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Chemist Reviews CMX Clean Machine

Posted by on Dec 16, 2015 in Miscellaneous, Tony's Tips |

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The following review of the CMX “Clean Machine” was performed by Charlie Miller, a retired chemist. We asked Charlie to do this review because as a chemist he would have a better technical basis to do so.


Track Cleaning – A Chemist’s Perspective

Few aspects of model railroading evoke as much controversy as track cleaning. Opinions on how to clean our rails are as varied as the ages of model railroaders. The one thing about this subject that we seem to agree on is dirty track interferes with engine performance and reduces the level of enjoyment of our hobby. From a model railroader who is also a chemist, the following opinion is presented:

When we say we have dirty track, we are really saying we have failed to achieve good electrical contact between the rails and the motive power pick-up wheels. This condition is obviously not the only cause of poor locomotive performance, but it may be the most common one. Unfortunately, most forms of “rail dirt” are very poor conductors of electricity. As I see it, dirty rails are the result of contamination from three sources. Each of these has its own set of characteristics, which are described briefly below.

Oxidation – Primarily an inorganic form of track contamination. Oxidative degradation occurs, over time, with most materials that are exposed to air. In many cases, this happens too slowly for us to notice, as with plastics and painted surfaces. With metal surfaces, however, oxidation is generally more rapid, and metal oxides are usually poor electrical conductors. Track manufacturers have minimized this oxidation tendency by using nickel/silver plating. Metal wheels on engines and on some brands of rolling stock are sometimes more susceptible to oxidation than the track itself. Friction between wheel and track can cause transfers of wheel oxidation to the track surface.

Organic contamination – Organic material (by the chemist’s definition) is composed of chemical compounds containing carbon. This covers a wide variety of both natural and synthetic materials. Sources of organic contamination include residual material from plastic wheel sets, nonvolatile residues from various cleaning preparations, fingerprints, and other oily substances.

External contamination – This category covers all other forms of contamination, which may be organic or inorganic. Single filament lint strands and other airborne particulates fall into this category. Other examples include smoke from tobacco products, hair spray aerosols, dust from various plaster-type modeling compounds, and overspray from air brushes. Any of these might contribute to the formation of a coating on the track, too thin to see, but thick enough to inhibit electrical contact. Because of this array of potential sources for what we broadly refer to as “dirt” on model railroading track, it is difficult, if not impossible, to define what we might call a “standard dirty track”.

Lacking such a standard, we are left with a rather subjective approach for measuring the effect of our cleaning efforts. For most model railroaders, the ultimate proof of a clean track lies in our ability to operate our locomotives in a consistent and trouble-free manner. The removal of dirt from our rails seems to be best accomplished through a combination of physical scrubbing and chemical softening of the rail dirt. Both of these techniques can be employed when using the “Clean Machine”. For inorganic contamination (primarily metal oxides), the physical scrubbing method is probably the best choice, in the form of some type of abrasion. As CMX Products has already discussed, the non-clogging sheet-rock sanding mesh pads work well for this. The CMX has adequate weight (even when the tank is empty) to provide constant abrasive force against the rails. Organic contaminants tend to be softer and more cohesive than inorganic oxides. These properties make them less likely to be removed by abrasion alone, and the assistance of chemical agents is usually needed. This means using solvents or liquid cleaning preparations which dissolve and/or dislodge the contaminating coating on the track surface. Since the CMX is designed to allow adjustable rates of solvent application, it is also ideally suited to this technique. The question remaining is: What chemical, or combination of chemicals, will provide acceptable all around results in the efficient removal of foreign organic material from the rail surfaces? To help us answer this question, let’s consider the properties of organic contamination in more detail.

Residual material from plastic wheels on rolling stock is a chief source of organic contamination. (I believe this has been analyzed and documented by the NMRA.) The plastic itself is subjected to friction as the wheels roll along the track. Think of how many revolutions each wheel makes in a complete circuit of your layout. When multiplied by the contact of the many wheels on even a short train, the gradual degradation occurring at a molecular level begins to build up.

Please be aware also that the plastic wheels have “additives”. To give the wheels their authentic color, carbon black or other dark pigment is usually added to the polymeric resin before it is used to form the wheels in the injection molding process. Thus, over time, tiny amounts of these pigments will accumulate at the wheel surfaces and transfer onto the track. Although some forms of elemental carbon can be good electrical conductors, when mixed with other residues, carbon is probably only a contributor to the overall dirty condition.

Also, the injection molding process usually requires something called a “mold release agent”, without which the manufacturer would have difficulty removing the cast wheels from the mold. Unless this release agent is removed from the wheel surfaces in some later step of the process, it too can transfer to the track.

