Do you measure metal temperature and how ?

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

  1. metallab

    metallab Silver

    Just curious.
    Does anybody measure temperature ? Infrared pyrometer, thermocouple ?

    I kick off.

    I use a type S (K is too unstable and not high temperature resistant) thermocouple sheathed in alumina but can only measure swirling air/ gas temperature around the crucible. This TC is very durable. I have no means of measuring metal temperature as the couple itself dissolves in the metal (when immersed without sheathing) or the sheathing gets wetted and when pulling it, the wetted sheathing freezes with a thin layer of metal on it.
    Using an infrared pyrometer cannot be used on bare metal because of the low emissin factor, so I can only measure on the slag layer which is only an indication (+/- 50 C) of the metal temperature.

    I saw in a thread of Petee716
    that he talks about "The stain is spit (poor man's pyrometer).".

    I once heard a similar story about that in the past iron casters spitted on the liquid iron and inspected how the spit reacts which can be an indication of the temperature. I don't believe it, because the spit vaporizes before reaching the crucible.
    Or is this true ?
  2. I use a Kane & May industrial digital pyrometer which is good for 13ooc
    & a type k thermocouple which I slide down a thinwall stainles steel tube with the end previously flattened & hammered over it's about 1/8" diameter & about 6" long but before I use it each time I paint it with a zircronium based refractory wash & dry it in the exhaust & after finish the alloy or bronze just taps off & it prevents any contamination of the metal & also the stainless lasts forever. I also coat my tools, ingot moulds or muffin tins as well because as you will know molten alloys dissolve steel,I've had my moulds & tins for years & no deteriation.Hope this helps.
  3. This chart may be of help??
  4. Zapins

    Zapins Gold

    I use a graphite sheath over k type probe from mifco and dip it the molten metal after preheating it for direct measurements:

    I hooked it to a horrible freight $5 multimeter. Works decently well. But I will upgrade the meter at some point.

    Use this chart (or any other k chart) to convert voltage to temperature:

    Also bend/build yourself a little handle for the probe to sit in. And shoot for 2150F for bronze pouring temp.

  5. Jason

    Jason Gold

    I dont measure temp anymore with any device except my eyes. I've learned to slow down, take my time and just pay attention to the metal. I still screw it up occasionally and might pour a bit on the hot side. You have to be kind of dumb to attempt to pour with chunks still floating around. I learn a lot when skimming and poking around with a piece of rebar.

    Zap, can you plug your thermocouple into one of those 5buck chinese meters from ebay?
  6. Zapins

    Zapins Gold

    I tried another meter which didn't work. Kept giving me numbers that didn't make sense.

    I noticed a big improvement in the repeatability of my castings when I started using a pyrometer compared with just eyeballing it. It doesn't make much of a difference in more block like castings but for some of the highly detailed and thin castings I've done more recently every little bit counts if you want a good casting.
    dennis likes this.
  7. HT1

    HT1 Gold Banner Member

    I use the Mifco 8 inch K probe... $46... I’m on my second in 10 years.... so I have to wonder about guys killing them.. my rig is 1/2 EMT conduit. The probe end was sliced with a hack saw and a hose clamp crimps the probe into place.. I put a plain handy box with a receptical in it and use the receptical as a convenient place to connect the wires. I use harbor freight cen tech meter 61593. $22. It comes with a cheap probe. I cut the end off the probes and wire it into the receptical box... so I can easily disconnect the probe from my meter if I need it... a lot of people are bad mouthing the Mifco probes for failing... I think you are using them poorly.. they are delicate and the probe always has to be downhill..: don’t just shove it into the melt in a running furnace and wait for a reading... preheat the probe try to only get the tip warm... my drain port is on the back of my furnace so that is perfect... you can only get the probe hot!!! protect the wires... learn how to interpret your meter... I almost always pour at 1094C. learn metric it is what the meter gives you! So I preheat the probe to over 1000c. Then go into the melt. watch about two seconds if temp not rising your heat is below 1000... if you leave it in it will start to rise a couple of degrees a second.. if you do that and it starts to rapidly rise I look for at least 1050 if it has not slowed any it’s over 1095... I can pour... I’ve only had the meter actually read 1095 on a heat once and i knew it as hot anyhow... zinc was billowing out... for yellow brass that’s good...

    V/r HT1
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  8. Zapins

    Zapins Gold

    I use mine the same way as HT1 and have had mine for at least 4 years now. My metal temp is often above goal so I just turn off the flames and keep the blower on until the temp of the metal in the furnace cools enough to pour then its go time.
  9. Jason

    Jason Gold

    Maybe I need to buy one of these probes and try it.
  10. dtsh

    dtsh Silver

    I have an IR thermometer which seems to work pretty well. It jives with the temps at which the aluminum melts and other items I've checked it against, but I don't have a way to determine exactly how accurate it is. It seems pretty accurate to me.
  11. Melterskelter

    Melterskelter Gold Banner Member

    I use a Type S thermocouple for my iron. I buy probes that are intended for use on commercial immersion pyrometers. I built a pyrometer consisting of a bent piece of SS tube with a shop-made brass plug that fits the probes. I purchased a dedicated millivolt panel meter as it reads much more prcisely than the mV scale on the typical VOM meters that most of us buy for 20 to 50 dollars. I enclosed the meter in a metal household wall-receptacle box along with a battery pack and cut a hole in the metal cover to fit the readout of the mV meter. I do have to have a printed table nearby to convert the mV reading to a temperature reading. But I have learned that 14.1 mV is about where I want to pour---2550 F as the reading assumes the wires of the couple are at 0C---so I add about 40 or 50 deg in the summer. Need to go to 14.3 or so in winter.

