Well mate you have a lot more energy than me or else wyou only have a small layout and not many locos or more free time on yopur hands than me and i'm retired.
rgds ian
Lionel collector, stuck in an N scaler's modelling space.
Chuck mate you are quite right, i have an unusual set of circumstances contaminating my rail.
!) I live near the ocean and i get salt laden air.
2) The track runs through tropical palms and ferns which have an exudation into the air.
3) and now i have this problem with ants. It only involves certain types of ants which leave a trail od acid on the rail the passage of electricity through it converts it to a sticky black substance and only certain locos are affected.
I clean my track weekly but i could weel do it twice per week.
Rgds ian
Getting back to the original statement, "Slightly dirty rails will improve traction," it really depends on what the rails are dirty WITH.
Oil, wet clay mud and dripped grill juice are unlikely to help anything - with the possible exception of vocabulary development.
Anything that interferes with getting power to the locomotive is bad - and whether or not it improves traction isn't the reason.
Scale plays a part. Something that would stop a G-gage train in its tracks probably wouldn't even be noticed by the engineer of a 1:8 scale live steamer.
Unless your loco has operating sanders, bright and shiny is probably the best available choice for rail condition.
OTOH, back about the time I was teething on a Lionel box car, one railroader (O scale, outside third rail) was reputed to deliberately apply 'scale sand,' (scouring powder) to one rail only, to convince his locos to make his worst grade. I'd be willing to bet that his track looked just like some of the sand-fouled rail seen under N&W Y6's in some half century old photos I have.
If somebody actually does some detailed research on the subject, I'd be happy to read the resulting paper, right after I wipe the metal polish off my rails.
Chuck
I agree I have proven in my own instance; that clean track has better traction than a dirty one. I have a short section of track that has a 4 % grade and somewhere between an R3 and an R2 curve and my Sachsen will spin its wheels with 4 box cars in tow, when rail is slightly dirty. When clean it will just pull 5 up the hill. Incidentally my Stainz with a powered tender will beat it and my Mallet pulls 7 carriages up the same incline.
Rgds Ian
Vic, that might work in G, if you can find enough space, but it didn't always work on the real thing. The B&O foisted off on to the Alton a 4-6-4 and a 4-4-4 named Lord and Lady Baltimore, respectively. The Lady was no lady; the weight on just 4 driving wheels spread the rails - not a good thing, at least for track. The Lady was retired in short order, and the Lord got replaced quickly by a slant nosed diesel so as to not have to stop for water and coal. Speed was of the essence in those days.
Art
Have fun with your trains
Is that TJ Kerry????
I just like clean rails! It's even better when you can get somebody else to do it for you!
My limited experiance and simple high school education would indicate that clean rails and wheels would work better!
Art, I voted to support friction before I voted against it. I supported the idea of molecular adhesion, then I flip flopped and unsupported it. I did not support school athletics, but now I am a jock supporter.
Donna, next time I'm on the Sunshine coast you got a date.........
The Dixie D Short Line "Lux Lucet In Tenebris Nihil Igitur Mors Est Ad Nos 2001"
There is a thread on this site that shows a foreign 2-10-0 with 7 - count'em, 7 - sand pipes coming down from the sand dome on just ONE side!! Probably a few of them are for reverse moves.
1/16 German RR w/troops & equip.
That must really run the sand bill up!
JACK,YOU SOUND REALLY INTERESTING .CAN WE MEET SOMETIME. LOVE DONNA(PS. I AM IAN"S SISTER IN LAW)
DONNA.
Very impressive, T-J, but I cannot determine if you're for or against friction. Friction is what we need; on a smooth clean rail, a little friction is helpful - going uphill anyway, and when sand doesn't get the job done, cogs come into play.
So the sand provides friction and once it's crushed to smithereens, we have to apply more and so we have more than one pipe per side delivering what's needed, clean rail or not.
And it helps even if we have grasshoppers or leaves all over the railhead. Now behind the engine, it's a different story, the less friction, the better. Opinions, though, must yield to tests, and I know I don't have the wherewith all for that.
Nuff said. Bye.
'There must be no barriers for freedom of inquiry. There is no place for dogma in science. The scientist is free, and must be free to ask any question, to doubt any assertion, to seek for any evidence, to correct any errors.'
J. Robert Oppenheimer(1904- 1966)
I did some more research on the subject of traction and I find no error in this argument. If anybody can dispute the following research with supportable facts and references I will be more than happy to change my position on the matter.
27 November 2006, Effects of friction on steel to steel contact as it applies to locomotive traction and the effects of the roughness of the surface.
Frictional resistance to the relative motion of two solid objects is usually proportional to the force which presses the surfaces together as well as the roughness of the surfaces. Since it is the force perpendicular or "normal" to the surfaces which affects the frictional resistance, this force is typically called the "normal force" and designated by N.
The frictional force is also presumed to be proportional to the coefficient of friction. However, the amount of force required to move an object starting from rest is usually greater than the force required to keep it moving at constant velocity once it is started. Therefore two coefficients of friction are sometimes quoted for a given pair of surfaces - a coefficient of static friction and a coefficient of kinetic friction. The force expression can be called the standard model of surface friction and is dependent upon several assumptions about friction.
While this general description of friction (which is refered to as the standard model) has practical utility, it is by no means a precise description of friction. Friction is in fact a very complex phenomenon which cannot be represented by a simple model. Almost every simple statement you make about friction can be countered with specific examples to the contrary.
Like all simple statements about friction, this picture of friction is too simplistic. Saying that rougher surfaces experience more friction sounds safe enough - two pieces of coarse sandpaper will obviously be harder to move relative to each other than two pieces of fine sandpaper. But if two pieces of flat metal are made progressively smoother, you will reach a point where the resistance to relative movement increases. If you make them very flat and smooth, and remove all surface contaminants in a vacuum, the smooth flat surfaces will actually adhere to each other, making what is called a "cold weld".
Once you reach a certain degree of mechanical smoothness, the frictional resistance is found to depend on the nature of the molecular forces in the area of contact, so that substances of comparable "smoothness" can have significantly different coefficients of friction.
An easily observed counterexample to the idea that rougher surfaces exhibit more friction is that of ground glass versus smooth glass. Smooth glass plates in contact exhibit much more frictional resistance to relative motion than the rougher ground glass.
One method to increase the coefficient of friction is to make the surfaces rough or less smooth. A shoe sole that contains a pattern of grooves or ripples will provide much more friction when walking on slippery ice than would a worn-out, smooth sole.
Polishing the surfaces that come into contact will reduce the coefficient of friction between the surfaces and thus reduce the amount of friction encountered. But note that if you polish the surfaces to be extremely smooth and flat, molecular effects may take place.
Molecular effects
When you slide two extremely flat and highly polished metal surfaces together, molecular attraction adds to the coefficient of friction. In other words, the coefficient decreases as you reduce roughness up to a certain point where it then increases due to the molecular effects.
Area now a factor
Once molecular effects come into play, the area of the surfaces in contact are a factor in the friction. Thus, the greater the area, the greater the friction caused by molecular effects.
Sticky materials
Some materials have a high coefficient of friction, not because their surface is rough, but because the material is "sticky" and molecular attraction adds to the common coefficient of friction. Rubber is a good example of molecular attraction adding to the standard coefficient of friction caused by surface roughness.
Dry surfaces
1. For low surface pressures the friction is directly proportional to the pressure between the surfaces. As the pressure rises the friction factor rises slightly. At very high pressure the friction factor then quickly increases to seizing
2. For low surface pressures the coefficient of friction is independent of surface area.
3. At low velocities the friction is independent of the relative surface velocity. At higher velocities the coefficient of friction decreases.
Lubricated (wet) surfaces
1. The friction resistance is almost independent of the specific pressure between the surfaces.
2. At low pressures the friction varies directly as the relative surface speed
3. At high pressures the friction is high at low velocities falling as the velocity increases to a minimum at about 0,6m/s. The friction then rises in proportion the velocity 2.
