Note: Descriptions are shown in the official language in which they were submitted.
~2~3~36C~
The present invention relates to a method of making dispersion
strengthened metal rods and tubes, and more particularly to a process for pro-
during a sheathed dispersion strengthened copper alloy or copper composite rod
or tube.
Dispersion strengthened copper is now a relatively well known
material which is particularly useful in the fabrication of electrodes for auto-
matte resistance welding machines used, for example, in the manufacture of
automobiles. Reference may be had to the patent to Nadkarni et at, 3,779,714
which discloses a method of dispersion strengthening copper by internal oxide-
lion. Patent Jo. 3,179,515 shows another method of internally oxidizing alloys
by surface oxidizing a powdered alloy and then diffusing oxygen into the
powder particles to preferentially oxidize a solute metal to solute metal oxide.
British patent 654,962 shows a method of internally oxidizing silver, copper
and/or nickel alloys containing solute metals by oxygen diffusion to increase
the hardness of the alloy.
Heretofore, bar stock for the production of dispersion strengthened
copper electrodes has been produced by a process for canning a dispersion
strengthened copper powder, and then extruding through a die to produce a disk
pension strengthened rod or bar. (See United States Patent No. 3,884,676
to Nadkarnie et at). Reference may also be had to united States Patent No.
4,045,644 to Shafer et at which shows a process for making a welding electrode
from dispersion strengthened metal to improve the grain structure in the
electrode tip portion and thereby improve the life of the product.
It has been found that extrusion of a "canned" dispersion strength-
eyed copper powder results in the formation of a densified dispersion strength-
eyed copper characterized by a grain structure in which the grains are sub-
staunchly in alignment and have a fibrous nature. This is caused by high
~22~396~
deformation ratios of the original cross-sectional area of can: cross-
sectional area of extradite used in the process of extrusion, e.g., from about
8:1 to about 200:1. As pointed out in the aforementioned Patent No. 4,045,644,
an upsetting operation is utilized in the manufacture of resistance wording
electrodes to disturb the axial alignment of the fibers and thereby minimize
failure of the electrodes by cracking generally in an axial direction long-
tudinally between the fibers as a result of impact in use.
The present invention provides an improved process for densifying
dispersion strengthened metal powder in a metallic sheath or container by
; 10 staged size reduction in a plurality of stages, some or all of which may be
carried out at elevated temperature, e.g., 1000F. or higher. Staged size
reduction alone has been found to be insufficient to assure complete densifi-
cation of powder and maximum electrode life unless a relationship between the
cold worked tensile strength of the outer sheath and the final tensile strength
; of the substantially fully densified dispersion strengthened metal is observed.
"Staged size reduction" as used herein contemplates relatively small size
reduction per pass, such reduction being in the range of from about 15% to 35%
of the cross-sectional area of the workups until at least about 90% of
theoretical density, and preferably full density has been achieved. Size
reduction may be accomplished by applying compressive force continuously during
a given pass, as with rolling or intermittently during a given pass as with
swaying. Usually extrusion is done with very much larger size reduction, i.e.,
of the order of from about 80% to 99% per pass see United States Patent No.
3,884,676~. Size reduction of this magnitude with containerized dispersion
; strengthened powder requires a large investment capital in extrusion apparatus.
The present process is less costly from the standpoint of investment and cost
of operation. Hence, products can be produced at reduced cost.
3~2~3~
Staged size reduction is keyword out preferably until
full density is achieved. Even during staged size reduction, it
has been found if these relative tensile strengths are too disparate,
relative deformation in an axial direction between the outer sheath
and the inner core is experienced to an extent sufficient to cause
cracking of the core. It has been found, therefore that the cold
worked tensile strength of the sheath should not be less than the
tensile strength of the fully densified core by more than about 22%
to I of the ultimate tensile strength of the core. In the case of
dispersion strengthened copper, this difference is about 15,000 psi.
The improved process utilizing a swaying machine or
rod rolling, involves a lower capital expenditure initially and a
: lower labor content than the previously practiced extrusion method.
According to one aspect of the present invention
there is provided a process for forming a elongated member of
substantially uniform cross-section and comprising a metal sheath
; surrounding a dispersion-strengthened metal core which comprises
the steps of:
(a) providing a sheath-forming metal container,
(b) filling said container with dispersion strength-
eyed metal powder having a particle size less than 20 mesh (Tyler
Screen Size) and said dispersion strengthened metal containing
from about 0.1% to about 5% by weight of a solute metal as a refract
tory oxide dispersed therein and having a predetermined tensile
; strength at full density,
(c) the metal of said container having a tensile
- 3 -
I
strength at room temperature in the cold worked condition no more
than about 22% to 25~ less than said predetermined tensile strength
: at full density of said core; and
(d) reducing the cross-sectional area of the powder
filled container by application of compressive force to said
container in a plurality of reduction stages each in the range of
from about 15~ to about 35% of the cross-sectional area until a
density of at least about 90% of theoretical density is achieved.
