Improvements in the Manufacture of Flexible Metallic Tubes.
Year: 1893

page_text: Date of Application, 10th Oct., 1893
Complete Specification Left, 10th July, 1894-Accepted, 25th Aug.. 1894
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Flexible Metallic Tubes.
1, PIERRE EUGÈNE SECRETAN of 16 Rue Drouot, Paris, France, Inventor, do
hereby declare the nature of this invention to be as follows:-
Flexible metallic tubes as hitherto constructed always comprise some foreign
elements for the purpose of giving the necessary flexibility as they cannot in any
other way resist the action of a fluid exerting even a small elastic force, or a high
temperature, as is necessary in the tubes of generators. Their application is thus
very limited. On the other hand it is not possible to combine flexible tubes thus
produced with ribs or gills either internal or external so as to obtain a greater
conductivity and a greater radiation of heat.
My invention which obviates these various inconveniences has for its object to
manufacture metallic flexible tubes with or without internal or external ribs or
gills preferably from a homogeneous material which is manipulated in different
ways according as it is of slight thickness and great malleability or on the other
hand thick and little malleable.
In the first case I submit the tube to a kind of screw threading or worming
internally or externally or both at once, by means of a mandrel or former of
progressive pitch which serves merely to press out and displace the metal. In the
second case I effect the same operation by making use of cutting tools to remove
the metal. The work in either case may be continuous or not, that is to say the
threads or spirals may be continuous or not, simple or mixed, may have more or
less pitch, and may be even parallel to the bore of the tube. According as the
threads are of greater or less pitch different types will be produced for various
adaptations.
I
The manufacture of these metallic flexible tubes can be effected in various ways.
may employ for instance a cylindrical tube of a thickness and exterior diameter
equal to that of the desired flexible tube, and 1 may fashion a mandrel which is a
screw with a diminishing thread of which the last turns correspond to the interior
of the flexible tube required. The initial pitch depends solely on the depth of the
last turns; it is about double at starting; then the pitch keeps diminishing whilst
the depth of the thread increases more and more. The diameter of the mandrel
is slightly less than that of the interior of the tube to be made, and it is fixed on a
rigid rod (of steel for example) of which the diameter is slightly less than that of
the interior of the finished flexible tube. Besides the mandrel I use a frame if
very thin tubes are in question which allows me by the help of screw tighteners to
force wires into the threads of my mandrel. Another form of frame which does
equally well, especially if the tube has a certain thickness, is composed of small
wheels or discs of various thickness forced by wedges or screws so as to penetrate
equally into the interior of the different threads of the mandrel of which they
take the respective forms.
In order to manufacture a flexible tube with this mandrel and one of these
frames I fix these two parts on a stage or framework taking care to fix both so
that they cannot turn and to make the rigid bar of the mandrel equal in length to
the finished tube. I place the cylindrical tube in the frame, slackening the wires
for its free passage, and I fix it on the other side of the frame by means of flanges
on a bush; this bush is somewhat smaller than the tube and revolves on the
mandrel bar. In this position I tighten the first wire until it penetrates into the
corresponding hollow of the mandrel, and I turn the tube by means of the clamped

page_text: bush until the impress made by the first wire faces the second wire; at thi
moment I tighten this second wire to make it impress the tube as far as the
bottom of the depression of the mandrel; then I again turn the tube until this
new impress faces the third wire, and so on until all the wires are tightened. From
this time I need only turn the tube until it has reached the necessary length. To
remove the flexible tube when finished I slacken all the wires, remove the clamping
bush and loosen the rod of the mandrel, then withdraw the whole from the frame.
If a smooth part of the rod be left I screw the mandrel until it is on the smooth
part and then it comes out of itself.
