I'm curious as to what steels are currently being used for constructing rods and motion. Also, does anyone know of any research conducted using other metals or lighter steel alloys in the construction of rods and motion.

Thanks,
Stephen Piwowarski
Berkshire Scenic Railway Museum, Inc.

A long time ago Kelly Anderson, or maybe Linn, posted photos of a new main rod they made for (?) WM 734. I can't find it.

n/m

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AISI 4340 is the same as "Timken High Dynamic Steel" used for roller bearing rods. As David Wardale seems content to use this for the 200 kmph AP5, I don't think there is a practical need for anything more exotic.

Something like 3135 matches an AAR/ARA specification I've seen in one of the Locomotive Cyclopedias for alloy steel rods. My library is in storage, so I can't give you the M specification number. In any case the 3000 series steels are obsolete. I think heat treated 4140 would be a good candidate for an intermediate strength rod between unheat treated 1045 and heat treated 4340. There were also some rods made with vanadium steel, but I don't know the chemical composition.

Alton & Southern (owned by Alcoa) had at least one locomotive with aluminum rods. I wasn't aware that Pennsy had tried aluminum. Aluminum is only 1/3 as stiff as steel which would make a given section more prone to column buckling. More important is that, unlike steel, it has no endurance limit and therefore has a limited fatigue life. Keep in mind that a billion revolutions is not an unreasonable life for a steam locomotive.

If you want to look at exotic materials for rods, I would suggest that titanium alloys seem to be a reasonable candidates as they do have an endurance limit. Carbon fiber would be difficult to engineer both from the standpoint of putting the right strength properties were they are needed and from the stanpoint of fatigue. You might also look at miraging steels which are hugely stong but don't have correspondingly high fatigue stengths and don't have an endurance limit. Trying any of these would require cubic bucks.

Andrew Adams

Thanks for the AAR standards and other information. I also find it interesting that the PRR did tests with aluminum rods and that the Alton and Southern ran an engine with aluminum rods.
My thought was that titanium or a titanium alloy might be an interesting candidate for experimentation due to its high strength to weight ratio, its corrosion resistance, and
hardness, though I am not sure if titanium has a suitable specific stiffness to be used in this way. It occurred to me that titanium was really not being produced on a wide scale until after the demise of steam in the U.S. and was very expensive to produce. Since then however, the cost of production has decreased significantly due to improved refining practices. If it could be used, I would imagine that the resulting locomotive would be much easier on the track and require less running gear maintenance.

Stephen Piwowarski
Berkshire Scenic Railway Museum, Inc.

Kelly,

Per your post and photo previously, I had a few questions.

1. In machining main rods of this size, what raw material state did you start? Hot rolled, cold drawn, forged? In doing the heavy material removal, especially the I beam pockets, have you run into warpage problems over the length of the rod? I believe cold drawn can get you into worse trouble due to drawing stresses in place from the steel supplier.

2. If you used 1045 or 4340, do you have any heat treatment done of just use them in the raw state?

Thanks.

Randy

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Technical trivial inquiry: IF we built a 3 cylinder simple with all components having the same weight for each set of running gear, and set the cranks at 120 degrees apart, would it essentially counterbalance itself without the need for additional counterweight?

dave

consider the 4-12-2, you will need inner rod connections to help counter the counter weight issues. I don't know if they did, a good question. The outside rods being 120 degrees off makes an unusual powering problem because your strokes are now not 1/4 off. So now you have to balance for 120 degrees off on non-third connected drivers, the 1/3rd connected drivers might balance better but remember you have siderods' weight on one side and that does not balance perfect for the other side, so the balancing not just for same side issues, but opposite transverse forces and your third power connection. Now thats getting tricky.

Its a good thing the more powerful engines were used for slower freight which reduces the motions (not counting your high speed freights like NKP). Passenger engines had their connections closer to the center of the wheel for higher speed and larger wheels and lighter rods as they did not need the extra power construction. Hence of course the Aluminum experiments.

The UP 4-12-2 was a compound, IIRC. if not, still the wrong example since the center running gear was markedly different that the outside running gear. Think about every driver axle being a crankshaft for all 3 cylinders with identical running gear - and, perhaps, some form of variable cam poppet valve gear to make it all happen with minimal additional reciprocating weight. Shays are the only steam locomotives I'm aware of using 3 simple 120 degree seperated power units on a commpn crank, albeit they use Stephenson gear and don't drive the drivers directly. They are, however, very smooth relative to 90 degree 2 cylinder rod engines.

Another think to think about: 4 simple cylinders each 90 degrees relative to the other closest 2, 180 to the opposite third. Can each 180 degree unit work as a dynamic counterweight to its counterpart?

dave

Kelly,

Just a minor quibble. While the theoretical problem is the reciprocating masses as the revolving weights can, in theory, always be balanced completely, it is sometimes useful to reduce revolving mass in order that the available counterweight mass can be applied toward reciprocating balance.

As a general matter, a 2 cylinder locomotive with no overbalance suffers from both yaw (nosing) and surge (fore and aft) accelerations. Adding overbalance creates roll and heave (up and down) accelerations. Cross-counterbalancing can deal with the part of these accelerations that result from the reciprocating masses being in different planes than the counterwighting masses. Most discussions of counterbalance present the trade off between yaw and heave (or more commonly nosing and dynamic augment) but ignore the surge and roll accelerations.

Interestingly, the last British Rail steam locomotive class, the 2 cylinder 9F 2-10-0 was balanced only against surge, having counterweights at 135 degrees to both crankpins.

Andrew Adams

Dave,

All of the US 1920 era 3 cylinder designs except the Baldwin 60000 were simple. The idea, as pushed by Alco, was get more tractive effort within the existing axle loading restrictions. Three cylinders allowed this through smoother torque requiring a lesser factor of adhesion. Three cylinders also reduced piston thrusts which meant smaller main rods, wrist pins, and main pins. Roadway improvements, simple articulateds, and superpower design concepts overtook the three cylinder movement.

As to balance, the center cylinder can't cause yaw, so I'm not sure if it makes sense to balance it. It would still have surge. If you wanted to balance it's surge, you would create a heave acceleration, but no roll acceleration. On the outside cylinders, the fraction of each revolution subject to surge, heave, yaw, and roll and their overlaps would change, but they wouldn't cancel. I'm sure there were British technical publications on three cylinder balancing that might give some idea where the consensus compromises were.

Four cylinders locomotives with opposing piston strokes could probably do without overbalance. Real world considerations of crank axle strength and cylinder centerline offsets might have required some overbalance, but, if so, it would be much less that in a 2 cylinder of equal tractive effort.

Andrew Adams

Thank you Andrew - I've never grokked the entirety of counterbalancing, and the idea of making it useful weight rather than just more weight has some appeal - even though the complications are obvious.

Let's see.....4 cylinders, 2 at the front, 2 at the rear, outside frames......

dave