Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
Extrusion Die for Biodegradable Material with Die Orifice Modifying Device and
Flow
Control Device
BACKGROUND OF THE INVENTION
This invention relates generally to the formation of shaped objects from
expanded
biodegradable materials, and, in particular, to an extrusion die for
ultimately forming sheets of
biodegradable material.
Biodegradable materials are presently in high demand for applications in
packaging
materials. Commonly used polystyrene ("Styrofoam" (Trademark)), polypropylene,
polyethyl-
ene, and other non-biodegradable plastic-containing packaging materials are
considered
detrimental to the environment and may present health hazards. The use of such
non-
biodegradable materials will decrease as government restrictions discourage
their use in
packaging applications. Indeed, in some countries in the world, the use of
styrofoam
(trademark) is already extremely limited by legislation. Biodegradable
materials that are
flexible, pliable and non-brittle are needed in a variety of packaging
applications, particularly
for the manufacture of shaped biodegradable containers for food packaging. For
such
applications, the biodegradable material must have mechanical properties that
allow it to be
formed into and hold the desired container shape, and be resistant to
collapsing, tearing or
breaking.
Starch is an abundant, inexpensive biodegradable polymer. A variety of
biodegradable
based materials have been proposed for use in packaging applications.
Conventional extrusion
of these materials produces expanded products that are brittle, sensitive to
water and unsuitable
for preparation of packaging materials. Attempts to prepare biodegradable
products with
flexibility, pliability, resiliency, or other mechanical properties acceptable
for various
biodegradable packaging applications have generally focused on chemical or
physio-chemical
modification of starch, the use of expensive high amylose starch or mixing
starch with synthetic
polymers to achieve the desired properties while retaining a degree of
biodegradability. A
number of references relate to extrusion and to injection molding of starch-
containing
compositions.
U.S. Patent No. 5,397,834 provides biodegradable, thermoplastic compositions
made of
the reaction product of a starch aldehyde with protein. According to the
disclosure, the resulting
products formed with the compositions possess a smooth, shiny texture, and a
high level of
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tensile strength, elongation, and water resistance compared to articles made
from native starch
and protein. Suitable starches which may be modified and used according to the
invention
include those derived, for example, from corn including maize, waxy maize and
high amylose
corn; wheat including hard wheat, soft wheat and durum wheat; rice including
waxy rice; and
potato, rye, oat, barley, sorghum, millet, triticale, amaranth, and the like.
The starch may be a
normal starch (about 20-30 wt-% amylose), a waxy starch (about 0-8 wt-%
amylose), or a high-
amylose starch (greater than about 50 wt-% amylose).
U.S. Patent Nos. 4,133,784, 4,337,181, 4,454,268, 5,322,866, 5,362,778, and
5,384,170
relate to starch-based films that are made by extrusion of destructurized or
gelatinized starch
combined with synthetic polymeric materials. U.S. Patent No. 5,322,866
specifically concerns a
method of manufacture of biodegradable starch-containing blown films that
includes a step of
extrusion of a mixture of raw unprocessed starch, copolymers including
polyvinyl alcohol, a
nucleating agent and a plasticizer. The process is said to eliminate the need
of pre-processing
the starch. U.S. Patent No. 5,409,973 reports biodegradable compositions made
by extrusion
from destructurized starch and an ethylene-vinyl acetate copolymer.
U.S. Patent No. 5,087,650 relates to injection-molding of mixtures of graft
polymers and
starch to produce partially biodegradable products with acceptable elasticity
and water stability.
U.S. Patent No. 5,258,430 relates to the production of biodegradable articles
from
destructurized starch and chemically-modified polymers, including chemically-
modified
polyvinyl alcohol. The articles are said to have improved biodegradability,
but retain the
mechanical properties of articles made from the polymer alone.
U.S. Patent No. 5,292,782 relates to extruded or molded biodegradable articles
prepared
from mixtures of starch, a thermoplastic polymer and certain plasticizers.
U.S. Patent No. 5,095,054 concerns methods of manufacturing shaped articles
from a
mixture of destructurized starch and a polymer.
U.S. Patent No. 4,125,495 relates to a process for manufacture of meat trays
from
biodegradable starch compositions. Starch granules are chemically modified,
for example with
a silicone reagent, blended with polymer or copolymer and shaped to form a
biodegradable
shallow tray.
U.S. Patent No. 4,673,438 relates to extrusion and injection molding of starch
for the
manufacture of capsules.
U.S. Patent No. 5,427,614 also relates to a method of injection molding in
which a non-
modified starch is combined with a lubricant, texturing agent and a melt-flow
accelerator.
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U.S. Patent No. 5,314,754 reports the production of shaped articles from high
amylose
starch.
EP published application No. 712883 (published May 22, 1996) relates to
biodegrad-
able, structured shaped products with good flexibility made by extruding
starch having a defined
large particle size (e.g., 400 to 1500 microns). The application exemplifies
the use of high
amylose starch and chemically-modified high amylose starch.
U.S. Patent No. 5,512,090 refers to an extrusion process for the manufacture
of resilient,
low density biodegradable packaging materials, including loose-fill materials,
by extrusion of
starch mixtures comprising polyvinyl alcohol (PVA) and other ingredients. The
patent refers to
a minimum amount of about 5% by weight of PVA.
U.S. Patent No. 5,186,990 reports a lightweight biodegradable packaging
material
produced by extrusion of corn grit mixed with a binding agent (guar gum) and
water. Corn grit
is said to contain among other components starch (76-80%), water (12.5-14%),
protein (6.5-8%)
and fat (0.5-1%). The patent teaches the use of generally known food extruders
of a screw-type
that force product through an orifice or extension opening. As the mixture
exits the extruder via
the flow plate or die, the super heated moisture in the mixture vaporizes
forcing the material to
expand to its final shape and density.
U.S. Patent No. 5,208,267 reports biodegradable, compressible and resilient
starch-
based packaging fillers with high volumes and low weights. The products are
formed by
extrusion of a blend of non-modified starch with polyalkylene glycol or
certain derivatives
thereof and a bubble-nucleating agent, such as silicon dioxide.
U.S. Patent No. 5,252,271 reports a biodegradable closed cell light weight
loose-fill
packaging material formed by extrusion of a modified starch. Non-modified
starch is reacted in
an extruder with certain mild acids in the presence of water and a carbonate
compound to
generate CO2. Resiliency of the product is said to be 60% to 85%, with density
less than 0.032
g/cm3.
U.S. Patent No. 3,137,592 relates to gelatinized starch products useful for
coating
applications produced by intense mechanical working of starch/plasticizer
mixtures in an
extruder. Related coating mixtures are reported in U.S. Patent No. 5,032,337
which are
manufactured by the extrusion of a mixture of starch and polyvinyl alcohol.
Application of
thermomechanical treatment in an extruder is said to modify the solubility
properties of the
resultant mixture which can then be used as a binding agent for coating paper.
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Biodegradable material research has largely focused on particular compositions
in an
attempt to achieve products that are flexible, pliable and non-brittle. The
processes used to
produce products from these compositions have in some instances, used
extruders. For
example, U.S. Patent Number 5,660,900 discloses several extruder apparatuses
for processing
inorganically filled, starch-bound compositions. The extruder is used to
prepare a moldable
mixture which is then formed into a desired configuration by heated molds.
U. S. Patent Number 3,734,672 discloses an extrusion die for extruding a cup
shaped
shell made from a dough. In particular, the die comprises an outer base having
an extrusion
orifice or slot which has a substantial horizontal section and two upwardly
extending sections
which are slanted from the vertical. Further, a plurality of passage ways
extend from the rear of
the die to the slot in the face of the die. The passage way channels dough
from the extruder
through the extrusion orifice or slot.
