Paper machines, based on the Fourdrinier machine, are used to make paper. They consist of four sections: the wet end, press section, dryer section, and calendar section. Different configurations are used to create papers of different qualities. The machine is supplied with a slurry of wood pulp and water, and the paper is shaped into flat sheets, dried, and smoothed.
A paper machine is used to make paper. Modern paper machines are based on the Fourdrinier machine, developed by Henry and Sealy Fourdrinier in the early 1800s. The design is based on a machine invented in 1798 by Louis Robert, although Fourdrinier machines are significantly more complex. Little has changed in paper machines since their initial development. Most paper machines are made up of four sections, which can all be in one piece of equipment or separate in some smaller machines.
This first section of the machine is called the wet end. Different configurations in this section of the machine are used to create papers of different qualities. In the wet end, the machine is supplied with a slurry of wood pulp and water. The pulp, which is up to 99% water, is placed against a screen so that the fibers are aligned in the same direction as the machine; fillers and colors can also be mixed with the pulp at this stage of paper production.
In the next section of the paper machine, the paper moves to the press section, which consists of two or more presses. The paper, still wet, is transferred from the screen onto a felt, which can be made from different materials to give the paper different textures. The purpose of this section is to remove water from the pulp by pressing the paper between the rollers. While removing excess water, the presses shape the paper into flat sheets which can later be cut by another machine. At the end of this stage, the paper may still contain up to 65% water.
The third section of the paper machine, called the dryer section, reduces the water content of the paper to about 5%. In this section, the paper is passed through steam heated rollers. Usually, there are two or more sets of these rollers, which are arranged in several tiers so as to press the paper through a narrower gap each time. At this point it is also possible to add starch, resin and glue to the paper to make the paper more resistant to water and improve its printability.
The final section of a paper machine is known as the calendar section. Here, the paper is smoothed and pressed to a more uniform thickness. The amount of pressure applied to the paper at this point will determine the finish on the paper.
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