Sub : Working of tamping machine in design mode.
All the tamping
machines are equipped with the system of working in smoothening mode and design
mode.
Working of tamping
machine in smoothening mode reduces the track defects viz. Cross level and
alignment to only limited extent. Working of tamping machine in smoothening
mode is desirable only when existing track parameters are not much beyond
prescribed limits otherwise it leaves appreciable residual defects in the track parameters after
tamping.
Working of tamping
machine in design mode is adopted to correct the track parameters upto a design
value thereby eliminating the track defects to a larger extent.
Thus
for achieving a good track geometry, it is desirable to work the tamping
machine in design mode which should be adopted under the following
circumstances:
1.
When the alignment
and unevenness/twist parameters fall below ‘B’ category or lower.
2. When TGI value of a km. falls below 50.
3. After every 2 cycles of tamping in smoothening mode.
For working of
tamping machine in design mode, following field works are mandatory:
I.
For straight track, location of high points
on track for both the rails are to be identified within a Chord length of
70-100 meters. P.Way Manual Chapter on MSP vide clause 1.2 elaborates the steps
to be followed in ascertaining the
location of high points.
II.
Rail having higher
points to be selected as reference rail/datum rail. Dip over the datum rail
between two high points is to be measured by the levelling instrument and
recorded for at least every 3rd sleeper. This record is to be
maintained in L- defect register.
III. Cross level defects in the track are to be measured at all
high points of both rails.
IV. The maximum cross level defect thus measured on high points
of non-datum rail should be choosen as general lift so that cross level
correction is done by lifting of rails as lowering of rail is not possible.
V.
The long level
defects measured on datum rail is to be written on respective sleepers and the
same value plus general lift is to be fed form front cabin as soon as front
tower reaches to that sleeper.
VI. For levelling on curve, inner rail is always be chosen as
datum rail. The same procedure as applicable for straight track to be followed
for working out lift values for different stations. While correcting level,
superelevation and gradient parameters to be considered wherever
applicable.
For
alignment correction of track in design mode of working, locations of Zero
alignment defect in straight track to be identified during field survey. For
curve track, calculation of designed versine by 3 point method for all the
station to be worked out for a given radius and transition length of curve as
per the chart available with the machine.
Following steps to be followed:
I.
Select good points of
alignment on straight track preferably within cord length of 70-100 meters.
II.
Measure alignment
defects between 2 good points as selected above. IRPWM chapter on MSP
elaborates the steps to be followed for identifying locations of zero defect in
straight track and measurement of alignment defect.
III. Record the measurement of alignment defects on straight
track at every 3rd sleeper in a alignment defects register and the
same to be written on the sleeper itself.
The value of alignment correction to be fed from a digital potentiometer
for lining provided in front cabin as soon as front trolly reaches to that
sleeper.This virtually shifts the location of front trolly to correct reference
position.
IV. The chord stretched between one corrected point and other
virtual correct point gives correct reference line and accordingly alignment is
corrected without any residual error.
V.
For curve track, the
design versine should be calculated as per three-point method, to be worked out
for all the stations and also for every third sleeper by interpolation of
values of adjacent stations. These values are to be written on respective
sleeper and to be fed from digital potentiometer for versine provided in front
cab of machines.
VI.
Slews for each
station is also worked out by adopting ROC
calculation. Software "Recur 999" can be used for calculation
of slews. These slew values are to be written on each station and to be fed
form lining potentiometer provided in front cab as soon as front trolly reaches
to that station. The virtual shifting of front trolly to correct position
eliminates the error in reference of measurement of versine and feeding of
designed versine from versine potentiometer provided in front cab to lining
trolly, align the track to a designed geometry w.r.t. chord stretched between a
corrected point and a virtual correct point.
VII Additional values for versine correction
in transition portion of curve are available in the charts provided with
machine. This value is to be worked out from the chart as per radius and
transition length of curve. It can be seen from this chart that correction
value of version for transition of curve is very nominal (maximum
value-3mm.) up to 20 of curve and therefore can be over looked up
to 20 of curve but should be applied for the sharper curves.
C.
Pre works in the field for good result in design
working :
To achieve the best results in the field, following preparations are required.
i) Before start of the work, zero defect track for a length of at least 21meters should be made so that machine starts the work with reference to zero defects and thus residual error during work will be minimum. Calibration of the machine should also be checked.
ii) If the condition of alignment is very bad so to say falling in ‘D’ category of CTR record, one round of lining correction in smoothening mode before correcting the alignment in the design mode helps to prevent heavy slew required at few isolated locations in the track.
iii) Shoulder ballast should be removed from the end of sleepers up to about 100mm away form track to prevent springing back of the track after slewing the track. This advance preparation will not allow springing back of track after correction of alignment and therefore disturbance in corrected alignment.
iv) Manuals available with the machines on the function of levelling and lining operation should be referred as stated above for working in design mode of machine.