Making mantles and glas-cols.

This all started with my "smelly glas-col" post
http://www.sciencemadness.org/talk/viewthread.php?tid=6754
where I discussed disassembling and reassembling a glas-col mantle. Since they sell for over $100 USD, I thought about making heaters. Here is what I found so far: will add more info as I find it.

I was inspired by the DIY stirrer link:
http://www.sciencemadness.org/talk/viewthread.php?tid=3056
In particular, BrainFever's mantle project which uses concrete. I bought a 10 pound bag of "quickcrete" for $1.88. Another useful material is muffler and tailpipe putty available at AutoZone or elsewhere. It is sodium silicate and crystaline silica. Somewhat brittle but still strong, useful as high temp "glue" and should withstand up to 1000 C.

For flexible heating elements as in glas-col, the elements are resistive wire wound around a fiberglass core, then sheathed with fiberglass insulation, then that element is circled in a spiral. The specification from glas-col gives a maximum element temperature of 450 C. Note: TYPICAL high-temp fiberglass wire insulation is usually acrylic coated, and therefore goes to something like 240 C. What is needed for direct contact with the heating wire is non-coated fiberglass. There is a product called "thermosleeve"
http://www.adlinsulflex.com/fire-sleeves/thermosleeve-b/
which is rated for 538 C continuous use. I don't know if the last link will sell small quantities. I found a different supplier of some kind of fiberglass sleeve, not sure what manufacturer, though:
http://www.sollerpaddles.com/composites/carbon%20fiber%20sle...
They sell 1/4" sleeve which they rate to around 650 C. Now, it seems that this size actually goes from .09" to .29" as it stretches. It is only 44 cents/ft.

It would be nice to find a supplier of that fabric they use in glas-cols. I still don't know if it might be asbestos? The only thing I've run across so far is the fiberglass cloth used for fiber/resin repair work. It will work, but it's just not as good as the official material.

Here's a rundown on HEATING ELEMENT DESIGN using nichrome or other wire:

I won't go into details, but V=IR, P=IV, and R=(rho)(s/A), where s is the total actual length of wire used.
1. Determine power limit
2. Choose max voltage (i.e. 115 v)
3. 1 and 2 determine the R (hot) needed, and the current I
4. you want a large r (wire radius) for strength & durability but..
5. Since R and rho (resistivity) are fixed, there's a tradeoff between length and diameter of wire (A=pi r^2)
6. Determine max temp Tm of the heating element
7. For a given wire gauge, R = s LR (LR, linear resistance, can be found from chart or calculated)
8. For coiling, s^2 / L^2 = 1+(pi d / p)^2 , where s is the wire length, L is the coiled element length, d is the winding diameter, p is the winding pitch

A regular light dimmer can usually control up to 600 watts (which I wouldn't use for more than 300-400), so power control is a consideration. The specs from glas-col have the 100 ml size hemisphere at 80 watts. For a straight wire in air, the radius actually needs to be determined from Tm and the current (from a chart). For the same power rating, a thinner, shorter wire will be hotter than a thicker longer wire. A table for temp-radius-current , as well as a gauge-LR chart exists here:
http://www.wiretron.com/nicrdat.html
However, in reality an element will not be straight, and will be in thermal contact with the mantle, so I think the temperature will actually depend in on how "compactified" the element is.
So, once you have the total wire length, you then need to figure out how to pack into the space available. That is why the heating element in a glas-col is coiled. Don't forget that nichrome's hot resistance (@~450 C) will be about 4% higher than the cold resistance.

Here's an example. For an 80 watt, 115 V heater, R(hot) will be 165.2 ohm. I think 36 gauge would be about as thin as I would want to go. I want Tmax=450 C (but not sure what actual will be). The cold resistance is therefore 158.6 ohm, and 30 gauge nichrome (6.5 ohm/ft) needs 24.4 ft. Then, if I want an element length of 3 ft, I should aim for a winding d of 0.1" and pitch of .039" . That 3 ft will be formed into a spiral.