According to a further aspect of the present invention
there is provided a process or forming an elongated member of
substantially uniform cross-section and comprising a metal sheath
surrounding a densified dispersion strengthened metal core which
comprises the steps of:
(a) providing a sheath-forming metal container;
(b) filling said container with dispersion strength-
eyed metal powder having a particle size less than 20 mesh (Tyler
Screen Size) and said dispersion strengthened metal containing from
about 0.1~ to about 5.0~ by weight of a solute metal as a refract
tory oxide dispersed therein and having a tensile strength at full
density of at least about 55,000 psi at room temperature;
(c) the metal of said container having a tensile
strength at room temperature in the cold worked condition of not
: more than about 15,000 psi less than the tensile strength of said
densified dispersion strengthened metal at maximum density; and
(d) reducing the cross-sectional area of the powder
filled container by application of compressive force to said
container in a plurality of reduction stages in the
_ _
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range of from about 15% to about 35% of the cross-sectional area
until a density of at least about 90% of theoretical density is
achieved.
According to another aspect of the present invention
there is provided a process as defined in claim 1 wherein the ten-
site strength of the dispersion strengthened copper at full density
is in the range of from about 55,000 psi to about 90,000 psi at
room temperature.
cording to a still further aspect of the present
invention there is provided a resistance welding electrode having
a proximal end and a distal end and formed from a swayed bar and
comprising (a) a cylindrical portion characterized by a core of
internally oxidized dispersion strengthened copper containing from
0.1 to 4.0% aluminum as refractory aluminum oxide dispersed therein,
said core having an ultimate tensile strength developed during
swaying to full density of at least about 55,000 psi, saidcylindri-
eel portion also having a thin metal sheath surrounding and tightly
adhering to said core, said sheath having a cold worked tensile
strength at room temperature no more than 15,000 psi below the
ultimate tensile strength of said core, said cylindrical body
also including a recessed water hole in the proximal end thereon,
and (b) a tip portion characterized by converging side surfaces
terminating in a circular work-contacting tip, the plan of said
circular tip being normal to the longitudinal axis of said electrode.
According to another aspect of the present invention
there is provided a magnetically responsive wireiproduct having
- pa -
~L22~3~6~
an outer sheath of copper, a contiguous inner ferruginous annuls
and a core of fully densified internally oxidized dispersion
strengthened copper filling said inner annuls, said core contain-
in from 0.1% to 0.7% aluminum as refractory aluminum oxide disk
pursed therein.
According to a further aspect of the present invention
there is provided a process for forming an elongated member of
substantially uniform cross-section and comprising a metal sheath
surrounding a dispersion strengthened metal core which comprises
lo the steps of:
(a) providing a sheath-forming metal container,
(b) filling said container with a metal powder come
prosing dispersion strengthened metal powder and having a particle
size less than 20 mesh (Tyler Screen Size and said dispersion
strengthened metal containing from about 0.1% to about 5% by weight
of a solute metal as a refractory oxide dispersed therein and having
a predetermined tensile strength at full density,
(c) the metal of said container having a tensile
strength at room temperature in the cold worked condition no more
than about 22% to 25% less than said predetermined tensile strength
at full density of said core; and
(d) reducing the cross-sectional area of the powder
filled container by application of compressive force to said
container in a plurality of reduction stages each in the range of
from about 15% to ~ut-35%of the cross-sectional area until a density
of at least about 90% of theoretical density is achieved.
- 4b -
A
Thus, briefly stated, the present invention is in a
process for forming an elongated member wherein dispersion
strengthened, or dispersion strength enable, alloy or metal composite
powder is enclosed in a tube or container which is then sealed.
Dispersion strengthening may occur within the tube or container
after it is sealed by application of heat. The container is then
submitted to a plurality of size reduction stages r for reducing
the cross-sectional area by application of compressive force to
the container until a powder density of at least about 90~ is
achieved. Size reduction is within the range of from about 15% to
about 35~ per pass of the c~oss-sectional area. Size reduction
: may be achieved by swaying, or rod rolling, or a combination of
these, e.g., swaying followed by rod rolling. After full density
is achieved, the product may be handled as a wrought metal and
shaped by any of the usual metal shaping processes including
drawing, milling, forging (hot or cold), turning, rolling, swaying,
: or the like. The reductions in cross-sectional area per pass are
designed to give initially rapid densification of the powder
through the cross-sectional area reduction with minimum lengthening
of the
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tube. Typically, these reductions are in the 20% to 30% range. Intermediate
sistering and annealing treatments may be utilized to develop inter particle
bonding and stress relief. The initial size reduction and powder consolidation
may be done cold or hot although initial cold swaying at a temperature which
attains less than 400F. followed by hot swaying at temperatures usually above
1000F. is a preferred process. A minimum relationship between the cold worked
tensile strength of the sheath and the ultimate tensile strength of the core,
measured at room temperature, is maintained whereby the tensile strength of the
sheath is no more than about 22% to 25% less than the tensile strength of the
10~ core. There does not appear to be an upper limit on the amount by which the
cold worked tensile strength of the sheath may exceed the tensile strength of
the core.
The swaying of metal powders within a tube is not per so new.
