RareEarth
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Heating mantle turning yellow/red upon heating?
I haven't used a heating mantle in a while, but I found one in storage. When I went to test it by boiling some water in the correct size flask, I
noticed that the some of the fabric area underneath parts of the flask started to turn dark red/yellow. As if it was burning, or something.
What could be causing this?
On a side note, is it safe to use a heating mantle if the flask inside is not filled up above the mantles edge? Such so that there are dry spots of
the glass being heated?
Edit:
Whoops, it appears it was the bottom of the glass turning red, not the mantle fabric. Maybe there was some residue on the bottom of it.
[Edited on 5-1-2016 by RareEarth]
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BromicAcid
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It's actually easy to get a mantle too hot like coils in a toaster oven. Let me guess, you were not using a variac and had it plugged directly into a
wall? If so, big problem, get some sort of regulator. If you did then you were pushing it too hard. If you do that too many times or for too long
you will fuse the glass in your mantle or burn it out. Fusing it is not a big deal in a hard mantle but for a soft mantle it certainly becomes
apparent quickly.
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RareEarth
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I thought most mantles couldn't get physically hotter than 450f?
I do have a temp controller but I don't think it can be used without a thermocoulple. I'd have to look at it again.
Wouldn't a variac only affect the rate at which it heats up, not the temperature the fabric gets to?
[Edited on 6-1-2016 by RareEarth]
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Ozone
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I've seen the glass fabric melt many times. Bad news. Fortunately, they will usually still work, but the exposed heating elements were worrisome. This
was common when we used to run 40 at a time (wall of liquid-liquid extractors)...one would often accidentally be left on. Toasty.
Just don't turn them on without some kind of means of removing the heat--usually via a condenser. Always use a variac.
As for the color, they seem to yellow naturally. A red color seems, to me, like something got spilled into it and has since burnt. Oops, nevermind.
O3
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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Dr.Bob
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Heating mantles can get hot enough to melt borosilicate glass, I have seen it happen... (No variac, no heat drain, left on overnight...) I would
guess that is more than 450F. The variac controls the voltage, which determines the amperage, which determines the rate of heating, but since heat
goes from high to low density, the rate of heating does help determine the ultimate temperature. I rarely use a mantle over 40-50 volts, even large
ones. The only exception might be heating water to boiling or a very high BP liquid. But they should never be used without either a voltage or
current regulator (thermostatic can work or just power cycle) or both, preferably.
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