U.S. patent application number 17/158249 was filed with the patent office on 2021-07-29 for thin-walled tube heater for fluid.
The applicant listed for this patent is LEXMARK INTERNATIONAL, INC.. Invention is credited to MAKOTO AOKI, JERRY WAYNE SMITH.
Application Number | 20210231345 17/158249 |
Document ID | / |
Family ID | 1000005416161 |
Filed Date | 2021-07-29 |
United States Patent
Application |
20210231345 |
Kind Code |
A1 |
SMITH; JERRY WAYNE ; et
al. |
July 29, 2021 |
THIN-WALLED TUBE HEATER FOR FLUID
Abstract
A tube heater for heating a fluid in an interior of the tube has
a stainless steel cylindrical core. The core ranges about 3 to 300
mm in length and about 100 to 200 microns in thickness with an
outer diameter of about 8 to 20 mm. An inner surface of the core
has dimples and a conductive coating. A patterned resistive layer
overlies the core in a thickness of about 9 to 15 microns. The
resistive layer is thin- or thick-film printed about a
circumference of the core. Two glass layers surround the resistive
layer. Each glass layer is electrically insulative. The glass
underlying the resistive layer has a thermal conductivity of more
than 2 W/mK while the glass overlying the resistive layer has a
thermal conductivity of less than or equal to 0.5 W/mK.
Inventors: |
SMITH; JERRY WAYNE; (IRVINE,
KY) ; AOKI; MAKOTO; (ISHIKAWA, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LEXMARK INTERNATIONAL, INC. |
Lexington |
KY |
US |
|
|
Family ID: |
1000005416161 |
Appl. No.: |
17/158249 |
Filed: |
January 26, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62966083 |
Jan 27, 2020 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B32B 2311/30 20130101;
F24H 3/002 20130101; F24H 9/1827 20130101; B32B 2311/09 20130101;
F24H 2250/02 20130101; B32B 2307/302 20130101; F24H 9/1872
20130101; F24H 1/142 20130101; B32B 2307/304 20130101; B32B 2250/04
20130101; B32B 15/017 20130101; F24H 1/102 20130101; B32B 2315/08
20130101; B32B 2311/24 20130101 |
International
Class: |
F24H 1/14 20060101
F24H001/14; F24H 3/00 20060101 F24H003/00; F24H 1/10 20060101
F24H001/10; F24H 9/18 20060101 F24H009/18 |
Claims
1. A tube heater for heating a fluid, comprising: a core in a shape
of a cylinder, the cylinder defining an inlet and outlet for the
fluid; a first glass layer on the core, the first glass layer being
in a range of about 40 to 50 microns thick; a patterned resistive
layer on the first glass layer, the resistive layer being disposed
about a circumferential surface of the core and formed of a
composition of silver and palladium or platinum and being in range
of about 9 to 15 microns thick; and a second glass layer on the
patterned resistive layer, the second glass layer having a thermal
conductivity lower than a thermal conductivity of the first glass
layer and being in a range of about 45 to 80 microns thick.
2. The tube heater of claim 1, wherein an inner surface of the core
has pluralities of dimples.
3. The tube heater of claim 1, wherein an inner surface of the core
is coated with aluminum.
4. The tube heater of claim 1, further including at least one
thermistor on the core.
5. The tube heater of claim 1, wherein the core is stainless
steel.
6. The tube heater of claim 1, wherein the stainless steel is 430
grade.
7. The tube heater of claim 1, wherein the core is 100 to 200
microns thick and has a length ranging from 3 to 300 mm.
8. The tube heater of claim 1, wherein the first glass layer has a
thermal conductivity of over 2 W/mK.
9. The tube heater of claim 1, wherein the second glass layer has a
thermal conductivity less than or equal to 0.5 W/mK.
10. The tube heater of claim 1, wherein the silver content is about
80% and the palladium is about 20% of the composition by
weight.
11. The tube heater of claim 1, wherein the silver content is about
60% and the palladium is about 40% of the composition by
weight.
12. A tube heater for heating a fluid, comprising: a stainless
steel cylindrical core; a first glass layer on the core, the first
glass layer being electrically insulative and having a thermal
conductivity of more than 2 W/mK; a patterned resistive layer on
the first glass layer, the resistive layer being circumferential
about a surface of the core; and a second glass layer on the
patterned resistive layer, the second glass layer being
electrically insulative and having a thermal conductivity of less
than or equal to 0.5 W/mK.
