DIY Silicone Heat Blanket

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chrismp
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Post by chrismp »

i found this rtv heat resistant silicone from a german source:

http://translate.google.de/translate?js ... t_213.html
fa
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Post by fa »

!, thats cheap, thanks chrismp
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MontuckyMadman
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Post by MontuckyMadman »

I have used several products from this company and they are an industry leader.
Overkill?
http://www.smooth-on.com/tb/files/MOLD_MAX_60_TB.PDF
leboeuf
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Post by leboeuf »

The silicon window sealant tubes I have laying around say the cured product is rated to 205C.
No idea how it would handle this application, but it is cheap enough for experimentation.

Found their spec sheet:
http://www.novagard.net/images/techspec/03mx1002.pdf
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chrismp
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Post by chrismp »

that mold max stuff is pretty inexpensive as well.

btw, why would you need that much resin? the fiberglass i was going to use needs about 150g of resin per m² to wet out completely.
leboeuf
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Post by leboeuf »

Well I was accounting for the fact that I usually get 90% of whatever I'm working with on me and not whatever its supposed to go on :D
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chrismp
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Post by chrismp »

MontuckyMadman wrote:I have used several products from this company and they are an industry leader.
Overkill?
http://www.smooth-on.com/tb/files/MOLD_MAX_60_TB.PDF
it's not overkill if you want to use your blankets for sublimation as well ;)
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chrismp
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Post by chrismp »

first small sample yesterday worked like a charm!!! :D so stoked!
a full size blanket is curing as i write this.
unfortunately I couldn't take any photos since I was working by myself, but here's a small write-up.

I used 320g/m² biaxial fiberglass that I had lying around.
First I stuck the resistance wire to the fiberglass using a fiberglass mesh sticky tape.
The resistance wire is 0.2mm thickness and has 15.6 ohms/m. Using five 8m long sections of wire connected in parallel I'll get about 2100 watts from one blanket.
Then I started wetting the second layer of fiberglass with the heat resistant silicone resin on both sides. After that I flipped the fiberglass with the wire over and put it on the other one wetting out only the outside of the layer with the wires.
That's it.
Last edited by chrismp on Sun Nov 28, 2010 7:26 am, edited 1 time in total.
jvangelder
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Post by jvangelder »

chrismp wrote:
MontuckyMadman wrote:I have used several products from this company and they are an industry leader.
Overkill?
http://www.smooth-on.com/tb/files/MOLD_MAX_60_TB.PDF
it's not overkill if you want to use your blankets for sublimation as well ;)
I dont know how to inturpret tech sheet die-electrical resistance, however they do state that the mold-max-60 containes iron oxide, just an FYI



If chrismp's blankets work out thats great info for all of us, looks like we could build blankets for a fraction of the cost of buying pre-made ones.

Ill deff be building a set for a pre-preg min press setup we want for our carbon

-Jacob
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MontuckyMadman
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Post by MontuckyMadman »

chris we need photos and more details. This is awesome. How did you get the rubber smooth and level?
Its thin also?
What is the hardness or durometer of the silicon?
artski
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Post by artski »

Ya mon, do tell!!
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richie
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heat blanket supplies

Post by richie »

Hi fellas, hey I have been hunting around and wonder if this is the stuff we need?

http://www.allstategasket.com/info_gask ... e-1117.asp

or this ?

http://www.right-tape.com/html/prod_sil ... tml#photo2
(thinking of part number 21400)

These are similar , seem to be vulcanisable too. 1/16" or 3/32" about right?

