Do you measure metal temperature and how ?

Discussion in 'Foundry tools and flasks' started by metallab, Oct 31, 2020.

  1. 0maha

    0maha Silver

    I had a conversation a few months ago with the guy who owns the company that makes the probes MIFCO sells. Good guy. Very helpful.

    He painted a picture that there are three things that impact the life of the probe in applications like ours:

    - The number of dips
    - The amount of time in the metal for a given dip
    - Whether or not you pre-heat the probe before dipping

    He's got a customer who uses the same probes we do in a continuous, brass casting environment. That guy replaces his probes every other day. That's pretty hard core.

    My specific question for him was this: Suppose I'm targeting 2200F, and I dip the probe and see 2160F. The furnace is still on, and the temp is still climbing. Am I better off just leaving it in the melt for the five or ten minutes (or whatever) as it gets up to temperature, or should I pull it and remeasure from scratch after a few minutes.

    His advice was to pull and remeasure.

    He was also very emphatic that pre-warming the probe in the furnace exhaust was essential to the long life of the probe. According to him, the thermal shock from dipping an ambient temperature probe into a 2000F melt is super hard on it.

    Thought I'd pass that along...
  2. Mantrid

    Mantrid Silver

    How long did he say to leave it in the exhaust?
  3. 0maha

    0maha Silver

    He didn't say exactly in terms of clock time. I told him my practice was to hang it over the edge and wait for it to read 2000F before plunging, and he approved.
  4. Zapins

    Zapins Gold

    Yup thats what I've always done too.
  5. Tops

    Tops Silver Banner Member

    Besides preheat and non-continuous use, are there any other care and feeding tips for the Mifco thermocouples? Anything special about gas furnaces and melting aluminum?
  6. HT1

    HT1 Gold Banner Member

    guys this is great advice, the explanation is really simple , the temp is "taken" at the little "tit" at the very end of the probe, , that is the ONLY part you want to get exposed to heat, which is pretty much impossible in our application(Fuel fired crucible furnaces), the rest of the probe is pretty well protected, but not perfectly, the wires in the ceramic "insulators/protectors" are not well protected at all, and thus a weak point, that is why the longer 12 inch probes for $10 extra dollars are really a GREAT bargain. and why your entire Pyrometer needs to be handled quite gently , those wires get hot and jostled, they may break

    V/r HT1
  7. 0maha

    0maha Silver

    Not that I know of.

    I think the bottom line for applications like what I think most of us are using is that if you follow those three guidelines, the probe should last a good long time. But it is still a consumable part that will not last forever. Depending on the particulars of your situation, having a spare on hand isn't a bad idea.
  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Make a good apparatus to hold the probe in position for preheat, taking temp, and storing it safely. I use Inconel sheathed k-types sheathed with carbon gouging rods but have broken several by dropping or walking into them. The carbon sheaths are only $1 but still a pisser to break one........much bigger pisser at $50-$60! Sort of a special case with an electric furnace plugging the entire vent. I don't preheat because they tolerate thermal shock and would be more difficult with an electric. It takes about 30 seconds to come to 90% of reading. I usually limit the dips to 60 seconds.. They last a lonnnng time if I don't break them.

    7 Good As New.JPG

    49 TC and Pyrometer.jpg 47 Furnace and Tool Holder.JPG

  9. Tops

    Tops Silver Banner Member

    Expecting the mini-K ends for the Mifco and some graphite rods to protect my little stainless Amazon probe to come in today.

    Is there a good way to remove dross from a stainless probe that was dipped in aluminum without a sheath?
  10. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Short answer....probably not if it's really dross. You can heat it up to say 1400F+ and see if it will wipe or scrape off but if it is dross aka aluminum oxide, it won't melt. It also won't sand off easily because Al2O3 is as hard as most common abrasives. It has probably alloyed at the SS steel surface. If the TC still works it will probably continue to do so and just be slighty slower responding so can be used as is (in non-contact service) unless you need the OD to be true, like to fit inside a close fitting hole.

