2790 



Chapter 23 



in which each fiber is freely movable to a sheet in which all fibers are fixed in 

 positions relative to one another that they will maintain through the rest of the 

 process. Since many of the qualities of the finished board are established here, 

 subsequent steps must not disturb this structure. 



The forming table slopes upward from the headbox towards the wet press. 

 This slope is adjustable and helps match the speed of the outflowing stock to the 

 speed of the wire. Any speed differential will cause drag on the fibers and biased 

 fiber orientation affecting directional mechanical and physical properties. A 

 double adjustable tilt permits a steeper slope at the exit from the headbox, then a 

 more gentle slope to the press section."^ 



On the machine shown in figure 23-32 the screen is supported by a series of 

 closely spaced idling steel table rolls 4 to 5 inches in diameter. These rolls are 

 designed to carry the considerable load of the stock and also contribute to 

 dewatering. Figure 23-33 graphs development of the considerable vacuum 

 caused by surface tension in the outgoing nip of a table roll running at peripheral 

 speeds of 2,000 to 2,500 feet/minute. Only paper machines run at such speeds. 

 A fiberboard machine operates at speeds less than 100 feet/minute and the 

 vacuum created will be much smaller. 



WIRE GUIDE 



TABLE ROLLS 



SAVEALL TRAYS 



Figure 23-32. — Fourdrinier board forming machine with wet press. (Drawing after Lyall 

 1969.) 



