Note: Descriptions are shown in the official language in which they were submitted.
~ 2~ g 49 3 4319-47
FLEXIBLE TUBING AND
METHOD OF MANUFACTURING SAME
Background of the Invention
Field of the Invention
The present invention relates to reinforced flexible
tubing of thermoplastic material and, more particularly, to rein-
forced flexible tubing having high resistance to bursting.
The present invention also relates to a method of manu-
facturing flexible tubing of thermoplastic material.
Description of the Prior Art
It is known to form a plastic tube, for example, by
extrusion through a circular die, to reinforce that tube by
applying a reinforcing material such as a textile or a metallic
material, normally in braid or lap form, over the exterior sur-
face thereof, and to apply a second (outer) tube, generally by
extrusion over the inner tube of the reinforcing material. Pre-
ferably, the outer tube is applied over the inner tube and the
reinforcing material while the inner tube is still warm from its
own formation, which is generally by extrusion, so that the mate-
rials of the inner and outer tubes can blend together and trap
the reinforcing material therebetween. It is desirable to en-
sure that the outer tube does adequately bond to the inner tube
in order to provide for sufficient peel strength of the finished
tubing and it is known to apply substances such as adhesives and
bonding agents to the exterior surface of the inner tube to
assist in the bonding of the outer tube thereto. Problems some-
times arise with known reagents and misbonding occurs, in which
event the inner and outer tubes are often separated from one an-
other with the reinforcing material being bonded to neither the
inner nor outer tube which reduces the strength and thus the
ability to withstand internal pressure.
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Summary of the Invention
According to the invention, there is provided rein-
forced flexible tubing of thermoplastic material comprising:
a) a tubular core of thermoplastic material having
on the outer surface thereof a multiplicity of contiguous forma-
tions integral with said core, said formations defining valleys
therebetween;
b) reinforcing material disposed on said outer sur-
face of said core in intimate contact with said surface of said
core; and
c) a coating of thermoplastic material covering said
outer surface of said core and said reinforcing material, said
thermoplastic material of said coating being directly and
intimately bonded to said thermoplastic material of said core.
According to another aspect of the invention, there is
provided a method for manufacturing reinforced flexible tubing
of thermoplastic material comprising the steps of:
a) providing a flexible tubular core of thermo-
plastic material;
b) supplying reinforcing material to the surface of
said core; and
c) extruding, by means of an extruder, a thermo-
plastic coating on the outer surface of said tubular core and
said reinforcing material while creating a positive air pressure
differential between the exterior and interior of said coating
in said extruder during extrusion to urge said coating into
intimate contact with said core and said reinforcing material.
Brief Description of the Drawings
The present invention will be further described with
reference to the following drawings which are merely illustra-
tive of the invention and are not intended to limit the inven-
tion.
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93
Figure 1 is a prospective, partly-cut away view of tub-
ing according to the present invention;
Figure 2 is a transverse cross-section of tubing
similar to that shown in Figure 1 but having more formations on
the inner tube;
Figure 3 is a prospective, partly-cut away view of tub-
ing of another embodiment of the present invention;
Figure 4 is a schematic diagram illustrating the
apparatus used in practising the invention;
Figure 5 is a sectional plan of an extruder forming
part of an embodiment of the apparatus;
Figure 6 is a transverse cross-section of an extrusion
die useful in an embodiment of the apparatus;
Figure 7 is a sectional plan view of nip rollers use-
ful in an embodiment of the apparatus;
Figure 8 is a transverse cross-sectional view of tub-
ing of an embodiment of the present invention; and
Figure 9 is a transverse cross-sectional view of tub-
ing of an embodiment of the present invention.
Description of the Preferred embodiments
Referring to Figures 1-3, reinforced flexible tubing 1
has a tubular core 2 of thermoplastic material having a multi-
plicity of contiguous formations 3 integral with the core. The
formations 3 define valleys, each of which contains (Figure 1)
or is bridged by (Figure 3) reinforcing material 4. Extruded
over and covering core 2 and reinforcing material 4 is coating 5
of thermoplastic material.
