Paper forming unit in which the sheet is first formed on a conventional fourdrinier table, and then a top wire is applied in some manner.
Definition source:
EN 9
Context:
In the hybrid former, much drainage occurs on a conventional fourdrinier before the web meets the top wire provided by the hybrid former. The top wire, by itself, does not add an extra ply, but it does provide dewatering elements (while improving formation). These are typically a forming roll (the 1st roll), which may or may not be a suction roll, plus a blade shoe (containing foil blades), and sometimes a form of vacuum box. Drainage above the wire (about 33% of the total) is complemented by a slight pulsating action on the web as it passes over blades below the wire.
