Patent Application
20150200032
Conductors are wires used to conduct electricity or signals in a variety of applications from building wire to medical devices to aerospace applications. The most common materials used as a conductor are copper and aluminum. Copper has a higher electrical conductivity relative to aluminum for the same size (volume) wire whereas aluminum has a higher electrical conductivity if the comparison is based on weight. With a density of 8.94 g/cm3 copper is 3.3 times heavier than aluminum with a density of 2.7 g/cm3. Electrical conductivity of copper is 100% IACS (International Annealed Copper Standard) whereas that of aluminum is 61% IACS. Aluminum has a much lower strength and is also prone to corrosion, but both materials have found application as conductors.
Although much stronger than aluminum, the strength of copper may not be adequate for higher demand applications. Copper alloys have been developed and are in use where strength of copper is inadequate for the application. Some of the traditional copper alloys used for higher demand applications have been cadmium-copper (C16200) and cadmium-chromium-copper (C18135). Both of these alloys, however, contain cadmium, a banned element for health and environmental concerns. Cadmium free environmentally friendly alloys (described below) have been developed to replace these alloys.
Copper clad aluminum (CCA) is a conductor with an outer layer of copper and an inner core of aluminum. This product can be produced with different ratios of copper and aluminum, but generally the copper outer layer constitutes 10% or 15% of the overall material by volume. The copper outer layer, while being conductive, provides a protective solderable outer layer for the wire.
Hybrid conductors have been used to obtain improved properties not attainable with a single material. Aluminum conductors steel reinforced (ACSR) are standard conductors used to carry current. Various constructions are in use, which utilize steel element/s at their core to support the aluminum conductor and prevent sagging. Another example of a hybrid conductor is disclosed in U.S. Pat. No. 7,105,740 B2 describing a seven strand conductor constructed with a central strength member surrounded by six strands of nickel plated copper clad aluminum. In both these cases of hybrid construction, the lighter but weaker aluminum or copper clad aluminum is supported by central strong member to increase the overall strength. Other examples of hybrid conductors are shown in U.S. Pat. Nos. 3,164,669 (Meyerhoff, 1965) and 5,483,020 (Hardie, 1996) and published U.S. patent application US2010/0196162 (Cerra 2010).
Copper clad aluminum has been used in the aerospace industry as a conductor in cable form. This material, however, has low strength and break load. In addition, crimping this material is problematic due to the low strength of aluminum. Combining a stronger material with the weaker copper clad aluminum can increase the strength, but at the sacrifice of weight. Hence the gain in strength must be sufficient to justify use of the stronger material.
Conductors are manufactured by twisting several wires together, typically in a geometric fashion. Common constructions consist of 7 or 19 strands. The requirements for such constructions in the aerospace applications are described in the European standard EN 4434, for example. In the seven strands construction six wires are twisted around a central wire. In the nineteen strands construction a third outer layer of twelve wires are wrapped around the seven ends core group of wires. Unilay construction is a common and more economical construction where the six wires of the first layer and the twelve wires of the second layer are wrapped around the central wire at the same time and with the same pitch (lay). Conductors can be manufactured with more than two layers of single end wire twisted around the central wire, but the seven and nineteen strand conductors are common. Preferably all the wires are of the same diameter, often in the ranges of AWG (American Wire Gauge) 30-50 (10 mil to about 1 mil) and typically about 4-5 mils.
U.S. Pat. No. 7,105,740 describes a hybrid conductor of copper clad aluminum with a “strength member”. This seven strand product consists of six strand outer layer of copper clad aluminum surrounding the central strength member. Crimping is applied to the outer soft copper clad aluminum with its complications. New costly contacts, crimping tools and crimping procedures had to be developed for this product to ensure proper crimping protection. The strength member is not described in this patent disclosure.
There has been a trend to reduce weight in many applications. This is especially true in the aerospace and automotive industries which strive to reduce weight in order to increase fuel efficiency. Wire harnesses make up a component of the weight in airplanes. Reducing weight has been a major requirement and a challenge in designing modern planes. Finding lighter conductors has been one of these goals. Tools for crimping the conductors are costly and attempts are made to maintain size to be able to use existing tools. This requires reducing cable conductor weight without changing the cable conductor size so that existing tools can be utilized.
It is a purpose of this invention to provide a solution by reducing the weight of the conductors currently used in the aerospace industry without degrading other attributes including size, break load, elongation or electrical conductivity. Where possible it is a purpose of this invention to additionally increase the strength of the conductor substantially beyond specifications and/or comparable state-of-the-art conductors, to thereby improve performance. Additionally it is a purpose of this invention to allow use of the existing tools for crimping and avoid the need for costly new devices to crimp the conductor.
The present invention provides a hybrid conductor of stranded wires with a core group of stranded wires and a second outer layer of stranded wires where the outer layer wires are trade of a strong copper base alloy and the wires of the inner core group layer/layers are wires of the weaker but lighter copper clad aluminum. The combined strength of the two members as a hybrid conductor equals or exceeds the strength of the conductors currently used in the industry while meeting or exceeding other criteria of modern standards exemplified by EN 4434.
Other objects, features and advantages will be apparent from the following detailed description of preferred embodiments taken in conjunction with the accompanying drawings in which:
An example of the cable construction is shown in
Tables 1 and 2 below list the requirements of the European aerospace industry for tight tolerance nickel plated AWG 26 and AWG 24 conductors. Most aerospace conductors are plated either with silver or nickel. Additionally these conductors require a minimum of 6% elongation.
