U.S. patent application number 10/445717 was filed with the patent office on 2004-12-02 for processing copper-magnesium alloys and improved copper alloy wire.
Invention is credited to Saleh, Joseph.
Application Number | 20040238086 10/445717 |
Document ID | / |
Family ID | 33131547 |
Filed Date | 2004-12-02 |
United States Patent
Application |
20040238086 |
Kind Code |
A1 |
Saleh, Joseph |
December 2, 2004 |
Processing copper-magnesium alloys and improved copper alloy
wire
Abstract
In accordance with the present invention, a copper alloy wire
having high strength and high conductivity is provided. The copper
alloy wire is formed from a copper base alloy containing from 0.05
to 0.9 wt % magnesium and more than 15 ppm impurities in total. The
wire has a single end diameter no greater than 0.10 inches, a
tensile strength of at least 100 ksi, and an electrical
conductivity greater than 60% IACS. A process for producing the
copper wire of the present invention is also described.
Inventors: |
Saleh, Joseph; (Morristown,
NJ) |
Correspondence
Address: |
BACHMAN & LAPOINTE, P.C.
900 CHAPEL STREET
SUITE 1201
NEW HAVEN
CT
06510
US
|
Family ID: |
33131547 |
Appl. No.: |
10/445717 |
Filed: |
May 27, 2003 |
Current U.S.
Class: |
148/684 ;
420/494 |
Current CPC
Class: |
C22C 9/00 20130101; C22F
1/08 20130101 |
Class at
Publication: |
148/684 ;
420/494 |
International
Class: |
C22F 001/08; C22C
009/00 |
Claims
What is claimed is:
1. A copper alloy wire having high strength and high conductivity
which comprises a copper alloy containing from 0.05 to 0.9 wt %
magnesium and more than 15 ppm impurities in total, said wire
having a single end diameter less than 0.010 inches, a tensile
strength of at least 100 ksi, and an electrical conductivity
greater than 60% IACS.
2. A copper alloy wire according to claim 1, wherein said tensile
strength is at least 110 ksi.
3. A copper alloy wire according to claim 1, wherein said
electrical conductivity is greater than 70% IACS.
4. A copper alloy wire according to claim 1, wherein said copper
alloy also contains from 0.01 to 0.3 wt % phosphorous.
5. A copper alloy wire according to claim 4, wherein said
phosphorous is present in an amount from 0.01 to 0.15 wt % and said
magnesium is present in an amount from 0.1 to 0.4 wt %.
6. A copper alloy wire according to claim 4, wherein a majority of
particles of said phosphorous are submicron in size.
7. A copper alloy wire according to claim 1, wherein said copper
alloy also contains at least one additional constituent selected
from the group consisting of from 0.01 to 1.0 wt % iron, from 0.01
to 0.5 wt % nickel, from 0.01 to 0.3 wt % phosphorous, from 0.01 to
0.2 wt % silver, from 0.01 to 0.2 wt % tin, and from 0.01 to 0.5 wt
% zinc.
8. A copper alloy wire according to claim 7, wherein said at least
one additional constituent includes iron in an amount from 0.01 to
0.5 wt %.
9. A copper alloy wire according to claim 7, wherein said at least
one additional constituent includes tin in an amount from 0.01 to
0.1 wt %.
10. A copper alloy wire according to claim 7, wherein said at least
one additional constituent includes phosphorous in an amount from
0.02 to 0.15 wt %.
11. A copper alloy wire according to claim 1, wherein said wire is
in a restructuring annealed and cold worked condition.
12. A copper alloy wire according to claim 1, wherein said single
end diameter is greater than 0.002 inches.
13. A copper alloy having high strength and high conductivity which
comprises a copper alloy consisting of from 0.05 to 0.9 wt %
magnesium, 0.01 to 0.3 wt % phosphorous, and the balance copper and
more than 15 ppm impurities in total, said wire having a single end
diameter no greater than 0.010 inches, a tensile strength of at
least 100 ksi, and an electrical conductivity greater than 70%
IACS.
14. A copper alloy according to claim 13, wherein said phosphorous
content is in the range of from 0.01 to 0.15 wt %, and said tensile
strength is at least 110 ksi.
15. A copper alloy wire having high strength and high conductivity
which comprises a copper alloy consisting of from 0.05 to 0.9 wt %
magnesium, at least one constituent selected from the group
consisting of from 0.01 to 1.0 wt % iron, from 0.01 to 0.5 wt %
nickel, from 0.01 to 0.3 wt % phosphorous, from 0.01 to 0.2 wt %
silver, from 0.01 to 0.2 wt % tin, and from 0.01 to 0.5 wt % zinc,
and the balance copper and more than 15 ppm impurities in total,
said wire having a single end diameter no greater than 0.010
inches, a tensile strength of at least 100 ksi, and an electrical
conductivity greater than 70% IACS.
16. A process for manufacturing a copper alloy wire having high
strength and high conductivity comprising the steps of: providing a
base material formed from a copper alloy containing from 0.05 to
0.9 wt % magnesium and more than 15 ppm impurities in total; cold
working said base material into a wire having at least a 40%
reduction in original cross section area; performing a
restructuring anneal after said cold working step; and cold working
said annealed material into a wire having a final gage of no
greater than 0.010 inches.
17. A process according to claim 16, wherein said restructuring
anneal is performed after said base material has been cold worked
into a wire having at least a 70% reduction in said original cross
section area.
18. A process according to claim 16, wherein said restructuring
anneal is performed at a temperature in the range of 650 to
1050.degree. F. for a time period in the range of 1 to 5 hours.
19. A process according to claim 18, wherein said restructuring
anneal is performed at a temperature in the range of 750 to
900.degree. F. for a time period in the range of 2 to 3 hours.
20. A process according to claim 16, wherein said base material
providing step comprises providing material formed from a copper
alloy consisting of from 0.05 to 0.9 wt % magnesium and the balance
copper and more than 15 ppm impurities in total.
21. A process according to claim 16, wherein said base material
providing step comprises providing material formed from a copper
alloy consisting of from 0.05 to 0.9 wt % magnesium, from 0.01 to
0.3 wt % phosphorous, and the balance copper and more than 15 ppm
impurities in total.
22. A process according to claim 16, wherein said base material
providing step comprises providing material formed from a copper
alloy consisting of from 0.05 to 0.9 wt % magnesium, at least one
constituent selected from the group consisting of from 0.01 to 1.0
wt % iron, from 0.01 to 0.5 wt % nickel, from 0.01 to 0.3 wt %
phosphorous, from 0.01 to 0.2 wt % silver, from 0.01 to 0.2 wt %
tin, and from 0.01 to 0.5 wt % zinc, and the balance copper and
more than 15 ppm impurities in total.
23. A process according to claim 16, wherein said final gage cold
working step comprises cold working said annealed material into a
wire having a diameter less than 0.010 inches.
24. A non-cadmium containing copper alloy wire having high strength
and high conductivity which comprises a copper alloy containing
from 0.05 to 0.9 wt % magnesium and more than 15 ppm impurities in
total, said single end wire having a diameter no greater than 0.10
inches, a tensile strength of at least 100 ksi, and an electrical
conductivity greater than 60% IACS.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to high strength, high
conductivity copper alloy wire and a method for manufacturing same,
wherein the copper alloy wire is a copper-magnesium based system
optionally with one or more additional elements.
[0002] Copper is the natural choice for conductor wire due to its
high electrical conductivity. High performance copper alloys are
required where the mechanical properties of copper are not
sufficient for a particular application. Thus, in addition to
electrical conductivity, these copper alloys must also meet a
combination of often conflicting properties. These properties may
include strength, ductility, softening resistance and flex life.
Indeed, ASTM B105 and B624 describe the requirements for hard drawn
and high strength, high conductivity copper alloy wire for
electrical applications.
[0003] Cadmium copper (alloy C162) is a copper alloy containing 1%
nominal cadmium with unique combination of properties. It has an
electrical conductivity greater than 80% IACS and when hard can
attain a tensile strength in excess of 100 ksi. These properties
make the alloy very useful for high strength conductor
applications, such as trolley wire or airframe wiring. In addition,
this alloy exhibits unusually long flex life as evidenced by the
number of cycles it can bend back and forth over a mandrel before
fracture. Consequently, it is used in many other high flex
conductor applications, such as those in antilock braking
harnesses, audio speaker and headset or telephone connecting
wire.
[0004] Cadmium has been known to be a health hazard and attempts
are being made to replace materials containing this element.
Cadmium appears on the list of bio-accumulative and toxic (PBT)
chemicals compiled by the Environmental Protection Agency (EPA).
The EPA considers cadmium as a possible human carcinogen. Various
proposals have been made in different countries to ban or restrict
the use of this element. Therefore it is very beneficial to provide
alternative alloys to Cu--Cd alloys.
[0005] Cu--Mg alloy base systems offer equally attractive
properties. Alloy C18661 with 0.1-0.7 percent Mg is a Cu--Mg alloy
listed by Copper Development Association (CDA). Alloy C18665 is
another listed alloy with 0.4-0.9% Mg. These alloys may also
contain a small amount of residual P which is typically used as a
de-oxidant. Although CDA does not list the applications of these
alloys, typical applications are as trolley wire or connectors.
These alloys are cast and drawn to finish size without any anneal
to obtain the highest strength possible.
[0006] It is, therefore, a principal object of the present
invention to develop a high strength, high conductivity copper
alloy and method for manufacturing same.
[0007] It is a still further object of the present invention to
develop an alloy and method as aforesaid, wherein the alloy is a
copper base alloy containing magnesium and other elements.
[0008] Further objects of the present invention will appear
hereinafter.
SUMMARY OF THE INVENTION
[0009] It has now been found that the foregoing objects can be
readily obtained in accordance with the present invention.
[0010] The present invention provides a process for manufacturing a
copper alloy wire having a high strength and high conductivity. The
process broadly comprises the steps of providing a base material
formed from a copper alloy containing from 0.05 to 0.9 wt %
magnesium and more than 15 ppm total impurities, cold working the
base material into a wire having at least a 40% reduction in
original cross section area, performing a restructuring anneal
after the cold working step, and drawing the annealed material into
a wire having a final gage size of 0.010" maximum. In a preferred
method, the magnesium content of the copper alloy is from 0.1 to
0.4 wt %.
[0011] Desirably, the restructuring annealing step is performed at
a temperature in the range of 650 to 1050.degree. F. for a time
period in the range of 1 to 5 hours, preferably 2-3 hours.
Desirably, also the copper alloy contains one or more additional
alloying ingredients, as
[0012] from 0.01-0.3 wt % phosphorous,
[0013] from 0.01-1.0 wt % iron, preferably less than 0.5 wt %
iron,
[0014] from 0.01-0.5 wt % nickel,
[0015] from 0.01-0.2 wt % silver,
[0016] from 0.01-0.2 wt % tin, and preferably less than 0.1 wt %
tin, and/or
[0017] from 0.01-0.5 wt % zinc.
[0018] The present invention also provides an improved copper alloy
wire having high strength and high conductivity which broadly
comprises a copper alloy containing from 0.05 to 0.9 wt % magnesium
and more than 15 ppm impurities, which wire has a single end
diameter less than or equal to 0.010 inches, a tensile strength of
at least 100 ksi, and an electrical conductivity greater than 60%
IACS.
[0019] Further features and advantages of the present invention
will appear hereinbelow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The present invention will be more readily understandable
from a consideration of the accompanying drawings, wherein:
[0021] FIG. 1 is a graph of tensile strength versus percent
reduction in cross sectional area for a copper-0.12% magnesium
alloy processed in accordance with the present and the same alloy
processed conventionally;
[0022] FIG. 2 is a graph similar to FIG. 1 for a copper alloy
containing 0.15% magnesium and 0.1% tin; and
[0023] FIG. 3 is a graph of tensile strength versus wire diameter
for a copper alloy containing 0.15% magnesium and 0.1% tin
processed in accordance with the present invention and the same
alloy processed conventionally.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0024] In accordance with the present invention the copper alloy
wire contains from 0.05 to 0.9 wt % magnesium, preferably from 0.1
to 0.4 wt %. Increasing the amount of magnesium will increase the
strength while reducing the electrical conductivity. This allows
the alloy to be tailored to a desired set of properties.
[0025] Additional alloying elements may be added to improve
strength or other properties of the alloy. Thus, for example,
phosphorous is an element that can be added to increase the
strength through precipitation of magnesium phosphide
(Mg.sub.3P.sub.2). The amount of phosphorus added to the alloy
should not exceed that needed to form the magnesium phosphide, or
phosphides of other elements when present. Therefore, the
phosphorus should be in an amount less than the amount of magnesium
present and generally from 0.01 to 0.3 wt % and preferably from
0.02-0.15 wt %. When phosphorous is added to form phosphide
particle, the composition, casting procedure and heat treatment
must ensure that the majority of the phosphide particles are
sub-micron size to provide high drawability and improved
performance at small wire diameters.
[0026] Iron is another beneficial element that may be added to the
alloy. For example, copper-magnesium alloys with iron and
phosphorus present will form phosphides of magnesium and iron,
which are quite beneficial. The amount of iron should vary between
0.01 to 1 wt %, and preferably less than 0.5 wt %.
[0027] Small amounts of tin are also beneficial and serve to
slightly improve the strength of the alloy. The amount of tin
should desirably vary from 0.01 to 0.2 wt % and preferably less
than 0.1 wt %. Very small amounts of tin may be considered as a
beneficial impurity. However, larger amounts of tin tend to reduce
the electrical conductivity of the alloy.
[0028] Naturally, other alloying additions and conventional
impurities greater than 15 ppm in total may be present. For
example, small amounts of silver will improve the performance of
the alloy without adversely impacting electrical conductivity.
Silver, when present, should be in the range of 0.01 to 0.2 wt %.
Other alloying additions for effecting specific objectives may
include nickel in amount from 0.01 to 0.5 wt % and/or zinc in an
amount from 0.01 to 0.5 wt %.
[0029] Thus, the present invention provides non-cadmium containing
copper alloy conductors containing magnesium which can readily be
used as a replacement for copper-cadmium alloys and in similar
applications. The processing of the copper-magnesium alloys to
desired final gage wire incorporates at least one restructuring
anneal before being drawn to the finish size wire required to
manufacture the desired conductor. The resultant wire is
characterized by a good combination of strength and conductivity,
as well as other desirable properties, such as good flex life and
resistance to thermal softening.
[0030] The copper alloy wire of the present invention may be
manufactured by the process of providing a base material formed
from a copper alloy containing from 0.05 to 0.9 wt % magnesium,
cold working the base material into a wire having at least a 40%
reduction in original cross section area, performing an anneal, and
drawing said material into a wire having a single end final gage of
0.010 inches maximum, preferably the final gage is more than 0.002
inches but less than 0.010 inches. If desired, the copper alloy may
also contain one or more of the additional elements discussed above
and the annealing step may be performed after the base material has
been cold worked into a wire having at least a 70% reduction in the
original cross section area.
[0031] The restructuring anneal may be performed at a temperature
in the range of 650 to 1050.degree. F. for a time period in the
range of 1 to 5 hours, preferably at a temperature in the range of
750 to 900.degree. F. for a time period in the range of 2 to 3
hours.
[0032] The cold working step may be performed by any suitable
technique known in the art including, but not limited to, rolling
and/or drawing.
[0033] Copper alloy wires formed in accordance with the present
invention exhibit a tensile strength of at least 100 ksi,
preferably at least 110 ksi, and an electrical conductivity at room
temperature of 68.degree. F. greater than 60% IACS, and preferably
greater than 70% IACS. This is an unusual set of properties for
copper alloy wire products having a single end diameter less than
0.010 inches.
[0034] The foregoing features and others will appear from the
following illustrative examples.
EXAMPLE 1
[0035] A copper-magnesium alloy was processed to wire incorporating
a restructuring anneal prior to being drawn to finish gage, and for
comparison without the anneal. The copper alloy contained 0.12%
magnesium. It was surprisingly found that the incorporation of a
restructuring anneal in the processing improved the rate of work
hardening and provided a stronger wire. Work hardening is the
increase in strength of an alloy due to plastic deformation.
[0036] The alloy was cast to 21 mm (0.827 inch) diameter rod and
rolled from the 21 mm diameter rod to 7.4 mm (0.291 inch) modified
square cross-section. The cross-section is equivalent to 0.312 inch
round diameter. The processing of the present invention then
provided an anneal at 700-850.degree. F. for 1-5 hours, and
generally 750-800.degree. F. for 2-3 hours, followed by drawing to
desired finish gage. The same alloy was drawn to finish gage
directly from the 7.4 mm rod using conventional processing which
does not employ any annealing.
