U.S. patent application number 11/322118 was filed with the patent office on 2006-05-18 for polymer processing system including compression chamber and method for using same.
This patent application is currently assigned to Extrutech International, Inc.. Invention is credited to Roderick E. Hughes.
Application Number | 20060105072 11/322118 |
Document ID | / |
Family ID | 36386646 |
Filed Date | 2006-05-18 |
United States Patent
Application |
20060105072 |
Kind Code |
A1 |
Hughes; Roderick E. |
May 18, 2006 |
Polymer processing system including compression chamber and method
for using same
Abstract
Polymer processing systems are provided including an extrusion
assembly, a specially configured decompression chamber assembly,
and a die assembly. Such systems are effective to provide shaped
polymer products having reduced extrusion markings. Methods of
using such systems are also provided.
Inventors: |
Hughes; Roderick E.;
(Newport Beach, CA) |
Correspondence
Address: |
STOUT, UXA, BUYAN & MULLINS LLP
4 VENTURE, SUITE 300
IRVINE
CA
92618
US
|
Assignee: |
Extrutech International,
Inc.
Costa Mesa
CA
|
Family ID: |
36386646 |
Appl. No.: |
11/322118 |
Filed: |
December 28, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10464285 |
Jun 18, 2003 |
|
|
|
11322118 |
Dec 28, 2005 |
|
|
|
Current U.S.
Class: |
425/131.1 |
Current CPC
Class: |
B29C 48/285 20190201;
B29C 48/267 20190201; B29C 48/21 20190201; B29K 2995/0073 20130101;
B29C 48/49 20190201; B29C 48/08 20190201; B29C 2948/92647 20190201;
B29C 48/25 20190201; B29C 48/305 20190201; B29C 48/2562 20190201;
B29C 48/39 20190201 |
Class at
Publication: |
425/131.1 |
International
Class: |
B29C 47/66 20060101
B29C047/66 |
Claims
1. A decompression chamber assembly comprising: an entrance block
including a through aperture structured to pass a flowable extruded
polymeric material; a decompression chamber in communication with
the entrance block and positioned to receive the flowable extruded
polymeric material passed from the through aperture, the chamber
having an outer wall defining a hollow space including an entrance
zone generally adjacent the entrance block, a generally oppositely
located exit zone and a central zone located therebetween, the
hollow space having an increased cross-sectional area perpendicular
to a central longitudinal axis of the hollow space at the central
zone relative to at at least one of the entrance zone and the exit
zone, the outer wall includes a first region defining increasing
cross-sectional areas perpendicular to the central longitudinal
axis of the hollow space and a second region, spaced apart from the
first region, defining decreasing cross-sectional areas
perpendicular to the central longitudinal axis of the hollow space,
wherein at least a portion of each of the first region and the
second region is oriented at an angle in a range of about
10.degree. to about 40.degree. relative to the central longitudinal
axis of the hollow space; and an exit block positioned to receive
the flowable extruded polymeric material from the exit zone of the
decompression chamber.
2. The decompression chamber assembly of claim 1 wherein the hollow
space has an increased cross-sectional area perpendicular to the
central longitudinal axis of the hollow space at the central zone
relative to at both the entrance zone and the exit zone.
3. The decompression chamber assembly of claim 1 wherein the
decompression chamber is structured to pass substantially all of
the flowable extruded polymeric material entering the entrance zone
out of the exit zone.
4. The decompression chamber assembly of claim 1 where the
decompression chamber is free of any rotatable component.
5. The decompression chamber assembly of claim 1 wherein the
decompression chamber is structured to cause the flowable extruded
polymeric material to be under reduced strain and/or stress as the
flowable extruded polymeric material passes through the
decompression chamber.
6. The decompression chamber assembly of claim 1 wherein the
decompression chamber is structured to reduce extrusion markings
present in the flowable extruded polymeric material entering the
decompression chamber.
7. The decompression chamber assembly of claim 1 wherein the outer
wall is substantially smooth.
8. The decompression chamber assembly of claim 1 wherein the
decompression chamber is in communication with no substantial
source of suction.
