Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
lZ73768
1 FIELD OF THE INVENTION
This invention relates to a met,hod of manufacturing discrete
fiber reinforced, plasf,ic tube and apparatus therefor.
More particularly the present invention relates to a method and
an apparatus for making plastic tube by a co--extrusion process.
BACKCROUND ART
It i3 known that the mechanical properties of plastic pipe can be
improved by incorporation of discontinuous reinforcing fibers ln it. It
is also known that properties of the fiber reinforced plastic tube are
strongly dependent on fiber orlentation. A s1gn1ficant lmprovement ln
certain properties of fiber reinforced p~astic tube occurs in the direc-
tion of preferential fiber or1entation.
There have been a number of methods and apparatus proposed rOr
making pla.stic tubes. Known in the art is a process for controlling
orientation of discontinuous fiber in fiber reinforced tube formed by
extrusion (U.S. Patent No. 4,056,591, November 1, 1977 Coettler). The
process described in this patent comprises extruding a mixture of fibers
and matrix material through a diverging channel of essentially constant
width rormed by stationary die members. The outlet area of the die chan-
nel being at least two or more times the channel lnlet area, this rela-
tion between outlet and inlet area provides plastic tube having improved
physical properties in the hoop direction.
Another known method of extruding fiber reinforced plastic tube
(U.S. Patent No. 3,933,960 January 20, 1976 Cameron et al~ comprises
continuously extruding at least one viscous material having reinforced
fibers therein through two concentric sets of converging discrete pas-
sages, producing laminar flow in the passages by causing the material to
- accelerate on entry into the passages and preventing deceleration thereof
within the passages whereby the fibers orientate themselves in the
material in a lengthwise direction of the passages, and then bringing
together the extruded material from the respective passages 90 as to form
two layers of material one within the other with the fibers of each layer
lying on helices of opposite hands with respect to one another by passage
through rotatlng die me~bers.
. , .
.:. . : ,
... ..
.. . .
:
. ' '
.. ,
.. .
~273D76~3
1 Although all the above processes are suitable for providing
plastic tubes with reinforced fibers, none of these processe~ can produce
in a satisfactory manner multi-layered plastic tubes having an inter-
mediate layer containing discrete fibers where a major portion of the
fibers is oriented to extend predominantly in a general direction lying
between the circumferential and the longitudinal axis of the tube with
the orientation of the fibers being generally the same throughout the
thickness of the intermediate layer. Theoretical and experimental
research have shown that while a die simllar to the one taught by
Coettler can give rise to a preferential circumferential orientation of
the fibers in a certain region of material, a significant longitudlnal
orientation in unavoidable in reeions near the walls of the die. The
reason is that the flow through such a dle involve3 a superposition of
shear and extentional components of deformation. While the shear com-
ponent tends to orient the fibers in the longitudinal direction, the
extensional comyonent tends to orient them in the circumferentlal direc-
tion. The magnitude of the extensional component becomes insignificant
near the wall of the die as the ~hear component approaches a maximum,
therefore the fiber~ tend to a longitudinal orientation near the inner
and outer walls of the die. This method does not provide fibers having
the same orientation throughout the thickness of the tube.
The process described by Cameron et al provides a multi-layered tube with
helically oriented fibers. The rotating die members taught by Cameron et
~al limits the process to providing reinforced fibers with helical orien-
tation as distinct from circumferentiaLly and longitudinal orientation.
There is a need for a method of, and an apparatus for, making
discrete fiber reinforced plastic tube having an improved overall frac-
ture toughness.
There is also a need for a method of, and an apparatus for,
making discrete fiber reinforced plastic tube having an improved
stlffnes3 and ~trength.
:
:,
~273768
1 There is also a need for a method of, and an apparatus for,
making discrete fiber reinforced plastic tube having an intermediate
layer of plastic material containing dLscrete fibers, where a major por-
tion of the fibers is oriented to extend predominantly in a general
direction lying between the circumferential and the longitudinal axis of
the tube with the orientation of the fibers being generally the same
throughout the thickness of the intermediate layer, by a simple and con-
tinuous process.
SUMMARY OF THE INVENTION
Accordin~ to the present inventLon there is provided a method of
extruding discrete fiber reinforced, p]astic tube, comprising:
a) introducing a first plastic material in an upstream
portion of an annular die channel for forming an inner
layer of the tube;
b) introduclng a second plastic material filled with
discrete fibers in the upstream portlon of the channel
and around the whole of the inner layer for forming
an intermediate layer of the tube;
c) introducing a third plastic material in the upstream
portion of the channel around the whole of the intermediate
layer for forming an outer layer of the tube; and
d) co-extruding the materials through a downstream
portion of the annular dle channel which is divergent
diametrically in a downstream direction so that at least
a major portion of the fibers are oriented to extend
predo~inantly in a general direction lyine between the
circumferential and longitudinal axis of the tube with
the orientation of the fibers being generally the same
throughout the thickness of the intermediate layer.
In some embodiments of the present invention the plastic materials
~r, ~, I s
~'~ are thermoplastic matcrial.
-,,;
1273768
1 In other embodiments of the present invention the discrete fj.ber9are of at least one material selected from the group consisting of glass,
high strength polymer, mineral, carbon and metal.
Further, according to the present invention there is provided a
discrete fiber reinforced, plastic tube extruding apparatus comprising a
casing assembly having a cavity and mandrel secured coaxially within the
cavity of the ca.sing assembly, the cavity and the mandrsl formine an
annular die channel, the annular die c~lannel having an upstream portion
and downstream portion; the upstream portion having a flrst inlet means
for introducing a first plastic material in the channel and forming an
inner layer of the tube therefrom adjacent to the mandrel, a second inlet
means for introducing a ~econd pla.stic materlal filled with discrete
fibers in the channel and around the whole of the inner layer to form an
intermediate layer of the tube and a third inlet means for introducing a
third plastic material in the channel and around the whole of the inter-
mediate layer to form an outer layer of the tube therefrom adjacent t~
the casing a.ssembly: and the downstream portion of the annular die chan-
nel diverging diametrically in a downstream direction so that, when the
materials are extruded through the downstream portion for forming the
plastic tube, at least a major portion of the fibers is oriented to
extend predominantly in a general direction lying betweeen the circumfer-
entlal and the longitudinal axis of the tube with the orientation of the
fibers being generally the same throughout the thickness of the inter-
mediate layer.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanylng drawings which illustrate, by way of example,
embodiments of the present invention,
Figure 1 is a sectional plan view of a portion of a discrete fiber
reinforced, pla.stic tube producing apparatus, the side view having been
cut along a plane passing through the central longitudinal axis of the
apparatus;
Figure 2 i8 a front view of another embodiment of a discrete
fiber reinforced plastic tube producing apparatus;
.. .
.
, ' ~
" ~ .
': . .
127376~3
Flgurs 3 is a sectional plan view along the line III - III,
Figure 2;
Figure 4 is a sectional plan view along the line IV - IV,
Figure 7;
Figure 5 is an end view a~ong line V - V, Figure 3 of an
intermediate casing member;
Figure 6 is a front view of` a spider construction of the
apparatus shown in Figures 2, 3, Jl, and 5; and
Figure 7 is a sectional plan view along the llne VII - VII,
Figure 6.
DETAILED DESCRIPTION OF THE DRAWINCS
In Fi~ure 1, there is shown a sectional plan view Or a portion of
a discrete fiber reinforced, pla.stic tube extrudir1g apparatus. The
apparatus showrl comprises a casing asc;emb].y 6 (partially .shown) having an
annu].ar die channel 8, the annll1.ar die chanr3el 8 ~laving an upstream
portion 2 an~ a downs~;ream portion 4; the upstream portion ~ l~aving a
first inlet means 10 by which a first plastic material, when in
operation, i9 introduced in the channel 8 for forming an inner layer of a
tube, a second inlet means 12 by which a second plastic material fllled
with discrete fibers, when in operation, is introduced in channel 8 and
around the whole of the inner layer for forming an intermediate layer of
- the tube and a third inlet means 14 by which a third plastic material,
when in operation, is introduced in the channel 8 and around the whole of
the intermediate layer for forming an outer layer of the tube; and the
downstream portion ll of the annular die channel 8 diverging diametrically
in the downstream direction so that, when the materials are extruded
through the downstream portion for forming the plastic tube, at least a
: 30 major portion of the fibers is oriented to extend predominantly in a
general direction lying between the circumferential and longitudlnal axis
of the tube with the orientation of the fibers being generally the same
throughout the thickness of the intermediate layer.
