Measures to increase the output of extruded aluminum

In the production of semi-finished products of aluminum and aluminum alloys, extrusion is one of the main forming processes. Extrusion products (profiles, tubes, and a small amount of wires and rods) account for about 30% of all semi-finished products. In 1998, the global output of aluminum semi-finished products was approximately 19,100 kt, of which the extruded product was 5,820 kt and the variety was nearly 40,000. There are more than 5,500 aluminum extrusion presses in the world, more than 2,500 in mainland China and about 190 in Taiwan. However, the extrusion pressure of 98% of the extruders in industrialized countries exceeds 15MN, but the extrusion pressure of 90% of China's extruders is below 15MN. The lack of operating rate of the extruder is a global problem. The average capacity utilization rate is about 65%, of which the highest in Japan is 91.6%, about 70% in North America and Western Europe, and about 35% in China.
In this situation, how to increase the productivity of the extruder has become a top priority. There are many measures to increase productivity, such as increasing the installed capacity, improving the quality of workers, and improving management standards. This article focuses on some of the more specific measures for improving production and quality.
1 Advanced Equipment and High-Quality Workers are Prerequisites for Increasing Outputs To improve the output of extruded products, advanced equipment, high-quality workers, and modern scientific management play a crucial role. In China's existing more than 2,500 extrusion presses, it is only about 25 sets of international standards, that is, about 1%, such as the 14.5MN (1600UStf.) extruder and 25MN (2750UStf.) of Nanping Aluminum Plant. Extrusion machine, 55MN (5500UStf.) extruder imported from Italy by Tianjin Nonferrous Metals Group Corporation, and 21 MN2 (2200/2500Ustf.) imported from SMS Sutton by Yuhua Aluminum Co., Ltd. Extrusion machines, 21MN (2350Ustf.) and 16.3MN (1800Ustf.) extruders imported from the Ube Japan Production Corporation (UBE) by Xi'an Aircraft Company.
China's aluminum extrusion industry is in the stage of structural adjustment, and it should avoid the low level of repeated introduction and construction. The existing remodeling value extrusion presses should be transformed into modern high-level extrusion presses. The newly-introduced positive extrusion machine shall be equipped with a computer-aided positive extrusion system (CADEX—Computer Aided Direct Extrusion) so as to minimize the actual extrusion time under the maximum extrusion force during isothermal extrusion; Ultra-precise hydraulic oil filter, and instruments for continuous monitoring of hydraulic oil quality and temperature; equipped with various process parameter display and monitoring electronic system PICOS (Process Information & Control System); should also have MIDIS system (management information and diagnostic display System-Management Information and Diagnostic Indication System) to display all kinds of information on various process parameters and production conditions, as well as to issue warnings and display signals in time for equipment failures, to guide maintenance and overhaul, to minimize downtime, and so on.
2 Relationship between temperature control and increased production Usually, if there is no unplanned downtime, then the maximum output depends mainly on the extrusion speed, while the latter is subject to four factors, three of which are fixed and the other is variable. . The first factor is the extrusion force of the extruder, which can be squeezed smoothly when the billet temperature is low. The second factor is the design of the mold. The friction between the metal and the mold wall during extrusion can usually be The temperature of the passing aluminum alloy is increased by 35-62°C. The third factor is the characteristics of the extruded alloy, which is an uncontrollable factor that limits the extrusion speed. The exit temperature of the profile generally cannot exceed 540°C, otherwise, the material surface The quality will drop, the pattern marks will obviously increase, and even sticky aluminum, gravure, micro cracks, and tears will appear. The last factor is the temperature and its degree of control.
If the extrusion force of the extruder is not enough, it is difficult to smoothly squeeze or even appear plug phenomenon and can increase the billet temperature, but the extrusion speed should be lower to prevent the outlet temperature of the material high. Each alloy has its own specific optimum extrusion (got) temperature. Production practice has proved that the billet temperature is best maintained at about 430°C (when the extrusion speed is ≥16mm/s). The temperature of 6063 alloy profile should not exceed 500°C, the maximum outlet temperature of 6005 alloy should be 512°C, and the maximum of 6061 alloy should not exceed 525°C. The slight change in die temperature will also affect the product's output and quality.
The temperature of the extruding cylinder is also very important. In particular, attention should be paid to the temperature rise in the preheating phase. Excessive thermal stress between the layers should be avoided. It is best to simultaneously raise the cylinder and the liner to the working temperature. The warm-up temperature should not exceed 38°C/h. The best preheating specifications are: raise to 235°C, keep warm for 8 hours, continue to heat up to 430°C, and keep warm for 4 hours before putting it into operation. This will not only ensure uniform internal and external temperatures, but also have enough time to eliminate all internal thermal stresses. Of course, heating the barrel in the furnace is the best way to preheat.
During the extrusion process, the extrusion barrel temperature should be 15 to 40°C lower than the ingot temperature. If the extrusion speed is so fast that the temperature of the barrel rises above the billet temperature, it is necessary to try to lower the temperature of the barrel. This is not only a troublesome task, but also the yield is reduced. During the increase of production speed, sometimes the heating elements controlled by the electric couple are cut off, but the temperature of the barrel is still rising. If the barrel temperature is higher than 470°C, the extrusion waste will increase. The ideal barrel temperature should be determined based on the different alloys.