Method for extruding an extrusion product and extrusion line

An extrusion line for extruding an extrusion product, the extrusion line comprising

• an extruder, which is configured to continuously receive bulk material and to extrude an extrusion product,
• a control device for controlling the extruder,
• a feeding device, which is designed and provided to receive a first bulk material and to pass it on to the extruder, and to output a first feed rate to a control device,
• a metering device, which is designed and provided to receive an additive bulk material and to pass it on to the extruder, and to output an additive measurement signal to the control device,
• a cooling device arranged downstream of the extruder for cooling the extruded product, and
• a stationary radar measuring device arranged downstream of the cooling device, which is designed and provided to continuously measure a layer travel time through a layer of the extrusion product,
• wherein the control device is configured to determine the layer thickness and the refractive index of the extrusion product in an initial measurement of the extrusion product and to calculate and control an additive content of the extrusion product from the refractive index and stored calibration values,
• wherein the control device is further configured to continuously or repeatedly control measurements of the stationary Radar measuring device during the extrusion and to record measured values of the current layer running time, in order to determine from a change in the measured current layer running time a change in the additive content and to control the additive content by controlling the metering device and changing the additive feed rate.