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https://en.wikipedia.org/wiki/Railgrinder

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= Rail Grinders =

Rail Grinders
Rail grinders were developed to increase the lifespan of the tracks being serviced for rail corrugation. Rail grinding is a process that is done to stop the deformation due to use and friction on railroad tracks by removing deformations and corrosion. Railroad tracks that experience continual use are more likely to experience corrugation and overall wear. Rail grinders are used to grind the tracks when rail corrugation is present, or before corrugation begins to form on the tracks. Major freight train tracks use rail grinder to maintenance based the interval of tonnage rather than time. Transit systems and subways in major cities continue to use scheduled rail grinding processes to combat the corrugation common to heavily used tracks.

Rail Corrugation
Rails that are heavily used and put under continual and constant wear will develop rail corrugation. Rail corrugation is represented in wavelength .Typically, heavily corrugated rails experience a concave deformation on the top of the railroad track in 20mm to 200mm intervals. Significant rail corrugation can decrease the service life span of tracks and make the replacement of the affected railroad track necessary. Rail corrugation is caused by the friction between the rail and the train wheels tangentially, vertically, and axially. Wear corrugation is a result of friction on the lower rail, which comes in contact with the train wheel. Excessive corrugation can be identified by the wavelength found on the higher, or outer, rail. Rail corrugation may be limited or lessened with the use of heat treated or alloyed rails, as oppose to the traditionally used carbon composite rail

Rail Corrugation Prevention
Rail corrugation may be prevented by selecting rails with material compositions that are more resistant to corrugation. Heat-treated alloy steel rails with relative hardness are the most resistant as opposed to Bessemer steels due to a greater relative hardness. Rails with a Brinell hardness of 320-360 are best for corrugation resistant rails. Trains may vary speed on the tracks in an effort to prevent corrugation from affecting sections or rail on a transit systems. Varying a train’s speed, direction, and tonnage are beneficial for combating the growth of rail, as corrugation is caused by continually uniform friction. On subways and major transit systems, it is not possible to vary the direction of trains, making the use of annual and bi-annual rail grinding processes more applicable.

Preventative Rail Grinding
Preventative rail grinding is done before any signs of rail corrugation development. Rail corrugation will develop exponentially if the first signs of rail corrugation are not ground or serviced. Preventative grinding removes the deformation from friction and the chemical breakdown of the tracks. Regular rail grinding is the primary maintenance operation used to combat roaring rail or short-pitched rail corrugation. Rail grinding operations occur periodically in order to prevent rail corrugation from occurring. Rail grinding cars can be taken down freight lines that traverse long distances in the same direction if the freight railway used continually Rail corrugation, the carbon growth of the rail which is increased by friction, grows exponentially.

Rail Corrugation Noise Treatment
Rail corrugation has become is a major point for community complaints noise level advocacy. Often, vibrations of the corrugated track will become progressively worse on the tracks, generating more friction and metal on metal contact. Roaring rail corrugation is a common reason for noise complaints in urban and suburban communities. Roaring rail corrugation is most prevalent when trains travel at moderate speed Often called short-pitch corrugation, this corrugation is responsible for the majority of community reaction. The vibration caused by rail corrugation on transit systems effects both the users of the transit system and local communities where the railroads intersect Rail corrugation is responsible for creating excessive noise and causes a tranit to become loud and uncomfortable for passengers.Short-pitch corrugation creates significantly more noise in comparison compared to nominal railroad track friction, with the tone it creates at about 500 to 800 Hertz . Short-pitch corrugation is most commonly seen on railroads that do not experience regular rail grinding maintenance, or that are rarely used. Rail support stiffness directly correlates with short-pitch corrugation.