PDF Publication Title:
Text from PDF Page: 015
Wire Coating In the wire coating process wire or a bunched cable core passes through a mandrel, mounted in a cross-head, which directs the conductor centrally into the die orifice. Here the conductor comes into contact and is coated with soft- ened plastic. The wire is drawn away from the die under conditions that pro- duce a predetermined insulation thickness (Figure 7.). The position of the tip of the mandrel relative to the die parallel is very important for most materials, because it controls the tightness of the covering of the wire. Some machines use a vacuum system to control the tightness of this covering. The insulated conductor then passes through one or more cooling baths to a haul-off, or capstan, maintained at constant speed, and from there to a wind-up drum. Generally, an accumulator is inserted between the capstan and the wind-up arrangements to allow completed reels to be changed without interfering with the extrusion operation. Cooling must be gradual, for if the insulation is cooled too rapidly the outer layers will freeze and contract, resulting in voids between the insulation and the conductor. Foamed coatings can be extruded directly onto wire using a com- pound containing a blowing agent; a chemical compound that will liberate nitrogen or some other inert gas on heating. Extrusion conditions should be such that the blowing agent decomposes on the last few flights of the screw. The melt issuing from the die is then in an un-blown state and expands to its final dimensions as it leaves the die. Premature expansion leads to a product with a rough external finish. Pay-Off (Input Drum) Input Capstan Preh Spark Tester Eccentricity Gauge Diameter Gauge Tension Controller Preheat er Figure 7. Wire Coating Sheet Preheater Extruder Cooling Trough Output Capstan Sheet is extruded through a slit die (See Figure 6.). After leaving the die it is cooled gradually by passing it over a serpentine of water-cooled rolls. With some materials, for example, polypropylene and polystyrene, it is desirable to use a series of polishing rolls to achieve sheet with a good surface finish. The haul-off equipment is designed to prevent distortion of the sheet during cool- ing and to minimize draw-down. Sheet is generally cut to length with a travel- ling circular saw or shear. Incorporating a corrugation unit in the haul-off produces corrugat- ed sheet, with transverse corrugations. A system is also available for forming longitudinal corrugations by using water-cooled forming dies. Embossed sheet, such as embossed acrylic sheet for lighting fit- tings, is produced by passing the extruded sheet between a pair of embossing rolls mounted close to the die. The sheet is air cooled as it leaves the die in order to retain a sharp impression. 9 section 1: introduction to extrusionPDF 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)