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Author: Subject: RBF heating blocks for hot plates
itsafineday
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[*] posted on 19-2-2020 at 09:01
RBF heating blocks for hot plates


I'm wondering if anyone has a source for heating blocks that can adapt a hot plate to heating a round bottom flask? I suppose cheap is the operative word since decent chinese stirring mantles are available. I would like to save some space and money and get a bit more use from my hot plates.

I am aware I can use baths of various types, the blocks just seem to be an elegant and tidy solution I'd love to make use of . I'm not experienced in using them so I suppose it would be good to hear about any shortcomings I'm overlooking as well. Thanks.




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12thealchemist
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[*] posted on 19-2-2020 at 10:49


I believe they're very expensive, but basically indestructable. They also only hold specific sizes of flask, like a heating mantle. You can pack out larger ones with eg sand, but at that point you may as well just use a squat tin can filled with sand. And much like sand baths, they usually take a while to heat up and cool down, though being aluminium they're a bit quicker.



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monolithic
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[*] posted on 19-2-2020 at 13:20


I've heard they can crack flasks if you let the flask cool in them. Just something to consider.
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draculic acid69
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[*] posted on 19-2-2020 at 23:16


Is there some reason you want this thing instead of a heating mantle?
What's the reason a heating mantle isn't sufficient?
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fusso
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[*] posted on 20-2-2020 at 01:03


What about casting one from aluminium yourself? It doesnt need perfectly even height, just sand the bottom to make it smooth.
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rockyit98
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[*] posted on 20-2-2020 at 16:01


you don't need a block ,what i use with my hot plate is bunch of small aluminium turnings in a container like a sand bath but much better. it works with every shape that out there so no need for casting.



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[*] posted on 21-2-2020 at 02:44


Quote: Originally posted by rockyit98  
you don't need a block ,what i use with my hot plate is bunch of small aluminium turnings in a container like a sand bath but much better. it works with every shape that out there so no need for casting.


best solution.

if you use a solid block of aluminium for each heating block, i hope you don't have many different sizes of flask, aluminium is "light" but a block for a 1L flask is not light at all





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draculic acid69
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[*] posted on 21-2-2020 at 03:30


Once again what's the advantage or need to use a block that a mantle couldnt be used for
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[*] posted on 21-2-2020 at 04:38


Quote: Originally posted by draculic acid69  
Once again what's the advantage or need to use a block that a mantle couldnt be used for


None that I can tell.
I have a 250ml block for my old hotplate and though I dont use it anymore it was very nice and didnt have those "inertia" problems mentioned here with sand.

Pros: the saved space compared to a heating mantle
Cons: Massively overpriced

My block is made from a machined piece of Al. Why not casting I dont know but that certainly plays a part in the price.




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rockyit98
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[*] posted on 21-2-2020 at 05:07


Quote: Originally posted by rockyit98  
you don't need a block ,what i use with my hot plate is bunch of small aluminium turnings in a container like a sand bath but much better. it works with every shape that out there so no need for casting.

you can use steel turnings with a inductive heater because you cant use aluminium ones.it's very handy in something like in a distillation.my inducting heater is 2kW but has 300W 700W 1200w 1500W settings.only problem is you can't use magnetic stirring.




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RogueRose
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[*] posted on 21-2-2020 at 06:10


Does anyone know how much these things cost? I'd be really interested in casting one from Al or Cu and casting the heater into it (like stainless cartridge heaters or something) and then using the lathe to cut the profile.

Aluminum would be a lot easier to work with as casting enough Cu (or even brass) to make one of these for a 500 or 1L+ flask can be a real PITA as Cu can be difficult to melt, especially in larger amounts.

I'm not sure how well these things would hold up without a ceramic coating but maybe an anodized coating on Al might be sufficient to give it some protection. Copper might be able to withstand the heat for a ceramic coating to be melted on.
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[*] posted on 21-2-2020 at 11:28


Optitherm makes aluminum blocks sort of like that. (anodized)

They're round bottomed and nest so you can use them stacked to use a (for example) 250 ml flask in a 500 ml mantle.

They cost more than many mantles, but are cheaper than Glas-cols.

