hOt Wire nEEded

[ELIEZER20]

HI to everyone!!

well i need to make some figures in a piece of solid dry ice , i was thinking to make the figure form with a coaxial wire, then to conect it to some device that heat it enough to cut the soild dry ice.

i use a 110v to 24v transformer to the TRY to heat the wire, but the transformer begun to throw smoke and smell funny,then i realize that the plastic protection of the wires were melting, so i stop it.

i really need something that can heat enough the coaxial wire,to cut the solid dry ice, but also need it to be working for at least 10-15 minutes ,because i need to cut some big stuff ,so if anyone can help me to build something that can help me i would really appreciate it, just wanna let you know that i don´t know a lot of electronics as you can see,
thanks for your time.!!

 

[Nigel Goodwin]

You can't use insulated wire, the insulation will melt and burn (as you've already found out. You also can't use copper wire, it's too low a resistance, and will take too much current - as you've also found out.

You need some kind of resistance wire, there are various types available, for cutting polystyrene I usually use wire from electric fire elements.

Once you've got your wire you need to find out how much voltage you need to feed it to give the heat you require - a variable transformer is EXTREMELY useful for doing this - my polystyrene cutter happens to require 24V, which is perfect as I have a 24V AC supply at work for the soldering irons.

With polystyrene it cuts fairly easily, if you drive the wire till it gets red hot it even cuts without touching - but makes a fairly large cut, probably about half an inch wide.

 

[gerty]

The type of wire you need is Nichrome wire , the same type used in heating elements. A heating element from a electric water heater will get fairly warm on 48v...

 

[Oznog]

Nichrome is the best stuff. Very thin stainless wire also has a high enough resistance to work, but nichrome is a higher resistance.

It expands a lot as it heats. You need a jig to keep tension on the wire even as its length changes.

The trouble I have with hot wire cutters is that the ends of the wire not inside the material get so hot they can glow and break. They carry the same current as the center of the wire but the heat has nowhere to go. The dissipation limits of the end limits the power you can put into the wire. Cooling the ends with moving air greatly improves it.