Author Topic: help with silver solder  (Read 693 times)

Offline cmitcham

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help with silver solder
« on: August 16, 2020, 01:29:35 AM »
obviously, i'm doing something wrong. in the picture below, i fluxed all the joints, and put pieces of solder in the flux for the bottom (right) fourth of the joints. i slowly applied heat, but after not very long, the flux just burns to a crispy black mess. this isn't how it looks in the few youtube videos i have found. any ideas what i need?

thanks!


Offline crueby

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Re: help with silver solder
« Reply #1 on: August 16, 2020, 02:08:19 AM »
Couple of questions:  which flux and which solder are you using, what percentage of silver? Some fluxes will last longer before burning off, and the silver content determines the temperature it needs to reach to flow. The flux and solder need to have a compatible temperature range, which is why I was asking for specifics


In general, you want to get the two parts up to temperature at the same time, so the solder flows evenly onto both. Heat from the back side, not putting the flame onto the solder, but getting the metal hot enough to melt the solder. Also, you need to heat quickly, not slowly, any flux will burn off if you go too slow. Most fluxes will melt and go clearer as they get to temperature, and the solder should go shortly after. 


Hope we can help you out, silver soldering does have some key techniques, but once mastered its an incredible tool.


Chris

Offline crueby

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Re: help with silver solder
« Reply #2 on: August 16, 2020, 02:10:57 AM »
Oh, and if you are doing a series of joints, best to do them a couple at a time, and pickle the last parts/joints and get them clean before doing them otherwise you will have oxidation in them that will mess up the flow.

Online tghs

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Re: help with silver solder
« Reply #3 on: August 16, 2020, 03:18:31 AM »
correct flux is very important,, I've had good luck with harris stay silver..  soldering in a darkened room can help as you can see your metals heating to the correct temp better and helps with bringing all the pieces up to temp evenly,, cleaning you solder and brushing or dipping it in flux can help greatly..
« Last Edit: August 16, 2020, 03:37:20 AM by tghs »
what the @#&% over

Offline crueby

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Re: help with silver solder
« Reply #4 on: August 16, 2020, 03:37:25 AM »
I started out using the Harris white flux, couple of years ago switched to the newer Harris Black, it has a longer working time. Both are good.

Offline Jasonb

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Re: help with silver solder
« Reply #5 on: August 16, 2020, 07:02:44 AM »
Heating slowly won't help as it will exhaust the flux faster.

As said a flux that is intended for higher temps and longer heating is best, I'll leave our US members to suggest the makes available.

Also use a hearth of proper insulating bricks as they throw the heat back into the work rather than absorbing it so work will get upto melting temp of solder a lot faster.

Offline derekwarner

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Re: help with silver solder
« Reply #6 on: August 16, 2020, 09:30:31 AM »
It would appeaar you have a high mass weight of parent material compared to the horizontal bands that themselves appear substantial in mass

Followingly along applying the heat source over the flux simply heats the flux to a burn off without any real heat attained within the mass

Builders of copper steam boilers often use a seperate preheat burner to elevate the mass of the boiler, then use a localised secondary heat source to achieve the individual solver soldered joints

A part of this selective silver soldering is performed in a darkened work area, where relative preheat temperatures can be seen as darkend purple or brown.......just prior to red/orange material temperatures

Just a left of centre question........do you need the horizontal blocks to have a high strength joint?.......or could soft solder suffice?

If all else fails, Cup Alloys UK provide a number of on-line silver soldering tutorials   :happyreader:

Derek

« Last Edit: August 16, 2020, 10:15:50 AM by derekwarner »
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Offline Mcgyver

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Re: help with silver solder
« Reply #7 on: August 16, 2020, 11:32:45 AM »
what flux are you using, what heat source are you using? 

curious what it is - could you use soft solder?  imo when the strength of SS or its ability to handle heat is not needed, tin/lead solder can be a better choice.  Its lower temps mean work doesn't distort (a problem with thin sections) nor does it anneal the brass

Offline gbritnell

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Re: help with silver solder
« Reply #8 on: August 16, 2020, 12:10:57 PM »
Silver soldering is fairly easily mastered once you know what's going on. If you're new to the art of silver soldering I would suggest taking 2 smaller pieces of the same metal, clean them good, apply flux and cut a small piece of solder but don't lay it on the joint, at least not initially. Now start heating the material, preferably from the back side or at least away from the joint. The solder will start to dry up and go from it's initial white color to little clear beads, like water droplets. Now lay your piece of solder into the joint. Slowly keep heating the material still staying away from the joint itself. With the flux in a liquid state it will only be a second or two before the solder goes liquid. The reason for not putting the piece of solder at the joint to begin with is because as the water boils out of the flux the piece of solder will move around. If you do lay the solder at the joint keep a small pice of steel rod handy to push it back in place. After a couple of practice sessions you will learn the steps of the process. The one thing you don't want to do is overheat the metal and burn it otherwise the solder will never wet and flow.
gbritnell
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Online tghs

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Re: help with silver solder
« Reply #9 on: August 16, 2020, 02:16:31 PM »
I use ceramic blocks to isolate my work from the surface for less heat loss,, also use fine wire solder as you can feed it into the joint and don't have to mess with trying to position solder chips,, you can get it "tinted" versions that can match you work,, leaves nearly invisible joints..https://www.riogrande.com/product/bronze-wire-solder-20-ga/132203  will be getting some black harris as my current jar of white is showing its age, at least 13 yrs old and has been re-wetted several times..
what the @#&% over

Offline cmitcham

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Re: help with silver solder
« Reply #10 on: August 17, 2020, 01:25:35 AM »
the flux in the picture is harris sta silv black. i will admit the solder is from ebay a couple years ago, so i don't remember which silver content. i did use it sucessfully with harris white flux when i got it, but that was stainless parts with very little mass. since the current parts are beefier, i guessed i would be heating longer so went with the black.

i did play with some scrap today, and found that the "crispy black mess" is simply the flux after the water is gone. i continue adding heat, and it melts back to a liquid, cleans the joint,and then solder starts to flow. excited with my breakthrough, i fluxed up my crankcase again for anothe try, but before the flux was ready, my propane tank died :(

thanks for the quick replies, i'll continue this thread after this week's vacation.


Offline crueby

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Re: help with silver solder
« Reply #11 on: August 17, 2020, 01:30:34 AM »
Great! Sounds like you are back in business, once Murphy's Law  leaves your propane tank alone!

Online tghs

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Re: help with silver solder
« Reply #12 on: August 17, 2020, 01:06:28 PM »
replace propane rig with mapp...
what the @#&% over