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Brazing Cast Steel to Brass

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Brazing Cast Steel to Brass

Unread postAuthor: timmy999 » Thu Feb 23, 2012 11:47 am

I've got a fire extingusher with a 30mm diameter thread and want to connect this to standard fittings. I started a topic about epoxy which allthough the methods seemed excellent, It required me to downsize the fitting from 3/4 to 1/2" to allow for a epoxy resin plug. Wanting maximum performance I wan't to keep the 3/4fitting.

Because the 3/4" fitting fits quite snugly but doesn't marry with the 30mm threads. I was thinking of soldering or Brazing.

Does any one have any tips. Would it be a good hold for 100psi - 150psi?

I've never brazed before. Is it easy to get it air tight and a strong weld with no prior experience. And is the steel of the fire extingusher ok to weld to a brass fitting?

Cheers
Tim
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Unread postAuthor: cammyd32 » Thu Feb 23, 2012 12:04 pm

You would have to take that paint off before you did anything, and getting the heat right would be hard. But apart from that I have seen it done quite successfully in the past.
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Unread postAuthor: battlelava » Thu Feb 23, 2012 1:04 pm

If its properly brazed it should hold up more then 150 psi with no problem. There was another topic similar expect with solder, which I think held up to 400 psi or more. If someone else can verify it you could do either.
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Unread postAuthor: MrCrowley » Thu Feb 23, 2012 2:10 pm

Some years ago I did something similar but when I took it to the shop to get brazed they suggested I pick up a galv. iron fitting instead of the brass one and they would remove the zinc coat and do it that way. Can't remember what the reason was that they gave me, perhaps it's something you may want to look in to. The fire extinguisher was aluminium by the way.
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Unread postAuthor: al-xg » Thu Feb 23, 2012 3:53 pm

What torch are you using ?

It shouldn't be too hard to do if you have a powerful enough torch.
The steel should be just on the edge of going red but just make sure you don't heat the brass too much, it will melt.
High content silver rods will make it pretty easy.

An iron fitting is a safer bet, try and get a black malleable iron fitting rather than the galvanised stuff (or have the coating removed as suggested), I've used a eutectic brass alloy rod for brazing an iron fitting to a steel tank.
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Unread postAuthor: Lazyboy » Thu Feb 23, 2012 4:06 pm

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Unread postAuthor: sharpshooter11000 » Thu Feb 23, 2012 4:11 pm

If the sides of the hole on the fire extinguisher are big enough you could tap 1 1/4" threads and use a 1 1/4" to 3/4" reducer. That's what I did with a 1" hole to 22mm.
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Unread postAuthor: Gun Freak » Thu Feb 23, 2012 5:19 pm

sharpshooter11000 wrote:If the sides of the hole on the fire extinguisher are big enough you could tap 1 1/4" threads and use a 1 1/4" to 3/4" reducer. That's what I did with a 1" hole to 22mm.


Dude you can't be serious. The lip on the sides of that fitting appears to be no greater than 2mm thick.

If I were you I would just gob it with JB Weld and torque the fitting in. Since you're only using 150 psi max it will be fine!
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Unread postAuthor: sharpshooter11000 » Thu Feb 23, 2012 5:30 pm

Ah, yeah I didn't notice that, my bad :oops:
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