electrical insulation for AC power at ~500F

[Admin]

I have this electrical heater that runs on AC power (which is part of a bigger robotic device). The leads are exposed, and so I need to cover them for safety reasons. I've measured the heater at 492F / 255C.

Plastics will all melt, and metals are conductive. I haven't looked into ceramics yet.

I tried using JB weld, which is better than nothing, but it cracked with the extreme heat. See attached images for the two screw terminals I need to cover up . . .

Anyone with better ideas?

[waltr]

Teflon?

[garrettg84]

vulcanized rubber? I am under the impression vulcanized rubber doesn't melt - it decomposes or simply breaks down. A quick google shows it doesn't break down (burn) until around 400-500C.

[Soeren]

Hi,

I have this electrical heater that runs on AC power (which is part of a bigger robotic device). The leads are exposed, and so I need to cover them for safety reasons. I've measured the heater at 492F / 255C.

Plastics will all melt, and metals are conductive. I haven't looked into ceramics yet.

There's always the old cermic beads found in eg. old toasters and room heaters,  etc. but This should do and won't shatter or chip like the ceramics might.

I have a reel of another type named Siligaine with a SiO₂ braidi and while I'm not sure about the max. thermal limits of the stuff I have, it should be at least as good as the Thermasleeve - Eg. Siligaine 33SI boasts the following data:

CHARACTERISTICS
Physical-chemical
● Continuous working temperatures: + 1050 °C,  Peaks at + 1200 °C.
● Fireproof.
● Highly flexible.
● Excellent resistance to radiation.
● Frays slightly when cut.
● Low heat expansion coefficient.
● Excellent thermal insulation properties.
● Low density.
● Very high chemical resistance, especially to acids.

I have no idea of the price, but I have a feeling that you're not picking up the bill anyway 

[Admin]

Soeren, not quite what I need, but your post gave me the key words to search for. I might still get some of that wire insulation as well, just in case (thank you tax payers! hehe).

What I'm current looking at are these:
http://www.stockcap.com/prod_detail.asp?id=99&cat=12

also this:
http://www.mcmaster.com/#push-on-caps/=cxlatm
(click Resilient Rubber Caps)

There are also these, but I haven't quite figured out the sizing, yet:
http://www1.mscdirect.com/eCommerce/SearchServlet?scrNtt=High+Temp+Wire+Joints&x=20&y=7&scrNtk=default
Any idea on what "Min. 3 No. 16, Max. 3 No. 14 " is referring to? Sounds like a metric or wire gauge rating . . .

I got a wire coming out the side, however. I've seen some of those right-angle rubber things on lead-acid batteries . . . see any for high temperatures?

edit: fixed typo

[Soeren]

Hi,

Any idea on what "Min. 3 No. 16, Max. 3 No. 14 " is referring to? Sounds like a metric or wire gauge rating . . .

They are for connecting ends. I haven't used them in high temp versions, but the rest is the same.
It means that the cap works with max. 3 wires of 14 gauge and should at least have (the equivaqlent of) 3 wires of 16 gauge to give a secure fit.

I got a wire coming out the size, however. I've seen some of those right-angle rubber things on lead-acid batteries . . . see any for high temperatures?

No, but I haven't been looking (and that's where you notice them the most). I would think some of the companies will make them on order though.

Would a high temp. RTV do (Not sure of the limits, but some of them are used for gaskets in racing engines).
If so, you could make them the way you want them.

[Kirk]

UL rated heaters use several different methods.
The most common is Air!  Tear apart a toaster oven and you will find many exposed conductors that are protected by steel that is a distance away. I forget the distances in the UL spec but 3/8" would be plenty for 120VAC.  Cooking appliances will use silicone insulated wire and fiberglass jacketed wire. 
As for plastics,
VESPEL is good to 500F and PEEK is good to (from memory) 425F
PEEK is half the price of VESPEL (still really expensive)

don't forget asbestos :-)
Kirk

[Admin]

Would a high temp. RTV do (Not sure of the limits, but some of them are used for gaskets in racing engines).
If so, you could make them the way you want them.

Awesome idea! I found plenty under < $10 that claim between 650F and 700F. I'll just buy that, makes life much easier.

[Gertlex]

Sounds like you're set, but though I'd mention a couple ideas...

There's that woven/cloth wire insulation they used before silicone/rubber, e.g. back in the 40s/50s/60s.  Maybe a kevlar version of this exists, for example.  I know there's kevlar rope, and kevlar is used for flexible heat shields...  Didn't find anything with quick searching, though.