Fourdrinier wire

Subsequent to stock preparation and proper dilution, the paper furnish usually is fed to the paper machine through one or more screens or other devices to remove dirt and fiber bundles. It then enters a flow spreader which provides a uniform flowing stream and which is the width of the paper machine. The flow spreader, or manifold, discharges the slurry into a headbox, where fiber flocculation is minimised by microturbulence and where the proper pressure head is provided to cause the slurry to flow at the proper velocity through the slice and onto the moving Fourdrinier wire. 

The pulp and paper additives enter the process first through a dump chest in their concentrated form. Adjustments are then made to the concentration in the stock chest just prior to transfer onto the Fourdrinier wire where the paper sheet is produced. Surface additives are sprayed after sheet formation and the final sheet is dried at high temperatures in dryers. The water from the wire is removed into underground tanks and in most cases, recirculated and reused. 

In some situations, if good plant hygiene is not maintained, fungal spores can also become established in and around the Fourdrinier wire. These can develop into large surface colonies which can become dislodged and transfer onto the paper sheet during formation. Again, this can lead to paper sheet failure. 

Paper machine Machine on which paper or paperboard is manufactured. The most common type is the fourdrinier machine using the fourdrinier wire as a felting medium for the fibers. 

Use Spark-resistant tools, springs, fourdrinier wire, paint, cosmetics (as powder), electrical hardware, vacuum dryers, blenders, water gauges, flow indicators, valves, drain cocks, fine arts. 

Use Springs, electrical switches, contact fingers, chains, fourdrinier wire. 

The furnish is fed to the headbox of a paper machine (Fig. 15.12), about the length of a city block. Sufficient additional fresh water (white water) is added to bring the pulp concentration in the headbox down to about 0.5%. White water, the water removed from the fibers as the paper sheet is formed on the machine, is continuously recycled. This low-concentration of pulp in water is necessary to obtain an even distribution of fiber (a smooth formation ) as the sheet is formed. The diluted furnish is fed through an adjustable horizontal slot (the slice) in the headbox onto an endless wire screen (the Fourdrinier wire), which moves rapidly away from the headbox. Direct drain-... 

At the end of the Fourdrinier wire a couch roll removes more water from the web before it is transferred to the press section. At this point the moisture content of the web is about 80% water (20% consistency, 200g/L). The white water from the Fourdrinier is continuously recycled 1000 kg of stock at 0.5% consistency is reduced to a 25 kg mat (5 kg fibre, 20 kg water) by the time it leaves the wire and 975 kg of white water is recycled to the make-up chest and thence back to the headbox. A 500 tonne a day papermachine recycles some 100 000 m of water a day. 

The wet-web is only a little stronger than where it left the Fourdrinier wire. It is still held together principally by van der Waals forces, surface tension, liquid cohesion and adhesion, and by Ifictional forces between the entangled fibres. Surface tension in particular plays an important part in sheet formation, in drawing the fibres into close contact within the fibre network. A closed draw is desirable. 

Some mills spray starch slurry to the Fourdrinier wire on single-ply webs. The position of the starch spray beam is critical in these applications spraying after the dry line results in starch sitting on the surface of the sheet with potential problems of felt filling and dryer sticking, while spraying close to the head-box results in the loss of most of the starch with the drainage water. The optimum lies somewhere between these positions and must be found by experimentation. 

The typical method of manufacturing paper involves feeding a mixture of fiber and water onto a travelling wire screen (Fourdrinier wire) so that most of the water drains through the screen and a wet web remains. The web is then subjected to vacuum and pressure (in the presses) to remove more water and receives the final drying by passing through a series of steam-heated cylinders. 

Fourdrinier wire section, the most common forming principle in the past and which has been continuously improved since its early invention, is a horizontal forming wire supported by different kinds of dewatering elements. 

Twin wire hybrid former where a rotating second wire is mounted on top of the fourdrinier wire, dewatering part of the suspension through the top wire. 

Wet suction boxes, which are dewatering elements that are located in front of the water line. They operate under vacuum and, in contrast to suction boxes, they mainly remove white water from the suspension. The water line is a line beyond which no free water is present on the surface of the freshly formed web and that is discernible on the fourdrinier wire by a change in light reflection. 

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-... 

The majority of paper machines worldwide produce graphic paper grades on fourdrinier wire sections or on hybrid formers. These kinds of conventional forming section usually satisfy the quaHty requirements. Their disadvantages are the limitation in machine speed of about 1200 m min and for some paper grades the nonsymmetry in the web z-direction. 

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