- Slides: 29
WEAR OF RAILS
TYPES 1. Wear on head of rail 2. Wear on ends of rail 3. Wear of rail on curve
WEAR ON HEAD OF RAIL n Wear on head of rail is due to abrasion on moving rails. n Due to grinding action of sand or dust between the rails and wheels of the train.
Cont… n When train starts or applies brakes, the wheel just slides on the rails causing wear on the head. n Load coming on to a track may exceed the carrying capacity of the section. Thus causing the wear in the head of rail.
WEAR AT THE ENDS OF THE RAIL n n It is much greater than the wear on the head of the rail. This type of the wear is resulted due to the blows which the rail receive when the wheel jumps the space between the rail ends. The ends are battered by such blows. The contact surface between the sleepers and the rail is worn as the effect of these blows increased.
CONT… n The ballast under the sleepers will loosen due to increase in the intensity of vibrations, also he sleeper will depressed due the displacement of ballast, also the fish plates will get loose under the constant impact of increasing vibrations
WEAR OF RAIL ON CURVE n On the curve the wear of the rail takes place in both inner and outer rails. n On the curve the, the outer wheel has to move through greater distance than the inner wheel. And the inner wheel has to slide over the inner rail. Curved Crossing
CONT… n n As a result of this sliding wear of the inner rail occur because the metal in the rail head is burnt. At the curve, flange of outer wheel will strike the inner surface of the outer wheel due to centrifugal force. Thus side of the head of rail wears out. Wheel Slope 1: 20 Flange of Wheel
TYPES OF CROSSING
TYPES OF CROSSING 1. Square Crossing 2. Diamond Crossing 3. Cross Over 4. Scissor Crossing 5. Symmetrical Split
SQUARE CROSSING n When to railway lines cross each other at 90 o it is called Square Crossing
DIAMOND CROSSING n Angle of intersection (crossing angle) of two tracks is when not 900 , then crossing is called diamond crossing
CROSS OVER n A cross over is introduced to transfer a train from one track to another track which may or may not be parallel to each other
SCISSOR CROSSING n If two cross overs are required between two parallel tracks and there is no sufficient space for crossing to be kept separate, then they are made to over-lap each other and result is a scissor crossing.
SYMMETRICAL SPLIT n If radius of main track is equal to the radius of turn out curve, then the turn out is known as symmetrical split.
CREEP OF RAILS
CREEP OF RAILS Definition: It is a horizontal movement of rails in a track. It can be minimized but cannot be stopped.
Causes Of Creep There are three main causes of Creep 1. Wave motion of trains. 2. Expansion and contraction of rails due to variation in temperature. 3. Due to starting, accelerating, slowing down (decelerating) and stopping of trains.
Wave Motion n When train passes on a track, the portion of rail length under the wheel of train will under more stresses and little depression will exist. n As a result, this depression will cause (set) a wave motion in the rail or track
Direction Of Creep Alignment Of Track: Creep is more on curve track than on a tangent portion (straight track). Grades: In upgrades tracks, creep will be less and in down grades track creep will be more. Direction of movement of trains: Creep will be more in the direction to which the loaded train moves more.
Extent Of Creep n Creep does not vary at some constant rate. (it is not constant) n Creep does not continue in one direction only. n Creep for two rails of the track will not be in equal amount.
Result Of Creep n Expansion gap is reduced, buckling of track take place. n Sleepers are moved out of a square. n Crossing points get disturbed.
Square Position of Sleeper out of square
SOME IMPORTANT TERMS
SUPER ELEVATION n The outer edge is raised with respect to the inner edge on curve rail section called super elevation. SUPER ELEVATION = Where, G = Gauge of track (ft) V = Design speed of train (ft/Sec) R = Radius of curvature (ft) g = Acceleration due to gravity (ft/sec 2)
Problem Fine the Design speed of railroad on a curve if Super elevation is 0. 5 ft, Gauge is 5’-6” and Radius of Curve is 3500 ft Sol: 101 Km/h
SLEEPER DENSITY It is the Number of Sleepers on track per rail length. n Sleeper Density is Expressed as “n + x” Where, n = Number of yards in rail length x = Number of sleepers more than “n” 1 yards = 3 ft n Note: n n Normally the Length of one rail section is 40 -42 ft Pakistan Railway sleeper density ranges from (n+3) to (n+6)
Problem Find out the sleeper density in a 420 ft railroad length, there are 3 more sleepers than Number of yards in 1 rail length. Find out the sleeper Density? Sol: Sleeper density = 17