Note: Descriptions are shown in the official language in which they were submitted.
81 10-55
\57596
2!18~o3
MOLDING MATERIAL UNDER THE APPLICATION OF SHEAR,
COMPRESSIVE AND/OR TENSILE LOADS
Field of the Invention
The present invention relates to apparatus for molding moldable
material while applying compressive and shear loads to a flow of the material
15 for transforming the material. More particularly, the apparatus and system use
an eccentric drive for creating and applying the compressive and shear loads.
Background of the Invention
The processing of deformable materials generally involves the
20 transformation of a starting material (i.e., in a solid state or a liquid state),
which is in a fungible form (e.g., powder, beads, granules, pellets, etc.), intoa final or intermediate product having a specific shape, dimensions and
properties. Processes useful in the transformation of moldable materials from
their initial fungible form to the form of the final or intermediate product are25 well known to those skilled in the materials processing industry. For instance,
if the moldable material is a plastic, examples of plastic transformation
processes include extrusion, transfer molding, calendaring, l~min~ting,
thermoforming, injection molding, compression molding, blow molding, and the
like. As used herein, such transformation processes and/or operations are
30 collectively referred to as "molding" processes. Similarly, the resulting final
. \17596 2 18~3q
or intermediate product is referred to as "molded," regardless of the specific
transformation process employed in its m:~nl-f~cture.
In order to produce molded products having a specific geometric
configuration, it is generally necessary to employ a mold or die. The primary
5 objective of a mold or die is to shape moldable material introduced therein byconfining the material to a preselected shape and rel~ining the material in thatconfined state until it cures.
The physical properties of a molded product depend, in part,
upon the specific molding process conditions and steps employed. It has been
10 observed that dirr~le~lL molding processes will often result in the final or
intermediate products having different physical properties. For example, the
amount of shear stress applied to the material during molding determines, in
part, the degree of molecular orientation and crystallization (in crystallizablematerials) within the molded product. This, in turn, has an effect on the
15 molded product's physical properties, such as yield strength.
One method of controlling the amount of shear stress applied
during molding of a molded product (and thereby controlling some of the
product's physical properties), is commonly referred to as "flow technology. "
The concept of "flow technology, " as it relates to plastic molding processes, is
20 concerned with the behavior of a moldable plastic material before, while, andafter it is introduced into a mold and/or being passed through a die. It has been
discovered that the properties of a final or intermediate molded product depend
largely upon how the moldable material flows prior to, and/or while, being
subjected to a molding process. For example, two products having identical
25 dimensions and made from the same basic starting material, but which are
molded under different conditions (e.g., different hydrostatic pressures and/or
shear stresses) and subjected to different flow patterns, will have different
physical properties.
This phenomenon is due, in part, to the fact that, as a moldable
30 material flows prior to, or while, entering a mold or passing through a die, it
81 10-55
\57596
- 3 -
is subjected to a shear stress, which is commonly referred to as "flow shear
stress." Flow shear stress induces molecular orientation in the plastic material(i.e., it results in the macromolecules in the material ~ligning themselves in the
direction of flow). The flow shear stress varies from a maximum level at the
outside surface of the flowing moldable material to a minimum level at the
center, where the material is slowest to cure.
A problem with existing molding processes is the inability to
simply and inexpensively provide thorough mixing of two constituent parts of
a moldable material. For example, the moldable material may consist of a base
polystyrene component material and a coloring agent. Alternately, the
constituent components could be a base resin or matrix material and an additive
or curing agent which, when mixed, form a moldable material as in a thermoset
material. A variety of other examples of moldable materials exist which consist
of two or more combined components and which must be mixed to form the
final product. In the prior art processes, mixing of the two components was
typically achieved either in a hopper or while conveyed by designated
processing machinery. In either case, it is important that the mixing be
thorough in order to achieve a structurally or cosmetically acceptable final
product. The uniformity in color of a final molded product is extremely
important in today's commercial marketplace. Since many products are
ultimately selected by a consumer based on their appearance, m:~mlf~cturers
strive to distinguish their products through specific coloring. The inefficient
manufacturing processes discussed above are perceived as drawbacks by these
manufacturers for generating the desired coloring.
Another problem with the prior art processes occurs when only
a small amount of one constituent is to be mixed with a large amount of a
second constituent. In this situation, the utilization of only the hopper to mixthe two constituents may not result in a homogeneous mixture. For example,
only one or two color pellets are typically needed to sufficiently color one
pound of uncolored polystyrene pellets. However, simply mixing one or two
81 10-55
\57596
2 ~ 8SQ~9
unmelted colored pellets into thousands of unmelted uncolored polystyrene
pellets and then melting the mixture will not provide an even color distributionin the final product.
The prior art processes are also inefficient when it is desirable to
combine dissimilar components which do not readily and easily mix with one
another. In order to produce the desired mixing, the prior art processes mix thematerials for an extended period of time or subject the materials to additional
m~mlf~cturing steps.
The screw in an extruder is generally used to provide additional
mixing of the constituent parts. The flights on the screw, acting in conjunctionwith walls of the extruder barrel, produce a rolling or kn~a(ling of the moldable
material as it is melted, compressed and driven toward the exit of the extruder.If a single screw does not provide sufficient mixing, multiple intermeshing
screws are utilized. The intermeshing of the screw flights more thoroughly
kneads the constituent parts of the material into a single homogeneous mixture.
A drawback to the use of multiple screws is the need for a complicated drive
mechanism for rotating the multiple screws. Furthermore, the multiple screws
produce excessive heat and compression of the moldable material, resulting in
degradation of the material.
