Sciencemadness Discussion Board

Heating mantle oopsie

Jome - 9-1-2021 at 06:41

Sorry for the rather unspecific topic.While searching the web I found a cheap heating mantle, a Faithful 98-III-B
Apparetly, finding equipment online from a zillion listings and models stresses and confuses me so much that I don't properly research what to buy; the mantle I bought has a metallic temperature probe, kind of like a steak thermometer, which must be immersed in the liquid in order for the heating mantle to start heating, otherwise it shows "HHH" (aka error).

So, I must either find a chemical-resistant probe to replace the metallic one (are they some kind of industry standard?), or make some kind of "pocket" for the probe out of borosilicate glass. Has anyone done this, or know someone who has? Any tips?



RustyShackleford - 9-1-2021 at 06:43

maybe you can replace the probe with a resistor of appropriate value.

Jome - 9-1-2021 at 07:28

Apparently, in ground glass terminology, both the threaded plastic things and the open "tube" type (one of which I used to have) are called "thermometer adapters", along with a sealed variety which is precisely what I need.

Now I feel even dumber. Sorry!

Maybe I should PTFE seal its upper end to prevent convection? Would that be an accuracy problem?

macckone - 9-1-2021 at 13:39

What you want is called a thermometer well or thermowell.

https://roccoscientific.com/product/thermowell-24-40/

I have ordered from rocco a few years back.
Good to work with.

Fyndium - 5-2-2021 at 11:03

Can one do distillations by putting the probe to measure the stillhead temp? At what level should the heater temp be set? I presume that putting it 10-20C above the bp would keep it running, but I'm not sure if the mantle element has on-off feature which either heats at full blast or is off or a progressive heating so it adjusts the power based on the desired set temp?

I'd use 3-neck flask anyway so the probe goes into the liquid via thermowell, but if I happen to use 1-neck, hence the question.

monolithic - 5-2-2021 at 17:05

Quote: Originally posted by Fyndium  
Can one do distillations by putting the probe to measure the stillhead temp? At what level should the heater temp be set? I presume that putting it 10-20C above the bp would keep it running, but I'm not sure if the mantle element has on-off feature which either heats at full blast or is off or a progressive heating so it adjusts the power based on the desired set temp?

I'd use 3-neck flask anyway so the probe goes into the liquid via thermowell, but if I happen to use 1-neck, hence the question.


Using a temperature probe to measure still head temperature works fine, you just have to be mindful of the thermal response of the probe. "Naked bead" in a thermowell work nicely because they respond rapidly. https://images.homedepot-static.com/productImages/af22876b-e... Something like a metal encased probe might not be so ideal due to much higher thermal mass. https://cdn.sparkfun.com//assets/parts/1/1/2/0/9/13715-01.jp...

Using the temperature probe in a closed loop / PID system probably isn't a good idea because there are too many variables at play. Most PID implementations just chop power on/off at the mantle and the PID tuning would be hunting for equilibrium that might not exist (e.g. during the transition of one fraction to another.) In cases like these, it makes more sense and yields cleaner fractions to just apply constant power to the mantle rather than turn the power on and off abruptly.

If the PID implementation was PWM rather than lengthy on/off cycles it might make more sense, but as far as I know most heating mantles don't do PWM.

[Edited on 2-6-2021 by monolithic]

draculic acid69 - 5-2-2021 at 19:14

Quote: Originally posted by Jome  
Sorry for the rather unspecific topic.While searching the web I found a cheap heating mantle, a Faithful 98-III-B
Apparetly, finding equipment online from a zillion listings and models stresses and confuses me so much that I don't properly research what to buy; the mantle I bought has a metallic temperature probe, kind of like a steak thermometer, which must be immersed in the liquid in order for the heating mantle to start heating, otherwise it shows "HHH" (aka error).

So, I must either find a chemical-resistant probe to replace the metallic one (are they some kind of industry standard?), or make some kind of "pocket" for the probe out of borosilicate glass. Has anyone done this, or know someone who has? Any tips?




