Brazing in an oven - Can I use an Inert gas?

[John E]

I need to braze stainless washers to brass hose ferrules, and based on what I have learned (and experimented with), doing these in an oven would be the ideal way to go.

My question is - can I use an inert gas to avoid the oxidation, but not impact the flux functionality? I'm using SRA STL-1205-655 Easy Brazing Paste - "Free Flowing Silver brazing alloy containing 56%Ag, 22%Cu, 17% Zn, 5% Sn with a strong flux." The melting temp is 1205F.

If this is a reasonable thing to do, what is the best gas to use? We don't use anything other than oxy in our normal course of business, so I I don't have any of the typical inert gasses on hand.

Thanks!
John

 

[starbolin]

No, the flux doesn't need anything else to work. In fact, since the joint no longer would need to be protected from oxidation, much less flux is needed, only enough to activate the metal surfaces.

Any gas non-reactive gas would suit the bill. Helium, Nitrogen, Argon and etc. Nitrogen is the cheapest but can react with the steels, Argon transfers heat well but is more expensive. Inert gas furnaces are more complex than simple ovens; what type of furnace were you contemplating using?

How big are the parts we're talking about? Insert a preform in the joint, wire up the assemble to prevent movement. Insert the assembly into a hand-made foil bad. Purge bag with Argon and close. Heat in oven. Not perfect but can greatly reduce the amount of scale.

 

[John E]

starbolin,
Thanks for the reply.

Parts are small, 620b ferrules (.450 OD x 9/16 long), 3/8 OD washer, and another part not mentioned before - a flared tube, .125 OD x .875 long in the hole of the washer. Kinda hard to describe it quick and easy, but ...

Ferrule open side down, washer on top, flared tube down through the hole. Flared tube will protrude beyond the open end of the ferrule.
They have to be staged, then set in the oven carefully to keep the centered. Not a precision deal, but it's got to be close. Probably only 20 pcs at a time, as needed.

The oven is small 'home made' (electric) deal about 9x4x6 inside, although heating elements are our business, so it's a fairly decent unit. No current facility for the gas, but that could be remedied quickly. I don't think with this size any fancy gas system is really needed. Flood it to start, then leave a low flow for the duration. Sounds like argon is the way to go.
Our big oven (L&L Hotbox, 2100F, 12x12x24 chamber) does have a gas fitting, but it's overkill.

Thanks again,
John