Reference may be had to British Patent No. 981,065 which teaches a method of
producing tubes or bars of circular cross sections composed of zirconium or
; niobium or both. These tubes are used in nuclear reactors as cladding tubes
for solid or hollow nuclear fuel elements composed essentially of ceramic
nuclear fuel materials, such as uranium dioxide and uranium carbide. Because
of the nature of zirconium or niobium or both, these tubes are produced by fill-in a container formed of zirconium or niobium with zirconium or niobium
powder, closing the ends of the tubular member or annular space and subjecting
the tubular member thus prepared to a swaying operation at a high temperature
(1000C) to stinter the mass of powder to a high density and thereafter removingthe tubular member by mechanical or chemical means or both.
Reference may also be had to United States Patent No. 4,030,919
to Lea, which teaches forming a bar from a powdered metal by compacting into
bar segments, sistering the bar segments and then swaying the sistered bar
I
segment. No outer sheath is utilized in the disclosed process.
Another prior art reference is the Patent to Fischmeister et at,
4,038,738. This patent teaches a method for producing a bar stock from iron
nickel or cobalt base alloy comprising the steps of introducing a powder of
the desired alloy into a tubular container together with a reducing agent and
an oxygen getter, sealing the container without evacuating it, heating the
container and the powder therein and compacting the heated container by pro-
gressive forging or swaying and rolling the forged blank.
None of these references contemplates the utilization of a dispel-
soon strengthened alloy or metal composite as the powder or the preservation of
a relationship between the ultimate tensile strength of the dispersion strength-
eyed core and the cold worked tensile strength of the container.
The present invention will now be further described, by way of
example only, with reference to the accompanying drawings, in which:
Figure 1 is a typical resistance welding electrode of the type used
in automatic welding machinery. It includes a water hold projecting inwardly
from the proximal end and a frusto-hemispherical tip at the distal end flatten-
Ed to about 1/4" diameter.
Figure 2 is a cross-sectional view on an enlarged scale of a
composite sheathed densified dispersion strengthened metal core useful in form-
in wire, e.g., magnetically responsive wire.
As indicated above, the present invention contemplates the use
of a dispersion strengthened alloy or metal composite, particularly including
copper, as the core material which is densified in the course of carrying out
the process of the present invention. Other dispersion strengthened alloys or
metal composites such as including nickel, steel, and the like may also be
used in the process of this invention. For most purposes, we prefer to use a
-- 6 --
9~6C~
dispersion strengthened metal powder which includes copper and has a particle
size of less than about 20 mesh (Tyler Screen Size) preferably from 40 to 800
microns, e.g., 600 microns average, which material has been internally oxidized
prior to its entry into the process. Dispersion strengthened copper produced
by other methods may also be used and in some cases may contain up to about 4%
or 5% aluminum as aluminum oxide. As we have stated above, internal oxidation
of the copper alloy (copper aluminum) may occur during the size reduction
operation by elevating the temperature during size reduction to a temperature
above about 1000F., for example, a temperature of from 1200 to 1800F. for a
period of time sufficient to cause reaction between the solute metal (aluminum)
and the oxidant (cuprous oxide), provided therein. Although the present invent
lion process will be described in connection with dispersion strengthened
copper, it will be understood that the principles and procedures of the present
invention are applicable as well to dispersion strengthened alloys and metal
composite powders. Iron, nickel, silver, etc., may be dispersion strengthened
with a refractory oxide such as, aluminum oxide, titanium dioxide, magnesium
oxide, silicon dioxide, zirconium oxide, beryllium oxide, and the like.
The advantages of the present mention are realized to the best
extent where the amount of solute metal in the form of refractory oxide disperse
Ed within the matrix metal, e.g., copper, iron, cobalt, nickel or alloys thereof,
is within the range of from about 0.1% to as high as about 5% by weight. Where
the dispersion strengthened metal is internally oxidized dispersion strengthened
copper, commercially available examples thereof are identified as "Glidcop"
AL-15, AL-20, AL-35, and AL-60. lid cop is a registered trademark of SCM
Corporation. These materials are copper based and contain respectively 0.15%,
0.2%, 0.35%, and 0.60% aluminum as aluminum oxide dispersed within the copper
matrix. They can be produced by internal oxidation as described in
Nadkarnie et at 3,77g,714, or Nadkarnie 4,315,770. An internally oxidized
dispersion strengthened copper composition wherein the aluminum content is 1.0%
may be produced and, although it is not presently commercially available, it
also can be used in the present process.
The dispersion strengthened metal core of the present invention
may, as indicated above, be an alloy which is prepared prior to introduction
into sheath as a powder, or, the powder may comprise powdered dispersion
strengthened copper and an additional powdered metal. If under the conditions
of consolidation and heating, the additional metal forms an alloy with the
dispersion strengthened copper, useful products can be produced. Thus, for
example, a mixture of 90% GLIPCOP AL-15 or AL-60, for example, with 10% tin
powder will yield quite readily a consolidated product of dispersion strengthen-
Ed copper/tin alloy in a metal sheath, and when the principles of the present
invention are applied, cracking during swaying or rolling is avoided.
