Any brazing hints?

**Norm.Mareeba** · 21st June 2006, 04:57 PM

Hi All;
Now that I’ve got the torch working right I’m ready to start brazing up my project. Before I start I thought I’d better check if there are any hints that would make my job easier or better.

I’m brazing up 25mm tubing, 1.6mm wall. The project will be a lot of "T" joints. I’ll make a "fish mouth" mitre to join one tube onto the another.

From what I’ve read, a good brazing joint starts with clean metal so the first step I’ll be doing is to remove any oil or grease. I’d thought of using mineral turps or alcohol but one site suggests using a degreaser.

Is that like the degreaser we use on engines and the like? Any other suggestions or am I on the right track here?

The next suggested step is to remove any rust or other impurities. I thought wire brush in angle grinder or emery cloth. A site suggested 50% HCL (hydrochloric acid) solution as the best cleaner. OK, I’m willing but where do I get HCL? Anyone care to comment on this?

The next step is to coat the joints with brazing flux. OK, I’ve got a black container of Comweld Brazing Flux (white granules like sugar). What do I dissolve the granules into to make a paste? The label is a bit messed up so I can’t read the directions.

I’m actually trying to do a "Braze Weld" to give each joint a bit of extra strength and make them look good. I’ve done some practice joints and I’m a bit concerned about them. They are strong enough but they aren’t very neat. I was hoping for a nice fillet but I can’t keep the fillet the same thickness. Some places I can see the outline of the base metal, other times I get a blob of bronze. Sometimes, when I try to "spread the blob", it just falls off. Other places have craters of flux, or the bronze looks grainy like a cold solder joint – not neat at all. Fortunately, other places look just perfect so I’m doing something right, just not all the time!

Finally, and if you’ve got this far I really appreciate it, I’m having difficulty removing the flux after the braze. I’ve tried hot water and a scrub brush, tried dipping the hot part (not red hot), tried wire brush on the angle grinder. Nothing works completely. I’ve noticed that the flux turns white and becomes furry when left overnight. Is that a clue? Should I be cleaning the part much later?

Thanks,

Norm

**DJ’s Timber** · 21st June 2006, 08:12 PM

G'day Norm

You are basically doing everything right, except for the flux
You lightly heat the end of the bronze rod, just enough to get it warm then dip it into the flux so that it coats the rod
By doing it this way you are putting the flux right where it needs to be ie right where the weld is
To get a nice even joint you have to lift the torch up and then back into the weld so that the bronze can settle and not run
It should look like you have lots of little balls melted together if that makes sense
There is no need to put flux on the tubing, by doing it this way you shouldn't get a build up of flux on the tubing
You could try wiping the flux off with a wire brush while it is still hot

Cheers DJ

**graemet** · 21st June 2006, 11:46 PM

G'day Norm,
I don't find I need to clean with degreasers etc, just hit the uncut bits of the joint with an angle grinder to get bright metal, no rust cause that causes pops and bangs and bits that stick on bare skin and hurt! The heat of the torch is enough to get rid of oil traces. If you use a coated rod, there is no need for flux (it's on the rod). If you are still getting blobs of braze rod, it means that the base metal isn't hot enough, or you don't have flux on the join. Heat the steel and let it melt the filler rod, don't put the flame on the blob, then as you get molten brass, slowly move the flame along the join away from the melt and the fillet will run after it making a nice thin join, with good penetration.
A lumpy glob of brass means the brass is all on the outside of the join and not between the pieces and this WON'T HOLD. When the joint is cold, the flux will look like a grey shiny paint, tap it with a sharp point or a screwdriver and it will flake off.
Cheers
Graeme

**Grahame Collins** · 22nd June 2006, 12:14 AM

Shiny clean is the way to go for brazing. Move the flux container well out of the way as sooner or later you will wave the flame over it and melt the plastic container.(ask me how I know?)

The is nothing wrong at all with applying the flux first to the joint. Heat the filler rod end slighty and dip it in the flux .
Most operators inadvertently blow most of it away with the flame.Heat the area to be brazed and deposit the grains of flux using pinched fingers.The flux will stick and fuse to the hot areas and will not be blown away by flame presure. Once the metal is molten, it will flow where ever you spread the flux.
As stated previously the bulk of the flux will readily clean off with a wire brush while everything is cooling down.If the remainder is not cleaned with water the left over flux after brushing can still corrode the metal.

An important point that has not been mentioned is not to overheat the molten metal. Zinc is part of the braze alloy and the is only a small tolerence between molten metal phase and the zinc turning into a gas and burning.

The indicator for this is when the zinc gasses it flashes off as a white powder.The result is a grainy surface of the cooled metal which lacks strength. Not having personally brazed with LP before is it a bit hard to tell how quickly it may happen, but I assume it would act similiar to the oxy acetylene. My guess is that oxy acetlene being hotter it will happen quickly but would take more time with LP

A correctly performed brazing operation will leave a flat rippled bead joint that blends smoothly into the components being brazed.

Grahame

**DanP** · 23rd June 2006, 03:14 PM

Originally Posted by Grahame Collins

(ask me how I know?)

How do you know?

**steve H** · 1st July 2006, 03:02 PM

i used to be a boilermaker and i used to warm the rod , dip the rod in the flux, then heat the area in the area u need it only. Once its hot, touch the rod on the steel use the tourch untill the brass melts , move the rod then using the flame heat the steel and the brass will follow the hottest point, then add more rod and do the same with the flame to heat and move . Try it,s not to hard......... Oh! move the flame in tiny circles this helps

**steve H** · 1st July 2006, 03:07 PM

Just remember i know lots of welders and all of them have there own little ways,You will your own

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