Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
1998-08-17
2001-07-10
Ip, Sikyin (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C148S684000, C029S527700
Reexamination Certificate
active
06258187
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of copper trolley wire, also known as the contact wire in overhead catenary rail systems. The invention relates to a copper trolley wire having improved mechanical properties and to a method of manufacturing the copper trolley wire with improved mechanical properties.
BACKGROUND OF THE INVENTION
Copper trolley wire has been in commercial use for a long time. There is a standard set forth by the American Society for Testing and Materials (ASTM), as ASTM B47-95a, which is titled the Standard Specification for Copper Trolley Wire and which is reproduced in the Appendix to this specification. It is well known and straight forward for those of skill in this art to make copper trolley wire in accord with this ASTM standard.
This ASTM standard lists the minimum acceptable mechanical properties for copper trolley wire at various wire sizes. For example, grooved wire of a copper and silver alloy having a nominal area of 300,000 circular mils(cmils) is required by the ASTM standard to have a minimum tensile strength of 48,000 pounds per square inch (psi).
Table 1 below contains the tensile requirements for silver bearing round wire found in Table 1 of ASTM 47-95a, which is reproduced in the Appendix as Table 3. Table 2 below contains the tensile requirements for silver bearing grooved wire found in Table 2 of ASTM 47-95a, which is reproduced in the Appendix as Table 4.
TABLE 1
ASTM B47-95a Tensile Requirements For
Silver-Bearing Round Wire
Tensile
Diameter,
Area,
Strength, min.
in.
cmils
psi
0.5477
300000
48500
0.4600
211600
51500
0.4096
167800
53000
0.3648
133100
54000
0.3249
105600
55000
TABLE 1
ASTM B47-95a Tensile Requirements For
Silver-Bearing Round Wire
Tensile
Diameter,
Area,
Strength, min.
in.
cmils
psi
0.5477
300000
48500
0.4600
211600
51500
0.4096
167800
53000
0.3648
133100
54000
0.3249
105600
55000
Typical methods for manufacturing copper trolley wire that meets the ASTM standard include methods such as continuous casting, rolling, and/or drawing (e.g., area reduction) and combinations thereof. Such methods are disclosed, for example, in Avitzur,
Handbook of Metal Forming Processes
(John Wiley & Sons 1983). These known methods are sometimes referred to as cold working and in some instances utilize an annealing step. Another known method for producing copper trolley wire meeting the minimum ASTM standards is to begin with a large wire bar, and drawing and/or rolling the wire bar to the desired dimension.
However, copper trolley wire manufactured in the typical way is limiting to the design of rail systems using such wire. For example, in a rail system using copper trolley wire, substations for electrical power must be placed at certain distances apart from each other. If it is desired to reduce the number of substations, copper trolley wire made to comply with the ASTM standard is inadequate because it lacks the desired tensile strength. Also for example, the advent of high speed rail and the desire to reduce costs have exposed practical limitations in copper trolley wire that has the mechanical properties listed in the ASTM standard.
Therefore, it has become desirable to have a copper trolley wire that has improved mechanical properties. It is also desirable to obtain such improved mechanical properties in copper trolley wire using a commercially acceptable manufacturing process, namely a process that is not cost prohibitive. Specifically, the need is to develop a trolley wire that can provide rail design options not currently available and that can withstand the rigors of high speed rail transit, while still providing sufficient transfer of electricity.
Therefore, it is an object of this invention to provide a copper trolley wire with improved mechanical properties. More specifically, it is an object of this invention to provide a copper trolley wire with tensile strength well exceeding the minimum listed in the ASTM standard.
It is also an object of this invention to provide a method of making copper trolley wire with improved mechanical properties. Further, it is an object of this invention to provide a method of making copper trolley wire in a commercially feasible manner.
SUMMARY OF THE INVENTION
These objects are met by the invention described herein by providing a high conductivity copper or copper alloy trolley wire used as an electrical contact with improved tensile strength. The increased tensile strength significantly exceeds industry standards and the ASTM standard allowing improved design and lower cost with regard to tensile loading on the wire. Typically, the copper trolley wire of this invention has a tensile strength of at least 10% greater than that listed in ASTM B47-95a. The copper content of this new trolley wire is about 99.90% (with this percentage optionally including small amounts of silver) and can be alloyed with various known alloying ingredients, such as silver, cadmium, magnesium, manganese, tellurium, chromium, zirconium titanium or tin. Preferably, the new copper trolley wire has a relatively fine grain size, generally not exceeding about 0.040 mm, which can be achieved through the manufacturing method disclosed herein. The copper trolley wire of this invention also has improved properties, as compared to the copper trolley wire in ASTM B47-95a, in the areas of ductility, yield point, hardness, and creep, while maintaining high conductivity. The new copper trolley wire of this invention has the same or better conductivity (also known as resistivity) as in ASTM B47-95a.
ASTM standard B47-95a requires a maximum resistivity at 20° C. of 900.77 &OHgr;-lb/mile
2
, which corresponds to a minimum conductivity of 97.16% IACS.
Also, this invention includes a cost effective method of manufacturing the improved copper trolley wire. Generally, the new method of making copper trolley wire utilizes a hot working step in addition to the known methods of cold working. Known methods also use an annealing step to recrystallize the copper trolley wire. However, the new method of this invention works the copper trolley wire while generating heat, and thus a heating (or annealing) step is not necessary to the method. Without being bound by any theory, it is believed that the new method which uses hot working, also referred to herein as conforming or extrolling, advantageously reduces the grain size of the copper trolley wire prior to the cold working steps. This is not to say that annealing cannot be used in conjunction with this invention. However, the method of this invention preferably excludes annealing as a separate step in the process of making the new copper trolley wire disclosed herein.
More specifically, this invention provides a method for making copper trolley wire comprising the steps of continuously casting a copper rod of about 99.90% copper, conforming the copper rod to arrive at a coil of wire, cold working the coil of wire to the desired dimension, optionally annealing the cold worked wire at known industry temperatures and cold working the wire again to a final desired dimension.
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Avitzur, B.,Handbook of Metal-Forming Processes, John Wiley & Sons, New York, 1983, pp. 35-248.
Boyer, H.E. et al., ed.,Metals Handbook, Desk Edition, American Society for Metals, Metals Park, Ohio, 1985, pp. 7-24 through 7-26.
“Standard Specification for Copper Trolley Wir
Chandler Thomas J.
Corrado John
Fish & Neave
Huang Eric H.
Ingerman Jeffrey H.
Ip Sikyin
Phelps Dodge Industries, Inc.
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