Brazing

Help please

About fifty years ago I remember using a brazing torch that was fuelled by town gas and compressed air.

Recently I was doing a job where my largest brazing torch, fuelled by my Camping Gaz bottle, was struggling to maintain the heat needed to make the braze run nicely.

I don't remember any trouble with maintaining heat with the gas and air torch and wondered whether they were still available?

I haven't been able to find any big torches on Google, although there are plenty of small torches for jewellers etc.

Also any ideas of what the domestic gas companies think about using their product for this sort of thing?

Thanks.

John

How big's your nozzle? I've got one that's nigh on two inches in diameter ( a Sievert branded one ), fueled solely by propane. I've seen bigger ones.

Regards,

What's in your camping gaz? If it's butane or a mainly butane mix then that's your problem.

Butane and propane both give about the same heat output (about 50 kj/g) but butane boils at -5 and propane at -40, so you can get much better gas delivery to the torch using propane (which is what the Sievert torches are designed for). Butane cylinders are usually blue and propane red.

AFAIK gas/air torches are still available though uncommon - they were needed in the days when town gas was carbon monoxide whose heat of combustion is much lower (10 kj/g). Our glassblowers at work use torches with air/natural gas fuel because they need very fine flame control.

MAPP gas will give you higher temperatures and faster energy delivery but won't run on ordinary propane torches.

Otherwise how about better insulation? The ceramic fibre blanket which CuP alloys sell does wonders for keeping heat where you want it.

John,

On the insulation front I use bricks from a storage heater as my hearth, all my Sievert kit runs on propane with no problem and as has been said there are some very large nozzles out there.

I braze and silver solder with no problems.

Martin, I don't have a brazing hearth so I could be wrong, but aren't storage heater bricks precisely the kind you don't want? I was under the impression that they have a high thermal conductivity and were designed to soak up the heat, whereas a fire brick supposely does the opposite?

Anyone who knows better feel free to correct me.

Peter

Hi Peter,

I don't profess to know better but ISTM there are 2 seperate possible uses for a forge : firstly being to quickly heat something up to temperature but secondly to slowly bring something down from temperature. Fire bricks would be ideal for the first purpose but I guess heater bricks are ideal for the second.

Peter,

All I know is that they work for me when brazing or soldering, they keep it warm as I assume their heat loss is slow so I don't waste heat.

Peter -

Storage heater bricks are indeed intended to do what it says on the tin - store heat - so they are designed for high thermal capacity and conductivity, rather than high insulation properties.

If you are trying to build a hearth that will allow you to rapidly bring something up to temp then you would be better off with "insulating firebrick" rather than the conventional solid firebrick - the insulating variety give good insulation and have low thermal mass. This is the type of brick that is used to build modern fast fire kilns for e.g., pottery use. I have a small hearth in my workshop made from some that I had left over from a pottery kiln project - wirks very well.

If you want to go even higher tech, then ceramic fibre is the stuff - better insulation properties & even lower thermal mass.

Regards, Tony

I'm not sure that conductivity is all that relevant for storage heaters

- high conductivity would lead to rapid cooling and cold heaters in the afternoon.

But on the high tech front I remember seeing a demonstration on TV a long time ago of the insulating properties of space shuttle tiles.

The demo involved picking up a piece of tile material that had been heated to red heat with a bare hand. Apparently it's conductivity was so low that it wouldn't conduct heat to the surface fast enough to cause a burn.

Russell

I recently bought two Gas/Air torches of different sizes from "Home and Workshop" at Footscray - =A320.00 each inc new hoses. Could have bought a brazing hearth with a torch for =A335.00, but I don't have any room in mt workshop for one.

Try [utl]

Manufacturers are Flamefast who do the RF10 & RF80 or T2 & T4 Torches. I'm running mine in Propane (32mBar) and a LPHV vane type blower. The RF types are designed to run from a LP air blower. The T types run on 4psi air. Mine were marked "NG" so they were obviously designed for "Natural Gas" but, they seem to be happy on Propane.

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Andy

Snipped

I had one of those "living flame" gas fires ripped out a while back and the whole thing is ceramic insulation in sheet and formed parts. It's awesome insulation properties and it allows a makeshift hearth for free. Next time the gas man comes round to do a service, I'm going to see if I can scrounge some more...

Steve

Whether it is relevant/desirable or not is another question, but the bricks used for heat stortage are in fact higher thermal conductivity than either conventional firebrick or the higher tech insulating refractories. The storage heater construction uses insulating materials around the storage bricks, and controls the airflow through/past the storage bricks, in order to control the rate of heat dissipation.

Regards, Tony

The firebacks from a Baxi Bermuda or similar radiant gas fire are well worth scrounging from a removed unit. Perfect for laying the part on whilst brazing.

Richard

Rather than buy, build.

which will melt cast iron in a foundry or try the Mini-Mongo burner by Rupert Wenig with the tapered flame retainer for brazing. Both are propane-air torches. I used the Mini-Mongo in my (Dave Gingery) foundry to melt a litre of aluminium in about 15 minutes. Should be fine for other purposes.

Mike in BC

When I went to tech school, the machine shop had two air gas torches. It was coal gas then. I have never seen torches like that since the 1950s.

Sigh! As far as I know, Sievert has no presence in Canada. Certainly not on the West Coast where I live.

Steve R.

The forge burners work really well. I've seen Rupert's burners in his furnace, and they really work well.

There are instructions available on various blacksmithing sites for propane burners in sizes from 1/2" pipe, on up to quite huge. They are very cheap to build, too.

Cheers Trev

I'm pretty sure that was a foamed ceramic, maybe silica. Also, it had a little time to cool off before it was picked up, you could see that the edges and corners were no longer glowing, although there was plenty of radiation coming out of the inside.

Yes, 'twas a lightweight fused silica - and very impressive in the early

80's.

'Course since then the advent of silica aerogels has changed things a bit - nowadays a 1/8 in layer of silica aerogel, which is too light to feel, can protect a bare hand from an oxy/acetylene torch indefinitely.

Hm, could do with some of that to insulate my garage door. Though no doubt would need a second mortgage.

David