ABSTRACT: Using the up-casting production line, the industrial test of the free-cutting high-conductivity tellurium copper alloy for the charging post of new energy electric vehicle was carried out, and the melting and up-casting technology of the alloy were explored and optimized, the results show that the optimized melting and drawing process can stabilize the alloy composition in the copper liquid and realize the up drawing method of 0.3% ~ 0.7% cu-Te alloy.

Key words: New Energy Electric Vehicle Charging Post; free cutting high conductivity tellurium copper alloy; upper drawing continuous casting; continuous melting and casting process; industrial test figure classification number: TG249 article number: 1009-3842(2021)01-0019-03

1. Introduction

The high conductivity tellurite copper alloy has excellent conductivity, heat conductivity, corrosion resistance and excellent arc performance. The domestic production method adopts semi-continuous casting + hot extrusion + drawing. The production efficiency and yield of this production process are low, can Not provide continuous length of blank, can not adapt to today's new energy vehicles and charging pile industry automated production needs. Three industrial tests of tellurium copper alloy have been carried out successively by using the up-drawing continuous casting method, and the continuous long tellurium copper alloy cast rod has been successfully developed, it is hoped to provide valuable practical experience for the large-scale production of tellurium alloy rods by up-drawing method.

2.New Trends in the production and use of tellurium-copper alloys

High conductivity tellurite-copper Alloy is an ideal material for high conductivity precise connector with excellent conductivity, heat conductivity, corrosion resistance and arc performance. It will have a wide application prospect in the field of new energy automobile charging pile. At present, however, the existing charging posts in China are mainly made of brass, and the low conductivity of brass results in long charging time. Tellurium, on the other hand, is a 60-year-old alloy that has not been widely used so far because of application requirements, materials and production costs, therefore, free-cutting copper alloys in the market mainly by lead brass and lead-free brass (conductivity in 20% iacs about) occupy the market. Therefore, the large copper processing enterprises at home and abroad almost have no research and large-scale production of tellurium copper alloy results. The domestic tellurium copper alloy bars and wires are mainly produced by some small copper processing plants using semi-continuous casting + hot extrusion + drawing. The production process is complicated, with high energy consumption, large investment, long construction period, low production efficiency and finished product rate, it can not realize continuous production, and can not meet the need of automatic production in new energy automobile and charging pile industry.

3. Experimental studies 

3.1 main contents of the experiment

According to the melting characteristics of tellurium-copper alloy, the key technology and process equipment for controlling the composition uniformity of tellurium are studied in this paper. Tellurium is expensive and volatile. In the melting process, special tellurium feeding device and stirring device are developed to ensure the even content of tellurium in copper liquid. At the same time, the continuous casting process of tellurium copper was optimized. The main feature of up-drawing continuous casting is that continuous copper bars can be produced directly from molten copper, which can effectively avoid the above shortcomings of the traditional iron mould casting process, however, it is the first time to be used in copper alloys, especially in tellurium alloys.

3.2 key technical issues to be addressed in the trial

Smelting and casting processes: Te is lighter than Cu, easily oxidizes and has a volatile temperature of less than 1000 °C (988 °c) , can be burned in air, and produces TEO2[2] . How to add Te to ensure that the burning loss of Te can be controlled, how to ensure that the alloy is strong getter, how to ensure that melting and casting melt does not getter, to ensure that the ingots are free of defects such as porosity and porosity, and to ensure that the rods are free from defects such as peeling and delamination.

4. Industrial test process 4.1 basic process flow of industrial test for tellurium-copper alloy by UPCASTING

According to the General Process Plan of the company, the Cu-Te Alloy Bar was obtained by the method of up casting, continuous extrusion and cold deformation. The effects of Te content, deformation and heat treatment on the microstructure and properties of the alloy were analyzed. The technical route and main method of the test are shown in Fig. 1. In this paper, the casting process is summarized. In this paper, different components of tellurium-copper alloy were prepared by up-drawing continuous casting and continuous extrusion. The process parameters of continuous up-drawing and continuous extrusion were improved, and the reasonable content of Te Element was determined. The technological route of this process is compared with the traditional method. The technical route and main method of the test are shown in Fig. 1[4] .

4.2 the industrial test of tellurium copper alloy by up-drawing continuous casting method was carried out by up-drawing melting and casting unit of Shanghai Qingpu Haoshen company with an annual production capacity of 8000t. The main technical parameters of the equipment were: UP-DRAWING SPEED: 600 ~ 800mm/min, h) , melting copper rate: 1200kg/h, take-up coil specification: 700mm 1500mm C) , casting rod diameter: 18mm.

