Screen Volume, Paste Deposit & Squeegee-Shear Viscosity

Open area is computed from a square-weave geometry, which describes a flat screen well and a rotary nickel screen only loosely - a galvanoformed rotary screen has round or hexagonal holes and its open area should be taken from the supplier specification rather than derived here. Theoretical volume is the paste the screen can hold, not the paste it delivers: transfer efficiency covers the fraction the squeegee actually pushes through and the fabric actually accepts, and it moves with squeegee pressure, blade hardness, printing speed and above all with how absorbent the ground is, so a value fitted on one construction does not transfer to another. The power-law fit describes the shear-thinning region and nothing else; it has no yield stress, so it will happily predict a finite viscosity at zero shear where a real paste has effectively infinite viscosity and does not flow at all, and that low-shear behaviour is exactly what governs whether a print bleeds after the blade has passed. Sharpness of line and bleeding are therefore not predicted here. The shear rate is a nominal blade estimate, taken as speed over film gap; the true rate varies steeply through the film and is much higher at the screen wall.