The principles of the present invention can be applied as well to
composites wherein the powdered dispersion strengthened metal, preferably copper
is mixed prior to consolidation with a non-alloyable powdered substance such
as a hard metal, for example, iron/nickel alloy to form a consolidated compost
tie structure. In these cases, the product is characterized by relatively high
mechanical strength, high electrical and thermal conductivity and a low co-
efficient of thermal expansion. For example, 60 parts of GLIPCOP AL-20 powder
screened Jo -80/+400 mesh is thoroughly mixed with 180 parts of -80/+400 mesh
nickel/iron ~42%:58% iron), and the powders thoroughly blended. The blended
powders may be consolidated by rolling to full density in a sheath provided in
accordance with the principles of the present invention.
Thus, the principles of the present invention are applicable to
dispersion strengthened copper powders; allowable compositions of dispersion
~2Z~
strengthened copper powder and a metal allowable therewith by heat; and come
posit compositions of dispersion strengthened copper powder and a non-
allowable discretely distributed particulate in a composite structure. Such
powders are consolidated to substantially full density by rolling or swaying
as described herein.
When the dispersion strengthened powders of the present invention
are substantially completely densified, i.e., I to 100% of theoretical density,
they should have a tensile strength at room temperature of at least about
50,000 psi. Obviously, in a partially densified state, the dispersion strength-
eyed copper or dispersion strength enable copper will not have a tensile strength
of this magnitude. When fully densified, "Glidcop" AL-15, for example,
develops a tensile strength in the range of from 55,000 to 60,000 psi at room
temperature. "Glidcop" AL-60, at the other end of the scale, develops a tensile
strength in the range from 80,000 to 90,000 psi. "Glidcop" compositions of
dispersions strengthened copper containing intermediate amounts of aluminum
oxide (calculated as the metal) have tensile strengths which are intermediate
to the limits stated above.
The metal container, which ultimately forms the tightly adhering
sheath surrounding the dispersion strengthened metal core, is desirably formed
of a metal which during the size reduction operation develops a cold worked
tensile strength relatively close to that of the ultimate tensile strength of
the dispersion strengthened metal core. For most purposes, tensile strength
of the sheath under cold working conditions has been found to be a tensile
strength no more than about 22% to 25% lower than that of the fully densified
core. In the case of dispersion strengthened copper cores this has been found
to be no more than about 15,000 psi lower than that of the fully densified core.
It has been found for dispersion strengthened copper DISC cores that the con-
I SHEA
trainer is conveniently formed, therefore, of a ferrous metal, such as, steel
or stainless steel, or alternatively of nickel, cobalt, copper or copper/nickel
alloys. These materials will have a cold worked tensile strength of at least
about ~10,000 psi. Accordingly, the lower cold worked tensile strength con-
tainer-forming metals will be used with the dispersion strengthened metal cores
which develop ultimate tensile strengths in the lower range, for example, those
dispersion strengthened copper materials which contain from 0.1% to 0.2% solute
metal as the refractory oxide. On the other hand, with the higher metal oxide
contents resulting in ultimate tensile strength at the higher end of the range,
for example, from 80,000 to 90,000 psi at room temperature for DISC cores, those
metals for forming the container having the higher cold worked tensile strengths,
such as, steel, stainless steel, nickel or cobalt or copper/nickel alloys will
more favorably be used. Following this schedule, the differential of no more
than about 22% to 25% or for DISC about 15,000 psi tensile strength lower than
that of the fully densified core can be observed. It should be borne in mind
that the tensile strength of the metal container will increase during the swag-
in operation due to working of the metal.
Composite sheaths are also contemplated hereby. For example, as
shown in Figure 2, there is provided a wire material 20. It has an outer
sheath 22 of copper metal (with the usual trace quantities of impurities) and
a contiguous inner sheath 24 of a ferrous, magnetically responsive metal, e.g.,
iron, steel, or owner iron alloy, e.g., iron/nickel. The core 26 is fully
densified dispersion strengthened metal, e.g., copper containing uniformly disk
pursed therein alumina in the range of 0.1% to .7% expressed as the equivalent
aluminum. Such wire is especially useful for semiconductor lead wire as it has
good conductivity and can be handled with magnets. It is formed conveniently
by drawing to wire diameter, e.g., .030" a fully densified bar having a cross-
- 10 -
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section such as shown in Figure 2.
The following schedule shows the important relationship of the
relative tensile strengths in accordance with this invention.
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From the foregoing schedule, it will be seen that the cold worked tensile
strength of the steel sheath (column I is less than 15,000 psi lower than
the ultimate tensile strength of the core. This indicates that a steel
sheath having a cold worked tensile strength of 80,000 psi is satisfactory
for use with the .60% aluminum-containing dispersion strengthened copper
material. Steel is, however, contra-indicated with the remaining lower
alumina containing OSC materials because the ultimate tensile strength of
the core is lower than the cold worked tensile strength of the sheath
instead of the opposite relationship.
In the case of the copper metal sheath, for the % Al = .60 core,
the cold worked tensile strength of the sheath is less, but by more than
about 15,000 psi. Copper metal is not satisfactory as a sheath material
for the owe Al core material. In practice, the core will crack under
swaying or rolling. The next example, using the 0.35% Al core is closer,
differing by 20,000 psi from the cold worked tensile strength of the copper
sheath. However, this material is not satisfactory also due to cracking of
the core during size reduction limits per pass stated above. The next two
examples, .20% and .15% Al, respectively, are well within the limit of
; 15,000 psi and the provision of copper metal sheaths for these lower oxide
content dispersion strengthened copper cores is found to be quite satisfactory
in swaying or rolling operation and at the size reduction levels hereof.
The tensile strength of useful sheath metals in the cold wormed
condition can be found in various handbooks, such as, for copper containing
sheath materials, the Standards Handbook, Wrought Metal Products, Part II -
Alloy Data ~1973) Copper Development Association for stainless steels see
..
- 13 -
I
Metals Handbook, Volume 1, Thea Edition, page 431 (1961), American
Society of Metals, for 1015 cold hard drawn low carbon steel see "Making,
Shaping and Treating of Steel, page 911 ~1971~; for copper/nickel alloy
~90:10) after 80% cold workln~ see Metals Handbook, Thea Edition Volume II
~1979) American Society for totals, page 374.
The cold worked tensile strength of the sheath may be higher
thin the full density or ultimate tensile strength of the dispersion strength-
eyed copper core, as illustrated in the following example.
The following Examples I through III show DSC/sheath combinations
lo that are useful in forming resistance welding electrodes. Example IV is
directed to a wire product.
EXPEL I
A Type 304 Stainless Steel tube with closed ends was filled with
"Glidcop" dispersion strengthened copper powder grade AL-60. The tube had a
starting outside diameter of 2.0 inches, a wall thickness of .065 inch, and
was 4 feet long. After 50% cold reduction this tubing had an estimated
tensile strength approaching 200,000 psi see Metals Handbook Thea Edition,
Vilely, page 413, C1961 by American Society for hletals), far in excess of
the minimum 75,000 psi tube strength necessary for this powder type.
The powder filled tube received a total of eight swaying passes
enroot to its final .620 inch diameter. Each pass delivered a 25% cross-
sectional area reduction. Two of the passes delivered at consecutive
intermediate diameters were performed while the rod was heated to 1650F,
: while the remaining passes took place at root temperature. At the final
diameter the powder was fully densified and of sound structure so as to
provide mechanical properties comparable to extruded form.
- 14 -
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- ~;22~3~6~
Slugs from this rod were cut and cold formed into resistance
welding electrodes. These electrodes performed very satisfactorily in
welding tests and give results indicative of substantially longer electrode
life. see Figure 1).
EN POLE II
Dispersion strengthened copper powder grade AL-60 was filled in a
cold dray tube of ASSAY 1015 steel. The tube dimensions and processing
route were identical to Example 1. The old worked tensile strength of the
tube was estimated as 80,000 psi (See The Making, Shaping and Treating of
lo Steel, 1971 by United States Steel Corporation, page 911), again greater
than the 75,000 psi tensile strength required by this invention.
Electrodes were again cold formed and tested as in Example I and
found also to be very satisfactory in terms of life expectancy.
EXILE III
A 90 Cut - long alloy tube with a starting diameter lo inch
diameter was filled with dispersion strengthened copper powder grade AL-35
; and processed and tested as in Examples I and II. The tensile strength of
the tube is 70,000 psi after 80% cold reduction metals Handbook, Ninth
Edition Volume 2, 1979 by American Society for Metals, p. 374~, age m
within the 15,000 psi margin of 80,000 psi for AL-35.
The weld test results should once more the wear of the sludgy -
consolidated electrodes equal to or surpassing the performance of standard
ext~llded product.
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EXPEL IV
A C-10200 oxygen-~ree copper tube was filled with DISC powder,
"Glidcop" grade AL-15. The tube had a starting diameter of 1.5 inches and a
Hall thickness of 0.032 inch. After 70% cold reduction, this tube has an
estimated tensile strength of 60,000 psi (See "Metals Handbook", American
Society for Metals, Volume 1, (1961) page 1009). Because the tensile
siren to of the fully densified core is 65,000 psi, the tube strength
disparity is 5000 psi which is within the limits of this invention.
The powder filled tube received a series of cold and hot swaying
cross-sectional area reductions each about 25%. The fully densified rod
was then drawn into a 0.014" diameter copper sheathed DISC wire. The tensile
properties or the wire were equivalent to or surpassed the properties of
AL-20 grade DISC wire produced by hot extrusion and drawing.
