Note: Descriptions are shown in the official language in which they were submitted.
~ ., L ')--4 /
~ ~273~
FL!EXIBLE 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 ~rt
It is known to form a plastic tube, ~or 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
reinforcincJ 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 o~ the outer tube there~o. 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 th~ reinforcing material being bonded to neither the
inner nor outer tube which reduces the strenqth and thas the
3Q ability to withstancl internal pre 5S ure.
~r,,~
Summa'ry of the Invention
According to the invention, there is pro~Jided rein-
forced flexible tubing of thermoplastic material comprising:
- a) a tubular core of thermoplastic material ha-~Jingon the outer surface thereof a multiplicity of contiguous forma-
tions integral with said core, said formations de~ining 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 inven-tion, 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 coatin~ into
intimate contact with said core and said reinforcing material.
~rief Description of the Drawings
The present invention will be further described with
reference to the followin~ drawings which are merely illustra-
tive of the inven~ion and are not intended to limit the inven-
tion .
,7~3~3
Figure 1 is a prospective, partly-cut awa~ vir--,/ 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 awa~ vie~l o tub-
ing of another embodiment of the present invention;
Figure 4 is a schematic diagram illustratinc3 the
apparatus used in practising the invention;
Figure 5 is a sectional plan of an extruder formin-~
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 ~ransverse cross-sectional ~iew of tub-
ing of an embodiment of the present invention.
Description of the Prefexred embodiments
Referring to Figures 1-3, reinforced flexibl~ tubin~ 1
has a tubular core 2 of thermoplastic material havinct a multi-
plicity of contiguous formations 3 integral with the core. The
formations 3 define valleys, each of which contains (Fic~ure 1)
or is bridged by (Flgure 3) reinforcinct material 4. E~truded
over and covering core 2 and reinForcinc~ material 4 is coatinc3 5
of thermoplastic material.
The out~r surface core 2 is formed with contic3uous
formations 3, such as, for example, ridctes, ribs or undulations.
Preferahly, th~ formations comprise a series o~ rid~3es or rihs
7~3
defining the valleys therebetween and, mos-t preferably, th~
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 valle~s defined therebet~/een to
~73~3
be V-shaped in cross-section, the ridges or ribs thus bein~3 cor-
respondingly tapered from their base. It is, howe~er, 005sible
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-
seetion 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 havincJ forma-
tions 3 on the outer surface thereof is preferably ~ormed by
extrusion.
The reinforcing material 4 disposed on the outer sur-
face of core 2 may be comprised o-E, for example, a textile mate-
rial, such as yarn or thread, or a metallic material, such as
wire. A kextile yarn, such as polyamide or polyester yarn, is
preferred. For many tubing constructions, a yarn size of 1100
cdecitex gauge is suitable. Other yarn sizes can be selected,
depending on the size of tubin~ and the reinforcement re~uired.
The reinforcing material ~ ma~ be dispased on the
outer surface of core 2 in lapped or braided fashion, for
example in criss-cross fashion~ ~hen reinforcin~ material ~ is
in lapped or braided form, it is preferable that a pluralit~ o~,
~or example, textile yarns be disposed on the core to procluce
the braid effect wlth half the reinforcin~3 material runnill~ in a
spaced apart, somewhat clockwise clirection ancl the otller h~lr
~73~3
running in a spaced apart, somewhat counterclocl~,Jis~ r--~tion,
the yarns crossing but leaving generally diamond-shape~ spaces
therebetween. However, if core 2 has the aforementioned longi-
tudinally disposed ribs or ridges, reinforcing material 4 ma~,~
also be conveniently placed along the length o-f valle~s ~ ned
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. ~lost pre$erably, both tubular
core 2 and coating 5 are polyvinyl chloride. ~hen both the
tubular core and coating are of polyvinyl chloride, the finished
tube is usable over a temperature range of at least about -20 C
to ahout 65C.
The thermoplastic material of coating 5 is directl~
and intimately bonded to the thermoplastic material of the core
2 and reinforcing tnaterial 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 prefs~rably he
achieved by extruding coating S over cor~ 2 and rein~orcinc3 mat~-
rial 4 with a positive air pressure diEferential bet~een the
exterior and in-terior of the coating, as will be described in ~le-
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 }-eing particularly so
when the material o~ the coatincl is extruds~d under pressure, an~'
in general the outer surfac~ of the coatinc3 will follow the con-
tours of the formatic>ns oE the S orS~ ancl~or the rS~in~orcins~3 n~S-~-
3~3
rial. Tubing of the p~esent invention havinc7 an outer su-- a-r
which is not smooth affords advantages in the coiling there3f.
This is because tubing having a smooth outer surface ten-ls to
stick to itself, especially with smooth polyvinyl chloride sur-
faces, and this causes problems in automatic coiling wnich do
not oceur 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 Eormations 3, reinforcing material
4A on the outer surface of tubular core 2, a coating 5A applied
over the core and its reinforcing material ~, reinforcing mate-
rial 4~ on the outer surface of the first coating and a second
coating 5B applied over the first coating 5~ 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
direetly 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 sincc tne ~lc:;-
ing shear load on the interface between the su~strate and the
subsequent layers is spread over a large percentacJe o~ the
resultant wall thickness of the whole tubing thereby rcducing
the necessity for high artificial bond strength ~f cour~e,
further layers of reinforciny material and thermoplas,ic mate-
rial may be provided as required for even greater strenyth.
A further embodiment of the present invention is la_
tubing of ribbon-like form as shown in Fig. 8. Such tubin~ is
substantially flat with the volume of the inside of the core be-
ing substantially zero and contains subs-tantially 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 sel~ 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, ~ue to -the
elastic memory of the tubing urging evacuation of the fluid with-
in the tubin~.
The present invention generally enables a recluction of
up to 30% of the material usecl to form the second tube in com-
parison ~ith prior art composite tubinq and still is capable o^
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 havin~ an
overall thickness of no more than about 3 mm and an inside dia-
meter of up to about 19 mm, with a capa~ility of working pres-
sures as high as ~0 BAR at 20 C.
The excellent fle~.ibilit~y of the tu~in~ of th~ ?res~n_invention is high due to the need for less material or a gi-~-n
strength.
The apparatus for manufacturing flexible reinforced
tubing of the present comprises a core supply for suppl~ing a
flexible tubular core, a reinforcing material suppl~ device for
supplying at least one reinforcing material to the outer sllrface
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 o~ manufacturing flexible reinforced tubing
of the present invention includes providing a flexible tubular
core of thermaplastic material, supplying reinforcing material
to the surfac~ of the core and extruding, by means of an
extruder, a thermoplas~ic 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 ~ond to form
directly bet~een the core and the coating.
Prefera~ly, the exterior of the coatin~ is at atmos-
pheric pre5sure, and a vacu~lm is applied ta the interior of the
coating as it is extruded. The coating is suitably extruded as
a tube uni~ormly spaced ~rom the surface o~ the core, the vacuum
drawinq the coatlng down onto the core while the coating is
still in a plastic state.
_g_
~7~1~
~ he core supply~ may be a reel, but is preferably an-
other plastics extruder, continuousl~ forminy a tubular cDre
which is cooled in water before passing through the winding d--
vice. The reinforcing material suppiy de~Jice 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 con~entional
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, incluces 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 de-tail, 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 re~ard to Figure 6.
The core 2 is preferably extruded at a temperature of about 140
to 150 C 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 ~ to about 70 C
before it reaches a reinforcing material supply, such as winding
device 1~ for the
--10--
application of reinforcing material. ~71ndin~ device 14 is CO,?s~
prised of two contra-rotating drums 14A and 14B, each OL ~Jnic--.
contain a plurality of reels 15 of reinforcing material. Th~
reinforcing material may be comprised of, for example, a te~.tile
material, such as yarn or thread, or a metallic ~aterial, 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 crossiny but leaving
generally diamond-shape spaces therebetween.
