Wire section, paper production

DRAINING ON THE WIRE SECTION. The differences obtained when beating or refining under neutral/alkaline conditions can produce some unexpected changes in the behaviour of the stock as it drains on the forming fabric of the paper machine - a specially critical region of the process in terms of product quality and uniformity. 

For production of woodfree uncoated and coated fine papers up to 40 kg starch per ton of paper are applied. 3 to 10 kg starch is added at the wet end, with the aim of internal strength improvement and retention increase. The major share of the starch is added to the sheet in surface treatment. A mass balance on a typical fine paper machine has shown, that more than 90% of the added starch is retained in the final paper product. Losses occur mainly during the sheet forming process in the wire section due to insufficient retention. Starch which is not held back in the paper is discharged with the process effluents to the waste water treatment plant, where a complete biodegradation process follows. 

Sheet formation on an inclined wire section is performed in the area where the wire is covered by a box filled with the suspension and is usually under pressure (Fig. 6.38D). Here the wire is supported by some type of forming board. The pressure under the forming board can be controlled. This type of forming unit is for low machine speeds and operates with low consistencies of down to about 0.01 %. It is used for the production of special papers and nonwovens. 

Figure 6.81 shows a schematic of a modem paper machine for LWC paper production started up in 2004. It includes a gap former wire section, a press section with a double-felted first press nip and a second press nip with felt and transfer... 

The paper machine itself is a single continuous production line with a length that today may exceed 200 m and comprises the following main sections headbox, wire section, pressing section, drying section, and finishing section. 

---