Track Machine Manual PDF

CHAPTER 2 TAMPING MACHINE AND DYNAMIC TRACK STABILIZER 201 General - Purpose of tamping and stabilization of track (ballast bed) is to produce well compacted sleeper supports in order to improve the load distribution across sleepers, restore track to correct geometry and have long...

CHAPTER 2 TAMPING MACHINE AND DYNAMIC TRACK STABILIZER 201 General - Purpose of tamping and stabilization of track (ballast bed) is to produce well compacted sleeper supports in order to improve the load distribution across sleepers, restore track to correct geometry and have long lasting retentivity of packing. Tamping machines are used for correcting the track geometry and tamp the ballast while Dynamic Track Stabilizer (DTS) is used for better anchoring of the track skeleton in the ballast bed to improve the durability of track geometry under running traffic. 202 Tamping machine - Tamping machine measures the existing track parameters and lifts it to enable correction of the cross level and alignment, to achieve target or pre-determined parameter values, with an aim to improve the track geometry. It simultaneously packs the ballast under sleeper(s), using tamping tools fitted on tamping unit, to provide well compacted ballast bed. (1) Functions - The main functions of tamping machines are- (a) Correction of alignment, (b) Correction of longitudinal and cross levels, (c) Tamping of ballast under the sleepers. Some of the tamping machines have additional fitments for track ballast stabilization also. (2) General Layout - General layout and important units of a tamping machine (09-32 CSM) are shown below- WORKING DIRECTION LEVELLING CHORD FRONT CABIN REAR/WORKING SATELLITE LIFTING AND LINING UNIT CABIN FRAME REAR BOGIE TAMPING FRONT TROLLEY REAR WHEEL LINING TROLLEY FRONT BOGIE UNIT TROLLEY MEASURING SATELLITE WHEEL TROLLEY Fig. 2.1 203 Important assemblies of tamping machines (1) Engine - Diesel engine is the main source of power. The engine converts chemical energy of fuel into mechanical energy, part of which is used directly 18  and remaining further converted into different forms of power for the working of machine. (a) Mechanical power through gear boxes - A part of mechanical power generated is used, by means of hydrodynamic gearboxes (in most of the machines), for movement of tamping machine. Remaining mechanical power is converted to other forms as mentioned below. (b) Hydraulic power through hydraulic pump - Hydraulic power is generated by means of hydraulic pump driven by mechanical power. It provides power for operations during working through various hydraulic motors and cylinders. (c) Pneumatic power through compressor - Pneumatic power is generated by means of compressor driven by mechanical power. It is used for brakes and locking/unlocking system of assemblies, up and down movements of feelers, operation of bogies for datum selection, horn operation and chord tension etc. (d) Electrical power through alternator and batteries - Electrical power is generated through alternator, or sourced from batteries. It is used to provide electrical power for sensing devices, feedback of corrected parameters, signals to hydraulic units, like directional valves, proportional valve and servo valve for operations. (2) Tamping units - Two or more independent tamping units are provided in tamping machine (one or more for each rail depending on the make and model of the tamper). These are mounted on the machine frame by means of vertical guiding columns. In some of the machines, the tamping units are fitted to the satellite frame. The tamping units on Indian Railways have the capability for tamping one/two/three sleepers at a time depending upon type and model of the tamping machine. The tools are arranged in pairs and each of the two sides of sleeper is tamped by four such pairs, four numbers on either side of each rail. The units are held on horizontal guide columns in order to slide sideways, which allow their manual/automatic centering over the rails in curves. The tools are vibrated by piston rods pivoted on eccentric shaft driven by hydraulic motors. A typical layout of tamping unit and its different components are shown as Fig 2.2 The lifting and lowering of tamping units is achieved by means of a hydraulic tamping units lifting/ lowering cylinder. The insertion depth of tamping tools and squeezing pressure can be varied for different types of sleepers. In case of simultaneous tamping of double/triple sleepers, the opening width of tamping tools can be changed pneumatically by changing the clapper piece to suit the sleeper opening and by pneumatic operation of clapper cylinders for joint sleepers. 