[0037] The resultant properties are shown in FIG. 1 which
illustrates the tensile strength of the Cu--Mg alloys processed as
aforesaid as a function of cold reduction. It can be readily seen
that those alloys given the restructuring anneal obtained an
increase of 10 ksi over those not given the anneal. This is a
significant increase. It was also found that these alloys could be
readily drawn to small diameter wire required for conductor
applications, typically less than 0.010 inch diameter.
EXAMPLE 2
[0038] Copper alloys containing 0.15% magnesium and 0.10% tin wire
processed in a manner after Example 1, with final gage wire being
38 American Wire Gage (AWG). The alloys were drawn to a final gage
either without any anneals (from rod) or after an initial rolling
operation followed by a restructuring anneal under the conditions
set out in Example 1.
[0039] The resultant properties are shown in FIG. 2 which
illustrates the tensile strength of the Cu--Mg--Sn alloys processed
as aforesaid as a function of percent reduction in area, and in
FIG. 3 which illustrates tensile strength as a function of wire
diameter.
[0040] The results also found that the rate of work hardening of
the annealed and drawn wire was greater than that of the wire
without any anneal. Work hardening of this alloy as a function of
cold reduction in the region of interest is illustrated in FIG. 2.
At the same cold reduction, an improvement of 20 ksi or greater is
observed when the alloy is annealed. When comparing the tensile
strength as a function of wire diameter as shown in FIG. 3, a
similar improvement is found. Depending on the size of the wire, an
improvement of 5-10 ksi is obtained when processing of the wire
incorporates a restructuring anneal. FIG. 3 illustrates that not
only can the alloy be drawn to small diameters, but that the
obtained tensile strength at 0.004 inch diameter exceeds 120 ksi.
The properties of the alloy of the present invention processed in
accordance with the present invention are quite attractive and
compare favorably with those of copper-cadmium alloy C162.
EXAMPLE 3
[0041] A copper alloy containing 0.15% magnesium was processed in a
manner after Example 1. The alloy was given a restructuring anneal
following rod rolling. The annealed wire was then drawn to 0.004
inch diameter in several steps. The resultant properties are shown
in Table 1, below.
1 TABLE 1 Reduction Tensile Electrical Diameter, in Strength,
Conductivity, inch Area, % ksi % IACS 0.3117 0.0 36.6 86.5 0.2573
31.9 55.0 86.4 0.2159 52.0 63.7 84.1 0.1921 62.0 64.6 83.7 0.1715
69.7 67.5 83.2 0.1583 74.2 65.3 84.6 0.1441 78.6 69.4 83.6 0.1203
85.1 72.2 84.3 0.1010 89.5 74.1 84.3 0.0359 98.7 87.8 84.0 0.0145
99.78 101.9 82.7 0.0040 99.98 121.6 80.8
[0042] Table 1 clearly shows that not only can the alloy be drawn
to small diameters, but also that the obtained tensile strength at
0.004 inch diameter exceeds 120 ksi. The properties are quite
attractive and compare favorably with those of copper-cadmium alloy
C162.
EXAMPLE 4
[0043] One of the major reasons for using high strength conductors
is their high flex life. ASTM B470-95 (paragraph 6) describes the
test procedures for the flex test. In this test, the conductor is
initially hung in a vertical position with a defined weight and is
repeatedly flexed back and forth over a pair of standard steel
mandrels held in a horizontal position. Flexing of the conductor is
repeated until fracture. The number of cycles to fracture defines
the flex life.
[0044] In accordance with this example similar conductors were
manufactured using alloy C162 (Cu-1% Cd) and a copper alloy
containing 0.15% magnesium, with the latter alloy using a
restructuring anneal in accordance with the procedure in Example 1.
The constructions consisted of 19 ends of 38 AWG wire (0.004 inch
diameter). The conductors were flex tested according to the
procedure outlined in ASTM B470 outlined above, the results are
shown in Table 2, below.
2 TABLE 2 Cu--1% Cd Cu--0.15% Mg Break Load, lb 30.9 28.0 Single
End Size, inch 0.0041 0.0040 Flex Life 23,617 35,038
[0045] In spite of the fact that the copper-cadmium alloy had a
higher breaking load (mainly due to a larger size), it showed a
lower flex life. Flex life of the copper-magnesium alloy processed
in accordance with the present invention is about 50% greater than
that of the copper-cadmium alloy. This is quite significant and
represents a valuable discovery since flex life represents a major
attribute in a high strength conductor.
