts that showed evidence of weld repairs on at least one occasion, thus requiring new pistons and piston rods. I would not hestitate to do it again, especially where the paying public is around the engine.

petitinc@nwlink.com

Why anyone would want to use original piston rods with any flaws is beyond me. Original pistons with antiquated ring designs or excessive tare (dead) weight can also be dealt with rather easily and inexpensively, as Mark can verify. He has designed new/modified pistons and valve spools for at least two of the engines, but I don't think the valve spools got installed on the 4501 before she was taken out of service (temporarily for all ye of little faith....).

Mike

> Hard Chrome Plating is an electrodeposition
> process. The substrate material is put in a
> chromic acid bath that is electrified with
> the proper polarity to pull material off the
> substrate. This "etches" the
> substrate to obtain a good surface for
> deposition of chrome. Then the electrical
> polarity is reversed. This deposits hard
> chrome on the substrate. The longer the
> current is maintained, the thicker the
> chrome layer. The resulting plating is tough
> and durable.

> Most chrome surfaces are only a few
> thousands of an inch thick. Chrome is hard
> and brittle. If it is too thick it will tend
> to fracture and delaminate from the
> substrate. Also, excessive strain
> (deformation) of the substrate may cause the
> plating to flake off because the chrome has
> a much higher modulus of elasticity than
> carbon steel. Most chrome plating is
> intended to provide a longer wearing rubbing
> surface where shafts slide or through or
> rotate around seals. It actually detracts
> from the strength of the substrate because
> it creates tiny surface imperfections that
> can spawn stress cracks if the part is
> stressed too highly beyond the fatigue
> threshold.

> Several pointers on steam locomotive piston
> rods: Remember, chrome plating is common on
> hydraulic cylinder rods, but these rods are
> usually brand new when plated. They have no
> history that might include fatigue or
> incipient cracks. Chrome plating will hide
> these imperfections on an old rod that is
> being built up. Steam locomotive piston rods
> are critical, high stress components. They
> should not be masked by chrome plating. They
> should be visually and NDT inspected at
> reasonably frequent intervals to look for
> trouble in the early stages. Plating
> inhibits the ability to watch out for
> problems.

> Furthermore, thin chrome plating works best.
> This means that the rods must be machined
> and ground to eliminate the imperfections
> before chrome plating and ground after
> plating to achieve a good, reliable surface
> finish without resorting to a thick chrome
> plate. Many times old, worn rods should not
> be turned smaller because they will no
> longer have the required cross sectional
> area to withstand the stresses they will see
> in service, thus aggravating the fatigue
> problem.

> Someone posted a suggestion that pits be
> built up with welding. NEVER, NEVER WELD ON
> STEAM ENGINE MOTION WORK!!! Such activity
> will essentially ruin the metallurgy of the
> part and create incipient cracks in most
> cases. This is setting up for disaster at
> some unpredictable time down the road. I
> have condemned motion work parts that showed
> evidence of weld repairs on at least one
> occasion, thus requiring new pistons and
> piston rods. I would not hestitate to do it
> again, especially where the paying public is
> around the engine.


Tennessee Valley Railroad Museum
newriver400@cs.com