Do Europeans lay welded rail differently than the U.S.?

Question

In a recent discussion of welded rail, a disagreement arose regarding how welded rail deals with thermal expansion. Some said the rails simply go into tension or compression and are held by the track; others said all this was absorbed by expansion joints like

http://en.wikipedia.org/wiki/Breather_switch

It became apparent that Americans favored the "tension" theory and the people floating the expansion-joint theory are from Europe.

So, do Europeans actually lay welded rail differently than Americans? Do they make widespread use of expansion joints, where America does not? (it is a fact that America does not.)

Answer 1

Taking into account the detailed answer above I can see differences and similarities between the US railroads and their European counterparts.

With respect to temperature, there are formulae that maintenance of way people use regarding ambient temperature when the rail is initially installed on pre-existing road bed, during up-grading from jointed rail to CWR.  The process for laying a totally new structure is different, however.

Most railroads employ “steel gangs,” that do only this kind of work as they travel around the country working on their railroad's right of way.  There are also “tie gangs” and “surfacing gangs.”

In the US the rails are 1320 feet (one quarter mile) in length and are transported to where they will be installed by special equipment designed for that purpose.  One end of a rail is secured to the ground via an anchor and heavy cable, and the train is moved from under it.  The rails are on rollers, something like five levels high and ten wide.  These are secured by the “tie down car” that is located in the middle of the train.  This way, the rail is secure during transport, yet still able to slide to negotiate curves that the train passes through.  When actually distributing the rail, there is radio contact with the tie down car and some one is instructed which rail to release to be taken off the train.  An example would be, unlock A-5 or C-7, ETC.  Several different types of rail are transported together with the carbon steel reserved for curved road way.  Sometimes the rail to be laid is distributed weeks in advance of the actual installation.

From that point, machinery called “speed swings” lift the rail and place it on top of the tie plates, which are between the base of the rail and the cross ties, which in the US are predominately wooden.  The scenario of heating the rail to the proper temperature sounds exactly the same, with a wheeled device that runs on propane to heat the rail to the desired temperature.  One difference to note is that rail is seldom laid in darkness, even during the summer.  Maintenance of way gets the railroad in the day light and the trains are run after their day is completed.  The lengths of rail are bolted together by the US equivalent of fish plates, called “angle bars”.

Welders follow and weld the joints by encasing the joint in a ceramic crucible which contains molten steel.  After the heat is removed and the molten material cools, the crucible is broken from around the weld and any excess is removed by grinding wheel.

Work on ribbon rail is also done in curvature where the  inside portion of the outside rail is worn to its limit.  The two rails are then swapped in a move called “transposition.”  When accomplished, there is nice new rail on the inside of the outside rail of the curve.

There is room for some expansion and contraction, of course.  Using wooden cross ties allows for some stress relief and the rail itself is engineered in such a way that some expansion also occurs laterally, as opposed to longitudinally.  The longitudinal expansion and contraction is further controlled by the use of “creepers,” which are steel devices shaped not unlike a candy cane.  These are hammered onto the base of the rail ahead of and behind the tie plates the further anchor the rail.  Stress is further dissipated in that the entire structure has a bit of “play” in it which allows for stresses to be relieved.  When walking along the right of way on US main line where ribbon rail is employed, from time to time one will notice a notation written in indelible chalk that indicates the temperature when the rail was laid.

But, in extreme temperatures, hot or cold, problems due to expansion and contraction occur.  The most common of these is the “sun kink,” which on extremely hot days will cause the rail and ties to shift in the ballast, usually on a curve.  Sometimes this shift is extreme, and can kick the ties and rail out of the ballast altogether.  When heat waves occur the tracks are patrolled several times each day over various districts by maintenance of way crews in hi-rail cars.  In one freak accident many years back, near Corning, California, the outside rail of a curve didn’t buckle laterally, but raised straight up, pulling the spikes out of the cross ties.  Later that night, when temperatures cooled, the rail laid back down exactly where it belonged, only no longer fastened to the rail.  Amtrak came along and took the ditch.  No one killed, but a very close call.

The flip side of the coin, and that which actually creates most of the problems, is the “pull apart” where contraction causes the rail to break.  In the winter during cold snaps these happen nearly every night in my neck of the woods.  Even so, 139 lbs rail is pretty tough stuff.

Usually, when extreme temperatures exist, track bulletins are issued to train and engine crews lowering speeds where sun kinks are likely, to minimize damage if there is a heat related derailment.

When building totally new roadbed, it is built in a fashion many would call, “backwards.”  The cross ties are put in place first, then comes the tie plates and rail.  The, the whole thing is covered in the rock ballast, then machinery comes along and lifts the rail/tie structure and allows the ballast to fall underneath.  This process is repeated until the desired amount of ballast and elevation are achieved.  Machines called “tampers” come along and, using a laser leveling system, pack the rock under the cross ties and level the rails.  A final load of rock is distributed when “ballast regulators” tidy up the top and create the shoulder of the ballast underneath.  This method is also used when adding ballast to existing road bed when needed.

There are areas of jointed rail here and there and always where there are switches (points).

All in all, a pretty straight forward business.  Good question, thanks for asking.

Answer 2

This is a description of how long welded rail is laid in the UK:-

Initially the long welded rails are joined by drilling holes in the web of the rail and bolting them together with fishplates. The holes affect the rail strength only minimally as they're on the centre of area. Later the rails will be welded to form continuous track from buffer to buffer many miles long. This raises the question of why it doesn't buckle during a change in temperature. After all, there used to be an expansion joint every 60ft and all construction work has to take temperature change into consideration

It is laid at a slightly lower than mean temperature, usually at night, and carefully expanded using special heaters until marks on the rail line up accurately with marks at the trackside. They are then securely tightened down on to heavy pre-stressed concrete sleepers which in their turn are held by tons per yard (or tonnes per metre) of ballast. Although there can be considerable internal stresses present within the rail it doesn't affect the geometry of the track.

To prepare for destressing, the track is released from its fastenings, raised slightly and supported on small diameter rollers at long intervals. Pegs are driven into the ballast at regular distances close up to the rail head. Each peg has a scribed line on its top running perpendicular to the rail.

From the difference between the ambient temperature and the mean temperature a distance is calculated or read from a table to assess how much the rail must be lengthened at each peg and the rail top carefully scribed to show this. When the two lines coincide the rail will be at its mean temperature length.

The trolley with burners is run along the rail manually as evenly as possible and a man stands by the peg watching the marks as the distance between them decreases. When they coincide the rails are rapidly fastened down and the procedure is repeated with the next peg.

As work progresses the long rail is welded at the joints so as to become continuous welded rail. This is usually done using the Thermit method.

When track maintenance is done there are strict regulations about how much manipulation is allowable at the ambient temperature. At very high Summer temperatures track maintenance which involves lifting the track may be banned altogether. Failure to observe these precautions can unleash tremendous forces which can do considerable damage to the track and may be difficult to remedy.