Note: Descriptions are shown in the official language in which they were submitted.
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"CONDUIT AND METHOD OF FORMING"
The present application is a divisional application of Canadian Patent
Application
Serial No. 2,439,762, filed September 8, 2003.
BACKGROUND TO THE INVENTION
1. Field of the invention
The present invention relates to components for breathing circuits and in
particular to conduits for use in the limbs of breathing circuits. The
invention also
relates to methods of manufacturing such conduits.
2. Summary of the prior art
In assisted breathing, particularly in medical applications, gases are
supplied and
returned through conduits. Such conduits are ideally light and flexible to
achieve the
highest possible level of comfort for the patient. In the prior art, thin
walled conduits
are known which include helical or annular reinforcing ribs which act to give
the
conduit better resistance to crushing and pinching, while still allowing the
conduit to be
light and flexible. A cross section of the wall of an example of such a
conduit is shown
in Figure 1.
It is advantageous to manufacture this type of conduit as a continuous
process. In
the prior art this is achieved by the spiral winding of a thin polymer tape
(ribbon or film)
onto a former such that the edges of adjacent layers overlap a small amount. A
bead of
molten polymer is then applied over top the overlapping edges welding them
together
and simultaneously forming the helical reinforcing ribs. A disadvantage with
this
forming technique is the difficulty welding several adjacent layers. This
problem is
especially severe when multiple layer conduit walls are to be formed. While
combining
the application of a molten bead with another secondary thermal welding
process or
applying the polymer to the former as a still molten plastic does go some way
to
alleviating this difficulty, these solutions add complexity to the tube former
and may be
difficult to achieve with very thin walls.
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SUMIVIARY OF THE INVENTION
It is an object of the present invention to provide a conduit, with particular
application to the limbs of a breathing circuit, which will at least go some
way towards
improving on the above or which will at least provide the public and the
medical
profession with a useful choice, and/or to provide a method of manufacturing
conduit
which will at least go some way towards providing the public and manufacturers
with a
useful choice.
In a first aspect the invention may broadly be said to consist in a method of
continuously forming conduit comprising:
continuously applying at least one thin fihn ribbon, each having "leading" and
"trailing" lateral edges, spirally around a former rotating and advancing said
conduit,
with the leading edge of each turn of ribbon overlapping the trailing edge of
a previous
turn of ribbon on the former and the trailing edge of each turn under lapping
the leading
edge of a succeeding turn, while,
in advance of said overlapping of said turns, applying a bead of molten
plastic
along the exposed trailing edge of the most recently applied turn on said
former, such
that a said bead is interposed between said trailing edges and said
overlapping leading
edges, and
said overlapping portion conforms to the contour of said bead, so that said
overlapping edge meets or substantially meets said underlapping ribbon at an
edge of
said bead.
In a further aspect the method of continuously forming conduit may include the
additional step of applying one or more heating wires to the exposed trailing
edge of the
ribbon prior to applying the bead, such that the bead encapsulates the one or
more
heating wires onto the said trailing edge.
In a further aspect the invention may broadly be said to consist in a method
of
continuously forming conduit wherein the former includes a plurality of
rotating rods
spaced about an axis and acting to support and advance the conduit during
forming,
further comprising:
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first applying a sacrificial layer of thin plastic around said former, before
said
conduit is formed on said former over top of said sacrificial layer, and
subsequent to forming said conduit, removing said sacrificial layer from
inside
said thin walled conduit after cooling.
In a further aspect the invention may broadly be said to consist in a conduit
formed in accordance with a method according to any one of the preceding
paragraphs.
In a still further aspect the invention may broadly be said to consist in a
conduit
comprising:
at least one thin plastic ribbon having a leading and a trailing lateral edge,
said
ribbon arranged helically with its face substantially parallel with the helix
axis, and,
apart from at its ends, the leading edge of each turn of ribbon overlapping
the trailing
edge of a previous turn, and the trailing edge of each turn of ribbon under
lapping the
leading edge of a succeeding turn,
a plastic reinforcing bead adjacent said trailing edge and interposed between
each
overlapping leading and trailing edge, such that said overlapping edge meets
or
substantially meets said underlapping ribbon at an edge of said bead.
In a still further aspect the invention may broadly be said to consist in
apparatus
for continuously forming conduit comprising:
a former for receiving at least one thin plastic ribbon, said former drawing
said
ribbon around and advancing said ribbon along to procure a helical arrangement
of said
ribbon, the pitch of said helical arrangement being somewhat less than the
width of said
ribbon,
means for delivering a ribbon to said former at a first position on said
former, and
means for continuously delivering a molten bead to said former at a second
position less than one turn pitch from the position of delivery of said
ribbon, said second
position corresponding to an expected position of the trailing edge of a
ribbon delivered
by said means for delivering a ribbon, such that an overlapping edge of the
ribbon meets
or substantially meets an underlapping edge of the ribbon at an edge of said
bead.
In still a further aspect the invention may broadly be said to consist in
apparatus
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for continuously forming conduit comprising:
a former for receiving plastic ribbon, said former drawing said ribbon around
and
advancing said ribbon along, to procure an overlapping helical arrangement of
said
ribbon, the pitch of said helical arrangement being somewhat less than the
width of said
ribbon,
a first means for delivering a first ribbon to said former, at a first
location
a second means for delivering a second ribbon to said former, at a location
subsequent to said first ribbon,
a means for continuously delivering a molten bead to said former at a position
less than one turn pitch from the position of delivery of said second ribbon
said position
corresponding to an expected position of the trailing edge of said second
ribbon, such
that an overlapping edge of the ribbon meets or substantially meets an
underlapping
edge of the ribbon at an edge of said bead.
In a further aspect the invention may broadly be said to consist in a method
for
removing a releasable inner layer from within a conduit comprising:
placing said conduit, including said inner layer around an elongate shaft
having a
longitudinal slot,
forming an adequate seal toward a first end of said shaft, effective for the
conduit
to at least substantially seal said slot, from the surroundings, apart from at
the other end
of said shaft,
applying suction to said slot,
initiating release of said inner layer from said conduit,
removing said conduit from said shaft after said inner layer is released from
said
conduit.
In a further aspect the invention may broadly be said to consist in an
apparatus
for assisting removal of a releasable inner layer within a conduit comprising:
an elongate shaft having a longitudinal slot,
a effective sealing means for making an adequate seal between said inner layer
and said shaft, toward a first end of said shaft,
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a means to suck gases from said slot, and release said inner layer from said
conduit.
To those skilled in the art to which the invention relates, many changes in
construction and widely differing embodiments and applications of the
invention will
suggest themselves without departing from the scope of the invention as
defined in the
appended claims. The disclosures and the descriptions herein are purely
illustrative and
are not intended to be in any sense limiting.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross sectional side elevation of a wall of a conduit according
to an
embodiment of the prior art.
Figure 2 is a cross sectional elevation of a wall of a conduit according to
one
embodiment of the present invention.
Figure 3 is a plan view of a conduit forming device for forming a reinforced
conduit according to a further embodiment of the present invention, such as
the conduit
pictured in Figure 2.
Figure 4 is a cross sectional elevation of a conduit wall showing a rough
inner
surface resulting from the tape not completely following the contour of the
molten bead.
Figure 5 is a side elevation of a conduit according to a further embodiment of
the
present invention including outer axial reinforcing threads.
Figure 6 is a plan view of a conduit forming device for forming a reinforced
conduit according to an embodiment of the present invention, such as the
conduit
pictured in Figure 5.
Figure 7 is a cross sectional side elevation of a conduit wall according to a
further embodiment of the present invention including a pair of heater wires
within the
conduit wall.
Figure 8 is a plan view of a conduit forming device for forming the conduit
pictured in Figure 7.
Figure 9a is a cross section of a tape or ribbon illustrating the assembly of
a pre-
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formed tape including a pair of heater wires according to a further embodiment
of the
present invention.
Figure 9b is a cross section view of the pre-formed ribbon of figure 9a, shown
assembled.
Figure 10 is a cross section view of a conduit wall including a pair of heater
wires formed from the pre-formed ribbon shown in figure 9b.
Figure 11 is a cross sectional elevation of a conduit wall showing a defect
caused
by the bead flowing between overlapping adjacent layers.
Figure 12 is a plan view of an apparatus for removing the sacrificial layer.
Figure 13 is a plan view of the apparatus of Figure 12, shown with a conduit
overtop.
DETAILED DESCRIPTION
The present invention relates to breathing conduits in general and in
particular to
improved methods of forming thin film (tape or ribbon) spiral wound conduits.
Consequently the present invention finds application in breathing conduits
fabricated
from a variety of materials which may include breathable and/or non-breathable
materials (breathable materials being capable of transmitting water vapour but
not liquid
water).
In assisted breathing, particularly in medical applications, gases having high
levels of relative humidity are supplied and returned through conduits of a
relatively
restricted size. Build up of condensation on the inside wall of the conduit is
a potential
result of this high humidity. The purpose of including a breathable region or
regions in
the conduit wall is to allow diffusion of water vapour from the expiratory
limb of the
breathing circuit along the path thereof. This can reduce the build up of
condensation
within the expiratory limb by drying the humidified gases during their flow
through the
expiratory limb. This furthermore reduces the humidity of the gases arriving
at ancillary
equipment, such as filters, ventilators and the like, reducing the risk of
condensation
accumulation, thereby improving their operation, or alleviating potential
detrimental
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effects.
The preferred breathable material is a hydrophilic polyester formed into a
homogeneous flat film or ribbon. This material has been found particularly
suited to
thin film productions having a wall thickness of less than approximately 50
microns, and
therefore fmd particular suitability in the manufacturing methods of the
present
invention. It will be appreciated that other breathable materials may also be
suitable for
forming breathable conduits. Such breathable materials may be breathable due
to their
composition, physical structure or a combination thereof.
The following embodiments will be described with particular reference to
breathable thin film wall construction from materials such as those referred
to above. It
will be appreciated however, that in the following described embodiments the
material
used to form the conduit walls may be either breathable or non-breathable and
may also
include combinations of both breathable and non-breathable materials. It will
be also
appreciated for the following described embodiments that the film(s) supplied
to the
former may be supplied either as a preformed flat ribbon wound onto a reel or
may
alternatively be supplied directly to the former from an extruder. Each of
these options
may have associated advantages and disadvantages which will be discussed
later. It will
also be appreciated by those skilled in the art that the materials supplied to
the former
may require a number of guides tensioners and/or rollers in order to position
the
materials accurately and provide the necessary tension.
As a corollary of material cost it is preferred that the conduit wall be
manufactured to have a relatively low wall thickness, so much so that the
conduit wall
membrane may be insufficiently sturdy to be self supporting. Spiral or helical
reinforcing members are therefore provided as part of the tubular membrane to
provide
support. The helical or spiral supporting members (beads) are formed from
polymer
materials and may be of the same material used in the wall of the conduit or
any other
compatible plastics material.
Referring to Figure 1, the lay-up arrangement of a flexible breathing conduit
known in the art is shown. Referring to Figure 2, a breathing circuit limb
wall cross
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section is shown with a thin film flexible wall. The thin film or ribbon is
arranged in a
spiral or helix such that the edge portions 45 and 46 of adjacent layers
overlap and form
the wall of a tube. Interposed the overlapping edges 45 and 46 of adjacent
winds of
ribbon, is a bead of polymer material bonded with the overlapping.portions of
ribbon
sealing the joint between windings and forming a continuous tube. The seam is
formed
between the edge of a first layer of film and the edge of a second, adjacent
layer of film
which is laid over top of the polymer bead while the bead is molten. The
overlapping
layer of film because it is so thin, closely follows the contour of the bead
and results in a
smooth inner conduit wall. It is desirable for the ribbon to be sufficiently
supple at least
laterally, to conform along its overlapping portion to the contour of the
bead, so that the
overlapping ribbon may meet or substantially meet the underlapping ribbon at
the edge
of the bead.
The accompanying figures show small gaps or spaces between the reinforcing
bead and the overlapping portion of ribbon. It is to be understood that these
spaces are
present for illustration purposes only, in order to differentiate the bead
from the
overlapping layer in the diagrams. In practice the overlapping layer conforms
to the
bead and bonds, without forming large gaps or bubbles.
An example of continuous forming apparatus suitable for manufacturing the
breathing tube according to a first embodiment of the present invention
described in
Figure 2 is shown in Figure 3. The apparatus includes a former 1 preferably of
a known
type including a plurality of rotating rods arranged around a central support
rod. The
rods extend from and are rotated by a gearbox within a machine stock 2. At
least in the
tube forming region the rotating rods follow a helical path. The pitch angle
of the rods
relative to the support rod controls the pitch angle of the tube being formed.
An example
of such a machine is a spiral pipeline mandrel available from OLMAS SRL of
Italy.
Tube being formed on the former is rotated and advanced in the direction of
arrow 3 by the movement of the rotating rods. The advance speed of the former
is
selected relative to the rotational speed so that the pitch of the helical
laying of the strip
or tape on to the former I is a little less than the width of the strip so
that adjacent turns
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narrowly overlap. A first extruder 4 supplies a tape or ribbon 5 of thin film
polymer
materials with a preferred width of approximately 10 millimetres. It will be
readily
understood that variation from this preferred ribbon width and size of overlap
is possible
in order to achieve reinforcing beads or conduits having varying pitches
and/or
dimensions. The ribbon 5 deposits on the former 1 in a helical fashion by
action of the
former. The pitch of the helical disposition of ribbon 5 is slightly less than
the width of
ribbon 5 and results in preferred overlap of approximately 2.5 millimetres.
The helical
deposition of ribbon 5 forms the wall 6 of the conduit.
An extruder 7 extrudes a bead 8 of molten or semi-molten polymer material. The
molten bead 8 deposits between the overlapping portions of adjacent winds of
ribbon 5
and is sufficiently heated to weld the strips of ribbon 5. In the preferred
embodiment of
the present invention the dimensions of the molten bead 8 are approximately
2.5
millimetres wide and 1.5 millimetres high. The conduit formed according to a
preferred
embodiment has an approximate internal diameter of 19 millimetres, although it
will be
appreciated that the methods of the present invention may be suitable for
forming
conduits having thin walls, irrespective of diameter of the conduit or the
dimensions of
the reinforcing bead.
For breathable wall conduits the thickness of the breathable film or ribbon 5
must
be thick enough so that the conduit does not become too flimsy in use, but
must also be
thin enough so that the conduit wall is sufficiently breathable. It has been
found that
with polyester block copolymers, such as those described above, a wall
thickness
between 15 and 35 microns fulfil these requirements. The preferred wall
thickness for
breathable conduits according to the present invention is approximately 25
microns. A
wall thickness of 25 microns has been found to provide a useful balance
between
breathability, flexibility and strength. The wall thickness for providing an
optimal
compromise of properties will ultimately depend on the specific material
employed. In
this regard the materials and preferred dimensions referred to in the
description are
illustrative and are not intended to be in any way limiting.
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During the continuous manufacture of breathing conduits according to the
method described above it has been found that overheating problems ma.y occur
when
thin film (whether breathable or not) is used in the conduit walls. Further,
the action of
the helical rods rotating and advancing the conduit, may wrinkle or even
damage the
thin ribbon deposited on the former and may reduce the fmish quality of the
conduit.
The mandrel temperature is raised by the continuing application of the molten
bead
which may also result in the thin film overheating and sticking to the mandrel
or rotating
rods, causing the quality of the conduit wall to suffer and/or disrupting the
forming
process. In order to overcome these potential problems it has been found that
a
sacrificial layer, wound onto the mandrel in an overlapping helix pattern
before the
application of the film reduces these problems and increases the quality of
the conduit
produced.
In order to accomplish this task the sacrificial layer of tape is
significantly more
rigid compared to the conduit wall and must not permanently stick to the
mandrel or to
the inside of the conduit wall. It has been found that a material such as bi-
axially
orientated polypropylene is ideally suited for the sacrificial layer. It will
be appreciated
that many alternative materials having a different base polymer to that of the
conduit
wall may also be suitable. The preferred thickness of the polypropylene
sacrificial layer
is between approximately 20 and 60 microns.
Referring to Figure 3, a sacrificial layer 17 is wound from reel 16 onto the
former
before the breathable extruded tape 5. The heat from the applied molten bead
may weld
the overlapping layers of sacrificial layer to each other, but does not result
in any
significant bonding between the sacrificial layer and the conduit wall.
Alternatively, a
secondary thermal welding process may be employed to weld the overlapping
layers of
sacrificial tape before the conduit is formed overtop. The sacrificial layer
may perform
many additional advantageous functions such as those described below:
l. The dummy layer protects the helically arranged rotating rods on the
mandrel from being fouled by molten plastic.
2. The sacrificial layer increases the stability of the process and may help
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prevent the overlapping layers that form the conduit wall from slipping
and moving relative to each other.
3. The sacrificial layer provides a protective barrier between sharp edges or
small protrusions on the mandrel or rotating rods, and the film or ribbon.
4. The sacrificial layer shields the thin film from the higher operating
temperatures of the mandrel and reduces overheating of the film.
It will be readily appreciated by those skilled in the art that the benefits
derived
from the application of a sacrificial layer onto the mandrel before forming a
conduit, are
not limited only to material lay-up and construction wherein the helical
reinforcing bead
is interposed the overlapping layers.
The polypropylene layer can be easily removed from the inner wall of the
fmished conduit product after cooling as it does not bond significantly to the
conduit.
Additional means such as water cooling of the mandrel may also be provided to
reduce
overheating.
A method of removing a releasable inner layer (for example the sacrificial
layer
17) from within a length of conduit 37, subsequent to forming the conduit,
will be
described with reference to Figures 12 and 13. A shaft 39 is provided having a
substantially hollow cylindrical shape of a length longer than that of the
desired conduit
product length. The shaft 39 has a longitudinal slot 40 and is cantilevered
from stock
42. The slot of shaft 39 is in fluid connection with a suction or vacuum
source 38 via
stock 42.
The outer diameter of the shaft is preferably smaller than that of the conduit
37.
A tapered shoulder region 41 is provided at the built-in end of the shaft 39
in order to
enable an effective seal to be formed between the inner layer and the shoulder
portion
when suction is applied. Alternatively, the seal may be formed between the
shaft and
the outside of the conduit. The effect is to seal (so far as necessary) at
least the inside of
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the releasable inner layer from the surroundings.
In use, and in order to remove the sacrificial layer 17 from the inner wall of
the
conduit 37,without damaging the conduit wall, the conduit (including
sacrificial layer) is
placed overtop the shaft as shown in Figure 13. An end of the conduit is slid
over the
shoulder portion 41 of the shaft 39 forming an adequate seal. The other end of
the
conduit is pulled back in an axial direction so that the conduit is contracted
as shown in
region 42, exposing and separating the end portion of sacrificial layer 17
from the
conduit. Vacuum source 38 applied to the inner space of the shaft, leads to a
pressure
differential between the inside and the outside of the inner layer where it
has separated
from the conduit. This urges the inner layer onto the shaft, and into the
slot, and the
separation propagates along the length of the section of conduit, sucking the
sacrificial
layer from the inner wall of the conduit 37. The portion of sacrificial layer
17
immediately opposite slot 40 is sucked so that it protrudes into the shaft
interior. It may
be necessary to initiate this release process at the exposed end (free end of
the shaft) of
the sacrificial layer 17 by hand (by bringing the separated end portion of the
inner layer
adjacent the slot. Helical reinforcing bead 43 prevents the conduit itself
from being
drawn into slot 40). After release of the sacrificial layer from the inner
wall of the
conduit 37, the conduit can be easily removed by sliding it off the shaft.
Removal of the
vacuum from the shaft allows removal of the remaining sacrificial layer more
easily.
Applying the molten bead between the overlapping layers of tape instead of
over
the top of the overlapping layers may improve the weld quality, as both layers
of tape
that are to be welded are in physical contact with the molten bead. This lay-
up may also
reduce overheating problems by lowering the temperature necessary to properly
bond
the molten bead. When the prior art forming method shown in Figure 1 is
employed to
manufacture conduits from very thin film or ribbon, (for example, having a
wall
thickness less than approximately 50 microns), consistently producing a high
quality
surface within the conduit has been found to be problematic.
Figure 4 and Figure 11 illustrates some potential problems which may occur
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during the production of conduit resulting in inferior wall smoothness. The
quality of
the surface finish for the inner surface of a breathing conduit is important,
because
rough inner surfaces may hinder gases flow and may cause more condensation to
build
up in the conduit. A protruding or flapping portion 33 may result if the
underlapping
layer of film is not completely bonded to the molten bead. This problem may
occur if
the underlapping portion of film is too wide or positioned on the former
incorrectly.
Similarly, overflow of molten bead 35, may result in a protrusion or defect
34, if the
underlapping portion 36 of the underlapping layer does not extend far enough
under the
bead. Small voids 9 or undulations, may result between adjacent strips of
ribbon if the
film does not closely conform to the contour of the molten bead. This may
occur if the
thin ribbon is not sufficiently supple. For this reason the construction
technique of the
present invention is especially suited to conduits fabricated from thin supple
film. The
thin film is highly flexible and able to conform closely to the shape of the
raised rib of
the applied molten bead 8 during fabrication. By lapping very closely on to
the bead
and wrapping around the bead, the thin film maintains a smooth inner surface
on the
fmished conduit product. A further defect 44, is shown where the overlapping
portion
of the layer overlaps the bead too much. The molten bead will also flow to
fill voids or
undulations between the lay-up, resulting in a smooth conduit wall. It will be
appreciated that the conduit wall cross section shown in figure 2 and figure 1
I is
illustrative and not meant to be interpreted strictly in regard to the space
shown between
the bead and the conduit wall layers. The application of a sacrificial layer
onto the
former before the conduit wall is formed, is especially suited to the conduit
forming
method wherein the molten bead is applied between overlapping layers. The
presence
of the sacrificial layer ensures that the helically arranged rotating rods on
the former do
not become fouled with molten polymer.
Throughout the diagrams, the helical reinforcing bead is shown as having a
substantially semi-circular cross section. It is however envisaged that the
actual cross
sectional shape of the reinforcing bead may vary. For example the presence and
thickness of the film which overlaps the reinforcing bead, may affect the
shape of the
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reinforcing bead by flattening the bead, resulting in a less rounded and more
square or
rectangular cross section. Further, rollers may be employed to shape the bead.
The
semi-circular reinforcing bead shown in the accompanying drawings is purely
illustrative and not intended to be in any way limiting.
It has been found that breathing conduits formed according to the first
preferred
embodiment described above are extremely light, flexible and provide good
crush
resistance. However conduits having very thin walls may have a reduced
resistance to
axial deformation and/or stretching. Due to the thin tape used to form the
walls of the
conduit, the resulting product may be prone to expansion and/or contraction
along the
axis of the conduit. In use axial forces arising from patient breathing are
capable of
producing axial extension/contraction along the length of the conduit. In
order to
improve the axial stiffness of such breathing conduits, a further embodiment
will now be
described.
In a further embodiment shown in Figure 5 a plurality of reinforcing threads
10,
running the length of the wall and spaced around the perimeter of the tube are
aligned
parallel to one another and substantially parallel to the major axis of the
conduit. The
threads 10 are supported by the helical bead 11, with the threads spanning the
spaces
between turns of the helical bead. In this embodiment it is may be desirable
to choose
the reinforcing threads (material, gauge, type and number) such that the
threads are
sufficiently stiff to improve the conduits ability to resist buckling under
the transiently
reduced internal pressures that could be expected during patient breathing.
Unrestrained
or excessive buckling of the threads may result in unacceptable levels of
conduit axial
contraction and/or extension. The axial threads 10 may be spun or braided
fibres or
drawn or extruded mono filaments or other equivalent forms. Tensile
reinforcement
may be provided by braided or spun fibres while compressive and/or flexural
reinforcement may be provided by drawn or extruded mono filaments.
A method of forming the tube according to the embodiment of Figure 5 is
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described with reference to the apparatus shown in Figure 6. In particular in
the machine
of Figure 6 the tube 12 is formed by helically wrapping a preformed tape or
strip of
polymer 13 on to a rotating former 14. The strip 13 unrolls from reel 15. In
an
analogous manner to that described previously for the first preferred
embodiment, a
sacrificial layer of polypropylene 17, is wound in an overlapping helix onto
former 14
from spool 16. The sacrificial layer 17, between the mandrel and the conduit
being
formed, allows the extremely thin film to be shielded from the mandrel and
higher
operating temperatures.
Tube being formed on the former is rotated and advanced in the direction of
arrow 3. The advance speed of the former is selected relative to the
rotational speed so
that the pitch of the helical laying of the strip or tape on to the former 14,
is a little less
than the width of the strip so that adjacent turns narrowly overlap. An
extruder 18
extrudes a bead 19 of molten polymer material. The molten bead 19 deposits
between
the overlapping portions of adjacent winds of tape 13 and is sufficiently
molten to weld
to the strips of tape 13. The molten bead becomes the helical reinforcement
for the
fmished conduit.
A freely rotatable thread laying head 20 is located over the former after the
bead
extruder 18. The rotating head 20 carries a plurality of spools 21 holding
reinforcing
thread. The head 20 is rotatable by an electric motor and drive belt 22 and 23
respectively. The head 20 is preferably rotated at a speed synchronized with
the speed
of effective rotation of the product 12. Advancement of tube along the former
14 draws
thread 24 from the spools 21 to be laid as parallel threads 10 on the outside
of the
reinforcing bead 19. Another thread 25 is drawn from spool 26 and wound onto
the
former overtop of the longitudinal threads 10, laid by thread laying head 20.
The thread
25 is laid on the former in a helical pattern such that the thread lies
between the helical
bead of molten polymer extruded from extruder 18. The purpose of thread 25 is
to
provide a temporary means of securing the plurality of longitudinal threads in
position
in preparation for permanent fixing. A second extruder 27 extrudes a second
bead of
molten polymer material 28 and deposits it over top the plurality of
reinforcing threads
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and directly on top of the first reinforcing bead 19 and bonds. The second
bead of
molten polymer sandwiches the plurality of longitudinal threads between itself
and the
first reinforcing rib formed by polymer bead 19. Thread 25 however, lies
between these
overlapping reinforcing beads and does not become permanently bonded to the
conduit
wall, allowing it to be removed. Thread 25, may be discarded or drawn from the
former
in a position subsequent to the application of the second reinforcing bead 28
and wound
onto a spool for re-use.
This embodiment of the invention provides a breathing circuit limb reinforced
against crushing by the helical bead and against longitudinal extension by the
axial
threads 10 as well as providing a breathing conduit having all the advantages
of the first
preferred embodiment. The spanning threads 10 also provide an additional
advantage
by reducing direct contact between the user/environment and the surface of the
tube,
therefore reducing the risk of punctures and damage. The threads effectively
provide an
additional barrier against potential damage around the conduit wall. It will
be
appreciated that the foregoing method of reinforcing a conduit is not limited
to conduits
wherein the helical reinforcing bead is interposed between the overlapping
layers.
A further breathing circuit component to which the present invention may be
applied is catheter mounts. A catheter mount connects between a patient
interfacing
component such as a mouth piece, nasal mask or endotracheal tube and the dual
limbs of
the breathing circuit. Connection with the dual limbs of the breathing circuit
is
generally via a wye connector. The extreme flexibility of very thin walled
tubes
manufactured according to the methods herein, makes them particularly useful
in a
catheter mount component.
It should be appreciated that with all of the forming methods described
involving
winding of a narrow ribbon or strip to create a tube, it would be possible to
wind two or
more ribbons or fihns simultaneously onto the former so that the turns created
by each
ribbon are interposed by turns of other ribbons, edges overlapping and being
bonded
together by an interposed extruded helical rib. For example a pair of ribbons
may be
laid as a double helix. This would require a multiplication in the number of
forming
CA 02624190 2008-03-27
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stations associated with the wound on components of the tube or conduit.
Further it is
envisaged that for methods where a preformed tape is supplied to a former, the
tape may
be provided as a laminate having a thin film layer and a reinforcing layer
bonded to it.
Where the thin film layer is a breathable layer, the reinforcing layer is also
permeable
and allows the passage of water vapour.
A further embodiment of the present invention is envisaged where thin walled
breathing conduits are manufactured in a similar manner as described above
but, where
the conduit wall also preferably contains at least one thin conductive wire. A
pair of
wires may be included in order to provide a means for heating the conduit and
or to
carry electrical signals to sensors or transducers. Heated conduits may reduce
the build
up of condensation in the conduit and may also offer a means to maintaining
the
temperature of humidified gases flowing through the conduit. Heated conduits
are most
often used in only the inspiratory arm of a breathing circuit but can also be
used in the
expiratory arm. Heated wall conduits may also be components of coaxial
(unilimb)
circuits, or be used in single limb applications such as for CPAP therapy. In
such
breathing conduits where the inspiratory arm includes heater wires, the
corresponding
connectors at at least one end of the conduit will include an electrical
connection
suitable for connection with the humidified gases source in order to supply
electrical
energy to the conduit heater wires. Referring to Figure 7, a breathing conduit
is shown
including a pair of heater wires 31, embedded in the helical reinforcing bead.
A method of forming a conduit according to this embodiment of the present
invention including a pair of heater wires will now be described with
reference to Figure
8. The method is similar to the method previously described and illustrated in
Figure 3,
but an additional stage is required to lay a pair of parallel wires in between
the
overlapping adjacent winds of film in the edge area of the film that will
become the
seam. A pair of wires 31 are supplied from two reels 29 and 30. The wires are
laid on
top of the first wind of film, towards the edge, after it is laid on the
former but before
the molten bead is applied. Figure 8 shows a pair of heater wires 31 in hidden
detail
CA 02624190 2008-03-27
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under the molten bead 8. The molten bead 8 is then laid over the wires on top
of the
first layer of film before the following overlapping wind of film wraps around
the
former and completes the tube. It will be appreciated that each of the film,
heating
wire(s), and reinforcing bead may be applied in a different plane in order to
achieve the
desired spatial lay-up.
The resulting conduit is shown in Figure 7 and is similar to the previous
embodiment shown in Figure 2, but includes an additional pair of heater wires
embedded in the helical reinforcing bead of the conduit wall. In this
embodiment, a
sacrificial layer 17 may also be wound in an overlapping helix onto the former
from
spool 16. The sacrificial layer 17 may be a polypropylene layer or some other
material
that will not weld to the conduit wall. The sacrificial layer 17 between the
mandrel and
the conduit being formed, allows the extremely thin film to be shielded from
the higher
operating temperature of the mandrel and alleviates overheating of the film.
A further method of forming a conduit according to the present invention
including a pair of heater wires will now be described.
The above method of forming a conduit discloses an online process for winding
a
pair of heater wires into the conduit wall. It is envisaged that a pair of
heater wires may
be included in a preformed tape which would then be used to form the walls of
the
conduit in a similar method to that described above and illustrated in Figure
3. Figures
9a and 9b show cross sections of such a tape being formed by laying a pair of
parallel
wires a distance x from one edge of the tape. The length x of tape between the
wires
and the edge is then folded over and back onto the rest of the tape so as to
enclose the
pair of parallel wires, as shown by arrow 32. A secondary thermal welding
process may
then be employed to bond the folded portion of tape so as to permanently embed
the
parallel wires. It will be appreciated however that a secondary thermal
welding process
may not be necessary if the extruded tape is molten or semi-molten when the
folding
occurs. In this case the two regions of molten layer, when folded and pressed
together
will bond.
Such a pre-formed folded tape including embedded wires may then be wound on
CA 02624190 2008-03-27
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to reels and supplied to a conduit forming process such as that described
previously and
illustrated in Figure 3 to produce a breathing conduit with a pair of integral
heating
wires. Figure 10 shows the lay-up of a breathing conduit formed by this
embodiment of
the present invention. The portion of thin film that wraps over the
reinforcing bead and
the adjacent wind on the former is only one layer thick and therefore is able
to conform
to the contour of the reinforcing bead. A tube formed according to this
embodiment of
the present invention therefore is able to retain all of the advantages of the
previously
described preferred embodiments, while having the additional advantage that a
forming
apparatus as described in Figure 3 may be employed to manufacture a conduit
including
embedded heater wires without substantial modification to the forming
apparatus. In
such a case the extruder 4 is replaced with a reel of pre-formed folded tape
such as that
shown in Figure 9b and supplied to the forming apparatus.
