Friday, March 23, 2018

Maintenance of Rail Joints

Maintenance Of Rail Joints –

(1) Special care is needed for maintenance of fish plated joints to get better rail life as well as improved running.

(2) The efficient maintenance of joint depends on:
(a) Efficiency of fastenings.
(b) The efficiency of packing and correct spacing of sleepers.
(c) The provision and maintenance of correct expansion gaps
(d) The proper lubrication and fishing of the joints.
(e) The correct maintenance of gauge and cross levels and proper packing.
(f) Efficient drainage.

Defects in rail joints –

Some of the major defects, noticed at the rail joints and the preventive measures suggested to rectify or minimize the deficiencies /defects noticed are detailed below

(a) Slack sleepers – Maintenance of joints by Measured Shovel Packing in case of flat bottomed sleepers improves the condition of the joints. In the case of conventional maintenance by beater packing it should be ensured that the sleepers do not get tilted.
(b) Loose Fish-Plates – Fish bolts must be kept tight, but not so tight as to prevent expansion or contraction of rails, by using standard spanners.

(c) Wear of Fish-Plates and Rails at fishing surfaces – When wear takes place on the fishing planes of rails and fish-plates, the joint dips down.The wear is generally greatest at the centre of the top of the fish-plates and least at the ends. Two types of devices are used for compensating the wear of the fishing planes.

(i) Repressed Fish-Plates – The repressed fishplates are those which are hot forged so as to form a bulge in the middle part of the fish-plate conforming to the wear most prevalent.

(ii) Tapered shims –Tapered shims are pieces of steel, shaped to fit the usual pattern of wear between the top fishing surfaces. They are made in varying thicknesses, each size being designated by the wear in mm. between the fishing surfaces multiplied by 10. Thickness of shim is varied in steps of 0.5 mm. from 1.5 mm. to 3.8 mm. Length of the shims should be determined on the basis of actual wear pattern of different sections of rails. Shims are tapered in thickness from one to the other to conform to the wear. The sketch shown as below indicates the type of tapered shim, which is commonly used:

(d) Battering of Rail ends – Battering can be avoided by packing the joint sleepers firmly and by maintaining correct expansion gaps. Battering of rail ends can be repaired by in situ welding. It can also be improved by end cropping.

(e) Hogged Rail Joints – De-hogging can be done by de-hogging machines. Dehogging of rail ends can be done by Measured Shovel packing. In this method the joint sleepers are normally packed to a specified height above the normal, taking into consideration the dip at the joint and voids below the sleepers, leaving the shoulder sleepers without packing. After allowing traffic for about two days, the shoulder sleepers are packed without lifting them. De-hogging is effected by traffic passing over the joints. Use of repressed fish-plates helps in improving the hogged joints. Hogging can also be eliminated by cropping the rail ends. 

(f) Broken Fish-plates – Broken or cracked fishplates must be replaced with new or reconditioned fish-plates.

(g) Cracked or Broken Rail ends – The fish bolt and bond holes at rail ends weaken the rails. When maintenance is poor, rail end fractures occur, the fractures almost always starting as a fine crack from the fish bolt or bond holes. During lubrication of rail joints, opportunity should be taken to observe the rail ends carefully for any fine cracks. If cracks are noticed rails should be replaced. Chamfering of bolt holes and bond holes should be done. Ultrasonic testing of rails helps in detecting the cracks which are difficult to detect by visual examination.

(h) Pumping of Joints – Immediately after the monsoon, the ballast at such joints
should be removed. Sand blanketing should be provided on the top layer of the formation which will prevent upward rise of clay slurry. On top of this blanket clean and adequate ballast should be put. Cross drains should be provided between first and second shoulder sleepers. Geotextiles can also be advantageously used.

Other important points regarding joint maintenance –
(a) Gap survey should be undertaken periodically and gap adjusted
(b) Use of wooden sleepers at fish-plated joints, on a metal sleepered road, is desirable.
(c) Ordinary fish-plated track could be converted into three rail panel, wherever all other conditions for SWR are satisfied.

Chamfering of bolt holes in rails-

(a) General :

(i) Chamfering of bolt holes work hardens the periphery of holes and thereby delays the formation of star cracks. The chamfering of hole takes 5 minutes per hole. Each drilled hole shall be chamfered.

(ii) Existing bolt holes in fracture prone zones should be chamfered if not elongated. In case of elongated holes, the chamfering bit will not be in contact with the full edge of the bolt holes and there will be uneven hardening of the metal resulting in stress concentration in weaker-zones. Therefore, such portion of rail should be removed; holes should be drilled and chamfered.

(b) Equipment for chamfering of bolt holes:

Work hardening of bolt holes should be done with chamfering kit of approved make. The chamfering kit consists of the following: Equipment (as per Fig.1) Qty.

(i) High tensile bolt M-20 1 No.
 (ii) High tensile nut for M-20 bolt 1 No.
(iii) Sets of 2 H.S.S. chamfering bits 1 set
(iv) 19mm sq. drive sockets size 32mm 8 Nos.
(v) Set of 2 packing pieces (sleeves) 1 set
(vi) T-400 torque-wrench with built-in ratchet Mechanism 1.25m length 1 No.