19  1. TAMPING BANK 7. PLATE GUARD 2. CENTER PIN 8. CLAPPER CYLINDER 3. BIG TAMPING ARM 9. SQUEEZING PLATE 4. BIG SQUEEZING CYLINDER 10. SMALL SQUEEZING CYLINDER 5. GUIDE ROD 11. SMALL TAMPING ARM 6. OIL BATH 12. TAMPING TOOL Fig. 2.2 (3) Tamping Tool - The size & shape of the blade of tamping tool has a bearing on the quality of compaction (tamping) of ballast. The size of tamping tools differs, depending on model/make of tamping machine. Tamping tool with carbide shield called Tungsten Carbide Tamping Tool (TCTT) are now being used for improving the performance of tools. The positions of tamping tools (TCTT) for various machines with important dimensions are depicted at Annexure 2.1. (4) Lifting and Lining unit - The lifting and lining unit is positioned in front of the tamping units. Lifting is carried out using one lifting cylinder with the help of roller clamps/hook on each side. The lining operation starts simultaneously with the lifting operation. As soon as the target values are reached, lining and lifting operations are automatically stopped. (5) Satellite unit - Continuous sleeper tamping machines have tamping & lifting cum lining unit, provided on the separate unit called satellite unit. Satellite unit is placed on an independent under-frame, which is mounted on wheels. 20  It can move independent of the main frame, capable of cyclic movement from sleeper to sleeper. (6) Trolleys - These are wheels mounted units provided with sensing feelers used for measurement and correction of the track parameters. Four trolleys are used in tamping machine, which are- front trolley, lining trolley, height transducer trolley, measuring trolley and rear trolley. (7) Brake system - Following types of braking system are provided on tamping machine- (a) Direct brake- It is applied only on machine during transit. (b) Indirect brake-This brake is used for application on machine and coupled camping coach/wagon while running. This brake system is provided in machines with KE valve. KE valve is available in all new tamping machines. It works with single piping system. (c) Emergency brake- This brake is applied on machine during transit alone or coupled with camping coach/wagon only when KE valve is in ‘ON’ position. It is applied through indirect brake system. (d) Safety brake- This brake is applied automatically by switching off hydrodynamic transmission gear (ZF Gear in Plasser machines). Normally this should not be used for service brake application. (e) Parking brake- This is hand operated mechanical brake, applied when machine is stabled. 204 Types of tamping machines (1) Tampers without Satellite unit - The tamping unit and the lifting cum lining unit are mounted on the main frame of the machine itself. The machine moves and stops at every sleeper for lining, levelling and tamping. One to two sleepers can be tamped simultaneously in one operation. Following machines fall in this category. (a) Duomatic (Plain Track Tamper) - It is a Plain track tamper and with 32 tamping tools to pack two sleepers at a time. These machines are also referred as Work Site Tampers (WST) for purpose of nomenclature. The names of the models of Duomatic tamping machines presently in use on Indian Railways; and the name of manufacturer, are given below- (i) 08-32 Duomatic (Plasser India). (ii) 08-32C Duomatic (Plasser India). (iii) 08-32 WST with flat car(Metex–JSC Moscow, Russia). (iv) VPR-02M without flat car(Kalugaputmash, Russia). The important features/dimensions of these machines are given at Annexure 2.2 21  (b) UNIMAT (Points and Crossing Tamper) - This is primarily a points and crossing tamping machine. Tamping unit of this machine is designed in a manner to allow independent operation of individual