Flashback arrestors for acetylene

[Sebculb]

Hey everyone,

So I gotta fix a piece of backhoe, thick cast iron. Decided to bronze braze it cuz I don't wanna heat it up with 5/8" thick by 8" long of nickel stick weld. Worried the thing'll warp like a potato chip if I do that.

Bought a used oxy acetylene kit off Facebook. Good deal in good shape according to everyone that's seen it. I dunno nuffin about it (yet, I learn quick though).

The kit doesn't have flame arrestors on it. It's obvious they'd been using it without them. Been looking all over but none of the welding stores or workshops here in SW Costa Rica have or use them. I'm talking big fancy commercial workshops too. Most haven't even heard of them. They say "less thinking, more working, keep it moving".

Anyone on here ever work without them? Everywhere on the internet in English says they are necessary. But I don't want to wait a week to even turn my new toy on while they ship from praxair in the capital.

I know it's not recommended. But who here has done it? Is flashback going up the hose a vague possibility or a real hazard?

Thanks!

 

[Menagerie-Manor]

Hey everyone,

So I gotta fix a piece of backhoe, thick cast iron. Decided to bronze braze it cuz I don't wanna heat it up with 5/8" thick by 8" long of nickel stick weld. Worried the thing'll warp like a potato chip if I do that.

Bought a used oxy acetylene kit off Facebook. Good deal in good shape according to everyone that's seen it. I dunno nuffin about it (yet, I learn quick though).

The kit doesn't have flame arrestors on it. It's obvious they'd been using it without them. Been looking all over but none of the welding stores or workshops here in SW Costa Rica have or use them. I'm talking big fancy commercial workshops too. Most haven't even heard of them. They say "less thinking, more working, keep it moving".

Anyone on here ever work without them? Everywhere on the internet in English says they are necessary. But I don't want to wait a week to even turn my new toy on while they ship from praxair in the capital.

I know it's not recommended. But who here has done it? Is flashback going up the hose a vague possibility or a real hazard?

Thanks!

They are not a necessity (although a good practice) and I doubt most users even have them installed.

 

[deereman75]

One caution I'd make (coming from someone who owns a shop that regularly repairs large cast iron parts) is that if you just bought a torch and don't have quite a bit of experience, I'd probably suggest not trying to fix this yourself if it is a structural part.
Proper repairs on large castings is really an involved process, you'll have to preheat and slow cool the entire piece, ect. Done improperly you can cause more cracks than you had to start with.

Also the brazing technique for large joints like that isn't really the same as for small thin parts. And you need a BIG tip to be able to get enough heat fast enough into the part to get the filler to flow properly and with control. And that means BIG cylinders to be able to run it. I have the largest cylinders available, and for a #6 welding tip like you'd be wanting to use for that, it's really pushing the limit even for them.

Not trying to discourage you from fixing it yourself, just be aware that brazing a big casting is far less simple than it seems. And if you try it and find you can't do it, it's very possible that you could cause enough damage to either render it unfixable, or at least make it far more expensive to have fixed professionally.

If it's a fairly simple part (IE not gigantic) you may only be looking at $3-500 to have it repaired and come back perfect.


As to the flashback arrestors, they are always recommended due to the liability of the people making those recommendations.
But if someone were inclined to look at how many torches are used every day without them, and how often you hear of a flashback occuring or a set of cylinders on a torch exploding, they could likely make their own conclusion about the risks.

 

[ROUSTABOUT]

I think you have cast steel. It possibly can be nodular cast but both are weldable.

 

[5030]

The only time flashback is an issue is when the operator don't cut the gas in the correct order.

 

[Sebculb]

One caution I'd make (coming from someone who owns a shop that regularly repairs large cast iron parts) is that if you just bought a torch and don't have quite a bit of experience, I'd probably suggest not trying to fix this yourself if it is a structural part.
Proper repairs on large castings is really an involved process, you'll have to preheat and slow cool the entire piece, ect. Done improperly you can cause more cracks than you had to start with.

Also the brazing technique for large joints like that isn't really the same as for small thin parts. And you need a BIG tip to be able to get enough heat fast enough into the part to get the filler to flow properly and with control. And that means BIG cylinders to be able to run it. I have the largest cylinders available, and for a #6 welding tip like you'd be wanting to use for that, it's really pushing the limit even for them.

Not trying to discourage you from fixing it yourself, just be aware that brazing a big casting is far less simple than it seems. And if you try it and find you can't do it, it's very possible that you could cause enough damage to either render it unfixable, or at least make it far more expensive to have fixed professionally.

If it's a fairly simple part (IE not gigantic) you may only be looking at $3-500 to have it repaired and come back perfect.


As to the flashback arrestors, they are always recommended due to the liability of the people making those recommendations.
But if someone were inclined to look at how many torches are used every day without them, and how often you hear of a flashback occuring or a set of cylinders on a torch exploding, they could likely make their own conclusion about the risks.

Thanks everyone for telling me I'd probably be okay without the flashback arrestors. However, when my buddy came over this afternoon to show me how to use the thing we actually found a pair of flashback arrestors (or at least check valves) attached to one of the cutting torches. Got a pile of extra cutting torches and hose thrown in for free.

Buddy showed me how to cut and get started melting, and said he doesn't think I'll blow myself up.

Deerman 75:
Thanks for the warning, I appreciate it. However I'm pretty thick headed and stubborn on some levels so I'll probably end up doing it myself.

For what it's worth I'm definitely not starting from zero in terms of metalworking, and I'm working under the guidance of people who really know what they're doing and they think I'll be fine.

Also I'm definitely gonna go build a couple pieces of furniture and a cart for the tanks for a few days to get a little practice manipulating the torches. Not gonna go to work on the unobtainium hub part as the first thing I do. Perhaps I'm naive but I stick weld for months straight sometimes on construction jobs and have welded plenty of cast iron with nickel rods and played with preheat and propane torches and lead and tin solder for "off label" usages and etc, like I say I'm not starting from zero. Perhaps negative one cuz I think I know something when I really don't ha ha.

Thanks again!

PS - thanks Deereman, in your warnings there were actually a lot of tips on how to do the job correctly, which I will be incorporating into whatever half cocked formula I decide on.

 

[deereman75]

Without getting into any real trade secrets, a good starting point is 600f preheat, cool as slow as you can. If you braze over a crack, it will crack. Joint prep is 90% of it.
Practice on a similar thickness piece of scrap steel to get a feel for how to make the bronze flow when you want and how to build up heavy when you want.

If you get comfortable with the torch and plan the job well it is certainly a doable project.