Anyone know how a train is weighed? Label on an engine cab the other day said 410,000 lbs. Do they travel over a scale at factory? Seems like there are lighter materials available. Space machines come to mind, capsules, etc. thanks. J
jschwendlerAnyone know how a train is weighed? Label on an engine cab the other day said 410,000 lbs. Do they travel over a scale at factory? Seems like there are lighter materials available. Space machines come to mind, capsules, etc. thanks. J
Building locomotives for hauling freight - lightweight is a disadvantage. The pulling power a locomotive generates is in part a function of its actual weight on the rail. CSX after running their GE AC fleet for several years at their 'as delivered' 392K weight, experimented with adding weight to the engines and testing the locomotive's pulling power at the new weight - the locomotives could pull several hundred tons more freight at the higher weight - thus CSX developed the 'Heavy' designation for their locomotives, before the project ended up in production GE stepped into the project and made software enhancements to help the operation. On one of the worst grades on CSX, a regular AC is rated for 2700 tons per unit, a Heavy is rated at 2900 tons per unit. Regular AC's have a tractive effort of 145K, Heavies 160K.
Railroads are bottom line operations - 200 tons means 2 more cars - 2 more cars mean 2 more cars REVENUE - it adds up, train after train after train.
Never too old to have a happy childhood!
jschwendlerAnyone know how a train is weighed?
Balt gave a nice discussion of loco weights. I will answer the more general question.
The tare (empty) weight of all freight cars are kept in an computer file. The weight in the file comes from the scale weight of each car at completion, and from later periodic reweighs. It is stencilled on the car, in pounds, as LT WT.
If a car is not loaded its gross weight is the tare weight. If a car is loaded, one of the elements of the waybill data is the weight of the load. The result is that the handling line always knows what the car's gross weight is.
After a train is built, a clerk will run a "train List" or "consist", which is an ordered list of all the cars in the train. The computer adds up all the gross weights and prints the total at the bottom of the list. That total is what the train (less power) weighs, a figure used for several operating purposes.
Mac McCulloch
Also, the base data tells the railroad when the customer has overloaded the car (LD LMT exceeded), which is detrimental to the car and the track structure.
Most railcar builders know what the design weights are, long before the car is built or modified. They still run them over a scale before turning them loose. Among other things, you want even weight distribution under load.
Lighter materials and metalurgy may not survive railroad conditions for long under the same number of cycles. (watched any pick-up truck commercials lately? Is the extra co$t worth it over the tried and true??)
In addition to the info already given, scales are used to weigh individual cars as needed. The scale house was a regular fixture in many yards. Today the weighing often goes on at the loading and/or unloading points.
Generally speaking, it's known how much a given commodity weighs, be it coal, oil, or rolls of paper. In the case of the paper, a car can hold X number of rolls and stay within its appropriate weight, so that's what will be loaded.
I don't know, so can't say authoritatively, but I suspect commodities like coal at in-motion loadouts involve a combination of known weight, known "flow", known speed of the train, and a scale there somewhere.
Occasionally, you'll hear of something being loaded into a car not designed for the cargo, like iron ore/pellets into standard hoppers. Adjustments are made regarding how much actually gets loaded.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
Railroads have been buying hoppers that are constructed with a lot of aluminum parts. It decreases the tare weight and allows more product weight in achieving maximum weight on rail. A ton or five per car adds up with a 130 car or more unit train. The ultimate aim of railroads is to move maximum revenue product with minimum car cost investment over the lifetime of the cars.
Then there is the Duffy St. Derailment that happened on May 12, 1989 when a Southern Pacific unit train loaded with Trona derailed after running away on Cajon Pass in San Bernadino, CA. The train was 69 open top hoppers loaded with 100 tons each. The cars were loaded by a sub-contractor to the mining company who failed to fill in the weight of the shipment on the waybill. For some reason the SP clerk who processed the shipment looked at the bulk in the cars and put down an estimate of the weight in each car and the total shipment weight as a 60 tons for each car and a total of 4140 tons, rather than contacting the shipper. The train was far too heavy for the locomotives assigned to bring the train down Cajon Pass. The train ran away on a 35 mph curve at an estimated 100 mph and destroyed seven houses and killed 2 young boys in one of the homes, and two of three crewmen on the head-end locomotives.
In response to the initial question, locomotives are usually weighed before being delivered; and there are considerable variances in the weights of the same model locomotive. The 410,000-pound weight shown on the locomotive in question was its "nominal" weight, not necessarily its actual weight. For example, CSXT's standard AC4400CWs all have nominal weights of 412,000 pounds; however their actual weights vary from around 408,000 pounds to around 419,000 pounds. The nominal weights of its high tractive effort AC4400CWs are 432,000 pounds; but their actual weights vary from around 423,000 pounds to around 437,000 pounds. In addition, the actual weight of a given locomotive, at any given time, depends on how much fuel and sand it's carrying. Because the performance improvement from added weight occurs primarily in the low speed range where tractive effort is a function of adhesion, all of CSXT's 432,000-pound units have been configured with advanced adhesion control software. The software on the first heavy units had been developed by GE for use on CSXT's AC6000CWs in order to maintain adhesion when high levels of horsepower were applied to the wheels. When CSXT requested an increase in AC4400CW weight, GE installed the same software in order to maximize the extent to which the weight would be translated into tractive effort.
