I am replacing a 110 volt 800 watt heating plate attached the bottom of a lab water bath. i have chosen to use two 400 watt nichrome coil elements controlled by the bath's three position analog rheostat heat the bath to 100 degrees F.
Question:
Is it feasible to use 1/8 inch thick HDPE sheets as insulation to enclose or other wise sandwich the nichrome heating coils, without reaching the melting temperature of HDPE (248 degrees F.)?

 

NO

The Nichrome will reach a higher temp than the water bath because the metal plate that distributes the heat will act as a heat sink to the nichrome wires. The wires will most likely operate at a low 'RED' heat. Get an old toaster, or buy a new one for $10 at Wally world and use the insulation backing boards that the toaster element wires are attached to.

In addition to all the above info I would add that unless the original element operated in free air with no attachment to the bottom of the heat plate, this scheme will likely not work as you envision it.

 

Get a Kevlar solder cloth in the homeDepot plumbing department or a sheet of Fiberglas cloth from an auto parts store. Otherwise, my best suggestion is to contact the hot plate manufacturer to get a replacement heating element.

 

Heater elements are typically insulated with some sort of metal oxide, such as TiO, and enclosed in a metal tube that is wound into a spiral or other shape that effects the best transfer of heat. Trying to make your own will most likely result in inferior performance.

 

My mind is aglow with whirling, transient nodes of thought careening through a cosmic vapor of invention. ~Hedley Lamarr

Ditto!

I think you mean ITO rather than TIO. I also think the point being is that what is desired is something that is a good electrical insulator but an excellent conductor of heat and/or is thermally transparent so the heat can be radiated through it.

 

Why on earth would they use ITO for something like this?

 

I think you mean ITO rather than TIO. I also think the point being is that what is desired is something that is a good electrical insulator but an excellent conductor of heat and/or is thermally transparent so the heat can be radiated through it.

No, I meant TiO. That's what was used in the heater manufacturer that I briefly worked in. After coiling the heating element and inserting it into the Ti tube, the space within the tube was filled with TiO, the ends capped, and then the tube diameter was reduced by a series of rollers, which compated the TiO and eleminated any remaining air space.

 

Thank you. The original heating elements were toaster-type tungsten elements connected in parallel from a common to two switch legs; watts are regulated by a low-medium-high selector switch and rheostat. The elements were insulated from metal surface contact by a sandwich of several sheets of mica.

The elements had shorted and burned due to a water leak soaking the rockwool insulation layer surrounding the stainless steel bath. That leak is sealed now with high temp epoxy.

I'll look into using kevlar sheets- 10" x 14"