When the aluminum extruder is reversely extruded, the direction in which the metal flows out is opposite to the direction in which the extrusion rod advances (relatively), and there is no relative movement between the extrusion barrel and the ingot.
The use of reverse extrusion has the following advantages:
1. Since there is no friction between the billet and the extrusion barrel, the pressing force is much lower than that in the forward extrusion. During the reverse extrusion process, the extrusion force remains constant over the full stroke of the extrusion bar. The hard-to-deform material can be extruded at a lower temperature with a higher extrusion coefficient.
2. The metal deformation is uniform, and the microstructure and mechanical properties along the length of the extruded product are basically the same.
3. Compared with the forward extrusion, the waste such as pressure residue is significantly reduced, and the yield is high; the larger ingot can be used, which helps to improve the efficiency of the equipment and the continuous production.
Of course, the reverse extrusion method also has the following disadvantages compared to the forward extrusion method:
1. The extrusion cylinder of the aluminum extrusion machine must be able to move. In order to ensure the production efficiency during reverse extrusion, the stroke of the extrusion cylinder should be slightly larger than the length of the extrusion cylinder. Therefore, not all extruders are suitable for reverse extrusion.
2. The surface quality of extruded aluminum is low.
3. The extrusion cycle is generally longer than the positive extrusion time. However, since the size and quality of the ingot can be increased, the residual loss is small, and the extrusion speed is high, the increase of the auxiliary time is compensated to some extent, and the reverse extrusion has higher production efficiency.
4. The maximum circumcircle diameter of extruded aluminum is limited by the strength of the hollow extruded rod.