Magpie
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mantle repair
I know that there is already a thread covering this but darned if I could find it. If a someone can find the original I'd be glad to have this post
moved.
My 500 mL Glas-Col mantle finally burned through the bottom (I bought it used) and disintegrated into small particles of fiberlglass. But this was
just at the very bottom over a circle of about 5cm in diameter. I wanted to just buy a new one but they are so darn expensive. So I'm going to give
repair a try using some sheet fiberglass and "high-temp RTV silicone" from the hardware store.
I shook out all the old fiberglass particles and then repacked the void with multiple patches of fiberglass. Now I'm sewing on an outer cover of
fiberglass reinforced on the perimeter with the silicone. Below is a picture of the nearly finished repair. I'll let you know how it holds up under
use.
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DJF90
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What are you using to sew the fiberglass on? I want to make a "glas-col" mantle at some point, and I have a source for decent heating elements but
have no idea how I'm going to contain them in the hemispherical shape. I was thinking a "firecement" hemisphere, with aluminium mesh on top.
Heres that thread: http://www.sciencemadness.org/talk/viewthread.php?tid=6764&a...
[Edited on 4-8-2008 by DJF90]
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Magpie
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I'm just using some "extra strong" thread from my wife's sewing basket - probably a polyester/cotton blend or some such. I wanted to use something
more heat resistant but thought I could get away with this ordinary thread because of the location of the stitching.
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DJF90
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What's inside the outer cover? I'm guessing theres some sort of insulation on the bottom of the element (to protect the worksurface at least)? Does
the element make the upper cover or is there a layer of fiberglass (or other stuff?) on top of it?
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Magpie
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I didn't root around inside the mantle too much but what I did see was this: there was a white fiberous "rope" about 3mm in diameter that was wound
with the wire element. This rope, in turn, was formed into a flat coil about 4cm in diameter. There was a little ceramic fiber-like packing above
this coil then some more below the coil. I replaced what ever was below the coil with multiple patches of fiberglass cloth.
There may well have been additional element and ceramic fiber packing inside that I did not see/disturb.
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Magpie
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My repaired mantle was tested by refluxing water for 1/2 hour at a 70% power setting. Everything appeared to hold up well.
I have since located a source of PTFE coated fiberglass thread (0.021" dia) rated for 1000F. Minimum purchase is 200 yards for $25. If my polyester
thread does not hold up this could be used instead.
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Panache
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okay i couldn't find the other thread either so i'm posting my question here.
i have had this old 10L heating mantle for some time but have never used it as it was fitted with UK plugs. So today i removed them and wired in Aus
kettle plugs and turned the thing on.
Well, the lights for the circuits came on but the mantle never heated on either circuit (it has two circuits with separate power inputs). Running a
Multi-Meter over the element from start to end gave me a high resistance reading of 620ohm on the 200K dial, testing the circuit didn't give me a
'bleep' however i figured this to simply be that the element run was too long. In all other manner, inspection shows the device to be sound and in
good order. In fact it looks hardly used.
the panel on the mantle asks for 200/250V ac/dc, which i assume would be fine with Aus 240V ac.
i then dismantled my 1L mantle to assess how it responded tot he multimeter. It gave a 'bleep' when testing the circuit, however it is much newer,
also i could not register a resistance reading for it. Deciding the element's where likely different materials i adopted to ask here rather than toss
the big boy 10l.
is the mantle expired?
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not_important
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620 ohm @ 240 V would pull a shade under 0,4 amps meaning 93 watts. Sounds a bit low for a 10L mantle, maybe enough heat to make a flask
uncomfortable to touch for long but not much more. The resistance is pretty low for a full break, check the connection points for a bad or corroded
connection.
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S.C. Wack
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Did you actually test just the heating elements themselves, or are there other connections to them involved? You say you tested the elements but I
just want this to be clear.
Interested, I found that a 3L Glas-Col has 25 ohms and a 250 ml. Thermowell 75 ohms of resistance at room temp., both are 120V. They both get very
hot.
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Panache
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bah this thing is driving me nuts, it could not possibly be a simpler circuit. Active pin goes to one end of the element, neutral to the other end,
two short cables between both or connections. The unit looks very new albeit dated in design
NI, i unravelled the connections and found that the cotton braiding had not been removed from the element before it was married to the cable via a
crimped stainless c-section piece. I have attempted to open the c-section but will destroy in process. What should i been looking for as a reading
either side of it so i can test it without removing all the fancy factory braiding etc. The multimeter tests a bleep for all the connections.
