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Plastic Product Material and Process Selection Handbook Part 12

Tham khảo tài liệu 'plastic product material and process selection handbook part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Q CALENDERING Introduction This process is used to convert thermoplastic materials into continuous sheets films and for applying plastic coatings to textiles paper or other supporting material. When coating the calendering line is also called a coating machine. Calendering is an alternative to extrusion with the usual film at three or more mils 75 microns thick Chapter 5 . For the production of sheet or film plastic melt is compounded and pressed as it passes through the nips of a series of three or more heated highly polished steel rolls. A plastic bank is formed into a web in the nip between the first pair of rolls. Passing through the second and third nips further reduces the thickness. Final thickness of the sheet is determined by the gap between the last pair of rolls called the gauging rolls. Finally a take-off roll pulls the hot sheet around a chilled roll to cool the sheet or film web Figure 9.1 . In this industry bank is identified as the quantity of plastic present in the nip formed between two rolls Figure 9.1 . Bank marks are surface roughness on sheet caused by incorrect temperature or sizes of banks. They can be minimized by optimizing formulations calendering speeds and roll temperatures so as to obtain the most orderly behavior of the rolling banks of stock at the calender-nip entrances. Calendering converts plastic into a melt and then passes the pastelike melt through roll nips of a series of heated and corotating speed-controlled rolls into webs of specific thickness and width. The web may be polished or embossed either rigid or flexible. Proper calendering requires precise control of the complete roll temperatures pressures and speed of rotations. An embossed design can be produced on the surface by using an engraved roll calendering a mixture of granular 370 Plastic Product Material and Process Selection Handbook Figure 9.1 Example of the sheet or film passing through nip rolls to decrease thickness plastic chips of varying color may produce .