U.S. patent application number 16/115831 was filed with the patent office on 2019-02-28 for high temperature monofilament articles.
This patent application is currently assigned to ADVANCED FLEXIBLE COMPOSITES, INC.. The applicant listed for this patent is ADVANCED FLEXIBLE COMPOSITES, INC.. Invention is credited to Barton Roy LEWIS, William Christopher Lewis, William James LEWIS.
Application Number | 20190062959 16/115831 |
Document ID | / |
Family ID | 65434169 |
Filed Date | 2019-02-28 |
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United States Patent
Application |
20190062959 |
Kind Code |
A1 |
Lewis; William Christopher ;
et al. |
February 28, 2019 |
HIGH TEMPERATURE MONOFILAMENT ARTICLES
Abstract
A fabricated part for a high temperature operation including a
non-metallic substrate formed of a polymer fabric of woven
non-absorbent polymer filament. The substrate is heat-resistant and
heat set at a temperature that is above a predetermined operating
temperature of an operation of the fabricated part. The heat
setting pre-shrinks/heat stabilizes the material, thereby reducing
failure during use in high temperature and/or wet applications. The
substrate is useful as an endless belt and other applications. The
invention further includes an apparatus with a heating device
configured to operate at the predetermined operating temperature,
and the fabricated part within or extending through the heating
device.
Inventors: |
Lewis; William Christopher;
(Saint Charles, IL) ; LEWIS; Barton Roy;
(Algonquin, IL) ; LEWIS; William James; (Naples,
IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ADVANCED FLEXIBLE COMPOSITES, INC. |
LAKE IN THE HILLS |
IL |
US |
|
|
Assignee: |
ADVANCED FLEXIBLE COMPOSITES,
INC.
LAKE IN THE HILLS
IL
|
Family ID: |
65434169 |
Appl. No.: |
16/115831 |
Filed: |
August 29, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62551563 |
Aug 29, 2017 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D03D 15/0011 20130101;
D10B 2331/14 20130101; D03D 9/00 20130101; D03D 2700/03 20130101;
D10B 2401/04 20130101; D10B 2321/021 20130101; D03D 1/0094
20130101; D10B 2505/00 20130101; D03D 19/00 20130101; D10B 2331/061
20130101; D10B 2331/301 20130101; D03D 15/0027 20130101; D03D 15/12
20130101; D03D 3/04 20130101 |
International
Class: |
D03D 3/04 20060101
D03D003/04 |
Claims
1. A fabricated part for a high temperature operation, comprising:
a non-metallic substrate formed of a polymer fabric of woven
non-absorbent polymer filament, wherein the substrate is
heat-resistant and heat set at a temperature that is above a
predetermined operating temperature of an operation of the
fabricated part.
2. The fabricated part of claim 1, wherein the substrate is
pre-shrunk at the temperature.
3. The fabricated part of claim 1, wherein the substrate is
pre-shrunk such that the product will not further shrink or
destabilize in the operation at or above 212.degree. F.
4. The fabricated part of claim 1, wherein the polymer fabric
comprises monofilament or multifilament PPS, PAI, PPSU, PES, PE,
LCP, or PEEK.
5. The fabricated part of claim 4, wherein the polymer fabric is
free of continuous fiber reinforcement of fiberglass, but the
monofilament or multifilament includes chopped or milled fiberglass
therein.
6. The fabricated part of claim 1, wherein the substrate is
connected at opposing ends to form an endless belt.
7. The fabricated part of claim 1, wherein the substrate is heat
set at a temperature of at least 212.degree. for at least 15
minutes, and preferably at least 30 minutes, or at least one
hour.
8. The fabricated part of claim 1, wherein the temperature is at
least 15.degree. over the predetermined operating temperature, and
preferably at least 50.degree..
9. The fabricated part of claim 1, wherein the polymer filament
comprises a high temperature chain extended or cured polymer
material.
10. The fabricated part of claim 1, comprising a conveyor belt for
steam treatment, article washing, oven drying, baking, or deep
frying.
11. The fabricated part of claim 1, wherein the substrate is formed
by heat setting the polymer fabric at the temperature that is above
the predetermined operating temperature of the operation for a
predetermined time period, to obtain the substrate.
12. The fabricated part of claim 11, wherein the substrate is
further formed by winding the polymer fabric with a non-stick layer
to form wound material layers, and heating the wound material
layers to the heat setting temperature.
13. The fabricated part of claim 11, wherein the substrate is
further formed by calendaring the polymer fabric at or above the
heat setting temperature.
14. The fabricated part of claim 13, wherein the calendaring is
performed with heated calendar rolls.
15. The fabricated part of claim 1, further comprising a
fluoropolymer or fluoroelastomer blended within the monofilament
and/or coating the substrate.
16. The fabricated part of claim 1, further comprising a non-stick
coating on the substrate.
17. The fabricated part of claim 1, further comprising an edge
material strip along or over opposing longitudinal edges of the
substrate to form an endless belt, the edge material comprising a
thermoplastic, fiber-reinforced material, or silicone material
capable of withstanding the predetermined operating
temperature.
18. The fabricated part of claim 1, comprising a piece of fabric
and an edge material along or over all side or peripheral
edges.
19. A fabricated part of claim 18, comprising a tray insert,
wherein the part is placed onto a tray in an oven used for
dehydration, curing, drying, baking, or pressing.
20. An apparatus comprising a heating device configured to operate
at the predetermined operating temperature, and an endless belt
comprising the fabricated part according to claim 1 and extending
through the heating device.
21. The apparatus of claim 20, wherein the heating device includes
steam microwave, or a heated liquid.
22. The apparatus of claim 20, wherein the apparatus is selected
from a washing apparatus, a drying oven, a deep fryer, or a yarn
treatment apparatus.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application, Ser. No. 62/551,563, filed on 29 Aug. 2017. The
co-pending parent application is hereby incorporated by reference
herein in its entirety and is made a part hereof, including but not
limited to those portions which specifically appear
hereinafter.
BACKGROUND OF THE INVENTION
[0002] This invention relates generally to high temperature polymer
materials and, more particularly, to high temperature fabrics made
from polymer filaments for use in various articles, such as belting
and tray liners.
[0003] Polyphenylene sulfide (PPS) is used in chemical and heat
resistant products. When PPS is drawn as a filament, whether as a
monofilament or as part of a multifilament yarn, the filament will
shrink at elevated operating temperatures, such as by 15% or more,
depending on grade and filament manufacturing process, and
application operating temperature. Furthermore PPS monofilament
generally can have a `roughness` after weaving that limits use in
applications such as steam bulking and heat setting of yarns,
various food applications, etc. There is a continuing need for
improved monofilament materials for belting and other articles.
SUMMARY OF THE INVENTION
[0004] A general object of the invention is to provide improved
polymer fabrics that can be used as a substrate with higher
temperature resistance and/or dimensional stability in various
fabricated parts for high temperature and/or liquid applications.
The invention provides, at least in part, a fabricated part for a
high temperature operation including a non-metallic substrate
formed of a polymer fabric of woven non-absorbent polymer
filaments, wherein the substrate is heat-resistant and heat set at
a temperature that is above a predetermined operating temperature
of an intended operation of the fabricated part. As used herein,
references to the term "non-metal" or "non-metallic" are to be
understood to refer to an element or material being devoid of
metal.
[0005] In embodiments of this invention, the polymer filament
includes a high temperature chain extended or cured polymer
material, desirably obtained by the heat setting. "Heat setting"
according to embodiments of this invention involves keeping the
material at the setting temperature for a period of time such that
a curing and/or crosslinking process occurs. This is discernable by
a color change in the fabric and the heat set material of this
invention has increased dimensional stability (little to no shrink)
at the in-use temperature after being subjected to the curing
temperature again.
[0006] The heat setting of the substrate according to this
invention provides benefits such as pre-shrinking the polymer
fabric and/or curing or chain extending the polymer material to
impart higher heat resistance. Heat setting the substrate above the
intended operating temperature, or the temperature of the intended
use, allows for heat resistance and dimensional stability at that
operating temperature. Without wishing to be bound by theory,
curing PPS with heat in the presence of oxygen results in property
changes that are a result of molecular chain extension and
formation of molecular chain branches via an oxygen ion bonded
between the aromatic rings of PPS. The curing increases the
molecular weight, resulting in some thermoset-like properties,
including good thermal stability, dimensional stability, and
resistance to harsh chemical environments. However, PPS is a
thermoplastic and does not suffer from many of the shortcomings of
thermosets. For example, whereas PPS monofilament belting is known
to shrink during high temperature use, the substrate and articles
of this invention are pre-shrunk or thermally stabilized via the
heat setting such that the product will not fail due to shrinkage
or other destabilization in the operation at, for example,
212.degree. F. (100.degree. C.) and higher.
[0007] In embodiments of this invention, the substrate is formed by
heat setting a polymer fabric (e.g., a fabric of polymer
monofilaments or multifilaments) at the temperature that is above
the predetermined operating temperature of the operation for a
predetermined time period, to obtain the polymer substrate. The
heat setting can be performed is any suitable method that
preshrinks/thermally stabilizes the fabric and/or otherwise imparts
dimensional stability. In one embodiment of this invention, the
substrate is formed by winding the polymer fabric with a non-stick
layer to form wound material layers, and heating the wound material
layers to the heat setting temperature, such as in a batch oven,
for a sufficient time. In another embodiment, the substrate is
formed by calendaring the polymer fabric at or above the heat
setting temperature, such as using heated calendar rolls.
[0008] The fabricated parts of this invention include endless
belts, trays, bakeware or cookware. Exemplary endless belts include
conveyor belts for, without limitation, steam treatment, article
washing, oven drying, baking, or deep frying. The conveyor belts
desirably include an edge material strip along or over the opposing
ends and/or longitudinal edges of the belt. The edge material can
be a thermoplastic, a fiber-reinforced material, or a silicone
material capable of withstanding the predetermined operating
temperature. Trays, such as cooking or baking sheets, can be formed
from a piece of fabric and an edge material along or over all side
or peripheral edges. The tray can be an insert for a cooking device
designed to be placed in an oven used for dehydration, baking, or
pressing. Other articles include thermoformed articles stamped from
the substrate, such for cooking, washing, and/or drying food, plant
material, or parts or articles (e.g., can washing).
[0009] The invention further provides an apparatus with a heating
device configured to operate at a predetermined operating
temperature, and a non-metallic endless belt as described above
extending through the heating device. In embodiments of this
invention, the heating device includes microwave, steam, and/or a
heated liquid. The apparatus can be, for example, a washing
apparatus, a drying oven, a deep fryer, or a yarn treatment
apparatus.
[0010] Other objects and advantages will be apparent to those
skilled in the art from the following detailed description taken in
conjunction with the appended claims and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a substrate according to one embodiment of this
invention.
[0012] FIG. 2 is a view of a fabric weave, according to one
embodiment of this invention.
[0013] FIG. 3 representatively shows a heat setting process
according to one embodiment of this invention.
[0014] FIG. 4 representatively shows a heat setting process
according to another embodiment of this invention.
[0015] FIG. 5 is an endless conveyor belt, according to one
embodiment of this invention.
[0016] FIGS. 6 and 7 each show a belt lacing, according to
embodiments of this invention.
[0017] FIG. 8 shows a tray, according to one embodiment of this
invention.
[0018] FIG. 9 shows a belt according to one embodiment of this
invention used in a can washing and drying apparatus.
[0019] FIG. 10 shows a belt according to one embodiment of this
invention used in a deep frying apparatus.
[0020] FIG. 11 shows a belt according to one embodiment of this
invention used in a yarn or other material treatment apparatus.
DETAILED DESCRIPTION OF THE INVENTION
[0021] The present invention provides a monofilament fabric having
dimensional stability and temperature resistance, and method for
making. The monofilament fabric is desirably woven, and can be
formed as a mesh with a plurality of mesh openings between the
woven monofilament strands.
[0022] FIG. 1 illustrates a substrate 20 formed from a polymer
monofilament mesh fabric. Substrate 20 includes a plurality of
parallel monofilament strands 22 extending between edges 30 and 32.
A second plurality of monofilament strands 24 extend perpendicular
to, and are woven alternatively between the strands 22 to form the
base polymer fabric and the mesh openings between the individual
monofilaments 22 and 24. Any suitable fabric weaving is suitable
for the polymer fabric. FIG. 2 shows an alternative monofilament
fabric substrate 20 where pairs of strands 24 are twisted together
and around alternating sides of a corresponding one of the strands
22. Mesh opening sizes can vary, depending on need, with a tighter
weaves with more strands forming smaller mesh openings.
[0023] The polymer filaments (monofilaments or multifilaments) of
this invention can be formed of suitable polymer material, such as
polyphenylene sulfide (PPS), polyaminde-imide (PAI), polyphenylene
sulfone (PPSU), polyethersulfone (PES), polyethylene (PE),
liquid-crystal polymers (LCP), and/or polyether ether ketone
(PEEK). The polymer material can include additives to impart
additional properties. Inclusion of chopped or milled fiberglass
within the polymer materials and within the individual filaments
can be used to increase strength or stiffness, thereby not
requiring separate, continuous fiberglass reinforcement of the
substrate or fabric as a whole. The opposing ends and/or edges 30
and 32 of the substrate 20 each include an edge material strip 36,
such as formed of a thermoplastic or silicone material, and
optionally fiber-reinforced, capable of withstanding the
predetermined operating temperature of the intended use of the
substrate 20.
[0024] In embodiments of this invention, the substrate 20 is heat
set at a heat setting temperature to obtain improved stability
and/or temperature resistance. Heat setting according to this
invention provides benefits such as curing or chain extending of
the polymer material, and/or preshrinking the polymer fabric. In
embodiments of this invention, the polymer fabric of the substrate
is heat set at a temperature that is greater than a predetermined
operating temperature of the intended use of the resulting
fabricated part including the substrate. The higher temperature
preshrinks/heat stabilizes the fabric before the substrate is put
into use, thereby reducing or eliminating shrinkage and rupture
during use, particularly at temperatures above 180.degree. F.
(82.degree. C.). In embodiments of this invention, the substrate
shrinks less than 2% during treatment. However, even 1% shrinkage
during use can result, for example, in an endless belt prematurely
failing on the conveyor rollers.
[0025] If the operating temperature of the final product is too
close to, or higher than, the heat setting temperature, then the
substrate fabric will likely still shrink, neck, distort, and/or
sometimes even elongate during use. The heat setting temperature is
above the glass transition temperature of the polymer, and in
embodiments of this invention the heat setting temperature is least
15.degree. over the predetermined operating temperature, and
preferably at least 25.degree., and desirably at least 50.degree.
over the predetermined operating temperature. For embodiments
including PPS monofilament, the heat setting temperature is
desirably 212.degree. F. (100.degree. C.) or above, more desirably
at least 250.degree. F. (121.degree. C.), for at least 15 minutes,
and preferably at least 30 minutes, and desirably at least one
hour.
[0026] Heat setting can be performed by any suitable heating
apparatus. In embodiments of this invention, the heat setting is
done in combination with a process to further provide stability
and/or reduce roughness. FIG. 3 illustrates heat setting according
to embodiments of this invention. Monofilament fabric web 20 is
calendared against one or more pairs of heated calendar rolls 40.
In the embodiment of FIG. 3, the rolls 40 are within an oven 42,
such as an oven able to reach a temperature of at least 50.degree.
over the intended operating temperature. Any suitable heated
calendar roll can be used, such as one or more heated rolls or
pairs of rolls. The fabric can also be first heat set, for example
in an oven, and then calendared at least once after heat set on
heated calendar rolls at or above the heat setting temperature.
[0027] FIG. 4 illustrated an alternative heat setting method that
also provides stability and/or reduces roughness. In FIG. 4, an
interleaf non-stick film or fabric 52, such as made from
polytetrafluoroethylene (PTFE), is layered between layers of the
monofilament fabric 20 wrapped tightly around roll 50. The wrapped
layers are secured about the roll, such as with PTFE tapes to hold
the tightness and shape, and placed in an oven at room temperature.
The oven is heated to the heat set temperature above the operating
temperature for a necessary time, such as near or to the melting
point for about 30 minutes. The resulting mesh material has
improved stability, decreased roughness, and improved temperature
resistance at the operating temperature. One or more monofilament
fabrics can be wound about the roll 50, with two fabric sheets 20
being shown in FIG. 4.
