Why is my silver solder not sticking at all to stainless?

[DeepSpaceGalileo]

I saw some people talking about the acidic fluxes, I couldn’t find that at my hardware store so I used some 80 grit sandpaper then muriatic acid to clean the surface of the key and ferrule. I put flux around the hole on the keg, clamped the ferrule to the keg and heated the keg (mostly) and ferrule but the solder wasn’t staying under the joint. It just rolls down to the edges of the keg. Do I need to order different flux? Or is there something else I’m doing wrong?


Edit: also it does appear the flux is evaporating before it gets hot enough to melt the solder. Could that be the issue?

[Saltbush Bill]

Wrong flux or wrong temprature. To hot causes solder to roll away at times from my experience.

[Forest Beekeeper]

Too hot.

[DeepSpaceGalileo]

Have any good vids on the topic? I assume I should keep testing until the solder just melts and then keep moving? I’ve never soldered something this large, just mic and instrument cables.

[Forest Beekeeper]

It may require 100 manhours of practice to acquire that skill.

Often times you can lead the puddle in the direction you want it to move by adding heat to that one spot only.

[Salt Must Flow]

Stop using muriatic acid. It's supposed to be really bad for stainless.

You can clean it with solvent or anything that degreases. I'd shop around for the proper flux. Everyone recommends using Harris Stay-Clean Liquid Soldering Flux.

I abrade both surfaces, make it clean and flux it. Begin heating the areas and if the flux starts to turn black I flux it again. Keep heating, flux if necessary and once the solder starts to melt, move the heat along the joint. Solder typically flows towards the heat. Touch it with solder where needed.

When the flux smokes, try not to breath it. It will knock the wind out of you, it's VERY nasty.

[Swedish Pride]

Deffo get Harris stay clean.

You won't need 100 hrs to get a hang of it, take it from someone who never yielded a torch before this hobby.

Scratch the surface up again, use Harris stay clean an normal lead free solder.

Lead free solder is cheaper, requires less heat, is plenty strong and is covering gaps better than silver solder.

When soldering something that big you have to be patient, it will take a while to get up to heat.

Yummyrum did a very similar solder job recently, see if you can find his post for clues

[shadylane]

Deffo get Harris stay clean.

You won't need 100 hrs to get a hang of it, take it from someone who never yielded a torch before this hobby.

Yummyrum did a very similar solder job recently, see if you can find his post for clues

viewtopic.php?p=7789930&hilit=soldering ... s#p7789930

Apply the majority of the heat to the thickest piece.
Don't overheat and burn the flux. If you do, clean off the burned flux add more, and try again.

[Yummyrum]

When I see a MAPP torch and hear of difficulties soldering SS I immediately thing “too much heat “

When I solder SS with my Mapp torch I have the flame turned right down to the point where the flame will almost go out . You just need a very gentle fluffy flame . The normal roaring Mapp flame will just cook the flux and the SS . Propane is more than enough heat for SS .

I also suggest you get the right liquid flux .
Incidentally , the acid flux is made by dissolving zinc in Hydrochloric acid which yields Zinc Chloride and a small percentage of remaining HCl . I’m not sure just using HCl on it’s own will work and as mentioned , it is pretty corrosive .
We had SS sinks in our Labs that have holes through them with just dilute HCl being in contact and not washed off .
We had a dish washer that was destroyed after 9months because teachers would put glassware in them that would drip dilute HCl waiting for a wash cycle .

Anyway , with the right flux , you need to reapply it during the soldering operation . The SS and solder will be around 350°C so you need a brush that won’t melt .
I use genuine Hog bristle brushes . You can use them to “wipe “ on more flux . Keeping fresh flux on the joint is key . Wiping on more flux also moves the molten solder around the joint and helps with the tinning of the SS surface .

Gently heat the area around the area but not directly on it . You will after a minute or two hear the flux start to sizzle . You want the SS to sizzle the flux ….not the flame .
When the flux starts to sizzle , it’s time to reapply the flux .
It also means that the SS is getting close to the melting point of the solder . You want the SS to slowly approach melting temp . If it quickly gets to melting point , you can guarantee it will well exceed it and you will cook the joint .

So, when that flux starts to sizzle , its time to start applying the solder . I wipe it on the joint like I am trying to paint it . If you have slowly heated the area , you will get a nice controlled time where the solder goes from not melting to …. Ohhh … it’s starting to leave a line on the SS . Thats the critical heat . Just enough to cause the solder to soften enough and adhere to the SS . At this point you can chase the heat and solder around the joint and keep applying more flux . The Flux etches and protects the SS just before the solder follows and bonds .

