Flash butt welding

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Mobile Flash Butt Welding Of Rail
s
Kuldeep Singh
Sr.ADEN/SIR

2. TABLE OF CONTENT
 Mobile Flash Butt Welding
 Uses of Mobile Flash Butt Welding
 Various Options in Mobile Flash Butt Welding
 Staff Requirement for Mobile Flash Butt welding
 Mobile Flash Butt Welding Procedure
 Pre Welding Checks
 Actual Welding Procedure
 Testing of Welds
 Precautions in Mobile Flash Butt Welding
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3. Mobile Flash Butt Welding
 Mobile Flash Butt Welding is a Rail cum Road Machine. M
obile Flash Butt Welding Plant is a four wheeled mobile ve
hicle, which can travel on roads with rubberised wheels an
d on rails with metal wheels in which the following are fitt
ed:
 Welding Equipment
 Welding Parameter Recorder
 Separate units for Grinding & USFD Testing Equipment
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4. Various Options in Mobile Flash Butt Welding
 FIXED SITE DEPOTS
 MOBILE DEPOTS
 MOBILE FBW PLANT
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5. Actual Welding Procedure at Depot
 Clamping the rail ends: The mobile flash butt welding machine is lowered fro
m the vehicle and the rail ends which are close together are clamped. The The rai
l ends are then brought together so that almost touch each other to create the fla
sh. The longitudinal and vertical alignment of the rail is corrected by suitable adj
ustments of the machine.
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The rail ends being clamped by the welding machine

6. The rail ends being clamped by the welding mach
ine at Depot
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7. Post straightening & Ultrasonic Testing at Dep
ot
 Post straightening: The rails are post straightened mec
hanically to remove horizontal and vertical kinks so as to gi
ve perfect alignment in both directions.
 Ultrasonic Testing: The welded rails are then ultrasonicall
y tested with normal 70° and 45° probes.
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8. Mobile Flash Butt Welding Plant moving on trac
k
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9. Unloading the welding Equipment from the vehicle Model
FBW-24 Made in India Thermit Corporation
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10. Unloading the welding Equipment from the vehicle Model K-900
Made In India Thermit Corp. Ltd.
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11. Uses of Mobile Flash Butt Welding
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1. The basic use of the Mobile Flash Butt Welding is to use
2. the flash butt welding technique in field which otherwise can
not be done using the static plant. The Mobile Flash Butt Wel
ding is preferable as the welds have much better fatigue stren
gth and performance as compared to the AT welding otherwi
se used.
3. It is basically used for the following purposes:
4. In construction works for converting free rails or 3 rail panels
(which is the maximum possible to be laid in new lines due t
o transportation constraints)to LWR.
5. In open Line for Through Weld renewal to replace welds whi
ch have completed their life

12. Staff Requirement for Mobile Flash Butt welding
 The Welding team may consist of one Supervisor and two
welders. The educational qualification of the Supervisor sh
ould be minimum Diploma in Mechanical / Electrical Engg
. or B.Sc and that of welder should be minimum Class X or
equivalent pass. Zonal Railways should ensure periodic trai
ning of welders on Mobile Flash Butt Welding Plant. The c
ompetency certificate of welder of Mobile Flash Butt Weldi
ng Plant is issued by the Zonal Railways.
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13. The Supervisor and Welder of the Plant should have acquaintan
ce in knowledge of the following.
 Welding parameters and its influence on quality of welding and heat af
fected zone
 Suitability of rails for welding
 Preparation of rails to be welded including pre straightening of rails
 Procedure of welding of rails
 Record of welds
 Post weld straightening of rails
 Finishing of joints
 Marking of joints
 Testing of welds
 Precautions to avoid defects in rail joints
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14. Mobile Flash Butt Welding Procedure
 There are three basic mechanisms in the machine:
 CLAMPING MECHANISM
 FORGING MECHANISM
 TRANSFORMER
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15. Basic Principle of Flash Butt Welding
 The basic principle is that heat is generated by electric resis
tance method at the ends of two rails to be welded which w
ere firmly clamped into the jaws of the welding machine. B
oth the jaws of the machine are movable and as such, the g
ap between the two rail ends can be adjusted.
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16. Straightening & Cleaning of rail ends
 Straightening of rails : The rails ends are required to be st
raightened with the help of hydraulic rams before welding s
o as to get good alignment of the welded rail .
 Cleaning of rail ends: The rail ends shall be cleaned using
grinders to get clean surface.
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17. Inspection of Rail ends
 A thorough inspection of rail ends shall be carried out and
the deviation of vertical and horizontal misalignment shou
ld be within the tolerable limits as given below:
 Individual welded ends may have a maximum difference in
height of 1.2 mm as in case of second hand rails.
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18. If the rail wear is not equal, the grouping of rails so that maximum dif
ference of height does not exceed 1.2 mm shall be done as shown in
figure
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19. Welding of second hand rails
 Second hand rails within the following limit of tolerance can
also be welded using Mobile Flash Butt Welding:
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Rail New Rail Second hand Rail
60Kg 172.00 mm 164 mm
52Kg 156.00 mm 150 mm
90R 142.88 mm 139 mm
Rail New Rail (Lateral ) Second hand Rail (w
ear)
60Kg 72.00 mm 66 mm
52Kg 67.00 mm 61 mm
90R 66.68 mm 61mm
The tolerance on the end bends in the vertical plane should be (+) 0
.7mm and (-) 0.0mm on a straight edge of 1.5 m.

