27-07-2012, 12:34 PM
SOLAR OPERATED RAILWAY TRACK CRACK DETECTOR
SOLAR OPERATED RAILWAY CRACK DETECTOR(REPORT).doc (Size: 539 KB / Downloads: 57)
SYNOPSIS:
The project relates to the location of singular points in the automatic control of railway tracks. According to a possible embodiment, the railway carriage carrying the control equipments is provided with sensor orientated to detect the crack.
CHAPTER – 1
INTRODUCTION
There are many reasons why rail tracks crack. In bygone days, it was common for a rail crack to start near the joint between discrete rail segments. Manufacturing defects in rail can cause fissures. Wheel burns can also contribute to rail cracks by changing the metallurgy of a rail. Rails are also more likely to crack when the weather is cold, when the ballast and ties/sleepers aren't providing as much support as they should, and when ground or drainage condition is such that 'pumping' occurs under heavy load. All of these conditions can contribute to a broken rail, and in turn a possible derailment.
MANUFACTURING DEFECTS IN RAIL:
The quality of rail steel has improved dramatically since the early days of railroading. The trend toward using continuously welded rail (CWR) requires a higher quality rail, due to the cyclic thermal expansion and contraction stresses that a CWR would be required to endure. In addition, rail operations in general have been trending toward higher speed and higher axle-load operation. Under these operating conditions, rail pieces rolled in the 19th century would likely break at an unacceptable rate. Despite the improved rail quality and rail metallurgy, if impurities find their way into rail steel and are not detected by the quality assurance process, they can cause rail breaks under certain conditions.
Recent rail-making processes have also been trending toward a harder rail, requiring less frequent replacements under heavy loads. This has the side-effect of making the rail more brittle, and thus more susceptible to brittle fracture rather than plastic deformation. It is therefore imperative that unintentional impurities in rail be minimized.
WHEEL BURN-RELATED RAIL CRACKS:
When a locomotive wheel spins without moving the train forward (also known as slipping), the small section of rail directly under the wheel is heated by the forces of friction between the wheel and itself. The wheel rests on an area of rail no larger than a dime in size, so the heating effect is very localized and occurs very quickly. While wheel burn typically does not cause the entire rail section to melt, it does heat the steel to red-hot temperatures. As the locomotive stops slipping and starts moving--or worse still, slips forward by a matter of inches and heats a different piece of rail--the heated spot cools down very quickly to normal temperature, especially when the weather is cold.
This heat-quench process results in annealing of the rail steel and causes substantial changes to its physical property. It can also cause internal stresses to form within the steel structure. As the rail surface cools, it may also become oxidized, or undergo other chemical changes by reacting with impurities that are on the surface of the rail. The net result of this process is that an area of the rail that is more susceptible to crackage is created.
WHEEL FLAT-RELATED RAIL CRACKS:
If the brakes are dragging or the axle ceases to move on a rail vehicle while the train is in motion, the wheel will be dragged along the head of the rail, causing a 'flat spot' to develop on the wheel surface where it contacts the rail. When the brakes are subsequently released, the wheel will continue to roll around with the flat spot, causing a banging noise with each rotation. This condition is known as wheel out of round.
The banging of flat wheels on the rail causes a hammering action that produces higher dynamic forces than a simple passage of a round wheel. These dynamic forces can exacerbate a weak rail condition and cause a rail crack.