tamping tool. This helps in tamping of almost all the sleepers in points and crossings. Tamping tool(s), which infringes any track component, can be tilted individually or in pairs and rest of the tools tamp the sleepers. Tamping unit in most of these machines can be rotated to align with the sleepers, which are laid at an angle e.g. Fan Shaped Layout design. Advanced models of UNIMAT have the arrangement for lifting of third rail and more advanced have the provision for both; lifting as well as packing under the third rail. Various models of UNIMAT machines presently in use on Indian Railways with the name of the manufacturers are as under- (i) 08-275 UNIMAT (Plasser India). (ii) 08-275-3S UNIMAT (Plasser India) with arrangement only for lifting of third rail. (iii) 08-475-4S UNIMAT (Plasser India) with arrangement for lifting and packing under the third rail. The important features/dimensions of these machines are given at Annexure 2.3 (c) Multi-Purpose Tamper (Plain and Points and Crossing Tamper) - This machine is designed for spot attention on plain track as well as point and crossing. These may have a flat platform at rear end with crane facility for loading, unloading and transportation of P.way materials. Various models of Multi-Purpose Tampers, presently in use on Indian Railways are as given below- (i) UNIMAT Compact (MPT) (Plasser India), (ii) UNIMAT Compact Split Head (MFI) (Plasser India). The important features/dimensions of these machines are given at Annexure 2.4 (2) Tampers with Satellite Unit - These machines are provided with a satellite unit, which moves independent of the main machine in working mode. Components required for tamping, aligning and levelling of track are provided on this satellite unit. While the main machine moves at a uniform speed continuously, the satellite unit moves and stops at every sleeper (sleeper set) for lining, levelling and tamping. These machines do twist correction also. Different models of these types of machines can tamp two/three sleepers in one operation. The machines falling in this category are- (a) 09-32 CSM (Plain Track Tampers) - It is a Plain track tamper designed for lining, levelling, twist correction and tamping of sleepers. It has 22  tamping unit with 32 tamping tools to tamp two sleepers at a time. Single chord lining and double chord parallel levelling systems are used. The important features/dimensions of this machine are given at Annexure 2.5 (b) Tamping Express (09-3X) (Plain Track Tampers) - It is a plain track tamper designed for lining, levelling, twist correction and tamping of sleepers. It has 48 tamping tools to tamp three sleepers at a time. Single chord lining and double chord parallel levelling systems are used. The important features/dimensions of these machines are given at Annexure 2.6 205 Tamping Mechanism - The tamping units work according to the asynchronous constant pressure tamping principle. The tamping tools penetrate the ballast and perform a closing movement with sinusoidal vibrations, as shown in Fig 2.3. SQUEEZING FORCES SQUEEZING FORCES ECCENTRIC VIBRATION FIXED PIVOT TO PICKUP THE SHAFT TAMPING REACTION FORCES 15 - 20 mm ASYNCHRONOUS ACTION SQUEEZING Fig. 2.3 The tamping tools continue to move, pressing the ballast till desired force is reached and thus each of the tools applies the same force on the ballast. Since each of the tools continue to move for different durations and presses the ballast till the desired pressure is reached, the process is known as asynchronous constant pressure tamping operation. Components of tamping unit are shown in Fig 2.3. All tamping tools, therefore, apply the same amount of pressure to the ballast being tamped; thus there is equilibrium of forces between the individual tool pairs and the specific surface pressure of all tools. During tamping of ballast, resistance gets built up in front of each pair of tools. The movement of the tool is completely 23  independent, according to the resistance encountered from the ballast. Once the resistance reaches the pre-selected value (hydraulic pressure in the squeezing cylinder), the corresponding tool pair stops squeezing automatically, however other tool pair(s) continue