Typically, without unscheduled downtime, maximum production is determined primarily by extrusion speed, which is subject to four factors, three of which are fixed and one of which is variable. The first factor is the extrusion pressure of the extruder. The high extrusion pressure can be smoothly extruded when the billet temperature is low. The second factor is the die design. The friction between the metal and the die wall during extrusion usually increases the temperature of the aluminum alloy through 35 ~ 62℃. The third factor is the characteristics of the extruded alloy, is to limit the extrusion speed of the uncontrollable factors, the exit temperature of the profile generally cannot exceed 540℃, otherwise, the surface quality of the material will decline, mold marks significantly aggravated, and even the appearance of aluminum, gravure, micro cracks, tearing, etc. The final factor is temperature and how controlled it is.
If the extrusion pressure of the aluminum extruder is not large enough, it is difficult to extrusion smoothly or even plug phenomenon and extrusion can not move, you can improve the billet temperature, but the extrusion speed should be low, to prevent the exit temperature of the material is too high. Each alloy has its particular optimum extrusion temperature. Production practice has proved that it is best to keep the billet temperature at about 430℃ (extrusion speed ≥16mm/s). The extrusion temperature of 6063 alloy profile shall not exceed 500℃, the maximum outlet temperature of 6005 alloy shall be 512℃, and the best outlet temperature of 6061 alloy shall be no more than 525℃. Little change of mold temperature will also affect the yield and quality of the product.
Extrusion cylinder temperature is also very important, especially attention should be paid to the temperature rise in the preheating stage, should avoid excessive thermal stress between the layers, it is best to make the extrusion cylinder and bushing at the same time to rise to the working temperature. The preheating rate shall not be greater than 38℃/h. The best preheating specification is: rise to 235℃, hold for 8h, continue to heat up to 430℃, hold for 4h, before putting into work. This not only ensures a uniform temperature inside and outside, but also gives enough time to eliminate all internal thermal stresses. Of course, in the furnace heating extrusion cylinder is the best way to preheat.
In the extrusion process, the extrusion cylinder temperature should be 15 ~ 40℃ lower than the ingot temperature. If the extrusion speed is too fast, so that the extrusion cylinder temperature rises above the billet temperature, it is necessary to try to make the extrusion cylinder temperature drop, not only a troublesome work, but also the yield will decline. In the process of production rate increase, sometimes the heating element controlled by the electric couple will be cut off, but the extrusion cylinder temperature is still rising. If the temperature of the extrusion cylinder is higher than 470℃, the extrusion waste 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. A factory in order to catch up with production, on the one hand with internal resistance element heating, on the other hand with liquefied gas burner heating. In this case, the temperature can not be measured and controlled, will produce a huge thermal stress, the lining temperature is high, expansion faster than the coat, so that the extrusion cylinder split, and heard the "burst" sound.
The extrusion shaft will accumulate internal stress in the working process, which will cause fatigue cracks to a certain extent, and will fracture 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, hold heat at 430 ~ 480℃ for 12h, and then cool down to 50℃ with the furnace. Unfortunately, few factories in our country do this.
The temperature of extrusion pad should also be strictly controlled when producing high quality surface building profiles, so as to reduce the amount of surface tone discordant waste. Fixed extrusion pads are of much better quality than mobile ones and accumulate more heat, thus reducing the billet end temperature and reducing the entry of impurities into the profile, helping to increase production. Castool, an American company, uses compressed air to cool the extrusion pads and shafts to about 50 ° C.
Mold temperature plays an important role in obtaining high yield, generally not less than 430℃; On the other hand, it should not be too high, otherwise, not only hardness may decrease, but also oxidation, mainly in the working belt. In the process of mold heating, should avoid mold close together, hinder air circulation. It is best to use box type heating furnace with lattice, each die is placed in a separate box.
The temperature rise of the billet in the extrusion process can reach 40℃ or higher, and the increase is mainly determined by the mold design. In order to obtain the maximum output, the temperature must not be ignored, should record each temperature and strictly control, in order to find the maximum output of the machine and the relationship between the temperature.
Finally, the staff of the extrusion plant should bear in mind that the precise control of temperature is essential to increase production.
