Help with Aluminium Pipe Soldering – Using Lumiweld + Dremel Torch, But Joint Fails

[Babs88]

Hi everyone,
I’m trying to solder two aluminium pipes together using low-temperature Lumiweld rods (flux is included in the rods). I’m using a Dremel torch as my heat source.


The solder appears to flow during the process, and the joint looks okay initially, but once it cools, the pipes easily come apart — the bond just doesn’t hold.


Has anyone successfully used Lumiweld for aluminium like this?
Any tips on:

• surface prep (I did light sanding)
• torch distance or heat control
• joint fit
• technique to improve adhesion or capillary action

Thanks in advance! Would really appreciate any insights before I try again. Barbara

 

[barracuda816]

That torch isn’t getting the pipe hot. Looks like you are just melting the rod.

The pipe should be hot enough for the rod to melt with just a bit extra help from the torch.

The lumiweld rods will melt lower than the parent material, but it’s still quite easy to overheat the aluminium. I’m not great with lumiweld rods either.

 

[brightspark]

its done with a wire brush and a stainless steel rod heated up dip the ally rod in till it melts and run the stainless rod along the join in the and it will run and fuse easily plenty of heat needed go on u tube plenty of demos there

 

[barracuda816]

I have never tried it with a ss rod.

But brightspark also brings up a good point. How are you prepping the pipes? Give them a good wire brush or going over with some scotch pad and a wipe with some acetone.

But generally from the photos. You have way to less heat.

 

[paradipiro]

Hi everyone,
I’m trying to solder two aluminium pipes together using low-temperature Lumiweld rods (flux is included in the rods). I’m using a Dremel torch as my heat source.


The solder appears to flow during the process, and the joint looks okay initially, but once it cools, the pipes easily come apart — the bond just doesn’t hold.


Has anyone successfully used Lumiweld for aluminium like this?
Any tips on:

• surface prep (I did light sanding)
• torch distance or heat control
• joint fit
• technique to improve adhesion or capillary action

Thanks in advance! Would really appreciate any insights before I try again. Barbara

Your heat source is way less powerful what you need. These rods as they get the right temperature, they will "flow into" the aluminium.. And thats where the alu will sag also.. Quite hard to hold the right temp. I have some pic, how a "good" not nice joint looks when it flows well,
just need some time to search for them.

 

[BrokenBiker]

You need a lot more heat, base metal isn't getting anywhere near soldering temperatures and that solder is just melting into a mess on top of the joint...brightsparks method seems like it would be good for smoothing out the solder after the initial joint had been soldered sufficiently.

I assume a dremel torch is butane? Aluminium is a massive heatsink and absorbs a lot of heat, the oxide layer requires more again...its why it's so tricky to weld and soldering, although an easier process, isn't necessarily any easier when aluminium is concerned

 

[paradipiro]

Your heat source is way less powerful what you need. These rods as they get the right temperature, they will "flow into" the aluminium.. And thats where the alu will sag also.. Quite hard to hold the right temp. I have some pic, just need some time to search for them.

 

[paradipiro]

If I remember well, the assembly was placed on the warm stove -winter times- and one fixed propane torch was directed to one side, and another was in my left hand, and the rod was in the right.. a HUGE amount of heat needed, although it was only a 400°C rod..

 

[Smallfry]

Not that it helps, but I have never had any success with Luminweld either. Given up on it, and the kit just sits on the shelf.

 

[not done it yet]

Not that it helps, but I have never had any success with Luminweld either. Given up on it, and the kit just sits on the shelf.

Exactly the opposite experience. Plenty of success. Got more at the Midlands Model engineering show a couple years back and my brother bought some last year.

There is no flux involved with these rods. If the poster has fluxed lumiweld rods, they are new to me!

 

[brightspark]

Exactly the opposite experience. Plenty of success. Got more at the Midlands Model engineering show a couple years back and my brother bought some last year.

There is no flux involved with these rods. If the poster has fluxed lumiweld rods, they are new to me!

the ones i use you just clean the job with a stainless steel wire brush melt the ally rod in and run a stainless steel rod along the molten metal joint making a nice weld = braze

 

[Pigeon_Droppings2]

Exactly the opposite experience. Plenty of success

Same here....I used mapp gas and stainless brush. Made a steel former and was able to remake an entire lug on an alternator!

The prep has to be good...and you need enough heat in the part itself such that the rod melts on contact with the part. I'd suggest do a trial on a small bit just to get a feeling for it. Should basically melt and look like molten silver.

 

[Babs88]

Hi!
Thanks so much for all your feedback on this! I bought a MAPP gas torch and cleaned the surfaces thoroughly with a stainless steel brush - and now the two pipes are finally bonded!
There’s definitely room for improvement in my brazing skills, but it's a solid start
Thanks again!
Babs

 

[not done it yet]

Aluminium is a quite reactive metal and easily oxidises in air, particularly when heated. This oxide layer prevents proper contact between the metallic parts. The scraping with a stainless steel ‘scratcher’ removes the oxidised layer and allows the melt to then ‘wet’ the surfaces, activating the surface which then spreads under the melt, to effect the joining process throughout the joint. Making the surfaces shiny, before heating, will not necessarily mean the surfaces are active at the time the lumiweld is molten.

 

[brightspark]

Aluminium is a quite reactive metal and easily oxidises in air, particularly when heated. This oxide layer prevents proper contact between the metallic parts. The scraping with a stainless steel ‘scratcher’ removes the oxidised layer and allows the melt to then ‘wet’ the surfaces, activating the surface which then spreads under the melt, to effect the joining process throughout the joint. Making the surfaces shiny, before heating, will not necessarily mean the surfaces are active at the time the lumiweld is molten.

yep need to scratch along the moten joint with the stainless rod to get a good clean weld

 

[Babs88]

Hi,

Thanks again for your help so far. I have another question: what are the most cost-effective, good-quality brazing rods for aluminium (low-temperature, with flux) currently on the market?

I’ve seen some very cheap options on Amazon but am concerned about their quality. I’m looking for recommendations that offer the best balance between value for money and reliable performance.

Thanks!