Some say the plastic wheels, being non-conductive, develop more low level static discharge and therefore attract the dirt. We've heard people say that metal wheels cut down on crud a lot. Some of my RR has metal wheels but many cars do not because they are not really worth changing. The track gets dirty regardless of which type I use.
By running a track cleaner car frequently (and keeping the wheels clean), I haven't had MAJOR problems with plastic wheels. In fact, if you clean frequently (recommended), I can't tell for sure if plastic are dirtier than metals.
I totally agree with you Frank, those metal wheels make a really nice "clack-clack-a-clack" when they run over a diamond or frog. I used to get sooooooo much crap build up on plastic wheels that at times you almost couldn't see the flange.
ALL wheels pick up SOME dirt. My experience, too, has been that plastic wheels pick up MORE dirt. I don't know why this is so, but I doubt the idea that static has much to do with it.
To generate static by friction one normally needs friction between two (relatively) non conducting items (plastic, rubber, cloth, fur, etc.). The wheel is effectively grounded to the metal rail. Also, the dirt that builds up on a wheel usually has a substantial metal content (from worn track and metal wheels), and would likely be conductive enough to further ground the wheel. Static electricity has high voltage but usually next to NO current delivery capability ... even materials with very high resistance will effectively ground it. Even AIR grounds it, especially moist air.
I could see plastic axles turning in plastic sideframes as a possible source of static, but, if so, then our plastic trucks would be collecting lots of dust and 'growing hair'in addition to the wheels. I don't see this happening.
I think the wheels just roll up dirt off the track. This dirt is mostly just settled dust, with a little dropped oil, and worn metal and plastic dust from the track and the wheels themselves. There's just enough moisture or oily residue to cause it to stick together, and imbed into or adhere to the wheel tread. My guess is that the softer plastic wheels are more prone to microscopic imbedding. Despite the light weight of our model cars, the actual contact pressure at the point where the wheels touch the rail is considerable (very small contact patch). Each wheel acts like a miniature laminating press, and rolls it's own 'dirt tire'.
I'd suspect that the dirt embeds itself into the plastic easier than the metal wheels. Actually, I've seen times that metal wheels have collected dirt faster than plastic wheels do. It all depends upon the type of dirt that you are dealing with.
-- Why isn't there an Ozone Hole at the NORTH Pole?
No doubt that's true. The type of dirt encountered is an 'environmental issue', and depends on the location.
What I get tends to be dust (mini fibers), grit (mineral?), oil, metallic dust, paint chips, and 'who knows what'. I suspect all manner of condensed vapors (paint, solvents, cleaning materials, outgassing plastics, etc.) also contribute. Particles of graphite from Kadee 'grease-em' shed from coupler pockets is likely also there.
We once used kerosene heaters in the building where our club layout is displayed at Christmas. It could get COLD 'back then' ... -10F degrees and 40 mph winds. WE were in a 'historic' building .. read: NO storm windows, NO insulation, free outside air flow beneath the floor. etc. FUN! Once we had FIVE such heaters going, and still had SNOW on the floor! The kerosene fumes condensed on the track something awful, like varnish. We had to clean the track about once an hour to get even barely acceptable operation.
If allowed to build up, the wheel 'gunk' rolls itself into 'tires' on the wheels. While a brittle material by nature, with care these can sometimes be chipped off in big curved segments. They often have a metallic sheen from the imbedded metal or graphite particles. I haven't tested it, but I suspect it's partially conductive (not enough to cause shorts, but maybe ground static).
I lean to the idea that plastic wheels are somehow more porous to attract and hold the crud. I'm surprised no one has mentioned the difference in metal wheels. Old Athearn compressed metal powder Diesel wheels are notorious for attracting crud as compared with NWSL machined solid metal replacements. I think the same is true with Lionel wheels - the sintered metal powder wheels used on postwar rolling stock seem to collect more black adherent crud than prewar pressed steel sheet metal wheels or "new Lionel" cast zinc alloy wheels (although this could be related to the fact postwar Lionel ran so much better (reliably and thus longer) than the prewar trains or many of the "new Lionel" offerings. Gary Q
If you want to find out if static is your problem try using some of that anti static spray to clean the wheels... it should be obvious when the dirt just falls off when you spray it...try monitor cleaner too...I believe that has antistatic stuff in it too!
And if you don't think static builds up without friction... static is the accumulation of excess electrons (or electron holes) and there has to be more than one way to do that.
I think most cars have metal axles and plastic sideframes/wheels. Accurail has a plastic wheelset though, because it's all one molded piece (and they really roll bad too...they were the first reason I went to replacement wheelsets)
The sintered ("grindstone" texture) wheels as used on Athearn locos, give an unusually high factor of adhesion (traction), and wear well. Their affinity for dirt and poor electrical contact more than compensates for these virtues. They are, as you say, especially good at collecting dirt, and are indeed porous, which may well explain the phenomena.