All we need is some nice heating wire, sounds like the right stuff is kind of nichrome wire wound around a fibreglass core, I think it is available but not found it yet.

cheers
Richard
MonkeyCAM and SnoCAD - https://github.com/mikemag
Ski binding mounting https://github.com/splitn2/DrillSki

Richard Harcourt | www.splitn2.com | Christchurch New Zealand
rich@splitn2.com | www.facebook.com/splitn2
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chrismp
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Post by chrismp »

for the rubber I didn't really need to do anything to get it smooth. i just worked it into the fiberglass like epoxy, so it's just as thick as the fiberglass.
hardness is 50A.
to answer the question in your mail, montucky:
when connecting wires in parallel you basically just take the same ends of each wire and connect it to one wire on your plug and do the same with the other ends on another wire on your plug.

the wire is nichrome wire, but any resistance wire will do. to get the desired amount of ohms you need to do some calculating.
I'll use our wires as an example.

We have wire with 15.6 ohms/meter. We figured we want to keep the connections easy so we had to choose the length of each wire in increments of 4m (our blankets are 2m long and you want the ends of the wire to end up on the same side of the blanket).
Another given factor was that we wanted our blankets to be approx. 45cm wide with a little free space on the sides and that we wanted our wires to be spaced about 2cm from each other. So for this blanket width we figured we needed five of the 8m long wires which would give us twenty wires running the length of the blanket with the desired spacing.
An 8m piece of wire has about 125 ohm (15.6x8=124.8).
I'll spare you with the formula to calculate the total resistance of a parallel circiut and give you this link instead (just scroll down to "input: a lot of parallel resistors" and enter your calculated resistance for one wire times the number of wires you have): http://translate.google.com/translate?j ... tm&act=url
In my case I entered 125 in five of the boxes (because we use five of the 8m long wires which have a resistance of 125) and the result was a total resistance for all the wires of 25 ohms.
Now we can calculate the power (=wattage) we will get with our chosen wire length and number using Ohm's Law..
Again, here's a calculator (use the third one listed under Calculate for Power): http://www.the12volt.com/ohm/page2.asp
In my case I enter 230V for voltage and our previously calculated value of 25 ohms which gives me 2116 watts of total power for my blanket. That's a good number for one blanket I guessed.

With this example you should be able to calculate the power you'll get for a certain length of wire with a certain resistance. Just input your own numbers.

As for controlling such a blanket you'd have to use dimmers to keep the power running through the wires low since they'll get way too hot and would melt the silicone.
We use two of these: http://www.kemo-electronic.de/en/Light- ... 000-VA.php one for each blanket.

If you want to use the regular PID/SSR method I'd recommend using a much higher resistance wire since they don't get that hot and just use a lot longer wires to get the desired amount of power (watts). (that's why the big manufacturers use wires wound onto a fiberglass core to get longer wires into their blankets)
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chrismp
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Re: heat blanket supplies

Post by chrismp »

richie wrote:Hi fellas, hey I have been hunting around and wonder if this is the stuff we need?

http://www.allstategasket.com/info_gask ... e-1117.asp

or this ?

http://www.right-tape.com/html/prod_sil ... tml#photo2
(thinking of part number 21400)

These are similar , seem to be vulcanisable too. 1/16" or 3/32" about right?

All we need is some nice heating wire, sounds like the right stuff is kind of nichrome wire wound around a fibreglass core, I think it is available but not found it yet.

cheers
Richard
You could use that stuff, but have you looked at their pricing? 20 USD for one foot, that's pretty steep. You can get the resin for much less (you'll need about 1kg for one blanket with 40x200cm using 300g/m² glass which costs about 30 USD). But buying this would save you some hustle ;)

Heating wire doesn't necessarily need to be wound around a fiberglass core. Just read my other reply in this thread and you'll see why ;)
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MontuckyMadman
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Post by MontuckyMadman »

Awesome. But when I do math for the wire on ebay with an average of 56ohms over the same distance as yours with a 110 power source I get 216 watts of power. That won't get me anywhere.
I need more resistance?
Bigger gauge wire?
I see the 32awg .2mm has 35ohm/meter. different from your stuff at the same gauge.

Seems like the thicker the less resistance as it carries the current more efficiently?

So I need tons of really thin stuff. Like 8 time the length you used for my 110V?

Thanks
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