PDF Publication Title:
Text from PDF Page: 016
10 Profile Profiles of open or hollow cross section can be extruded from specially designed dies. Each shape presents its own problems of die design and post- extrusion handling. Profile dies are frequently intricate and thus difficult and expensive to make. Unless CAE is used, a lengthy process of trial and error is required to establish both die design and extrusion conditions (A case in point, is to prevent preferential flow in the thicker sections). Such dies can be used for small sections, but a simpler technique is desirable for larger profiles (for example, for diffusers for fluorescent light- ing fittings). One technique involves post-forming sections extruded from tube dies. Compared with profile dies, these large tube dies can be made at low cost and their symmetry facilitates uniform flow. The inner lip of the die can have a reeded surface that imparts a pattern to the extrudate. A knife mounted in the die face, slits the emerging reeded tube and the tube passes to a shaping and cooling jig. Alternate inner and outer formers do the shaping with polished forming surfaces. Cooling is accomplished by internal and external perforated copper rings through which is directed a gentle flow of air. The haul-off may be the rubber caterpillar-band type, and an on-demand knife cutter can cut off sections. Trial and error will again be necessary to establish conditions and former design, but adjust- ments to formers are made more quickly and cheaply than changes to a pro- file die. Extrusion Blow Molding Hollow articles (such as bottles) are produced using the blow molding process. This process normally starts with the extrusion of a short thick- walled tube, or “parison”, from a tube die mounted in a cross-head. This tube is extruded vertically downward between the two halves of a split, water- cooled mold. The two halves of the mold are closed, sealing the ends of the molten tube. Air is then applied to the interior of the tube, blowing it outward against the inner surface of the mold. Frequently, as one molding is cooling another is made ready to receive a fresh parison. The split molds may be mounted on a turntable below the extruder die. Alternatively, the melt can be delivered to two or more static molds by arranging for melt to be diverted, in turn, to different dies connected to the same extruder. All extrusion-blown moldings involve welds of the open-ended parison which are potential sources of weakness. Thus care must be taken in the design of the mold to ensure the formation of strong, bead-type, welds. In the blow-molding field it is possible to combine co-extrusion with bi-axial orientation and so produce strong, lightweight bottles which give a long storage life to the products. Fiber from Film The extrusion process can be used to produce fibers or tapes from film. Such products are usually based on polyethylene or polypropylene and they may be used as string, rope or as a woven product (such as a sack). The polymer may be extruded on a single screw machine into a flat sheet using the chill roll process. The sheet may is then slit into tapes by either stationary or rotat- ing knives. Godet rolls are then used to stretch the tape (mono-axial orienta- tion) while it is heated in a hot air oven or on a hot stretching table. In the production of film tape, the width of the tape may decrease to 1/3 of its origi- nal slit width as a result of this stretching process. This imparts a significant strength to the tape, in the machine direction. Annealing may then be per- formed on the tape before it is wound into packages suitable for weaving.PDF Image | Dynisco Extrusion Processors Handbook
PDF Search Title:
Dynisco Extrusion Processors HandbookOriginal File Name Searched:
27429_Legacy_Txt.pdfDIY PDF Search: Google It | Yahoo | Bing
Development of a solar powered Electric Ship The Electricship website originally started off as a project to develop a comprehensive renewable, affordable, modular electric ship... More Info
Modular Boat Hull Composite The case for a unsinkable, modular composite hybrid boat hull... More Info
MS Burgenstock Hybrid Electric Catamaran Lake Lucerne Unique shuttle servicing Lucerne to the Burgenstock Resort... More Info
Ground Power Unit GPU Powered by Lithium Ion Batteries The goal of the Ground Power Unit is to provide a readily accessible, modular, ready-to-power solution for remote power... More Info
CONTACT TEL: 608-238-6001 Email: greg@electricship.com (Standard Web Page)