to squeeze till the resistance for those also becomes equal to preselected pressure. Individual tools may have different closing movements as shown in Fig 2.4 W1 W2 W3 W4 Fig. 2.4 206 Tamping parameters (1) Squeezing pressure - Squeezing force per unit effective area of squeezing piston is called squeezing pressure. The force at face of tamping tool for consolidation of ballast will correspond to this squeezing force. For tamping units, presently available with Indian Railways, the squeezing pressure for different track structure is as below: Table 2.1 Type of Track and Sleeper Squeezing Pressure Plain Track (CST9) 90-100 Kg/cm2 Plain track (ST& wooden) 100-110 Kg/cm2 Plain track (PSC) 110-120 Kg/cm2 P & C (ST/Wooden) 110-115 Kg/ cm2 P & C (PSC) 125-135 Kg/ cm2 The squeezing pressure should be kept on higher side of the stipulated range for caked ballast, however for deep screening sites and newly laid tracks with unconsolidated ballast bed, it could be on lower end of the range. (2) Tamping depth - For effective tamping of the ballast below the sleeper bottom, under the rail seat, the gap between top edge of the tamping tool blade and bottom edge of sleeper in closed position of the tamping tool should be adjusted depending upon the type of rail and sleeper. The desirable gap between top edge of the tamping tool blade and bottom edge of sleeper for different types of sleepers will be as under- 24  Table 2.2 Type of Sleeper Desirable gap between top edge of the tamping tool blade and bottom edge of sleeper Flat bottom sleeper 15-20 mm Metal sleeper 22-25 mm To obtain the correct depth of tamping tool during packing of sleepers, the initial (Zero) position of tamping tool is set as shown in Fig 2.5 Fig. 2.5 Tamping tool depth is calculated as: Tamping tool depth = Sleeper depth at the rail seat location + Rail height + rubber pad thickness Example 2.1: For a track with 60 Kg rail and sleepers, the tamping depth will be = 172 mm (rail height) + 210 mm (sleeper depth) +6 mm (thickness of rubber pad to drawing no. RDSO T-3711) = 388 mm (Fig 2.6) Fig. 2.6 (3) Tamping Tool Vibration, Amplitude & Frequency - The tamping tools are vibrated by piston rods pivoted on eccentric shaft driven by hydraulic motors with following parameters- 25  Table 2.3 Parameters Value Rate of revolution of vibration shaft 2000 to 2100 RPM (approx.) Vibration frequency of tamping tool 33 to 35Hz. (approx.) Amplitude of oscillation 3-5 mm These values may vary depending on design/model/make of tamping machine. Technical manual of the machine may be referred for details of all such parameters. (4) Vibration pressure - The vibration pressure of tamping tool is so adjusted that vibration does not slow down or stop even while penetrating the ballast. The vibration pressure varies from machine-to-machine and ranges from 150 to 210 Kg/cm2. (5) Tamping cycle & squeezing time - A complete tamping cycle involves lowering of tamping unit to the desired depth, squeezing of ballast (till all tool pairs reach pre-defined squeezing pressure), holding of tamping tools in that position, releasing and lifting of tamping unit & travelling of tamping unit to the next sleeper location. Time taken in squeezing the ballast with preset pressure is called the squeezing time. Normal setting of machine is such that lifting and lining of track starts when the tamping unit is lowered by about 100 mm from its zero position. Squeezing action commences about 30 mm before the tool reaches the target depth. Squeezing 100M LIFTING & LINING TAMPING DEPTH SQUEEZING & HOLDING 30MM TIME SQUEEZING LIFTING OF TRAVELLING LOWERING T/UNIT AHEAD OF T/UNIT TAMPING CYCLE Fig. 2.7 26  circuit is cut-off as the preset squeezing time is completed. The tamping unit is then lifted in succession. Lifting and lining circuit is cut-off when tamping unit, while in lifting operation, is 100 mm before the Zero position. For maintenance packing, squeezing time of 0.8 second to 1.2 second should normally be adequate. Higher value of the above range of squeezing time is required for track with caked up ballast. (6) Tamping tool surface area - Surface area of tamping tools blade of different machines is given in Annexure 2.1. Tools with more than 20% wear of the original surface area should not be used. The worn out tools are to be reconditioned/replaced. 