Previously, in order to form clam shells, trays and other food product
containers,
biodegradable material was extruded as a flat sheet through a horizontal slit
or linear extrusion
orifice. The flat sheet of biodegradable material was then pressed between
molds to form the
clam shell, tray or other food package. However, these die configurations
produced flat sheets
of biodegradable material which were not uniformly thick, flexible, pliable
and non-brittle. The
packaging products molded from the flat sheets also had these negative
characteristics.
As the biodegradable material exited the extrusion orifice, the biodegradable
material
typically had greater structural stability in a direction parallel to the
extrusion flow direction
compared to a direction transverse to the extrusion flow direction. In fact,
fracture planes or
lines along which the sheet of biodegradable material was easily broken,
tended to form in the
biodegradable sheet as it exited from the extrusion orifice. Food packages
which were molded
from the extruded sheet, also tended to break or fracture along these planes.
Therefore, there is a need for a process which produces a flexible, pliable
and non-brittle
biodegradable material which has structural stability in both the longitudinal
and transverse
directions
SUMMARY OF THE INVENTION
According to one aspect of the present invention, there is provided a
extrusion die
through which biodegradable material can be extruded which has structural
stability in both the
longitudinal and transverse directions of the material, which has a flow
control device which
controls flow of biodegradable material through the extrusion die, and which
allows the inner
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and outer walls of the extrusion orifice to be adjusted relative to each other
to modify the
circumferencial wall thickness of the cylindrical extrudate.
According to one embodiment of the invention, the die extrudes a tubular
shaped
structure which has its greatest structural stability in a direction which
winds helically around
the tubular structure. Thus, at the top of the tubular structure, the
direction of greatest stability
twists in one direction while at the bottom the direction of greatest
stability twists in the
opposite direction. This tubular structure is then pressed into a sheet
comprised of two layers
having their directions of greater stability approximately normal to each
other. This 2-ply sheet
is a flexible, pliable and non-brittle sheet with strength in all directions.
According to another embodiment of the present invention, the flow rate of the
biodegradable material is regulated at a location upstream from the orifice
and at the orifice
itself to provide complete control of extrusion parameters. In particular, the
head pressure of the
biodegradable material behind the extrusion orifice is controlled to produce
an extrudate having
desired characteristics.
According to a further embodiment of the invention, an annular extrusion die
allows the
inner and outer walls of the extrusion orifice to be adjusted relative to each
other to modify the
circumferencial wall thickness of the cylindrical extrudate.
According to one aspect of the present invention, there is provided an
extrusion die for
extruding biodegradable material, the extrusion die comprising: a mandrel; an
outer member
positioned near the mandrel; an extrusion orifice between the mandrel and the
outer member; a
member in communication with at least one defining member of the extrusion
orifice, wherein
the member is capable of producing relative movement between the outer member
and the
mandrel, wherein the relative movement has a component transverse to an
extrusion direction of
biodegradable material through the extrusion orifice; a flow control device
which controls flow
of biodegradable material through the extrusion die; and a positioning device
which positions
the outer member and the mandrel relative to each other.
According to another aspect of the invention, there is provided an extrusion
die for
extruding biodegradable material, the extrusion die comprising: a cylindrical
mandrel; a
cylindrical outer ring positioned around the mandrel; an annular extrusion
orifice between the
mandrel and the outer ring; a member in communication with at least one
defining member of
the annular extrusion orifice which produces angular relative movement between
the outer ring
and the mandrel; a flow control device which controls flow of biodegradable
material through
the extrusion die, wherein the flow control device comprises a mechanism which
translates the
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outer ring to adjust the width of the annular extrusion orifice; and a
positioning device which
positions the outer ring and the mandrel relative to each other.
According to a further aspect of the invention, there is provided an extrusion
die for
extruding biodegradable material, the extrusion die comprising: a mandrel; an
outer member
positioned near the mandrel; an extrusion orifice between the mandrel and the
outer member; a
mounting plate having a flow bore which conducts biodegradable material toward
the extrusion
orifice, wherein the mandrel is fixedly mounted to the mounting plate and the
outer member is
movably mounted to the mounting plate; a shearing member which moves the outer
member
relative to the mandrel in a direction having a component transverse to an
extrusion direction of
biodegradable material through the extrusion orifice; a flow control device
which controls flow
of biodegradable material through the extrusion die, wherein the flow control
device comprises
a flow control channel upstream of the extrusion orifice, wherein the flow
control channel
throttles flow of the biodegradable material through the die, wherein the
mandrel is attached to
the mounting plate with at least one spacer between, wherein the mounting
plate and the
mandrel define the flow control channel; and a positioning device which
positions the outer
member and the mandrel relative to each other, wherein the positioning device
comprises a
shifting device for moving the outer member and the mandrel relative to each
other and a fixing
device which fixes the relative positions of the outer member and the mandrel.
According to another aspect of the invention, there is provided an improved
process for
the extrusion of biodegradable material wherein the extrusion comprises
flowing the
biodegradable material in a flow direction through an orifice, the improvement
comprising:
moving or shearing the biodegradable material, in a direction having a
component transverse to
the flow direction, during extrusion; controlling the flow rate of
biodegradable material through
the extrusion die during extrusion, wherein the controlling comprises
adjusting the head
pressure of the biodegradable material in the extrusion die and adjusting at
least one cross-
sectional area of a biodegradable material flow path within the extrusion die;
and modifying the
orifice geometry.
According to another aspect of the invention, there is provided a process for
manufacturing biodegradable shaped products of increased strength, the process
comprising:
extruding a biodegradable material, wherein the extruding comprises moving the
biodegradable
material in a first direction through an orifice to produce an extrudate;
modifying the orifice
geometry; shearing the biodegradable material, in a second direction having a
component
transverse to the first direction, during the extruding; controlling the flow
rate of biodegradable
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material through the extrusion die during the extruding, wherein the
controlling comprises
adjusting the cross-sectional area of an extrusion orifice and wherein the
controlling further
comprises adjusting the cross-sectional area of a biodegradable material flow
path at a location
upstream of the extrusion orifice; compressing the extrudate; and molding the
compressed
extrudate of biodegradable material into a structure.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is better understood by reading the following
description of non-
limitative embodiments, with reference to the attached drawings wherein like
parts in each of
the several figures are identified by the same reference character, and which
are briefly
described as follows.
Figure 1 is a cross-sectional view of a rotating die embodiment of the
invention fully
assembled.
Figure 2 is a cross-sectional view of a rotating embodiment of the die fully
assembled
with orifice modifying and flow control devices.
Figure 3 is an exploded perspective view of the several parts which comprise
the die
shown in Figure 2.
Figure 4 is a cross-sectional exploded view of a mandrel, mounting plate and
spacers.
Figure 5 is a cross-sectional exploded view of a gap adjusting ring, a bearing
housing
and an end cap.
Figure 6 is an exploded cross-sectional view of a seal ring, an outer ring and
a die wheel.
Figure 7A is a cross-sectional side view of an embodiment of the invention
having a
motor and belt for rotating an outer ring about a mandrel.
Figure 7B is an end view of the embodiment of the invention as shown in Figure
7A.
Figure 8 is a side view of a system for producing molded objects from
biodegradable
material, the system comprising an extruder, a rotating extrusion die, a
cylindrical extrudate,
rollers, and molding devices.
Figure 9 is a flow chart of a process embodiment of the invention.
Figure 10A is a perspective view of a cylindrical extrudate of biodegradable
material
having helical extrusion lines.
Figure l OB is a perspective view of a sheet of biodegradable material
produced from the
extrudate shown in Figure 10A.
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Figure 11 is an end view of an embodiment of the invention for rotating the
die wheel of
the rotating die, the device having a rack gear.
Figure 12A is a perspective view of a cylindrical extrudate having sinusoidal
extrusion
lines.
Figure 12B is a top view of a sheet of biodegradable material produced from
the
extrudate shown in Figure 12A.
