propane brazing

has anyone had experience of oxy /propane brazing using hobbyweld oxygen cylinder

Any oxygen with propane will give a good flame, most commercial users working on sites nowadays don't use acetylene but propane as acetylene is not allowed on site.

dont know about hobbyweld but in my commercial boiler business I only ever use oxy propane...no messing with fire bricks to keep it all hot, no multi stage silver solder, direct and intense localised heat.

thanks fizzy , that what I hoped for . I am having trouble silver soldering steel components , taking too long to heat up by propane alone and the flux dies , regards Phil

Philip, if you are having problems with flux on long heating cycles then try Tenacity No 5. It's made to cope with this.

Brian

"don't use acetylene but propane as acetylene is not allowed on site"

Never heard that one it's usually just cost propane is far cheaper (unless you're outside the UK then i wouldn't know, never been told this on any site I have and do work on ever...)

Acetylene is only needed for welding steel and aluminium, otherwise propane is hot enough for all other tasks.

I was intrigued by that too, but it does make sense depending on the Site. For example it's not allowed at Heathrow as per this Instruction.

If you're running the world's busiest airport and want to minimise the disruption caused by a fire I can see it pays to guarantee that Acetylene Cylinders aren't involved. When an Acetylene Cylinder is overheated they sometimes start an internal process of decomposition ending in an explosion up to a couple of hours later. So the procedure is to keep 200 metres away from hot Cylinders for several hours after the fire's out and everything's cooled down.

I suppose most 'ordinary' sites don't need to restrict the use of acetylene because the impact of an incident on them is much lower.

Dave

Edited By SillyOldDuffer on 27/11/2017 09:18:03

How about Mapp gas? **LINK** if you want a higher temperature without using oxygen. This is easily obtainable in plumbers merchants in the yellow canister. John

I thought "original" mapp gas was not available anymore, the stuff in yellow canisters now appears to be a different compound.

Edited for spelling

Edited By V8Eng on 27/11/2017 10:40:14

Yes, you're right, as mentioned in that very link. So instead, they sell products that look and sound very similar but aren't as good. More cynical marketing there. They call it "MAP / Pro" (one less "P" ) but some retailers seem to misspell it, accidentally or on purpose.

Pity, 'cos you could easily braze with the "real" MAPP gas.

Murray

Edited By Muzzer on 27/11/2017 10:33:19

Yes I used the original MAPP at work, it was great stuff

Hi Phil, you don't say how big you components are or what size burner you have on your propane torch. As everyone is saying propane is not the hottest gas, however, problems may be overcome by simply increasing the size of the burner. The heat comes from the energy, ie gas burnt. Think of an electric bar fire, put on another bar, they are both the same temperature but combined produce twice the heat. As Brian says immediately switch to a longer life flux (we call it HT5). There is a small torch using what is called MAXY gas/Oxygen, I believe this to be a 'rose by another name' as we get very good reports. Please see http://www.cupalloys.co.uk/torch-kits/index.asp

I use oxy-propane all the time, using hobbyweld oxygen but mostly with a medical oxygen concentrator. The concentrator is man enough for most things - bicycle frame brazing in my case - an dyou can sometimes find one cheap on ebay or glass bead making people use them a lot. When you get one it means free oxygen for life!

The one drawback with oxy-propne is that the flame, while just as hot as oxyacetylene, is more diffuse so you need to use a large nozzle for the same effect.

Hywel

Yes - work size is the key here - for smaller items you can SIF-bronze with just Propane but you do need a burner designed for this use - I have the Bullfinch 404 which I find works well for small steel parts.

"This Autotorch brazing kit can give temperatures up to 950c under general conditions and up to 1200c in ideal conditions only. The burners can therefore bronze braze under most conditions as well as being able to make faster soft and silver soldered joints."

Regards,

IanT

As I understand it premises rented from Network Rail normally have this as a restriction so that any fires are less likely to cause delays to the trains.
​Baldric

yep, can confirm that network rail specifically outlaw acetelyene use by anyone renting or using one of their railway arches. Was a dealkiller for a friend of mine looking into one.

The potential probem with acetylene is that under certain circumstances it can start to decompose within the bottle, which creates a lot of heat and pressure. The only thing you can do about it is cool the bottle and wait till it's finished. Note it doesn't need an oxygen supply to do this. Yes it's pretty unlikely, but it has happened. For boiler work I'd stick to propane, with oxy if you do enough to justify it. If you really must have acetylene, I'd check with your house insurer, and keep the bottle outside

When I worked in the motor trade many years ago we were told that it takes several hours for an Acetylene cylinder to explode if you get a blow back. I read a report some years back though where a cylinder exploded about 5 minutes after a blow back. Luckily no one was injured in the explosion but the building was damaged.

the parts I have been trying to silver solder are steel bar about 1/2 dia to 1 inch wide by 1.8 thick steel strip . it turns black before getting hot enough to solder . Using a severt gun , Does flux go off in the tub unmixed ?

regards Phil