Flux for soft soldering steel

[Red'n'Black]

I'm trying to put a patch on a pressed steel cover. It's far too thin to weld, by me at least, I'd say about 0.6 mm.

It doesn't need to be particularly neat so I was just going to soft solder it. I've had success doing it this way with electronic rosin cored flux before, but this time I got a bit too aggressive with the blowtorch half way round and it turned blue. It's a really hard layer, a glass fibre pencil doesn't touch it.

Is there a flux that will cut through the oxide layer, and is better for soldering steel generally? Or will I have to dismantle it all, sand back to bare metal and start again?

 

[JEZGUZ]

I'd take it apart and have another go, give it a really good clean up and tin both parts, when you re-solder put the heat into the steel cover, not the patch

 

[voipio]

Which flux did you use? Zinc chloride would be the preferred flux on steel, but it needs cleaning to bare metal before starting to solder. The blowtorch needs to be just played over the surface, and kept moving, until the part comes up to temperature. Baker's Fluid no.3, is a trade name for the flux, and contains zinc chloride and ammonium chloride. Solder paste is quite useful, spread between the parts to be joined, and then "sweated" gently with the blowtorch until a liquid solder line appears at the edges of the parts being joined.

 

[Red'n'Black]

Which flux did you use? Zinc chloride would be the preferred flux on steel, but it needs cleaning to bare metal before starting to solder. The blowtorch needs to be just played over the surface, and kept moving, until the part comes up to temperature. Baker's Fluid no.3, is a trade name for the flux, and contains zinc chloride and ammonium chloride. Solder paste is quite useful, spread between the parts to be joined, and then "sweated" gently with the blowtorch until a liquid solder line appears at the edges of the parts being joined.

Thanks, I'll get some on order.

I just used rosin cored electronic solder, which was all I had lying around and has worked OK for smaller jobs before.

At some point, not on this job, I'd like to give silver soldering a go, for where soft solder doesn't have the strength. We did some in metalworking classes 30+ years ago, I forget the name of the flux we used but it was a powder that you made up into a paste with water.

 

[voipio]

Borax is used as a flux for silver soldering and brazing. It only has low solubility in water, so forms a paste.

 

[tom2207]

the pre mix plumbers flux and paste solution works well ,, its expensive but handy.

 

[Martin-Sy]

For silver solder I always use Johnson Matthey Easy-Flo or Tenacity 5 (for st steel).
It's not a difficult process once you get the hang of it. Cleanliness is important tho.

 

[Brad93]

Bakers for soft solder

 

[graffian]

I use phosphoric acid as flux when I am soldering holes in petrol tanks.

 

[Agroshield]

Bakers for soft solder

Presumably the Ginger version for red metals.

 

[Eric the chicken]

Presumably the Ginger version for red metals.

Where did you drum that up from?

 

[Hopefuldave]

Presumably the Ginger version for red metals.

Is that one fluid or Cream?

 

[Martin-Sy]

Only need a Spoonfull

 

[graffian]

Only need a Spoonfull

Or Blind Faith.