Paper and Board Machines

The majority of paper machines worldwide produce graphic paper grades on fourdrinier wire sections or on hybrid formers. These kinds of conventional forming section usually satisfy the quaHty requirements. Their disadvantages are the limitation in machine speed of about 1200 m min and for some paper grades the nonsymmetry in the web z-direction. 

The paper machine layout and operating conditions differ according to the special requirements of the grades produced as regards 

An example of woodfree paper is copy paper. The most important properties are high bulk at a certain roughness, and good formation. Here the whole paper-making process has to be considered to meet the high bulk requirements of the 

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Although the Fourdrinier machine is used for making almost all grades of paper and board, other designs are sometimes more advantageous. The cylinder machine, invented at about the same time as the Fourdrinier, consists of a rotating cylindrical mold covered with a wire screen and partially submerged in a vat. The stock flows into the vat, and a mat is formed on the cylinder under a hydraulic head difference between the stock level in the vat and the white-water level inside the cylinder. The... 

ASTM D1922, usually known as the Elmendorf tear strength (related to test originally devised for paper and board), is carried out in the machine (MD) and cross (CD) direction of the material. Measured as kN/m. Test D689-44 also applies for films. 

All aspects of the stock flow system and the paper or board machine equipment will have an effect on the retention and drainage aid. 

The two major types of synthetic size employed at the wet-end of a paper or board machine, AKD and ASA, will be dealt with jointly as in many respects the wet-end chemistry is the same. Individual problems related to tlie sizes thanselves will be dealt with later in this section. 

The task of the paper machine is to produce paper or board of the quality required by the end user - or by the intermediate process steps such as converting or printing. The paper and board properties have to be uniform in machine direction (MD) as well as in cross machine direction (CD). Further, the paper machine has to make the best use of the quality potential of the entering stock The paper machine includes... 

By tradition and technical feasibihty, coating and supercalendering for surface quality improvement have been off-hne processes. Today both are increasingly integrated into the paper machine. The final activities in paper and board production are shtting of the full width reels into smaller rolls at the winder followed by packaging the rolls for shipment... 

In 2002 the world production of paper and board was ca. 331 x 10 t Although paper and board are used in some form or other in all parts of the inhabited world, the production is left to a limited number of countries. More than 9000 paper machines are responsible for production in 111 of the approximately 200 countries in the world, whereby the 15 largest producer countries alone account for 82% of total world production (Table 1.2). 

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