Getting a solder bond to the SS is key .

[Chauncey]

From the looks you used too high of heat. Clean it with a mild acid like a citric solution, scuff it up,apply Harris liquid flux, and slowly bring the stainless to temp. Flux the fitting too. Basically it's like making a roux, you wanna keep it moving but not so fast it doesn't cook and not so slow it burns. That's my advice anyway ymmv

[Tammuz]

You have definitely picked a flux that would be hard to work with. Not aggressive enough for ss. I would go out of my way to get some staybrit and stay clean from Harris. It's a bitch to start with the wrong product. Use this on your copper.

Nokorode Regular Paste Flux
Nokorode Regular Paste Flux is a lead-free, all purpose, soft soldering paste flux ideal for use with 95/5 and other common solders. Nokorode special oil base protects the solder joint against corrosive attack. It cleans and fluxes all at one time.


Features
Cleans and fluxes in one operation saving time and money
Flows smoothly into even the smallest cavity
Multipurpose for use with 95/5, 60/40, 50/50, and 40/60 solder
Lead free and acid free - safe to use on potable water systems
Special oil base protects the solder joint against corrosive attack.

[kiwi Bruce]

I would go out of my way to get some staybrit and stay clean from Harris.

+1 to all who quoted using Harris.

If your a cow cocky you'll find this at your farm supply, it was developed for the dairy industry. If your close one of the "Big Smokes" Auckland, Wellington or ChCh you'll find it at one of the jewelry supply houses. We jewelers were PDQ to grab this stuff, it's a God send. As a "new bee" get the Harris solder and flux, yes it's more expensive but it is VERY forgiving. DO go gentile on the heat too. Take your time, patience is KEY in this hobby, just slow down and you'll see, it'll work out fine. Good Luck! From a Kiwi "far far away"

[Twisted Brick]

Have any good vids on the topic? I assume I should keep testing until the solder just melts and then keep moving? I’ve never soldered something this large, just mic and instrument cables.

All good advice above, especially using patience. Another good practice is to flatten your solder with a hammer (for smaller joins further reduce by splitting the length of solder down the middle) prior to application. This reduces both the amount of heat needed to melt your solder and the possibility of overheating your join.

I too had no prior soldering experience but followed the advice here to use Harris silver solder and liquid flux. Many dozens of builds later I am still using it along with MAPP gas. It will take a little practice but following the advice listed here you should see improvements with each session.

Soldering stainless is kicking my ass

Joining stainless to copper

[DeepSpaceGalileo]

Thanks all, I’m in the process of reading the replies. I switched to propane, “stay silv white brazing flux” because I assumed it would have higher heat tolerance but maybe I should use some of the liquid acidic stuff. I thought I had tacked the ferrule to the keg but when I unclamped it has zero resistance. No hold at all. I tried unclamped but there’s too much room between the rounded keg top and the 8” ferrule bottom. I’m going to clean off, sand again and try one more time focusing on heating the ferrule. I was definitely heating the keg top directly. Weird there’s absolutely no adhesion though.

[DeepSpaceGalileo]

For solder I’m using Sterling lead free solder from lowes. Maybe I need to spring for the expensive Harris stuff on Amazon too

[DeepSpaceGalileo]

Sorry for triple post. Wrapping solder around as in the video was very helpful. As was heating from afar. I’m still sketched to put a bunch of weight on this thing with the column…. I might just pay someone to weld it..

[DeepSpaceGalileo]

Oops. Yeah no adhesion after cleaning, sanding, wiping down, flux applied then solder wire down and the ferrule was clamped to the keg.

[shadylane]

As a "new bee" get the Harris solder and flux, yes it's more expensive but it is VERY forgiving. DO go gentile on the heat too. Take your time, patience is KEY in this hobby, just slow down and you'll see, it'll work out fine.

Flux is similar to mashing with malt. Don't overheat and denature. Instead, slowly raise the temp.
Use the solder to test if the metal is hot enough by touching it to the SS.
Don't use the flame on the solder in an attempt to force it to melt like you would brazing.

[SaltyStaves]

“stay silv white brazing flux” because I assumed it would have higher heat tolerance but maybe I should use some of the liquid acidic stuff.

That is absolutely the wrong product for this application. That is for brazing rods that are well beyond the flow temperatures of silver solder.
Stick to the liquid fluxes that others have already recommended.

