Through the control of heating and extruding process in the production of oxygen-free copper tube and Bar, the entry of oxygen is reduced as far as possible, and the possibility of unqualified oxygen content caused by processing production is reduced, so as to raise the qualified rate of oxygen content in oxygen-free copper. With the increase of demand for oxygen-free copper, the output of oxygen-free copper is increasing year by year, especially the oxygen-free copper tube and bar has become an important product. The production capacity and product quality of the pipe and bar are greatly improved, the production process is gradually improved, and the comprehensive yield is greatly improved. However, the oxygen content of oxygen-free Copper Tube Rod is not qualified is a long-term trouble for oxygen-free copper production. A large proportion of oxygen content in the sample after extrusion is often not up to standard, or even the whole batch is not up to standard, which not only increases the cost, delays the delivery date, but also affects the image of the product, therefore, it is very important to explore the extrusion process of oxygen-free copper tube and bar and the qualified rate of high oxygen content of oxygen-free copper.

1. Improve the status quo

Before improvement, the overall yield of oxygen-free copper tube and bar was 57.5% . The average yield of oxygen-free copper in extrusion process is 60.36% , the highest is 67.85% , the lowest is 45.76% . There are two methods to collect data and test oxygen content in oxygen-free copper: one is YS/T335-94《 metallographic examination of oxygen-free copper content in electric vacuum devices 》 , the test results are divided into 1 ~ 6 grades, 1,2 and 3 grades to judge qualified, the second is GB/T5152-1996"high frequency pulse heating infrared absorption gas analysis method" , is a quantitative detection method. Data collection. Sampling inspection of ingots showed that all ingots with 1-grade feed were found to contain oxygen. (1) a total of 19 pieces of TU1 Bar (85) were sampled one by one. The sampling position is shown in Fig. 1. The oxygen content is 4 ~ 6 grade, and some of the results are shown in Table 1. The samples of the unextruded 295 ingot were then examined. The oxygen content varied from 3 to 6 grades. The sampling sites were shown in Fig. 2 and some of the results were shown in Table 2. (2)21 samples of 410mm Ingot (7 pieces) with the serial number 3130 were sampled at the center, 1/2 radius and near the edge. All of them were grade 1, and all the products produced were grade 1. The test results are shown in Table 3. 245mm ingots of 3314 and 360mm ingots of 3297 were drawn

Check, 245 ingots are all grade 4(this batch is also all grade 4) . One sample of 360 INGOT IS GRADE 4, three samples are grade 1. The report is shown in Table 3. (3) the oxygen content in the bottom and the gate of 102 furnaces is different from that in the gate. The oxygen content in the bottom of 60 furnaces is higher than that in the gate. Some results are shown in Table 4. (4) from Table 1 to Table 4, the results show that the oxygen content in the INGOT is obviously uneven. If the INGOT is qualified, it may be unqualified. From Table 4, it can be seen that for the same ingot (furnace) , different sampling positions (gate and bottom) also exist the phenomenon of inconsistent oxygen content, especially the oxygen content of gate is obviously lower than

Oxygen content at bottom of Ingot. 2. Oxygen Permeation and desquamation test. (1) oxygen permeation test. Oxygen penetration tests were carried out on oxygen-containing qualified (grade 1) oxygen-free copper extrudates in the laboratory. Firstly, the products were annealed at 600 °C ~ 800 °C for different time in the oxidation annealing furnace, then the products were grinded and treated, and the oxygen penetration depth was measured by special instrument. The annealing test was carried out by simulating the heating process of the ring heating furnace and the induction heating furnace, and then the oxygen penetration depth was measured. (2) peeling test. The surface of the annealed product is covered with 0.75 mm ~ 1.5 mm (simulated peeling and extruding process) , and then the oxygen content on the surface of the product is detected. The results are shown in Table 6. (3) the results show that the oxygen content of the sample decreases from Grade 1 to grade 4 to Grade 5 and the depth of oxygen penetration is 0.5 mm to 1.5 mm due to the oxygen penetration during heating, and the heating time is controlled within the range of technological requirements, during extrusion, oxygen permeation can be eliminated by peeling. Depending on the type of heating furnace, the amount of peeling can be controlled between 0.75 mm and 1.5 mm.

The heating time is less than 2 hours, the micro-reduction atmosphere is maintained in the heating furnace, and the oxygen penetration depth is less than 1.5 mm. 3. The process improvement of oxygen-free copper tube bar is as follows: Melting and heating (reducing atmosphere)—— extrusion. Combined with the test and the actual production, the improvement measures such as spot check of ingots and adjustment of heating process were taken. 1. In consultation with the quality department, the method of oxygen-containing sampling for ingots was changed from the original ingots gate to the bottom of the ingots to make the ingots more representative and reduce the unqualified ingots to enter the next process. 2. The ingots entering the processing procedure are selected for inspection, according to the melting number of each melting times sampling inspection 1 ingot of 4 points. Check the unqualified ingots and do not arrange production. Reduce the decline in the pass rate due to ingot problems. 3. Heating Process. (1) inspect the tools and equipment, make sure that the tools are ready and the equipment is in good condition, then allow the furnace to be installed and the production can not be interrupted. (2) on the premise of ensuring automatic control, the annular furnace heating can reduce the air intake, increase the gas volume, and keep the furnace for reducing atmosphere. (3) keep positive pressure in the furnace, preferably above 5Pa. (4) to organize mass production as far as possible. Oxygen-free copper production in accordance with the extrusion schedule furnace, to ensure that the ingot heating within 2 hours can be extruded. Installing a furnace, heating a furnace, reducing the number of charging furnace door opening, so that the furnace to maintain micro-reduction atmosphere, prevent ingot heating oxygen infiltration. The principle is: slow heating, less furnace, fast extrusion. 4. Extrusion process. In order to prevent the oxygen permeated into the product during the heating process, the peeling amount of the ingot heated by the induction furnace is controlled by 0.75 mm ~ 1.5 mm, and that of the ingot heated by the annular gas furnace is 1.0 mm ~ 1.5 mm, make sure the products are oxygenated and qualified. At the same time should ensure that the equipment during production in good condition, stability, the indicators set according to the requirements of the regulations. Productivity 1. Oxygen-free copper because of oxygen unqualified, and the return rate dropped significantly. 2. The yield of extrusion process increased greatly, reaching 75% , 14.64% higher than before. 3. After the improvement, the output and yield of oxygen-free copper extrusion process were greatly increased, and the average yield was 62% , which was 4.5% higher than before. 5. Conclusion 1. By changing the location of oxygen-containing sample and sampling the ingots in the process, the sample sent to the ingots is more representative and the unqualified ingots in the process can be effectively reduced. 2. The results showed that the oxygen content of the sample decreased from 1 grade to 4ー5 grade, and the oxygen penetration depth was 0.5 mm ー1.5 mm, during extrusion, oxygen permeation can be eliminated by peeling. Depending on the type of heating furnace, the amount of peeling can be controlled between 0.75 mm and 1.5 mm. The oxygen penetration depth of induction heating furnace is 0.5 mm, and the oxygen penetration caused by heating can be completely eliminated by peeling and extruding. The oxygen penetration caused by heating can also be eliminated by peeling and extruding in ring heating furnace after 90 minutes The oxygen infiltration caused by heating can not be completely eliminated by dehulling and extruding. The improvement measures are as follows: ensure that the INGOT can be extruded within 2 hours of heating; Reduce the opening times of charging furnace door to keep the micro-reduction atmosphere in the furnace. As long as the oxygen penetration depth is less than 1.5 mm, the oxygen penetration can be basically eliminated by dehulling extrusion. 3. Due to the change of gas source and composition in ingot heating in pipe and bar production, it is necessary to explore a better process to control furnace atmosphere and reduce oxygen penetration. 

Source: Chinanews.com, by Zhao Wanhua

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