I might buy some of the fiberglass tubing, and ebay seems a good source for nichrome wire. Then, a heating element could be as simple as winding the right length onto some fiberglass tube, then pulling more tube over that, and then forming a spiral. This could also be a way to replace the element in a glas-col (if you're willing to take one apart! No, that's the easy part - I mean if you're willing to sew one together.)

[Edited on 10/1/2006 by BeerChloride]

[Edited on 10/2/2006 by BeerChloride]

This design works fine but takes quite awhile to construct and has a limited lifespan:
lugh
(Moderator)
02-02-03 00:53
No 403446
DIY OTC Heating Mantles

Heating mantles can be constructed using easily available materials. They're quite brittle, but very serviceable and are based on the fact that Johns-Mansville marketed insulating bricks called Sil-O-Cel made from diatomaceous earth in days of yore

1) Obtain a suitable length of nichrome wire, and wind it into a coil.

2) Support your flask with the neck down, and paint the bottom (which is now up) with melted paraffin/wax.

3) Mix equal volumes portland cement and diatomaceous earth in a suitable container, such as a plastic gallon milk jug with the top cut out, add a little water at time and mix until you get a thick paste of cement, then apply it to the waxed portion of the flask, building up a thin layer of insulating cement

4) Once you have a dry layer of cement, mix up more and start to embed the coil of nichrome wire in the cement, you may have to use various mechanical means to force the coil to stay in place, such as starting out in a plastic bucket a little wider than the flask, and use shims to hold the coil in place, or plastic ties, or weights on the unembedded coil etc

5) Continue to mix and apply cement until you have a mass of cement with just two ends of the nichrome wire sticking out, it's best to keep them relatively close, without actually touching.

6) Once it's dried, stick the end of a steam generator line into the flask, which will melt the paraffin/wax, and release the flask.

7) Remove as much of the wax from the mantle as possible.

8) Bake the mantle in the electric oven for a few hours at 250 degrees Fahrenheit.

9) Attach an electrical cord to the two ends of your nichrome wire coil, using aluminum/copper crimp on connectors with the plastic removed.

10) Use a variable transformer/rheostat/dimmer switch to control the amount of heat generated.



[Edited on 1-10-2006 by leu]

Sounds like some good fairly inexpensive materials. I wish they had some pictures - their fiber "rope" might be a candidate for stitching for a glas-col. I may be requesting samples..

I sheepishly post this:
Use of house insulation
I wondered about wall insulation for stuffing, etc. Owens-Corning "pink" insulation is made with a phenolic resin binder which makes it pink. Phenol and formaldehyde I believe. Thus it should not be heated as is. However, phenolic resin decomposes with strong acid. So if you REALLY wanted to maybe put some of that yukky brown drain-cleaner sulphuric acid to use, you could soak pink fiberglass in it to clean it. I tried it with a sample, and in a few minutes made it lose most of the color. It would probably need more time/heat though. Then maybe some final cleaning step.

However - it's probably ridiculous to do that. Insulation with no binders added should be obtainable at home improvement centers.

Yeah. Actually Allied's maximum discount price is down to the $8 range. But anyway ultimately it's just a connector. I mean you could use anything. I've got insulated spade terms on mine. But the twist lock would sure be one of those niceties. As I find again and again, you can easily spend as much as the item itself trying to make one to spec, so it's almost always comprimise for homebrew. Oh well.

I was looking at a "jones plug" as a decent substitute for the connector. It doesn't lock though:
2 prong Jones plug

Anyway, I just bought 25 ft of 31 ga nichrome for $6 with ship., and I'm going to order some fiberglass sleeve. So I'll just start by playing with making a heating element and see where that goes...

