Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Method for forming a tubular body, undulating tubular body and use of same
According to a first aspect, the present invention relates to a method for
forming a tubular
body. According to another aspect, the invention relates to a meandering
tubular body
produced by such a method. According to another aspect, the invention relates
to the use
of a tubular body of this kind.
Forming tubular bodies is a widely known process. After being produced,
tubular bodies
are generally in an elongate, substantially uncurved form. However, since
tubular bodies
are not used only along straight delivery sections in practice, the
installation locations
may sometimes require fluids to be delivered along curved paths, e.g. around
corners, by
means of tubular bodies, and it is not always possible or desirable to use
branch lines,
flanged-on pipe elbows and the like in these situations, there is, on the one
hand, the
need to be able to bend tubular bodies, by means of forming for instance. On
the other
hand, there is a need to be able to form tubular bodies in respect of their
cross-sectional
shape in order to be able to lay them through predefined opening cross
sections or to be
able to shape the cross section of the tubular bodies as closely as possible
to
predetermined opening cross sections. The latter is significant especially
when using the
tubular bodies as cooling elements in order to be able to achieve the best
possible heat
transfer between the tubular body and the body to be cooled.
One particular challenge when forming tubular bodies is to prevent collapse or
buckling of
the tubular body or unwanted deformation of the tubular body in some other way
and to
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obtain only the deformation which is intended in the forming process. To
achieve this,
sand is used as a filler in the prior art. The sand fills the internal cross
section of the
tubular body and prevents collapse or unwanted indentation of the tubular body
during
forming, given an adequate packing density.
Even if this method is feasible for simple forming processes, such as the
production of
individual bending radii or the production of non-circular cross sections of
the tube, there
is the problem, in the case of more complex forming processes, such as the
production of
meandering tubular bodies, that it may no longer be possible to remove the
sand
completely from the tubular body after the forming process. Consequently, it
is not
possible in the prior art to produce complex tubular body shapes, such as
meandering
tubular bodies, in one piece.
In the German patent application on which priority is based, the German Patent
and
Trademark Office identified the following documents: DE 694 02 051 T2, DE 196
16 484
A1, EP 0 099 714 A1, DE 199 52 508 A1 and DE 10 2010 018 162 B3.
It was therefore the underlying object of the invention to indicate a method
for forming
tubular bodies which as far as possible eliminates the disadvantages described
above. In
particular, it was the underlying object of the invention to indicate a method
for forming
tubular bodies which allows higher flexibility for complexity in forming.
The invention achieves the underlying object in the case of a method of the
type
designated at the outset by means of the features of Claim 1. In particular,
the method
according to the invention has the following steps: making available a tubular
body having
a first and a second tube end, filling the tubular body with a liquid,
preferably water,
closing the tubular body, and forming the tubular body. The invention makes
use of the
insight that water can be removed from the tubular body without leaving
residues after the
forming of said body, especially in the liquid or gaseous state, irrespective
of the
complexity of the tubular body, as long as one end or preferably both tube
ends are
opened again after forming. Moreover, the invention makes use of the fact that
liquids,
such as water or suitable oils, can be compressed only with difficulty and
therefore
ensure adequate stabilization of the internal tube volume, despite being in
the liquid state,
if the tube is completely filled and closed.
In a particularly preferred development of the method, this method furthermore
comprises
the following step: pressurizing the liquid in the tubular body before the
forming step.
Through the pressurization of the liquid, the liquid is as it were preloaded.
Physically
speaking, liquids are not completely incompressible. However, it has been
found that
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sufficient incompressibility or sufficiently low compressibility for the
purposes of the
method according to the invention is available when using water, and this can
be even
further improved by subjecting the water to pressure before forming.
Pressurization as it
were provides an indicator of the complete filling of the tubular body. One
particular
advantage associated with pressurization is the following: if a leak, e.g. in
the form of a
crack, develops during the forming of the tubular body, the pressurized liquid
would
immediately escape from the interior of the tubular body. This escape would be
easy to
detect. Thus, pressure checking can simultaneously be performed during
forming. If no
liquid escapes until the forming process is complete, the operator knows
immediately that
the tube is pressure tight at least up to the pressure to which the tubular
body has
previously been subjected from the inside. This represents a significant
economic
advantage.