207 Optional equipment - The use of optional equipment like Laser Beam System, Geometry Value Assessment (GVA), and ALC etc. simplifies working and reduces error-proneness associated with manual system of data collection and feeding. These systems are briefly described below- (1) Laser beam system - A pair of photocells mounted on tamping machine receives a fanned-out laser beam from laser emitter. In case of unbalanced laser input received by photocells, a corresponding differential signal activates an electric motor, to move the whole receiver assembly along with front end of the chord to the centre of the laser beam. Thus, front tower end of chord is shifted laterally by the amount of error to enable design lining and levelling. Working of Laser Beam system is explained in Annexure 2.7. (2) Geometry Value Assessment (GVA) - It is a small computer, which eliminates the feeding of adjustment values from tables and marking on sleepers. The locations of main points of curve i.e. starting of transition, transition length, radius, super elevation data etc. are fed into the computer. The use of GVA eliminates the necessity of attention by operator for feeding values and thus avoids possible mistakes in calculations and/or feeding, which result in better progress with improved quality. (3) Automatic Guiding Computer (ALC) System - It is advanced system, which automatically calculates the values of various track parameters, to be fed into machine on the basis of target track geometry. It has the capability to measure and record existing track parameters during a measuring run, in advance of working, and also allows flexibility to choose the desired track geometry. It also saves the operator from entering various parameters to be fed, as it does automatic feeding of parameters. The detailed working of this system is explained in Annexure2.8. ALC’s are being provided with fault finding diagnostic software also. (4) Data Recording Processor (DRP) System - It is a system for recording track parameters during working operation, at the working speed of the machine. It records the parameter of tamped track, like unevenness, alignment, cross- level, twist. The measuring sensors are so mounted that tamped track parameters are recorded in the working direction of the machine. It has a 27  system to predefine the limits of individual parameters and it is possible to evaluate and classify the measurement results. The parameters can also be displayed graphically along with calculated standard deviations of different parameters in small lengths (say 200 meter section). Apart from the track parameters, it can also be designed to record the machine working parameters like squeezing time, squeezing pressure and squeezing depth. (5) Computerized Measuring System (CMS) - This is on board computer used for displaying track parameters measured i.e. super elevation, versine and Longitudinal level etc. It also displays the nominal value fed by the operator. It also displays lifting and lining values fed manually, through Laser system and through ALC separately. It is used for digital calibration of lining and levelling system (For calibration of systems controlled by servo valve) & diagnosis of signals for proper working of these units. (6) Computerized Working System (CWS) - This computer receives the various machine working parameter (controlled by proportional valve) from its circuit some of which are listed below and displays it on monitor- (a) Driving: RPM of engine, work drive speed, run drive speed etc. (b) Tamping: tamping depth, tamping position, speed of up and down of tamping unit, squeezing pressure, squeezing time etc. (c) Satellite drive (if provided): satellite speed etc. (d) Automatic positioning: Sleeper distance setting during automatic working. It is also used for setting of the above parameters i.e. tamping parameter like tamping depth, squeezing time, squeezing pressure, satellite forward and reverse speeds etc. 208 Lining system - Lining system is for measuring and correction of track alignment. Single chord lining