Steam Locos & Track Wear

It's not that the rail is necessarily damaged at the joints. The pounding a poorly-balanced engine can produce actually dents the rail corresponding to the wheel's circumference--welded or not.

Converting a horizontal motion(pistons & rods) to a circular  rotational motion(the axles) is inherently  an unbalanced arrangement and it will never be  absolutely smooth.  Diesels and the rail car wheels pound, too. The rails today are heavy but some were very heavy in steam days. The Bessemer rails were 132 lbs but the steam engines were heavy, too.  The engines and rail cars are a lot heavier today than before. It comes down to "axle loadings".

I love this passage from "The Steam Locomotive" (Johnson, 1944):

"As an example of the results obtained in the use of this type of wheel (disc type -  [smd]), the case is cited of a 2-10-2 type locomotive built in 1916, with 63-inch driving wheels, which was placed in service requiring higher speeds than the engine had originally been designed for. The railroad engineers found over 700 bent rails in a distance of 100 miles, occurring always at the foot of a decending grade. The kinks occurred at a distance apart equal to the circumference of the 63-inch drive wheel, namely 16 feet 6 inches. The wheels were statically balanced in accordance with the practice at the time the locomotives were built. According to the original calculations the main balance was about 295 pounds less than required to balance the revolving parts. When the difference in planes were considered, as in cross-balancing, this underbalance increased to 780 pounds. When the railroad engineers checked the old wheels, they found that, due to the loss of lead or some unknown cause, the underbalance in the main wheels had increased to 1155 pounds for the left wheel and 1095 pounds for the right wheel. By substituting cross-balanced, disc type centers on the main wheels the underbalance was reduced to 260 pounds and the rail trouble was eliminated."

The chapter goes on to talk abut how the dynamic augment can be greater than the weight of the wheel itself. "Under these conditions each wheel would be lifted clear of the rail when the pin was up and would return to the rail with a tremendous blow within the next half revolution."

By the end of steam, the major players in the steam market had things figured out. We know for a fact that none of the big engines running today have any effect on the rails they ply, and at the speeds 844 and 765 ran this year, if there was a problem it would have shown up a long time ago. There have been engines in the past that were poor designs, Norfolk and Western had a 4-8-2 class that was horribly balanced and caused rail trouble.

 When they moved 2156 speeds were limited to 25mph since they moved it without the main rods on her. Even at that speed you could feel the ground move up and down when she passed.

The dynamic augment problem was well solved by the 30s.

None of the big engines running today (765, 611, 1225, 4449, 844, etc.) have a dynamic augment problem.

steam fan posted:

 Norfolk and Western had a 4-8-2 class that was horribly balanced 

That would have been the K3. From what I understand a big issue was the extra long main rod connecting to the third drive wheel instead of the 2nd. It had a speed limit on the order of 35 mph. When WWII broke out, the N&W (gladly) sold them off to other roads that in were need of locomotives.

OGR Webmaster posted:

The dynamic augment problem was well solved by the 30s.

The PRR must have forgotten this when they built its Q1, a 4-6-4-4 Duplex in 1942.  The first group of six driving wheels was driven by a pair of cylinders mounted conventionally in front of them, while the rear four driving wheels were driven by cylinders mounted behind them on either side of the firebox.  Apparently that rear set of driving wheels pounded the rails pretty good, and was one of a couple of reasons they went to a conventional arrangement with the Q2. 

In the steam age, both the PRR and the B&LE used 152 lb. rail. Since it was a US Steel road, B&LE used it almost everywhere.....

There was an article in the SP TRAINLINE about the 3 cylinder 4-10-2's.  On Donner Pass at night one could see hot pices iron coming off the rail head.  True?  Anyway, SP got them out of the Mountains.