ABSTRACT: This paper briefly introduces the application of continuous extrusion technology in copper processing, with emphasis on its application in oxygen-free copper strip, copper bar, special copper bar, oxygen-free copper bar, contact wire and copper flat wire. Key words: continuous extrusion; oxygen-free Copper Strip; Copper Bar; Special Copper Bar; oxygen-free Copper Bar; contact wire Middle Diagram classification number: TG 375.25 Literature Identification Number: a article number: 1671-6795(2010)02-0030-03

Continuous extrusion is a new method of plastic processing proposed by Mr. D. Guerin of United Kingdom Atomic Energy Authority in the early 1970s, which is known as a revolution of Non-ferrous metal processing technology. The continuous extrusion technology in China has been developed for more than 20 years, and it has been copied and improved at the beginning, and innovated again with independent property right.

1. How continuous extrusion works

The working principle of continuous extrusion technology is as shown in Fig. 1: The die cavity is located on the side of the extrusion wheel, and the billet is driven into the extrusion cavity by the rotating extrusion wheel, after a certain value is reached, the product is extruded from the die hole. The size and shape of the product depends on the mold, simply replace the mold can produce different specifications of the product. The basic principle of continuous extrusion cladding is shown in Fig. 

2[1] : based on the continuous extrusion process method, the shoe seat is placed on the upper part of the extrusion wheel, which allows the core wire to pass through the cavity, thus, the coating material is directly or indirectly coated on the core wire, and the core wire is simultaneously extruded from the die opening to form a coating product.

2. Application of continuous extrusion technology in copper processing

2.1 oxygen-free copper tape oxygen-free copper tape is used to make high-end product components and is widely used in electric power, electrical appliances, communications, electronics, computers and other industries, such as optical cable, coaxial RF cable, computer micro-radiator, soft printed circuit board and so on

Oxygen-free copper tape is a kind of material with high technology content and special performance, there are strict requirements for electrical properties, oxygen content, chemical composition, mechanical properties, dimensional tolerance accuracy, profile accuracy, Surface roughness and edge quality. The production of oxygen-free Copper Strip has been puzzled by oxygen content exceeding the standard and uneven oxygen content distribution. There are two traditional production methods of oxygen-free Copper Strip: Vertical semi-continuous casting or full continuous casting-hot rolling-cold rolling and horizontal continuous casting-cold rolling. The first process has the disadvantages of long production flow, high energy consumption, large investment and long construction period. The second process has the advantages of short flow, energy saving and less investment, but it has the disadvantage of low production efficiency. The annual production capacity of a single line is about 2000 tons, the process stability and quality need to be further improved and perfected.

Continuous extrusion process is a kind of processing method which uses 20 ~ 30mm oxygen-free copper rod as raw material to obtain strip billet by continuous extrusion and extension deformation, and then produces oxygen-free copper strip by cold rolling, annealing and surface treatment. The key of the process is to obtain a wide strip blank by means of extended deformation, which is an innovation in strip production. At present, the width of 630 continuous extruder produced by Libo group can reach 320mm. The oxygen-free Copper Strip produced by this process has the following characteristics: 1. The continuous extrusion technology transforms the useless friction force in the pressure processing into the driving force and the heating source of the deformation. The direct extrusion molding of the Strip billet reduces the processes of heating, hot rolling, milling and so on, which has the advantage of high efficiency and energy saving. The as-cast microstructure of the top-drawing Copper Rod was transformed into fine and uniform recrystallized microstructure with average grain size of 0.020 mm after continuous extrusion. 3. High Purity, low oxygen content, high conductivity. Cu + Ag ≥99.97% , conductivity ≥101% IACS, oxygen content ≤8 PPM.

