FIELD OF THE INVENTION
The present invention generally relates to a process for upsetting of seamless
tubes made of carbon steels, alloy steels, stainless steels for power boiler
applications. More particularly, the invention relates to a method of heating tube
ends by using induction coil inline and integrated with a swaging and upsetting
hydraulic press.
BACKGROUND OF THE INVENTION
In manufacturing of super-heater or re-heater coils for sub-critical or super-
critical power boilers, various materials of tubes are used at various levels across
the length of the coils depending on the temperature and pressure. As the
material changes from higher grade to lower grade, at a particular location, the
thickness used for the lower grade is higher and for the higher grade is lower. To

weld the tubes with lower wall thickness to the higher wall thickness, the
thickness of lower wall has to be matched with higher wall thickness. The
upsetting process is employed to attain a higher wall thickness, in the tube end
having lower wall thickness, where it is welded with the next tube. As a
substitute for upsetting, according to prior art, a small tube known as "tube
insert" with higher wall thickness, is machined in such a way that one end
matches with the lower wall thickness and other end matches with the higher
wall thickness tube. This increases the quantum of welds and also an additional
insert is introduced into the circuit, which is not desirable. Hence, the inventors
recognized that if the wall thickness of the tube with lower wall thickness can be
increased by upsetting at its end, it can avoid "tube inserts" and reduce the
quantum of welds. While upsetting of tubes according to prior art, where the
heating is done outside the machine, it has been observed the temperature falls
below the forging temperature by the time the mandrel approaches the tube,
resulting in tube failures in the upset portion.
Upsetting of tube ends is a metal forming process involving thickening of the
tube wall on one or both ends of the tube utilizing a mandrel in a hydraulically
operated ram.
In order to perform upsetting of tube ends, the tube ends to be heated to a
temperature where the metal attains a plastic state, fit for deformation. The
heated tube is then gripped in a die and a force is applied on the heated end
through a mandrel connected to the hydraulically operated ram, to get the
desired wall thickening.
The upsetting process of tube ends for various industrial applications are known
in the art. However, heating the tube separately and then positioning between
the clamping dies, clamping it, involves a time lag resulting in drop in
temperatures before the tube end is subjected to upsetting. The effect of this
time lag is not brought out, in prior art. Due to the drop in temperature, the
metal tends to stiffen and the application of force becomes either inadequate to

achieve the desired wall thickening or the tube wall fails through development of
microscopic cracks or often the mandrel gets stuck inside the tube ultimately
damaging the tube or the mandrel. The prior art mainly deals with the upsetting
method rather than the heating technique before the upsetting is done and its
effects.
Figure 1 shows an outline sketch of the machine (with modification now
incorporated), which is basically a horizontal hydraulic press designed to perform
swaging and upsetting of tuber ends. The upsetting process requires the tube
end to be heated to a forging temperature and swaging process does not
require heating. According to the prior art, the tube when heated separately
outside the machine, the time taken to insert the tube through the cavity of
clamping dies and gripping it for upsetting resulted in drop in temperature. If the
temperature falls below the forging temperature, then the tube either does not
yield properly or liable to crack under the force by the mandrel. Sometimes the
upset mandrel gets stuck inside the tube and breaks while retracting.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method for rapid heating
of tube ends to produce improved weld-joint between the tube ends, which
eliminates the disadvantages of prior art.
Another object of the invention is to propose a method for rapid heating of tube
ends to produce improved weld-joints between the tube ends, which provides an
improved heating technique to enable the tube ends to be heated inside the
swagging and upsetting the machine to avoid cooling down of the tube ends
before upsetting operation.
A further object of the invention is to propose a method for rapid heating of tube
ends to produce improved weld-joints between the tube ends, which is capable
of producing an improved product.

SUMMARY OF THE INVENTION
The rate of cooling of metal at higher temperatures is rapid. Therefore it is
essential that the tube ends are to be subjected to upsetting at the quickest
possible time before there is any drop in temperature. Since the drop in
temperature due to time lag has a deterioratory effect on the final quality of the
upset end, the present invention provides a method by which the time lag can be
reduced. Accordingly, the invention improves the quality of the product and ease
of handling.
According to the invention, the tube end is heated by means of an induction coil
mounted on a swagging an upsetting machine, inline with the axis of the tube,
and clamping a die and an upset mandrel. The tube end is heated, after inserting
it into the induction coil, to a preset temperature by switching on the power of
the induction coil. On attaining the preset temperature, the tube is pushed into
the clamping die without any delay by the upset mandrel. The tube is clamped
and the mandrel moves further to complete the upsetting and retracts
immediately. By this process, the time lag is reduced to a few seconds, wherein
the temperature drop is minimized.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: shows an outline sketch of a swaging and upsetting machine indicating
the positions of the tube, the upsetting mandrel and the induction coil.
Figure 2: shows an arrangement of the induction coil and its movement relative
to position of the tube and the upset mandrel.
Figure 3 to 10: illustrates a sequence of operation followed in the machine for
upsetting of the tube end.
Figure 11: shows the tube with a thicker wall at the tube end, subsequent to the
upsetting operation.
DETAILED DESCRIPTION OF THE INVENTION
As illustrated in Figure 1, an induction coil (1) which is the main heating source is
provided adjacent and close to the area where upsetting is done. The induction
coil (1) is in line with the axis of the tube (2), a clamping die (3) and a mandrel
(4). Figure 2 provides the details of an induction coil mounting frame (5) with a
HF transformer (6). The induction coil (1) can be moved up and down, forward
and reverse by means of a screw rod (SR) and hand wheel (HW) arrangement.
Hence, during the swaging operation, the induction coil (1) can be moved away
from the axis of the tube (XI). During upsetting operation, the induction coil (1)
can be moved into position in line with the axis (XI) of the tube (2).
Figures 3-10 provides the sequence of operation for upsetting of tube ends.
The sequence is as follows:
Figure 3 - The tube (2) is inserted through the clamping jaws (3) which are in
open position. The clamping jaws are provided with high temperature resistant
pads (7) in the zone where it comes in contact with the heated tube ends. The
end of the tube (2) is positioned in such a way that the portion of the tube end
to be heated is within the width of the induction coil (1). The upset mandrel (4)
initially is in retracted position. The power switch for the induction coil is in the
OFF mode as indicated by (8).
Figure 4 - The power is switched ON (indicated by 9) for the induction coil. The
portion of the tube within the width of the induction coil is heated. The heating is
done for a pre-set time, which is determined through trials done earlier, to attain
the forging temperature, for a particular tube diameter, thickness and material.
Figure 5 - Once the tube end attains the forging temperature OFF for the
induction coil. The upset mandrel advances. The front portion of the mandrel
inserts through the tube and the step provided on the mandrel which is equal to
the outside diameter of the tube touches the end of the tube.

Figure 6 - The mandrel advances pushing the tube backward and positions the
tube end to coincide with the edge of the clamping jaws. The distance to which
the mandrel has to advance is programmable in the machine. The movement
and stopping is automatic.
Figure 7 - As the mandrel stops, the clamping jaws close, gripping the tube. This
is also done automatically through a position sensor.
Figure 8 - The mandrel advances further providing the necessary force to
compress the heated portion of the tube wall. The metal flows into the annular
space between the inside diameter of the tube and the mandrel portion inserted
inside the tube. The amount of length reduction determines the amount of wall
thickening. The length by which the mandrel has to advance is pre-programmed
in the machine. The mandrel stops after it has advanced by the pre-programmed
length.
Figure 9 - The mandrel is quickly retracted to the home position before the
temperature drops.
Figure 10 - The clamping jaws are opened and the tube is released and
withdrawn.
Figure 11 - The tube with the upset end with desired wall thickening.
EXAMPLES / PREFERRED EMBODIMENT
The clamping dies and upsetting mandrels for tube diameters 51mm and
63.5mm were made. The tubes tested for thickening of tube diameter 51mm and
wall thickness of 7.1mm of stainless steel SA213 - 347H. Several trials were
done successfully with upset lengths varying from 47mm to 53mm.
Similarly using the clamping dies and upsetting mandrel for tube diameter of 63-
5mm, tubes with all thickness of 8mm were thickened to 12.5mm of stainless
steel SA213 - 347H. Several trials were done successfully with upset lengths of
40mm.

WE CLAIM:
1. A method for rapid heating of tube ends to produce improved weld-joint
between the tube ends, comprising the steps of:
providing a swaging and upsetting machine comprising clamping
jaws, with cavities, a plurality of high temperature-resistant pads
provided to the clamping jaws, an upsetting mandrel to apply force
on the heated end of a tube, a mounting frame having a screw rod
and wheel arrangement, a high frequency transformer, and an
induction coil;
inserting the tube through the clamping jaws when in open
position, the tube end being positioned to be adjacent to the
induction coil;
switching on the induction coil through the transformer and heating
the tube end to a forging temperature;
switching off the induction coil and activating the upsetting mandrel
to advance and push the tube backward till a programmed time
period elapses, the mandrel being deactivated after the initial
pushing;

allowing the clamping jaws to grip the tube upon stoppage of
mandrel movement;
reactivating the mandrel to further advance and provide force to
compress the heated portion of the tube ends during a period
predetermined depending upon material composition, the desired
reduction of length and wall thickness; and
deactivating the upsetting mandrel and retracting the mandle at
home position.
2. A method for rapid heating of tube ends to produce improved weld-joint
between the tube ends, substantially as herein described and as illustrated in the
accompanying drawings.

1. A method for rapid heating of tube ends to produce improved weld-joint
between the tube ends, comprising the steps of: providing a swaging and
upsetting machine comprising clamping jaws, with cavities, a plurality of high
temperature-resistant pads provided to the clamping jaws, an upsetting mandrel
to apply force on the heated end of a tube, a mounting frame having a screw
rod and wheel arrangement, a high frequency transformer, and an induction coil;
inserting the tube through the clamping jaws when in open position, the tube
end being positioned to be adjacent to the induction coil; switching on the
induction coil through the transformer and heating the tube end to a forging
temperature; switching off the induction coil and activating the upsetting
mandrel to advance and push the tube backward till a programmed time period
elapses, the mandrel being deactivated after the initial pushing; allowing the
clamping jaws to grip the tube upon stoppage of mandrel movement;
reactivating the mandrel to further advance and provide force to compress the
heated portion of the tube ends during a period predetermined depending upon
material composition, the desired reduction of length and wall thickness; and
deactivating the upsetting mandrel and retracting the mandle at home position.