Usually when there is no unscheduled downtime, the maximum output is mainly determined by the extrusion speed, which 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 ingot temperature is low when the extrusion force is large; The second factor is the mold design, the friction between the metal and the mold wall during extrusion can usually increase the temperature of the aluminum alloy by 35~62°C; The third factor is the characteristics of the extruded alloy, which is an uncontrollable factor that limits the extrusion speed, and the outlet temperature of the profile generally should not exceed 540 °C, otherwise, the surface quality of the material will decrease, the die marks will be significantly aggravated, and even aluminum sticking, gravure, microcracks, tears, etc. will appear. The last factor is temperature and how well it is controlled.
If the extrusion force of the aluminum profile extruder is not large enough, it is difficult to squeeze smoothly or even the die plugging phenomenon cannot be squeezed, the temperature of the ingot can be increased, but the extrusion speed should be lower to prevent the outlet temperature of the material from being too high. Each alloy has its own specific optimal extrusion temperature. Production practice has proved that the temperature of the ingot billet should be kept at about 430°C (when the extrusion speed ≥ 16mm/s). The mold temperature of 6063 alloy profiles shall not exceed 500 °C, the maximum outlet temperature of 6005 alloy is 512 °C, and the best temperature of 6061 alloy should not be greater than 525 °C. The small change in mold temperature will also affect the output and quality of the product.
The temperature of the extrusion cylinder is also very important, especially attention should be paid to the temperature increase in the preheating stage, and excessive thermal stress between the layers should be avoided, and it is best to raise the extrusion cylinder and bushing to the working temperature at the same time. The preheating rate shall not be greater than 38°C/h. The best preheating specification is: raise to 235°C, keep warm for 8h, continue to heat up to 430°C, keep warm for 4h, and then put it into work. This not only ensures uniform and consistent internal and external temperatures, but also gives enough time to eliminate all internal thermal stress. Of course, heating the extrusion cylinder in the furnace is the best way to preheat.
During the extrusion process, the extrusion cylinder temperature should be 15~40°C lower than the ingot temperature. If the extrusion speed is too fast so that the extrusion cylinder temperature rises above the ingot temperature, it is necessary to try to reduce the extrusion cylinder temperature, which is not only a troublesome task, but also reduces the output. During the increase in production speed, the heating element controlled by the couple is sometimes cut off, but the extrusion cylinder temperature is still rising. If the extrusion cylinder temperature is higher than 470°C, the extrusion scrap will rise. The ideal extrusion cylinder temperature should be determined according to different alloys.
Don't think that preheating the extrusion cylinder is a waste of time and energy. In order to catch up with the production task, a factory heats with internal resistance elements on the one hand, and on the other hand, it heats with liquefied gas burners. In this case, the temperature cannot be measured and controlled, and huge thermal stress will be generated, and the lining temperature is high, and the expansion is faster than that of the jacket, causing the extrusion cylinder to crack and hear a "popping" sound.
The extrusion shaft will accumulate internal stress during the working process, which will cause fatigue cracks to a certain extent, and will break once subjected to non-axial radial force. Therefore, after the cumulative working time of the extrusion shaft reaches 4500h, it is best to carry out a stress relief treatment, keep warm at 430~480°C for 12h, and then cool it down to below 50°C with the furnace.
When producing surface building profiles, the temperature of the extrusion pad should also be strictly controlled to reduce the amount of scrap with inconsistent surface tone. The quality of the fixed extrusion pad is much better than that of the moving, and it can accumulate more heat, so it can reduce the temperature of the ingot end and reduce the entry of impurities into the profile, which helps to increase the yield.
The mold temperature plays an important role in obtaining high output, generally not lower than 430°C; On the other hand, it should not be too high, otherwise, not only the hardness may decrease, but also oxidation, mainly in the working zone. During the mold heating process, avoid close contact between molds to obstruct air circulation. It is best to use a box heating furnace with a grid, and each mold is placed in a separate box.
The temperature of the ingot billet during the extrusion process can reach about 40°C or higher, and the increase is mainly determined by the mold design. In order to obtain the maximum output, each temperature must not be ignored, and each temperature should be recorded and strictly controlled to find out the relationship between the maximum output of the machine and each temperature.
Employees of aluminum extrusion production plants should keep in mind that precise control of temperature is essential to increase output.