Organic chemical solvents are available in a bewildering assortment. Solvents vary in strength according to their chemical nature, characterized by a chemist’s term called “polarity”. Unfortunately, “stronger” is not always better, since it depends on what type of contamination we are attacking. A simple rule of thumb to remember when dissolving a solid is “like dissolves like”. This approach can be quite effective in a chemical laboratory, where we often know what material we are trying to dissolve. Two practical examples of solvent polarity effects come to mind: Sugar is freely soluble in water (water and sugar both being highly polarized chemicals) but totally insoluble in something like lighter fluid or mineral spirits. On the other hand, ordinary paraffin wax is fully soluble in relatively on-polar solvents like lighter fluid or mineral spirits, but virtually insoluble in water.

Since we, as model railroaders, have no means of identifying the individual track contaminants, we may as well proceed in a “worst case” orientation. In doing so, we can simply assume that there could be some of all three categories of contamination present on our rails. Because we are usually dealing with such a “hodgepodge” of contaminants, we need something that covers a wide range of solvent strengths. The best we can hope for is to partially dissolve and loosen most of the foreign matter and have it transfer onto the cleaning pad.

As one of my fellow model railroaders is quick to point out, if we soften the foreign matter on the rails without removing it, we are simply “making mud”, which will dry out and remain on the rails after the solvent evaporates. My recommendation for this broad utility cleaning agent is lacquer thinner. Lacquer thinner usually contains a mixture of petroleum distillates, methanol, toluene, acetone, methyl ethyl ketone, propylene glycol monomethyl ether acetate, ethyl acetate and xylene. Some of these chemicals are not even available to the general public in their pure form. (Further reading will also inform you that this mixture “cannot be made non-poisonous” and that it is highly flammable. These properties of lacquer thinner mean that it must be used with utmost caution.) Because of the array of solvent strengths represented here, lacquer thinner is well suited for track cleaning, and in conjunction with the CMX, it is probably more effective than any single component solvent.

Perhaps the issue of volatility should be addressed here. Many organic solvents, such as the lower molecular weight alcohols (methanol, ethanol, propanol) and ketones (acetone, methyl ethyl ketone) have boiling points well below that of water. The lower the boiling point, the more readily a solvent will evaporate. Very volatile solvents are sometimes referred to as “fast” solvents. With the exception of toluene and xylene, all the listed ingredients of lacquer thinner are fast solvents. This is why the adjustable flow control on the CMX unit comes in handy. The user can adjust the flow to compensate for evaporative loses, thereby keeping the pad wet during the entire cleaning operation.



So here (finally) is the bottom line:

To me, from the chemist’s perspective, the CMX, when used with lacquer thinner on the absorbent pad, is the best method of mechanized track cleaning presently available. It allows you to apply constant and consistent wiping pressure against the track surfaces, even in places (like tunnels) where you can’t easily reach by hand. It allows you to dispense a continuous stream of fresh solvent onto the pad, replacing the solvent lost to evaporation and keeping the pad at a suitable “wetness”. The large reservoir assures long operation between refills. Finally, using the Clean Machine is much more enjoyable than going along the track with a finger wrapped in a cloth. It’s also safer, because you would not want prolonged skin contact with lacquer thinner. And after all, isn’t “having fun safely” what this hobby is all about?

Having said all this, it is obvious to me (and hopefully to you) that it makes very little sense to clean the track so thoroughly unless you also clean your locomotive wheels and your rolling stock wheels. During my evaluation of them, I looked closely (under 3X magnification) at some of my n-scale plastic wheel sets. I was appalled at the visual difference between freshly cleaned and “uncleaned” wheels. For cleaning black plastic wheels, I recommend only methanol (methyl alcohol). Some of the solvents contained in lacquer thinner are strong enough to soften and distort some types of plastics. (If you don’t believe this, try pouring a little lacquer thinner into an ordinary Styrofoam coffee cup, but make sure you have a more suitable catch basin under it.) Just to test this, I soaked a discarded black plastic wheelset in lacquer thinner for about one half hour. When removed from the solvent, it was a gooey mass, with no resemblance to its original shape. Although better-quality rolling stock wheels are usually either Nylon or Delrin, some cheaper brands appear to use polystyrene. Nylon and Delrin are relatively impervious to most solvents; polystyrene is not. So, to be on the safe side, I believe it’s best to use methanol.

Comments and Suggestions:

I spent several days trying to make the CMX fail by doing things I thought others might attempt to do. (Well, only some of the things they might do… I didn’t try dropping the unit or throwing it against the wall. And I didn’t eat the spare set of O-rings.) I did not experience any “failure” that I could expressly attribute to the machine itself.

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