Title: Reinforced thermoplastic storage vessel manufacture
Abstract: A method is disclosed for reinforcement of thin wall hollow thermoplastic storage vessels with one or more wraps of continuous fibers. This method requires thermal bonding between the reinforcement fibers and the outer surface of the thermoplastic storage vessel while the interior cavity of the storage vessel is being pressurized. The fiber wraps can also be oriented in spatial directions further resisting internal stress on the storage vessel walls when put in service.
Patent Number: 6,893,604 Issued on 05/17/2005 to Hauber
| Inventors:
|
Hauber; David E. (Troy, NY)
|
| Assignee:
|
ADC Acquisition Company (Schenectady, NY)
|
| Appl. No.:
|
267122 |
| Filed:
|
October 10, 2002 |
| Current U.S. Class: |
264/516; 156/156; 156/172; 220/589; 220/590; 264/257; 264/258; 264/314; 264/324 |
| Intern'l Class: |
B29C 070/44 |
| Field of Search: |
264/257-258,516,324,314
156/156,172
220/589,590
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Staicovici; Stefan
Parent Case Text
This is a division of application Ser. No. 09/726,252 entitled Method to Reinforce
Thin Wall Thermoplastic Storage Vessels filed Nov. 30, 2000, now U.S. Pat. No. 6,716,503.
Claims
1. A method to reinforce a thin all hollow storage vessel formed with a solid
thermoplastic organic polymer while being physically suspended in a hollow condition
which comprises:
(a) wrapping a plurality of continuous juxtapositioned reinforcement fibers formed
with a material composition selected from the group consisting of ceramics, metals,
carbon and organic poloymers while in an unbonded condition about the outer surface
of said suspended storage vessel, said reinforcement fibers being applied at a
predetermined spatial angle for maximum effectiveness in withstanding the applied
internal stress when the reinforced storage vessel is subseguently put into service,
(b) externally heating the outer fiber wrapped vessel surface sufficiently to
cause thermal bonding between the reinforcement fibers and said outer vessel surface
while not further melting said underlying suspended storage vessel,
(c) contemporaneously pressurizing the interior cavity of said suspended fiber
wrapped storage vessel with a coolant medium during said heating steps, and
(d) allowing the suspended fiber wrapped storage vessel to cool upon terminating
said heating step before discontinuing pressurization of the vessel interior cavity.
2. The method of claim 1 which includes rotation of the suspended fiber wrapped
storage vessel during said heating step.
3. The method of claim 1 wherein the reinforcement fibers are provided in a matrix
formed with a solid thermoplastic polymer.
4. The method of claim 1 wherein the thermal bonding includes melting of the
fiber matrix.
5. The method of claim 1 wherein the thermal bonding includes radial expansion
of the suspended fiber wrapped storage vessel.
6. The method of claim 1 wherein the thermal bonding includes melting of the
outer vessel surface as well as melting of the reinforcement fiber matrix while
still averting further melting of the underlying suspended vessel.
7. The method of claim 1 wherein the reinforcement fibers are preheated when
wrapped about the outer surface of the suspended storage vessel.
8. The method of claim 1 wherein pressurization of the vessel interior cavity
of the suspended storage vessel is instituted prior to said heating step while
being further retained during said heating step.
9. The method of claim 1 wherein the suspended storage vessel is allowed to cool
below the melting temperature of the outer vessel surface upon terminating said
heating step.
10. The method of claim 4 wherein the suspended storage vessel is allowed to
cool below the melting temperature of the fiber matrix upon terminating said heating step.
11. The method of claim 1 wherein the reinforcement fibers are wrapped about
the outer surface of said suspended storage vessel while being subjected to a selected
amount of externally applied mechanical force.
12. The method of claim 11 wherein the reinforcement fibers are subjected to
an external applied tensile force.
13. The method of claim 11 wherein the reinforcement fibers are subjected to
an externally applied compression force.
14. The method of claim 1 wherein the coolant medium is a gas.
15. The method of claim 1 wherein the coolant medium is a liquid.
16. The method of claim 15 wherein said coolant medium is removed from the interior
vessel cavity upon terminating said heating step.
17. The method of claim 1 wherein the suspended storage vessel has a cylindrical configuration.
18. The method of claim 1 wherein the suspended storage vessel has a spherical configuration.
19. The method of claim 17 wherein the reinforcement fibers include fibers wrapped
in the hoop direction.