It is to be understood that a frame having small wheels or discs as herein before
described gives the same result and so will other means capable of pressing the
metal of the tube to the bottom of the hollows or depressions of the mandrel. By
this method of manufacture I obtain a tube with spiral depressions having every-
where the original thickness of the metal, the first turns of the spiral only drawing
out the necessary metal and the following bending it more and more so that there
is no need for any rolling. It is necessary to use a cylindrical tube larger than
the spiral tube that is required. This method of manufacture is particularly useful
for a tube with deep spirals to render it flexible, but for a tube with shallow spirals
for generators the mandrel can have but one spiral either uniform or preferably
wide to start with, then more and more deep.
When a frame is used having wheels or discs as above described there are as
many of them as practicable bearing on the circumference of this spiral and these
wheels may be alike if the spiral is uniform, but it is much preferred to have the
first wheel wider so that it may penetrate less into the recess, the second a little
smaller, and eventually the last giving the final form.
By this method the same phenomenon is produced on a plain circumference, and
the metal of the tube being drawn equally to the various generatrices of its surface
arranges itself and renders rolling here also unnecessary.
Moreover a spiral tube being obtained by a preliminary process one can employ
two or more sets of mandrels and frames, the second diminishing the pitch and
increasing the depth of the threads of the first tubular screw obtained.
This process is useful for manufacturing spiral tubes for steam boilers. The
apparatus placed at the mouth of the furnace, the tube of iron, steel or other
metal once heated is drawn on the mandrel, clamped by the bush and immediately
revolved; the wheels or discs are forced into the recesses and the tube is drawn
and formed.
Instead of turning the tube round the mandrel a rotating movement can be
given to the frame and mandrel; the tube in this case will be clamped on the bush
so as not to partake of this movement.
This mode of manufacture can also be carried out more especially in the case
where cutting tools are used for making gills or ribs in the form of spirals of a
greater or less pitch or in rectilinear form; and equally in the case where the tool
employed is not a cutting tool, in which latter case I may use :-
1. A lathe, by arranging the tube so as to make it turn and causing to press
upon it during its rotation a wheel, disc or other like tool, either cutting or not, to
which is given a forward movement according to the pitch required, and a pressure
varying with the depth of the straight or helical ribs as desired. This wheel or
like tool may be single, or more than one may be used to obtain a more rapid
production. The apparatus should be momentarily stopped when a rib or gill of
varying form is required.
2. A shaping machine for forming external ribs in the direction of the length of
the tubes; this machine can work either by cutting out the metal or by having a
tool fitted to it which will simply fold the metal instead of cutting it.
3. A draw bench with draw plates sharp at the edges according to the require-
ments of the desired ribs and mandrels with interual cutting section. These
operations can be performed at one or more passages, the importance and number
of which will depend upon the depth required in the ribs.

page_text: 4. I can take a tube of known thickness generally strong and cut from it
externally either in the form of a screw or in separate rings a quantity of metal
sufficient to form the tubes with ribs and to produce as great a heating surface or
rings as may be desired. This cutting can be performed in a lathe and the smallest
or the largest pitch may be given to it so as to form if necessary only a single
spiral continuous or broken. The tubes thus obtained will give a heating surface
and a conductivity greater than that hitherto manufactured but they will have
besides the great advantage of possessing a certain flexibility which will allow
them (which cannot be done at present) to be employed in every sort of way. To
obtain a greater flexibility it will always be necessary to have internal spirals.
5. Another method consists (in case of longitudinal ribs) in taking a tube of a
greater diameter than the final diameter and in forming ribs in it by folding the
excess diameter by means of a draw bench with special draw plates and specially
placed mandrels. In the case of internal ribs the mandrel is made with concave
parts and the draw plates or formers with convex parts. In the case of external
ribs the mandrel has external projections and the draw plates or formers are
countersunk so as to receive the projections on the mandrel. Finally, to
hermetically join up or close the ribs thus formed, I pass the whole through a draw
bench with a single draw plate having the final dimensions and with or without an
internal mandrel. The tube so finished is of a perfect construction. These tubes
can also be produced by hammering, stamping, rolling or by these various means
combined.
