The production of profiles in the extrusion process requires uniform and precise heating of the starting material. Aluminium of various alloys is used as the starting material. This is fed into the process in the form of billets or logs. Both gas furnaces and induction systems can be used for heating. A hybrid form of heating is also possible, in which the basic heating is carried out using gas and the precise temperature setting is carried out using induction.
Depending on the extrusion process, the heating is uniform over the length of the billet or a temperature profile is set over the length of the billet. Setting an axial temperature profile allows isothermal extrusion.
The extrusion press itself can only process billet-shaped starting material, so that each rod is cut into several billets. This can be done in the cold state using a cold saw or in the warm state with a hot saw.
Depending on the form of the starting material and the heating technology used, various plant concepts can be described.
Log-shaped starting material is often heated in a gas furnace, at the outlet the logs are then cut to length using a hot saw or shears and transferred to the press as billets. It is also possible to use a cold saw or shear and to heat billets in a gas furnace. In principle, it is possible to set a temperature profile over the length of the billets, but this is limited in terms of accuracy.
When heating exclusively by means of induction in a TEM-PRO heater® billets are used, which are individually heated in an induction coil. The division of the coil into several zones depending on the billet length in connection with the precise power control for each individual zone enables a precise temperature setting. Uniform heating over the length can be set, as well as an axial temperature profile for isothermal extrusion.
The advantage of precise temperature setting using induction is also used in the hybrid form, in which the basic temperature of typically 400 °C is reached in a gas furnace.
In the inline configuration with HybroHeat developed and patented by IAS®, logs are preheated in a gas furnace, at the outlet of which an induction coil forms the last zone before the log is fed to the saw, which is also arranged in line.
In the standalone configuration a separately arranged TEM-PRO heater® is used and takes over preheated billets coming from the gas furnace. This configuration can be planned from the outset for new systems in order to use the advantages of both energy sources. Also the later retrofitting of a TEM-PRO heater® is possible to achieve more precise heating or an increase in throughput.
The main differences between the various concepts are: