Method and device for determining a layer property of a layer in an extrusion process

Method according to one of the preceding claims, characterized in that, as electro-magnetic radiation, Terahertz radiation (S), in particular in a frequency range between 0.1 and 50 THz is irradiated.

Method according to one of the preceding claims, characterized in that said extrusion product (2) is measured electro-magnetically during the conveyance involving relative adjustment of said extrusion product (2) in its direction of conveyance, preferably without rotation of said extrusion product (2).

Method according to one of the preceding claims, characterized in that the feed-in rate (z) is measured gravimetrically and/or involving measurement of a supply mass per time, e.g. by means of a scales device (9), and/or involving measurement of a supply volume per time.

Method according to one of the preceding claims, characterized in that, further, a retraction velocity (v) of said extrusion product (2) is determined and used for determining said at least one layer property (n16, wd16).

Method according to one of the preceding claims, characterized in that, as layer property of said mixed layer (16), a refraction index (n16) and/or a wall thickness (wd16) is determined.

Method according to one of the preceding claims, characterized in that, upon determining the layer property (n16, wd16), further, at least one dimension, e.g. a diameter (D), of said extrusion product (2) or of a layer of said extrusion product (2) is included.

Method for manufacturing an extrusion product (2) from a plastics material, where

• at least one supply material (7) is continuously fed to an extruder (3) and foamed at least in part, and an extrusion product (2) is continuously extruded and extracted, whereby said extrusion product (2) contains at least one layer (16) to be determined,
• at least one layer property (n16, wd16) of said the layer (16) to be determined is determined using a method according to one of the preceding claims, and
• as a function of said at least one determined layer property (n16, wd16) the feed-in rate (Z) or feed-in volume of said supply material (7) is adjusted for regulating said at least one layer property (n16, wd16).