Rolls in Paper and Board Machines
6.2 Rolls in Paper and Board Machines
Different types of rolls are used throughout the paper or board machine as well as in off-line machines and fulfill a variety of functions:
. • Guide rolls give a stable run either to the paper web or to wires, felts or belts. They are about 400 to 1000 mm in diameter and are covered with coatings (Sec¬tion 6.2.4). They are also used in tension control devices to ensure that the fabrics operate at adequate tension in the machine direction and in wire and felt guide systems for continuous control of the fabric position in the cross machine direction.
. • Suction rolls apply controlled vacuum at a certain angle to the roll circumference to dewater the web or for pick up and transfer (Section 6.2.2).
. • Press rolls form a loaded press nip for mechanical dewatering of the paper web.
. • Calender rolls equipped with special covers and coatings generate web smooth¬ness and gloss (Sections 6.2.4 and 6.9).
. • Spreader rolls spread the paper web or fabrics in the width direction in order to avoid wrinkling or flutes. They consist of several short cylindrical roll sections which are covered by one common flexible hose. The overall axis can be bent for spreading.
. • Deflection control rolls (Section 6.2.3) overcome the disadvantages of deflection of the conventional rolls resulting from internal and external forces.
Depending on their application these rolls are made from steel, cast iron, bronze or fiber reinforced plastics. Each roll may be driven by its individual drive, and thus may drive in turn the paper web, the wire, felt or belt. Alternatively, the rolls are driven through friction by a wire, felt or belt. Depending on their application the rolls are equipped with varying covers and coatings (Section 6.2.4). Increased ma¬chine speeds make good roll balancing ever more important in order to avoid machine vibrations with their negative effect on paper quality and machinery.
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