papr17 - Operational variables The selection of nip width...

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1 Paper Machine Dry-end Lecture 17 PAPR 1000 Introduction to Pulp and Paper Manufacturer
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2 Types of Papermaking Machines ± Cylinder Machine – Oldest, can use poor fiber mix, heaver caliper possible, can bury inferior furnish in the center of the sheet ± Fourdrinier Machine – Most widely used, suitable to wide variety of papers ± Twin Wire Machines – Newest type, can produce thick calipers, can bury inferior furnish in the center of the sheet,
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5 Fourdrinier Machine
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7 Twin Wire Formers
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9 Pressing ± More water removal by squeezing ± Water from the sheet transfers to the press felt which is then cleaned with water jets and dewatered by vacuum boxes ± Consolidate matt to bring fibers into close contact
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10 Press - Variables ± There are large number of factors that affects dewatering at press: –Layou t – Nip configuration – Nip load – Roll covering and crowns – Stock and sheet characteristics
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Unformatted text preview: Operational variables The selection of nip width and dwell time can be related to sheet basis weight and speed 11 Presses- Types Plain press Two smooth rolls, capacity of water removal depends on void volume of felt (s) Grooved press Helical grooves cut in the bottom roll, provide additional volume and path for water transfer Suction press Bottom press roll is equipped with a suction box to remove water Extended nip press Better compaction of the web and increased water removal 12 13 14 15 16 Press Felt The press felt normally runs underneath the paper web going through the press section It is designed to absorb water squeezed out of the sheet and to support the sheet through the presses A variety of mechanical and/or chemical conditioning treatments are used to clean press felt...
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papr17 - Operational variables The selection of nip width...

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