The only advice I can give about these mantles I can give is:
DO NOT BUY they are cheap shit and mine didn't come
with instructions nor could any be found for it nor did it
have any non English writing nor a stirrer and it never worked
as it should.massive temperature spikes and an inability to
sit at the set temp made me gut the electronics and replace with
reliable stuff.dont buy.if U already bought cancel

[Edited on 6-2-2021 by draculic acid69]

Fyndium - 6-2-2021 at 00:46

I went and bought Joanlab 2L mantle from AliExpress and did two distillation runs with it using 1L 3n flask stripping IPA and toluene clean from a synthesis. It seemed to work actually quite decently by setting the temp to the boiling point of the desired substance. With toluene it sat steadily all the way, with IPA there seemed to be more like boiling range, but I don't think it has to do with the mantle. I also used a parallel set of thermometers for calibration, and the probe seemed to be on point with 1-2C error at max. I immersed the mantle probe into the boiling liquid via one of the 3n flask joints using thermowell. Remote probe was used for stillhead.

The stirrer worked well from the package at first. It does not give very high rpm, but likely enough for vacuum distillation not to bump excessively. When I did set it up, the stirrer messed up and it was either at full rpm or off, which always caused the bar to disengage. I quickly noted that it was because of a loosened connection by accident when lifting the mantle, and I opened the bottom and reclamped the loose connection back tightly and it worked again.

Chinese 2L 3n flask does not quite fit into the mantle, but the actual volume of this flask is closer to 3L actually. There will be 1-2cm gap between the bottom. This likely has most effect on magstir stability at higher rpm. Schott duran 1n flask fits like a glove.

is a still head temperature sensor suitable for PID control of heating ?

Sulaiman - 6-2-2021 at 02:26

... I've not tried because to the level of my understanding,
sill head temperature is determined by vapour mixture/content,
not by heating rate.

Why try ? ... and does it work well ?

(I choose constant (but manually adjustable) heating power by using a 'dimmer' or for my 5l mantle the inbuilt mechanical controller)

{have others noticed that there is no thermal connection between the heating element and these types of bi-metalic 'temperature' controllers ?
They are just very slow pwm controllers }

Fyndium - 6-2-2021 at 10:05

I would love a manual adjust mantle for this matter. It is easy to find a sweet spot with every device I've got quickly. Electronic controllers appear fancy and cool, but they're prone to malfunction and tend to work poorly in general, unless they're severely priced brand models.

Well, if it blows up someday, it's good time to learn manual wiring with dimmer. I've got a full carton of them I ordered 10 years ago from china and used a couple for kanthal electronic furnaces, the smaller are 2000W and bigger 3500W.

zed - 6-2-2021 at 20:42

Ummm. Stirring problems. Seems to be an eternal problem. Some plates and mantles, incorporate a kind of sophisticated speed controller to prevent magnetic uncoupling.

Wrong approach, to my way of thinking. Mechanical simplicity=Less possible screw ups.

Create greater magnetic coupling, by utilizing a stronger magnet as a stir-bar.

I like Neodymium Magnets, but for higher temperatures, they lose their mojo. Boiling water, is much too hot.

Next up, Samarium Cobalt; not as strong as Neodymium and very expensive, but if you utilize a magnet with a larger cross-section, it'll do the trick.

I recently purchased something like this.

Those 1/2x1/2 cylindrical Samarium cobalt magnets, will do the job. On the edge, in terms of diameter, with an inert coating.

They can be stacked 2, 3, or 4... and enveloped in HDPE.

http://www.ebaystores.com/CMS-Magnetics/_i.html?_nkw=samariu...

As stated before, a 1/4 inch diameter, Neodymium magnet, makes a brilliant stir-bar, but only for cold solutions.

[Edited on 7-2-2021 by zed]

[Edited on 7-2-2021 by zed]

Mateo_swe - 13-2-2021 at 09:38

You could try find out what type of temp probe that is mounted on the mantle.
Maybe you can replace it with the "Naked bead" type if its the same type.
If so you can make a temperature probe from glass tubing.
First sealing one end using a torch then deposit some thermal compound inside the tube at the sealed end using a drinking straw.
Put some thermal compound in the end of the straw, insert it into the glass tubing down to the sealed end and deposit it there by inserting something into the straw and push the heat compound out.
Then put your "Naked bead" sensor down into the thermal compound and tape the top so the wire doesnt come out so easily.
If you have the same diameter glass tubing as ordinary lab thermometers it will fit into thermometer adapters.
There are videos on this on YT.

