FIELD OF INVENTION
The invention generally relates to the field of precision manufacturing procedure
for obtaining flat-faced elliptical section including process of manufacturing flat-
faced tubes and apparatuses therefor. More particularly, the present invention
relates to a device and method for producing a consistently and precisely
flattened tube loop on a tubular section in a single pressing.
BRIEF DESCRIPTION OF THE INVENTION
Usually elliptical shaped or flat-faced tube is derived from a circular shaped tube
by suitable forming technique. Then this flattened tube is used in panel type heat
exchangers, where it is joined to flat heat transfer surfaces.
Many heat exchangers use flat-faced tubes for heat transfer applications, whence
the fluid flowing through the tube absorbs heat energy from the surface or
supplies heat energy to the flat surface to which they are attached to. Usually
such flat tubes are attached to a flat surface by a conventional joining process
like brazing or soldering or welding to form heat exchanger panels. For better
heat exchange efficiency between the flattened surface of the tube and the sheet
surface a very precise flat surface contact has to be ensured.
Flat surfaces on tubular section can be obtained either by mechanical flattening
of a cylindrical tube or by manufacturing a square or rectangular section tubes or
by machining the curved surface to attain a flat surface. Of the above three
processes, mechanical flattening is the most sought after and economical,
though the degree of flatness achievable in the other two methods are inherently
superior. So it is mostly the quality of flatness of the surface that is achievable
that decides the employability of mechanical flattening process. Different
techniques of tube flattening therefore focus on improving the quality by
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reducing the attendant side effects of flattening, specifically wrinkling or
buckling. Tube flattening or forming is normally achieved by one of the different
methods described below. In one method, fine Sawdust power is packed inside
the tube and the tube ends are closed with the temporary end plugs. After
mechanically forming the tube, the end plugs are cut and the sawdust powder is
removed by poking and blowing compressed air. Another method uses Sieved
sand that is packed inside the tube. The tube ends are closed with temporary
end plugs. After forming the tube, the end plugs are cut and poking and blowing
of compressed air removes the sieved sand. In yet another method, low-melting
rigid plastic compound is poured inside the tube to be flattened and the ends are
closed with rigid end plugs. Then tube is flattened or formed. After forming the
tube is heated till the plastic melts and by blowing compressed air the plastic
material is removed. Alternately, Lead shots mixed with the sieved sand are
packed inside the tube and the ends are closed with temporary end plugs. After
forming the tube, the end plugs are cut and poking and blowing of compressed
air removes the sieved sand and the lead shots. Another method employs a
Gupolan compound consisting of a hardener and resin that is properly mixed and
poured inside the tube to be formed and allowed to solidify. Then tube is
flattened or formed. After forming the entire assembly is kept in hot water bath
so that the filler material is melted out and removed from the flattened tube.
The above processes however suffer from failures to establish a perfect flat
surface. This is more so when thin walled tubes are flattened. Dumbbell shape is
formed irrespective of filler material used especially when wall thickness of the
tube is very less; say below 2mm.
On the other hand, use of rectangular shaped tubes for the above purpose has
the following problem. Camber at the central face of the rectangular tube, which
gets generated during rolling process, is generally not suitable for the heat
exchangers due to lesser percentage of area contact for the given shape.
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Secondly, flow through such tubes will not be uniform clue to stagnating flow at
the corners. Rectangular tubes are costlier then the circular tubes to
manufacture. Forming of multiple loops, i.e. bending to circular radii will be very
difficult. Rectangular shaped tubes normally not employed in high-pressure
application.
Certain special applications catering to Nuclear industry, Space research etc.,
may not permit use of sand as filler material. In certain cases (multiple bend
panels) removal of filler material will be very difficult after flattening process is
over. Lead shot filler material produces indentation marks on the inside surface
of the tubes on critical bend locations. All the above processes in addition also
have some limitation on the minimum achievable flattening height.
Further US patent no. 6,032,501 discusses a method of obtaining multi-lateral
(walled) members from round tubes, employing fluid pressure as well a specially
designed cavity die. This patent describes a process that is substantially forming
oriented, ie. involving plastic flow of metal & forcing such metal to required
shapes using specially designed cavity dies as in a moulding process, thereby a
lot cumbersome to configure and difficult to practice and thus substantially
costlier on the whole. Additionally the specific aspects of avoiding stress
concentrations at corners are not effectively addressed in this said US patent.
Further, the method described in the US patent No. 6,032,501 needs specific die
for each and every unique shape of the panel pressed. Moreover US pat. #
6,032,501 is suitable only for open-ended tubes.
OBJECTS OF THE INVENTION
An object of the invention is to provide a device and method for producing a
consistently and precisely flattened tube loop on a tubular section in a single
processing.
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Another object of the invention is to provide a device and method for producing
a consistently and precisely flattened tube loop on a tubular section in a single
processing which eliminates dumbbell formation at the center of flattened
surfaces.
