RogueRose
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Small hat plate attempt from nichrome coil & clay
I had a 400w nichrome coil that had some fiberglass or asbestos like fibre inside the coil that I thought I would try to use to make a mini hot plate
for small beakers and flasks (50ml - 500ml) or 3-4" diameter.
I have some VERY fine kaolin clay powder/dust which is supposed to be excellent for very high temperature applications so I thought I would be able to
use this as the material for the hotplate surface.
What I did was take a mason jar narrow mouth lid ring (doesn't have the flat part that seals) and lined it with saran wrap on the inside of the ring
so it could be filled with clay.
I mixed the clay powder with water until proper consistency and then placed it inside the ring and tamped it down with the bottom of a flat glass
"jar" - making the whole thing level and filling in all the crevices on the side to a depth of about 3/8". I then took the nichrome and starting from
the center made a spiral outwards keeping each outer ring consistent distance from each other. I then tamped the wire into the clay so that it was
flush with the surface.
I then placed some more clay on top of the wire and added about another 1/4", tamping down and making sure it reached the sides of the lid. When
doing this I had to make sure that there were wire leads from both ends of the wire to connect power.
Once tamped down as much as possible and making sure no air bubbles were present I pulled the clay out of the lid ring and flattened out the plastic
wrap. I then used an exacto knife and thin metal ruler to smooth the edges and any part that needed smoothing. After this, it is ready to "fire" or
cure (which is where I messed up I think). I flipped the clay over onto a small cast iron pan with a couple newspaper sheets separating the clay from
the pan then placed on a grill/forge.
I think my clay heated to fast and I had some cracking on the top. Here are the pics of the process and the results. I'm interested in what people
think about this idea of making small hot plates for small beakers/flasks. If anyone knows how I could fire this without a kiln or some other
suggestions I would be much appreciative.
(NOTE) the flat side where the beaker sites is not seen on the pics, but it is very flat.
  
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Dank
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I did something similar with a corning pc-351 which had a burnt out heating element. However, I did not use any core for the coil and I used kanthal
wire. I've been using it for about 2-3 months and the coil still works just fine, but I would worry about hotspots with a setup like yours. What are
you planning on using for your heating surface?
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RogueRose
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Quote: Originally posted by Dank  | | I did something similar with a corning pc-351 which had a burnt out heating element. However, I did not use any core for the coil and I used kanthal
wire. I've been using it for about 2-3 months and the coil still works just fine, but I would worry about hotspots with a setup like yours. What are
you planning on using for your heating surface? |
Well IDK if theceramic an be used by itself (I would find a high temp glaze) or I would probably find something like 304SS or Al plate possibly -
maybe interchangable depending upon what I am going to be heating.
I only tried this b/c I had the extra nichrome sitting around and wanted to try a little experiment to see if it would work. I've never seen small
hot plates for 50-250ml beakers and I hate using a 6"-8" plate when the beaker diameter is 3" - it wastes so much heat.
On another note, I posted this in the longer thread that was "homemade lab gear" did anyone see it there or did someone move it? I've been trying to
be better at placing posts where they should be so I'm a little confused.
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Melgar
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Chinese suppliers sell "coffee cup warmers" on ebay for between $2 and $3. The AC ones get to about 80C, although they come with shitty cords that
don't stay plugged in easily. I got one and it's been convenient for speeding reactions up where you need to make sure it doesn't reach 100C or so.
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