Increase the output of extruded aluminum profiles through temperature control

Typically, if 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 variable. The first factor is the extrusion force of the extruder, which can be extruded smoothly when the temperature of the ingot is low; 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 passing 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 cannot exceed 540 °C, otherwise, the surface quality of the material will decline, the mold marks will be significantly aggravated, and even the appearance of sticky aluminum, gravure, micro-cracks, tears, etc. The last factor is the temperature and how well it is controlled.

If the extrusion force of the aluminum extruder is not large enough, it is difficult to squeeze smoothly or even the mold plugging phenomenon can not 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 (ingot) temperature. Production practice has proved that the temperature of the spindle billet should be kept at about 430°C (when the extrusion speed ≥ 16mm/s). The die temperature of 6063 alloy profile shall not exceed 500 °C, the maximum outlet temperature of 6005 alloy is 512 °C, and the best temperature of 6061 alloy shall not be greater than 525 °C. A small change in the ejection temperature can also affect the yield and quality of the product.

The temperature of the extrusion cylinder is also very important, special attention should be paid to the temperature increase in the preheating stage, excessive thermal stress between the layers should be avoided, and it is best to make the extrusion cylinder and the bushing rise 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 8 hours, continue to heat up to 430 °C, keep warm for 4 hours, and then put into work. This not only ensures that the internal and external temperatures are uniform, but also has enough time to eliminate all internal thermal stresses. Of course, heating the extrusion drum in the furnace is the best way to preheat.

In the extrusion process, the temperature of the extrusion cylinder should be 15~40°C lower than the temperature of the spindle. If the extrusion speed is too fast, so that the temperature of the extrusion drum rises to a higher temperature than the spindle billet, it is necessary to try to make the temperature of the extrusion cylinder drop, which is not only a troublesome job, but also the output will decrease. As the production speed increases, sometimes the heating element controlled by the galvanic is cut off, but the temperature of the extrusion barrel is still rising. If the temperature of the extrusion cylinder is higher than 470°C, the extrusion scrap will rise. The ideal extrusion barrel temperature should be determined according to the different alloys.

Don't think that preheating the drum is a waste of time and energy. In order to catch up with the production task, a factory uses internal resistance elements to heat on the one hand, and liquefied gas burners on the other hand. In this case, the temperature cannot be measured and controlled, and there is a huge thermal stress, and the temperature of the liner is high, and it expands faster than that of the jacket, so that the extrusion cylinder cracks and a "popping" sound is heard.

During the working process, the extruded shaft will accumulate internal stress, which is large enough to produce fatigue cracks, and will break once it is subjected to non-axial radial forces. Therefore, after the cumulative working time of the extrusion shaft reaches 4500h, it is best to carry out a stress relief treatment, keep it warm at 430~480 °C for 12h, and then cool it to below 50 °C with the furnace. Unfortunately, very few factories in our country do this.

In the production of high-grade and high-quality surface building profiles, the temperature of the extrusion pad should also be strictly controlled to reduce the amount of waste products with inconsistent surface tones. The quality of the fixed extrusion pad is much better than the active one, and it can accumulate more heat, which can reduce the temperature of the spindle end and reduce the amount of impurities entering the profile, which can help to increase the yield.

The mold temperature plays an important role in obtaining a high output, which is 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, it should be avoided to be close to each other and obstruct air circulation. It is best to use a chamber furnace with a grid, with each mould placed in a separate chamber.

The temperature of the spindle can rise to about 40°C or higher during the extrusion process, and the amount of increase is mainly determined by the mold design. In order to obtain the maximum output, the temperature should not be ignored, and the temperature should be recorded and strictly controlled to find out the relationship between the maximum output of the machine and the temperature.

Personnel in aluminium extrusion production plants should keep in mind that precise temperature control is essential to increase output.