6. I can also operate in the lathe in the following manner: In the interior of the
tube hot or cold, is placed a mandrel which is either smooth or engraved or stamped
or has grooves, according to the ribs required. In the case of a smooth mandrel a
powerful wheel or former is used which will mark on the tube the gills or ribs
required; if these are to be deep or broad they should be produced when the tube
is hot, the interior surface will then be smooth. If the grooves be at right angles
to the bore of the tube they are obtained by means of mandrels or fixed draw
plates and by turning the tube or by revolving one or more of these parts. In
the case of longitudinal grooves or ribs they are produced by fixing the tube and
causing the wheel or other tool to move along its length. In the case on the
contrary of tubes to be ribbed or grooved internally or externally, I use mandrels
of suitable form, concave or convex, and I cause to roll on the metal thus prepared
the necessary wheel or tool of a like section and form to the mandrel, taking count
of course of the thickness of metal and the result to be obtained. These shapes
can also be effected by rolling, hammering or forging. In the case of steam
tubes I can also make them by taking a round tube manufactured in the usual way
but unfinished and I complete it by forming an internal groove either by a
mandrel fitted to receive a core or by a cutting draw plate having the same object;
then I place inside it a transverse plate having ribs more or less long and having
on the longitudinal edges the form of the groove traced on the tube; then I pass
the tube through a draw bench or rolling mill and the tube is finished by applying
the sides of the internal plate against the inner sides of the tube.
This form of plate constitutes a diaphragm which can consist of various gills of
various or multiple sizes or in the form of a cross. The draw plates which I use
for the method above mentioned may be, as is easily understood, in one or more
pieces. The spiral tube obtained has in its length sufficient flexibility to aliow of
its being mounted and dismounted inside boilers, the pressure helping to make it
joint tight. As this kind of tube possesses a certain elasticity its length has not
to be mathematically precise.
Tubular or semi-tubular boilers and even boilers with removable grates are able
with this tube to be cleaned more easily as it will be sufficient to bend the tube
a little to detach the scale. In "field" boilers it will allow of reducing the height
of the boiler the tube being capable of being bent a little in order to dismount it.
For locomotive boilers or marine boilers where the heating suface is always
insufficient, the spiral tube is particularly applicable since it will increase this

page_text: surface without otherwise altering the boiler; it can be made with cylindrical ends
like an ordinary tube.
Lastly, for the conveyance of water, steam or gas, the spiral tube being capable
of bending easily even on the smallest radius without the necessity of being heated
or filled with anything is particularly adapted for use in many industries, as any one
will be able to fit up his own tubes by making use of pieces of spiral tubes where
it is necessary to form elbows, the same straight piece of spiral tube being able to
take various forms.
Dated this 10th day of October 1893.
J. C. MEWBURN,
55 & 56, Chancery Lane, London, Chartered Patent Agent.
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Flexible Metallic Tubes.
I, PIERRE EUGÈNE SECRETAN of 16 Rue Drouot, Paris, France, Inventor 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 :-
Flexible metallic tubes as hitherto constructed always comprise some foreign
elements for the purpose of giving the necessary flexibility, as they cannot in
any other way resist the action of a fluid exerting even a small elastic force, or a
high temperature as is necessary in the tubes of generators. Their application is
thus very limited. On the other hand it is not possible to combine flexible tubes
thus produced with ribs or gills either internal or external so as to obtain a greater
conductivity and a greater radiation of heat.
My invention which obviates these various inconveniences has for its object to
manufacture metallic flexible tubes with or without internal or external ribs or gills
from a homogeneous material manipulated in different ways according as it is of
slight thickness and great malleability, or on the other hand thick and little
malleable.
