Glue gun nozzle? Gordon Williams ----- Original Message -----=20 From: "Denny Esterline" To: "Microcontroller discussion list - Public." Sent: Friday, June 07, 2013 1:56 PM Subject: Re: [OT] Best way to attach uninsulated NiCr wire to a copper pipe= ? > At a slightly different scale this problem has been worked over quite > thoroughly by the RepRap community - heating element connected to a tubular > melt chamber. > A rough overview in order of successfulness (did I just make up a new word?) > > Wrapping uninsulated element wire with various barriers (PTFE tape, > barbecue paint, Kapton, fire putty, etc) > Using _insulated_ element wire > Using a heat transfer block and using a power resistor as heater element > Using a heat transfer block and using commercially available cartridge > heater > > State of the art at the moment seems to be the Prusa nozzle which is an > aluminum block with sensor and cartridge heater clamped to a tubular melt > chamber. > May require a bit of machine work, but should scale easily to paraffin in a > 3/4" tube. > > Also noteworthy for this discussion is flexible "sheet heaters". Easily > flexible enough to wrap this size of tubing. > > -Denny > > > > On Fri, Jun 7, 2013 at 7:19 AM, Spehro Pefhany wrote= : > > > At 04:52 PM 06/06/2013, you wrote: > > >On 2013-06-06 12:08 PM, Dwayne Reid wrote: > > > > 2) Consider using the copper tube as a shorted 1-turn secondary on = a > > > > transformer. In other words, wrap however many turns of insulated > > > > wire you need around the pipe and feed with enough high-frequency > > > > current as you need to bring the pipe up to the desired temperature= .. > > > > > > > > Note that the primary wire does NOT get hot, so space it away from > > > > the copper tube if desired. Better yet, wrap the copper tube with > > > > insulation, then wrap the primary coil over top of that insulation. > > > > > > > > Details left as an exercise for the student . > > > > > >I was considering this, and if done right, would be ideal. But it woul= d > > >complicate the electronics. With the NiCr wire, I could get away with = a > > >MOSFET and switch it to control temperature. With the induction heatin= g > > >method, I'd need at least an H bridge and potentially complicated PWM > > >control to shape the output signal into a sine wave. > > > > > >Also, how would I go about calculating the inductance, coupling, numbe= r > > >of turns, frequency, etc...? I'm assuming this is far from an ideal > > >transformer and losses will be great. > > > > Sure, since that is where the heating comes from. > > > > If you're interested, have a look at the work of Tim > > Williams- he has built rigs that work up into the kW range. > > > > http://www.mindchallenger.com/inductionheater/induction10.html > > > > If you want to buy a resistive heater, something like shown on page 509 > > here: http://www.watlow.com/products/heaters/cable-nozzle-heaters.cfm > > would be good. For even better coupling, buy a wound MgO-insulated > > coil and braze it to the outside of a relatively thin (to minimize > > the heat capacity) copper tube. Stainless sheath is fine for your > > low-temperature application. > > > > Hmm... since you say you want fast heating it seems inevitable that a > > failure of the controller would cause the flash point of the wax to be > > exceeded. Suggest some kind of reliable safety agency approved thermal > > fuse (cutoff) in the circuit if this is a concern. > > > > --sp > > > > > > -- > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > --=20 > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .