Chromel to Chromel

Discussion in 'General foundry chat' started by Jason, Nov 15, 2019.

  1. Jason

    Jason Gold

    Just about everyone here uses a thermocouple in some sense of the word. I've got a 16ga alumal/chromal wire that's about 20feet in length and snakes through hell and back. Long story short, a small pin on the end of a chromal is broken. The pin resides in a 1inch sized cannon plug with about 20 other pins. The factory originally soldiered or brazed the chromal pin to the chromal wire with a silver looking material. I know all the stories about crimps only, blahs blahs blahs. But this pin must be attached in the same manner. What is the mystery silver stuff???

    and no, off the shelf silver soldier doesnt work, it just balls up and falls off. I need a silver for high heat. To attach anything to chromal, you have to get it red/ orange hot. So far, only mapp was able to release the factory silver from the broken chromal pin. Should I just say f it and use gold???
     
  2. I would try some plumber's zinc chloride based flux and 60-40 rosin flux core solder, that combo will even soft solder 316 stainless steel which is also a nickel chrome based alloy. I use Ezi Weld 801 which has zinc chloride, hydrochloric acid and sal ammoniac (ammonium chloride).

    https://www.hampdon.com.au/soft-soldering-flux-x-250g-jar

    If you're joining two identical alloys together in a thermocouple circuit then any alloy of solder that will solder it will work, as any thermocouple voltage effect at the join will cancel out. I went into meltdown when I first saw someone make T thermocouple junctions by soft soldering the two thermocouple wires together but it turns out he was right and it doesn't matter: a third alloy between the two thermocouple wires has it's voltages cancel out as if it wasn't there.
     
    Last edited: Nov 15, 2019
  3. Jason

    Jason Gold

    What do I use for heat?
     
  4. Just an electric soldering iron. You could improvise the Ezi Weld 801 by mixing cloudy ammonia with hydrochloric acid to get ammonium chloride, you could then "kill" some hydrochloric acid with pieces of zinc to get zinc chloride and then mix the zinc chloride with the ammonium chloride and some hydrochloric acid to get the same mix as Ezi Weld 801.
     
    Last edited: Nov 15, 2019
  5. DavidF

    DavidF Administrator Staff Member Banner Member

    Stay silv. 85-15-5 that last 5 is phosphorus and acts like a flux. I'm pretty sure that's what you need.
     
  6. Jason

    Jason Gold

    David, do I need high heat with the 85=15=5??
     
  7. I got curious about this and ran the experiment with 60-40 electornics solder and the Ezi Weld 801 plumber's flux. The badly corroded thermocouple wires needed to be completely scraped to bare metal before dipping in flux and soldering straight away. I won't say it's a pretty solder join but it is definitely wetting the chromel and alumel wires of an old corroded K type thermocouple. It's almost reluctant to wet the wires but it does work, probably because chrome, nickel and aluminium all self passivate with an oxide layer. There are active flux cored aluminium solders (tin lead based ) that would probably work well on clean wires.

    solder chromel alumel 1.jpg


    solder chromel alumel 2.jpg
     
    Jason likes this.
  8. DavidF

    DavidF Administrator Staff Member Banner Member

    Yes over 850 f
     
    Jason likes this.
  9. joe yard

    joe yard Silver

    Can you spot weld it?
    Joe
     
  10. Jason

    Jason Gold

    That's impressive mark.

    I thought about that too Joe, but there is some high dollar stuff all around the area. I cannot remove the thermocouple wires. Just running any kind of torch in this hell hole is going to be a challenge. I'll have to use some kind of heat shield to protect everything else. Kaowool to the rescue.
     
  11. Jason

    Jason Gold

  12. Jason

    Jason Gold

    I have some silfoss 15 so I heated a pin with a butane torch and tried that. It definitely bonds to the chromal.
    This is the cup end of a 32dollar pin. Seeing I cant find what you recommended Dave, I guess I'll try this.

    20191115_215310.jpg
     
  13. Jason

    Jason Gold

  14. Jason

    Jason Gold

    I was able to get safety silv 56% and the white flux. The pins went on easily and wetted out. Finger crossed I didnt add too much resistance. For now I'm seeing less than 1 ohm difference so it should be a non event.
    20191118_173431.jpg
    20191118_172818.jpg
     
    Mark's castings likes this.
  15. That one ohm reading is probably the lead resistance of the digital multimeter, I'd say it'd be lucky to be 0.2 Ohms for a soldered joint although the resistance of the alloys suck compared to copper. It's a pity you didn't have access to one of those teeny oxy-acetylene torches that jewellers and orthodontists use. Are you going to do a rough calibration check with another digital thermocouple temp unit?.
     
    Last edited: Nov 19, 2019
  16. Jason

    Jason Gold

    Yeah Mark, I've got a barfield box to check the resistance on the wire. It also allows me to dial in an egt and it can be read on the indicator. It acts as the engine's "rake" or thermocouple group which there are 10 individual sensors.... Pretty slick box, Cost about 4grand and goes out for calibration every 90days.:eek:

    We had some funkiness going on last night during testing. I have to check today, but I have a feeling either the tech pinned the connector wrong or the alpha numeric designations might have changed over time. A company in NY tried to sell me 60%silver with cadmium for this job. I decided to pass. From what I read, its nasty stuff and I was the guy making the connection. If anyone was going to burn down my shit, it was going to be me.:oops:

    We have those little hydro torches in florida, would have been sweet on this job.:rolleyes: I used a butane torch from HD like the one I use for wax work. It was plenty of heat, fast and controllable. It was 25bucks and makes our snap-on butane torch look like a joke. Nothing like getting screwed by the red rape truck.:(
     
  17. Cadmium vapour in a confined space is not my idea of fun :confused: and it comes off with not much heat too.
     
  18. Jason

    Jason Gold

    Funkiness found! It appears someone crossed an alumel and chromel and things were going apeshit. For the moment, I think I might be outta the woods. Fingers crossed.
    After what I read on cadmium, I was out. I did hear back from engineering at the manufacturer and they said silver solder. I told them there is about 50flavors of silver solder and need more clarification. Some how, I think they don't have a clue.:rolleyes:
     
  19. Jason

    Jason Gold

    Mission complete! I could not ask for a more perfect setup.... It makes 650 in a blink of an eye and will plant you back in the seat on takeoff.
    I took this in cruise yesterday. Thanks guys for the help on this one. I never would have thunk chromel was such a finicky bastard!
    20191122_162846.jpg
     
    Tobho Mott and Mark's castings like this.

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