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chuckzeiler (154 posts)
Aug-23-01, 04:31 PM (EST) "The Friction of friction bearing trucks" Am looking for research information on the friction coefficients of friction bearing trucks (aka bogies) versus roller bearing trucks. This info to be used in a friction calculator program by Joseph Realmoto (available in the File Library). My guess is that the AAR or perhaps individual railroads must have conducted tests sometime in the 1930's or 1940's to determine the cost effectiveness of replacing friction bearings with roller bearings nationwide, and as history bears out, that's exactly what happened. I would also guess it would take considerable more horsepower to move a train of friction bearings. I've looked through my copies of Railway Age, but I don't have a whole lot of issues. The AAR web site wasn't much help, nor were the bearing manufacturers' sites. Alert Edit | Reply | Reply With Quote | Top
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Subject Author Message Date ID RE: The Friction of friction bearin... Nels_Anderson Aug-23-01 1 RE: The Friction of friction bearin... krswen Aug-23-01 2 RE: The Friction of friction bearin... jerseycentral Aug-23-01 3 RE: The Friction of friction bearin... jtr1962 Aug-25-01 4 RE: The Friction of friction bearin... HAC Aug-27-01 5 RE: The Friction of friction bearin... chuckzeiler Aug-27-01 6 RE: The Friction of friction bearin... jtr1962 Sep-07-01 7

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Nels_Anderson (487 posts)
Aug-23-01, 06:42 PM (EST) 1. "RE: The Friction of friction bearing trucks" This probably isn't going to be all that helpful...But I recently read something about this. Timken (the company that makes roller bearings) apparently had quite a hard sell at first. They even offered to demonstrate the effectiveness for individual railroads but at first had a hard time getting any takers. I would have to think, though, that Timken did the research that proved to themselves the relative effectiveness, so maybe using their name as a search term would be helpful.
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krswen (3 posts)
Aug-23-01, 07:36 PM (EST) 2. "RE: The Friction of friction bearing trucks" I'm still trying to find the source, but I remember reading that a properly lubricated journal bearing actually has LESS friction than a roller bearing. Problem with journal bearings is that they can't handle the (normal) heat that builds up in cars over 70 tons. So they were replaced for maintenance reasons more than energy reasons. I'll keep looking for the source .. it surprised me when I read it. Remove | Alert Edit | Reply | Reply With Quote | Top
jerseycentral (385 posts)
Aug-23-01, 10:40 PM (EST) 3. "RE: The Friction of friction bearing trucks" well, a little OT but still a bit on topic..railroads HATE adapting unproven technology..for example...6000HP A.C. units...dieselization AFTER WWII when EMC/EMD and others were already making units in the 30's, and even Westinghouse Air Brakes...to keep this on topic...i cant even tell the difference between the different trucks in MSTS, on my models yes but not in MSTS... Remove | Alert Edit | Reply | Reply With Quote | Top
jtr1962 (5 posts)
Aug-25-01, 00:42 AM (EST) 4. "RE: The Friction of friction bearing trucks" I'm not necessarily surprised that the friction of properly lubricated journal-bearing trucks might be less than that of roller-bearing trucks, at least after they are rolling. A very smooth, lubricated metal shaft will be riding on a microscopic film of oil or grease as opposed to a roller-bearing which will have a definite contact point. The key words here are "properly lubricated", which in practice might be impossible to do with a 100-car freight train with 400 axles and 800 bearings spread out over a mile of train. The equations that I used for my friction calculator program are, by definition, averages derived from empirical measurements of large numbers of cars. I highly doubt that a set of such average measurements for large numbers of cars with journal-bearing trucks will be less than an equivalent set of such numbers for cars with roller-bearing trucks. The starting friction of journal-bearing trucks is definitely higher than roller-bearing trucks due to metal-to-metal contact when the bearing is not in motion, hence the old locomotive engineer's adage of "If I can start it, I can pull it". With roller bearings, there is little difference in static or rolling friction. I have heard that journal-bearing trucks will sometimes roll down an 0.3% grade while roller-bearing trucks will occasionally roll down an 0.1% grade, so we have static friction coefficients of 0.003 and 0.001, respectively. I haven't been able to find rolling coefficients for journal-bearing trucks as of yet, either. For comparison purposes, a car tire has a rolling coefficient of about 0.01 while a high pressure bicycle tire can vary from 0.0035 on asphalt to about 0.002 on concrete. Tests I conducted on HO scale models with needlepoint axles(a form of journal bearing), gave rolling coefficients from 0.01 down to as low as 0.004.As for speculation on the reasons why railroads were slow