In a multi-billet furnace, also known as a pusher furnace, in contrast to a single billet furnace there are always several billets in the coil section. Multi-billet furnaces are used for basic heating up to a temperature of typically 650 °C, after which the preheated billets are transferred to a single-billet furnace for precise setting of the final temperature, or for heating to the final temperature required for the pressing process.
The cold billets are pushed one behind the other as a closed column of material through the coil section by means of an electrically or hydraulically driven cylinder. The length of the coil section is essentially dependent on the billet dimensions, the required throughput and the desired temperature.
The coil section is typically divided into several zones, which can be individually regulated in terms of power and temperature, therefore enabling alloy-dependent heating curves. For this purpose, there is an optical temperature measurement in each zone, the measured value of which is transferred to the IGBT converter used and leads to an automatic adjustment of the power value in the event of a deviation between the setpoint and the actual value.