9. The decompression chamber assembly of claim 2 wherein the
cross-sectional area perpendicular to the central axis of the
hollow space defined by the outer wall varies substantially
continuously across the entire central zone.
10. The decompression chamber assembly of claim 1 wherein the
decompression chamber includes no inner wall.
11. A method of processing a polymeric material, which method
comprises: passing a flowable extruded polymeric material through a
decompression chamber having an outer wall defining a hollow space,
the hollow space including an entrance zone through which the
flowable extruded polymeric material passes in entering the
decompression chamber, a generally oppositely located exit zone
through which the flowable extruded polymeric material passes in
exiting the decompression chamber and a central zone located
therebetween, the hollow space having an increased cross-sectional
area perpendicular to a central longitudinal axis of the hollow
space at the central zone relative to at at least one of the
entrance zone or the exit zone.
12. The method of claim 11 wherein the passing step is effective to
pass substantially all of the flowable extruded polymeric material
entering the decompression chamber out of the decompression
chamber.
13. The method of claim 12 wherein the cross-sectional area of the
outer wall is varied so as to facilitate substantially all of the
flowable extruded polymeric material entering the decompression
chamber passing out of the decompression chamber.
14. The method of claim 11 wherein the hollow space has an
increased cross-sectional area perpendicular a central longitudinal
axis of the hollow space at the central zone relative to at both
the entrance zone and the exit zone.
15. The method of claim 11 wherein the passing step is effective to
relax the flowable extruded polymeric material in the decompression
chamber.
16. The method of claim 11 wherein the passing step is effective to
reduce extrusion markings present in the flowable extruded
polymeric material entering the decompression chamber.
17. The method of claim 11 which further comprises: extruding a
polymeric material to form the flowable extruded polymeric
material.
18. The method of claim 17 wherein the extruding step occurs in at
least one screw extruder.
19. The method of claim 17 wherein the extruding step occurs in two
or more screw extruders.
20. The method of claim 19 herein each screw extruder produces a
ribbon of extruded polymeric material and the method further
comprises combining the ribbons of extruded polymeric material into
a combined ribbon of polymeric material.
21. The method of claim 11 which further comprises, after passing
the flowable extruded polymeric material through the decompression
chamber, passing the flowable extruded polymeric material through a
die to form the flowable extruded polymeric material into a desired
shape.
22. The method of claim 21 wherein the desired shape is a sheet.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of U.S. patent application
Ser. No. 10/464,285, filed Jun. 18, 2003, the entire contents of
which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to polymer processing systems
and methods for using same. More particularly, the invention
relates to polymer processing systems including decompression
chambers preferably structured to provide products which are more
aesthetically pleasing, and methods for using such systems.
[0003] Polymer processing to produce articles, such as sheets,
films, other profiles and the like, has become increasingly
important as the use of such articles become more prevalent.
Production of polymer products often involves the use of extrusion
processing, for example, using screw extruders, other types of
extruders and the like, to produce a workable or flowable extruded
polymeric material. This extruded polymeric material is often
passed through a die configured to produce a polymer product of a
desired shape or configuration from the extruded polymeric
material.
[0004] One disadvantage of such processing is the presence of
visually apparent markings, blemishes and the like, such as
extrusion marks or markings, in the final product. Such markings
and the like are the result of processing in the extrusion
assemblies, e.g., the extruder or extruders in which the extruded
polymeric material is produced. Because the polymeric material
leaving the extrusion assembly is under a substantial degree of
stress resulting from work done on the material in the extruder,
extrusion markings are produced on this material leaving the
extruder. Since the die assembly is often substantially adjacent
the extruder or extruders, the extrusion markings often are present
in the final shaped polymer product from the die assembly. Such
extrusion markings in the final product is aesthetically
disadvantageous, may reduce the value of the product and may be so
severe as to require expensive reprocessing.
[0005] Various approaches have been suggested to avoid such
extrusion markings. For example, the production rate of a product
can be reduced to allow for less stress to be placed on the
polymeric material being passed through the extruder or extruders.
