Extrusion head for aluminum extrusion
The extrusion head is the most critical extrusion equipment used in the aluminum extrusion process (Fig 1). The quality of the pressed product and the overall productivity of the extruder depend on it.
Fig 1 Extrusion head in a typical tool configuration for the extrusion process
Fig 2Typical design of extrusion head: extrusion cake and extrusion rod
Fig 3 Typical design of extrusion head: valve stem and extrusion cake
Good performance of the extrusion head depends on factors such as:
Overall alignment of the extruder
Temperature distribution of the extrusion barrel
Temperature and physical properties of the aluminum billet
Proper lubrication
Regular maintenance
Function of the extrusion head
The function of the extrusion head seems very simple at first glance. This part is like a continuation of the extrusion rod and is designed to push the heated and softened aluminum alloy directly through the die. The extrusion cake must perform the following functions:
Transmit pressure to the alloy in each extrusion cycle under high temperature conditions;
Quickly expand under pressure to a predetermined limit (Figure 4), leaving only a thin layer of aluminum alloy on the container sleeve;
Easy to separate from the billet after extrusion is completed;
Not trap any gas, which could damage the container sleeve or the dummy block itself;
Help to solve minor problems with the alignment of the press;
Able to be quickly mounted/dismounted on the press rod.
This must be ensured by good extruder centering. Deviations in the movement of the extrusion head from the extruder axis are usually easily recognized by uneven wear, which is visible on the rings of the extrusion cake. Therefore, the press must be aligned carefully and regularly.
Fig 4 Radial displacement of the extruded cake under extrusion pressure
Steel for the extrusion head
The extrusion head is the part of the extrusion tool that is subjected to high pressure. The extrusion head is made of tool die steel (e.g. H13 steel). Before starting the press, the extrusion head is heated to a temperature of at least 300 ºС. This increases the steel’s resistance to thermal stresses and prevents cracking due to thermal shock.
Fig5 H13 steel extrusion cakes from Damatool
Temperature of the billet, container and die
An overheated billet (above 500ºC) will reduce the pressure of the extrusion head during the extrusion process. This can lead to insufficient expansion of the extrusion head, which causes the billet metal to be squeezed into the gap between the extrusion head and the container. This can shorten the service life of the dummy block and even lead to significant plastic deformation of its metal by the extrusion head. Similar situations can occur with containers with different heating zones.
Sticking of the extrusion head to the billet is a very serious problem. This situation is especially common with long work strips and soft alloys. The modern solution to this problem is to apply a lubricant based on boron nitride to the end of the workpiece.
Maintenance of the extrusion head
The extrusion head must be checked daily.
Possible aluminum adhesion is determined by visual inspection.
Check the free movement of the rod and the ring, as well as the reliability of the fixing of all screws.
The extrusion cake must be removed from the press every week and cleaned in the die etching groove.
During the operation of the extrusion head, excessive expansion may occur. It is necessary to control this expansion not to be too large. Excessive increase in the diameter of the pressure washer will significantly shorten its service life.
Post time: Jan-05-2025
