Seamless rails: no wheel knocking?

The butt joint is probably the weakest point in the design of a railway track. Throughout the history of the existence of the "iron", engineers have not been able to find the best way to connect the rails. Joints are still sources of negative dynamic impact on the locomotive and the cars following it.


Of all the costs of maintaining a railway, approximately 40% are attributable to joints that need constant maintenance. Yes, today's tracks, of course, cannot be compared to those of 100 or more years ago. However, the negative impact of rail joints has not been completely eliminated. There is only one way out - to create a seamless ("velvet") railway track. Of course, it will not be possible to completely get rid of joints. But it is quite possible to reduce their number to a minimum, which is being done today.

History of continuous welded railways

The idea of ​​such a rail connection first occurred to the Russian engineer Stetsevich in 1896. To compensate for the forces of tension and compression, he proposed making the tracks wavy (curved). In 1907, the German Otto Gronau developed a technology for welding rails into a single long whip. The method began to be used in many countries, but the further development of continuous tracks was prevented by the First World War.


By the early 1930s, most countries had gradually switched to laying long rails. This was facilitated by the VII Congress of Railways, which confirmed the possibility of using products up to 60 m long without any negative consequences in terms of thermal expansion and contraction. Around the same time, special mobile machines appeared that could weld rails directly on the railway bed.


In the USSR, 1932 was marked by the laying of continuous welded track 215-225 m long on the bridges across the Volga (Kalyazin) and Oka (Serpukhov). In 1933, a 477 m long section was first built at Podmoskovnaya station. By 1966, the country already had 5,5 thousand km of such railway. In 1982, they began to use 850 m long whips. The rails were made heavier; inserts were used during welding that resisted rupture under a force of 2,5 MN.

How does a continuous welded track work?

The main problem is the thermal expansion of the railway in summer and its contraction in winter. It occurs, but only at the ends of the welded rail. These sections are called equalizing. To minimize the effect of temperature, the I-beam is fastened more often: there are more joints in the middle than at the ends.


However, not everything is so ideal: in extreme heat, a so-called surge may occur, which is a sharp horizontal curvature of the rail. In severe frost, the weld may break. Therefore, the length of the continuous track is limited, most often to 1700 m - the standard length of the block section. In practice, an equalizing span of 850-2 ordinary rails is inserted between the strings (4 m). Their standard length is 12 m.


There is another reason why a continuous track cannot be made "endless". This is the need to isolate the rails from each other, since static voltage can arise in them. And the current that feeds the locomotives is either alternating or direct. And they cannot be "mixed".

How rails are welded

The procedure is quite complicated, since high-carbon steel is used. Therefore, such work is carried out only by highly qualified specialists in companies that have permission to perform this operation. There are several methods of connecting whips using welding.

Electrical contact

The most reliable method, which involves joining through preliminary heating and melting of the rail ends. The procedure is carried out continuously or in a pulsed mode, when the seam is periodically cooled and settled. A special machine is used to carry out the work.


The method is characterized by a high degree of automation and is most often used in the arrangement of main lines. The strength of the connection, compared to a whole rail, is from 90 to 110%.

Gas press

Preliminary preparation consists of mechanical cutting of the ends to ensure a tight fit. The rail is also treated with dichloroethane. Then both ends are clamped with a hydraulic press, heated to 1200°C and the ends are pressed together, bringing them closer to each other. This method is popular in the USA: it provides 90-100% strength.

Electric arc welding

The connection is made by filling a gap of 14-16 mm with a molten electrode. It is placed between the ends and current is passed through it.


This method is used to connect tracks at stations. The quality of the work depends on the electrode, the achieved strength of the connection is 55-70%, compared to a solid metal product.

Thermite welding

The chemical essence lies in the reduction of iron from its oxide in the "neighborhood" of aluminum. During the reaction, a lot of heat is released, which heats up the ends of the rails. The technology is specially designed to connect untreated ends. Moreover, they can be made of different grades of steel. Preparatory work is necessary: ​​cleaning, installation of forms in which the thermite is placed (and then ignited). A torch is used for this. When the process begins, the material melts and flows into the seam.


Everything happens within 15-20 minutes. Then the joint is ground. The technology is simple and efficient: no bulky machines, rail welding trains, or energy sources are needed. Everything is done manually by professionals. The total joining time is no more than an hour. The strength, compared to the previous connection method, is higher - from 65 to 70%.

Maintenance of continuous welded rails

As mentioned earlier, the main concern of railway workers here is temperature control, which is intensified in summer and winter. Portable thermometers are used for this. In hot weather, the position of the rail is measured over a length of 8 to 15 m.


If the deviation is more than 10 mm per 10 m of track, the dangerous section must be fenced off with installation signals and measures must be taken to discharge the temperature stress. Work is carried out on the nearest equalizing span. If this cannot be done promptly, a piece of rail is cut out and replaced with another.


In frosty weather, when the metal is compressed, the welds are checked: if necessary, the fasteners are tightened at the ends of the strings. If necessary, the sections of rails are replaced with longer ones at the equalizing sections.

Conclusions

Despite some difficulties in maintenance, it is easier and cheaper to maintain a continuous track than a classic one. In addition, it is worth considering the advantages of "solid" rails:

✅ smooth movement of passenger trains: less noise, shaking
✅ increased service life of both rails and wagons, locomotives
✅ lower costs for track repair and maintenance
✅ saving metal in the construction of railways
✅ the resistance of the train's wheels decreases: its speed increases
✅ increased safety: the likelihood of a train derailing is reduced

The disadvantages include the comparative complexity of repairing a damaged section of track. And also the need to arrange a thick (at least 45 cm) ballast layer. Moreover, it can sag, which must be monitored. Nevertheless, the length of continuous tracks in the Russian Federation is gradually increasing: according to data for 2003, they accounted for 40% of the total length of railways.