Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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REINFORCED THERMOPLASTIC PIPE MANUFACTURE
BACI~GROUND OF THE INVENTION
This invention relates generally to the
manufacture of fiber reinforced thermoplastic pipe
lengths and more particularly to a novel continuous
processing means for the manufacture of these
articles.
The fiber reinforcement of pipe members
.formed with both thermoset and thermoplastic organic
polymers has already gained wide commercial
acceptance attributable to affording high strength
and stiffness per unit weight when compared to pipe
fabrication with the conventional materials
previously used for transporting various fluids such
as concrete, steel and the like. A variety of
fabrication procedures are also well lcnown to
produce the composite pipe member with continuous
fiber filaments which are commonly applied to the
outer pipe surface. In one example, a tension
winding process is commercially employed whereby a
thermoplastic pipe or coupler member is rotated on a
mandrel while the reinforcing fiber is being applied
under heat and tension. The fiber tension during
winding or wrapping around the underlying
thermoplastic member provides a compaction force
therebetween to secure thermal bonding of the fibers
after the heating has melted or softened the outer
surface of the thermoplastic material. This process
has been found limited to relatively high fiber
angles with respect to the longitudinal axis of the
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pipe or coupler member, typically greater than 15
degrees because the radial component of the fiber
tension provides this compaction force. While
tension winding can be augmented with a use of
compaction roller means to increase the radial
compaction force, the resulting low fiber angles
produce undesirable fiber build-up at the mandrel
ends since the continuous fibers being applied
cannot be cut for a restart of the filament winding
process. A further need to apply _relatively high
pressure as well as provide mandrel rotation during
said tension winding process requires robust and
expensive mandrels together with significant; mandrel
handling labor. In a different manufacturing
process for the production of reinforced plastic
pipe members, continuous glass fibers in a thermoset
epoxy matrix are employed. Still other
manufacturers produce a reinforced thermoplastic
pipe construction having the thermoplastic pipe
member as an innerlayer which is surrounded by
various ~uterlayers of the reinforcement material.
For example, one such manufacturer surrounds the
thermoplastic liner with a fiberglass layer in an
epoxy resin matrix and provides a_n_ exte_rior
protective layer thereover of a still different
fiber material which is again contained in an
organic polymer matrix. Using thermoset polymers in
the reinforcement of a thermoplastic pipe member
frequently creates additional manufacturing
problems. The curing required of these polymers
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occasions contamination as well as time delay and
these materials are not recyclable.
Another complex reinforced thermoplastic
pipe construction is disclosed in United States
Patent No. 4,850,395. As therein described, a core
member of thermoplastic material is wound with an
inner aramid fiber layer while being covered with
still additional tape and metal outer layers. Such
end product is understandably found to be both
cumbersome and expensive to manufacture. In United
States Patent No. 4,469,138 there is disclosed
polypropylene pipe lengths reinforced by simply
mixing discrete carbon fibers in the starting
polymer composition. The resulting product lacks
the mechanical strength afforded with continuous
fiber reinforcement as well as laclcs the ability to
orient continuous fibers in a predetermined spatial
direction for maximum effectiveness in withstanding
applied stress when the pipe member is in service.
In the latter regard, such controlled directional
orientation of the continuous fiber component in the
reinforced thermoplastic pipe member enables the
fiber placement to be fixed for such maximum
effectiveness since the fiber materials being
employed are generally stronger than the
thermoplastic polymers forming the pipe member. The
fiber reinforced end product is thereby only as
strong as the spatial direction of the applied
fibers with respect to the direction of the external
stress when applied to said reinforced pipe member.
Thus, when the fiber reinforced pipe member is
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stressed by internal fluid pressures in the
direction of the fiber placement, the applied load
is withstood primarily by the included fibers and
the strength of said pipe member is at maximum
value. Conversely, when the composite member is
stressed in a perpendicular direction to the fiber
direction, the applied force must necessarily be
resisted primarily by the polymer pipe member so
that pipe strength is at a minimum. From such
consideration and a further analysis of the expected
stress during pipe service employing recognized
shell theory calculations, it has been determined
that certain installations of the present fiber
reinforced thermoplastic pipe members dictate a
fiber orientation in the hoop direction whereas
dissimilar pipe installations require the fiber
direction to be oriented at lesser angles with
respect to the longitudinal axis of the reinforced
pipe member.