    There was a member here (OldIronFarmer IIRC) that reported being able to use a common SS sheathed TC (or maybe just TC wire) for many dips because the dross served as a protective layer against further attack by the molten aluminum, but most report rapid failure.

    Tops likes this.
  11. 0maha

    0maha Silver

    AND...right on schedule I aborted a melt this morning because my thermocouple died.
  12. Tops

    Tops Silver Banner Member

    Bummer. If you weren't a state and a half away I'd loan you mine...

    The new mini-K's from Amazon are working. Hooked to a 12$ 4-inch SS probe the HF meter clocked an ice cube at -4 C.
    I have yet to try the MIFCO.
    When I am back at work next week I will make an adapter to assemble one of the graphite's over that 4" probe.
    0maha likes this.
  13. 0maha

    0maha Silver

    That's nice of you to say.

    The good news is I checked the function of the lance before the melt had really started. Was just pre-warming on propane at that point. Able to abort things before I had any actual melt in the crucible.

    And it gives me an opportunity to tighten up a few things in my process and equipment that I've been putting off.
    Tops likes this.
  14. Tops

    Tops Silver Banner Member

    Got my 'burger flippah' put together...most of the metal came off the probe with gas stove heat and a Stanley knife. The rest filed off pretty easily, enough to slide into the graphite sleeves and coupler they machined for me at work. Paddle end is about 4 inches in diameter plus a small laser-burned chart on the handle since I do not know any of these temps by heart yet.
  15. HT1

    HT1 Gold Banner Member

    pointing out the obvious
    those are melting temperatures not pouring temperatures

    V/r HT1
    Tops likes this.
  16. Tops

    Tops Silver Banner Member

    Thanks, true, it's worth mentioning for sure. I should find a different table and redo it.

    "Proper pouring temperatures for a given metal vary with the casting size, design, and desired rate of pouring. For this reason, the pouring ranges given below should be taken as a general guide only:
    Pouring-Temperature Range
    In general, thin-walled castings are poured on the high side of the range and thick-walled castings on the low side."
    Source: USN Foundry Manual 1958, page 142, with added Celsius conversions
    Last edited: Jun 11, 2022
  17. Tops

    Tops Silver Banner Member

    I worked on my Mifco thermocouple today. The lead machinist at work made made me a .500" bore x 2" long x 1 end @ .700" or so OD coupler to clamp into a piece of old 1/2" EMT with a 'free' bend. There is a 10-24 set screw in the coupler to catch the probe. I am trying to decide to keep using the HF meter or get something just for the foundry. If I picked up a 2 channel one I could test them both (this one and the one make previously) at the same time.


    0maha and Tobho Mott like this.
  18. Foundry Rat

    Foundry Rat Silver

    to Jason
    I use those, they are good tips, but not good for constant emersion.
    I am currently using a Rex C100 process controller set to type K with a 10 foot shielded lead with an emersion tip. I melt aluminum and I like to get my temp from the center of the bath.
    I am accurate plus or minus 1 degree at 1500F.
  19. john h

    john h Copper

    Another temp measuring question. I have two boron nitrite sprayed 6" SS ridged probes plugged into my hand held OMEGA digital thermometer ( I trust it) both probes are within 2 deg up high and down low.
    For regular thermometers I know freezing and boiling water is a calibration method since the 32f and 212f is stable during the phase change.

    The problem is we know AL melts at 1224f and when I dip my probes in the crucible right as the AL has gone molten I should expect to see 1230f or there abouts.
    My problem is they consistently read 1120f with no way to calibrate the OMEGA.
    Is this normal or what am I missing?

  20. That water calibration has to be with distilled water, not tap water to be accurate and having a decent amount of the ice-water is best, like half a bucket. So when I was doing that calibration on a regular basis, we had an industrial blender to shave the distilled ice cubes and then add distilled water to make a slush mix in an insulated container.

    Your aluminium temperatures would be for pure aluminium: 1220.58 deg F according to wikipedia. Adding other alloying elements would change the melting point, according to the Engineer's toolbox, aluminium alloys melt between 865-1240 deg F.

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