tailieunhanh - Plastic Product Material and Process Selection Handbook Part 9

Tham khảo tài liệu 'plastic product material and process selection handbook part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 264 Plastic Product Material and Process Selection Handbook ratio and to reduce polymerization costs and emissions. The final polymer plastic may or may not be soluble in the solvent. Dry spinning involves a solution of plastics. The solution is then heated above the boiling temperature of the solvent and the solution is extruded through a spinneret. The solvent evaporates into the gas stream. With wet spinning the fiber is directly extruded into a coagulation bath where solvent diffuses into the bath liquid and the coagulant diffuses into the fiber. The fiber is washed free of solvent by passing it through an additional bath. Each process step generates emissions or wastewater. Solvents used in production are recovered by distillation. Extruders have their part in producing fibers or filaments. There are many variations and combinations of the basic processes that include 1 reaction spinning 2 dispersion emulsion and suspension spinning 3 fusion-melt spinning 4 phase-separation spinning 5 gel spinning. During processing molten melt spinning plastic is forced by just a gear pump or an extruder through fine holes in a spinneret die Figure . The spinneret holes may be simple cylindrical bores but may also be profiled to create fibers with improved wicking properties. Common profiles include trilobal quadrilobal delta and dogbone shapes. The land length of the spinneret holes is typically in the range 5 to 15 times the hole diameter. In turn they are immediately stretched or drawn oriented cooled and collected at the end of the line. During this process they may be subjected to other operations such as 1 thermal setting and thermal relaxation processes to provide dimensional stability 2 twisting and interlacing to provide cohesion of the filaments with or without sizings 3 texturing 4 crimping and cutting to provide staple products. Speeds of certain lines using the melt and dry spinning processes can go from 2 000 m min 6 600 ft min to at least 4 000 m min 13 .

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