Good formation means fibers, fines and filler are spread evenly at scales from a few millimeters to a few centimeters; poor formation shows as flocs and thin spots. It is judged by eye in look-through or measured with light transmission or beta radiography and expressed as a formation index. Formation affects opacity uniformity, print mottle and strength, and it is set mainly at the headbox and forming section.
Formation went cloudy when they raised headbox consistency, you can see it in the look-through.
Formation and retention pull against each other: more retention aid usually means more flocculation and a cloudier sheet.
Also heard as
- sheet formation
- formation uniformity
Related terms
Floc
Clump of entangled fibers in stock or in the finished sheet, the building block of poor formation.
Look-through
Visual check of formation made by holding a sheet up to a light and judging how even or cloudy it looks.
Wild formation
Very uneven, blotchy formation with obvious flocs and thin areas when the sheet is held to the light.
Headbox
Pressurized box that spreads stock in a thin, even jet across the full width of the forming wire.
Mottle
Uneven, blotchy appearance in a print or coating, seen as cloudy patches of density or gloss.