The liquid is preferably subjected to a pressure of 20 bar or more,
particularly preferably
in a range of from 50 bar to 200 bar.
In a preferred embodiment of the method, the forming step comprises
introducing one or
more bending radii into the tube. In brief, the advantage of using liquid as
an internal
stabilizer is all the more effective, the more complex is the geometry of the
tubular body
and consequently the more bending radii are introduced into the tube.
In another preferred embodiment, the bending radius or at least one of the
plurality of
bending radii, preferably a plurality of the bending radii or all of the
bending radii, is/are
less than three times the tube diameter. Whereas, in the case of conventional
tube
bending methods in the prior art, a minimum bending radius of about five times
down to a
maximum of easily three times the tube diameter is taken as a basis, the
method
according to the invention allows significantly greater bending owing to the
use of liquid,
in particular pressurized liquid, as an internal stabilizer, and this results
in significantly
tighter possible bending radii. In preferred embodiments, the achievable
bending radius is
in a range of from less than three times the tube diameter to about twice the
tube
diameter, wherein, as before, the bending radius also depends, as is known, on
the
material used for the tubular body and especially on the wall thickness
thereof. In the
case of a tube with a diameter of 12 mm, a wall thickness of 1 mm and
stainless steel as
a material, the abovementioned bending radii can be achieved, for example.
In another preferred embodiment of the method, the forming step comprises:
changing
the tube cross section of one or more segments of the tubular body or of the
entire
tubular body, preferably to a substantially polygonal cross-sectional shape,
particularly
preferably to a substantially rectangular shape. A substantially polygonal or
substantially
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rectangular shape is taken to mean that the angularity of the cross section is
within the
range of what is technically possible. If a tube cross section is deformed in
such a way by
means of forming that it has one or more edges which give the cross section a
polygonal,
in particular rectangular, shape overall, it must be expected that a small
edge radius will
remain on the inside and on the outside. This can be ignored for purposes of
understanding the concept of the substantially polygonal or substantially
rectangular
cross-sectional shape.
Changing the tubular cross section into a substantially polygonal or
substantially
rectangular cross-sectional shape is preferably achieved by placing a segment
or
segments of the tubular body or the complete tubular body in a die and then
forming it to
match the die by the application of force. According to the invention, force
is applied
either externally to the die or the tubular body and/or by means of the die
itself, which
acts in the manner of a punch, for example. According to the invention, there
is a
preference, for example, for deforming the tubular body by means of a punch or
a roll, by
means of levelling rolls for instance.
In another embodiment, the method is developed in that a plurality of bending
radii is
introduced into the tubular body and in that the forming step furthermore
comprises:
bending the tube into a meandering shape, wherein the meandering shape has one
or
more substantially uncurved tube segments, which each adjoin one or more of
the
bending radii.
As another preferred option, the method comprises the following step:
discharging liquid
from the tubular body, preferably by means of a pressure relief valve, if the
pressure
exceeds a predetermined value during forming. This is preferably carried out
by closing at
least one of the ends of the tubular body using an excess pressure limiter
valve, which
discharges liquid whenever the pressure rises significantly, preferably by 1
to 10% or
more, owing to the progress of forming. The following is thereby achieved:
when
changing the tube cross section by applying force from the outside, the volume
of the
tubular body is sometimes reduced. To ensure that the liquid medium escaping
from that
segment of the tubular body which has just been deformed does not cause
bulging or
unwanted deformation of the tubular body at some other point, liquid is
selectively
discharged according to this embodiment in order to keep the pressure in the
tubular
body substantially constant. Depending on the design of the tubular body,
different limit
values can be defined here. At a wall thickness of 1 mm and with stainless
steel as a
material, a limit value for the pressure limit of about 50 bar has proven
appropriate, for
example.
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In another preferred embodiment of the method according to the invention, said
method
furthermore comprises the following step: monitoring the liquid pressure
during forming,
preferably by means of a pressure sensor. Apart from the fact that visual
monitoring of
the liquid pressure can, of course, take place through observation of the
pressure relief
valve, there can also be a preference for quantitative detection of the
pressure rise within
the tubular body for the sake of more accurate control of the forming process,
and a
widely known pressure measuring transducer is preferably used for this
purpose.
