An Improved Method of Bending Metal Pipes, and Apparatus therefor.
Year: 1893

page_text: Date of Application, 17th Apr., 1893
Complete Specification Left, 17th Jan., 1894-Accepted, 17th Feb., 1894
PROVISIONAL SPECIFICATION.
An Improved Method of Bending Metal Pipes, and Apparatus
therefor.
I, GUSTAV OESTEN, of 55, Stromstrasse, Berlin, in the Empire of Germany,
Engineer, do hereby declare the nature of this invention to be as follows:-
My invention relates to the bending of metal pipes, the object being to effect
such bending without interfering with the circular section of the pipes. This is
especially true of pipes with thin walls, which easily become indented and lose their
circular form.
In order to avoid this it is necessary to fill up the tube with as firm a material or
as rigid a body as possible, which will follow the intended curvatures without
yielding longitudinally or laterally, so that it will prevent any buckling of the wall
of the pipe.
It has hitherto been found most advantageous to employ for this purpose resin,
which is poured into the pipes in a fluid state. This is then allowed to set, after
which the tube is bent, and the resin is removed again when the bending is finished.
This is a very troublesome process, and has at the outset the disadvantage that it
cannot in most cases be carried out on the spot, but only in the workshop. More-
over, on account of the rigid nature of the core the force required to effect the
bending is disproportionately great, and the repeated melting of the resin adds
greatly to the expense.
According to my invention the pipe to be bent is charged with fluid under high
pressure, and is then curved under the influence of this pressure, the fluid under
pressure then acting upon the pipe as a solid body, and preventing it from under-
going any change in its cross section.
A suitable means of carrying out my invention is as follows:-
An elastic tube is inserted into the pipe to be bent, the outer diameter of the
former being somewhat less than the inner diameter of the latter. The tube is
inade very thick at its ends, so that they can be completely closed by metal plugs.
The plugs are bored through in the direction of their length. One of them is
connected with a tube which communicates with a force pump, whilst the perforation
in the other plug can be closed by a screw plug. Both the metal plugs end in
hooks at the inner part, so that they can be connected together by a chain, a cord
or a rod.
IS
Fluid is forced through the small tube into the elastic tube and the screw plug is
inserted as soon as the air has escaped and the fluid begins to issue from the passage
closed thereby. The fluid being continuously forced into the elastic tube the
latter consequently dilates and becomes closely applied to the wall of the metal
pipe, the longitudinal expansion of the tube being prevented by the chain which
now tightly strained. The pressure is raised to a point near the limit of
elasticity of the substance of the wall of the pipe. The pipe and its contents
then form a solid rod which allows of being bent in any desired manner without
undergoing alterations in cross section or receiving indentations in its walls, since
effectual resistance is offered to such efforts by the fluid under pressure in the
interior of the pipe. When the desired curve has been given to the pipe the fluid
under pressure can be let out of the interior of the elastic tube, which returns to
its original size by virtue of its elasticity, and may in consequence be easily
withdrawn from the curved pipe, the pipe itself retaining the form given to it.
Only a small expenditure of force is required to bend the pipe when subjected to
the internal pressure, inasmuch as it is expended only in stretching the metal of

page_text: the wall of the pipe on the outside of the curve and thickening it up on the inner
side, since the force required to bend the chain, the fluid, and the inner tube, may
be disregarded. The force required is thus much smaller than when the pipe is
filled with a solid substance.
In place of the closed tube, two sleeves or plungers connected by a chain or the
like can be employed; in this case the sleeves or plungers must fit the internal
diameter of the tube to be bent. Other methods of closing the ends of the tube
may also be used for example caps placed over them or the like.
Dated the 17th day of April 1893.
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicant.
An Improved Method of Bending Metal Pipes, and Apparatus
therefor.
I, GUSTAV OESTEN, of 55, Stromstrasse, Berlin, in the Empire of Germany,
Engineer, do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by
the following statement :-
My invention relates to the bending of metal pipes, the object being to effect
such bending without interfering with the circular section of the pipes which is
especially difficult with pipes having thin walls, which easily become indented and
lose their circular form.
For this purpose it is necessary to fill up the tube with as firm a material or as
rigid a body as possible, which will follow the intended curvatures without
yielding longitudinally or laterally, so that it will prevent any buckling of the wall
of the pipe.
It has hitherto been found most advantageous to employ for this purpose resin,
which is poured into the pipes in a fluid state. This is then allowed to set, after
which the tube is bent, and the resin is again liquefied when the bending is finished.
This is a very troublesome process, and has at the outset the disadvantage that
it cannot in most cases be carried out on the spot, but only in the workshop.
Moreover, on account of the rigid nature of the core the force required to effect
the bending is disproportionately great, and the repeated melting of the resin adds
greatly to the expense.
According to my invention the objections above referred to are obviated by
charging the pipe to be bent with water or other fluid under high pressure, and
then curving the pipe under the influence of this pressure, the fluid under pressure
then acting upon the pipe as a solid body, and preventing it from undergoing any
change in its cross section.
In this manner the pipe can be very easily bent and the process neither requires
disproportionate power, nor gives rise to great expense. The fluid can be placed
either in the pipe itself or in a tube inserted into the pipe, and this fluid is then
subjected to so high a pressure that in submitting the pipe to be bent to this strain
the material of the same very nearly attains its limit of elasticity, and when the
pipe is being bent the material of which it is made stretches on the outside of the
curve and thickens up or folds from within outwards without there being any
diminution in the area of the cross section.
In the accompanying drawings which illustrate various means for bending metal
pipes according to my invention and the various stages of the process-
Figures 1 to 3 are sections illustrating the process where a tube inside the pipe
is used:
Figure 4 is a section shewing the fastening formed at the end of the pipe by
means of a sleeve or bushing:

