IM brass wheelsets - conductivity

[Bill H]

Group;
I was adding some SMD resistors to some older IM cars for detection this past week, cars that had been in storage for some time, and the cars all had IM "brass" wheel sets. These are the IM wheel sets at least 10 years old with a dark finish on them - not the new "high detail" wheelsets. Usually I give the conductivity paint 12-24 hours to dry and then test to make sure the resistor install went correctly. Without exception, each wheel set I was testing with the IM "brass" wheels, was not showing the resistance I was expecting on my multi-meter i.e. 10k ohms. In fact, the wheel sets were not showing any conductivity at all. So, just to cross check in case my multi-meter was out to lunch or I set something wrong, I put the wheel set on some clean track that is connected to a BDL168 and again, no detection. The wheels had no gunk, had never been run, regardless I tried cleaning the wheels anyway with IPA "just in case". No change. No conductivity. Only after some time lightly brushing the wheel with a Dremel and very soft wire brush did the wheel set show some conductivity and the correct resistance. It seemed like whatever coating IM used to darken the wheels really impacted conductivity. I have never had a problem in this regard with FV or ESM wheel sets. Has anyone else experienced this with the IM "brass" wheels?

Kind regards,
Bill

[peteski]

Wile I have not had any experience with IM wheels, I know that certain blackening layers can act like insulation.  In my example it was the blackening used on the drivers of the poorly running Kato American Freedom Train GS4 loco.  It was only that specific roadname.  I have other GS4s (Southern Pacifiic) and the drivers of those had no conductivity issues and run very smoothly.

Visually, the AFT loco driver's blackening layer looks different than the SP ones.  The AFT's blackening is much darker, seems thicker and it is flat in sheen, where the blackening layer on SP model drivers looks like typical Kato blackening: brownish in color with a slight sheen.

When I used my multimeter on the blackened AFT drivers, there was no continuity at all until I actually scraped the black layer to expose bare metal. Once I removed the driver blackening (using a rotary wire brush in a Dremel tool), the loco ran as well as the SP units.

I wrote this all up on the Atlas forum, and also notified Kato USA, giving them a link to that thread.  I didn't really get an explanation of why they used that particular blackening on that model, but it seems that subsequent runs of GS4 went back to the standard (problem free) blackening.

Bottom line is that yes, certain blackening solutions can very negatively affect electrical conductivity.  Did you also scrape the blackening in the resistor area?

[Bill H]

Peteski:
I had conductivity in the area of the resistor i.e. back of the wheel and axle shaft.  It was wheel tread to wheel tread that lacked connectivity. Hence my question about the coating on the wheel treads.

Kind regards,
Bill

[peteski]

Peteski:
I had conductivity in the area of the resistor i.e. back of the wheel and axle shaft.  It was wheel tread to wheel tread that lacked connectivity. Hence my question about the coating on the wheel treads.

Kind regards,
Bill

Hmm, in my experience the entire wheel is blackened using the same blackening solution. As I understand it, is a chemical process where the entire wheels are immersed into blackening liquid. I nave encountered just the wheel thread being different.  Interesting.

[Bill H]

Peteski;
I think I have gotten to to bottom of the issue. The set of IM cars I have been working on were run on a friend's layout that used a lot of graphite to inhibit dirty track. Then the cars sat in their boxes for more than two decades while I was moving. They were thoroughly cleaned with IPA before I started applying resistors but still did not have any conductivity at the treads, but the back of the wheels and the axles were OK. It took a lot of time with a wire brush only on the wheel treads, before conductivity at the treads returned. Once that was done the wheels were fine, and those other IM boxcars that were never run on that layout have not been an issue. No clue as to why, but that seems to be the resolution.

Kind regards,
Bill

[peteski]

Peteski;
I think I have gotten to to bottom of the issue.
. . .
 No clue as to why, but that seems to be the resolution.

Kind regards,
Bill

I'm glad you found a solution Bill.  The only odd thing I find is that graphite is conductive, so it a layer of graphite should show some resistance, not open circuit. But if removing the graphite (plus I assume gunk) from the threads, solves the problem, that's all that counts, especially since the unused wheels do not show any conductivity problems.

[mmagliaro]

Graphite on a stick has some kind of binder in it, doesn't it?  To keep the stick from just crumbling.  Maybe the graphite was long gone or cleaned off, but the binder stubbornly clung to the wheels.

[Bill H]

Max;
The only thing I can figure is that something in the graphite pencils that person was using reacted with the coating on the IM wheels. As Peteski noted, graphite is a conductor, but there was zero gunk on the wheels and they were very clean from a visual standpoint, in the sense that nothing was coming off the wheels during aggressive cleaning with IPA. But. The treads had a different color than the rest of the wheel, they sorted of looked like, from a wood working perspective, like they had a coat of varnish or something on them. It took a lot of time to get that color change on the treads back to "normal" i.e. the color of the treads on IM wheels of the same generation that were not run on that graphited track. As i continue to add resistors to some of the fleet that have been in storage for a long time, I will have to take extra time with the IM wheelsets if they look like they ran on that other layout.

I think I can conclude that whatever graphite pencil my friend was using, and I think it was some sort of artists' graphite pencils, does not play well with older IM wheelsets. FWIW, of the new runs from IM, their "high detail" wheel sets, they are no longer darkened but have a bright metallic appearance.

Kind regards,
Bill