Forming Station Physics: Meniscus, Edge Dam, Slurry Rheology Window
Where the board becomes a board. Three forces, one window of survival.
The forming station is geometry imposing chemistry. The slurry must flow into the edge dams, wet the paper, hold the bottom and top facings parallel, and begin to set before the knife — all in roughly thirty seconds of belt travel.
The rheology window
A slurry that is too thin pours through the edge dams and produces a wavy edge profile. Too thick, and the meniscus tears, leaving a starved bottom paper and a poor bond. The window is narrower than most plants realize. With a modern PCE you can hold flow at lower water demand, but the trade-off is a longer induction period — the slurry takes longer to start setting after it leaves the mixer.
If you have switched dispersant chemistry recently and started seeing edge cracking, the diagnosis is almost always that your accelerator hasn't been re-tuned to the new induction period.
The forgotten variable
Belt speed. Plants will adjust slurry chemistry rather than belt speed because chemistry is "soft" and mechanics are "hard." The right answer is the opposite. Find the belt speed that gives your knife a clean cut at your target board weight, then tune chemistry to that speed.