A further object of the present invention is to provide a device and method for
producing a consistently and precisely flattened tube loop on a tubular section in
a single processing which does not employ any specially designed complicated
dies for each and every shape, thereby simple to configure and substantially
cheaper.
A still further object of the present invention is to provide a device and method
for producing a consistently and precisely flattened tube loop on a tubular
section in a single processing which sufficiently addresses the problem of stress
concentrations at corners of the tubes.
An yet another object of the present invention is to provide a device and method
for producing a consistently and precisely flattened tube loop on a tubular
section in a single processing which respectively uses a flat bed and a plate at
the bottom and top of the device enabling precise surface flattening of a plurality
of tube panels.
An yet further object of the present invention is to provide a device and method
for producing a consistently and precisely flattened tube loop on a tubular
section in a single processing which simultaneously employs mechanical force
from outside and hydraulic force from within in the form of high pressure liquid.
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SUMMERY OF THE INVENTION
Accordingly there is provided a tube flattening device having at least one tube
releasably disposed thereon for surface flattening, the device comprising: at least
one end plug removably insertable at one end of the at least one tube; a fluid-
pressurizing pump connected to the other end of the at least one tube via a
flexible hose, the flexible hose being provided with a pressure gauge and an
isolation cum pressure regulation valve; a flat bed to accommodate the at least
one tube such that a major portion of the flattenable surface being covered by
the flat bed; a flat rigid top plate connected to a hydraulic ram being movable on
the at least one tube in registration with the movement of the hydraulic ram. The
at least one tube is filled over the entire length with a pressurized fluid by means
of the fluid-pressurizing pump followed by sealing of the built-up pressure via
closing of the isolation-cum-pressure regulating valve. The hydraulic ram in
association with the top plate flattening the fluid-fitted at least one tube. A
plurality of stopper pieces disposed over the at least one tube in a spaced-apart
relationship such that the movement of the top plate is being controlled to
configure the desired flattened end of the at least one tube.
The method of production of flat-faced tubes and tube panels according to the
invention results in very high precision (higher percentage) flat surface on a
single pressing. Specifically, this invention uses a high-pressure liquid, as filler
material to achieve such high flatness over a very large sized tube panels.
Particularly this method is unique in its efficacy of flattening multi looped large
sized panels in one go.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 - Shows a dumbbell-shape formation on a tube section during pressuring
according to prior art.
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Fig. 2 - shows a very large size tube section formed with multi-loop
configuration according to the present invention
Fig. 3 and 4 - shows the device according to the invention for tube-flattening
Fig 5 - shows a sectional view of the flattened tube configured according to the
invention.
DETAILED DESCRIPTION OF THE PREFERED EMBODIMENT OF THE
INVENTION
The invention is described in greater detail with reference to the accompanying
drawings referred herein. Fig. (3 & 4) shows tube-flattening setup with pumping
arrangement Fig. (5) shows sectional view of flattened tube so achieved. Fig. 1.
shows formation of dumbbell shape on the tube wall according to prior art
method. Fig. 2. depicts a typical tube panel used for high-precision jobs having
large size and multiple loop panels. The device for tube flattening has the
following components. Circular loop tube (1) to be flattened is fitted with
pressure-tight but easily removable end plug (2) on one end and the other end is
connected through a flexible hose (3) to a hydraulic system comprising a
hydraulic pump (4), a pressure regulating cum isolation valve (5), and a pressure
gauge (6) to control and monitor the actual pressure during tube flattening.
The tube (1), either in a single piece or as a bent coil is kept on a flat bed (7),
which accommodates a major portion of the tube to be flattened. Stopper pieces
(8) are placed in between the loops at a number places such that during
flattening, the movement of a flat rigid top plate (9) fitted to a hydraulic ram
(10) is controlled to the flattened end upto the needed tube height.
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The tube (1) is pressurized to a suitable pressure using the pump (4) that fills a
pressurized fluid like water throughout the tube length. To seal the pressure, the
valve (5) is closed. Then the top plate (9) fitted to the ram (10) is slowly lowered
down. This movement is continued till the stopper pieces (8) resist the
movement. During this process the fluid filled tube is flattened by the top plate
(9) in association with the hydraulic ram (10). The ram (10) is then released to
allow the flattened tube thus produced to be taken out.
The fluid pressure is to be so maintained such that a perfect flat face is achieved
and at the same time preventing formation of 'Dumb Bell' shape and/or wrinkles.
For a tube wall thickness range of 0.5 mm to 2 mm a pressure range of 3 bars to
15 bars is recommended as optimal Till-up' pressure.
A tube-flattening device of the present invention can be used for any tube with
wall thickness lesser than the range indicated with ease and at appropriate lesser
'fill up' pressure.
The device of the invention is further capable to accommodate any tube panel
having a large span with any complicated shaped loop structure, such large tube
panels can also be flattened within desired flatness on the entire surface of the
tube panel in one single sequence.
The device can be employed for the manufacture of ornamental tubular
applications by adapting contoured flat bed (7) and top plate (9).