20. The method of claim 18 wherein the reinforcement fibers are wrapped in a
different spatial direction.
21. The method of claim 1 wherein multiple wraps of the reinforcement fibers
are employed.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to a method for reinforcement of hollow thermoplastic
storage vessels with one or more wraps of continuous fibers and more particularly
to a means for improved bonding between the applied fibers and the outer vessel
surface for storage vessels having relatively thin walls.
In a co-pending application Ser. No. 09/327,003 entitled "Reinforced Thermoplastic
Pipe Coupling" and filed Jun. 7, 1999, now U.S. Pat. No. 6,164,702 in the names
of David E. Hauber, Robert J. Langone and James A. Mondo which is also assigned
to the present assignee, there is disclosed a continuous fiber reinforced thermoplastic
pipe coupling having improved resistance to applied stress when used with pipe
lengths being joined together. The fiber reinforcement is aligned during placement
in a particular manner and placed at predetermined fiber angles dictated by mechanical
forces being applied such as by internal fluid pressure in the coupled pipe lengths.
Said already known method for construction of said reinforced thermoplastic pipe
coupling includes a controlled directional orientation of the fiber component to
enable the fiber placement to be fixed for maximum effectiveness in withstanding
the particular stress being generated when the joined together pipe lengths are
customarily used for the transfer of pressurized fluids. Since the fiber materials
currently used in this manner are generally stronger than the polymer matrix compositions
also being employed, the overall strength produced in the composite member depends
largely upon the fiber placement direction for the particular end product. The
fiber reinforced coupler is thereby only as strong as the spatial direction of
the included fibers with respect to the direction of the internal stress when applied
to said member. Thus, when the fiber reinforced coupler is stressed by internal
fluid pressures in the direction of the fiber placement, the applied load is withstood
primarily by the included fibers and the coupler strength in resisting such stress
is at a 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 matrix so that the coupler strength is at minimum. The
relative amounts of the individual stresses being applied to the fiber reinforced
coupler must also necessarily be considered for proper fiber placement direction.
For an externally unconstrained installation of said previously disclosed pipe
couplings, such as encountered with above ground pipe installations, the applied
loads can be examined by treating the joined pipe lengths as a pressure vessel.
From such analysis it was found that the stress applied to the pipe wall in the
hoop direction is twice an amount as the applied stress in the pipe's axial direction.
Employing well recognized shell theory calculation, it was further found that a
fiber-angle of 55 degrees was needed to balance these applied loads assuming 90
degrees to be in the pipe hoop direction and 0 degrees to be aligned in the direction
of the pipe longitudinal axis. For constrained pipe installations, however, such
as in-ground or having the pipe ends being held there, there can only be need for
resisting hoop stress. Accordingly, fiber placement at or near a 90 degree angle
with respect to the longitudinal pipe axis was dictated while further recognizing
that some angle less than 90 degrees may only be achievable with the fiber winding
in the customary manner. The entire contents of said referenced co-pending application
are hereby specifically incorporated into the present application.
It can readily be appreciated that thermoplastic storage vessels undergo similar
internal stress when being utilized. Accordingly, the effectiveness of fiber reinforcement
for thermoplastic storage vessels will also depend to a considerable degree upon
the same factors previously considered with respect to said reinforced thermoplastic
couplings. For example, a thermoplastic storage vessel having a cylindrical configuration
can generally have the fiber wraps applied in a hoop direction for maximum reinforcement
whereas a spherical storage vessel will understandably have the fiber placement
angle varied in different spatial directions. It has now been found, however, that
thermal bonding the reinforcement fibers to the outer surface of the thermoplastic
storage vessel in the same manner previously employed for reinforcement of said
thermoplastic pipe couplings produces inferior results. Specifically, the previously
employed bonding method provided sufficient thermal expansion of the thermoplastic
inner coupling member when being carried out that an effective thermal bonding
with the applied fiber reinforcement took place. This does not reliably occur for
various shaped thermoplastic storage vessels having a lesser wall thickness. It
thereby becomes necessary for said relatively thin wall storage vessels to adopt
an improved thermal bonding procedure for the fiber reinforcement to have the desired effectiveness.
It is an important object of the present invention, therefore, to provide a novel
method to reinforce thin wall thermoplastic storage vessels with one or more wraps
of applied continuous fiber.
It is still another object of the present invention to provide a novel method
to secure the applied fibers to the outer surface of a thin wall thermoplastic
storage vessel so as to better resist internal stress when the storage vessel is
in use and prevent delamination when pressure is released.
Still another object of the present invention is to provide a novel method
for reinforcement of a thin wall thermoplastic storage vessel which includes a
plurality of continuous juxtapositioned fibers being reliably secured to the outer
surface of said storage vessel so as to be aligned in a predetermined spatial direction
resisting applied internal stress during vessel use.
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 now been discovered by the present applicant that a contemporaneous pressurization
of the internal cavity in a thin wall thermoplastic storage vessel while the applied
reinforcement fibers on the outer surface of said storage vessel are being thermally
bonded thereto overcomes the problem previously experienced with inadequate joinder
of said reinforcement means. The internally applied pressure is seen to avert buckling
or wrinkling of the thin storage vessel wall while being heated sufficiently for
joinder between the reinforcement fibers and the outer vessel surface thereby enabling
a sufficient bonding action therebetween. Internal pressurization of the storage
vessel can thereafter be discontinued in the present reinforcement method allowing
the fiber wrapped storage vessel to cool upon termination of said thermal bonding
action. Accordingly, the present method to reinforce said type thin wall hollow
storage vessel comprises wrapping a plurality of continuous juxtapositioned reinforcement
fibers formed with a material composition selected from the group consisting of
ceramics, metals, carbon and organic polymers while in an unbonded condition about
the outer surface of said storage vessel, heating the outer vessel surface sufficiently
to cause thermal bonding between the reinforcement fibers and said outer fiber
wrapped vessel surface, contemporaneously pressurizing the interior cavity of said
rotating fiber wrapped storage vessel with a coolant medium during said heating
step, and allowing the fiber wrapped storage vessel to cool upon terminating said
heating step before discontinuing pressurization of the vessel interior cavity.
Various liquid or gaseous coolants can be employed in the present method to include
water, air, nitrogen or the like, while removal of said coolant medium from the
storage vessel after being heated during the present thermal bonding step can assist
final cooling of said reinforcement fiber wrap vessel. Thermal bonding in the present
method involves some melting of the thermoplastic materials being employed so that
melting of the thermoplastic outer vessel surface occurs which can be accompanied
by melting of a thermoplastic matrix included in the applied fiber reinforcement.
Accordingly, a softening or melting action takes place during the present thermal
bonding step between the outer surface of the thermoplastic storage vessel and
any thermoplastic polymer materials serving as the matrix composition in selected
preformed tape embodiments having the continuous reinforcement fibers thereafter
becoming permanently bonded therein.
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 vessel polymer
and has a glass transition or melting temperature higher than the surface temperature
of the thermoplastic vessel during use. Selected polymer fibers can understandably
include continuous bare filaments and commingled continuous fibers which can be
wetted by polymer melt flow in the above described heat bonding procedure. For
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 vessel polymer. Any suitable heating source can be
used in the present method to reliably bond the applied fiber reinforcement to
the outer thermoplastic vessel 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 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 heating source provides economical heating with high-energy densities
and with the gas burner or burners being suitably designed so as to heat the outer
circumference of the fiber wrapped thermoplastic vessel. In a preferred embodiment,
the wrapped storage vessel is rotated about the selected heat source while having
the interior cavity of said storage vessel being subjected to a pressurized condition.
The applied pressure can desirably produce some radial expansion of the storage
vessel wall thereby further enhancing the thermal bonding action taking place.
The applied pressurization can also be initiated prior to said heating step in
the present method with applied pressures of ten pounds per square inch or more
having been found effective.
The fiber alignment selected in the present method can also vary with the particular
shape of the thermoplastic storage vessel being reinforced in said manner. Thus,
a cylindrically shaped thermoplastic water heater can have one or more wraps of
the reinforcement fibers aligned in a hoop or helical direction whereas a spherical
thermoplastic storage vessel for the same use can understandably be wrapped in
different spatial directions. A means of preserving the fiber alignment in the
present method until the melted polymer in physical contact therewith again becomes
solid can require that said fibers be subjected to appropriate applied mechanical
force during the thermal bonding action. Such manner of fiber placement can be
carried out by employing external tension winding means to guide the fiber reinforcement
while being wound around the outer vessel surface. An alternate means for retaining
the fiber alignment is a compaction roller to apply mechanical pressure to the
heated fiber and polymer materials while being bonded together. Use of a compaction
roller in such fiber placement can apply an external compaction force with zero
tension force being applied if desired although it is within contemplation of the
present invention for both forms of external mechanical energy to be employed together
when found beneficial. Another advantage of compaction roller use is the ability
to orient such means in any spatial direction enabling fiber placement at a predetermined
fiber angle dictated by the contour of the particular storage vessel being reinforced
in said manner. Thus, a cylindrical shaped thermoplastic pressure vessel can have
one or more wraps of the reinforcement fibers aligned in a hoop or helical direction
whereas a spherical thermoplastic storage vessel for such use can be wrapped in
different spatial directions.
Following termination of said thermal bonding step in the present method,
the fiber wrapped storage vessel can be allowed to cool in the ambient atmosphere.
Such cooling can be carried out in various ways to include removal of any pressurizing
liquid or gas coolant heated during the thermal bonding procedure as well as actively
cooling with an applied coolant medium. The completed fiber reinforcement can now
serve to enable sufficiently higher operating pressures in said storage vessels
than otherwise permissible. Employment of the present method upon an otherwise
conventional thermoplastic pressure vessel having a closed end cylindrical configuration
has produced this result. Additionally, an outer protective or decorative coating
to include heat shrinkable tubing, wrap or extruded coatings and the like can be
applied to said fiber reinforced thermoplastic storage vessel in a conventional
manner for protection of the fiber reinforcement from environmental or mechanical
damage and/or corrosion.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating successive processing steps which can
be employed in carrying out the method of the present invention.
FIG. 2 is a side view for a representative thermoplastic storage vessel being
reinforced according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings, FIG. 1 is a block diagram representation illustrating
the sequence of processing steps employed according to the present invention for
fiber reinforcement of a representative thermoplastic storage vessel having a closed
end cylindrical configuration. The depicted fiber reinforcement process
10
employs a typical six inch diameter, thirty-two inch long thermoplastic liquid
container
12 having a 0.14 inch wall thickness which has one or more wraps
of the thermoplastic reinforcement fibers
14 helically wound about the outer
cylindrical surface of said storage vessel. One or more tie wraps
16 of
said thermoplastic reinforcement fibers can also be subsequently applied in the
hoop direction for the purpose of carrying the radial stress in the cylindrical
pressure vessel. Said fiber wrapped vessel
18 next undergoes thermal bonding
of the applied fiber reinforcement to the outer vessel surface. In a preferred
embodiment, the fiber wrapped vessel is rotated about its central axis
20
while heating the outer vessel surface with a conventional heat source
22.
Heating of the fiber wrapped vessel in said manner produces some melting of the
outer vessel surface which upon vessel cooling retains the originally applied spatial
orientation of said fibers. During said heating step the hollow interior cavity
of said fiber wrapped storage vessel
18 is pressurized
24 by various
means to avoid any significant wrinkling or collapse of the vessel wall that could
understandably deter a fully bonded condition for the applied fiber reinforcement.
Internal pressurization of the storage vessel can be initiated before thermal bonding
of the fiber reinforcement while thereafter being discontinued when the thermal
bonding step has been completed and the reinforced storage vessel then being allowed
to cool
26. Terminating pressurization of the storage vessel
28 can
also be carried out in various ways. To further illustrate a suitable vessel pressurization
in the present method, the interior cavity of the fiber wrapped storage vessel
18 can be filled with a liquid coolant, such as water, glycol, alcohol and
the like before the above described heating step is begun as well as thereafter
being removed from the storage vessel after becoming heated during said processing
step. Alternately, the interior cavity of said storage vessel
28 can be
actively cooled with a suitable gaseous coolant to include air, nitrogen or other
inert gas while the thermal bonding step is being carried out and with said cooling
action being discontinued when the reinforced storage vessel is thereafter allowed
to cool. Active cooling of the fiber wrapped storage vessel in said manner at a
pressure of 10 PSI or more has been proven satisfactory in the present method.