If you can use the "bead type" sensor then maybe you could place the sensor at the bottom of the mantle, making it a ordinary heating mantle with a temp knob.
Anybody done this and would the heating be good?
As the sensor isnt inside the heated liquid anymore and it bypasses the thermal resistance of the glass and the heated liquid itself it maybe doesnt work good and heating will be slow and weak.

macckone - 16-2-2021 at 22:52

Another solution than the thermowell, is making an aluminum block with a groove for the bottom of the flask.
Then you are measuring the flask bottom temperature.
Just use a regular glass thermometer for measuring the reaction mix or head temperature.

The probe should not be reading 'HHH' if it is not immersed.
That indicates an error with the probe.
I suspect it has a short and only functions in a reasonably upright position.
Otherwise how would it tell it is immersed?

One test would be to put a cork in a test tube and push the probe through the cork into a liquid and lay it on its side.
If it doesn't work then it is the position not the liquid.

Fyndium - 17-2-2021 at 00:47

My mantle states HHH when the probe is not plugged in. When it is, it states the current temperature of the probe - which is the room temp in this instance.

I've found the probe not at all an issue, BUT it mandates you have at minimum 2-neck flask and a thermowell. It measures the temp of the reaction meanwhile commanding the mantle heating circuit, which is beneficial because I'd just use a separate thermometer for that. The cord for the probe is not too long though, it is barely long enough to fully lower the mantle with jack from the flask and at that position requires deplugging from the mantle to pull it up from the well.

For stirring open pots or single neck flasks it is an issue though. I find myself somewhat annoyed seeing all those pics on eBay and else where the probe is just immersed in an open beaker or a wide-neck erlenmeyer - ain't no one heating anything in an open vessel in real chemistry.

Rainwater - 1-1-2022 at 08:51

Wish i had found this thread before christmas
Was trying to dissolve some silicate gel catlitter and as soon as i started mixing in the naoh. Baaaam. H2 production
The stainless steel probe is aluminum.
Waiting on the seller to message me back

16410558131124940558774365086682.jpg - 1.4MB

organicchemist25 - 1-1-2022 at 11:07

I had one of those a few years ago and I put the probe down on the outside of the RBF and still recorded the temp with a glass thermometer noting what the differences was. It was about a 20° difference, but I was still able to use it.

Rainwater - 1-1-2022 at 11:41

how come the simplest solutions never occur to me until i have fubar'ed something.
Thanks for the tip.

Rainwater - 2-1-2022 at 16:34

So after following organicchemist25's suggestion. I have discovered that by controlling the temp of the heating mantle independently of the solution my frictional distillation have become much easier to control.
Tho getting the solution up to the first fraction takes longer. Thanks for the tip

Fyndium - 3-1-2022 at 01:51

Ah, this topic.

Get thermowells. I don't remember if I mentioned, but I long gone solved this problem with these. The probe can be made from any reactinium metal and be good. Wells also seal well for vacuum.

For stirring, I've moved to overhead stirring long time ago. They allow for huge efficiency leap over any other stirring method, and they seem to work great with vacuum too, at least as long as the substance is not very sensitive to oxygen, as small leaks through the bearing are just overcome with powerful vacuum pump.
Quote: Originally posted by Rainwater  
frictional distillation


Damn, you must run some serious RPM there. ;)

ManyInterests - 4-1-2022 at 10:08

I've had that problem with my JoanLabs heating mantle (1 liter. I wish I got the 2 liter). The heating of the mantle is dependent entirely on the reading it gets from the metal thermometer. What this means is when I am distilling something I cannot put the thermometer where it needs to be and I have to perform the on-off dance with my power bar. I should mention that the only distillation I did was nitric acid, and nitric acid will be destroyed if the heating mantle gets too hot (and it can very quickly get hot enough to boil sulfuric acid). So I have to wait until the nitric acid starts to boil and then turn it off and let it cool before turning it on again and repeating the process until all nitric acid is extracted.

It is extremely annoying and I wish it wasn't so dependent on the thermometer. It would have processes like what I did previously much easier. It will also mean that other concentrations/distillations will need me to figure out another on-off dance to make sure everything goes well.