SAMPLE V
A C-10200 oxygen-free copper tube having an outside diameter
of 1.50" and a wall thickness of 0.065" end 4 feet in length, was filled with
dispersion strengthened copper powder: Glidcop AL-60. The ends of the tube
were closed and then it was cold swayed to 1 125" diameter rod in two passes
of about equal reductions in the area of cross section. During this process
the density of metal powder in the tube increased from about 50% to about
85% of theoretical ull-density. Metallographic examination of a sample
of the 1.125" diameter swayed rod showed the rod to be completely free of
cracks. The swayed rod was when cut into four pieces of approximately
; equal length. All four samples were heated in a gas fired fur m ace for
one hour, at 1650F, in preparation for hot-rolling. Rolling was conducted
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in a Fern made 2-High reversing rolling mill Ludlow Noah) having a pair
of 14" diameter x 14" Lange grooved rolls. These rolls offered a number of
choices for roll pass schedules between the starting size of 1.125" and
finish size of 0.625". Table V-l lists the various groove sizes, shape and
cross-sectional area. Each of the four sample rods was rolled in a specific
- pass schedule. However, three basic rules were adhered to in selecting the
roll pass schedules and in carrying out the experiments. These were I the
stock was rotated by 90 between successive passes, it the stock was fed
alternately between grooves having different shapes ego., round oval round
10 diamond, etc.) to allow for some amount of lateral spread, along with
reduction in cross-sectional area, and (iii) no more than two passes were
taken without reheating the sample at 1650F., for at least 30 minutes.
ale test schedules and the results are shown in Table V-2.
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As may be noted in the Table V-2, cracking was observed in all samples,
some even after the very first pass. The cracks were limited to the core
material only and ran generally in a direction perpendicular to the length
of the rod.
Since none of the material made here was free of visible cracks, no
further testing touch as hardness, density, cold formability measurements)
err carried out.
EXAMPLE VI
A 304-L Stainless Steel tube having an outside diameter of 1.50"
and a wall thickness of 0.065l' and 4 feet in length, was filled with
dispersion strengthened copper powder: Glidcop AL-60. The ends of the tube
were closed and then it was cold swayed to 1.125" diameter rod in two passes
of about equal reductions in the area of cross section. During this process
the density of metal powder in the tube increased from about 50% to 85~ of
theoretical full-density. Metallographic examination of a sample of the '
1.125" diameter swayed rod showed the rod to be completely free of cracks.
The swayed rod was then cut moo three pieces of approximately equal length.
These rods were heaved in a gas fired furnace for one hour, at
1650F., in preparation for hot-rolling. Rolling was conducted in a Fern
made 2-Hlgh reversing rolling mill idyll Noah) having a pair of 14"
diameter x 14" long grooved rolls. These roils offered a number of choices
for roll pass schedules between the starting size of 1.125" and finish size
of 0.625". Table V-l lists the various groove sizes, shape and cross-
sectional area. Each of these sample rods was rolled in a specific pass
schedule. However, three basic rules were adhered to in selecting the roll
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past schedules and in carrying out the experiments These were: (i) the
Slick was rotated by 90 between successive passes, it the stock was fed
alternately between grooves having different shapes (e.g., round oval round
diamond, etc.) to allow for some amount of lateral spread, along with
reduction in cross-sectional area, and lit no more than two passes were
taken without reheating the sample at 1650F., for at least 30 minutes.
The test schedules and the results are shown in Table VI-l.
As may be noted in Table VI-l, all metallographic samples were
free of cracks. Further evaluation and testing was carried out to determine
the suitability of the finished rod material for making resistance welding
electrodes. As shown in Table VI-2, all three samples passed the test.
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As indicated above, a characterizing feature of the present
invcn~ion is that dispersion strengthened metal it compacted within the
metal container sheath to an extent approaching theoretical density by
staged size reduction. Swaying machines capable of handling containers
having a diameter of as much as 6 inches are available. Reference may
be had to United Staves Patent 3,149,50g and its corresponding British
Patent 925,494 for description of one type of swaying machine useful in
carrying out the process of the present invention. Other machines are
available from the Torring~on Company, Machinery Division and the Abbey
Eta illusion Company. Rolling machines are well known.
It is desirable to carry out the initial stages of staged size
reduction at low temperatures, it without application of heat, because
if the container should rupture during impacting, damage to the dispersion
strengthened copper by ambient air is minimized, whereas if the staged
size reduction were conducted hot to begin with where the core has a large
amount of interconnected porosity rupture at this point would expose the
powdered core material to an undue amount of oxidation by ambient air.
After the initial size reduction and at the time of the dispersion
strengthened metal has reached from 80 to-90% of theoretical density,
Jo subsequent staged size reduction is carried out hot, that is, at a
temperature in excess of about 1,000F. and preferably in the range from
1450~ to }650P. In some cases cold swaying or rolling after a sistering
treatment between 1400 and 1$00F is satisfactory, for example with the
vower aluminum oxide grades such as AL-15 and AL-20. With increasing
aluminum content, dispersion strengthened copper materials, ego AL-35 or
- 24 -
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AL-60, for example, higher temperatures above 1000F. are required for
swaying and rod rolling to offset the increasing brittleness of these
materials and reduce the tendency to core cracking. These temperatures
are also sufficient to promote internal oxidation. Where the powder
utilized to fill toe container has not been internally oxidized prior to its
insertion into the container, internal oxidation may be carried out in the
container during hot rolling or swaying if desired. However, best results
are obtained when the internal oxidation is carried out prior to the
can filling operation.
