I think I understand the theory behind friction bearings from my days working on machinery: The axle rests in a cylindrical sleeve and the lubricant (oil) acts as a very small wedge between the bearing surfaces, thus preventing metallic contact and resulting heat.
My question is, why don’t railroads like friction bearing equipment? I hear about friction bearing issues every time a piece of historic equipment has to be moved. As long as the bearing on that equipment is properly lubricated, shouldn’t it travel just fine?
Maintenance. A roller bearing can go great distances with little or no maintenance. Friction bearing have to be checked for proper lubricant levels. If a friction bearing isn’t getting the proper lubrication, it’s metal on metal and a hotbox in short order.
That’s not to say that a roller bearing can’t fail - they do. But the probability is much lower than with friction bearings.
The elimination of friction bearings is likely one of the reasons the caboose is no more - there is far less need to monitor the train for that telltale odor.
I recall an incident some years ago where a small holding yard near here was flooded. The bulk of the cars had friction bearings at the time, which meant that each and every one had to be inspected, and very possibly repacked…
Friction bearings need much more mechanical care than roller bearings. these days there is nobody checking journal boxes anymore and withut Cabooses a hotbox may not get detected. In old days many more eyes observed trains from rear end crews to Block operators, tower operators etc, these days no such observations are made anymore.
It’s not just that railroads dislike the friction bearings, they’ve been outlawed for interchange for some time now. A good example of this was an off line excursion from Steamtown several years back. The train was delayed for a few hours at (I believe) Binghamton NY while a car knocker opened every bearing cover on every car. All the cars in use for the excursions are equipped with roller bearings, but to maintain the historic appearance of the cars, the traditional journal cover was left in place. The railroad (Canadian Pacific, I believe) had to be sure all cars were properly equipped with roller bearings. (Don’t tell anybody, but so are the tenders)
Another couple technical points about the differences: 1) roller bearings are sealed against dirt, friction bearings aren’t; 2) Roller bearings use all hardened steel components (axle ends, races, rollers) friction bearings have a softer metal sleeve for the bearing sometimes called a babbet material (tin, brass, lead in different ratios for different hardnesses). This soft sleeve was designed to be the wear point and were a lot easier to change than a whole wheelset.
How would you like to re-grease friction bearings on your car every 100 miles…? That’s how often friction bearings on steam locomotives had to be regreased. Not very efficient when you have a load going the distances they travel on the high iron today.
26 years ago we had a major derailment and fire involving a chemical train in Mississauga, Ontario. (I posted the story here on the 25th anniversary).
The cause was a friction bearing that overheated and burned off the end of the axle. The cause of that was thought to be the installation of the wrong size pad in the journal box, so that it did not properly wick up the oil into the bearing. Much of a large suburban city was evacuated for a week until they were sure that the chlorine and other chemicals wouldn’t spread out.
You are right on the money tree, failuers with roller bearings can happen in most cases that is only after the seals fail and all the grease has been spun out of the bearing.
The reason museums and railroads have problems is that when cars or engines sit for long periods of time that film of oil gets squeezed out leaving metal on metal. Since they are dissimilar they will almost invariably weld themselves together and gall upon any attemop to move them resulting in catostrophic failure, flattened wheels, derailments and a host of other serious problems. And it doesn;t take that long for it to happen.
interesting comment, and to flush it out some more, let’s recall from Physics 110 that there are two kinds of friction: Static and Kinetic. Getting something to move from a standstill involves pushing against a Static friction force, which is greater than the Kinetic friction force felt while the object is in motion.
I’m guessing, then, that starting a train from standstill with friction bearings took quite a bit of Ummpff, and that once moving, the Ummpff needed to counter friction was much less. Certainly, more Umpff was needed to start an all-friction-bearing train than an all-roller-bearing train (roller bearings having nearly no friction). If so, I wonder if there were tricks of the trade for getting trains started back in the era of friction bearings – like perhaps starting with a bit of a jolt so that momentum of the car in front got the one behind moving. I’m just hypothesizing here, and have no idea if what I’m talking about is valid or not. I have heard it said there was more art to train handling a half century ago than today, though.
Afterthought [edit]: Once a friction bearing train is moving, and the oil is doing its job, I wonder if the amount of friction is minimal?
I wonder if most of the friction is felt only during starting when you have metal to metal contact due to oil being mostly squeezed out of the contact surfaces?
One reason that railroads do not like to move “friction bearing” cars is that they are just not set up for them anymore. Cars with those bearings had their journal lids opened at every major yard, a visual inspection of the bearing was made, the oil was topped off, the "waste was checked and replaced if necessary, and finally the jornal lid was closed and if there were no other problems the car was deemed fit by the “car knockers”. The workers necessary to perform these tasks do not exist in modern railroading. Any significant distance movement with “friction bearing” equipment would require a lot of special care and provision of not normally available equipment and supplies. People would have to be identified, trained and scheduled to do this at every yard.
It was important in the days of friction bearings that all slack was out of a standing train so you had that extra little pull of the slack running out to start it moving. This can be very important if starting uphill even today. They will start with a small amount of air still applied to prevent the back of the train rolling backwards as the front was starting forward. Keeping the slack in till you started would have helped overcome the dry bearings resistance to this initial movement. Even when not dry these bearings had more resistance than roller bearings.[2c] As always ENJOY
rrandb beat me to the slack answer. Anyone who ever heard a train of empty hoppers being started in the friction bearing era can attest to the racket as the slack was taken out of the train…
Since the engines at Golden Spike are replicas of the original 1869 locomotives, the tenders have friction bearings. These are checked every day during operating seasons – and they require oil every day. Even though the typical day’s movement is only about 3 to 5 miles, the friction bearings still consume sufficient oil that it is noticable in the journal boxes.
The rolling resistance of friction vs. roller was also shown in the tonnage ratings. rollers I think have a resistance of about 4-6 lbs. per ton,and friction was somewhere near 8-10 lbs. per ton. I most likely will be corrected,but that’s why were’re here. To learn from each other.