13. The tube heater of claim 12, wherein the first glass layer
contains conductive filler particles of aluminum oxide, aluminum
nitride, or boron nitride.
14. The tube heater of claim 12, wherein the resistive layer has a
thickness in a range of about 9 to 15 microns.
15. The tube heater of claim 12, wherein the first glass layer has
a thickness in a range of about 40 to 50 microns.
16. The tube heater of claim 12, wherein the second glass layer has
a thickness in a range of about 45 to 80 microns.
17. The tube heater of claim 12, wherein the stainless steel
cylindrical core has a thickness in a range of about 100 to 200
microns, an outer diameter of the stainless steel cylindrical core
being in a range of about 8 to 20 mm.
18. The tube heater of claim 12, wherein the stainless cylindrical
core has a length in a range from about 3 to 300 mm.
19. The tube heater of claim 12, wherein the stainless cylindrical
core has an inner surface with dimples, the dimples being coated
with aluminum.
20. A tube heater for heating a fluid, comprising: a stainless
steel cylindrical core having a thickness ranging from about 100 to
200 microns and a length ranging from about 3 to 300 mm and further
having an inner surface with dimples, the dimples being coated with
a conductor; a first glass layer on the core, the first glass layer
being electrically insulative and having a thermal conductivity of
more than 2 W/mK, the first glass layer including conductive filler
particles and having a thickness ranging from about 40 to 50
microns; a patterned resistive layer on the first glass layer, the
resistive layer being serpentine about a circumferential surface of
the core and having a composition of silver and palladium or
platinum, the resistive layer having a thickness ranging from about
9 to 15 microns; and a second glass layer on the patterned
resistive layer, the second glass layer being electrically
insulative and having a thermal conductivity of less than or equal
to 0.5 W/mK, the second glass layer having a thickness ranging from
about 45 to 80 microns.
Description
[0001] This utility application claims priority from U.S.
Provisional Application Ser. No. 62/966,083, filed Jan. 27, 2020,
whose entire contents are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present disclosure relates to a tube heater for a
variety of uses. It relates further to a relatively thin-walled
tube that heats fluid such as gas and liquid when the fluid passes
through the interior of the tube. The tube defines a base
composition or core having a circumferentially thin- or thick-film
printed resistive layer thereon, including electrically insulative
glass layers about the resistive layer one with relatively high and
one with relatively low thermal conductivity.
BACKGROUND
[0003] Tube heaters have many and diverse applications for heating
fluid. Large numbers in the marketplace today, however, suffer slow
warm-up times and have safety issues depending upon use. Typical
tubes consist of ceramics (e.g., aluminum oxide) or metal (e.g.,
aluminum or stainless steel) that become thick-film printed with a
resistive material that serves as a heating element. The tubes are
also generally very thick, greater than 1 mm, which limits the
speed of thermal transfer from the heating element to the interior
of the tube. When metal, an insulating layer of glass exists
between the tube and heating element, but typically such has a low
thermal conductivity of less than 1 W/mK further slowing the rate
of thermal transfer from the heater element to the fluid. A
compromise does exist, though, whereby the thickness of the glass
is thinned so that the high potential operating voltage is lowered
to approximately twice the operating voltage of the tube heater,
e.g., the high potential is set at 440V for a tube heater rated at
an operating voltage of 220V. This approach, unfortunately, has an
ability to compromise safety. The inventors, thusly, identify a
need to overcome these and other problems. The inventors further
note that any solutions in the technology of tube heaters should
further contemplate the competing design constraints found in power
consumption, safety features, warm-up characteristics, operating
temperatures, heating speeds, thermal conductivity, materials,
costs, electrical requirements, construction, materials
to-be-heated, temperature control, installation/integration with
other components, size, shape, and dimensions, and the like.
SUMMARY
[0004] A tube heater for heating a fluid in an interior of the tube
has a stainless steel cylindrical core. The core ranges about 3 to
300 mm in length and about 100 to 200 microns in thickness with an
outer diameter of about 8 to 20 mm. An inner surface of the core
has dimples to increase surface area and a conductive coating, such
as aluminum, to improve thermal transfer. A conductive mesh, such
as aluminum, copper, or brass, can be also placed in contact with
the inner surface to improve thermal transfer. Overlying the core
is a heater in the form of a patterned resistive layer in a
thickness of about 9 to 15 microns. The resistive layer is thin- or
thick-film printed about a circumference of the core. A conductor
layer connects ends of the resistive layer to form a serpentine
path about the core and provide a means to connect the resistive
layer to power for heating during use. Two glass layers surround
the resistive layer. Each glass layer is electrically insulative.
The glass underlying the resistive layer has a thermal conductivity
of more than 2 W/mK. The glass overlying layer it has a thermal
conductivity of less than or equal to 0.5 W/mK.
[0005] As a result, the glass thickness of the underlying layer
need not be made too thin, thus improving safety, yet matching
heating rates of modern tube heaters. The overlying layer prevents
heat loss of the tube heater. Various filler particles may also
accompany the glass, such as thermally conductive filler particles
like aluminum oxide to maintain a coefficient of thermal expansion
in the underlying layer that closely matches the materials of the
resistive layer, conductor layer, and tube. It is noted that a tube
heater of the foregoing type greatly improves over the art the rate
of heat transfer to the fluid from the resistive layer. Various
embodiments teach the material compositions and relative dimensions
of the tube and layers and the process conditions for the
manufacture thereof.
[0006] One or more thermistors attach to the core on either a
proximal or distal end or both. The thermistor(s) provide closed
loop thermal control of the heater. A representative technique to
attach the thermistor(s) to the core includes directly welding the
lead frame legs of the thermistor lead frame to the core or any
conductors thereof.
BRIEF DESCRIPTION OF THE FIGURES
[0007] FIG. 1 is a tube heater according to a representative
embodiment of the present invention;
[0008] FIGS. 2A-2J are diagrammatic views of a representative
sequence of creating a tube and preparing it to become a tube
heater;
[0009] FIGS. 3A-3F are diagrammatic views of a representative
sequence for layering a glass when forming a tube heater;
[0010] FIGS. 4A-4F are diagrammatic views of a representative
sequence of patterning a resistive layer when forming a tube
heater, including a conductor layer; and
[0011] FIG. 5 is a graph of a representative heating profile of a
heating unit according to embodiments of the invention.
DETAILED DESCRIPTION
[0012] FIG. 1 teaches a tube heater 10 for a variety of uses,
especially heating a fluid flowing through an interior 12 thereof.
The fluid comprises liquids or gases. Water and air are common. The
tube heater has a variety of applications. It is envisioned the
tube heater will find utility in kitchen appliances, such as
dishwashers, coffee makers, washing machines, and like appliances
requiring hot air or water. Appliances currently using reservoirs
to hold water for pre-heating will find particular advantage using
the tube heater herein as fluid can be heated on-demand. The tube
heater gives rise to further utility in on-demand water heaters and
kitchen faucet usage. Heating of air in the tube heater also allows
for direct or auxiliary heating, e.g., for a heat pump in an HVAC
system. Rather than requiring a centralized heating source, which
suffers significant heating loss when moving air from a centralized
heater to points of usage, the tube heater herein can be used
on-demand as needed in residential and commercial buildings or
similar environments. It is even envisioned that the tube heater
can be placed over existing tubes and heat water, such as a tube
heater 10 that heats water flowing through existing copper water
pipes placed in the interior 12.
[0013] As will be seen, the tube heater 10 utilizes a material set
in a manner to overcome the problems of the prior art having
inefficient warm-up times and/or safety issues. At its essence, the
tube heater 10 includes a variety of layers, such as glass 16, 18,
resistive traces 20, and conductors 22 on a core 14. The core
typifies a metal or metal composition with stainless steel grade
430 being a preferred instance. Typical properties of grade 430
include, but are not limited to: thermal conductivity of about 26
W/mK; tensile strength greater than 500 MPa; melting temperature in
a range of 1425.degree. to 1510.degree. C.; and a coefficient of
thermal expansion equal to 5.7.times.10.sup.-6. As such, stainless
steel grade 430 can be deep drawn to form a very thin tube, e.g.,
having a wall thickness as low as 35 microns at a seamless tube
length of at least 300 mm. The steel is also known for having good
corrosion resistance and formability. Grade 430 stainless steel is
usually provided in bar form.
[0014] The core used herein is also relative thin compared to known
tube heaters and has an outer diameter (o.d.) ranging from about 8
to 20 mm. Its inner diameter ranges such that a thickness of the
core from the inner diameter to its outer diameter is less than
1000 microns, with 100 to 200 microns being optimal. A length (l)
of the core ranges variously, but about 3 to 300 mm has been
prototyped and is representative. On an inner surface 30 of the
core is one or more dimples 32 to increase the surface area of the
core. The dimples are optionally coated with a conductor, such as
aluminum, to improve heat transfer into the interior 12. The
construction of the core, its dimples and coating will be described
below in relation to the process of preparing the core for its
overlying layers for use as a tube heater. One or more thermistors
40 may be also configured with the core to provide a relative
temperature. The thermistors may be attached by welding. Also, in
instances where the stainless steel core has a wall thickness less
than about 750 microns, the tube should be processed for layering
with an inside rod or mandrel during the printing, drying (e.g.
80.degree. C. for approximately 10 minutes), and firing (e.g., ramp
up from room temperature to over 800.degree. C. for at least 10
minutes and controlled cooling back to room temperature--about a 1
hour cycle) process steps.
[0015] With continued reference to FIG. 1, and the processes of
manufacture in FIGS. 2A-2J, the core begins as a blank 50 (FIG. 2A)
of raw material, such as stainless steel. The blank is set in a
deep-draw configuration including a die 52 for supporting the
blank. A punch 54 is supported by a punch holder 56 and moves in a
direction (A) toward the blank to deep draw a cylindrical shape of
the core. For longer tubes, however, spinning the tubes takes place
with outside rollers with support on the inside of the tubes with a
rod (not shown). The spinning process thins and lengthens the tube,
as in the case of deep drawing. As seen in FIG. 2B, the punch 54
travels into an interior of the blank as the punch holder and die
are brought closer together which results in an intermediate
configuration 60 of the core having a longitudinal extent in the
direction of movement of the punch. In FIG. 2C, excess material 64
is excised 65 from the configuration 60 as is a closed end 66 cut
open along 67 to result in a core in FIG. 2D having a cylindrical
or tube shape 70 with open ends 72, 74. At FIG. 2E, the tube is
cleaned 80 with cleanser and fluid and/or polished 82 to finish the
inner and outer surfaces 30, 31 of the tube.
[0016] At FIG. 2F, one open end 74 of the tube 70 is closed with a
cover 83 and the interior 12 of the tube is filled 85 with various
sized balls 86. The other open end 72 is closed with another cover
87 to seal inside the balls 86 in the interior of the tube. As in
FIG. 2G, the tube is agitated 90, such as by spinning or shaking so
that the balls in the interior impact the inner surface of the tube
and create a variety of dimples 32 in the inner surface 30 as seen
in FIG. 2H. Of course, the dimples could be of any size and be
varied or uniform. The balls used to create the dimpling are
ceramic, such as aluminum oxide, or metal, such as stainless steel.
In either, the interior 12 of the tube is (optionally) next
arc-sprayed 90 with a conductor 92 to coat the dimples 32 and inner
surface 30 with a conductive coating as seen in FIG. 2I. The
conductor can be aluminum, for example. The core is thusly prepared
and ready for layering, such as by thick- and thin-film printing.
At FIG. 2J, a conductive mesh 90, such as aluminum, copper, or mesh
can be optionally placed into contact with the inner surface to
improve heat transfer to the fluid flowing through the tube heater
during use.
[0017] With further reference to FIG. 1, and the processes of FIGS.
