Soft soldering flux

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Soft soldering flux

This topic has 9 replies, 8 voices, and was last updated 5 March 2013 at 18:10 by nigel jones 5.

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4 March 2013 at 12:27 #15627
Speedy Builder5
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@speedybuilder5
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4 March 2013 at 12:27 #113680
Speedy Builder5
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@speedybuilder5
I need to soft solder a 3" x 8" piece of gauge plate onto the face of a heavy bronze casting. I would assume that it is best to tin both surfaces first, but which flux would be better suited, a past flux such as FLUXITE, or acid flux as BAKERS FLUID.

Are there better alternatives. Would a lead based or lead free be better.

I don't want to use epoxy type glues and want a metal to metal contact.

Your ideas would be appreciated.

Bob
4 March 2013 at 13:40 #113688
JohnF
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@johnf59703
Hi Bob, Either of the fluxes will be OK but the Bakers fluid is not recommended for non ferrous metal so I would go for the resin flux [Fluxite] you could also use the type of flux available for plumbing, these are very mildly acidic but clean non ferrous material extremely well. Make sure you wash well with water when finished.

The solder — use tin, same as available from plumbers merchants, tin flows to a very thin layer and is stronger than lead / tin alloys. We use this for fixing ribs on shotgun barrels and fitting new tubes into the breech, used with a resin flux and it is of course subjected to stress when the gun is fired. Tin both your components and strap together with wire then heat with a gas torch and feed in some extra solder when you see the tinning go "wet".

John.

PS Bakers fluid = killed sprites = hydrochloric acid + zinc.
4 March 2013 at 16:01 #113692
colin hawes
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@colinhawes85982
Tinning is the right way to go. I would use Bakers fluid to ensure a reliable adhesion to both parts .Wash the job in water afterwards and apply a little oil to minimise chance of rusting . Colin
4 March 2013 at 16:04 #113693
Gordon W
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@gordonw
I would use Bakers fluid on the steel, tin it and then wash. Use resin paste on the bronze and then as John above.
4 March 2013 at 17:08 #113697
Sub Mandrel
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@submandrel
The tin solder is the 'lead free' sold in places like wickes/B&Q not the same as the sort sold as lead free electronic solder. If you look at the composition it is about 99% tin and 1% copper.

Neil
4 March 2013 at 17:31 #113699
Speedy Builder5
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@speedybuilder5
Thanks all for some good advice.

Bob
4 March 2013 at 19:34 #113713
MICHAEL WILLIAMS
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@michaelwilliams41215
Hi Bob ,

Gauge plate doesn't soft solder very easily at all because of the alloying metals in it . In small pieces its generally ok but with large pieces and long heating you may need stainless steel flux .

Joint may separate end wise on cooling .

If you don't actually need gauge plate use something easier to solder .

Personally I'd redesign the job to use screws – these can be partial csk with the slot ground away after assembly if you want near invisible fixing .

Regards ,

Michael Williams .
4 March 2013 at 23:10 #113738
merlin
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@merlin98989
PS Bakers fluid = killed sprites = hydrochloric acid + zinc.

Some years ago I saw a formula for a home-made tapping fluid known as 'Angels Tears'. Were these in response to the fate of JohnF's elves?
5 March 2013 at 18:10 #113800
nigel jones 5
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@nigeljones5
killed sprites?? It will be dead gremlins next!
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