Beating of Chemical Pulps

The first operation in the paper mill involves stock preparation the slushing of baled pulp, the refining or beating of chemical pulps, the blending of pulp stocks and additives prior to forming paper. 

This discussion will be eonfined principally to the well-established Fourdrinier papermachine and will only touch upon twin-wire machines that are now common in the industry. 

Paper made from unbeaten chemical pulps is bulky, porous and has less tensile strength than from beaten pulps. This is because the unbeaten fibres tend to be stiffer, springy and resistant to collapse on pressing, so that there is comparatively little interfibre bonding in the sheet. 

Low consistency refining, with some fibre cutting at the bars 

High consistency refining, with more fibre-fibre contact 

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The Beating of Chemical Pulps - the Action and the Effects , D.H. Page in Transactions of the 9th Fundamental Research Symposium , ed. C.F. Baker and V. Punton, Volume 1, pp. 1-38, Mechanical Engineering Publications Ltd, London, 1989, ISBN 0-85298-706-4. 

Page, D.H. (1989) The beating of chemical pulp - the action and effect. 9th Fundamental Research Symposium Notes, Pulp and Paper Fundamental Research Society, Cambridge, UK, 1989. 

Paper is made by the wet laying of a mass of cellulose fibres onto a woven wire band, which is effectively a filter through which the water drains and the fibres settle down to produce a continuous sheet. A slurry of cellulose fibres, or pulp, is formed by disintegrating and beating (or chemically treating) wood chips, and is then slowly and evenly fed onto the woven wire. The fibres settle in a random manner to form the sheet of paper, which has to be pressed and dried to achieve the required moisture content. 

Before the pulp can be made into paper, it is necessary to mechanically beat or refine it. It is also usually bleached with chlorine and calcium hypochlorite. Unbleached kraft pulp is used for grocery bags and heavy wrapping paper. Other materials may also be added to the pulp depending on the type of paper to be made. For book paper, fillers such as white clay and titanium oxide may be added to provide opaqueness and extra whiteness. Size may be added for stiffness and smoothness. Dyes are added for tinted papers. The specific combination of pulp and additives used to produce a particular type of paper is called the furnish for that paper. With better grades of paper, care is taken to produce a furnish that is chemically neutral (pH 7 on the acid-base scale). For a paper to have long life, it must be acid-free. 

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