Copper pipe silver solder or brazing... yes on an aircraft. 1

[RoarkS]

Okay this is a new one for me. This is part of an air conditioning system that handles R-134a refrigerant for an aircraft cabin AC system.
One of the options I was given was to fabricate a manifold out of copper pipe fittings. Now I have to make a print for it.

Anyone have any idea what to use for a spec on the solder/brazing??? joint? I got "figure it out"

 

[MintJulep]

This is a common spec for passenger trains

silver solder conforming to AWS B2.2, BAg-5 or BCuP-5

 

[RoarkS]

I'll run that up the chain. See what happens.

Anyone else?

 

[WKTaylor]

RS... a few specs to consider...
NOTE. Copper tube/pipe alloys You are brazing may require low temperature silver brazing alloys to ensure copper is not heat damaged, thus...

CAUTIONs/NOTEs.
Some low temp silver-braze alloys have added cadmium to reduce solder melt temperatures and improve 'flow'... suggest avoiding AMS4770 and AMS4771.
Consider using AMS4763 or AMS4773... low temp silver braze alloys WO cadmium.
Always use brazing flux [AMS3410].
Your weld/braze techs should be able to assist in brazing alloy selection.

AMS2665 Brazing, Silver, For Use Up to 400 °F (204 °C)
1. SCOPE
1.1 Purpose
This specification covers the engineering requirements for producing brazed joints in parts fabricated from steels, iron
alloys, nickel alloys, cobalt alloys, and copper alloys by use of silver alloys, and the properties of such joints.
1.2 Application
This procedure has been used typically for joints requiring high strength up to 400 °F (204 °C), but usage is not limited to
such applications.
1.3 Warning
Numerous scientific studies have determined that cadmium, which is used in some brazing alloys, presents a health
hazard to persons if inhaled

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[MintJulep]

Nice resource showing the matching of AMS and AWS spec fillers:

https://princeizant.com/silver-brazing-filler-metals

In general, more Ag --> "easier" to use. At obvious cost disadvantage. Given no other guidance a brazing technician would likely tend to select an easier to use filler.

The P in BCuP-5 makes this filler self-fluxing on copper. A nice bonus. At the cost of a higher brazing temperature. However it has no match in AMS world.

Perhaps AMS4761 / BAg-34 warrants consideration.

 

[RoarkS]

How do you all feel about
AWS C3.4M/C3.4:2007 ?

 

[berkshire]

One of the most common on copper tube is Phos Copper brazing alloy, 0% Silver, 7.1% Phosphorus, Balance Copper. this is used by most heating and ventilating mechanics on air conditioning systems. Now whether or not you can use it on an aircraft is an entirely different matter.
B.E.

You are judged not by what you know, but by what you can do.

 

[MintJulep]

We invoke AWS B2.2/B2.2M.

It's a framework for establishing and qualifying brazing procedures and qualifying individuals to braze in accordance with those procedures.

Great stuff for producing fodder to keep the file cabinets of the QA/QC departments full.

I don't see much difference between the scope of that and AWS C3.4M/C3.4 based on the abstracts.

AWS C3.4M/C3.4 appears to have been developed at the request of SAE for use in aerospace.

Note that the current version of AWS C3.4M/C3.4 is 2016.

 

[WKTaylor]

CAUTION/NOTE. Berkshire may have an important point RE high copper-alloy pipe/tube brazing...

In aerospace, brazing is RARELY done on high copper-alloy pipes... almost exclusively on SStl [3XX, 21-6-9, etc], Inconel, Monel, etc... pipes/tubes, which can take the heat of furnace and torch silver brazing.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[SAITAETGrad]

AC43-13.1B Paragraph 4-88 may provide some help.