Alternatively, or in addition, the distance between the extruder or
extruders and the die assembly can be lengthened to allow the
extruded polymer material more time before final shaping so that
the extrusion markings may become less apparent. However, such
approaches reduce production rates and/or increase production
costs. In addition, providing longer distances between the
extruder(s) and die assembly can be disadvantageous in that
polymeric material can hang up within, or even block, the
processing system, which can result in system shutdown, leading to
substantial additional costs and system downtime.
[0006] There continues to be a need for polymer processing systems
which reduce extrusion markings in the final shaped polymeric
products while, at the same time, avoiding reduced production rates
and increased costs.
SUMMARY OF THE INVENTION
[0007] New polymer processing systems and methods for using such
systems have been discovered. The present systems are
straightforward and advantageously provide for effective reduction
of extrusion markings, other visually apparent blemishes and the
like caused by processing a polymeric material prior to passing the
material through a shape-forming die. The present systems provide
for such advantages substantially without reducing production rates
or increasing operating costs. The present systems take advantage
of the flow characteristics of extruded polymeric materials, while
being easy to operate and control.
[0008] In one broad aspect of the present invention, polymer
processing systems are provided which comprise an extrusion
assembly, a decompression chamber assembly, and a die assembly. The
extrusion assembly is structured to extrude a quality of polymeric
material into an extruded polymeric material, preferably a flowable
extruded polymeric material.
[0009] The decompression chamber assembly of the present system is
positioned and structured to receive the extruded polymeric
material from the extrusion assembly. The decompression chamber
assembly includes a decompression chamber which has an outer wall
defining a hollow space including an entrance zone, a generally
oppositely located exit zone and a central zone located
therebetween. The entrance zone and the exit zone preferably,
though not necessarily, are substantially longitudinally aligned,
for example, along a central longitudinal axis of the hollow space.
The entrance zone is positioned such that the extruded polymeric
material enters the decompression chamber through the entrance
zone. Extruded polymeric material leaves the decompression chamber
through the exit zone. The hollow space has an increased cross
sectional area perpendicular to the central longitudinal axis of
the hollow space at the central zone relative to at at least one
of, and preferably at both of, the entrance zone and the exit
zone.
[0010] Such configuration of the decompression chamber
advantageously provides a location where the extruded polymeric
material can relax or be subjected to reduced strain and/or stress
or otherwise be subjected to conditions effective to reduce, or
even substantially eliminate, unwanted extrusion markings,
blemishes and the like defects often formed in the polymeric
material during extrusion processing.
[0011] The die assembly is positioned and structured to receive the
extruded polymeric material from the decompression chamber assembly
and form the extruded polymeric material into a desired shape, for
example, sheet, film or the like.
[0012] Advantageously, the decompression chamber, as described
herein, is structured to pass substantially all of the extruded
polymeric material entering the decompression chamber out of the
decompression chamber. In this embodiment, substantially none of
the polymeric material entering the decompression chamber is held
up or hangs up in the decompression chamber. Of course, the
configuration of the decompression chamber may cause the polymeric
material to remain in the decompression chamber for a longer period
of time relative to the period of time the material remains in an
identical decompression chamber without an increased cross
sectional area perpendicular to the central longitudinal axis of
the hollow space at the central zone, as in the present invention.
However, after steady state operation is achieved, the rate at
which the polymeric material enters the present decompression
chamber preferably is substantially equal to the rate at which the
polymeric material exits the decompression chamber and
substantially no polymeric material is held up or hangs up in the
decompression chamber.
[0013] In one very useful embodiment, the decompression chamber is
free of any rotatable component. In certain prior art systems, a
so-called decompression zone was provided in a space within a
rotating extruder, for example, a screw extruder, with a rotating
central element located within the decompression zone and
screw-like blade located on either side of the decompression zone.
In the present embodiment, no screw-like blades or central
rotatable element is provided within the decompression chamber. A
decompression chamber having a hollow space without screw-like
blades and/or a rotatable component is highly advantageous in
allowing the extruded polymeric material to relax or otherwise be
subjected to conditions so as to reduce extrusion markings and the
like defects.
[0014] The decompression chamber preferably includes no inner wall.
In a more preferred embodiment, the hollow space defined by the
outer wall of the decompression chamber is substantially completely
hollow and has no member or other elements located therein.
[0015] The outer wall of the decompression chamber advantageously
is substantially smooth. This feature is effective in facilitating
passing substantially all of the polymeric material entering the
decompression chamber through and out of the decompression chamber.
The decompression chamber preferably is in communication with no
substantial source of suction. Thus, preferably, the force provided
by the extruder or extruders, for example, the screw extruder or
extruders, is sufficient to cause the extruded polymeric material
to pass from the extruder or extruders through the decompression
chamber and through the die assembly to provide a product of a
desired shape and configuration.
[0016] In addition, the cross sectional area perpendicular to the
central longitudinal axis of the hollow space defined by the outer
wall of the decompression chamber advantageously varies so as to
facilitate the passing of substantially all of the extruded
polymeric material entering the decompression chamber out of the
chamber.
[0017] In one useful embodiment, the outer wall of the
decompression chamber includes a first region defining increasing
cross sectional areas perpendicular to the central longitudinal
axis of the hollow space and a second region, spaced apart from the
first region, defining decreasing cross sectional areas
perpendicular to the central longitudinal axis of the hollow space.
At least a portion, preferably a substantial portion, and more
preferably a major portion (at least about 50%) of the first region
and the second region is preferably oriented at an angle in a range
of about 10.degree. to about 40.degree., more preferably about
15.degree. to about 30.degree., for example, about 20.degree.,
relative to central longitudinal axis of the hollow space. It has
been found that such orientation is highly effective in providing
for or in facilitating the passing of substantially all of the
extruded polymeric material entering the decompression chamber out
of the chamber.
[0018] The specific configuration chosen for the decompression
chamber depends, for example, on the type of extruded polymeric
material being processed, the processing conditions being employed,
the flow properties, e.g., viscosity, of the extruded polymeric
material being processed and the like and other factors. In any
event, it has been found that the use of the present systems,
including the decompression chambers and decompression chamber
assemblies as set forth herein, cost effectively provide
aesthetically pleasing polymer products.
[0019] The present systems preferably further include an entrance
block including a through aperture structured to pass extruded
polymeric material from the extrusion assembly to the decompression
chamber. The present systems may further include an exit block
structured to receive the extruded polymeric material from the
decompression chamber and provide the extruded polymeric material
to the die assembly.
[0020] The present extrusion assemblies may include one or more
extruders, for example and without limitation, at least one screw
extruder, or two or more screw extruders. If two or more screw
extruders are used, individual decompression chambers, as described
herein, may be used for each screw extruder or the plurality of
screw extruders can be used to provide extruded polymeric material
to the same decompression chamber, as described herein.
[0021] In one embodiment, where two or more extruders are provided,
each of the extruders advantageously produces a stream, for
example, a so called ribbon, of extruded polymeric material, and
the system further comprises an orifice block positioned and
structured to combine the streams or ribbons of extruded polymeric
material into a combined stream or ribbon of extruded polymeric
material to be passed to the decompression chamber.
[0022] The present methods of processing polymeric material
generally comprise passing an extruded polymeric material through a
decompression chamber, as described elsewhere herein. Such methods
are highly effective in providing aesthetically pleasing, shaped
polymeric products at commercially acceptable production rates in a
cost effective manner.
[0023] In another broad aspect of the present invention,
decompression assemblies are provided which comprise an entrance
block, a decompression chamber and an exit block. The entrance
block includes a through aperture structured to pass extruded
polymeric material, for example, flowable extruded polymeric
material into the decompression chamber.
[0024] The decompression chamber is as described elsewhere herein.
The exit block is structured to receive extruded polymeric material
from the exit zone of the decompression chamber.
[0025] Each and every feature described herein, and each and every
combination of two or more of such features, is included within the
scope of the present invention provided that the features included
in such a combination are not mutually inconsistent.
[0026] These and other aspects of the present invention are set
forth in the following detailed description, examples and claims,
particularly when considered in conjunction with the accompanying
drawings in which like parts bear like reference numerals.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1a is a schematic flow diagram of a polymer processing
system in accordance with the present invention.
[0028] FIG. 1 is a cross sectional view of a portion of the system
shown in FIG.a.
[0029] FIG. 2 is a cross sectional view of another portion of the
system shown in FIG. 1.
[0030] FIG. 3 is a cross sectional view of a bracket structure used
to hold the decompression chamber shown in FIG. 1 together.
[0031] FIG. 4 is the schematic view of a system in accordance with
the present invention of an alternate embodiment of a system in
accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0032] The present invention relates to systems for processing
polymeric materials.
[0033] Although any suitable type of polymeric material may be
processed using the present systems, advantageously thermoplastic
polymeric materials effective to be die formed into products, such
as sheets, films and the like shapes, are used. FIG. 1a is a
schematic view showing one embodiment of such a system in
accordance with the present invention. In FIG. 1A, the system 10
includes a polymer extrusion assembly 12, a decompression chamber
assembly 14 and a die assembly 16. The result of processing a
polymeric material through the system is a shaped polymer product
18.
[0034] The polymer extrusion assembly 12 may be any suitable
polymer extrusion assembly, for example, a conventional or
substantially conventional assembly, such as an extrusion assembly
including one or two or more conventional or substantially
conventional screw extruders. The function of polymer extrusion
assembly 12 is to produce a workable or flowable extruded polymeric
material for further processing in system 10.
[0035] The extruded polymeric material from polymer extrusion
assembly 12 passes into decompression chamber assembly 14, to be
described in detail hereinbelow. Passing the extruded polymeric
material through the decompression chamber assembly 14 is effective
to relax and/or otherwise condition the extruded polymeric material
so as to reduce extrusion markings and/or other blemishes and/or
other visually apparent defects or distortions in the extruded
polymeric material, for example, caused or formed during the
extrusion processing in the extrusion assembly 12.
[0036] The extruded polymeric material passes through the
decompression chamber assembly 14 and is processed through a die
assembly 16. Die assembly 16 may be any suitable such assembly, for
example, a conventional or substantially conventional polymeric
material die assembly, effective to form the extruded polymeric
material from the decompression chamber assembly 14 into a polymer
product of the desired shape/configuration, such as shaped polymer
product 18. In one useful embodiment, die assembly 16 is effective
to produce a sheet or film of the extruded polymeric material which
has enhanced aesthetic appearance relative to such a polymer
product produced by a system identical to system 10 without
decompression chamber assembly 14.
[0037] As noted above, one or both of the polymer extrusion
assembly 12 and the die assembly 16 may be selected from
conventional such assemblies. However, the decompression chamber
assembly 14 of system 10 is particularly structured/configured in
accordance with the present invention to advantageously provide
shaped polymer products, such as shaped polymer product 18, which
have enhanced aesthetic appearance and can be produced cost
effectively.
[0038] Thermoplastic polymeric resins processed in accordance with
the present invention include without limitation, high-density
polyethylene, low-density polyethylene, polypropylene, copolymers
between ethylene and propylene and between ethylene, propylene and
another a-olefin, polystyrene, acrylonitrile/butadiene/styrene
(ABS) copolymers, acrylonitrile/styrene/acrylic (ASA) copolymers,
polyamides, polyesters, polycarbonates, polyvinyl chloride,
polyvinylidene chloride, polyphenylene oxide, polyimides,
polysulfones, polyphenylene sulfide, and the like and mixtures
thereof.
[0039] The feed portion of screw extruder 20 of polymer extrusion
assembly 12 is shown in some detail in FIG. 2. Pellets of
thermoplastic polymeric material are fed through port 30 and are
passed, using feed screw 32, through feed portion 34 into the main
screw compartment 36. It is often not necessary to use a feed
screw, such as feed screw 32, particularly if pellets of polymeric
material are fed to extrusion assembly 12. The pellets are melted
as they are passed through main screw compartment 36 of extrusion
assembly 12. The system 10 advantageously is heated from the main
screw compartment 36 through the decompression chamber assembly 14
and die assembly 16 to facilitate melting the polymeric material
particles and to maintain the polymeric material being passed
through the system in a suitable flowable state. The polymeric
material is fed under pressure in the main screw compartment 36
from left to right in FIG. 2, while being kneaded by the propelling
force of the main screw 38.
[0040] The main screw 38 can be exemplified as having a compression
ratio in the range of about 0.5 to about 2, preferably about 0.6 to
1.5. The term "compression ratio" means the depth of the screw
channel at the start portion of polymeric material flow/the depth
of the screw channel at the end portion of polymeric material
extrusion, when the pitch of the screw is constant in each of the
sections of the screw. The compression ratio at the beginning of
the screw is determined by the type of polymeric material being
processed, the rate of extrusion, the condition of the remainder of
the system 10 and the like. In one useful embodiment a straight
screw is provided having a compression ratio of about 1.
[0041] The power or force provided by the screw should be such as
to provide proficient propulsion for the extruded polymeric
material to pass through the decompression chamber assembly 14 and
the die assembly 16.
[0042] The main screw 38 employed in the polymer extrusion assembly
12, shown partially in FIG. 2, may be of any type, for example, a
straight type, a type of an equidistant pitch and variable in the
depth of screw channel, a type of a constant depth of screw channel
and variable in the pitch, a rapid compression type and the
like.
[0043] Although excessive force on the polymeric material and
kneading of the polymeric material by main screw 38 are to be
avoided, it is important that the polymeric material be provided
with sufficient propulsion so that the final shaped product is
effectively formed and that the polymeric material be substantially
uniform. Because the decompression chamber assembly 14 is effective
to reduce markings in the polymeric material caused by the
extrusion processing, adequate and effective amounts of propelling
force and mixing force can be applied to the polymeric material by
main screw 38 and polymer extrusion assembly 12 substantially
without adversely affecting the aesthetic appearance of the final
shaped polymer product.
[0044] It should be noted that the screw extruders employed in the
present systems may be similar to those screw extruders which are
conventionally used in polymer processing.
[0045] Referring now to FIG. 1, the distal end portions of screw
extruders 40 and 42 are shown joined to an entrance block 44. Each
of the screw extruders 40 and 42 is structured substantially
similarly to extruder 20 described previously. The extruders 40 and
42 are positioned so as to provide a ribbon or stream of extruded
polymeric material to the aperture 46 of entrance block 44.
[0046] It should be noted that a single screw extruder can be used
to provide extruded polymer material to aperture 46. In addition,
although one or more screw extruders are very useful, the present
systems may include one or more extruders of other types and such
systems are included in the scope of the present invention.
[0047] The extruded polymeric materials from screw extruders 40 and
42 are combined in aperture 46 of entrance block 44 and pass
through entrance opening or inlet 48 into decompression chamber 50
of decompression chamber assembly 14.
[0048] Decompression chamber 50 includes inlet 48, entrance zone
52, outer wall 54, exit zone 56, and exit opening or outlet 60. The
cross sectional areas of the entrance zone 52 and exit zone 56
perpendicular to the longitudinal axis 62 of hollow space 64 of the
decompression chamber 50 are substantially equal, although such
cross sectional areas can be unequal in accordance with the present
invention. The decompression chamber 50 includes a central zone 66
where the cross sectional area of the hollow space 64 is increased
relative to the cross sectional area of either the entrance zone 52
or the exit zone 56.
[0049] Thus, the cross sectional area of the hollow space 64
perpendicular to the longitudinal axis 62 at the entrance zone 52
increases as you move toward the maximum cross sectional area
substantially at the center 70 of the hollow space. As you move
further towards the exit zone 56, the cross sectional area of the
hollow space 64 (perpendicular to the longitudinal axis 62)
decreases.
[0050] Substantial portions, even major portions, of the outer wall
54 between the entrance zone 52 and the central zone 66, and
between the central zone 66 and the exit zone 56 are oriented at an
angle of about 200 relative to the central longitudinal axis 62 of
the hollow space 64. In addition, the outer wall is substantially
smooth, for example, includes substantially no sharp or protruding
edges.