    I tested my meter against a couple of commercial foundry meters at the the foundries. The reading was within 20 degrees of agreement with their $4K units---good enough for the girls I date.

    The probes are about 4 bucks each and need to be handled very carefully as they are very fragile. I can get about ten readings out of them if I am careful. I do make sure the melt is skimmed and no unmelted metal is below the surface as that will kill the probe instantly.

    I'll put some pics up in the next day or two.

  12. $4 is pretty darn good for an S type thermocouple, I can't imagine how fine the wires must be on that. Been meaning to try out some K types I bought with about 3mm wire gauge and alumina insulator body but it'll need an outside shell of some kind.
  13. metallab

    metallab Silver

    Indeed, I got an S for $15 incl shipping. It are 0.2mm Pt/Rh wires and the alumina sheathing is included. And, despite the thin wires, it is very durable and reacts quickly. I have two other 'S'-es with 0.5mm wire for decades and they respond more slowly, but are accurate. All three measure ordinary room temperature matching the values of ordinary thermometers within the degree. That won't say that they are so accurate at 1400 C, probably not. But better than 'K'-s, the latter even don't withstand 1400 C.
    But 3mm wire gauge ? That is very thick and will respond very slowly. I have a few 'K'-s with only 0.2mm gauge.
  14. Melterskelter

    Melterskelter Gold Banner Member

    I have never measured the wires, but I can say you really have to look carefully to see them with the unaided eye.

    Edit: I measured today Nov 1 and the one wire is .0015" diameter---thinner considerably than a human hair on someone's head which is .004 to .006" on average though some blonds have hair as fine as .0015"

    Last edited: Nov 1, 2020
  15. Melterskelter

    Melterskelter Gold Banner Member

    I went out tot he foundry today and made some photos of my shop-made immersion pyrometer.

    These are the tips I use. Several manufacturers make interchangeable ones. Mine cost me roughly 4 dollars as purchased in a case from a foundry supply. One case will likely last me for as long as I want to/am able to cast.
    The cleat tip is a quartz tube with the thermocouple in it
    The end that plugs into the pyrometer

    Cutaway tip on the plug side showing the plastic plug casting holding the copper contacts connected to the couple.
    The brass plug parts I enclosed in the outer SS tube. Inner bar is 1/8" and outer contact is about 1/2"
    The outer tube crudely bent by just racking it multiple times in a vise. It would have been nice but unnecesary to roll it.
    View of the electrical box and its attachment to the tube. I am clumsy enough that I wanted a robust idiot-proof attachment. The square barstock has holes that are sliced on one side and pinched shut by the SHCS's. The panel meter uses 4 AA batts.

    The pyrometer without a tip.

    The panel meter let into the metal box plate. I highly recommend a backlit meter as reading it in sunlight is otherwise a challenge. One toggle is on-off. The second is the back light and the push button is a momentary swuiutch that captures the highest reading.

    Here is abrief video showing the inner contact point of the pyro tips supplied by Reliacheck and others. If a person were to make a pyrometer, I would suggest either getting a defunct tip from someone using them or sacrifice a tip to tune the measurements of the plug

    This pyrometer has been extremely reliable, precise, and very robust save for the necessarily fragile tips. I mic'd a couple wire a .0015" and that may have been the larger of the two. The other wire on the broken tip I was checking was too short to mic.

    Panel meters are available from various sources. I think I got mine from Mouser. It was about 15 or 20 bucks.
    Here is an example of what I think I used:

    The bent tube could be any convenient steel or SS tube. You have to get the OD of the plug portion of the tube right (I nested a thicker walled machined tube in the outer tube) so that it is a reasonably snug fit so the tip won't fall off and yet is not too tight for easy assembly. I spray my tips with silicone or teflon. Graphite is conductive.

    Last edited: Nov 2, 2020
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  16. Melterskelter

    Melterskelter Gold Banner Member

    Oops, I see I had failed to embed the tip video above. Fixed it.

  17. Jim Edgeworth

    Jim Edgeworth Silver

    I knocked them one up with a AliExpress digital thermometer with K type probe ($3.5) inside a graphite rod (5 for $3) bored to take the probe, steel tube with hardwood grip and sleeve to protect the graphite rod. Seems to work well, but only tried it out with aluminium so far.

    Attached Files:

  18. Billy Elmore

    Billy Elmore Silver

    Yall are going to think this is crazy but one of our former owners used to lick his fingers and then run them through the stream of iron while it was being poured form a transfer ladle to a pouring ladle to check the temp. He was way more accurate than you could imagine as they checked against him several times with a probe and he was very close...which tells me he had lots of experience doing that. I never saw it but have spoken to many eye witnesses who say he was crazy. I would not recommend anyone trying this but it is an option for those who dare or just don't like their fingers very much.
  19. rocco

    rocco Silver

    You were right, I think that's crazy.
  20. Jason

    Jason Gold

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