The solid bolsters were only used on locomotives which were ordered with extremely heavy axle loadings. They were solid because EMD needed the extra weight to achieve the BN's specification. BN was one of the few railroads that specified 70,000 lbs. axle loadings. That gave the BN SD40-2s a total weight of 420,000. A basic (standard) SD40-2 had a total weight of 386,000 lbs. or an axle loading of 64,333 lbs. and was equipped with a hollow bolster which was standard. Very few locomotives had solid bolsters. BN's justification for the heavy weight was tractive effort for coal service. An SD40-2 had an adhesion factor of 22% which translated into a tractive effort or drawbar pull of 92000 lbs. An SD40-2 weighing in at 386000 would have the same adhesion factor, but only about 85000 lbs of tractive effort. More tractive effort translates to more trailing tonnage.
Amtrak's SDP40F couldn't and didn't need to be be as heavy. Their trailing tonnage was never that great and Amtrak was more interested in speed and acceleration. In addition, Amtrak locomotives had to run all over the country on various track conditions. Many railroads didn't have track structure that could support 70,000 lbs per axle, so Amtrak locomotives had to be built toward the lighter weight. They were delivered at about 390,000 lbs; an axle loading of 65,000 lbs. That was a difficult task since the SDP40Fs, were specified with a lot of equipment that added additional weight. These included the steam generator, a significant water supply (water is heavier than fuel oil) electronics to operate on all of the different signal systems that they would or could encounter and they were four feet longer than a standard SD40-2. In addition, they had also been built with electrical equipment that was intended to allow for future conversion to head end power.
BN didn't start buying EMD heavy SD40-2s for coal service until about 1975. They bought about 200 per year in 1978, 79 and 80. Prior to the first coal SD40-2s, almost all of the coal power purchases were for GE U30Cs and C30-7s. BN SD40-2 purchased earlier than 1975 were lighter at about 396,000 and were equipped with standard hollow bolsters as were all previous Q, GN and NP six axle EMD power.
Bill Barber
Gravois Mills, MO
Wed Apr 3, 2013 9:37 am (PDT) . Posted by:
The SDP40F used a hollow truck bolster, which standard SD40's did not.
This was suspected, though never proved, to be the cause of the
derailments.
Thanks!
--
Brian Ehni