In order to compensate for the inefficient mixing that occurs with
the prior art processes, excessive amounts of one or more component part of the
moldable material are sometimes added. For example, as discussed above, one
or two coloring agent pellets would, under proper mixing conditions, be
sufficient to color a pound of uncolored polystyrene pellets. However, since
most mixing systems do not adequately mix the component materials, it is
typically required that more coloring pellets be used per pound of uncolored
polystyrene. This increases the cost of manufacturing the final colored product.Another problem in the prior art relates to mixing of recyclable
materials. There is a trend to increase the amount of recyclable material
30 incorporated into a final molded part. In many instances, the recyclable
81 10-55
\57596
~8s~3q
- 5 --
material must be combined with virgin material prior to solidification. If the
recycled material is not adequately mixed with the virgin material, flaws or
we~kn~sses can develop in the final product.
The prior art devices are also deficient when it is desired to mix
5 multicomponent systems with more than one polymer component (e.g., rubber
or plastic) and/or more than one additive. For example, prior art devices do notefficiently mix filler material, such as reinforcing materials or plasticizers,
which are used to improve one or more of the properties of the final product.
Prior art devices incorporate dry reiforcing fibers into the material either in the
10 hopper or while in the extruder barrel. Neither method provides an effective
method for reiforcing the material. On the contrary, mixing the fibers with the
molten material prior to or during conveyance in the extruder causes fiber
breakage and excessive extruder wear. To minimi7e the damage to the
extruder, prior art devices incorporate the fibers near the end of the screw.
15 However, this results in poor mixing of the plies into the melt and still results
in wear of the last few flights of the extruder screw.
A need therefore exists for an appa~ s and system which
facilitates the mixing and transformation of a moldable material prior to and/orduring solidification. Furthermore, a need exists for a system for reinforcing
20 a moldable material flow without causing excessive wear of the extruder screw.
Sumrnary of the Invention
The present invention relates to an al~par~lus
and a system for subjecting a flow of moldable material to shear, compressive
25 and/or tensile loads.
In another aspect the present invention provides an app~lus
and system for thoroughly mixing a flow of moldable material.
- In yet another aspect the present invention provides an
apparatus and system for displacing a flow of moldable material so as to
30 produce mixing of the material.
81 10-55
~- \S7596 ~1 ~5~34
These and other aspects and advantages of the present invention
are achieved by the novel apparatus and system for molding a flow of moldable
material under the application of shear, compressive and/or tensile loads. The
apparatus comprises a mold housing that has a flow of moldable material
S supplied to it. A first boundary element is located within the mold housing and
defines a first side of the flow of moldable material. A second boundary
element also positioned within the mold housing defines a second side of the
flow of moldable material. A driver in driving contact with the first boundary
element is adapted to produce a deflection of the first boundary element in a
10 direction subst~nti~lly perpendicular to the flow of the moldable material. The
deflection of the first boundary element imposes shear, compressive and tensile
loads on the flow which function to transform the moldable material. In one
embodiment of the invention, the applied shear, compressive and tensile loads
produce mixing of the moldable flow of material. In another embodiment of the
15 invention, the shear, compressive and tensile loads are controlled for effecting
the rheological properties of the moldable material prior to and during curing.
The imposed forces also function to increase the mixing of the moldable flow
without the need for further mixing devices.
A flexible joint is incorporated into the apparatus to allow the
20 first boundary element to deflect. In one embodiment of the invention, the
flexible joint is configured as a cylindrical wave or bellows. This cylindrical
wave attaches to the first boundary element or mandrel which may also be
cylindrical in shape.
In one configuration, the driver comprises an eccentric portion
25 of a drive shaft. The rotation of the drive shaft causes the eccentric portion to
rotate eccentric to the shaft's axis of rotation. This eccentric rotation causes the
deflection of the first boundary element. The amount of deflection may be
varied as desired by means of a bearing assembly which includes a rotatable
eccentric bearing journal.
85l75965 2 ~ ~03~
A system for transforming a flow of moldable material is also
disclosed. The system includes the steps of mixing a first material component
and a second material component so as to produce a mixture. The mixture is
then melted to form a moldable material. The moldable material is conveyed
5 between a first and second boundary element of a molding apparatus. A portion
of the first boundary element is deflected in a direction substantially
perpendicular to the flow of moldable material. The deflection of the first
boundary element imposes shear, compressive and tensile loads on the flow of
moldable material which produce further mixing of the moldable material. The
10 moldable material is then cured into a final product.
The novel apparatus and system result in moldable material which
is more thoroughly and efflciently mixed than has heretofore been possible by
prior art processes. The novel apparatus and system also controls the
rheological properties of the moldable material for reducing the residual stress15 and/or elimin~ting the melt fracture in the final product.
The foregoing and other features and advantages of the present
invention will become more apparent in light of the following detailed
description of the preferred embodiments thereof, as illustrated in the
accompanying figures.
Brief Description of the Dldwi~
For the purpose of illustrating the invention, the drawings show
a form of the invention which is presently preferred. However, it should be
understood that this invention is not limited to the precise arrangements and
25 instrumentalities shown in the drawings.
Figure 1 illustrates the present invention as it is utilized in a die
molding system.
Figure 2 is a section view of an extruder used to feed a moldable
material into a die housing.
81 10-55
\57596
2 1 ~5~34
- 8 -
Figure 3 is a schematic representation of a prior art molding
apparatus.
Figures 4A-4D are schematic representations of a molding
apparatus made according to the present invention for use in applying shear and
5 colllplessive loads to a flow of moldable material.