So far as we art now aware, the present invention is best
practiced in the following manner. A metal container, preferably steel,
closed at one end by any suitable means such as forming a conical point
is filled with dispersion strengthened copper powder having a particle
size of less than 20 mesh Tyler), e.g., 600 microns average. The powder
use is "Glidcop'~ AL-35. The metal container is formed of regular carbon
steel having a cold worked tensile strength at room temperature of about
80,000 psi. The dispersion strengthened copper has a tensile strength at
lull density of about JOY psi at room temperature. Hence, the cold
worked tensile strength of the steel sheath is equal to the ultimate
tensile strength of the core and thus provides a satisfactory combination.
The container has an OX of 2.0 inches to begin with, a wall thickness of
0.065 inch, and a length of 6 feet. The container is filled with the
powdered internally oxidized dispersion strengthened copper and closed at
the opposite end, by any suitable means, e.g., a conical point. Sealing
or end closure may be accomplished on the swaying machine and need not be a
hermetic seal. The container is submitted to from 7-9 passes through the
- 25 -
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swaying machine with a cross-sectional area reduction of about 25~ per pass.
In a specific example, 8 passes are used. The first 3 passes are done cold
ire " without applied heat and tile powder brought to about 90% of full
density. The next 3 passes are hot at 1650F. The final two passes are
done not or cold as may be desired. In the present case, size reduction
is from I" diameter to S/8" diameter. The dies are changed after each pass
to achieve the next cross-sectional area reduction, preferably about 25%
per pass. The containers or tubes are conveniently S Jo 6 feet in length,
.
although any length that may be accommodated by the machine may be used.
In the case of "Glidcop:'AL-60, the same procedure is followed
espy that the container may be formed of steel or stainless steel having
cold wormed tensile strengths of about 80>000 psi for steel and up to
200,000 psi or stainless steel. ye dispersion strengthened copper has
a final tensile strellgth of 85,000 to guy psi, and thus maintains the
strength relationship described above.
The final densities in each case are in excess of 99% of
theoretical> and the resulting rods have an OX of 5/8" and a tightly
adhering steel or stainless steel sheath surrounding a dispersion
strengthened copper core.
The 5/8" diameter rod may then be formed into a welding
electrode by tapering or rounding by machine turning one end of the rod
leaving, preferably, at one end a small transverse flat surface and
severing the body by any suitable means from the balance of the rod to
provide a tip 0.8~0" long. ale portion of the electrode body which has
been tapered or rounded to a frusto-conical shape or frusto-hemispherical
- I -
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shape has the characteristic copper color. ale balance of the electrode
byway his cellular metallic color characteristic of steel. A water hole may
be machined into the proximal end of the electrode zip. Upsetting of the
try is not necessary to achieve improved tip life. Alternatively, the tip
may be formed by cold forging a nose and water hole into a billet cut from
a swayed rod produced in accordance herewith.
These electrodes in use have been found to last substantially
longer than similar electrodes produced by an extrusion process. This we
believe occurs by reason of the fact that swaying avoids to a substantial
extent the formation of fibrous structure within the body of the electrode
which in use is subject to splitting or grading in an axial direction.
By utilizing the swaying process and controlling the difference in tensile
strength as indicated above, we avoid to a fame extent the formation of
leers in axial alignment. This results in a product with much lower grain
aspect ratio (length to diameter) than extruded product and is better
able to withstand compressive forces as experienced in automatic welding
machines for a much longer period of time.
Modifications in the process may be made without departing from
the invention For example, the container may contain also an inner core
so that when filled with the dispersion strengthened powder metal, the
powdered metal fills an annuls around the core member.
The present process may also be used to produce dispersion
strengthened copper wire with copper or nickel sheathing for use in
electrical incandescent lamps as lead wires. (See United States Patent
4,203,603). In this respect, the use of a swains process is far superior
to an extrusion process because the extrusion process is incapable of
- 27 -
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producing a uniformly coated or clad product. Swaying on the other hand,
provides a very thin cladding of uniform thickness. Both clad and unclad
products aye be made my the process hereof. Decladding can be done after
so e reduction in accordance herewith by any suitable means, e.g., grinding,
leaching, etc.
'Rowley the process has been illustrated with dispersion
strengthened copper, the advantages of the invention will be achieved with
dispersion strengthened metals in general and in particular, as in the
case of resistance welding electrodes where the final product must be able
to withstand a primary compressive stress and secondary tensile stress.
The foregoing disclosure has been concerned principally with
sieging and rod rolling. The invention hereof is applicable also to sheet
rolling. It has been found that the principles of this invention apply to
rolling of containerized dispersion strengthened copper compositions across
the range of aluminum contents of 0.1% to 5% when the rolled CROSS section
is a rod or bar as well as a sheet where the thickness is much less than
the width and the edges unconstrained.
With the lower aluminum content dispersion strengthened copper
powders, i.e., less than about 0.35~ Al, no special procedures in strip
roiling appear to be required. However with the higher aluminum contents,
hot rolling is beneficial in reduc1no the snowiness to cracking. The
following examples illustrate sheet rolling:
Example VII
A copper (C-10200) billet container measuring 8" in length, 3"
in width and 0.75" in overall thickness, with 0.065" thick wall on all sides,
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was filled with dispersion strengthened copper powder: "Glidcop" AL-15 grade,
and the ends of the container were closed. It was then cold rolled to a
thickness of 0.37", by taking four rolling passes of approximately equal
amount of redllction. The density of powder mass in the billet at this
point was estimated to be approximately 90% of its theoretical full-density.
