Table rolls

Variable, high-torque machine hains operating at moderate speeds Run-out table rolls Vertical pump shafting... 

Foils, table rolls and suction boxes aid the natural drainage through the wire... 

Figure 13.20. (a). Fourdrinier papermachine. (b) Drainage effects of foils and table rolls. 

Table rolls contribute a gentle suction in the downstream expansion zone between wire and roll, while some of the water pulled through clings as a film on the underside of the fabric to be pushed up through the wire on the upstream side of the next roll this vertical pressure pulse helps consolidate the web. Where wire speeds exceed about 25 m s the suction increases excessively and rolls are no longer used. 

The diluted stock may then be pumped by the fan pump through a series of cleaners and into the machine headbox. An inlet distribution header spreads the stock flow evenly over the width of the headbox. The flow is stabilised by the headbox and passes from the headbox through an adjustable orifice plate called the slice. It is discharged onto the moving wire screen (which is usually of plastic construction), dewatered by a series of devices called table rolls, foils and flat boxes leaves the wire as a formed web of paper. It is further dewatered and dried in the succeeding operation before being wound on the reel at the dry end of the machine. 

Paper and Board Manufacturing Tables. Roll cover applications. 

Table roUs (Fig. 6.39), used in the fourdrinier section for drainage and to generate turbulence. Pressure is developed in the upstream wedge between the wire and roU, and a vacuum is induced in the downstream nip. With increasing machine speeds the pressure and vacuum pulses increase over-proportionally and thus hmit the application of table rolls to machine speeds of about 500 m min. ... 

The short-wave turbulence (micro-turbulence), generated in the suspension in the headbox to maintain fiber deflocculation, dissipates rapidly. For this reason, good formation requires either the fiber web to be fixed very quickly or additional turbulence to be generated in the suspension to be dewatered. This can be achieved by means of pressure and vacuum impulses from table roUs, foils and blades. However, impulses that are too strong are harmful, for example by table rolls at machine speeds above approx. 500 m min or by foils with too high a foil angle at elevated machine speeds. In special cases, on fourdrinier wires, formation is improved by agitating the wire. A shaker vibrates the breast roll and thus the fourdrinier wire horizontally in the cross machine direction with a frequency of up to 10 Hz and an ampHtude of up to 25 mm. It is used at low machine speeds and... 

The fourdrinier wire (Fig. 6.38A) is the classical method of sheet formation. Speeds up to about 1200 m min are achieved with the fourdrinier. This is a reasonable limit due to excessive turbulence on the free suspension surface and dewatering capacity. Normally, the fourdrinier is equipped with a forming board, foils and/or table rolls, suction boxes, wet suction boxes, and suction rolls. Drainage proceeds in the direction of gravity. A dandy roll is often used just in front of the water line to improve formation. This is a wire-covered open roll, with a honey-... 

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