1273768
- 1 The portion of casing assembly 6 forming the downstream portion 4
of the annular die channel 8 also comprises coextruding inlet means 30 by
which plastic materials are injected in the downstream portion 4, an
inner mandrel 32 tapering outwardly in the downstream direction and form-
ing an inner boundary surface of the annular channel 8, and an outer
member 17 with a cavity tapering outwardly in the downstream dlrection
and forming an outer boundary surface of the annular channel 8 80 that
the downstream 4 portion of the channel 8 diverges diametrically in the
downstream direction.
In operation, the apparatus shown in Figure 1 extrudes discrete
fiber reinforced, plastic tube by:
(a) introducing a first plastic material in the upstream portion 2
of the annular die channel 8 for forming the inner layer of the
tube;
(b) introducing a second plastic material filled with discrete
fibers in the upstream portion 2 of the channel 8 and around the
whole of the inner layer for forming the intermediate layer of the
tube;
(c) introducing a third plastic material in the upstream portion 2
of the channel 8 and around the whole of the intermediate layer for
forming the outer layer of the tube;
(d) co-extruding the materials through the downstream portion 4 of
the annular die channel 8 which is divergent diametrically in the
downstream direction so that at least a major portion of the fibers
is oriented to extend predominantly in a general direction lying in
between the circumferential and longitudinal axis of the tube with
the orientation of the fibers being generally the same throughout
the thickness of the intermediate layer.
The presence of the lnner and outer layer on the inside and outside of
the intermediate layer durlng co-extrusion through the downstream portion
4 of the channel 8 reduces the effect of the shear components of deforma-
tion, which occur near the inner and outer boundary surfaces of the chan-
nel 8, on the intermediate layer so that the orientation of the fibers
i273768
1 is substantially the same throughout the thickness of the intermediate
layer.
The orientation of the fiber~ depends on the rheological proper-
ties of the plastic materials used for the inner, outer and intermediate
layers Or the tube and on the length and angle of divergence of the down-
stream portion 4 Or the channel 8. L,arger differences in viscosities of
the materials, diverging ang1e and length of the downstream portion 4
will provide a greater extent of circumferential orientation, up to a
limit.
In Figures 2 to 7 there is shown another discrete fiber rein-
forced, plastic tube extruding apparatus.
Figure 2 shows the front end of the apparatus where the exit
opening 33 of an annular channel is formed between a mandrel 32 and an
outer hollow member 17. Also shown is an exhaust opening 44 of an air
channel. The casing assembly 6 is made of six casing me~bers (only a
front casing member 15 is shown in Figure 2) held together by eleven
mechanical fasteners 1. Six centering screws 3 allow the centering of
- the outer hollow member 17 with respect to the mandrel 32 for adjusting
the width of the annular channel 8 in it;s downstream portion.
In Figure 3 there is shown a sectional plan view of the apparatus
along line III - III of Figure 2 and in Fieure 4 there is shown a sec-
tional plan view of the apparatus along line IV- IV of Figure 2. Refer-
ring to Figures 3 and 4 the apparatus comprises six casing members which
are the front end casing member 15, a back end casing member 5 and four
intermediate casing members 7, 9, 11 and 13. All the casing members are
held together by eleven mechanical fasteners 1 (one of which is shown in
Figure 3). A first feed channel 16 can sllpply plastic material con-
taining discrete fibers to a second inlet means 12 via three channel3 18
; (one of which i3 shown in Figure ~) para1lel to the longitudinal axis ofthe channel 8. The second inlet means 12 comprises a first annular
hollow ring portion, delimitated by two intermediate casing member~ 11
and 13, for receiving the plastic material containing fibers from the
three channels 18. A second feed channel Z0 can supply plastic materials
1273768
-- 8 --
1 to a first inlet means 10 and a third inlet means 14 of the annular chan-
nel 8 via a divider 40. The plastic material is conveyed from the
divider to the first inlet means 10 via a central channel 42 and to the
third inlet means 14 via three channels 22 (one of which is shown in
Figure 3) parallel to the longitudinal axis of the annular channel 8,
The third inlet means 14 comprises an annular hollow ring portion, delim-
itated by one intermediate casing member 13 and the outer hollow member
17, for receiving the plastic material from the three channels 22 ex-
tending from the divider 40. A spider construction 19, which is shown
with more details in Figures 6 and 7, is used for holding the mandrel 32
with respect to the oute- hollow member 17. ~he spider constructlon 19
has a threaded cavity into w~ich a threaded portlon of the mandrel 32 can
be screwed. The central channel 42 extends through the spider construc-
tion 19 up to the first inlet means 10.
The annular channel 8 has an upstream portion 2 and a downstream
portion 4. The upstream portion 2 of the annular die channel 8 ls
delimitated by an outer boundary surface, formed by two intermediate
casing members 11, 13 and a portion of the outer hollow member 17, and an
lnner boundary surface formed by the mandrel 32. The downstream portion
4 is delimitated by an outer boundary surrace formed by the outer hollow
member 17 and an lnner boundary surface formed by the mandrel 32. The
upstream portion 2 has a constant diameter and the downstream portion 4
diverges diametrically in the downstream direction. The wldth of the
channel in the downstream portion can be adjusted by six centering screws
3 (two of whlch are shown ln Figure 4), The air channel 28 has an alr
inlet means 23 by which pressurized air can be in~ected into the air
channel 28. The air channel 28 extends from the inlet means 23
perpendicularly to the longitudinal axis Or the annular channel 8 up to
the threaded portion of the mandrel, from there it extends along the
longitudinal axis of the annular die channel 3 and inside the mandrel 32
up to the exhaust opening 44.
Pressurized air can be fed into the tube as it is being extruded
from the exhaust opening 44 for controlling the size of the tube.
~Z73768
In figure 5 there is shown an end view of intermediate casing
member 9 showing the distribution of the channels 18, 22 and 42 and
fa3tener holes 25.
The mechanical fasteners 1 of Figure 2 hold the front end casing
member 15, the bac~ end casing member 5 and the four intermediate casing
members 7, 9, 1 1, 1 3 by means of the holes 25.
A first plastic material containing discrete fibers is brought to
the annular die channel 8 by means of the three channels indicated as 18.
A second plastic material is brought to the annular die channei 8
by means of the central channel 42 and the three channels indicated as
22.
In Figure 6 there is shown a ~ront view of the spider construc-
tion 19 of the apparatus shown in Figures 3 and 4. The spider construc-
tion has an outer ring member 31 and a hub portion 43. The outer ring
member 31 supports the hub portion 43 by means of three legs 27. Arcuate
channels 42 carry the plastic material (not shown) to the first inlet
means 10 and extend between the three legs 27 and are bounded by the
outer ring member 31 and the hub portion 43. The hub portion 43 has a
threaded cavity 29 into which the threaded portion of the mandrel is
screwed.
In Figure 7 there is shown a sectional plan view of the spider
construction of Figure 6 along the line VII - VII. The outer ring member
31 supports the hub portion 43 by means of three iegs 27 (one of which is
shown in this drawing and through which air inlet means 23 extends).
The central channel 4Z is delimitated by the outer ring member
21 and the hub portion 43. The air channel 28 that carries pressurized
air extends throughout the outer ring member 31, one of the legs 27 and
the hub portion 43 up to the threaded cavity 29.
While the embodiment of the present invention shown in Figures 2
to 7 shows a discrete fiber reinforced, plastic tube apparatus for pro-
ducing a three layer tube, it will be appreciated that it is within the
scope of the present invention to provide at least one more additional
layer on ~he inside or the outside of the three layers, or at least one
additional layer on both sides of the thrs- layers.