3A-3F, glass is next layered on the core 14. The glass is any of a
variety, but typically defines a glass having a viscosity of 100
Pas or less. More particularly, the viscosity exists at 90 Pas or
less, especially 65 Pas or less. Its solid content, on the other
hand, exists at 65% or more. In various specific embodiments, the
glass is purchased commercially from AGC, Inc. (formerly the Asahi
Glass Company). A representative glass from AGC is identified
commercially as AGC Class Sato 31H. Importantly, the glass is also
electrically insulative and has a thermal conductivity of 2 W/mK or
greater. As such, heat transfers effectively through the glass from
the resistive trace but does not electrically short the core to the
trace. The glass is also layered to a thickness of about 40 to 50
microns. Conductive filler materials may reside in the glass to
enhance thermal conductivity. These include, but are not limited,
to metals and nitrides or oxides thereof, such as aluminum,
aluminum oxide, or aluminum nitride or, alternatively, boron
nitride. Such a filler maintains a coefficient of thermal expansion
closely matching the resistive traces, conductor, and core
materials of the tube heater.
[0018] The general process steps for layering the glass, or any of
the layers, includes one or more of thick- or thin-film printing
and instances of settling, drying, and firing or heating the layer
so printed. As shorthand from the industry, the steps are generally
known as print, dry, and fire, or PDF. In more detail, FIG. 3A
shows a core 14 being provided after one or more of the process of
FIGS. 2A-2J. A glass paste 100 is next deposited over a mesh
stencil 102. In FIG. 3B, a leveling device 104, such as a squeegee
or other scraper, levels the paste on a surface of the stencil upon
passing the device from position 104a to 104b. In FIG. 3C, the
paste falls 120 through the mesh of the stencil in a direction of
the arrows (B). In FIG. 3D, the glass paste 100 comes to contact an
exterior surface 130 of the core 14. As the paste contacts the
surface circumferentially, the torque from the paste allows the
core 14 to rotate by gravity in the direction of the arrow (C). The
core is mounted on spindles (not shown) or other such device
enabling the rotation. Alternatively, FIG. 3D' shows the core 14
attached to a motor 140 that rotates the core in the direction of
the arrow (C) upon the paste contacting the surface 130. In either
embodiment, the rate of rotation of the core 14 matches a rate of
falling of the paste from the stencil. Eventually, an entirety of
the circumferences of the core is coated with the glass paste
forming glass layer 18 on the core 14 as seen in FIG. 3E. The glass
is then allowed to settle and dry at room temperature e.g.,
20.degree.-25.degree. C. for about 5 to 30 minutes followed by
drying at about 80.degree. to 120.degree. C. (100.degree. C.,
typical) for about 30 to 60 minutes. In FIG. 3F, the core and glass
layer 18 are provided to a curing or drying unit 150 for
application of heat 151. The drying unit typifies a box oven or
blast furnace and the core is provided to the unit along a
conveyor, typically.
[0019] The drying unit begins drying the glass layer 18 at around
room temperature followed by a curing or drying cycle of about 30
minutes reaching peak temperatures of about 800.degree. to
830.degree. C. for about 5 minutes around the halfway mark of the
drying cycle. In one embodiment, the drying cycle includes applying
infrared heat or hot air (both given generically as heat 151).
Thereafter, the core and glass layer is removed from the drying
unit. Both are allowed to settle at room temperature.
[0020] With continued reference to FIG. 1, and the processes of
FIGS. 4A-4F, resistive traces are next applied to the
circumferential surface of the core on top of the glass layer 18.
In FIG. 4A, the resistive traces 20 result from first providing a
resistive paste 160 to a mesh stencil 162. The stencil may be
patterned to a width and length matching the width and length of
the traces. Next, the paste 160 is leveled through the stencil with
a leveling device 64 moving from positions 64a to 64b in FIG. 4B.
The resistive paste is then allowed to fall through the stencil at
168. Similar to the instances of rotating the core in FIG. 3D or
3D', the core 14 rotates and the resistive traces 20 are patterned
on the core 14 on top of the glass layer 18. A representative
pattern of the traces is a plurality of longitudinally extending
traces paralleling one another about an entire circumference of the
core. Their width and length is variable depending upon the
dimensions of the core. In FIG. 4C, the resistive traces 20 are
dried at room temperature for a period of time from about 5 to 30
minutes and dried at about 80.degree. to 120.degree. C.
(100.degree. C., typical) for about 30 to 60 minutes. The traces
are next fired with heat 151 in the heating unit 150. The traces
are heated for about 30 minutes with a peak temperature of about
850.degree. C. for about 5 minutes. The heating unit may also fire
with a heating profile for at least 40 total minutes starting at
about 25.degree. C. and ramping up to 850.degree. C. by 20 minutes
and maintaining 850.degree. C. for at least 10 minutes and
decreasing the temperature for at least 10 minutes. In any profile,
the traces settle for a period of time ranging up to one hour upon
removal from the heating unit.
