Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
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In recent years, much effort has been expended
in the metallurgical field to develop techniques for con-
tinuously casting molten metal into continuous metal rod.
The advantages of continuous casting over batch casting are
well known in the art and include the elimination of such
prior art batch casting operations as initially casting
individual bars of the metal, cooling the bars and casting
molds, stripping the bars from the casting molds, an~ then
reheating the bars to a sufficient temperature so that they
may be rolled into lengths of rod.
For example, the prior art production of copper
rod from cast copper wire bars, typically weighing 250
pounds, included reheating the cast bars to 1700F in order .
to homogenize the metal and condition it for the subsequent ~ `
hot-forming operation, and thereafter rolling the bars i~ a
so-called "looping mill" which was a long, slow operation
that permitted the rod to completely recrystallize between
rolling passe.s. After rolling, the copper rod would be . ~:
completely co~ered with a black oxide coating, and no cold
work (stored energy) would remain in the rod as it exited
the mill at 1000F. The 250 pound length of rod emitting
from the looping mill was taken-up on a coiling device and
immediately quenched to facilitate subsequent handling~ .
Inasmuch as no stored energy remained in the rod as it :
exited the mill, the quenching operation did not affect
its metallurgical properties.
In the continuous production of-metal rod ~;~
according to present practice, on the other hand, molten ~
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metal passes from a holding furnace into the mold of a
casting wheel where it is cast into a ~etal bar. The
solidified metal bar is removed from the casting wheel and
directed into a rolling mill where it is rolled into con-
tinuous rod. Depending upon the intended end use of the
metal rod product, the rod may be subjected to cooling
during rolling or the rod may be cooled or quenched
immediately upon exiting from the rolling mill to impart
thereto the desired mechanical properties. As disclosed in
U.S. Patent 3,395,560 to Cofer et al, a continuously-
processed rod is preferably cool~d as it exits the rolling
mill and prior to being coiled. Because the continuous
casting and rolling oparation does not include the inter-
vening homogenizing step of the prior art batch casting of
wire bars, and because the rolling operation is relatively
rapid as compared with the prior art looping mill, the
continuous rod emitting from the rolling mill will have a
substantial amount of cold work retained therein and thus
the immediate quenching operation will serve to retain the
same and freeze impurities in solid solution thus improving
the tensile strength of the product~
Conventional cooling techniques include immers-
ing the rod in a coolant, and spray-cooling the rod with
coo ant. In all cases, however, it is standard practice
to cool or quench the continuously produced rod prior to
its coiling and rods ormed in this manner are hereinafter
referred to as cold-coiled rods in contrast to the hot-
coiled rods of the present invention.
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In some instances, it is desirable to have
uniformly dispersed copper oxide inclusions throughout the
rod product whereas in other instances, it is neceqsary to
remove such oxide by shaving or scalping operations. The
oxide and other surface scale may be removed from the rod
product by pickling the surface of the rod in a liquid such
as sulfuric, nitric or other acids. The pickling operation
aLso performs a cooling function so that it is possible
to both cool and pickle the rod in one operation ancl one
example of such a system for quench-pickling cast rod is
shown in U.S. Patent 3,623,532 to Cofer et al. Rods formed
in this manner are also cooled, due to the pickling
operation, prior to their delivery to a coiling apparatus
and therefore are cold-coiled.
One disadvantage of the prior art systems for
continuous production of metal rod is that due to the ;
cooling operation, the rod becomes harder and hence more
difficult to coil. This is particularly disadvantageous
with large diameter rod. Another disadvantage of quenching
the high temperature rod prior to coiling is that the
retained vacancies and lattice defects which are present
after quenching remain in the rod since the temperature of
the quenched rod is too low to enable these defects to
be rectiied through thermal vacancy diffusion. For many
applications, such as wire drawing, rod which is quenched
prior tc coiling becomes too hard and will have too high
a yield tensile streng~hand too high a de~ree of residual !
stress to be commercially suitable.