to adapt to roller bearings, I would tend to think it was partly force of habit, and partly very low fuel prices. Until the 1970's, nobody cared about energy consumption(or pollution, for that matter) since coal and diesel fuel were ridiculously inexpensive. Roller bearings started to be used on new freight cars from the early 1960's initially because they were more reliable, and they allowed higher speeds. Hotboxes caused by failed journal bearings were the source of a number of derailments, and this is what eventually lead to the phasing out of journal bearings more than any savings in fuel consumption. In the course of my research I came across an article at:http://www.tsb.gc.ca/ENG/reports/rail/esr9401.htmlwhich describes the causes of derailments in some detail.Another reason mentioned for the phaseout of journal bearings is the 70-ton weight limit. If the weight on the axle is too great, the bearing will fail to maintain a film of oil when rotating, and will fail due to sliding metal-to-metal contact. High speeds will also cause bearing failure due to overheating and oxidation of the lubricant. Hence, journal bearings were not used in passenger service after about the 1930's due to both the appearance of heavy metal passenger cars and the 80+ mph speeds reached by the more powerful locomotives developed at the time.In any case, if anyone has access to detailed studies on journal-bearing trucks vs. roller-bearing trucks, please post a message here. I strived to make the friction calculator program as representative of real world performance as possible, and would also like to be able to represent older equipment accurately in the next version(actually, there won't be any need for a new version unless I can obtain this information). Joe Realmuto
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HAC (231 posts)
Aug-27-01, 05:05 PM (EST) 5. "RE: The Friction of friction bearing trucks" I'll dig through a copy of "Car Builders Cyclopedia".. should be something in there...cheers
Harold Remove | Alert Edit | Reply | Reply With Quote | Top
chuckzeiler (154 posts)
Aug-27-01, 08:26 PM (EST) 6. "RE: The Friction of friction bearing trucks" I hope you have dates that I don't have, because I couldn't find anything in the 1940, 1943, 1957, 1966 editions. After that, I don't expect anything. There is a lot there on seals, so I would guess that the railroads must have recognized that the loss of lub oil was their basic problem, but their simple solution was to replace the friction bearings with roller bearings. I intend to inquire to Timken about research conducted in the 1930's (about the time of the Four Aces 4-8-4 that the NP ultimately bought), but you can imagine the reaction I'll get when I tell them I need the info for a game. Remove | Alert Edit | Reply | Reply With Quote | Top
jtr1962 (5 posts)
Sep-07-01, 02:20 AM (EST) 7. "RE: The Friction of friction bearing trucks" I found some general information about train resistance here:http://www.uwm.edu/~horowitz/PropulsionResistance.html There are also some scattered bits and pieces on this subject in several forums at http://www.Railroad.net but I haven't yet found anything specific regarding tests Timken may have run in the 1930's or 1940's. I did learn that train resistance was first measured empirically in 1926 by a GE engineer named Davis on the PRR, and the differences between the equation derived by him and two others in common usage today are summarized below(all equations are for standard freight cars).
Original 1926 Davis Equation:R = 1.3T + 29N + 0.045TV + 0.045V²Modified Davis Equation:R = 0.6T + 20N + 0.01TV + 0.07V²AAR Recommended Equation:R = 1.5T + 18.125N + 0.015TV + 0.055V²In all equations R=resistance(pounds), T=weight(U.S. tons), N=number of axles, V=speed(mph)I used the AAR Recommended equations for my MSTS Friction Calculator. Since these are in common use today they are correct for cars with roller-bearing trucks, and as the original Davis equation was derived in 1926 it is presumably correct for journal-bearing trucks. Neglecting the term proportional to V², which is air drag, we can infer that friction per axle is around 10 pounds more with journal-bearing trucks, and that this increases with speed at a faster rate than for roller-bearing trucks(the term proportional to V).I thought it was interesting that the term proportional to V²(air drag) is actually less for the 1926 equation than for the other two. I assume this is because most freight cars were 40 feet or less in 1926 compared to 50 feet and up for modern freight cars-this obviously would give the modern cars more aerodynamic drag.Unless anybody here can find any more information, I'll probably have to base the next version of the MSTS Friction Calculator on the information outlined above when I add calculations for journal bearing equipment. I also plan to include calculations for intermodal cars. I treated intermodal cars the same as trailer on flat cars (TOFC) but it turns out that they have a somewhat lower air drag. This change only affects two cars in MSTS(US2DbleHgtFrghtBl and US2DbleHgtFrghtRd). Remove | Alert Edit | Reply | Reply With Quote | Top

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