Figure 5 is a detail view of one arrangement of the driver for use
in deflecting or eccentrically offsetting a mold surface.
Figure 6 is a section view of the molding apparatus taken along
lines 6-6 in Figure S.
Figure 7 is a side view of the molding apparatus taken along lines
7-7 in Figure 5.
Figure 8 is a detail view of one arrangement of the flexible joint
for accommodating the deflection of the mandrel.
Figure 9 is a illustration of a test sample produced according to
a prior art method.
Figures lOA and lOB illustrate two test samples produced
according to one embodiment of the present invention.
Figure 11 illustrates an embodiment of the present invention as
it is utilized in a blow molding system.
Figure 12 illustrates an embodiment of the present invention
wherein the extruder and the drive shaft are formed as an integral unit.
Figure 13 illustrates an embodiment of the present invention as
it is utilized in fabricating flat die molded sheets of material.
Figure 14 illustrates a section view of the flat die molded sheet
embodiment of the present invention.
Figures l5A and l5B illustrate two eccentric positions of the
driver for use in deflecting or eccentrically offsetting a mold surface.
Figure 16 illustrates an embodiment of the present invention for
use in m~mlf~cturing a molded product made with fiber reinforced molded
material.
8 1 10-55
` \57596 ~ g3
Figure 17 illustrates another embodiment of the present invention
for use in m~nllfacturing a molded product made with fiber reinforced molded
material.
Figure 18 illustrates an embodiment of the present invention
S wherein the mandrel is eccentric with respect to the die mold.
Detailed Des~ Jtion of the Preferred Embodillle--ls
Referring now to the drawings, wherein like reference numerals
illustrate corresponding or similar elements throughout the several views, Figure
10 1 illustrates one embodiment of the present invention as it is incorporated in a
die molding assembly 10. The die molding assembly 10 includes an extruder
12, a mold housing 14, and one or more mold dies 16. A power unit 18 is used
to rotate an internally mounted drive shaft 20 which will be discussed in more
detail below.
The extruder 12 is illustrated in more detail in Figure 2. The
extruder 12 generally includes a hopper 22 for supplying a preferably unmelted,
fungible moldable material into a extruder housing or barrel 24. A screw 26
is located within the extruder barrel 24 and is rotated by a motor drive 27. Thescrew 26 contains one or more flights 26' which, when the screw is rotated,
20 drive or feed the moldable material from the hopper 22 to an extruder port 28in the extruder barrel 24. The screw 26 also functions to melt, compress and
homogenize the moldable material during translation from the hopper 22 to the
port 28. At least one heater 30 is located on or adjacent to the extruder barrel24. The heater 30 transmits heat to the moldable material causing it to melt as
25 it is translated by the screw 26 to the port 28.
In one plerelled embodiment, the extruder port 28 directs the
flow of moldable material from the extruder 12 into the mold housing 14. A
flow divider (not shown) channels the incoming flow of moldable material into
the mold dies 16 which define the external shape or boundary of the final
30 product. In the embodiment illustrated, the mold dies 16 define the external
81 10-55
\57596 ~ 1 85~3~
- 10 -
surface of a cylindrical tube. A mandrel 32 is located within the die molds 16
and forms an internal mold boundary along which the moldable material flows.
Hence, in this embodiment, the moldable material flows or is channeled
between the inner surface of the outer mold dies 16 and the outer surface of theS inner mandrel 32 which define the final product shape. In the illustrated
embodiment, the final product shape is a tube or cylinder such as a pipe.
Alternate shapes may also be practiced within the scope of the invention.
As discussed above, the screw 26 compresses and conveys the
moldable material while in the extruder 12. The moldable material is fed into
the mold housing and is forced to flow between the mold dies 16 and the
mandrel 32 by pressure from the continuous rotation of the screw 26. Hence,
the speed of the screw 26 determines the speed that the final product is output
from the die molding assembly 10.
A series of temperature control units (not shown) may be
positioned on or adjacent to the outer surface of the die molds 16. Both coolingand heating of the moldable material can be applied through the temperature
control units. Those skilled in the art would readily be able to determine
whether to cool or heat the material depending on the specific material being
processed and/or the objectives sought. For example, cooling can be applied
to shorten the solidification or curing time of the moldable material. Although
the mold dies 16 are depicted as being relatively long in length, it should be
appreciated that the desired length will depend at least on the amount of cooling
required to solidify or cure the final molded product, and on the final product
shape.
In order to more thoroughly mix the component parts of the
moldable material, the present invention subjects the flow of moldable material
to a load or deflection which is substantially perpendicular to the direction ofmaterial flow so as to impose compressive and shear loads on the flow.
Referring to Figure 1, in one embodiment of the invention, the material flowing
between the mandrel 32 and the mold die 16is subjected to force caused by the
81 10-55
\57596
as~34
eccentric rotation of a portion of the internal drive shaft 20. That is, a portion
of the internal drive shaft 20 is eccentric to and in driving contact with the
mandrel 32 so as to function as an eccentric driver. The eccentric driver
produces an eccentric motion or deflection of the mandrel 32 with respect to thelongitudinal axis of rotation of the shaft so as to result in relative motion
between the mandrel 32 and the die mold 16. This motion or deflection of the
mandrel 32 is substantially perpendicular to the axial direction of the flow of
moldable material between the mandrel 32 and the mold die 16. The deflection
of the mandrel 32, in turn, subjects the flow of moldable material to shear,
compressive, and tensile forces which result in further mixing of the moldable
material just prior to and during solidification.
A better underst~n(ling of this eccentric motion can be had by
reference to Figures 3 and 4A-4D. Figure 3 illustrates a section view of a priorart die mold system during operation. The mandrel 32 is concentric with the
mold die 16. There is no internally mounted drive shaft since the prior art die
molding assemblies typically do not apply rotational motion to the mandrel or
the mold dies. As a consequence, there are no forces applied to the flow of
moldable material (designated by numeral 34) by eccentric rotation of a drive
shaft.
Referring to Figures 4A-4D, one embodiment of the present
invention is shown wherein the drive shaft exerts an eccentric motion on the
mandrel 32. Figures 4A-4D show the rotation of the drive shaft in 90 degree
increments. In the embodiment illustrated, a portion 20' of the internal drive
shaft 20 rotates eccentric to the shaft's longitudinal axis of rotation (designated
by numeral 36 and shown in Figure 1). The eccentricity, 'e', is shown in
Figure 1. As the eccentric portion 20' rotates, it deflects the mandrel 32
causing the mandrel 32 to move toward and away from the die mold 16. This
motion produces compression, tension and shear forces in at least a portion of
the moldable material flow 34. These applied compression, tension and shear
81 10-55
\57596
~18~
- 12 -
forces produce, as one consequence, an omni-directional mixing of the moldable
material.
The applied compression, tension and shear forces also produce
changes in the rheological properties of the molten material. That is, the
S eccentricity of the drive shaft 20 with respect to the mandrel 32 can be tailored
to produce compression and shear forces in the moldable material which, for
example, alter the orientation and/or the flexural and tensile strength of the
material. Transforming the physical characteristics of a moldable material is
well known and is described in detail in U.S. Pat. Nos. 4,469,649 and
5,306,129 which are both incorporated herein by reference. The disclosed
embodiments provide a novel means for achieving the change in the rheological
properties of the material. It is contemplated that a controller may be utilizedto control the eccentric driving to produce the desired rheological properties.
Those skilled in the art would readily be capable of l]tili7ing the teaching of the
15 present invention for altering the rheological properties of the moldable material
and, therefore, no further discussion is needed.
It is also well known that, during the flow process, molten
polymers store a significant amount of elastic energy when subjected to
pressure, such as from the screw of an extruder. This stored elastic energy in
20 the polymer melt could cause a high level of residual stress, die swell and/or
melt fracture in the final molded article. The application of the compressive,
tensile and shear loads on the molten polymer prior to and/or during
solidification or curing can be used to control the level of elastic "memory" byinducing relaxation of the polymer molecules. This would result in the control
25 of the residual stress and/or elimin~tion of the melt fracture in the final molded
part. Prior art methods of reducing the residual stress or melt fracture stress
included reducing the applied pressure, increasing molding cycle time, ~nn~ling
the molded article after it is already molded, etc. The present invention
elimin~tes or reduces the need for such expensive and time-consuming
30 m~m-f~blring solutions.
81 10-55
\57596
~ 1 35~3q
As stated above, in one embodiment of the invention, a portion
of the drive shaft 20 is formed eccentric to the longitll~lin~l axis of rotation 36
of the shaft. This embodiment is shown in Figures 1 and 5. As illustrated in
Figure 5 and discussed above, the eccentric portion 20' of the drive shaft has
a centerline 38 that is eccentric to the axis of rotation 36 of the shaft 20.
The eccentric portion 20' of the shaft is engaged with the mandrel
32 by means of a bearing assembly 40. The bearing assembly 40 includes a
bearing journal 42 which has an inner surface 44 disposed around an outer
surface 46 of the eccentric portion 20'. The bearing journal 42 also has an
outer surface 48 which is in contact with an inner race 50 of a bearing 52.
Generally a tight fit is desired between the bearing journal 42 and the inner race
50 of the bearing 52 such that rotation of the bearing journal 42 produces
rotation of the inner race 50. The bearing 52 also has an outer race 54 which
is located between the inner race 50 and an inner wall or surface 56 of the
mandrel 32. Preferably the outer race 54 is fit snug against the inner wall 56
of the mandrel 32 so as to prohibit or minimi7e motion therebetween.
Alternately, a second bearing journal (not shown) could be located between the
outer race 54 and the mandrel 32 to minimi7e the size of the bearing needed.
The bearing assembly 40 permits the drive shaft 20 and eccentric portion 20'
to rotate with respect to the mandrel 32 while m~int~ining engagement between
the eccentric portion 20' and the mandrel 32.
In the illustrated embodiment, it is desirable that the bearing
journal 42 rotate with the drive shaft 20. To achieve this, the bearing journal
42 may be directly locked into engagement with the drive shaft 20 and/or the
eccentric portion 20' by means of a screw or pin 58 (shown in Figure 6).
Alternately and more preferably, a locking mechanism 60 may be utilized to
attach the bearing journal 42 to the eccentric portion 20'. Referring to Figures5 and 7, the locking mechanism 60 is positioned adjacent to the bearing journal
42 and is disposed around the eccentric portion 20' of the shaft. The locking
mechanism 60 is attached to the bearing journal 42 by means of the pin 58.
81 10-55
\SîS96 2 1 ~34
- 14 -
The locking mechanism 60 furthermore has a slot 62 formed therein, the width
of which can be adjusted by a locking screw 64. Tightening of the locking
screw 64 causes the width of the slot 62 to decrease. This, in turn, causes the
locking mechanism to tighten around the eccentric portion 20 ' of the drive shaft.
5 As a result, rotation of the drive shaft 20 produces corresponding rotation of the
bearing journal 42 and the inner race 50 of the bearing.
Alternate methods for eng~ging the eccentric portion 20' with the
mandrel 32 are also within the purview of this invention. For example, the
inner race 50 of the bearing 52 could be disposed directly on the outer surface
46 of the eccentric portion 20' elimin~ting the need for a bearing journal 42.
Furthermore, in an alternate arrangement, the locking mechanism 60 may be
formed integral with the bearing journal 42 or, instead, the bearing journal
could be attached to the eccentric portion 20' through a splined, keyed or
similar type arrangement. In still yet another embodiment, a cam arrangement
15 similar to the one shown in Figures 4A-4D may be incorporated into the
invention for functioning as the eccentric driver to produce the offset of the
mandrel 32. It is also contemplated that the drive shaft can be formed without
an eccentric portion 20'. Instead, the eccentric driver for producing the offsetof the mandrel is attached directly to the mandrel 32 itself. For example, the
20 bearing 52 can be mounted to the mandrel 32 in a non-concentric manner.
Normal rotation of the drive shaft 20 would result in the eccentric motion of the
mandrel 32.
In one embodiment of the die molding assembly, the eccentricity
e of the shaft 20 is preset and non-adjustable. In this embodiment, the bearing
25 journal 42 is shaped such that its outer surface 48 is concentric with the outer
surface 46 of the eccentric portion 20'. As a result, the mandrel 32 will alwaysbe eccentrically driven by the drive shaft 20.
In a second, and more preferable, embodiment the amount of
eccentricity e produced by the driver is adjustable depending on the amount and
30 type of loading desired on the moldable material. For example, in one
81 10-55
\57596 ~ 1Q34j
- 15 -
configuration, the eccentricity is adjustable from about zero inches to more than
0.125 inches. The amount of adjustability will, of course, differ depending on
the configuration of the molding process and the shape of the resulting product.In order to achieve this variability in eccentricity, the outer surface 48 of the
5 bearing journal 42 has a shape which is not concentric with the outer surface 46
of the eccentric portion 20'. This bearing journal configuration is illustrated in
Figures 5 and 6. It should be apparent that rotation of the bearing journal 42
with respect to the eccentric portion 20' will alter the amount that the mandrelis displaced or eccentrically offset. The combination of the bearing journal 42
and the eccentric portion 20' define a driver centerline 300. The amount of
deflection of the mandrel 32 is a function of the distance between the driver
centerline 300 and the longitudinal axis of rotation 36 of the shaft 20. Figure
15A illustrates one position of the bearing journal 42 and eccentric portion 20'combination. In this position, the driver centerline 300 lies substantially in line
15 with the longitlldin~l axis of rotation 36 of the shaft 20. Accordingly, there is
substantially no eccentric offset of the mandrel 32 by the eccentric driver.
Figure 15B illustrates the bearing journal rotated into a second position. In this
position, the driver centerline 300 is spaced apart from the longitudinal axis of
rotation 36 of the shaft 20 by an eccentric distance e. Accordingly, the
20 eccentric offset of the mandrel 32 will be a function of this eccentricity e.Varying the eccentricity e, produces varying compression, tension and shear
loads on the flow of moldable material.
In order to rotate the bearing journal 42 with respect to the
eccentric portion 20', the locking mechanism 60 has flat surfaces 66 formed on
25 it to permit grasping of the locking mechanism 60 by a wrench or similar typeimplement. The drive shaft 20 is held in place while the locking mechanism 60
and the bearing journal 42 are rotated to produce the desired eccentricity e.
In the alternate splined or keyed arrangement discussed above,
the bearing journal 42 is engaged with the proper splines or keys on the
30 eccentric portion 20' so as to provide the desired eccentricity e. In the alternate
81 10-55
\57596
~ I ~S~ ~4-
- 16 -
embodiment discussed above where the bearing journal 42 is pinned directly
into the drive shaft 20, multiple pin holes could be formed in the drive shaft in
a circumferential pattern, each hole representing a different eccentric position.
Accordingly, the bearing journal would be pinned into the appropriate hole to
5 provide the desired eccentricity. It is also contemplated that the eccentric
portion 20' of the shaft be removable such that portions with different
eccentricities may be substituted as needed. Alternately, a portion of the
mandrel 32 itself could be formed non-concentric with the die mold 16. Motion
of the mold (e.g., rotational or lateral) would result in compression and shear
10 loads being applied to the moldable material flow. Those skilled in the art
would readily appreciate the various alternate methods of adjusting the
eccentricity that can be practiced within the scope of this invention. For
example, a motor drive (not shown) could be mounted within the mandrel 32
for permitting automated adjustment of the eccentricity e.
As discussed above, rotation of the drive shaft 20 causes the
eccentric portion 20' to produce a deflection or eccentric offset of the mandrel32. In the embodiment illustrated in Figure 1, the eccentric offset of the
mandrel 32 occurs at a location apart from the point where the mandrel 32
attaches to the mold housing 14 and where the extruder 12 feeds the moldable
20 material into the mold housing 14. In order to permit the mandrel 32 to be
displaced, the end of the mandrel 32 closest to the point where the moldable
material enters the mold housing 14 is attached to the mold housing 14 through
a flexible joint 68. The flexible joint 68 permits the mandrel 32 to remain
relatively straight. Tn~te~(l, the offset or displacement of the mandrel 32 is
25 accommodated by angular flexure of the flexible joint 68. The flexible joint 68
preferably also biases the mandrel back to its undeflected position.
The incorporation of the flexible joint 68 reduces or elimin~tes
the stresses which would otherwise develop in the mandrel 32 from the eccentric
offset or deflection. Additionally, the angular flexure of the flexible joint and
30 resulting angular orientation of the mandrel 32 subject the flow of moldable
81 10-55
\57596
~ 1 85b34
- 17 -
material to an additional axial shear force which acts along substantially the
entire longitl-~lin~l length of the mandrel 32. This added shear force helps to
mix the moldable material and reduce the slip-stick behavior of the flow.
In one preferred embodiment, the flexible joint 68 comprises an
internal wave 70 similar to a bellows. This type of configuration permits the
internal wave 70 to flex radially in all directions. The bellows shape also
allows the moldable material to flow relatively unobstructed through the mold
housing 14 and onto the mandrel 32. During a standard molding process,
pressures of up to 10,000 psi can be generated as the extruder 12 forces the
moldable material into the mold housing 14. Accordingly, the internal wave 70
must be designed to with~t~nfl this applied pressure while also permitting the
required angular flexure produced by the displacement of the mandrel 32. In
the preferred embodiment, the internal wave 70 is made from 17-4PH stainless
steel with a thickness of about 0.125 inches. A variety of other configurations
and materials may be substituted for the preferred embodiment. For example,
the wave could instead be constructed from fiber reinforced composite matrix
material.
Referring to Figures 1 and 8, the internal wave 70 is attached to
the mandrel 32 preferably through a threaded arrangement designated by the
numeral 72. Alternate methods for attaching the mandrel 32 to the internal
wave 70 can be utilized in the present invention. However, the selected method
of attaching the mandrel 32 to the internal wave 70 should be designed to
prevent or minimi7~ leakage of the moldable material into the interior of the
mandrel 32 and onto the drive shaft 20 and its associated bearings.
The internal wave 70 is preferably attached to the mold housing
14 by means of a spindle 74. The spindle 74 is positioned within the flow
divider (not shown) and can be threadingly engaged with the internal wave 70
or, as shown in the figure, can attach the internal wave 70 to the mold housing
through a thrust type arrangement. Axial adjustment of the spindle 74 pulls the
internal wave 70 toward the mold housing 14. Bearings 76 are located between
81 10-55
\57596
- ~ ~ 35~34
- 18 -
the spindle 74 and the drive shaft 20 so as to permit the shaft 20 to rotate within
the spindle 74.
Alternately, the flexible joint 68 may comprise a universal joint
arrangement (not shown). The universal joi~t accommodates the angular
5 deflection of the mandrel 32. In this embodiment of the invention, the flow ofmaterial is fed into the mold housing 14 downstream of the universal joint so
as to prevent the moldable material from interfering with the operation of the
joint. In another embodiment of the invention, the flexible joint is simply a less
rigid portion of the mandrel 32. That is, the mandrel is attached directly to the
10 mold housing 14 and has a portion which has a reduced flexural stiffness. As
a consequence, the applied eccentric offset will result in the bending or flexing
of the portion of the mandrel 32 with the reduced stiffness. Those skilled in the
art can readily appreciate the variety of modifications to the exemplary
embodiments that are possible within the scope of the present invention.
It is also contemplated that the mandrel 32 can be rotated instead
of, or in addition to, the rotation of the shaft 20. For example, the drive shaft
20 may be fixedly mounted to the mold housing 14. The flexible joint 68 and
the mandrel 32 are then rotated with respect to the drive shaft 20. An eccentricdrive, such as an eccentric portion 20' of the shaft, would be positioned within20 the interior of the mandrel 32 in contact with the inner surface of the mandrel
32. As the mandrel 32 rotates, the eccentric drive displaces the mandrel 32.
The rotation of the mandrel 32 also produces a natural conveyance of the
moldable material between the mandrel 32 and the mold die 16. Thus, less
pressure from the extruder 12 would be needed to drive the moldable material
25 through the mold die 16. Rotation of the mandrel also results in omni-
directional stresses being generated in the material. That is, the displacement
of the mandrel 32, in combination with the mandrels rotary motion, impose
shear, compressive and tensile loads in various directions. These stresses assist
in thoroughly mixing the melt and/or properly controlling the rheological
30 changes and stick-slip behavior of the moldable material. In another
8sl7s96 ~ ~ 85~3~1
- 19 -
embodiment of the invention, the mandrel is non-concentric with the die molds.
Accordingly, rotation of the mandrel results in relative movement between the
mandrel and the mold die so as to induce compressive, tensile and shear loads
on the moldable material.
In yet another embodiment, the mandrel has two distinct portions
which are rotatable with respect to one another. During the molding process,
one mandrel portion is rotated in a clockwise direction while the other mandrel
portion is rotated in a counter-clockwise direction. As the moldable material
flows from one mandrel portion to the other, the counter-rotation of the
mandrels causes the material to further mix. In order to prevent the mandrels
from separating, a hydraulic cylinder is incorporated to provide a counterforce.It is also possible to rotate both the mandrel 32 and the drive
shaft 20 at the same time. In this embodiment, the mandrel 32 can be rotated
in the same direction as the drive shaft 20 or in the opposite direction depending
on the shear loading that is desired. The mandrel 32 can also be rotated at the
same or a different speed than the shaft 20. For example, it may be desirable
to step the mandrel 32 around while the drive shaft 20 is continuously rotating.This can be accomplished by lltili7.ing a stepper motor or similar type of driving
unit. Alternately, the mandrel 32 and/or drive shaft 20 may be oscillated back
and forth instead of completely rotating in one direction. Each of these
embodiments produces distinct shear and compressive loads on the moldable
material prior to and/or during solidification.
If the mandrel 32 is rotated alone or in conjunction with the drive
shaft 20, then it may be desirable to form one or more conveyor flights 150 on
the mandrel 32. The conveyor flights 150 would operate similar to the flights
26' on the screw 26. That is, the flights 150 would convey the moldable
material between the mandrel 32 and the mold die 16. The incorporation of
flights 150 onto the mandrel would reduce the amount of conveying pressure
needed by the extruder screw 26. It is also possible to completely elimin~te theextruder and, instead, melt, compress, convey and mix the moldable material
81 10-55
\57596
~85~34
- 20 -
with only the mandrel 32. Alternately, the conveyor flights may be formed on
the internal surface of the mold dies 16 to provide the desired flow mixing.
Referring to Figure 18, an alternate embodiment for rotating the
mandrel is shown. In this embodiment, the power unit 18 does not drive an
5 internal shaft. Instead, the power unit 18 directly drives the mandrel 32. Therelative displacement between the boundary layers of the material is provided
by an eccentric portion of the mandrel 32'. That is, a portion of the mandrel
32' is formed eccentric to the mold housing 14 and/or the mold die 16.
Accordingly, rotation of the mandrel 32 causes the eccentric portion of the
10 mandrel 32' to subject the moldable material flow to compressive, shear and/or
tensile loads for mixing the material. Preferably, the eccentric portion of the
mandrel 32' is located at a position spaced from the end of the mold die 16.
This permits the post-mixed material to conform to the shape of the mold die
16 while solidifying. Positioning the eccentric portion of the mandrel 32' too
15 close to the end of the mold die 16 could produce inconsistencies in the surface
finish. For example, in the illustrated embodiment the eccentric portion of the
mandrel 32' is located within a first section of the mold die 16. This is where
the compressive, shear and/or tensile loads are applied to the material. The
portion of the mandrel located within the downstream portion of the mold die
20 (identified as 16') is concentric with the mold die. This portion of the die
mold/mandrel forms the moldable material into its final shape. By
incorporating an eccentric portion onto the mandrel 32, it is possible to provide
a significant degree of displacement between the mandrel 32 and the mold die
16. Also, more than one eccentric portion can be formed on the mandrel if
25 desired.
Vanes or flow separators (not shown) may be mounted on the
mandrel and/or the mold die to add instability to the flow. The instability
produces further kn~ ing and mixing of the moldable material flow.
Test samples were prepared using one embodiment of the present
30 invention and compared with a sample made with a standard die molding/mixing
81 10-55
\s7596 ~ 1 8S~3~
process. Referring to Figure 9, a sample of colored polystyrene is depicted
which was produced using a prior art method. One colored pellet was added
to a pound of uncolored polystyrene pellets in a hopper. The components were
melted and mixed in a standard extruder and forced though a mold die. The
5 resulting sample had large pockets of uncolored polystyrene (lln~h~ded portion).
Figures 10A and 10B depict two test samples made according to one
embodiment of the present invention. In both samples, one colored pellet was
placed in the hopper with a pound of uncolored polystyrene. The combination
was then melted in the extruder 12 and fed through the mold die 16. An
10 eccentric loading from the drive shaft 20 was imposed on the mandrel 32 so asto generate compressive, tensile and shear loads on the flow of moldable
material prior to solidification. As can readily be seen, the samples produced
according to the present invention are more thoroughly mixed (less ~ln~h~ded
area) than the prior art sample. The differences in mixing between the sample
15 in Figure 10A and the sample in Figure 10B is due to variations in frequency.The sample illustrated in Figure 10A was for a drive shaft running at a low
rotational speed and, therefore, low frequency of eccentric loading. While the
sample illustrated in Figure 10B was the result of a drive shaft running at highrotational speed and, thus high frequency of eccentric loading. The properties
20 that are desired in the end product will govern the frequency/speed of rotation
chosen.
As stated above, the present invention may be utilized to change
the rheological properties of the moldable material. By tailoring the amplitude
and frequency of the eccentric load, it is possible to modify the physicochemical
25 properties of the moldable material. For example, by properly tailoring the
eccentric offset and the speed of the rotation (i.e., frequency) a vibratory load
can be imposed on the moldable material so as to increase the resulting flexuraland tensile strength. In the illustrated embodiment, the amount of displacement
of the mandrel produced by the combination of the eccentric portion 20' and
81 10-55
\57596
2 11 8~Q3~
bearing journal 42 determines the amplitude of the vibratory load and the speed
of rotation of the shaft 20 determines the frequency of vibration.
The above embodiments relate to the use of the present invention
in a die molding assembly. The present invention, however, can be utilized in
various other molding processes, such as blow molding. For example, Figure
11 illustrates the present invention as it is utilized in conjunction with a blow
molding assembly 100. The construction and operation of the assembly is
generally the same as in the die molding embodiment. However, a conduit 110
is preferably formed through the center of the drive shaft 20. The conduit 110
is attached to and in fluidic communication with a source 112 of a pressurized
medium, such as air. A blow mold 114 is positioned at a location downstream
from where the moldable material is subjected to the displacement or offset.
During operation, the moldable material is melted and conveyed
through the extruder 12 and into the mold housing 14 as discussed above. The
lS moldable material is then subjected to a displacement or offset so as to apply
compressive, shear and/or tensile loads on the moldable material. After being
subjected to the offset, the moldable material is fed into the blow mold 114.
A means for closing off the end of the moldable material so as to form a
parison is not shown but may be incorporated into the system and is
conventional in the art. When a sufficient quantity of the moldable material is
within the blow mold 114, the pressurized media is channeled from the pressure
source 112 through the conduit 110 and into the blow mold 114. As a
consequence, the moldable material or parison expands onto the surface of the
mold.