The method according to the invention has proven itself especially also with
tubular
bodies which are formed by a steel material, in particular stainless steel or
structural
steel.
According to the second aspect of the invention, the underlying object of the
invention
was to indicate a tubular body which is suitable for cooling a generator,
wherein the
generator is used for producing an electric current, in particular in the form
of a multi-pole
synchronous generator of a wind power plant.
The invention achieves the object in that the tubular body is designed with
the features of
Claim 12. In particular, the meandering tubular body has a plurality of
bending radii,
preferably with a bending radius of less than three times the tube diameter,
and a plurality
of substantially uncurved segments, which adjoin the bending radii, preferably
without
kinks, wherein at least one, preferably a plurality or all, of the
substantially uncurved
segments has/have a substantially rectangular cross section.
Where substantially uncurved segments of the tubular body are referred to
above and
below, this is to be taken to mean that the tubular body is designed to be
free from
curves, i.e. straight, in these segments or at least has so little curvature
that it can be
introduced into the groove of the generator and preferably rests there against
the
opposite walls of the groove in order to allow heat transfer. If there is a
slight curvature in
the direction of the depth of the groove, the curvature is insignificant here.
According to
the invention, even if there is a slight curvature transversely to the depth
of the groove,
i.e. in a direction toward the groove walls or away from them, a substantially
uncurved
segment is assumed if the segment can be moved into the groove by elastic
deformation.
The tubular body according to the invention preferably has a wall thickness in
a range
between 0.5 and 3.5 mm, particularly preferably in a range of from 1-2 mm.
As another preferred option, the tubular body according to the invention is
formed by a
steel material, in particular stainless steel or structural steel. Admittedly,
there are
materials which allow significantly greater changes in shape owing to higher
ductility, e.g.
copper tubes. However, the preference according to the invention is to design
the tubular
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body with the minimum possible electrical conductivity, especially for use in
a generator
for producing electric current. Fundamentally, the tubular body in its
meandering shape
also acts like a coil and, during the operation of the generator, when the
pole shoes are
moved past the grooves provided with the meander, can cause power losses or
interference fields, it being possible to keep these low by a suitable choice
of material.
Thus, according to the third aspect, the invention relates to the use of a
meandering
tubular body according to one of the embodiments described above in a
generator.
In particular, the invention achieves the object of implementing the cooling
of the
generator by means which are as economical as possible and of allowing coolant
to be
carried as far as possible without leakage.
Given the above considerations, the use of the meandering tubular body
according to one
of the preferred embodiments described above is particularly preferred because
the
tubular body has (implicitly) already been checked for pressure-tightness
during the
production thereof.
According to the invention, the meandering tubular body is particularly
preferably used in
a generator which is designed as a multi-pole synchronous generator of a wind
power
plant. The generator, particularly preferably the stator of the generator, has
a multiplicity
of grooves, in which a winding, which is preferably the stator winding, is
arranged. The
plurality of substantially uncurved tube segments of substantially rectangular
cross
section of the tubular body is introduced into the grooves. When cooling
liquid then flows
through the tubular body, the heat produced by the stator winding can be
dissipated
directly from the groove and, at the same time, the development of heat in the
stator can
be stemmed.
In the case of a synchronous ring generator of a gearless wind power plant,
the term
"multi-pole" is taken to refer to a multiplicity of stator poles, in
particular a design having
at least 48 stator teeth, often even with significantly more stator teeth, in
particular 96
stator teeth or even more stator teeth. The magnetically active region of the
generator,
namely both of the rotor, which can also be referred to as an armature, and of
the stator
is arranged in an annular region around the axis of rotation of the
synchronous generator.
Thus, in particular, a range of from 0 to at least 50 percent of the radius of
the air gap is
free from materials which carry the electric current or electric field of the
synchronous
generator. In particular, this internal space is completely free and, in
principle, can also be
accessed. This region can often also make up more than 0 to 50 percent of the
air gap
radius, in particular up to 0 to 70 percent or even 0 to 80 percent of the air
gap radius.
