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Polymeric sand has a metallic component to it and is attracted to magnets. Just a little bit of it in a motor could chew it up in no time.
I'm not disagreeing with the potential magnetism of the product, nor the destructive results that could occur if particulate matter were to get into a bearing. I do wonder if it's that significant of a danger in this particular application. The magnetic field would have to be pretty strong for it to draw up the particles. Since the idea with this product is that it forms a very solid base, you'd have to have a magnetic field capable of not only attracting loose particles, but loosening them in the first place. (I'll accept that the weight of the train moving over the track could release [i]microscopic[/i] particles from the roadbed.)
When our motors are near the track where the magnetic field has the greatest potential of being remotely close enough, they’re usually in sealed cases, keeping the nasty stuff on the outside. The motor’s magnets might attract it, but it doesn’t give the particles a roadmap on how to navigate through the plastic case. On other locomotives without sealed motor blocks, the motors are typically mounted above the frames, which puts them between 1 - 2" above the ballast. I question whether that’s close enough to attract anything. I can’t get a magnet to fall towards the fridge at that distance. I seriously doubt the magnets at that distance would have the strength needed to separate particles from the roadbed.
Also, there’s the simple fact that if a magnetic particle is attracted to the motor, it’s going to be attracted directly to the magnets on the motor. The law of attraction doesn’t allow for detours, so the particles will most likely attach themselves to the outside of the case, away from the bearings. Larger particles–whose potential for damage is greater–are by nature heavier, and would need a stronger magnetic field to draw them up. Particles small enough to make such a voyage would cause no more damage than the dust in the air around them.
Obviously there’s the potential for damage, but I seriously doubt it’s any greater than the risk posed by other nasties we deal with. The oil and grease we put on the locomotives will attract far more dust and debris–magnetic or not–than any large-scale motor ever will. That stuff’s right next to the ballast, in the open with nothing getting in the way. If you’re worried about particulate matter contamination, magnetic draw from our motors is pretty far down on the list of causes.
Getting the binder separately and mixing it yourself with non-magnetic media is an ideal solution. At that point, though, are you just as well served mixing a bit of cement in the ballast and wetting it down? That’s a solution that’s worked for a number of folks over the years, too. I don’t see the sand as posing enough of a realistic threat to worry about its use in the garden.
Later,
K