4. The friction is not so dependent of the surface materials
5. The friction is related to the temperature which affects the viscosity of the lubricant
Some variables
1. smoothness (grove pattern from previous wear)2. water content in steel wear groves3. water viscosity - function of temperature of steel which will be a function of the energy in the friction which has already occurred (time dependent).4. steel to steel pressure
Conclusion:
Friction and thus traction increases with a scoured and rough rail head, to a certain point. Likewise, a smooth rail head has equivalent traction, assuming it’s free of contamination, that is to say clean. Adding sand to a smooth rail will not change the coefficient of friction; merely place it back into a useable form by changing the point at which it takes effect by roughening up the surface to compensate for something like rain or ice. For our modeling purposes we can either polish the rail heads and properly weight the engines to create the required friction coefficient, or scour the rails to roughen the surface. Dirt is a non standard variable that will affect the traction unpredictably and therefore should be removed from the equation.
Reference:
Jones & Childers, 2nd EdSec 4.8
Krim, J., "Friction at the Atomic Scale", Scientific American, October 1996.
Standard Handbook for Mechanical Engineers, seventh edition, Baumeister & Marks
Hey Snoc you sound like Tedd Bullpitt, you forgot to add on to the end"and I'm king of the castle".
I will tell you now, i would be very surprised if anything my mate Jack said was too far off the mark.
It is possible for a metal surface to appear quite clean and shiny but in fact be be pitted with microscopic highs and lows which make it quite resistive to anything sliding along it. I think it is to do with coefficient of depth of molecular penetration and surface tension; which is of course as we all know is very much affected by temperature and humiidty.
Snoq. Pass RR, sure have no arguments with your response. I worked for a railroad for 4 plus years but not out on the line, just towers and stations. But the rails around where sand was used sure weren't shiny in my memory. I cleaned my HO track with kerosene; of course I had no grades so that worked, and it sure stopped oxidation. Wahls clipper oil was touted in the MR at the time but my budget was the beer kind, not champaigne.
Wouldn't be a bit surprised that if the rails were 'abraided' slightly using 600 trimite paper crosswise, not longitudinally, would improve traction. When tracks are cleaned by sliding something gritty along the rail, it should actually reduce the surface area in contact with the wheel as there are now grooves. admittedly near microscopic, in the rail.
Very true, Art. The sand does have a positive effect on traction, this is a known fact. But it is like giving a hot rod a shot of nitro, it's something you don't want to do all the time, but when you need a little extra ooph it's there for you. Obviously a textured surface will give better traction, but how long will texturing last before a 400 car steel wheeled train reduces it yet again to a smooth rail head? If it were practical the railroads would be doing it already.
Now the question is, how do we get sand down on our miniature rails without getting it stuck in the motor gears???
Tangerine-Jack, your points are well taken. You mention in a prior post that the sand is pressure sprayed onto the rail. Having watched a few, it appeared to me that the sand drops onto the rail by gravity.
The effect of the sand does not appear to be long lasting as many engines had two or more sand valves on each side applying sand to more than one driver. Some Santa Fe Mikados had two sand domes with each sand dome having two pipes on each side thereby supplying sand at 4 places on both rails.
I have never checked rails after only the one driver had passed over the sand. Looking at the rails after the entire train has passed is not a satisfactory method of checking the efficacy or the results of sanding.
So I still think grit does it, not shiny clean.
artschlosser wrote: IMHO, there is something else at work when it comes to sand on the rails. Back when I lived where there was snow and ice, kitty litter was purchased even though I had no cats; it was kept in the car. When stuck on ice, which is slippery - the essence of clean, a little kitty litter spread in front of and back of the wheels provided the necessary traction to get the car moving. Rather analogous to paint and shiny, polished, really clean surfaces; the surface must have 'tooth' for the paint to grab hold of. I have always thought that the sand textured the rail and produced a non-slip surface. Masons always use sharp sand, not the beach stuff which has been polished by the ocean waves. Just my two cents. Art
IMHO, there is something else at work when it comes to sand on the rails. Back when I lived where there was snow and ice, kitty litter was purchased even though I had no cats; it was kept in the car. When stuck on ice, which is slippery - the essence of clean, a little kitty litter spread in front of and back of the wheels provided the necessary traction to get the car moving. Rather analogous to paint and shiny, polished, really clean surfaces; the surface must have 'tooth' for the paint to grab hold of.
I have always thought that the sand textured the rail and produced a non-slip surface. Masons always use sharp sand, not the beach stuff which has been polished by the ocean waves.
