Mechanical Engineering Handbook: Special Machinery Volume (IV)

Author: Editor-in-Chief: Qi Fujiang
Publisher:
Publish Date: 1997-11-01
Features: The Mechanical Engineering Handbook (Second Edition) consists of 18 volumes and 152 chapters, divided into sections such as fundamentals, engineering materials, design, processing and equipment, electrical and electronic instruments, general mechanical products, and specialized mechanical products. This volume is one of the sections on specialized mechanical products, including pulp and paper machinery, beer and carbonated beverage machinery, dairy production equipment, rubber and plastic processing machinery, printing machinery, packaging machinery, and environmental protection machinery, totaling 7 chapters. It primarily introduces the classification, applications, working principles, typical structures, key technologies, main technical parameters, and selection principles of products. This handbook is mainly intended for a broad range of mechanical engineering technicians with intermediate to advanced technical skills, serving as a reference for comprehensive research and handling of technical issues in their field and related disciplines, as well as for university teachers and students and other relevant personnel. Excerpt:
Chapter 1 Introduction Paper is an indispensable product in daily life and also a fundamental material in industrial and agricultural production. Modern papermaking industry includes three interconnected or independent production processes: pulp production from fiber raw materials, paper (including paperboard) production from pulp using appropriate types of pulp, and processed paper production that gives new properties to raw paper through appropriate processing.
1 Pulp Production Raw Materials and Methods [1]–[6] Pulp is generally made from plant fiber materials. Among plant fiber raw materials, wood is the primary source, but grass fiber materials and recycled fibers from waste paper or paperboard are increasingly being developed. For the production of certain special types of paper, other fiber materials are also used. Common pulp fiber raw materials are listed in Table 1·1－1. Pulp production includes processes such as preparation, pulping, bleaching, and screening. Methods of pulping for plant fibers and recycled fibers are shown in Table 1·1－2. Pulp that has been bleached is called bleached pulp, while pulp that has not been bleached is called unbleached pulp. The variety of pulp is first distinguished by pulping method and then by raw material. Pulp produced by chemical mechanical or mechanical methods is both referred to as high-yield pulp. When producing certain special types of paper, such as asbestos paper, mica paper, or wool paper, mineral, animal, or synthetic fiber materials are broken, cut, washed, degreased, and stirred to form liquid suspensions, which are used alone or mixed with plant fiber pulp for papermaking.
2 Production and Classification of Paper and Paperboard The production of paper and paperboard includes processes such as pulp preparation, papermaking, and finishing. Paper is divided into handcrafted paper and machine-made paper based on whether it is made by hand or mechanically. It is also classified into wet and dry methods based on the composition and state of the fiber suspension. Handcrafted paper is one of the wet papermaking methods. The differences between wet and dry papermaking production methods are as follows:
(1) Wet Papermaking. Pulp in water suspension is treated with processes such as beating and purification, then mixed with recycled pulp. It is formed into wet paper on a forming wire through filtration and concentration. The wet paper is further pressed to remove water and dried to become paper. On the papermaking machine, it is formed into an endless sheet and then rolled into a paper reel. Handcrafted paper, however, is made into sheets.
(2) Dry Papermaking. Dry pulp or other dry fiber materials are loosened or cut and combed to form an air suspension. The fiber suspension is then retained and spread on a forming wire to form a fiber layer, which is combined into paper through sizing and dried into a paper web. Dry papermaking is used to produce materials such as mineral wool paper and sanitary napkins. Dry papermaking production methods are similar to those of nonwoven fabrics (woven fabrics). The papermaking production method described in this section is the wet machine-made paper production method.
Paper with a basis weight (i.e., mass per unit area) of 225 g/m2 or greater or a thickness of 0.1 mm or greater is generally referred to as paperboard. Paper or paperboard used specifically for further processing into processed paper is called raw paper. The main classification of paper and paperboard is shown in Table 1·1－3.