As herein pointed out, the fiber direction of the underlying fiber layers for
the illustrated cylindrical storage vessel is dictated primarily by the ability
of said reinforced storage vessel to withstand internal fluid pressures when such
vessel is-put into service. It can readily be appreciated, however, that other
storage vessels having a different shape, such as a sphere, can have the fiber
alignment in an overall hoop direction for better resistance to internal fluid
pressures during use. Additionally, the continuous fiber reinforcement can be applied
in the present method by various means. A selected amount of tension can be exerted
upon the continuous fibers when being applied to assist with retention of the predetermined
or juxtapositioned fiber angle with respect to the vessel longitudinal axis in
the herein illustrated embodiment. Similarly, a mechanical compaction force exerted
upon said fibers during initial placement or subsequent thermal bonding can be
employed for this purpose. A wide variety of thermoplastic polymers can also be
selected as the material of construction for storage vessels being reinforced according
to the present method. Suitable organic polymers include but are not limited to
polyethylene such as high density polyethylene and medium density polyethylene,
polypropylene, polyphenylene sulfide, polyetherketoneketone, polyamide, polyamideimide
and polyvinylidene difluoride. A similar wide variety of materials are found suitable
as the fiber reinforcement in the present method to again include but not be limited
to ceramics, metals, carbon aramid and other organic polymer fibers having softening
temperatures above that of the storage vessel in use and glass compositions such
as E type and S type glasses. Moreover, said fiber materials can also be applied
in various structural forms to include a parallel alignment of the bare fibers
and conventional fiber tapes having the continuous parallel oriented fibers bonded
together in a thermoplastic polymer matrix. The optional use being made of tie
layers
16 in the presently illustrated embodiment can also serve to help
retain the juxtapositioned spatial orientation of the applied fiber reinforcement
when selected thermoplastic polymer materials being employed are not miscible during
the heating step.
FIG. 2 is a side view for a representative thermoplastic storage vessel being
reinforced according to the present invention. More particularly, the depicted
cylindrical thermoplastic storage vessel
30 is repeatedly illustrated during
each processing step described in the preceding preferred embodiment. As shown,
said storage vessel
30 comprises an elongated thermoplastic cylinder
32
having a closed end
34 and an open end
36 fitted with a conventional
inlet coupling
38. There is next depicted the manner whereby the continuous
reinforcement fiber
40 is deposited on the outer surface
42 of the
rotating thermoplastic storage vessel in a helical pattern
44 while also
being subjected to a tensile force being applied in the customary manner. The next
processing step being illustrated depicts further rotation of the fiber wrapped
storage vessel
46 while additional fiber wraps
48 are applied in
a hoop direction enabling better retention of the underlying reinforcement fiber
40. The still further depicted processing step in the herein illustrated
method of fiber reinforcement demonstrates the heating step being employed to cause
thermal bonding between the applied unbonded reinforcement fibers and the outer
surfaces of said storage vessel. In doing so, a conventional heat source
50
positioned in relatively close proximity to said fiber wrapped storage vessel
46
supplies the needed thermal energy during said bonding procedure and which is further
accompanied by having the interior cavity
52 of said fiber wrapped storage
vessel pressurized with a selected liquid cooling medium
54 while said thermal
bonding step is being carried out. Following said latter procedure, the reinforced
storage vessel
56 is allowed to cool in the ambient atmosphere which further
include removal of the pressurizing fluid after sufficient time has elapsed for
solidification of the polymers thermally bonded together.
It will be apparent from the foregoing description that a broadly useful and
novel
method has been provided to reinforce thin wall thermoplastic storage vessels with
one or more wraps of applied continuous fiber. It will be apparent, however, that
various modifications can be made in the disclosed process without departing from
the spirit and scope of the present invention. For example, it is contemplated
that some heating of the unbonded reinforcement when being initially applied to
the outer surface of the storage vessel can assist in having the fiber conform
more closely to the particular contours of the vessel surface. Likewise, it is
contemplated that other organic polymers, other vessel shapes and other processing
equipment than herein specifically disclosed can be substituted in carrying out
the present method. Consequently, it is intended to cover all variations in the
disclosed reinforcement method which may be devised by persons skilled in the art
as falling within the scope of the appended claims.
*
