FIELD OF INVENTION
The present invention generally relates to the field of welding engineering. More
particularly, the invention relates to an improved process for flash butt welding
of BOILERtubes. The invention further relates to an improved flash butt welding
system for welding of thick-walled boiler tubes.
BACKGROUND OF THE INVENTION
In the prior art there are many methods of welding the tube to tube joints. One
of the popular welding method is the Flash butt welding process. In this process,
the tubes to be welded are clamped on the machine, and an electric current is
passed between them. The joint gets heated up due to resistance heating and
once the edges are sufficiently heated, an upsetting force is applied and the joint
gets welded. The problem here is to ensure that an uniform heat energy
distribution takes place during the flashing cycle, which is indeed difficult. As a
result, in the majority of the cases, most of the time, weld defects occur in the
joint interface. Thus, a need exists to provide a technical solution to this prior art
problem, for example, the lack of uniform heat distribution throughout the
surface of the faying edges during the solid state welding of boiler tubes.
United States Patent 4417121 disclosesan apparatus and method for solid state
welding of machine components. According to the cited invention, the parts to
be welded together are caused to continuously approach each other and their
ends are fused by an alternating current, and concurrently an oscillatory motion
along the direction of approach is imparted to one of the parts, whereby additional relative movements of the parts towards and away from each other
are accomplished. During the stage of a relative movement of the parts being
welded together away from each other, the welding voltage is reduced to within
a range of 0.7 to 0.0 of its working value, and during the stage of a relative
movement of the parts towards each other, the voltage is restored to its initial
value. Reducing the voltage is carried out in a time interval of not less than 1/8
of the period of the oscillatory motion from the beginning of the relative
movement of the parts away from each other, and restoring it, in a time interval
of not more than 1/8 of the period of the oscillatory motion from the beginning
of the relative movement of the parts towards each other. The voltage may be
reduced to within the same range for the periods when the resistance across the
contacts exceedsa predetermined value.
In gist, the cited reference disclose one of the improved flash butt welding
machine where the movement of the components towards each other is done in
an oscillatory manner.
United States Patent 6294752 describes a method of flash-butt welding in which
the travel speed (Vt) of the machine mobile plate and the welding voltage (U2)
are changed (by preset programs) and the travel speed is controlled through a
negative feedback by the welding current. The voltage is simultaneously changed
discretely for each flashing at a fixed interval of tm which is a function of the
increment of the actual average speed of the parameters of shortening (Va)
during the previous flashing interval. The Va value is maintained at the preset
level, which is lower than Vm• The cited invention enVisages a change of the
coefficient of enhancement of the negative feedback in a discrete manner for each preset flashing interval of to, as a function of Va increment during the
previous flashing interval. The invention further adapts an increased value of Uz
and a decrease of the coefficient of negative feedback to the set value until the
speed has reached the set value of speed Vf at which the upsetting is switched
on. Alternatively, Uzis increased after the set value of Qm has been reached, and
the coefficient of negative feedback is decreased to the set value, these values
remaining constant until the upsetting is switched on.
In gist, according to this cited patent, the travel speed is controlled by a negative
feedback by the welding current.
United States Patent 4159408 describes a continuous flash butt welding
machine. According to the cited invention, a continuous flash butt-welding
machine is supplied with power from a mobile diesel-generator power plant, and
comprises a rectifier-charger, the input of which is connected to the dieselgenerator.
The machine has a storage battery provided with a charge-discharge
sensing element connected to the rectifier-charger. The machine also has an
inverter with a unit for controlling the frequency and amplitude of the voltage at
the inverter output. The inverter is connected to the welding transformers and to
a current transducer. A control unit is connected to the charge-discharge sensing
element, the current transducer and a flashing value sensing element. The cited
invention makes it possible to reduce the installed power of the diesel-electric
units of mobile power plants and thereby, to increase the life of the diesel
engines and the thermal efficiency of the welding process. In gist, this cited patent deals about supplying power to the flash butt welding
through an inverter.
OBJECTS OF INVENTION
It is therefore an object of the present invention to propose an improved Flash
butt welding system for welding of boiler tubes which ensures uniform heat
distribution at the faying edges.
Another object of the invention is to propose an improved Flash butt welding
system for welding of boiler tubes, which is capable of introducing an arc
rotation by means of at least two permanent magnets.
A still another object of the invention is to propose an improved Flash butt
welding system for welding of boiler tubes, which ensures a uniform and
consistent weld joint between the tubes and solid rods.
Yet another object of the invention is to propose an improved Flash butt welding
system for welding of boiler tubes, which achieves a defect free tube to tube
joints.