EXAMPLE 5
[0046] Conductors with 19 ends of 38 AWG construction as in Example
4 were prepared using the copper-0.15% magnesium-0.1% tin alloy of
Example 2. Two conductors were prepared, one utilizing the no
anneal condition and the second utilizing the rod rolled and
annealed condition of the wire outlined in Example 1. The
conductors were tested for flex life according to ASTM B470 and the
results are shown in Table 3, below.
3 TABLE 3 Annealed after No Anneal Initial Rolling Condition Break
Load, lb 29.0 27.3 Single End Size, inch 0.0041 0.0041 Flex Life
34998 28137
[0047] As evidenced by a higher break load the above results
clearly show a higher strength and a superior flex life for the
wire with the restructuring anneal.
EXAMPLE 6
[0048] A copper-0.59% magnesium alloy was given a restructuring
anneal following initial rod rolling in a manner after Example 1.
The annealed wire was then drawn to 0.004 inch diameter in several
steps. The resultant properties are shown in Table 4, below.
4 TABLE 4 Reduction Tensile Electrical Diameter, in Strength,
Conductivity, inch Area, % ksi % IACS 0.0874 92.1 100.3 64.5 0.0359
98.7 119.9 64.9 0.0145 99.78 132.8 62.3 0.0040 99.98 160.0 61.4
[0049] The 160 ksi tensile strength is very high for a copper alloy
with an electrical conductivity of greater than 60% IACS. Indeed,
this represents a unique combination of tensile strength and
electrical conductivity for a copper alloy. Although the electrical
conductivity of this alloy is less than that of copper-cadmium, the
combination of properties is excellent and is quite useful.
EXAMPLE 7
[0050] A copper-0.12% magnesium-0.1% tin-0.02% phosphorus was given
a restructuring anneal of the present invention in accordance with
the procedure of Example 1. The alloy was annealed following
initial rod rolling, the annealed wire was then drawn to a 0.004
inch diameter in several steps and the resultant properties shown
in Table 5, below.
5 TABLE 5 Reduction Tensile Electrical Diameter, in Strength,
Conductivity, inch Area, % ksi % lACS 0.3117 0.0 39.2 81.9 0.2573
31.9 56.8 81.7 0.2159 52.0 64.8 80.8 0.1921 62.0 66.4 80.8 0.1715
69.7 70.2 0.1583 74.2 68.7 80.9 0.1441 78.6 71.4 80.7 0.1203 85.1
74.9 81.4 0.1010 89.5 77.5 81.1 0.0359 98.7 91.4 78.9 0.0145 99.78
108.6 77.1 0.0040 99.98 128.8 74.4
[0051] The alloy could easily be drawn to 0.004 inch diameter. The
results shown in Table 5 clearly indicate that at 0.004 inch
diameter a significant improvement in tensile strength is
obtained.
EXAMPLE 8
[0052] In accordance with this example a 19/38 AWG conductor was
made using the single end 0.004 inch diameter wire obtained in
Example 7. This conductor was tested to determine its flex life
according to the procedure outlined in ASTM B470. Flex life of this
conductor, as shown in Table 5, below, was superior to that of
copper-1% cadmium and a base copper-0.15% magnesium which was
processed with the restructuring anneal of the present
invention.
6 TABLE 6 Cu--0.12% Mg-- Cu--1% Cd Cu--0.15% Mg 0.1% Sn--0.02% P
Break Load, lb 30.9 28.0 29.4 Single End 0.0041 0.0040 0.0040 Size,
inch Flex Life 23,617 35,038 45,738
[0053] While the present invention has been described in the
context of single end wires, it should be recognized that the
invention is applicable to and covers cables formed from multiple
wires processed in accordance with the techniques described
hereinbefore.
[0054] It is to be understood that the invention is not limited to
the illustrations described and shown herein, which are deemed to
be merely illustrative of the best modes of carrying out the
invention, and which are susceptible of modification of form, size,
arrangement of parts and details of operation. The invention rather
is intended to encompass all such modifications which are within
its spirit and scope.
* * * * *