Coil Ohms

[crxess]

Sorry actually got distracted and missed a part of my intended post.

The devices that seem to suffer the most(fastest) are Chrome plated.
Chrome is a Very Hard Coating, but not actually a true part of the overall structure. Thin chrome finishes start to bubble and separate under heat/cooling. We see this as flaking.

As to Kanthal oxidation - not really an issue. it is the other metals that are more effected and become coated.

Break down a well used T3 Base - Remove center pin, grommet and coil.
Shine a light into the opening from the base end.
What you will see is Carbon build up and even carbon bumps.

Another example of oxidation causing contact loss is burning of the insulator. This if from increased heat on the poorly contacting leg.

Tossing a new coil into this will result in a so so build and a shorter use cycle.
Cleaning first - Tiny brass brush is handy - will give the Wire a good clean surface to make contact.

I have also noted if the wire is not torched just a bit to clean, ohms will vary on first use until a solid contact is established. I am speculating heat plays a role in cleaning during initial use.
Wires I have torched and wiped tend to be very close and stay there over the break-in period.

 

[generic mutant]

Well if there is a conclusion to this thread, it seems like "Several plausible mechanisms - more rigorous testing needed."

 

[Ryedan]

Oxidation and dissimilar metals.

Coil resistance greatest increase is caused by a loss of clean contact between the coil lead ends and the device.
As heat is induced, especially on longer draws, the outer shell starts to oxidize.
The wire ends touching the SS housing(or other metal) start to lose contact. Carbon starts to form and contact continues to be reduced until the coil finally reads open, even if not broken.
Even at this point the coil may be good, but will not function do to contact loss. Cleaning the leads of oxidents would bring it back to normal function.
Problem is working on tiny coils in many applications and getting them reattached properly. Most are not worth the effort compared to quick replacement.

Items like Kanger bases need to be inspected and cleaned when rebuilding or coils tend to read higher than actual build.

Very interesting crxess. How are cartos made? I thought the resistance wire was soldered to leads, but I could be completely wrong here.

 

[AttyPops]

I'm still in the "wire erosion" camp. Think "microcoil" for a minute.

They (excuse the "they" thing, MC fans) make them and actually squish the coil loops together. Yet they don't get shorts across the coil wires. Thus there's a layer of oxides protecting the wire from shorting. Now, as they "pulse" the coil, it starts to glow more evenly. Why? Building up more non-conductive coating on the outside of the wire by transforming the wire material into something less conductive. So it's not just a coating "from the air" but rather a reaction with the air and the wire and you could view the wire cross section as a "bulls eye" type of thing where the center is still conductive and there's a ring around the outside that's not very conductive. This thin outside layer is the area that pits/cracks/fissures.

So after continual use and cleaning the wire basically gets narrower, thinner, and higher resistance...albeit only slightly. There may be some change to the structure of the crystals in the material too, IDK. Also, don't ask me if that has any effect to the vapor we inhale...IDK that either.

/hypothesis