Soldering/Welding Techniques

Discussion in 'General Electronics Chat' started by cmartinez, Jul 15, 2019.

  1. cmartinez

    Thread Starter AAC Fanatic!

    Jan 17, 2007
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    I need to solder a few very small mechanical pieces of stainless that will be part of an electronic device that I'm currently working on. From what I gather, silver soldering is the right technique for this task.

    So I bought some supplies in the form of the flux composites shown below.



    upload_2019-7-15_7-59-41.png upload_2019-7-15_8-0-0.png

    I also acquired different samples of silver wire so that I can try and see which one works best.
    Here's a brief the description of a couple of those wires:

    • Silver Solder Wire 20 Gauge 0.032"
    • Silver content: 56%; Density: Extra Easy
    • Solidus temperature : 1,145°F (618°C)
    • Liquidus temperature : 1,207°F (653°C)
    • Silver Solder Wire 20 Gauge 0.032"
    • Silver content: 70%; Density: Medium
    • Solidus temperature : 1,275°F (691°C)
    • Liquidus temperature : 1,360°F (738°C)
    I then began to test things using a miniature butane (lightener fluid) torch that I have, shown below.

    Image00001.jpg


    Now, I know that the torch is quite capable of reaching the temperatures needed for this task, because if point it directly at the silver wire it will easily melt it, and it can also turn the SS parts red hot if they're heated for a few seconds. (I read somewhere that heating the parts red hot is undesirable when soldering with silver)

    After applying flux to the part, I then used the torch to heat it and waited until the flux went from a paste to a liquid, and then applied the solder. The solder did melt alright, but it curled into a ball, and did not turn into a liquid as I've seen in the videos available in YouTube, and it didn't adhere to the parts at all.

    What gives? Am I using the wrong flux? Or is it the wire I chose? Or perhaps the torch I'm using is too small and does not produce the amount of heat needed?

    @shortbus , I have a feeling that this sort of thing is right up your alley. Any thoughts?
     
  2. SamR

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    Mar 19, 2019
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    Everyone I have ever seen doing silver solder work was using a small oxyacetylene brazing torch.
     
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  3. SLK001

    Senior Member

    Nov 29, 2011
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    The torch seemed to have burned off the flux before the solder reached liquidus, because the solder isn't wetting at all. Maybe apply the flux to a hot surface. Did you scour the surfaces to be soldered with a SS brush first? The oxides on SS can be harder than a witches heart.
     
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  4. Wolframore

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    Jan 21, 2019
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    It's all in the correct flux and prep. Stainless steel creates a Chromium oxide barrier (Passivation film) that makes it resistant to corrosion. You need to cut through that layer with a proper flux. I've seen it done but haven't done it myself. The flux I've seen looks like a rust colored paste.
     
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  5. shortbus

    Expert

    Sep 30, 2009
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    Any silver solder that has the percentage of silver in it that you're using needs to get the part to red temperature. Melting (balling of the solder) will take place without getting to red temp, but it won't bond until red temperature.
    Compare the liquidus temperatures of your solders to the chart of red temperatures below, liquidus needs to be, at the minimum reached to bond, but getting too much past it will "burn" the part and no bond will happen.

    Colour Temperature [°C] Temperature [°F]
    Red: Just visible 525 977
    Dull red 699 1,290
    Dull cherry red 800 1,470
    Full cherry red 900 1,650
    Clear cherry red 1,000 1,830
    Deep orange 1,100 2,010
    Clear orange 1,200 2,190
    White heat 1,300 2,370
    White bright 1,400 2,550
    White dazzling 1,500 2,730
     
    Last edited: Jul 15, 2019
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  6. cmartinez

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    Thank you all for your very helpful responses. Maybe I'm making the mistake of not preheating the part before applying the flux?
    And shortbus, I'd say that the color reached by the part is between dull red and dull cherry red. Maybe that means that not enough temperature is being reached?

    On the other hand, I found this solder that seems to be a marvel:


    https://www.muggyweld.com/product/ssf-6-silver-solder/
     
  7. Wolframore

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    Jan 21, 2019
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    There's a difference between soldering and brazing.
     
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  8. cmartinez

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    I confess myself a complete neophyte... mind elaborating?
     
  9. Wolframore

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    Brazing is higher temprature than soldering:

    The American Welding Society (AWS) defines brazing as such a process which involves a filler metal which has a liquidus above 450°C (842°F). Soldering, on the other hand, involves filler metals with a liquidus of 450°C or below.

    Soldering is a low-temperature analog to brazing. Metals that can be soldered include gold, silver, copper, brass, and iron. The filler, called solder, melts. When it solidifies, it is bonded to the metal parts and joins them. The bond is not as strong as brazed joint or welded one. Solder was once made mainly of lead, but environmental concerns are pushing industry to lead-free alternatives.

    You can solder stainless steel... it is easier to do than brazing... Stainless steel absorbs heat but does not conduct it well. It is difficult material to weld, braze or solder...
     
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  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I have never tried stainless, but evidently it is a bear to SS or Braze. Similar to cast iron, about the only success I have had with that is brazing.
    But for stainless, any silver solder is OK , but I gather you need an acid-based flux made specifically for nickel or stainless steel.
    Max.
     
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  11. cmartinez

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    That's why I bought two different flux types, to see which one works best. And both claim that they can be used for SS. So far, my biggest suspicion lies on the material not getting hot enough.

    According to this manual:
    • "If the rod balls up, the base metal is too cold-- back the brazing rod up and heat the base metal in a broad fashion."
     
  12. jpanhalt

    Expert

    Jan 18, 2008
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    For stainless I have used:

    Filler:
    Easy-Flo 3 (alloy 31-503), Lucas-Milhaupt (very good and easy)
    or
    Prince & Izant (cadmium free)
    McMaster-Carr #76965A62

    Flux:
    Superior 601 (used most often)
    https://superiorflux.com/spec/TDS_No_601.pdf
    (I believe the above flux is McMaster-Carr #7693A1 . At least when I ordered that number years ago, it came labeled ,"Superior 601.")

    There is also a 601B (very limited experience with it)
    https://superiorflux.com/spec/4_12/TDS_No_601B.pdf

    Temperature control is critical. Too hot or cold, and the filler tends to ball up. Just right, and it flows well. I do not do it often and each time requires practice. In my experience, once you overheat stainless, you are screwed unless you do an awful lot of clean-up.

    As for the McMaster filler wire, wow has that price increased. Current price for that quantity is about 10x what it was earlier this century.
     
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  13. Zeeus

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    Apr 17, 2019
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    @cmartinez Sorry for asking here..forgive for sake of Sertillanges

    Please trying/ tried to solder with "lead free" silver solder using copper clad but it does not work...worked with solder that contains lead...

    Is there any available lead free solder to work with copper clad ?

    Thanks
     
  14. cmartinez

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    It worked!

    What I did is I increased a little bit the flame, and then applied the other flux that I had. That is, I used Harris Stay-Silv instead of the Lucas-Milhaut brand. The first one looks like a dark gray mush, whilst the latter is a white colored thick cream.

    What I did was cut a very small ring of low-temp soldering wire (Silver content: 56%), wrapped it around the 5/32" rod of SS, and slid it down to the part I wanted to solder. See below.

    Image00002.jpg

    Notice how the solder flowed down through the very narrow gap between the part's hole and the rod.

    When I opened the Stay-Silv jar its contents had separated, with a thick dark brownish mud at the bottom and lots of water at the top. So I stirred it thoroughly with a plastic spoon, and then applied a couple of drops on top of the solder ring.

    Image00001.jpg

    Here's an interesting bit: as I was heating the parts, the flux began to boil and it started sparkling a bit in tiny bright red spots! So there's definitely some metal dust mixed in.

    I'm going to keep practicing and see if I can use even less solder for this joint, but the solder wire that I'm using (about 1/32" diam) is too thick to make that easy.
     
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  15. SamR

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    I saw a lot of stainless steel piping being fabricated over the years and one very critical step was prepping the pipe. They spent a large part of their time cleaning the area around the joint with angle grinders to remove any hint of oxidation and get down to bare shiny metal before TIG welding. I would assume the same prep is necessary for SS albeit by sanding instead of grinding. Make sure you have a clean bright surface before soldering. Sand it down.
     
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  16. Wolframore

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    Awesome... that's the brownish flux I was talking about! Nice.

    When you take the oxide layer off it's important you put flux on it right away... stainless chormium oxide layer happen extremely quick! That's why it's so resistant to corrosion.
     
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  17. cmartinez

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    I'm guessing that this type of solder that I'm using should work for what you want.
     
  18. cmartinez

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    Yup ... that's exactly what I did before starting this whole process. Thanks for emphasizing how important this is.
     
  19. Wolframore

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    that looks interesting... what are you making?
     
  20. cmartinez

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    Test #2. I used #30 Ga (really thin) pure sterling silver. It didn't work.

    Image00002.jpg


    Here's how the part looks with the flux applied.

    Image00003.jpg



    The picture below clearly shows that not enough temp was reached for the silver wire to melt.

    Image00004.jpg




    Test #3. This time I used medium alloy (70% Ag) #20 gauge silver wire. It's easy noticeable that the wire's way too thick for the part.

    Image00005.jpg


    And it didn't work either, also for lack of enough heat.

    Image00001.jpg



    My problem is now clear. I need a far better torch than the puny toy that I've been playing with. I'm setting my eyes on something similar to this:

    Image00001.jpg
    Now that I've found a miniature torch, my next question is, where can I find miniature oxyacetylene tanks? The only ones I know are humongous!
     
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