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Aug 30, 2001 12:00 AM
A typical machine extends the length of a city block and is two stories high
In 1798, Nicholas-Louis Robert, while working for a French paper mill owned by the Didot family, invented a machine that used a belt of wire screen to produce a continuous web of paper. He was backed in England by the Fourdrinier brothers, who built and sold the first paper machines.
By 1810, the Fourdrinier brothers were bankrupt. Their engineer, Bryan Donkin, however, continued to improve the basic design. Soon he was successfully manufacturing a machine that mechanized the process of making paper. A water and pulp mixture flowed across a moving, vibrating web of woven wire cloth, forming a wet mat of interlocking fibers. From the wire, the newly formed paper transferred to a moving web of woolen cloth (the felt), before being dried.
The following are basic steps of the papermaking process, courtesy of Mohawk Paper (Cohoes, NY).
One of the most important aspects of papermaking takes place in large beaters before the paper machine. Each paper requires its own special mix of fibers and fillers to achieve its unique characteristics. The furnish, which consists of the finest available wood pulps, fillers and internal sizing, is mixed with water in large beaters until the mixture (a slurry called “stock” or “stuff”) resembles oatmeal.
The slurry is about 99 percent water and one percent fiber. It moves from the headbox, which evenly distributes the mixture, onto a fine wire mesh. At Mohawk Paper, the wire travels at speeds up to 1,800 fpm. The wire's gentle shaking motion mats the fibers together. Water drains off as the wire moves forward.
This mechanism rides on top of a moving web of paper. Its functions are to help remove water from the web, and to lay down and compact the fibers. It may also be used for watermarking via designs in wire sewn to its surface, or for reproducing the surface of laid paper with a laid watermark.
The partially dry web of paper leaves the wet end of the paper machine here. It is now strong enough to support itself.
The paper at this point is still about 50 percent water. For genuine felt marks, the paper web is run against special textured marking felts, which impart their finish to the paper.
Most of the remaining moisture is removed from the paper by steam-heated drums.
In this section, surface sizing is added to uncoated paper to provide surface strength and to prevent feathering and picking when ink is laid down in the offset printing process.
The coating process can be performed either while the paper moves through the papermaking machine, or when it comes off the machine. Coating improves ink holdout, reducing dot gain for sharper, brighter printed images.
The calender stack controls the caliper, smoothness and gloss of paper.
Paper is wound up into rolls and taken off the paper machine.
Paper is cut into smaller web rolls, precision-sheeted, and packed in cartons or on skids.