The oldest and still the most prevalent machine for making paper that utilizes a continuously moving wire mesh belt to produce long rolls, or webs of paper.
Following stock preparation and refining, the papermaking furnish—a water suspension of paper pulp fibers and any non-fibrous additives or fillers—is diluted to a concentration of about one part fibers to 200 parts water and delivered to the fourdrinier machine's wet end. Here, the pulp solution is kept in the machine's headbox, which keeps the fibers from bonding together prematurely. From the headbox, the furnish is sent through the slice—an adjustable rectangular slit—to the continuously moving forming wire. The headbox and slice ensure that the furnish is deposited on the wire with a uniform speed, thickness and consistency.
The forming section consists of the moving forming wire made of bronze or plastic. As the furnish is deposited on the wire, water drains through the mesh. Suction cup-shaped foils or table rolls beneath the wire increase water removal by suction. Some paper machines also oscillate the wire back and forth, producing a shake that also contributes to water drainage. As the water is removed, the fibers bond together forming the paper web. Additional layers of fibers are then deposited on top of previous ones. As the web forms, the side that forms in contact with the wire—called the wire side—will have a somewhat different texture than the top side—called the felt side. This two-sidedness of paper has consequences in certain types of printing, and new techniques and devices—in particular, a twin-wire former, an alternative to the traditional fourdrinier machine—have been developed to reduce differences in the wire and felt sides of paper. After the foils, table rolls, shake, and gravity itself have removed as much water as possible, the web passes over vacuum boxes which suck out more water. At this point, the web may pass beneath a dandy roll, a wire-covered cylinder that compresses the web fibers. In some papers, a watermark is produced utilizing a raised design on the dandy roll. (Watermark-like designs on the dandy roll also impart laid-like marks to some paper.) At the end of the forming section of the fourdrinier machine is a couch roll, a perforated cylinder that uses a vacuum to suck out more water before the web is sent to the press section.
The paper is 80:85% water when it reaches the press section. As its name implies, the purpose of the press section is to compress the fiber web to improve fiber bonding and regulate the ultimate thickness, bulk, and finish of the paper. The degree of pressing at this stage can be adjusted, depending on the desired bulk and finish of the paper. When the web leaves the press section, it is 60:70% water, and is ready to be sent to the drying section, where a series of heated cylinders evaporate residual moisture. The method of drying also depends on the desired characteristics of the paper. (See also Yankee Dryer and Air Drying.) The drying section also includes a size press, which adds a sizing solution to many types of papers. Following drying, paper may be subjected to various degrees of calendering to impart the desired finish, thickness, or other characteristics.
The difficulties created by the two-sidedness of paper has resulted in the search for modifications or replacements to the conventional fourdrinier machine. (See also Twin-wire Former and Cylinder Machine, as well as Paper and Papermaking: Papermaking.)
The fourdrinier machine has a fairly complex history that begins around the period of the French Revolution in a papermill run by St. Leger Didot. During the Napoleonic Wars, most of his skilled papermakers were conscripted into the army. Didot hired a new personnel director, Nicholas Robert, who had a talent for engineering and told Didot his idea for an automated papermaking machine. Didot agreed to financially support Robert in this endeavor. Robert produced a working model, and applied for a French patent. Soon, Didot and Robert fought over who actually held the rights to the machine, the result being that Didot agreed to buy the rights from Robert. A short time later, Robert sued to regain the rights and won, but Didot bought them back again. Robert, never actually getting paid by Didot, tried for the rest of his life to sell his invention but failed, and died broke. Meanwhile, Didot, having come to believe that there was no market for a papermaking machine, gave the idea to his brother-in-law, John Gamble, in London. There, Gamble took the idea to two stationer brothers, Henry and Sealy Fourdrinier, who agreed to help build the machine. In 1801, Gamble received a patent for the machine in Britain and the Fourdriniers started getting the machines manufactured. The man employed in their mill who was put in charge of the project also ran a foundry elsewhere, and passed all the paper-machine work to one of his foundry employees—Bryan Donkin—who was coerced into building the machine based on Robert's original design. Donkin improved on the machine, and set it up in a papermill at Frogmore in Hertsfordshire in 1803, primarily to manufacture wallpaper. The new papermaking machines, however, did not sell well, and other manufacturers infringed on the patent. Eventually, the court costs of the patent infringement suits drove the Fourdrinier brothers into bankruptcy.