system is used in all tampers working on Indian Railways. The chord stretched between front and rear trolley is used for measuring alignment of track by means of measuring transducers. The track is, then slewed by lifting-cum-lining unit to the target alignment. For the purpose of lining - Machine measures alignment of only one pre-selected reference rail and rectifies that rail i.e. reference rail. The alignment of other rail, being fixed with the sleeper, automatically gets rectified except for correcting the gauge defect. Versine on curved track depends on radius of curves, chord length for measurement and location of measurement. (1) Reference Rail - The reference rail for carrying out attentions to alignment should be selected as given below- 28  (a) On curved track – outer rail (however, if outer rail is highly worn out, inner rail should be taken as reference rail). (b) On straight track on single, double and middle line in multiple line section –Any of the two rails of the track being tamped, which is less disturbed. (2) Lining method - Tamping machines follow two methods of alignment correction; 3-point & 4-point. Some of the latest machines have provision for only 3-point lining method. (a) 4- Point Lining method - The selected reference rail is measured at four points on the curve taking two measurements for versines. These values are then compared to correct the geometry. This method reduces existing error significantly to improve the track alignment. (b) 3- Point Lining method - The selected reference rail is measured using 3- points and the lining is performed until the measurement at middle measuring point reaches the target versine value. This method restores the geometry to almost perfect provided correct measurements are fed. 209 4 Point Lining method (1) Lining principle - This method can be used for correcting alignment of only the curved track. In this method track is measured at 4 references point and versines measurements of two intermediate points are compared (using geometrical versine ratio relation) to control the lining. The principle followed is that, in a circular curve, versines measured at two pre-decided locations on a chord of given length will have a fixed ratio, depending on the position of measuring points. This versine ratio is constant and is independent of the radius of the circular curve. The four points in machines are as below- DIRECTION OF WORK TAMPING UNIT LIFTING & LINING UNIT A MEASURING POINT B C D LINING POINT TARGATED CURVE H2 H1 REAR TROLLEY CHORD EXISTING CURVE FRONT TROLLEY Fig. 2.8 Here A is the rear trolley location, B is the location of measuring trolley (where versine is measured), C is lining trolley (where also versine is measured and correction is done), and D is the front trolley location. 29 Trolleys at A, B, C and D are pneumatically pressed against the outer rail (reference rail selected for alignment). A wire forming the chord is stretched between A and D representing the ‘base Line'. The transmitting potentiometers (transducers), which are fixed to the measuring trolley B and lining trolley C are connected to this wire by means of forks and the wire drives for measurement of versines. The geometrical property used in this method is explained below- DIRECTION OF WORK A B C D H2 H1 R Fig 2.9 From the above figure, 𝑨𝑨𝑨𝑨.𝑪𝑪𝑪𝑪 Theoretical Versine H1 = 𝟐𝟐𝟐𝟐 𝑨𝑨𝑨𝑨.𝑩𝑩𝑩𝑩 Theoretical Versine H2 = 𝟐𝟐𝟐𝟐 𝑯𝑯𝑯𝑯 𝑨𝑨𝑨𝑨.𝑪𝑪𝑪𝑪 Versine Ratio i = = (is independent of radius of the curve) 𝑯𝑯𝑯𝑯 𝑨𝑨𝑨𝑨.𝑩𝑩𝑩𝑩 𝑯𝑯𝑯𝑯 = 𝒊𝒊. 𝑯𝑯𝑯𝑯 Machine does the curve correction by slewing point C, until Versine H1 is in the correct ratio to H2 (H1 =i.H2). The Versine Ratio ‘i’ is the property of machine and depends on respective distance between the trolleys. The value of ‘i’ for various machines are listed in Annexure 2.9 In a four point lining system, location of A is taken as first reference point for subsequent corrections. It is, therefore, important to choose initial point, on the track with correct geometry, as pre-existing error at the initial point will get transmitted to track location being corrected. All subsequent corrections will also have accumulated errors. Points A & B of the machine always remain on the