20. Tolerances for rail in vertical plane
 The tolerance on the end bends in the horizontal plane s
hould be (+) or (-) 0.7mm
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21. Tolerances specified for rail ends
 The dimensions of the head width of rail should be check
ed and should be less than 0.5 mm deviation
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22. Rail head checking gauge for 60Kg rail
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23. Tolerances for rail ends
 The rail ends shall be cut vertically and these shall be as
per tolerances given below:
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24. Setting up the flash
 The rails are brought towards each other till the flash starts. Th
e flash will lead to heat generation which will soften the steel.
 The electric energy is switched on and thereby allowing and el
ectric current of about 5 volts and 35,000 Amperes to pass bet
ween interfaces of two rails. Lot of flashing takes place and co
nsiderable heat is generated by the passage of electric current
between the rail ends.
 The rail ends are moved to and fro automatically by the machi
ne till the temperature rises to the fusion limits in the range of
1000° C to 1500° C.
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25. Work Starting in track
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26. Flashing for welding
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27. Applying force
 The rail ends are then hydraulically pressed so that the s
oftened rail ends fuse together to form weld.
 At this juncture, the rail ends are pressed together with
an upset pressure of about 37 T.
 The final flashing takes place joining the two rail ends t
ogether. The welding is so regulated that any steel that
might have been oxidized during the heating process ge
ts completely squeezed out.
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28. Applying hydraulic force at Depot
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29. Stripping the weld
 As soon the rails are welded, they are made to pass
through a stripping Unit where all the extra metal
called upsets is chipped off. The removal of metal
by stripping is so good that except the head no oth
er portion require any finishing.
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30. Weld completed
 The average time taken for welding a joint is about 7 to 8 minutes per j
oint and No. of joints that can be welded is about 40 to 50 joints per 8
hrs shift.
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31. Grinding rail ends
 The rail table and gauge face of the joints thus welded, are finally ground t
o correct rail profile, by means of a trolley grinder for the rail table and by
pneumatic grinders for other portions.
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32. Weld numbering and identification
 Weld recorder: The machine has a weld recorder which measures and stores the weld
ing parameters. The results are stored in machine and can be retrieved later on also.
Print out can also be obtained of the welding parameters which can be used as perm
anent record. The following parameters are recorded (figures in brackets are standar
d values):
 Testing of Welds
 Pre Flash Time (47 sec)
 Flash Time (95 sec)
 Boost Time (07 sec)
 Up set Time (1.8 sec)
 Forge Time (2 sec)
 Current Set (190 – 280 Amps)
 Forge Force (38 – 65 Tons)
 Up set Rail Use (12.7 mm)
 Welding parameters will depend on section and metallurgy of rail to be welded. The
se are, normally, specified by the manufacturer of the plant. Before adoption, the wel
ding parameters shall be got approved from RDSO. RDSO shall consider parameters
suggested by the manufacturer while fixing the parameters.
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Each weld shall be given a number so as to identify the weld, welder and correlati
on can be established between the field weld and the weld record.

33. Testing of Flash Butt Welded Joints
 Hardness Test: Brinnel hardness test shall be conducted on the test
weld sample before conducting transverse load test. The hardness
value in HAZ shall not vary from the hardness of the parent rail by
more than + 20 HB. Results shall be maintained as per proforma gi
ven in Annexure – VI C.
 Extent of heat affected zone (max value in mm)
 Head
 38 mm
 Web
 39 mm
 Foot
 36 mm
 The results of tests shall be maintained.
 VALUES OF MINIMUM BREAKING LOAD AND DEFLECTION IN
TRANSVERSE
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34. Testing Frequency of Flash Butt Welded Joints
 “Sample joints for first 1000 Joints welded by a Mobile Flash butt welding p
lant will be tested at a frequency of 1 in 100 joints and subsequently at a fre
quency of 1 in 500 joints.” As Per RDSO Manual
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Rail section S Span Min. Breakin
g Load (tone
s)
Min. Deflec
tion At cent
re(mm)
Frequency of testing
Stationary &
plant
Mobile FBW
P
60 Kg. (UIC) NHH 1.25m 115 30 1 IN 500 1 in 100
60 Kg (UIC) Cr. Mn. Allo
y steel
1.25m 110 12 1 IN 500 1 in 100
60 Kg (UIC) (90 UTS) 1 m 150 20 1 IN 1000 1 in 100
52 kg. 90 UTS 1 m 100 15 1 IN 1000 1 in 100
60 Kg (UIC) MM (72 UT
S)
1 m 135 30 1 IN 1000 1 in 100
52 Kg MM (72 UTS) 1 m 100 30 1 IN 1000 1 in 100