The device of the invention including the tube flattening method can be
employed for achieving any surface flattening or surface contouring of tubes,
wherein such tubes could be of any wall thickness below 2mm employing any
suitable fluid including water, mineral oil, organic compounds like glycerine,
glycol, etc. said fluid pressurized to any pressure in the range of 3 bar to 15 bar.
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The tubes are kept between a flat bed (7) or any contoured bed, and a top plate
(9) or any matching contoured plate, and plates are pressed together by a
hydraulic ram (10) or any other adaptable forcing mechanism.
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WE CLAIM
1. A tube flattening device having at least one tube (1) releasably disposed
thereon for surface flattening, the device comprising:
- at least one end plug (2) removably insertable at one end of the
at least one tube (1);
- a fluid-pressurizing pump (4) connected to the other end of the
at least one tube (1) via a flexible hose (3), the flexible hose (3)
being provided with a pressure gange (6) and an isolation cum
pressure regulation valve (5);
- a flat bed (7) to accommodate the at least one tube (1) such that a
major portion of the flattenable surface being covered by the flat
bed (7);
- a flat rigid top plate (9) connected to a hydraulic ram (10) being
movable on the at least one tube (1) in registration with the
movement of the hydraulic ram (10), characterized in that the
at least one tube (1) is filled over the entire length with a
pressurized fluid by means of the fluid-pressurizing pump (4)
followed by sealing of the built-up pressure via closing of the
isolation-cum-pressure regulating valve (5), the hydraulic ram (10)
in association with the top plate (9) flattening the fluid-fitted at least
one tube (1), and in that a plurality of stopper pieces (8) plates
disposed over the at least one tube (1) in a spaced-apart
relationship such that the movement of the top plate (9) is being
controlled to configure the desired flattened end of the at least one
tube (1).
2. The device as claimed in claim 1, wherein said pressurized fluid is selected
from a group comprising water, mineral oils, organic compounds like
glycerin, glycol.
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3. The device as claimed in claim 1, wherein the fluid is pressurized between
3 bar to 15 bar.
4. The device as claimed in claim 1, wherein said flat bed (7) and said top
plate (9) are contoured to match the desired flattered end of the at least
one loop (1).
5. The device as claimed in any of the preceding claims, wherein the wall
thickness of the at least one tube is below 2.0 mm.
6. A method for tube flattening in a tube flattening device as claimed in
claims 1 to 5, comprising the steps of:

- placing the tube (1) between a flat bed (7) or a contoured bed, and
a top plate (9) or a correspondingly configured plate, the tube
being equipped with an end plug (2);
- providing a plurality of equidistantly disposed stopper pieces (8) in
registration with configurable height of the flattened tube;
- supplying a pressurized fluid into the tube (1) by means of a pump
(4) having a control value (5) to achieve a flat surface; and
- a forcing means (10) causing the top plate (9) or the
correspondingly configured contoured plate to pressurize the tube
(1) on the flat bed (7) or the contoured bed till the tube (1) gets
flattened to the configurable height.
7. The method as claimed in claim 6, wherein the pump (4) and the control
valve (5) are employed corresponding to the span size and the contour of
the tube loop (1).
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12-
8. The method as claimed in claim 6, wherein the flat bed (7) and the top
cover (9) are configurable such that orhamental tubular loop can be
developed.
9. A tube flattening device having at least one tube releasably disposed
thereon for surface flattening as substantially herein described and
illustrated with reference to the accompanying drawings.
10. A method for tube flattening in a tube flattening as substantially herein
described and illustrated with reference to the accompanying drawings.

Accordingly there is provided a tube flattening device having atleast one tube
releasably disposed thereon for surface flattening, the device comprising: at least
one end plug removably insertable at one end of the atleast one tube; a fluid-
pressurizing pump connected to the other end of the atlesat one tube via a
flexible hose, the flexible hose being provided with a pressure gauge and an
isolation cum pressure regulation valve; a flat bed to accommodate the atleast
one tube such that a major portion of the flattenable surface being covered by
the flat bed; a fiat rigid top plate connected to a hydraulic ram being movabfe on
the atleast one tube in registration with the movement of the hydraulic ram. The
atieast one tube is filled over the entire length with a pressurized fluid by means
of the fluid-pressurizing pump followed by sealing of the built-up pressure via
Closing of the isolation-cum-pressure regulating valve. The hydraulic ram in
association with the top plate flattening the fluid-fitted atleast one tube. A
plurality of stopper pieces disposed over the atleast one tube in a spaced-apart
relationship such that the movement of the top plate is being controlled to
configure the desired flattened end of the atieast one tube.
The method of production of flat-faced tubes and tube panels according to the
Invention results in very high precision (higher percentage) flat surface on a
single pressing. Specifically, this invention uses a high-pressure liquid, as filler
material to achieve such high flatness over a very large sized tube panefs.
Particularly this method is unique in its efficacy of flattening multi looped large
sized panels in one go-