Design coeffient of friction of steel wheel on steel rail is approximately .25 but can range from .75 (ideal lab conditions) to .05 (wet, slippery rail). The pulling power of a locomotive is limited by the loco's weight times the coefficient of friction. Typically a 400,000 lb locomotive can pull 100,000 on the coupler. Add a few of these and the stress on the first few couplers exceeds their design strength and the coupler knuckle (the weak part of the train -- you hope) will break. Couplers are usually rated at 240,000 lbs breaking strength so that is your limit on how much you can pull on the train. Of course the first coupler behind the locomotives is the one with the most stress and hopefully that doesn't have a casting flaw that makes it weaker than specs. Come to the Jackson Street Roundhouse in St.Paul, MN and I will show you a broken knuckle with a nice casting flaw that made it fail on the Westminister Hill of the BNSF Midway sub. I think it was 5 cars back from the locos. Of course you could make the locomotives heavier but then the weight on the rail would start to stress, break and split rails.
jschwendlerLabel on an engine cab the other day said 410,000 lbs. Do they travel over a scale at factory? Seems like there are lighter materials available.
Something I think has been left out of this discussion are weight limits imposed by things like HAL. Up to a comparatively high point, the weight of a locomotive can be used for additional adhesion, with the assumption being that the locomotive can develop enough horsepower to justify the weight used for adhesion.
This is why older locomotives for high-speed service were often designed with B-B trucks but high horsepower (the U36B being a good example) - the assumption being that some percentage of the available "horsepower" would be used to accelerate to and maintain relatively high speed, rather than start the heaviest possible train. On the other hand, in early diesel days six-motor units could 'guarantee' slow operation with heavier consists with minimum derating of developed TM power for a given prime-mover hp.
As an aside, it is NOT true that weight saving as in automotive practice gives you a better locomotive. One of the arguments advanced for the Krauss-Maffei "Amerika-Loks" in the early '60s was that the lower mass inherent in high-speed engines and hydraulic transmission would make for a better engine. What happened was that the locomotives had to be ballasted to the proper adhesive weight, proportional to expected hp at speed (probably in the hyperbolic part of the power curve).
Some steam locomotives had weight-saving measures applied to them - the T1 being a particular case in point - or were severely compromised in their design by excess weight (the Lima Alleghenies might be in this category, and a number of ATSF designs clearly were) but this isn't due to optimizing adhesion, it's due to the basic structure at acceptable factor of safety being too heavy for the civil limits on the track and bridges that have been set by that side of the railroad company.
Modern AC units can develop high TM torque even at zero rpm, and have more sophisticated approaches to wheelslip. This can permit them a far lower factor of adhesion (FA) than the 4 that a previous post mentioned (that being a rule of thumb that applied more appropriately to reciprocating steam power). So there can be advantages in ballasting locomotives to the point where they most effectively use their available hp at the most cost-effective speed for overall operation on a particular train and stretch of a particular railroad.
But there are increasingly nonlinear limits to what the contact patch between a locomotive wheel and the railhead can absorb, in the combination of tractive effort and weight. Beyond that point you get added wear and also added defects in the steel of the railhead, and obviously (to me) this puts relatively hard limits on how "heavy" you want the weight for a given area of contact patch to be. (Limiting this is one of the reasons modern locomotives use larger diameter wheels.)
Well, thanks, folks! I learned a lot. I appreciate all of you taking the time to answer and explain in understandable terms.
J
RMEThis is why older locomotives for high-speed service were often designed with B-B trucks but high horsepower (the U36B being a good example) - the assumption being that some percentage of the available "horsepower" would be used to accelerate to and maintain relatively high speed,...
The "fast forties" (GP40, and possibly the SD40) I've heard that horsepower is necessary for speed, not hauling. The 600 HP SW1 could pull a lot of cars, but not very fast.
I've also heard that the GP40 (and I'm sure others of its ilk) was "slippery," antislip technology notwithstanding. I would presume this was on the low end of the speed scale.
Even steamers built for speed had problems at the low end.
Apparently Al Krug's website has been 'taken down' sometime in the last few years. Fortunately, a copy's been saved in an archive (kudos to MikeF90 for looking for and posting this link, from "Al Krug's site taken down?"at: http://cs.trains.com/trn/f/111/t/245838.aspx ) - this link is to the Home page:
https://web.archive.org/web/20150205123806/http://www.alkrug.vcn.com/home.html
"Table of Contents Page" (my label):
https://web.archive.org/web/20150509041056/http://www.alkrug.vcn.com/rrfacts/rrfacts.htm
Tractive Effort vs Horsepower - this one is the best pertinent to this discussion:
https://web.archive.org/web/20150426114142/http://www.alkrug.vcn.com/rrfacts/hp_te.htm
How Much Force can a Coupler Withstand?
https://web.archive.org/web/20090408192716/http://www.alkrug.vcn.com/rrfacts/drawbar.htm
Amperage to Tractive Effort table for an SD40-2 and Dynamic Braking Force vs Locomotive Speed
https://web.archive.org/web/20111204213958/http://www.alkrug.vcn.com/rrfacts/amps_te.htm
- Paul North.
Another factor was the "Dynamic Braking" was not workinng on two of the locomotives, and the weight of train was 10,000 tons. SP was famous for using fewer units than needed.
CHIPSTRAINS Another factor was the "Dynamic Braking" was not workinng on two of the locomotives, and the weight of train was 10,000 tons. SP was famous for using fewer units than needed.
In the documentary on this wreck it was stated that the clerk 'guesstimated' the weight based on his prior experience with coal - which is much lighter per unit volume. Then the rear end engineer went to emergency air, and the train became a long, jointed bobsled.
Then, during the cleanup, a backhoe operator hooked a gasoline pipeline - and the pipeline's duty engineer responded to the falling pressure by speeding up the pumps! IIRC, several more lives were lost to the inevitable fireball.
An absolutely classic case of how to do everything wrong.
Chuck (Former USAF Disaster Control technician)
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