Depending on the construction, there may be a supporting structure in this
inner region,
but this can be of axially offset design in some embodiments. By virtue of
their
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functioning, such synchronous generators of a gearless wind power plant are
slowly
rotating generators. Here, the term "slowly rotating" is taken to mean a speed
of less than
40 revolutions per minute, in particular of about 4 to 35 revolutions per
minute, depending
on the size of the plant.
The invention is described in greater detail below by means of preferred
illustrative
embodiments with reference to the attached figures, of which:
Fig. 1 shows a first method state during the production of a meandering
tubular body,
Fig. 2 shows a second method state of the method according to Fig. 1, and
Fig. 3 shows a third method state of the method according to Figures 1 and
2.
In its undeformed state, the tubular body 1 shown in Figures 1-3 has a
substantially
cylindrical cross section and is uncurved, as can be seen in Fig. 1. To
prepare the
forming step, the tubular body 1 is closed pressure tightly in a first end
segment 2 by
means of a closure 3, e.g. a blind plug. A second closure 5 is fitted in an
opposite, second
end segment 4. The second closure 5 is designed as a check valve with an
excess
pressure limiter, for example.
The tubular body 1 is filled with liquid, preferably via the second closure 5,
and
pressurized, e.g. with a pressure in a range of from 50 to 200 bar. The
tubular body is
then closed pressure tightly by means of the optionally provided check valve,
wherein the
optionally provided pressure limiter is designed to discharge liquid from the
interior of the
tubular body 1 if a predetermined pressure within the tubular body 1 is
exceeded.
It is then possible to carry out the forming step with the filled and closed
and preferably
pressurized tubular body 1. In the illustrative embodiment shown, the tubular
body 1 is
first of all placed in a tube bending device 100, as shown in Fig. 1. The tube
bending
device 100 holds a first leg of the tubular body 1 against a stop 101. A lever
103 brings
about the bending of the tubular body 1 around a retention pin 105 in the
direction of the
arrow A. Owing to the filling of the tubular body 1 with the liquid, tube
bending takes place
without the tube cross section collapsing, and a state as shown in Fig. 2 is
achieved when
the bending process is carried out several times.
The tubular body shown in Fig. 2, which is bent in a meandering shape and
represents an
intermediate product of the method of the illustrative embodiment shown, has a
plurality
of substantially uncurved segments 7, which are each arranged adjoining the
bending
radii 9 without kinks.
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Starting from the state shown in Fig. 2, the tube cross sections of the
substantially
uncurved segments 7 are then preferably changed. This is accomplished as shown
in Fig.
3 by placing the substantially uncurved segments 7 successively in a die 203
of a
punching device 200. The die 203 consists of two parallel bars, for example,
which
between them define a gap of rectangular cross section, e.g. in the form of a
square with
the slot width C and preferably the same slot depth.
By moving a punch 201 repeatedly up and down in the direction of the arrows B,
the
tubular body 1 is subjected to an external force in the die 203, said force
leading to
deformation in such a way that the tube cross section is shaped to match the
cross
section of the slot.
A pressure-measuring transducer 11, which is designed to monitor the internal
pressure
of the liquid, is preferably arranged on the second closure 5. If a
predetermined pressure
value is exceeded, there is the possibility either of discharging liquid
manually or of
automatic opening of a pressure relief valve if said pressure is exceeded in
order to take
account of the reduction in volume in the interior of the tubular body 1 due
to the change
in shape brought about by the punching device 200.
As can be seen from the above illustrative embodiment, the method according to
the
invention can be used for both the combined bending and the changing of the
shape of
the tube cross section. However, the advantages according to the invention of
stabilizing
the volume of the tubular body 1 by means of, preferably pressurized, liquid
also come
into play in both individual processing steps, i.e. when only bending of the
tube cross
section is taking place or only a change in the shape of the tube cross
section is taking
place. It has been found that the use of water allows adequate stabilization,
and the
environmental compatibility of water is regarded as advantageous for the use
thereof.
As an alternative, the use of oil or the like is likewise envisaged.
