silver plate over super finished gear profiles 6

[mfgenggear]

The subject is
super finished gear teeth which then require silver plate over gear teeth profiles, including the major diameter, roots, & end faces.

the issue I am having is I have customers that wants a 4 micro
on their tooth profiles. similar process to ISF Isotropic Super finish Process. However my suppliers complain that the plating process will not adhere to the parent material. It will peel off after the post embrittlement bake operation. the bake can only be 275 Deg F because these are Carburized parts.

what the suppliers normally do is an abrasive (glass bead peening) which roughs out the surfaces to make the plate stick.
which of course this is not acceptable because it violates the 4 micro.

what is this boards recommendations, I looking for constructive suggestions. or is there a process which will make the plating stick to the super finished gears.
can the super finish be 15-20 micro. so the plating will adhere.
I am at a loss with this scenario.

Thanks in Advance

Mfgenggear

 

[mfgenggear]

TVP

thanks for the reply
but could you please elaborate more on the Manganese phosphate.
You have star

Thanks & respectfully
Mfgenggear

 

[israelkk]

Manganese phosphate produces hydrogen too, See "MIL-DTL-16232G Phosphate coating, heavy, manganeese or zinc base" for instructions.

 

[tbuelna]

Nice catch israelkk. Attached are the relevant pages from MIL-DTL-16232 regarding hydrogen embrittlement relief requirements.

 

[mfgenggear]

Terry & Israelkk

true OK post embrittlement is required but would it stick (adhere) to the super finish.
that is what I was inquiring to TVP

seems no way out of some type of plating. did you gentlemen see my post above about
the Army core of engineers, data.

Respectfully

Mfgenggear

 

[spigor]

This maybe sounds funny to some of you, but what does the term "baking" (used in MIL-DTL-16232) mean? Is this some kind of a heat treatment? Many thanks for a hint.

 

[TVP]

spigor,

Yes, baking means heating to an elevated temperature, usually in the range of 100-220 C.


mfgenggear,

Phosphating adhesion is improved somewhat with surface roughness, but since this is a chemical process in an acidic bath, there is a degree of etching that takes place, which is why adhesion should be better than with an electroplated metal coating. This acid etching is also why embrittlement is a concern, albeit a small one given that inhibitors are used in the bath. Just follow the relief requirements in the appropriate specification.

 

[mfgenggear]

TVP
thanks for your reply

Terry & Israelkk

If selective Carburizing is required, then masking with copper plate in accordance with AMS 2418 type 2 is normally used.
prior stress relief & post embrittlement is required.

Just saying that since I have been making gears for selective gears copper plating has been used even before my time.
what are your thoughts on this.

Mfgenggear

 

[israelkk]

Copper plating for shielding is done prior to Carburizing. Therefore, there is no problem of hydrogen embrittlement during Carburizing. However, if the base metal hardness is 35RC and more there is a need for a stress releive prior to copper plating and hydrogen embrittlement relief after the copper plating (prior to Carburizing). See attached MIL-C-14450B Copper plating that was replaced by the AMS 2418. Note that the 44RC in para. 3.7 was changed later on to 35RC in amendment 3 of MIL-C-14450B.

 

[mfgenggear]

Terry

My Parts are normally Normalized, Subcritical anneal, then Harden to 27-36 prior to carburize.
it allows for better control of broaching & gear cutting.

Mfgenggear

 

[mfgenggear]

israelkk

Sorry that above comment was for you too.
thanks for the explanation

Take Care

Mfgenggear

 

[tbuelna]

mfgenggear,

First, yes I did read the document you linked from the US Army Corp of Engineers. The document recommends some useful practices for running-in new gear drives. Unfortunately, I think the recommendation of applying silver plate to the tooth flanks as scuffing protection during break-in is a bit of an old-wive's tale legacy. Even under part load operation, the soft silver plating on the tooth flank surfaces would be largely displaced within only a few load cycles. So any scuffing protection it provided would be extremely short term.

Second, I don't see why electroplated copper or silver would have trouble adhering to a 4 microinch surface roughness. I don't have a copy of AMS 2412 (silver) handy, but I read thru AMS 2418 (copper) and there was no mention of minimum surface roughness on the basis metal. However, AMS 2418 section 3.4.3 does briefly discuss acceptance test criteria for plating adhesion.

The only reasons I can speculate on for lack of plating adhesion with your ISF gear surfaces is either due to residue from the ISF process contaminating the surface, or possibly that the plating is being applied too thick. Sometimes a nickle strike can also promote better adhesion of the silver or copper plate with certain alloys.

Good luck to you.
Terry

 

[mfgenggear]

Terry

I am gratefully for the comments You and Israelkk
are willing to take time and share with us.

Respectfully

Mfgenggear