4.2.1 the main test parameter 

(1) is the design of the tellurium-copper Alloy composition. In order to optimize the up-drawing process of tellurium-copper Alloy and obtain reasonable process parameters, six groups of different composition tellurium-copper alloys were designed and studied. The calculated and measured components are shown in Table 1. From the measured results, the stability of tellurium can be ensured by adopting reasonable technology in the up-drawing equipment.

(2) according to the alloy composition, the tellurium copper rod was made by up-casting. The continuous casting experiments of six groups of tellurium copper alloys with different composition have been carried out. The reasonable parameters of upcasting can ensure continuous upcasting, and the tellurium copper alloys with good surface quality and excellent properties have been obtained. High Purity Copper (GB/T467-2010) and copper tellurium master alloy were used as raw materials to prepare 12.5 mm tellurium copper alloy bar continuously. (3) The tellurium copper bars were fabricated by up-casting with different pitch. In order to optimize the process and obtain the process parameters, the project has studied the process of continuous casting of tellurium-copper alloy, different traction parameters and pitch are designed for different composition tellurite copper alloys, as shown in table 2,7 different pitch and 7 different traction speeds. Six groups of tellurium-copper alloys with different compositionsDo not use different traction speed in each pitch to prepare, observe the quality of the casting Rod.

4.2.2 optimization results of surface quality tests for rods with different pitch and speed according to previous research conclusions, in order to improve production efficiency, the selection of pitch and traction speed is based on the premise that high quality tellurium alloys can be produced continuously, the larger the pitch and traction speed, the better. Taking cu-0.7 Te Alloy as an example, first fixed pitch of 2.0 mm, try 8 groups of different traction speed, determine the best traction speed at this pitch. Then the optimum technological parameters were determined by using different traction speeds at the pitch of 2.5 mm, 2.8 mm, 3.0 mm, 3.5 mm, 4.0 mm and 4.5 mm. If the pitch and the drawing speed are too large, it will cause the cooling intensity of the cooling water in the mould to be too low, and the surface of the upper guide rod will be oxidized, red and dark, as shown in Fig. 3.

Under a certain cooling intensity and a reasonable casting temperature, different pitch and reasonable traction speed are adopted to increase the cooling intensity of the solidification front in the mould. The results show that the cooling strength is the most sensitive parameter in the drawing-up process of tellurium-copper Alloy. 4.2.3 the microstructure of different "internode" and "internode" bars was observed in order to observe the microstructure of the bars, especially the distribution of tellurium. In addition, Cu-Te alloy bars with high Te content were selected because of the obvious mark between each pitch, such as the Yellow Arrow in Fig. 4(a) , and the segregation easily occurred in Te element copper, samples were taken at the "section" and "section" of the casting Rod, and the microstructure was observed as shown in Fig. 4(b) and Fig. 4(c) . There are more black particles in the node than in the internode. It can be inferred that the black particles are probably due to the Te cooling crystallization, which tends to cluster on the node and makes the obvious mark between the nodes

4.2.4 the parameters of Te continuous casting on the high conductivity cu-Te alloy rod have been tested for many times. The Te content is 0.3% ー0.7% , the pitch is 2.0ー2.5 mm, the traction speed is 250ー300 mm/min, and the Te content is 0.1% ー0.3% , the pitch is controlled from 2.5 mm to 3.0 mm, the traction speed is controlled from 350 mm to 450 MM/MIN, the Te content is 0.02% to 0.1% , the pitch is controlled from 3.0 mm to 4.0 mm, the traction speed is controlled from 550 mm to 650 MM/MIN, it can continuously prepare the top guide rod of tellurium copper alloy with excellent performance. As shown in Fig. 5, a tellurite copper alloy (0.3% Te) with 0.30% Te content, different pitch and different traction speed has been cast [6] .

5. Summary (1) with suitable melting-casting process, the continuous up-drawing of tellurium-copper alloy with different composition can be realized, which can provide qualified continuous billet for continuous extrusion in the next step and a new process for preparation of tellurium-copper Alloy is provided; (2) the top drawing of tellurium-copper alloy is especially sensitive to the cooling strength and this parameter, so it is necessary to control the drawing pitch. 

Source: Chinanews.com, by Wei Anxiang

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