[Tammuz]

The Harris black paste flux would have been a better pick if you can't get stay clean.

[acfixer69]

The Harris black paste flux would have been a better pick if you can't get stay clean.

If he was silver brazing that would work but He is soldering and not brazing. He needs a silver bearing solder like stabrite or stabrite 8 for the solder. For flux use liquid Harris staclean or equivalent. There are many other brands but those are by far the most commonly found.

[acfixer69]

I checked the Harrris website and Harris sterling is not a silver bearing solder.Sterling® tin-copper-selenium lead-free low melting point solder provides a melting range for filling and capping solder connections used for plumbing applications.
From their website:
"Sterling® tin-copper-selenium lead-free low melting point solder provides a melting range for filling and capping solder connections used for plumbing applications.
Stainless needs silver to bond and acid to etch. No way around it.
Also Nokorode will not etch stainless.

[Tammuz]

A Harris representative suggested the black flux when I was having problems locating liquid flux. She thought the black flux would handle the temperatures better when heating two different pieces of stainless steel thickness. I was fortunate enough to find three bottles of liquid flux for the price of one on eBay.

[acfixer69]

There is a black paste but not used for stainless or carbon steel.

[Tammuz]

From Harris website:

STAY-SILV BLACK BRAZING FLUX
The black flux formula includes powdered boron which gives the flux a black color. This ingredient provides two features:

A. Flux absorbs oxide during heating. There is a maximum amount of oxide absorption the flux provides, after which it becomes saturated and is no longer effective. This formulation allows the flux to withstand longer heating cycles without breaking down. These applications may include specific types of concentrated localized heating (induction, for example), or may occur during torch heating of large parts. In these cases the black brazing flux is a good choice.

B.Some metal oxides are more difficult to flux. These include stainless steel, nickel alloys and tungsten carbide. The black flux helps dissolve these oxides and assists in filler metal wetting.

BLACK FLUX is primarily used with the Safety-Silv high silver brazing filler metals (you’ll often find it used with the nickel containing 40Ni2 or 50N products).

Black flux conforms to AWS A5.31 class FB3-C and has an active temperature range of about 1050 - 1700°F (565 - 925°C).

[SaltyStaves]

Black flux conforms to AWS A5.31 class FB3-C and has an active temperature range of about 1050 - 1700°F (565 - 925°C).

And Harris Sterling Solder has a Solidus of 419°F (215°C) and Liquidus of 660°F (350°C).

Black, white, it doesn't matter. Its not a suitable combo.

[Salt Must Flow]

A Harris representative suggested the black flux when I was having problems locating liquid flux. She thought the black flux would handle the temperatures better when heating two different pieces of stainless steel thickness. I was fortunate enough to find three bottles of liquid flux for the price of one on eBay.

I suspect THAT'S where the screw-up originated.

[OtisT]

Hi Deepspace. I don’t envy you. As you are learning, soldering stainless is a bit of an art. Getting two stainless parts of greatly different mass up to the right temp at the same time requires patience and persistence. Lots of good advice above on that.

I do want to warn you, before you go further, to check your ferrule for squareness before you try to solder it on again. Too much heat in one spot, too fast, can warp one of those thin walled weld ferrules pretty significantly. It would be a travesty for you to figure out how to get that thing soldered securely only to find out it has been warped and you need to start over again. For this reason I like to heat ferrules fully, not just in one spot, at the same time you are bringing the boiler up to temp. (It is a juggling act with the torch in constant motion.) Get the whole ferrule warmed up evenly, well below your working temp, before trying to get one point up to working temp.

[kiwi Bruce]

DeepSpaceGalileo...I looked at your images again and I don't think the gap between the work pieces posses a problem. That said, if your still having a problem closing the gap get a piece of 12 gauge copper wire (strip it out of heavy house wire) and make a collar to ring the two pieces. The collar will help you flow the solder between the two joints and direct some of the heat away as the solder starts to flow. The solder will completely cover the wire so don't worry about it corroding.

[Yummyrum]

DeepSpaceGalileo...I looked at your images again and I don't think the gap between the work pieces posses a problem. That said, if your still having a problem closing the gap get a piece of 12 gauge copper wire (strip it out of heavy house wire) and make a collar to ring the two pieces. The collar will help you flow the solder between the two joints and direct some of the heat away as the solder starts to flow. The solder will completely cover the wire so don't worry about it corroding.

Thats exactly what I did kiwi Bruce .
It also provides a “Meatier “fillet of solder z

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