2.2 Copper Bar (copper bus bar) and special-shaped copper bar

Copper bar is a kind of high current conductive copper, used for high and low voltage electrical appliances, switch contacts, distribution equipment, bus slot and other electrical equipment, also widely used in metal smelting, electrochemical plating, chemical caustic soda and other large current smelting or electrolytic equipment [4] . There are two traditional methods of manufacturing Copper Bar in China: Rolling Method and traditional extrusion method. The disadvantages of these two methods are long process flow, long working procedure, high energy consumption, low yield and difficult quality control. The technology of continuous extrusion for producing copper bar is: Top drawing copper bar-continuous extrusion-stretch finishing-fixed length sawing. Compared with the traditional method, the technology has the advantages of short flow, less investment, high efficiency and energy saving, compact product structure and fine grain, advantages of superior mechanical and electrical properties. The special-shaped copper bar is the main raw material for making the commutator of DC motor, excitation motor, motor amplifier, switch contacts of high and low voltage electrical apparatus and conductors for power transmission and distribution installation. Die Design is the key of continuous extrusion technology to produce profiled copper bar. The design of the shape and size of profiled copper bar extrusion die is not only based on the shape and size of the finished product, the ratio of height to width and the angle between inside and outside should be considered.

2.3 oxygen-free Copper

 Rod oxygen-free Copper Rod is widely used in electric vacuum devices. The oxygen content is strictly controlled because the electric vacuum device must be sealed in hydrogen during the manufacturing process. At present, the widely used production technology of oxygen-free Copper Rod is: melting-semi-continuous casting-hot extrusion-drawing, continuous extrusion technology to produce oxygen-free Copper Rod is: drawing-continuous casting-continuous extrusion-drawing; The technology has the advantages of short flow, high efficiency and energy saving, low oxygen content, good comprehensive performance, low equipment investment and flexible organization and production.

2.4 contact line

The contact wire is a bare wire for the transmission of power from the traction substation to the equipment through its direct contact with the pantograph. It is the main component of the railway electrification system. With the development of high-speed and electrification of railway in our country, the performance of contact wire is required higher and higher. Copper and copper alloy contact wire materials have been developed from pure copper into copper silver alloy, copper tin alloy, copper magnesium alloy and so on. The main methods of producing copper and copper alloy contact wire are: Top drawing casting-drawing method, continuous casting-rolling-drawing method, continuous extrusion method. The general process of up casting-drawing is up casting-multi-pass drawing-rolling-annealing-multi-pass drawing-finished product. The cast rod produced by this process has the advantages of good quality, low oxygen content and low cost. The continuous small off-line spark will be produced when the product is used, which reduces the quality of the locomotive flow and the life of the contact line.

Continuous casting and rolling-drawing method is to use continuous casting and rolling production line to produce 20mm billet, and then cold drawing forming by drawing machine. The advantage of this method is that the continuous casting and rolling billet is hot-rolled wire billet, the casting structure is eliminated completely and the billet is fine equiaxed grain. However, the contact wire produced by this method has high oxygen content and is easy to form brittle Cuprous oxide on the grain boundary, resulting in poor bending and fatigue resistance of the contact wire. The contact wire with 120mm 2 or 150mm 2 cross-section is produced by continuous extrusion, which is made of 16mm up-drawn oxygen-free copper rod as blank, continuous extrusion and expansion to 22mm or 24mm billet, rolling and cold drawing. The contact wire produced by continuous extrusion method has fine grain structure, uniform grain distribution and good mechanical properties, all properties are better than those produced by traditional process, and the index is obviously higher than the standard [6] . Copper-aluminum composite contact wires are produced by continuous extrusion (Fig. 4) , which are mainly used in rail and Maglev train. The key of this technology is to realize semi-cladding forming of metallurgical bond between aluminum alloy and copper billet.

2.5 copper flat wire

Copper flat wire is the main material of electromagnetic wire used in transformer. Its conductivity, tensile strength, ductility and surface quality directly affect the performance and manufacturing quality of transformer winding. The traditional processing method of copper flat wire is rolling-drawing-annealing, which has many processes, long cycle and high cost, and the size of raw material is related to the product specification. The copper flat wire produced by up-drawing continuous casting-continuous extrusion process has fine grain structure, uniform grain distribution and good performance. The utility model omits the annealing process, not only saves electric energy, but also completely avoids the product performance change caused by the uneven furnace temperature during the annealing process, which can ensure the product performance uniformity along the whole length, and has good surface quality, and greatly improve the production efficiency, reduce the production cost and production cycle.

3. Conclusion continuous extrusion technology is widely used in copper processing because of its advantages of high efficiency, low investment and good product performance. 

Source: Chinanews.com, by Yao Youfu

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