May. 06, 2024
The object is to melt 3mm pvc, UMHW, or abs rods in a brass nozzle tip 6 mm diameter and which has an exit hole 1mm or smaller.
I estimate that the nichrome wire would be wrapped around the nozzle over 40mm of its length, and the thermistor would be near the end, so I could tell when the plastic is sufficiently melted to extrude it.
PVC and ABS melt around 180° C to 220° C , so that's the lower end, and the material can't get hotter than 260° because itstarts to break down. In addition, according to the REP-RAP folks, parts of the extruder need to be made of Teflon to reduce the friction of the rods being pushed into the nozzle, acting like a piston to force the plastic out the 1mm hole. teflon starts to degrade at 280° and gives off toxic gasses ( including Phosgene) at 330°, according to Dupont. That's what caused the big hubub over Teflon pots.
a website that has the general arrangement is here:
<A href='http://reprap.blogspot.com/2006_10_01_archive.html' Target=_Blank>External Web Link</a>
The nozzle tip length is variable. It might need to be longer to be able to wrap more wire around it, but that's OK, I can turn them out in about an hour's work.
My question is, do I need to depend on the thermistor or am I understanding you correctly that I could accurately measure the temperature of the wire when it's not being powered? I could turn off the nichrome wire, measure the resistance, then turn it back on.
What kind of repeatability and accuracy could one expect?
I figure that measuring a large section of the nozzle by knowing the temperature of the wire wrapped around it might be better than measuring just one spot near the tip of the nozzle.
My guess is that 5° range of accuracy would be fine. 10° might do, but I guess it would take some running to really find out.
did I give you enough information?
Edited by - Larry on 11/02/2007 06:37:49
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The NiCR wire itself is worth somewhere in the ballpark of $6.00 a pound.
Elements that that look like wire are NiCR. They are insulated by hanging from ceramic insulators.
For example the the element from a hair dryer is a bare wire element.
Water heater elements are like stove top burners. Burners have a heavy insulation on them so you don't get electrocuted when you set the pan on it! You can just picture what the result would be if the water heater element was to contact the water directly.
I never tried but I'm sure you would have to beat the hell out of it to get to the center wire.If you want to learn more, please visit our website 80x80 steel building.
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