It is shown that many physical properties of paper vary significantly in the CD, as much as 10% or more. These variations are believed to be due to the great dependence of sheet properties on the jet minus wire speed differential, and on the large random variations in the headbox discharge velocity, especially from older, air-padded headboxes run at speeds greatly exceeding their design capacity. These jet velocity variations arise both from partially plugged tube bundles feeding the headbox, and from eddy currents created by the slice rectifier roll.
Instead of replacing such headboxes to overcome these problems, it is proposed that two elements of slow ( 100 m/min), early 20th century Foundriniers missing from modern high speed machines be re-introduced . One is a “stilling” Zone on the first part of the wire, once supplied by an apron; this can now be provided by a wide non-dewatering forming board. The second element is a unique Formation Shower which generates CD shear-inducing (like that due to a shake) repetitive ridges, and keeps the stock dispersed throughout the forming zone. The excellent results obtained in the first commercial installation employing these concepts at 650 m/min on light weight papers are presented.