Comparative Study of Forces in Blade Coating, 1991 Forest Products Symposium Proceedings

Previous analyses of blade coating have considered many different forces that act on a stiff bevelled blade including hydrodynamic lubrication, impulse, and the lateral forces. The objective of this work was to quantitatively compare

each one of these forces with results from controlled pilot-plant experiments. A technique was developed to estimate the total dynamic force (TDFe) from curves of coat weight as a function of blade pressure at three web speeds ranging

from approximately 150 to 300 m/min. Under the conditions investigated, the impulse force accounted for more than

90% of the TDFe , while the rest was attributed to hydrodynamic lift in the vicinity of the blade tip. Furthermore, the contribution of the impulse force increased with web speed. Lubrication flow in the blade nip alone was not sufficient to explain coat weight development since hydrodynamic lift represented less than 47% of the TDFe. Experimental results also indicated that the sum of impulse and hydrodynamic lubrication forces described coat weight accurately.

Therefore, the pressure force should be omitted from calculations of impulse in blade coating. Finally, the recently

proposed lateral force at the nip represented only 4 to 8 percent of TDFe within the speed range studied.