The Amazing Fourdrinier Machine
The Fourdrinier machine was invented in 1798 by a Frenchman of the name of Louis Robert. It was further developed in England by Brian Donkin by the request of Henry and Sealy Fourdrinier and put to work in the papermaking process in 1804. Today, the same basic design is used as an integral part in the papermaking process. The machine itself consists of four sections: wet end, press section, dryer section, and calendar section.
The Wet End
The wet end of the Fourdrinier machine is where the wood pulp in its slurry form, which is pulp mixed with water, is delivered to the machine. The pulp is usually brought here directly after the pulping process takes place, but it can also be delivered in dried sheets that are broken down in water in order to create a similar slush.
While in the wet end, the pulp is combined with fillers, sizing, and colors. Sometimes, waste paper, called broke, is passed on to the refiner. Here, the fibers are subject to rubbing and brushing. As a result, the fibrils of the smaller wood fibers become partially detached and bloom outward. Then, the pulp is washed some more and moved into the headbox, which is a unit responsible for loading the pulp onto a moving conveyer made of wire mesh.
As the pulp moves on the conveyer, a gate called the slice is used to determine the weight and thickness of the paper with the help of a series of tubes or table rolls. From here, it revolves around the Fourdrinier table and vibrates, which causes the fibers to become aligned. Beneath the table are suction boxes, which remove the water from the pulp with the help of a mild vacuum.
The Press Section
As the name suggests, the press section is made of two or more presses. The purpose of the press section is to remove more of the water that remains in the pulp. It accomplishes this by pressing the rolls against each other. Some of the squeezed out water is carried out by what is known as “press felt.” The rest is removed by suction with a vacuum chamber. In addition to helping remove more of the water, the press section smoothes and flattens out the pulp in the shape of a sheet.
The Dryer Section
When the pulp enters the dryer section, it still has a water content of approximately 65%. The drier section finishes reduces this content to about 5% with steam-heated rollers. Generally there are two or more of these rollers, which are tiered, within the machine.
Sizing agents are also added to the pulp at this time, such as starch, resins, and glue. This sizing process helps make the paper more resistant to water. It also reduces the abrasiveness, decreases its ability to fuzz, and improves the printing properties of the paper.
The Calendar Section
Not all Fourdrinier machines have a calendar section, though most do. This area consists of a series of rollers in which the web of papers is run. This helps to further smooth it out and creates a more uniform thickness. The pressure placed on the paper at this time determines the finish of the paper.
There are three possible finishes that can be placed on the paper in the calendar section of the Fourdrinier machine: machine finish, supercalendered finish, and plater finish. The machine finish can range from a rough antique appearance to a smooth and high quality look. The supercalendered finish is high degree and is usually used for fine-screened halftone printing. The plater finish is an even higher quality and is accomplished by removing the paper from the calendar and placing it between copper or zinc plates. Here, it is put under pressure and usually heated.
The Fourdrinier machine is at the heart of the paper making process. With the help of this machine, the paper making process is sped up dramatically as the drying and smoothing process is simplified.