Blonde Girl Strips Her Red Underwear On The Railway

Most modern railways use continuous welded rail (CWR), sometimes referred to as ribbon rails. In this form of track, the rails are welded together by utilising flash butt welding to form one continuous rail that may be several kilometres long, or thermite welding to repair or splice together existing CWR segments. Because there are few joints, this form of track is very strong, gives a smooth ride, and needs less maintenance; trains can travel on it at higher speeds and with less friction. Welded rails are more expensive to lay than jointed tracks, but have much lower maintenance costs. The first welded track was used in Germany in 1924 and the US in 1930 and has become common on main lines since the 1950s.
Flash butt welding is the preferred process which involves an automated track-laying machine running a strong electrical current through the touching ends of two unjoined pieces of rail. The ends become white hot due to electrical resistance and are then pressed together forming a strong weld. Thermite welding is a manual process requiring a reaction crucible and form to contain the molten iron. Thermite-bonded joints are also seen as less reliable and more prone to fracture or break.
If not restrained, rails would lengthen in hot weather and shrink in cold weather. To provide this restraint, the rail is prevented from moving in relation to the sleeper by use of clips or anchors. Anchors are more common for wooden sleepers, whereas most concrete or steel sleepers are fastened to the rail by special clips which resist longitudinal movement of the rail. There is no theoretical limit to how long a welded rail can be. However, if longitudinal and lateral restraint are insufficient, the track could become distorted in hot weather and cause a derailment. Distortion due to heat expansion is known in North America as sun kink, and elsewhere as buckling. In North America a rail broken due to cold-related contraction is known as a pull-apart. Attention needs to be paid to compacting the ballast effectively, including under, between, and at the ends of the sleepers, to prevent the sleepers from moving. In extreme hot weather special inspections are required to monitor sections of track known to be problematic.
After new segments of rail are laid, or defective rails replaced (welded-in), the rails are artificially stressed. The stressing process involves either heating the rails causing them to expand, or stretching the rails with hydraulic equipment. They are then fastened (clipped) to the sleepers in their expanded form. This process ensures that the rail will not expand much further in subsequent hot weather. In cold weather the rails try to contract, but because they are firmly fastened, cannot do so. In effect, stressed rails are a bit like a piece of stretched elastic firmly fastened down.