Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invent~on relates to a method of manufacturing
a double-walled tube for transporting solid ~aterials, and also
to a double~walled tube.
Double-walled tubes are used, for example, in mining under-
ground operations for pneumatic transportation of small-piece min-
erals which are brought in the excavated longwall face space as
filling material. Moreover, the double-walled tubes are provided
during hydraulic transportation of sands for use particularly in
the case of excavating works. The properties of the solid mater-
ial to be transported require tubes with a wear-resistant inner
surface having a long service life. On the other hand, the same
tubes must be designed so that they grow under the action of
inner pressure loads and particularly during transportation of
construction materials to the place of use under the action of
rough impact loads. For satisfying both these extreme xequire-
ments, for years double-walled tubes have been utilized in which
a core tube is designed especially for wear loads, whereas a
casing tube is designed for pressure and impact loads~ It is
required that the core tube and the casing tube are fixedly
connected wIth one another. In one proposal for manufacturing
such double-walled tubes the co~e tube is expanded ~:n the casing
tube under the act~on of cold deformation and simultaneously fixed
relative to the outer surface. In another proposed method a tube
is composed of a plurality of steel layers whnse heat expans~on co-
efficient decreases from ins;de outwardly~ In accordance with
another proposed method a glass hard ;`nner layer ~s welded with a
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hardenable tough outer layex to form a two-layer tube. Another
method involves a high-hardened wear-resistant core tube over which
a sheet of a tough non-hardenable metal is bent to form a slotted
casing tube, and the cas;ing tube is f~nally welded along ~ts
longitudinal edges. The cas~ng tu~e is shrunk on the core tube
because of welding and p~ovides for the desired immo~able assembly.
Moreo~er, core tubes of slotted springy wear-resistant steels
are used whose slotted edges prior to the insextion into a casing
tube of a tough steel are overlapped. The slotted core tu~e is
then expanded by the inner pressure and pressed against the casin~
tube, whereas finally the slot edges abut against one another.
A pressure expansion is also possible without longitudinal slots.
The expansion of ~he core tube in the cas~ng tube is carried out
by a respective tool.
Finally, in accordance with another method, a slotted
core tube of a hardenable tube is used whose outer diameter
prior to insertion into a casing tube is greater than the inner
diameter of the casing tube. The slot width and the outer dia-
meter are so determined relative to one another that after the
pressing-in of the core tube, because of radial compression, the
return spring effect provides for firm lying of the core tube in
the caslng tube with tight abutment of the slot edges. After this,
hardening of the core tube takes place, and volume increase result~
ing from the hardening of the core tube no longer presses against
the cas~ng tube~ In addition, there is also a possib;lity to cool
the casing tube similarly, to increase the pressing force.
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The above discussed developments, which have taken place
over several decades, make clear that the experts have not in
practice been able to come to a completely satisfactory concept
for manufacturing a double-walled tube with a wear-free core tube
and a tough casing tube. Allproposals as a whole, regardless of
whether slotted or unslotted tubes are used, deal with a core
tube and a casing tube which are designed such that the outer
diameter of the core tube
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only insignificantly deviates from the inner diameter of the casing tube. Only
by maintenance of these narrow tolerances do the experts see a possibility to
press the core tube in the required manner against the casing tube. The ex-
penditures both related to accurate manufacture of tubes and also to the devices
for insertion of the tubes into one another and hardening are relatively high.
Accordingly, i~ is an object of the present invention to provide a
method of manufacturing a double-walled tube for transporting solid materials,
and a double-walled tube produced thereby, which avoid the disadvantages of the
prior art.
More particularlyl it is an object of the present invention to
provide a method of manufacturing a double-walled tube which has consider-
ably lower manufacturing expenditures as compared with known methods, and
both with respect to the utilized materials and the manufacturing method.
rloreover, it is also an object of the present invention to produce by
this highly advantageous method a suitable double~walled pipe for solid material
transport.
In keeping with these objects and with others which will become
apparent hereinafter, one feature of the present invention rasides, briefly
stated, in that, with consideration of manufacturing tolerances and/or non-
cir~ularity duringmanufacture of the ~ube, the outer diameter of the circum-
ferentially closed core tube is sufficiently smaller than the inner diameter
of the casing tube and/or the inner diameter of the casing tube is sufficiently
greater than the outer diameter of the core tube that the core tube with a
sufficient p]ay can be easily inserted into the casing tube, and the core tube,
under the action of repeatedly following hardening steps with step-like radial
expansion, is brought to firm surface abutment against the inner surface of the
casing tube.
The invention uses the kno~n phenomenon that during hardening of
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suitable carbon steels a volume increase takes place. However it has in un-
predictable manner been found that this volume increase is not limited to one-
time hardening. Moreover, it has been determined in a surprising manner that
an already hardened tube, in the event of further repeated hardening steps,
expands in a further progression and in the sense of its outer diameter con-
tinuously increasing. This unexpected result leads to inventive fea~ures which
are not known in the prior art, that the core tube is fixed in the casing tube
unobjectionably only by hardening, and tubes can be utilized whose manufactur-
ing and/or transporting requirements have great deviations in outer and inner
diameter and/or noncircularity. The invention deals with the assumption that
now also tubes with very high tolerances of simple quali.ty standards can be
used for manufacture of double-walled tubes.
