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silver soldering


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Arthur Goodwin10/05/2021 16:00:30
59 forum posts
40 photos

Hi all

I have today had my first attempt at silver soldering and it was an abject failure.

I cleaned both parts to the nth degree finishing off in pickle bath.

The flux I used was J & M tenacity 5 and the filler was 55% silver 0.5 mm wire.

I was using a rothernberger torch and Mapp gas. The copper got plenty hot enough (dull red)but the flux never "glassed" over and the filler would not run.

Any suggestions would be much appreciated

Dave Halford10/05/2021 16:02:46
1507 forum posts
16 photos

How big was the part?

Where did you get the solder from?

CUP allots has a video that shows what should happen.

Edited By Dave Halford on 10/05/2021 16:04:07

Bob Stevenson10/05/2021 16:06:17
514 forum posts
7 photos

Arthur,.....I suspect that "Dull-red" needs to be 'brighter red' it sounds like the workpiece did not reach sufficient temp to melt the solder, which it must.

Nigel McBurney 110/05/2021 16:17:19
875 forum posts
3 photos

more heat required,cpper should be bright red, I would use easy flo flux for copper pipe, get the part up to heat quickly the flux should melt ,them move the torch flame away and touch the copper with the solder,the heat in the copper has got to be able to melt the solder,when the solder just starts to melt re apply the heat and feed the solder into the joint.

Dave Halford10/05/2021 16:21:23
1507 forum posts
16 photos

Flux melts at 560C, 55% melts at 630+C. so you are more than 100C too low at 'dull red'.

Tim Stevens10/05/2021 16:28:38
1430 forum posts

I guess that you were concerned about getting the job too hot and destroying it. For reassurance, do the same things but with a piece of scrap copper (or perhaps an old penny etc?) and you will be better able to judge how hot is hot enough. And see what melted flux looks like, etc.

hope this helps

Regards, Tim

Bo'sun10/05/2021 17:06:53
444 forum posts

Another vote for the info' from CUP.

JA10/05/2021 17:43:08
1154 forum posts
72 photos

Advice not posted (too close to Tim’s)


Edited By JA on 10/05/2021 17:47:51

bernard towers10/05/2021 18:23:54
188 forum posts
71 photos

Ditch the tenacity 5 for easy flow especially on small jobs. Flux will go glassy and then seem to disappear that’s the point when it all happens.

Arthur Goodwin10/05/2021 19:03:51
59 forum posts
40 photos


Thanks for all the advice. did,nt realise it had to be bright red. Having watched numerous you tube videos and not one of them made reference to it.

will try again with the easy flow flux. any reccomended suppliers.

I got the tenacity from ebay. It had the proper label on it but white powder in a jiffy bag could be anything.

Bill Phinn10/05/2021 19:25:04
512 forum posts
81 photos

Arthur, to minimize the risk of ongoing frustration, can you at least show us a close-up photo of the parts in the position you were attempting to solder them in, and also of your torch alongside?

I'm sceptical whether getting the parts bright red as opposed to dull red was the solution you needed; your torch being too small and/or being directed at and played over the parts in a less than optimal way, or your joints being too gappy or too tight or too dirty are a more likely cause of failure.

On another note, I too have bought Tenacity [and Easyflo] off eBay in nondescript packaging; they worked exactly as expected. I bought a 500g tub of Easyflo from Zoro recently when it was on offer at £19.99, and the 250g tub was selling [or probably not selling] at £29.99. Price-setting algorithms are clearly convenient for the big-volume sellers, and sometimes for their customers too.

Andrew Johnston10/05/2021 19:27:45
6055 forum posts
671 photos
Posted by Arthur Goodwin on 10/05/2021 19:03:51:

Thanks for all the advice. did,nt realise it had to be bright red.

You don't, I made that mistake and messed up several attempts because of it.

For stainless steel I use a high temperature flux such as HT5 but for copper alloys and mild steel I use an Easy-Flo flux. The flux should go clear and runny when the correct temperature is reached.

I've learnt several lessons the hard way. First you need plenty of heat (not the same thing as temperature) to get the job up to temperature quickly. The flux going clear and running tells you the temperature is correct. I've also found that holding the rod in the edge of the flame to heat it up, but not melt it, before applying to the job makes all the difference. On the last job i did, the bodies and flanges at the back, in this photo:

singling valve parts me.jpg

the silver solder flowed properly but you couldn't see any redness in the heated parts, although that was in dull sunlight rather than shade.


JasonB10/05/2021 20:14:18
20637 forum posts
2296 photos
1 articles

Watch this one by CuP, not particularly bright but hot enough. If you are having a job getting the work hot enough with your small burner then HT5 flux may well be the better option as it will not get exhausted during the excessively long heating process.

fizzy10/05/2021 21:04:23
1792 forum posts
120 photos

As someone who buys their silver solder by the kilo (from the cup twins no less) take it from me that if you get your copper bright red there will be no flux left to flux. An easy way to ensure you dont over do the heat is to apply flux - HT5 is more forgiving - then cut off a snippet of solder from your rod and place it in the joint area. Evenly heat the job and at the point the snippet starts to turn liquidus apply flux rod. You may find it easier using 1mm or 1.5mm rod. And the super clean part - maybe years ago but technology has moved on since thene. It just needs to be free from surface debris, the flux does the job of cleaning far better that we can. And on a small item, dont be tempted to try to make a gap for the solder to run in to. capillary action and ipmerfect metal finish will ensure it finds its way everywhere it needs to. Wont be long before you crack it.

J Hancock10/05/2021 21:55:20
617 forum posts

I suspect you may have been worried about melting the copper ?

With air/propane that will not happen.

Avoid the temptation to melt the silver solder with the torch flame !

Arthur Goodwin11/05/2021 09:36:46
59 forum posts
40 photos

Thanks for all your comments.

Re photos Bill will add later, got an 18th Birthday on today so have been banned from workshop ha ha

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