Experimental Study of NIP Dynamics in Metered Size Press Coating, 2002 Coating Conference Proceedings

J. Poranen, J. Grön, M. Kataja and A. Niemistö

The pressure distribution in both the metering nip and the film transfer nip was measured using handmade pressure sensors placed under the roll cover material. The influence of the roll speed, the linear load, and the coating suspension on the measured pressure profile was studied. The influence of the roll speed on the measured pressure profile was found to be minimal, whereas the effect of the linear load was evident. Even though the pressure profile was measured under the roll cover material, the measured values were relatively high. This sets high requirements for the roll cover materials.

Strain profiles of the roll cover material in the nip contacts and the heat build-up of the cover material during the coating process were measured with strain gauges and thermocouples installed inside the roll cover material. It was observed that the temperature of the roll cover material increased several tens of degrees depending on both the linear load and the machine speed. Such a temperature increase has a distinct effect on the dynamic mechanical properties of the roll cover material and, thus, probably on the whole coating process. The measured strain profiles of the roll cover material in the nip contacts were consistent and correlated realistically with the pressure profile and temperature measurements.