Copper-clad aluminum wire is a bimetallic composite wire which covers the lead core wire with a copper layer and forms a metal bond at the copper-aluminum interface. It is the "replacement" product of pure copper conductor of CATV coaxial cable, which has the advantages of reasonable utilization of natural resources, stable transmission of TV signals, reducing cable production cost, and convenient network construction. CATV cables in the United States have used copper-clad aluminum wires since the 1970s.
In recent years, due to the appearance of domestic copper-clad aluminum wire, CATV cables produced in China, such as 75-9, 75-12 and 540, have also started to use copper-clad aluminum wire as internal conductor in large quantities. With the rapid development of China's information industry, the cable TV network will be constantly built or updated, and will develop the cable TV, telephone and computer network, coaxial cable using copper-clad aluminum wire will have a broad application prospect. Therefore, this paper mainly introduces the knowledge of copper-clad aluminum wire, the characteristics of domestic copper-clad aluminum wire and the characteristics of coaxial cable with copper-clad aluminum wire as the inner conductor for the reference of network construction personnel.
1. Specification of aluminum wire and its quality and performance requirements
1.1 Specifications of copper-clad aluminum wire: Copper-clad aluminum wire can be divided into two types according to the volume ratio of copper layer (the volume of copper layer accounts for the percentage of volume of copper layer) : The volume ratio of copper layer within the range of 8 ~ 12% is 10% (abbreviated as 10); The volume ratio of copper layer is 15% in the range of 13 ~ 17% (abbreviated as 15). According to the different soft and hard states, copper-clad aluminum wires can be divided into two types: those without fire opening after drawing are hard (denoted by H); The annealed after drawing is soft (denoted by A). Therefore, copper-clad aluminum wires can be divided into four categories: 10H, 10A, 15H and 15A.
Various copper - clad aluminum wires can be drawn into different nominal diameters. Copper Clad Aluminum wire is denoted as CCA(Copper Clad Aluminum).
For example, for soft copper-clad aluminum wire with a diameter of 2.77 and a volume ratio of copper layer of 15%, its specification is marked as CCA-15A-2.77.
1.2 for the quality of copper-clad aluminum wire :(1) the thickness of copper layer should be evenly distributed along the circumference direction. The standard specifies the thinest point of the copper layer along the circumferential direction. For 10A and 10H copper-clad aluminum wire, it should not be smaller than 3.5% of the radius of the dry conductor. For 15A, 15H should not be less than 5% of the wire radius, otherwise it will affect the TV signal transmission. (2) The copper layer should have good tightness to ensure no cracking during use. Take a section of copper-clad aluminum wire, clamp the two ends at 15 times its diameter, twist it forward three times and then reverse three times to check.
(3) An interatomic bond should be formed on the interface between the copper layer and the aluminum core, that is, good copper-aluminum adhesion. Generally, copper - clad aluminum wire can be bent in any way to observe its breaking back for inspection. If the fracture is laminated with copper and aluminum, it indicates that the two are not bonded well.
1.3 The performance of copper-clad aluminum wire: (1) the requirements of tensile strength and elongation. The tensile strength and elongation of hard and soft copper-clad aluminum wires with different diameters have different requirements, which are clearly stipulated in the standards of foreign and Domestic copper-clad aluminum wires. The tensile strength and elongation of hard copper coated aluminum wires are higher. The soft state has lower tensile strength and higher elongation. The choice of hard state and soft state mainly depends on the requirement of cable manufacturer. (2) Requirements for DC resistivity. Dc resistivity depends on the quality of copper village, thickness of copper layer, copper-aluminum adhesion and softening annealing process, which reflects the material and processing technology level of copper-coated aluminum wire.
2. Main industrial production mode of copper-clad aluminum wire and its product characteristics
2.1 Industrial production modes of copper-colored aluminum wire: There are mainly three industrial production modes of copper-covered aluminum wire. (1) Copper plating method for aluminum wire. It is a method to electroplate copper layer on the surface of aluminum core wire to obtain copper clad aluminum wire. This method is simple, but the composition of copper plating layer is impure and the performance is brittle. And copper coating and aluminum core wire often different core, it is difficult to meet the coaxial cable production and use requirements. It is no longer produced in China.
(2) Roll bonding. Two cleaned and heated copper strips are coated with aluminum core wire from top and bottom directions, and the copper strip is pressed together with the aluminum core wire by the strong pressure of the roller. Then remove both lugs at the copper band seam to form a line back. Then the wire is drawn to obtain the required diameter, and the required properties are given by heat treatment. This kind of process is more complicated, and the investment of rolling equipment is larger. (3) Cladding welding method. The cleaned copper strip is gradually formed into a round tubular shape, which is coated around the cleaned aluminum core wire, and the longitudinal joint of the copper tube is continuously welded to form a line blank by argon arc welding. Then the required diameter and properties are obtained by technical drawing and heat treatment. This process model is relatively simple, the equipment is not too complex, less investment. The quality of copper-clad aluminum wire is better, which is the main production method in China. The coated welding device used in this method has obtained the national patent. The innovative technology of copper-clad aluminum wire production by cladding welding has been gradually industrialized and commercialized, and filled the gap in China.
2.2 Characteristics of copper-Clad aluminum wire produced by color coating welding: Taking the copper-clad aluminum wire produced by our company by coating welding as an example, its quality and performance are introduced. (1) Structure of copper-clad aluminum wire. The distribution of copper layer along the circumferential direction is very uniform. Therefore, copper layer and aluminum core wire have better concentricity. (2) Metallurgical bonding at the interface between copper and aluminum. Due to the thorough cleaning and strict protection of copper strip and aluminum core wire before cladding welding, there is no black nonmetallic inclusion on the boundary between copper layer and split-core wire, which creates conditions for bonding between two kinds of metal atoms. When the finished product is bent or broken, the phenomenon of coating stratification cannot be seen from the fracture. (3) Performance of copper-clad aluminum wire. The mechanical properties (tensile strength and elongation) and dc resistivity of the copper-clad aluminum wire are listed in Table (1) after being tested by the electronic industry information transmission line quality supervision and Testing Center. The mechanical properties and DC resistivity requirements of copper-clad aluminum wire in ASTM B 566-93 and China's electronic industry standard Copper-clad Aluminum Wire are also given in the table for comparison. The annealing process has great influence on the mechanical properties and resistivity of soft copper-coated aluminum wire. During the annealing process, a layer of white bright metal compound (CuA12) is formed on the boundary between copper and aluminum due to heating. This kind of compound layer is very brittle, when its thickness is large, it will reduce the elongation and conductivity of silver-coated aluminum wire. Considering the practical application, if the annealing process is appropriate, the thickness of the compound layer is small 2pm, and the performance of the copper-coated aluminum wire will not be adversely affected.