Unlike Ni200 or Tit the NiFe 52 can & should be oxidized prior to use (This is a good thing). It is a mandatory if configured as either a contact coil or Clapton. IE everything I build!!
If you try to dry burn NiFe like it's Kanthal you'll just burn the legs right off. It takes a different technique to get them dry pulsed & successfully glowing inside out.
It makes sense if you consider a kanthal coil typically has a final resistance 4+ x higher then the NiFe 52 so a hot leg/arch on a .4 Kanthal might bring it down to a .15Ω, whereas a hot leg on a .12Ω NiFe might fire at .05 & I've had a .1Ω target (unoxidized) NiFe 52 contact coil (pictured) so low without pre-torching it wouldn't even fire to try dry pulsing.
Uwell Crown RBA 26ga parallel .1Ω would not fire on DNA to pulse, unoxidized ohms below DNA safety limit.
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I now wrap the coils first & then torch before installing (I have the exact torch dwcraig1 just posted a pic of). I then dry pulse in watt mode starting at 10 watts till its acting right. Then for good measure pulse a few times at 30+ watts to make sure it's glowing reliably middle out. If I don't have a torch with me I just start pulsing with 5 - 10 watts.
TheothersteveS beat me to it with the description of torching.
The only thing I do differently is to wrap the coils first and then torch. I did the same test as TheothersteveS torching the hell out of a straight piece & then wiped with IPA to confirm no residue resulted from torching. The rational for torching
after wrapping is that I don't want to damage the newly oxidized surface when winding the coil with my coil-master. I polished the serrations off the hex screws that guide the wire around the mandrels, but they still leave a stripe if I pre-torch the wire & then wind.
1st pic torching a NiFe Reactor coil.
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2nd pic. coil pair 26ga Reactor NiFe 52 one is oxidized with torch shown with unoxidized match & Black mandrel background for Color Ref. NiFe 52 is dark Gray/Blue after torching & color lightens when dry pulsing
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3rd Picture (Compressor coils) showing how color lightens when dry pulsing. Had to replace the one on the right. I zapped a leg off while pulsing on a series mech @ 300+ watts.
Coil on the left has been torched & dry pulsed. Coil on the right has been torched only.
My theory is that torching creates oxide by heating from the exterior, whereas pulsing heats from within causing additional oxide formation (druckle thoughts? Am I off the reservation here?)
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If NiFe 52 contact type coils are not oxidized the resistance will be low & or erratic. Of coarse same goes for good old A1 kanthal (pre-torching & dry pulsing was the key to success when Kanthal micro coils first caught on).
For spaced NiFe 52 coils (including single wire core claptons) I've seen the initial unoxidized cold resistance match the final resistance after oxidizing.
From that it would seem OK to run a
spaced NiFe without pre-torching or dry pulsing,
however:
- the emissivity would be significantly lower on a bright polished coil vs oxidized & may result in a cooler then expected vape??
People are always gushing over how much warmer the vape & faster ramp times with Nichrome 80 vs Kanthal.
FWIW - emissivity, fully oxidized condition for A1 Kanthal is .70, for Nichrome 80 it's 25% higher @ .88, & for NiFe 52 also .88
I'd love love to have some of the experts on here share their knowledge on the topic of emissivity & and its affect on our application. How does it correlate to heat flux on Steam Engine?
- I am of the opinion that the safety level of one coil alloy vs another in our wet application is directly tied to the below characteristics of the oxidized layer formed prior to use. This is not a complete list, but may provoke some good discussion.
- Oxide layers performance as an electrical insulator. (Will the coil perform as micro coil/Clapton?)
- Oxide layer formation. (Does the process of oxide formation result in flaky crust or sooty residue that may be soluble in the e-juice?)
- Oxide layers ability to heal itself when damaged or spalled off. (How many times can you dry burn before oxide can no longer regenerate?) There is a limit with Kanthal A1 & you can tell when you've hit it.
- Oxide layers coefficient of thermal expansion vs that of the base metal. (Is the likely-hood of oxide spallation increased due to dissimilar expansion coefficients & heat pulse cycling?)
- Oxide layers ability to bond to the base metal. (Ability to prevent boundary layer infiltration from liquid, moisture, & vapor; thus preventing or allowing oxide layer fracturing & spallation due to boundary layer vapor pressure when heated.)
- Oxide layers grain structure how fine or coarse. (How well does it protect base metal from corrosive oxidation?) & (Does the oxide layer effectively seal the base metal, thus preventing any leaching?)
- Oxide layers malleability. (How delicate is it? Will it be easily damaged when wicking?)
In a future post I'll try to plug all the available TC wires into the above oxide layer characteristic/questionnaire.