(d) Procedure for chamfering of bolt holes:

(i) The nut of high tensile steel bolt is removed and one packing piece is inserted in the shank followed by one side of the H.S.S. chamfering bit.
(ii) The high tensile steel bolt is inserted with 2 pieces in the rail hole.
(iii) On the other face of the rail hole, the second half of the HSS chamfering bit is inserted over the shank followed by the second packing piece.
(iv) The nut on the high tensile steel bolt is replaced.
(v) Pre-set torque-wrench on nut at torque value of 52 Kg-m equivalent to an axial force of 12.5 tonnes, is applied. The nut is tightened with the torque wrench. As soon as the preset torque is attained, the torque wrench will automatically trip indicating complete tightening to preset torque value.
(vi) The nut by reversing the torque wrench is unscrewed and HTS bolt is removed. The process is repeated on other rail holes.

(e) Chamfering of each hole should be done under the supervision of Mate/Keyman.

Lubrication of Rail Joints –

(1) The purpose of lubricating rail joints is not only to facilitate expansion of rails but also to retard wear on the fishing planes of the rail and the fish plate. Reduced wear on the fishing planes is one of the preventives of the low joints.

(2) The lubricant to be used should be specified by the Chief Engineer. A stiff paste of plumbago (Graphite) and kerosene oil, made in the proportion of 3 Kg. of plumbago to 2 Kg. of kerosene oil may be used. Black oil or reclaimed oil may be used for fish bolts and nuts. Alternatives to the above may be used, with the specific approval of Chief Engineer.

(3) All rail joints should normally be lubricated once a year on a programmed basis during the cold weather months after the monsoon, from October to February. Lubrication should not be carried out in extremes of weather both hot and cold. In yards this period may be extended to 2 years with the approval of the Chief Engineer.

(4) Creep in excess of 150 mm. should be adjusted before the work of lubrication of rail joints is undertaken.

(5) The lubrication of rail joints should normally be carried out by gangs working under the direct supervision of at least a qualified Permanent Way Mistry. The work should be carried out under caution orders arranged to be issued daily by the Permanent Way Inspector and under protection of engineering signals. In this case the procedure to be followed for lubrication of rail joints will be as follows:

(i) The nuts are unscrewed and the fish bolts and fish-plates are removed.
(ii) The fishing surfaces of the fish-plates and rail are then cleaned with a wire brush.
(iii) The rail ends are inspected for cracks, and the fishing surfaces of rails and fishplates are checked for wear. A magnifying glass and a mirror should be used for detecting cracks in rail ends and fish-plates.
(iv) The fishing surfaces of the rails and fish-plates are then lubricated.
(v) The fish bolts are then put back in reverse position and tightened using a standard fish bolt spanner, the inner two bolts being tightened first.
(vi) While tightening overstraining of bolts shall be avoided.
(vii) Spare fish-plates and bolts should be available for replacement of cracked ones.

(6) Alternatively, the work of lubrication may be carried out by the Keymen of the gang, assisted by one or more men on such sections as may be specified by the Divisional Engineer. In such cases the Keymen shall exhibit a red signal flag at the site of the work and act as lookout man also. Normally not more than one joint should be opened at a time under this procedure. In this case the lubrication of rail joints and reversing of fish bolts should be carried out as follows:

(i) The nuts are unscrewed and the fish-plate on the nut-side is then removed leaving the other fish plate and bolts in position.
(ii) The fishing surfaces of the fish-plate and the rails are cleaned with a wire brush. The rails ends are examined for cracks and fishing planes of rails and fish-plates for wear, a mirror and a magnifying glass should be used to detect cracks. Such conditions shall be brought to the notice of Permanent Way Mate/Mistry for
necessary action. The fishplates are lubricated and put back in position.
(iii) The fish bolts are taken out one at a time, and then put back, after oiling.
(iv) The other fish-plate and fishing surface of the rail is treated similarly.
(v) The nuts are replaced and tightened to the extent possible with the standard fish bolt spanner without overstraining the bolts.
(vi) Two joints opposite each other or consecutive joints shall not be opened out at the same time. It should be particularly noted that at no time during the operation there is less than one fishplate and three fish bolts without nuts connecting the two rails. The men should sit facing the direction of train while doing the work.
(vii) Both fish-plates should be fixed and at least one fish bolt and nut on either side of each joint should be tightened when a train is approaching the site of Work.
(viii) Spa re fish-plates and bolts should be carried for renewal of cracked ones. 

(7) The Chief Engineer may issue subsidiary instructions as necessary.

(8) The lengths over which the rail joints are lubricated together with dates shall be recorded in the gang chart of the section and in the Permanent Way Inspector’s section register. In the month of April, Permanent Way Inspectors should submit to the Assistant Engineers certificates of lubrication of rail joints giving reasons for any exception. Copies of these certificates should be forwarded with the Assistant Engineer’s comments to the Divisional Engineer for scrutiny and record.

(9) During all works such as relaying, rail renewals and renewals of turnouts, etc. rail joints should be lubricated. The imp. of going over and re-tightening the bolts after the fish-plates have taken a bearing under traffic should be impressed on the staff. 

(10) Insulated fish-plates should not be greased.

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