here in particular the shear rate especially but not exclusively in the region of the screw closure the viscosity or shear rate values are determined by way of the detection of the melt front this either takes place with the aid of pressure or temperature sensors or it is equally conceivable to use what are known as digital binary switches for example light guides for detecting the melt front the basic concept is that the flow profile changes fundamentally if only one melt flows through this region instead of two different melts since the injection volume of each individual component or each individual layer does not change while this is happening the shear rate of the individual layers must inevitably change at a lower shear rate there is no barrier layer at a higher u201c optimized u201d shear rate the barrier layer is present with preference of course the shear rate of each layer is monitored so that the actual layer of plastic and the barrier layer are differentiated very precisely in order only to determine the shear rate it would be conceivable to use some combination of pressure and temperature sensors since it is especially the time difference that the melt requires to flow through the flow path between the two sensors that is determined the easiest and lowest cost variant would be that of arranging two temperature sensors since these are on the one hand small and on the other hand also less expensive than pressure sensors instead of monitoring or controlling.