The outer surface core 2 is formed with contiguous
formations 3, such as, for example, ridges, ribs or unduiations.
Preferably, the formations comprise a series of ridges or ribs
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defining the valleys therebetween and, most preferably, the
formations comprising a series of ridges which run longitudin-
ally of the core 2 so that the ridges 3 are parallel to the main
central axis of core 2. When a series of ribs or ridges are pro-
vided, it is convenient for the valleys defined therebetween to
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be V-shaped ln cross-section, the ridges or ribs thus being cor-
respondingly tapered from their base. It is, however, possible
to provide ribs or ridges having other shaped cross-sections
such as trapezoidal cross-section. Where a trapezoidal cross-
section is used, the shortest side of the trapezoidal cross-
section is preferably adjacent to the outer surface of core 2.
The provision of the aforementioned formations increases the
external surface area for a given outer diameter of core 2.
Tubular core 2 may be formed of any suitable thermo-
plastic material. A preferred thermoplastic material for form-
ing core 2 is polyvinyl chloride. Tubular core 2 may be formed
of an anti-static thermoplastic material where anti-static pro-
perties are required in the final product, such as in some types
of tubing for medical purposes. Tubular core 2 having forma-
tions 3 on the outer surface thereof is preferably formed by
extrusion.
The reinforcing material 4 disposed on the outer sur-
face of core 2 may be comprised of, for example, a textile mate-
rial, such as yarn or thread, or a metallic material, such as
wire. A textile yarn, such as polyamide or polyester yarn, is
preferred. For many tubing constructions, a yarn size of 1100
decitex gauge is suitable. Other yarn sizes can be selected,
depending on the size of tubing and the reinforcement required.
The reinforcing material 4 may be disposed on the
outer surface of core 2 in lapped or braided fashion, for
example in criss-cross fashion. When reinforcing material 4 is
in lapped or braided form, it is preferable that a plurality of,
for example, textile yarns be disposed on the core to produce
the braid effect with half the reinforcing material running in a
spaced apart, somewhat clockwise direction and the other half
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running in a spaced apart, somewhat counterclockwise direction,
the yarns crossing but leaving generally diamond-shaped spaces
therebetween. However, i~ core 2 has the aforementioned longi-
tudinally disposed ribs or ridges, reinforcing material 4 may
also be conveniently placed along the length of valleys defined
thereby, thus increasing the longitudinal as well as hoop
strength.
A coating 5 of thermoplastic material covers reinforc-
ing material 4 and tubular core 2. The thermoplastic material
of coating 5 is generally similar to or compatible with that
used for tubular core 2. Preferably, coating 5 is of the same
thermoplastic material as core 2. Most preferably, both tubular
core 2 and coating 5 are polyvinyl chloride. When both the
tubular core and coating are of polyvinyl chloride, the finished
tube is usable over a temperature range of at least about -20C
to about 65 C.
The thermoplastic material of coating 5 is directly
and intimately bonded to the thermoplastic material of the core
2 and reinforcing material 4 is securely entrapped between core
2 and coating 5. This direct intimate bonding of the material
of coating 5 to the outer surface of core 2 may preferably be
achieved by extruding coating 5 over core 2 and reinforcing mate-
rial 4 with a positive air pressure differential between the
exterior and interior of the coating, as will be described in de-
tail hereinafter with regard to the method of the invention.
Often the coating of the tubing of the present inven-
tion does not have a smooth surface, this being particularly so
when the material of the coating is extruded under pressure, and
in general the outer surface of the coating will follow the con-
tours of the formations of the core and/or the reinforcing mate-
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120~493
rial. Tubing of the present invention having an outer surface
which is not smooth affords advantages in the coiling thereof.
This is because tubing having a smooth outer surface tends to
stick to itself, especially with smooth polyvinyl chloride sur-
faces, and this causes problems in automatic coiling which do
not occur with tubing of the present invention having a non-
smooth surface.
If it is desirous to provide tubing of very high
strength, reinforcing material may be applied on the outer sur-
face of the coating, and a second coating applied thereover asshown in Fig. 9. The tubing thus formed includes a tubular core
2 having the aforementioned formations 3, reinforcing material
4A on the outer surface of tubular core 2, a coating 5A applied
over the core and its reinforcing material 4A, reinforcing mate-
rial 4B on the outer surface of the first coating and a second
coating 5B applied over the first coating 5A and its association
reinforcing material 4B. The first and second coatings are
applied so as to entrap the reinforcing materials between the
core and first coating, and first and second coatings, respec-
tively. The thermoplastic material of the first coating isdirectly and intimately bonded to the thermoplastic material of
the core and the thermoplastic material of the second coating is
directly and intimately bonded to the thermoplastic of the outer
surface of the first coating.
The outer surface of this second coating may be smooth
or non-smooth, although any tube produced in the aforementioned
manner greatly reduces the interface bond stress since the flex-
ing shear load on the interface between the substrate and the
subsequent layers is spread over a large percentage of the
resultant wall thickness of the whole tubing thereby reducing
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1~2094~3
the necessity for high artificial bond strength. Of course,
further layers of reinforcing material and thermoplastlc mate-
rial may be provided as required for even greater strength.
A further embodiment of the present invention is flat
tubing of ribbon-like form as shown in Fig. 8. Such tubing is
substantially flat with the volume of the inside of the core be-
ing substantially zero and contains substantially no air within
the inner part of the tubing when not in use. The tubing is cap-
able of assuming a tubular form by introduction of internal
fluid pressure. Such flattened tubing may be used as hosepipe,
being self draining, by virture of the elastic memory of the
material for the ribbon-like form. This tubing is more easily
formed into a roll and occupies less space for storage than con-
ventional round tubing.
The ridges and valleys provide an additional function
in this flat embodiment in that they act as hinge-like parts,
allowing the hose to readily assume a traditional shape under
internal pressure. When the pressure is removed, the hose re-
turns to a substantially completely flat profile, due to the
elastic memory of the tubing urging evacuation of the fluid with-
in the tubing.
The present invention generally enables a reduction of
up to 30% of the material used to form the second tube in com-
parison with prior art composite tubing and still is capable of
achieving the same resistance to bursting as the conventional
tubing. For example, fully flexible polyvinyl chloride tubing
according to the present invention can be produced having an
overall thickness of no more than about 3 mm and an inside dia-
meter of up to about 19 mm, with a capability of working pres-
sures as high as 60 BAR at 20 C.
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The excellent flexibility of the tubing of the presentinvention is high due to the need for less material for a given
strength.
The apparatus for manufacturing flexible reinforced
tubing of the present comprises a core supply for supplying a
flexible tubular core, a reinforcing material supply device for
supplying at least one reinforcing material to the outer surface
of the core and an extruder arranged to extrude a tubular coat-
ing of thermoplastic material onto the outer surface of the core
in the reinforcing material, the extruder being adapted to en-
able a positive air pressure differential to be applied between
the exterior and the interior of the coating around the core dur-
ing extrusion of the coating.
The method of manufacturing flexible reinforced tubing
of the present invention includes providing a flexible tubular
core of thermoplastic material, supplying reinforcing material
to the surface of the core and extruding, by means of an
extruder, a thermoplastic coating on the outer surface of the
tubular core while creating a positive air pressure differential
between the exterior and interior of the coating in the extruder
during extrusion to urge the coating into intrinsic contact with
the core and the reinforcing material. This positive air pres-
sure differential during extrusion causes a bond to form
directly between the core and the coating.
Preferably, the exterior of the coating is at atmos-
pheric pressure, and a vacuum is applied to the interior of the
coating as it is extruded. The coating is suitably extruded as
a tube uniformly spaced from the surface of the core, the vacuum
drawing the coating down onto the core while the coating is
still in a plastic state.
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~ rhe core supply may be a reel, but is preferably an-
other plastics extruder, continuously forming a tubular core
which is cooled in water before passing through the winding de-
vice. The reinforcing material supply device is preferably
arranged to apply a plurality of reinforcing threads, half the
thread running in the opposite direction to the other half.
The apparatus and method are capable of producing tub-
ing having typically one third less material than conventional
tubing of the same general structure, internal diameter and
burst pressure. The amount of tubing which has to be discarded
through bond failure is substantially reduced and higher produc-
tion speeds can be achieved.
The apparatus, shown in Figure 4, includes a first
extruder 11 which is a conventional screw feed extruder receiv-
ing thermoplastic material, such as polyvinyl chloride, in the
form of granules. The arrangement of the granule feed hopper
and feed screw barrel is conventional and these parts are there-
fore not shown in detail, only a part of the barrel being shown.
The granules are melted and the molten thermoplastic material is
forced through an annular die to extrude a tubular core 2, pre-
ferably having an external surface consisting of longitudinal
ridges and valleys of generally triangular configuration around
the tube. Dies suitable for extruding tubular core 2 are des-
cribed in further detail hereinafter with regard to Figure 6.
The core 2 is preferably extruded at a temperature of about 140
to 150C and at a linear speed of about 2000 ft/hr (170 mm/s)
and passes through a cooling bath 13 containing a flow of cool-
ing water. The cooling bath 13 cools the core 2 to about 70 C
before it reaches a reinforcing material supply, such as winding
device 14 for the
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application of reinforcing material. Wlnding device 14 is com-
prised of two contra-rotating drums 14A and 14B, each of which
contain a plurality of reels 15 of reinforcing material. The
reinforcing material may be comprised of, for example, a textile
material, such as yarn or thread, or a metallic material, such
as wire. The reels are arranged to feed the reinforcing mate-
rial to the core under a very light tension and spaced apart so
as to produce a braided effect, the yarns crossing but leaving
generally diamond-shape spaces therebetween.
The core with the reinforcing material thereon passes
from winding device 14 into a second extruder 16 of similar
general configuration to the first extruder 11. The coating
material is a thermoplastic material, preferably a material
which is similar to or compatible with that used for the core.
Most preferably both the core and the coating material are poly-
vinyl chloride. The coating material is supplied to an annular
die which is described hereinafter in more detail with reference
to Fig. 5. A vacuum pump 17 is connected to the extruder 16 by
means of a vacuum pipe 18. The coated core passes through a
second cooling bath 19 whose length, coolant flow rate and tem-
perature are selected to reduce the temperature of the coating
from the extrusion temperature, which may be from about 140 to
150 C, to a suitable temperature to permit manual handling of
the tube, for example, forming into rolls such as on a reel 10.
Referring to Fig. 5, the extruder comprises an elon-
gated screw 20 which drives the molten thermoplastic coating
material into the extrudina head 21. Head 21 comprises a two
part extruding tool 22, having an outer part 22A containing a
frusto-conical bore 22B therethrough and a generally frusto-
conical inner part 22C whose conical surface contains an angle
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smaller than that contained by the surface of the bore 22B. Theinner part 22C has a cylindrical bore 22D therethrough, the dia-
meter of which is larger than the external diameter of the core
2 with the reinforcing material wound onto the surface thereof
so that the prevailing gas pressure at the rear face 22E of the
inner part 22C is substantially the same as that of the opposite
end of the bore 22D.
The rear face 22E is attached to one end of a tubular
vacuum chamber 23 which is in turn attached to an adjusting ring
24 which is externally screw-threaded and screws into a corres-
pondingly-threaded socket 25 in the body of extruding head 21.
Rotation of the adjusting ring 24 thus moves the inner part 22C
of the extruding tool relative to outer part 22A which in turn
alters the thickness of the coating extruded.
A vacuum connector piece 26 extends axially from
adjusting ring 24 and has a bore 27 therethrough which communi-
cates with the interior of vacuum 23 and with vacuum tube 28
which is connected by flexible hose 8 to vacuum pump 7 (see Fig.
4). An inlet tube 29, having a tube guide, typically of PTFE,
in sealing bushing 30 in the end thereof, extends axially from
connector piece 26 and the interior of the tube communicates
with the interior of connector piece 26.
Bushing 30 makes sealing contact with the core as it
enters the inlet tube 29 and passes through the vacuum chamber
to the extruding tool, thus maintaining the vacuum.
The coating material delivered to the extruding head
21 by screw 20 passes into an annular space 31 surrounding the
vacuum chamber 23 and from there into the space between the
inner and outer parts 22C and 22A of the extruding tool. The
material is extruded at a rate such that it flows out of the
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annular gap at the outlet of the extruding tool 22 at substanti-
ally the same speed as out of the annular gap at the outlet of
the extruding tool 22 and substantially the same speed as that
at which the core 2 passes through the extruder, typically
170 mm/sec. The vacuum in the vacuum chamber is communicated to
the inside of the coating at the point of extrusion. The coat-
ing is extruded substantially parallel to the core and the
vacuum, of the order of about 20 to 40 inch water gauge, draws
the coating into intimate contact with the core and with the
reinforcing material wound onto the core. The coating thickness,
after being drawn onto the core, is less than the thickness of
the core, and the texture of the reinforcing material may be
felt and may also be seen after coating.
In a first alternative embodiment, the coated tubing
passes from the second extruder 16 through cooled nip rollers 32
as shown in Fig. 7 before entering cooling bath 19. Nip rollers
32 flatten the tubing into a ribbon-like form which may be re-
turned to a tubular form by internal fluid pressure. Such flat-
tened tubing 33 may be used as hosepipe, being self-draining, by
virtue of the elastic memory of the material for the ribbon-like
form, more easily formed into a roll, and occupying less space
for storage than conventional round tubing.
In a second alternative embodiment, the coated tubing
from the second extruder 6 passes through a cooling bath which
brings the temperature down to about 70C then to a second wind-
ing device identical to the first winding device 4 where a
second set of reinforcing material is applied, and from there to
a third extruder, of a generally identical construction to the
second extruder 16, where a final outer coating is applied,
again of a thin thermoplastic material, such as polyvinyl
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chloride. Tubin~ produced in this manner is suitable for ~Jery
high pressure applications, with operating pressures, for
example, for a 10 mm internal diameter tube, in excess of 60 BAR
at 20 C.
The apparatus for and the method of manufacturing of
reinforced flexible tubing of thermoplastic material provides
efficient low cost production because production may be carried
out in a continuous manner. Such continuous production permits
a thin outer coating to be applied over the braid and core and
in multilayer tubing prevents problems such as "cold flow" when
the tubing is assembled with connectors. Further, tubing pro-
duced according to the present invention can be produced at
lower cost due to tremendous saving in material weight. Work in
progress is non-existent as tubing may be continuously produced
and scran levels are exceedingly low.
In a preferred embodiment of the invention, approxi-
mately 80% of the thermoplastic material is in the inner core
and a maximum of about 20% of the thermoplastic is in the outer
coating. This allows the outer coating to assume the configura-
tion of the ribbed inner core giving the tubing an abrasionresistant cover since the contact point at any abrasion area is
reduced.
In a preferred embodiment of the invention, tubular
core 2 may be extruded utilizing a die of the type shown in
Figure 6 to produce the tubular core 2 having an external sur-
face consisting of longitudinal ridges and valleys of generally
triangular configuration extending longitudinally on the tube.
Reinforced flexible tubing of thermoplastic material has been
successfully produced utilizing dies 34, having the configura-
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tions shown in Table 1, in first extruder of an apparatus
similar to that shown in Fig. 4. The inside diameter of the
core thus produced is also shown in Table 1.
Table I
Die Dimensions
Die Core
Right Angle Bore Width of Ridge Ridge Peak Inside
A(degrees) Diameter Valley Base Height Angle Diameter
B(in.) C(in.) D(in.) E(degrees) (in.)
1 84 0.480 0.012 0.035 18 0.937
2 84 0.550 0.009 0.035 15 0.937
3 84 0.725 0.035 0.023 12 0.875
4 84 0.915 0.013 0.028 8 0.812
5 84 0.980 0.014 0.035 9 0.750
6 84 1.512 0.003 0.035 5
The present invention will be further illustrated by
the following examples which are intended merely to illustrate
the present invention and are not intended to limit the scope of
the invention which is defined in the claims.
EXAMPLE
A flat hose was produced in accordance with the method
described hereinbefore with reference to Figures 4 and 7, as the
first alternative embodiment. The internal diameter of the tube
before passage through the nip rollers was 12 mm. The nominal
overall wall thickness was 2 mm, with the height of the ridges,
relative to the valleys, being 0.58 mm. The outer coating thick-
ness was approximately 1 mm relative to the valleys. The over-
all weight of the hose was 93 g/m. Samples of the tube were
tested for burst pressure by applying gradually increasing hydro-
static pressure to a sealed section of the tube. The minumum
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burst pressure out of a number of samples was found to be 450
p.s~i.g. (3.1 MNm ) and burst pressures were generally in ex-
cess of 500 p.s.i.g. (3.45 MNm ).
COMPARATIVE EXAMPLE 1
Round hoses were prepared in accordance with the main
method hereinbefore described with reference to Figures 4 and 5.
Hoses of exactly the same nominal dimensions were produced by a
similar process, but without the application of vacuum. Each
hose was tested for burst pressure as in the Example herein-
before.
The results were as follows:
BURST PRESSURE
(at 20C) (psig)
Nominal Internal COATING COATING
Diameter (mm) WITHOUT WITH
VACUUM VACUUM
6 1190 1300
1160 1250
12 790 ~50
19 575 6~5
COMPARATIVE EXAMPLE 2
Hoses were produced using the methods as in
Comparative Example 1, but, in the case of the hoses coated with-
out application of vacuum, the coating thickness was such that
the burst pressures of the hoses coated with the without vacuum
were generally the same. The resulting weights of the hoses for
a unit length were compared, and Table 2 gives the result.
20Nominal Internal WEIGHT (g/m)
Diameter (mm) COATING COATING
WITHOUT WITH
VACUUM VACUUM
6 90.8 54
165 ~5
12 223 126
19 334 ~58
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COMPARATIVE EXAMPLE 3
A hose manufactured in accordance with the method here-
inbefore described with reference to Figures 4 and 5 was tested
to compare the strength of bonding between the coating and the
core with a conventional gas hose having a similar general con-
struction, but a smooth core tube and coating applied without
vacuum. The hoses were both high pressure gas hoses of 10 mm
internal diameter.
300 mm lengths of each type of hose were used as test
specimens. A hypodermic needle was inserted at one end of the
hose at the junction between the coating and the core. The hose
was plugged and secured with hose clips, the needle extending
beyond the clip at one end. Each sample was immersed in water
during the test, and air was supplied under pressure to the
hypodermic needle.
Samples in accordance with the invention were pres-
surized for 20 hours at 50 p.s.i.g. (343 kNm 2), and for one
hour at 60 p.s.i.g. (414 kNm 2) at 80 p.s.i.g. (552 kNm 2), and
no leak was detected at the end of this time.
A sample of the conventional hose showed air leaks
from both ends, from between the layers, after only a few
minutes at a pressure of 10 p.s.i.g. (69 kNm ).
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