In the first case I submit the tube to a kind of screw threading or worming
internally or externally or both at once, by means of a mandrel or former of
progressive pitch, which serves merely to press out and displace the metal. In the
second case I effect the same operation by making use of cutting tools to remove
the metal. The work in either case may be continuous or not, that is to say the
threads or spirals may be continuous or not, simple or mixed, may have more or less
pitch, and may be even parallel to the bore of the tube. According as the
threads are of greater or less pitch different types will be produced for various
adaptations.
The example shown in Figure 1 of the annexed drawing is specially adapted
for locomotive, marine or other steam boilers. Its shape augments its power to
resist the pressure and back pressure, whilst the heating surface is doubled for an
equal length. That shown in Figure 2 on the contrary by its extreme flexibility
solves the much desired problem of a flexible metallic tube to take the place of
caoutchouc, and can be used for brakes, water pipes, steam pipes, gas pipes and the
like.
I
The manufacture of these metallic flexible tubes can be effected in various ways,
may employ for instance a cylindrical tube of a thickness and exterior diameter
equal to that of the desired flexible tube, and I fashion a mandrel as shown in
Figure 3 which is a screw with a diminishing thread of which the last turns
correspond to the interior of the flexible tube required. The initial pitch depends
solely on the depth of the last thread. It is about double at starting, then the
pitch keeps diminishing whilst the depth of the thread increases more and more as

page_text: indicated in Figure 3. The diameter of the mandrel is slightly less than that of
the interior of the tube to be made and it is fixed on a rigid rod (of steel for
example) of which the diameter is slightly less than that of the interior of the
finished flexible tube. Besides the mandrel I use a frame like that shown in
Figure 4, if very thin tubes are in question, which allows me by the help of screw
tighteners to force wires into the threads of my mandrel which is shown in the
centre. These wires are shown in section in Figure 3 opposite the corresponding
threads. Another form of frame shown in Figure 5 which does equally well,
especially if the tube has a certain thickness, is composed of small wheels or discs a
of various thickness forced by screws b or by wedges so as to penetrate equally
into the interior of the different threads of the mandrel of which they take
the respective forms. These wheels are shown in section opposite the threads
(Figure 3).
In order to manufacture a flexible tube with this mandrel and one of these
frames, I fix these two parts K, E on a stage or framework D, Figure 6, taking
care to fix both so that they cannot turn and to make the rigid bar K' of the
mandrel equal in length to the finished tube, and by fixing it in position by means
of the support F. I place the cylindrical tube in the frame (as shown in Figure 4)
slackening the wires for its free passage, and I fix it on the other side of the
frame by means of flanges N on a bush M, Figure 6; this bush is somewhat
smaller than the tube and revolves on the bar K. In this position I tighten the
first wire until it penetrates into the corresponding hollow of the mandrel, and I
turn the tube by means of the clamped bush M until the impress made by the first
wire faces the second wire; at this moment I tighten the second wire to make it
impress the tube as far as the bottom of the depression of the mandrel; then I
again turn the tube until this new impress faces the third wire and so on until all the
wires are tightened. From this time I need only turn the tube until it has reached
the necessary length. To remove the flexible tube when finished I slacken all the
wires, remove the clamping bush M and loosen the rod of the mandrel, then
withdraw the whole from the frame.
If a smooth part of the tube be left as at P I screw the mandrel until it is on
the smooth part and then it comes out of itself.
It is to be understood that a frame having small wheels or discs as herein before
described gives the same result, and so will other means capable of pressing the
metal of the tube to the bottom of the hollows or depressions of the mandrel. By
this method of manufacture I obtain a tube with spiral depressions having
everywhere the original thickness of the metal, the first turns of the spiral only
drawing out the necessary metal and the following bending it more and more so
that there is no need for any rolling. It is necessary to use a cylindrical tube
larger than the spiral tube that is required. This method of manufacture is
particularly useful for a tube with deep spirals to render it flexible but for a tube
with shallow spirals for generators such as Figure 1, the mandrel R can have but
one spiral either uniform or preferably wide to start with, then more and more deep
(see Figure 7).