page_text: Figures 5 and 6 are sectional elevations shewing another method of fastening the
pipe:
Figures 7 to 10 are views of details of the apparatus shewn in Figures 5 and 6.
I will first describe my invention by reference to Figures 1 to 3.
An elastic tube B is inserted into the pipe to be bent, the outer diameter of the
former being somewhat less than the inner diameter of the latter. The tube is
made very thick at its ends, so that they can be completely closed by metal
plugs a and b, Figure 1. The plugs are bored through in the direction of their length.
One of the plugs a is connected with a tube c which communicates with a force
pump, whilst the perforation in the other plug can be closed by a screw plug d.
Both the metal plugs end in hooks at the inner part, so that they can be connected
together by a chain C, or a cord or a rod.
Fluid is forced through the small tube c into the elastic tube B and the screw
plug d is inserted as soon as the air has escaped and the fluid begins to issue from
the passage in the plug 6 closed thereby. The fluid being continuously forced into
the elastic tube B the latter consequently dilates and becomes closely applied to the
wall of the metal pipe A as shewn in Figure 2, the longitudinal expansion of the
tube B being prevented by the chain which is now tightly strained. The pressure
is raised to a point near the limit of elasticity of the substance of the wall of the
pipe.
For brass tubes of about an inch in diameter and with walls of a thickness of
one fiftieth of an inch for example a pressure of about one hundred atmospheres is
required.
The pipe and its contents then form a solid rod which allows of being bent in any
desired manner without undergoing alterations in cross section or receiving indenta-
tions in its walls, since effectual resistance is offered to such efforts by the fluid
under pressure in the interior of the pipe. When the desired curve has been given
to the pipe the fluid under pressure can be let out of the interior of the elastic
tube B, which returns to its original size by virtue of its elasticity, and may in
consequence be easily withdrawn from the curved pipe, the pipe itself retaining
the form given to it. Only a small expenditure of force is required to bend the
pipe when subjected to the internal pressure, inasmuch as it is expended only in
stretching the metal of the wall of the pipe on the outside of the curve and
thickening it up on the inner side, since the force required to bend the chain, the
fluid, and the inner tube, may be disregarded. The force required is thus much
smaller than when the pipe is filled with a solid substance.
In place of the closed tube, two sleeves or bushings connected by a chain or the
like can be employed as illustrated in Figure 4 which shews one of the said sleeves
similar to the thickened ends of the tube B shewn in Figures 2 and 3; in this case
the sleeves or bushings must fit the internal diameter of the tube to be bent.
Other methods of closing the ends of the tube may also be used, for example, caps
placed over them or the like. Or as illustrated in Figure 6 the edge of the ends
of the pipe g may be curved outwards and on each of these ends a divided ring h,
Figures 5, 6, 8 and 10 is fitted provided at one end with catches or projections
and also formed with flanges whereby the two parts can be screwed together as
clearly shewn in Figure 10. The rings in consequence of the curving of the
edges of the pipe ends cannot be removed from the same. On each of the divided
rings ha cap k, Figures 5, 6, 7 and 9, is placed having projections which catch
over the projections of the divided ring after the manner of a bayonet-joint.
In the cap works a screw-threaded rod m provided with a square n to receive a key
or spanner for turning the rod and with a plunger or piston o working in the
interior of the pipe end and covered with an elastic material.
After one end of the pipe has been closed by means of one of the rings, caps
and plungers it is filled with a suitable liquid and the other end of the pipe is
then similarly closed. The hydraulic pressure is obtained by forcing one of
the plungers o inwards by means of the screw-threaded rods m. The bending of

page_text: the pipe is effected in the manner hereinbefore described with reference to
Figures 1, 2 and 3.
If it is desired to measure the pressure or tension of the liquid a passage is bored
through the rod m to a pressure gauge s, Figures 5 and 6.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. A process for bending metal pipes in which liquid under high pressure is
introduced into the pipe to be bent and the pipe is bent under the influence of this
pressure, the liquid then acting like a solid body on the sides of the tube whereby
the latter is prevented from undergoing any change in cross section, substantially
as hereinbefore described.
2. The means for carrying out the process claimed in Claim 1 consisting of an
elastic tube designed to be inserted in the pipe to be bent, and plugs closing the
ends of the elastic tube and provided with hooks so that they can be connected by
a chain, cord or rod, one of the said plugs forming a communication between the
interior of the tube and a force pump, substantially as herein before described and
illustrated in Figures 1 to 3 of the accompanying drawings.
3. The modified arrangement illustrated in Figure 4 in which the elastic tube is
dispensed with and the ends of the pipe to be bent are closed by sleeves or bushings
connected by a chain or the like, substantially as set forth.
4. The means for carrying out the process claimed in Claim 1 consisting of a
piston or plunger covered with elastic material and which can be moved along in
the pipe by means of a screw-threaded rod and a cap k provided with projections !
catching after the manner of a bayonet-joint over projections on a divided ring h
situated at the outwardly turned end of the pipe with the object of stopping or
pluging the ends of the pipes and causing compression of the liquid through the
movement of the piston, substantially as herein before described and illustrated in
Figures 5 to 10 of the accompanying drawings.
Dated this 17th day of January 1894.
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicant.