Disassembling a 17-4ph part, nickel alloy braze

[mjohnsonaero]

I need to disassemble a 17-4 ph part, it assembled with nickel alloy braze. I want to dissasemble this using acid strips to remove the braze and leave me with pieces, that i can then repair, then put back together using the nickel braze. I have looked and found that an initial strip of a water soluable alkali cyanide and a nitro-substituted aromatic compound in an 185 degree bath for 20-30 minutes. Then a rinse, and the acid strip of 50% nitric acid, small amount of hydrocloric acid for about 30 seconds to 5 minutes. My question is , does this seem right? What else do we need to know, do? Thank you
mjohnsonaero

 

[rb1957]

would it take too much heat to melt the braze with a blow torch ?

"gently, gently; catchee monkey"

 

[mjohnsonaero]

Would probably warp it, sheet metal parts put together to make a bigger part, I need to get it apart to repair, then be able to put it back together.

 

[rb1957]

i guess i'd prefer the blow torch to playing with cyanide ... i guess it's "pick your poison".

wait for will talyor to reply, he'll set you straight !

 

[WKTaylor]

mjohnsonaero...

1. Joint info... Devil is in the details.

17-4PH in what condition(X) [SHT, H1000, H1100, etc]? Heat treated to condition(X) before or after brazing?

What braze alloy? What braze process? What braze class [A, B, C]?

Joint design? Thick or very thin details?

Engine or airframe part?

Operating environment?

Why is it so crucial to disassemble and reassemble... as opposed to replacing?

Regards, Wil Taylor

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.

 

[mjohnsonaero]

1. Joint info... Devil is in the details.

17-4PH in what condition(X) [SHT, H1000, H1100, etc]? Heat treated to condition(X) before or after brazing?Has been heat treated and final aged, 1922 deg ht and then the final age.

What braze alloy? What braze process? What braze class [A, B, C]?BNi-2, AMS 4777, Hi-Temp 820

Joint design? Thick or very thin details? thin, .080 thick

Engine or airframe part?Engine

Operating environment? flying

Why is it so crucial to disassemble and reassemble... as opposed to replacing? Trying to come up with a repair for the part, my job. I'm development Eng here. Right now we are burning the old vanes out, EDM, but it is many steps to get this done, if I could seperate by this means, it would be a bit faster.

 

[mfgenggear]

Is this an after market Illegal repair?
The part being salvage, does it meet the original dimensional criteria.
Playing with fire my Friend.

Mfgenggear

 

[mjohnsonaero]

No, it's not an illegal repair, we are an FAA repair shop. There is no good current repair for the part, we are looking to develop a better repair and then be able to submit it. I'd like to cut the repair steps, hopefully in half by use of the stripping of the braze, seperating the part, fixing the parts that need to be fixed, then put it back together, and rebraze.

 

[KirbyWan]

I would think a process that can etch a braze metal would etch the 17-4PH material as well. I don't know what the part design is, but if instead of trying to keep the parts and put them back together, are some of the parts able to be fabricated from simple operations, from flat stock or a simple stretch forming process so that a skin can be removed and discarded and then use a locally fabricated replacement to the original material spec.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[berkshire]

Is there enough copper in the braze material to use an ammonia etch?
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[mfgenggear]

mjohnson

my apologies
Just that when used parts that are tac welded, brazed have very close fitting requirements for brazing. "I been there done that."
& are very close tolerance components. it is very difficult to salvage.
a brazed unit to my experience is an inseparable assembly. in other words it would destroy it to disassemble it.
with out knowing the details of it's fit form & function. I would guess this will not be a successful salvage.
if you have bridged that then I tip my hat to your facility.

OK I got that out of my system.
what is the brazing temperature. are there any close tolerances that will be affected.
sometimes some dimensions are finished after braze. I have done that.
so that is the question of braze temperature, and are the parts not distorting after braze.

"when there is way there is a will". although I don't agree with salvaging parts of this nature
it is probably done more often than not.

Masking of all areas that are not be etched is mandatory. you must work with a supplier who is willing do it.
etch only the braze joints of the parts that are to be scraped.
this is not any easy task.
ultimately machining is probably the best choice.

Mfgenggear

 

[mjohnsonaero]

The part I have is a diffuser, top and bottom plate with vanes in between, I want to seperate the top plate from the vanes and bottom plate, fix the vanes and put the top plate back on. Right now we EDM through the top plate, bench, put in new vanes, bench, alloy, braze furnce, finish dims, and ship, essentially. The part I have is a bit more difficult and needs to be taken apart, in order to fix correctly. It has been brazed AMS 4777, Temp I believe is at 1922 Deg F, I have thought about heating it up and taking it aprat a high temp, but not sure how that will work, So I thought if there was a way to use acid strip the braze away, bench the tack welds out, I could then get it apart and fix it, put it back together. That is my hope anyways. I have a method that I have found online, and it is similar to what we do to another part here, I just wanted to see if anybody else had any ideas.

 

[mfgenggear]

mjohnson

your best bet is to take a scrap assy & work with it.
you are breaking new ground and you will develop the best method.
I forgot to mention berksire idea of using ammonia. it eats copper with out attacking the base material.
it may work. It "ammonia" is used often to strip copper plated parts.

Mfgenggear

 

[mjohnsonaero]

Thats a good idea, I like that. I am working with a scrap part first, not looking to buy a new part to replace something that I have ruined. I'll try the ammonia too. I'll keep everyone posted. Thank you
Please keep the ideas coming!!!!

 

[WKTaylor]

mjohnsonaero...

NOTE.
I believe that this question would be better addressed in the metals and metallurgy forum [

http://www.eng-tips.com/threadminder.cfm?pid=330

] or welding, bonding and fastening forum [

http://www.eng-tips.com/threadminder.cfm?pid=725

].

NOTE.
You gave such low-grade answers to my questions, I hesitate to get involved. In my opinion You need to do a LOT of basic braze process research prior to going forward. There are many tricky elements to high temp/strength brazing You need to be aware of before proceeding. You also need to understand the exact environment these parts see [temperatures, gas flow, vibrations, etc] before proceeding. Then there is the element of qualification testing to verify all aspects of a process in real world environements. ETC, ETC...

NOTE.
Major engine manufacturer's, such as PW, GE, etc, usually have detailed process manuals for every significant operataion. I checked a PW manual used by DoD and found NO references for brazed assembly tear-down for rework, much less tear-down after thousands of hours in-service use. In this case it is obvious Your company has no such Brazing process manual system and is hunting for one.

A few useful starting documents may be as follows.

AWS [Americamn Welding Society]
AWS A2.4 Standard Symbols for Welding, Brazing, and Nondestructive Examination
AWS A3.0 Standard Welding Terms and Definitions Including Terms for Adhesive Bonding, Brazing, Soldering, Thermal Cutting, and Thermal Spraying
AWS A5.8 Specification for Filler Metals for Brazing and Braze Welding
AWS A5.31 Specification for Fluxes for Brazing and Braze Welding
AWS B2.2 Specification for Brazing Procedure and Performance Qualification
AWS C3.2 Standard Method for Evaluating the Strength of Brazed Joints
AWS C3.5 Specification for Induction Brazing
AWS C3.6 Specification for Furnace Brazing
AWS BRH Brazing Handbook

ASM [American Society for Metals/Materials] Books on "Brazing"

http://www.asminternational.org/portal/site/

http://www/GoogleSearch_2010/?qOld=brazing&q=brazing&collection=www_only&searchQueryString=

NOTE. ASM has an excellent forum for members to technical questions of ASM experts/members.

Also, suggest You get Your engine manufacturer's (or any other reputable manufacturer's) general processes manual(s) if they are available.

Regards, Wil Taylor

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.

 

[Screwman1]

I would also be careful about Hydrogen pick-up after the disassembly soak. Generally you should be OK, but I not sure after in service exposure and if I am on the aircraft I would want to be sure.