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We are working on a project requiring a temperature-controlled oven for melting lead, tin and other low-temperature metals. The inner cylinder is aluminum. The heat comes from Kanthal wire, for which we needed an electrical insulator capable of withstanding the heat. The problem is, something must hold the fiberglass in place. We just tried to melt the stuff end-to-end (does not hold) and with an overlap (gets blackened, shrinks, but does hold a tiny bit). We have thought of a couple of alternative ideas:

  1. Add glass powder, sand, or broken glass to the area of the joint and have more glass available to melt
  2. Get some kind of glass fiber and "sew" the layers together somehow
  3. Some kind of chemical adhesive that can handle the same extremes of temperature

The plan is to wrap a thin layer of fiberglass around the inner aluminum, then wrap with Kanthal wire. Then wrap more fiberglass around that and cover with aluminum, and do enough layers that the outside is not hot to the touch. An Arduino will control the circuit, and slowly bring the inside up to exactly the temperature we want using a thermocouple.

How can we hold the fiberglass insulation in place without interfering with or shorting out the Kanthal wires that will go around the fiberglass?

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    $\begingroup$ What temperatures will the holder material be required to withstand? $\endgroup$
    – hazzey
    Aug 24 '15 at 11:18
  • $\begingroup$ The fiberglass and aluminum can handle 1000C so that's an upper limit. $\endgroup$
    – Dov
    Aug 25 '15 at 0:14
  • $\begingroup$ What type of insulation are you using? What's the diameter of the tube? Could you just use some stainless steel straps to hold it on? $\endgroup$
    – GisMofx
    Aug 25 '15 at 1:46
  • $\begingroup$ If we are wrapping the fiberglass with kanthal wire, using stainless steel straps is not appealing because it is conductive. On the other hand, if it only crosses one loop of wire, that's not a bad solution. I will think about that. $\endgroup$
    – Dov
    Aug 25 '15 at 12:12
  • $\begingroup$ Aluminium alloy with a melting point above 1000C....really ? $\endgroup$ Mar 17 '16 at 23:58
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First I recommend you use mineral wool or ceramic wool instead of fiberglass as they are rated for higher temperatures.

Material Temperature
Glass wool 230 - 260 °C
Stone wool 700 - 850 °C
Ceramic fiber wool 1200 °C

https://en.wikipedia.org/wiki/Mineral_wool

Second, using insulation to separate the aluminum and resistance heating wire is not a reliable solution. You should use ceramic rods, ceramic insulator rigs or something similar to space the wire away from the aluminum. You may even consider not using aluminum and directly wrapping a ceramic container with the wire.

There are lots of options for securing the insulation around the outside. A thin sheet of aluminum or stainless would be a nice clean way to keep the insulation protected.

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  • $\begingroup$ What kind of ceramic container can withstand being wrapped with kanthal wire and heated to 1400C, then air cooled? I obviously don't want it to shatter. $\endgroup$
    – Dov
    Mar 18 '16 at 17:16

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