[0051] All of these features are designed to provide all of the
extruded polymeric material entering the decompression chamber 50
exits the decompression chamber 50 without hanging up in the
chamber. The shape and configuration of the decompression chamber
50 is very effective in providing a location for the extruded
polymeric material to relax or otherwise be subjected to conditions
so that unsightly markings or blemishes, for example, formed in the
extruded polymeric material in the screw extruders 40 and 42, can
be reduced. Such reduction in extrusion markings and/or other
blemishes enhances the aesthetic quality of the final polymer
product obtained by system 10.
[0052] It is important to note, unlike many prior art decompression
chambers, the present chamber includes no screw extruder mechanism,
for example no screw or no rotating shaft. Thus, the extruded
polymeric material in decompression chamber 50 is subjected to
reduced stress which has been found to be effective in reducing
extrusion markings and the like.
[0053] Moreover, it is somewhat surprising that extruded polymeric
material advantageously passes through the decompression chamber 50
without material hang-up. Without wishing to limit the invention to
any particular theory of operation, it is believed that the
configuration of the decompression chamber 50 facilitates effective
passage of substantially all of the polymeric material through the
decompression chamber. One or more features, such as a
substantially smooth-outer wall, a properly angled outer wall, and
the like are believed to be effective in facilitating the passage
of the material through the decompression chamber 50 while, at the
same time, allowing the extruded polymeric material to effectively
reduce extrusion markings and the like blemishes.
[0054] An exit block 74 is coupled to the decompression chamber
component 76 so that the extruded polymeric material from the
decompression chamber 50 passes through opening 78 on its way
toward die assembly 18.
[0055] With reference to FIGS. 1 and 3, one construction of a
bracket structure, shown generally at 80, used to hold
decompression chamber 50 together is shown. In this construction,
the decompression chamber components 76 and 77 are formed and are
brought together. Collar elements 82 and 84 are placed over the
joint 86 between the components 76 and 77. Using conventional screw
and nut combinations 87 and 88 the two collar elements 82 and 84
are tightened around the joint 86 to securely join components 76
and 77 together, as shown in FIGS. 1 and 3.
[0056] It should be noted that other constructions may be employed
to provide the compression chamber in accordance with the present
invention. For example, and without limitation, the decompression
chamber components 76 and 77 can be formed with outwardly extending
flanges including a plurality of apertures. Bolts can be passed
through the apertures and secured in place using nuts and the like,
thereby directly coupling components 76 and 77 together. Additional
constructions may be employed to provide the present decompression
chambers and systems. All such constructions are within the scope
of the present invention.
[0057] As the extruded polymeric material passes from the
decompression chamber assembly 14 to the die assembly 16, the
material continues to be propelled by the force of the screws in
screw extruders 40 and 42. The present systems are associated with
no other source of suction. The extruded polymeric material passes
through the die assembly 16 to shape the extruded polymeric
material into a desired form, such as a film or sheet.
[0058] With reference to FIG. 4, a portion of an alternate system
110 in accordance with the present invention is shown in which each
of two streams of extruded polymeric material, from individual
screw extruders, is passed through an individual decompression
chamber 150, 150a configured similarly to that described
previously. In this embodiment a composite, shaped polymer product,
for example, a two layer film or sheet is produced, in a die
assembly such that both layers have reduced extrusion markings or
other visually apparent blemishes.
[0059] Additional processing, such as that conventionally employed
in producing polymeric shapes or products through die assemblies,
may be employed with the present systems to produce the final
shaped polymeric product. In any event, it has been found that the
final shaped polymeric product, for example, film or sheet product,
has a reduced degree of extrusion markings and/or other blemishes
relative to an identical product produced using an identical system
without the present decompression chamber. Moreover, such
aesthetically pleasing product is provided without reducing
production rates and in a cost effective way without polymeric
material hang up in the system. In short, the present invention is
highly cost effective, performance effective and provides a product
having an enhanced appearance which promotes saleability and
reduces or even eliminates the need for reprocessing.
[0060] While this invention has been described with respect to
various specific examples and embodiments, it is to be understood
that the invention is not limited thereto and that it can be
variously practiced within the scope of the following claims.
* * * * *