Research Progress of Isothermal Extrusion Technology for Industrial Aluminum Profiles

The theoretical basis for achieving isothermal extrusion is the extrusion limit diagram. The extrusion limit diagram describes the relationship between extrusion temperature (T), extrusion speed (V), extrusion capacity (P), and surface quality (Q) of the article, as shown in FIG. Extrusion limit diagram contains two limit curves, one is the limit curve of the extrusion capacity, when (T, V) is located in the shadow area above the extrusion capacity curve, the extrusion can not be achieved; the other is the extrusion product surface defects The limit curve, when (T, V) is located in the shadow area above the surface quality curve of the extruded product, the surface of the product will have defects such as cracks and adhesion. The window between the two curves provides a feasible range for the (T,V) extrusion of the corresponding product. When (T,V) is in the isothermal extrusion zone, the extrusion speed is higher than that of the conventional extrusion at the same extrusion temperature. The nip is much higher and at the same time avoids defects on the surface of the product. At the intersection of the two curves, the theoretical maximum extrusion speed and the optimum outlet temperature are provided.

 

The principle behind the temperature gradient of the cast rod is that the temperature at the radius of the cast rod is very fast, and the axial temperature gradient of the cast rod can be maintained for several minutes. The basic equation of heat transfer shows that the heat transfer rate of the solid is inversely proportional to the square of the distance. For a cast rod with an aspect ratio of about 100, the radial heat transfer rate is about 64 times that of the two ends. Gradient heating of the cast rod means that a temperature gradient is formed in the length direction of the cast rod before it is loaded into the extruder. Due to the large thermal conductivity of aluminum alloys, it is difficult to generate a precise temperature gradient in the cast rod using conventional fuel heating methods, and the gradient cannot be maintained. Therefore, an electromagnetic induction heating system must be used, which heats one end of the cast rod. Or heat the cast rods in stages. Extrusion speed control is a key factor in keeping the exit temperature of industrial aluminum profiles constant.