A still more arduous method for
reinforcement of a thermoplastic pipe member is
disclosed in United States Patent No. 4,347,090
which employs a fabric sleeve applied about the pipe
member for this purpose. The method requires an
inner liner to be filled with liquid which is then
heated causing said liner to expand as well as
become partially molten for thermal bonding to an
overlying glass fabric layer. An outermost layer
comprising a thermoset resin impregnated glass cloth
completes the reinforcement. Such final product and
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its method of fabrication are understandably bath
complex and expensive.
In United States Patent No. 4,770,443
there is also disclosed a rather complex
electrofusion type coupler being employed to join
synthetic resin pipe lengths together. Said coupler
member employs a cylindrical thermoplastic sleeve
which includes a metal heating wire being disposed
adjacent the inside surface while being reinforced
on the outside surface with a winding or covering
formed with a material composition exhibiting a
.lower thermal expansion than that of the
thermoplastic sleeve material. Such reinforcement
is said to limit any outward radial expansion of the
composite sleeve during subsequent thermal bonding
of said member to the pipe lengths being joined
together by this means.
It is an important object of the present
invention, therefore, to provide a more effective
means for the fiber reinforcement of a thermoplastic
pipe member in a continuous manner.
It is another important object of the
present invention to provide a novel fiber
reinforced thermoplastic pipe member having the
fiber placement physically incorporated therein so
as to better resist the applied stress encountered
during use in a significantly improved manner.
Still another important object of the
present invention is to provide a novel method for
continuous fabrication of a fiber reinforced
thermoplastic pipe member.
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A still further important object of the
present invention is to provide novel apparatus
means for the continuous fabrication of a fiber
reinforced thermoplastic pipe member.
These and still further objects of the
present invention will become more apparent upon
considering the following more detailed description
of the present invention.
SUMMARY OF THE INVENTION
It has been discovered, surprisingly, that
fiber reinforcement of a thermoplastic pipe length
can be carried out more effectively in a continuous
manner by reversing the customary relative rotation
between the fiber when applied and the pipe member.
More particularly, the processing procedure of the
present invention continuously moves the pipe length
in a linear direction without rotation while
wrapping a plurality of continuous juxtapositioned
reinforcement fibers formed with a material
2Q composition selected from the group consisting of
ceramics, metals, carbon and organic polymers in an
unbonded condition about the outer surface of said
moving pipe member in a predetermined spatial
direction and thereafter heating the fiber wrapped
pipe length sufficiently to cause thermal bonding
between the reinforcement fibers and the pipe outer
surface while said fiber wrapped pipe length
continues to move in the same linear direction. To
impart increased mechanical strength for said fiber
reinforcement requires that the fiber placement be
carried out with the fibers being oriented in a
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particular spatial direction depending upon end use
of the wrapped pipe length as previously pointed out
herein. In accordance therewith, the fibers can be
wrapped in a hoop direction about the pipe length as
well as wrapped at lesser or interim angles with
respect to the longitudinal axis of said pipe
length. Additionally, multiple wraps of the
reinforcement fibers can be applied continuously in
accordance with the present processing procedure to
include one or more overwraps being applied to serve
as a protective covering from exposure of the final
product to environmental or mechanical damage.
Likewise, having the individual fiber wraps applied
continuously in different spatial directions is
contemplated in accordance with the present
processing procedure and with the individual wraps
all being bonded to the underlying thermoplastic
pipe member after placement with a single heating
step. The present processing procedure can
similarly be carried out with multiple pipe lengths
that have been joined together at the pipe ends in
an in-line configuration before continuous fiber
placement by employing conventional means such as
butt-welding, adhesive bonding and the like as well
as possibly being joined 'together with only a
physical abutment existing therebetween. Suitable
thermoplastic organic polymer materials forming the
pipe member in the present composition construction
include but are not limited to polyethylene such as
high density polyethylene and medium density
polyethylene, polypropylene, polyphenylene sulfide,
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polyetherketoneketone, polyamide, polyamideimide,
and polvinylidene difloride. Similarly, a wide
variety of materials are found suitable as the fiber
reinforcement in the present processing procedure to
again include but not be limited to ceramics,
metals, carbon, aramid and other polymer fibers
having softening temperatures above that of the pipe
service temperature in use and glass compositions
such as E type and S type glass.
Basically, the present thermal bonding of
continuous fibers after having been wrapped in an
unbonded condition about the outer periphery of the
thermoplastic pipe length or lengths involves an
operative cooperation between the applied fibers and
the outer surface of said pipe member. A softening
or melting action takes place during the thermal
bonding step between the outer surface of the
thermoplastic pipe member and any thermoplastic
polymer materials serving as the matrix composition
in selected preformed tape embodiments having the
continuous reinforcement fibers bonded therein. In
this manner, the applied fibers become physically
joined to the pipe member with softened or melted
thermoplastic polymer when the fiber wrapped pipe
member is heated in the present method such as
occurs when melting said outer pipe surface. The
present heating step also produces a significant
radial expansion of the pipe member upon heating
which further promotes the physical adherence of the
applied fibers to the outer pipe surface. In so
doing, a radial compaction or compressive force is
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generated in the joined components with the maximum
benefit being imparted by having the coefficient of
thermal expansion for the selected fiber material
being lower than that for the thermoplastic pipe
polymer. The herein defined fiber reinforcement
method understandably enables a wide variety of
fiber materials to be selected as previously pointed
out. Thus, a reinforcement fiber material can be
selected from the aforementioned class of suitable
materials so long as it is mechanically stiffer than
the selected thermoplastic pipe polymer and has a
glass transition or melting temperature higher than
the service temperature of the thermoplastic pipe
member during use. Selected polymer fibers can
understandably include continuous bare filaments and
comingled continuous fibers which can be wetted by
polymer melt flow in the above mentioned compaction
zone during heating. ror selection of a suitable
preformed continuous fiber material or prepreg tape
having a matrix formed with a thermoplastic polymer,
said matrix polymer is desirably chosen to have a
softening or melt temperature equal to or lower than
the softening temperature of the selected pipe
polymer.
Any suitable heating source can be used in
the present method to continuously bond the applied
fiber reinforcement to the outer thermoplastic pipe
surface. Contemplated heat sources include but are
not limited to inert gases, oxidizing gases and
reducing gases, including mixtures thereof, infrared
heating sources, such as infrared panels and focused
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infrared means, conduction heating sources such as
heated rollers, belts and shoe devices, electrical
resistance heating sources, laser heating sources,
microwave heating sources, RF heating sources,
plasma heating sources and ultrasonic heating
sources. An external flame heat source provides
economical heating with high energy densities and
with the gas burner or burners being suitably
des.i_gned so as to surround the outer circumference
of the fiber wrapped thermoplastic pipe member.
Understandably, the employment of a continuous
heating step in the present method can further
advise auxiliary equipment means to be operatively
associated therewith in the event of process
interruptions such as fast responsive heating
devices or cooling means averting meltdown of the
materials being processed. It is also contemplated
that the present method of thermally bonding the
applied reinforcement fibers continuously to the
outer surface of said thermoplastic pipe member can
be modified in a still further manner. Accordingly,
roller members rotatably mounted so as to press
against the already heated fiber wrapped
thermoplastic pipe member can be-employed to help
generate the aforementioned compaction force found
beneficial in carrying out the present method. Such
compaction rollers can be cooled, heated or remain
at ambient temperatures in the present method
depending upon the process requirements being
carried out as well as the physical characteristics
desired in the final product.
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As above indicated, the present continuous
method necessarily further includes provision being
made for both start-up as well as termination and
possible process interruption. Satisfactory start-
s up of the present processing procedure can be
conducted in various ways to include starting with a
single thermoplastic pipe length or multiple pipe
lengths and feeding these members with continuous
linear motion at a relative constant velocity to
suitable fiber winding means. A continuous
thermoplastic pipe length can be suitably provided
employing conventional extruder means while the
feeding of discrete pipe lengths to the operatively
associated fiber winding means can preliminarily
involve having the discrete pipe lengths simply
butted together physically in an in-line
configuration as well as having the respective pipe
ends fused or welded to each other. Conventional
means can be employed for continuous transport of
the thermoplastic pipe member during processing in
said manner including known moving belt drive
mechanisms and motor driven rollers. Suitable
start-up would also optionally include having the
initial continuous fiber being physically secured to
the outer surface of the first moving thermoplastic
pipe member being processed with conventional
clamping or adhesive bonding means. Following a
continuous thermal bonding of the applied
reinforcement fibers in the manner previously
described, the present method can be terminated with
conventional cut-off means being employed to suspend
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any further fiber placement. Satisfactory cut-off
means can utilize a moving cutter device traveling
in the same linear direction as the moving pipe
member or members and to include a cutter severing
the pipe along with the applied fiber reinforcement.
Novel apparatus means are employed to
provide continuous fabrication of the present fiber
reinforced thermoplastic pipe member. Basically,
the present apparatus employs pipe feeding means
which continuously transports the pipe length in a
linear travel direction for operative association
with rotating fiber supply means, fiber supply means
which rotate about the circumference of said moving
pipe length to continuously apply a plurality of
juxtapositioned reinforced fiber wraps in a
predetermined spatial direction on the outer surface
of said moving pipe length, and heating means which
causes thermal bonding to be continuously formed
between the applied reinforcement fiber wraps and
the outer surface of the moving pipe length. Said
apparatus can further include a plurality of
individual fiber supply means to serve various
purposes such as applying successive fiber wraps at,
different fiber placement angles, reversing the
application direction of successive fiber wraps, and
applying overwraps of continuous fiber or tape
material to serve as a protective covering against
environmental or mechanical damage to the final
product. A satisfactory embodiment for said
individual fiber supply means can be a conventional
cylindrical winder mechanism operatively associated
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with a rotary fiber or tape spool. The pipe feeding
means in the present apparatus can also be of
conventional construction, as previously pointed
out, to include known moving belt drive mechanisms
as well as motor driven rollers and the like. While
a further previously mentioned wide variety of
heating sources can be employed in the present
apparatus for continuous thermal bonding of the
applied fiber or tape wraps, it remains advisable
for the selected heat source to uniformly provide
heat about the entire circumference of the fiber
wrapped pipe length in doing so. In the apparatus
embodiments to be more fully described hereinafter,
the particular heating means being employed consists
of a stationary cylindrically shaped heater that
surrounds the entire circumference of the fiber
wrapped pipe member and which is equipped with
appropriately disposed internal gas burners. Moving
cutter means are also employed in the illustrated
apparatus embodiments for the purpose of severing
the moving fiber wrapped pipe member into one or
more suitable lengths upon completion of the herein
described thermal bonding procedure. The entire
apparatus in said illustrated embodiments is further
operated automatically with known robotic control
means employing a conventional velocity
servomechanism system.
BRIEF DESCRTPTION OF THE DRACn~INGS
Figure 1 is a schematic view depicting
typical processing equipment which can be employed
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to continuously fabricate the fiber reinforced
thermoplastic pipe member of the present invention.
Figure 2 schematically depicts
representative automatic control means for the
Figure 1 processing equipment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings, Figure 1 is a
schematic drawing depioting a representative
processing apparatus which can be employed to
continuously fabricate the present fiber reinforced
thermoplastic pipe member. The depicted equipment
means further illustrates the individual process
steps being employed for said continuous fabrication
according to the present invention. Said combined
equipment and process flow chart 10 first utilizes a
conventional tractor type feed mechanism 12 to
continuously transport the supplied bare
thermoplastic pipe length 14 in a horizontal linear
direction at constant speed through the depicted
apparatus 16. The bare pipe member 14 proceeds in
said manner to a first cylindrical winder mechanism
18 which employs a motor driven rotating drum member
20 surrounding the pipe circumference to
continuously wrap a first ply of the reinforcement
fiber 22 about the outer surface of the moving pipe
length. The reinforcement fiber comprises a
plurality of the selected continuous length
juxtapositioned fibers being supplied from a rotary
spool 24 operatively associated with said winder
mechanism and which feeds the supplied fiber
material at a relatively constant rotational speed.
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As further shown in the present drawing, said first
wrap or ply of the fiber reinforcement has been
applied in an unbonded condition at a predetermined
spatial angle with respect to the longitudinal axis
of the moving pipe length in response to a
counterclockwise rotation of drum member 20. While
not specifically identified in the present drawing,
the particular reinforcement fiber material 22 being
applied in the illustrated embodiment consists of
continuous length glass filaments embedded in a
thermoplastic polymer matrix but still other
commercially available prepreg or preformed
reinforcement tapes of similar construction are
deemed equally suitable for processing in the
illustrated apparatus.
The initially fiber wrapped moving pipe
length 26 is next transported to a second
cylindrical winder mechanism 28 with the same type
rotating drum member 30 and rotary spool 32
previously employed for application of a second ply
of the same fiber reinforcement 34. In doing so, it
can be seen that said fiber reinforcement is now
aligned in an unbonded condition at a different
predetermined placement angle with respect to the
longitudinal axis of the moving pipe length than
previously employed and with said placement of the
second ply being in response to a clockwise rotation
of drum member 30. The now two-ply fiber wrapped
pipe length 36 is next further transported to a
third cylindrical winder mechanism 38 again having
the same rotating drum member 40 and rotary spool 42
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where a final ply 44 of protective overwrap 46 such
as a thermoplastic film tape is applied over the
moving fiber reinforced pipe length to protect the
fibers from handling and/or environmental
degradation. As can again be noted from the present
drawing, said protective overwrap has been applied
at a predetermined reverse spatial angle from that
employed 'in the preceding fiber wrap and with drum
member 40 rotating again in a counterclockwise
direction. Zt becomes possible in such manner to
help improve the overall mechanical strength of the
applied fiber reinforcement while still further
enabling the protective overwrap to add to the
compaction force generated when the fiber
reinforcement is thereafter thermally bonded to the
pipe member. Said thermal bonding is carried out
continuously with the now protected fiber wrapped
pipe member 48 being transported to a stationary
heating means 50 which again encloses the pipe
member while being spaced apart therefrom and which
consists of a hollow cylinder provided with suitable
internal heating elements of the type hereinbefore
disclosed. Passage of the pipe member in the same
linear direction at constant speed through the
length of said heated chamber in the present
apparatus embodiment causes thermal bonding of all
wraps on the pipe circumference to become secure to
the underlying outer pipe surface and with the
individual fiber wraps retaining the applied spatial
direction. A movable cut-off mechanism 52
mechanically severs the now completed fiber
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reinforced thermoplastic pipe member 54 into
suitable lengths without interrupting continuous
movement of the remaining pipe construction through
the illustrated apparatus. Such cut-off operation
can be carried out with various known saw or knife
devices such as already employed in existing plastic
pipe extrusion apparatus. The illustrated traveling
cutter could use a knife means including a circular
knife if only the reinforced fiber is to be severed
whereas a saw device is deemed preferable if an
entire fiber reinforced pipe length is desired to be
removed from the remaining pipe construction.
Additionally, it is contemplated that said traveling
cutter mechanism could still further include router,
planar, or chamfer means and the like to provide a
customized profile at one or more cut-ends of the
severed pipe length if desired for a particular end
use application.
In Figure 2 there is shown schematically
in block diagram form a representative automated
control system for the Figure 1 processing
apparatus. Basically, said control system 60
includes a conventional velocity type servomechanism
to regulate the pipe movement and fiber wrapping
operations conducted in said apparatus as dictated
by an operator activated interface. Identification
numerals employed in the present drawing further
include the same numerals previously used in the
Figure 1 apparatus description for the purpose of
herein denoting the operative association between
controlled components of said apparatus and
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components of the presently illustrated control
means. The overall control system 60 herein
depicted is of the known master-slave type whereby
the tractor feed component 12 operates as the master
control component with all cylindrical wrapping
components 18, 28 and 38 being slaved thereto. In
accordance therewith the velocity or speed ratio
between the master and slave servo control means 62
is determined by main control component 64 in the
illustrated control system as regulated by settings
in the operator interface component 66.. Heater
control component 68 in the illustrated control
system automatically handles all heating
requirements while also signaling the main control
(~4) and operator interface (66) components in the
illustrated control system of both process operating
conditions and any fault conditions discovered
during apparatus operation. Cut-off control 70, if
used, is actuated by main control 64 with a setting
established through the operator interface component
66. Remaining power control component 72 in the
illustrated control system~is operated in the
conventional manner with settings controlling power
input from a customary power supply (not shown) to
the illustrated apparatus.
It will be apparent from the foregoing
description that a broadly useful and novel means to
continuously fabricate a fiber reinforced
thermoplastic pipe member in a more effective manner
has been provided. It is contemplated that already
known modifications can be made in the fiber wrapped
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pipe member produced in such manner than herein
specifically recited as well as process end
apparatus modifications being made in carrying out
such continuous fabrication procedure.
Consequently, it is intended to cover all variation
in the disclosed fabrication procedure which may be
devised by persons skilled in the art as falling
within the true spirit and scope of the herein
claimed invention.
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