Discussion in 'Foundry tools and flasks' started by Jason, Aug 25, 2017.
Did you realize that probe is "Only" 1.96" long?
Does the graphite rod get burned at these temps, or absorbed into the molten metal? Noob showing his colours
Coke auto ignites at 700 deg C so you'd need to quench it once it's out of bronze at least, aluminium might be ok.
Here's a photo of carbon gouging rod sheath consumption at somewhere between 4-8 hours exposure in air up to 1800F (982c). The one I have now looks about the same after ~50 dips in molten aluminum several minutes at a time. I've had it at 1800F metal temps and although it glows bright read when removed, if there is any ignition, it quickly self extinguishes. I'd add that I seem to have a 25-50F discrepancy between my other TCs and the carbon sheathed version (carbon sheathed is higher) and this appears to be real, and may very well be a reaction occurring on the surface of the carbon slightly elevating the measured temp. -Cant attest to brass/bronze service but I think others here seem to do fine with them.
That level of erosion looks acceptable and the cost of the rods is economical, about the only alternative would be those aluminium oxide/alumina tubes on Ebay which would need the end plugged.
What about these?
The premade t-couple from Mcmaster Carr come in that same ceramic tube. The wires are exposed on both ends so no dipping those in metal. The wires will also burn up if left exposed just poked into a kiln. The gouging rods are cheap, but drilling is a pain. So for checking the temp of the "air" in a kiln, the best option is the stainless steel sheethed probe. They make those 1.96" probes in a longer version. Here's the link on that one. https://www.amazon.com/0-600C-Tempe...sr=8-6&keywords=k+type+thermocouple+stainless
Kelly and I both made the mistake of just using the carbon sheeth as a covering in an electric "kiln". It kinda funny to see how the carbon just disappears in a short time. Mine lasted maybe about an hr and it disintegrated and left my t-couple exposed and melted it. Hence the reason I switched to the SS probe. Something that helps the carbon last longer when dipping is keep it out of the flame, don't preheat it and go straight for the molten metal. That time in the air burns off the carbon faster than the dunking.
I use Inconel sheathed K-Type TC as the furnace temp control sensor. It's 1/8" diameter 6" long poking through 4" of IFB and I'm still on my original probe. Many such probes will also specify the max operation temp at the cable interface.....and some are suitable for this type of service and some are not even though the probe itself is capable such.
Ya-know, the interesting thing is, in my present use the sheath is mounted in a stainless steel tube and I insert the whole assembly into the furnace through the hole in the lid with the furnace at temperature. I made a little stand to control the probe insertion depth.
The sheath is not fully immersed in molten metal yet the 4-5" portion above the molten metal exposed to hot air is not reduced while the immersed portion is. Granted, this may occur when it is withdrawn and still at temperature but no doubt the exposure time of the air exposed portion is greater than the immersed portion of the sheath.
Sorry for the Resurrection but with so much pyrometer talk at AA I’ll show my rig here ... 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...
Hope this helps someone
P.S. remember keep the probe downhill... the pic above shows exactly where mine is at all times
If I try to preheat my graphite rod before dunking, I won't have one. It disintegrates in side my kiln. What's your probe made outta?
Here is all the Information, my eyeball says it is a low grade of Stainless
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