Flash butt welding of rails

1. Flash-Butt Welding
The welding process is in principle a regulated electric short
circuit with the two rail ends functioning as D.C. poles. The
high current produces an arc between the rails ends, the two
rail cross-sections are heated to melting temperature due to
the high input of current.

2. • During the following upset stroke the rails are pressed
together under high pressure causing the ends to coalesce.
The upset metal is trimmed off immediately after the upset
stroke.
• The result is an accurate weld without filler metal with a very
small heat-affected zone and a more or less consistent
progression of the hardening process with a favorable crystal-
line structure.

3. Preparing the weld – the slight inclination

4. Principle of Flash Butt Welding of Rails
I. One end of the joint begins moving towards the other.
II. Voltage is applied but current is not yet flowing.
III. When high spots touch current and rapidly molts the metal at the point of contact.
IV. The high current causes rapid expansion which expels the molten metal.
V. Heat is also conducted into the area around the point of contact.
VI. As the joints keep closing, the next two high spots touch to allow current to flow.
VII. As flashing continues, perhaps hundreds of flashes, the joint area is heated.
VIII. At the end of the flashing cycle the joint area is at forged welding temperature, ready for
‘butting’.
IX. Because the largest proportion of material is in the rail head, this cools down far more
slowly. The natural consequence is a depression of the rail in the area of the welded joint.
X. However, this result would have very negative effects on the track geometry and the
operational safety. For this reason, a slight upward inclination of the two rail ends is
performed, adapted to the respective rail profile, so that an ideal position of the rail is
achieved when the weld has cooled down.

5. Flash Butt Welding & Alumino Thermic Welding
a) Alumino Thermic Welding
– Strength of AT joint is app. only 56% of parent rail.
– More prone to corrosion.
– High failure rate.
– Poor Quality of Weld.
b) Flash Butt Welding
– Strength of FB joint is almost equal to parent rail.
– Less prone to corrosion
– Failure rate < 10 %.
– Excellent Quality of Weld. The defects like porosity,
inclusions and lack of fusion are eliminated.

6. Mobile Flash butt welding Machine
I. It is rail cum road machine that can be driven to site.
II. The mobile Flash butt welding machines are either
built in Standard railway vehicle or as containerized
units.
III. In case of m/c built on Railway Vehicle the welding
head is Positioned between the bogies and can be
lowered for welding in running track.
IV. The containerized units can be used for welding in
track or on cess on the other hand the standard
vehicle machine can be used only on running line.
V. New machine is fully computerized.
VI. Once the welding head is in position, the entire
process is carried out automatically at the push of
button.

7. Welding Parameters
– Welding Current,
– Upset force Pressure,
– Displacement,
– Welding time,
– Programmed identification
and setting details.

8. Procedure Approval Tests
I. Weld alignment.
II. Weld Trimming.
III. Weld appearance.
IV. Non-Destructive testing.
V. Bend testing.
VI. Hardness testing.
VII. Macro Examination.
VIII.Statements of the result and procedures.
IX. Maintenance of the records.

9. Related Standard
• BS EN 14587-2 – Railway applications. Track.
Flash butt welding of rails.
Prepared By-Sujit Sen, Kolkata(India).
Thank You