corrected track (corrected w.r.t previous positions). Point D always remains on the portion of track, which is yet to be corrected. Lining correction is done at point C. The machine system feeds H2 in system, where it is multiplied with constant i, to give H1. This value (H1) is then fed in difference amplifier and error, if any, is indicated on the galvanometer. The alignment is corrected at C by lining 30  units so that H1 becomes equal to H2.i or the ratio H1/ H2 = i is maintained and galvanometer indicates zero reading. In the machine having satellite units, the constant value ‘i’ may vary due to relative movement of position C. To overcome this problem a compensation system is provided to automatically adjust for measuring locations. (2) Application of 4-Point Lining Method - 4- point lining method can be used in following situations- (a) When theoretical track geometry is either not known or not required to be known, track is aligned according to geometrical properties of existing curve. (b) When, due to the location of track defects, the track slewing values are expected to be so large that they cannot be implemented without additional measures, and it is decided to smoothen the curve and rather than bringing it to the targeted/design profile. Lining can also be carried out according to reference points or previously set slewing values, as explained below- 210 Corrections to be applied in 4 Point Lining method - The curve to be corrected as explained above has to be further compensated for following errors- The error due to front trolley being on disturbed track, At variable curvature where front trolley and rear trolley are on curve of different radii and the ratio of H1/H2 equal to ‘i’ does not remain true, like transitions portion of the curve or while exiting and entering from one curve to another. (1) Correction (FD) in 4 Point Lining due to Front trolley on Disturbed track Fig. 2.10 In figure 2.10, curve marked 1 shows the targeted alignment, 2 shows existing position of track (disturbed) being attended and 3 is corrected alignment with front trolley on disturbed track. 31  Points A and B in figure 2.10 are on the previously aligned track, point D is the front end of the chord i.e. front trolley is on the disturbed track with an error FD, resulting in incorrect measurement of versine H2. Point C is slewed until H1 is in the correct ratio to incorrectly measured H2. Depending on the distances of the measuring points (which are fixed for a given machine), an error remains at lining Point C, as shown in the figure, which is also called left over error or residual error ‘FR’. Left over error FR = 𝑭𝑭𝑫𝑫 /𝒏𝒏𝟒𝟒𝟒𝟒𝟒𝟒 𝑨𝑨𝑨𝑨.𝑩𝑩𝑩𝑩 Error reducing ratio n4pt = 𝑨𝑨𝑨𝑨.𝑩𝑩𝑩𝑩 Value n4pt depends on trolley distances and its value for various machines are given in Annexure 2.9. A Correction equal to FD in the direction opposite to it needs to be fed in front tower to eliminate this left over error, to apply FR at lining trolley. The FD value has to be computed from the readings taken during field survey to be done prior to tamping. Either of the two methods may be adopted for the field survey. Measurement of versine on reference rail of the track (which is generally termed as disturbed track) and calculating slews by suitable software for realignment of curves, for deciding target curve which will be termed as desired curve. Survey with respect to fixed references like reference post, OHE masts etc. This is to bring the track on targeted alignment which is termed as design lining. (2) Versine Compensation (V) in 4 Point Lining at location with changing curvature For simple curves with transition at either end, the corrections are applied at following sections of the curves: For entry of machine from straight to transition and existing from transition to straight. Machine working in transition. For entry of machine from transition to circular curve and existing from circular to transition curve. When machine enters from straight to (leading) transition with front trolley on transition and rear trolley on straight, the measurement of H2 and H1 are as shown below: 32  DIRECTION OF WORK A B C D V H2 H1=H2xi Fig. 2.11 The correct versine at C will be H2.i +V, where V is the versine compensation required to bring track to target position. In the above curve, this compensation will be towards outside of the curve. The value of compensation increases as transition curve is parabolic of third degree and will become maximum (Vm) when entire machine is on transition curve and will then remain constant. When the machine enters from leading transition to circular curve, the compensation reduces from Vm and will eventually become zero when the entire machine enters the circular curve. Similarly, when the machine enters from curve to trailing transition and from trailing transition to straight, the versine compensation is applied in opposite direction as shown below: CORRECTION FOR TRANSITION CURVES WITH LINEAR CURVATURE CIRCULAR DIRECTION OF WORK Lo Lo CT TC R Vm1 Vm2 L1 L2 Lo ST TS Lo Fig. 2.12 Note: Versine correction is applied at trolley C but is to be fed by operator in front cabin and therefore to be written for front trolley D location i.e CD distance ahead of where it is applied. The above graph has been made accordingly. 33 Here R is the radius of circular curve, L1 and L2 are the transition length at either end, Lo is the chord length of machine, and Vm1 and Vm2 are maximum versine compensations at the two ends. The value of Vm depends on 3 factors i.e. position of different trolleys of the tamping machine, length of transition and radius of circular curve and worked out by formula: 𝑽𝑽𝑽𝑽 = 𝑴𝑴𝑴𝑴𝑴𝑴𝑴𝑴𝑴𝑴𝑴𝑴𝑴𝑴 𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪/𝑳𝑳. 𝑹𝑹 𝑴𝑴𝑴𝑴𝑴𝑴𝑴𝑴𝑴𝑴𝑴𝑴𝑴𝑴 𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪 = (𝑨𝑨𝑨𝑨. 𝑪𝑪𝑪𝑪. 𝑩𝑩𝑩𝑩)/𝟔𝟔(AC, CD, BC are shown in Fig 2.8) Variation of V is not linear from zero to maximum value (Vm). The value of Vm for different lengths of transitions and radii of curves along with corresponding values of V at intermediate locations are given in machine manufacturer’s instruction manual. A sample distribution for V in the chord length of Lo as given manufacturer’s instruction manual is given in Annexure 2.10 for guidance. In machines with ALC, radius of curve and transition length can be fed into ALC, and feeding of V value is done by ALC itself. Example-2.2 below explains the method of calculating V and Vm value. Example 2.2: To attend a curve of radius R=583 m with transition length 70 m by DUOMATIC 08-32C using 4 Point method. For DUOMATIC 08-32C from Annexure 2.9 AB=5.0 m, BC=5.3 m, CD=9.35 m, AC=10.3 m, BD=14.65 m and AD=19.65 m. Machine constant= (10.3x9.35x5.3)/6=85.06, Hence Vm=85.06/70x583=0.002 m i.e. 2.0 mm From Annexure 2.10 V value from straight to transition- Distance from ST 0 to 8 m 9 to 13 m 14 to 19.7m and CT (Meter) V in mm 0 1 2 Distance from TC 0 to 8 m 9 to 13 m 14 to 19.7m and TS (Meter) V in mm 2 1 0 ST, CT, TC and TS stands for straight to transition, curve to transition, transition to curve and transition to straight respectively 34 For remaining portion of transition length V=Vm should be fed. Direction of feeding will be as shown in Fig 2.12. Note: These values are to be written on sleepers to be fed in versine potentiometer in front cabin when front trolley is above that location The general principle followed in deciding the direction of feeding (toggle switch) versine compensation is as below: If machine is entering:-  From large radius (straight has infinite radius) to low radius ­towards outside  From Low radius to large radius ­towards inside Versine compensation and its direction in different curve layout are as below: (a) Curve with Transition (i) Straight to Transition to Curve to Transition to Straight DIRECTION OF WORK STRAIGHT TRANSITION CURVE END OF DIRECTION OF TRANSITION ADJUSTMENT START OF TRANSITION CHORD LENGTH Vm CHORD LENGTH STRAIGHT TRANSITION “L” CURVE ST TC Fig. 2.13 CURVE TRANSITION STRAIGHT DIRECTION OF WORK START OF TRANSITION DIRECTION OF END OF ADJUSTMENT TRANSITIO CHORD VM CHORD LENGTH LENGTH TRANSITION “L” TS STRAIGHT CT Fig. 2.14 35 (ii) Compound Curve R1>R2 V0=V2-V1 Fig.2.15 If R1R2) Fm0=Fm2-Fm1 (Fm1 and Fm2 are corrections as given by machine manufacturer for curve 1 and 2 respectively) 37  DIRECTION OF WORK Fm0 R2 R1 CURVE 1 CHORD LENGTH CURVE 2 Fig. 2.19 CURVE 1 TO CURVE 2 (R1