[0021] With reference to FIG. 4E, without showing the instances of
printing, drying and firing, conductors 180 are applied to the core
140 and interconnect the terminal ends 181, 183 of the
longitudinally-extending resistive traces 20. The result is a
serpentine pattern about the circumference of the core. During use,
the conductor at 180' receives power from an external voltage
source to power the resistive trace 20. In turn, the resistive
trace heats and provides heating to the tube heater to heat fluid
in the interior of the tube. In dimensions, the thickness of the
resistive trace is about 9 to 15 microns and has a length that
varies according to the length of the core, but typically resides
at about 50% to 90% of the length of the core. A width of each
trace 20 ranges about 0.5 to 1 micron. Also, the resistive trace
has a resistance of about 10-12 ohms at 195.degree. C. The
resistive trace is formed in a layer from the resistor paste
comprised of silver and palladium or platinum as is the conductor
formed from a conductive paste comprised of silver and palladium or
platinum. In one embodiment, the resistor paste includes content of
about 60% to 80% silver with the balance (other than impurities)
being made up by the palladium or platinum. Also, skilled artisans
will note that the process steps for layering the resistive traces
followed by the conductors could be reversed.
[0022] In FIG. 4F, a second glass layer 16 is applied over the
resistive traces and conductors. It is applied in a thickness of
about 45 to 80 microns. Unlike the glass underlying the resistive
traces, however, the second glass of the second glass layer has a
thermal conductivity in a much lower range of less than or equal to
0.5 W/mK. In process steps similar to layering the layer of glass
18 underlying the resistive layer, the glass overlying the
resistive layer is similarly applied. One or more thermistors 40
may be also welded to the core 14 at a distal or proximate end of
the tube heater. They are positioned to measure the temperature of
the resistive traces and the conductor connects the thermistors to
external sources (not shown) to measure, store and control the
temperature of the tube heater. The thermistors are preferably
resistance welded.
[0023] With reference to FIG. 5, a representative firing or heating
profile for any layer is shown in graph 200. Namely. the heating
profile for a resistive or conductive layer is shown by the solid
line 202, whereas a dashed line 204 depicts the heating profile for
layering a glass. In general, the heating profile of the heating
unit includes a total heating time of about 40 total minutes
starting at about 25.degree. C. and ramping up to a peak
temperature (part of zones 5-8) by 20 minutes and maintaining the
peak temperature for at least 10 minutes and decreasing the
temperature of the heating unit (post zone 8) for at least 10
minutes thereafter. Cooling continues even further thereafter (post
zone 12) until completely cooled. For the resistive or conductive
layers, the peak temperature reaches about 850.degree. C. The glass
layers, on the other hand, have a peak temperature in a range from
800.degree. to 830.degree. C.
[0024] Without reference to any Figure, once the tube heater is
formed, the resistive trace of the becomes tested under voltage
conditions of 1.75 KVAC applied to the conductor layer. Resistance
of the trace is tested cold at room temperature and upon heating to
about 200.degree. C. Its resistance is about 10 ohms at room
temperature and about 11 ohms upon heating with a variance of about
+/-2 ohms.
[0025] Advantages should be now readily apparent to those skilled
in the art. Among them, a thin walled, deep drawn stainless tube
serves as a core for a tube heater. Its wall thickness is multiple
times thinner than anything known by the inventors. The first layer
of glass on the core is a di-electric glass developed specifically
for higher thermal conductivity while maintaining high di-electric
strength for electrical resistivity. The second layer of glass or
cover glass is developed for improved thermal insulation in order
to reduce thermal losses in the tube heater. Such design improves
safety over the state of the art and minimizes heat loss between
the resistive trace and the fluid, thereby increasing the heating
efficiency of the tube heater.
[0026] The foregoing description of several structures and methods
of making the same has been presented for purposes of illustration.
It is not intended to be exhaustive or to limit the claims.
Modifications and variations to the description are possible in
accordance with the foregoing. It is intended that the scope of the
invention be defined by the claims appended hereto.
* * * * *