When a frame is used having wheels or discs as above described there are as
many of them as practicable bearing on the circumference of this spiral and these
wheels may be alike if the spiral is uniform, but it is much preferred to have the
first wheel wider, so that it may penetrate less into the recess, the second a little
smaller, and eventually the last giving the final form.
By this method the same phenomenon is produced on a plain circumference, and
the metal of the tube being drawn equally to the various generatrices of its
surface, arranges itself. Moreover a spiral tube being obtained by a preliminary
process, one can employ two or more sets of mandrels and frames, the second
diminishing the pitch and increasing the depth of the threads of the first tubular
screw obtained.
This process is useful for manufacturing spiral tubes for steam boilers. The
apparatus is placed at the mouth of the furuace; the tube of iron, steel or other

page_text: metal once heated is drawn on the mandrel, clamped by the bush and immediately
revolved; the wheels or discs are forced into the recesses and the spiral tube is
thus formed.
Instead of turning the tube round the mandrel a rotating movement can be given
to the frame and mandrel; the tube will be clamped on the bush so as not to
partake of this movement.
Instead of employing the wires or the wheels or discs as hereinbefore described
I can use dies acting in the same manner and as illustrated in Figures 15 to 28.
Figure 15 is a sectional elevation on the line 1-2 of Figure 16 of the apparatus
as it is used to produce upon the tube by means of dies the first spirals, wide but
shallow. Figure 16 is a sectional plan of the same apparatus on the line 3-4 of
Figure 15.
Figure 17 is a sectional elevation on the line 5-6 of Figure 18, showing the
apparatus as it is used to produce on the tube by means of the dies deep spirals but
diminishing more and more in width.
Figure 18 is a sectional plan on the line 7-8 of Figure 17.
Figures 19 to 28 inclusive are views in plan and in elevation showing a series of
dies such as I make use of in carrying out my invention.
1
The apparatus comprises a kind of support D to which is fixed by any convenient
means a frame E in the interior of which are placed the dies C C' which can be
brought together at will by means of a screw A or equivalent means in such a way
as to squeeze between them the tube P. I will explain later on the manner in which
these dies are arranged.
It
The tube P which is to be worked upon has as previously one of its ends pl free,
the other end p is firmly fixed in a wrench or in a device such as a jaw M, for
which purpose there may be inserted in the interior of the tube so that it is not
damaged a sleeve B which will give the necessary resistance to ensure a good grip
of the wrench on the tube. Moreover, there is placed in the interior of the same
tube a mandrel R fixed at the extremity of a rod G which can be firmly secured in
position (as represented at 9 in the drawing) so that the mandrel cannot turn.
has helical grooves (diminishing or otherwise) which grooves will serve (as will be
explained later) by their action combined with the dies C C' to produce the spirals
of the tube. The dies C C₁ are constructed in wood or metal. I prefer to make
use of lignum vitæ for the dies to be used at the commencement of the operation,
whilst those to be used at the end of the operation I prefer to make of metal. The
pieces forming the dies are inclined with reference to the axis of the tube in such
a way as to take the direction of the spiral which it is desired to produce and their
edges are rounded having preferably a semi-elliptic section." The die C is
composed of two or three pieces whilst the die C¹³ is composed of one or two
corresponding to the depressions of the die C, as will be clearly understood by
reference to Figure 16.
The method of working is effected as follows:-The tube P, in which the
mandrel R has been placed, having been previously passed into the frame is fixed
in the wrench M. This having been done, the dies C C¹ are applied on the part of
the tube corresponding to the mandrel and brought into operation by squeezing
them by means of the screw A in such a way that they penetrate respectively into
the corresponding grooves of the mandrel. When this first operation has been
effected the tube P is rotated by means of the wrench M; a movement which by
the action of the spiral grooves of the mandrel is transformed into a forward
movement of the tube towards the wrench at the same time producing spiral grooves
as will be clearly seen by referring to Figure 6. In this way the mandrel should
be worked backwards and forwards once or oftener, then the tube having acquired
a certain resistance the mandrel is drawn out and a new impression is made by the
lignum vitæ dies of the smallest dimensions in width, but deeper as represented in
Figures 11 and 12. It is a good plan to leave in the interior of the tube, in order
to support it, a rod G as shown in Figure 18; but this is not absolutely necessary.
Three impressions are now made with the metal dies decreasing in pitch but

page_text: increasing in depth as shown in Figures 23 to 28. During this part of the operation
it is desirable to grease by means of oil or soapy water.
The operation such as I have just described consists of five distinct impressions,
but it is understood that the number can be increased or diminished without altering
the process.
The tube which is obtained after these operations is furnished with spirals very
close and very deep such as is shown in Figure 18 which imparts to the tube very
great flexibility.
This mode of manufacture can also be carried out more especially in the case
where cutting tools are used for making gills or ribs in the form of spirals of a
greater or less pitch or in rectilinear form; and equally in the case where the tool
employed is not a cutting tool, in which cases I may use :-
1. A lathe, by arranging the tube so as to make it turn, and causing to press
upon it during its rotation a wheel, disc or other like tool, either cutting or not, to
which is given a forward movement according to the pitch required, and a pressure
varying with the depth of the straight or helical ribs desired. This wheel or like
tool may be single or more than one may be used to obtain a more rapid production.
The apparatus should be momentarily stopped when a rib or gill of varying form
is required.
2. A shaping machine for forming external ribs in the direction of the length of
the tubes; this machine can work either by cutting out the metal or by having a
tool fitted to it which will simply fold the metal instead of cutting it.
4
3. A draw bench with draw plates sharp at the edges according to the require-
ments of the desired ribs, and mandrels with internal cutting section. These
operations can be perforined by producing one or more impressions the extent and
number of which will depend upon the depth required in the ribs.
4. I can take a tube of known thickness generally strong and cut from it
externally either in the form of a screw or in separate rings a quantity of metal
sufficient to form the tubes with ribs and to produce as great a heating surface or
rings as may be desired. This cutting can be performed in a lathe and the smallest
or the largest pitch may be given to it so as to form if necessary only a single
spiral, continuous or broken. The tubes thus obtained will give a heating surface
and a conductivity greater than those hitherto manufactured, but they will have
besides the great advantage of possessing a certain flexibility which will allow
them (which cannot be done at present) to be employed in every sort of way. To
obtain a greater flexibility it will always be necessary to have internal spirals.
5. Another method consists (in the case of longitudinal ribs or gills) in taking
a tube of a greater diameter than the fiual diameter and in forming ribs in it by
folding the excess diameter by means of a draw bench with special draw plates and
specially placed mandrels. In the case of internal ribs the mandrel is made with
concave parts and the draw plates or formers with convex parts. In the case of
external ribs the mandrel has external projections and the draw plates or formers
are countersunk so as to receive the projections on the mandrel. Finally to
hermetically join up or close the ribs thus formed, I pass the whole through a draw
bench with a single draw plate having the final dimensions and with or without an
internal mandrel. The tube so finished is of a perfect construction. These tubes
can also be produced by hammering, stamping, rolling, or by these various means
combined.