~273768
1 Thus the inner and outer plastic layers produced by the apparatus
need not be the inner and outer most layers of the tube.
While in the embodiment of the present invention shown in Figures
2, 3 and 4, the end of the downstream portion of the annular die channel
8 forms an exit for the co-extruded materials, it will be appreciated
that it is within the scope of the present invention to provide a
straight ann~lar channel section downstream to the downstream portion 4
of the annular die channel 8, for example, to improve the surface finish.
If the straight channel section is not too long, the inner and outer
layers will continue to reduce the efrect of shear components on fiber
orientatLon in the intermediate layer during the rlow through the
straight channel section and thus prevent major change in fiber orienta-
tion developed in the downstream portion 4 of the annular dle channel 8.
While in the embodiment of the present invention shown in Figures
3 and 4, the first feed channel 20 supplies plastic material to both the
inner and outer layers of the tube, it will be appreciated that it is
- within the scope of the present invention to provide two separate feed
channels for providing independently plastic materials to the first inlet
means 10 and the third lnlet means 14 whereby different plastic materials
may be used for the inner and outer layers of the tube.
EXPERIMENTAL RESULTS
An apparatus similiar to the one shown in Figures 2 to 7 was
experimented. The apparatus in question is further defined by an annular
die channel 8 having a uniform width, between the mandrel 32 and the
outer hollow member 17, of about 3 mm ar1d an angle of divergence with
respect to the longitudinal axis of the channel 8 of about 50. Diameter
expansion of the downstream portion 4 is about 2.6, which is the ratio of
the diameter at the end of the downstream portion 4 to that of the up-
stream portion 12.
A first extruder is used to supply plastic materials containing
, .
~Z73768
"
1 discrete fibers, the screw having a diameter of about 63 mm and a screw
length to diameter ratio of 30. The barrel temperature of the first
extruder i~ 190-205 and its feed rate i9 9.5 cm3/s. A second extruder
ls used to supply plastic materials for the inner and outer layers, it
has a screw diameter of 32 mm and a scrcw length to diameter ratlo of 21l.
The barrel temperature o~ the second extruder is 170-200 and its feed
rate is 3.1 cm3/s. The extrudate tube emerginB from the downstream por-
tion 4 of the annular die channel 8 is cooled in a cooling tank, having a
desired length, flooded with water and maintained under vacuum.
A three layer coextruded tube with a nominal diameter of 50 mm
and a nominal thickness of 1.6 mm was pr-oduced with the apparatus
described above. T~le inner and outer layers of the tube are made of
polyethylene resin and the middle layer i9 made of composite material
comprislng polyethy]ene resin toeether with 30% (by weight) short glass
fibers as reinforcement.
In order to determine the fiber orientation pattern in the tube,
the tensile strength of the tube was measured in longitudinal and cir-
cumferential directions of the tube. For this purpose, test pieces were
cut from tube sample3 in two directions (longitudinal and circumferen-
- s1, L~ ec~ed
tial) and ~ub~ect to a tensile test in accordance with standard test
method ASTM D 638. The ratio of the tensile strength in the longitudinal
direction to that in the circumferential direction provides an indication
of the fiber orientation pattern present in the tube. A greater ratio
than unity implies a preferential orientation in the longitudinal direc-
tlon. The larger this ratio is, the greater is the orientation in this
direction. A ratio less than one indicates a preferential orientation in
the circumferential direction. It is understood that the fibers can be
oriented at various angles with respect to the longitudinal and circum-
ferential directions and can contribute to the measured tensile strength
in the two directions. A ratio equal to one indicates a balanced fiber
orientation with respect to the two directions.
1273~6~3
12 -
1 The average value of the tensile strength in the longitudinal
direction is 26.4 MPa and in the circumferential direction is 27.7 MPa,
therefore the ratio of the tensile strength in longitudLnal direction to
that in the circumferential direction is 0.95. The data show that the
fibers are oriented preferentially in the circumferential direction, the
orientation being generally the same throughout the thickness of the
intermediate layer.
1 0
3o
. .