Choices of the copper alloy wires 14 for an outer ring of wires can include, for example, wires made of the PERCON® 28 (P28) and PERCON® 24 (P24) alloys and made and sold by Fisk Alloy, Inc. The P28 alloy has a minimum of 80 ksi (103 lbs./in.2) tensile strength, a minimum of 85% IACS conductivity, and a minimum of 6% elongation. The density of P28 is 0.323 lbs/in3. P28 is described in a white paper of Fisk Alloy, Inc: (http://www.fiskalloy/wp-content/uploads/2012/04/percon—28_whitepaper.pdf). P24 alloy is described in U.S. Pat. Nos. 6,053,994 and 6,063,247. It was discovered that it is possible to combine P28 or P24 wires, or other wires of similar properties, with copper clad aluminum in a specific conductor construction to obtain the desired properties of the alloy conductors described in EN 4434 as a whole while saving weight. This applies to base conductors of copper alloy and copper clad aluminum or such conductors as coated with nickel or silver or other metals in customary cable construction practice. The nickel coating thickness is typically specified as 50 μin (in×10−6) minimum and silver typically in the order of 40 μin minimum. These conductors are typically further over-coated with insulation materials preferably high temperature materials such as polyimides, in one layer or multiple layers.
Copper clad aluminum wires usable as wires 12 in the above described conductor are available with various ratios of copper to aluminum. One of the more common and useful ratios is 15% copper (as to overall volume of the material). This is the CCA wire used in the examples shown in this application but the invention is not limited to this ratio of copper and other CCA choices can also be used preferably in the range of 5 to about 30%. Density of 15% copper clad aluminum wires is 0.1312 lbs/in3. Minimum electrical conductivity of this material is 64.4% IACS. Tensile strength of annealed CCA conductors in the diameters of interest (typically less than 0.010″ or 30 AWG) is in the range of 20 to 2.5 ksi (1000 lbs/sq in).
Based on the values for P28 copper alloy wire and CCA wire components, expected properties for the hybrid construction shown in
These conductors are required to have a minimum of 6% elongation, they are used in the soft temper and require annealing following the last wire drawing operation. Since the two materials of the two wire types do not have the same softening characteristics they must be annealed at different steps. When CCA wires at smaller diameters, especially smaller than 0.010″ (10 mils), are batch annealed formation of brittle Cu—Al intermetallic results in reduced ductility (elongation) of the wire. Hence, annealing of the CCA wires is conducted by operations Which expose the material to high temperature for only a short time, such as strand (tube) annealing or resistance annealing. The two wire components (copper alloy wires and CCA wires) can either be individually annealed prior to stranding or alternatively the copper alloy wires can be annealed separately and then hard CCA and soft copper alloy wires can be stranded followed by annealing the entire conductor at lower temperatures for annealing the CCA wires to impart elongation. Annealing the whole conductor at finish is a preferred operation to allow the strands of the conductor to relax in place and prevent out of pattern geometry.
Percon® 2.8 with its superior tensile strength is an ideal alloy for outer strand wires 14 to be combined with the CCA wires 12. This fact, however, does not exclude use of other high strength alloys such as Percon® 24. Although Percon® 24 has a lower strength, it is possible to combine Percon® 24 and CCA and obtain the required properties for aerospace applications while saving weight under same likely specifications with advantage over prior art cables used under such specifications.
The requirements for AWG 24 and AWG 26 conductors with silver plating are listed in Tables 4 and 5, below. These requirements are the same as those listed in Table 1 and 2 except for the resistance which is lower due to silver plating as opposed to nickel plating. The silver plated option is used here for demonstration of the concept. Other plating options may also be used.
Calculations for a hybrid conductor comprising Percon® 24 copper alloy wire as a ring of outer strands and copper clad aluminum as a core group as illustrated in
Table 6 indicates that superior properties and weight saving can be achieved even with Percon 24. A 16% weight saving can be obtained with the AWG 26 construction and 19% weight saving with the AWG 24.
Copper clad aluminum (CCA) wires 12 and Percon® 28 wires 14 were plated with sufficient nickel to provide the minimum plating thickness of 50 μin at the final size for the AWG 24 (19/36, i.e. 19 wire strands, each of AWG 36 diameter) construction. Twelve strands of the P28 were batch annealed to provide a minimum of 6% elongation. These twelve strands of the annealed P28 wires and seven strands of as drawn CCA wires were stranded according to the diagram in
This conductor was crimped using standard crimping tools. Evaluation of the crimp quality in terms of strength and electrical resistance indicated equal to superior performance compared with state-of-the art cables tested. The hardness of the wires 14 relative to the CCA wires 12 affords this crimping amenability.
Copper clad aluminum (CCA) wires and Percon 28 wires (P28) were plated with sufficient nickel to provide the minimum plating thickness of 50 μin at the final size for the AWG 26 (19/38, i.e. 19 wire strands, each of AWG 38 diameter) construction. Twelve strands of the P28 were batch annealed to provide a minimum of 6% elongation. These twelve strands of the annealed P28 wires and seven strands of as drawn CCA wires were stranded according to the diagram in
It will now be apparent to those skilled in the art that other embodiments, improvements, details, and uses can be made consistent with the letter and spirit of the foregoing disclosure and within the scope of this patent, which is limited only by the following claims, construed in accordance with the patent law, including the doctrine of equivalents.
The present application relates to cable conductors. The application claims priority from U.S. provisional Ser. No. 61/927,676 filed Jan. 15, 2014.
| Number | Date | Country | |
|---|---|---|---|
| 61927676 | Jan 2014 | US |