35. Testing of Flash Butt Welded Joints
 Macro Examination test: One test joint for every 1000 joints weld
ed in case of mobile flash butt welding plant shall be subjected to
macro examination. 150 mm length of rail with weld at centre sha
ll be cut and the sample shall be sectioned in vertical, longitudina
l directions through the weld. One of the sections shall be etched
with 5 – 10% Nitric acid and also subjected to magna flux test to
ensure freedom fro cracks, lack of fusion or oxide inclusion. Exte
nt of heat affected zone shall be measured for head, foot and we
b of the rail. These values should not be more than the values ac
hieved during standardization of welding parameters of the partic
ular rail section and chemistry of particular make of FBW Plant.
Results shall be maintained as per performa.
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Tolerance after Final Welds Position
A. Welds with new Rails
(i) Vertical misalignment: +0.3mm at the centre of a 1m - 0 mm strai
ght edge.
(ii) Lateral misalignment: +0.3mm at the centre of a 1m straight edg
e.
(iii) Head Finishing (in width) Side of rail head should be finished to:
+- 0.25 mm on gauge side at the centre of
10 cm straight edge.
(iv) Fishing of top table surfac
e
+ 0.2mm at the centre of 10 cm straight ed
ge -0.0mm
(v) Web zone (underside hea
d, web, top of base ,both f
illet each side)
+-3.0 mm of the parent contour –0 mm

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Tolerance after Final Welds Position
B. Welds with Old Rails
(i) Vertical misalignment: +-0.5mm at the centre of a 1m straight edg
e.
(ii) Lateral misalignment: +-0.5mm at the centre of a 1m straight edg
e.
(iii) Head Finishing (in sides) +-0.3 mm on the gauge side at the centre o
f a 10 cm straight edge.
(iv) Head finishing ( on top tab
le surface)
+- 0.2mm on the gauge side at the centre o
f 10 cm straight edge
(v) Web zone (underside hea
d, web, top of base ,both f
illet each side)
+ 3.0 mm
- 0.0 mm of parent contour –0 mm

38. Precautions in Mobile Flash Butt Welding
 End squareness of rail faces must be ensured. Better weld strength with minimum value and m
erely parallel shape of heat affecting zone can be achieved using perfect matching of rail ends.
 Secondary out put of current should be sufficient enough to achieve complete fusion of butting
faces.
 Butting stroke should be sufficient for complete coalescence (not less than 12 mm)
 Throughout Uniform and smooth auto trimming of the squeezed out metal and complete grind
ing using profile grinder.
 Minimum and nearly parallel heat affected zone of the joint should be achieved.
 Facilities for auto recording of weld parameters including final butting pressure shall be availa
ble.
 When weld is carried out in situ, minimum 20 minutes time after trimming is required to pass t
he first train through the weld with proper packing and support below the joint.
 Track should be levelled.
 Excess butting pressure leads to high joints. These are strictly prohibited and shall be closely m
onitored by trained departmental staff.
 To avoid buckling of track, the continuous welding is prohibited in skeleton track and a gap sho
uld be left at every 500 m interval which will be used for destressing. (In new line works)
 Night welding and welding during rainy session to be avoided as far as possible for obtaining be
tter results.
 Target should not be fixed more than 40 joints per working day in order to keep sufficient time
gap before moving allowing the machine over the newly welded joints.(In new line works)
 Computer printout has to be obtained for each weld just after the execution in order to rectify t
he variations in various parameters as recommended before commencement of the next joint..
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39. 39
The different options have their own advantages & disadvantages:
S.
N.
FIXED SITE DEPOTS MOBILE DEPOTS MOBILE FBW PLAN
T
1 Panels can be made at one
point only. Transportation
has to be done.
At convenient locations, the depots ca
n be setup and the panels will require t
o be transported from this location onl
y
Plant moves and reaches
every point of welding.
2 Time for welding is less. Ti
me for transportation of pa
nels maximum.
Time for welding is min but setting up
of plants takes some time at each locati
on. Transportation of panels takes less
er time.
Time for welding maxim
um as plant to be setup f
or each weld. No transpo
rtation of panels.
3 Suitable for smaller lengths
of track where one set up c
an serve the entire stretch i
n construction as well as o
pen line.
Suitable for construction projects if the
welding work to form panels is to be d
one in parallel with the other works. In
open line, suitable for TWR and the pl
ant can be setup near any level crossin
g or approachable location.
Suitable for construction
projects if the track poss
ession can be given for t
he plant to work. Work
will commence only afte
r the rails are laid on co
mpleted formation.

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