Plastic wheels, on the other hand, are not particularly porous, yet they still collect dirt. It may be that the softer (compared to metal) plastic just allows dirt to imbed into it's surface more easily. Or, perhaps it gets (microscopically) scratched more easily, leaving pockets for the dirt to collect into. As I've stated, I don't think static has much to do with it, though it can't be ruled out entirely as a contributor.
And, as others have observed, it also depends on the nature of the 'dirt' in your layout room. Some even report more dirt on metal wheels, but that's sure NOT been my observation.
But many, MANY people use Kadee or P2K wheelsets in Athearn (or similar) sideframes. That's plastic on plastic. It causes wear and friction problems over time, but I've NOT seen it produce static (though in principal it could).
A few otherwise decent kits come with all plastic trucks, and Life Like (not P1K or P2k), Bachmann, and several other low-end train set models use, or have used, all plastic trucks commonly.
Acually, plastic is porous, at a microscopic level. This is why plastic cutting boards need regular dousing with bleach -- they provide good hiding places for kitchen bacteria, better than wood. Also, all plastics are "filled" with additional compounds to increase wearability, hardness, rigidity, etc. In effect, plastics are alloys. This means that at the surface there wil be different substances exposed to the crud on the rails, and some of these will simply pick it up easier. Some stuff just sticks more easily to other stuff, is all.
True, but your description also applies to many metal wheels. Brass and Nickel-Silver are both alloys (mixtures of two or more materials), have a highly variable grain structure, and frequent microscopic voids. The sintered metal wheels are HIGHLY porous. Plating, too, can be very rough to start with, and frequently wears through, leaving an even rougher surface.
Since several different plastics are in common use in model railroading (Styrene, ABS, Polycarbonate, and Acetal, at least), and the quality of both the 'mix' and molding technique likely vary a lot, most anything is possible. Some plastics have low porosity, and make excellent moisture barriers. Others, like Nylon, are quite porous and actually soak up water like a sponge.
A smoothy TURNED fine-grained solid metal wheel is undoubtedly harder and less porous than many plastic wheels. I suspect this has a lot to do with their resistance to 'gunk' build up.
One of our group has access to an electron microscope who advised the "crud" is made up of "humus" (lint and dust - plant and fiber) and the solvent is "Water".
What a surprise!
So, instead of dissolving it, John Allen and Linn Westcott "sloughed" it off of the track.
They "floated " a masonite block on a stock car to "slough" the reside to one side to effect good electrical connections.
I will throw another theory out here (and it may not be valid). Pretty much all plastics constantly excrete some of their base solvents (oils). This is why many plastics become brittle with age. The amount may be incredibly small, but there is still some. Is it possibly that this excretion is what is attracting the initial coat of dirt and continued use is of course adding more dirt to the dirt that has already collected (dirt attracting dirt). This would explain the difference between metal and plastic...
Newer plastics last longer and therefore excrete less oils, but I would always assume that they will put out more than a metal wheel.... The oil is also partially bonded to the wheel and should therefore be worse than oil that was applied to a metal wheel.
An excellent point. Most plastics, especially most softer plastics, outgass and 'weep' to some extent. This is the plasticize coming out of the material. One way of thinking of it is that the softer plastics are partly dissolved all the time, saturated with a solvent of sorts, thus they become soft and spongy. Even many hard plastics have some of this. As the plasticizer is released, the materials warp, shrink, and become brittle.
This could indeed contribute to the dirt collection problem (as well as indoor air pollution, etc.). And, some plastics, especially older plastics, depolymerize (the structure of the molecules breaks down) with time, and become brittle, or "grow hair" (usually a white, crusty substance with a strong odor). Some of the old Varney plastic items are noted for this, as are many drafting templates.
On 15 Feb 2005 10:47:29 -0800, snipped-for-privacy@mailcity.com (Jason) purred:
You have the basis of the problem. I, too wondered and all I saw were opinions so I decided to ask an environmental chemist. He says basically what you do then adds this combines with the "indoor pollutants" like oil and grease from cooking, smoke, cosmetic vapours,the naturally excreted oils in human breath, etc to form the crud we see on the wheels. Since metals do not release plasticizers they are less prone to attracting the pollutants. Also he says the round shape helps retain the crud as edges would cause it to break off before a heavy layer built up. With no weak spot (point) it becomes more homogeneous and tenacious. That was something I had never imagined, that the shape of the wheel was part of the problem. ah well, live and learn.. Oh, he says the crud will not build up if we run our trains in a vacuum. Scientifically accurate but hardly practical. =^-^=
outgass and 'weep' to some extent< An excellent point. It has been analyzed that much of the crud on the rails (discounting climate conditions) is plastic from plastic wheels.
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