In each of the above embodiments the extruder 12 has been
illustrated as being adjacent to the side of the mold housing 14 and powered by
a separate power unit. However, it is also within the purview of the present
invention that the screw 26 of the extruder 12 and the drive shaft 20 are drivenby the same power unit. This configuration is illustrated in Figure 12. The
flow is first conveyed, compressed and melted along the screw portion 26" of
8110-55 2185~3~1-
the shaft. The flow is then directed between the mandrel 32 and the mold die
16. An eccentric portion 20' is formed on the shaft at a downstream location.
Alternately, the screw 26 may have an eccentric portion formed at its
downstream end. The eccentric portion would serve to further mix the flow of
moldable material. In this alternate embodiment, a drive shaft with an eccentricportion would not be required for mixing the flow since the mixing would occur
while the moldable material is being conveyed by the screw.
As stated above, the present invention is not limited to forming
circular shaped structures. For example, Figures 13 and 14 illustrate the
utilization of the present invention in an assembly 200 for manufacturing flat
sheets of material. Figure 13 is an isometric illustration of two parallel flat
sheet mold dies 210. A controller 212 provides signals along lines 214 to a
driver 216, such as a linear actuator. The driver or linear actuator is in driving
contact with one surface of each of the mold dies 210. Actuation of the driver
causes deflection of the surfaces in a direction perpendicular to the direction of
flow of the moldable material. Figure 14 is a sectional view showing one
surface of each of the mold dies 210 conn~ctecl to the linear actuator 216.
These surfaces also attach to a flexible joint 218 which permits the surfaces tobe angularly deflected.
It should be readily apparent that the amount of deflection of the
mandrel or inner surface determines the amplitude of the applied vibratory load.Similarly, the frequency of the vibration is determined by the speed of rotationof the drive shaft. By controlling the frequency and amplitude of the applied
vibratory load, it is possible to control the rheological properties of the
moldable material.
Referring now to Figure 16, an embodiment of the present
invention is illustrated wherein reinforcing fibers are fed into the moldable
material prior to mixing. As discussed above, the prior art devices add
reinforcing fibers either when the material is in the hopper or while the material
is conveying through the extruder. In Figure 16, a fiber feeding assembly 400
8110-55 2 1 ~S~3~
\57596
- 24 -
is shown which feeds reinforcing fibers directly into the melt prior to mixing
and after conveyance by the extruder. The fiber feeding assembly 400 includes
a conveyor 402 mounted between the extruder port 28 and the mold housing 14.
The conveyor 402 translates in a direction (as shown by the arrow) which is at
S an angle to the material flow so as to locate at least a portion of the conveyor
402 within the material flow. Preferably the direction of travel of the conveyor402 is about 90 to the direction of flow. The conveyor 402 can be translated
in a reciprocating manner or, alternately, may be a unidirectional feed. In the
latter case, the conveyor 402 may be supplied in the form of a large spool or,
10 more preferably, may be a continuous belt. A power source (not shown) may
be used to control the travel of the conveyor 402. The speed of the conveyor
402 may be controlled so as to be proportional to the extruder motor and/or
anticipated speed of the material flow.
As shown in the figure, the conveyor 402 has a plurality of open
cells 404 formed through it. The open cells 404 are oriented so as to permit themolten material to flow therethrough when the conveyor 402 is placed within
the flow. Short or chopped fibers 406 are deposited within the open cells 404.
A vacuum source 407 is preferably utilized to draw the chopped fibers into the
open cells. Once the cells 404 are filled with the fibers 406, the conveyor 402
is translated so as to placed the filled cells 404 within the material flow.
Accordingly, as the molten material passes through the open cells 404 it picks
up the loose fibers 406. The combination of the molten material and the fibers
then enters into the mold housing 14 wherein the fibers are thoroughly mixed
with the molten material.
In one preferred embodiment, the conveyor 402 is a continuous
screen changer. Continuous screen changers are used in molding devices to
filter out cont~min~nt~ from the molten material as it flows through the screen.One suitable type of continuous screen changer is produced by High Technology
Corp., Hackensack, New Jersey. The present invention uses the continuous
81 10-55
\57596
~ 5~34
screen changer to incorporate the reinforcing fibers 406 into the melt while at
the same time removing any cont~min~nt~ in the flow.
In an alternate configuration shown in Figure 17, the fiber
feeding assembly is designed to incorporate long reinforcing fibers into the
S material flow. A conveyor 410 is again mounted between the extruder port 28
and the mold housing 14. The conveyor 410 travels in a direction, as shown
by the arrow, which is preferably at an angle to the material flow. As with the
configuration discussed above, the conveyor 410 is preferably a continuous
screen changer for filtering cont~min~tçs out of the material flow. Long
reinforcing fibers 412 are positioned on the downstream side of the conveyor
410 prior to placement within the material flow. Accordingly, when the
conveyor 402 is translated through the material flow, the reinforcing fibers 412are picked off the conveyor 410 by the flow of material and carried along into
the mold housing for further mixing. One method for attaching the fibers 412
to the conveyor 410 is through the use of a vacuum source 414. The vacuum
source 414 draws the fibers 412 against the downstream surface of the conveyor
410. Alternate methods for feeding the reinforcing fibers into the material flowmay be substituted for the disclosed embodiments and are well within the
purview of the claims.
Although the invention has been described and illustrated with
respect to the exemplary embodiments thereof, it should be understood by those
skilled in the art that the foregoing and various other changes, omissions and
additions may be made therein and thereto, without parting from the spirit and
scope of the present invention.