A further object of this invention is to propose an improved Flash butt welding
system for welding of boiler tubes, which reduces the cycle time for welding as
comparedto the conventional flash butt welding. A still further object of the invention is to propose an improved Flash butt
welding system for welding of boiler tubes, which reduces the flashing cycles and
introduces an arc rotation which interalia reduces the total energy consumption.
Yet further object of the invention is to propose an improved process for flash
butt welding of boiler tubes.
SUMMARY OF THE INVENTION
According to the invention there is prOVidedan improved flash butt welding
(FBW) system and a process for welding of boiler tubes.
Thus, the present invention discloses an improved Flash butt welding system
which ensures uniform heat distribution at the faying edges. The system employs
an arc rotation by the interaction between a set of permanent circular magnets,
and the welding current is then passed between the tubes to be welded. The
system and process of the invention achieves uniform and consistent weld joint
between the tubes and solid rods, which produces a substantially defect free
tube to tube joints.
According to another aspect of the invention, the cycle time for welding is
reduced as compared to the conventional flash butt welding, and the flashing
cycles are eliminated, and the total energy consumption is reduced by
introducing the arc rotation. The process of the tube joints maintains a high
efficiency (time of welding of tube of 46 mm 00 6 mm wall thickness is approx.
35 s), and achieves narrow heat-affected zones (3-5 mm). Metal structure is fine grained in the joint zone and no grain coarsening is found. The strength and
ductility properties of the welding joints is almost at the level of the base metal.
According to a further aspect of the invention, in the tube joint, there will not be
any pores, extraneous inclusions or other volume defects typical for fusion
welding processes.The system and process maintains an insignificant dimension
(not more than half of the pipe wall thickness) of the outer and inner
reinforcement which is uniformly distributed around the perimeter of the tubes
being welded. According to the invention, it is easy for control and monitor the
welding parameters. The improved FBW machine lends itself easily to
automation and that the improved FBWmachine does not require a highly skilled
operator.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Fig 1 shows an improved FBWwelding system.
DETAILED DESCRIPTION OF THE INVENTION
As shown in Fig. 1 according to the invention, the improved FBW system
comprises a welder unit (1), a welding power source (2), a Pumping unit (3), a
Controller (4), and a remote controller unit (5). The welding power source (2)
prOVidesthe welding current. The pumping unit (3) gives necessary force for
clamping the weldable components including an upsetting force. A set of
permanent magnets (6) provide the arc rotation. The controller (4) controls the
timing and sequence of the welding process. Additionally, the set of magnets (6) makes the arc to rotate around the periphery of the tubes. After heating by the
arc rotation, after a preset time, a defect - free weld joint is achieved by
upsetting.
An improved flash butt (IFB) welding is a pressure butt welding technique where
the heat is generated prior to the forging of the weldable component by a rapid
movement of an arc over the ends of the weldments by a magnetic field. The arc
is drawn between the adjacent ends of the two weldments and is rotated around
the weld line by a force (F) resulting from the interaction of a welding current (I)
and a magnetic field (B). At least two constant magnets (6) of opposite polarity
are arranged and the radial component of magnetic induction gives the required
field. Arc initiation, arc rotation, upsetting are controlled in a sequence by a set
of timers in the process controller unit (4). During the upsetting, a high current
pulse is given to get a good quality weld.
WE CLAIM
1. An improved flash butt welding (FBW) system for welding of boiler tubes
in particular thick-walled boiler tubes, comprising:
- a welder unit (1) connected to a welding power source (2) which
provides the welding current;
- a pumping unit (3) supplying the necessary hydraulic force to
clamp the weldable tubes on the welder unit (1);
- at least two permanent magnets (6) of opposite polarity are
arranged in order to rotate an welding arc which is generated
between the weldable boiler tubes;
- a controller (4) controlling the timing and sequence of welding; and
- a remote controller unit (5) for controlling the welding parameters
from a remote location.
2. An improved process for flash butt welding of boiler tubes in an improved
flash butt welding (FBW) system, the process comprising the steps of :
- providing an improved flash butt welding (FBW) system;
clamping the weldable boiler tubes by using a hydraulic force
provided by the system on an welder unit of the system;
- providing the welding current from a welding power source to the
welder unit of the system;
- generating an arc over the ends of the weldments, and rotating the
arc around the adjacent ends of the weldments by utilizing a
magnetic field created by at least two permanent magnets;
- controlling the timing and sequence of welding by utilizing a
controller and/or a remote controller; and
generating an upsetting force by said pumping unit through
transmitting a high current pulse to remove extra materials around
the weld-joint.
3. An improved flash butt welding (FBW) system for welding of boiler tubes
in particular thick-walled boiler tubes, as substantially described and
illustrated herein with reference to the accompanying drawings.
4. An improved process for flash butt welding of boiler tubes in an improved
flash butt welding (FBW) system, as substantially described and illustrated
herein with reference to the accompanying drawings.