For this purpose, a core tube can be used whose outer diameter is
smaller than the inner diameter of the casing tube by so much that the core
tube can be inserted with sufficient play into the casing tube, or the inner
diameter of the casing tube is held such that an easy problem-free insertion
of the tubes is guaranteed. It is to be understood that both features can be
used in combination.
Even the problem-free insertion of the core tube into the casing tube
can eliminate a lot of known problems during manufacture of the double-walled
tubes for the solid material transport. Further problems are eliminated in
that, exclusively by a repeatedly performed hardening with stepped radial
expansion, the arresting of the core tube in the casing tube takes place and
simultaneously the desired wear-free condition of the core tube is attained.
In accordance with another feature of the present invention, it is
~ossible that the heating tem~eratures of the hardening steps are identical.
In dependence upon the requirements, it is also possible that the heating
temperatures of the hardening steps are different from one another.
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A double-walled tube for transporting of solid materials in accordance
with the invention has a flame-hardened core tube and a casing tube of a tough
material, which are pressed against one another by hardening, wherein in
accordance with the invention with consideration of manufacturing and/or trans-
port requirement tolerances and/or noncirclllarity the outer diameter of the un-
slotted core tube is smaller than the inner diameter of the casing tube) and
under the action of repeated successive hardenings, and thereby acting step-like
radial expansion of the core tube, it is brought to firm adhering surface abut-
ment against the inner surface of the casing tube.
Such a tube is easy to manufacture, since core and casing tubes have
relatively high tolerances, and for connection of the core tube and the casing
tube as well as for manufacturing a wear-free inner surface repeatedly succes-
sive hardening steps are used. In addition to drawn tube, also tube welded by
longitudinal seams or spiral seams can be utili~ed. The tube diameter is in-
significant so that the double tube of greater diameter can be manufactured in
an economical manner. Transport-conditional noncircularity is automatically
eliminated during the tube mounting.
The novel features which are considered characteristic of the present
invention are set forth in particular in the appended claims. The invention it-
self, however, both as to its construction and its method of operation, together
with additional objects and advantages thereof, will be best understood from the
following description of specific embodiments when read in connection with the
accompanying drawlng.
BRIEF DESCRIPTION OF Tl~ DRAWING
Figure 1 is a view showing a vertical section of one sector of a
circumferentially closed double-walled tube after insertion of both tubes into
olle another, but prior to hardening; and
Figure 2 is a view substantially corresponding to the view of Figure
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1, but showing the tube after the hardening.
The drawings partially and schematically show a double-walled pipe 1
which serves for hydraulic or pneumatic transport of solid materials. It has
an inner core tube which is identified with reference numeral 2 and composed of
a hardenable carbon steel, for example C35, and an outer casing tube which is
identified with reference numeral 3 and composed of a tough material, for ex-
ample structural steel. At each end of the tube flanges, not shown, can be
provided.
As can be seen from Figure 1, the dimensions of the core tube 2
and the casing tube 3 are selected such that, with consideration of the manu-
facturing and transport-conditional tolerances and/or noncircularity, the outer
diameter AK of the circumferentially closed or unslotted core tube 2 is dimen-
sioned so much smaller than the inner diameter IM of the casing tube 3, that
the core tube 2 can be inserted with a sufficient play Sp easily into the casing
tube 3. For insertion of the core tube 2 into the casing tube 3 therefore no
special steps or means are required.
After the insertion of the core tube 2 into the casing tube 3, the
core tube 2 is repeatedly successively subjected to hardening steps. As a re-
sult of this, the core tube 2 expands and particularly such that, after an
appropriate number of hardening steps ~which depends on the play Sp between
the core tube 2 and the casing tube 3), the outer surface ~ of the core tube 2
is pressed tightly against the inner surface 5 of the casing tube 3. This is
shown in Figure 2. In this manner, not only the desired wear-free condition
takes place Oll the inner surface 6 of the core tube 2, but also a firmly ad-
hering surface abutment of the core tube 2 against the casing tube 3 is provid-
ed.
It will be understood that each of the elements described above, or
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two or more together, may also find a useful application in other types of con-
structions differing from the types described above.
While the invention has been illustrated and described as embodied
in a double-walled tube, it is not intended to be limited to the details shown,
since various modifications and structural changes may be made without depart-
ing in any way from the spirit of the present invention.
Without further analysis, the foregoing will so fully reveal the
gist of the present invention that others can, by applying eurrent knowledge,
readily adapt it for various applications without omitting features that, from
the standpoint of prior art, fairly constitute essential characteristics of the
generic or specific aspects of this invention.
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