The core with the reinforcin~ material thereon passes
from winding device 14 into a second eY~truder 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 care pol~
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 lenyth, coolant flow rate and tem-
perature are selected to reduce the tempera~ure oE the coatinc3
from the extrusion temperature, which may be from about 1~0 ~o
150 C, to a suitable temperature to permit manual handlir.g of
the tube, for example, forming into rolls such as on a reei 10.
Referring to Fig. 5, the extruder comprises an elon-
gated screw 20 which drives the molten thermoplc~stic coatîng
material into the extruding head 21. Elead 21 comprises a ~wo
part extruding tool 22, havin~ an outer part 22~ containin~ a
frusto-conical bore ?2B therethrougtl an~i a ~enerally rus~o-
conical inner part 72C whose conical sur~ce contains all an{31e
--11--
~ ~ ~ 7 ~ 1t~
smaller than that contained by the surface of the ;~Gre~ 22~ ,einner part 22C has a cylindrical bore 22D therethrougn, 'h-e di--
meter of whieh is larger than -the external diameter of .ne co e
2 with the reinforcing material wound onto the surface thereo
so that the prevailing gas pressure at the rear face 22E o. the
inner part 22C is substantially the same as that of the opposite
end of the bore 22D.
The rear faee 22E is attached to one end of a tubular
vaeuum ehamber 23 whieh is in turn attached to an adjusting ring
24 whieh is externally serew-threaded and screws into a corres-
pond.ingly-threaded soeket 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 whieh in turn
alters the thiekness of the eoating extruded.
A vaeuum eonnector piece 26 extends a~ially from
adjusting ring 24 and has a bore 27 therethrough whieh eommuni-
cates with the interior of vaeuum 23 and with vaeuum tube 28
whieh is eonneeted by flexible hose 8 to vaeuum pump 7 (s~e Fi~.
4). An inlet tube 29, having a tube guide, typically of PTFE,
in sealing bushing 30 in the end thereof, e~tends axially from
eonneetor pieee 26 and the interior of the tube communieates
with the interior of COnneCtGr 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 eoating material delivered to the extrudin~ head
21 by screw 20 passes into an annular space 31 surrounclincJ the
vaeuum chamber 23 and Erom there into the space bet~.~een the
inner and outer parts 22C and 22A of the e:;trllclincJ tool. The
matèrial is extruded at a rat~ such that it fl.ows out of the
~12-
annular gap at the outlet of the e~truding tool 22 a~ s~ s~an-i-
ally the same speed as out of the annular ga? ~t the outle' 'J--
the extruding tool 22 and substanti~ the same sDeed as _ha-
at which the core 2 passes through the extruder, t~picall,~
170 mm/sec. The vacuum in the vacuum chamber -is com~unicated to
the inside of the coating at the point of e.~trusion. Tn~ coat-
ing is extruded substantially parallel to thc core and the
vacuum, of the order of about 20 to 40 inch ~.Jater gauge, draws
the coating into intimate contact with the core and with the
reinforciny 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. `.~ip rolle-s
32 flatten the tubing into a ribbon-like form ~hich may be re-
turned to a tubular form by internal fluid pressure. Such flat-
tened tubing 33 may be used as hosepipe, being self-clraining, ~y
virtue of the elastic memory of the material for the ribbon-like
form, more ea~ily Eormed into a roll, and occup~ing less space
for storage than conventional round tubing.
In a second alternative embodiment, the coated tuDing
from the second extruder 6 passes through a cooling bath wnich
brings the temperature down to about 70 C then to a second wind-
ing device identical to the first windin~ device ~ whcre a
second set of reinforcing materi,ll is applied, and from thcre to
a third extruder, of a generally identical construction to thc
second extruder 16, where a final outcr coating is applicd,
again of a thin thermoplastic material, such as ~oly~inyl
-13-
chloride. Tubing produced in this manner i~ suitable for J---ry
high pressure applications, ~ith operating presa~1res, or
example, for a 10 mm internal di~meter tube, in e~cess of ~0 ~A~
at 20 C.
The apparatus for and the method of ~anufacturing o'
reinforced flexible tubing of thermoplastic material provides
efficient low cost production because production ma~ 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 COât due to tremendous saving in material weic3ht. Work in
progress is non-existent as tubing may be continuously pro~uce~
and scran levels are exeeedinyly low.
In a preferred embodiment of the invention, appro~i-
mately 80~ of the thermoplastic m~terial is in the inner corr-
and a maximum of about 20~ of the thermoplastic is in ~he outer
coating. This allows the outer coating to assume the confic3ura-
tion of the ribbed inner core giving the tubing an abrasiQnresistant cover since the contact point at any abrasion arecl is
reduced.
In ~ preferred embodiment of th~ invention, tubular
core 2 may be extruded utilizing a die o the type shc~wn in
Figure 6 to produce the tubular core 2 having an external sur-
ace consistiny of lonyitudinal ridqes and valleys of generally
triangular confiyuration extending longitudinally on ~he tube.
Reinforced flexible tubiny o~ thermopl~stic material has been
successfully produced utilizing dies 3~ "la~in~ t;ne con~icjura-
13
tions shown in Table 1, in first extruder of an appara~l,similar to that shown in Fig. 4. The inside diamPtrr of -.~se
core thus produced is also shown in Table 1.
Table I
Die Dimensions
Die Core
Right Angle Bore W1dth of Ridge Ridge Peak Inside
A(degrees) Diameter Valley Base Height Anyle Diameter ,
B(in.) C~1n.) D(in.) E(degrees) (in.)
_
1 84 0.480 0.012 0.035 la 0.937
2 84 0.550 0.009 0.035 15 0.937
3 ~4 0.725 0.035 0.023 1~ 0.875
4 84 U.915 0.013 0.028 ~ 0.81~
5 84 0.980 0.014 0.035 9 0.750
6 84 1.512 0.003 0.~35 5 0.593
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 o
the invention which is defined in the claims.
EXAMPLE
A 1at 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 passaye through the nip rollers was 12 mm. The nominal
overall wall thickness was 2 mm, with the height of the ridqes,
relative to the valleys, being 0.58 mm. The outer coating thic~-
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 sectlon o~ the tube. The minumum
-15-
~73~3
burst pressure out of a number of samples "as found to D" 4~
p.s.i.g. (3.l ~INm ) and burst pressures .~ere generally in ex-
cess of 500 p.s.i.g. (3.45 MNm ).
COMPARATIVE EX~MPLE 1
Round hoses were prepared in accordance with the main
method hereinbefore described with reference to Figures 4 and ~.
Hoses of exactly the same nominal dimensions were produced by a
similar process, but without the application of ~Jacuum. Each
hose was tested for burst pressure as in the Example herein-
before.
The results were as follows:
BURST PRESSURE
lat 20C) (psig)
Nominal Internal COAT:[NG COATING
Diameter ~mm) WITHOUT WITH
VACUUM VACUU~
6 ll90 1300
1160 1250
12 790 ~50
19 575 6~5
COMPARATIVE EXAMPLE 2
-
Hoses were produced using the methods as in
Comparative Example l, but, in the case of the hoses coated with-
out application of ~acuum, 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 th~ hoses 'or
a unit length were compared, and Table 2 gives the result.
Nominal Internal ~EIG~T (g~m)
Diameter ~mm) COATING COATING
WITHOUT WITH
VACUUM VACUU~`I
6 ~0.8 5
165 '~
l~ 22~ 126
19 331~ ~5
-16-
COMPARATIVE EX~PLE 3 1
A hose manufactured in accordance with the me~ od .-:ere-
inbefore described with reference to Figures 4 and 5 was tested
to compare the strength of bonding between the coating and ~he
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 extendin~
beyond the clip at one end. Each sample was immersed in ~ater
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. (3~3 kNm 2), and for one
hour at 60 p.s.i.g. (414 kNm 2) at 80 p.s.i.g. (552 kNm 2), an~l
no leak was detected at the end of this time.
A sample of the conventional hose showed air leak~s
from both ends, from ~e-tween the layers, after only a few
minutes at a pressure of 10 p.s.i.g. (69 kNm ).
