Sizing
Box concentration is add-on divided by pick-up. Change the squeeze and you have changed the recipe.
— %
Add-on divided by wet pick-up. Not a free choice
Wet pick-up is taken as litres per kilogram of yarn on the assumption that the size liquor is close enough to water in density for the two to be interchangeable, which holds at ordinary concentrations and drifts at high solids or with heavy filler loadings. The add-on this delivers is the add-on at the squeeze rolls, not the add-on on the beam: some size is lost at the drying cylinders as the sheet separates, and a little is carried back at the split rods, so the beam figure is usually a fraction of a point below what the box arithmetic predicts. Box turnover time is worth watching as much as concentration; a long turnover means size sitting hot for hours, and starch that has been held at temperature loses viscosity and film strength in a way that no addition of solids recovers. Where the turnover exceeds an hour or two the answer is a smaller box or a higher speed rather than a stronger cook. The concentration derived here assumes the box is at steady state with a constant feed; on start-up and after a stop the box is at whatever it drifted to, and the first hundred metres of warp are sized to a recipe nobody wrote.
Size Box Concentration & Stock Make-Up — free, with the formula and a worked example, at Textile School.