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  1. #1
    precisionmetal's Avatar
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    Default Cutting tungsten/water conductivity

    A question for anyone that's cut tungsten in decent amounts.

    I had a wire job that ran for a good number of days cutting tungsten (significant cutting using .010" wire). The resin in my machine was quite new before the job, and I turned conductivity up during the cutting and turned it back down after the water cleaned up. The conductivity would not come down significantly.

    I chalked it up to something the tungsten did to the resin (?).

    So... did a resin change... and had a stainless job I ran for a few days (very light cutting, not much "debris"). But... even after the water is clean from the stainless job, I still can't seem to pull the conductivity down where I'd like.

    Has anyone encountered this? Is there something going on with cutting tungsten that I'm missing?

    Any insight appreciated.

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  2. #2
    EDM AE is offline Aluminum
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    You have probably already considered this, but in case you haven't... Have you verified that the conductivity sensor contacts are clean? Also, it would be a good idea to check that there are no obstructions to the inlet of the D.I. pump such as a piece of paper, shop rag, etc.

  3. #3
    precisionmetal's Avatar
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    No... everything checked (I check that stuff all the time... not just if/when there's a problem).

    Conductivity sensor is clean. Machine conductivity is reading 2 points off my handheld meter like it always has. Good flow through the DI can. Everything double checked (vs. the "single check" which happens on a daily basis ).

    I normally get very fast response from the D.I. system... can pull the water down from a conductivity of 10+ to under 2 in a few hours without any problem. After this tungsten job though; it's just hanging at about 8.

    The only thing I have NOT done is change the filters (bypass pressure still quite low and the filter are still quite new).

    I guess the only thing I have not ruled out is that the tungsten in the filters is "re"contaminating the water in some way that is preventing the D.I. system from fully doing its job.

    Maybe I'll put a piece of aluminum in the machine and make a few cuts... that usually pulls the conductivity right down.

    Still searching......

  4. #4
    BrianA is offline Plastic
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    Have never wired carbide for more than a few days, so never noticed a problem.

    But, this from my Agie manual,

    The water's conductivity will increase sharply when eroding carbide, the following will result:

    Greater demand upon the DI resin
    Rapid ageing of the water
    Corrosion of the workpiece material

    Therefore the DI resin should always be replaced at an early stage.

    and this,

    .......... causing a reduction in the life of the resin and of the FILTER.

    So your contamination theory (from the filters) could be the cause.

  5. #5
    TheMetalDoctor is offline Titanium
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    Default Tungsten, conductivity problem

    Precision Metal...

    Sounds like you have covered all the bases. There has to be a skunk in the woods if you "smell-em". Let us know what you find. We all gain from the shared information here...

    Sorry I have nothing to offer.

    TMD

  6. #6
    precisionmetal's Avatar
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    Brian,

    Thanks for your input. Yes... I've read the same section in the manual as well. I'm not sure how the D.I. or the filters "feel" about tungsten -- whether it is similar to carbide or not. To be 100% precise, the material I was cutting was a tungsten copper alloy... though the percentage of copper was very low.

    TMD,

    I'll definitely post what I find. If nothing obvious surfaces on this, I'll probably change the filters and the water in the machine... and if that doesn't do it, it must be planet alignment or sunspots. <big grin>

    PM

  7. #7
    Jay Cee's Avatar
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    I cut a lot of tungsten (I mean a LOT!!) and have never had a problem with it killing my DI at any insanely abnormal rate. And I especially have not had a problem where the machine would not come back after the resin has been changed. The only DI - tungsten relation that I've seen that is note worthy is tungsten will not cut at all if your DI is bad. As a matter of fact, you can always tell when the DI is going bad by the cutting speeds. A couple of points high and your speeds drop by half.
    FWIW, I cut everything from 99.98% pure tungsten to a 80/20 tungsten/copper. Cuts vary from 4" thick to .039" thick.
    Curious... do you use virgin or regenerated? I use regenerated... Not sure it has any relevance... Just exposing another possible variable.
    Wasn't it discussed here before that the aluminum cut dropping DI is a false reading?

  8. #8
    precisionmetal's Avatar
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    Virgin resin here. I've never used regenerated.

    Yes... the aluminum dropping the conductivity has something to do with hydrogen being liberated or something like that?

    Thanks for your input, Jay Cee.

  9. #9
    EDM AE is offline Aluminum
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    Yes, Jay Cee, we have discussed the apparent effect on water conductivity when cutting aluminum in the past. Below, I'm pasting a copy of one of my earlier posts addressing this common misconception:

    "Gents, I'll make this as short and sweet as possible, as there could be volumes written on this topic. This "deionizing" effect you're witnessing when cutting aluminum is a false security. In the mixed bed of resin, the aluminum ion is accepted by the cation bead, which releases hydrogen in this exchange. Chloride ions, which carry the bulk of conductivity, are exchanged by the anion bead for hydroxide. The basic principle is that the combination of these two reactions produces one H and one OH (H2O) maintaining water purity. In reality, cutting aluminum makes your water hydrogen rich, and resultingly more acidic. This will not be readily apparent just by glancing at your conductivity level, as Hydrogen is a very poor conductor. Aluminum not only destroys your filters, but also the cation portion of your mixed bed DI resin."

  10. #10
    precisionmetal's Avatar
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    As a follow-up and closure to this thread... I found the problem.

    Or more precisely; I eliminated any other possibilities, and finally concluded that I must have a filter that was leaking (or was damaged in some way) so that it would contaminate the water supply just enough to keep the conductivity up.

    And that's what it was. Bypass pressures on both banks appeared equal and normal for the time the filters had on them, so there was no clear indication that I had a problem.

    But... put new filters in the machine, and the conductivity dropped like a rock...

    So all is well, and next time I have "stubborn" conductivity when everything else looks good, I'll change the filters.

    I appreciate the input of everyone that pitched-in suggestions/ideas on this thread. Thanks!
    Last edited by precisionmetal; 03-15-2008 at 12:27 AM.

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