[0028] After heat setting, the monofilament fabric can be further
processed according to the intended use. The mesh can be spliced or
cut into the necessary length/shape, and include necessary edge
materials, such as described above in FIG. 1. In some embodiments
of this invention, coating materials can be applied to the
monofilaments or the heat set mesh, such as a silicon,
fluoropolymer and/or fluoroelastomer (e.g., PFA, MFA, PTFE, or FEP)
coating to provide further non-stick properties. Other exemplary
coatings include quartz or silicone polyesters to provide release
properties. The coating materials can be applied as additives in
the monofilament material, and/or applied before or after the heat
treatment, such as by spray coating, dipping, curtain coating,
and/or roller coating, and then cured as needed.
[0029] The monofilament fabric/mesh of this invention is useful in
forming many articles for use. In embodiments of this invention,
the monofilament fabric can be formed into conveyor belts, such as
shown in FIG. 5. The fabric can be cut and spliced to form endless
belt 60, that when assembled around rollers 62 can convey objects
64. As shown in FIGS. 6 and 7, the opposing longitudinal ends and
edges of the belt can include an edge material strip 66, such as
formed of a thermoplastic or silicone material. The ends 65 of the
belt 60 can includes an attachment mechanism for connecting the
opposing ends together, such as with an overlapping and connected
ends, a male to female connection mechanism, the lacing 68 shown in
FIG. 6, or the alternative spiral lacing 70 shown in FIG. 7.
[0030] In addition to an endless belt, the monofilament fabric/mesh
can be cut and edged as needed to form a sheet, tray, or other
fabricated part. FIG. 8 illustrates a representative sheet or tray
80, useful as a food support made from the substrate of this
invention. The food support 80 is formed from the substrate of this
invention, and includes a mesh fabric 82, with an edge material 84
covering all four sides. Various shapes and configuration are
available for food support, such as a flat sheet or with raised
`basket` edges as shown in FIG. 8.
[0031] The food support 80, which can be formed, for example, as a
cooking basket/tray or a planar cooking sheet, and is useful for
placing and removing food items from, and holding food items while
in, an oven. The food support of this invention is desirably
durable for multiple heating cycles, high temperature and water/oil
resistant, easy to clean, stain resistant, and dissipates heat
quickly; all while desirably not having any or much effect on the
cooking of food. The food support can include a tight weave as a
more solid bottom substrate sheet, such as to prevent liquids from
dripping on heating elements, or a more open mesh substrate sheet
to allow hot air through. The thickness of the substrate and/or the
size of the mesh openings provide the ability to cook different
food items and provide, for example, the desired food browning,
toasting and/or heating characteristics.
[0032] The temperature-resistant materials of this invention are
also non-absorbent, non-wicking, and resistant to chemicals, steam,
and wet conditions, thereby making them particularly useful in
numerous applications. Exemplary uses for the belting or other
articles made according to this invention include, without
limitation, food processing (drying, cooking (oven or microwave)),
washing and/or drying of parts or materials (e.g., cans, plant
materials (hemp, tobacco, etc.)), yarn bulking/heat setting,
high-temperature insulation manufacture, non-woven manufacture,
textile drying/shrinking/lamination, screen printing, industrial
microwave/RF application, dehydration/drying, bacon cooking,
doughnut and corn dog production, pasta belting and pasta screen,
extruding corn puffs, and manufacturing pet food.
[0033] FIG. 9 illustrates one exemplary use of the fabric/mesh
according to this invention as a conveyor belt 92 in a can, or
other article, washing and drying apparatus 90. The conveyor belt
92 carries cans 95 through a washing device 94 and then through a
drying device 96, such as a hot air dryer or oven. The high
temperature substrate of this invention is particularly useful in
such part washing and/or drying, particularly due its
non-absorbent, preshrunk properties.
[0034] FIG. 10 illustrates one exemplary use of the fabric/mesh
according to this invention as a conveyor belt 102 in a deep frying
apparatus 100. The conveyor belt 102 carries food items (not shown)
through a deep fryer 104 filled with oil and then through any
downstream device for further cooking or application of additional
ingredients (e.g., toppings). The high temperature substrate of
this invention is particularly useful in deep frying, or other
submersed or liquid-based cooking processes (e.g., water boiling),
due its non-absorbent, preshrunk properties.
[0035] FIG. 11 illustrates one exemplary use of the fabric/mesh
according to this invention as a counterband 112 in a yarn
production or treatment apparatus 110. Exemplary treatment
apparatuses include heat setting or bulking machines available from
Superba SAS (Mulhouse, France) and/or Spindelfabrik Suessen GmbH
(Sussen, Germany). The counterband 112 extends around rollers 114
and between pinch rollers 116, and holds a bundle of yarn against
the conveyor belt 118, which also can be formed of the substrate of
this invention, as the bundle of yarn is treated with the oven 115.
Traditional counterbands are formed from woven textile webbing. The
monofilament fabric of this invention is particularly useful as a
counterband due to resistance of the operating temperature of the
oven 115. In addition, the monofilament fabric will not absorb any
moisture from the heated fluid 117, such as steam, within the oven
115.
[0036] The counterband holds a bundle of yarn in place as the
conveyor carries it through the oven and any yarn cooler. There are
several places and mechanisms by which the yarn can become
displaced or snagged, which reduces the production efficiency of
the entire system. At each end of a steam chamber of the heat
setting oven, there is a set of pinch rollers 116 that squeeze the
yarn between the counterband 112 and the conveyor belt 118. The
rollers 116 substantially seal the chamber at both ends, preventing
the pressurized steam from escaping. As the rollers are constantly
exposed to the steam and moisture, the counterband also keep the
yarn from sticking to the rollers 116.
[0037] The monofilament fabrics of this invention can also be
thermoformed (i.e., heat pressed) into shaped articles. Due to the
temperature resistance, microwave safe, and non-stick capabilities,
the monofilament materials are particular suitable for use in or
forming cookware or bakeware. Exemplary thermoformed articles
include, without limitation, cooking sheets, bread pans, and trays
and baskets, particularly for use in high speed ovens.
[0038] The present invention is described in further detail in
connection with the following examples which illustrate or simulate
various aspects involved in the practice of the invention. It is to
be understood that all changes that come within the spirit of the
invention are desired to be protected and thus the invention is not
to be construed as limited by these examples.
Examples
[0039] As a control, a fabric material was heat processed using
conventional methods of running the material in a tenter frame
through an infrared oven set to 210.degree. C. (410.degree. F.),
such that the filament/yarn in the fabric did not reach the actual
oven set-point temperature. This process was then followed by the
material being calendared at 220.degree. C. (428.degree. F.) using
a heated steel two roll calendar. A piece of this material
10''.times.218.5'' was then placed into a conventional oven set at
220.degree. C. (428.degree. F.) for 8 hours to simulate use. The
material was a dull yellow in color after processing. When removed
and measured, the material lost 3.75% in the width and 4.75% in the
length and the material had changed color to a dull amber
color.
[0040] Another piece of fabric 11.875''.times.1142'' that went
through the heat setting and calendaring process above was rolled
up a layer of PTFE coated fiberglass fabric between each layer of
PPS monofilament fabric like displayed in FIG. 4. This roll was
tightened so that the roll could not move during processing and
then the outside of the roll was wrapped completely with fiberglass
tape and placed into a conventional hot air oven at 220.degree. C.
(428.degree. F.) for 8 hours. After removing from the oven and
measured. The roll lost 0.1% in length and 3.75% in the width for
the first three wraps of the material (about 120'') and 0% in width
the remaining length of the roll (or 1020''), and the material had
a dull amber color. A piece of this heat-stabilized material
according to this invention was then put in the oven unsupported,
without any tension, for 8 hours at 220.degree. C. (428.degree.
F.). This material lost 0% in width and 0% in length, indicating
that the material was fully heat stabilized so it can be processed
without tension.
[0041] Thus, the invention provides a non-absorbent polymer fabric
substrate having many uses in heated and/or wet environments. By
heat setting the polymer fabric of the substrate at a temperature
above the intended use temperature, the substrate is preshrunk and
stabilized for belting applications at higher temperatures than
generally thought.
[0042] The invention illustratively disclosed herein suitably may
be practiced in the absence of any element, part, step, component,
or ingredient which is not specifically disclosed herein.
[0043] While in the foregoing detailed description this invention
has been described in relation to certain preferred embodiments
thereof, and many details have been set forth for purposes of
illustration, it will be apparent to those skilled in the art that
the invention is susceptible to additional embodiments and that
certain of the details described herein can be varied considerably
without departing from the basic principles of the invention.
* * * * *