Figure 13 is an end view of a device for rotating the die wheel of an
embodiment of the
invention wherein the system comprises a worm gear.
Figure 14A is a perspective view of an extrudate of biodegradable material
wherein the
extrudate is cylindrical in shape and has zigzag extrusion lines.
Figure 14B is a top view of a sheet of biodegradable material produced from
the
extrudate shown in Figure 14A.
Figure 15 is a cross-sectional view of a flow control embodiment of the die
fully
assembled.
Figure 16 is a cross-sectional view of an orifice modifying embodiment of the
die fully
assembled.
It is to be noted, however, that the appended drawings illustrate only typical
embodiments of this invention and are therefore not to be considered limiting
of the inventions
scope, as the invention may admit to other equally effective embodiments.
DETAILED DESCRIPTION OF THE INVENTION
Referring to Figure 1, a cross-section view of an embodiment of the invention
is shown.
The die 1 is made up of several discrete annular members which share the same
longitudinal
central axis 3. A mounting plate 20 is located in the center of the die 1 and
is the member to
which most of the remaining parts are attached. At one end of the mounting
plate 20, an
extruder adapter 10 is attached for connecting the die 1 to an extruder (not
shown). A backplate
11 is attached between the extruder adapter 30 and the mounting plate 20. At
an end opposite to
the extruder adapter 10, several spacers 100 are positioned in counter sunk
holes in the
mounting plate 20 at various locations equidistant from the longitudinal
central axis 3. A
mandrel 30 has counter sunk holes which correspond to those in the mounting
plate 20. The
mandrel 30 is fixed to the mounting plate 20 with the spacers 100 between, the
spacers being
inserted into the respective counter sunk holes. On the same side of the
mounting plate 20 as
the mandrel 30, a seal ring 40 is inserted into an annular spin channe122 of
the mounting plate
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20. At the periphery of the mounting plate 20, the mounting plate 20 has a
bearing portion 71
which extends around the seal ring 40. An end cap 80 is attached to the distal
end of the bearing
portion 71 of the mounting plate 20 to lock the seal ring 40 in the spin
channel 22. An outer
ring 50 is attached to the seal ring 40 around the outside of the mandre130 to
form an extrusion
orifice 5 between the outer ring 50 and the mandrel 30. Finally, a die wheel
90 is attached to the
outer ring 50. As described more fully below, a motor and drive system drive
the die wheel 90
to rotate the outer ring 50 about the mandrel 30.
Biodegradable material is pushed through the die 1 under pressure by an
extruder (not
shown) which is attached to the extruder adapter 10. The biodegradable
material passes through
flow bore 23 which conducts the material through the extruder adapter 10 and
the mounting
plate 20 to a central location at the backside of the mandrel 30. The
biodegradable material is
then forced radially outward through a disc-shaped cavity called a flow
control channel 4 which
is defmed by the mounting plate 20 and the mandrel 30. From the flow control
channel 4, the
biodegradable material is pushed through the extrusion orifice 5 defined by
the mandre130 and
the outer ring 50. According to one embodiment of the invention, the
biodegradable material is
forced through the extrusion orifice 5, the die wheel 90, outer ring 50 and
seal ring 40 are
rotated relative to the stationary mounting plate 20 and mandrel 30.
Referring to Figures 2 and 3, cross-sectional and exploded views,
respectively, of an
embodiment of the invention with orifice shifting and flow control devices are
shown. The die
1 is made up of several discrete annular members which share the same
longitudinal central axis
3. A mounting plate 20 is located in the center of the die 1 and is the member
to which most of
the remaining parts are attached. At one end of the mounting plate 20, an
extruder adapter is
attached for connecting the die 1 to an extruder (not shown). A gap adjusting
ring 60 is placed
concentrically around the cylindrical exterior of the mounting plate 20. A
bearing housing 70
lies adjacent the gap adjusting ring 60 and the mounting plate 20. A seal ring
40 is placed
within the bearing housing 70 and is inserted into an annular spin channel of
the mounting plate
20. At an end opposite to the extruder adapter 10, several spacers 100 are
positioned in counter
sunk holes in the mounting plate 20 at various locations equidistant from the
longitudinal
central axis 3. A mandrel 30 has counter sunk holes which correspond to those
in the mounting
plate 20. The mandrel is fixed to the mounting plate 20 with the spacers 100
between. An outer
ring 50 is attached to the seal ring 40 around the outside of the mandrel 30
to form an extrusion
orifice 5 between the outer ring 50 and the mandre130. Finally, a die wheel 90
is attached to the
outer ring 50 for rotating the outer ring 50 about the mandrel 30.
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Referring to Figure 4, a cross section of the mounting plate 20, spacers 100
and the
mandre130 are shown disassembled. The mounting plate 20 is basically a solid
cylinder with a
cylindrical flow bore 23 cut in the middle along the longitudinal central axis
3. One end of the
mounting plate 20 comprises a mounting shoulder 21 for engagement with the
extruder adapter
10 (shown in Figs. 2 and 3). Opposite the mounting shoulder 21, the mounting
plate 20 has a
annular spin channel 22 for receiving the seal ring 40 (shown in Figs. 2 and
3). Between the
cylindrical flow bore 23 at the center and the spin channe122, the mounting
plate 20 has a disc-
shaped flow surface 25. The mounting plate 20 also has several mounting plate
counter sunk
holes 24 for receiving spacers 100 such that the counter sunk holes 24 are
drilled in the flow
surface 25. In Figure 4, only two counter sunk holes 24 are shown because the
view is a cross
section along a plane which intersects the longitudinal central axis 3. All of
the mounting plate
counter sunk holes 24 are equidistant from each other and from the
longitudinal central axis 3.
According to one embodiment of the invention, the mandrel 30 is a bowl shaped
structure having a base 31 and sides 32. As shown in Figure 4, the mandrel 30
is oriented
sideways so that the central axis of the mandrel is collinear with the
longitudinal central axis 3
of the die. Unlike the mandrel 20, which has a flow bore 23 through the
center, the mandre130
has a solid base 31. The outside surface of the base 31 is a base flow surface
33. The mandrel
30 has several countersunk holes 34 which are cut in the base flow surface 33.
In Figure 4, only
two mandrel countersunk holes 34 are shown because the view is a cross-section
along a plane
which intersects the longitudinal central axis 3. All of the mandrel
countersunk holes 34 are
equidistant from each other and from the central axis 3. The inside of the
mandrel 30 is
hollowed out to reduce its overall weight.
Spacers 100 are used to mount the mandrel 30 to the mounting plate 20. Each of
the
spacers 100 comprise male ends 102 for insertion into mounting plate and
mandrel countersunk
holes 24 and 34. Of course, the outside diameter of the male ends 102 is
slightly smaller than
the inside diameters of mounting plate and mandrel countersunk holes 24 and
34. Between the
male ends 102, each of the spacers 100 comprise a rib 101 which has an outside
diameter larger
than the inside diameters of the mounting plate and mandrel countersunk holes
24 and 34. The
rib 101 of each spacer 100 has a uniform thickness in the longitudinal
direction to serve as the
spacer mechanism between the assembled mounting plate and mandrel.
The mandrel 30 is attached to the mounting plate 20 with mandrel bolts 36. The
mandrel bolts 36 extend through the base 31 of the mandre130, through the
spacers 100 and into
treaded portions in the bottom of the mounting plate counter sunk holes 24.
While the heads of
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the mandrel bolts 36 could be made to rest firmly against the inside of the
base 31 of the
mandrel, in the embodiment shown, the mandrel bolts extend through risers 35
so that the heads
of the mandrel bolts 36 are more accessible from the open end of the mandrel
30. In this
embodiment, one end of each of the risers 35 rests securely against the inside
of the mandrel
base 31 while the other end of each riser is engaged by the head of a mandrel
bolt 36.
Referring to Figure 5, a cross-sectional view of the gap adjusting ring 60,
the bearing
housing 70, and the end cap 80 are shown disassembled. The gap adjusting ring
60 is a ring
shaped member having a longitudinal central axis 3 and an inner diameter
slightly greater than
the outside diameter of the mounting plate 20 (shown in Figs. 2 and 3). The
gap adjusting ring
60 also has several lock screws 61 which extend through an inner portion 62 of
the gap
adjusting ring 60 for engagement with the mounting plate 20 once the gap
adjusting ring 60 is
placed around the outside of the mounting plate 20. Also, the gap adjusting
ring 60 has an outer
portion 63 for engagement with the bearing housing 70. At the outer edge of
the outer portion
63, the gap adjusting ring 60 has shifting lugs 64 which are attached via lug
bolts 65. In the
embodiment shown, four shifting lugs 64 are attached to the outer portion 63
of the gap
adjusting ring 60. The shifting lugs 64 are spaced around the gap adjusting
ring 60 so that one
is at the top, bottom, and sides, respectively. The shifting lugs 64 extend
from the outer portion
63 in a longitudinal direction for positioning engagement with the bearing
housing 70. The
shifting bolts 66 poke through the shifting lugs 64 in the part of the
shifting lugs 64 which
extend from the outer portion 63 in the longitudinal direction. The shifting
bolts 66 poke
through in a direction from outside the die toward the longitudinal central
axis 3. Finally, the
gap adjusting ring 60 has threaded holes 67 at various locations around the
outer portion 63 for
receiving screws 74.
The bearing housing 70 is an annular ring which has a longitudinal central
axis 3. The
bearing housing 70 has a bearing portion 71 and a support portion 72. The
support portion 72 is
annular with is greatest cross-section in a direction transverse to the
longitudinal central axis 3.
The bearing housing 70 is attachable to the gap adjusting ring 60 by the
support portion 72
which engages the outer portion 63 of the gap adjusting ring 60. In the
embodiment shown, this
engagement between the bearing housing 70 and the gap adjusting ring 60 is
accomplished by
screws 74 between these two members. The support portion 72 has several slip
holes 75 which
protrude through the support portion 72 in a longitudinal direction. In one
embodiment, twelve
slip holes 75 are positioned equidistant from each other around the support
portion 72 and are
positioned equidistant from the longitudinal central axis 3. The inside
diameter of each slip
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hole 75 is larger than the outside diameter of screws 74 so that there is
substantial "play"
between the screws 74 and the slip holes 75. While the slip holes 75 are
larger than the screws
74, the slip holes 75 are small enough so that the heads of the screws 74
securely engage the
support portion 72 of the bearing housing 70.
The other major part of the bearing housing 70 is the bearing portion 71 which
is an
annular section having its greatest thickness in the longitudinal direction.
The interior surface of
the bearing portion 71 is a bearing surface 76 for engaging lateral support
bearings 42 (shown in
Fig. 6). The bearing surface 76 supports the lateral support bearings 42 in a
plane normal to the
longitudinal central axis 3. Protruding from the bearing surface 76 near the
support portion 72,
the bearing housing 70 has a bearing housing lateral support flange 73 which
supports a lateral
support bearing 42 of the seal ring 40 (shown in Fig. 6).
When the. bearing housing 70 is attached to the gap adjusting ring 60, the
relative
positions of the two devices may be adjusted. In particular, during assembly,
the shifting bolts
66 of the gap adjusting ring 60 are relaxed to provide enough space for the
support portion 72 of
the bearing housing 70. The bearing housing 70 is then placed directly
adjacent the gap
adjusting ring 60 with the support portion 72 within the extended portions of
shifting lugs 64.
The screws 74 are then inserted through the slip holes 75 and loosely screwed
into threaded
holes 67 in the gap adjusting ring 60. The shifting bolts 66 are then adjusted
to collapse on the
support portion 72 of the bearing housing 70. The shifting bolts 66 may be
adjusted to push the
bearing housing 70 off center relative to the gap adjusting ring 60. Because
the slip holes 75 are
larger than the screws 74, the shifting bolts 66 freely push the bearing
housing 70 in one
direction or the other. By varying the pressure of the shifting bolts 66
against the outer surface
of the bearing housing 70, the bearing housing 70, seal ring 40 and outer ring
50 may be
perturbed from their original positions to more desirable positions. Once the
desired relative
position of the bearing housing 70 to the gap adjusting ring 60 is obtained,
the screws 74 are
tightened to firmly attach the two members.
The end cap 80 is preferably a ring which has a longitudinal central axis 3.
The interior
portion of the end cap 80 is a stabilizer 81 and the exterior is a fastener
flange 82. Fastener
holes 83 are drilled in the fastener flange 82 for inserting fasteners which
secure the end cap 80
to the bearing portion 71 of the bearing housing 70. The outside diameter of
the stabilizer 81 of
the end cap 80 is slightly smaller than the inside diameter of the bearing
portion 71 of the
bearing housing 70. This allows the stabilizer 81 to be inserted into the
bearing portion 71. At
the distal end of the stabilizer 81, there is an end cap lateral support
flange 84 which supports a
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lateral support bearing 42 (shown in Fig. 6). Therefore, when the end cap 80
is securely
fastened to the bearing housing 70, the bearing housing lateral support flange
73 and the end cap
lateral support flange 84 brace the lateral support bearings 42 (shown in Fig.
6) against
movement in the longitudinal directions.
Referring to Figure 6, a cross-sectional view of the seal ring 40, the outer
ring 50 and the
die wheel 90 are shown disassembled. The seal ring 40 is a cylindrical member
having a
longitudinal central axis 3. The seal ring 40 has an interior diameter which
decreases from one
end to the other. At the end of the seal ring 40 which has the smallest inside
diameter, the seal
ring 40 has a notch 47 for engaging the outer ring 50 as discussed below. On
the outside of the
seal ring 40, there are four superior piston rings 41 for engaging the
mounting plate 20 and the
end cap 80 (both shown in Figs. 2 and 3). The seal ring 40 also comprises two
lateral support
bearings 42. The lateral support bearings 42 are separated by a bearing spacer
flange 43 which
is positioned between the two lateral support bearings 42. The seal ring 40
further comprises
two retaining rings 44 which are positioned on the outsides of the lateral
support bearings 42.
Thus, the seal ring 40 is assembled by slipping one of the lateral support
bearings 42 over each
end of the seal ring 40 until they are each adjacent opposite sides of the
bearing spacer flange
43. Next, retaining rings 44 are slipped over each end of the seal ring 40
until they snap into
grooves 45 at the outsides of the lateral support bearings 42. Thus, the
lateral support bearings
42 are secured between the bearing spacer flange 43 and the retaining rings
44. Finally, the
superior piston rings 41 are placed in piston slots 46.
The outer ring 50 is a cylindrical member having a longitudinal central axis
3. The outer
ring 50 has a ring portion 51 and a fastener flange 52. Longitudinal holes are
cut through the
fastener flange 52 for inserting fasteners which secure the outer ring 50 to
an end of the seal ring
40. The outside diameter of the ring portion 51 is slightly smaller than the
inside diameter of
the notch 47 of the seal ring 40. This allows the outer ring 50 to be
assembled to the seal ring
40 by inserting the ring portion 51 into the notch 47. The inside diameter of
the ring portion 51
tapers from the end which attaches to the seal ring 40 to the other. At the
end of the ring portion
51 having the smallest inside diameter, the outer ring 50 comprises a lip 53
which defmes one
side of the extrusion orifice 5 (shown in Fig. 2).
The die wheel 90 is a cylindrical member with a wheel flange 92 and a drive
section 93.
Holes are drilled through the wheel flange 92 for inserting wheel fasteners 91
which secure the
die wheel 90 and the outer ring 50 to the seal ring 40. The drive section 93
is a device which
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engages a drive mechanism for rotating the die wheel 90. In the embodiment
shown in the
figure, the drive section is a pulley for engaging a drive belt.
Assembly of the complete die 1 is described with reference to Figures 2 and 3.
First, the
extruder adapter 10 is secured to the mounting plate 20 with a back plate 11
between. Next,
with further reference to Figure 4, several spacers 100 are placed in the
mandre130 by inserting
a male end 102 of each spacer 100 into a mandrel counter sunk hole 34, until
all the mandrel
counter sunk holes 34 have a spacer 100. The mandrel 30 is then placed
adjacent the mounting
plate 20 with the protruding male ends 102 of the spacers 100 being inserted
into the mounting
plate counter sunk holes 24. The mandrel 30 is then attached to the mounting
plate 20 with
spacers 100 between the mandrel bolts 36. In particular, the risers 35 are
slipped over the
shanks of the mandrel bolts 36 and the mandrel bolts 36 are inserted through
the mandrel base
31, the mandrel counter sunk holes 34, the spacers 100, and the mounting plate
counter sunk
holes 24. The bottoms of the mounting plate counter sunk holes 24 are threaded
so that the
mandrel bolts 36 may be screwed into the mounting plate 20. The mandrel bolts
36 are then
screwed into the threaded bottoms of each mounting plate counter sunk hole 24
to fasten the
mandrel 30 to the mounting plate 20. With further reference to Figure 5, the
gap adjusting ring
60 is slipped over the exterior of the mounting plate 20. The lock screws 61
are then tightened
against the exterior of the mounting plate 20. The bearing housing 70 is then
positioned with
the support portion 72 against the outer portion 63 of the gap adjusting ring
60. The shifting
bolts 66 are adjusted to center the bearing housing 70 about the longitudinal
central axis 3 and
the screws inserted through slip holes 75 and tightened into the threaded
holes 67 of the gap
adjusting ring 60. Next, with further reference to Figure 6, the seal ring 40
having superior
piston rings 41, lateral support bearings 42 and retaining rings 44 attached
thereto, is rotatably
attached to the bearing housing 70. In particular, the seal ring 40 is
inserted into the bearing
housing 70 and then into the spin channel 22 of the mounting plate 20. The
seal ring 40 is
pushed all the way into the spin channel 22 of the mounting plate 20 until the
first of the lateral
support bearings 42 rests firmly against the bearing housing lateral support
flange 73. In this
position, two of the four superior piston rings 41 form a seal between the
seal ring 40 and the
spin channel 22 of the mounting plate 20. The seal ring 40 is held in this
position by inserting
the stabilizer 81 of the end cap 80 into the bearing portion 71 of the bearing
housing 70. The
end cap 80 is pushed all the way into the bearing housing 70 until the end cap
lateral support
flange 84 contacts the second of the lateral support bearings 42 of the seal
ring 40. Once in
place, the end cap 80 is fixed to the bearing housing 70 by inserting
fasteners through the
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fasteners holes 83 of the fastener flange 82 and into the bearing portion 71
of the bearing
housing 70. The interior surface of the stabilizer 81 of the end cap 80
engages the remaining
two superior pistons rings 41 of the seal ring 40 so that the seal ring 40 is
completely stabilized
and allowed to spin freely about the longitudinal central axis 3. With the end
cap 80 securely
fastened to the bearing housing 70, the seal ring 40 is securely fastened in
the lateral direction
between the lateral support flanges 73 and 84. With the seal ring 40 securely
in place, the outer
ring 50 and die whee190 are then attached to the end which protrudes from the
mounting plate
20. In particular, the ring portion 51 of the outer ring 50 is inserted into
the notch 47 of the seal
ring 40 and the wheel flange 91 of the die whee190 is positioned adjacent the
fastener flange 52
of the outer ring 50. Wheel fasteners 91 are then inserted through the wheel
flange 92 and the
fastener flange 52 and locked into the seal ring 40.
Once assembled, both the extruder adapter 10 and the mounting plate 20 further
comprise a flow bore 23 which extends from the extruder (not shown) to the
flow surface 25, as
shown in Figures 2 and 4. Thus, the die 1 operates such that biodegradable
extrudate material is
pushed by the extruder through the flow bore 23 until it reaches the base flow
surface 33 of the
mandrel 30. The biodegradable extrudate then flows radially outward around the
spacers 100
between the flow surface 25 of the mounting plate 20 and the base flow surface
33 of the
mandrel 30. This disc-like space between the mounting plate 20 and the
mandre130 is the flow
control channel 4. From the flow control channel 4, the biodegradable
extrudate then enters a
cylindrical space between the seal ring 40 and the mandrel 20 and is pushed
through this space
toward the extrusion orifice 5 between the mandrel 30 and the outer ring 50.
As the
biodegradable extrudate moves toward the extrusion orifice 5, the die wheel 90
is rotated to
rotate the outer ring 50 and seal ring 40 around the stationary mandrel 30.
Thus, the
biodegradable extrudate is twisted by the rotating outer ring 50. As the
extrudate exits the
extrusion orifice 5, a tubular product of twisted biodegradable material is
produced. As
described fully below, because the seal ring 40 is rotatably mounted within
the bearing housing
70, the seal ring 40 may be made to rotate about the mandrel 30 as the
extrudate is pushed
through the orifice 5.
Flow of the biodegradable material through the die 1 is controlled in two
ways: (1)
adjusting the width of the flow control channel 4, and (2) controlling the
size of the extrusion
orifice 5. Regarding the flow control channel 4, as noted above, biodegradable
material is
passed from the extruder through a flow bore 23 in the mounting plate 20 until
it reaches the
base flow surface 33 of the mandrel 30. From the central location, the
biodegradable material is
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pushed radially outward between the base flow surface 33 of the mandrel 30 and
the flow
surface 25 of the mounting plate 20. Of course, as the biodegradable material
flows between the
surfaces through the flow control channel 4, it passes around each of the
spacers 100 which
separate the mandrel 30 and the mounting plate 20. The width of the flow
control channel 4 is
adjusted by using spacers which have larger or smaller ribs 101 (See Figure
4). In particular, if
it is desirable to decrease flow of the biodegradable material through the
flow control channel 4,
spacers 100 having ribs 101 which are relatively thin in the longitudinal
direction are inserted
between the mounting plate 20 and the mandrel 30. Alternatively, if it is
desirable to increase a
flow rate of biodegradable material through the flow control channel 4,
spacers 100 having ribs
101 with relatively larger thicknesses in the longitudinal direction are
inserted between the
mounting plate 20 and the mandrel 30. Therefore, in a preferred embodiment,
the die 1 has
several sets of spacers 100 which may be placed between the mounting plate 20
and the mandrel
30 to control the width of the flow control channel 4.
Additionally, flow of the biodegradable material through the extrusion orifice
5 is
controlled by altering the width of the extrusion orifice 5. The thickness of
the extrusion orifice
5 between the mandrel lip 37 and the outer ring lip 53 is adjusted by sliding
the gap adjusting
ring 60, the bearing housing 70, the seal ring 40, and the outer ring 50 along
the longitudinal
central axis 3 out away from the stationary mandrel 30. Since the interior
diameter of the ring
portion 51 of the outer ring 50 is tapered from the end which attaches to the
seal ring 40, the
outer ring 50 has its smallest interior diameter at the outer ring lip 53. To
produce a
biodegradable extrudate with a very thin wall thickness, the gap adjusting
ring 60 is pushed all
the way onto the mounting plate 20 until the outer ring lip 53 is directly
opposite the mandrel lip
37. To produce a thicker biodegradable extrudate, the gap adjusting ring 60 is
moved slightly
away from the mounting plate 20 along the longitudinal central axis 3 in the
direction of
direction arrow 6 (shown in Figure 2), so that the outer ring lip 53 is
positioned beyond the
mandrel lip 37. Thus, a wider section of the ring portion 51 is adjacent the
lip 37 of the mandrel
so that the extrusion orifice 5 is thicker. Once the desired orifice size is
obtained, lock
screws 61 are screwed into the gap adjusting ring 60 to re-engage the mounting
plate 20. This
locks the gap adjusting ring 60, the bearing housing 70, the seal ring 40, and
the outer ring 50 in
30 place to ensure the thickness of the extrusion orifice 5 remains constant
during operation. A
thicker extrusion orifice 5 increases flow through the die.
Referring to Figures 7A and 7B, side and end views of portions of an
embodiment of the
invention for rotating the outer ring of the die are shown, respectively. The
mandrel 30 is
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WO 99/44806 PCT/US99/04774
attached to the mounting plate 20 so that the mandrel 30 is locked in place.
The seal ring 40 and
outer ring 50 are rotatably mounted around the mandrel 30. A die wheel 90 is
also attached to
the outer ring 50. All of these members have longitudinal central axes which
are collinear with
longitudinal central axis 3. The device also has a motor 110 which has a drive
axis 113 which is
parallel to longitudinal central axis 3. Attached to a drive shaft of motor
110, there is a drive
wheel 111. The motor 110 and drive wheel 111 are positioned so that drive
wheel 111 lies in the
same plane as the die wheel 90, the plane being perpendicular to the
longitudinal central axis 3.
Opposite the drive wheel 111, the system further has a snubber wheel 115 which
is also
positioned in the perpendicular plane of the drive wheel 111 and the die wheel
90. The snubber
wheel 115 has a snubber axis 116 which is also parallel to the longitudinal
central axis 3. Thus,
the drive wheel 111 and the snubber wheel 115 are positioned at opposite ends
of the system
with the die wheel 90 between. A drive belt 112 engages the drive wheel 111,
the die wheel 90
and the snubber wheel 115. The snubber wheel 115 has no drive mechanism for
turning the
drive belt 112. Rather, the snubber wheel 115 is an idle wheel which only
turns with the drive
belt 112 when the drive belt 112 is driven by the motor 110. The snubber wheel
115 serves only
to evenly distribute forces exerted by the drive belt 112 on the die wheel 90.
Because the drive
wheel 111 and snubber wheel 115 are positioned on opposite sides of the die
wheel 90, forces
exerted by the drive belt 112 on the die wheel 90 are approximately equal in
all transverse
directions. If the snubber wheel 115 were not placed in this position and the
drive belt 112
engaged only the drive wheel 111 and the die wheel 90, a net force would be
exerted by the
drive belt 112 on the die whee190 in the direction of the motor 110. This
force would pull the
die wheel 90 and thus the outer ring 50 out of center from its position about
the stationary
mandrel 30. Of course, this would have the detrimental effect of producing an
extrudate tube of
biodegradable material which would have a wall thickness greater on one side
than on the other.
Therefore, the snubber wheel 115 is positioned in the system to prevent the
die wheel 90 from
being pulled from its central location around the mandrel 30.
In a preferred embodiment, the drive belt 112 is a rubber belt. Alternatively,
chains or
mating gears may be used to mechanically connect the motor 110 to the die
whee190. A typical
one-third horse power electric motor is sufficient to produce the necessary
torque to drive the
drive belt 112. Further, the gear ratios between the drive wheel 111 and the
die wheel 90 are
such that the die wheel 90 may preferably rotate at approximately 15 rotations
per minute.
Depending on the particular gear system employed, alternative embodiments
require more
powerful motors.
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Referring to Figures 8 and 9, system and method embodiments of the invention
are
described for producing a biodegradable final product, respectively. The
system 130 has a
hopper 131 into which biodegradable material is initially placed (step 140).
The hopper 131
supplies (step 141) biodegradable material to an extruder 132 which
pressurizes (step 142) and
cooks (step 143) the biodegradable material. The extruder 132 pushes (step
144) the
biodegradable material through an extrusion die 1. The extrusion die 1 is an
embodiment of the
rotating extrusion die of the present invention and is driven by a motor 110
with a drive belt
112. As the biodegradable material is pushed (step 144) through the extrusion
die 1, an outer
ring of the die 1 is rotated (step 145) around an inner mandrel. The
biodegradable material is
pushed (step 146) from the extrusion die 1 through an extrusion orifice to
form a cylindrical
extrudate 15. The cylindrical extrudate 15 is then pulled (step 147) from the
extrusion orifice by
a pair of press rollers 133. Next, the press rollers 133 flatten (step 148)
the cylindrical extrudate
into a sheet 17 of biodegradable material. The sheet 17 of biodegradable
material is then
molded (step 149) between corresponding molds 134 to form the biodegradable
material into
15 final products. The shaped final products are then deposited in bin 135.
According to alternative embodiments of the invention, it is desirable to
stretch the
cylindrical extrudate 15 as it exits the extrusion orifice 5. This is
accomplished by rotating the
press rollers 133 slightly faster than a speed necessary to keep pace with the
exit rate of the
cylindrical extrudate 15 from the extrusion orifice 5. As the press rollers
133 rotate faster, the
cylindrical extrudate 15 is pulled by the press rollers 133 from the extrusion
orifice 5 so that the
cylindrical extrudate 15 is stretched in the longitudinal direction before it
is flattened into a flat
2-ply sheet.
Referring to Figure 10A, an example of a biodegradable extrudate from the
extrusion die
of the present invention is shown. The extrudate 15 exits from the extrusion
orifice 5 (see
Figure 2 for die components) as a cylindrical structure. Typically, while not
meant to be limited
thereby, it is believed the polymer chains of the biodegradable material are
aligned in the
direction of extrusion to produce an extrudate which has its greatest
structural integrity in the
extrusion direction. If the extrudate 15 exits the extrusion orifice 5 as the
outer ring 50 is
rotated around the mandrel 30, the extrudate 15 orients along extrusion lines
16.
Preferably, the cylindrical extrudate 15 is collapsed to form a sheet of
biodegradable
material having two extrudate layers. As shown in Figure l OB, a perspective
view of a sheet of
extrudate material produced from the tubular extrudate of Figure 10A is shown.
The sheet 17 is
produced simply by rolling the extrudate 15 through two rollers to compress
the tubular
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WO 99/44806 PCT/US99/04774
extrudate 15 into the sheet 17. The sheet 17 consequently comprises extrusion
lines 16 which
form a cross-hatch pattern. The sheet 17 is comprised of two layers, one of
which previously
formed one side of the tubular extrudate 15 while the second layer of the
sheet 17 previously
formed the other side of the extrudate 15. Therefore, because the extrusion
lines 16 were
helically wound around the extrudate 15, when the sheet 17 is formed, the
extrusion lines 16 of
the two layers run in opposite directions. The extrusion line angle 18 of the
extrusion lines 16
may be adjusted by controlling the flow rate of the extrudate 15 from the
extrusion orifice 5 of
the die 1 (see Figure 2 for die components), and controlling the speed of
angular rotation of the
outer ring 50 about the mandre130. If it is desirable to increase the
extrusion line angle 18, the
die is adjusted to increase the angular speed of the outer ring 50 relative to
the mandrel 30,
and/or to decrease the flow rate of the extrusion material from the extrusion
die. As noted
above, the flow rate of the biodegradable material through the die is
controlled by adjusting the
size of the extrusion orifice 5 and/or the flow control channel 4.
According to one embodiment of the invention, the outer ring 50 of the die 1
is made to
rotate in both clockwise and counter-clockwise directions about the mandrel 30
to produce a
biodegradable extrudate wherein the extrusion lines have a wave pattem. To
produce this
extrudate, the outer ring 50 is first rotated in one direction and then
rotated in the opposite
direction. Depending on the rates of direction change, the pattem produced is
sinusoidal,
zigzag, or boxed. The periods and amplitudes of these wave patterns are
adjusted by altering
the rate of rotation of the outer ring 50 and the flow rate of the
biodegradable material through
the extrusion die 1.
Many different drive systems are available for alternating the direction of
rotation of the
outer ring 50. For example, the motor 110 of the embodiment shown in Figures
7A and 7B is
made to alternate directions of rotation. As the motor 110 changes directions
of rotation, the
drive wheel 111, drive belt 112 and die wheel 90 consequently change
directions.
Alternatively, as shown in Figure 11, the die wheel 90 is a spur gear with
radial teeth
parallel to the longitudinal central axis 3. The teeth of the die wheel 90 are
engaged by teeth of
a rack gear 117. Opposite the rack gear 117, an idler gear 124 is engaged with
the die wheel 90
to prevent the rack gear 117 from pushing the outer ring 50 out of alignment
with the mandrel
30 (See Figure 2). The rack gear 117 is mounted on a slide support 118 and
moves linearly
along a slide direction 120 which is transverse to the longitudinal central
axis 3. The slide
support 118 is connected to a drive wheel 111 via a linkage 114. In
particular, one end of the
linkage 114 is connected to an end of the slide support 118 and the other end
of the linkage 114
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is connected to the drive wheel 111 at its periphery. The slide support 118 is
braced by brackets
125 so that slide support 118 is only allowed to move along slide direction
120. As the drive
wheel 1 I 1 rotates clockwise around rotation direction 119, the linkage 114
pushes and pulls the
slide support 118 back and forth along slide direction 120. The back and forth
movement of the
slide support 118 rotates the die wheel 90 and the outer ring 50 aiternatively
in clockwise and
counter-clockwise directions.
Since the linkage 114 is connected to the drive wheel 111 at its periphery, as
noted
above, the alternative clockwise and counter-clockwise rotation of the outer
ring 50 is a
sinusoidal oscillatory type motion. Thus, this embodiment of the invention
produces a
biodegradable extrudate 15 with extrusion lines 16 which have a sine wave
pattem as shown in
Figure 12A. As described above, the extrudate 15 is rolled into a sheet 17
having two layers as
shown in Figure 12B. The period of the sine waves are identified by reference
character 19 and
the amplitude is identified by reference character 14. The period 19 and
amplitude 14 of
extrusion lines 16 may be adjusted by controlling the flow rate of the
extrudate 15 from the
extrusion orifice 5 of the die I (see Figure 2 for die components), and
controlling the speed of
angular rotation of the outer ring 50 about the mandrel 30. If it is desirable
to increase the
period of the sine waves, the die is adjusted to decrease the angular speed of
the outer ring 50
relative to the stationary mandrel 30, and/or to increase the flow rate of the
extrusion material
from the extrusion orifice 5. As noted above, the flow rate of the
biodegradable material
through the die is controlled by adjusting the size of the extrusion orifice 5
and/or the flow
control channel4. Further, if it is desirable to increase the amplitude 14 of
the sine waves, the
angular range of motion of the outer ring 50 is increased so that the outer
ring 50 rotates further
around the stationary mandre130 before it stops and changes direction. While
many parameters
may be altered to produce this result, a simple modification is to use a drive
wheel 111 which
has a relatively larger diameter.
A similar embodiment of the invention which rotates the outer ring in
clockwise and
counter-clockwise directions is shown in Figure 13. As before, the die whee190
is a spur gear
with radial teeth parallel to the longitudinal central axis 3. The teeth of
the die wheel 90 are
engaged by teeth of a worm gear 122 which is positioned with its axis of
rotation transverse to
the longitudinal central axis 3. Opposite the worm gear 122, an idler gear 124
is engaged with
the die whee190 to prevent the worm gear 122 from pushing the outer ring 50
out of alignment
with the mandrel 30 (see Figure 2). The worm gear 122 is driven by a motor 110
with a
transmission 121 between. A drive shaft 123 of the motor 110 is connected to a
power side of
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the transmission 121 and the worm gear 122 is connected to a drive side of the
transmission
121. While the motor 110 rotates the drive shaft 123 in only one direction,
the transmission 121
rotates the worm gear 122 in both clockwise and counter-clockwise directions.
Further, in one
embodiment, the transmission 121 rotates the worm gear 122 at different speeds
even though
the motor 110 operates at only one speed. A similar embodiment comprises a
motor and
transmission which drive a pinion gear which engages the die wheel 90. Since
the worm gear
122 is rotated at a constant speed in each direction, this embodiment of the
invention produces a
biodegradable extrudate which has a zigzag pattem of extrusion lines 16.
Since the motor 110 runs at constant angular velocity and the transmission is
used to
change the direction of rotation of the worm gear 122, the alternative
clockwise and counter-
clockwise rotation of the outer ring 50 is an oscillatory type motion. Thus,
this embodiment of
the invention produces a biodegradable extrudate 15 with extrusion lines 16
which have a linear
oscillatory wave patteln or zigzag wave pattem as shown in Figure 14A. As
described above,
the extrudate 15 is rolled into a sheet 17 having two layers as shown in
Figure 14B. The period
of the zigzag waves are identified by reference character 19 and the amplitude
is identified by
reference character 14. The period 19 and amplitude 14 of extrusion lines 16
is adjusted by
controlling the flow rate of the extrudate 15 from the extrusion orifice 5 of
the die 1(see Figure
2 for die components), and controlling the speed of angular rotation of the
outer ring 50 about
the mandre130. If it is desirable to increase the period of the zigzag waves,
the die is adjusted to
decrease the angular speed of the outer ring 50 relative to the stationary
mandrel 30, and/or to
increase the flow rate of the extrusion material from the extrusion orifice 5.
As noted above, the
flow rate of the biodegradable material through the die is controlled by
adjusting the size of the
extrusion orifice 5 and/or the flow control channel 4. Further, if it is
desirable to increase the
amplitude 14 of the zigzag waves, the angular range of motion of the outer
ring 50 is increased
so that the outer ring 50 rotates further around the stationary mandrel 30
before it stops and
changes direction. While many parameters may be altered to produce this
result, a simple
modification is to control the transmission 121 to allow the worm gear 122 to
run longer in each
direction before reversing the direction.
Referring to Figure 15, a cross-sectional view of an embodiment of the
invention for
controlling the flow of biodegradable material is shown. The die 1 is made up
of several
discrete annular members which share the same longitudinal central axis 3. A
mounting plate
20 is located in the center of the die 1 and is the member to which most of
the remaining parts
are attached. At one end of the mounting plate 20, an extruder adapter 10 is
attached for
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WO 99/44806 PCT/US99/04774
connecting the die I to an extruder (not shown). Opposite to the extruder
adapter 10, several
spacers 100 are positioned in counter sunk holes in the mounting plate 20 at
various locations
equidistant from the longitudinal central axis 3. A mandrel 30 has counter
sunk holes which
correspond to those in the mounting plate 20. The mandre130 is fixed to the
mounting plate 20
with the spacers 100 between. The spacers 100 create a gap between the mandrel
30 and the
mounting plate 20, the thickness of which is dependent upon the thickness of
the spacers 100.
This gap is the flow control channel 4. An outer die structure 55 is attached
to the mounting
plate 20. The outer die structure 55 has a gap adjusting ring 60 at one end
which is positioned
concentrically around the cylindrical exterior of the mounting plate 20 and an
outer ring 50 at
the other end. The outer ring 50 of the outer die structure 55 and the mandrel
30 combine to
form an extrusion orifice 5. The gap adjusting ring 60 secures the outer die
structure 55 to the
mounting plate 20 with lock screws 61 which engage the outer surface of the
mounting plate 20.
Flow of the biodegradable material through the die 1 is controlled in two
ways: (1)
adjusting the width of the flow control channel 4, and (2) controlling the
size of the extrusion
orifice 5. Regarding the flow control channel 4, as noted above, biodegradable
material is
passed from the extruder through a flow bore 23 in the mounting plate 20 until
it reaches the
mandrel 30. From the central location, the biodegradable material is pushed
radially outward
between the mandrel 30 and the mounting plate 20 through the flow control
channel 4. Of
course, as the biodegradable material flows between the surfaces through the
flow control
channel 4, it passes around each of the spacers 100 which separate the mandrel
30 and the
mounting plate 20. The width of the flow control channel 4 is adjusted by
using spacers which
have larger or smaller thicknesses in the longitudinal direction. In
particular, if it is desirable to
decrease flow of the biodegradable material through the flow control channel
4, relatively thin
spacers 100 in the longitudinal direction are inserted between the mounting
plate 20 and the
mandrel 30. Alternatively, if it is desirable to increase a flow rate of
biodegradable material
through the flow control charuiel4, relatively thick spacers 100 in the
longitudinal direction are
inserted between the mounting plate 20 and the mandrel 30. Therefore, in a
preferred
embodiment, the die I has several sets of spacers 100 which may be placed
between the
mounting plate 20 and the mandrel 30 to control the width of the flow control
channel 4.
Additionally, flow of the biodegradable material through the extrusion orifice
5 is
controlled by altering the width of the orifice. The thickness of the
extrusion orifice 5 between
the mandrel 30 and the outer ring 50 is adjusted by sliding the outer die
structure 55 along the
longitudinal central axis 3 out away from the stationary mandrel 30. Since the
interior diameter
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of the outer die structure 55 is tapered from the outer ring 50 toward the gap
adjusting ring 40,
the outer die structure 55 has its smallest interior diameter at the outer
ring 50. To produce a
biodegradable extrudate with a very thin wall thickness, the gap adjusting
ring 60 is pushed all
the way onto the mounting plate 20. To produce a thicker biodegradable
extrudate, the gap
adjusting ring 60 is moved slightly away from the mounting plate 20 along the
longitudinal
central axis 3 in the direction of direction arrow 6, so that the outer ring
50 is positioned beyond
the mandrel 30. Thus, a wider section of the outer die structure 55 is
adjacent an orifice fomiing
portion of the mandre130 so that the extrusion orifice 5 is thicker. Once the
desired orifice size
is obtained, lock screws 61 are screwed into the gap adjusting ring 60 to re-
engage the mounting
plate 20. This locks the outer die structure 55 in place to ensure the
thickness of the extrusion
orifice 5 remains constant during operation. Of course, a thicker orifice 5
allows the
biodegradable material to flow more freely through the die 1.
Referring to Figure 16, an embodiment of the invention for modifying the
geometry of
the die orifice is shown in cross-section. The die I is made up of several
discrete annular
members which share the same longitudinal central axis 3. A mounting plate 20
is located in
the center of the die 1 and is the member to which most of the remaining parts
are attached. At
one end of the mounting plate 20, an extruder adapter 10 is attached for
connecting the die 1 to
an extruder (not shown). At an end opposite to the extruder adapter 10,
several spacers 100 are
positioned in counter sunk holes in the mounting plate 20 at various locations
equidistant from
each other and from the longitudinal central axis 3. A mandre130 has counter
sunk holes which
correspond to those in the mounting plate 20. The mandrel is fixed to the
mounting plate 20
with the spacers 100 between. An outer die structure 55 is also attached to
the mandrel 30. The
outer die structure 55 has a support portion 72 at one end and an outer ring
50 at the other. The
outer ring 50 and the mandrel 30 combine to form an extrusion orifice 5. The
support portion
72 is used to attach the outer die structure 55 to an outer portion 63 of the
mounting plate 20.
The mounting plate 20 also has shifting lugs 64 which are screwed to the outer
portion 63 of the
mounting plate 20 with lug bolts 65. In this particular embodiment, four
shifting lugs 64 are
used, spaced equidistant from each other around the outer portion 63 of the
mounting plate 20.
The shifting lugs 64 extend from the mounting plate 20 in a longitudinal
direction toward the
mandrel 30. Shifting bolts 66 extend through distal ends of the center lugs 64
in directions
transverse to the longitudinal central axis 3. The support portion 72 of the
outer die structure 55
is positioned within the shifting lugs 64 so that the shifting bolts 66 engage
an outer surface of
the support portion 72 of the outer die structure 55. The outer die structure
55 is actually
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secured to the mounting plate 20 with screws 74. Threaded holes 67 extend
through the outer
portion 63 of the mounting plate 20 in directions parallel to the longitudinal
central axis 3.
Corresponding slip holes 75 extend through the support portion 72 of the outer
die structure 55
in directions parallel to the longitudinal central axis 3. The slip holes 75
have a larger inside
diameters than the threaded outside diameters of the screws 74 to allow "play"
between the
screws 74 and the slip holes 75.
The orifice 5 geometry is modified by moving the outer die structure 55
relative to the
mandrel 30. In the above described embodiment, this is accomplished by
loosening screws 74
slightly to allow the outer die structure 55 to move relative to the mounting
plate 20. Shifting
bolts 66 are then adjusted against the support portion of the outer die
structure 55 to push the
outer ring 50 to a desired position relative to the mandrel 30. Once the outer
die structure 55 is
properly positioned, the screws 74 are tightened to securely fix the outer die
structure 55 to the
mounting plate 20.
While the particular embodiments for extrusion dies as herein shown and
disclosed in
detail are fully capable of obtaining the objects and advantages herein before
stated, it is to be
understood that they are merely illustrative of the preferred embodiments of
the invention and
that no limitations are intended by the details of construction or design
herein shown other than
as described in the appended claims.
LIST OF CHARACTER DESIGNATIONS
1. Die 30. Mandrel
3. Longitudinal Central Axis 31. Mandrel Base
4. Flow Control Channel 32. Mandrel Sides
5. Extrusion Orifice 33. Base Flow Surface
6. Direction Arrow 34. Countersunk Holes
10. Extruder Adapter 35. Risers
11. Back Plate 36. Mandrel Bolts
14. Extrusion Wave Amplitude 37. Mandrel Lip
15. Extrudate 40. Seal Ring
16. Extrusion Lines 41. Superior Piston Rings
17. Sheet 42. Lateral Support Bearings
18. Extrusion Line Angle 43. Bearing Spacer Flange
19. Extrusion Wave Period 44. Retaining Rings
20. Mounting Plate 45. Grooves
21. Mounting Shoulder 46. Piston Slots
22. Spin Channel 47. Notch
23. Flow Bore 50. Outer Ring
24. Countersunk Holes 51. Ring Portion
25. Flow Surface 52. Fastener Flange
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53. Outer Ring Lip 100. Spacer
55. Outer Die Structure 101. Rib
60. Gap Adjusting Ring 102. Male Ends
61. Lock Screws 110. Motor
62. Inner Portion 111. Drive Wheel
63. Outer Portion 112. Drive Belt
64. Centering Lugs 113. Drive Axis
65. Lug Bolts 114. Linkage
66. Centering Bolts 115. Snubber Wheel
67. Threaded Holes 116. Snubber Axis
70. Bearing Housing 117. Rack Gear
71. Bearing Portion 118. Slide Support
72. Support Portion 119. Rotation Direction
73. Lateral Support Flange 120. Slide Direction
74. Screws 121. Transmission
75. Slip Holes 122. Worm Gear
76. Bearing Surface 123. Drive Shaft
80. End Cap 124. Idler Gear
81. Stabilizer 125. Brackets
82. Fastener Flange 130. Biodegradable Product Producing System
83. Fastener Holes 131. Hopper
84. Lateral Support Flange 132. Extruder
90. Die Wheel 133. Press Rollers
91. Wheel Fastener 134. Molds
92. Wheel Flange 135. Bin
93. Drive Section
