When the aluminum extrusion machine presses reverse direction, the direction of the metal outflow is opposite to the direction in which the extrusion rob advances (relatively speaking), and there is no relative movement between the extrusion cylinder and the billet.
As shown above, the part of the original extrusion bar was converted into a blocking plate 1 and the section of the inner liner 2 of the extrusion cylinder was sealed. At the original position of the mold holder, an immovable hollow extrusion bar 4 is installed, and the mold 3 is set at the head of the extrusion rod. When the main plunger advances in the direction of the arrow, the extrusion cylinder moves together with the aluminum ingot, forcing the metal aluminum ingot to flow out of the holes of the mold 3 to form the extruded product 5 .
Using reverse extrusion has the following advantages
1. Since there is no friction between the aluminum rod and the extrusion cylinder, the pressing force is much lower than the forward extrusion. In the reverse extrusion process, the extrusion force remains unchanged over the entire stroke of the squeeze bar. The harder deformable material can be extruded with a higher extrusion coefficient at a lower temperature.
2. Metal deformation is uniform, and the structure and mechanical properties along the length of the extruded product are basically the same.
3. Compared with forward extrusion, waste materials such as residual pressure are significantly reduced and have a higher yield; larger aluminum ingots can be used, which contributes to the improvement of equipment efficiency and continuous production.
Of course, the reverse extrusion method also has the following disadvantages compared to the forward extrusion method:
1. The extrusion barrel of the aluminum extrusion machine must be able to move. In order to ensure the production efficiency in reverse extrusion, the stroke of the extrusion barrel should be slightly larger than the length of the extrusion barrel. Therefore, not all extruders are suitable for reverse extrusion.
2. Surface quality of extruded aluminum is lower.
3. The extrusion cycle is generally longer than the forward extrusion. However, since the size and quality of the aluminum ingot can be increased, the residual pressure loss is small, and the extrusion speed is high, the supplemental time is compensated to a certain extent, and the reverse extrusion has a higher production efficiency.
4. The maximum circumcircle diameter of extruded aluminum is limited by the strength of the hollow extruded rod.