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leizhanpapermachine-blog · 7 years

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HOW PAPER IS MADE

Paper is simple material. It is essentially a mat held together by the fiber’s roughness, and can be made from almost any fibrous material like wood or recycled paper.

The process for making paper was invented in China in the second century A.D., and all paper was made one sheet at a time until 1798. To learn more about the history of paper, clickhere.

The process of making paper has not changed – at least, fundamentally – since its discovery. But with almost two centuries of improvements and refinements, modern papermaking is a fascinating, high tech industry. Wisconsin has led the nation in papermaking for more than 50 years.

STEP 1: FORESTRY

Typically, trees used for papermaking are specifically grown and harvested like a crop for that purpose. To meet tomorrow's demand, forest products companies and private landowners in Wisconsin plant millions of new seedlings every year.

STEP 2: DEBARKING, CHIPPING AND/OR RECYCLING

To begin the process, logs are passed through a debarker, where the bark is removed, and through chippers, where spinning blades cut the wood into 1" pieces. Those wood chips are then pressure-cooked with a mixture of water and chemicals in a digester.

Used paper is another important source of paper fiber. Thanks to curbside recycling programs in many communities, we recover 40% of all paper used in America for recycling and reuse. The paper is shredded and mixed with water.

STEP 3: PULP PREPARATION

The pulp is washed, refined, cleaned, screened and sometimes bleached, then turned to slush in the beater. Color dyes, coatings and other additives are mixed in, and the pulp slush is pumped onto a moving wire screen.

Computerized sensors and state-of-the-art control equipment monitor each stage of the process.

STEP 4: PAPER FORMATION

As the pulp travels down the screen, water is drained away and recycled. The resulting crude paper sheet, or web, is squeezed between large rollers to remove most of the remaining water and ensure smoothness and uniform thickness. The semidry web is then run through heated dryer rollers to remove the remaining water.

Waste water is carefully cleaned and purified before its release or reuse. Fiber particles and chemicals are filtered out and burned to provide additional power for the mill.

Papermakers carefully test for such things as uniformity of color and surface, water resistance, and ink holding ability.

STEP 5: PAPER FINISHING

The finished paper is then wound into large rolls, which can be 30 feet wide and weigh close to 25 tons. A slitter cuts the paper into smaller, more manageable rolls, and the paper is ready for use.

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leizhanpapermachine-blog · 7 years

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Paper Making Process

Pulpwood normally arrives at the paper mill in the form of very thick sheets and recovered paper normally arrives in the form of large, compressed bales. Both these materials have to be broken down so that the individual fibres they contain are completely separated from each other. This process is performed in large vessels, known as ‘pulpers', where the raw materials are diluted with up to 100 times their weight of water and then subjected to violent mechanical action using steel rotor blades.

The resulting slurry (known as papermaking pulp) is then passed to holding tanks. During this preliminary stage, auxiliary chemicals and additives may be added. The auxiliary chemicals are usually combined with the fibrous raw materials at levels from below 1% to 2% and can be sizing agents, which reduce ink and water penetration, and process anti-foaming agents. Common additives consist of clay, chalk or titanium dioxide that are added to modify the optical properties of the paper and board or as a fibre substitute. The stock is then pumped through various types of mechanical cleaning equipment to the paper machine.

In the pulp and papermaking industry 95% of the water used is cleaned and reused on-site and all waste water is treated in accordance with European legislation and standards. Paper mills have state of the art wastewater treatment installations to the extent that in some cases water in lakes close to paper mills is now cleaner than it was in the past. Since 1994, the paper industry has reduced annual water consumption by over 14% per year.

On the paper machine, more water is added to produce a fibre suspension of as little as 1-to-10 parts fibre to 1000 parts water and the resulting mixture is passed into a headbox which squirts it through a thin, horizontal slit across the full machine width (typically 2 - 6 m) on to a moving, endless wire mesh.

The water is then removed on this wire section by a mixture of gravity and suction in a process known as sheet formation where the fibres start to spread and consolidate into a thin mat, which is almost recognisable as a layer of paper on top of the wire mesh.

This web of wet paper is then lifted from the wire mesh and squeezed between a series of presses where its water content is lowered to about 50%. It then passes around a series of cast-iron cylinders, heated to temperatures in excess of 100ºC, where drying takes place. Here the water content is lowered to between 5% and 8%, its final level. Throughout its passage from the wire mesh to the drying operation, the paper web is supported by various types of endless fabric belts moving at the same speed. After drying, some papers may also undergo surface treatments e.g. sizing and calendaring - a process consists of smoothing the surface of the paper by passing it between a series of rotating, polished, metal rollers to produce a glazed or glossy appearance. The paper is then wound into a reel.

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