I kind of worry about the sizing problem though.
RBFs vary in size a bit these days, and the difference is often tolerable with floppy mantles, but the firmer "bird's nest' designs can make for a bad fit, and a metal block could be worse.

Maybe less of a problem with major manufacturer's flasks, but potential trouble perhaps with no-name glass as there have been reports of poor fitting from some of our posters.

Somebody used to make flasks with integral heaters.
I believe they were potted in epoxy on the outside of the flask in some cases.
Instatherm.

There was at least one Eastern European maker too.
Rasotherm made flasks with the heating element inside the flask.
Never handled one myself, so I'm not entirely sure how that worked.

They look like the element might be glass or quartz coated.

Heating mantles aren't all that expensive used if you shop around.
A couple of sizes will go a long way.

I've got sizes 25, 50, 100, 150, 250, 500, 1000, 2000, 3000, 5000 in hemispherical mantles but I hardy ever use most of them. It's the 250 or the 500 for most ordinary uses.

Before I had all this crap (and my reaction chamber, spherical, and concentrator flask mantles), I used flat bottom flasks instead.

They work fine for just about anything and go right on your hotplate.
I'd use the flats that look like RBFs for vacuum, and jointed Erlenmeyers for everything else as they're easier to clean.


EDIT: Hey, if your heating block was gallium it'd always fit fine when you were heating it!







[Edited on 21-2-2020 by SWIM]

[Edited on 21-2-2020 by SWIM]




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draculic acid69
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[*] posted on 21-2-2020 at 20:23


Gallium 'wets' everything it touches.also what's it's b.p.? I'm guessing not high enough
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SWIM
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[*] posted on 21-2-2020 at 20:59


You're right.
BP is only 2400 degrees C

This gallium doesn't really seem to be wetting this glass either.

gallium.jpg - 102kB

[Edited on 22-2-2020 by SWIM]




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draculic acid69
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[*] posted on 22-2-2020 at 05:18


Shit didn't realize b.p. was so high.was thinking
low m.p.= low b.p.
Also does the gallium wet the glass when heated or not?
Someone's YouTube clip led me to believe that heated gallium wets everything it touches.obviously this doesn't happen at room temperature.

[Edited on 22-2-2020 by draculic acid69]
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[*] posted on 22-2-2020 at 14:52


I honestly had no Idea what gallium's BP was when I posted.
The post was meant sort of tongue-in-cheek as I assume gallium is a little pricey for that sort of use.

I am also surprised at the high BP.

I don't know much about gallium. The clip you saw is probably right.

I have since recalled that they do, or at least used to, use molten metal baths for heating flasks sometimes.
Wood's alloy and such.

Really, if I wanted to mess around with some uncommon heating method for RBFs I'd probably look into heating with hot air.
They have fairly cheap hot air guns now with thermostatic control.

They claim to be accurate to a few degrees or less, and blowing air at any temperature you choose from one of these into something like a steam bath with adjustable rings, or even just a simple can to fit each flask you have, might work pretty well.

There is at least one post on here where somebody made a simple hot air bath from an analog controlled hot air gun and what looks like a tin can with a tube soldered to the side and a screen on the top.
Very cheap, simple and, according to the poster, effective.

For high temps I suppose you'd want to put the flask in the can with a lid covering the top except a hole for the neck with enough clearance for the hot air to escape. With those hot air guns putting out up to 500C you ought to have all the heat you'd need for almost anything you'd do in glass, but evenly distributed around the surface.

Infra- red was discussed a bit here a couple of years ago. I don't recall any prototypes being built, but I find it an interesting Idea. With a quartz flask you'd be heating the contents directly and I wonder if this would have certain advantages in pyrolysis reactions involving solids.





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[*] posted on 23-2-2020 at 02:17


Quote: Originally posted by SWIM  
You're right.
BP is only 2400 degrees C

This gallium doesn't really seem to be wetting this glass either.



[Edited on 22-2-2020 by SWIM]


That's because its special gallium oxide coated glass.
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draculic acid69
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[*] posted on 23-2-2020 at 02:57


Graphite, quartz and teflon are apparently the only other thing liquid gallium won't stick to.
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[*] posted on 23-2-2020 at 03:24


Liquid Gallium is a PITA, I have a sample that once liquefied during the summer, the plastic container it was in kept at least 2 grams sticking to it.
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