DIY Silicone Heat Blanket

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chrismp
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DIY Silicone Heat Blanket

Post by chrismp »

Just throwing around some ideas.
Has any of you guys ever thought about making your own silicone heat blankets á la MEI?
The construction seems pretty straightforward with resistance wire laid up in loops laminated between some fiberglass mats impregnated with heat resistant rtv silicone resin.
The materials aren't that expensive and building one doesn't seem overly complicated to me.
Am I missing something?

Richuk
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Post by Richuk »

I think plywood do some work in this - using CF tows? Can't find the thread right now : (

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chrismp
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Post by chrismp »

i remember his thread, but CF is pretty expensive and harder to connect compared to resistance wire. with wire you just have to figure what length you need and how much wattage you want and then you simply choose the wire with the correct resistance for these needs. plus, i think he didn't mention any kind of insulation.

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MontuckyMadman
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Post by MontuckyMadman »

You make it sound easy.
if it was that easy I'm all for it. I talked to a builder who said he uses plumbers heat tape for years in the cassettes but I don't have a comprehension of electrical stuff so I have no idea how he ramped the temp, more resistance?

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chrismp
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Post by chrismp »

well, i talked to an electrical engineer and he said that it should work the way i described it.
ramping the heat could be done via a PID just like everyone else on here uses, or you could ramp manually by using a dimmer to adjust the wattage.

i guess i'll have to shell out the bucks and try building one. a rough estimate came out at about 70-80 EUR for materials worth two blankets with 40x200cm.
won't happen till the end of this year though, since university needs all my attention now.

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MontuckyMadman
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Post by MontuckyMadman »

I am all for it. Post some links to some materials. I have done allot of work with RTV silicons and Polyurethanes for mold making. Just need a high heat pourable silicon.
I have a PID for my single blanket but I need it wider and longer and another for the top with the new press.
Could I use the pid to ramp the temp on heat tape you suppose?

twizzstyle
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Post by twizzstyle »

MontuckyMadman wrote:I am all for it. Post some links to some materials. I have done allot of work with RTV silicons and Polyurethanes for mold making. Just need a high heat pourable silicon.
I have a PID for my single blanket but I need it wider and longer and another for the top with the new press.
Could I use the pid to ramp the temp on heat tape you suppose?
I am in the EXACT same boat as you. I've got one nice blanket, but its just big enough, would be nice if it were a little larger... and I'd like a second to heat from both sides. Very curious about the DIY route now too!

leboeuf
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Post by leboeuf »

I've been looking into picking up some nichrome wire to mess with...

It won't be hard to get a parallel/series combo to get a desired wattage.

I was thinking of getting some cotton fabric or burlap and stitching the wire to it, then coating the top and bottom in silicon. Then you could literally press the laminate like a ski with a waxed cassette.

Unfortunately I have negative free time right now... I may get to this during the holiday season...

Cost should be ~$20 for the tubes of Si, ~$20 for the wire... At least it looks good on paper!

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chrismp
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Post by chrismp »

yep, a pid should work for heat tape as well.
leboeuf, i wouldn't use fabric since it doesn't take heat that well. fiberglass has the advantage of being an electrical insulation and a very good heat conductor at the same time. plus, it's not that expensive compared to cotton fabrics.

here's some links:
www.resistancewire.com (US)
www.distrelec.com (Europe)

you can find the silicone on ebay or amazon.
and i'm pretty sure you all know where to find fiberglass ;)

one thing that came to my mind: does silicone resin stick to fiberglass?

leboeuf
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Post by leboeuf »

Yeah, I'm not too sure how fiberglass and silicon mix... kinda why I was leaning towards canvas or something.

I know from a couple of bathroom remodel jobs that silicon sticks very well to canvas pants lol.

IIRC tight weave canvas should be able to handle fairly high temps, a lot higher than ski pressing temps at least ;)

leboeuf
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Post by leboeuf »

This is straight off the MEI website, looks like they use fiberglass as the bonding medium 8)


Technical Information



Silicone Rubber Flexible Heating Blankets


Michaels Enterprises flexible heaters are constructed using UL and CSA approved materials and components. Silicone flexible heaters are constructed for temperatures up to 450 degrees F.

Heating Element


The resistance heating element is high temperature Copper-Nickel and Nickel-Chrome alloy wire, wound around a fiberglass cord to provide added strength and flexibility.

Sheath Material


The prewound heating element is vulcanized between two layers of fiberglass reinforced silicone rubber to form a strong flexible assembly. Vulcanizing agents are removed during the hot press and out-gassing cycles to produce a flexible heater with high dielectric strength that is resistant to moisture, chemicals and acids.

Heater Sizes


Flexible heaters are available in sizes up to 37" x 143" without splicing. Longer heaters are available 30" wide or less. Complex shapes, contours and power densities in single or multi-zoned heaters are available with voltages ranging from 6 volt single phase to 480 volt three phase.

Heater Fasteners and Attachments:

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chrismp
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Post by chrismp »

yep, i found that info too. unfortunately that doesn't rule out the possibility of a special process to bond silicone to fiberglass.

edit: just found this http://www.answerbag.com/q_view/2284631

leboeuf
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Post by leboeuf »

In hindsight its funny to poke fun at the fact that I was wondering if RTV type silicon would stick to fiberglass.

RTV type silicon is engineered to adhere to SiO2.... as in textile fiberglass...

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MontuckyMadman
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Post by MontuckyMadman »

leboeuf wrote:In hindsight its funny to poke fun at the fact that I was wondering if RTV type silicon would stick to fiberglass.

RTV type silicon is engineered to adhere to SiO2.... as in textile fiberglass...
That's funny, I was thinking silicon? Doesn't that have silica in it in some form? But In my chem-jongness I said nothing.

fa
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Post by fa »

very interesting project!
i was thinking about the same things last winter, but i never thought using FG for reinforcement (!)
after reading this thread, i looked for some draft notes i kept.
plan was for 170x40cm blnkt.
0.2mm dia nichrome wires running length wise, parallel connected on the 40cm sides.
27 wires in total, at 15mm intervals.
i had in mind to run a low dc current for safety, with a dimmer.
if my notes are right, with some 14~17 volts (8~9 amps) i could get it to ~90 oC.
the temp on the wire will increase inverse to the heat flow out of it.
so probably a thermostat is a must have to control the circuit when the environment (mold, laminate) approach to target temp.
i never did a test, but that thread warms up the idea!
cheapest 2-parts heat resistant silicon i 've found, was quite expensive, >50euros/kg. a bit less was standard silicon film sheets.
rtv si weights ~1.25kg/lt, so for a mm of thickness 1 kg will give 0.8m2.
The cheap, standard -not high temp, 1-part silicon (caulking tubes) wont burn at 90C, so it might be a viable alternative for the low temps im after.
(during this summer i experiment with 1 part Si for a different project, and I've found that it can be thinned with acetone, or some paint thinners.
this silicon sets with air moisture, so curing time is accelerated by mixing in very small amounts of glycerin that holds water -i came up with 1 or 2 drops per 100cc.
A friend gets good results by adding some drops of acrylic paint as well, but i never tried it.
People use it for mold making and they prepare it not to be sticky, by working it inside a bucket of water).
I know 1 part silicon contains acid (that's where that smell comes from) so it might be corrosive for the wire. It stings so bad, i would n dare to experiment inside the shop ever again with this stuff.
Silicon bonds very well to silicon.

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