Fourdrinier former

Making paper by a eontinuous proeess dates back to 1798, with Robert s invention of the foremnner of the modem Fourdrinier former. Many different types of formers are in use today. They are of three basic types, the Fourdrinier former, the twin wire former, and the cylinder former. Eaeh has many variations on the basic design, and is especially suited to partieular papers. Fourdrinier and twin wire formers are used to make papers that range from extremely lightweight tissue grades to linerboard. Cylinder maehines are used to make heavyweight papers and paperboards that are formed in several layers. 

The Fourdrinier former is likely the most widely used forming method employed in modem papermaking. It has proven uniquely versatile in the variety of paper grades it can produce. Wire speeds up to 5000 feet per minute are possible with some lightweight grades. The following description follows the pulp flow fi-om the headbox to the couch roll just prior to the press section. A Fourdrinier wet end is shown in Figure 3. 

The slurry is pumped into another stock chest, where wax in emulsion form, usually about 0.5—1.0% wax-to-fiber weight, and 1—3% PF resin are added. PF resin is also added on the basis of resin solids-to-dry fiber. Then a small amount of alum is added, which changes the pH (acidity) of the slurry, causing the resin to precipitate from solution and deposit on the fibers. Resin is required in greater quantity than in the Masonite process because only light bonding occurs between fibers prepared in a refiner. The fiber slurry is then pumped to the headbox of a Fourdrinier mat former, and from this point the process is similar to the Masonite process. 

Centrifugal Former. The use of a centrifugal former allows for the preparation of a sheet of paper that posseses a fiber orientation similar to the orientation present in commercial papers. With this apparatus, the fiber suspension is sprayed onto a fast rotating screen. The dynamic motion of the screen mimics the moving wire of the Fourdrinier machine and induces fiber orientation. In addition, by independently varying the flow of the fiber suspension and the speed of rotation of the screen, different degrees of fiber orientation can be obtained. 

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. 

C (a) suction former with rotating wire on a fourdrinier, (b) Suction breast roll former in tissue production,... 

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. 

As the fourdrinier vtire sections have sufficient speed potential gap formers are seldom used in cartonboard production. Nevertheless gap former installations can be found for certain applications of specialty board like gypsum board. 

The base sheet forming concept for specialty papers is the fourdrinier. It can be used for the whole basis weight range and up to a machine speed of about 1200 m mimf In order to achieve best results concerning formation and dimensional stability Dandy rolls or hybrid formers and effective vidre shaking units are frequently used. New machines however can exceed the speed limit of fourdri-niers, so gap former concepts are used in this case. 

The twin wire formers are a variaton of the Fourdrinier. The Fourdrinier tends to make a sheet that is two-sided, beeause drainage occurs in only one direetion. The sheet is imeven in distribution of fine fibers, dyes, and filler pigments. This can be especially undesirable in colored papers, since dyes have a greater affinity for the finer fibers and pigment particles. Because water drainage on the Fourdrinier eoneentrates these fines on the wire side of the sheet, the color of darkly dyed papers tends to be imeven with the bottom and top sides distinctly different. 

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