Just my two cents. Art
True, but ice is slippery not because of the clean ice, but because the pressure of an object (your boot for example) compresses the ice and forms a microscopic film of water between your boot and the ice. The water acts as a lubricant, that is what makes ice slippery. Using kitty litter or sand interferes with the ability of the ice to form the water film, creating a good grip.
As an aside, my surf buddies refer to this as "gription"- used in a sentence: "Dude, I wiped because I lost my gription on the board"
Paint sticks to a surface through chemical adhesion, which is similar to friction but more like a molecular velcro.
Great thread Ian!
Now I am thinking what is the weight of the loco need to be, or is there one?!
And what about modern ones?! Both can/could pull abit of weight if balanced?!
William
Interesting counterpoint Snoq Pass. Do you have experimental data to support, or is it just observation? I am interested in another view point if there is some empirical data to compare.
Of course with track power clean rails are required for conductivity, battery power and live steam who cares, but the topic is on traction. Sand is used by locos to scrub the rails free of ice, oil and other contaminates. It is reasoned that if you can increase the coefficient of friction by 10% or more by artificial means (sand), in effect cleaning the rails by sandblasting. I wonder what track looks like after it was hit by sand and a 100 ton loco runs over it, I expect clean and shiny? How much sand remains on the rail head after being sprayed there under pressure? Surely not enough to help anything but the first set of drive wheels on the loco. What about the other drivers, seems they would not be running on sand, but on the now cleaned rails left behind by the first set of road wheels. The optimum traction happens with molecule to molecule contact from steel rail to steel wheel. The same physics apply to the garden railroad, albeit on a far smaller scale.
For most of our miniature railroads this just is never an issue. It only comes into play when we haul long trains and have steep grades. In these instances adding weight to the loco and cleaning the rails shiny (regardless of power source) WILL increase traction. My money is on the millions of dollars and pounds the railroads have spent on research and specialized equipment to find the answer to traction problems, as well as my own degree in physics which verifies the data presented earlier.
Again, I am interested in other view points, with supporting documentation. There may be another answer, but in my mind the solution is clear that clean rails improve traction.
Caveat: It's your railroad, so whatever works for you do it.
If you are running track power, then you MUST clean the track. If you put RCS into the locomotives and then who gives a crap about the track. If you have batteries then you could run the locomotives on the floor (Not always the best idea though). On REAL railroads, yes slightly dirty rails will improve your traction. Heck even the locomtives are making the track dirty by them putting sand on the rail for improved traction.
Don't thank me, it was your question Ian that made me realize I was ignorant of something that seemed to be important, so I merely corrected my own ignorance by applying information and fact to the problem.
It would seem that for our G scale concerns clean rail and heavier locos are the cure for traction problems. Adding weight to a loco is an art and a voodoo at the same time, we want a heavy loco for traction, but not so heavy it won't pull the load that it's intended to. Seems that we must do as the full sized railroads and use the trial and error method to obtain useful results.
You can see the level of interlect on this forum; that was absolutely brilliant Jack and also a very good comment Robert and i have learnt a lot. I am sorry the other comment was so childish and illinformed that i didn't learn anything from it all.I have tried not to use the word ignorant.
That dissertation Jack was so well informed and i can see in came from a proper research base and of course many of the points they raise are applicable to our hobby; and i have been so impressd i have printed them out and saved them for distribution to associates.
Well done gentlemen
Is it REAL? or Just 1:29 scale?
Long live Outdoor Model Railroading.
I did some research and what I found was that clean rails maximize traction. In fact real railroads spend a huge sum of money researching this very problem. Interestingly wheel slip is used to clean the rails and optimize traction during heavy pulls, along with a shot of sand to help clean the rail of grease and oil. See for yourself:
“……… electrical control systems graduated from slip control to adhesion control. This is because newer control systems were designed that actually allow the wheels to slip slightly, on purpose. It is called creep control. On a heavy pull the wheels will typically by turning a couple of miles an hour faster than the locomotive is moving, and thereby gain the greatest pulling power from the locomotive. You can sometimes hear the effect on a heavy pull when the wheels begin to sing. This means the control system is working hard. The theory is that the slipping wheels will burn off any contamination between the wheels and the rail and thus give a better grip on the rails. With this type of system installed on DC locomotives the adhesion ratings jumped to 25 or 28 percent dispatch adhesion……….”
In front of each wheel is a nozzle that uses compressed air to spray sand, which is stored in two tanks on the locomotive. The sand dramatically increases the traction of the drive wheels. The train has an electronic traction-control system that automatically starts the sand sprayers when the wheels slip or when the engineer makes an emergency stop. The system can also reduce the power of any traction motor whose wheels are slipping.
“The process of adhesion is complex, possibly consisting of a combination of the effects of small scale roughness of the two surfaces and the attraction between the molecules near the surface of the two faces in contact. Whatever the underlying cause, the effects can be represented quite simply. Usually, we only need to predict when sliding occurs, or if the vehicle relies on sliding for its operation, how large the propulsive force must be.
Usually the force needed to start sliding is greater than that needed to continue sliding. The former is concerned with static friction, referred coloquially to as 'stiction', or more pretentiously as 'limiting friction', whilst the latter is called 'sliding friction'. At what speed the situation ceases to be 'static' and becomes 'sliding' is never defined, as the process of transition between the two is not particularly well understood.
Experience shows that the heavier an object is, the harder it is to drag. Newton's Second Law dictates that we should expect the acceleration of the heavy object to be less, because it has the greater inertia, but in the absence of friction, some motion is to be expected. So our simple model of static friction defines a resisting force parallel to the surface, which is proportional to the force perpendicular to the surface, the object will not move until the applied motive force exceeds this resisting force. The constant of proportionality is called the coefficient of friction. Values for typical engineering materials are given in the Engineer's Handbook [2].
When a wheel rolls, the point of contact is stationary with respect to the rail, so under normal conditions, an adhesion railway is governed by static friction. For steel on steel the coefficient of friction can be as high as 0.78, under the best of conditions, whilst under extreme conditions it can fall to as low as 0.05. A 100 tonne locomotive could have a tractive effort of 78tonnes , under the ideal conditions (assuming the power can be matched to the load), falling to a mere 5 tonnes under the worst conditions.
A well turned (railway) wheel, in good bearings should achieve a lift to drag ratio as high as 50:1, so the locomotive would require 2 tonnes of tractive effort just to move itself, leaving just enough to pull two 60 tonne coaches, provided the train doesn't encounter a gradient. More typically, we should expect the coefficient of friction to be in the region of 0.25, implying that the 100 tonne locomotive could pull 21 coaches on the level. Alternatively, the same locomotive could pull ten coaches up a 12% gradient.
Safety, however, would dictate that railway brakes should still be effective in the worst adhesion conditions, so gradients would normally be restricted to roughly 5% or less, unless measures are taken to ensure adequate adhesion under all circumstances.
The behaviour of adhesion railways is determined by the forces arising between two surfaces in contact. This may appear trivially simple from a superficial glance, but it becomes extremely complex when studied to the depth necessary to predict useful results.
The first error to address is the assumption that wheels are round. A glance at a parked car will immediately show that this is not true; the region in contact with the road is noticeably flattened, so that the wheel and road conform to each other over a region of contact. If this were not the case, the contact stress of a load being transferred through a point contact would be infinite. Rails, and railway wheels, are much stiffer than pneumatic tyres and tarmac, but the same distortion takes place at the region of contact. Typically, the area of contact is elliptical, of the order of 15 mm across.
The distortion is small and localised, but the forces which arise from it are large. In addition to the distortion due to the weight, both wheel and rail distort when braking and accelerating forces are applied, and when the vehicle is subjected to side forces. These tangential forces cause distortion in the region where they first come into contact, followed by a region of slippage. The net result is that during traction the wheel does not advance as far as would be expected from rolling contact, during braking it advances further. This mix of elastic distortion and local slipping is known as "creep" (not to be confused with the creep of materials under constant load). In analysing the dynamics of wheel sets, and complete rail vehicles, the contact forces are treated as linearly dependent on the creep.
The forces which result in directional stability, propulsion and braking may all be traced to creep. It is present in a single wheel set, and will accommodate the slight kinematic incompatibility introduced by coupling wheel sets together, without causing gross slippage, as was once feared…..”
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