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Additionally, rod quenched at high temperatures
as it exits the rolling mill will exhibit a high recrystal-
lization temperature because impurities contained in the
metal will be trapped or frozen in solid solution. Conse-
quently, the rod will have a high annealing temperature
which obviously necessita~es appropriate process equipment
and energy requirements capable of effecting the high
temperature anneal. Moreover, when the rod is drawn into
wire intended to be subsequently fabricated into magnet
wire by coating the same with enameling composition in an
annealing tower, a high temperature anneal ~e.g., greater
than 500F) will cause the enamel to blister on the surface
of the wire. Consequently, under these circumstances the
annealing and enameling would have to be effected in
separate operations.
STATEMENT OF THE INVENTION
,
According to the present invention, a continuous
length of copper or copper alloy rod is coiled as it exits
from a rolling mill and prior to any quenching or cooling
operations, and thereafter gradually cooled to room tempera-
ture. The rod is hot-coiled under temperature-controlled
conditions to selectively impart desired characteristics to
the rod before the rod has had an opportunity to cool. By
coiling the rod in this manner, a much lesser degree of
vacancies and lattice defects are ultimately retained in
the final rod product, the ductility of the rod is improved,
the recrystallization temperature is lowered, the yield
tensile strengthis lowered and the rod has a lesser degree
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of residual stress than rods of similar composition which
are cold-coiled.
More particularly, there is provided in
accordance with this invention a methocl of producing a con-
tinuously processed copper rod comprising the steps of:
a) continuously casting molten copper con-
taining normal impurities into a cast bar at a rate at
which said impurities are trapped in solid solution;
b) substantially immediately hot-rollin~ the
cast bar in the as-cast condition into continuous rod at a
rate at which said impurities are retained in solid solu-
tion;
c) cooling the rod after rolling; and
d) coiling the rod;
characterized in that in order to improve the ductility of
the rod and to lower the residual stresses therein the rod
is hot-coiled prior to any substantial cooling thereof from
the hot-rolling temperature, and thereafter gradually cooled
to room temperature to permit precipitation of substantially
all of said impurities thereby lowering the recrystalliza-
tion termperature of the rod.
In addition, another aspect of this invention
concerns the production of enamel-coated magnet wire.
Because the method ~f this invention yields a rod having a
lower recrystallization temperature than cold-coiled rod,
it is possible to simultaneously anneal wire drawn down
rom the rod while coating the wire wi~h an enameling
composition at a temperature of approximately 500F.
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Having in mind the above and othex objects,
features and advantages of the invention that will be
evident from an understanding of this disclosure, the
present invention comprises the method and resultant
product as illustrated in the presently preferred embodiment
o~ the invention which is hereina~ter set forth in suf~i-
cient detail to enable those persons skilled in the art
to clearly understand the function, operation, and advan-
tages of it when read in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a block diagram depicting the major
operations of a continuous casting system employing the
method of the present invention; and
Figure 2 is a schematic view of a continuous
casting system arranged to carry out the method of the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
According to one aspect of the present invention
and with reference to Figure 1, the method of the invention
comprises the steps of continuously casting 5 molten metal
into a cast metal bar, rolling 6 the cast bar while at high
temperature into a metal rod, and coiling 7 the metal rod
be~ore subjecting the same to any quenching or cooling
operations. In ~his fashion, the metal rod is hot-coiled
immed~ately after being rolled and while at the high temper-
ature at which it was rolled. The coiled rod may then be ;
gradually cooled 8 to room temperature.
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One type of apparatus which may be used to
carry out the method of the inven~ion is shown schematically
in Figure 2. The apparatus comprises a continuous casting
system comprising a delivery device 10 which receives molten
copper metal containing normal impurities and delivers the
metal to a pouring spout 11. The pouring spout 11 directs
the molten metal to a peripheral groove contained on a
rotarv mold ring 13. ~n endless flexible metal band 14
encircles both a portion of the mold ring 13 as well as a
portion of a set of band-positioning rollers 15 such that
a continuous casting mold is defined by the groove in the
mold ring 13 and the overlying metal band 14 between the
points A and B. A cooling system is provided ~or cooling
the apparatus and effecting controlled solidification of
the molten metal during its transport on the rotary mold
ring 13. The cooling system includes a plurality of side
headers 17, 18, and 19 disposed on the side of the mold -
ring 13 and inner and outer band headers 21 and 22, respec-
tively, disposed on the inner and outer sides of the metal
band 14 at a loca~ion where it encircles the mold ring. ~
A conduit network 2~ having suitable valving is connected ~;
to supply and exhaust coolant to the various headers so ;
as to control the cooling of the apparatus and the rate of
solidification of the molten metal. For a more detailed
showing and explanation of this type of apparatus, reference
may be had to U.S. Patent 3,596,702 to Ward et al. ~ `
By such a construction, molten copper metal
containing normal impurities is fed from the pouring spout
11 into the casting mold at the point A and is solidified
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and partially cool~d during its transport between the points
A and s by circulation of coolant through the cooling sys~
tem. Thus by the time the cast bar reaches the point ~,
it is in the form of a solid cast bar 25. The solid cast
bar 25 is withdrawn from the casting wheel and fed to a
conveyor 27 which conveys the cast bar to a rolling mill
28. It should be noted that at the point B, the cast bar
25 has only been cooled an amount sufficient to solidify
the bar and the bar remains at an elevated temperature to
allow an immediate rolling operation to be performed thereon.
The rolling mill 28 comprises a tandem array of rolling
stands which successively roll the bar into a continuous
length of wire rod 30 which has a substantially uniform,
circular cross-section.
In accordance with the invention, the wire rod
30 is not quenched or cooled after its formation but rather
is immediately fed to a coiler 31. The coiler in the em-
bodiment shown comprises a coiling basket which receives
the wire rod 30 and coils the same into extremely long
lengths of coiled rod. The coiling operation occurs immedi-
ately downstream from the rolling operation without any
intervening quenching or cooling. After the rod is coiled,
it is delivered to a subsequent cooling station for gradual
cooling to room temperature to permit precipitation of sub-
stantially all of the impurities from solid solution thereby
lowering the recrystallization temperature of the rod.
It is a metallurgical postulate that impurities
in solid solution will raise the recrystallization tempera-
ture of the product. Moreover, the impurlties in copper
(e.g., iron, silver, tin and lead) are additive in in-
creasing the recrystallization temperature. Consequently,
by permitting precipitation of substantially all -the
impurities from solid solution as above-described, the
recrystallization temperature of the copper rod will be
substantially lowered as compared with the recrystalli~a-
tion temperature of rod produced by prior art processes
wherein the rod is immediately quenched upon exit from the
rolling mill. As a result of the lowered recrystallization
temperature, the continuously-produced rod may be annealed
at lower temperatures in order to achieve minimum elongation
requirements. It should be apparent that the low tempera-
ture anneal is desirable in order to reduce oxidation and
also to conserve energy and increase the life of process
equipment. Moreover, in the production of ma~net wire
having an enameled coating thereon, it is advantageous if
the annealing and enameling can be effectuated simultaneous-
ly in the annealing tower. If annealing at temperatures
greater than 500F is required, the enamel will blister
on the surface of the rod. On the other hand, if the
annealing can be accomplished at temperatures lower than
500F, enameling and annealing can be effectuated simultan-
eously in an annealing tower at about 500F.
A significant feature of the present invention
resides in the discovery that rolled rods which are first
quenched and then coiled are at too low a temperature to ,
permit vacancy difusion to occur and therefore such rods
possess certain mechanical properties which are undesirable.
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From an examlnation of cold-coiled rods, it was learned
that they possessed a hi~h degree of vacancies and lattice
defects which were quenched in the rods and since vacancy
concentrations in most metals increase with increasing
temperature, the high degree of vacancies is believed to be
due to the fact that the temperature of the quenched rods is
too low to permit these defects to be rectified through .
thermal vacancy diffusion or thermal recovery of the exist-
ing high dislocation density material. When the metal is
hot rolled, the last 2 or 3 rolls produce a high dislocation
density in the metal matrix due to the act that a great
portion of this deEormation is "warm rolling" which produces
a high p~rcentage o~ cold work to the matrix. This cold
work is produced by the ~eneration of dislocations and
defects which would be held-in by a quick water quench. As
a result, the rod is hard and not easily bendable and as a
consequence, it is difficult to coil such rods, especially
those o larger diameter~ The present i.nvention allows
thermal recovery of these defects to a certain degree so as
to provide improved mechanical properties in the coiled rod.
By way of example only, the results of two
comparative tests will be given so that the advantages of
the invention will be more readily apparent. In both exam-
ples, the chemical composition of the copper alloy rod, in
paxts per million, is as follows:
Pb Sn Ag Sb Fe Mn As Bi
1 1 1 1 1 < 1 < 1
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X~PLE~ COI.D-C'OIL13D RO
A length of copper alloy rod having the fore-
going chemical composition was formed by continuous casting
of molten metal into cast bar followed by rolling the bar
into metal rod of 3/8 inch diame-ter. The metal rod was
then quenched and cooled to room temperature, between 80-
100F., after which the cooled rod was coiled in a coiling
apparatus. The following mechanical properties of the rod
were measured:
Ultimate tensile strength 31-32 KSI
Yield tensile strength 16.5-17.5 KSI
Elongation (10") 40-4~1%
Rockwell F. Hardness 50
EXA~IPLE 2 HOT-COILED ROD
A copper alloy rod was formed by casting and
rolling in the same manner as described above in Example 1
only in this case, the rolled rod was in~ediately fed to the
coiling apparatus and coiled in a hot condition before any
quenching or cooling operation. The copper alloy rod was
delivered directly from the rolling mill and coiled while
at a temperature of 1110F. and after the rod was gradually
cooled to room temperature, the following mechanical
properties were measured: ,
Ultimate tensile strenyth 30-31 KSI
Yield tensile strength 12-13 KSI
~ .:
Elongation (10") 43-44~ ;~
Rockwell F. Hardness 42
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From a comparison of the two Examples, the
improved results obtained Erom hot-coiling the copper alloy
rod as oRposed to cold-coiling the copper alloy rod are
readily seen. One significant result is that the yield
tensile strength decreased from the 16,000 psi range to the
12,000 p~i range. This lower yield tensile strength results
in a more ductile rod which is easier to process, especially
easier to draw into wire.
Another significant result is that the Rockwell
F Hardness decreased from about 50 to about 40 with the
attendant result that the ductility of the rod was increased
thereby making the rod easier to cold form, such as by
drawing. This is evidenced by the increase in elongation
of the hot-coiled rod as opposed to the cold-coiled rod.
The Examples given above are representative only and similar ~-
result3 are obtained using any copper and copper alloy
mat:erials which are currently employed in the art and com-
paring thP mechanical properties of col,d-coiled versus hot-
coiled rods made from those materials.
In accordance with the present invention, it has
been found that the rod-coiling temperature should lie
within 700F. to 1200F. in order to permit adequate thermal
vacancy diffusion to occur since the vacancies are not
quenched at this temperature range and recovery of the
re idual cold working imparted during rolling of the rod
will therefore nccur. This temperature ran~e is suitable
particularly ~or copper and copper alloy rods. ~lso, the
region within 950F. to 1150F. has been found to be especi-
ally effeative in impartinq the foregoing desirable
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mechanical properties to the rod and therefore the preferred
temperature range ~or the rod-coiling is ~rom 950F. to
1150F.
It has also been found in accordance with the
invention that the hot-coiled rod should be gradually
cooled to room temperature at a cooling rate not exceeding
300F. per minute in order to permit precipitation of sub~
stantially all of the impurities from the copper rod. ~ -
Thus it will be seen that in accordance with the
present invention, a copper rod is produced which hascertain
predetermined mechanical properties which were not hereto-
fore obtainable by coiling the rod in the conventional
manner. The rod product formed in accordance with the
method of the invention is annealable at a lower temperature
than a cold-coiled rod and has a low~r yield tensile strength
and lower hardness than corresponding rod which is cold-
coiled.
While the invention has been disclosed with
reference to one preferrea embodiment, it is understood that ~ ~;
many modifications and changes will become apparent to those
ordinarily skilled in the art and the present invention is ;~
intended to cover all such obvious modifications and changes ~ ;
which fall within the spirit and scope of the invention as
deined in the appended claims.
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