I saw a BNSF loaded coal train eastbound through Eola today with virtually all of the cars being CEFX cars in the 67000 series. All of the cars were seemingly identical except the load limits painted on the sides of the cars were different by a few hundred pounds…i.e. 236,300, 236,400, 236,500 and 236,600. My question is what minor differences in each car would account for such a small difference in each cars load limit?
Differences in the tare (empty) weight of each car. Steel castings used in truck sideframes, bolster, and draft gear have some variability in wall thickness; steel plate, sheet and structural shapes also have allowed tolerance in thickness. Individually these differences are small (e.g., plus or minus 1/100th of an inch) but over something as large as a freight car they do not entirely cancel out between cars.
For instance, suppose the steel mill rolls 1/4" plate with a tolerance of +/- 0.001". One day the 1/4" steel plate emerging from the steel mill is 0.251 inches in thickness and another day it is 0.249 inches in thickness, a difference of 2/1000th of an inch. One car is built with 0.249" plate and the next one off the assembly line is built with 0.251" plate. Suppose the car consumes 2,000 square feet of 1/4" steel plate. That 1/1000" variation in the thickness of the steel from nominal to actual (plus or minus) results in a difference between the two cars of 164 pounds. (Steel weighs 495 lbs. per cubic foot.)
The car is weighed when manufactured in order to properly stencil it for its allowable net lading without exceeding the car’s gross weight limit or the wheel bearing weight limit.
Tolerances of materials and dimensions is a not-small consideration in engineering and manufacturing. It’s possible to get materials manufactured to tighter tolerances but the cost goes up dramatically the smaller the tolerances become.
RWM
Is each car weighed after it’s filled? Years ago, my dad was a trucker. When he loaded at the S.D. cement plant, they would fill what they thought was the right amount, then run the truck accross the scales. Too heavy, and they took some back out. Too light, and they added more. Does a railcar get that much scrutiny?
Yup, they do.
Here at the PTRA, we make a goodly amount weighing cars for the industries we serve…each shift has a track or two the drag across the scales.
Most of the time, we are weighing empty tanks, because most of the time, they are not really empty, but have a small amount of residue left in them.
Shell is a big scale customer…because most of their tank cars are filled with the same product over and over, they need to know how much is still in the car before they begin to fill it.
The product has a weight per volume formula, so once they know what the car weighs they can calculate how much product to put in to bring it up to the allowable weight.
Phillips Plastic has us weigh a certain group of covered hoppers on a regular basis for them after loading…not real sure of the type of plastic, (it is in pellet form) but it is particularly heavy/dense for its size, and the FRA will/has fined them if their cars are overweight.
Plus, a lot of these cars go to a SIT yard, so knowing exactly how much product by weight is in the car lets them fill orders better.
Some industries have their own in house scale.
Four I can think of off the top of my head are Auto Fina, Dow Chemicals, Hampshire Chemicals and VoPac Industries, simply because of the volume of cars they ship it is cheaper for them to weigh them in house.
We have a little CNW scale car running around on the PTRA, has been here several months, going from industry to industry checking their scales.
Some day we might send it home, maybe…
It depends upon the commodity. Many commodities such as lumber, canned goods, etc., that are unlikely to overload the car and are sold by unit, not by weight, are “agreement weight” and are not weighed. Commodities that are sold by weight or have significant ability to overload the car such as coal, aggregates, cement, and dry bulk minerals are usually weighed. Most shippers of these commodities are responsible for weighing the cars on loading and electronically transmitting the scale weights to the railroad. The receivers demand these weights too, and usually reweigh the car on arrival.
Many coal mines use weigh-in-motion scales in conjunction with the loading chute and gates. The operator types in the car number into his console and the computer uses a look-up table to display the maximum net weight allowable for that particular car. As the coal is loaded the scale tallys the total weight and the computer counts down the weight of coal remaining to be put into the car. The operator manipulates the chute and gates to cut off the coal flow when the car is just shy of being an overload. A good operator can consistently load the car within 100 lbs. of maximum weight with no overloads; an inexperienced operator or difficulties with the machinery will result in overloads that are trimmed with a wheel loader after the train emerges from the loadout. Some coal mines use batch loaders that preweigh the coal to be put into each specific car, then dump it into the car. The advantage of a batch loader is it will rarely
Anybody know the allowed tolerance for a certified electronic weigh-in-motion scale? I recall 5%, but that could be high. 5% on a 283,000 load limit car would be 14,000 lbs and change, and I suspect would produce a car that could turn rail defects from hidden to visable.
Ah, the wonders of modern technology. We fixed over loads with men and coal shovels. [^]
Most but not all rail traffic is handled under Weight Agreements. In many cases the Shippers Load & Count defines the weight of a loaded car and the the rate is applied against this weight. In other cases the Consignee determines the weight transported upon unloading the car. There are various rules and regulations that apply to both the Shippers & Consignees to be able to obtain and use a Weight Agreement on their shipments. The Shippers and Consignees will routinely have their methods for determining the billed weight tested. The third method for determining billed weigh if for the carrier to weigh the car and subtract the tare weight (as stenciled on the car) from the gross weight determined on the scale to extract the weight to be billed.
Carriers may use single car balance scale, electronic hump scales and weigh in motion scales to perform this function. Where Railroad weights are required on unit train type commodities they are normally obtained from a weigh in motion scale, where the entire train operates over the scale at speeds between 1 & 4 MPH and the weights are electronically sent to a control center where they are compared to the electronically obtained tare weights for the cars in the train consist and the net weight of each car is calculated. In normal circumstances this action will take 1 hour or less. Each railroad has it’s own rules concerning how much of an overload condition can be tolerated for continued movement of the cars. Overloads that exceed the tolerance must be set out of the train for adjustment. Overloads may be set out at the scale location, or they may be taken to the next terminal to be switched out.
? “All trains over 80,000# gross take next exit when yellow lights are flashing”? How are they caught?
(1) Defect or failure in railcar (1-spot requests weight, HBD takes issue with the car or impact detector catches it.)
(2) In motion scale catches it en-route.
In-motion scales are found all-over, the issue is keeping them in-tolerance as the strain gauges and wheatstone bridges etc. can get funky in a tough railroad service environment. For a while, the scales seemed to be close to the IES/RFID scanners until many failed.
Thanks guys, your answers and explanations are both logical and very helpful in my understanding.
SL&C (shipper load and count) is a phrase I havent heard in nearly 20 years.
In looking at railroad tariffs, many are rated on carload, some by weight. Is the shipper normally charged a minimum carload rate, subject to weight.
RWM, that was a great explanation as to the weight differences of a car, based on tolerances of the steel. At the UTC factory in East Chicago each car was weighted to the nearest 100 pounds prior to the decals (stencils) applied. The LD LMT/LT WT number was filled in based on that weight. It varied several hundred pounds and it made sense that it would…but I never really knew exactly WHY it occured.
ed