FIELD OF THE INVENTION
The invention relates to application of solid state high frequency generating
source for induction pressure welding of steel tubes. More particularly, the
invention relates to an improved solid state high frequency electronic device in
an induction pressure welding machine for producing quality welding Joints of
boiler tubes.
BACKGROUND OF THE INVENTION
Induction pressure welding (IPW) is a process of joining steel tubes by upsetting
the tube - tube joint at a high temperature just below the melting point of the
material, to form a homogenous structure.
The known IPW machine comprises a motor- alternator set for high frequency
generation at Constant frequency for induction heating. The power capacity of
such motors is very high, and consumes high amount of power. The productivity
of such machines is very less.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved solid state high
frequency electronic device in an induction pressure welding machine for
producing quality welding joints of boiler tubes.

Another object of the invention is to propose an improved solid state high
frequency electronic device in an induction pressure welding machine for
producing quality welding joints of boiler tubes which is enabled to provide
higher productivity.
A further object of the invention is to propose an improved solid state high
frequency electronic device in an induction pressure welding machine for
producing quality welding joints of boiler tubes which substantially eliminates the
power wastage.
SUMMARY OF THE INVENTION
According to the invention solid state inverter produces high frequency electricity
which is used to drive a large alternating current through a work coil to a high
frequency output transformer. The passage of current through the work coil
generates a very intense and rapidly changing magnetic field in the vicinity to the
tube-tube joint, which generates a high temperature just below the melting point
to form a joint.
In the improved IGBT Based Solid State System, it s possible to control the
frequency over a range, depth of penetration of heat & HAZ (Heat Affected
Zone) over the job can be controlled precisely. This system is with PLL (Phase
lock loop) control and hence automatically tune to the resonant frequency within

the pre-mentioned range, thereby reactive power consumption is considerably
reduced & Power Factor Improves. Power is consumed only during welding and
soaking time, remaining time only control elements consumes a very low amount
of power, where as in the old method 70% of the power goes for idle running of
the motor(prime mover) and the remaining 30% only goes for welding process.
The improved machine employs hydraulic system which reduces the setting time.
Process status can be seen through a Human - Machine Interface. The new
machine allows improvement in the Quality of the weld joints.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: Shows a schematic diagram of a motor-alternator set of prior art
IPW - machines.
Figure 2 : Shows a solid state electronic device according to the invention
replacing the motor - alternator set of prior art IPW machines.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
As shown in figure - 1, according to the prior art machines, a control panel is
used for controlling the motor - alternator, field devices, excitation and Power
transmission (1, 3). The motor and Alternator is disposed on a mono-block body
(2) which generates a high frequency. An external capacitor bank increases the

frequency level for different materials (4). A high frequency Output transformer
(5) is provided for a split-type which inductor (6) which heats the metal tube. A
hydraulic power pack (7) for upsetting the solenoid of the upsetting and tube
clamping cylinders which hold the tube. A secondary copper bus bar (8)
connects the output transformer (5) and the inductor (6).
As shown in the figure 2, a converter and inverter panel generates high
frequency in the order of 10KHZ. A Human - Machine Interface (HMI) with a
touch panel (11) is used to program six type of welding parameters and for the
operator interface. An Output HF transformer (5) is connected through a water
cooled co-axial cable to an inductor (12). The Inductor heats a tube (14). A
hydraulic power pack for upsetting and tube clamping cylinders (15). A Control
panel controls the solenoid of the hydraulic motors and clamping and upsetting
cylinders.
The energy transfer to the tube-tube joint to be heated occurs by means of
electromagnetic induction. It is known that in a loop of conductive material, an
alternating current is induced, when this loop is placed in an alternating
magnetic field.
A solid state inverter (10) shown in figure 2, produces a high frequency
electricity which is used to drive a large alternating current through a work coil
(14), through the high frequency output transformer (12). The alternating
magnetic field induces a current flow in the conductive tube-tube joint. The work
coil (14) acts as an electrical transformer in the IPW machine in combination of

the tube-tube joint The work coll acts as a primary coll where electrical energy
is fed in, and the tube-tube joint acts as a single turn secondary coil that is
short-circuited.
This configuration generates a high current to flow through the tube-tube joint.
These are known as eddy currents.
In addition to this, the high frequency used in induction heating applications
gives rise to a phenomenon called skin effed. This skin effed forces the
alternating current to flow in a thin layer towards the surface of the tube-tube
joint This skin effed increases the effective resistance of the metal to the
passage of the large current Therefore it greatly increases the heating effed
caused by the current induced in the tube-tube joint The Skin effed helps to
control the depth of penetration of heat & Heat affeded zone (HAZ) in the
welding processes. With the rise in the frequency, the width of Heat affeded
zone (HAZ) can be reduced precisely. HAZ of the job is equally prone to failure
as like joint Hence by properly tuning the Frequency, the HAZ band an be
reduced, there by weld defed reduces & Quality improves.
The HMI panel (11) used to store different sets of programmed parameters for
different materials, which can be called back for different jobs and it Is also used
as a handheld operator control for the entire system.

According to the invention the Quality of the joints from the IPW Machines is
improved to meet the present standard relating to boiler pressure parts welding
applications. Moreover, a static electronic device with Insulated Gate Bipolar
Transistor is used as a fast acting switch with high current handling capacity to
act as an inverter. The present invention provides a relatively easy and in-
expensive machine to improve productivity and reduce cost.

WE CLAIM:
1. An improved solid state high frequency electronic device in an induction
pressure welding machine (IPW) for producing quality welding joints on
boiler tubes, the device comprising a converter and inverter generating
high frequency power, a human- machine interface incorporated with data
relating to welding parameters adaptable by an operator interface, an
output high frequency transformer connected to an inductor for heating
the weldable boiler tube, and a hydraulic power pack for upsetting and
clamping the solenoids of an upsetting and clamping means, characterized
in that the inverter constitutes a solid state inverter generating high
frequency electricity which electricity is capable to drive a large alternating
current via a work coil to said output high frequency transformer, and in
that the work coil acting as a primary coil of the electrical transformer and
the tube-tube joint acting as a secondary coil of the transformer which is
short-circuited.
2. An improved solid state high frequency electronic device in an induction
pressure welding machine for producing quality welding joints of boiler
tubes substantially as herein described and illustrated with reference to
the accompanying drawings.

The invention relates to induction pressure welding is a process of joining steel
tubes by upsetting the tube - tube joint at a high temperature just below the
melting point of the material, to form a homogeneous structure. The solid state
inverter produces high frequency electricity which is used to drive a large
alternating current through the work coil through high frequency output
transformer. The passage of current through this work coil generates a very
intense and rapidly changing magnetic field in vicinity to the tube-tube joint,
which generates a high temperature just below the melting point to form a joint.
By controlling the frequency, depth of penetration & Heat affected zone of the
tube, the invention allows producing the quality welding joints.