Destressing of LWR

1. Manually. 2.Using Rail Tensor

Manually

1. A traffic block of adequate duration should be arranged at such d time that the rail temperature will be within the temperature range specified for td during the fastening down operations. The entire work shall be done under personal supervision of the PWI.

2. Before the block is actually taken, a speed restriction of 30 km/h should be imposed and fastenings on alternate sleepers loosened. 

3. When the block is taken, the closure rails shall be removed, the SEJs adjusted and fastened.

4. The remaining, sleepers, fastenings on both running rails shall be loosened/removed starting from the ends near the SEJs and proceeding towards the centre of LWR. The rail shall be lifted and placed on rollers at every 15th - sleeper to permit the rails to move freely. While destressing on curved track, side rollers are provided. The rails shall be struck horizontally with heavy wooden mallets to assist in their longitudinal movement.

5. The rollers shall then be removed, the rails lowered to correct alignment and fastenings tightened, starting from the middle of LWR and proceeding towards both hands simultaneously. The tightening of fastenings shall be completed within

the temperature range for td. The actual range of temperature during the period of tightening shall be recorded by PWI along with the time and date.

6. Simultaneously with the tightening of fastening, arrangements for insertion of cut rails between the SEJ and LWR shall be started. The four gaps shall be measured individually and the rails of required length cut by saw keeping required gaps for AT welding. The cut rails shall then be placed in position, fastened to the sleepers and welded at each end, Fastenings for 20 metre on each end of the LWR shall be removed before welding. Joints shall be clamped for 20 minutes after welding.

Using Rail Tensor

Sequence of operations

The procedure to be adapted for destressing consists of the following steps: 

(i) Remove impediments to free movement of rail such as rail anchors, guard rails, check rails etc.

ii) Create gap of about 1 metre at the centre of LWR during a traffic block and insert a closure rail there, at a restricted speed.

iii) Mark anchor lengths at either end of the proposed LWR in accordance

 Notes:

a) Anchor length shall be determined on the basis of the fewest value of tp at which destressing is likely to be carried out.

b) Anchor length shall be increased suitably if the fastenings, rubber' pads, liners or ballast conditions are poor.

iv) Erect marker pillars at the ends of anchor lengths on either side and at 100 metre intervals thereafter.

v) Obtain a traffic block when tp is less than the desired installation temperature (to),  remove the closure rail at the centre and unfasten the full length of rails leaving only the anchor lengths at either end. Mount the rails on the rollers.

Notes: Side rollers shall also be used while under taking destressing on curved track. Side supports on the inside of curve should be spaced at every nth sleeper.

Outside supports shall be used in addition at the rate of one for every three inside

supports. 

vi) Fix rail tenser across the gap at the centre and apply tension so as to get the required amount of extension as provided.

vii) Re-fasten the rails starting from the anchor lengths at either end after removing the rollers progressively and adjusting tension at the rail tensor to make sure that the required extension has been achieved at each marker pillar.

viii) Put paint marks on either side of the gap at the centre, spanning over the gap at a distance of 6.5 metre. Insert a closure rail of a length equal to (6.5 metre - 2 gaps for welding +l mm for saw cut ends) and clamp as per arrangements.

ix) Release and remove the rail tenser. 

x) During another traffic block, weld both the joints of the closure rail at the centre.

xi) Equalise stress at the centre and at the anchor lengths.

DESTRESSING OPERATION-OF LWR WITH THE USE OF RAIL TENSORS

Far destressing of LWR with the use of rail tenser, the following procedure shall be adopted:

i) During the first traffic block, create a gap of 1 metre at location B i.e. centre of

LWR Introduce rail closure as required and fasten with special fishplates and clamps. Allow traffic at restricted speed.

ii) Mark the anchor length A1 A2 and C1 C2 each equal to la at either end or the length A2 C2 to be destresed.

Note: The anchor length 'la' should be determined on the basis of the lowest value of tp at which the Destressing is likely to be carried out.

iii) Erect marker pillars Wo W1 etc., on each of the length A2 B. and C2B. Transfer the marks Wo onto the rail foot 

Note: The distances WoW1, W1 W2 etc. shall be marked at about 100 metre intervals, the distance from the previous pillars and the last pillar WB may be less than 100 metre.

iv) During the second traffic block, when tP is less than the desired To destressing operation shall be carried out for the lengths A2 B and C2 B as described below.

a) Remove the closure rail from location B. Unfasten and mount on rollers the portion from A2 C2

b) Fix the rail tenser across the gap at B and apply tension so as to obtain some movement at Wo to remove any kinks or misalignment and to minimise the friction in the rollers etc. Release the tension and note the movement Yo at Wo. 

c) Transfer marks W1, W2. ……onto the rail foot and note temperature tp. 

d) Calculate the required movement at W1 as under: -

Movement at W1 =Yo + elongation of length Wo W1 (L) due to temperature difference (to - tp) = Yo+L a (to -t p)

Calculate the required movement at W2 as under: -

Movement W2 = Movement at W1 elongation of length W1 W2 (L) due to temperature difference (to - tp).

Similarly, calculate the required movements successively at each of the remaining points. Mark the above calculated extensions with respect to the transferred marks referred at (c) above on the rail foot on the side away from the tenser. Apply the tension by means of rail tenser till the mark of required extension comes opposite to the mark on the marker pillar W1. Fasten down the segment Wo W1.

Then check at W2, bring the mark of required extension at this location opposite to the mark on the marker pillar W2, by adjusting the tenser either by reducing or

Increasing tension and fasten down the segment W1W2 Similarly, check the remaining marks, adjust the tension as required and fasten down each segment before proceeding to the next.

Note:

i) Annexure VII gives the value of L a (to - tp) for different values of L and (to - tp).

ii) Only one value, of tp has to be taken at the time of marking W1W2 etc. on the rail foot. The value of tp is not required to be taken thereafter. The variation of temperature, if any during the destressing operation shall automatically be taken care of by reducing or increasing the tensile force from the tenser, while coinciding the reference mark on rail with the corresponding mark on pillars. 

iii) If for any reason, both the lengths A2B and C2B can not be fastened down simultaneously, the final adjustment in pull and fastening down of the individual

segments may be done in series, first from A2 to B and then, from C2 to B. 

e) After the fastening down of the last length A2B and C2B is completed, make a

paint mark near free end of one rail at a distance of (6.5 metre + 2 % 25 mm -1 mm), measured from the end of, the other rail across -the gap spanned by the rail

tenser.

f) Remove the tensor, close the 1 metre gap temporarily and allow traffic at restricted speed.

v) During-.another traffic block, cut the rail at the paint mark, insert a rail closure of length exactly equal to 6.5 metre and weld one end thereof. If the gap at the other end is also 25 mm, it can be welded in the same block. Other wise, fasten with special fishplates and clamps and allow traffic at restricted speed. In the latter case I during a subsequent block, when tp is not greater than to release rail fastenings on either side to the required extant and pull the rails with rail tensor to get the desired gap of 25mm, refasten the rail and weld the joint. Release the tensor after a lapse of a minimum of 20 minutes after pouring of the weld metal. 

vi) During subsequent traffic block, when tp is less than td, equalise the forces in the rail by releasing the fastenings over a length of 100 metre on either side of location B and tapping with wooden mallets etc. Fasten down the rail and allow traffic.

vii) During another traffic block, when tp is within the range of temperature specified for td, destress end 100 metre from SEJ. There after, weld the closure rail next to SEJ duly ensuring setting of the SEJ.

In case rail temperature at the time of destressing is within the range specified

detailed procedure as given without using rail tenser, may be adopted.