Hot rolling was performed subsequently, with the aim of attaining theoretical
full density in the powder mass and good inter particle bonding.
Two hot rolling passes were taken, each resulting in 20%
; reduction in area of cross section. The strip was heated at 1650F. for
}0 45 minutes, in an atmosphere of nitrogen, for each hot rolling pass. After
the two ho rolling passes, the metallographic examination of a sample
of the strip showed the material at the core to be free of crackles. The
strip was then cold-rolled to 0.050" in thickness, by taking 15% reductions
per pass. Tensile test specimens were prepared from this strip material,
per ASTM specifications. Two specimens were tested in the as-rolled
condition and the other two were tested after annealing at luff. in
nitrogen atmosphere for 30 minutes. Toe results are shown in liable VII-l
below.
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EASE VIII
A plain carbon steel ASSAY lows) billet container measuring
8" in length, 3" in width and 0.75" in overall thickness, with 0.065"
thick wall on all sides, was filled with dispersion strengthened copper
powder: Glidcop AL-60 grade, and the ends of the container were closed.
It was then cold rolled to a thickness of Q.36"~ by taking four rolling
passes of approximately equal amount of reduction. The density of the
powder mass in the billet, at this point, was estimated to be approximately
90 of its theoretical full density. Hot rolling was performed subsequently,
with the aim of attaining theoretical full density in the powder mass and
good inter particle bonding.
Seven hot rolling passes were taken, each resulting in 20%
reduction in the area of CROSS section. The strip was heated at 165QF.
for 45 minutes, in an atmosphere of nitrogen, for each hot rolling pass.
hletallographic samples were taken after the end, the Thea and the -Thea passes.
An examination of these samples showed the material at the core to be free
of cracks. The thickness of the strip after the Thea hot rolling pass was
O.Cg9". It was then cold rolled to .070", in two passes, each having a
reduction of 15%. Tensile test specimens were prepared from samples of
this strip, as per Asps specifications. These specimens were tensile tested
and the results are shown in Table VIII-l below.
- 31 -
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A copper ~C-10200) billet container measuring 8" in length, 3"
in width and 0.75" in overall thickness, with 0.065" thick wall on all
sides, was filled with dispersion strengthened copper powder: GlidCop
AL-60 grade, and the ends of the container were closed. It was then cold
rolled to 2 thickness of Q.37"~ by taking four rolling passes of
approximately equal amount of reduction. The density of powder mass in
the billet at this point was estimated to be approximately 90% of its
theoretical full density. Hot rolling way performed subsequently, with
the aim of attaining theoretical pull density in the powder mass and good
inter particle bonding.
TAO hot rolling passes were taken, each resulting in 20%
reduction in area of cross section. ale strip was heated at 1650F. for
45 minutes, in an atmosphere of nitrogen, for each hot rolling pass.
After the two hot rolling passes, metallographic examination of a sample of
the strip showed presence ox transverse cracks in its cross section.
Attempts were made to cold roll the strip with taking 15% reduction per
pass. However the strip developed cracks during the 3rd pass and hence
further rolling was not possible.
The invention may also be modified to yield a deoxidized
internally oxldi~ed dispersion strengthened copper rod or bar or tube or
sheet by blending the dispersion strengthened copper powder with from Oily
to 0.1% by weight of boron metal powder, titanium metal powder, or zirconium
powder, or the powdered hydrides thereof, prior to compacting and swaying.
- 33 -
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72304-5
Hot swaying or sistering is used to cause the boron or titanium
to react with free oxygen in the matrix copper metal. Such
deoxidized internally oxidized dispersion strengthened copper rod
or bar may be drawn into wire useful as lead wire in electric
lamps as disclosed in United States Patent No. 4,426,598, issued
January 17, 1984 by Charles I. Whitman as sole inventor.
Prime uses for the consolidated-from-powder dispersion
strengthened copper stock of this invention include lamp leads,
components for X-ray and microwave apparatus, and magnetrons,
generally traveling wave tube helixes, components of vacuum
tubes and hydrogen-cooled electrical generators, semiconductor
lead wires and frames, particularly those that need brazing,
electric relay blades and contact supports and electric
switch gear components in general, components of electrical
generators and transformers for resisting mechanical and thermal
surges as occur in their short-circuiting, hemostatic
surgical scalpels and other components where the dispersion
strengthened copper is bonded to high carbon steel, wire and
strip electrical conductors generally, components of vacuum
interrupters and circuit breakers, wide sheets or strips as for
making shadow mats for TV tubes, and improved resistance welding
and MUG (Metal Inert Gas) electrodes and the like, generally
all for getting high temperature strength and improved
stress-rupture qualities, non-blistering qualities, brazing
quality, and improved mechanical properties.
-34-