6. I can also operate in the lathe in the following mauner: In the interior of the
tube hot or cold, is placed a mandrel which is either smooth or engraved or
stamped, or has grooves according to the ribs required. In the case of a smooth
mandrel a powerful wheel or former is used which will produce on the tube the
gills or ribs required; if these are to be deep or broad they should be produced
when the tube is hot; the interior surface will then be smooth. If the grooves be
at right angles to the bore of the tube they are obtained by means of mandrels or
fixed draw plates, and by turning the tube or by revolving one or more of these

page_text: parts. In the case of longitudinal grooves or ribs they are produced by fixing the
tube and causing the wheel or other tool to move along its length. In the case on
the contrary of tubes to be ribbed or grooved internally and externally I use
mandrels of suitable form, concave or convex, and I cause to roll on the metal thus
prepared the necessary wheel or tool of a like section and form to the mandrel,
regard being had of course to the thickness of the metal and the result to be
obtained. These shapes can also be effected by rolling, hammering or forging, or
by any other means capable of giving sufficient force to the draw plate and
mandrel. In the case of steam tubes I can also make them by taking a round tube
manufactured in the usual way but unfinished, and I complete it by forming an
internal groove either by a mandrel fitted to receive a core or by a cutting draw
plate having the same object; then I place inside it a transverse plate having ribs
more or less long, the longitudinal edges thereby causing the form of the groove
to be left on the tube; then I pass the tube through a draw bench or rolling
mill and the tube is finished by applying the sides of the internal plate against the
inner sides of the tube.
This form of plate constitutes a diaphragm which consists of various gills of
various or multiple sizes or in the form of a cross. I then pass the whole through
the draw plate with or without a mandrel inside. The draw plates which I use for the
method above mentioned may be, as is easily understood, in one or more pieces.
The spiral tube obtained has in its length sufficient flexibility to allow of its being
fitted in and removed from boilers, the pressure helping to make it tight (Figure 8).
As this kind of tube possesses a certain elasticity, its length has not to be
mathematically precise.
Tubular or semi tubular boilers, and even boilers with removable grates are able
with this tube to be cleaned more easily, as it will be sufficient to bend the tube a
little to detach the scale. In "Field "boiler tubes (see Figure 9) it will allow of
reducing the height of the boiler, the tube being capable of being bent a little in
order to dismount it. For locomotive boilers or marine boilers where the heating
surface is always insufficient the spiral tube is particularly, applicable, since it will
increase this surface without otherwise altering the boiler; it can be made with
cylindrical ends like an ordinary tube (Figure 10).
Lastly, for the conveyance of water, steam or gas, the spiral tube being capable
of bending easily even on the smallest radius without the necessity of being heated
or filled with anything, is particularly adapted for use in many industries, as any
one will be able to fit up his own tubes by making use of pieces of spiral tubes
where it is necessary to form elbows, the same straight piece of spiral tube
(Figure 11) being able to take various forms shown in Figures 12, 13 and 14.
Having now particularly described and ascertained the nature of my said iuven-
tion and in what manner the same is to be performed, I declare that what I
claim is
1. The manufacture of flexible metallic homogeneous tubes by forming the body
of the tube with spirals, grooves, ribs or gills projecting on the inside or on the
outside or on both sides either for the purpose merely of giving flexibility to the
tube or for the purpose of increasing the conductivity or the radiating power of
the tube, substantially as described and illustrated in the accompanying drawings.
2. The manufacture of flexible metallic tubes such as referred to in the preceding
claim by submitting the tube to a kind of screw threading or worming action
internally or externally or both obtained (a) by causing the tube to pass
successively between a series of tightening wires of different section, of wheels or
of dies of decreasing pitch and of increasing depth inclined relatively to the axis
of the tube, these wires, wheels or dies serving merely to press out or displace the
metal corresponding to grooves of the same form on a mandrel placed inside the tube
during the first impressions and removed during the subsequent impressions, or
(6) by means of cutting tools for cutting away the metal, the work in either case

page_text: being continuous or not, that is to say to form spirals continuous or not, simple or
mixed, with more or less pitch and even parallel to the bore of the tube, substantially
as described and illustrated in the accompanying drawings.
3. The employment in the manufacture of flexible metallic tubes of apparatus
having dies inclined to the axis of the tube in such a way as to form ribs and
hollows constituting helical grooves of increasing depth, and which impart great
flexibility to the tube, substantially as herein before described and shown in the
accompanying drawings.
Dated this 10th day of July 1894.
J. C. MEWBURN & ELLIS,
55 and 56, Chancery Lane, London, Patent Agents.