BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 - Shows an embodiment of the apparatus according to the
invention.
Figure 2 - Shows a schematic diagram of the tube to fin welding process.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF
THE INVENTION:
Referring now to the drawings. Wherein like reference numerals designate
identical or corresponding parts throughout the several views. The welded
joint shown in FIG. 1 can be made with the least possible outlay by the
process according to the invention. For the fabrication of gas-tight boiler-
tube walls, the tubes (1) have to be welded to the flat steel fins (2) arranged
in between.
As shown in Fig. 1, to produce boiler membrane panel of tube to fin, one
tube (1) and one fin (2) are fed from the modified spiral fin welding
machine. The tube (1) is fed in the usual way through a plurality set of
rollers (8) and the fin (2) is fed from the conventional uncoiling equipments.
As shown in fig-2, a first copper contact (3) is placed over the tube through
pneumatic pressure and a second copper contact (4) is placed over the fin (2).
The HF current source is connected between the contacts (3,4) to enable heating
between the fin and the tube, the pressure between the fin and the tube being
maintained continuously by a roller guide (7) having slot for locating the fin (2).
By continuously feeding the tube (1) and the fin (2), the longitudinal fin (2) to
the tube (1) welding is achieved. Further, the fin to fin butt welding shall be
carried out by laser hybrid welding.
As shown in figure 1, the fin (2) is fed via the first set of rollers (8) and the tube
(1) is fed through the second set of rollers (8) and allowing the second set of
rollers (8) to come in contact. The tube (1) is fed by the first set of rollers (8) as
shown in fig. 1 and the fin (2) is fed by another set of rollers parallel to the tube
(1), while not touching the tube upon the point of welding zone from the
conventional uncoiling equipments (not shown). A welding station is provided at
which the fins (2) are welded to the tube (1) at welding point. The prior art
techniques of high frequency electrical resistance heating are utilized to provide
the heat necessary to cause the weld at welding point. Sliding contacts or
electrodes are slidingly contacted with the advancing tube (1) and the fins (2) in
advance of the welding point so that the high frequency oscillating current is
passed along the surface of the materials and through the welding point. The
first and second copper contacts (3,4), including a third and fourth copper
contacts (4,6) are connected to a high frequency oscillating current source (not
shown).
For carrying out the welding and for the proper control of the flow of the high
frequency current in advance of the weld point, it is necessary to bring the tube
(1) and the fin (2) together at a sight angle known as V angle. In order to
assure that a good weld is formed at welding point, the fins (2) are held and
guided by rollers (7,8) providing a firm contact with the tube (1) at the weld
point. As best seen in FIG. 2, fins (2) are moved into a line parallel to the axis
of the tube (1) by guiding the rollers (8). A suitable forging pressure is
applied at the point of welding through guide rolls. The third and the fourth
copper contacts (5,6) are provided to facilitate preheating of the fin (2) and
to ensure better deformation and formation of V angle prior to welding point.
The invention thus provides a process for high-frequency longitudinal welding
of a tube to a flat steel fin comprising:
- feeding of atleast one tubes (1) through a set of rollers (8); feeding a steel
flat fin (2) in the longitudinal direction of the tube (1); pressing the tube and
the flat steel fin (2) to be joined against one another; and welding between
the tube (1) and the fin (2) by HF (100-800 KHZ) welding procedure.
WE CLAIM:
1. A process for high frequency longitudinal welding of a tube to a flat
steel fin comprising the steps of:
- feeding of at least one tube (1) through a set of rollers (8);
- feeding a flat steel fin (2) in the longitudinal direction of tube
(1);
- pressing the tube (1) and the flat steel fin (2) against one
another; and
- welding the tube (1) and the fin (2) together by HF (100-800
kHz) welding procedure;
characterized in that,
- the boiler tube (1) is welded to the flat steel fin (2) in a single
operation by positioning a plurality of HF copper contacts (3, 4,
5, 6) over the tube (1) and the fin (2); and
- in that the welding is carried out at a feed rate in the range of
6 m/min-10 m/min & preferably 8 m/min .
2. The process as claimed in claim 1, wherein the magnitude of the feed
rate is selected as a function of a wall thickness of the tube.
3. The process as claimed in claim 1, wherein the welding parameters
are selected in such a way that a non-through welding thickness of
the flat steel fin (2) is at most 0.1 times of the thickness of the flat
steel bar, wherein a sum of weld thicknesses on a top side and an
underside of the joints is at least 0.90 times of the thickness of the flat
steel bar, and wherein a thickness of molten portion of the tube
material is restricted to 1 mm.
4. The process as claimed in claim 1, wherein the welding and bending
of the fin is achieved simultaneously.
5. A process for high-frequency longitudinal welding of a tube (1) to a
flat steel fin (2) as substantially described herein with reference to the accompany drawings.

A process for high-frequency longitudinal welding of a tube to a flat steel fin Comprising:
- feeding of at least one tubes (1) through a set of rollers (8); feeding a steel flat fin
(2) in the longitudinal direction of the tube (1); pressing the tube and the flat steel fin (2) to be joined against one another; and welding between the tube (1) and the fin (2) by HF (100-800 KHZ) welding procedure,
Characterized in that the boiler tube (1) is welded to the fin (2) in a single operation.