[Edited on 10/2/2006 by BeerChloride]

A heating element

Well I got my 31 ga nichrome and the 0.25" fiberglass sheath from Soller. I measured out 19.3 ft of nichrome for 158.6 cold ohms (80 watts @115 V) and wound it on a cardboard tube to. I then made a mock heating element spiral from cheap wire which determined 28.5" for the heating element. I cut a similar length of the .25" fiberglass to use as a core. The nichrome was then wound onto the fiberglass core, producing a 0.1" diameter coil. Here's a photo of a section of that (sorry it's hard to see the nichrome):



It was challenging to wind the exact pitch for the length to end up at 28.5" (the pitch needed to be .039"). I went beyond 28.5", and ended up having to eliminate about 8" from the nichrome wire. So the resistance was a little lower, but I relaxed a little when I calculated that the design was only slightly changed to 87 watts.

I then attached non-copper wires with high-heat sleeves to the nichrome ends, and then wrapped the connections with silver wrapping wire. After that, I used another piece of the same fiberglass material used for the core, and worked it onto the element as a sleeve. This was much easier than I thought would be, because when you push on the sleeve, it expands in diameter. The sheathed element was then shaped into a spiral. I held it on a 100 ml scrap flask, and put foil on it. This keeps the spiral immobile until I make the rest of the mantle, and also let me test it.


NOTE: The foil is temporary, and could pose a shorting hazard as wire whiskers can poke through this type of sheath.

I boiled some water - it works! The fiber material has something like glycerin or maybe pva on it, but it seems to heat off easily. The heat was very even, and I was almost surprised to see how the bubbles came very uniformly from everywhere throughout the flask. I'd post the picture but you've all seen boiling water before. Of course the foil would tend to even out the heat. I use a regular light dimmer installed in a box for control.

I'm still working on the rest of the mantle. I have a few ideas but still looking for small quantities of just that right fabric! I'm experimenting with silicone coating some fabric for the bottom of the mantle.

Concrete Mantle Body

I decided to try a concrete shell for the heating element I made. I cut the top off a bottle and used it as an outer mold. The inner mold was a 100 ml flask padded with .1" of paper towels, wrapped in foil. Two holes were punched in the outer mold and straws used to keep the holes in the concrete. After curing (concrete needs days of moisture to cure!) the heating element was put in:





The heating element was sealed in place with small amount of automotive exhaust sealant, and then burned in for about an hour. The temperature of the heating element maxed out at about 430 C (it was 57 F outside). At that temperature, the outside of the concrete was too hot to hold onto. Concrete definitely has a lower R value than fiberglass.

Anyway, the hard part was how to attach some fabric. I thought about using silicone or a thin aluminum strip to seal the fabric edge right to the concrete. I decided on steel epoxy which (JB weld) goes to 260 C, so I hope the outside of the thing won't get that hot.

It was a hassle. First I tied a steel wire around to hold the fiberglass on which I thought I had quite tight. To my dismay it simply fell off later. I tried to use thin foam as masks to form a neat strip of epoxy, but because I had the seam so close to the top, the mask would tend to slide off. So I took the masks off before the epoxy was set, and the fiberglass seam kept lifting off. Well, the final solution of all this is that I wrapped a sheet of plastic (polyethylene) around it. Epoxy will not bond at all to PE so when it set I just peeled it off. No nice, straight masking though.

I used double fabric and also layed another piece down inside before installing. Also, I used two sections of silicone insulation to cover the fiberglass sheath fray used to cover the heating element. Here it is, ready for some type of connector:







EDIT: Just did the final burn-in. Dissapointed. The steel epoxy on the outside kept giving off fumes and eventually was scorching, I doubt it will cease to smell. The temperature of the epoxy was measured to be only around 160 C during this.

[Edited on 10/11/2006 by BeerChloride]

Quote: Originally posted by entropy51

Fine Cu metal shot, or Cu powder (made by displacement with steel wool and CuSO4 solution)

I only mentioned it to try to reassure myself that I didn't waste the money I just spent on Cu powder when I have CuSO4 and steel wool coming out of my ears

I'm pretty sure you wasted your money!

Age and cunning will win out over youthful enthusiasm every time.

Well, 40 years beyond where you are now.

Life is a funny game. By the time you learn the rules, you're too old to play.

[Edited on 13-9-2009 by entropy51]