Also if you had not already noticed i know more about Jesus than i do about electronics and i'm not even a Santa Clausian, actually using a multimeter
is an exercise is guessing for me. It just seems too coincidental that both circuits appear undamaged, yet both do not work
Mr Wack, yes the first thing i did was plug it into 240V wall supply nothing happened, well the little light came on thats ganged parallel to the
element. Could it need greater amperage than i am providing, which is the same amperage that comes out of the wall.
Also to clariy the multimeter read 620 but the scale was on one labelled 200K, therres also a 2000K, 20K etc setting
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Magpie
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Is there a watt rating for either of the elements? That will help greatly in determining what the resistance (ohms) and amperage should be.
I'm assuming that since it's British made the proper operating voltage is right at 240 Volts, as you have indicated.
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Panache
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sorry yes i should have mentioned it, it is 500W per circuit and a third stated spec of 1000W, however i assume this third one is a addon as there are
ports for another in the body of the mantle however they are plugged up, i assume they just printed one spec panel to cover both power options.
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Magpie
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| Quote: |
it is 500W per circuit
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That makes it easy since P=EI. From Ohm's Law E=IR, or R=E/I = E/(P/E) = (E^2)/P = [(240V)^2]/500w = 115 ohms.
So you should be mearsuring a resistance of about 115 ohms with your multimeter for each circuit.
Also from above P = (E^2)/R so if your resistance reads quite a bit more than 115 ohms it will cut your power output significantly. Let's assume that
the reistance is 620 ohms, then the power output would be P = [(240V)^2]/620 = 93 watts. Hope this helps.
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watson.fawkes
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Warning: almost all heating elements have strong changes in resistivity with temperature. Temperature coefficients can be both positive and negative.
Simply using Ohm's law to compute an expected resistance only works if you're measuring the hot resistance.
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Panache
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So why would an element lose such considerable power, i figure its not as simple as use in this case because the weaving around the element and the
bed would also show signs of ageing and they are pristine-ish.
I have discovered something further however. There are two points for thermocouples in the body of the mantle, on the inside of the mantle they
terminate, ie nothing attached to them. On the specification plate it says
thermocouple terminals should be connected to electrothermal pyrometer cat no mp 301 or 302 with colour coded compensating leads
i had dismissed this as irrelevant however when i placed the entire element/braiding over a light box to inspect it thoroughly i discovered two things
1-that indeed the braiding is pristine throughout
2-at one point, halfway around thee spirally element loop a small braid, not connectted with the element had woven what appears to be a small
thermouple wire into the mantle bed it is about an 1inch long and has one end effectively 'sealed' within the braid, the other end produces two
exposed wires.
So is it possible some device exists (ie an elctrothermal pyrometer cat no 301) that would ramp up the power considerably when cold and diminish it
when getting closer to the set temperature. I have always know temp controllers to be effectively on/off type devices.
Now that i think of it i have a very old lab equip catalogue, i'll check if it carries electrothermal gear but any other ideas?
edit-wow i just found the exact mantle in this old catalogue,
'the safety mantle have a co-axial element with an earthing facility in the sleeve such that any moisening will earth the current, stopping heating
and protecting the operator. '
however the temperature controller is simply an on/off type one so the answer does not lie there it would appear.
[Edited on 11-9-2008 by Panache]
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Magpie
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Today I dismembered a 100mL RBF Glas-Col mantle. I picked up 3 on an eBay purchase and never have used but one so felt I could sacrifice one for
another project. Even so I felt like a criminal as I was doing this.
I must say that these are very well constructed. I wanted to salvage all parts, including the thread, so made as few cuts as practical to the
threads. It took me over an hour.
I thought others might be curious as to its components:
The single most important condition for a successful synthesis is good mixing - Nicodem
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entropy51
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Snuff porn. How could you?
Actually if one of my mantles ever dies, I sort of look forward to the necropsy to see what's in there that could be so darned expensive.
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Sedit
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| Quote: | | I thought others might be curious as to its components: |
Indeed.
Thank you for your sacrifice for science Magpie. So what kind of electronics you got there? Just a thermocouple and a controller?
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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Magpie
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There's no electronics. The parts in the little nest in the upper right all go to the plug. There was a TC but I snipped it off first thing. The
coil on the lower left is a woven fiberglass encased nichrome wire I'm guessing. The rest is just various forms of fiberglass.
I think the high cost comes 50% for the sewing handwork - a lot of stiches and knots. The other 50% is Fisher Scientific's fee for
being so gracious as to sell it to you.
The single most important condition for a successful synthesis is good mixing - Nicodem
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